UTG/18/ERG/CT/217/RResearch+Project+No+379... · Since this method directly measures the dry...

UTG/18/ERG/CT/217/R

VERIFYING FLUE GAS FLOW RATE CALCULATION AT POWER PLANTS, FOR

EMISSIONS REPORTING PURPOSES, BY MEANS OF STACK TESTING AND DATA

EVALUATION TO EN ISO 16911:2013

Ratcliffe-on-Soar, Arnhem, Linkebeek, April 2018

Authors

D P Graham, J Spence Uniper Technologies, United Kingdom

F Blank, P Wolbers DNV GL - Energy, The Netherlands

N Faniel, J Annendijck Laborelec, Belgium

Under supervision of

VGB Technical Group: Emissions Monitoring

Supported by

VGB PowerTech e.V., Germany

VGB RESEARCH PROJECT NO. 379: Verifying Flue gas flow rate calculation

Uniper Technologies Uniper Technologies Limited, Technology Centre, Ratcliffe-on-Soar, Nottinghamshire, NG11 0EE T+44 (0) 2476 192900 www.uniper.energy

Registered office Compton House, 2300 The Crescent, Birmingham Business Park, Birmingham, B37 7YE. Registered in England and Wales No: 2902387.

UNRESTRICTED UTG/18/ERG/CT/217/R Job No: 2122.C40223.003

April 2018

VGB RESEARCH PROJECT NO. 379 VERIFYING FLUE GAS FLOW RATE CALCULATION AT POWER PLANTS, FOR

EMISSIONS REPORTING PURPOSES, BY MEANS OF STACK TESTING AND DATA EVALUATION TO EN ISO 16911:2013

prepared for VGB POWERTECH

by D P Graham, J Spence (Uniper Technologies)

F Blank, P Wolbers (DNV GL - Energy) N Faniel, J Annendijck (Laborelec)

SUMMARY Operators of combustion plants need to know the stack gas flow rate in order to calculate the mass release of pollutant emissions for inventory reporting purposes and also for compliance reporting in certain circumstances. EN ISO 16911 is a two-part CEN standard for stack gas flow rate measurement, published in 2013. For many standard fuels, the calculation of stack gas flow rate gives reliable, accurate results and this approach is used at many power stations for continuous stack flow monitoring. A stack flow rate calculation procedure, based on previous VGB research results, is specified in Part 1 of the standard (Annex E). If this is used as an Automated Measuring System (AMS), for continuous flow rate calculation, then it must be verified by annual stack testing using Standard Reference Methods (SRM) implemented by accredited Test Laboratories. However, installed stack gas flow monitors need to be calibrated using an SRM. The SRM can be based on multiple (20 point) stack velocity surveys, conducted using Pitot tubes or Vane Anemometers; the average velocity from each survey is then multiplied by the stack cross-sectional area to give the volume flow rate. Alternatively, the average velocity can be measured using time-of-flight radioactive tracers or the stack gas flow rate can be measured directly using rapid injection tracer gas dilution techniques. The standard does not provide a detailed assessment procedure for verifying stack gas flow rate calculations. Neither was the standard validated for ‘wet’ stacks, common at coal fired power stations across Europe, or for gas turbines, which present additional challenges related to the high temperature of the turbine exhaust gases and their relatively short stacks. The main objectives of this project are therefore to provide further guidance on verifying stack gas flow rate calculations at power stations and to provide practical guidance on the choice of SRM and the evaluation of test results. Proposals for the ongoing Quality Assurance (QA) of stack gas calculation approaches are also presented.

http://www.uniper.energy/

ii UTG/18/ERG/CT/217/R

The project was based on field trials at a Combined Cycle Gas Turbine (CCGT) plant in the UK and a coal fired power plant with a ‘wet’ stack in Holland. All of the available SRM, except the radio-active tracer injection method, were employed at both locations. Two different types of Pitot tube and a Vane Anemometer were evaluated and also the tracer gas dilution technique - using a chemically inert and insoluble tracer. Prior to the field test campaigns, the calibration of the tracer flow meter was checked, by an accredited test laboratory, to an expanded uncertainty of ±0.5%, noting that the tracer calibration gas has an expanded concentration uncertainty of ±1.0%. The overall expanded uncertainty of the tracer method is better than ±2.5%. The calibrations of L-type and S-type Pitot tubes and a Vane Anemometer were also checked at two accredited calibration laboratories (a 3D Pitot was not checked since this service if not yet offered in Europe). The results were generally encouraging, with Pitot coefficients and Vane Anemometer performance being confirmed to within ±1% expanded uncertainty, although additional effort would be required for measuring velocities below 5 m/s. The overall expanded uncertainty of the velocity methods, in the field, is of the order of ±2 to ±3%. Whilst various new Quality Assurance requirements for the velocity methods are not yet recognised or reported by calibration laboratories (linearity, repeatability and impact of mis-alignment with the flow direction) these aspects were checked where possible and the results were generally encouraging. The first field trial, at a CCGT plant in the UK, was successfully completed in August 2014. In most cases, a full set of 15 velocity traverses was obtained - using a 3 D Pitot, an S type Pitot and a Vane Anemometer - with an L type Pitot providing a reference reading at a fixed location. Testing was conducted at maximum and minimum plant loads. A set of 33 tracer gas injections was aggregated to give 20 test results. The AMS calculation, based on the metered fuel flow and calorific value, was successfully verified by all of the SRM except the S type Pitot which was reading too high with no obvious explanation for this behaviour. Otherwise, the results were broadly in line with previous validation studies with the tracer gas dilution and the 3D Pitot being closest to the AMS (± 0.5%) and the Vane anemometer reading about 4% higher than the AMS. The fixed L type Pitot was also about 4% higher than the AMS. The second field trial, at a coal fired power plant in Holland, commenced in November 2014 but operational issues at the plant curtailed the velocity testing to 9 - 11 test points and the tracer gas injection work was not completed until March 2015 (19 injections in total). Since testing was conducted at both maximum and minimum plant loads, a minimum of 9 test points remained in compliance with the flow standard. The AMS calculation is based on the plant thermal output and boiler efficiency which are calculated on-line within the plant control system. The AMS was successfully verified by all of the SRM but the testing was slower than before since the Pitot impulse lines required regular purging in the wet stack. As before the tracer and 3D Pitot were closest to the AMS with the Vane Anemometer and S type Pitot being 3 to 4% higher. The performance of the, mostly unattended, L type reference Pitot, was erratic due to problems with water droplets. It can be concluded that all of the test methods can be used to verify stack flow rate calculations and can be used in wet stacks and for gas turbine testing. However, the tracer gas dilution method appears to have the least bias, takes the least amount of test time and does not require any knowledge of the plant geometry or flue gas characteristics (other than the oxygen content). Since this method directly measures the dry volumetric stack gas flow rate, at 273K 101.3 kPa, it is particularly well suited to verifying calculations performed on the same basis. Provided that the tracer gas can be well mixed with the flue gas, sampling arrangements that are non-compliant with EN 15259 can also be considered. Good mixing can be achieved by injecting the inert tracer at the gas turbine air inlet or upstream of an FGD unit at a coal fired power

iii UTG/18/ERG/CT/217/R

station. However, high pressure cylinders of tracer gas are required along with the additional equipment to measure tracer gas flow rate and concentration. The Vane Anemometer provides the next quickest and most reliable alternative for non-swirling flows since this gives a direct velocity reading, although gas temperature, pressure and composition are still required for normalisation to reference conditions. S type Pitots are commonly available and can also perform satisfactorily in non-swirling flows although they tend to further over-read when compared with the other techniques. Whilst a 3D Pitot accurately measures swirling flows, it is relatively difficult and time consuming to use and requires calibration in the United States. Adaptation of the Quality Assurance (QA) requirements, for an AMS flow calculation, is considered in some detail. EN 14181 defines three Quality Assurance Levels - QAL1, QAL2 and QAL3 - along with an Annual Surveillance Test (AST) in order to correctly certify, calibrate and control Automated Measuring Systems. The pass/fail criteria embedded within the QA process are based on the Daily Emission Limit Value (Daily ELV) which, in this case, is 120% of the maximum measured flow rate, with the uncertainty requirement, σ0, equal to about 5% of the maximum flow rate, equivalent to a 95% Confidence Interval of about 10%. Note that the ‘ELV’ should be increased to 125% of maximum measured flow to be consistent with a Confidence interval of 10%. QAL1 requires that AMS are suitable for their intended application and AMS instruments must be certified according to EN 15267 which requires that the AMS uncertainty should not be more than 75% of the Confidence Interval for an hourly average value. This equates to about 7.5% of the maximum flow rate. QAL1 should therefore consist of a validation of the calculation against the requirements of EN ISO 16911-1 (Annex E) by means of an uncertainty assessment. Annex E requires that the expanded uncertainty is ≤ 2% for gas, ≤ 3% for oil and ≤ 7.5% of the flow rate for solid fuel firing. These uncertainties are achievable for large, new plants within the EU ETS. However, for existing plants with non-ETS meters, and for smaller plants, it may not be possible, or justifiable, to demonstrably achieve these uncertainties. From a practical point of view, it should then be sufficient to meet the over-arching ±7.5% uncertainty requirement and demonstrate compliance by means of a QAL2 verification. This follows the approach specified in EN 14181 (Annex H) which addresses the situation of a pre-existing uncertified AMS that can be used for the rest of its design life with the agreement of the Competent Authority. QAL2 requires that AMS based on flow calculations are verified by means of stack testing. A QAL2 Excel workbook has been developed in order to implement the EN ISO 16911-2 requirements and to define an assessment approach. This workbook is freely available from the VGB web site and contains additional information and tools for implementing flow calculations. Since QAL2 factors are not applied to a flow calculation, it is recommended that the AST Validity test is applied instead. This requires that the absolute mean difference (|D|) between the SRM and the AMS must be within about 5% to 8% of the maximum measured flow rate - dependent upon the number of test points and the standard deviation of the differences between the AMS and the SRM (sD). The QAL2 Variability test must also be passed which requires sD to be less than about 5% of the maximum flow rate. EN ISO 16911-2 allows a linear regression between SRM and AMS data to be forced through zero and places requirements in the coefficient of determination (R2 > 0.9) unless the data are narrowly clustered around the mean value. AST requirements are the same as those defined in EN 14181 and require the absolute agreement between the SRM and the AMS to remain within about 5 to 12% of the maximum flow rate - dependent upon the number of test points and the standard deviation of differences between the SRM and AMS. Provided that the QAL2 verification has tested the whole reporting

iv UTG/18/ERG/CT/217/R

chain, with a direct comparison between the SRM and the outputs from the Data Acquisition and Handling System, then it may be appropriate to reduce the frequency of AST testing in favour of ongoing QA applicable to the calculation inputs. Experience to date suggests that most of the benefit of applying EN ISO 16911-2 is obtained when conducting the QAL1 validation and the QAL2 verification since the calculation is critically reviewed at that point and any errors identified as a result of this review, or as a result of QAL2 testing, are corrected. QAL3 for a flow calculation principally requires that the quality of the calculation inputs is maintained. When fuel flow rate and calorific value are already subject to EU ETS verification then no further action is needed. Other meters should have a current calibration certificate, i.e., the meter is calibrated and maintained at the frequency specified by either the manufacturer or an appropriate flow standard or code of practice. When thermal efficiency is used for flow calculation then this should be checked annually using EU ETS fuel input data and annual production data supplemented by plant performance testing when this is available. Finally, plant performance calculations can be used to provide additional cross-checks of calculated flow rates and it is recommended, in any case, that the calculation is manually checked by the operator every year. Prepared by Approved for publication Master copy signed by D P Graham & H D Jones (18/04/2018) D P Graham H D Jones GT Combustion Team Leader Testing & Measurement

UNRESTRICTED This document was prepared by Uniper Technologies Limited. Neither Uniper Technologies Limited, nor any person acting on its behalf, makes any warranty, express or implied, with respect to the use of any information, method or process disclosed in this document or that such use may not infringe the rights of any third party or assumes any liabilities with respect to the use of, or for damage resulting in any way from the use of, any information, apparatus, method or process disclosed in the document. Telephone +44 (0) 2476 192900 (please ask for Proposal Management) E-mail [email protected] © Uniper Technologies Limited 2018 No part of this publication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means electronic, mechanical, photocopying, recording or otherwise, without the written permission of the Directors of Uniper Technologies Limited, Technology Centre, Ratcliffe on Soar, Nottingham, NG11 0EE.

CLIENT DISTRIBUTION LIST EF Mr S Göhring Advisor, VGB PowerTech EF Ms S Polenz Business Support, VGB PowerTech

mailto:[email protected]

UTG/18/ERG/CT/217/R

CONTENTS

Page NOMENCLATURE / SUBSCRIPTS / SYMBOLS

1 BACKGROUND ................................................................................................................ 1

2 PROJECT OBJECTIVES .................................................................................................. 2

3 PROJECT DESCRIPTION ................................................................................................ 2 3.1 General Issues and Rationale .................................................................................. 2 3.2 Experimental Techniques ......................................................................................... 3 3.3 Instrument Calibration .............................................................................................. 5

3.3.1 Pitot and Vane Anemometer – Calibration ....................................................... 5 3.3.2 Pitot and Vane Anemometer – Other QA Requirements .................................. 7 3.3.3 Tracer Dilution Method - Calibration Standards ............................................... 8

3.4 Field Trial Requirements .......................................................................................... 9

4 QUALITY ASSURANCE PROCEDURES ........................................................................ 10 4.1 General Considerations .......................................................................................... 10 4.2 Quality Assurance Level 1 (Validation) ................................................................... 10 4.3 Quality Assurance Level 2 (Verification) ................................................................. 12 4.4 Annual Surveillance Test (Verification) ................................................................... 15 4.5 Quality Assurance Level 3 (Control) ....................................................................... 16

4.5.1 Annual Surveillance Test ............................................................................... 16 4.5.2 Calculation Inputs .......................................................................................... 16 4.5.3 Control Charts ............................................................................................... 16

5 FIELD TRIAL 1 (NATURAL GAS FIRED CCGT PLANT IN THE UK) .............................. 17 5.1 SRM Implementation .............................................................................................. 17 5.2 AMS Implementation .............................................................................................. 18 5.3 Field Trial Results .................................................................................................. 20

6 FIELD TRIAL 2 (COAL FIRED POWER PLANT IN HOLLAND)....................................... 21 6.1 SRM Implementation .............................................................................................. 21 6.2 AMS Implementation .............................................................................................. 21 6.3 Field Trial Results .................................................................................................. 22

7 FURTHER GUIDANCE ON COMPLIANCE WITH EN ISO 16911 ................................... 23 7.1 Sample Location Requirements ............................................................................. 23 7.2 Choice of Reference Method .................................................................................. 23 7.3 Common Causes of Bias in Calculation Procedures .............................................. 24

8 SUMMARY ...................................................................................................................... 25

9 REFERENCES ................................................................................................................ 26

TABLES ................................................................................................................................... 27

FIGURES ................................................................................................................................. 35

UTG/18/ERG/CT/217/R

APPENDIX A Calibration Data

APPENDIX B Calculation of Flue Gas CO2 and H2O

APPENDIX C CCGT Field Trial QAL2 Sheets

APPENDIX D Coal Power Plant Field Trial QAL2 Sheets

UTG/18/ERG/CT/217/R

NOMENCLATURE a AMS AST b BL

Calibration line offset Automated Measuring System(s) Annual Surveillance Test Calibration line gradient Base load

BREF C

Best Available Techniques REFerence document Concentration of tracer in flue gas

CCGT Combined Cycle Gas Turbine CEMS CEN

Continuous Emissions Monitoring System(s) Comité Européen de Normalisation (European Committee for Standardization)

CO2 cst CUSUM Davg D |D|

Carbon dioxide Pitot constant (equivalent to k) Cumulative sum control chart Mean of differences between SRM and AMS pairs of values Difference between a pair of SRM and AMS values |Absolute| mean of differences between SRM and AMS pairs of values

DAHS DCS DIN E EN ETS

Data Acquisition and Handling System Distributed Control System Deutsches Institut für Normung (German Institute for Standardization) Electrical output Euronorm Emissions Trading System

EU EWMA

European Union Exponentially Weighted Moving Average control chart

FGD H2O HRSG

Flue Gas Desulphurisation Water Heat Recovery Steam Generator

IED Industrial Emissions Directive ISO LCP k

International Organisation for Standardization Large Combustion Plant Coefficient of discharge (Pitot)

kv M Max Min MM

Variability test value based on a 2-test with a value of 50% for N tests Mass flow rate Maximum Minimum Molecular mass

MPU Maximum Permissible Uncertainty N NCV

Number of tests or Normal reference conditions (273 K, 101.3 kPa) Net Calorific Value

NTI Net Thermal Input O2 Oxygen P PL PP Q QA

Pressure Part load Power Plant Volumetric flow rate of flue gas Quality Assurance

QAL R Rs RSS

Quality Assurance Level Coefficient of determination Specific gas constant Root sum of squares

s Standard deviation

UTG/18/ERG/CT/217/R

S Fuel factor SRM T

Standard Reference Method Temperature

t0.95;N-1

TNP U u UK UV V VA x y ycal z

Value of the t distribution for N-1 degrees of freedom at 95% confidence Transitional National Plan Expanded Uncertainty Standard uncertainty United Kingdom Ultra-violet Velocity Vane anemometer Abscissa Ordinate Calibrated AMS value Applicate or Compressibility factor (non-ideal gas)

SUBSCRIPTS a AMS b D dry est i ISO

Assumed value Automated Measuring System Background value Differences between parallel measurements (SRM and AMS) Dry flue gas condition Estimated (calibrated) value Indicated (test) value ISO reference conditions

m min max o

Metering condition Minimum value Maximum value In the flow direction

r ref rep

Reference value Reference reporting condition Reported value

SYMBOLS

0

Probe angle or Pitot factor (incompressible flow)

Delta (difference)

Pitot correction factor for compressibility

Electrical or thermal efficiency

Density

Uncertainty requirement derived from legislative requirements

1 UTG/18/ERG/CT/217/R

1 BACKGROUND Operators of combustion plants need to know the flue gas flow rate to calculate the mass release of pollutant emissions. This is required for reporting to the European Pollutant Release and Transfer Register (E-PRTR) or compliance reporting under the Transitional National Plan (TNP) derogation within the Industrial Emissions Directive (IED) [1]. For many standard fuels, the calculation of flue gas flow rate gives reliable results, with a defined uncertainty, using relatively simple procedures. A two-part CEN standard on stack gas flow rate measurement was published in 2013, noting that European standards refer to Continuous Emissions Monitoring (CEM) systems as Automated Measuring Systems (AMS). The scope of the standard, based on the original mandate from the EU, is linked to the requirements of European Directives, including the IED which requires CEN standards to be employed where available. This standard is entitled EN ISO 16911-1:2013 Stationary source emissions - Manual and automatic determination of velocity and volume flow rate in ducts. Part 1: Manual Reference Method defines manual Standard Reference Methods (SRM) to be used for the calibration of continuous stack flow monitors and for other compliance purposes, such as periodic testing [2]. The manual methods include: velocity traverses obtained with Pitot probes or vane anemometers; tracer (dilution) and tracer (time-of-flight) methods. Under certain circumstances, flow calculation can be used to perform periodic compliance checks and a harmonised calculation method is provided in Annex E (Calculation of flue gas volume flow rate from energy consumption). This calculation approach was defined in a previous VGB Research Project (No. 338 Validated methods for flue gas flow rate calculation with reference to EN 12952-15) [3], [4]. Part 2: Automated measuring systems applies to continuous monitoring and specifies the requirements for the certification, calibration and control of continuous flow monitors [5]. Part 2 also allows the use of calculation methods as an alternative to the continuous measurement approach (using the calculation methods specified in Part 1 above). Most power plants calculate flue gas flow rate from the net energy consumption derived from the fuel flow multiplied by the Net Calorific Value (NCV). Alternatively, the power or heat output is divided by the electrical or thermal efficiency, as appropriate, in order to determine the net energy consumption. As with all automated measurement systems, this calculation approach is subject to prescribed Quality Assurance (QA) procedures, in line with EN 14181:2014 [6] which defines three Quality Assurance Levels (QAL1, QAL2 and QAL3) and an Annual Surveillance Test (AST). QAL2 defines the initial calibration of a flue gas flow monitor (if installed), as performed by an accredited Test Laboratory, and the AST defines the annual calibration check, also conducted by the Test Laboratory, to check that the calibration has not deteriorated. However, the performance criteria specified in EN 14181 for all of the Quality Assurance Levels are modified by EN ISO 16911-2 to be suitable for flow measurement. When the flow rate is calculated from energy consumption, a QAL2 is required to verify the calculation, again requiring manual flow measurements at different load conditions. This is again checked annually, by means of an AST, whereby the calculation procedure is again checked against manual test measurements, restricted to base load operation if necessary. The standard specifies the required level of agreement between the measured (periodic) and the calculated (continuous) flow rates but the assessment procedure is not specified. Applying this new standard to existing large combustion plant is the subject of this VGB Research Project and this poses a number of challenges relating to a) sample port provision and access; b) choice of manual reference methods for both coal fired boilers and Combined Cycle Gas Turbine (CCGT) plant and c) implementation of the QA requirements in a consistent and meaningful way.


2 PROJECT OBJECTIVES This VGB Research Project has been supported and supervised by the VGB Technical Group: Emissions Monitoring - the project being led by Uniper Technologies (formerly E.ON Technologies) with the participation of two additional partners: DNV GL - Energy and Laborelec. The overall aim of the project was to clarify the way in which EN ISO 16911 is used for verifying the calculation of flue gas flow rate at power plants and to provide advice regarding the associated Quality Assurance (QA) requirements. The project has three main objectives: 1. Define a common approach to verifying flue gas flow rate calculation at power plant by

means of field trials, data evaluation and interpretation of the standard. 2. Provide guidance on the choice of stack testing methods for use at coal and gas fired

power plant, taking into account access restrictions at existing plant. 3. Provide a tool for applying Quality Assurance requirements to stack gas flow rate

calculation in compliance with the appropriate standards (EN ISO 16911 and EN 14181). The power industry will benefit from a standardised compliance approach and an understanding of how to apply the requirements of this relatively new standard. The overall experimental approach, including pre-calibration of field trial instruments, is described in Section 3. A Quality Assurance (QA) approach is then defined - based on the EN 14181 framework of Quality Assurance Levels: QAL1, QAL2, QAL3 and the AST - and this approach is described in Section 4. In particular, an Excel tool, developed within this project, is described for implementing the QAL2 requirements. The Excel tool is then applied to the results of the field trials in Sections 5 and 6 before further generic guidance is presented in Section 7. Normal (N) conditions refers to 237 K and 101.3 kPa. 3 PROJECT DESCRIPTION 3.1 General Issues and Rationale The project incorporates two field trials at i) a CCGT plant in the UK and ii) a coal fired power plant with a ‘wet’ stack in Holland. This site selection is intended to expand on the CEN validation field trials at a coal fired power plant in Germany, with a ‘dry’ stack, and a waste incinerator in Denmark, also with a ‘dry’ stack. The CEN validation trials are summarised in Annex G of Part 1 to the standard [2]. The CEN validation trials did not address measurement issues related to ‘wet’ stacks that are saturated with water and potentially contain droplets. This is commonly the case downstream of flue gas abatement equipment, such as Flue Gas Desulphurisation (FGD) units at coal fired plants, when the flue gas is not re-heated to a temperature above the water dew point. The degradation of performance of Pitot probes and anemometers in wet stacks is not well understood. In principle, it should be possible to make reliable Pitot measurements for flow measurement, since this is already done when measuring dust concentrations and when assessing the flow uniformity at a measurement location. However, this measurement is not commonly undertaken with precision vane anemometers due to concerns related to the


potential impact of droplets on the rotating components. Tracer methods can be used provided that the injected tracer gas is insoluble, especially when contacted with weakly acidic solutions in wet FGD systems. The CEN validation trials also did not address measurement issues related to gas turbines. In particular, the high exhaust gas temperature which makes it difficult to inject conventional tracer gases, such as methane and nitrous oxide, since these compounds combust or decompose explosively at gas turbine exhaust temperatures. Gas turbines present other challenges related to stack height, noting that the base of the stack is already at the top of the boiler, leading to relatively squat stacks in which it is more difficult to meet the recommended upstream and downstream lengths either side of the measurement location (specified as multiples of the stack diameter). Gas turbines are usually built to a unitised design, with separate stacks, i.e., wind-shields are not normally used and stack testing platforms are exposed to the elements. In some cases, gas species monitoring is therefore conducted at a representative point, or through a multi-point sampling rake, at the gas turbine exhaust location. It is difficult to measure velocity in the gas turbine exhaust duct since this operates at positive pressure and, typically, at 500 to 600°C. Ducts are often rectangular in section and are not fitted with the horizontal or vertical ports that are required for a multi-point grid measurement. It is also more difficult to find a suitable tracer to inject at this location, as noted above. It is therefore important to investigate a range of techniques that can be employed when full compliance with the standards is not possible. Since this project was focussed on verifying the stack flow rate calculation, typically employed at power plants, the methods already used by the sites were reviewed and cross-compared with the EN ISO 16911 calculation approach. The required calculation inputs were also reviewed and checked. Ideally, the flow at these stack locations should also have had a high swirl velocity component (> 15°) since it is known that high swirl causes an over-estimate of the axial velocity profile close to the wall (the profile is flatter than it should be) resulting in an over-estimate of the stack flow rate (up to 25% of reading based on published data) [7]. This can be addressed by using ‘3D’ Pitots, that take account of the tangential velocity component, or tracer techniques that are completely insensitive to the flow field in the stack. However, high swirl was not observed in either of the selected stacks. 3.2 Experimental Techniques The project incorporates two field trials at i) a CCGT plant in the UK and ii) a coal fired power plant. The experimental techniques are all described in detail in EN ISO 16911-1 [2]. Three basic approaches are defined in Part 1:

• Perform a stack velocity survey at 20 points (in a large duct). The points are defined at centres of equal area as specified in EN 15259 [8] as shown in Figure 1, so that an arithmetic mean of the point velocities directly yields the average velocity which is then multiplied by the cross-sectional area of the stack to obtain the volumetric flow rate. This requires a stack diameter measurement. The moisture content of the flue gas must also be known in order to correct the measured SRM ‘wet’ flow rate to dry reporting conditions for comparison with the calculated ‘AMS’ dry flow rate, also the static temperature and pressure of the flue gas for correction to reporting conditions. In the case of Pitot measurements, the full composition, temperature and pressure are also required in order to calculate the flue gas density so that a velocity can be calculated from the measured


pressure drop. All of the velocity measurement techniques listed in Part 1 of the standard are employed in this study: 3D Pitots (Figure 2), S type Pitots (Figure 3), L type Pitots and Vane Anemometers (Figure 4) which provide direct point velocity readings.

• Measure the volumetric flow rate directly using a tracer dilution method. A known flow rate of tracer gas is injected at a location upstream of the stack, for a short duration (typically 1 to 2 minutes), such that the tracer gas is well mixed with the flue gas. The concentration of tracer in the stack gas is then measured and a simple dilution calculation, given below, yields the volumetric flue gas flow rate directly at the normal temperature and pressure reference condition (273K, 101.3 kPa). If there is a background concentration of the tracer gas within the process, this is measured prior to the injection and subtracted from the test measurement. In this study, an inert insoluble tracer gas (helium) is used to avoid problems related to high temperatures and wet conditions. The injected flow is measured using a mass flow meter and the concentration in the flue gas is measured with a mass spectrometer, both meeting the performance characteristics specified in Part 1 of EN ISO 16911. The stack diameter is not required since the volume flow is measured directly. In this study, the tracer gas concentration is measured on a dry basis so the moisture content of the flue gas is not required, nor the temperature and pressure, for comparison with calculated dry AMS flow rates. However, the flue gas dry O2 concentration is required in order to correct to the reference O2 concentration. A schematic showing the application of the method at a CCGT plant is shown in Figure 5.

The use of an inert tracer gas allows a number of different injection options to be considered: i) single point injection at the combustion air inlet with multi-point sampling at the GT exhaust or stack; ii) multi-point injection at the combustion air inlet (through the compressor wash system for example) combined with single point sampling at the GT exhaust or stack; iii) multi-point injection at the GT exhaust with single or multi-point sampling in the stack. Any of these approaches provide uniform mixing between the tracer and the flue gas.

𝑄 =𝑀

𝜌𝑜· (1 − 𝐶

𝐶) · (

20.95 −%𝑂2𝑑𝑟𝑦

20.95 −%𝑂2𝑟𝑒𝑓)

Where Q = Flue gas volumetric flow rate at reference conditions, Nm3/s M = Tracer mass flow rate, kg/s ρo = Tracer density at reference conditions (273 K, 101.3 kPa), kg/Nm3 C = Ci - Cb Ci = Tracer indicated concentration in the stack gas, mole fraction Cb = Tracer background concentration, mole fraction %O2dry = Oxygen content of stack gas sample, % by volume dry %O2ref = Reference oxygen content (15% for gas turbines), % by volume dry

• Measure the bulk average velocity directly using a tracer time-of-flight measurement. A tracer is injected into the stack at a low level and the time of arrival is measured at a high level. The vertical separation between the injection and detector locations is measured and divided by the time of flight to obtain the average velocity which is then multiplied by the cross-sectional area of the stack to obtain the volumetric flow rate. Again, the stack diameter, flue gas composition, temperature and pressure are required in order to correct the velocity to a normalised flow rate. Part 1 defines a radioactive tracer technique but since this requires a special authorisation from the Competent Authorities, when allowed in a given country, this approach was not considered to be generally applicable for power plants and is not considered further within this project.


3.3 Instrument Calibration 3.3.1 Pitot and Vane Anemometer – Calibration The velocity probes used in this study are listed in Table 1. A pre-trial pitot calibration exercise on the Pitots and the Vane Anemometer was conducted at two accredited laboratories. Firstly, a witnessed calibration at Aerometrologie, in Paris, France, on a free jet wind tunnel; Figure 6 shows the small reference calibration Pitot (L type) and a larger test Pitot (S type) under calibration. Secondly, an unwitnessed calibration at the Young Calibration laboratory at Shoreham-by-Sea, UK, with a variable nozzle diameter free jet wind tunnel and a reference device comprised of an x, y, z automated traverse system with integrally mounted, laser doppler anemometer. For the Pitots, velocity is determined from the Pitot tube pressure drop (ΔP) in the usual way:

V = k [2 ΔP / ρ] 0.5 Where V = velocity, m/s k = coefficient of discharge, - ΔP = pressure drop at the Pitot tip, Pa ρ = gas density, kg/m3 The measured coefficient of discharge is reported from the reference velocities using the same formula. The French laboratory used three multiplexed reference ΔP sensors, depending on the magnitude of the measured ΔP, with ranges of: 0-13 Pa, 13-130 Pa and 130-1300 Pa. In this case, the same pressure sensors were used for the reference L type pitot which has a resolution of 0.01 m/s (k = 1.00 with 1% expanded uncertainty) and for the test Pitots. Each instrument was calibrated at five pre-selected nominal velocities of 2.5, 5, 15, 25, and 40 m/s. Three measurements were taken at each velocity and each of these was the average of six instantaneous readings. The French calibration certificates quote the atmospheric pressure (hPa) and relative humidity (%), the wind tunnel air temperature (°C) and the calculated air density (kg/m3). The calibration certificate for each Pitot tube (APPENDIX A), at each velocity, also contains the following information:

• Pr - reference Pitot average ΔP, Pa

• Vr - reference Pitot average velocity, m/s

• Pi - test Pitot average ΔP, Pa

• Standard Deviation - of the three averaged values of (Pr – Pi), Pa

• Stability - average of three standard deviations of each set of six instantaneous values, Pa

• α (1-ε) - the test Pitot coefficient of discharge (k) incorporating compressibility, i.e., k as derived directly from the above equation, -

• Uncertainty - the expended uncertainty (95% confidence) taking into account the standard deviation, the stability, the uncertainty of the reference reading and the uncertainty in the air density. The uncertainty is assumed to apply to the discharge coefficient and this was, typically, ±1% in the range 15 ≤ Vr ≤ 40 m/s, increasing to ±2% below 15 m/s. This does


not incorporate any additional uncertainty related to the ΔP measurement device used in field trials.

A summary of the French results is given in Table 2. The S type Pitot coefficients are very close to the expected ‘standard’ k value of 0.84 (within 0.25%) at ≥ 15 m/s. The L type Pitot coefficient is 1% higher than the reference coefficient (k = 1.01). The Höntzsch vane anemometer is also included based on direct velocity readings from the anemometer. The results in Table 2 indicate that the agreement between the Vane Anemometer and the reference system velocities was also very close (typically within 0.3%). However, the 3D Pitot could not be calibrated due to the inability to accurately set the yaw and pitch angles of the Pitot head. The UK laboratory evaluated performance at the same nominal calibration points with the probe heads aligned perpendicular to the flow direction at 140mm from the wind tunnel exit plane, taking a minimum of ten readings at each measurement point. The calibration certificates (APPENDIX A) contain similar information to the above list, except for the uncertainty which is not assigned to each point but is given as a range in each of the uncertainty components (pressure, velocity and density). The implied maximum expanded uncertainty is within ±1%. A comparison with the UK results is given in Table 3 for the S type, L type and Vane Anemometer probes used in the field trials. For the ‘S’ type Pitot, both calibration checks produced Pitot coefficients within ±0.5% of the expected coefficient (0.84). In the UK results, this tight agreement was maintained down to 5 m/s with the coefficient dropping by about 1.5% at 2.5 m/s. In the French results, the agreement held down to 15 m/s, with the coefficient dropping by about 2% at both 5 and 2.5 m/s. For the L type Pitot, both calibration checks produced agreement within ±1.0% of the expected coefficient (1.0) at all velocities except 2.5 m/s where the coefficient was slightly higher than at the other velocities at both laboratories (by about 0.5%). However, agreement between both sets of results was within ±0.5% across the velocity range. For the Vane Anemometer, the French results were significantly closer to the velocity reading from the instrument, being within ±0.3%, except at 5 m/s (-0.8%). The UK results showed a greater departure of about 1% at the two highest velocities, about 2.5% at the lowest velocity and about 0.5% at the intermediate velocities. This is somewhat surprising since the UK calibration is velocity based. However, differing instrument performance on the two occasions, or instrument misalignment, cannot be completely ruled out. Overall, the calibration results indicate that the underlying calibration of the L type and S type Pitots and the Vane Anemometer can be checked or determined to typically within ±0.5% (i.e., within the declared expanded calibration uncertainty of ±1%) across the velocity range of interest in power station stacks. However, caution needs to be exercised when measuring velocities below 5 m/s. In these situations, the Pitot coefficient determined by the calibration laboratory could be used but the reported deviation may be within the increased calibration uncertainty at the lower velocities. In the field trials reported here, the stack velocities were always above 5 m/s and so a constant Pitot coefficient has been used for each probe, following usual practice. However, if a specific application requires low velocity measurement, it is recommended that a detailed multi-point calibration is performed by a calibration laboratory that can deliver a low uncertainty under

these conditions. Great care must also be taken to select a field P instrument with a low uncertainty.


3.3.2 Pitot and Vane Anemometer – Other QA Requirements The required performance characteristics for velocity measurements are given in Table 4. Those directly relevant to the Pitot and Anemometer calibration are:

• Uncertainty due to calibration (< 2% of full scale)

• Linearity (< 2% of value - maximum deviation at five velocities)

• Repeatability (standard deviation) (< 1% of value Vmin < V < Vmax)

• Effect of angle of sensor to flow (≤ 3% at ±15°) Uncertainty. The uncertainty requirement is considered above and is easily satisfied under all conditions. Linearity. This is not normally considered by calibration laboratories and it is not clear in the standard how this should be evaluated. In this study, the test velocity at each measurement point, Vi, has been re-calculated, assuming a constant test Pitot coefficient (0.84 for the S type and 1.01 for the L type). It is clear that the linearity is generally excellent, on this basis, as shown graphically in Figure 7. The results are given in Table 5 which shows the relative differences in velocity at each measurement point. The straight-line regression equation between the reference (Vr) and re-calculated velocity (Vi) is also shown for each probe and this relationship has been used to calculate a ‘calibrated’ velocity, Vest, at each reference velocity, Vr. It can be seen that the relative differences between Vi and Vest are then within the required value of 2% of reading, apart from the two lowest velocity readings for the S type calibration conducted at Aerometrologie, which have been commented on above. The above approach is based on that given in EN 14181. Repeatability. The method for determining the laboratory ‘repeatability’ is not specified in the standard but the field ‘repeatability’ defines this as the standard deviation of the differences in velocity, between the test probe and the reference probe, across five paired readings; or the standard deviation of five consecutive one-minute readings of velocity from the test probe only if a reference probe is not used. The UK calibration laboratory did not report a standard deviation associated with the individual measurements. The French calibration laboratory evaluated

differences in P between the test and reference probes based on six readings over 30s, repeated three times, and reported two standard deviations based upon these differences. This does not comply with the standard but does give a, more conservative, estimate of repeatability

(< 0.5% of the test P for the Pitots and < 0.5% of the test velocity for the Vane Anemometer). For Pitot repeatability, it is therefore recommended that the Pitot velocity, Vi, is calculated, as above, based upon a constant Pitot coefficient, for at least five consecutive readings, each of one-minute duration, at both the minimum and maximum reference velocities. The standard deviation of the differences between the test velocity and the reference velocity, at each flow rate, must then be less than 1% of the reference velocity in each case. Further guidance on these aspects is required. Effect of angle of sensor to flow. The calibration laboratory does not normally investigate the impact of turning the Pitot head away from the normal flow direction. At the French calibration laboratory, an inclinometer was used to make a rough assessment of turning the measurement head by ±15° (Figure 8). One S type Pitot and the L type Pitot passed the test (<3% deviation) at the minimum and maximum velocities. A second S type Pitot showed a 6% deviation (fail) at the highest velocity and the anemometer failed at -15°, even though the nominal characteristics from the manufacturer indicate acceptable performance (Figure 9). This evaluation is not sufficiently robust to draw firm conclusions. However, it does reinforce the need to properly


evaluate the impact of flow misalignment, during calibration, across the velocity range of interest.

Overall, the performance of all of the P/velocity instruments tested was satisfactory. However, certain performance requirements are not yet routinely evaluated by calibration laboratories and the plant operator needs to carefully specify the tests that are required. In particular, the velocity deviation due to changing the flow direction by ±15° needs further evaluation. Based on the above calibration results, an expanded uncertainty of circa ±3% should be achievable in the field, when taking into account the measured performance characteristics. This uncertainty would increase to circa ±5% if all of the performance characteristics are assumed to be at the maximum values allowed in the standard. 3.3.3 Tracer Dilution Method - Calibration Standards Tracer gas flow rate EN ISO 16911-1 requires that the expanded uncertainty of the tracer flow meter shall be ≤ 1 % of value, taking into account any relevant influencing parameters such as ambient temperature. The manufacturer’s original calibration states an expanded uncertainty of ±0.35%. However, when influencing factors are taken into account, as required by the standard, this increases to ±0.54%. The mass flow meter calibration was verified by the Young calibration laboratory in the UK, using dry air as the reference medium, to an expanded uncertainty of ±0.41% (APPENDIX A). The individual test points and relative differences between the reference and indicated flow rates are shown in Table 7, indicating that the relative differences are well within the claimed expanded uncertainty of ±0.41%. The only other requirement is to perform an on-site leak check of the injection system immediately prior to injection. The standard uncertainty of the tracer flow measurement is therefore ±0.205% [=0.41%/2]. Tracer gas concentration The performance characteristics required by the standard are given in Table 8. The calibration gas for the tracer concentration measurement is supplied at ±1% uncertainty (95% confidence) by gravimetric preparation, as required by the standard, giving a standard uncertainty of 0.577%

[=1%/3]. The linearity of the mass spectrometer response had previously been checked by Uniper, according to EN 14181, with a pass of the ±1.5% criterion, giving a standard uncertainty

of 0.866% [=1.5%/3]. Cross-interference effects are considered to be zero since the target mass:charge ratio within the mass spectrometer is unique to the tracer gas. Sample loss is considered to be zero since the tracer gas is insoluble, for all practical purposes, and the sampling system is leak checked on site. The mixing of the tracer with the flue gas is considered to be perfect if a grid sample is used for the tracer concentration measurement. Calibration drift due to ambient temperature variations is addressed by frequent calibration and

drift correction but a residual standard uncertainty of 0.577% [=1%/3] is nevertheless assumed. Combining the above component standard uncertainties gives an overall expanded uncertainty

of about ± 2.4% [=2 * (0.2052 + 0.5772 + 0.8662 + 0.5772)].


3.4 Field Trial Requirements

EN ISO 16911-2 requires that a range of flow rates (related to minimum and maximum generation) are included in the QAL2/AST measurements. Two approaches are defined.

1. Flow surveys are not performed. In this case, 15 tests are required and the minimum flow condition must be included in the QAL2.

2. Two flow surveys are performed at the min/max plant flow rates in order to check that the shape of the velocity profile does not change between the min/max plant load points. If these pre-surveys are undertaken, it is possible to restrict the number and range of the subsequent QAL2 measurements, reducing the number of tests to 9 that can be conducted at any flow rate (the base load condition only if it is not practical to change the plant load).

When verifying the calculation method, it is not meaningful to perform the pre-surveys since the shape of the flow profile does not affect the calculation in the way that a flow monitor could potentially be affected.

If the tracer method is used (faster individual measurements), then Option 1 is preferred. However, if velocity surveys are used as the SRM, it is better to choose Option 2 since this minimises the number of (time-consuming) velocity traverses and one of these must be at the minimum load in both cases.

Since all SRM techniques are used for this study, the aim is to perform a full QAL2 (15 measurements at different loads), noting that, for the probe techniques, each one of these measurements is a 20-point velocity survey. At least four large (>100mm diameter) access ports, spaced at 90° around the stack circumference, and one reference port, at the same plane, are required for the velocity based measurements.

For the tracer measurements, at least one small (> 13 mm) access port is required for the injection, as far upstream of the stack as possible to ensure good mixing between the tracer and the main exhaust flow (preferably upstream of a forced draught or induced draught fan). For the concentration measurement, at least four small (> 13 mm) stack access ports are required. These should ideally be different to the velocity ports but could be the same ports (the short injections can then be performed in-between the velocity traverses).

Note that the tracer dilution method, as implemented by Uniper, gives a direct measurement of the dry volumetric stack gas flow rate at 273 K and 101.3 kPa. Following correction to the reference oxygen condition, this can be compared directly with the flow calculation.

Note also that the velocity traverse results, when averaged, must be corrected to reference conditions using a measured oxygen, water vapour, temperature and absolute pressure. Representative readings from plant instruments can be used (in which case the site QAL2/AST reports and EN15259 reports must then be made available). In the case of water vapour, this can be calculated from either the FGD absorber outlet temperature or the stack gas oxygen if water is not measured. The test laboratories need to check the site readings and also measure O2 (dry), temperature and pressure. The stack diameter (cross-sectional area) is also required and this must be checked by the test laboratories.

The sites must provide representative fuel analyses, corresponding to the trial periods, in addition to the required stack flow calculation inputs, stack emissions, plant data and stack drawings. All of the above requirements were met by both test sites as described in Sections 5 and 6.


4 QUALITY ASSURANCE PROCEDURES 4.1 General Considerations EN ISO 16911-2 is applicable, in conjunction with the generic standard EN 14181 (Quality Assurance of AMS), and defines additional requirements that are specific to stack flow measurements. EN ISO 16911-2 follows, as far as possible, the structure of EN 14181 but notes that an emission limit value (ELV) and the required uncertainty limit, specified as a 95% confidence interval, are not defined for flow by any EU Directive. Since these parameters are required by the procedures prescribed in EN 14181, surrogate values are given in EN ISO 16911-2. Since volume flow rate has no prescribed ELV, 120% of the maximum volume flow rate during the QAL2 test shall be used as the ELV unless the Competent Authority has given other instructions. The ELV is not to be lower than 10 m/s. Since flow rate has no prescribed uncertainty in an EU Directive, σ0 = 4 % of the ELV shall be used unless the Competent Authority has given other instructions. Since the ELV is 120% of the highest measured value, σ0 is effectively 4.8% of the highest measured value. The definition of σo in EN 14181 is based on pollutant concentrations expressed at normalised conditions of dry flue gas at 273K, 101.3 kPa and the reference O2 applicable to the process. However, in EN ISO 16911-2, σ0 is calculated at the stack gas conditions prevailing at the time of the AMS calibration. The uncertainty therefore includes contributions related to the plant operating conditions (actual moisture, temperature, pressure and O2). For a calculation approach, which produces the stack flow at reference conditions, it makes more sense to revert to reference conditions for QA purposes as specified in EN 14181. The stack flow rate is calculated from the plant thermal input which, in turn, is calculated from either the fuel flow multiplied by the net calorific value or the plant thermal/electrical output divided by the thermal/generating efficiency. It should be noted that this flow rate calculation is given on the ‘Plant Calculations’ tab of the VGB Excel workbook described in Section 4.3. EN 14181 defines three Quality Assurance Levels - QAL1, QAL2 and QAL3 - along with an Annual Surveillance Test (AST) in order to correctly certify, calibrate and control Automated Measuring Systems (AMS). The pass/fail criteria embedded within the QA process are based on the Daily Emission Limit Value (Daily ELV) which is 120% of the maximum measured flow rate, with σ0 equal to 4.8% of the maximum flow rate, as noted above. EN ISO 16911-2 requires that the calculation method shall follow EN ISO 16911-1 (Annex E) and that the calculation shall be verified by means of a QAL2 and checked yearly by means of an AST in accordance with EN 14181. However, the exact means of verification are not described. It is important to clarify how verification should be performed since QAL2 ‘calibration’ factors are not applied to calculation results. This contrasts with the installation of a flow monitor which is subject to calibration and requires QAL2 factors to be applied. 4.2 Quality Assurance Level 1 (Validation) QAL1 requires that AMS are suitable for their intended application and AMS instruments are certified according to EN 15267 which specifies both performance requirements and type testing requirements. EN ISO 16911-2 gives additional performance specifications and type testing requirements for flow monitors.


EN 15267-3 [9] requires that the AMS uncertainty should not be more than 75% of the Confidence Interval for an hourly average value. This equates to about 7.5% of the maximum flow rate since the Confidence Interval is 2 * σo (rounding σo to 5% of the maximum flow rate). Note that the ELV should be increased to 125% if the maximum measured flow to be consistent with a Confidence Interval of 10%. EN ISO 16911-1 (Annex E) gives performance specifications for flow rate calculation as an expanded uncertainty, at 95% confidence, applicable to the hourly average flow rate, as shown in Table 9. It can be seen that the maximum uncertainty requirement of 7.5%, specified for solid fuels, is equivalent to the EN 15267 requirement. Additional uncertainty requirements are applicable to the calculation inputs (fuel flow rate etcetera) as shown in Table 10 and the uncertainty of the fuel factor is given for standard fossil fuels and biomass, as shown in Table 11 and Table 12, respectively. It should be noted that a range of tools for calculating non-standard fuel factors is given on the ‘Fuel Properties’ tab of the VGB Excel workbook described in Section 4.3. EN ISO 16911-2 also makes it clear that it is important to minimise systematic errors in the context of reporting mass emissions of CO2 under the EU Emissions Trading System (ETS). However, power stations are expected to comply with the highest tier measurement requirements specified by the EU ETS, i.e., the most demanding uncertainty requirement of ±2.5% for the reporting of CO2 mass emissions. This represents the combined uncertainty of both stack flow and stack CO2 measurement. Given that the ensemble average uncertainty of the flow reference methods is ±5% and the best flow reference methods have an uncertainty of circa ±1 to ±2% it is unlikely that power stations would switch from the current approach, based on annual fuel consumption and carbon content, which delivers an uncertainty of circa ±1.6%. It is therefore proposed that QAL1 for a flow calculation is simply a validation of the calculation approach against the requirements of EN ISO 16911-1 (Annex E). This validation consists of an uncertainty assessment of the hourly average stack flow rate following the approach given in Annex E which also presents various examples. It should be noted that each input parameter has an equivalent influence on the calculated stack flow rate which simplifies the uncertainty assessment. For example, ±2% relative uncertainty in either the thermal efficiency or the fuel flow gives rise to ±2% relative uncertainty in stack flow rate.

The building block for the uncertainty assessment is the relative standard uncertainty which is

equivalent to the standard deviation for a normal distribution. Standard uncertainties are

combined using a root sum of squares (RSS) approach, according to the law of propagation of

uncertainty, and then multiplied by a coverage factor of 2 in order to obtain the overall expanded

uncertainty at 95% confidence.

This approach is illustrated below for the first CCGT field trial example below:

Stack Flow = Thermal Input * Fuel factor (m3/s) (MJth/s) (m3/MJth)

Expanded to:

Stack Flow = Fuel flow * Net Calorific Value * Fuel factor (m3/s) (kg/s) (MJth/kg) (m3/MJth)

The fuel flow meter is a fiscal quality turbine meter with a current calibration certificate calibrated to better than ±1% expanded uncertainty. This is conservatively increased to ±1.5%


to account for the additional uncertainty related to pressure and temperature correction. The calorific value is measured using a gas chromatograph calibrated annually under EU ETS to better than ±0.5% expanded uncertainty and the fuel factor for natural gas has an expanded uncertainty of ±0.7% (Table 11). In line with usual practice, these component uncertainties are first converted to standard uncertainties, dividing by a coverage factor of 2, before combining these using the RMS approach. The combined standard uncertainty is then multiplied by the coverage factor to obtain the overall expanded uncertainty.

For this example, the overall expanded uncertainty is then 2(0.752 + 0.252 + 0.352) = ±1.73%. This is within the overall hourly average expanded uncertainty of ±2% specified for gas fired installations by EN ISO 16911-1 (Annex E), as shown in Table 9. For large power stations that comply with EU ETS requirements, it is relatively easy to demonstrate compliance with the EN ISO 16911-1 requirements and this would be expected for new installations. However, this is less likely to be the case for existing plants where, for example, the EU ETS site meter supplies multiple plants and each plant has a unit meter that is not EU ETS compliant. Smaller plants may not have a gas chromatograph and may use a fixed calorific value with an expanded uncertainty of typically ±5% in the hourly average value. It may not be possible, or reasonably necessary, to fully quantify this uncertainty for smaller plants with lower tier EU ETS requirements. Similar issues apply when considering existing liquid and solid fuel fired plants. In these circumstances, it must be remembered that the monitoring method must be fit for purpose and that the target uncertainty requirements in EN ISO 16911-1 (Annex E) are focused on EU ETS reporting. From a pragmatic point of view, for existing installations, it should be sufficient to meet the EN 15267-3 requirement of ±7.5% for the hourly average stack flow rate and then demonstrate compliance by means of a QAL2 verification. This follows the approach specified in EN 14181 Annex H (Implementation of QAL1) which addresses the situation of a pre-existing uncertified AMS that can be used for the rest of its design life with the agreement of the Competent Authority. 4.3 Quality Assurance Level 2 (Verification) ISO 16911-2 Section 9.2 (Selection of calibration method, if calculation methods are used), describes the main principle as follows: ‘When the AMS is based on a calculation method, this shall follow EN ISO 16911-1:2013, Annex E and the calculation shall be verified according to this clause by means of a QAL2 and checked yearly by means of an AST in accordance with EN 14181. If QAL2 or AST fails, the calculation procedure shall be investigated and if necessary rectified prior to retesting by QAL2.’ ISO 16911-2 Section 9.3 (Calibration procedure): ‘EN 14181:2004, 6.1 and 8.1 apply with the following modifications. The calibration of an AMS volume flow rate monitor is performed as described in EN 14181, with the exception that the flow monitor shall be calibrated in units of volume flow rate, m3/s, under the actual operating conditions.’ ISO 16911-2 Section 9.5 (Parallel measurements with a standard reference method): ‘EN 14181:2004, 6.3 and 8.2 apply with the following modifications. EN 14181 states that the results obtained from the SRM shall be expressed under the same conditions as those measured by the AMS, which is normally m/s. NOTE 1 The calibration is normally expressed in m3/s in operation condition if the dilution tracer method is used.’


The stack flow calculation formulas of EN ISO 16911-1: Annex E deliver normalised values at the stoichiometric condition (zero % oxygen, dry). This flow is commonly recalculated to the reference oxygen concentration of the installation at normalised reference conditions. Pollutant concentrations will, in most cases, also be recalculated to the reference oxygen concentration. The multiplication of the flow and the concentration directly gives the mass emission. When using flue gas flow calculation as an AMS it therefore follows that the QAL2 flow verification should be conducted at normalised conditions and at the reference oxygen concentration. In ISO 16911-2 Section 9.5, if a pre-investigation of the velocity profile at maximum and minimum plant loads has been performed, the number of paired measurement points required for a QAL2 calibration is reduced. However, stack gas flow rate calculation is insensitive to any flow non-uniformity in the stack. The flow/velocity profile does not adversely affect flow calculation performance and so a pre-investigation of the velocity profile should therefore not be required. According to EN ISO 16911-2 Section 9.5, the minimum number of paired data points when a pre-investigation has been performed is 9, rather than 15, and there are no restrictions on the upper or lower limit of calibration range. This should be the same for a flow verification provided that the calculated flow rates at the maximum and minimum plant loads are included in the verification. The QAL2 and AST procedure shall be performed to obtain data points that are evenly spread out over a minimum of 5 hours. The EN 14181 minimum requirement of performing the calibration over a minimum of 3 days is not required. If QAL2 or AST fails, the calculation procedure shall be investigated and if necessary rectified prior to retesting by QAL2. In ISO 16911-2 Section 9.9.2, an alternative calibration method has been added (method D) using linear regression and forcing the regression line through the zero point. In ISO 16911-2 Section 9.12 there is also a new requirement that the linear fit parameter, R2, is greater than 0.9. However, this test does not need to be passed if the flow rate spread (Max – Min) is less than 15% of the average flow rate for both the SRM and the AMS. All of these aspects have been incorporated into the Excel workbook that has been developed as part of this project. This file (VGB Research; ISO 16911-2 Calculation Verification or AMS Calibration.xlsx) is available free of charge through the VGB website. The second QAL2 example from EN ISO 16911-2 Annex A is included in the Excel workbook. This allows the user to follow all of the calculations and graphs from Example A.2 in the standard. As illustrated in the VGB field trial example below, the main options in the Excel workbook (QAL2 and AST tab) are: Choice of method:

- ‘Measured’ Performs the default quality assurance tests of EN ISO 16911-2

- ‘Calculation’ o The calibration function becomes obsolete and is only provided for information o The block “Validity of calculation” becomes active and tests the absolute difference

(|D|) between the SRM and AMS, as shown below Choice of verification or calibration unit:

- ‘m/s’ If velocity measurement - typically for calibration of AMS (‘Measured’)

- ‘m3/s’ Applicable for verification in normalised flow at reference conditions (‘Calculation’) or calibration of AMS (‘Measured’)


Below the data entry table, there is an additional option as illustrated below. Calibration function - Force through zero:

- ‘Empty’ Method A of ISO 16911-1 is applied; Regression line intercept (a) and regression line slope (b) are calculated

- ‘✓’ Method D of ISO 16911-1 is applied; Regression line intercept (a) is fixed at zero and regression line slope (b) is calculated

The results of the Variability, Validity and R2 tests are displayed in the relevant calculation boxes as shown.


The Variability test, as defined in EN 14181, is:

sD ≤ o * kv

Where sD is the standard deviation of the differences between the SRM test results and the calibration line at normalised conditions. Since the calibration is not applied for a verification procedure, sD is the standard deviation of the differences between the SRM and AMS pairs of results. kv depends on the number of tests, N, as defined in Annex I of EN 14181. For 15 QAL2 tests, kv = 0.9761 and sD ≤ 4.7% of the maximum flow value. For 9 QAL2 tests, kv = 0.9581 and sD ≤ 4.6% of the maximum measured flow rate. The Validity test, as defined in EN 14181, is:

|D| ≤ [ t 0,95;N-1 * sD/N ] + o

Where |D| is now the absolute value of the mean of the differences between the SRM and calibration line or, in this case, the mean of the differences between the SRM and AMS pairs of test results. The Student t-factor, t 0,95;N-1, depends on the number of tests, N, as defined in Annex I of EN 14181. For 15 QAL2 tests, t 0,95;N-1 = 1.761 and |D| ranges from 4.8% to 6.9% of the maximum flow rate depending on the value of sD (0 to 4.7% of the maximum flow rate). For 9 QAL2 tests, t 0,95;N-1 = 1.860 and |D| ranges from 4.8% to 7.7% of the maximum flow rate depending on the value of sD (0 to 4.6% of the maximum measured flow rate). Since sD is generally low, the absolute agreement between the AMS and the SRM is normally required to be within about 6% of the maximum measured flow rate. 4.4 Annual Surveillance Test (Verification) An AST analysis is included below the QAL2 analysis within the Excel spreadsheet. This part of the sheet copies the General Data, AMS and SRM information from the QAL2 data input. There are no options given for the AST test. The AST Validity and Variability tests are the same as those defined in EN 14181. For a smaller number of test points, the extremes in the Validity criteria become:

i) sD = 0, then |D| o 4.8% of the maximum measured flow rate

ii) sD = the maximum allowed value of the AST Variability test, i.e., sD ≤ 1.5 * o * kv. For 5 AST tests, kv = 0.9161 and t 0,95;N-1 = 2.132 therefore sD ≤ 1.5 * 4.8% * 0.9161, i.e., sD ≤ 6.6% and |D| 11.1% of the maximum measured flow rate. For 4 AST tests, kv = 0.8881 and t 0,95;N-1 = 2.353 therefore sD ≤ 1.5 * 4.8% * 0.8881, i.e., sD ≤ 6.4% and |D| 12.3% of the maximum measured flow rate.

So the absolute maximum that |D| could reach is about 2.5 times larger than the lowest possible QAL2 difference (4.8%). In practice the standard deviation of differences is relatively small and would deliver a test |D| target value in the range of 6 to 7% of the maximum measured flow rate.


4.5 Quality Assurance Level 3 (Control) 4.5.1 Annual Surveillance Test Experience to date suggests that most of the benefit of applying EN ISO 16911-2 is obtained when conducting the QAL1 validation and the QAL2 verification since the calculation is critically reviewed at that point and any errors identified as a result of this review, or as a result of QAL2 testing, are corrected. However, AST verification should continue at least until the stack flow calculation has been fully implemented in the Data Acquisition and Handling System (DAHS) and the Test Laboratory has directly compared the SRM results with the DAHS outputs1,2. The whole of the measurement and reporting chain is then verified. After this level of verification, simplified QA may be appropriate as discussed below. 4.5.2 Calculation Inputs Integrity of the calculation. In all cases, an annual manual calculation check of the DAHS reported stack flow rate based on the DAHS input data should be documented to ensure that the calculation has not been modified. This is especially important if an AST is not performed. Otherwise, QAL3 for a flow calculation principally requires that the quality of the calculation inputs is maintained, recognising the stated uncertainty requirements of EN ISO 16911-1 Annex E (Table 10). Fuel flow rate. Flow meters that are used for EU ETS reporting require no further QA. Other meters should have a current calibration certificate, i.e., the meter is calibrated and maintained at the frequency specified by either the manufacturer or an appropriate flow standard or code of practice. Fuel heating value. Natural Gas chromatographs that report the Net Calorific Value for EU ETS reporting require no further QA. An assumed Net Calorific Value must be checked and updated annually in line with EU ETS recommended values. Electricity and steam flow meters must be of fiscal quality and calibrated and maintained at the frequency specified by either the manufacturer or an appropriate flow standard or code of practice. Thermal efficiency. The thermal efficiency of the plant that is used for stack flow rate calculation should be checked and updated annually using EU ETS fuel input data and annual production data supplemented by plant performance data as required. The thermal efficiency may also be updated based on plant performance testing, noting that heat accountancy can provide useful supplementary information. 4.5.3 Control Charts EN 14181 allows different types of control charts to be used in order to keep an AMS under control. Control charts are not particularly useful for a calculation based AMS. However, the relevant sections of EN 14181 are reviewed below in order to compare the required calculation uncertainties with control chart limits and sAMS values. In any case, the control chart information is useful if AMS instruments are used for continuous flow monitoring in the stack. 1 When the averaging period of the DAHS output is not suitable for direct comparison with the SRM data, then the Test Laboratory may directly calculate the stack flow rate from the DAHS input parameters. In this case, the Test Laboratory must separately perform a manual check that the DAHS stack flow output is consistent with the DAHS inputs and document this check within the test report. 2 AST testing must continue until the full measurement and reporting chain within the DAHS has been verified.


In case of Shewhart control charts which determine the combined drift and precision of the AMS, ±50 % of the maximum permissible uncertainty shall be used to establish the alarm limits of the control chart. The maximum permissible uncertainty is equal to the Confidence Interval defined previously. For both flow calculations and measurements, this criterion therefore implies an alarm limit of 4.8% of the maximum measured flow rate. Alarm limits for Shewhart charts are defined as 2 * sAMS-span, which means sAMS-span would be 2.4%, for hourly measured values. In addition, warning limits may be established e.g. at ±25 % of the maximum permissible uncertainty to provide early information on necessary adjustment or maintenance of the AMS. A warning limit of 1.2% of the maximum measured flow rate follows. In case of more sophisticated methods (e.g. EWMA or CUSUM) the control chart limits shall be calculated by use of the specific control chart parameters and 50% of the maximum permissible uncertainty. The control chart parameters shall be chosen to ensure early information on necessary adjustment or maintenance of the AMS. This criterion was derived in an E.ON / DNV GL investigation. The sAMS-span value to ensure early information on necessary adjustment is typically 15% of the maximum permissible uncertainty (0.15 x 9.6%) = 1.44%. This value implies that the quality control contributes 10% to the

maximum permissible uncertainty √((2 x 1.44)2 + 9.22) = √(8.3 + 84.62) = 9.6% and 8.3 / 84.6 10%. The maximum sAMS-span would be 0.25 x 9.6% = 2.4% for the hourly values, contributing roughly 33% to the maximum permissible uncertainty. We conclude that if a metering system complies with the EU ETS uncertainties it complies with the maximum calculated QAL3 limits. In that case, QAL3 procedures can be replaced by quality assurance of fuel metering under EU ETS. It is also the case that the annual sequence of AST measurements can be regarded as a pseudo QAL3. In any other situation, the above approach for calculating sAMS-span is preferably used for either flow measurements or flow calculations. 5 FIELD TRIAL 1 (NATURAL GAS FIRED CCGT PLANT IN THE UK) 5.1 SRM Implementation The first field trial was conducted in August 2014 at a 435 MWe (Gross-generated) CCGT plant in the UK fitted with an Alstom GT26 gas turbine (about 285 MWe Gross gas turbine output). The CCGT stack gas temperature is ~ 90°C so the flue gas is therefore ‘dry’, i.e., well above the water dew point of ~ 40°C and the acid dew point of ~ 60 to 70°C. All stack measurements were conducted at a stack sampling location fully compliant with EN 15259 (Figure 10 and Figure 11). The diameter of the steel stack is 7.00 m, confirmed by laser range finder measurements, giving a cross-sectional area of 38.485 m2. Fifteen velocity traverses, with each measurement incorporating 20 traverse points, were performed from 12 – 15 August employing the Uniper S type and 3D Pitots and the Laborelec Vane Anemometer, described earlier in Section 3. During each traverse, a Laborelec L type Pitot was used to obtain a reference velocity at a fixed point. The reference point was chosen to be 0.236*Stack Radius from the stack inside wall since the velocity measured at this location should be equal to the average velocity for a fully developed flow profile in a power station


stack [7]. This is slightly different to the generic position of 0.242*Stack Radius recommended by ISO 7145 [10]. The test times are given in Table 13 for which it can be seen that a typical stack velocity traverse lasted about 1 hour. The last two test points were obtained at the minimum plant load condition of about 230 MWe, as shown in Figure 12. The test duration was dictated by the operation of the 3D Pitot which requires longer at each test point in order to determine the required flow angles. The S type Pitot was aligned with the flow direction at each point. The measurements proceeded uneventfully, apart from an issue with the Vane Anemometer during the first test when a probe extension became loose, causing misalignment with the flow direction (Test 1 excluded). An L type reading was not obtained for Test 5 due to logistical issues. The static temperature (~90°C) and pressure were measured by the test teams and the dry flue gas O2 content was supplied by the installed certified AMS (ABB AO2000-Limas11UV) following checks conducted by the test teams. The flue gas dry CO2 concentration was calculated from the dry oxygen concentration using an assumed stoichiometric CO2 content as described in APPENDIX B. The flue gas water vapour concentration was calculated using a simple approach, used in the UK for compliance purposes, employing the ambient air relative humidity and temperature, reported by site, and assuming standard natural gas properties (APPENDIX B). This approach compared well with the full flue gas composition calculated from the natural gas composition and enabled the density of the flue gas to be calculated for the Pitot traverses. The average velocity was typically about 17.7 m/s at base load, giving a flow rate of about 680 m3/s at duct conditions (about 615 Nm3/s, dry basis, at 15% O2, dry). Tracer injection work was performed on the 20 – 21 August since the same sampling ports were required for both test methods. A total of 33 tracer injections were performed and some of these were combined to obtain 20 test points for the QAL2 analysis, from the original 33 injections, as shown in Table 13. It can be seen that the injections are rapid and it is important to synchronise time between the tracer data collection and the process data that is used for the flow calculation. It is also important that the process is stable during the tracer injection. Flue gas sampling for the tracer method employed 20 fixed sample points, located on four sample probes, specified according to EN 15259 [8]. The sample streams were extracted using an ABB SCCF pump and dried using an ABB chiller; the tracer concentration was measured using a portable mass spectrometer, as discussed in Section 3.2. The inert tracer gas was supplied from a bank of 50 L internal volume pressurised cylinders and was injected at the gas turbine air inlet (Figure 13). The injection flow rate was about 10 kg/h, resulting in a tracer flue gas concentration in the range 50 to 75 ppm by volume (incorporating a background concentration of about 20 ppm). 5.2 AMS Implementation The ‘AMS’ plant stack gas flow rate calculation is based on the net thermal input of the plant, as required by EN ISO 16911-1, and is calculated from the flow rate of natural gas and the net calorific value of the fuel. Q = M * NCV * S

Where:

Q = Flue gas volumetric flow rate at 15% O2, dry, 273 K, 101.3 kPa, Nm3/s


M = Mass flow rate of natural gas, kg/s NCV = Net Calorific Value, MJ/kg S = Fuel factor for natural gas, Nm3/MJ = 0.845 Nm3/MJ at 15% O2, dry The fuel factor is the value specified by EN ISO 16911-1 at 0% O2 (S = 0.24 Nm3/MJ) corrected to the CCGT reporting conditions of 15% O2, dry (S = 0.845 Nm3/MJ). The calculation inputs were reviewed prior to the field trial. The natural gas composition and NCV are reported by dual gas chromatographs. The mass flow rate of natural gas is calculated within the plant Distributed Control System (DCS) from the measured natural gas volumetric flow rate using the density of the gas at the flow meter conditions:

= P / (Rs .T. Z) Where:

= Real gas density, kg/m3 Rs = Specific gas constant, kJ/kgK P = Pressure, kPa T = Temperature, K Z = Compressibility, - It became apparent that an assumed compressibility factor (based on an assumed supply pressure and temperature) and an assumed molecular mass (17.04 kg/kmol) is specified in the DCS since fixed values of Rs and Z are specified (Rs = 0.48794172 kJ/kgK, Z = 0.9067388). The fuel mass flow rate was therefore corrected as follows: M = Mrep * (Za / Zm) * (MMm / MMa) and Zm = ZISO * (1 + 0.000025 * (T - 288.15)) / (1 + 0.00002 * (P - 101.3)) Where: M = Corrected metered mass flow rate of natural gas, kg/s Mrep = Reported mass flow rate of natural gas, kg/s Zm = Compressibility factor at the meter, - Za = Assumed compressibility factor = 0.9067388 MMm = Molecular Mass of natural gas as metered, kg/kmol MMa = Assumed Molecular Mass of natural gas = 17.04 kg/kmol ZISO = Compressibility at 288.15K and 101.3 kPa, - (= 0.9976) The natural gas flow rate, and therefore the calculated stack flow rate, was increased by, typically, 3%. Across the range of natural gas supply conditions expected at this site, the correction could be as high as 5 to 6% which would cause a fail in the verification process. This correction was later applied to the emissions reporting system. The stack flow rate calculated from the corrected natural gas flow rate was also cross-checked against the plant output and generating efficiency:

Q = E / * S Where:


E = Electricity output, MWe

= Plant efficiency (-) The steady-state results were in very close agreement (±0.5% relative) across the min-max load range between fuel flow and electricity output readings. 5.3 Field Trial Results The plant conditions were stable in each test period, as indicated by the load profile in Figure 12. On average, the standard deviation of the L type (fixed point) results was 2.9% of the mean traverse value for each test (ranging from 1.7 to 3.7%) thus demonstrating stability during individual tests. The velocity profiles for Test 13 (Base-Load) are shown in Figure 14, indicating some asymmetry in the profile across all measurement techniques. The flow on one radius is about 13% higher than the other radius, for one diameter (A-C), and about 20% higher for the other diameter (B-D). When each profile is normalised by its average velocity, the results in Figure 15 show similar profile shapes. The Part Load (PL) profile from Test 14 has also been added, indicating that the shape of the flow profile does not change as the load is varied. In each case, the average velocity from each traverse is multiplied by the cross-sectional area to obtain the stack gas volume flow rate at duct conditions. This flow is then corrected to reference conditions (15% O2, dry at 273K, 101.3 kPa). The velocity results are multiplied by a Wall Adjustment Factor of 0.995 as required by EN ISO 16911-1. The average of each of the traverses is plotted in Figure 16, along with all of the tracer results. The results are very closely grouped together, at base load and minimum load, apart from the S type Pitot results which are consistently high. There is no explanation for these higher values since the levels of swirl were low (<5°). The QAL2 verification of the calculated flow rate is presented in detail in APPENDIX C, for each reference method, using the Excel spreadsheet tool developed by DNV GL as described in Section 4.3. The following testes must be passed in order to verify the flow ‘AMS’, as described in Section 4:

• the AST Validity test: |D| ≤ limit (|D|)

• the QAL2 Variability test: sD ≤ Max sD

• the R2 test: R2 > 0.9 The full set of QAL2 verification results is summarised in Table 14, in flow units, and Table 15, in velocity units. It can be seen from the slope of the calibration lines that the closest agreement is achieved with the 3D Pitot and tracer methods (± 0.5% of the AMS) with the Vane anemometer and the L-type Pitot being about 4% higher than the AMS. All of the reference methods pass the linear regression test (R2 > 0.9) and the Variability test (sD < Max sD). However, the S type Pitot results are about 8% higher than the AMS and this causes a fail of the Validity test (the mean deviation is 45.17 and this is higher than the pass criterion of 39.40 Nm3/s). Otherwise, all of the methods pass the Validity test. For two of the reference methods, it was only possible to obtain 14, rather than 15, tests points. However, provided that the flow profile is characterised at maximum and minimum loads, the flow standard allows the number of QAL2 test points to be reduced from 15 to 9 tests. It can be concluded that the reference method performance is very similar to that observed in the CEN validation trials on an incinerator and a coal fired power plant. Tracer injection at the gas turbine air intake using an inert tracer gas was successfully demonstrated. Provided that


the tracer is well mixed with the flue gases, there is no need to perform a full EN 15259 grid concentration measurement so it then possible to measure flow at non-compliant sampling locations. 6 FIELD TRIAL 2 (COAL FIRED POWER PLANT IN HOLLAND) 6.1 SRM Implementation The second field trial was conducted in November 2014 at a coal fired power plant (PP) in Holland with a ‘wet’ stack (800 MWe nominal output). All stack measurements were conducted at a stack sampling location fully compliant with EN 15259 (Figure 17). The diameter of the Glass Reinforced Plastic stack is 8.00 m, confirmed by laser range finder measurements, giving a cross-sectional area of 50.266 m2. The aim was to perform at least nine velocity traverses, with each measurement incorporating 20 traverse points, and these were performed from 11 – 13 November, again employing the Uniper S type and 3D Pitots and the Laborelec Vane Anemometer, described earlier in Section 3. Unfortunately, not all of these tests were coincident as shown in Table 16. During each of the Vane Anemometer traverses, a Laborelec L type Pitot was again used to obtain a reference velocity at a fixed point. The reference point was again chosen to be 0.236*Stack Radius from the stack inside wall since the velocity measured at this location should be equal to the average velocity (for a fully developed flow profile). The test times are given in Table 16 for which it can be seen that a typical stack velocity traverse lasted about 1.25 hours. Testing was slower than before since the Pitot impulse lines needed to be purged on a regular basis to prevent plugs of water from causing erratic measurements. This was done successfully for the traversing Pitots but not for the reference Pitot which suffered from blockages from time to time. The static temperature (~50°C) and pressure were measured by the test teams and the flue gas composition (O2, CO2 and H2O) was supplied by the installed certified AMS (Sick MCS100FT). The average velocity was typically about 14.5 m/s at base load, giving a flow rate of about 725 m3/s at duct conditions (about 600 Nm3/s, dry basis, at 6% O2, dry). Tracer injection work was begun on the 13 November since the same sampling ports were required for both test methods. However, further velocity and tracer testing was curtailed by a plant upset and the tracer testing was completed at a later date (20 March 2015). Flue gas sampling for the tracer method employed 20 fixed sample points, located on four sample probes, specified according to EN 15259. The sample streams were extracted using an ABB SCCF pump and dried using an ABB chiller; the tracer concentration was measured using a portable mass spectrometer, as discussed in Section 3.2. The inert tracer gas was supplied from a bank of 50 L internal volume pressurised cylinders and was injected at the ID fan inlet (Figure 17). 6.2 AMS Implementation The ‘AMS’ plant stack gas flow rate calculation is based on the net thermal input of the plant, as required by EN ISO 16911-1 (Annex E). The net thermal input is calculated within the Distributed Control System (DCS) using a full mass and heat balance approach according to the performance standard DIN 1942 (subsequently replaced by EN 12952-15). The thermal output of the boiler is divided by the calculated thermal efficiency of the boiler in order to obtain the net thermal input. The flue gas flow rate is also calculated by the DCS using a standard coal composition. However, for the purposes of this field trial, the flue gas flow rate was calculated


directly from the reported thermal input using the approach specified in Annex E of Part 1 to the flow standard: Q = NTI * S Where: Q = Flue gas volumetric flow rate at 6% O2, dry, 273 K, 101.3 kPa, Nm3/s NTI = Net thermal input, MJ/s S = Fuel factor for coal, Nm3/MJ [= 0.359 Nm3/MJ at 6% O2, dry] The fuel factor is the value specified by EN ISO 16911-1 for coal at 0% O2 (S = 0.256 Nm3/MJ) corrected to the plant reporting conditions of 6% O2, dry (S = 0.359 Nm3/MJ). The flue gas flow rate reported by the DCS was typically within 0.5% of this independently calculated flow rate that was used for subsequent QAL2 analysis. A flue gas flow monitor in the stack was typically 2% lower than the independently calculated value. 6.3 Field Trial Results In each case, the average velocity from each velocity traverse is multiplied by the cross-sectional area to obtain the stack gas volume flow rate at duct conditions. This flow is then corrected to reference conditions (6% O2, dry at 273K, 101.3 kPa). The velocity results are multiplied by a Wall Adjustment Factor of 0.995 as required by EN ISO 16911-1. The average of each of the traverses is plotted in Figure 18, along with the tracer results. With the exception of the L type fixed reference Pitot, the results are very closely grouped together at all load conditions: base load (8 tests); minimum load (2 tests) and an intermediate load (1 test). Tracer testing was conducted at base load only due to commercial operating constraints. The L type results were affected by impulse line blockages caused by water droplets in the flue gas. The reference Pitot could not be blown back as frequently as the traversing probes which were continuously attended. The QAL2 verification of the calculated flow rate is presented in detail in APPENDIX D, for each reference method, using the Excel spreadsheet tool developed by DNV GL. The full set of QAL2 verification results is summarised in Table 17. It can be seen from the slope of the calibration lines that the closest agreement with the AMS flow calculation is again achieved with the 3D Pitot (- 2.3%) and the tracer method (+1.1%) with the Vane anemometer and the S-type Pitot being about 3 to 4% higher than the AMS. All of the reference methods result in a successful verification of the AMS. However, the fixed position L type Pitot failed the Variability test and the linear regression test due to some of the points being affected by impulse line blockages, as noted previously. For the velocity based reference methods, it was only possible to obtain between 9 and 11 test points. However, provided that the flow profile is characterised at maximum and minimum loads, the flow standard allows the number of QAL2 test points to be reduced from 15 to 9 tests. It can be concluded that the reference method performance is very similar to that observed in the CEN validation trials on an incinerator and a coal fired power plant. Inert tracer gas injection upstream of the FGD was successfully demonstrated. All of the methods performed well in the wet stack environment although greater care is required with Pitot methods to manage impulse line blockages.


7 FURTHER GUIDANCE ON COMPLIANCE WITH EN ISO 16911 7.1 Sample Location Requirements In large ducts, four sample ports, fully compliant with EN 15259, are required for point velocity traverses. The ports should be located at a sample plane that does not have significant flow non-uniformity. EN 15259 recommends that the sample plane should be located at least five stack diameters downstream of the nearest flow disturbance and at least two stack diameters upstream of the nearest flow disturbance or the stack exit plane. This is particularly difficult to achieve in gas turbine stacks since the base of the stack is often already at the top of the boiler and the stack is generally squat. Platforms need to accommodate the long probes needed for traversing, in order to avoid Health & Safety issues, or sectional probes need to be assembled during each traverse in order to achieve the required insertion depth within the stack. Ideally, the same sampling arrangements should be available for tracer gas dilution testing since a full 20-point tracer concentration traverse, or 20-point grid sampling, is required in order to ensure that any inhomogeneity of the tracer gas mixing is accounted for. However, if the tracer can be injected at a far upstream location through a 20-point grid, or at the inlet to a fan, so as to guarantee perfect mixing, then non-ideal tracer sampling arrangements can be considered in the stack or exhaust. This has obvious advantages for existing plants that do not have compliant sampling platforms or locations. 7.2 Choice of Reference Method From the field trial testing, it can be concluded that all of the test methods can be used to verify stack flow rate calculations and can be used in wet stacks and for gas turbine testing. However, the tracer gas dilution method has the following advantages, especially at existing plants:

• Direct determination of the stack gas volumetric flow rate at the reference temperature and pressure, either on a ‘wet’ or dry basis depending on the sample handling adopted for the tracer concentration measurement.

• Reduced method uncertainty and reduced complexity of testing since o Stack diameter and cross-sectional area are not required o Stack gas temperature and pressure are not required o Stack gas density (composition) is not required o When the tracer concentration is measured on a dry basis, only the oxygen content

needs to be measured in order to give a direct comparison with the calculated stack flow rate.

• Complete independence from the plant geometry provided that the tracer is well mixed with the flue gas. Non-compliant sampling locations and platforms can therefore be accommodated, as noted above.

• Complete independence from the axial velocity profile and the other velocity components, including the tangential (swirl) velocity.

• Rapid measurement when compared with Pitot traversing. A dilution tracer measurement can be completed in less than 5 minutes when compared with a Pitot traverse which may take up to 60 minutes. A QAL2 test requires up to 15 data points (traverses). This results in:


o Reduced overall duration and cost of testing o Greater flexibility when testing at low load conditions o Wider range of flow conditions for the flow calibration or verification o Reduced environmental impact since plant operation at non-optimal conditions is

minimised o Reduced financial impact on the operator since lost generation, associated with low

load operation, is minimised. However, the tracer gas dilution method does require specialist equipment to measure the tracer gas concentration. At a large site, several cylinders of tracer gas are required to complete a QAL2 test. All the other methods require the internal area of the duct at the measurement plane. ISO 16911-1 Section 7.2 requires this area to be defined with a performance criterion ≤ 2%, which means, for example, for a circular stack that the stack diameter has to be measured with an uncertainty lower than 1% of the value. This is difficult to achieve in practice. The Vane Anemometer provides the next quickest and most reliable alternative for non-swirling flows since this gives direct velocity and gas temperature readings and no other information is required. However, the Vane Anemometer tends to over-read by about 4% when compared with other techniques, based on these field trials. S type Pitots are commonly available and can also perform satisfactorily in non-swirling flows although they tend to over-read more significantly when compared with the other techniques. Whilst a 3D Pitot accurately measures swirling flows, it is relatively difficult and time consuming to use and requires calibration in the United States. 7.3 Common Causes of Bias in Calculation Procedures Various examples of bias in the calculation procedures at CCGT plants have been encountered in the UK recently. The stack gas flow rate is calculated from the fuel flow, multiplied by the Net Calorific Value and then multiplied by the fuel factor for natural gas. Common problems have included:

• Gross (upper) Calorific Value mistakenly was used instead of the Net (lower) Calorific Value, resulting in a 10% over-reading

• Volumetric fuel metering temperature was incorrectly assumed to be 15°C when it was 0°C, or vice-versa, resulting in a 6% over- or under-reading

• High pressure fuel meter with a fixed compressibility factor was used instead of a pressure-compensated compressibility factor, resulting in a 5% under-reading

• Performance calculations of flue gas flow rate were on a ‘wet’ basis, rather than the assumed dry basis, resulting in an 8% over-reading

Calculation performance at coal fired power stations has generally been very good since a protocol for flow calculation has been established for many years. The gross generated electrical power output is divided by the gross generated efficiency to obtain the thermal input which is then multiplied by the fuel factor for hard coal. The generated efficiency is specified as a function of load and is updated annually in line with EU ETS reporting.


At other solid fuel stations, there have been issues with both the efficiency and the fuel factors not being updated on a regular basis. It should also be remembered that, when stack flow rate is measured directly, the normalisation of the flow to reference conditions must be implemented correctly. The correction for temperature, pressure, moisture and oxygen content are the inverse of those required when correcting concentrations to reference conditions. 8 SUMMARY EN ISO 16911 Part 1 defines manual methods for the measurement of flue gas flow rate and also an approach for the calculation of flow rate from plant thermal input. The manual methods incorporate a multi-point stack velocity measurement method and a tracer dilution method that determines volume flow rate directly. EN ISO 16911 Part 2 defines how these manual test methods can be used to calibrate continuous in-stack flow meters or to verify continuous flow calculations, following the QA structure defined in EN 14181. For many standard fuels, the calculation of flue gas flow rate gives reliable, accurate results and this approach is used at many power stations. However, further guidance is required on how to apply EN 14181 to a calculation based AMS and, in particular, how to verify a flow calculation. QAL1 Validation. An uncertainty assessment of the AMS calculation against the requirements of Part 1 (Annex E) can be used to check that the overall calculation approach is consistent with Annex E and to validate that the calculation uncertainty is acceptable. Individual gas- and oil-fired plants that are compliant with top tier EU ETS uncertainty requirements should automatically satisfy the Annex E performance requirements. However, individual plants that cannot satisfy top tier EU ETS requirements should instead have an uncertainty within ±7.5% of the maximum plant flow rate, equivalent to the certification requirement of a flow meter. This is broadly consistent with a 95% Confidence Interval of 10%, noting that this agreement would be exact if the ‘ELV’ is increased from 120% to 125% of the maximum flow. QAL2 Verification. The AST Validity test assesses the absolute difference between the AMS and the SRM with the required agreement being of the order of 5%. This should be used to verify a calculation based AMS using QAL2 data. The QAL2 Variability test assesses the combined scatter of the AMS and SRM data points and this should also be passed. A VGB Excel spreadsheet tool has been developed to perform this assessment. Since most of the benefit is obtained from performing the initial validation and verification, it may be appropriate to reduce the AST frequency subject to alternative QA processes being in place. Any of the SRM can be used to perform the AMS verification and the VGB field trials have further demonstrated this for ‘wet’ stacks and for gas turbines. However, the tracer dilution method has a number of advantages relating to the direct determination of the volume flow rate, the speed of testing and suitability for non-compliant sampling locations. Whilst the tracer method appears to be unbiased, additional equipment, tracer gas cylinders and sampling probes are required. Amongst the velocity based methods, the Vane Anemometer is very easy to use and does not require the full flue gas composition but tends to over-read. The S type Pitot appears to be the least reliable method and also tends to further over-read, particularly in swirling flows. Recommendations are made regarding the calibration of Pitot tubes to EN ISO 16911-1. The 3D Pitot appears to be unbiased and is particularly suitable for swirling flows but it is difficult to use and calibration facilities are not available in Europe.


QAL3 Control. The quality of the calculation inputs should be maintained in addition to periodic checks that the calculation continues to be properly implemented. Fiscal quality fuel metering and calorific value measurement under the EU ETS is already well controlled. Other fuel meters should have a current calibration certificate. When the plant output and efficiency are used for flow calculation then this should be checked annually using EU ETS fuel input data and annual production data supplemented by plant performance testing when this is available. Finally, plant performance calculations can be used to provide additional cross-checks of calculated flow rates and it is recommended, in any case, that the calculation is manually checked by the operator every year. 9 REFERENCES [1] Directive 2010/75/EU of the European Parliament and the Council of 24 November 2010

on industrial emissions (integrated pollution prevention and control), Official Journal of the European Union, L334/17 - 119, 17 December 2010.

[2] EN ISO 16911-1:2013 Stationary source emissions - Manual and automatic determination

of velocity and volume flow rate in ducts - Part 1: Manual reference method. [3] Graham D, Harnevie H, van Beek R, Blank F, Validated methods for flue gas flow rate

calculation with reference to EN 12952-15, KEMA Report 55106284-PGR/R&E 12-7222, 2012.

[4] EN 12952-15:2003, Water-tube boilers and auxiliary installations – Part 15: Acceptance

tests. [5] EN ISO 16911-2:2013 Stationary source emissions - Manual and automatic determination

of velocity and volume flow rate in ducts - Part 2: Automated measuring systems. [6] EN 14181:2014, Stationary source emissions. Quality assurance of automated measuring

systems. [7] Graham DP, Jones HD, Stack gas flow rate measurement using a tracer gas injection

technique, CEM 2007, 8th International Conference on Emissions Monitoring, Zurich, Switzerland, Sep 5-6, 2007.

[8] EN 15259:2007 Air quality. Measurement of stationary source emissions. Requirements

for measurement sections and sites and for the measurement objective, plan and report. [9] EN 15267-3: 2007 Air quality. Certification of automated measuring systems. Performance

criteria and test procedures for automated measuring systems for monitoring emissions from stationary sources.

[10] ISO 7145:1982 Measurement of fluid flow in closed conduits. Velocity area methods.

Method of measurement of velocity at one point of a conduit of circular cross section.


TABLES Table 1: Velocity Probes

Type Calibrated in Owner

(Serial No.) France UK

S Pitot (T4223) X X Uniper

L Pitot (1) X X Laborelec

Vane Anemometer (666) X X Laborelec

S pitot (2950) X _ Laborelec

3D pitot _ _ Uniper

Table 2: Pitot calibration summary (France)


Table 3: Pitot calibration summary (France and UK)

France UK Average

Vr Vr

m/s Pitot cst. m/s Pitot cst. Pitot cst.

L pitot

2.56 1.012 2.515 1.015

5.11 1.01 4.992 1.008

15.05 1.01 14.968 1.008

24.61 1.01 24.97 1.005

38.93 1.01 39.967 1.002

avg 1.010 1.008 1.009

stdev 0.001 0.005

Maximum differences between both calibarations

max diff % of avg

all values 0.013 1.3

on avg 0.003 0.3

S pitot

2.53 0.8222 2.478 0.828

5.14 0.8206 4.971 0.842

15.19 0.8421 15.038 0.843

24.6 0.8403 25.011 0.843

38.58 0.8419 39.987 0.839

avg 0.833 0.839 0.836

stdev 0.011 0.006

Maximum differences between both calibarations

max diff % of avg

all values 0.0224 2.7

on avg 0.006 0.7

Vane anemometer

Vr Vr Average

m/s vi-vr m/s vi-vr vi-vr

2.581 -0.006 2.552 -0.062

5.114 -0.041 5.023 -0.013

15.524 -0.05 15.026 -0.076

24.39 0.071 25.037 -0.287

39.923 0.129 37.475 -0.395

avg 0.021 -0.167 -0.073

stdev 0.077 0.165

Maximum differences ((vi-vr)/vr)*100

% -0.8 2.4

@ 5m/s @ 2m/s


Table 4: Performance characteristics for velocity measurement in EN ISO 16911

Parameter Criterion Method of determination

Standard deviation of repeatability of measurement in the laboratory

< 1 % of value Performance evaluation in wind tunnel at values spanning

Lack- of-fit (Linearity)

< 2 % of value

Maximum deviation from linear fit at five velocity levels in wind tunnel

Uncertainty due to calibration < 2 % of full scale From calibration certificate for measurement equipment

Lowest measurable flow (limit of quantification)

No criterion, but should be determined

This parameter shall be determined, but is not a performance requirement. The sensor shall not be used to measure flows below its limit of quantification

Sensitivity to ambient temperature Note: Only external components are affected by ambient conditions

≤ 2 % of range per 10 K

Performance evaluation of measurement device.

Sensitivity to atmospheric pressure

pressure ≤ 2% of range per 2 KPa

Performance evaluation of the measurement device

Effect of angle of sensor to flow ≤ 3% at 15° Performance Evaluation of measurement device


Table 5: Linearity comparison (Vi recalculated for Pitots)

LType (1) Aerometrologie = 1.172 kg/m3 k = 1.010

Vr (m/s) P (Pa) ki (-) Vi (m/s) (Vi - Vr) /Vr Vest (m/s) (V i - Vest) /Vest

2.56 3.76 1.012 2.56 -0.1% 2.56 0.1%

5.11 14.99 1.010 5.11 0.0% 5.10 0.2%

15.05 130.47 1.010 15.07 0.1% 15.02 0.3%

24.61 348.26 1.010 24.62 0.0% 24.56 0.3%

38.93 866.59 1.010 38.84 -0.2% 38.85 0.0%

Gradient 0.9979 Offset 0.0012 R2

1.0000

L Type (1) Young = 1.205 kg/m3 k = 1.010


2.515 3.70 1.015 2.50 -0.5% 2.54 -1.4%

4.992 14.78 1.008 5.00 0.2% 5.04 -0.7%

14.968 132.89 1.008 15.00 0.2% 15.10 -0.7%

24.970 372.08 1.005 25.10 0.5% 25.19 -0.4%

39.967 959.25 1.002 40.30 0.8% 40.32 -0.1%


1.0000

S Type (T4223) Aerometrologie = 1.174 kg/m3 k = 0.84


2.53 5.57 0.822 2.59 2.3% 2.51 3.0%

5.14 23.05 0.821 5.26 2.4% 5.10 3.2%

15.19 191.19 0.842 15.16 -0.2% 15.07 0.6%

24.60 503.21 0.840 24.59 0.0% 24.40 0.8%

38.58 1224.07 0.842 38.36 -0.6% 38.27 0.2%


1.0000

S Type (T4223) Young = 1.205 kg/m3 k = 0.84


2.478 5.40 0.828 2.51 1.5% 2.48 1.3%

4.971 21.01 0.842 4.96 -0.2% 4.98 -0.3%

15.038 191.79 0.843 14.99 -0.3% 15.05 -0.4%

25.01 530.09 0.843 24.92 -0.4% 25.02 -0.4%

39.987 1369.62 0.839 40.05 0.2% 40.01 0.1%


1.0000

Vane Anemometer Aerometrologie = 1.170 kg/m3


2.581 - - 2.57 -0.3% 2.59 -0.8%

5.114 - - 5.07 -0.8% 5.14 -1.3%

15.524 - - 15.47 -0.3% 15.59 -0.8%

24.390 - - 24.46 0.3% 24.50 -0.2%

39.923 - - 40.05 0.3% 40.10 -0.1%


1.0000

Vane Anemometer Young

Vr (m/s) P (Pa) i (kg/m3) Vi (m/s) (Vi - Vr) /Vr Vest (m/s) (V i - Vest) /Vest

2.552 - 1.194 2.49 -2.4% 2.53 -1.4%

5.023 - 1.197 5.01 -0.3% 4.97 0.8%

15.026 - 1.193 14.95 -0.5% 14.87 0.6%

25.037 - 1.181 24.76 -1.1% 24.77 0.0%

37.475 - 1.168 37.08 -1.1% 37.07 0.0%


1.0000


Table 6: Effect of mis-alignment from flow direction

Table 7: Tracer mass flow meter calibration

Table 8: Tracer concentration performance requirements

Type of device Reference # Owner +15° -15° +15° -15°

L type Pitot 1 Laborelec 0.99 0.97 0.99 0.98

S type Pitot T4223 Uniper 0.98 0.99 1.02 1.08

S type Pitot 2950 Laborelec 1.02 1.04 1.06 1.06

Vane Anemometer 666 Laborelec 1.00 0.93 0.98 0.95

2.5 m/s

Relative velocity reading at

40 m/s

Reference Indicated M

Mr Mi (Mi - Mr)/Mr

kg/h kg/h %

0.000 0.000 0.00%

9.957 9.946 -0.11%

20.069 20.005 -0.32%

30.017 30.009 -0.03%

40.050 39.998 -0.13%

Parameter Criterion Method of determination

Calibration gas

concentration≤ 1 % of value

Traceable calibration gas standard (standard

uncertainty).

Linearity

≤ 1.5 % relative to the

calibration gas

concentration

Laboratory evaluation according to EN14181

using traceable calibration gases or a calibrated

dilution system. The five concentration levels

are 0, 25%, 50%, 75% and 100% of the

calibration gas concentration.

Repeatability≤ 1 % of calibration

gas concentration

Laboratory evaluation using calibration gas

(standard deviation).

Interference≤ 2 % of calibration

gas concentration

Cross-interferences of stack gas components

determined from instrument certification or

laboratory evaluation according to EN15267-3.

Leak/sample loss≤ 2 % of calibration

gas concentration

Field evaluation - passing calibration gas

through sampling system.

Drift≤ 2 % of calibration

gas concentration

Field evaluation by periodic calibration gas

check. Correct drift if > 2% and declare invalid

if > 5%.


Table 9: EN ISO 16911-1 Uncertainty requirements for flow rate calculations

Table 10: EN ISO 16911-1 Uncertainty requirements for flow rate calculation inputs

Table 11: EN ISO 16911-1 Fuel factor uncertainty for fossil fuels

Table 12: EN ISO 16911-1 Fuel factor uncertainty for solid biomass fuels


Table 13: CCGT Velocity traverse and Tracer test times

Velocity

Tracer Table 14: CCGT Summary results (flow units)

Test # Date Start End

1 12-Aug-14 11:10 13:58

2 12-Aug-14 14:04 15:18

3 12-Aug-14 15:28 16:35

4 12-Aug-14 17:07 18:14

5 13-Aug-14 09:10 10:16

6 13-Aug-14 10:25 11:20

7 13-Aug-14 11:28 12:20

8 13-Aug-14 13:20 14:21

9 13-Aug-14 14:28 15:20

10 13-Aug-14 15:36 16:28

11 14-Aug-14 08:59 09:56

12 14-Aug-14 10:03 10:55

13 14-Aug-14 11:03 11:53

14 14-Aug-14 13:01 15:00

15 14-Aug-14 15:05 15:55

Q Nm3/s

N Slope Max |D| limit |D| sD Max sD R2

Limit R2

Ref. L-Pitot 14 1.034 650.0 19.88 36.50 11.21 30.41 0.986 0.90

3D Pitot 15 1.005 629.6 2.66 32.69 5.75 29.37 0.996 0.90

S-Pitot 15 1.078 691.8 45.17 39.40 13.62 32.42 0.979 0.90

Vane anemometer 14 1.042 648.9 24.04 33.23 4.40 30.34 0.998 0.90

Tracer Gas 20 0.998 652.6 0.93 36.61 13.66 30.78 0.986 0.90

15 vol % O2 Dry, 0°C, 101.3kPa


1 20-Aug-14 16:28:26 16:28:46

20-Aug-14 16:54:21 16:54:41

2 20-Aug-14 17:06:34 17:06:54

20-Aug-14 17:28:49 17:29:09

3 20-Aug-14 17:39:13 17:39:33

20-Aug-14 17:55:35 17:55:55

4 21-Aug-14 09:29:21 09:29:41

21-Aug-14 09:36:09 09:36:29

5 21-Aug-14 09:45:17 09:45:37

21-Aug-14 10:05:04 10:05:24

6 21-Aug-14 10:11:00 10:11:20

21-Aug-14 10:24:31 10:24:51

7 21-Aug-14 10:30:04 10:30:24

21-Aug-14 10:35:58 10:36:18

8 21-Aug-14 11:43:24 11:43:44

21-Aug-14 12:12:05 12:12:25

9 21-Aug-14 12:17:33 12:17:53

21-Aug-14 12:31:04 12:31:24

10 21-Aug-14 13:30:00 13:30:20

21-Aug-14 13:34:59 13:35:19

11 21-Aug-14 13:40:35 13:40:55

21-Aug-14 13:47:01 13:47:21

12 21-Aug-14 13:52:47 13:53:07

13 21-Aug-14 14:37:32 14:37:52

14 21-Aug-14 14:43:51 14:44:11

15 21-Aug-14 14:49:15 14:49:35

16 21-Aug-14 14:54:20 14:54:40

17 21-Aug-14 14:59:11 14:59:31

18 21-Aug-14 16:03:31 16:03:51

19 21-Aug-14 16:09:25 16:09:45

21-Aug-14 16:14:35 16:14:55

20 21-Aug-14 16:25:35 16:25:55

21-Aug-14 16:30:36 16:30:56


Table 15: CCGT Summary results (velocity units)

Table 16: Coal PP Velocity traverse and tracer injection test times

Velocity Tracer Table 17: Coal PP Summary results (flow units)

V m/s


Limit R2

Ref. L-Pitot 14 1.034 18.6 0.57 1.04 0.318 0.870 0.981 0.90

3D Pitot 15 1.005 17.7 0.08 0.92 0.165 0.830 0.994 0.90

S-Pitot 15 1.078 19.6 1.29 1.11 0.371 0.917 0.973 0.90

Vane anemometer 14 1.042 18.0 0.68 0.92 0.114 0.844 0.997 0.90

Actual measured speed

Test # SRM Date Start End

1 S, 3D 11-Nov-14 15:40 16:59

2 S, 3D 11-Nov-14 17:05 18:48

3 S, 3D 11-Nov-14 18:50 19:40

4 S, 3D 12-Nov-14 08:55 10:02

5 S, 3D 12-Nov-14 11:01 12:05

6 S, 3D, VA 12-Nov-14 13:32 14:48

7 S, 3D, VA 12-Nov-14 15:46 16:50

8 S, 3D, VA 13-Nov-14 09:24 10:27

9 S, 3D, VA 13-Nov-14 10:38 11:50

10 S, 3D, VA 13-Nov-14 14:20 15:21

11 S, 3D, VA 13-Nov-14 15:29 16:26

12 VA 13-Nov-14 16:42 17:20

13 VA 13-Nov-14 17:23 17:58

Q Nm3/s


Limit R2

Ref. L-Pitot 10 1.015 563.0 7.27 52.31 43.62 26.04 0.84 0.90

3D Pitot 11 0.977 574.3 11.39 34.02 11.81 26.66 0.99 0.90

S-Pitot 11 1.032 601.0 16.61 34.57 10.47 27.90 1.00 0.90

Vane anemometer 9 1.039 602.9 18.60 40.12 18.04 27.76 0.99 0.90

Tracer Gas 19 1.011 592.5 6.35 30.98 6.38 27.92 N/A 0.90

6 % O2 Dry, 0°C, 101.3 kPa


1 13-Nov-14 18:54 18:55

2 13-Nov-14 19:04 19:05

3 13-Nov-14 19:13 19:14

4 13-Nov-14 19:21 19:22

5 13-Nov-14 19:32 19:33

6 20-Mar-15 13:58 14:00

7 20-Mar-15 14:20 14:22

8 20-Mar-15 14:31 14:33

9 20-Mar-15 15:33 15:35

10 20-Mar-15 15:45 15:47

11 20-Mar-15 15:57 15:59

12 20-Mar-15 16:10 16:12

13 20-Mar-15 16:22 16:24

14 20-Mar-15 16:29 16:31

15 20-Mar-15 16:37 16:39

16 20-Mar-15 16:48 16:50

17 20-Mar-15 16:54 16:56

18 20-Mar-15 17:01 17:03

19 20-Mar-15 17:10 17:12


FIGURES

Figure 1: Centres of equal area "Tangential Method" in EN 15259

Figure 2: Spherical (5 hole) Pitot head

Figure 3: S type Pitot head


Figure 4: Vane anemometer (Höntzsch)

Figure 5: Inert tracer gas injection at the CCGT air intake


Figure 6: Free jet calibration wind tunnel

Figure 7: Linearity of all velocity probes

0

10

20

30

40

50

0 10 20 30 40 50

Vi(m

/s)

Vr (m/s)

S type - Aero

S type - Young

1:1 agreement

L type - Aero

L type - Young

Vane - Aero

Vane - Young

Laboratory reference Pitot (L type)

Pitot under test (S type)


Figure 8: Pitot rotation (left image) with angle setting using an inclinometer (right image)

Figure 9: Hontzsch Vane Anemometer performance with mis-alignment


Figure 10: CCGT stack test location

Figure 11: CCGT stack test location showing platform extension

Platform extension

Test platform


Figure 12: CCGT test periods and plant load

Figure 13: CCGT tracer injection location at the combustion air inlet


Figure 14: CCGT Velocity Profiles at Base Load

Figure 15: CCGT Normalised Velocity Profiles at Base and Part Load (PL)


Figure 16: CCGT Flow results (all methods)

Figure 17: Coal fired power plant stack test location and tracer injection location

Stack sample port

Tracer injection port


Figure 18: Coal PP Flow results (all methods)

0

200

400

600

800

0 200 400 600 800

y (

SR

M)

Nm

3/s

@ 6

% O

2, d

ry

x (AMS) Nm3/s @ 6% O2, dry

Tracer

y=x

3D Pitot

Vane

S Pitot

L Pitot Ref

UTG/18/ERG/CT/217/R

APPENDIX A

Calibration Data

A-1 UTG/18/ERG/CT/217/R

B-1 UTG/18/ERG/CT/217/R

APPENDIX B

Calculation of flue gas CO2 and H2O Symbols and abbreviations are listed at the end of the Appendix. The flue gas dry CO2 concentration of UK natural gas can be calculated from the dry oxygen concentration using an assumed stoichiometric CO2 content of 12.3% by volume:

%CO2 = 12.3 * [1 - (%O2 / 20.95)] The flue gas water vapour concentration can be calculated form the dry oxygen concentration and the ambient relative humidity, combined with standard natural gas combustion properties, as follows. Calculate the moisture content from the stoichiometric flue gas parameters, given in Table B1, as follows.

1) Calculate the excess air factor, from the dry O2 reading:

= 1 + [CFRs / AFRs] . [O2,dry / (0.2095 - O2,dry)]

Where CFRs is the ratio of dry combustion products to fuel and AFRS is the ratio of dry combustion air to fuel, both at stoichiometric conditions (Table B2). 2) Calculate the actual air:fuel ratio from the air factor and the stoichiometric air:fuel ratio:

AFR = AFRs

3) Calculate the water:fuel ratio of any additional moisture associated with the combustion

air, WaFR, using the moisture volume fraction of the ambient air, Bwa, noting that ISO air (60% relative humidity at 15°C) contains 1% by volume of water vapour (Bwa= 0.01):

WaFR = AFR / (1/ Bwa - 1)

The ISO default Bwa value may be acceptable. However, Bwa can be calculated from the ambient temperature, t (°C), fractional relative humidity, RH (-), and pressure, Pa (mbar absolute), as follows, noting that RH = %RH/100:

Bwa = RH . 10 {[7.5 t / (237.3 + t) ] + 0.78571} / Pa

4) Calculate the water vapour content of the flue gas knowing the ratio of combustion derived

water:fuel at stoichiometric conditions (WFRs) from Table B1.

Bw = {[WFRs + WaFR] / [CFRs + WFRs + (– 1). AFRs + WaFR]} Table B1: Combustion parameters

Fuel CFRs AFRs WFRs

m3/kg m3/kg m3/kg

Coal 6.61 6.80 0.60

Natural Gas 11.57 12.88 2.67

B-2 UTG/18/ERG/CT/217/R

The stoichiometric data in Table B1 are taken from standard combustion handbooks for solid and liquid fuels [Rose & Cooper, 1977] and natural gas [Rhine & Tucker, 1991], noting that the parameters for coal are based on Rank 702. Alternatively, the combustion properties given in Table B1 can be calculated from the full fuel composition as described in EN 12952-15. Symbols and abbreviations AFR ratio of dry combustion air to fuel (m3/kg) AFRs ratio of dry combustion air to fuel at stoichiometric conditions (m3/kg) Bwa concentration of water vapour in ambient air by volume (m3/m3) Bw concentration of water vapour in flue gas by volume (m3/m3) Bws concentration of water vapour in stoichiometric flue gas by volume (m3/m3) CFRs ratio of dry flue gas to fuel at stoichiometric conditions (m3/kg)

excess air factor (-) O2a concentration of oxygen in ambient air by volume (m3/m3) O2s,wet concentration of oxygen in flue gas by volume, on a wet basis (m3/m3) O2s,dry concentration of oxygen in flue gas by volume, on a dry basis (m3/m3) Pa absolute pressure of ambient air (mbar) PT absolute pressure of saturated flue gas (Pa) Pv vapour pressure of water (Pa)

RH relative humidity (-) T temperature of saturated flue gas (K) t temperature of ambient air (°C) WFRs ratio of combustion water vapour to fuel at stoichiometric conditions (m3/kg) WaFR ratio of ambient water vapour to fuel (m3/kg) References Rose, J.W., Cooper, J.R., Technical Data on Fuel, 7th edition, Scottish Academic Press, 1977. [Table 5.45 solid fuels, Table 5.25 liquid fuels. Rhine, JM, Tucker, RJ, Modelling of gas-fired furnaces and boilers, McGraw-Hill, 1991.

C-1 UTG/18/ERG/CT/217/R

APPENDIX C

CCGT Field Trial QAL2 Sheets

G eneral Data AMS S ystem 0.995

Installation type C C G T Method C alculation T ype R eference L -P itot

C ompany ANO N R ange 0-800 Nm3/s R ange 0-20 m/s

F uel G as L ocation F rom DC S L ocation At s tack

S R M company L aborelec 95 % C .I. 0.70% 95% C onf. Interval 2.00%

Accredited yes S tandard IS O 16911-1; Anx. E S tandard IS O 16911-1

x (AMS ) y (S R M)

No. m3/s m3/s ycal D (D-Davg) 2̂

1 608.61 638.99 629.597 30.375 110.2017

2 610.40 640.14 631.446 29.744 97.3594

3 610.43 622.84 631.482 12.402 55.8721

4 609.80 609.24 630.830 -0.561 417.6854

5 607.00 645.96 627.930 38.958 364.0859

6 606.05 627.81 626.952 21.756 3.5319

7 606.37 628.20 627.278 21.826 3.8001

8 607.28 621.43 628.220 14.154 32.7534

9 607.70 631.14 628.655 23.438 12.6804

10 621.92 637.34 643.369 15.415 19.9080

11 620.66 644.73 642.065 24.068 17.5693

12 617.19 649.95 638.477 32.757 165.8947

13 368.31 375.39 381.013 7.077 163.8383

14 368.45 375.32 381.158 6.867 169.2637

15

16

17

18

19

20

21

avg 576.44 596.32 596.319 19.88

N 14 O rigin through 0 T R UE R 2̂-test required? Y es

Min 368.3 375.3 a (for verification) 0.000 R 2̂ 0.986

Max 621.9 650.0 b (for verification) 1.034 Min R 2̂ 0.90

Max-Min 253.6 274.6 Valid C alibr. R ange 779.9 R 2̂ test P ass

S pread 44.0% 46.1%

E L V (120% of S R M Max) 779.9

σ0 4%

kv 0.975

sD 11.213

Max sD 30.405

Variability test P ass

19.88

36.50

Validity test P ass

T est parameter

|D|

QAL 2: C alc ulation Verific ation

or AMS C alibration (IS O 16911-2)S R M S ystem

Date S tart T ime E nd T ime

S pread of data C alibration func tion R ^2 tes t

V ariability tes t

V alidity of c alc ulation

0

100

200

300

400

500

600

700

800

900

0 200 400 600 800 1000

y (

SR

M)

x (AMS)

Function

Data

Function

y=x

F orce through z ero

C alculation

m3/s



Installation type C C G T Method C alculation T ype 3D P itot





x (AMS ) y (S R M)


1 608.61 596.49 611.406 -12.122 218.4393

2 610.40 616.67 613.201 6.271 13.0550

3 610.43 616.04 613.236 5.605 8.6879

4 609.80 618.67 612.603 8.864 38.5107

5 610.82 610.15 613.624 -0.666 11.0461

6 607.00 613.06 609.787 6.061 11.5802

7 606.05 610.75 608.837 4.695 4.1479

8 606.37 606.61 609.154 0.245 5.8210

9 607.28 602.16 610.069 -5.115 60.4177

10 607.70 617.58 610.491 9.880 52.1527

11 621.92 626.55 624.780 4.624 3.8674

12 620.66 624.83 623.513 4.169 2.2835

13 617.19 623.99 620.029 6.797 17.1287

14 368.31 370.17 370.004 1.857 0.6418

15 368.45 367.16 370.145 -1.296 15.6355

16

17

18

19

20

21

avg 578.73 581.39 581.392 2.66





S pread 43.8% 44.6%

E L V (120% of S R M Max) 751.9

σ0 4%

kv 0.976

sD 5.753

Max sD 29.365


2.66

32.69

Validity test P ass

T est parameter

|D|





V ariability tes t


0

100

200

300

400

500

600

700

800

0 200 400 600 800

y (

SR

M)

x (AMS)

Function

Data

Function

y=x


C alculation

m3/s



Installation type C C G T Method C alculation T ype S -P itot



S R M company E .O N UK 95 % C .I. 0.70% 95% C onf. Interval 2.00%


x (AMS ) y (S R M)


1 608.61 650.37 656.116 41.761 11.6439

2 610.40 660.99 658.042 50.589 29.3359

3 610.43 667.47 658.080 57.035 140.7195

4 609.80 691.78 657.400 81.980 1354.7373

5 610.82 638.50 658.496 27.677 306.1099

6 607.00 655.94 654.379 48.943 14.2104

7 606.05 654.61 653.359 48.557 11.4534

8 606.37 652.40 653.699 46.035 0.7428

9 607.28 653.31 654.681 46.035 0.7428

10 607.70 654.72 655.134 47.016 3.3959

11 621.92 665.40 670.468 43.477 2.8752

12 620.66 662.32 669.109 41.655 12.3722

13 617.19 659.34 665.369 42.146 9.1624

14 368.31 390.03 397.061 21.721 549.9861

15 368.45 401.42 397.212 32.967 148.9830

16

17

18

19

20

21

avg 578.73 623.91 623.907 45.17





S pread 43.8% 48.4%

E L V (120% of S R M Max) 830.1

σ0 4%

kv 0.976

sD 13.618

Max sD 32.422


45.17

39.40

Validity test F ail

T est parameter

|D|





V ariability tes t


0

100

200

300

400

500

600

700

800

900

1000

0 200 400 600 800 1000

y (

SR

M)

x (AMS)

Function

Data

Function

y=x


C alculation

m3/s



Installation type C C G T Method C alculation T ype Vane anemometer





x (AMS ) y (S R M)


1

2 610.40 626.97 635.845 16.571 55.7599

3 610.43 636.01 635.882 25.575 2.3608

4 609.80 635.69 635.225 25.890 3.4292

5 610.82 624.59 636.283 13.768 105.4724

6 607.00 632.57 632.305 25.575 2.3608

7 606.05 633.98 631.320 27.922 15.0837

8 606.37 632.22 631.648 25.855 3.3006

9 607.28 633.73 632.597 26.451 5.8194

10 607.70 633.87 633.035 26.170 4.5457

11 621.92 648.87 647.852 26.941 8.4264

12 620.66 648.90 646.538 28.237 17.6323

13 617.19 643.36 642.925 26.170 4.5457

14 368.31 388.56 383.668 20.250 14.3541

15 368.45 389.61 383.814 21.161 8.2817

16

17

18

19

20

21

avg 576.60 600.64 600.638 24.04





S pread 44.0% 43.3%

E L V (120% of S R M Max) 778.7

σ0 4%

kv 0.975

sD 4.397

Max sD 30.356


24.04

33.23

Validity test P ass

|D|





V ariability tes t


T est parameter0

100

200

300

400

500

600

700

800

900

0 200 400 600 800 1000

y (

SR

M)

x (AMS)

Function

Data

Function

y=x


C alculation

m3/s


G eneral Data AMS S ystem

Installation type C C G T Method C alculation T ype T racer G as

C ompany ANO N R ange 0-800 Nm3/s R ange 0-800 m3/s




x (AMS ) y (S R M)


1 626.85 622.48 625.808 -4.366 11.7854

2 625.61 622.97 624.578 -2.641 2.9162

3 623.54 613.85 622.504 -9.683 76.5574

4 632.09 599.45 631.046 -32.640 1005.3136

5 633.85 606.99 632.803 -26.865 672.4804

6 633.92 618.22 632.873 -15.704 218.1715

7 633.96 620.75 632.909 -13.204 150.5704

8 631.21 633.85 630.167 2.641 12.7722

9 629.66 637.34 628.620 7.676 74.1126

10 628.18 641.18 627.144 12.993 193.9220

11 628.61 639.59 627.565 10.986 142.0533

12 627.44 652.62 626.405 25.175 681.6421

13 369.21 367.42 368.602 -1.796 0.7442

14 367.10 369.42 366.493 2.324 10.6076

15 367.07 365.52 366.458 -1.549 0.3797

16 367.10 376.43 366.493 9.331 105.3443

17 368.12 378.90 367.512 10.774 137.0621

18 628.61 628.75 627.565 0.141 1.1533

19 627.76 632.87 626.722 5.105 36.4638

20 627.83 630.47 626.792 2.641 12.7722

21

avg 563.89 562.95 562.953 -0.93





S pread 47.3% 51.0%

E L V (120% of S R M Max) 783.1

σ0 4%

kv 0.983

sD 13.663

Max sD 30.780


0.93

36.61

Validity test P ass

|D|





V ariability tes t


T est parameter0

100

200

300

400

500

600

700

800

900

0 200 400 600 800 1000

y (

SR

M)

x (AMS)

Function

Data

Function

y=x


C alculation

m3/s

D-1 UTG/18/ERG/CT/217/R

APPENDIX D

Coal Power Plant Field Trial QAL2 Sheets


Installation type B oiler Method C alculation T ype R eference L -P itot


F uel C oal L ocation F rom DC S L ocation At s tack



x (AMS ) y (S R M)


1 575.00 563.00 583.645 -11.999 371.1171

2 408.40 498.17 414.540 89.767 6806.4810

3 569.30 547.98 577.859 -21.324 817.3252

4 569.40 545.61 577.961 -23.792 964.5372

5 228.30 298.25 231.733 69.951 3929.5346

6 230.60 274.97 234.067 44.368 1376.6326

7 563.20 547.87 571.668 -15.333 510.6854

8 563.90 540.75 572.378 -23.147 924.9262

9 561.80 552.64 570.247 -9.157 269.6936

10 562.30 535.62 570.754 -26.682 1152.3852

11

12

13

14

15

16

17

18

19

20

21

avg 483.22 490.49 490.485 7.27




Max-Min 346.7 288.0 Valid C alibr. R ange 675.6 R 2̂ test F ail

S pread 71.7% 58.7%

E L V (120% of S R M Max) 675.6

σ0 4%

kv 0.963

sD 43.619

Max sD 26.037

Variability test F ail

7.27

52.31

Validity test P ass

|D|





V ariability tes t


T est parameter0

100

200

300

400

500

600

700

800

0 200 400 600 800

y (

SR

M)

x (AMS)

Function

Data

Function

y=x


C alculation

m3/s



Installation type B oiler Method C alculation T ype 3D-P itot





x (AMS ) y (S R M)


1 569.00 535.27 555.851 -33.730 499.0864

2 569.80 564.40 556.633 -5.396 35.9204

3 568.50 561.61 555.363 -6.892 20.2267

4 574.00 574.33 560.736 0.334 137.4395

5 575.40 563.95 562.104 -11.454 0.0041

6 408.60 386.73 399.158 -21.873 109.9099

7 569.60 559.80 556.438 -9.803 2.5170

8 227.90 202.15 222.634 -25.746 206.1031

9 230.60 216.41 225.271 -14.188 7.8285

10 563.60 569.33 550.576 5.729 293.0468

11 564.70 562.43 551.651 -2.266 83.2339

12

13

14

15

16

17

18

19

20

21

avg 492.88 481.49 481.492 -11.39





S pread 70.5% 77.3%

E L V (120% of S R M Max) 689.2

σ0 4%

kv 0.967

sD 11.812

Max sD 26.661


11.39

34.02

Validity test P ass

T est parameter


V ariability tes t


|D|




0

100

200

300

400

500

600

700

800

0 200 400 600 800

y (

SR

M)

x (AMS)

Function

Data

Function

y=x


C alculation

m3/s



Installation type B oiler Method C alculation T ype S -P itot





x (AMS ) y (S R M)


1 569.00 590.62 587.022 21.622 36.1312

2 569.80 581.21 587.847 11.409 17.6549

3 568.50 580.05 586.506 11.545 16.5317

4 574.00 600.97 592.180 26.970 129.0252

5 575.40 599.91 593.625 24.505 79.1082

6 408.60 422.11 421.542 13.509 4.4196

7 569.60 592.53 587.641 22.932 53.6018

8 227.90 224.57 235.118 -3.329 358.7093

9 230.60 230.73 237.904 0.131 239.6481

10 563.60 591.87 581.451 28.266 160.1409

11 564.70 578.86 582.586 14.161 2.1024

12

13

14

15

16

17

18

19

20

21

avg 492.88 508.49 508.493 15.61





S pread 70.5% 74.0%

E L V (120% of S R M Max) 721.2

σ0 4%

kv 0.967

sD 10.474

Max sD 27.897


15.61

34.57

Validity test P ass

T est parameter


V ariability tes t


|D|




0

100

200

300

400

500

600

700

800

0 200 400 600 800

y (

SR

M)

x (AMS)

Function

Data

Function

y=x


C alculation

m3/s


G eneral Data AMS S ystem no WAF

Installation type B oiler Method C alculation T ype T racer G as

C ompany ANO N R ange 0-800 Nm3/s R ange 0-800 m3/s




x (AMS ) y (S R M)


1 568.01 578.08 574.306 10.070 13.8697

2 561.57 566.50 567.795 4.930 2.0045

3 566.60 560.76 572.880 -5.840 148.4935

4 564.40 575.31 570.656 10.910 20.8320

5 558.52 576.42 564.711 17.900 133.4998

6 574.90 567.60 581.272 -7.300 186.2076

7 575.30 582.00 581.677 6.700 0.1255

8 583.20 586.10 589.664 2.900 11.8735

9 574.00 584.70 580.362 10.700 18.9591

10 576.50 582.40 582.890 5.900 0.1987

11 576.00 580.30 582.385 4.300 4.1853

12 573.80 582.50 580.160 8.700 5.5423

13 576.70 592.50 583.092 15.800 89.3821

14 575.70 578.20 582.081 2.500 14.7901

15 575.80 584.40 582.182 8.600 5.0815

16 576.30 575.70 582.688 -0.600 48.2440

17 574.30 583.00 580.666 8.700 5.5423

18 573.90 578.70 580.261 4.800 2.3895

19 572.10 583.00 578.441 10.900 20.7408

20

21

avg 572.51 578.85 578.851 6.35

N 19 O rigin through 0 T R UE R 2̂-test required? No




S pread 4.3% 5.5%

E L V (120% of S R M Max) 711.0

σ0 4%

kv 0.982

sD 6.377

Max sD 27.917


6.35

30.98

Validity test P ass

T est parameter


V ariability tes t


|D|




0

100

200

300

400

500

600

700

800

0 200 400 600 800

y (

SR

M)

x (AMS)

Function

Data

Function

y=x


C alculation

m3/s

Uniper Technologies Ltd Technology Centre Ratcliffe-on-Soar Nottingham NG11 0EE United Kingdom

T +44 (0) 2476 192900

www.uniper.energy

UTG/18/ERG/CT/217/RResearch+Project+No+379... · Since this method directly measures the dry...

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