Coal quality Impacts-FinalJan_2010.pdf

7/27/2019 Coal quality Impacts-FinalJan_2010.pdf

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EE n g i n e e r i n g C o n s u l t a n t s G r o u p , I n c . A k r o n , O h Page 1

Coal

QualityImpacts

Matching Coal Quality

to LoadDemand/Emissions &

Cost Targets with

AccuTrack

James Mooney


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Engineering Consultants Group, Inc | 1236 Weathervane Lane

Akron, Ohio 44313

CONTENTS:

Introduction

Applications:

AccuTrackTM Z

8

AccuTrackTM

As Fire

10

AccuTrackTM

W ..12

COAL QUALITY ISSUES BEGIN WHEN THE FUEL

ARRIVES AT THE PLANT


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Abstract:

Putting aside the critical function of the corporate fuel procurement section, plant-site coal

management begins when the fuel arrives at the plant and ends with the combustion in the boiler; the

boiler status then being unrestricted for continued operations. / and thereabouts, most of

coal fired power plants were designed and built to use readily available fuels. Utilities

pass-through fuel costs obviated the economic incentive to manage costs as long as the as-received coal

conformed to the design fuel specifications. d brought environmental

considerations and deregulation of the electric utility industry so that fuel and fuel related costs went to

the top of the priority list. With lowest cost production economics came the assortment of coal qualities

that have significant impact to the boiler operations, economic dispatch and emissions. Although the

desirability of enhanced on-site fuel management would seem apparent, the entrenched practices,

limited equipment capabilities and process complexities has made the transition difficult and slow - and

with the consequences still painful.

The need to bring together extensive operating experience with the capabilities of the computer

advances in real-time fuel analysis, fuel flow modeling, and understanding of combustion chemistry and

coal quality consequences has prompted the development of a patented advanced plant site fuel

management tool called AccuTrack. With this AccuTrack tool, available fuel can be received, segregated,

reclaimed, blended (if required) and loaded for delivery to the boiler for optimal time-dependant

considerations of dispatch economics, demand capability and reliability with detailed operator

information regarding controllable real-time and projected fuel/combustion parameters.

Introduction:

In the coal-fired

of the boiler for projected life of 30-40 years. This fuel was generally either locally mined or the delivery

facilitated by transportation access. With the execution of long term contracts for the design fuel, fuel

received at the plant was expected to be relatively unifor

1. A simplistic fuel

management by the plant consisted of tracking tonnage in receiving, maintaining adequate inventory in

storage (usually a 30-60 day usage) and then delivery to the boiler. Coal quality was often accepted from

the vendor supplied analysis. But circumstances were about to alter the fuel picture.

A driver causing utilities to change their fuel supply in the 1990 was the Clean Air Act tightening of

environmental regulation for emissions of sulfur dioxide and nitrogen oxides. Coal fired facilities had to

evaluate alternatives including switching to lower sulfur fuel or installing Flue Gas Desulfurization (FGD)

systems. In the case of fuel switching, the implications to boiler operations was not (and often still is

not) fully appreciated.

1 ready


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In the same time period, extensive deregulation of the electric utility industry forced the generation

facilities into the open market of competition. The cost of fuel became very important as it is on the

order of 75-85% of the variable cost of generation. Economic fuel sources were sought and contracts

signed for available fuels including low cost coal, waste oil, biomass, and petcoke to replace some or all

of the design fuels. In the case of the low cost coal, this was often low grade fuel but attractive on a

$/MMBtu measure, hence referred to as High Value fuel. But in the rush to acquire environmental

compliance and economic fuels, insufficient consideration either through ignorance or the absence of

due diligence - was often given to implications for capabilities in fuel processing and boiler operations,

particularly at higher loads.

In fuel selection, it is clear that boilers were designed to burn a specific quality of coal or narrow range

thereof. Any consideration of a change to a different fuel mix requires an adaptive fuel management

review as well as a complete evaluation of appropriate equipment requirements to address the fuel

handling and operational implications. This greater attention is essential if the plant is to consistently

achieve targeted performance metrics for least-cost generation with reliability and availability. If these

goals are to be attained, extensive modifications or upgrade replacements are usually required to theequipment as well as to the procedures for receiving, stacking, reclaiming, blending and loading of the

coals to each unit. In addition, boiler considerations must address combustion monitoring/tuning,

sootblower requirements and emission consequences.

Having the appropriate fuel mix to meet peak demands is critically important to the company looking to

maximize the contribution of their generating resources through time-dependant economic dispatching.

Matching load with the most economical system resources generates profit to the market dispatched

entities. To the plant, meeting targets for availability, reliability and production costs means

determination and management to assure the correct fuel mix, both physical and economic. Operation

and maintenance must enable the installed process equipment capabilities to match the demand forproduct; electric generation.

To meet these demanding production requirements with diverse implications, a sophisticated

adaptation of state-of-the-art equipment, process understanding and extensive data must be

manipulated by the capabilities of the computer to provide usable real-time information as well as

projections for proactive intervention. This objective brought about the development of the AccuTrack

technology, a patented process now available for the day to day implementation in opportunity-driven

progressive generation entities.

AccuTrack technology was developed with many resources including experienced power plant

operators, advanced R&D academia, equipment suppliers and engineers to get it right. Among theelements of the AccuTrack System are on-line coal analyzers, conveyor scales, level transmitting devices,

belt speed monitoring, coal quality Impact blend expert calculations and silo/bunker stochastic flow

modeling to enable delivery of the right fuel at the right time. The AccuTrack system along with

precursor elements has tracked millions of fuel tons and combustion related reagents (e.g., limestone,

aqua ammonia, and sodium sulfite) to support initiatives for fuel flexibility, opacity control,

environmental emissions, and cost optimization.


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.

Figure 1 Overview of AccuTrack display graphic; flow schematic and status data.

The Day Ahead generation demands for utilities is a projection by the operating company using many

variables such as historical demand, weather, time of day, etc. Figure 2 is from Texas Market Nodal

implementation plan and describes the emerging Day Ahead market forecast. The qualifying generation

suppliers in this zone will bid to proDt(generating plants) in the zone. The system Day Ahead demand will vary seasonally and market

participants might take advantage of off-system sales opportunities or lower demand periods to

postpone or expedite planned maintenance activities as appropriate. Power plants project their

generation capabilities to the owners who in turn bid the production into the regional market. The plant

commitment is based on the equipment conditions at the time and the fuel quality/economics that will

be available to operate at the demand loads.


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Figure 2 Matching Coal Quality to ERCOT Day Ahead Market Demands

AccuTrackTM advises the plant operating staff of the fuel quality available in the As Received System to

manufacture fuel matching targets of the day ahead market peaks, then tracks through the blending

process to assure coal quality will match peak demand. Failure to match coal quality cascades through

the processes at full load as demand places stress first on pulverizers to grind the fuel to the proper size

distribution resulting in larger than desired particle sizing to the furnace, increased air flow required for

combustion, operating above design furnace exit gas temperatures and reheat temperatures, creating

slagging conditions in furnaces and additional sootblowing, increased demand on Limestone to FGD

scrubbers can exceed the design requirements causing an environmental derate of the unit.

Operating the units at full load with a coal quality that is below design is often possible for the short

term, but never desirable because it leads to future outages. Multiple days of high MW operation with

below design fuel may have a deleterious effect over time from high temperature corrosion as metal is

lost from furnace slag and continuous sootblower operation.

Utilities are increasingly looking to real time coal analyzers to identify the coal quality as received;

dh to make the coal acceptable for

full load.


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/dh

inadequate for the design of the equipment, the plant is charged with a derate. Managers, in order to

meet availability and reliability targets, must manage the fuel to the unit in a manner consistent with

Dt

When all of the fuel received by the plant does not meet the requirements either for Emissions or MWproduction at full load, it is a plant challenge to match the new fuels to the load and process equipment

demands, by gaining understanding of the coal quality impacts. If the plant has been receiving one

source of coal for its entire existence it is necessary for the staff to gain an understanding of the

potential impacts from the new sources. Often times this entails closer scrutiny, beyond the normally

supplied BTU/Ash/Sulfur/Volatile/Moisture quality usually provided with the original source.

AccuTrack facilitates the matching of the coal quality to demand in two interrelated systems known as

the As Received System, and the As-Fired System, using quality assurance manufacturing techniques to

match Coal Quality to Load Demand.

A fuel source example is Powder River Basin (PRB) coal that is attractive with its lower sulfur content

and easy mining methods (i.e., lower mine-mouth cost) compared with most eastern bituminous

sources. With enhanced rail and barge capabilities in place, PRB and similar plains states coals are widely

used in generation plants across the continental USA. Burning straight PRB, however, can limit unit

capabilities due to the low Btu/lb and consequent increased tonnage that must be processed. Of even

more consequence is the ash chemistry and combustion process that is critical to the slagging/fouling

vulnerability of the boiler. If properties and constituents such as Base-Acid ratios (a property used to

determine slagging tendencies) are not fully understood, forced outages or derates due to slagging, tube

leaks from erosion/ash corrosion, opacity upsets and/or emission constraints are to be expected. The

PRB low sulfur content might be utilized in a tailored fuel blend with a high BTU coal to achieve a full

load fuel/boiler capacity with compliance sulfur criterion. All other blended fuel properties calculated

must be available to the fuel management personnel and unit operator the designed mission

capability of AccuTrack.

Plant management must make routine, prudent decisions as the fuel is being unloaded in the As

Received area of the plant to adjust fuel quality to projected requirements, by blending from

appropriate storage piles if necessary. AccuTrack Unloading Advisory is ready to identify and source

quality blending solutions and loading times commensurate with the identified demand projections and

through continuous monitoring of the performance recommend adjustment through computerized

algorithms to change the blend for equally effective but less costly solutions at lower demand periods.


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As-Received System_______________________________________________________________

The plant staff is responsible to operate and maintain all fuel process equipment including fuel

analyzers, stackers/reclaimers, conveyors, scales, crushers, pulverizers, furnaces, instruments, and

environmental control systems. Management of the fuel conversion processes according to optimized

criteria is the key to meeting performance targets.

The AccuTrack unload advisor assists the plant staff from receipt through consumption, or from As-

Received to As Fired. The advisor software maintains segregated fuel storage data within the Yard

handling area by quality and quantity. Fuel being received but not meeting current loading criteria must

either be blended or directed to its appropriate storage area for future use. Fuel matched to current

loading quality characteristics can bypass yard storage and proceed direct to unit silo.


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Figure 3 Coal segregated by quality within fuel processing area

The tasks addressed on receipt of the coal with the patented AccuTrack System include:

1. Measuring quality with real-time coal quality analyzers,2. Directing the fuel to the proper area (storage, blending station or direct to bunker,3. Tracking fuel analysis and quantity by source and destination,

For the purpose of illustration, figure 3 above depicts three typical categories of fuel qualities:

Performance (higher quality but higher cost), Mid-range and Value Fuel (lower quality but low

$/MMBtu). The Performance fuel is high quality fuel that enables peak capacity from the boiler without

vulnerability to derates (e.g.; slagging). High Value fuel is used to produce low cost megawatts, typically

at lower demand periods to correspond to time dependant economic dispatch. At lower loads, furnaces

might operate at lower temperatures as less demanding boiler conditions making the High Value fuel

the economic imperative. Figure 4 is a typical summary display of the plant fuel inventory.


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Figure 4 AccuTrack Inventory Tracking Display.

As Fired System________________________________________________________________________

The As-Fired system is defined as the point where modification to the fuel is essentially no longer

feasible. Fuel loaded to the bunker or silo is committed and must be burn ready. AccuTrack modeling

captures the limited blending that takes place depending on the loading profile within the bunker, the

geometry and the flow rate to the pulverizer as described in the following pages.

Large utility boilers are equipped with fuel bunkers or silos of various capacities and designs. It is critical

to understand the complex coal flows through these short-term storage structures, the storage

capacities typically ranging in from 4 hours to 24 hours. Figure 5 shows individual silos with their

respective projected fuel characteristics based on the current bunker inventory and the programmed

fuel consumption forecast. This intricate model is a critical element of the AccuTrack technology and is a

stochastic flow calculation with several characteristics inputs unique to the fuel geometry and analysis.

Other bunker flow modeling is available but virtually all are severely handicapped by processing time, an

attribute making them useless in a real-time demand scenario.


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Figure 5. AccuTrack Bunker Flow modeling with combustion property projections.


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Figure 5. AccuTrack modeling of Funnel Flow and Plug Flow conditions.

The modeling of fuel flow in silos or bunkers is critical to the time-dependant match of boiler coal quality

delivery to the economic load demand. Managing the flow through the silos as is done in the AccuTrack

technology involves the understanding of many factors including the structure geometry, particle

characteristics, existing content profile and loading/extraction rates.


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Figure 6 Bunker as seen in Operator As-Fired Advisory screen grid

Calculations are graphically presented to plant operators through Advisory Screen grids within the

AccuTrack Software. Figure 7 displays a bunker feed to four pulverizers that has been loaded

with three different fuels with their respective qualities represented by yellow, green and orange.Pointing at any area of the grid provides a pop-up screen identifying the coal source, and other relevant

data indicated below:


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Continuous monitoring through the bunker flow model is available is performed by the AccuTrack

Software as the fuel flow proceeds through the pulverizers and then to the boiler. Details of the

modeling within the coal bunkers is described in previous pages for the fuel loaded at all times up to the

point of delivery to the furnace.

AccuTrack for Performance______________________________________________________________

Figure 7 Operator Advisory Screen alerts

The color coded screen uses a stoplight based formula to advice operators of projected coal and

associated combustion characteristics. Operators can d regarding

appropriate response to advisory or alarm. This unit specific advice is based on field proven calculations

as well as heuristic experience on the units past performance. The NOW column in the table of figure

8 is showing the current fuel exiting the silo and associated combustion properties. Correspondingly, the

past 8 hours in 2 hour intervals is displayed on the left and similar 8- hour projections are on the right.

GREEN indicates a match of coal quality to current load demand, of full load, YELLOW is a caution

indication, and RED is a high risk situation recommended for appropriate operator attention. A sampleof a combustion / slagging reference material incorporated into the AccuTrack software is shown in

figure 9 below.


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Figure 8 Hensel-Halfinger boiler cleanliness predictor

COAL QUALITY ISSUES END WHEN THE PLANT

ACHIEVES ALL TARGETED PERFORMANCE

GOALS

Coal quality Impacts-FinalJan_2010.pdf

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