The 37th International Technical Conference on Clean Coal & Fuel Systems, Clearwater, Florida, USA June 3-7, 2012

USE OF CFD MODELING IN DESIGNING ADVANCED NOX CONTROL TECHNOLOGY FOR

UTILITY BOILERS

Guisu Liu1, Baiyun Gong

1, Brian Higgins

1, Muhammad Sami

2

1Nalco Mobotec Inc., 1601 W. Diehl Road, Naperville, IL 60563 2ANSYS Inc., 1007 Church St., Suite 250, Evanston, IL 60201

ABSTRACT

In this paper, a 350 MW tangential coal-fired utility boiler in China was studied using ANSYS FLUENT

Computational Fluid Dynamics (CFD) code to evaluate the application of Nalco Mobotec advanced

ROFA® system for NOx reduction. The simulations showed that ROFA, which delivers a large amount of

air up to the upper furnace, significantly reduces the NOx through deep staging. Due to enhanced

turbulent mixing, CO and LOI are rapidly burned out in the upper furnace. Heat transfer becomes stronger

than the baseline case due to mixing. An overall 50%-60% NOx reduction is achieved during

performance test. The boiler efficiency has been slightly increased by 0.38%. All these results are the

consequence of strong mixing from ROFA system. These results have been validated against the

performance testing results in great detail.

INTRODUCTION

China’s rapid economic growth has led to concerns about environmental protection. The state utilities are

facing more aggressive and stringent regulations for SO2, NOx and particulate matter. In accordance with

the new regulations of China State Environmental Protection Administration come into effect on January

1, 2012, the coal-fired boilers have to meet the stringent NOx emissions requirements by January 1, 2014.

Therefore, there is an urgent task for the power plants to employ advanced NOx reduction technologies.

Existing NOx reduction technologies are typically classified into three categories: low NOx combustion

technologies (e.g. Low-NOx Burner, Over-Fired Air, etc), selective non-catalytic reduction (SNCR), and

selective catalytic reduction (SCR) technology. In all these technologies, low NOx combustion

technologies are low capital cost, and are preferred to be installed in all units.

The Nalco Mobotec advanced ROFA® system is a deep-stage combustion technology to reduce NOx

emissions. Meanwhile, the high-speed ROFA air can increase the upper furnace mixing to burn out CO

and LOI to improve combustion performance. The ROFA system air flow, air pressure and nozzle

position are designed and optimized through CFD simulation to achieve the best NOx reduction

performance and combustion performance1,2,3,4

. ROFA was selected to be implemented on a 350 MW

tangential coal-fired utility boiler in China.

1 Liu, G., et al., “CFD Evaluation of ROFA on Limestone Utilization in a Circulating Fluidized Bed”, CIBO Conference, April 2005 2 Higgins, B., et al., “Evaluation of ROFA and Sorbent Injection on NOx and SOx Reduction at Hoosier Energy’s Frank E. Ratts Unit 1”, Coal-

Gen, August 20, 2009 3 Higgins, B., Gong, B., Pozzobon, E., Liu, G., “ROFA and Rotamix Systems Reduced NOx below 200 mg/Nm3 at Elektrownia Opole”, the 35th

International Clean Coal Conference, Clearwater, Florida, June 6-10, 2010 4 Gong, B., Liu, G., Higgins, B., Williamson, T., et al., “CFD-based Design and Installation of Cost-effective ROFA/Rotamix System for NOx

Reduction at RPU Silver Lake Unit 4”, ”, the 35th International Clean Coal Conference, Clearwater, Clearwater, Florida, June 6-10, 2010

In this paper, the details of the project are presented. First, the technology is evaluated through a

Computational Fluid Dynamic (CFD) modeling. The actual performance of ROFA system is also

presented to validate the model predictions.

BOILER INFORMATION

The boiler is a Japanese Mitsubishi company's 1160 t/h subcritical reheat forced circulation furnace built

in 1998. The unit main parameters are as follows: unit capacity: 350MW, main steam flow: 1210 t/h,

main steam temperature: 541℃, main steam pressure: 17.5Mpa, flue gas volume 1,200,000-1,600,00

Nm3/h, exhaust gas temperature: 130-200℃. The boiler is equipped with three induced fans, flue gas

exhausts into the atmosphere through the 200-meter-hige chimney.

The design coal is Shenfu Dongsheng coal, the check coal is Datong coal; The unit usually fires a blended

coal. Blast furnace gas (BFG) and coke oven gas (COG) are often fired as auxiliary fuel. Under normal

circumstances, the amount of blast furnace gas is about 100-200 kNm3/h, and in extreme case the BFG

co-firing capacity is of 350kNm3/h. The baseline NOx is in a wide range of 400-900 mg/Nm

3 with an

average of 650 mg/Nm3. NOx level is lower when co-firing blast furnace gas, and it becomes high when

100% coal firing.

ROFA SYSTEM DESIGN

The ROFA system was installed to reduce NOx through furnace staging. In the meantime, the ROFA

system was designed to increase mixing in the upper furnace for CO and LOI burnout. As shows in Fig. 1,

a ROFA system includes a boosted-pressure ROFA fan, interconnecting air ducting, and air injection

nozzles. The ROFA air is taken from ducts at the outlet of the air preheaters. It is boosted in pressure by

the ROFA fan and delivered through specially located nozzles into the furnace. The air pressure at the

nozzles is optimized as required to achieve mixing as determined during the CFD modeling. All air flow

to the ROFA nozzles is controlled based on a relationship to boiler steam flow to maintain tuned box

pressures as load changes. Additionally, feed-forward and feed-back control strategies can be

implemented to reduce system upsets during load fluctuations.

The ROFA system consists of a variable frequency drive (VFD) controlled centrifugal ROFA fan. The

ROFA fan takes air through an individual duct from the outlet of the air preheater. Each duct has a venturi

flow meter to allow the boiler control system to account for air flow through the ROFA system.

Figure 1: ROFA system design

Extensive on-site investigations were carried out to determine the most efficient and cost effective way to

redirect secondary air to the upper furnace ROFA ports. The ROFA air suction and discharge duct routing

was meticulously engineered as the existing boiler and building structure contained significant duct path

interferences particularly adjacent to the furnace walls.

CFD MODELING

Combustion Model Overview

ANSYS FLUENT has been selected as the CFD code for this project because it is likely the best

commercially available CFD package. Grids (or meshes) used in the CFD simulations are first

constructed using FLUENT’s companion software, GAMBIT. FLUENT then solves for the density,

velocity, temperature, and species (including coal volatiles) concentrations fields of the gas phase and

coal particle properties and combustion within the furnace to steady state. The gas phase conservation

equations are solved using a variable density, quasi-incompressible formulation embedded in an Eulerian

reference frame. These governing equations are the gas phase continuity, momentum, turbulent kinetic

energy, turbulent dissipation, enthalpy, and the species conservation equations for each gas species in the

turbulent combustion model. These conservation laws have been described and formulated extensively in

standard CFD textbooks. A k-ε turbulence model was implemented in our simulations. Standard Eddy-

Breakup (EBU) turbulence combustion model is used. The following two step mechanism was utilized for

coal combustion:

Coal + a O2 → b CO + c CO2 + d H2O + e SO2

CO + 0.5 O2 → CO2

where the stoichiometric coefficients (a, b, c, d, and e) were determined from the fuel proximate and

ultimate analyses. For lower temperatures found in the back-pass, a modification to the carbon monoxide

reaction is also included to more accurately predict CO concentration.

Coal is injected through the burners by specifying a Rosin-Rammler particle size distribution and a

particle velocity slightly less than the gas phase velocity within the primary injectors. Parameters for this

distribution are derived from sieve data collected onsite. Gas phase air flow rates are specified at the

primary, fuel air, auxiliary air and CCOFA, and ROFA ports using appropriate inlet velocities,

temperatures, turbulence intensities.

The CFD model solves the particle/liquid phase (coal, limestone, water/urea, etc.) in a Langrangian

reference frame. The gas phase and particle phase conservation equations are solved separately by

FLUENT in order to make the computation more tractable; however, these two phases are strongly

coupled through iterative updates of the source terms that occur less often than the iterative updates of the

gas phase variables. Particle motion is obtained through solutions of the bulk gas velocity. Turbulent

dispersion of particles was modeled using the stochastic discrete-particle approach.

The CFD model uses different expressions for particle heating and reaction at each stage of the process.

An inert heating law applies when particle temperature is less than the onset temperature for

devolatilization. Particle heating is caused by convective heat transfer from the gas phase and the radiant

flux from the furnace. During devolatilization and char oxidation, the particle energy balance also

includes a heat of devolatilization and heat of combustion, in addition to the convective and radiative heat

transfer rates. Both diffusion and intrinsic kinetics were included in the char oxidation sub-model.

FLUENT NOx submodel involves sophisticated fuel-N conversion pathways. After fuel devolatilization,

fuel-N is partitioned into volatiles-N and char-N. HCN is the dominant nitrogen species in volatile-N

released from coal. Char-N is released into the gas phase at a rate that is proportional to the carbon

burnout rate. Because char-N conversion chemistry is complex, we used a fixed fraction of char-N

directly converted to NO with the rest of N converted to N2. This assumption is often used in literature5.

The gas phase NO can be reduced by CO, on the char surface, or through ammonia/urea injection.

Geometry

The CFD computational domain is shown in the left panel of Fig. 2, respectively. Coal is fed into the

furnace through rows of burners in each of four corners. Secondary air comes from the windbox, and the

flow is generally above, below, and between the coal pipes. The superheater and reheater pendants are

suspended above the nose, leaving the open radiant furnace free of any obstructions.

Figure 2: The CFD domain (left) of the furnace and surface mesh (right).

The furnace enclosure or CFD model domain for baseline and ROFA cases is defined as beginning at coal

burners and ending at the vertical plane right after the tertiary reheater (as shown in Fig. 2). The same

geometry was used for both baseline and ROFA cases; however, the baseline and ROFA cases were

distinguished by switching off and on the boundary conditions for ROFA ports. The waterwall, and all

superheat and reheater pendants are included in the model to account for heat absorption and flow

stratification, and are accurately depicted with equivalent surface areas of each of the sections. The burner

geometry including primary air flow and secondary air flow was well represented in the model.

An isometric view of the furnace surface mesh is shown in the right panel of Fig. 2. This furnace is

represented by about 1,440,000 computational cells. Most of the cells are unstructured, hybrid, hexahedral

cells. This large number of computational cells is adequate to resolve the most relevant features of the

three-dimensional combustion process. The grid size is relatively uniform over the entire domain, except

the burner region. Because the near-burner zone combustion is complex and important, an extra care was

taken when burner zone was meshed, and the burner zone is subject to much finer mesh.

5

Niksa, S., and Liu, G.-S., “Incorporating detailed reaction mechanisms into simulations of coal-nitrogen

conversion in p.f. flames”, Fuel 81(18), pp. 2371-2385 (2002)

Model Inputs

Key inputs for the furnace CFD baseline simulations at full load (350 MW) are listed in Table 1. The coal

proximate and ultimate analysis, fineness are listed in Table 2. Coal flow for full load were provided in

the performance data during testing, and the firing rate (i.e. total heat input) for both cases are calculated

based on the fuel flow and the fuel high heating values. The exit O2 for two cases were also taken from

the performance data during testing and the total air flow (TAF) was calculated based on the

stoichiometric (S.R.) analysis with given fuel flow and exit O2.

Table 1: Baseline System Operating Conditions

Thermal Firing Rate [MWt] 917.0

Load [MWe gross] 350

Excess Air [%] 22

Excess O2 [% dry] 3.84

Excess O2 [% wet] 3.50

Coal Flow [t/h] 138.1

Total Air Flow [t/h] 1322.9

Table 2: Coal Analysis and Fineness

Proximate Analysis

Volatiles Matter [wt % ar] 27.33

Fixed Carbon [wt % ar] 47.67

Moisture [wt % ar] 14.0

Ash [wt % ar] 11.0

HHV [kJ/kg] 23919

Ultimate analysis

C [wt % ar] 60.33

H [wt % ar] 3.62

O [wt % ar] 9.94

N [wt % ar] 0.70

S [wt % ar] 0.41

Fineness

< 297 µm (50 mesh) [wt %] 100

< 149 µm (100 mesh) [wt %] 99.5

< 74 µm (200 mesh) [wt %] 85

Modeling Results

Baseline Validation

The baseline model results are compared with the testing data in Fig. 3. The testing was conducted at nose

elevation for full load 350 MW and mid load 260 MW. Only the full load data is compared here. The x-

axis of the plots in Fig. 3 represents the testing port locations from A at left wall, A1 through A6 on front

wall and B on right side wall. All testing ports are located around nose elevation. There were two

temperature measurements obtained during testing: one by thermocouple at the tip of the HVT probe and

the other by a portable infra-view pyrometer, which measures the maximum and minimum temperatures

around the view port region. Modeled gas temperature, O2, CO and NOx at furnace exit (F.E.) are also

included in the plot. In this case, the furnace exit is between tertiary superheater pendants and second

reheater pendants. No HVT measurements were taken at furnace exit location due to lack of accessible

viewports. Overall, modeling results are in good agreement with the testing data.

In Table 3, the CFD modeled FEGT is almost exactly the same as the OEM design value of 1317 K,

indicating that the heat distribution feature in the furnace and backpass in the model is well captured.

CFD modeled O2 and NOx data at the furnace outlet is also in good agreement with the tested emission

data at the stack for furnace outlet comparison.

Figure 3. Comparison of temperature, O2, CO and NOx between testing and CFD modeling

Comparison at Furnace Exit and Model Outlet

The baseline model results are compared with other data in this section. Two locations are compared. One

is the furnace exit which is typically defined as the vertical plane in between radiant and convective

section of steam tubes. In this case, the furnace exit is between tertiary superheater pendants and second

reheater pendants. The other location is the furnace outlet in CFD which is immediately after the tertiary

reheater pendants. No HVT measurements were taken in these locations due to lack of accessible

viewports. Instead, we used the furnace exit temperature in a design document for furnace exit

comparison and the tested emission data at the stack for furnace outlet comparison.

In Table 3, the OEM design document indicated that at full load the furnace exit gas temperature (FEGT)

is 1317 K. The CFD modeled FEGT are almost exactly the same, indicating that the heat distribution in

the furnace and backpass in the model. CFD modeled O2 and NOx data at the furnace outlet is also in

good agreement with the reported data.

The following conclusions can be drawn from the comparisons.

• CO decreased from baseline to ROFA. As discussed later, even though in the lower furnace a large

amount of CO is formed, it is burnt away rapidly and results in even lower CO at the exit in ROFA

cases. Upper furnace combustion is greatly improved by high turbulent ROFA jets.

• The furnace exit gas temperature decreased about 25°C from baseline to ROFA case. The heat transfer

rate however increased slightly from baseline to ROFA case. This indicates that the heat transfer in

ROFA case is stronger than that in baseline case due to the high turbulence induced by high velocity

ROFA jets and better use of the furnace volume.

• The outlet NOx concentration reduced 56% from baseline, due to air staging.

• LOI also went down in the ROFA case.

Table 3: Comparisons of results between baseline and ROFA case

Baseline Testing CFD Baseline CFD ROFA

Fur. Exit

O2 [%] 3.8 3.8

H2O [%] 7.3 7.3

CO [ppm] 122 129

CO2 [%] 14.1 14.1

Temp [K] 1317 1320 1296

NO [ppm] 323 141

Outlet

O2 [%] 3.5 3.7 3.7

H2O [%] 7.3 7.3

CO ppm [ppm] 58 39

CO2 [%] 14.1 14.1

Temp [K] 1109 1091

NOx [ppm] 307 324 141

NOx Red. [%] - 56

LOI [%] 2.7 1.1

Temperature Distribution

The temperature distributions for seven horizontal planes are shown in Fig. 4. These figures show that the

majority of the combustion occurs in the region well below the nose. In fact, by the ROFA level the

majority of the coal is combusted, though high CO levels still need to be burned out. The maximum flame

temperature in the baseline furnace is about 2100 K. This is also true for the ROFA case but the

temperature is more evenly distributed through the lower furnace as the mass flow in the lower furnace is

approximately 30% less. The temperature distribution also shows that coal ignites soon after being

injected into the furnace. As can been seen from looking into the furnace (and from the control room

furnace camera), the flames are not attached to the coal nozzles (as is usual for T-fired boiler). Fig. 2 and

later illustrations also show how the ROFA jets penetrate deep into the flue gas cross flow.

O2 Distribution

The O2 distribution in the furnace in the left panel of Fig. 5 shows high O2 in the near-wall region of the

furnace that does not quickly mix with the combustion products until well after the nose. These O2

inhomogeneities persist well into the upper furnace. For the ROFA case, the lower furnace is clearly

staged sub-stoichiometrically. This is, of course, the mechanism for NOx reduction. The key to efficient

NOx reduction is the ability to stage sub-stoichiometrically and still burn out the CO before exiting the

furnace. CO burnout requires an evenly mixed O2 concentration in the ROFA case. The O2 at furnace

outlet is more evenly distributed in the ROFA case than in the baseline case, as evidenced in Fig. 6.

Figure 4. Gas temperature of baseline and ROFA. Figure 5. O2 distribution of baseline and ROFA.

CO Distribution

CO is the primary intermediate species during the oxidation of coal. In general, all of the coal carbon that

eventually burns must first be partially oxidized to CO before further oxidized to CO2. In fact, half of the

heat release from combustion occurs during this CO to CO2 oxidation. Therefore CO is as important as O2

to characterize the combustion in furnace. In Fig. 7, the CO is formed but burnt progressively as the flow

moves upwards to the upper furnace in the baseline. Clearly there is much more CO in the ROFA case

below the nose. This is again a desirable effect of staging. The key is to burn it all out before leaving the

furnace. The deep penetration by the ROFA jets is seen to quickly react with CO. Not all the CO is

burned in the model before it exits. Stack CO with ROFA is typically below 20 ppm, and we expect this

to be the case after ROFA is installed in this unit.

Figure 6. Furnace outlet O2 distribution of (left) baseline and (right) ROFA.

NOx Distribution

The CFD analysis can calculate NOx reduction using the chemistry described above. While each coal and

boiler geometry leads to different NOx generation, the fundamentals remain the same. The baseline NOx

model parameters were adjusted within normal ranges to model the measured base case NOx rates and

then these model parameters were fixed when the ROFA case was modeled.

The NOx results of baseline and ROFA are compared in Fig. 8. Clearly the ROFA case shows reduced

NOx. Importantly, the NOx reduction comes directly from affecting the conversion of the fuel-bound

nitrogen. In a staged environment, HCN comes off the coal and preferentially reduces to N2, where in the

baseline case much of the HCN forms NOx. This is particularly evident in the horizontal plane between

the ROFA nozzles and the burners, where the NOx concentrations for the ROFA case are clearly lower

across the entire horizontal plane. Due to air staging of ROFA, the lower furnace is overall reducing. As a

result, the NO concentration is dramatically lower in the entire furnace as shown in the right panel of Fig.

8. Even with the secondary combustion after injection of ROFA air, NO is not increased significantly.

Figure 7. CO distribution of baseline and ROFA. Figure 8. NO distribution of baseline and ROFA.

Turbulent Kinetic Energy

One of the two variables in the turbulence model - kinetic energy is plotted in Fig. 9. Coal combustion is

“mixing limited”. That is, in the open furnace, it is the mixing of the fuel and air that limits the progress

of combustion. Once mixed, combustion occurs quickly at high temperatures. Turbulence is a very

instructive method of gauging mixing. As a fluid body moves, turbulence dissipates through mixing.

Large eddies break into smaller eddies and the smaller eddies break into many more smaller eddies. Each

eddy functions to mix unburned carbon or CO with O2. In Fig. 9, it is obvious that there is significant

kinetic energy in the burner zone in both baseline and ROFA case, but once the coal leaves the burner

zone in the baseline case there is nothing left to continue the mixing. The one exception to this is the nose,

which is why the nose is so important in boiler designs. In the ROFA case, there are not only high levels

of kinetic energy in the upper furnace, but it is clear that the turbulence is dissipated throughout the upper

furnace.

Upper Furnace Temperature Distribution

For tangentially fired boiler, furnace outlet steam temperature is usually biased, this problem is universal.

This is due to the reason of the fluid in one direction of rotation. Overheating discipline and reheater tubes

serious temperature deviation will increase the thermal stress of the pipe and gradually make the tubes

leak, eventually had to replace the pipe. Frequent replacement of the steam pipe cost is expensive.

Figure 9. Kinetic energy of baseline and ROFA.

In ROFA the design, the introduction of air to the upper part of the furnace again can effectively solve this

problem. Figure 10 shows the upper furnace temperature distribution of before and after ROFA. In the

boiler right side of the wall and two and three overheating near region, compared with the early-mode

model, the entire furnace within the flue gas temperature distribution is more uniform. The flue gas

temperature cannot be a good adjustment, but such a comparison also shows that, of ROFA the flexible

design for this problem. A large number of on-site commissioning according to customer needs, so as to

solve the corresponding problem

Figure 10. Upper furnace temperature distribution of baseline and ROFA.

FIELD PERFORMANCE

The entire ROFA installation includes ROFA fan, the air duct, boiler water wall openings, ROFA air

dampers, and control system. The installation took approximately 3-4 months. ROFA air duct installation

is difficult, mainly due to the transformation of the old units, insufficient space on-site construction, and

the larger ROFA duct size. During the unit outage, the boiler water wall openings, ROFA dampers, and

the connection between air duct and dampers were installed. Special attention was paid to the boiler

thermal expansion installation.

Turbulent mixing of the high-speed ROFA airflow enhanced the upper furnace combustion; as a result the

boiler system can be operated in a relatively low oxygen conditions. The original O2 curve was then

corrected. Figure 11 shows the O2 curves before and after ROFA in service. Over the entire range of

steam load, the O2 is reduced by 0.5%-1.5%, due to improved combustion by ROFA. This reduction of O2

has resulted in the increase of thermal efficiency by 0.38%.

Figure 11. The furnace O2 operating curves of baseline and ROFA.

Furnace flue gas temperatures were measured through the front wall viewport (right above nose elevation)

using infra-view pyrometer. Table 4 shows the temperature measurements between ROFA on and off

conditions. The average furnace temperature reduced about 12°C when ROFA is in service. CFD model

predicted the flue gas temperature reduced by 25°C. While there is some discrepancy between prediction

and actual performance, the qualitative trend is consistent. The reduction on flue gas temperature is

caused by enhanced heat transfer due to strong mixing by ROFA air jets.

The ROFA fan is turned on, the NOx concentration decreased significantly, as can be seen from Figs. 12

and 13. When the ROFA air increased from 70 t/h to 380 t/h, the NOx concentration reduced from 680

mg/Nm3 to 300 mg/Nm3. When the ROFA air flow reduced from 380 t/h to 60 t/h, NOx increased from

about 300 mg/Nm3 to 600 mg/Nm

3. In general, ROFA system reduced NOx by 50% to 60% based on

various operating conditions. Similar level of NOx reduction was achieved when co-burning BFG and

COG gas. This is in good agreement with CFD predictions.

The boiler fly ash LOI increased slightly, but remained to below 4.0% limit. The increase of LOI is

thought to be due to lowered O2 from baseline to ROFA case. The CO content measured at the inlet of the

air preheater reduced from about 22 ppm to 2ppm when ROFA is in service. This is consistent with CFD

prediction in Table 3.

Superheater steam temperature deviation from left to right is a common operational problem. Due to

enhanced mixing through ROFA box setting, ROFA improved the steam temperature deviation by

reducing from 20°C to 10°C.

Table 4: Comparisons of Measured Upper Furnace Temperatures

Figure 12. NOx change when ROFA is tuned on. Figure 13. NOx change when ROFA is tuned off.

CONCLUSIONS

A ROFA system has been designed and installed on a 350-MWe tangential coal-fired boiler to reduce

NOx emission. Over 50% NOx reduction was achieved and NOx level remained at or below 300 mg/Nm3

when ROFA is in service. The combustion was improved by reduced CO and reduced furnace O2, and the

boiler efficiency increased by 0.38%. Due to enhanced mixing in upper furnace, the flue gas temperature

became much more uniform with less potential to form slagging at the bottom of superheater platens.6

Nalco and the logo are Registered Trademarks of Nalco Company.

Nalco Mobotec and the logo are Registered Trademarks of Nalco Mobotec, Inc.

Ecolab is a trademark of Ecolab USA Inc.

ROFA and Rotamix are Trademarks of Mobotec AB, used with permission.

© 2012 Ecolab USA Inc. All Rights Reserved.

Condition Infra-view Temperatures Measured Through Front Wall Viewports

F1 F2 F3 F4 F5 F6

ROFA

Out of

Service

Run1 1176 1204 1315 1319 1287 1154

Run2 1209 1256 1338 1333 1226 1129

Run3 1237 1247 1365 1348 1348 1166

Mean 1259

Standard

Deviation 209

ROFA In

service

Run1 1182 1196 1261 1322 1328 1211

Run2 1206 1241 1242 1260 1298 1179

Run3 1206 1223 1292 1307 1312 1186

Mean 1247

Standard

Deviation 146