METHODOLOGY, ASSUMPTIONS, AND REFERENCES

PRELIMINARY NOx CONTROLS COST ESTIMATES

FOR

INDUSTRIAL BOILERS

By Sikander Khan 

Environmental Engineer, U.S. EPA 

 

OCTOBER-NOVEMBER 2003 
Preliminary NOx Controls Cost Estimates 

2

PRELIMINARY COST ESTIMATES FOR NOx CONTROLS

INDUSTRIAL BOILERS

1.0 METHODOLOGY

The cost estimates covered in this report were developed as part of the investigations 

conducted for the proposed Interstate Air Quality Rule (IAQR) for industrial boilers. 

These costs are preliminary and are being reviewed further by the EPA. 

The costs were developed for three boiler sizes, with heat inputs of 100, 250, and 1,000 

MMBtu/hr. The following NOx control technologies were included in these estimates for 

coal-, natural gas-, and oil-fired boilers (except as noted below): 

Low-NOx burner (LNB) 

Overfire air (OFA) 

Gas recirculation (GR) (only for gas- and oil-fired boilers) 

SCR 

SNCR 

It is to be noted that the purpose of this evaluation was to develop cost information for a 

large range of industrial boiler sizes and associated NOx control technologies. The 

decision on the use of this information in the proposed IAQR will be made as part of the 

Rule itself. 

The methodology can be divided into two major activities: 1) Developing design basis for 

each NOx control system and determining its operating impacts on the boiler 

performance and 2) determining capital and operating costs associated with retrofitting 

the NOx control system. These two activities, along with the associated assumptions and 

references, are described below. 

2.0 DESIGN BASIS AND PERFORMANCE IMPACTS

Combustion and boiler efficiency calculations were performed using standard 

procedures(1,2), for the three boiler sizes of 100, 250, and 1,000 MMBtu/hr. Tables 1 and 

2 summarize the key data determined from these calculations for the three boilers firing 

coal, oil, and gas. In addition, the average uncontrolled, baseline NOx levels for these 

boilers were established as follows (see Attachments 1 and 2): 

1. Coal-fired boilers (bituminous and sub-bituminous coals): 0.72 lb/MMBtu 

2. Gas-fired boilers: 0.25 lb/MMBtu 

3. Oil-fired boilers: 0.22 lb/MMBtu 

The above NOx levels are mainly based on the ICI database. Based on a further 

clarification provided by ICF(3), the NOx levels provided in Attachment 1 for oil firing do 
Preliminary NOx Controls Cost Estimates 

3

 not represent the maximum levels reported in the ICI database. Therefore, the costs 

were calculated for two additional baseline NOx levels of 0.36 and 0.5 lb/MMBtu. ICF 

indicated that these costs would be applied selectively to the oil-fired boilers with the 

reported baseline levels around these two high values. 

The above information was used to determine the NOx reduction levels and the boiler 

performance impacts, as described below separately for each type of control technology: 

2.1 LNB, OFA, and GR 

The NOx reduction levels achievable with LNB, OFA, and GR technologies for different 

fuels are summarized in Table 3, along with the supporting references. The following 

assumptions and criteria were used to establish the impacts of these technologies on the 

plant performance: 

1. With the use of OFA on coal firing, the unburned carbon level at the boiler outlet 

increases by 50 percent. This increase in the unburned carbon level reduces the boiler 

efficiency and results in an increased coal consumption and auxiliary power 

consumption associated with the draft fans. 

2. The GR systems for the gas- and oil-fired boilers are designed for a recirculation rate 

of 20 percent. For full-load operation, a gas recirculation rate of 15 percent is used to 

estimate the fan power consumption requirement. 

3. LNB and OFA do not result in a change in the gas- and oil-fired boiler efficiencies. 

In general, the gas recirculation does not have a substantial impact on the heat 

transfer within the boiler and the original steam temperatures can be maintained. It is 

recognized that some boiler would require modification of the heating surfaces for 

these temperatures. 

The plant performance impacts associated with the use of LNB, OFA, and GR are 

summarized in Table 4. These impacts were used for the estimation of operating 

resulting from the use of these technologies. 

2.2 SCR 

The SCR technology is considered applicable to all three fuel (coal, gas, and oil) 

applications. A conservative NOx reduction effectiveness of 80 percent was selected for 

this estimating effort. The following assumptions and criteria were used to establish the 

SCR design parameters and the impacts on the plant performance: 

1. The methodology described in Attachment 5 was used to estimate the catalyst 

volumes for various boiler applications. The space velocities (1/hr) used were 3,750 

for coal, 16,800 for gas, and 11,800 for oil. The ammonia slip levels used were 5 

ppm for coal and oil and 10 ppm for gas. 
Preliminary NOx Controls Cost Estimates 

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2. The reagent was assumed to be anhydrous ammonia with electrical heating for 

vaporization. 

3. The pressure drop through the SCR reactor and additional ductwork was assumed to 

be 6 in. wt. 

4. Catalyst replacement requirement was based on a very conservative assumption of 

1/3rd of the catalyst being replaced every year. There is substantial industry 

information available that the average catalyst life span, especially with catalyst 

management schemes, is substantially more than the 3 years assumed for these 

estimates (see Attachment 6). 

The above assumptions were used to determine the impacts of the use of SCR on plant 

performance, which are summarized in Table 5. 

2.3 SNCR 

The cost estimates have been developed for SNCR systems for all three fuel applications. 

However, it is recognized that SNCR technology may not, in general, be effective for 

small, shop-assembled gas- and oil-fired boilers (the physical constraints associated with 

such boilers may not permit proper location of the SNCR reagent injection nozzles). 

The SNCR system design and boiler performance impacts have been estimated, based on 

the methodology provided in an EPRI report(4). Additional assumptions and criteria used 

are as follows: 

1. A NOx reduction effectiveness of 40 percent was used for all boiler cases. 

Attachment 7 lists information on many SNCR installations, especially for the smaller 

boiler sizes, which supports the 40 percent effectiveness level selected for this study. 

2. The reagent was assumed to be urea. 

3. Because of the injection of water within the boiler, as part of the SNCR process, there 

will be a reduction in boiler efficiency. This reduction will result in increased fuel 

consumption and ash generation, as applicable(4). 

Table 6 summarizes the plant performance impacts resulting from the use of SNCR. 

3.0 CAPITAL AND LEVELIZED COSTS

The capital costs ($/MMBtu/hr) for the application of the NOx control technologies for 

various boiler sizes included in this evaluation were based on recent industry data(5) and 

Attachments 3 and 5. In general, these costs were identified for one boiler size and then 

scaling factors were used to project these costs for other boiler sizes. The costs are based 

on 1999 dollars. 
Preliminary NOx Controls Cost Estimates 

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The levelized costs ($/ton of NOx removed) were calculated using the estimates of the 

capital costs and increased consumable rates associated with each technology, as shown 

in Tables 4 through 7. The economic factors used in these calculations(5-9) were as 

follows: 

Anhydrous ammonia, $/ton 260 

Urea, $/gal 0.95 

Water, $/gal 0.0006 

Bituminous coal, $/MMBtu 1.45 

Sub-bituminous coal, $/MMBtu 1.20 

Oil, $/MMBtu 3.5 

Gas, $/MMBtu 5.0 

Power, mills/kwh 25.0 

Solid waste disposal, $/ton 12 

Operator cost, $/hr 30 

SCR catalyst, $/cu. ft. 396 

Useful life, years 30 

Carrying charges, % 12.00 

Levelization factor 1.0 

Maintenance cost (% of capital cost) 1.5 

A US Department of Commerce, Bureau of Economic Analysis(10), price index was used 

to adjust cost basis from one year to another. The levelized costs for various technology 

retrofits are presented in Table 8. 

3.1 Sensitivity Cases 

Two sensitivity cases were evaluated to see the effect of changes in the study 

assumptions on the technology costs: 1) increased cost of power from 25 mills/kwh to 50 

mills/kwh and 2) an increase of 25 percent in the SCR capital cost. Only a few retrofit 

options were evaluated to see the impact of these changes – the impact on other options 

will be similar. Table 9 presents the results. A comparison of Table 9 and corresponding 

values in Table 8 shows that: 

1. Increase in the cost of power has virtually no impact on the LNB/OFA option, since 

the increase in power consumption for this option is quite small. 

2. Increase in the cost of power has a relatively small impact on the SCR option. This 

impact ranges from approximately 0.8 to 6.8 percent of the total cost in $/ton of NOx 

removed. 

3. Increase in the capital cost of SCR results in an increase of approximately 13 to 19 

percent in the total cost in $/ton of NOx removed. It is to be noted that, with a 25 

percent increase in capital cost, the levelized cost remains around $2000 per ton of 

NOx removed for boilers 250 MMBtu/hr and larger, with a capacity factor of 50 

percent or higher. 
Preliminary NOx Controls Cost Estimates 

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5.0 REFERENCES 

1. “Steam Its Generation and Use,” Babcock and Wilcox, 40th Edition 

2. “Power Test Code – Steam Generating Units,” ASME PTC 4.1, 1991 

3. “Personal Call from S. Khan of EPA to B. Galef of ICF,” 9/29/03 

4. “SNCR Feasibility and Economic Evaluation Guidelines for Fossil-Fired 

Utility Boilers,” EPRI TR-103885, May 1994 

5. “Status Report on NOx Controls for Gas Turbines/Cement Kilns/Industrial 

Boilers/Internal Combustion Engines, Technologies & Cost Effectiveness,” 

NESCAUM, December 2000 

6. “Coal Utility Environmental Cost (CUECost) Workbook User’s Manual, 

Version 1.0,” EPA-600/R-99-056 (NTIS PB99-151938), June 1999 

7. “EPA Modeling Application Using The Integrated Planning Model,”, 

http://www.epa.gov/airmarkets/epa-ipm/index.html

8. “Annual Energy Review 2000,” DOE, http://www.eia.doe.gov/aer/aerpdf.html

9. “Electric Power Monthly September 2003,” DOE, 

http://www.eia.doe.gov/cneaf/electricity/epm/epm.pdf

10. “Implicit Price Deflator,” Table 7.3. Quantity and Price Indexes, 

http://www.bea.doc.gov/bea/dn/nipaweb/TableViewFixed.asp
Preliminary NOx Controls Cost Estimates 

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TABLE 1

COMBUSTION CALCULATIONS- COAL-FIRED BOILERS

Parameter Bituminous Coal Sub-Bituminous Coal 

Boiler –100 

MMBtu/hr 

Boiler –250 

MMBtu/hr

Boiler –

1000 

MMBtu/hr

Boiler –100 

MMBtu/hr

Boiler –250 

MMBtu/hr

Boiler –

1000 

MMBtu/hr

Fuel carbon, wt. % 67.94 67.94 67.94 42.22 42.22 42.22 

Fuel ash, wt. % 12.71 12.71 12.71 7.41 7.41 7.41 

Fuel sulfur, wt. % 3.43 3.43 3.43 0.73 0.73 0.73 

Fuel heating value, 

Btu/lb 

11922 11922 11922 7090 7090 7090 

Steam flow, lb/hr 86455 205750 822978 81680 194500 777500 

Steam temp., F 460 600 600 460 600 600 

Unburned carbon, % 0.5 0.5 0.5 0.5 0.5 0.5 

Stack gas temp., F 330 330 330 280 280 280 

Boiler efficiency, % 87.798 88.028 88.098 82.981 83.211 83.281 

Fuel use, lb/hr 8424 21005 83955 14160 35324 141086 

Flue gas temp. at 

boiler outlet, F 

685 685 685 650 650 650 

Flue gas from 

combustion, lb/hr 

99,500 248,130 991,730 104,810 261,200 1.101,660 

TABLE 2

COMBUSTION CALCULATIONS- GAS- & OIL-RED BOILERS

Parameter Natural Gas Oil 

Boiler –100 

MMBtu/hr 

Boiler –250 

MMBtu/hr

Boiler –

1000 

MMBtu/hr

Boiler –100 

MMBtu/hr

Boiler –250 

MMBtu/hr

Boiler –

1000 

MMBtu/hr

Fuel ash, wt. % NA NA NA 0.06 0.06 0.06 

Fuel sulfur, wt. % NA NA NA 0.99 0.99 0.99 

Fuel heating value, 

Btu/lb 

22548 22548 22548 18268 18268 18268 

Steam flow, lb/hr 79580 189900 797410 81930 196190 824460 

Steam temp., F 460 600 600 460 600 600 

Stack gas temp., F 480 480 250 480 480 345 

Boiler efficiency, % 81.131 81.361 85.439 83.554 84.081 88.338 

Fuel use, lb/hr 4437 11091 44349 5475 13685 54740 

Flue gas temp. at 

boiler outlet, F 

650 650 650 650 650 650 

Flue gas from 

combustion, lb/hr 

78,840 197,080 788,060 93,422 233,530 934,100 
Preliminary NOx Controls Cost Estimates 

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TABLE 3

NOx REDUCITON CAPABILITIES OF VARIOUS TECHNOLOGIES

Boiler Fuel NOx Level At Boiler Outlet, lb/MMBtu 

LNB LNB/OFA LNB/OFA/GR 

Bituminous coal(1) 0.45 0.35 NA 

Sub-bituminous coal (1) 0.35 0.25 NA 

Natural gas(2) See note 0.1 0.05 

Oil (0.36 lb/MMBtu)(3) NA NA 0.25 

Oil (0.5 lb/MMBtu)(2) See note 0.35 0.25 

Notes

1. The NOx levels achievable for bituminous and sub-bituminous coals are based on 

information provided in Attachments 3 and 4, which takes into account the limitations 

caused by the relatively smaller sizes of the industrial boilers compared to the utility 

boilers. Also, gas recirculation technology is not considered applicable to coal-fired 

boilers. 

2. It is recognized that some of the smaller boilers (especially the shop-built boilers) 

may not have space to add OFA. The NOx reduction capability is conservatively 

selected for the gas- and oil-fired boilers, so that the boilers, which cannot be 

retrofitted with OFA, would still, on an average, be able to achieve the NOx level 

listed for the LNB/OFA. 

3. For oil firing with the baseline emission of 0.36 lb/MMBtu, the LNB and LNB/OFA 

technologies may not provide significant NOx reduction. 
Preliminary NOx Controls Cost Estimates 

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TABLE 4

BOILER PERFORMANCE IMPACTS OF LNB, OFA, AND GR

Technology Boiler Size 

MMBtu/hr 

Reduction 

in Boiler 

Efficiency 

% 

Increased 

Auxiliary 

Power 

kW 

Increased 

Fuel Use 

lb/hr 

Increased 

Ash 

Generation 

lb/hr 

100 0.23 0.5 19 20 

250 0.23 1.0 48 51 

LNB/OFA on 

bituminous coal 

1000 0.23 4.5 193 204 

100 0.23 0.5 33 20 

250 0.23 1.0 81 51 

LNB/OFA on subbituminous coal 

1000 0.23 4.5 325 203 

100 NA 18 NA NA 

250 NA 45 NA NA 

LNB/OFA/GR on 

gas 

1000 NA 159 NA NA 

100 NA 21 NA NA 

250 NA 52 NA NA 

LNB/OFA/GR on 

oil 

1000 NA 197 NA NA 
Preliminary NOx Controls Cost Estimates 

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TABLE 5

BOILER PERFORMANCE IMPACTS OF SCR

Fuel Boiler Size 

MMBtu/hr 

Anhydrous 

Ammonia Use 

lb/hr 

Increased 

Auxiliary 

Power 

kW 

Catalyst 

Replacement 

Ft3

/yr

100 20 72 138 

250 49 184 345 

Coal 

1000 195 691 1380 

100 9 65 21 

250 21 140 58 

Gas 

1000 83 425 247 

100 15 67 39 

250 38 144 97 

Oil, 0.5 

lb/MMBtu Inlet 

NOx 

1000 150 538 387 

100 11 62 42 

250 27 131 102 

Oil, 0.36 

lb/MMBtu Inlet 

NOx 

1000 109 488 406 
Preliminary NOx Controls Cost Estimates 

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TABLE 6

BOILER PERFORMANCE IMPACTS OF SNCR

Technology Boiler Size 

MMBtu/hr 

Reduction 

in Boiler 

Efficiency 

% 

Urea 

Use 

gph 

Water 

Use 

gpm 

Increased 

Fuel Use 

lb/hr(1)

Increased 

Auxiliary 

Power 

kW 

Increased 

Ash 

Generation 

lb/hr 

100 0.48 13 3 40 3 5 

250 0.48 34 7 100 6 13 

Coal 

1000 0.48 134 29 399 26 52 

100 0.18 5 1 169 0.4 NA 

250 0.18 13 3 423 3 NA 

Gas 

1000 0.18 52 11 1776 10 NA 

100 0.37 10 2 19 1 0.14 

250 0.35 26 6 48 5 0.34 

Oil, 0.5 

lb/MMBtu 

Inlet NOx 

1000 0.35 103 22 202 19 1.43 

100 0.27 7 2 14 1 0.1 

250 0.26 19 4 35 5 0.25 

Oil, 0.36 

lb/MMBtu 

Inlet NOx 

1000 0.25 74 16 145 14 1.1 

Notes

1. The fuel use is expressed in lb/hr for coal and oil and scf/hr for gas. 
Preliminary NOx Controls Cost Estimates 

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TABLE 7

CAPITAL COSTS FOR NOx CONTROL TECHNOLOGY APPLICATIONS 

Capital Costs, NOx Control Retrofits 

$/MMBtu/hr 

Technology Fuel 

Boiler Size 

100 MMBtu/hr

Boiler Size 

250 MMBtu/hr

Boiler Size 

1000 

MMBtu/hr 

LNB Coal (bit. and 

sub-bit.) 

5097 3872 2554 

LNB/OFA Coal (bit. and 

sub-bit.) 

7281 5531 3649 

LNB/OFA Gas 2554 1940 1280 

LNB/OFA/GR Gas 3991 3031 2000 

LNB/OFA Oil 2554 1940 1280 

LNB/OFA/GR Oil 3991 3031 2000 

SCR Coal 14562 11062 7298 

SCR Gas 8009 6084 4014 

SCR Oil 11067 8407 5547 

SNCR Coal 5266 4000 2639 

SNCR Gas 4212 3200 2111 

SNCR Oil 4081 3100 2045 

Notes

1. The cost for each technology was established based on recent industry data(5) and 

Attachment 3. 

2. A scaling factor of 0.3 was used to project costs for different boiler sizes. 
Preliminary NOx Controls Cost Estimates 

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 TABLE 8

 NOx Technology Retrofit Costs

 COAL-, GAS- & OIL-FIRED INDUSTRIAL BOILERS

Fuel Technology NOx Reduction 

%

Capacity Factor 

%

$/Ton of Pollutant

1000 MMBtu/hr 250 MMBtu/hr 100 MMBtu/hr

Coal LNB, sub-bituminous 51 14 1520 2304 3033

50 426 645 849

83 256 389 512

Coal LNB/OFA, sub-bituminous 65 14 1727 2608 3428

50 496 743 972

83 306 454 593

Coal LNB/OFA, bituminous 51 14 2197 3317 4358

50 634 947 1239

83 392 581 757

Coal SCR 80 14 4481 5924 7262

50 1359 1766 2141

83 876 1123 1349

Coal SNCR 40 14 2962 4015 4970

50 1510 1814 2073

83 1285 1473 1625

Gas LNB/OFA 60 5 5260 7973 10521

50 526 797 1052

94 280 424 559

Gas LNB/OFA/GR 80 5 6204 9415 12374

50 656 981 1278

94 368 543 700

Gas SCR 80 5 14815 21095 26859

50 1670 2330 2933

94 986 1354 1689

Gas SNCR 40 5 14,165 20,870 27,105

50 2,452 3,116 3,735

94 1,842 2,193 2,521

Oil LNB/OFA (0.5 lb/MMBtu 30 10 2630 3986 5260

inlet NOx) 50 526 797 1052

86 306 464 612

Oil LNB/OFA/GR (0.5 lb/MMBtu 50 10 2505 3790 4973

inlet NOx) 50 533 791 1028

86 326 477 615

Oil LNB/OFA/GR (0.36 lb/MMBtu 30 10 5694 8613 11303

inlet NOx) 50 1210 1798 2337

86 741 1085 1399

Oil SCR (0.36 lb/MMBtu inlet NOx) 80 5 14,601 20,113 25,838

50 1,622 2,178 2,767

86 1,017 1,343 1,694

Oil SCR (0.5 lb/MMBtu inlet NOx) 80 5 10,458 14,443 18,544

50 1,191 1,595 2,014

86 760 997 1,245

Oil SNCR (0.5 lb/MMBtu inlet 40 10 4271 5892 7399

NOx) 50 1749 2070 2367

86 1485 1670 1840

Oil SNCR (0.36 lb/MMBtu inlet 40 10 5497 7753 9842

NOx) 50 1995 2444 2853

86 1628 1889 2123
Preliminary NOx Controls Cost Estimates 

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TABLE 9

COST SENSITIVIY EVALUATIONS – NOx TECHNOLOGIES

Fuel Technology Sensitivity $/ton of NOx 

Parameter(1) 

NOx 

Reduction 

% 

Capacity 

Factor 

% 

1000 

MMBtu/hr 

250 

MMBtu/hr 

100 

MMBtu/hr 

Coal LNB/OFA, 

bituminous 

Increased 

power cost 

51 14 

50 

83 

2198 

635 

393 

3318 

948 

582 

4359 

1240 

758 

 

Coal SCR Increased 

power cost 

80 14 

50 

83 

4541 

1418 

936 

5988 

1830 

1187 

7325 

2203 

1412 

 

Coal SCR Increased 

capital cost 

80 14 

50 

83 

5179 

1554 

994 

6981 

2062 

1301 

8653 

2531 

1584 

NOTES

1. Two sensitivity parameters were evaluation: 1) increased power cost from 25 mills/kwh to 50 mills/kwh 

and 2) an increase of 25 percent in the SCR capital cost.