TO: Petroleum Refinery NSPS Docket No. EPA-HQ-OAR-2007-0011 

FROM: Bob Lucas, EPA/SPPD 

DATE: July 6, 2010 

SUBJECT: Revised NOX Impact Estimates for Process Heaters 

I. Purpose

This memorandum documents the revised nitrogen oxides (NOX) impact estimates for petroleum 

refinery process heaters that become subject to 40 CFR part 60, subpart Ja. 

II. Background

The impacts for various control techniques for NOX from process heaters were considered 

previously (Coburn, 2008), but the impacts did not account for differences in the draft design of 

the process heater (forced versus natural draft). This memorandum provides additional 

information to support the development of NOX emission standards for process heaters when 

considering the differences between baseline emissions for natural and forced draft process 

heaters. Additionally, the EPA is considering providing NOX emission limits in terms of pounds 

per million British thermal units (lb/MMBtu) as an alternative to the concentration-based NOX

emission limits. This memorandum provides additional information regarding the appropriate 

NOX emission limits in terms of lb/MMBtu that are equivalent to a given concentration-based 

NOX emission limit. 

III. Cost Estimates of Process Heater NOX Control Systems

The cost analysis for process heaters was similar to the cost analysis performed previously 

(Coburn, 2008), except that costs were estimated for two different scenarios. Scenario 1 assumes 

all of the process heaters are natural draft process heaters and Scenario 2 assumes all of the 

process heaters are forced draft process heaters. We do not have much data on the precise 

proportion of process heaters that are forced versus natural draft, so the nationwide impacts are 

expressed as a range bounded by these two scenarios. 

The cost factors, model plant sizes, and the number and size distribution of process heaters per 

model plant are identical to those used previously. However, the control option effectiveness 

and the baseline emissions are slightly different based on whether the process heater is natural 

draft versus forced draft. Table 1 provides a summary of the distribution of baseline NOX

concentrations for different types of process heaters. 
Memo: Revised NOX Control Cost Estimates for Process Heaters 

July 6, 2010 

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Table 1. Summary of Representative Baseline NOX Concentrations for Affected Process 

Heaters 

Representative Average 

NOX Concentration 

(ppmv) 

Fraction of Affected Natural 

Draft Process Heaters 

Represented by Average NOX

Concentration 

Fraction of Affected Forced 

Draft Process Heaters 

Represented by Average NOX

Concentration 

80 0.40 0.00 

100 0.40 0.50 

150 0.15 0.35 

200 0.05 0.10 

240 0.00 0.05 

Various NOX concentration limits were evaluated for process heaters with a capacity greater than 

40 MMBtu. The costs include costs for O2 monitoring equipment for process heaters with a 

capacity less than 100 MMBtu /hr and the costs for a continuous emission monitoring system 

(CEMS) for NOX. Table 2 provides the projected impacts for new or modified natural draft 

process heaters. Table 3 provides the projected impacts for new or modified forced draft process 

heaters. The incremental cost effectiveness for natural draft process heaters is reasonable at an 

emission limit of 40 ppmv, but jumps to over $30,000 per ton of NOX removed at an emission 

limit of 20 ppmv. For forced draft process heaters, incremental cost effectiveness is reasonable 

at an emission limit of 60 ppmv, but jumps to approximately $14,000 per ton of NOX removed at 

an emission limit of 20 ppmv. Based on these impacts, the performance level for the best system 

of emission reduction (BSER), which is a combination of enhanced combustion monitoring 

controls and ultra-low NOX burners, is 40 ppmv for natural draft process heaters and 60 ppmv for 

forced draft process heaters. 
Memo: Revised NOX Control Cost Estimates for Process Heaters 

July 6, 2010 

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Table 2. Summary of Nationwide Impacts of Various NOX Regulatory Alternatives for 

Scenario 1: All Natural Draft Process Heaters 

Regulatory 

Alternative 

NOX Emission 

Limit (ppmv) 

Total Capital 

Investment 

($1,000) 

Total 

Annualized 

Costs 

($1,000/yr) 

NOX Emission 

Reduction 

from Baseline

(tons/yr) 

Overall 

Option Cost 

Effectiveness 

($/ton) 

Incremental 

Cost 

Effectiveness 

($/ton) 

Nationwide Costs for Newly Constructed Units (70% of affected units) 

80 6,460 3,050 2,390 1,280 1,280 

60 7,570 5,410 4,140 1,310 1,350 

40 8,050 7,440 5,000 1,490 2,360 

20 34,100 13,300 5,200 2,560 30,200 

Nationwide Costs for Modified or Reconstructed Units (30% of affected units) 

80 5,070 1,570 1,030 1,540 1,540 

60 10,300 3,120 1,770 1,760 2,070 

40 15,200 4,520 2,140 2,110 3,800 

20 28,000 7,230 2,230 3,250 32,500 

Table 3. Summary of Nationwide Impacts of Various NOX Regulatory Alternatives for 

Scenario 2: All Forced Draft Process Heaters 

Regulatory 

Alternative 

NOX Emission 

Limit (ppmv) 

Total 

Capital 

Investment 

($1,000) 

Total 

Annualized 

Costs 

($1,000/yr) 

NOX Emission 

Reduction 

from Baseline

(tons/yr) 

Overall Option 

Cost 

Effectiveness 

($/ton) 

Incremental 

Cost 

Effectiveness 

($/ton) 

Nationwide Costs for Newly Constructed Units (70% of affected units) 

80 7,450 4,900 4,840 1,010 1,010 

60 8,050 7,440 6,030 1,230 2,120 

40 14,600 8,910 6,140 1,450 13,600 

20 75,300 22,400 6,830 3,290 19,700 

Nationwide Costs for Modified or Reconstructed Units (30% of affected units) 

80 9,060 2,770 2,070 1,340 1,340 

60 15,200 4,520 2,600 1,750 3,420 

40 18,400 5,200 2,630 1,980 14,700 

20 48,500 11,500 2,930 3,910 21,300 

The nationwide impacts for Scenarios 1 and 2 provide a range of potential impacts. Table 4 

presents the nationwide impacts combined for new, modified, and reconstructed process heaters 

for the two scenarios. The costs of the control systems are identical for the two scenarios 

because the scenarios are based on identical controls (enhanced combustion monitoring controls 
Memo: Revised NOX Control Cost Estimates for Process Heaters 

July 6, 2010 

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and ultra-low NOX burners). The projected emission reductions differ due to the different 

baseline emission distribution. In the June 2008 final rule, total nationwide emission reductions 

were estimated to be 7,500 tons/yr. In the current analysis, the emission reductions are projected 

to range between 7,100 and 8,600 tons/yr. If natural draft process heaters are approximately 75 

percent of the newly affected process heaters, then the originally projected emission reductions 

are in agreement with the revised estimates. 

Table 4. Range of Nationwide Impacts of Selected Regulatory Alternatives for Process 

Heaters 

Regulatory 

Alternative NOX

Emission Limit 

(ppmv) 

Total Capital 

Investment 

($1,000) 

Total 

Annualized 

Costs 

($1,000/yr) 

NOX Emission 

Reduction from 

Baseline 

(tons/yr) 

Overall Option 

Cost 

Effectiveness 

($/ton) 

Nationwide Costs for Scenario 1: All Natural Draft Process Heaters 

40 23,000 12,000 7,100 1,700 

Nationwide Costs for Scenario 1: All Forced Draft Process Heaters 

60 23,000 12,000 8,600 1,400 

IV. Comparability of NOX Emission Standards

The proposed concentration emission limits of 40 or 60 ppmv are to be determined on a dry basis 

at 0 percent oxygen. The stoichiometric combustion of most fuel gases will produce a fairly 

constant volume of exhaust gas on a dry basis unless the hydrogen content is very high. Table 5 

of this memorandum is a copy of the proposed Table 1 to 40 CFR part 60, subpart Ja and 

contains the molar exhaust volume and molar heat content of typical compounds that make-up 

part of the fuel gas. 

Looking at each constituent as the only fuel available, a 40 ppmv concentration can be converted 

to a lb/MMBtu basis using the following equation. 
Memo: Revised NOX Control Cost Estimates for Process Heaters 

July 6, 2010 

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EmissLimit MMBtulb  Conc ppmv  MEV /)()/(  MWMHC  /2045.2 MGV (Eq. 1) 

Where: 

EmissLimit = the emission limit in lb/MMBtu equivalent to a concentration limit, lb/MMBtu 

 Conc = the NOX concentration limit, ppmv dry basis, corrected to 0% excess air 

 MEV = molar exhaust volume, dry standard cubic feet per mole (dscf/mol) at standard 

conditions of 68°F and 1 atmosphere, 0% excess air. 

 MHC = molar heat content (higher heating value basis), Btu per mole (Btu/mol) 

 MW = Molecular weight of NOX = 46 kg/kg-mol 

 2.2045 = unit conversion, lb/kg 

 MGV = molar gas volume, scf/kg-mol 

Table 5. Molar Exhaust Volumes and Molar Heat Content of Fuel Gas Constituents 

Constituent MEVa dscf/mol MHCb Btu/mol 

Methane (CH4) 7.29 842 

Ethane (C2H6) 12.96 1,475 

Hydrogen (H2) 1.61 269 

Ethene (C2H4) 11.34 1,335 

Propane (C3H8) 18.62 2,100 

Propene (C3H6) 17.02 1,947 

Butane (C4H10) 24.30 2,717 

Butene (C4H8) 22.69 2,558 

Inerts 0.85 0 

a

 MEV = molar exhaust volume, dry standard cubic feet per mole (dscf/mol) at standard conditions of 68°F and 1 

atmosphere, 0% excess air. 

b

 MHC = molar heat content (higher heating value basis), Btu per mole (Btu/mol) 

Applying Equation 1 to the various constituents of fuel gas (other than inerts, which do not 

contribute to the heating value of the fuel gas stream) yields the values presented in Table 6. 
Memo: Revised NOX Control Cost Estimates for Process Heaters 

July 6, 2010 

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Table 6. Emission Limit Conversion Factors for Fuel Gas Constituents 

Constituent 

NOX Concentration 

Limit (ppmv) 

Equivalent NOX

Emissions Limit 

(lb/MMBtu) 

Methane (CH4) 40 0.041 

Ethane (C2H6) 40 0.042 

Hydrogen (H2) 40 0.029 

Ethene (C2H4) 40 0.041 

Propane (C3H8) 40 0.042 

Propene (C3H6) 40 0.042 

Butane (C4H10) 40 0.043 

Butene (C4H8) 40 0.042 

Based on typical gas composition (mixture of C1 to C4 hydrocarbons with some hydrogen), a 

NOX concentration of 40 ppmv is essentially equal to 0.040 lb/MMBtu. Only when the 

hydrogen content exceeds 20 or 30 percent does a 0.040 lb/MMBtu emission limit becomes less 

stringent than the 40 ppmv emission limit. At high hydrogen concentration, the water content in 

the exhaust gas becomes significant, so that the dry basis correction of the concentration limit 

makes the concentrations limit more stringent even though the mass emission rate is the same. 

As the other factors in Equation 1 are constants for each constituent of fuel gas, a 60 ppmv NOX

concentration limit is similarly equivalent to a 0.060 lb/MMBtu emissions limit. 

V. References

Coburn, J. 2008. “Documentation of Final NOX Control Cost Estimates.” Memorandum to Bob 

Lucas, EPA/SPPD. Docket Item No. EPA-HQ-OAR-2007-0011-0222. April 28.