FROM: David Randall, RTI International 

TO: Brenda Shine, EPA/OAQPS 

FOR: EPA Docket No. EPA-HQ-OAR-2007-0011 

DATE: March 12, 2012 

SUBJECT: Impact of Turndown on NOx Emissions from Process Heaters at Petroleum 

Refineries 

1. Purpose

This memorandum presents an evaluation of the effect of turndown on nitrogen oxide (NOx) 

emissions from process heaters at petroleum refineries. 

2. Background

On December 28, 2008, EPA proposed amendments to the NOx emission limits for process 

heaters in 40 CFR part 60, subpart Ja (73 FR 78522). In comments on the proposal, several 

industry representatives noted that the proposed concentration-based NOx emissions limits would 

be difficult to meet during turndown, which is a period of time when a process heater is firing 

below capacity (Cade, 2009; Hunter, 2009; Chittim, 2009a; and Chittim, 2009b). Typically, the 

commenters suggested that problems would occur when process heaters are fired at less than 50 

percent of the rated capacity, but one commenter suggested that meeting the NOx concentration 

limit becomes problematic at firing rates less than 70 percent of the design rate. As an 

alternative to the proposed concentration limits, the commenters suggested that EPA develop 

mass-based limits that would apply either at all times or at least on the days when the process 

heaters operates at turndown. One example suggested by a commenter was to set a daily mass 

limit based on the mass of NOx emitted while operating at the design firing rate and meeting the 

lb/MMBtu emission limit specified for that type of process heater. 

This analysis is focused on characterizing the performance of combustion technologies for 

reducing NOx emissions from gas-fired process heaters or boilers in a petroleum refinery. To aid 

in the analysis, the following information on burner technologies is provided (MACTEC, 2005). 

 Low-NOx Burners. Low-NOx burner (LNB) technology utilizes advanced burner design 

to reduce NOx formation through the restriction of oxygen, flame temperature, and/or 

residence time. The two general types of low NOx burners are staged fuel and staged air 

burners. Staged fuel LNBs are particularly well suited for boilers and process heaters 

burning process and natural gas which generate higher thermal NOx. The estimated NOx

control efficiency for LNBs where applied to petroleum refining fuel burning equipment 

is generally around 40 percent. 
2 

 Ultra-low NOx Burners. Ultra-low NOx burners (ULNB) are similar to LNB but are 

specific to gas-fired units. These burners use a higher percentage of staged fuel to 

achieve lower flame temperatures and lower NOx concentrations. The estimated NOx

control efficiency for ULNBs is 50-60 percent. 

 “Next generation” ultra-low NOx Burners. Next generation ultra-low NOx burners 

(NGULNB) may incorporate a variety of techniques including induced flue gas 

recirculation (IFGR), steam injection, or a combination of techniques. These burners 

combine the benefits of flue gas recirculation and low-NOx burner control technologies. 

Rather than a system of fans and blowers (like external flue gas recirculation), the burner 

is designed to recirculate hot, oxygen depleted flue gas from the flame or firebox back 

into the combustion zone. This leads to a reduction in the average oxygen concentration 

in the flame without reducing the flame temperature below temperatures necessary for 

optimal combustion efficiency. These NGULNBs have yielded reduction efficiencies of 

between 75-85 percent. 

3. Analysis

To evaluate the effect of turndown on emissions, we examined NOx CEMS data for 27 process 

heaters. The 27 process heaters are owned by 3 refiners and are located at 9 refineries. Most of 

the process heaters have either low NOx burners or ultra low NOx burners (the type of burner was 

not available for a few of the process heaters). Over half of the process heaters are designed with 

forced draft, four have natural draft, and the design is not available for five. The amount of 

CEMS data per process heater ranges from 4 months to 34 months. Nearly all of the forced draft 

process heaters have combustion air preheat, which is expected to lead to higher NOx emissions 

than no preheat. Various details of design and operation of the process heaters are summarized 

in Table 1 (Chittim, 2009c; Feerick, 2008; Laughlin, 2008; Marathon, 2008a; Marathon, 2008b; 

and Wagner, 2008). 

A previous analysis determined that, for normal operation, the incremental cost effectiveness of 

control is reasonable at an emissions limit of 40 ppmdv for natural draft process heaters and 60 

ppmdv for forced draft process heaters, with both concentration limits corrected to 0 percent 

excess air (Lucas, 2010). The same thresholds were also used in this analysis of the effect of 

turndown. All of the 30-day averages in this analysis were based on valid data for the preceding 

30 calendar days, which meant the averages for some days were based on data for much less than 

30 days. (The effect of calculating the averages based on the preceding 30 valid daily values was 

also examined, and the results were essentially the same.) All available data were included in the 

analysis, including SSM, except for data related to a CEMS malfunction. 
3 

Table 1. Process heater data 

Process 

heater 

ID Company Refinery 

Draft 

typea Burner typeb

Design 

firing rate 

(MMBtu/hr) 

CEMS data 

dates 

Unit in which 

heater is used 

FD-1 Marathon Detroit F ULNB 417 5/07 – 4/08 Crude and vacuum 

units (common 

stack) 

FD-2 Marathon Canton F ULNB 193 5/07 – 4/08 Crude 

FD-3 Marathon St. Paul Park F ULNB 116 10/07 – 4/08 Gas Oil Hydrotreater 

FD-4 Marathon St. Paul Park F LNB 178 5/07 – 4/08 Crude 

FD-5 Marathon Catlettsburg F ULNB 177 5/07 – 4/08 Crude 

FD-6 Marathon Catlettsburg F ULNB 178 5/07 – 4/08 Sat. Gas 

FD-7a Marathon Texas City F ULNB 182 5/07 – 4/08 Topper 

FD-7b Marathon Texas City F ULNB 182 5/08 – 4/09 Topper 

FD-8 Marathon Garyville F LNB 283 5/07 – 4/08 Coker 

FD-9 Marathon Garyville F LNB 295 5/07 – 4/08 Alky 

FD-10 Marathon Garyville F LNB 226 5/07 – 4/08 Rose Oil 

FD-11 Marathon Garyville F LNB 323 5/07 – 4/08 Crude 

FD-12 Marathon Garyville F LNB 315 5/07 – 4/08 Crude 

FD-13 ConocoPhillips Ponca City F ULNB 180 1/06 – 10/08 Crude Topping 

FD-14 ConocoPhillips Ponca City F ULNB 110 3/06 – 10/08 Crude Topping 

FD-15 ExxonMobil N/A F ULNB 500 1/08 -8/08 N/A 

FD-16 ExxonMobil N/A F ULNB 340 1/08 – 8/08 N/A 

FD-17 ExxonMobil N/A F ULNB 340 1/08 – 8/08 N/A 

ND-1 Marathon Canton N ULNB 242 5/07 – 4/08 CCR 

ND-2 Marathon Garyville N N/A 231 5/07 – 4/08 N/A 

ND-3 ConocoPhillips Ponca City N ULNB 330 1/06 – 10/08 Catalytic reforming 

ND-4 ConocoPhillips Ponca City N ULNB 180 4/06 – 10/08 Catalytic reforming 

UD-1 Marathon Robinson N/A ULNB 154 1/08 – 4/08 HF Alky Isostripper 

UD-2 Marathon Garyville N/A N/A 152 5/07 – 4/08 Crude Vacuum? 

UD-3 Marathon Garyville N/A N/A 152 5/07 – 4/08 Crude Vacuum? 

UD-4 Marathon Garyville N/A N/A 71 5/07 – 4/08 N/A 

UD-5 Marathon Garyville N/A N/A 187 5/07 – 4/08 FCC Charge? 

a

 ”F” means forced draft or balanced, and “N” means natural draft. 

b

 ULNB” means ultra low NOx burner, and “LNB” means low NOx burner. 

“N/A” means not available. 

Effect of Averaging Period and Exhaust Oxygen Levels on Performance 

Table 2 shows firing rate and NOx CEMS emission data for the 27 process heaters. Overall, 18 

(67 percent) of the process heaters exceeded at least one daily threshold, and 11 (41 percent) 

exceeded the daily threshold 10 or more times. Because short-term fluctuations resulted in fairly 

frequent exceedances of daily thresholds, we also examined the effect of 30-day averaging 

periods on moderating the impact of these fluctuations. On this basis, 9 (33 percent) of the 
4 

process heaters exceeded the applicable threshold on at least one day, and 7 (26 percent) 

exceeded it 10 or more times. The percentages are the same if the results for each process heater 

are normalized to an annual operating period. See Attachment A for plots of the daily firing 

rates, NOx concentrations, and oxygen concentrations for the 9 process heaters. 

Of the 7 process heaters that exceeded 30-day average thresholds on 10 or more days, 5 operated 

with high oxygen levels normally (FD-11, FD-12, FD-13, ND-3, and ND-4). Although these 5 

process heaters often exceeded 30-day thresholds, all except ND-3 met the limits most of the 

time, generally when operating at lower exhaust oxygen levels. One of the 7 process heaters 

(FD-14) exceeded the 30-day threshold only on days when the exhaust oxygen levels were much 

higher than normal and the firing rate was 50 percent of design or less. These high oxygen levels 

(6 percent to 11 percent) are higher than typically required for flame stability at reduced firing 

rates, and the unit usually operated with NOx concentrations less than 60 ppmdv while firing at 

less than 50 percent of design capacity on days when the oxygen levels were less than 6 percent. 

One process heater (ND-2) exceeded the 30-day threshold on every operating day. This process 

heater operated with exhaust oxygen levels less than 5 percent, but we do not have confirmation 

that this process heater was equipped with low NOx burners. 

Of the two process heaters with fewer than 10 days exceeding the 30-day average threshold, 

process heater (FD-7b) exceeded the threshold only when the exhaust oxygen levels were much 

higher than normal (i.e., 10 percent or higher) and firing rates were less than 50 percent of 

design. As noted previously, such oxygen levels are much higher than needed to ensure flame 

stability. See Figure A-2 for a plot of the daily emissions data for this process heater. 

Only one process heater (FD-5) had a few exceedances of the 30-day threshold even though it 

was equipped with ultra low NOx burners and it generally operated with exhaust oxygen levels 

less than 5 percent (even during the period when the exceedances occurred, although the oxygen 

concentrations during the exceedance periods were slightly higher than during compliant 

periods). This process heater also almost never operated with a firing rate less than 50 percent of 

design (2 percent of operating days) and infrequently operated with a firing rate less than 75 

percent of design (20 percent of operating days). Therefore, its performance issues were not 

related to turndown. Based on the limited number of exceedances for this process heater, it is 

expected that this unit could meet a 30-day average 60 ppmdv emission limit if such a limit were 

required. 
5 

Table 2. Summary of process heater firing rates and NOx emissions 

Process 

heater 

ID 

Total no. 

of days 

with both 

firing 

and 

CEMS 

data 

No. of days 

firing relative 

to design rate 

Percent of 

days firing 

relative to 

design rate 

Preheat

? 

No. of days 

applicable 

threshold was 

exceededb

<50% <75% <50% <75% Comments 

Individual 

days 

30-day 

rolling 

average 

Process heaters with forced draft 

FD-7a 356 356 356 100 100 Y 0 0 

FD-4 338 338 338 100 100 No 10 0 

FD-7b 329 329 329 100 100 Y 16 8 Oxygen on days with NOx

>60 ppmdv are much higher 

than for other days with 

similar and lower firing rates. 

FD-14 952 195 952 20 100 Y 53 30 

FD-3 196 189 196 97 100 Y 1 0 

FD-8 341 69 341 20 100 Y 3 0 Very scattered NOx for only 5 

days with firing <30% of 

design. 

FD-2 366 15 298 4 81 Y 0 0 

FD-10 338 15 53 4 16 Y 0 0 

FD-17 182 12 28 7 15 Y 9 0 No trend >40% of firing rate. 

All 7 days with high NOx and 

lower firing rate are clustered 

at about 22% of design. The 

7 days also have the highest 

oxygen levels. 

FD-5 365 9 74 2 20 No 32 8 

FD-1 359 6 231 2 64 Y 0 0 

FD-16 229 4 38 2 17 Y 3 0 

FD-6 366 4 68 1 19 No 11 0 

FD-13 1026 4 88 0.4 9 Y 255 271 Trend is more pronounced 

for firing <50% of design, but 

based on only four data 

points. 

FD-9 341 1 195 0.3 57 Y 0 0 

FD-12 340 1 10 0.3 3 Y 66 52 Very scattered NOx for firing 

rates <50% of design rate. 

FD-11 340 1 9 0.3 3 Y 78 74 NOx data very scattered for 

firing rates <75% of design 

rate. 

FD-15 227 0 12 0 5 Y 0 0 NOx increases as firing rate 

increases above 75% of 

design. 

Process heaters with natural draft 

ND-3 979 254 979 26 100 No 762 855 Oxygen usually >5%, often 

over 7%, and higher during 

periods of greatest turndown.
6 

Process 

heater 

ID 

Total no. 

of days 

with both 

firing 

and 

CEMS 

data 

No. of days 

firing relative 

to design rate 

Percent of 

days firing 

relative to 

design rate 

Preheat

? 

No. of days 

applicable 

threshold was 

exceededb

<50% <75% <50% <75% Comments 

Individual 

days 

30-day 

rolling 

average 

ND-4 917 148 899 16 98 No 268 306 Oxygen usually between 5% 

and 7%; higher during 

periods of greatest turndown.

ND-1 366 12 355 3 97 No 0 0 

ND-2 327 3 7 1 2 No 343c 316 Very slight trend based on 

only 7 data points. Process 

heater may not have a low 

NOx burner. 

Process heaters for which the type of draft is unknown 

UD-3 337 5 122 1 36 N/A 1 0 NOx increases as firing rate 

decreases to about 50% of 

design, then 3 data points 

with lower firing rate have 

low NOx. 

UD-2 341 4 10 1 3 N/A 3 0 Same comment as for UD-3. 

UD-1 118 2 118 2 100 N/A 0 0 Only 1 data point for firing 

rate <50% of design, and it is 

within wide range of NOx

values for firing rate >50% of 

design. 

UD-4 340 1 4 0.3 34 N/A 2 0 Nearly all days firing >100% 

of design. 

UD-5 341 0 166 0 49 N/A 0 0 

a

 See the text for descriptions of each category. 

b

 The applicable threshold is 60 ppmdv for forced draft process heaters and 40 ppmdv for both natural draft process 

heaters and process heaters for which the draft type is unknown. 

c

 The number of exceedances of the applicable threshold exceeds the number of days for which both firing rate data 

and CEMS data were available because firing rate date were unavailable for several days while NOx CEMS data 

were available. 

“N/A” means not available. 

Daily average NOx concentrations are plotted versus daily average exhaust oxygen levels for 

each of the 27 process heaters in Attachment B. The data show that 8 of the 27 process heaters 

never exceeded an applicable 30-day average threshold when oxygen levels were less than 5 

percent. Another 4 process heaters occasionally exceeded an applicable 30-day threshold, but 

when oxygen levels were less than 5 percent, the daily NOx concentrations were always or nearly 

always less than the applicable threshold. Ten additional process heaters had no exceedances of 

an applicable 30-day threshold even though oxygen levels were generally greater than 6 percent. 

Three process heaters had numerous exceedances of the 30-day thresholds and generally 

operated with oxygen levels greater than 5 percent to 6 percent; however, NOx concentrations 

nearly always were below the thresholds on days when oxygen levels were less than 6 percent to 

6.5 percent. One process heater operated with oxygen levels less than 5 percent nearly every day 
7 

while NOx concentrations were over 80 ppmdv; however, this process heater may not be 

equipped with low NOx burners. Only one process heater known to be equipped with low NOx

burners nearly always exceeded the applicable 30-day NOx threshold regardless of the exhaust 

oxygen level, which was nearly always greater than 5 percent. This process heater also operated 

with firing rates that were less than 50 percent and 75 percent of the design rate on 26 percent 

and 100 percent of the operating days, respectively. If this process heater cannot be operated 

safely at lower oxygen levels during turndown operations, then it is the only process heater that 

could have difficulty meeting an emission limit based on the applicable threshold on a 30-day 

rolling average basis. However, it would also have difficulty meeting the applicable emission 

limit regardless of the number of days included in the rolling average. Additionally, while this 

unit does use ULNB, it does not use the latest technology (i.e., NGULNB). It is also unclear if 

this unit could meet a 60 ppmdv emission limit during turndown if it had the best available 

burner technology. Table 3 identifies the process heaters in each group. 

Table 3. Comparison of NOx concentrations and Exhaust Oxygen Levels 

Process heater ID 

Frequency of 

30-day 

threshold 

exceedances Exhaust oxygen levels Comments 

FD-2; FD-4; FD-6; 

FD-7a; FD-10; UD-1: 

UD-3; UD-4 

None Always or nearly always <5% 

FD-5; FD-7b; FD-14; 

ND-4 

Occasional Varied • Typical oxygen levels were <5%, 

<6%, <8%, and <10% for the four 

process heaters 

•Daily NOx was always or nearly 

always less than the threshold 

when oxygen was less than 5 

percent 

FD-1; FD-3; FD-8; 

FD-9; FD-15; FD-16; 

FD-17; ND-1; UD-2; 

UD-5 

None Generally >6% 

FD-11; FD-12; FD-13 Often generally >5 percent to 6 percent Daily NOx levels were always or 

nearly always less than the 

threshold when oxygen levels were 

less than 6 percent to 6.5 percent 

ND-2 Always Always <5% May not have low NOx burners 

ND-3 Nearly always Typically >5% 

Effect of Turndown Operation on NOx Emissions 

As shown in Table 2, only 4 of the process heaters operated with firing rates less than 50 percent 

of design all or nearly all of the time, and 10 operated with firing rates less than 75 percent of 

design all or nearly all of the time. Of the 4 process heaters that typically operated with firing 

rates less than 50 percent of design, 3 never exceeded the applicable 30-day threshold, and the 

fourth exceeded the 30-day threshold on only 8 days (or 2 percent of the time). Of the 10 

process heaters operating at less than 75 percent of design all or nearly all of the time, 6 never 
8 

exceeded the 30-day threshold, 2 exceeded the threshold on 2 percent to 3 percent of the days, 

and 2 exceeded the threshold on a significant number of days. Of the remaining 17 process 

heaters that infrequently operated at turndown, 12 never exceeded a 30-day threshold, and 5 

exceeded a 30-day threshold between 2 percent and 97 percent of the operating days. As noted 

in the preceding section, exceedances generally correlated with high exhaust oxygen levels. In 

addition, 4 of the 9 process heaters that exceeded 30-day thresholds operated at turndown on 

very few days relative to the number of exceedances. Details are noted below: 

 Three process heaters (FD-3, FD-4, and FD-7a) never exceeded the applicable threshold 

even though they operated with firing rates less than 50 percent of design on all or nearly 

all days. 

 Fifteen process heaters that operated with firing rates less than 50 percent of design on 

between 0 and 69 days (generally over the course of 12 months of operation) also never 

exceeded an applicable 30-day threshold. These same process heaters also operated with 

firing rates less than 75 percent of design on between 4 and 355 days over the same time 

periods. 

 One process heater (FD-7b) operated at firing rates less than 50 percent every day and 

exceeded the 30-day rolling average threshold on 8 days. However, as noted above, these 

exceedances correlate with a series of days where the oxygen level was high. 

Furthermore, although firing rates were less than 50 percent of design on every day, the 

days with high oxygen levels had some of the highest firing rates. 

 One process heater (FD-5) had 8 exceedances of the 30-day rolling average threshold. 

This process heater and operated with firing rates less than 50 percent of design for only 

9 days, and the NOx concentrations on these 9 days did not contribute to any of the 8 

exceedances. 

 Over nearly 3 years of operation, one process heater (FD-14) had 30 exceedances of the 

30-day rolling average threshold and operated with firing rates less than 50 percent of 

design on 195 days. The days of turndown operation did affect the number of 

exceedances. However, as noted previously, the high NOx correlated with high oxygen, 

and many days with similar or lower firing rates had both lower exhaust oxygen levels 

and lower NOx concentrations. 

 Four process heaters (FD-11, FD-12, FD-13, and ND-2) had between 52 and 316 

exceedances of the applicable 30-day threshold, but they operated with firing rates less 

than 50 percent of design on only 1 to 4 days. Three of these process heaters operated 

with firing rates less than 75 percent of design on up to 10 days, and the fourth operated 

with firing rates less than 75 percent of design on 88 days. In all cases, the number of 

days operating at reduced firing rates was much less than the number of exceedances. 

Thus, turndown operation had little effect on the number of exceedances. 

 Two process heaters (ND-3 and ND-4) both had a large number of exceedances (nearly 

every day for ND-3), and they operated with firing rates less than 50 percent of design on 

numerous days. They also operated with firing rates less than 75 percent of design on all 

or nearly all days. The highest NOx concentrations were associated with the lowest firing 

rates. Thus, turndown did affect the 30-day average concentrations, and likely affected 
9 

the number of exceedances as well. We do not have data for operation with firing rates at 

75 percent to 100 percent of design for these process heaters and thus, we cannot 

determine whether they would have difficulty meeting the 30-day threshold only on days 

of turndown operation. 

To get another perspective, we plotted the daily NOx concentrations versus the daily firing rates 

and then classified the process heaters in one of the following five categories based on the 

correlation or trend in the data: 

 Category 1. No correlation or trend between NOx concentrations and firing rates, and all 

or nearly all of the daily NOx concentrations are below 40 ppmdv for natural draft units 

and 60 ppmdv for forced draft units. 

 Category 2. No correlation or trend between NOx concentrations and firing rates, but 

daily NOx concentrations often exceed the 40 ppmdv or 60 ppmdv thresholds. 

 Category 3. NOx concentrations decrease with decreasing firing rates. Generally the 

decrease is slight, and the NOx data for such process heaters fall in a wide band (i.e., 

some days with the highest NOx concentrations have the same firing rates as other days 

with much lower NOx concentrations). The days with the highest NOx also generally 

have the highest exhaust oxygen levels. 

 Category 4. NOx concentrations increase with decreasing firing rates, and daily NOx

concentrations are always or nearly always less than the 40 ppmdv and 60 ppmdv 

thresholds. 

 Category 5. NOx concentrations increase with decreasing firing rates, but daily NOx

concentrations often exceed the 40 ppmdv or 60 ppmdv thresholds. 

Attachment C contains the plots of the daily NOx concentrations versus the daily firing rates for 

each of the 27 process heaters. Table 4 identifies the correlation category that applies to the data 

for each process heater. 

Ten of the process heaters show increasing NOx concentrations with decreasing firing rates, but 7 

of those process heaters had no exceedances of the applicable 30-day threshold. The other three 

process heaters (FD-13, ND-3, and ND-4) each had more than 270 exceedances of the applicable 

30-d threshold out of more than 900 days of data. As discussed above, these three process 

heaters generally operated with high exhaust oxygen levels, even during normal operation. If 

those process heaters are being operated as recommended for safe operation such that lower 

excess air levels cannot be achieved consistently, then they may have difficulty meeting emission 

limits based on the applicable thresholds, regardless of the averaging period. 

Four of the process heaters showed no trend between NOx concentrations and firing rates, but the 

30-day concentration limits were not met on some days. This suggests that the cause of the 

exceedances is due to something other than turndown. 
10 

Table 4. NOx correlation with firing rate 

Process 

heater ID 

No. of days firing 

<50% of the 

design rate 

No. of days 

applicable 30-

day threshold 

was exceeded 

Category of NOx correlation with firing ratea

1 2 3 4 5 

Forced draft process heaters 

FD-7a 356 0 1 

FD-4 338 0 3 

FD-7b 329 8 3 

FD-14 195 30 2 

FD-3 189 0 1 

FD-8 69 0 4 

FD-2 15 0 1 

FD-10 15 0 3 

FD-17 12 0 4 

FD-5 9 8 2 

FD-1 6 0 4 

FD-16 4 0 4 

FD-6 4 0 1 

FD-13 4 271 5 

FD-9 1 0 1 

FD-12 1 52 2 

FD-11 1 74 2 

FD-15 0 0 1 

Natural draft process heaters 

ND-3 254 855 5 

ND-4 148 306 5 

ND-1 12 0 1 

ND-2 3 316 3 

Process heaters for which the type of draft is unknown 

UD-3 5 0 4 

UD-2 4 0 4 

UD-1 2 0 1 

UD-4 1 0 4 

UD-5 0 0 1 

 a See the text for descriptions of each category. 

Effect of a Mass-Based Emission Limit for Turndown Operation 

The analysis above shows that some process heaters generate higher NOx concentrations when 

operating under turndown conditions than under normal conditions. Eight of the 27 process 

heaters in the analysis also would exceed emission limits set at 60 ppmdv for forced draft units 

and 40 ppmdv for natural draft units, with both limits calculated as 30-day rolling averages. 

Although NOx concentrations may be above such limits on some days of turndown operation, the 
11 

mass of emissions may be less than on days with normal firing rates (and lower NOx emissions 

levels) due to lower gas flow rates. Thus, a mass-based emission limit may be more appropriate 

than a concentration based limit, at least on days of significant turndown. To evaluate this 

possibility we developed a regulatory alternative that combines a mass-based limit and the 30-

day rolling average concentration limit. 

The general concept of the alternative is that a facility could choose to comply with either limit 

on days when the firing rate is less than 50 percent of the design rate. The facility would then be 

subject to the otherwise applicable 30-day average concentration limit on all other days. The 

mass limit in this alterative was calculated as the mass of NOx that would be emitted by a process 

heater that is meeting the applicable concentration-based limit and operating at 50 percent of its 

design firing rate for the entire day. Because the mass limit is related to the capacity of the unit, 

the limits would vary from one process heater to another. For example, a forced draft process 

heater with a design firing rate of 200 MMBtu/hr would have a mass-based emissions limit of 

144 lb/d (0.06 lb/MMBtu x 0.5 x 200 MMBtu/hr x 24 h/d = 144 lb/d). 

To evaluate the effect of the alternative, we applied it to each of the 8 process heaters described 

above that would not meet applicable concentration-based 30-d average emission limits every 

day. The choices that result in the fewest number of exceedances will depend on the specific 

NOx concentrations for days in 30-day averages that are affected by excluding certain days that 

meet the mass limit. In this analysis we considered two approaches for the 8 facilities. First, we 

assumed the facility would demonstrate compliance with the mass limit on all days when the 

mass limit was met (and the firing rate was less than 50 percent of the design rate). These days 

would then be excluded from the calculation of 30-day rolling averages of the NOx

concentrations for comparison with the applicable 60 ppmdv or 40 ppmdv limit on all other days. 

The second approach is similar to the first approach except that the facility would demonstrate 

compliance with the mass limit only if the average NOx concentration on that day exceeded 60 

ppmdv or 40 ppmdv. The results are presented in Table 5. 

As shown in Table 5, the alternative would eliminate exceedances for only 1 of the 8 facilities. 

(However, this process heater always operated at less than 50 percent of the design firing rate 

and met the concentration-based limit on days when the oxygen levels were normal. Thus, 

exceedances for this process heater also could likely be eliminated by better control of excess 

air.) The alternative (either approach) had little effect on the number of exceedances for the 

other 7 process heaters. The primary reason for the minimal impact was that most of these 

process heaters had few days of turndown operation. In addition, when they did operate at 

turndown, relatively few of those days (in comparison to the number of exceedances) also met 

the applicable mass limit. Process heater FD-14 did have numerous days firing less than 50 

percent of design and meeting the mass limit, but most of those days also had NOx

concentrations less than 60 ppmdv, so excluding those days from the 30-day averages had little 

effect on the number of exceedances. 
12 

Table 5. Effect of regulatory alternative on the number of exceedances 

Process 

heater 

ID 

No. of days 

exceeding 

applicable 

NOx ppmdv 

threshold 

based on 30-

day 

averages 

Total no. 

of days 

firing 

<50% of 

design 

(A) 

Total no. of 

days firing 

<50% of 

design and 

meeting 

lb/d limit 

(B) 

Total number of 

days firing <50% 

of design, meeting 

lb/d limit, and 

exceeding 

applicable NOx

ppmdv threshold 

Total number 

of daily 

exceedances if 

using the lb/d 

limit to comply 

on days in 

column (B) 

Total number of 

daily 

exceedances if 

using the lb/d 

limit to comply 

on all days in 

column (A) 

FD-7b 8 329 329 16 0 0 

FD-14 30 195 170 9 20 9 

FD-5a 8 9 8 1 8 8 

FD13 271 4 0 0 271 271 

FD-11b 74 1 1 0 74 85 

FD12 52 1 1 0 52 52 

ND-3 855 254 44 35 811 806 

ND-4 306 148 68 28 239 252 

a

 The one day that meet the conditions in column (B) does not cause any exceedances of a 30-d average. 

b

 The number of exceedances is higher for the approach in column (A) because the one day that meets the specified 

conditions for complying with the lb/d limit has low NOx and the following days have relatively high NOx. 

4. Conclusions

 A majority of existing forced draft process heaters cannot continuously meet a daily 

average emission limit of 60 ppmdv corrected to 0 percent oxygen, and (although the data 

sample was small) most existing natural draft process heaters cannot continuously meet a 

daily average emission limit of 40 ppmdv corrected to 0 percent oxygen. 

 Based on current operating procedures, most forced draft and natural draft process 

heaters can meet the emission limits based on the applicable 60 ppmdv and 40 ppmdv 

thresholds if compliance is determined on a 30-day rolling average basis, even when 

including data from periods of turndown in the averages. 

 Under normal operation or turndown, some process heaters experience numerous 

exceedances when exhaust oxygen levels are relatively high, but few or no exceedances 

when the oxygen levels are lower. Better control of excess air levels likely would reduce 

the number of exceedances. 

 An alternative daily mass-based emission limit calculated as the mass of NOx that would 

be emitted when a process heater meets the applicable concentration and operates with a 

firing rate at 50 percent of design for an entire day would do little to reduce the number 

of exceedances among process heaters that are unable to meet the 30-day rolling average 

emission limit. 
13 

5. References

Cade, R. 2009. Letter and Attachments from R. Cade, Marathon Petroleum Company LLC, to 

EPA Docket Center. Comments on Proposed Amendments to 40 CFR part 60, subparts J 

and Ja. February 3, 2009. Docket Item No. EPA-HQ-OAR-2007-0011-0296. 

Chittim, R. 2009a. Letter and Attachments from R. Chittim, API, to EPA Docket Center. 

Comments from API, NPRA, and WSPA on the Proposed Amendments to 40 CFR part 60, 

subparts J and Ja. February 5, 2009. Docket Item No. EPA-HQ-OAR-2007-0011-0311. 

Chittim, R. 2009b. Letter from R. Chittim, API, to EPA Docket Center. Supplemental 

Comments from API, NPRA, and WSPA on the Proposed Amendments to 40 CFR part 60, 

subparts J and Ja. April 8, 2009. Docket Item No. EPA-HQ-OAR-2007-0011-0315. 

Chittim, R. 2009c. Letter and Attachments from R. Chittim, API, to K. Hustvedt, EPA/OAQPS. 

Follow-up to August 12 Call Regarding Process Heaters. September 10, 2009. Docket No. 

EPA-HQ-OAR-2007-0011. 

Feerick, C. 2008. Email communications from C. Feerick, ExxonMobil, to K. Hustvedt, EPA. 

EM Process Heater NOx Raw Data. September 9 and 12, 2008, and August 27, 2008. 

Docket Item No. EPA-HQ-OAR-2007-0011-0261. 

Hunter, D. 2009. Letter from D. Hunter, ConocoPhillips, to EPA Docket Center. Comments on 

Proposed Amendments to 40 CFR part 60, subparts J and Ja. February 5, 2009. Docket 

Item No. EPA-HQ-OAR-2007-0011-0305. 

Laughlin, J. 2008. Email communication with attached data files from J. Laughlin, 

ConocoPhillips, to, B. Shine, EPA. Refinery Heaters—NOx Emissions. October 27, 2008. 

Docket Item No. EPA-HQ-OAR-2007-0011-0283. 

Lucas, B. 2010. Memorandum from B. Lucas, EPA/SPPD, to Petroleum Refinery NSPS Docket 

No. EPA-HQ-OAR-2007-0011. Revised NOx Impact Estimates for Process Heaters. July 6, 

2010. 

MACTEC Engineering and Consulting, Inc. 2005. Midwest Regional Planning Organization 

(RPO) Petroleum Refinery Best Available Retrofit Technology (BART) Engineering Analysis. 

Prepared for The Lake Michigan Air Directors Consortium (LADCO). March 30, 2005. 

Docket Item No. EPA-HQ-OAR-2007-0011-0036. 

Marathon Petroleum Company LLC. 2008a. NSPS Ja Process Heater NOx Concerns. June 6, 

2008. Docket Item No. EPA-HQ-OAR-2007-0011-0256. 

Marathon Petroleum Company LLC. 2008b. Presentation slides. NSPS Subpart Ja Process 

Heater NOx. July 15, 2008. Attachment to Docket Item No. EPA-HQ-OAR-2007-0011-

0264. 
14 

Wagner, J. 2008. Email communication from J. Wagner, API, to, K. Hustvedt and B. Shine, 

EPA/OAQPS. Process Heater Information. October 15, 2008. Docket Item No. EPA-HQOAR-2007-0011-0280. 
Attachment A
A-2 

Figure A-1. Plot of daily data for Process Heater FD-5 

Figure A-2. Plot of daily data for Process Heater FD-7b 
A-3 

Figure A-3. Plot of daily data for Process Heater FD-11 

Figure A-4. Plot of daily data for Process Heater FD-12 
A-4 

Figure A-5. Plot of daily data for Process Heater FD-13 

Figure A-6. Plot of daily data for Process Heater FD-14 
A-5 

Figure A-7. Plot of daily data for Process Heater ND-3 

Figure A-8. Plot of daily data for Process Heater ND-4 
A-6 

Figure A-9. Plot of daily data for Process Heater ND-2
Attachment B 
B-2 

 

Figure B-1. Plot of daily NOx versus daily oxygen for Process Heater FD-1 

 

Figure B-2. Plot of daily NOx versus daily oxygen for Process Heater FD-2 
B-3 

 

Figure B-3. Plot of daily NOx versus daily oxygen for Process Heater FD-3 

 

Figure B-4. Plot of daily NOx versus daily oxygen for Process Heater FD-4 
B-4 

Figure B-5. Plot of daily NOx versus daily oxygen for Process Heater FD-5 

 

Figure B-6. Plot of daily NOx versus daily oxygen for Process Heater FD-6 
B-5 

 

Figure B-7. Plot of daily NOx versus daily oxygen for Process Heater FD-7a 

 

Figure B-8. Plot of daily NOx versus daily oxygen for Process Heater FD-7b 
B-6 

 

Figure B-9. Plot of daily NOx versus daily oxygen for Process Heater FD-8 

 

Figure B-10. Plot of daily NOx versus daily oxygen for Process Heater FD-9 
B-7 

 

Figure B-11. Plot of daily NOx versus daily oxygen for Process Heater FD-10 

 

Figure B-12. Plot of daily NOx versus daily oxygen for Process Heater FD-11 
B-8 

 

Figure B-13. Plot of daily NOx versus daily oxygen for Process Heater FD-12 

Figure B-14. Plot of daily NOx versus daily oxygen for Process Heater FD-13 
B-9 

 

Figure B-15. Plot of daily NOx versus daily oxygen for Process Heater FD-14 

 

Figure B-16. Plot of daily NOx versus daily oxygen for Process Heater FD-15 
B-10 

 

Figure B-17. Plot of daily NOx versus daily oxygen for Process Heater FD-16 

 

Figure B-18. Plot of daily NOx versus daily oxygen for Process Heater FD-17 
B-11 

 

Figure B-19. Plot of daily NOx versus daily oxygen for Process Heater ND-1 

 

Figure B-20. Plot of daily NOx versus daily oxygen for Process Heater ND-2 
B-12 

Figure B-21. Plot of daily NOx versus daily oxygen for Process Heater ND-3 

Figure B-22. Plot of daily NOx versus daily oxygen for Process Heater ND-4 
B-13 

Figure B-23. Plot of daily NOx versus daily oxygen for Process Heater UD-1 

Figure B-24. Plot of daily NOx versus daily oxygen for Process Heater UD-2 
B-14 

Figure B-25. Plot of daily NOx versus daily oxygen for Process Heater UD-3 

Figure B-26. Plot of daily NOx versus daily oxygen for Process Heater UD-4 
B-15 

Figure B-27. Plot of daily NOx versus daily oxygen for Process Heater UD-5 
Attachment C 
C-2 

 

Figure C-1. NOx emissions versus firing rate for process heater FD-1 

Figure C-2. NOx emissions versus firing rate for process heater FD-2 
C-3 

Figure C-3. NOx emissions versus firing rate for process heater FD-3 

Figure C-4. NOx emissions versus firing rate for process heater FD-4 
C-4 

Figure C-5. NOx emissions versus firing rate for process heater FD-5 

Figure C-6. NOx emissions versus firing rate for process heater FD-6 
C-5 

Figure C-7. NOx emissions versus firing rate for process heater FD-7a 

Figure C-8. NOx emissions versus firing rate for process heater FD-7b 
C-6 

Figure C-9. NOx emissions versus firing rate for proces heater FD-8 

Figure C-10. NOx emissions versus firing rate for process heater FD-9 
C-7 

Figure C-11. NOx emissions versus firing rate for process heater FD-10 

Figure C-12. NOx emissions versus firing rate for process heater FD-11 
C-8 

Figure C-13. NOx emissions versus firing rate for process heater FD-12 

Figure C-14. NOx emissions versus firing rate for process heater FD-13 
C-9 

Figure C-15. NOx emissions versus firing rate for process heater FD-14 

Figure C-16. NOx emissions versus firing rate for process heater FD-15
C-10 

Figure C-17. NOx emissions versus firing rate for process heater FD-16 

Figure C-18. NOx emissions versus firing rate for process heater FD-17 
C-11 

Figure C-19. NOx emissions versus firing rate for process heater ND-1 

Figure C-20. NOx emissions versus firing rate for process heater ND-2 
C-12 

Figure C-21. NOx emissions versus firing rate for process heater ND-3 

Figure C-22. NOx emissions versus firing rate for process heater ND-4 
C-13 

Figure C-23. NOx emissions versus firing rate for process heater UD-1 

Figure C-24. NOx emissions versus firing rate for process heater UD-2 
C-14 

Figure C-25. NOx emissions versus firing rate for process heater UD-3 

Figure C-26. NOx emissions versus firing rate for process heater UD-4 
C-15 

Figure C-27. NOx emissions versus firing rate for process heater UD-5