APMM Unit Recommendations/Considerations for AQP Unit Reasonable Progress 

Determination for Devon Energy Blaine County #1 Compressor Station 

Prepared by Claudia Smith 

Emission Limit for 5,500 HP Ingersoll Rand 616 Natural Gas-Fired Compressor Engines 

AP-42 specifies a NOx emission factor of 2.21 lbs/MMBtu for rich-burn natural gas-fired 

reciprocating internal combustion engines. Based on 90% control efficiency typically predicted 

for NSCR add-on control equipment, that would translate to a controlled emission factor of 0.22 

lbs/MMBtu. 

The APMM unit typically sets emission limits as a mass per unit time limit, such as lbs/hr. 

Review of the permit analysis for a since modified version of Montana DEQ’s air pollution 

control permit for this facility (permit number 1626-05) indicated that uncontrolled NOx

emissions from these engines were estimated at 956.13 tpy, or 218.06 lbs/hr. Considering 90% 

control efficiency, that would translate to a controlled emission rate of 95.6 tpy or 21.8 lbs/hr. 

Typical MRR Permit Requirements for Rich Burn Natural Gas-Fired Engines with NSCR 

Note: emission limit is typically a short term mass per unit time limit, such as lbs/hr (this could 

be calculated and recorded as a rolling 30-day average). 

Work Practice and Operational Requirements

1. Each engine shall be equipped with a non-selective catalytic reduction (NSCR - three 

way catalyst) with air-to-fuel ratio control system capable of reducing uncontrolled 

emissions of NOx by at least 90% at maximum operating rate (90% to 110% of engine 

capacity at site elevation). 

2. Install a temperature-sensing device (i.e. thermocouple or resistance temperature 

detectors) before the catalyst in order to monitor the inlet temperatures of the catalyst for 

each engine. 

3. The engine exhaust temperature at the inlet to the catalyst for each engine, shall be 

maintained at all times the engine operates at at least 750oF and no more than 1250oF in 

accordance with manufacturer’s specifications. [Comment: The catalyst inlet 

temperature is important; it has to be hot enough to work, but not so hot as to damage 

the catalyst – the actual temperature range would be dependent on the specifications of 

the manufacturer of the control – the range above is what is found in MACT ZZZZ for 

rich burn RICE with NSCR].

4. Install gauges before and after the catalyst for each engine in order to monitor pressure 

drop across the catalyst. The pressure drop shall not change by more than ± 2” water at 

100% load plus or minus 10% from the pressure drop across the catalyst measured during 

the initial performance test. [Comment: Pressure drop is a good indication of catalyst 

operation; too low, the catalyst may be blown out; too high and it may be clogged].

5. Follow, for each engine and its respective catalyst, the manufacturer’s recommended 
APMM Unit Recommendations/Considerations for AQP Unit Reasonable Progress 

Determination for Devon Energy Blaine County #1 Compressor Station 

Prepared by Claudia Smith 

maintenance schedule and procedures to ensure optimum performance of each engine and 

catalyst. 

6. All engines shall be fired only with natural gas. The natural gas shall be pipeline-quality 

in all respects except that the CO2 concentration in the gas shall not be required to be 

within pipeline-quality. 

[Note: The purpose of requirement 6, above, is to ensure that there are no contaminants in the 

fuel that might foul the catalyst. In general, pipeline-quality natural gas is (1) within ± 5% of the

heating value of pure methane, or 1,010 Btu/per cubic foot under standard atmospheric 

conditions, and (2) free of water and toxic or corrosive contaminants. However, CO2 is not a 

potential foulant of the catalyst and has therefore been excluded from the requirement.]

Testing Requirements

1. An initial performance test shall be conducted for each engine for measuring NOx

emissions from the engines to demonstrate initial compliance with the emission limits. 

The initial performance test shall be conducted within 90 calendar days of the effective 

date of the permit (or in this case, the reasonable progress determination?). 

2. Upon change out of the catalyst for each engine a performance test shall be conducted for 

measuring NOx from the engines to demonstrate compliance with the emission limits and 

re-establish temperature and pressure correlations. The performance test shall be 

conducted within 90 calendar days of the date of the catalyst change out. 

3. The performance tests for NOx shall be conducted in accordance with the test methods 

specified in 40 CFR Part 60, Appendix A. EPA Reference Method 7E shall be used to 

measure NOx emissions. 

4. All tests for NOx emissions must meet the following requirements: 

(a) All tests shall be performed at a maximum operating rate (90% to 110% of engine 

capacity at site elevation). 

(b) During each test run, data shall be collected on all parameters necessary to 

document how NOx emissions in pounds per hour were measured or calculated 

(such as test run length, minimum sample volume, volumetric flow rate, moisture 

and oxygen corrections, etc.). The temperature at the inlet to the catalyst and the 

pressure drop across the catalyst shall also be measured and recorded during each 

test run for each engine. 

(c) Each source test shall consist of at least three 1-hour or longer valid test runs. 

Emission results shall be reported as the arithmetic average of all valid test runs 

and shall be in terms of the emission limits (pounds per hour) and grams per 

horsepower-hour. 
APMM Unit Recommendations/Considerations for AQP Unit Reasonable Progress 

Determination for Devon Energy Blaine County #1 Compressor Station 

Prepared by Claudia Smith 

(d) A source test plan for NOx emissions shall be submitted to EPA at least 45 

calendar days prior to the scheduled performance test. 

(e) The source test plan shall include and address the following elements: 

(i) Purpose of the test; 

(ii) Engines and catalysts to be tested; 

(iii) Expected engine operating rate(s) during test; 

(iv) Schedule/dates for test; 

(v) Sampling and analysis procedures (sampling locations, test methods, 

laboratory identification); 

(vi) Quality assurance plan (calibration procedures and frequency, sample 

recovery and field documentation, chain of custody procedures); and 

 (vii) Data processing and reporting (description of data handling and 

quality control procedures, report content). 

Monitoring Requirements

1. Measure NOx emissions from each engine at least semi-annually or once every 6 month 

period to demonstrate compliance with the emission limits. To meet this requirement, 

measure NOx emissions from the engines using a portable analyzer and a monitoring 

protocol approved by EPA. Submit the analyzer specifications and monitoring protocol 

to EPA for approval within 45 calendar days of the effective date of the permit (or in this 

case, the reasonable progress determination?). Monitoring for NOx emissions shall 

commence during the first complete calendar quarter following the permittee’s submittal 

of the initial performance test results for NOx to EPA. 

2. Measure the engine exhaust temperature at the inlet to the oxidation catalyst at least once 

per week. The pressure drop across the oxidation catalyst shall be measured monthly. 

Each temperature-sensing device shall be accurate to within plus or minus 0.75% of span 

and the pressure sensing devices shall be accurate to within plus or minus 0.1 inches of 

water. 

II.E. Recordkeeping Requirements [40 CFR 71.6(a)(3)(ii)] 

1. Comply with the following recordkeeping requirements: 

(a) Records shall be kept of all temperature and pressure measurements required by 

this permit. 

(b) Records shall be kept of vendor specifications for the thermocouples and pressure 

gauges. 
APMM Unit Recommendations/Considerations for AQP Unit Reasonable Progress 

Determination for Devon Energy Blaine County #1 Compressor Station 

Prepared by Claudia Smith 

(c) Records shall be kept of vendor specifications for the NSCR catalyst and the airto-fuel ratio controller on each engine. 

(d) Records shall be kept that are sufficient to demonstrate that the fuel for the 

engines is pipeline-quality natural gas in all respects, with the exception of the 

CO2 concentration in the natural gas. 

2. Records shall be kept of all required testing and monitoring. The records shall include 

the following: 

(a) The date, place, and time of sampling or measurements; 

(b) The date(s) analyses were performed; 

(c) The company or entity that performed the analyses; 

(d) The analytical techniques or methods used; 

(e) The results of such analyses or measurements; and 

(f) The operating conditions as existing at the time of sampling or measurement. 

3. Records of all required monitoring data and support information shall be maintained for a 

period of at least 5 years from the date of the monitoring sample, measurement, or report. 

These records shall be made available upon request by EPA Region 8. Support 

information includes all calibration and maintenance records, all original strip-chart 

recordings for continuous monitoring instrumentation, and copies of all reports required.

II.F. Reporting Requirements [40 CFR 71.6(a)(3)(iii)] 

Submit to EPA a written report of the results of the required performance tests. This report shall 

be submitted within 90 calendar days of the date of testing completion.