United States Environmental Protection Agency National Risk Management Research Laboratory Cincinnati, OH 45268 Research and Development EPA/600/SR-96/020 April 1996 EPA Project Summary Criteria Pollutant Emissions from Internal Combustion Engines in the Natural Gas Industry Gerald S. Workman Jr., Rachel G. Adams, and Gunseli Sagun Shareef This report contains emission data for oxides of nitrogen, carbon monox- ide, methane, ethane, nonmethane hy- drocarbons, and nonmethane-ethane hydrocarbons from stationary internal combustion (1C) engines and gas tur- bines used in the natural gas industry. The emission factors calculated from test results were from five test cam- paigns conducted as part of the Gas Research Institute's air toxics study, three of which were cofunded by the U.S. Environmental Protection Agency (EPA). Test results for individual en- gines tested are presented, along with full load engine family-specific factors, and the calculated emission factors are evaluated relative to the emission fac- tors published in EPA report AP-42. Units tested included eleven 2-stroke engines and five 4-stroke engines, with and without controls, and two gas tur- bines. This data will enhance the cur- rent data base in AP-42 for stationary 1C engines. It will not only enlarge the population of engine types covered, but will enhance the emission factor qual- ity of several engine categories which have a limited data set. This Project Summary was developed by the National Risk Management Re- search Laboratory's Air Pollution Pre- vention and Control Division, Research Triangle Park, NC, to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back). Background One function of the Air Pollution Pre- vention and Control Division (APPCD) of the U.S. Environmental Protection Agency's (EPA's) Office of Research and Development is improving current air pol- lutant emission inventory methodologies, especially for pollutants associated with tropospheric ozone formation. As part of the improvement of emission inventory methodologies, APPCD supports field emission measurement efforts. These data are used by EPA's Office of Air Quality Planning and Standards (OAQPS) to en- hance their reference document "Compi- lation of Air Pollutant Emission Factors" (AP-42), which contains emission factors for oxides of nitrogen (NOX), carbon mon- oxide (CO), methane (CH4), ethane (C2H6), nonmethane hydrocarbon (NMHC), and nonmethane-ethane hydrocarbon (NMEHC) emissions from the large, stationary inter- nal combustion (1C) reciprocating and tur- bine engines used in the natural gas in- dustry. In AP-42, emission factors for some types of engines, especially those with air pollution controls, are based on an inad- equate amount of emissions test data. To improve the understanding of emissions from these sources, additional testing is needed to enhance the emissions data- base, giving OAQPS the ability to revise AP-42. Emissions characterization of 1C engines in the natural gas industry is currently underway through a program sponsored by the Gas Research Institute (GRI), with the primary focus on determining the po- tential for air toxics emissions. Since in- formation on NOx, CO, CH4, C2H6, NMHC, and NMEHC emissions is needed to com- pletely characterize the 1C engine emis- sions, EPA/APPCD provided cofunding to the GRI program to support gathering such data for enhancement of the emissions ------- database currently used in AP-42 for the development of emission factors. The work described in this document was conducted as part of this joint effort between GRI and EPA and involved: • Field measurements of NOx, CO, CH4, C2H6, and total hydrocarbon (THC) emissions at three test sites (joint EPA/GRI effort); • Incorporation of field data, collected by GRI at two earlier test sites, into the data set for evaluation; and • Evaluation of all test data for use in enhancing the emissions database currently in AP-42. Results Table 1 summarizes full load emission factors for NOx, CO, CH4, C2H6, THC, NMHC, and NMEHC expressed in grams per horsepower-hour and pounds per mil- lion British thermal units. The emission factors were averaged by engine family, and are presented for 2-stroke, lean-burn; 2-stroke, clean-burn; 4-stroke, lean-burn; 4-stroke, clean-burn; and 4-stroke, rich- burn engines; and gas turbines. Separate emission factors were calculated for en- gines using emission control equipment; e.g., nonselective catalytic reduction (NSCR) selective catalytic reduction (SCR), CO oxidation catalyst, or precom- bustion chamber (PCC). Only data from test periods during which the engines were operated within 90% of rated load and 95% of rated speed were used to calcu- late the average emission factors, except when the engine tested was the only one of a particular classification included in the test program, and the engine did not meet the minimum load and speed criteria during any of the test periods. The NOx, CO, and THC emission fac- tors are based on continuous emissions monitoring system (CEMS) measurements while the CH4 and C2H6 emission factors are based on gas chromatography (GC). Emission factors expressed as NMHC and NMEHC are calculated by subtracting the CH4 and CH4/C2H6 concentrations, respec- tively, from the THC concentrations. In some cases, the difference between the measured THC and CH4/C2H6 concentra- tions was less than the analytical preci- sion of the instruments. In these cases, NMHC/NMEHC emissions were not quan- tified. Except for the 2-stroke, lean-burn en- gine family, the information presented in Table 1 is considered limited since the emission factors are based on tests con- ducted on only one to three engines/tur- bines. As expected, there are differences between the emission factors calculated in this study and those in AP-42. The differences between the data from this study and AP-42 can be attributed to the variability associated with the population of engines tested, and differences in the type of instrumentation used during the two studies. Conclusions Based on examination of the test re- sults from this study, the following conclu- sions are offered to enhance the emis- sions database currently in AP-42: • Incorporate emissions data used to develop the emission factors for un- controlled 2-stroke, lean-burn; 4- stroke, lean-burn; and 4-stroke, rich- burn engines; and gas turbines into the current AP-42 emissions data- base. Although the current factors are "A" quality, incorporation of these data will broaden the population of the en- gines covered. Incorporate the data used to develop the emission factors for 2-stroke, clean-burn engines into the current AP-42 emissions database. The cur- rent AP-42 factors are "C" quality. The additional data may upgrade the emission factor quality rating for this category. Use data for NSCR-controlled 4- stroke, rich-burn engine, PCC-con- trolled 4-stroke, lean-burn engine, and the 2-stroke, clean-burn engine with a CO oxidation catalyst to build and/ or improve an emissions database for these categories. The current version of AP-42 has separate emission factors for "clean- burn" and "PCC" controlled engines. "Clean-burn" is a trade name used by one manufacturer to describe modifi- cations to a lean-burn engine to lower emissions. A PCC is a primary com- ponent of the "clean-burn" modifica- tion to these engines. An engine equipped with PCC may also have all of the other clean-burn modifications, as did the one engine with PCC tested under this program. Consideration should be given to combining the emissions database for these control scenarios under a single generic de- scription. ------- Table 1. Full Load Average Emission Factors Engine Family 2-stroke; lean-burn Emission Control — No. of Engines/ Runs? 7/16 Units (g/hp-hr)" (Ib/MMBtu) N0x 14 3.4 CO 0.63 0.15 CH4 4.6 1.1 C2H4 0.31 0.059 THC 5.7 1.4 NMHC 1.1 0.28 NMEHC 0.80 0.19 2-stroke' clean-burn 4-stroke; lean-burn 4-stroke; clean-burn 4-stroke; rich-burn Gas turbine — CO catalyst — SCR catalyst PCC — NSCR catalyst — 1/3 1/1 3/6 1/2 1/1 P/1 1f/2 2/4 (g/hp-hr) (Ib/MMBtu) (g/hp-hr) (Ib/MMBtu) (g/hp-hr) (Ib/MMBtu) (g/hp-hr) (Ib/MMBtu) (g/hp-hr) (Ib/MMBtu) (g/hp-hr) (Ib/MMBtu) (g/hp-hr) (Ib/MMBtu) (g/hp-hr) (Ib/MMBtu) 0.48 0.14 0.54 0.17 14 3.7 5.0 1.3 0.56 0.14 18 5.2 0.050 0.015 1.4 0.31 1.4 0.41 0.11 0.030 0.83 0.21 0.43 0.11 2.0 0.51 15 4.2 0.26 0.075 0.1& 0.03& NA NA NA NA 5.5 1.5 NA NA NA NA NA NA NA NA ND ND 0.38C 0.1 1C NA NA 0.16 0.044 0.15 0.036 NA NA NA NA NA NA ND ND 6.8 2.0 6.3 1.9 4.1 1.1 2.7 0.69 8.0 2.0 3.0 0.85 1.7 0.49 ND ND — c — c — c — c c,d c,d c,d c,d —c C —c — c — c —c ND ND — c — c c c _,,<* c,d c,d —C'" C c —c c c — c ND ND NA = Not available. ND = Not detected. NSCR = nonselective catalytic reduction. SCR = selective catalytic reduction. PCC = Pre-combustion chamber. 'For some pollutants, the number of engines/runs used in the average is less than the total number tested. "There is uncertainty in the horsepower measurements made by the engine analyst for 4 of the 16 runs. CGC hardware malfunction during Campaign 4 prevented collection of data for methane and/or ethane. ''Difference between recorded methane and THC measurements was less than the precision of either instrument. 'Based on one engine tested at 91 % speed and below 90% load. 'Based on one engine tested at 90% speed. gTest results below the detection limits were averaged as zero. ------- G. Workman, R. Adams, andG. Shareefare with Radian Corp., Research Triangle Park, NC 27709 Charles C. Masser is the EPA Project Officer (see below). The complete report consists of two volumes, entitled "Criteria Pollutant Emissions from Internal Combustion Engines in the Natural Gas Industry:" "Volume I. Technical Report" (Order No. PB96-168265; Cost: $25.00) "Volume II. Appendices A-l" (Order No. PB96-168273; Cost: $57.00) The above reports will be available only from: (cost subject to change) National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Air Pollution Prevention and Control Division National Risk Management Research Laboratory U. S. Environmental Protection Agency Research Triangle Park, NC 27711 United States Environmental Protection Agency National Risk Management Research Laboratory (G-72) Cincinnati, OH 45268 Official Business Penalty for Private Use $300 BULK RATE POSTAGE & FEES PAID EPA PERMIT No. G-35 EPA/600/SR-96/020 ------- |