Clearstone Engineering Ltd.
January 11, 2016
Executive Summary
Limited data is currently available on N2O emissions from natural gas-fired equipment in the upstream oil and gas (UOG) industry and the N2O emission factors presently in use have high uncertainties. The primary objective of this study was to determine N2O emission factors for selected types of natural gas-fired equipment commonly used in the UOG industry, namely, process heaters, reciprocating engines, and stationary gas turbines. In addition, emission factors were determined for CH4, CO, CO2, and NOx. Measurement campaigns were conducted in May 2014, December 2014, and April 2015 at five sweet gas processing plants in southern Alberta. A total of twenty-one sources were surveyed including ten process heaters, eight reciprocating engines, and three stationary gas turbines. A mobile combustion laboratory featuring an array of continuous analysers and temperature sensors was used to monitor the fuel and flue gas compositions and exhaust gas temperature for each source. Three cavity ringdown spectrometers were used to measure N2O, CO, CO2, CH4, O2, and H2O concentrations in the flue gas and a chemiluminescence analyser was used to measure NO and NO2 concentrations. The fuel gas was analyzed for CO2 and C1 to C5+ compounds using an optical gas chromatograph. A heated filter, heated sample line, and chiller were used to condition the sample gas in accordance with US Environmental Protection Agency (EPA) Recommended Operating Procedure (ROP) No. 56. The setup described above is the final version; modifications were made after the first two campaigns to enhance the system capabilities. Measurements at each source were conducted for an average of 25 minutes. Flue gas concentrations of N2O were <1 ppm for all but one source (i.e., a 4-stroke leanburn reciprocating engine). N2O flue gas concentrations are expected to be <5 ppm from all combustion sources except for fluidized beds due to the fast destruction reactions of N2O during combustion at high temperatures (Hayhurst and Lawrence 1992). N2O emission factors determined from the measurements were less than 1.5 ng/J for all sources expect for one 4-stroke lean-burn reciprocating engine. N2O emission factors for gas turbines agree with those published by the US EPA, while measured N2O emission factors for process heaters and reciprocating engines are about five times less than reference values published by the US EPA and Environment Canada (EC), but within the assessed uncertainty bounds of those values. The reference US EPA and EC values are based on studies of limited sources conducted during the 1990s. A sampling bias is known to be present in N2O measurements conducted in this era using grab samples (Ryan and Karns 1993; Hayhurst and Lawrence 1992). This may explain the discrepancy between the reference emission factors and those determined in the present study.
13-AU-ARPC-01