Emissions control from stationary engines has been mandated to varying degrees over the years, depending on factors such as engine size, location, site limits, operating hours, annual emissions rates, and regional nonattainment status. Emissions of nitrogen oxides (NOx), carbon monoxide (CO) and volatile organic compounds (VOCs) specifically have been targeted. In addition to the proposed NSPS, the Environmental Protection Agency already has issued the National Emission Standards for Hazardous Air Pollutants (NESHAP) to control formaldehyde, acetaldehyde, acrolein and methanol emissions from stationary internal combustion engines.
Stationary reciprocating internal combustion engines provide the horsepower to compress natural gas in a variety of applications at every stage of the gas supply chain–from production and gathering, to processing and storage, to natural gas transmission and distribution. The spark-ignited engines packaged with gas compressors typically burn natural gas as the feedstock in both rich-burn (stoichiometric) and leanburn configurations.
Primary measures to reduce exhaust emissions involving in-cylinder modifications can be effective, but they also can adversely impact performance. Increasingly, secondary measures such as installing catalytic conversion technologies are being specified to meet local and national emissions standards. Applying exhaust gas treatment to stationary sources can be particularly challenging because of the vast array of applications, with different duty cycles, durability demands, packaging constraints and regulatory requirements. However, reliable solutions are available for both rich- and lean-burn stationary engines that provide high conversion efficiencies to reduce emissions of CO, hydrocarbons, VOCs, HAPs, NOx, and where applicable, particulate matter. Although lean-burn engines may offer operational advantages to the owner, such as improved fuel efficiency, compared to a rich-burn design, the cost to install emissions control can be significantly higher for lean-burn engines.