Potential Reduction of Fugitive Methane Emissions at Compressor Stations and Storage Facilities Powered by Natural Gas Engines

The American Gas Association (AGA) and the United States (US) Energy Information Administration (EIA) report that natural gas reserves, production, and consumption are increasing. Current estimates show over 100 years worth of recoverable reserves. As production increases, the natural gas pipeline interstate will grow or at least experience increased throughput. With the industry expanding at rapid rates and the high global warming potential of methane (21 over a 100 year period), it is important to identify potential sources for reductions in fugitive methane emissions. This research group conducted leak and loss audits at five natural gas compressor station and storage facilities. The majority of methane losses were associated with the operation of the lean-burn, natural gas engines (open crankcases, exhaust), compressor seal vents, and open liquid storage tanks. This paper focuses on the potential reduction in fugitive methane emissions of the discovered industry weaknesses through application of various proven technologies. As engines are not perfectly sealed, blow-by of intake air, fuel, and combustion gases occurs past the piston rings. In order to prevent a build-up of pressure within the crankcase, it must be vented. Diesel engines have lower hydrocarbon emissions from their crankcases due to the short duration of fuel addition after compression of the intake charge. Lean-burn, natural gas engines, like conventional gasoline engines, compress both the fuel and intake air during the compression stroke. During the 1960s, many passenger vehicles adopted positive crankcase ventilation (PCV) or closed crankcase ventilation (CCV) systems to reduce significantly hydrocarbon emissions from engines. Currently, some heavy-duty on-road engines still have open crankcase systems and most off-road engines have crankcases simply vented to the atmosphere. In this paper, researchers will examine the potential reduction in methane emissions that could be realized with the installation of retrofitted CCV systems at these locations. In addition to the reduction of methane losses from the crankcase, it is realized that with proper plumbing, flow control, and safety parameters, all of the losses typically vented to atmosphere could be ducted into the engine intake for combustion. Preliminary results show that applications of closed crankcase systems could reduce emissions from these sites by 1–11% while modifying these systems to include the losses from compressor seal vents and storage tanks could yield potential reductions in methane emissions by 10–57%.