RDE610 Methane Slip - Exhaust Gas Treatment Options

Descriptions

Methane slip is the term used to describe the portion of methane (fuel) that passes through a gas engine without being combusted and is emitted to atmosphere via the engine exhaust. It may also describe methane that is not captured during biogas upgrading and is emitted with the off-gas via the process vent stack. This project is primarily concerned with methane slip from (stationary, reciprocating) lean-burn gas engines used to generate electricity or for cogeneration (CHP). Lean-burn gas engines are commonly deployed at landfill sites, wastewater treatment facilities and anaerobic digestion plants to generate electricity from the methane rich biogas produced by those sites. The gas engines are typically in the 500kWe to 2MWe range. Lean-burn engines are generally favoured over other types due to their higher fuel efficiency and lower NOx emissions. However, the combustion conditions that favour lower NOx formation typically result in higher methane slip rates as an inherent part of the engine operation. Historically, the options to treat exhaust gases to remove unburned methane have been limited. The low exhaust temperatures associated with lean-burn engines hindered the operation of the 2 or 3-way catalyst systems often used for emissions reduction. However, the Environment Agency is aware that considerable research has been taking place on methane slip reduction and that viable exhaust treatment techniques may now or may soon be commercially available. The Environment Agency proposes to let a project to review current and emerging techniques for the abatement of methane in lean-burn engine exhausts.