Siloxanes in Biogas and Landfill Gas White Paper

The waste feedstock used to generate biogas and landfill gas (LFG) often produces siloxanes; silicon-based organic materials that are widely used in industry, e.g. water repellents, cosmetics, deodorants and shampoos. Siloxanes become a significant problem when combusted in combined heat and power (CHP) gas engines; they form silicon dioxide, an abrasive glass-like material which can damage the engines.

There are several filters and clean-up systems available for the removal of siloxanes from biogas, these include chillers, regenerating materials, solvents and activated carbon based filters. All of these systems have a finite capacity to capture organic compounds; once spent, the organic compounds already trapped will begin to leach from the media. Hence the timing of when the filter materials are changed or regenerated is important for maintaining efficient performance of the gas engines.

In order to make judgements on the lifetime of the filter media, it is important to be aware of changes in the VOC (Volatile Organic Compound) content of the inlet and outlet gas, the siloxane content of the inlet and outlet gas, and the moisture content (particularly in the summer) of the inlet gas. Gas chromatography-Mass Spectrometry (GC-MS) can analyse for these compounds, confirm the identity of the siloxane and provide information on other contaminants within the gas.

Biomethane is a purified form of biogas with a higher concentration of methane, which can be injected into natural gas pipelines and used as a fuel for vehicles. There are many benefits to the use of biogas and biomethane as fuel sources, including the reduction of greenhouse gas emissions from organic waste decomposition, the replacement of fossil fuels, and the diversion of waste from landfills for sustainable waste management.