Biogas/Biomethane Quality and Requirements for Combined Heat and Power (CHP) Units/Gas Grids with a Special Focus on Siloxanes-a Short Review

Abstract

The presence of siloxanes in biogas and biomethane is a major barrier to using them as renewable energy sources in Combined Heat and Power (CHP) units and national grid systems. Siloxanes in the form of methyl siloxanes (including L2, L3, L4, D3, D4, D5, D6), Trimethylsilanol (TMSOH), as well as other contaminants such as H₂S, NH3, relative humidity (rH), halogenated compounds (including organic chlorine and fluorine), and volatile organic compounds (VOCs) present in biogas upgraded to biomethane quality are detrimental to engines, turbines, and gas grids; therefore, it is necessary to remove them before their high-value utilization. Under oxidation, siloxanes are converted into microcrystalline silicon dioxide (SiO₂) deposits that can shorten the lifetime of the engine and affect the gas grids. The review presents the actual requirements for biogas and biomethane quality in the context of their utilization in CHP units and national gas grids. Moreover, the methods of siloxane removal based on adsorption, absorption, cryogenic condensation, membranes, and biofiltration are described.