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 use them as renewable energy sources in Combined Heat and Power (CHP) units and national grids systems. Siloxanes in the shape of methyl siloxanes (incl. 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) presented in biogas upgraded to biomethane quality are detrimental to engines, turbines and gas grids, therefore it is necessary to remove them before its high-value utilization. Under the oxidation, process 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 of biogas and biomethane quality in context to their utilization in CHP units and national gas grids. Moreover, the methods of siloxanes removal based on adsorption, absorption, cryogenic condensation, membranes, and biofiltration are described.