While composed primarily of methane and carbon dioxide, biogas also contains a host of contaminants including moisture, hydrogen sulfide, and Non Methane Organic Compounds (NMOCs). The most problematic NMOCs are called “siloxanes” which are a family of man-made organic compounds used in the manufacture of cosmetics, hygiene products, foods, and industrial coatings. The use of these compounds is increasing rapidly - and so is their presence in landfills and waste water.

 

As the material in a landfill or digester decomposes and generates biogas, the siloxane molecules enter the biogas stream as a vapor. During combustion these siloxanes undergo a phase change from a vapor to a solid silicon dioxide powder. This abrasive powder adheres to all surfaces downstream of the point of combustion, reducing heat transfer, blocking flow and increasing wear. Frequent overhaul is often required to prevent total equipment failure. The increased equipment maintenance and parts failures can significantly increases project costs while the downtime and reduced efficiency significantly decreases revenue.

 

The reduction of siloxane vapors prior to combustion to eliminate siloxane powder build up may be critical to the profitability of your biogas to energy project. In projects requiring the use of post combustion catalysts, siloxane vapor reduction is an absolute necessity.

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Siloxane and VOC reduction is also often necessary to protect biogas upgrading processes including membranes, or water / amine washes, and to meet the necessary gas quality specifications for pipeline injection or vehicle fueling.