Trace compounds affecting biogas energy utilisation

Why it matters

According to the researchers, the demand for renewable fuels is increasing with growing concern about climate change, air quality and energy import dependence and depletion of fossil fuels. Biogas is a versatile renewable fuel which can be used for power and heat/cool production or it can be upgraded to biomethane and used as vehicle fuel. Biogas can be used on a production site, or it can be distributed through the gas grid and it can also be liquefied. Biogas production potential is significant; it has been suggested that major part of the EU 27 renewable energy target for year 2020 will originate from bioenergy and at least 25% of bioenergy could be met with biogas produced from wet organic materials including animal manure, whole crop silages, wet food and feed wastes. The main components of biogas are methane and carbon dioxide, but typically biogas also contains hydrogen sulphide and other sulphur compounds. In some production sites biogas may also contain compounds such as siloxanes and aromatic, halogenated and other volatile organic compounds and ammonia. Various volatile organic compounds have been identified especially in landfill gas. In several cases landfill gas has been reported to contain more than one hundred different trace compounds such as halogenated and aromatic hydrocarbons. Trace compounds in biogas are sampled and analysed using several different methods, although currently there is no standardised method either for sampling or analysis. The authors reviewed information about trace compounds in biogas affecting energy utilisation in various biogas production sites. In previous research publications, organic silicon compounds have been mentioned as the most harmful compounds affecting energy utilisation in biogas produced from waste materials. The authors also included a brief discussion of organic silicon compounds.

Reference

The article appears in the November/December 2011 issue of the Energy Conversion and Management journal (volume 52, issue 12, Pages 3369-3375). Authors: S. Rasi, J. Läntelä & J. Rintala.

Abstract

This paper investigates the trace compounds affecting energy utilisation in biogas that come from different production sites. With biogas being more widely used in different energy applications more interest has arisen for the specific composition of biogas. In traditional energy applications, methane and hydrogen sulphide contents have had the most influence when energy utilisation application has been considered. With more advanced processes also the quantity and quality of trace compounds is more important. In regards to trace compounds, it was found that the concentrations and the variations of volatile organic compounds (VOCs) can be high in different landfills, especially, with compounds originating from the biological degradation process (like aromatics and terpenes) as seasonal variations affect the biological degradation. Trace compounds produced by direct volatilisation (halogenated and silicon compounds) show a smaller seasonal variation. Halogenated compounds are rarely present in high concentrations in waste water treatment plant (WWTP) biogas, but the concentrations of organic silicon compounds and their variation is high. Organic silicon compounds are usually detected only in low concentrations in co-digestion plant biogas, when no WWTP sludge is used as a raw material.