Technical Report

Biogas upgrading technologies – developments and innovations

October 2009

Biogas is produced during anaerobic digestion of organic substrates, such as manure, sewage sludge, the organic fractions of household and industry waste, and energy crops. It is produced in large scale digesters found preliminary in industrial countries, as well as in small scale digesters found worldwide. Biogas is also produced during anaerobic degradation in landfills and is then referred to as landfill gas. The worldwide biogas production is unknown, but the production of biogas in the European Union was estimated to be around 69 TWh in 2007. The biogas production in the European Union has steadily increased over the last years (Fig. 1).

Biogas consists mainly of methane and carbon dioxide and it can be utilized as a renewable energy source in combined heat and power plants, as a vehicle fuel, or as a substitute for natural gas. The methane in the biogas can also be utilized in industrial processes and as a raw material in the industry.

• Production and utilization of biogas has several environmental advantages such as:
• It is a renewable energy source.
• It reduces the release of methane to the atmosphere compared to e.g. traditional manure management or landfills.
• It can be used as a substitute for fossil fuels.
• A high quality digestate that can be used as a fertilizer is produced simultaneously with biogas.

Depending on the end use, different biogas treatment steps are necessary. For some applications, where it is important to have a high energy content in the gas, e.g. as vehicle fuel or for grid injection, the gas needs to be upgraded. The energy content of biogas is in direct proportion to the methane concentration and by removing carbon dioxide in the upgrading process the energy content of the gas is increased.

Upgrading of biogas has gained increased attention due to rising oil and natural gas prices and increasing targets for renewable fuel quotes in many countries. New plants are continually being built. The number of upgrading plants was around 100 in 2009 (Fig. 2).

The process of upgrading biogas generates new possibilities for its use since it can then replace natural gas, which is used extensively in many countries. However, upgrading adds to the costs of biogas production. It is therefore important to have an optimized upgrading process in terms of low energy consumption and high efficiency giving high methane content in the upgraded gas. It is also very important to minimize, or if possible avoid, emissions of methane from the upgrading process, since methane has a greenhouse gas effect 23 times greater than that of carbon dioxide. This means that the methane content in the reject gas, in the water from a water scrubber, or in any other stream leaving the upgrading plant should be minimized.

Several techniques for biogas upgrading exist today and they are continually being improved. In parallel, new techniques are under development. These new developments, both for new and more traditional techniques, can lower investment costs and operational costs. The developments can also lead to other advantages such as lower methane emission which is important from both an economical and environmental perspective. In this brochure the latest developments in biogas upgrading are reviewed.

This publication is produced by IEA Bioenergy’s Task 37: “Energy from biogas and landfill gas”. More information about the group as well as publications can be found on www.iea-biogas.net.