Efficient biogas processing with membrane technique
Biogas produced from grass or energy crops is a gas mixture containing methane (50-75%), carbon dioxide (23-48%), hydrogen (up to approx. 2%) and traces of hydrogen sulphide and ammonia. Biogas, when produced is saturated with water. Biogas can be used for several purposes: direct energetic usage (combustion), combined heat and power generation (gas engines, gas turbines), compression and usage as fuel, and the usage as a natural gas substitute after upgrading and compression.
For the usage as a natural gas substitute it is important to develop an efficient and robust technology to remove carbon dioxide, humidity and traces of ammonia and hydrogen sulphide for the specific requirements in rural areas.
Current technologies have certain disadvantages: using water absorption, for instance, it is difficult to reach the required methane concentration according to the Austrian gas quality directive G31 for the direct usage as a natural gas substitute. Investment costs are usually high and the specific energy consumption as well as the consumption of other resources (e.g. cooling water or fresh water for water scrubbers) are rather high.
It was the main goal of this project to develop a modern and efficient method based on membrane separation technology and to test the technology in combination with a biogas fermentation for the digestion of energy crops. An innovative process design required only one compressor; additionally, the methane losses could be reduced down to below 2%.
For this purpose a mobile pilot plant unit was designed, built and transported to an agricultural biogas production facility using energy crops as fermentation feed source. During the demonstration phase of the project a small bypass raw biogas stream of up to 1 m³/h was upgraded to meet the requirements of the Austrian natural gas quality directive ÖVGW G31. The product gas quality was analyzed and confirmed by an independent laboratory. The results achieved are the basis for a future full-scale design of a biogas upgrading facility. Although the membrane lifetime cannot be estimated from the runs so far, only a small performance decline of the membrane modules was observed.
Another goal of the project involved the screening of new gas analysis techniques for the online monitoring of the product gas. A new technology based on a photoacoustic signal generation was tested by constructing a suitable prototype for the measurement of carbon dioxide. The results are promising and they may be the basis for further development.
Safety measures for the scale up of the technology and suitable control techniques were investigated and recommendations were given for the fully automated plant operation. A concept was developed for the quick shutdown of the upgrading facility.
Finally, a simulation tool was developed to model and scale up the investigated technology. The simulation model considers all the individual unit operations (compression, condensation, gas permeation, adsorption) and will be the basis for a future scale-up.
Project leader (Contact address)
Univ.Ass. Dipl.-Ing. Dr. Michael Harasek
Technische Universität Wien, Institut für Verfahrenstechnik
Getreidemarkt 9/1662, A-1060 Wien
Tel: +43 (0) 1/58801-15925
Fax: +43 (0) 1/58801-15999
Internet: TU-Wien : thermische verfahrenstechnik und simulation
Wien Energie Gasnetz GmbH (Projektpartner)
Axiom Angewandte Prozesstechnik Ges.m.b.H. (Projektpartner)
Biogas Produktionsges.m.b.H. (Projektpartner)
Technische Universität Wien, Institut für Chemische Technologien und Analytik (Werkvertragspartner)