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Why using biogas?

Today, biogas is understood to be a renewable and sustainable energy carrier being produced at a high number of sites throughout Europe in the meanwhile. As a substrate, various substances like energy crops, organic residuals or agrarian side products and wastes are used. Beside the numerous trace components like ammonia or hydrogen sulphide the main components of biogas are methane (45 to 70vol%) and carbon dioxide. The state-of-the-art technology for using the energy content of this biogas is the combustion in gas engines together with the generation of electric energy with a normal efficiency of 35 to 40%. Due to the rising prices for energy and raw materials the utilisation of the produced waste heat becomes more and more important in order to achieve an ecologically and economically efficient operation of the biogas plant. As a result, regionally used district heat is produced in many cases together with the electric power. The feasibility and profitability of such biogas plants have been demonstrated frequently and as a result, a considerably high number of these plants have been commissioned during the last decades.

Figure: Conventional utilisation of biogas in Bruck an der Leitha; left: Gas engine (CHP); right: Thermal image of the container for the production of district heat

The upgrading of biogas shows an alternative way of using the energy content of the gas instead of the conventional way of generating electric power and heat. Upgraded biogas can be used as a fully-fledged natural gas substitute in all the natural gas applications like fuel for households and industry as well as propellant for the automotive sector (CNG-vehicles, compressed natural gas). Doing this, the already well-established natural gas infrastructure like pipelines, gas storage tanks and fuelling stations can be utilised to transport the produced gas to the consumers.

According to numerous experts, the utilisation of upgraded biogas as an alternative to the imported natural gas has three major advantages. First of all, the dependency of the European gas market on non-European natural gas producers could be reduced and thus, a higher flexibility in European economy and policy could be achieved. Secondly, the usage of green-house-neutral biogas would strongly support the European efforts on reducing the emission of greenhouse gases and reducing the share of fossil energy carriers on the primary energy consumption. Thirdly, mainly small and locally operating companies would benefit from biogas upgrading resulting in increasing the local added-value of the specific region and the survivability of these companies.

Today, natural gas is a very popular energy carrier throughout Europe and in the whole world, still having high rates of economic growth. The European industry, electric power supply and the households depend to a significant amount on this energy source. The main advantages of natural gas used as an energy carrier are as follows: low transportation costs due to the use of pipelines as well as low emissions of carbon dioxide and other pollutants per unit of produced secondary energy compared to other primary energy carriers. The reorientation of a part of today’s transportation sector towards the utilisation of natural gas (and furthermore, utilisation of biogas) as a vehicle fuel, would result in a significant reduction of emissions (carbon dioxide, nitrous oxides, unburnt hydrocarbons, dust, noise) according to multitudinous experts. The area of CNG power train engineering currently is a field of intense national and international research in order to enhance the efficiency of the engines and the storage capacity of the vehicles. As a result, the range of coverage for vehicles propelled by methane (from natural gas or from biogas) will be extended to the today’s needs.

As a consequence of the named facts, efficient processes for the upgrading of biogas have to be applied. Usually, the production of sustainable and renewable energy carriers show a disadvantageous ratio of produced to invested energy amount. Therefore, the costs for investment and operation of the plants have to be decreased as far as possible. Furthermore, the operation of the biogas upgrading has to be highly automated and the effective personnel requirements have to be minimised to assure controllable personnel cost for the usually relatively small plants.