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At the Vereinigte Ville landfill site in Erftstadt-Liblar close to Cologne a test plant was situated.
© AVG Köln
Gas purification with catalytic separation and activated carbon
Projektinfo 11/2014
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Clean use of landfill gas

In the production of landfill gas, other gases are produced alongside the desired methane that damage motors and turbines. To protect these plant components, trace compounds of organic silicon contained in the gases are separated beforehand, e.g. by means of adsorption. The high consumption of the adsorbent, however, endangers the efficiency of the process. A research team has developed an on-site regeneration method for the adsorbent. This can increase the efficiency of the energy recovery of landfill gas.

Biogas is produced in landfill sites, sewage treatment plants and agricultural biogas facilities. It is produced through the biological decomposition of organic waste under exclusion of oxygen. Its primary constituents are carbon dioxide and up to 60 per cent methane. Owing to the high methane content, biogas is used for energy generation. Trace compounds of organic silicon contained in the gases, however, damage motors and turbines. In the combustion process within the engine compartment, these are converted into silicon dioxide owing to the prevailing high temperatures and deposited there. This leads to greater wear of the components and results in reduced operating hours. An upstream gas purification method is consequently employed. Various technical solutions exist, such as scrubbing, refrigeration drying, adsorption with activated carbon and molecular filtering. Adsorption with activated carbon is the most commonly used method.

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A research project conducted by Siloxa Engineering and Fraunhofer UMSICHT investigated how the gas treatment process could be made economically and technically more efficient. Two method variants were tested in this regard, one involving activated carbon adsorption with subsequent regeneration and the other catalytic separation from activated aluminium oxide. Activated carbon absorbs not only the trace elements of organic silicon, but also other organic trace compounds present in abundance in landfill gas and non-hazardous for engine operation, such as hydrocarbons, terpenes and sulphur compounds. The result is poor utilisation of the adsorbent. For this reason, the activated carbon must be frequently exchanged. This high rate of consumption results in added costs, which to a certain extent endanger the economic utilisation of the landfill gas. As a solution, the research group has successfully tested an on-site regeneration method for the activated carbon. The idea is to increase the service life of the activated carbon and consequently to reduce the number of exchanges by regenerating the adsorbent on site. The combination of thermo and vacuum desorption lends itself to this endeavour. In this process, the absorbed compounds are cast out by generating a vacuum with simultaneous temperature increase.

In the test plant, the desorbent was collected using an adsorber filled with activated carbon, termed a control filter. Disposal of the desorbent using a high-temperature gas burner is envisaged for the industrial implementation of the process.

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Addresses

Project management, planning, development and commissioning of mobile test plant
Siloxa Engineering AG

Scientific support for gas analytics and plant operation
Fraunhofer UMSICHT

Links

Funding programme Biomass energy use
Website of the Funding programme of the German Federal Ministry for  Economic Affairs and Energy (BMWi)

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