Future Combustion Engine Power Plant WP4 Fuel - Fuel Flexibility: Minimum limit for biogas upgrading

The task on minimum limit for biogas upgrading for medium speed engines concentrated on siloxanes, which were deemed to be a weak spot. A review of costs of siloxane removal techniques, and construction of a test bench to study a few siloxane removal techniques were performed. This report describes performed cost assessment, constructed removal test facility and removal test results. Cost assessment results covered biogas plants with total energy (electricity + heat) capacities of 1 MW, 4 MW, 20 MW and 40 MW. According to the results, siloxane removal in capacity of 1 MW biogas plant had lowest costs with replaceable activated carbon. As low siloxane removal cost in biogas plant with capacity of 4 MW was shown to be with regenerable polymer adsorption and with replaceable activated carbon. In plant capacity of 20 MW or more the regenerable polymer adsorption was seen to have lowest costs. Commonly in plants having high biogas production capacity the regenerable siloxane removal medias have lower costs due to their long usage time before media needs to be replaced.

Experimental work covered the construction of the test facility and siloxane removal tests of three different siloxane removal systems. Tested removal systems were: Activated carbon, Siloxane removal system and Silicagel based media. Tests were performed in nitrogen matrix and injected impurities were siloxane D5, siloxane D6, limonene and toluene. As a result, the activated carbon had the highest siloxane removal capacity in these tests. Silica gel media had a siloxane removal capacity of almost as high as activated carbon. Siloxane removal system had a siloxane removal capacity of half when compared with activated carbon.

Utilisation of biogas is increasing rapidly and research data for removal capacities are needed for different biogas mixtures. Results of this research can be used when choosing best available and cost-effective siloxane removal system into biogas applications. Growing and versatile business of the biogas utilisation needs removal system test facilities in future to ensure comparable removal capacity informations. Test facilities are ready for further siloxane removal tests. Additional tests for other removal systems and with different gas matrix are possible arrange with existing test bench setup.