Saija Rasi

Bio: Saija Rasi is an academic researcher from University of Jyväskylä. The author has contributed to research in topics: Biogas & Anaerobic digestion. The author has an hindex of 14, co-authored 32 publications receiving 1644 citations.

Biogas composition and upgrading to biomethane

Abstract: Rasi, Saija Emilia Biogas composition and upgrading to biomethane Jyvaskyla: University of Jyvaskyla, 2009, 76 p. (Jyvaskyla Studies in Biological and Environmental Science ISSN 1456-9701; 202) ISBN 978-951-39-3618-1 (PDF), 978-951-39-3607-5 (nid.) Yhteenveto: Biokaasun koostumus ja puhdistaminen biometaaniksi Diss. The feasibility of biogas in energy production was evaluated in this thesis by determining the composition of biogas from different sites and evaluating the effectiveness of water absorption for landfill gas upgrading. Methane, carbon dioxide, oxygen, nitrogen, volatile organic compounds (VOCs), including organic silicon compounds, halogenated compounds and sulphur compounds, were measured in biogas samples from landfills, waste water treatment plants (WWTP) sludge digesters and biogas plants processing different material. Methane content in the studied landfills, WWTPs and biogas plants ranged from 47 % to 70 %, carbon dioxide from 32 % to 43 % and nitrogen from < 1 % to 17 %. Oxygen content in all the measured gases was < 1 %. The highest methane content was found in the gas from one of the biogas plants while the lowest methane and highest nitrogen contents were found in the gases from landfills. Hydrogen sulphide and other sulphur compounds were found in higher amounts in the gases from landfills and biogas plants than in the WWTPs. The total amount of organic silicon compounds was highest (up to 10 mg/m3) in one of the studied WWTP, and lowest (24 μg/m3) in the biogas plant processing grass and maize. Organic silicon compounds were also detected in all the biogases produced in the batch assays from energy crops, with higher yields in the grass (from 21.8 to 37.6 μg/kg-volatile solids (VS)) than grass silage or maize assays (from 14.7 to 20.4 and from 7.4 to 12.1 μg/kgVS, respectively). A counter-current absorption process upgraded the landfill gas near to or above 90 % methane content. The carbon dioxide content of the product gas ranged from 3.2 to 4.8 %. With a high pressure water absorption system product gas with methane content ranging from 83 to 92 % was achieved. The carbon dioxide content of the product gas ranged from 4 to 6 %. Hydrogen sulphide was removed from the raw landfill gas with over 99 % efficiency with both upgrading systems, and halogenated compounds with 96 % efficiency with the counter-current process and from 83 to 91 % efficiency with the high pressure process. The silica gel gas drying unit, used in the high pressure process, removed about 66 % of volatile organic compounds from the gas. The results of this study show the feasibility of biogas upgrading for energy production. However, depending on the gas utilization application, the occurrence of trace compounds should be taken into account when planning an upgrading unit for biogas.