A study of upgrading technologies of biogas for a biogas plant

The biogas production in Sweden year 2014 was 1,8 TWh where almost 1 TWh was upgraded to biomethane for use in vehicles. The production of biomethane is mainly located at the biogas plants that have a production over 200-400 Nm3/h. This is mainly due to the fact that the investment and operating costs becomes too high for the small producers with low biogas flows. The government of Sweden has a highly ambitious goal of having a vehicle fleet that runs on at least 80 % renewable fuels in the year 2030. To reach that goal even the small biogas producers needs to start upgrading their gas to be able to replace fossil fuels with renewable biomethane. The aim of this master thesis has been to supply enough information to Norrmejerier about whether or not to upgrade the biogas by summarizing relevant research papers and calculate energy flows and costs for each upgrading technology.The limitation of the thesis has been that the production of biogas with different incoming substrates have been neglected due to it being constant in each scenario that has been compared. After a thorough literature study about relevant upgrading technologies the water scrubber and membrane technology was chosen as the best fit for Norrmejerier’s biogas plant. This was mostly due to that the water scrubber is in no need for chemicals duting operation and that some waste water could be used from the dairy plant at Norrmejerier. In the case for the membrane technology it had a low investment cost coupled with a stable operation without the need for surveillance. A relatively new ash upgrading technique was also considered briefly where the need for ash was estimated to 10 000 – 17 000 metric tonnes a year with the assumed biogas production of Norrmejerier. The supply of ash in Umeå municipality were about 5000 metric tonnes which is far below the demand for the biogas upgrading plant. The production of biogas at Norrmejerier is enough to sustain all their own truck transports with biomethane plus that they can sell the excess to the public. The cost-estimates were calculated for the scenario if Norrmejerier builds their own refilling station and in the scenario if they would sell it to a fuel supplier instead. The cost of upgrading for both upgrading technologies ranged from 0,53 to 0,54 SEK/kWh independent of the two previously mentioned scenarios. Both technologies had a payback period of two years and a few months. The membrane technology however gave a higher economical value with a greater yearly capital income mainly because of its longer economical lifetime. The limited lifecyle assessment compared the different uses of the produced biogas to calculate the emissions of carbon dioxide equivalents for each scenario. The assessment revealed that the emissions can be reduced by about 1700 metric tonnes carbon dioxide equivalents per year if the biogas is upgraded to biomethane and Norrmejerier supplies its own trucks with this renewable fuel.