Biogas is a renewable source of energy which when used does not contribute any net emissions of carbon dioxide into the atmosphere. Biogas can be produced in many different ways, including anaerobic digestion, landfill, gasification or Power to Gas.
Biogas production through anaerobic digestion
The majority of biogas in Sweden is produced at anaerobic digestion plants. At an anaerobic digestion plant, microorganisms break down the substrate, e.g. food residue, sludge from wastewater facilities or energy crops, and in doing so forms a biogas (raw gas), which comprises approximately 60% methane and 40% carbon dioxide. In order to be able to use the biogas as a fuel in vehicles the gas needs to be upgraded, i.e. the carbon dioxide is removed using, for example, a water scrubber.
The Jordberga biogas facility, which is located inTrelleborg, is the largest anaerobic digestion plant in Sweden. The raw material comprises mainly locally produced energy cereals that are grown in integrated cultivation systems. The surplus biogas from Jordberga is injected into Swedegas transmission grid.
Biogas production through thermal gasification
Thermal gasification means that wood residue and carbon waste, e.g. residual forest products, are heated up under controlled conditions whereupon the hydrocarbon compounds in the fuel are broken down into mainly carbon monoxide and hydrogen gas (synthetic gas). The temperature in the gasifier is normally 500-1,400°C. Through methanisation of the synthetic gas, biogas can be produced with a level of quality similar to natural gas.
Göteborg Energi is focusing on implementing this gasification technology on a commercial scale through GoBiGas (Gothenburg Biomass Gasification Project). The raw material in biogas production will comprise residual forest products in the form of wood chips and branches and treetops. The biogas from GoBiGas will be fed into the Swedegas gas grid.