EXPANDING CENTRALIZED BIOGAS PLANTS IN DENMARK FOR PURPOSES OF ENERGY PRODUCTION, REDUCING GREENHOUSE GAS EMISSIONS, WASTE RECYCLING, AND OTHER ENVIRONMENTAL AND AGRICULTURAL BENEFITS

Abstract

The concept of centralized biogas plants has been developed over a 10 year period. Manure, mainly as slurry, is transported to the biogas plant from a number of farms. It is co-digested with “clean” organic wastes from abattoirs, food industries and municipalities. The average mixture consists of 75% manure and 25% organic wastes. After digestion the slurry is returned to the farms that delivered the manure or to other crop farmers as a nutritionally defined fertilizer. The gas is used mainly for co-generation of electricity and heat; the electricity production is sold to the grid and the heat is used for district heating of urban communities. The benefits include renewable energy production, reduced greenhouse gas emissions, cheap and efficient organic waste recycling, and improved utilization of the manure as fertilizer. At present (June 1996) 18 plants are in operation serving approx. 600 farms. The plant capacities range from 50 to 500 tonnes biomass feedstock per day. A total of about 1 million tonnes are digested per year. Important preconditions for financial competitiveness of centralized biogas plants include: enhanced gas production and reception fees from co-digestion with organic wastes, high quality key components leading to operational stability and low costs of operation and maintenance, firm plant management, and energy sales prices at the level of DKK 2.5 per m 3 methane. Operational and capital costs as low as DKK 50 per tonne of feedstock are attainable. Thus, centralized biogas plants provide a link to organic waste recycling, which in many cases is cheaper than other options. In April 1996 the Danish government presented its new energy action plan “Energy 21”. Long-term transition to substantial renewable energy supply is one of the key elements. According to the plan, biogas production is to be doubled by the year 2000 and increased 10-fold by the year 2020. A major part of this increase is expected to come from new centralized biogas plants. On average the action plan implies an annual increase of 0.8 PJ biogas. However, for the next few years “only” 0.6 PJ production increase per year is expected.