Firing straw for the production of electricity with/without producing of district heating

摘要

Like other western countries Denmark has, during the past decade, assigned considerable resources to research and demonstration projects of new energy sources to replace the traditional fossil fuels. In Denmark this has resulted in increased industrial competence within several fields. The power production based on biomass is such a newly developed area of industrial competence. During the last 10 years the power generating companies in Denmark erected five (5) purely straw fired plants and three (3) plants fired with a mixture of straw and other fuels for a combined production of electricity and district heating. The straw consists of baled residues from the agricultural production of grains such as wheat, barley, rye, oat and linseed rape. Up till now, straw was regarded as a valueless product and simple burning of the straw in the fields was conducted. Law now prohibits this and the power generating companies are obliged - from the year 2000 - to utilize more than 1.2 million tons of straw and 0.2 million tons of wood chips in the production of electricity. Plant sizes up to 10 MWe with drum type boiler and one 40 MWe with a once-through boiler are in commercial operation. The 40 MWe plant is the world's first straw-fired once-through steam boiler with steam parameters of 122 t/h, 210 bar and 542°C. The steam boiler is connected in parallel to an existing coal-fired 2000 t/h steam boiler serving the same steam turbine which produces 630 MWe in total. By firing 120,000 tons of straw and 30,000 tons of wood chips yearly the coal consumption can be reduced by 80,000 tons. Nature is in that way spared 190,000 tons of carbon-dioxide (CO_2) yearly. This paper will deal with following items: - Straw as fuel; - Straw handling and storage; - Firing system for straw; - Combustion principle; - Control of fouling; - Straw price; - Power Plants; - Problems when firing straw; - Governmental initiatives; - Economy; - References.