BIOMASS CFB GASIFIER CONNECTED TO A 350 MWTH STEAM BOILER FIRED WITH COAL AND NATURAL-GAS - THERMIE DEMONSTRATION PROJECT IN LAHTI IN FINLAND

The successful experience in developing the advanced Foster Wheeler En ergia Oy's (former Ahlstrom Pyropower) Circulating Fluidized Bed combu stion system subsequently led to the development of the CFB Gasificati on Technology in the early 80 s. The driving force for the developing work was the dramatically increase in oil price during the oil crises. The primary advantage of CFB gasification technology is that it enabl es the substitution of expensive fuels e.g. oil or gas with cheap soli d fuels. These cheap fuels are typically different types of waste wood s, bark or other biofuels. In the CFB gasifier these solid fuels are c onverted to gaseous fuel which can be used instead of other expensive fuels. In some cases this also solves a waste disposal problem, provid ing a secondary economic and environmental benefit. Foster Wheeler Ene rgia Oy has supplied four commercial scale atmospheric CFB gasifiers i n the mid 80 s to the pulp and paper industry with capacities from 17- 35 MW based on fuel input. These applications utilize waste wood as fe edstock and the units are still successfully operational today. Lahden Lampovoima Oy is a Finnish power company producing power and district heat for the city of Lahti. The company is 50% owned by the city of L ahti and 50% by Imatran Voima Oy, which is the largest utility power c ompany in Finland. Lahden Lampovoima Oy operates the Kymijarvi power p lant locating nearby the city of Lahti in Southern Finland. To keep th e energy prices as low as possible, Lahden Lampavoima is continuously looking for the most economical fuel sources, and simultaneously, tryi ng to improve the environmental acceptability of the energy production . At the moment, about 300 GWh/a different type of biofuels and refuse fuels are available in the Lahti area. On an annual basis, the availa ble amount of biofuels and refuse fuels is enough to substitute for ab out 15% of the fuels burned in the main boiler equaling max 30% of coa l. The aim in this Lahden Lampovoima Oy's Kymijarvi power plant gasifi cation project is to demonstrate the direct gasification of wet biofue l and the use of hot, raw and very low-calorific gas directly in the e xisting coal-fired boiler. The gasification of biofuels and co-combust ion of gases in the existing coal-fired boiler offers many advantages such as: recycling of CO2, decreased SO2 and NOx emissions, efficient way to utilize biofuels and recycled refuse fuels, low investment and operation costs, and utilization of the existing power plant capacity. Furthermore, only small modifications are required in the boiler, pos sible disturbances in the gasifier do not shut down the power plant. ( C) 1998 Elsevier Science Ltd. All rights reserved.