Power boiler fuel augmentation with a biomass fired atmospheric circulating fluid-bed gasifier

Abstract

The successful experience in developing the advanced Foster Wheeler atmospheric circulating fluidized-bed (ACFB) combustion system subsequently led to the development of the ACFB gasification (ACFBG) Technology in the early 1980s. The driving force for the development work was the dramatic increase in oil price during this period. The primary advantage of the ACFBG technology is that it enables the substitution of expensive fuels (e.g. oil or gas) with cheaper solid fuels. Prior to this Lahti project, Foster Wheeler had supplied four waste wood fired commercial scale ACFBGs in the mid-1980s to the pulp and paper industry with capacities from 17 to 35 MW th based on fuel input. These units are still in successful operation today. Lahden Lämpövoima Oy (LLOy) is a Finnish power company producing power and district heat for the City of Lahti. The company is jointly owned by the city of Lahti and by Fortum Oy, the largest utility power company in Finland. LLOy operates the Kymijärvi Power Plant located nearby the city of Lahti in Southern Finland. To keep the energy prices as low as possible, Plant personnel are continuously looking for the most economical fuel sources, and simultaneously, trying to improve the environmental aspects of the energy production. Currently, about 300 GW h/a of different types of biofuels and refuse fuels are available in the Lahti area. On an annual basis, the available amount of biofuels and refuse fuels is enough to substitute for about 15% of the fuels burned in the main boiler, equaling up to 30% of the coal typically used. The aim of the LLOy Kymijärvi Power Plant gasification project is a commercial scale demonstration of direct gasification of wet biofuel and the use of hot, raw and very low calorific gas directly in the existing coal fired boiler. The gasification of biofuels and co-combustion of gases in the existing coal-fired boiler offers many advantages such as: recycling of CO 2, decreased SO 2 and NO x 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 were required in the boiler and process upsets in the gasifier do not shut down the power plant. The first two years of operation (1998 and 1999) have been excellent with good availability for the gasifier and its related components. During 1998 several measurements and tests with different fuel combinations were performed. This paper presents the project in detail as well as the most important results of the first measurements. The EU Thermie program has supported this project.