Valmet's solution to utilize high ash coals in CFB boiler

摘要

Valmet has a long history supplying boilers for high ash coal firing. Technology is based on circulating fluidized bed (CFB) technology. CFB's biggest benefit is fuel flexibility - it can burn fuels from high moisture content to high ash content. Valmet has delivered several CFB boilers burning waste or high ash coal starting on 80's. CFBs burning anthracite waste (ash content 65 %) and bituminous coal (ash content 50%) have been in operation over twenty years meaning that there is a long term experience from these plants available. Recently Valmet studied the possibility to fire even higher ash content coal i.e. residue coming from coal washing plants. In India, for example, coal washing is mandatory for high ash coal in order not to transport ash. Pre-study of this kind of concept lead to the conclusion that coal washing process can be fine-tuned so that reject's calorific value is only 1100 kcal/kg and that was set as a target for boiler design. Valmet shipped 200 tons of washery reject to its own research centre in Finland. Wide range of fuel characterization tests were done in lab-scale following with a week test run in 4 MW CFB pilot boiler. Test run proved that 1100 kcal/kg can fired without any support fuel in CFB boiler with a little modified design. Test run results gave a good set of data regarding combustion efficiency, emission performance and boiler dynamic behaviour when burning this kind of fuel. Beside of high ash coal experience this paper will introduce some Valmet's most recent coal firing CFB boiler projects globally - two times 135 MWe unit with Indonesin coal, one 90 MWe unit in Czech Rebublic and one 150 MWe multifuel unit in Finland designed to burn also 100% coal.