Abstract
This paper presents a research on ash-related problems and emissions during co-firing low-rank Bosnian coals with different kinds of biomass; in this case woody sawdust and herbaceous energy crops Miscanthus. An entrained-flow drop tube furnace was used for the tests, varying fuel portions at a high co-firing ratio up to 30%wt woody sawdust and 10%wt Miscanthus in a fuel blend. The tests were supposed to optimize the process temperature, air distribution (including OFA) and fuel distributions (reburning) as function of SO2 and NOx emissions as well as efficiency of combustion process estimated through the ash deposits behaviors, CO emissions and unburnt. The results for 12 co-firing fuel combinations impose a reasonable expectation that the coal/biomass/Miscanthus blends could be successfully run under certain conditions not producing any serious ash-related problems. SO2 emissions were slightly higher when higher content of woody biomass was used. Oppositely, higher Miscanthus percentage in the fuel mix slightly decreases SO2 emissions. NOx emissions generally decrease with an increase of biomass co-firing rate. The study suggests that co-firing Bosnian coals with woody sawdust and Miscanthus shows promise at higher co-firing ratios for pulverized combustion, giving some directions for further works in co-firing similar multi-fuel combinations.
Highlights
Specific Objectives and State-of-the-ArtTransition of traditional fossil-fueled power stations into multi-fuel power plants is ongoing.Multi-fuel operation of coal-fired power stations, running different kinds of biomass in co-firing with coal, is nowadays aimed to provide fuel mix diversity to reduce CO2 emissions, improve security of supply and reduce operational costs by fuel cost optimization
For biomass co-firing Tuzla coal blends TET5 and TET7 with woody biomass and Miscanthus, it can be noticed that the increase of the unburnt carbon content (UBC) in the ash deposits collected in
In the slag collected at the bottom of the furnace, the UBC is increased from 0.45% at 15% biomass co-firing, over 3.58% at 20% biomass co-firing to 6.92% at 25% biomass co-firing with TET7 coal
Summary
Multi-fuel operation of coal-fired power stations, running different kinds of biomass in co-firing with coal, is nowadays aimed to provide fuel mix diversity to reduce CO2 emissions, improve security of supply and reduce operational costs by fuel cost optimization. Significant progress was made in biomass co-firing in coal-fired power stations, [1]. Coal is often replaced with up to 30% of biomass by weight in pulverized coal (PC) fueled power stations. Most of these projects refer to co-firing of biomass with high-rank coal (both bituminous and anthracite), (e.g., [3]), while projects with biomass co-firing with low-rank sub-bituminous coal, brown coal or lignite are more scarce, like the project involving
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