Co-firing Bosnian coals with woody biomass: Experimental studies on a laboratory-scale furnace and 110 MWe power unit

Thermal Science

卷:16

关键词: co-firing;    coal;    woody biomass;    ash;    deposits;    slagging;    NOx emission;    SO2 emission;   

DOI  :  10.2298/TSCI120120122S

来源: DOAJ

【 摘 要 】

This paper presents the findings of research into cofiring two Bosnian colatypes, brown coal and lignite, with woody biomass, in this case sprucesawdust. The aim of the research was to find the optimal blend of coal andsawdust that may be substituted for 100% coal in large coal-fired powerstations in Bosnia and Herzegovina. Two groups of experimental tests wereperformed in this study: laboratory testing of co-firing and trial runs on alarge-scale plant based on the laboratory research results. A laboratoryexperiment was carried out in an electrically heated and entrainedpulverized-fuel flow furnace. Coal-sawdust blends of 93:7% by weight and80:20% by weight were tested. Co-firing trials were conducted over a range ofthe following process variables: process temperature, excess air ratio andair distribution. Neither of the two coal-sawdust blends used produced anysignificant ash-related problems provided the blend volume was 7% by weightsawdust and the process temperature did not exceed 1250ºC. It was observedthat in addition to the nitrogen content in the co-fired blend, the volatilecontent and particle size distribution of the mixture also influenced thelevel of NOx emissions. The brown coal-sawdust blend generated a furtherreduction of SO2 due to the higher sulphur capture rate than for coal alone.Based on and following the laboratory research findings, a trial run wascarried out in a large-scale utility - the Kakanj power station, Unit 5 (110MWe), using two mixtures; one in which 5%/wt and one in which 7%/wt of browncoal was replaced with sawdust. Compared to a reference firing process with100% coal, these co-firing trials produced a more intensive redistribution ofthe alkaline components in the slag in the melting chamber, with aconsequential beneficial effect on the deposition of ash on the superheatersurfaces of the boiler. The outcome of the tests confirms the feasibility ofusing 7%wt of sawdust in combination with coal without risk to the efficiencyof the unit, its combustion process and with the benefits of emissionsreductions. Furthermore, they show that no modification to the existing coaltransport system and boiler equipment is necessary to achieve this outcome.

【 授权许可】

Unknown