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

Abstract

This paper presents the findings of research into cofiring two Bosnian coal types, brown coal and lignite, with woody biomass, in this case spruce sawdust. The aim of the research was to find the optimal blend of coal and sawdust that may be substituted for 100% coal in large coal-fired power stations in Bosnia and Herzegovina. Two groups of experimental tests were performed in this study: laboratory testing of co-firing and trial runs on a large-scale plant based on the laboratory research results. A laboratory experiment was carried out in an electrically heated and entrained pulverized-fuel flow furnace. Based on and following the laboratory research findings, a trial run was carried out in a large-scale utility - the Kakanj power station, Unit 5 (110 MWe), using two mixtures; one in which 5 wt.% and one in which 7 wt.% of brown coal was replaced with sawdust. Compared to a reference firing process with 100% coal, these co-firing trials produced a more intensive redistribution of the alkaline components in the slag in the melting chamber, with a consequential beneficial effect on the deposition of ash on the superheater surfaces of the boiler. The outcome of the tests confirms the feasibility of using 7 wt.% of sawdust in combination with coal without risk to the efficiency of the unit, its combustion process and with the benefits of emissions reductions. Furthermore, they show that no modification to the existing coal transport system and boiler equipment is necessary to achieve this outcome.