MITIGATION ASH-RELATED PROBLEMS BY COFIRING COAL WITH WOODY BIOMASS IN CASE OF KAKANJ THERMAL POWER PLANT – EXPERIMENTAL AND TRIAL RUN

摘要

Thermal power plant Kakanj (2x118 MWe, 1x230 MWe) uses blend of brown coals of Middle Bosnia –rnfrom a coal basin with huge coal reserves. Principally it is low grade brown coal with very high percentage of ash -rnover 40%, high sulphur content and inconvenient ash composition, exhibiting a strong tendency to slagging andrnfouling. The very high percentage of ash particularly makes clear certain differences between this coal type comparedrnwith some other world coal types, providing a strong argument for investigating the specific ash-related problems asrnwell as ways to improve combustion behavior. Co-firing with woody biomass is one of the possible solution for thernimprovement and that is the subject of investigation in this study. Two groups of experimental tests were performedrnin this study: laboratory testing of co-firing and trial run on a large-scale plant based on the laboratory researchrnresults. A laboratory experiment was carried out in an electrically heated entrained pulverized-fuel flow furnace.rnCoal-woody biomass blends of 93:7% by weight and 80:20% by weight were tested. Biomass used in this case isrnspruce sawdust. Co-firing trials were conducted over a range of the following process variables: process temperature,rnexcess air ratio and air distribution. Neither of the two coal-sawdust blends used produced any significant ash-relatedrnproblems provided that the process temperature did not exceed 1250 ℃. Based on and following the laboratoryrnresearch findings, a trial run was carried out in a large-scale utility - the Kakanj power station Unit 5 (118 Mwe),rnusing two mixtures; one in which 5%/w and another in which 7%/wt of brown coal was replaced with the woodyrnsawdust. Compared to a reference firing process with 100% coal, these co-firing trials produced a more intensivernredistribution of the alkaline components in the slag in the melting chamber, with a consequential beneficial effect onrnthe deposition of ash on the superheater surfaces of the boiler. The outcome of the tests confirms the feasibility ofrnusing 7%w of woody sawdust in combination with the coal without risk to the efficiency of the unit, its combustionrnprocess and with the benefits of emissions reductions as well as reducing ash deposits problems. Furthermore, theyrnshow that no modification to the existing coal transport system and boiler equipment is necessary to achieve thisrnoutcome.rnKeywords: