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 cola 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. Coal-sawdust blends of 93:7% by weight and 80:20% by weight were tested. Co-firing trials were conducted over a range of the following process variables: process temperature, excess air ratio and air distribution. Neither of the two coal-sawdust blends used produced any significant ash-related problems provided the blend volume was 7% by weight sawdust and the process temperature did not exceed 1250ºC. It was observed that in addition to the nitrogen content in the co-fired blend, the volatile content and particle size distribution of the mixture also influenced the level of NOx emissions. The brown coal-sawdust blend generated a further reduction of SO2 due to the higher sulphur capture rate than for coal alone. 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

Experimental researches of the effect of vegetable oil addition on the emissions during combustion of coal liquid fuels

“…The known works [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] are devoted to co-combustion of coal with all sorts of biological additives. As additives to coal fuels are used waste wood (sawdust, chips) [11,12], straw [13], vegetable oils (e. g. sunflower and olive oils) [14,15], olive cake [16,17], fruits stone [18], coconut shell [19], sunflower husk [20,21], rapeseed oil [22], glycerol [23], rice husk [24]. The processes of preparation, ignition, combustion, and formation of gaseous emissions and ash have been considered at cocombustion of coal and biomass (with varying mass fractions of each component of the mixture).…”

“…The processes of preparation, ignition, combustion, and formation of gaseous emissions and ash have been considered at cocombustion of coal and biomass (with varying mass fractions of each component of the mixture). The vast majority of the results indicate a significant reduction in the amount of emissions due to the involvement of plant additives in the process of energy generation [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. However, much less works aim at studying the combustion processes of composite liquid fuels with an admixture of a vegetable component.…”

Requested characteristics of new sustainable coal-fired thermal power plants in Bosnia and Herzegovina

“…Preporu~eno je da se u pogonu budu}ih termoenergetskih blokova u Termoelektrani "Kakanj" ograni~i udio pepela u smjesi ugljeva na 30% kako bi se pove}ala energijska efikasnost procesa. Istra`ivanje u prethodnom smislu se nastavlja [20][21][22][23][24][25]. U skladu s rezultatima ovih istra`ivanja kao najprikladnija tehnologija sagorijevanja za novi blok u Termoelektrani "Kakanj" preporu~uje se tehnologija sagorijevanja ugljene pra{ine u letu sa suhim re`imom odvo|enja {ljake.…”

“…Mije{anje biomase s ugljem je izvr{eno na depou uglja, a tako stvorena mje{avina je dopremana trakama do bunkera i uvo|ena u kotao kroz postoje}e mlinove i gorionike. Nije uo~en nepovoljan uticaj na energijsku efikasnost, proces sagorijevanja i fleksibilnost pogona [11,22].…”

Ash related problems with biomass combustion – application to co-firing in large scale boilers

“…Little operating experience on co-firing of wood has been published. Results from pilot-scale test facilities and full scale tests vary: no change, increasing or decreasing problems [75]; [76]; [77]. An attempt to use standard fusibility correlations to evaluate the influence of co-firing wood on boiler slagging gave non-equivocal results [75].…”