The use of additives and fuel blending to reduce emissions from the combustion of agricultural fuels in small scale boilers

Effect of Additives and Fuel Blending on Emissions and Ash-Related Problems from Small-Scale Combustion of Reed Canary Grass

“…Pure wood pellets, in comparable combustion conditions, produced almost half of this amount (621 mg·Nm and 983 mg·Nm −3 , signifying that additives allowed a decrease of particles ranging from 17% to 29% compared to pure reed canary grass. These numbers almost correspond with particle drops (31%-57%) obtained by Bäfver et al [20], Tissari et al [11] and Carroll and Finnan [17] when kaolin was added (2-5 wt%) to agricultural products (oat grain, miscanthus, or tall fescue). As the latter authors stated, addition of additives with very low concentration of K or high amounts of Al and Si counteracts K volatilization from energy crops during the heating process and thus reduces PM emissions.…”

“…Kaolin mainly acts by binding alkali compounds in ash and by forming K-or Na-Al silicates that have a higher melting temperature than pure K or Na silicates [17][18][19]. Some works [20,23,28,29] also reported that the addition of kaolin almost eliminated Cl in fly-ash particles whereas HCl levels raised.…”

“…Since the primary cause of emissions is the elemental composition of the feedstock, an alternative, which does not imply possible modifications to the heating system and can act on ash-related problems, is modifying the biomass chemical properties through the use of additives or fuel blending [17]. Additives refer to a group of minerals or products that can alter the ash chemistry, convert problematic species to less troublesome forms and enhance the ash melting temperature in thermal processes.…”

“…Additives can be introduced before combustion by blending them with the fuel prior to pelletizing the admixture produced [18]. Based on their reactive compounds, additives can be classified as aluminum silicates, calcium, or sulfur based additives [17][18][19].…”

“…Aluminum (Al) silicates based additives, such as kaolin, have been exhaustively studied and have shown an ability to abate particle emissions [11,17,[20][21][22][23][24] and ash sintering [25][26][27] during combustion of agricultural crops and residues. Kaolin mainly acts by binding alkali compounds in ash and by forming K-or Na-Al silicates that have a higher melting temperature than pure K or Na silicates [17][18][19].…”