Ash transformations in pulverised fuel co-combustion of straw and woody biomass

Abstract

Ash transformation processes have been studied during co-firing of wheat straw and pine stem wood and softwood bark. Pilot-scale trials in a 150 kW pulverised-fuel-fired burner were performed. Thermodynamic equilibrium calculations were made to support the interpretation of the results. The results show that fast reactions involving gaseous ash compounds are favored at the expense of reactions where condensed components participate. Accordingly, the conditions promote gas phase reactions resulting in the formation of chlorides, sulfate and carbonates whereas reactions involving condensed reactants are suppressed. Both the slagging and fouling propensity of all co-firing mixes was reduced compared to that for pure straw. For the wood/straw mixes this was mainly due to a dilution of the ash forming elements of straw whereas for straw/bark, an additional effect from interaction between the fuel ash components was observed to primarily reduce slagging. In general it can be concluded that under powder combustion conditions equilibrium are approached selectively and that the ash matter are strongly fractionated. The general results in this paper are useful for straw-fired power stations looking for alternative co-firing fuels.

Toxicological characterization of particulate emissions from straw,Miscanthus, and poplar pellet combustion in residential boilers

“…Previous studies have reported high particulate emissions and increased slagging tendencies of straw pellets, even with improved air staging in domestic appliances ( € Orberg et al 2014;Kortelainen et al 2015), which has limited their use to mainly medium-and large-scale combustion systems (Nordgren et al 2013). When the toxicity of the emissions was evaluated, we found that straw pellet combustion induced the most pronounced inflammatory effects of the pellet fuels, but otherwise the responses were on a similar level to the emissions from the Miscanthus sp.…”

The grate-kiln induration machine - history, advantages, and drawbacks, and outline for the future

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A Study on the Migration Behavior of K, Na, and Cl during Biomass Gasification

“…Biomass resources are favored because they are clean, renewable, contain low levels of nitrogen, and can effectively address the pollution and global warming problems presented by traditional energy sources (Ma et al 2008;Khan et al 2009;Qin et al 2010;Kirtay 2011). Biomass gasification technology is an advanced means of biomass energy conversion; however, the high alkali metals content in straw wastes, such as corn straw and rice straw, can accumulate in the ash on gasifier heating surfaces, from slag-bounding in a furnace, and from agglomeration of bed material and similar technologies Niu et al 2010;Nordgren et al 2013) because of the sticky deposition layer of sodium and potassium (Doshi et al 2009). Therefore, it is essential to study the migration and conversion of alkali metals during biomass gasification.…”