生物质中矿物质在气化条件下的演变行为研究

以稻秸秆和玉米秸秆为原料,考察了弱还原性气氛以及550-1 300℃生物质中矿物质的变化,并采用Fact Sage软件对生物质中矿物质在高温下的演变行为进行了模拟。结果表明,生物质灰中Na和K元素的存在形式相对稳定,部分以气态氯化物的形式挥发出去,部分存在于低熔点硅酸盐或硫酸盐中;Si元素与Ca、Fe、Mg和Al四种元素形成的硅酸盐的变化形式较多,主要形成辉石(Ca,Mg,Fe)_2Si_2O_6]、橄榄石(Ca,Mg,Fe)_2SiO_4]和黄长石Ca_2(Al,Mg)(Si,Al)SiO_7]三类物质,随着温度的升高,部分辉石会转化为橄榄石与黄长石,此三类物质相互作用易形成熔点较低的共熔体而导致矿物质的熔融。方石英和莫来石Al_6Si_2O_(13)]是导致稻秸秆流动温度高于玉米秸秆的主要原因,莫来石最终转化为斜铁辉石FeSiO_3]、铁尖晶石FeAl_2O_4]和钙长石CaAl_2Si_2O_8]等熔点较低的矿物质。

Evolution behaviors of mineral matters in biomass under gasification conditions

The composition and reaction of mineral matters in rice straw and corn stalk were investigated in weak reducing atmosphere at temperature range of 550-1300℃. The FactSage was also used to simulate the evolution behaviors of mineral matters under high temperatures. The results show that the existing form of Na and K in biomass is relatively stable, including volatilized chlorides, silicates and sulphates with a lower melting point. The silicates made up of Si, Ca, Mg, Fe and Al have various forms, mainly including pyroxene, olivine and melilite. Pyroxene is transformed into olivine and melilite with the increasing of temperature. The interaction of the three kinds of materials could result in the generation of eutectics which could lead to the melting of mineral matters in biomass. The formation of cristobalite and mullite leads to a higher flow temperature of rice straw ash than corn stalk ash, the mullite ultimately is transformed into low melting point materials like clinoferrosilite, iron spinel and anorthite.