烘焙生物质燃烧过程中钾的赋存形态及析出迁移特性

Occurrence form and release and migration characteristics of potassium during combustion of torrefied biomass

选取稻秆和棉秆为原料,在烘焙预处理后,通过固定床燃烧实验结合HSC Chemistry热力学平衡计算,获得了烘焙生物质燃烧过程中碱金属K的析出和迁移规律。结果表明:烘焙过程中存在着少量水溶性K的释放及其向醋酸铵溶态K的转化,而其转化和释放能力与Cl/K呈正相关。烘焙生物质的成灰率随着燃烧温度的升高而下降,而K的释放率随温度的变化则相反,其主要释放形式为K的氯化物和KOH;此外,600℃时,水溶性K和醋酸铵溶态K主要转化为char-K,700~900℃时其主要转化为K的硅酸盐,随着温度的上升,其转化量不断增加。相比于原生生物质,烘焙生物质有更高的成灰率;此外,烘焙促进了生物质燃烧过程中醋酸铵溶态K向酸溶态或残渣态K转化,同时抑制了水溶性K的释放,这些使得烘焙生物质燃烧过程中K的释放率更低,而烘焙对生物质燃烧过程中K释放的抑制与烘焙过程中Cl的释放率呈正相关。

Rice straws and cotton stalks were selected as raw materials.After torrefaction pretreatment,the fixedbed combustion experiment and HSC Chemistry thermodynamic equilibrium calculations were conducted to obtain the release and migration characteristics of alkali metal K during the combustion of torrefied biomass.The results showed that there was a small amount of water-soluble K release and its conversion to ammonium acetate dissolved K during torrefaction,and its conversion and release capacity was positively correlated with Cl/K.The ash formation rate of torrefied biomass decreased with the increase of combustion temperature,while the release rate of K changed with the temperature on the contrary;K was released in the form of water-soluble K,ammonium acetate dissolved K and acid-soluble K,and its main release form was K chloride and KOH.In addition,water-soluble K and ammonium acetate dissolved K were mainly converted to char-K at 600℃,and mainly converted to K silicate at700—900℃.As the temperature rose,its conversion volume continued to increase.Compared with the raw biomass,torrefied biomass had a higher ash formation rate;in addition,torrefaction promoted the conversion of ammonium acetate dissolved K to acid-soluble K or potassium silicate during the combustion of biomass,and at the same time inhibited the release of water-soluble K.Therefore,the release rate of K during the combustion of torrefied biomass was lower.The inhibition of K release during the combustion of biomass by torrefaction is positively correlated with the release rate of Cl during the torrefaction.