Oxidative Torrefaction of Some Biomass Kinds in a Fluidized Bed

Recent years have seen increasingly growing attention to decarbonizing the energy sector and decreasing, owing to this policy, the consumption of fossil fuels. Since recycling of waste is among the urgent problems at present, then, seeing that biomass accounts for a significant fraction of waste, efforts taken to more efficiently use it as fuel are becoming of issue. Torrefaction is one of the most acceptable technologies for obtaining high-quality fuel from biomass, the application of which makes it possible to increase the heating value of biofuel, decrease its hydrophilicity, and improve its grindability, all with relatively moderate energy expenditures. The torrefaction process can be further improved by performing it in a gaseous medium with some content of oxygen. This will make it possible to decrease both the energy expenditures for conducting the process and the time taken to perform it. The article presents the results from studying the oxidative torrefaction of three kinds of finely dispersed biomass: ground sunflower husk, chicken litter, and wood sawdust. The process is performed in a fluidized bed with biomass fluidization by subjecting it to smoke gases at a temperature of 250 degrees C and with the oxygen content equal to 2-3 vol %. The study results have shown that, given the polydispersed composition and complex shape of biomass particles, their stable fluidization is possible in a rather narrow range of gas velocities. The oxidative torrefaction process itself takes from 5 to 15 min for its completion, depending on the biomass kind. Such a wide interval of time is due to the presence or almost complete absence of exothermal reactions developing in the process depending on the kind of raw material used. The maximal and minimal exothermal effects take place in performing oxidative torrefaction of sunflower husk and chicken litter, respectively.