Study On The Combustion And Pollutant Emission Characteristics Of Steam Coal Blent With Biomass

In this paper, the combustion characteristics of three different ranks of steam coal and six common biomass (including sunflower-seed husks, bagasse, furfural residue, vinasse, platanewood and corncob) and their blending were studied using thermo-gravimetric analysis technique respectively, and impacts of biomass type, heating rate and the blending ratio on the combustion characteristics of samples were researched, which led to the dynamics of the sample combustion; a tube heating furnace was applied to study the pollutant emission characteristics of separate biomass, coal and their blending, and analyze the impacts of furnace temperature and blending ratio on the pollutant emission characteristics.First, this paper utilized TGA/SDTA851e comprehensive thermal analyzer to study the combustion characteristics of steam coal blended with biomass. Weight loss of biomass combustion fell into two stages:the first stage (240～380℃) was cellulose and lignin pyrolysis and release and combustion of volatile; the second one (＞380℃) was the coke combustion stage. The scope of weight loss in the first phase was large, with a narrow temperature range, which was the main phase of biomass combustion. In the region, the weight loss rate of agricultural waste (sunflower-seed husks, bagasse, platanewood and corncob) was as high as 70%, and that of industrial waste (furfural residue and vinasse) was 50% or more. The weight loss in the second stage was relatively smoothing, with a wide reaction temperature range, whose weight loss and weight loss rate were significantly lower than those of the first stage. The actual burning rate curves of coal blended with biomass in various ratios were basically in agreement with calculated ones, but slightly different:the experimental data of devolatilization stage was slightly lower than the calculated value, and that of coke combustion stage was higher than the calculated value. With the increase of heating rate, to whether single coal, biomass or their blending, TG curves moved to higher temperature, DTG curve peak position was also deviated to the right, the maximum weight loss rate correspondingly increased, while the combustion time reduced, and flammability index increased. Secondly, in this paper, different treatments of thermal analysis curves containing Freeman-Carroll method, improved Coats-Redfern method and Ozawa method were utilized to compute the experimental data, solving the kinetic parameters of its combustion. According to the improved Coats-Redfern method, the best'n'value of combustion mechanism function of six kinds of biomass and three different ranks of coal were calculated, solving the apparent activation energy of their various stages. With a combination of three kinds of dynamic analysis methods, it was found that for the combustion of biomass and coal alone, in the initial stages of combustion, the reaction activation energy and frequency factor of biomass and coal were large, and for the main stage of combustion, as the heating rate increased, the activation energy and frequency factor were gradually reduced, so that burning rate of biomass and coal gradually increased with the increased heating rate, indicating the increase of heating rate was conducive to biomass and coal activity. Ozawa method results further showed from another side, in different stages of combustion, combustion activation energy of biomass and coal was different, and as the reaction degree'a'increased, the activation energy of biomass increased first and then decreased, while activation energy of coal and blending of coal and biomass was decreased.Finally, using the tube heating furnace the sulfur and nitrogen emission characteristics of combustion of steam coal blended with biomass, and influence laws of factors such as furnace temperature and blending ratio were investigated. The results showed that in coal combustion, SO2 release was divided into two phases:the first one corresponded to the combustion stage of devolatilization in coal, which was formed by combustion of the organic sulfur and part of pyrite sulfur in coal; the second one was formed by organic sulfur, pyrite sulfur and a small amount of sulfate sulfur, whose combustion needed a high temperature. In biomass combustion except furfural residue, one single peak of SO2 release was formed, and SO2 release characteristics of furfural residue were similar to coal. Except furfural residue, in the combustion of coal blended with biomass, as the proportion of biomass increased, there was a reduction in SO2 release peak, SO2 emissions, and SO2 emission time; for furfural residue, with the increase of the furfural residue ratio, SO2 emissions reduced when its sulfur content was lower than coal; when higher, SO2 emissions increased. For coal blended with biomass, in the former combustion, the lower furnace temperature was, the faster the precipitation of easily decomposable organic sulfur was, the faster SO2 release was, and in the latter combustion, the higher the furnace temperature was, the faster the precipitation of refractory organic sulfur was, the faster SO2 release was, which was consistent with the rule of single coal; Except bagasse and platanewood, with the rise of furnace temperature, SO2 emissions first increased and then decreased, while for coal blended with bagasse and platanewood, SO2 emissions increased gradually; With the increase of furnace temperature, SO2 emission time decreased, and SO2 conversion ratio first increased, then decreased.In single coal combustion, NO release of bituminous coal formed two peaks, while that of lean coal and anthracite both formed one relatively flat peak; While in single biomass combustion, except vinasse and furfural residue, the NO release of all biomass was one peak, while that of vinasse was apparent double peak structure, and that of furfural residue was uneven, with a overall double peak trend. Compared with coal, the NO release time of biomass was short, and mainly concentrated in the former combustion. In combustion of coal and biomass alone, with the increase of nitrogen content in samples, the NO conversion ratio of coal and biomass decreased overall, but the NO emissions had no obvious regularity with nitrogen content of the sample itself. In combustion of coal blended with biomass, the biomass made NO release earlier, and release time decrease, and with the increase of the biomass ratio, NO emission time reduced. Except vinasse, with the increase of biomass ratio, NO emissions decreased, while for vinasse whose nitrogen was higher than that of coal, NO emissions first increased, then decreased.