| Biomass/coal co-combustion and oxy-fuel combustion technology both contribute to the reduction of CO2 emission, and it is significant to alleviate the current energy shortage and the greenhouse effect by the relevant feasibility study which combining the two technologies. So far, the gradual heated TGA has widely been adopted to study the co-combustion characteristics of coal and biomass blends which do not coincide with practical industrial application. In this paper, the co-combustion characteristics, NO and SO2 release laws of coal and biomass blends in the oxygen enriched atmosphere have been studied by means of a improved constant-temperature thermogravimetric test rig. Besides, the effects of biomass on coal combustion characteristics are mainly embodied in the effects of volatile matter on coal char since volatile content of biomass is far greater than that of coal. So the coupling action between volatiles and char combustion has also been studied. The results show that:Volatiles can accelerate burning rate but also can rob the oxygen around char particle during combustion process. With the decrease of temperature, the accelerated burning rate enhances and the robbing oxygen due to volatiles reduces. As the coal rank decreases, the effect of volatiles on accelerating burning rate and robbing oxygen become much stronger. As environmental oxygen concentration decreases, the burning process of volatiles and coal char shows a tendency of separation. The co-combustion of coal and biomass blends can be divided into two stages: i.e., the devolatilization and the combustion of char. It has little effects on the stage of devolatilization when changing oxygen concentration. Compared to air atmosphere, the sample in the oxygen enriched atmosphere leads to a slighter burnout time delay at 21% oxygen concentration. As environmental oxygen concentration increases, the average weight loss rate of coal enhances. Along with the blending biomass ratio increasing, the coal combustion promoting effect enhances while the coal combustion promoting effect weakens with the coal rank decreasing. With the increase of temperature, the promoting effect of blending biomass on coals reduces, which is most obvious for Indonesia coal. With blending three kinds of biomass, the samples’ burnout time is significantly reduced, in which the burnout time of blending corn cob is the shortest. In NO and SO2 instantaneous release curves of Yangquan coal blending corn cob, two peaks are appeared both in air and oxygen enriched atmosphere at 21% oxygen concentration. NO and SO2 cumulative emissions in oxygen enriched atmospheres less than that in air atmosphere. As oxygen concentration increases, NO instantaneous release curve with two peak was changed into one peak, and NO and SO2 cumulative emissions increases. At 30% O2/CO2 atmosphere, only corn cob exists two peak obviously in NO instantaneous release curves of coal, biomass and their blends, and SO2 instantaneous release curves of all samples show a strong release peak and a slow release peak. As the blending biomass ratio increases, NO and SO2 cumulative emissions show a decreasing tendency. NO and SO2 cumulative emissions of all samples increase with the temperature rising. NO and SO2 cumulative emissions of three kinds of coal blending corn cob decrease in different degree. And NO and SO2 cumulative emissions of Yangquan coal blending three kinds of biomass decrease. Besides, the two-component stage reaction kinetics model applying to biomass/coal combustion at constant temperature is established, where some parameters which can reflect the differences between volatile and char combustion reaction mechanism and the difficulty degree of two stages can be obtained. The simulated value and experimental value can be fitted well using this model under different temperature, oxygen concentration, biomass blending ratio and coal types. |
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