Study Of Combustion Kinetic Properties Of Rice Husk,High-Alkali Coal And Their Coke Products By Rapid Heating

Rice husk is a biomass fuel with high yield,high ash and high silica content.Combustion of rice husk mixed with high alkali coal can not only reduce carbon emissions,but also can utilize the ash properties of rice husk ash to prevent the staining and caking problems of high alkali coal.In-depth study of the combustion differences between rice husk and high alkali coal and the unique role of rice husk as an important biomass fuel are of great value to the safe production and carbon reduction of thermal power generation.In this study,we analyzed the differences between the exothermic combustion processes of rice husk and high alkali PRB coals in Anhui Province using differential scanning calorimetry(DSC),produced rice husk coke and high alkali coal coke by rapid pyrolysis using a wire mesh reactor,and calculated the combustion kinetics of rice husk and high alkali coals and their coke products based on the combustion heat release fluxes using the Coats-Redfern integration method to investigate the effects of different pyrolysis temperature conditions on the combustion of rice husk and coal coke.The effects of different pyrolysis temperatures on the combustion characteristics of rice husk coke and coal coke were investigated,and the microscopic morphology and surface Si and K enrichment characteristics of rice husk coke produced by different pyrolysis temperatures were also analyzed by electron scanning microscopy and energy spectroscopy(SEM-EDS).The results showed that the DSC exothermic curve of rice husk combustion showed obvious bimodal characteristics,while the PRB coal had a short combustion temperature region and presented a stronger combustion intensity during the combustion process.The peak temperature of combustion exotherm at 10%rice husk blending ratio was 8.6℃ lower than that of PRB coal alone,and the combustion intensity was 1.4 lower than that of PRB coal alone.kinetic parameter analysis indicated that rice husk blending in PRB coal combustion could reduce the activation energy in the second stage of combustion,and with the increase of rice husk blending ratio,the activation energy could be reduced from 84.066 kJ/mol The rice husk blending ratio of 10%not only reduced the activation energy of the second stage,but also had the least effect on the first stage of PRB coal combustion,and the blending combustion effect was the best.Compared with the slow pyrolysis,the fast pyrolysis process in the wire mesh reactor and the combustion characteristics of its coke products better reflect the pyrolysis and coke combustion characteristics of the fuel during the combustion in the furnace.The combustion characteristics of both rice husk coke and PRB coal coke decrease with increasing fast pyrolysis temperature,but the exothermic heat of PRB coal shows a trend of increasing and then decreasing.The analysis of combustion kinetic parameters showed that the reaction activity of the rapidly produced PRB coal coke and rice husk coke was high,and the activation energy of both rice husk coke and PRB coal coke had a tendency to increase with the increase of pyrolysis temperature.The activation energy of rice husk coke at a pyrolysis temperature of 700℃ was closest to that of rice husk coke at the combustion stage.The activity of PRB coal coke with a pyrolysis temperature of 900℃ is closest to that of PRB coal in the second stage of combustion.PRB coal is more difficult to pyrolyze than rice husk for their coke to have such combustion variability.Microscopic morphological analysis showed that the original rice husk had a distinct protruding structure on the outer surface,while the inner surface was smoother relative to the outer surface.With the increase of pyrolysis temperature,the pores of microstructure on the side of coke grains increased,the combustible material decreased,and the heat that could be released also decreased.Si element was mainly enriched on the outer surface of rice husk coke,and when the pyrolysis temperature was 815℃,the Si element content on the outer surface increased about one time than that on the inner surface.The molten substance attached to the surface of rice husk coke mainly contains C,Si,and K elements,as the pyrolysis temperature increases,and the difference of K element content on the inner and outer surfaces is related to this.