Experimental Study On Pyrolytic Semi-Coke Combustion Characteristics Based On High-Speed PLIF Diagnostic Techniques

In the current context of energy structure,coal resources still occupy a major part of China's energy consumption.Due to the shortcomings of traditional coal utilization methods,such as low recycling efficiency and excessive discharge of pollutants,it is in conflict with the current shortage of energy resources in China.Therefore,how to make a cascade utilization of coal resources to achieve an efficient and clean utilization has become an important issue that needs to be resolved.In order to solve the problem of utilization of ultra-low volatile carbon-based fuels,the project had investigated the ignition and combustion behaviors of pyrolysis semi-coke under different combustion conditions based on an optical diagnostic type of portable flow combustion reaction system.The combustion law of the pyrolysis semi-coke with temperature(1600K-1800K),oxygen concentration(5%-30%)and different blending ratio were analyzed in depth,which had certain guiding significance for the pure semi-coke combustion technology and the application of cooperative combustion technology with coal.In this project,the ignition and combustion characteristics of Shenmu pyrolysis semi-coke were studied by means of optical measurement and coal char test,respectively.In the experiment,high-speed ICCD camera was used together with a high-repetition-frequency,high-energy and tunable laser system to collect OH stimulated radiation fluorescence signals in single particle flames and particle group jet flames.The flame information of the pyrolytic semi-coke in the combustion process was obtained by analyzing the intensity and distribution range of the OH signal.The experimental results show that because of the small amount of volatile matter in the semi-coke,the ignition mode was mainly based on the heterogeneous ignition mode that occured on the surface of the particles,and the ignition delay decreased with increasing oxygen concentration and temperature,but combustion reaction intensity increased.In addition,by comparing the normalized curve of CH* spontaneous emission signal intensity and the signal distribution pseudo-color map under different combustion conditions,the displaying results also proved the correctness of the conclusion.It is noteworthy that the full-band black body radiation flame images taken by the SLR camera show that as the oxygen concentration rose above the medium oxygen concentration(20%),the semi-coke particles underwent thermal burst due to their structural characteristics,and the phenomenon was alleviated during the process of blending and co-combustion with Shenhua coal.In view of the differences in combustion performance of the blended fuels,this project was equipped with seven different blending ratios for OH-PLIF experiments.The results show that when blending ratio was around 30%,the mixed fuel had the shortest ignition delay and maintained sufficient combustion intensity.Moreover,the flame deflagration phenomenon had also been weak.According to the changes of burnout rate and pore characteristics of pyrolytic semi-coke under different combustion conditions,carbon residue samples were collected during the experiment for research.The carbon content calculation results show that both the volatilization precipitation rate and the fixed carbon conversion rate increased with the increasing oxygen concentration and temperature.By the analysis of the nitrogen adsorption experiments results combined with microscopic surface images under scanning electron microscopy(SEM),it was found that a large number of broken and collapsed pore structures were distributed at low oxygen concentrations,and the micro and mesopores were extensively consumed as the oxygen concentration increased which led to a sharp reduction in specific surface area and a substantial increase in pore volume,and the surface become smooth and mellow;In the case of oxygen concentration remained constant but the temperature rose,the ash melting on the surface of the residual char appeared,and the impact on pore structure and the burnout rate of semi-coke was not significant,which meant that simply increasing the temperature of the flue gas to improve the combustion characteristics of semi-coke under high temperature conditions was not very profitable.