Study On Combustion Characteristics Of Low-Rank Coal Pyrolysis Semi-Coke For Industrial Utilization

Low-rank coal pyrolysis-based staged conversion technology is in line with China's energy structure and policy guidance,which can achieve efficient and clean utilization of low-rank coal.As one of the products of staged conversion technology,the large-scale utilization of low-rank coal semi-coke is beneficial to the large-scale and large-scale staged conversion technology.Based on the national key research and development program of China,this thesis carried out a systematic experimental study on the combustion characteristics of this kind of semi-coke and obtained the differences between the semi-coke and the original low-rank coal,aiming to provide a basis for the relevant equipment transformation and combustion organization of the large-scale utilization of this kind of specific semi-coke and to expand the application scope of the technology of pyrolysis-based staged conversion technology of the low-rank coal.Firstly,the physical and chemical properties of semi-coke,such as coal quality,pore structure and micro surface structure,were obtained,which laid a foundation for the further study of combustion characteristics.Subsequently,a preliminary study on the forming characteristics of semi-coke in industrial boilers was carried out.The results showed that the chemical composition and pore structure of the semi-coke had changed greatly after pyrolysis.Due to the poor forming characteristics of semi-coke,it was difficult to obtain the formed semi-coke with the use strength by cold pressing without binder.Based on the thermo analysis method,an experimental study was conducted on the intrinsic combustion characteristics of the semi-coke and the difference between the intrinsic combustion characteristics of semi-coke and coal was obtained.After that,the blending experiment was carried out.Subsequently,a kinetics study was carried out,which provided a basis for the subsequent setting of the experimental conditions of suspension combustion and model calculation.The results showed that the firing temperature and burn-out temperature of the semi-coke were significantly higher than those of the raw coal.The semi-coke had worse combustion characteristics and the activation energy was slightly higher.The utilization of semi-coke in industry should pay more attention to the problem that it was difficult to burn out.Relying on the self-made drop tube furnace test system to simulate the suspension combustion conditions of pulverized coal boilers,a detailed study was carried out on the burnout characteristics and NO_x emission characteristics of the semi-coke.From the perspective of the quality of combustible conversion rate and the perspective of energy loss of incomplete combustion heat,the difference between the burnout characteristics of semi-coke and coal was analyzed.After that,the differences in furnace temperature,oxygen concentration and particle size were explored.The results showed that,compared with coal,the burnout rate of semi-coke was lower,the heat loss of incomplete combustion was higher,but the NO_x emission concentration was lower.Under reasonable operating conditions,the semi-coke was expected to achieve clean and efficient combustion.A model calculation of the movement and combustion process of semi-coke in the drop tube furnace was carried out and a multi-stage equal-density nuclear shrinkage combustion model was constructed.Then,the model was used to study the combustion of semi-coke in the furnace.