Characteristics Study On Pyrolysis And Gasification Of Typical Coals

Flue gas of coal power plant is the main resourcese of atmospheric pollution in China, and the fundamental way to improve the efficiency of coal utilization and reduce environmental pollution caused by coal utilization is to research and develop optimal utilization technologies, which has become the development direction of the coal industry, one of the possible ways is to research, develop and apply the coal gasification technology. Although various coal gasification technologies had been developed successfully in foreign countries, advanced coal gasification technology in China is still in development stage. Therefore, the research of coal gasification technology that suitable for our country's situations is of particular practical significance to satisfy the requirement of the economic development to coal clean utilization.This thesis provided an overview of the present researches on coal gasification. It revealed the key factor of the coal gasification process. The following investigations are made in this thesis:Thermal gravimetric analyzer STA 409C with portable infrared spectrometry (FTIR) GASMET DX-4000 is used to investigate the pyrolysis processes of some typical coals, including the reaction kinetics and the analysis of gas products. A comprehensive study on pyrolysis temperature and coal properties is analyzed, at the same time, pyrolysis products of the combustible gases and pollutants are mainly detected in this chapter.Rapid-pyrolysis cokes and slow-pyrolysis cokes are made in a tube furnace, and coal samples are dematerialized by pickling. Thermal gravimetric analyzer and tube furnace are used to perform coal gasification characteristic respectively with the help of FTIR on-line measurement, to study the impact of gasification temperature, coal property, devolatilization, demineralization by pickling, the coal particle size and the reaction rate on the yields of the product gas in the gasification progress. According to the TGA gasification experiments, it's indicated that, compared with coal and slow-pyrolysis cokes, rapid-pyrolysis cokes gasification can make the mineral influence more remarkable. It points that when the coal particle size is over 0.15mm, instead of smaller than 0.074mm, the differences of CO2 gasification conversion rates are not obvious. Meanwhile the study also indicated that raising the concentration of CO2 in the coal gasification process can increase the concentration of combustible gas products and pollutants NO and SO2.The physical structures of coals with different ranks have been studied by surface area analysis and low-temperature ashing experiments. It finds that high ash coal is very easy to felt at high temperatures, seriously affecting the pyrolysis and gasification reaction. In the char-making process, there are multi-molecular layer adsorption and capillary condensation phenomenon in the inner of char, and the pore types are various. The Fourier transform infrared spectroscopy have also been used to studied the chemical structures of coal and char. Detailed characteristics of coal properties, demineralization, char-making temperature and heating rate on coal/char chemical structure are studied. It pointed that pickling process mainly removed crystalline SiO2 and soluble salt. With the increase of coal rank, minerals in coal are in combination with the molecular structure more closely, resulting in dematerializing by pickling more difficult. Moreover, the lower the coal rank is, the more complex the coal structure is, the more serious peaks association is. In addition, the effects of pickling, char-making temperature and heating rate on the coal groups are selectivity. Comparing with the infrared parameters to characterize the molecular structure of coal, it is found that pickling would affect certain groups, but has little effect on the molecular structure of coal.Based on the experiments, kinetics parameters of typical coals pyrolysis were detemined, and a multi-step reaction mechanism of pyrolysis was used to simulate coal pyrolysis. There is good correlation between the experiments and the simulation results. It is important to investigate the reaction mechanism of pyrolysis and gasification.