Characteristics Study On Pyrolysis And Gasification Of Zhundong Coal

Zhundong coalfield is the most abundant basin of coal resources in Xinjiang, which is also the largest integrated coalfield in China and in the world. Sodium content in Zhundong coal is very high, which is rare in China. Recently, with the large scale development and utilization of Zhundong coal, the contamination and agglomeration problems induced by sodium have attracted widespred attention.To improve the utilization efficiency of Zhundong coal, the research on clean coal technology should be strengthen. Coal pyrolysis and gasification are important clean coal technologies, which can improve the utilization efficiency of coal, reduce pollutant emission, and make easier for the subsequent conversion and transportation.Circulating fluidized bed (CFB) gasification is a mature coal utilization technology. In the dissertation the pyrolysis and gasification characteristics of Zhundong coal, the forms of sodium in Zhundong coal and the migration of sodium during fast pyrolysis are studied. In addition, a comparative study on gasification reactivity of Zhundong coal and other type of coals is also carried out.TG-MS-FTIR experimental platform was applied to study the effect of heating rate, particle size on weight loss of Zhundong coal during pyrolysis process, and the releasing characteristics of H2, CH4, CO, CO2 were also studied. Several pyrolysis kinetics models were applied to fit coal pyrolysis data, and pyrolysis gas kinetic parameters were also calculated. The maximum weight loss rate during Zhundong coal pyrolysis is in the temperatures between 450-470 ℃; the order of the starting temperature of pyrolysis gas releasing is CH4, CO2, CO, H2; F2 model can fit Zhundong coal pyrolysis process.Four kinds of pretreatment methods, step wise extraction,815℃ high temperature ashing,575℃ low temperature ashing, direct digestion, were applied to determine the total sodium content in Zhundong coal. The content and distribution of sodium and other matel elements in Zhundong coal were also obtained. Fast pyrolysis experiments of Zhundong coal was carried out in a horizontal tube furnace and the chars were characterized with X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray (SEM/EDX), fourier transform infrared spectroscopy (FTIR), inductively coupled plasma-optical emission spectroscopy (ICP-OES). The 575℃ low temperature ashing is an accurate and rapid pretreatment for measurement of sodium content in Zhundong coal. More than 70 percent of the sodium in Zhundong coals is water-soluble. Temperature has important influence on sodium content in Zhundong chars, and pyrolysis temperature and pyrolysis time affect the pore structure, functional groups, aromatic structure of char.TG was utilized to study the influence of pyrolysis temperature, pyrolysis time, heating rate, gasification temperature, atmosphere, etc., on the gasification reactivity of Zhundong coal char. Distributed activation energy model (DAEM) was used to calculated coal gasification activation energy. Compared with the pyrolysis temperature, gasification temperatures can significant influence coal CO2 gasification reaction rate. Rising gasification temperatures from 850℃ to 1050℃, the maximum gasification reaction rate increases thirty times. Steam can promote coal gasification reactivity comparing with CO2, and the effect is more obvious at lower temperatures. The activation energy of char gasification with CO2 increases with the increase of carbon conversion.Coal gasification characteristics are not only relevant to reaction conditions but also relevant to coals feature. Based on circulating fluidized bed gasification projects, the CO2 gasification characteristics with different coal chars were studied by TG. The effects of coal types and gasification temperatures were explored. Random pore model (RPM) and distributed activation energy model (DAEM) were used to fit the gasification reaction. The impact of temperatures on the gasification is more obvious for coals with poor gasification reactivities. Based on circulating fluidized bed gasification operating parameters, the CO2 gasification rate with the variation of carbon conversion can be fitted well with RPM model.This dissertation studied systematicly slow pyrolysis, fast pyrolysis, char sodium element content, the structure and gasification characteristics of Zhundong coal and char, which can provide reference for the application of the circulating fluidized bed gasification of Zhundong coal.