Abstract
The process of steam gasification of three coals of various rank and three chars obtained from these coals by the ex-situ method at 900 °C was compared. In the coal gasification process, the pyrolysis stage plays a very important part, which is connected with its direct impact on the kinetics of gasification of the resulting char. What is more, taking into consideration the impact of pyrolysis conditions on char properties, it should be anticipated that the gasification kinetics of coal and char, formed from it by the ex situ method, will be different. In order to examine and compare the process of gasification of coals and chars, an isothermal thermovolumetric method, designed by the authors, was applied. For all the examined samples the measurements were performed at three temperatures, i.e. 850, 900, and 950 °C, and at the pressure of 0.1 MPa. An evaluation of the impact of raw material on the steam gasification of the examined samples was made. The carbon conversion degree and the kinetic parameters of CO and H2 formation reaction were calculated. It was observed that the course of gasification is different for coals and chars obtained from them and it can be concluded that coals are more reactive than chars. Values of kinetic parameters of carbon monoxide and hydrogen formation calculated for coals and corresponding chars are also different. Due to the observed differences the process of gasification of coals and of chars with steam should not be equated.
Highlights
Coal gasification is a clean and effective method of coal conversion to a gas which has a very broad range of applications in the synthesis of chemicals, substitutes of petroleum and natural gas as well as in power generation [1,2,3]
In the era of dwindling resources of primary energy carriers and increasing consumption, a revival of interest in the gasification technology can be observed, which is reflected in the recent rapid growth of the number of coal gasification plants [4] and the number of works devoted to problems of coal gasification [5,6,7,8,9,10]
One of the fundamental problems is getting to know the impact of the applied raw material on the kinetics of the gasification process
Summary
Coal gasification is a clean and effective method of coal conversion to a gas which has a very broad range of applications in the synthesis of chemicals, substitutes of petroleum and natural gas as well as in power generation [1,2,3]. In order to further develop and optimise the operation of gasification reactors it is necessary to acquire a thorough knowledge of the process and factors which influence it. One of the fundamental problems is getting to know the impact of the applied raw material on the kinetics of the gasification process. In spite of the fact that the gasification of char, limiting the course of the entire process, is the slowest stage, the coal pyrolysis stage, which directly influences char properties, should not be underestimated. Factors having an effect on the reactivity of char, apart from the properties of the applied coal, include: the final temperature of pyrolysis, the rate of its growth, pressure, and the character of the atmosphere [11-23]
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