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THE INFLUENCE OF CHEMICAL COMPOSITION OF ASH ON THE COAL GASIFICATION PROCESS
Abstract
The coal gasification process is currently developed as one of clean coal technologies. Gasification is a high-temperature process (above 800 пїЅC) in which the coal reacts with a gasifying agent, e.g. air, oxygen, or water vapor. As a result, under conditions of elevated temperature and pressure, chemical bonds in the molecular structure of coal break up and the mixture of water vapor, oxygen, carbon monoxide, and hydrogen, commonly known as syngas, is produced. The chemical composition of the obtained syngas is dependent on the type and quality of the used coal, gasification factors, gasification conditions (heating rate, residence time, temperature, and pressure), and the installation configuration. The important factors influencing the possibility of using coal in a given technology include the ash content, oxide composition, and the ash melting point. The ash melting point was correlated with the base-acid ratio R, defined as the ratio of the sum of CaO, MgO, Na2O, K2O, and Fe 2 2 3 2 2 2 2 3 SiO +Al O + TiO CaO+MgO + Na O+ K O+ Fe O R ? 2O3 and the total sum of SiO2, Al2O3, and TiO2 in the ash. On this basis it is possible to determine whether the examined coal exceeds the fluid point of ash. The obtained results have confirmed that the fluid point was exceeded in only a few lignites and bituminous coals from Polish deposits. In most cases, the R value was below 1, which allowed indicating their acidic nature. The results of the analysis have shown that the type and properties of mineral matter in coal make it particularly suitable for the use in fluidized bed gasification reactors.
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