- Wall, TF; Liu, GS; Wu, HW; Roberts, DG; Benfell, KE; Gupta, S; Lucas, JA; Harris, DJ
- Advanced clean coal technologies, e.g. power generation from integrated gasification combined cycle (IGCC) and pressurised fluidised bed combustor, have attracted increased interest from the scientific and technological communities over the last few decades. Pressures up to 40atm have been applied to these technologies, which inherently result in an increase in coal throughput, a reduction in pollutant emissions and an enhancement in the intensity of reaction. Therefore, fundamental understanding of the effect of operating pressure on coal reactions is essential to the development of these technologies. In this paper, the pressure effect on a variety of aspects of coal reactions reported in the open literature has been reviewed. Major emphasis of the paper is given to experimental observations, although some theoretical modelling is reviewed. The pressure has been found to significantly influence the volatiles yield and coal swelling during devolatilisation, hence the structure and morphology of the char generated. More char particles of high porosity are formed at higher pressures. Char structure appears to play a significant role in burnout of residual char and ash formation. In general, at higher pressures, coal particles burn quicker and form finer ash particles. Increasing reactant pressure enhances char combustion and gasification reaction rate, which can be understood by an adsorption-desorption mechanism. These factors have been applied to the understanding of a practical high-pressure gasifier. Most of the work published has been at the lower temperatures (typically < 1000°C), which can be achieved in experiments involving captive particles or coal samples. Experiments in pressurised TGA and wire mesh systems at these low temperatures are the most commonly reported, with some experiments for entrained flow system reported at the higher temperatures typical IGCC conditions in entrained flow reactors. Although the difficulty and cost have restricted these experiments, the entrained flow work is the current research need. The structure of the char generated has recently been related to char reactivity and the ash formed, but the mechanisms leading to the effect of pressure on this structure are not understood. Progressing the understanding of the formation of char structure at pressure and its relation to coal properties is an obvious research need. © 2002 Elsevier Science Ltd. All rights reserved.
- January 1, 2002
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