Energy and exergy analyses of an intensified char gasification process
Conventional coal gasification technologies have been widely used in chemical synthesis and power generation industries, and are regarded as clean technologies for utilising fossil fuel resources. Although it has not yet realised widespread commercial application, fluidised bed gasification technology has the potential for high energy utilisation efficiency if the high carbon content in discharged ash can be decreased. This article introduces a novel concept for an intensified gasification process, and provides a comprehensive energy and exergy analyses comparing this with a conventional fluidised bed gasification process, to demonstrate potential improvements in terms of energy and exergy efficiencies. The results show that the intensified gasification process can increase the energy and exergy efficiencies by 8.1% and 7.1%, respectively, in the gasification temperature range from 850 to 1100 °C, compared with the conventional process. Increasing gasification temperature improves the energy utilisation efficiency, and consumes more oxygen and less steam. It also increases CO yield from 0.957 to 0.997 and lowers H2 yield from 0.498 to 0.442. The exergy analysis shows that irreversible gasification reactions are the major source of exergy destruction. Hence, this should be the focus for improvements in energy utilisation of coal gasification processes.
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