Exergy Destruction Mechanism of Coal Gasification by Combining the Kinetic Method and the Energy Utilization Diagram

Gasification is the core unit of coal-based production systems and is also the site where one of the largest exergy destruction occurs. This paper reveals the exergy destruction mechanism of carbon gasification through a combined analysis of the kinetic method and the energy utilization diagram (EUD). Instead of a lumped exergy destruction using the traditional "black-box" and other models, the role of each reaction in carbon gasification is revealed. The results show that the exergy destruction caused by chemical reactions accounts for 86.3% of the entire carbon gasification process. Furthermore, approximately 90.3% of exergy destruction of chemical reactions is caused by the exothermal carbon partial oxidation reaction (reaction 1), 6.0% is caused by the carbon dioxide gasification reaction (reaction 2), 2.4% is caused by the steam gasification reaction (reaction 3), and 1.3% is caused by other reactions under the base condition. With increasing O₂ content α and decreasing steam content β, the proportion of exergy destruction from reaction 1 decreases due to the higher gasification temperature (a higher energy level of energy acceptor in EUD), while the proportions of other reactions increase. This shows that the chemical efficiency is optimal when the extent of reactions 1 and 3 is equal and the shift reaction extent approaches zero at the same time.