Thermal Plasma Gasification of Different Coals with Carbon Dioxide

Carbon dioxide emissions from conventional coal-fired power plants constitute the majority CO₂ emissions in the U.S. Mitigation of CO₂ by chemical conversion provides an alternative method to reduce the CO₂ emissions from coal gasification process with the benefit of eliminating energy-intensive CO₂ sequestration step. A CO₂ emission reduction process, which utilizes CO₂ as oxygen source by reacting CO₂ with coal to produce CO via the reverse Boudouard reaction (CO₂ (g) + C (s) → 2CO, DH^o = +172.6 kJ/mol, DG^o = +119.9 kJ/mol) in a thermal plasma reactor, is reported in this paper. Since the reaction has a positive DG^o, high temperature from thermal plasma shifts the equilibrium favorably to the right. A thermal plasma spray system was adapted for this application. The reaction temperature can be changed by adjusting the thermal plasma amperage. Three different coals were tested with CO₂ under thermal plasma condition (650 A, 28 V), and the CO₂ conversion rate was lignite coal 73%, subbituminous coal 77%, and bituminous coal 88%, respectively. Temperature effect study shows that the CO₂ conversions increased with the temperatures, which is in accordance with the fact that the reaction of CO₂ with carbon is an endothermic reaction.