Thermochemical CO_2 Gasification of Coal Using a Reactive Coal-In_2O_3 System

摘要

A number of coal--metal oxide systems were examined for a thermochemical CO_2 gasification of coal in a two-step cyclic redox mode, as well as in a normal single-step mode for the purpose of utilizing solar high-temperature heat below 1173 K. In the two-step cyclic redox mode, metal oxide was reacted with coal powder as an oxidant in the absence of CO_2 at 1173 K to produce CO, H_2, and the component metal which was reoxidized with CO_2 to generate CO at lower temperatures in a separate step. In_2O_3 was found to be the most reactive metal oxide among the thermodynamically promising metal orides. The two-step cyclic CO_2 gasification could be repeated using the In_2O_3/In redox system by resupplying the consumed coal to the system. About 80/100 of the coal supplied to the system was gasified at the temperature range of 1023--1173 K. The In_2O_3 phase was completely regenerated without the formation of other solid phases after repeating the two-step gasification. In a normal single-step, continuous feeding mode of CO_2 at a constant temperature of 1173 K, the coal--In_2O_3 system also showed the most reactivity for the Boudouard reaction of C + CO_2 -- 2CO in the CO_2 gasification of coal at the metal content of 17 wt /100 in the coal and metal oxide mixture. Depending on the indium content in the mixture, the initial coal-conversion rates with the coal--In_2O_3 system were 2.5--4 times as fast as that in the coal--CO_2 reaction without any catalysts. The separation of used In_2O_3 from the remaining coal ash by In_2O evaporation was also proposed.