Reactive metal-oxide redox system for a two-step thermochemical conversion of coal and water to CO and H 2

Abstract

A number of metal-oxide redox systems were examined for a two-step thermochemical conversion of coal and water to CO and H 2 for the purpose of utilizing solar high-temperature heat below 900°C: metal oxide+CH n (coal)→metal+CO+ n/2H 2, metal+H 2O→metal oxide+H 2. In 2O 3 and SnO 2 were found to be the most reactive oxidants for coal under an N 2 gas stream below 900°C. These reactive metal oxides were tested for the proposed two-step cyclic process in the pulse feeding mode of H 2O, with a temperature swing and under an N 2 gas stream. The two-step cyclic process using the In 2O 3/coal mixture could be repeated with high coal conversions of about 80% in the temperature range of 600–900°C by resupplying the consumed coal to the system. The repeated two-step process via the In 2O 3/In redox system resulted in efficient performance of the net reaction CH n (coal)+H 2O→CO+( n/2+1)H 2, while hydrogen was scarcely produced in the continuous feeding mode of H 2O/N 2 over the In 2O 3/coal mixture, at a constant temperature of 900°C. The separation of recovered In 2O 3 from the remaining coal ashes by In 2O evaporation was also proposed.