Process of reducing higher metal oxides to lower metal oxides

A process of reducing the higher valencies of a metal oxide to lower valencies of the metal oxide comprising:

• (a) calcining in a circulating fluidized bed reactor fine-grained solids which contain metal oxides of higher valency at at a temperature of 800.degree. to 1100.degree. C. under oxidizing conditions with hot gases, in which the solids are suspended;
• (b) reducing the calcined solids at a reduction temperature in a rnage of from 800.degree. to 1100.degree. C. in a stationary fluidized bed which is supplied with a carbonaceous reducing agent and oxygen-containing gases to reduce the higher metal oxides to lower metal oxides;
• (c) supplying the carbonaceous reducing agent to the stationary fluidized bed and removing discharge matter from said bed, the carbonaceous reducing agent being supplied at a rate effective to reduce the higher valency metal oxide to a lower valency metal oxide, to maintain the reduction temperature, and to maintain a carbon content in the discharged matter;
• (d) removing exhaust gas from the stationary fluidized bed and introducing the exhaust gas as a secondary gas in the circulating fluidized bed in the calcining step;
• and
• (e) supplying fuel to the calcining step (a) and substantailly completely combusting the fuel and the exhaust gas, the fuel being supplied at such a rate that the total of the heat generated by the substantially complete combustion of said fuel and of the heat supplied to the calcining step by the combustion of the exhaust gas from step (d) is sufficient to effect the calcination.