Improvements in or relating to heating ferrous oxide

摘要

As a preparatory step to the production of pure iron powder by reduction of ferrous oxide with hydrogen, the ferrous oxide is preheated to 600-800 DEG C. in two fluidized bed stages, in the first of which its temperature is raised to about 100 DEG C. by means of a fluidizing moisture-free gas consisting of carbon dioxide, nitrogen or mixtures thereof and in the second stage the hot oxide is passed to a series of fluidized beds through which it passes in an overall countercurrent direction to a gas consisting of carbon monoxide, carbon dioxide, nitrogen, hydrogen and steam which enters at 850 DEG C. and which has an overall composition such that it is in equilibrium with FeO at temperatures above 550 DEG C. The second gas stream is suitably obtained by the incomplete combustion of methane. As shown in Fig. 1, ferrous oxide is fed from a hopper 3 to a fluidized bed 4 through which a carbon dioxide/nitrogen stream passes upwardly to be recirculated through a heat exchanger 7. The ferrous oxide, now at 100 DEG C., is fed through a conveyer 8 to a plurality of successive fluidized beds 10. Hot gases obtained by the partial combustion of methane in burner 11 pass upwardly and fluidize the successive beds and are withdrawn through a fan 14 and passed in part through line 15 and the tubes 19 of a heat exchanger back through line 21 to the bottom of the second heating zone, and in part through line 16 where, at the foot of the heat exchanger 17 they are burnt with oxygen to heat the tubular heat exchanger 19. The ferrous oxide powder then passes from the lowermost fluidized bed through a gas-tight conveyer 22 to the apparatus where it is reduced with hydrogen to iron powder. The conveyers 8 and 22 linking the first and second heating stages and the heating and reducing stages respectively are preferably gas tight and differential pressure gauges may be placed thereacross. Responsive to such a gauge, the pressure in one or other of the stages may be adjusted to prevent gas leak between stages. Specifications 980,425 and 980,426 are referred to.