Carbon Monoxide Reduction of Iron Ore

C ERTAIN attention is paid today to the weaknesses of the classical blast furnace process, and interest is continuously increasing in methods for direct reduction without melting. Several different methods have been developed or suggested in the past, but so far only a few have been adopted for practical use. Another tendency in the iron industry of today is the change-over to concentrates, with an agglomeration as the first stage before reduction. It would mean a big step forward if this agglomeration process could be avoided, as it is often difficult to carry lt out. A practical solution of these two problems-direct reduction in a continuously operating process adapted to large scale production, and based on fine-grained raw materials without previous agglomeration, would certainly be of great importance. But due to the many difficulties of various kinds which arose when the sponge iron methods were brought into practical use, some skepticism is natural. There are many reasons for the comparatively slow progress in the sponge iron field. One is the gangue content in the raw material, which naturally is also to be found in the sponge iron. However, with a still further concentration, this problem might not be too serious. Perhaps the biggest problem is to proceed far enough with the reduction without the material sticking to the furnace wall or sintering, both of which cause operational difficulties. The sticking can be avoided by decreasing the reduction temperature, but the speed of reaction is also diminished. The conditions would, however, be different, depending on whether hydrogen or carbon monoxide is used as a reducing agent. When using hydrogen, the reduction can be cayried through at 500°C with suitable speeds of reaction, but with a very unsatisfactory utilization of the hydrogen. With carbon monoxide, there is spontaneous decomposition into carbon dioxide and carbon, and the speed of reaction is also lower compared to that obtained with hydrogen.' The further decomposition of carbon dioxide however, made it impossible to investigate the speed of reduction with carbon monoxide to temperatures below 8 0 0 " ~ . The fluidized bed, where a gas is pressed through a bed of fine-grained material with velocity so high that the solid particles make a turbulent movement, is characterized by a very intimate mixing of the solid material so that a constant temperature is acquired within the entire bed. Fluidization is reached at a certain linear gas velocity, determined by the physical properties of particles-and. gas, and occurs within a rather large speed interval. The particle size generally used in fluidized beds is 0.03 to 3 mm; the linear gas velocities generally range