Fundamental Research On Coal Hot-Air Rotary Hearth Furnace Process

For environmental and economic consideration, it is necessary for ironmaking industry to use iron ore concentrates and coal directly instead of coking and sintering. So the research and development of the smelting reduction process are being paid more and more attention. The Coal Hot-Air Rotary Hearth Furnace Process (CHARP) has been developed by University of Science and Technology Beijing since 1997, which is a new iron-making process evolved from the direct reduction of ore/coal composite pellets in rotary hearth furnace (RHF). At the temperature of 1350℃ to 1450℃, iron oxides in pellets are reduced by coal to iron. After carburization, melting and separation between liquid iron and slag components, iron bead without gangue can be formed, which is different from direct reduced iron (DRI). The present work mainly concentrates on a fundamental study on the CHARP process by thermal simulation experiment. The behavior of the reduction and melting in ore/coal composite pellets has been investigated at high temperature, as well as the distribution of sulfur and the behavior of sulfur during the reduction, melting and separation of pellets have been studied. Methods how to decrease or control the sulfur content in iron bead have been proposed. During the experimental process, a series of samples have been taken for chemical analysis in the partially or completely reacted specimens. These results have brought about a better understanding of the reduction process at high temperature. In order to the comprehensive utilization of titanium resource, the reduction and melting in vanadium titano-magnetite/coal or ilmenite/coal composite pellets have been studied in the laboratory. A new process and two routes on titanium resource utilization have been put forword. By the numerical simulation on the turbulent flow, combustion and radiative heat transfer in rotary hearth furnace (RHF), the distribution of temperature and flow in the furnace has been determined. The main new viewpoints of the author are as follows: The reduction of iron oxides, melting and separation of iron and slag in pellets have been investigated at the temperature of 1350℃ to 1450℃. The behaviour of sulphur and the control of sulphur during the reduction and melting process in pellets have been investigated. The research on the beneficiation of titanium oxides from Panzhihua ilmenites by means of the reduction of coal bearing pellets has been carried out. Two routes of utilizing the titanium resource by RHF are proposed: one is to produce iron bead and slag containing about 50 percent titanium oxides after the reduction and melting of vanadium titano-magnetite concentrates with sodium sulfate as the flux; while another is to produce the slag containing about 75 percent titanium oxides and granular iron with sodium sulfate and lithium carbonate as the composite flux. The size of granular iron is ranged from 3 millimeter to 8 millimeter after reduction, melting and magnetite separation. The temperature field and flow field in RHF have been calculated by using CFX software, which would be helpful for engineering design.