A new generation of rotary hearth furnace technology for coal based DRI production

摘要

The rotary hearth furnace (RHF) allows the production of direct reduced iron out of various iron ores and other iron bearing materials (such as steel mill wastes). Key-points for a flexible and efficient operation are a proper raw material preparation and a RHF, which provides ideal reduction conditions in each zone. During the last years, great effort has been put in the technological improvement and innovation of the rotary hearth furnace for coal based direct reduction. Basically, all key components, which control the atmosphere, temperature, gas velocity and pellet distribution had been optimised with the help of computer-supported simulation and various test campaigns. A newly designed feeding system provides a uniform pellet distribution on the hearth. The combination of sidewall burners, roof-burners and specially designed wicket air nozzles allow individual atmosphere, temperature and gas composition control in each zone of the furnace. The hearth is equipped with a new driving system and the hearth weight is minimised. A new water seal system prevents air penetration to the inside of the rotary hearth furnace and improved refractory concepts lead to a long life of the furnace wall, sealing and hearth. A discharge screw removes the DR smoothly from the hearth with low fine formation. The multi function off-gas conditioner completes the list of recent major innovations. Process parameters and set points are determined with a test laboratory furnace, which is located in Genova, Italy. The rotary hearth furnace produces DR at lowest cost, in comparison to other direct reduction units. Highly metallised DRI (>92 % metallisation) can be charged into several iron and steel making furnaces or can be hot-briquetted. DRI with a metallisation of 85% is suitable for the Redsmelt concept.