The direct reduction technology of rotary hearth furnace has been developed for nearly forty years, and the device was firstly used in the heating furnace of steel rolling, and later used to treat the iron containing waste materials. The direct reduction technology of rotary hearth furnace is characterized by low fuel quality, no need for deep processing of raw materials, simple process, good utilization of waste resources, and protection of the human environment, therefore, it has received more and more attention from the industry.

RHF direct iron smelting can be divided into INMETCO method, DRYIRON method, FASTMET method and ITKM3 process due to the different raw material processing conditions and product quality requirements.In the last article we have introduced the INMETCO method, this article will introduce the DRYIRON method.

In the last article, we compared the advantages and disadvantages of several coal-based reduction processes, and concluded that the rotary hearth furnace process is more suitable. This article will introduce the development of rotary hearth furnace process and the INMETCO method in rotary hearth furnace process.

At present, there are mainly the following technical routes for direct reduced iron. Coal-based direct reduced iron and gas-based direct reduced iron,Among them, gas-based reduction technologies include: COREX, Midrex, FINEX, HIsmelt, etc.Among them, coal-based reduction technologies include: tunnel kiln, RHF, rotary kiln, etc. Gas-based reduction technology can achieve large-volume industrial production. The comprehensive economic indicators are good, but the investment is relatively large. Coal-based reduction technology generally has low output and relatively low investment.

Non-blast furnace iron making technology has grown significantly in recent years, driven by increasing environmental requirements, the need for high-quality steel materials, and especially the Chinese government's commitment to "carbon neutrality" to the world. Non-blast furnace iron-making technology is dominated by the gas-based shaft furnace process, because the gas-based shaft furnace can use hydrogen reduction technology, which greatly reduces carbon emissions, In addition to the gas - based shaft furnace process, rotary kiln, tunnel kiln, RHF and other technologies are also used.

Rotary hearth furnace technology (RHF) was developed and built in the United States in 1978 by the International Metal Company affiliated to INCO Group of Canada in order to treat and utilize metallurgical wastes. It can not only be used to treat dust produced by metallurgical plants and other wastes containing iron, chromium， and zinc, but also be used to reduce iron ore.