Direct Reduction processes produce a solid product which substitutes for residual scrap in the EAF process. Most Direct Reduction processes produce either Direct Reduced Iron (DRI) or Hot Briquetted Iron (HBI). DRI and HBI are generally cleaner and more consistent product than residual scrap for use in the Electric Arc Furnace (EAF) process, but depending on the purity of the iron oxide used to produce it, tends to contain more gangue material.
DRI can be used directly in the EAF as either a hot or cold charge, but cannot be traded easily as a merchant product due to its pyrophoric nature. For this reason the DRI is “compressed” to reduce its porosity using a hot briquetting process to produce HBI. In the form of HBI the porosity of the material has been reduced to a level where it is no longer pyrophoric and can be safely transported as a merchant product.
Another product being developed as a merchant product is iron carbide (Fe3C). Iron Carbide is relatively inert in atmospheric conditions, requiring no further treatment once it is produced. The carbide is also a source of energy which can be used in the downstream processing of the material in the EAF.
The Midrex shaft process leads the field, due mainly to its level of commercialisation and known risk. The major limiting factor for this technology is its lack of flexibility in feed materials, requiring lump ore or indurated pellets and natural gas as the fuel and reductant. The HYL processes which follow closely have the same issue with flexibility and are not considered to be at the same level of commercialisation as the Midrex process.
Fastmet, which now has 2 commercial applications is considered as having a high chance of success due to its capability of using oxide wastes and residues and uses coal as the reductant and fuel for the process.
Two other processes which show promise are Comet and Primus. Both of these processes can use iron oxides in several forms in an unprocessed (ie no agglomeration) form, and use coal as the reductant and fuel for the process. Neither of these processes have however been trialled at any significant scale.
Fluid bed technologies are still too complex to be considered as any threat to the Midrex and HYL processes.
Kiln based processes are limited by their size (throughput) to be economically viable, but have however found an industry niche for processing some materials, eg iron sands.
Direct reduction processes can be categorized into the following groups:
- Fluidized Bed Reactors
- Rotary Hearth Furnaces