Carbon Capture Options for MIDREX® Plants

The MIDREX® process for direct reduction can include a carbon capture system in its initial engineering or be retrofitted to existing plants. All CO₂ in a MIDREX®* direct reduction plant is generated by direct reduction of the iron oxide in the reduction shaft furnace with carbon-containing process gases and by combustion of top-gas fuel in the reformer to generate the heat required for reforming natural gas. This offers the advantage of centralized carbon capture, which can be done before or after combustion, unlike other direct reduction and blast furnace processes. There are two options for integrating an amine-based carbon capture system into a MIDREX® plant. One option involves integrating the carbon capture system into the top-gas fuel stream. The other option processes the reformer flue gas. At both options, the captured CO₂ can be compressed and delivered to a take-over point. The compressed CO₂ can be sequestrated or sold as a by-product, e.g., for direct use in oil and gas recovery (enhanced oil recovery), the chemical industry, the food industry, or converted into biofuels.

Carbon Capture from Top-Gas Fuel

Top gas exiting the MIDREX® reduction shaft furnace is scrubbed and cooled in the top-gas scrubber. Subsequently, a part of the top gas, the so-called top-gas fuel, is branched-off and used in the reformer to generate the heat required to reform natural gas. In the case of carbon capture, the top-gas fuel is pressurized and fed to a CO₂ separation system before the reformer, where CO₂ is scrubbed out. The produced CO₂-lean gas is then used again as a fuel gas in the reformer or can be returned into the process gas cycle. Recirculation of the CO₂-lean gas to the process gas cycle reduces natural gas consumption by approximately 5%, resulting in lower required reforming work and a smaller reformer size. This option can capture approximately 50% of the total CO₂ emissions.

Carbon Capture from Reformer Flue Gas

The CO₂ from the plant can also be captured from the reformer flue gas system. This solution is also the easiest to retrofit to existing MIDREX® direct reduction plants. Since all the carbon in the flue gas is fully oxidized to CO₂, this option substantially reduces net CO₂ emissions by approximately 85-90% compared to a natural gas-based MIDREX® plant without carbon capture technology.

Advanced KM CDR Process

The advanced KM CDR Process™ is an amine-based CO₂ capture process based on Mitsubishi Heavy Industries' proprietary solvent, which can recover 95% or more of the CO₂. The capture process is similar to other amine-based carbon capture processes, but is equipped with several proprietary features that are integral to its design.

Main Advantages of Carbon Capture for MIDREX® Direct Reduction Plants

• Possible installation from the beginning or later retrofitting of a carbon capture system for further reduction of CO₂ emissions

• In the MIDREX® process, CO₂ emissions can be captured at a single point

• Two possibilities for carbon capture installation:

• Top-gas fuel with approx. 50% CO₂ reduction

• Flue gas with 95% CO₂ reduction

*MIDREX® is a registered trademark of MIDREX Technologies, Inc.