Carbon Capture Options for MIDREX® Plants

All CO₂ in a MIDREX® direct reduction plant is generated by using carbonaceous gases in the reduction shaft for direct reduction and by combustion of the top gas in the reformer to generate the heat required for reforming. This offers the advantage of centralized carbon capture, which can be done before or after combustion, unlike other direct reduction and blast furnace processes. As a result, there are three options for integrating an amine-based carbon capture system for a MIDREX® plant. Two options involve integrating the carbon capture system into the top-gas fuel stream, either with or without an upstream CO shift reactor. The third option processes the reformer flue gas exhaust. In each option, the captured CO₂ is fed to a CO₂ compressor, compressed to approximately 150 bar, and delivered to a take-over point. The compressed CO₂ can be sequestered or sold as a by-product for direct use in oil and gas recovery (enhanced oil recovery), the chemical industry, or converted into biofuels.

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

Carbon Capture from Top-Gas Fuel

The CO₂ in the top-gas fuel is separated before it is combusted. After cooling, the top-gas fuel is pressurized and fed to the CO₂ separation system. After preheating, the CO₂ lean top-gas is used as a fuel gas in the reformer and as a reduction gas in the reduction shaft. Most of the preheated lean gas is returned back into the reduction gas cycle. Recirculation of the CO₂-lean top gas to the process gas cycle reduces natural gas consumption by approximately 5%, resulting in lower reforming work and a smaller reformer size. The remaining portion of the preheated lean gas stream serves as the primary fuel in the reformer. This option can capture approximately 50% of the total CO₂ emissions.

Carbon Capture from Top-Gas Fuel After CO Shift

The top-gas fuel still contains significant amounts of carbon monoxide (CO), which a CO₂ scrubber cannot separate. To increase the CO₂ capture rate and the content of decarbonized fuel in the form of H₂, the CO gas can be converted to CO₂ via the homogeneous water-gas shift reaction. This is done by increasing the water vapor content of the top-gas fuel and converting it into a high-temperature CO shift reactor vessel. Therefore, the gas flow rate and CO₂ content of the top gas fed to the capture plant is increased. With this proprietary solution developed by Primetals Technologies, it is possible to almost double the amount of CO₂ captured in a carbon capture plant. This method can capture approximately 70-80% of 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 if the flue gas is extracted from the reformer flue gas stack. 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. However, higher CAPEX must be considered, as the flue gas flow exceeds the top-gas fuel flow.

Advanced KM CDR Process

The Advanced KM CDR process™ is an amine-based carbon capture process utilizing a proprietary solvent developed by Mitsubishi Heavy Industries. It can recover 95% or more of the CO₂ from the flue gas for further compression to the required pipeline conditions. The process is similar to other amine-based carbon capture processes but is equipped with several advantageous and proprietary features that are integral to its design.

Main Advantages of Carbon Capture for MIDREX® Direct Reduction Plants

• Selective carbon capture in top-gas fuel (pre-combustion) or flue gas (post-combustion)
• CO₂ emissions can be captured up to a high percentage, approximately 90% of total CO₂ emissions, at a single point, and the CO₂ concentration in the feed gas is higher compared to other DR processes.
• KM CDRs KS-1™ and KS-21™ performance amine solvents used in the plant offer several advantages over conventional processes, including low energy consumption, low corrosiveness, and high stability.