Midrex: Next-Generation Ironmaking

Hydrogen, Heat Recovery, and Proven Innovations

Sustainable steelmaking has become an undeniable trend in the industry as more producers worldwide transition to electric steelmaking and increasingly shift their demand for high-quality input materials toward direct-reduced iron. For reliable direct reduction, producers have trusted Midrex® Plants to deliver. Moreover, as the global shift has increased focus on environmental impacts, energy efficiency, and recyclability, the combined expertise of Primetals Technologies and Midrex ensures the development of highly advanced Midrex Plants, including the landmark 2.0 mtpy Midrex Flex™ plant for Dillinger in Germany.

Besides hydrogen utilization, another option to reduce the Midrex Plant’s carbon footprint is the installation of a carbon capture system. In new or existing Midrex Plants, a carbon capture system can be included at a single extraction point to capture the pre- or post-combustion CO₂.

Building on forty years of cooperation, Primetals Technologies and Midrex Technologies are currently delivering one of Europe’s flagship decarbonization projects with the 2.0 mtpy Midrex Flex™ plant for Dillinger and ROGESA in Germany, supporting the producers’ long term sustainability goals. The consortium of Primetals Technologies and Midrex Technologies provides, in close cooperation, process engineering, mechanical equipment, material handling systems, a water treatment plant, electrical and automation systems, training, and advisory services for implementation and start-up. Working closely as partners ensures that Midrex Plants from Primetals Technologies are built for the next generation.

In the pressure-proven Hot Fines Recycling (HFR) system, HBI fines are screened in hot condition below the briquetting presses and sent back via bucket elevators to the inlet of the briquetting machines, turning fines into valuable yield.

Without the Hot Fines Recycling (HFR) system, fines smaller than 6.3 millimeters would account for 3–4 percent of production. With the implementation of an HFR system, the total production fines are below 1.5 percent.

The HFR system has recently been proven in operation and successfully implemented at reference plants, including ArcelorMittal Texas (formerly voestalpine Texas) and Cleveland Cliffs. For new Midrex HBI plants under construction or in development, the system is already included.

By combining experience in environmental innovations and recycling and applying this expertise to Midrex Plants, a by-product utilization plant from Primetals Technologies improves yield and reduces environmental impacts.

The by-product utilization plant at ArcelorMittal Texas recycles iron ore pellet fines, DR sludge, and DRI/HBI classifier fines. The plant produces cold briquettes that can be used in the reduction furnace as part of the feed mix.

For existing or new plants, the by-product utilization plant can be implemented as a permanent or temporary mobile installation.

While the transition to sustainable steel involves increased adoption of direct reduction plants and the replacement of blast furnace operations, integrated steel plants still operate closely with highly integrated energy-efficiency systems that recycle waste heat from existing processes. Midrex Plants provide several possibilities for waste heat recovery in the direct reduction process, indicating ample opportunities for electricity generation and steam recycling for other processes.

Examples of waste heat recovery in Midrex Plants are top gas, reformer flue gas, and seal gas heat recovery.

1. Top Gas Heat Recovery

In top gas heat recovery systems, top gas at a typical temperature of 350-400 °C is sent to a waste heat boiler, generating about 40–70 tons per hour of steam. The cooled gas is then returned to the top gas scrubber, where coarser dust is removed at the bottom of the waste heat boiler. A soot blower system can also be installed to clean the heat-exchange bundles.

2. Reformer Flue Gas Heat Recovery

Following a standard heat recovery system, flue gas still maintains a high temperature that can be con verted into valuable steam. Flue gas temperatures can be reduced from about 325 °C to about 220 °C by installing additional heat-recovery bundles. For exam ple, a Midrex Plant producing 2.5 mtpy DRI can recover an additional 18 MW of thermal heat, generating about 22 tons per hour of steam.

3. Seal Gas Heat Recovery

A portion of the reformer flue gas is used as seal gas in the Midrex process. This seal gas is about 1,150 °C before it cools in a direct-contact cooler. However, this heat can also be recovered, reducing the seal gas temperature to about 220 °C and generating about 16 MW of thermal energy, equivalent to 19 tons per hour of steam.

4. EAF-Off-Gas Heat Exchanger

When the Midrex Plant is integrated with electric arc furnace (EAF) operations, the EAF off-gas provides an additional opportunity for heat recovery. Off-gas tem peratures of 1,400 °C can be reduced to just 300 °C, generating around 90 tons per hour of steam.

Combined, the systems potentially integrated in a Midrex Plant (points 1-3 above) can produce more than 80 tons per hour of low- or medium-pressure steam, which can be used in various applications, including steam heat tracing in cold climates. The modular nature of modern plant design means that waste heat recovery systems can be installed during construction or retrofitted later, as economic conditions warrant, provided waste heat recovery is considered in the initial design. Alternatively, these additional waste heat recovery systems can be used to pre-heat other pro cess streams or in a CO2 removal system.

With Midrex Plants operating in various countries around the world where water is scarce, preserving this precious resource and making optimal use of it in industrial applications are essential. Thus, experts at Primetals Technologies have developed technologies to address key areas of water loss, including evaporation, slurry handling, and blowdown.

The implementation of air coolers reduces evaporation in Midrex Plants by using axial fans to draw air through cooling pads, reducing the temperature of incoming process fluids. Next, using a water heat exchanger, an ideal cold-water temperature is reached within the circuit. The heat exchanger can then be re-cooled with fresh water or seawater, depending on the plant location.

Additionally, slurry and water treatment systems developed by Primetals Technologies have been applied in integrated steelworks across various stages of the steelmaking process. For Midrex Plants, wastewater containing materials from the plant’s water loops is treated and can be dried through a chamber filter press to recover water for reuse in the process. The remaining by- product can then be reused.

Finally, blowdown water can be reused in adjacent steelmaking operations, including pelletizing plants, supporting closed-loop water management that focuses on reducing environmental impacts. Combining evaporation and centrifugal separation, these systems ensure minimal liquid discharge (MLD) or zero liquid discharge (ZLD), providing water suitable for reuse.

Water conservation is a key component of modern Midrex Plants. Advanced water treatment, recycling, and discharge technologies help maximize water reuse while minimizing environmental impact.

Building on the advanced technology of Midrex Plants, experts at Midrex and Primetals Technologies have taken these plants to new heights in digital operations. From enhancing production processes to enabling digital training systems for operators, Midrex Plants are built for the next generation and designed to support operators through automation, modernization, optimization, and digitalization.

Modern Midrex Plants come equipped with industry-standard automation hardware integrated with process safety and designed for high availability. Moreover, the next-generation Midrex Plant has improved instrumentation, sensors, automation devices, cameras, and monitors to ensure smooth production and easy monitoring by human operators. DRIpax DR Optimizer and the related expert system optimize production by consolidating data, providing insights into future operations, offering process diagnoses, corrective actions, and supporting standardized operation.

Beyond advancing ongoing operations, Operator Training Simulation (OTS) provides a training environment based on digital twin technology. These systems allow operators to enhance their skills, improve decision-making, and ensure they can handle real-world operations. The result is a more efficient plant that operates safely and effectively. With this system, new operators can be trained on a plant before it is built, and current operators can learn new systems while maintaining peak skill levels. Additionally, thanks to digital twin technology, the virtual environment can be used for software commissioning, production testing, and life-cycle management, since it mimics the real-world plant.

The Virtual Plant meets the demands of steel producers regarding operator training, thoroughly tested systems, and a well-prepared workforce ready for rapid startups.