*3.6. Mini-Pilot Reactor Testing*

In this section, we describe a mini-pilot reactor called the Large-Scale Bench Reactor (LSBR) operating at 1200–1600 ◦C and a concentrate feeding rate of 1–7 kg/h, installed at the University of Utah and shown in Figure 12.

**Figure 12.** The Large Bench Reactor installed in the University of Utah.

The LSBR consists of a reactor vessel, a vessel roof with various feeding and auxiliary ports, burners, a quench tank, off-gas piping, a flare stack, an off-gas analyzer, a gas valve train, a water cooling system, gas leak detectors, a concentrate feeding system, and human machine interface. Figure 13 shows the main components of the reactor body.

**Figure 13.** Schematic diagram of the Large-Scale Bench Reactor (LSBR).

The reactor vessel was built with a carbon steel shell and lined with three wall layers: 0.3 cm of alumina-silica fiber blanket, 8 cm layer of high fired and pressed silica, and 18 cm of 99.8% alumina castable refractory layer with high hot strength. The inner diameter of the vessel was 80 cm and the length was 210 cm, as shown in Figures 13 and 14. Figure 14 also shows photos of the main reactor and the burner as well as other details by schematics.

The LSBR had three burners: a preheat burner, the main burner, and a plasma torch. The preheat burner was used for preheating the reactor to the target temperature using a natural gas and industrial oxygen combustion flame. The preheat burner contained a pilot burner that generated a small flame to ignite the preheat burner. The pilot burner had a fiberglass flame detector that detected the pilot flame and started the flow of natural gas and oxygen through the preheat burner. Through the main burner, natural gas and industrial oxygen were injected to produce a flame and reducing gas mixture by partial

oxidation. The plasma torch was installed to provide heat, if needed, without affecting the process gas flow rates.

The Human Machine Interface consisted of the programmable logic controller (PLC) and a computer. The main PLC was connected to all the different parts of the system and to the computer where the operator could monitor the various parts and run the reactor. The programming in the main PLC was responsible for all the safety and emergency steps.

During preheating, combustion of natural gas with industrial oxygen was used to heat the reactor at a ramp rate of 90–95 ◦C/h to the operating temperature of 1200–1550 ◦C. The reactor was preheated by burning natural gas with oxygen. The wall temperature was measured by B-type thermocouples imbedded 2.5 cm inside of the inner wall surface. The concentrate was fed to the reactor using a pneumatic feeder with a rate of 1–7 kg/h through 2 feeding ports 0.28 m away from the center of the roof.

The gas analyzer used an NDIR (infrared) detector for measuring the CO, CO<sup>2</sup> and CH<sup>4</sup> contents, a thermal conductivity cell for measuring the H<sup>2</sup> concentration, and an electrochemical sensor for measuring the O<sup>2</sup> content. The partial oxidation of natural gas produced H<sup>2</sup> and CO, but CH<sup>4</sup> and O<sup>2</sup> contents in the off-gas were always less than the detection limits.

The experimental conditions were selected to represent the industrial conditions and to produce a gas mixture that had sufficiently high reducing power and temperature. In addition, the gas flow rates were set to generate sufficient heat and residence time for high degrees of reduction.

The results of the LSBR runs will help in designing an industrial reactor in terms of the identification of the technical hurdles and improvement of the operation. This reactor was simulated by 3-D CFD to optimize the operating conditions for an industrial reactor [50]. Six runs with the LSBR listed in Table 5 were simulated. The results obtained from the CFD model was in satisfactory agreement with the results of the reactor runs, especially considering the complexity of the process and the size of the facility. This work further identified potential safety issues and solutions that are needed in the design and operation of an industrial flash ironmaking reactor.



(a) Volumetric flow rates are presented at 298 K and 0.85 atm, the atmospheric pressure at Salt Lake City (1 atm = 101.32 kPa). (b) The measured wall temperature varied in the shown range during a run and the average value was selected for Computational fluid dynamics (CFD) simulation.

### *3.7. Computational Fluid Dynamics Simulation*

3-D Computational fluid dynamics (CFD) technique was used to simulate the fluid flow, heat transfer and chemical reaction of the concentrate in the shaft of a flash ironmaking reactor. Flash reactor runs to test the effects of different powder feeding schemes, different flame configurations, and hydrodynamic conditions of an industrial flash ironmaking reactor were simulated using the CFD technique. Temperature and species contours, gas flow patterns, and particle trajectories inside the reactor were computed while incorporating the rate expressions.

The Euler-Lagrange approach was used in this simulation, in which the gas phase was described in the Eulerian frame of reference while the particles were tracked in the Lagrangian framework. Particle spread by turbulence was described using the stochastic trajectory model. Detailed description of the CFD model for LSBR can be found elsewhere [50].

Experimental reduction degrees and the corresponding computed values are presented in Table 6. A reasonable agreement in the reduction degrees is seen in the first three runs. The disagreements for the last three runs were attributed to possible particle agglomeration at higher temperatures, which was not considered in the simulation [50].


**Table 6.** Experimental vs. computed reduction degrees.

#### *3.8. Economic Analysis*

Sohn and coworkers [20–22,51] studied the economic and environmental aspects of the FIT by using the METSIM software to assess different process configurations for a plant that produces 1 million tons per year of solid iron powder. These authors constructed the flow sheet for an industrial-scale plant based on the Flash Ironmaking Technology and carried out detailed material and energy balances. They also calculated the net present value (NPV) after a 15-year operation.

These results suggested that the flash ironmaking process would be economical if it is operated with natural gas. Although the use of hydrogen was not economical at the 2010 price, sensitivity analyses indicated that it could become economical with the development of hydrogen economy with mass production for application as an automobile fuel or with some publicly imposed CO<sup>2</sup> penalty.

Thus, this transformative technology has a significant economic potential in addition to considerable energy saving and reduced CO<sup>2</sup> emissions relative to the current blast furnace process.

#### **4. Concluding Remarks**

With the immediate and increasing gravity of global warming caused by anthropogenic CO<sup>2</sup> emissions and similarly serious increasing costs for energy, the steel industry faces a dire need for developing drastically new technologies to respond to these issues. These two issues are coupled in that current energy production is largely dependent on fossil fuels that generates CO<sup>2</sup> emissions and the sequestration of CO<sup>2</sup> requires energy. The amounts of emissions and energy requirements in current ironmaking processes including BF, DR, and SR were compared.

The Flash Ironmaking Technology developed at the University of Utah to address many of the disadvantages of BF and current alternate processes was introduced. This transformative technology removes the energy intensive cokemaking and pelletization/sintering steps by using iron ore concentrate without any further treatments, which allows considerable energy saving and reduced CO<sup>2</sup> emissions. It can be adopted in large enough scales (of the order of millions of tons of iron per year) to compete with the currently available ironmaking technologies or to feed EAF operations for steelmaking. This technology is expected to have an economic advantage over the BF route when it is operated with natural gas as the reducing agent as well as a fuel. Furthermore, the technology may be able to recover iron from fine feed materials other than iron ore concentrates such as dusts, precipitates, and other sources.

**Funding:** This research was funded by the U.S. Department of Energy under Award Numbers DE-EE0005751 (2012–2018) and DE-FC36-971D13554 (2005–2007) with cost share by the American Iron and Steel Institute (AISI) and the University of Utah, and by American Iron and Steel Institute during 2008–2011.

**Acknowledgments:** I wish to thank all my undergraduate and graduate assistants plus postdoctoral associates, too many to name all here, who worked with me during the development of the Flash Ironmaking Technology at the University of Utah over the years. Funding from the U.S. Department of Energy, the American Iron, and Steel Institute (AISI), and the University of Utah is gratefully acknowledged.

**Conflicts of Interest:** The author declares no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

**Disclaimer:** This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

#### **References**


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