Strategic Selection of a Pre-Reduction Reactor for Increased Hydrogen Utilization in Hydrogen Plasma Smelting Reduction

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This review discusses the different types of reactors used in the process of direct reduction of iron using hydrogen, and suggests optimal solutions to increase the efficiency of this process. Highlights include: Cyclone cascade: It is proposed to use a cyclone cascade with at least three stages due to its low complexity, reliability and flexibility. This type of reactor is able to handle particle agglomeration, as larger particles can freely fall down through the funnel into the next cycle. The problems associated with moving-load reactors are discussed, such as the need for a hermetically sealed rotating drum to prevent hydrogen leakage. These reactors are less susceptible to sticking effects, but require complex structures. It is mentioned that a critical component of a fluidized reactor is the gas distribution system, and that agglomeration can lead to the formation of "dead" zones, which complicates the process. The publication highlights the need for experimental determination of the residence time of particles in reactors in order to optimize their design and operation. It is proposed to build a demonstration reactor for further research and optimization. In conclusion, the authors emphasize that although the proposed design procedures are based on empirical correlations, further research is needed to accurately determine the parameters and behavior of materials in reactors before they can be integrated into existing demonstration facilities. Here are some critical comments that can help improve the article.: 1) The article could benefit from a more detailed comparison of the various technologies used to restore iron. Including data on the performance, cost-effectiveness, and environmental aspects of each technology will help readers better understand the advantages and disadvantages. 2) The mention of the need for experimental research is important, but the article could be more convincing if it included preliminary results or data from similar studies. This would add weight to the arguments and show that the authors have already begun work in this direction. 3) The article should pay more attention to the environmental consequences of the proposed technologies. How do they affect carbon emissions and other environmental factors? This is especially relevant in light of global efforts to reduce environmental impacts. It is necessary to supplement the article with existing analyzers for the emission of various gas mixtures. See for example: 10.1088/1361-6595/ac91a1 10.1021/acs.analchem.1c03499 4) Figures 4 and 6 should be improved. 5) The conclusion must be structured.

Comments on the Quality of English Language

This review discusses the different types of reactors used in the process of direct reduction of iron using hydrogen, and suggests optimal solutions to increase the efficiency of this process. Highlights include: Cyclone cascade: It is proposed to use a cyclone cascade with at least three stages due to its low complexity, reliability and flexibility. This type of reactor is able to handle particle agglomeration, as larger particles can freely fall down through the funnel into the next cycle. The problems associated with moving-load reactors are discussed, such as the need for a hermetically sealed rotating drum to prevent hydrogen leakage. These reactors are less susceptible to sticking effects, but require complex structures. It is mentioned that a critical component of a fluidized reactor is the gas distribution system, and that agglomeration can lead to the formation of "dead" zones, which complicates the process. The publication highlights the need for experimental determination of the residence time of particles in reactors in order to optimize their design and operation. It is proposed to build a demonstration reactor for further research and optimization. In conclusion, the authors emphasize that although the proposed design procedures are based on empirical correlations, further research is needed to accurately determine the parameters and behavior of materials in reactors before they can be integrated into existing demonstration facilities. Here are some critical comments that can help improve the article.: 1) The article could benefit from a more detailed comparison of the various technologies used to restore iron. Including data on the performance, cost-effectiveness, and environmental aspects of each technology will help readers better understand the advantages and disadvantages. 2) The mention of the need for experimental research is important, but the article could be more convincing if it included preliminary results or data from similar studies. This would add weight to the arguments and show that the authors have already begun work in this direction. 3) The article should pay more attention to the environmental consequences of the proposed technologies. How do they affect carbon emissions and other environmental factors? This is especially relevant in light of global efforts to reduce environmental impacts. It is necessary to supplement the article with existing analyzers for the emission of various gas mixtures. See for example: 10.1088/1361-6595/ac91a1 10.1021/acs.analchem.1c03499 4) Figures 4 and 6 should be improved. 5) The conclusion must be structured.

Author Response

Thank you for your critical review. Please see the attachment for our changes and responses.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

1.  In the Introduction section:

Please provide more background information in the introduction section. For example, readers may not understand why the authors focus on the HPSR process method. There are various plasma reduction methods for iron ore, including several recent studies from the last two years. The authors should consider listing the advantages of the HPSR process to clarify its significance and highlight its benefits over other methods.

2. In Section 4.3:
The authors have devoted significant effort to evaluating the Cyclone cascade. To enhance clarity, I suggest including a schematic diagram illustrating how particles move within the reactor and the forces acting on them. This visual representation will help readers better understand the ~30 equations discussed in this section.

3. In Section 5:
The authors have discussed the evaluation criteria for the three reactor types. However, it appears that the Cyclone cascade scores higher in "Mixing of reactants" and "Overall complexity," while the Rotary Kiln performs better in "Sensitivity to grain size enlargement" and "Sensitivity to operation with sticky material," resulting in an even score of 2-2. The authors should provide additional explanation to justify why they selected the Cyclone cascade over the Rotary Kiln, focusing on which criteria they consider most critical for this application.

4. Residence Time in Section 5:
In Section 5, the authors include "residence time" as one of the evaluation criteria. However, on page 10, it is stated that "a TR provides good heat and mass transfer between phases, reaction kinetics need to be fast to reach the desired conversion because of the low particle residence time." Since longer residence times are generally considered beneficial for reactions, the authors should clarify their rationale. If fast reaction kinetics are required, then "residence time" might not be a relevant criterion and could potentially be omitted.

Author Response

Thank you for your critical review. Please see the attachment for our changes and responses.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have eliminated some of the comments.

And the paper already looks much better.

However, possible emissions of impurities and modification of reactors with an additional unit for analyzing the composition of harmful emissions still remain unassessed. It is clear that this work is for the future, but it is necessary in any case.

In my opinion, the references to works 10.1088/1361-6595/ac91a1 10.1021/acs.analchem.1c03499 (and other works) suggested by the referee in the previous review would help the authors to pay attention to this and include a small paragraph on the topic of detecting harmful emissions during processing in plasma reactors.

 

After elimination, the review paper can be accepted for publication.

Author Response

Reviewer comment: However, possible emissions of impurities and modification of reactors with an additional unit for analyzing the composition of harmful emissions still remain unassessed. It is clear that this work is for the future, but it is necessary in any case. In my opinion, the references to works 10.1088/1361-6595/ac91a1 and 10.1021/acs.analchem.1c03499 (and other works) suggested by the referee in the previous review would help the authors to pay attention to this and include a small paragraph on the topic of detecting harmful emissions during processing in plasma reactors.

Author's response: First of all, thank you for reviewing the manuscript and your comment! However, we still do not agree with the opinion, that an explanation of the detection of harmful emissions of plasma-reactors is within the scope of our review. We do not even focus on the plasma reactor itself with our paper, but on the selection of a suitable pre-reduction reactor and the proposal of this new reactor concept. Conducting a thorough review on the compounds that may be formed in the plasma reactor itself and their methods for detection is a very important work, but not at the present state of the process development. This vast subject is best investigated in a separate paper, since mentioning some analysis methods for the detection of harmful emissions in the plasma-reactor's off-gas would not provide any benefit/argument to the conclusion. Furthermore, if we mention only some analysis methods, we would need to explain why we chose those specific ones. Since there is no sufficiently convincing short answer to this question, we would need to include as many different technologies as possible, which in turn would result in a review about analyzing methods for traces of harmful compounds in the off-gas of plasma-reactors. Besides exceeding vastly the scope of our review, including a small "mini-review" about this subject would most likely only bloat our article with irrelevant explanations, making it more difficult to read and understand, in our opinion.