A Study on the Stability Fields of Arc Plasma in the HPSR Process
Round 1
Reviewer 1 Report
The manuscript is well written and structured. It summarizes the work performed to determine the effect of various parameters on the arc stability, this being important to optimize the hydrogen plasma smelting reduction process for steel production. The publication of such know-how will be useful for the research community working in this field. I recommend publication in Metals.
Author Response
Thank you for this comment. We appreciate your positive feedback. Some changes were made to the paper. You can find the yellow marked changes in the attached document
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript written very clearly and neatly. Submitted data have great interest for progress of plasma metallurgy processes. It would be better if authors add more relevant data about CO2 emission on 2018-2019 years.
Author Response
Thank you for this comment. We appreciate your positive feedback. The CO2 Emission Data are updated with the following sources:
- World Steel Association. Steel’s contribution to a low carbon future and climate resilient societies. worldsteel position paper, 2020. https://www.worldsteel.org/en/dam/jcr:7ec64bc1-c51c-439b-84b8-94496686b8c6/Position_paper_climate_2020_vfinal.pdf (accessed on 9 October 2020). https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5_full.pdf (accessed on 15 July 2020).
- Le Quéré, C.; Jackson, R.B.; Jones, M.W.; Smith, A.J.P.; Abernethy, S.; Andrew, R.M.; De-Gol, A.J.; Willis, D.R.; Shan, Y.; Canadell, J.G.; et al. Temporary reduction in daily global CO2 emissions during the COVID-19 forced confinement. Nature Climate Change 2020, 10, 647–653
Some changes were made to the paper. You can find the yellow marked changes in the attached document
Author Response File: Author Response.pdf
Reviewer 3 Report
Dear Authors,
The reviewed manuscript prepare in a logical way and organized well to transfer the main idea of the research to the readers which is absolutely fine for such a publication however considering the following recommendation can improve the quality of the paper more to fit the Journal criteria as well as final output.
1) Half of the references used in the introduction are back to more than 10-20 years ago which I think could be substitute with more current relevant findings.
2) In section 2, the advantage of Arc plasma is mentioned however no financial comparison is not made. Better would point out this fact as well as other add/disadvantages.
3) Section 3.1: all facilities and equipment used should mention with manufacturer company details. check journal template and instruction.
4) Section 4: the presented results are fine however a lack of technical discussion is clear. The results should explain in a quantitative model as well as deep in reasons why they achieved. As a technical-scientific paper, this would be the most important section of the paper.
5) Section 5 should also revise base on the previous comments.
Author Response
- The reviewed manuscript prepare in a logical way and organized well to transfer the main idea of the research to the readers which is absolutely fine for such a publication
Response: Thank you for this comment. We appreciate your positive feedback.
- Half of the references used in the introduction are back to more than 10-20 years ago which I think could be substitute with more current relevant findings.
Response:
According to Reference 1 to 3: We updated the data to 2018/19 Values
According to Reference 5 to 9 and 22: These are the latest publications in this field according to the used facilities. To make this long period of time easier to understand, it should be mentioned that the laboratory reactor was shut down in the period 2009-2018. References 11-16 show the most recent investigations with this facility which focused mainly on theoretical aspects of the process.
The number of research groups in the field of HPSR is limited. The most relevant publications are cited in the references
- In section 2, the advantage of Arc plasma is mentioned however no financial comparison is not made. Better would point out this fact as well as other add/disadvantages
Response:
In this special case, it is really hard to calculate the financial advantages and disadvantages of the process, because the current status of development is at a rather low technology readiness level. In section 1 line 40-42 an assumption for a cost advantage is mentioned.
The mentioned 15-20% lower costs are connected to the usage of non-agglomerated ultra-fine ores and the one-step process concept for the industrial application
- Section 3.1: all facilities and equipment used should mention with manufacturer company details. Check the journal template and instruction.
Response:
For all purchased plant components (charging system, mass spectrometry, camera system, ampere meter, voltmeter, and mass flow controllers) type and manufacturer are mentioned. All other parts were manufactured in house or built up out of several small bought parts (silica wool, molecular sieves…). In particular, the entire reactor system including the electric power supply was manufactured in house. The authors have interpreted the template in such a way that no specifications are necessary for parts built by the operator.
- Section 4: the presented results are fine however a lack of technical discussion is clear. The results should explain in a quantitative model as well as deep in reasons why they achieved. As a technical-scientific paper, this would be the most important section of the paper
Response:
Thank you very much for your suggestion to improve the paper.
In section 3.4 the details of the methodology by the means of arc stability maps and fields of stability are explained. The Results and the discussion are presented in section 4.
We added in this section further explanations on the influence of the hydrogen content on the supplied power and on the voltage drop in the arc zone. These are important findings for the scale-up of the technology.
In Section 5 additional conclusions were made.
You can find the yellow marked changes in the attached document
Author Response File: Author Response.pdf
Reviewer 4 Report
Dear authors,
I would like you to make comments on the following issues:
- Being a complex phenomena, which would be the process parameters that help to scale-up your resuts to an industrial furnace?
- How the dynamic variations of the megnetic field are related with the stability of the field?
- The presence of the particles of iron ore decrease the stability of the field. What is the mechanism of this effect?
- The presence of hydrogen ions and the influence of nitrogen affect the stbility of the field. Will you please elaborate why is that?
Author Response
- Being a complex phenomenon, which would be the process parameters that help to scale-up your results to an industrial furnace?
Response:
For the scale-up, further investigations are in progress.
Based on the experimental results a dimensionless number representing the arc stability is under development. For this purpose, a detailed analysis of the voltage curves while the operation I needed. Methods that are applied are e.g. FFT-methods and curve analysis for skewness and kurtosis. This dimensionless arc stability number should be independent of the scale of the facility.
A new bench-scale testing facility with a capacity of 100kg/h of operated ore is under construction and commissioning. In the coming trials, the stability fields and map should be determined with the developed methods of this publication. Also, the firstly mentioned ASI will be again determined.
We added in section 4 further explanations on the influence of the hydrogen content on the supplied power and on the voltage drop in the arc zone. These are important findings for the scale-up of the technology.
In Section 5 additional conclusions were made.
- How the dynamic variations of the magnetic field are related to the stability of the field?
Response:
This is a very complex issue, especially considering that there is an additional particle stream(ferromagnetic at certain rates of reduction) in the process gas.
Basically, a solution of the magnetohydrodynamic equilibrium equations (only valid for single fluids) of the System (∇p=j x B, ∇*B=0, and ∇ x B= μ0j) can be used to describe the relationship. In this context, a relation between the magnetic force field and the defined stability fields should be possible.
Unfortunately, this kind of solution would be only a qualitative assumption for the interaction of those two phenomena due to the fact that the used plasma gas is neither a single fluid nor free of particles in the case of ore charging trials. The authors are sorry to be unable to answer this question with a satisfying amount of information, but we thank you for your question because it could start a new field of research in relation to a better understanding of the process.
- The presence of the particles of iron ore decreases the stability of the field. What is the mechanism of this effect?
Response
The quick, short, and easy answer to this question would be the lower amount of conductive argon ions in the gas/solid mixture and therefore a higher resistivity of the system. For a detailed and more sophisticated answer, the points of the former response should be clarified. With a fundamental description of the process physics, this effect could probably be visualized in a simulation.
- The presence of hydrogen ions and the influence of nitrogen affect the stability of the field. Will you please elaborate why is that?
Response
The authors think that this behavior is directly connected to the needed amount of energy for the ionization of the gas. Argon is already monovalent and therefore needs no energy for the breakage of the molecule bonds like nitrogen and hydrogen do. Therefore, it is a better-conducting gas, and with the decrease of the amount of this better conduction gas, the stability decreases
Some changes were made to the paper. You can find the yellow marked changes in the attached document
