Review Reports

Round 1

Reviewer 1 Report

This is a very interesting subject area and relevant to low CO2 ironmaking which makes it a very useful and necessary piece of research.  It has been carried out to a high standard, although I have a few points to make and some questions.

• It would be a good idea to use subscripts for the accuracy of representing compound formulas e.g CH₄
• Line 255: Could you define recycled H2, or did I miss it?
• Lines 258-263: I found the following wording very confusing, I suggest that this needs rewording to clarify what you are saying.  "Natural gas was considered as 98.1% CH4 (1 mol% of 258 C2H6 is equivalent to 2.6 mol% of CH4 in heat production and 2 mol% of CH4 in hydro-259 gen and carbon monoxide production, both for generating a representative hot gas mix-260 ture from the partial combustion. Thus, considering these two factors, 1 mol% of C2H6 261 was treated as being equivalent to 2.3 mol% of CH4) and 1.9% N2 to avoid the complexity 262 of including the small amount of C2H6 in the combustion calculations."
• Why were the gas flow rates higher for at the lower preheat temperature?
• You use different quantities of H2 at the different pre-heat temps, because the iron oxide reduction reaction using H2 is endothermic, does this have any effect on process performance and heat loss?
• I must say that these flame temperatures are higher than I might expect considering you are running in partial oxidation conditions. Any comment why this might be the case?
• Line 328: I assume that the 'sensible heat ' of the input gases is due to preheating.  Is this what is meant by this term? Could this be defined more clearly for the reader?
• Just out of interest, why aren't the powder feeding ports angled towards the centre line considering the concentration of reducing gases is highest in this zone and they need to avoid particle sticking to the walls? Is this due to increased melting and less particle reduction?  
• The burner configuration (fig9 line 220) indicates gas flow exiting the burner head at an angle of 60^o (also shown in fig 11) but the CFD in the other figures doesn't seem to indicate flow at this angle for very long at all, and doesn't seem to have much effect on the powder flow. Why has the directional momentum seemed to have dissipated, why might this be?
•   Did you get turbulent flow in any of these configurations?  You mention a recirculation area but laminar flow seems to be dominant.  Do you not get turbulence at the reactor exit?

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear authors,

Congratulation to you and your team for the intense and comprehensive work about new efficient iron ore reduction processes, that are important in order to transform the global steel industry to lower CO2 emissions.

The publication of the presented paper in Metals is  recommended.

And I strongly recommend to consider other R&D on flash reactors in the first part of the paper and to discuss the results of your work against other designs of direct reduction reactors.

There is neither any remark nor discussion with other R&D work in the entire paper. 23 out 30 references are from Sohn and co-workers, 2 other references from general associations (USGS and world steel institute), a bit self-referred (although there are only few other papers). E.g., papers from R&D group of J. Schenk in Austria, or recent R&D from metallurgy group at USTB Beijing (Zhangcheng Guo) or about arc flash reactors in Japan, some time ago.

1. The sentence in lines 46-48 about inefficient DRI technology requires one or more references, for all propositions, or replaced by a less offensive phrase. DRI is running already at steel plants with a million tons annual productivity. An established competitor to the proposed FIT. Current DRI processes have to be improved, though.

2. In Section 4 (lines 117-139) results from other iron oxide flash reactors could be mentioned.

One suggestion for text editing:

line 16: ... and 35 m with... -> and 35 m height with...

Best regards.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

This article is devoted to the generalization of a new ironmaking technology. The paper presents extensive and well-founded material. The authors of the article have extensive experience in the subject area. In general, I believe that the article can be accepted in the current version. However, I would recommend that the authors pay attention to some illustrations. For example, Figure 6 is unreadable. Despite this, the present manuscript meets high standards.

Author Response

Thank you for your comments. Figure 6 is to give a general picture of what the screen showed and not meant for reading the detail.