Supercritical Carbon Dioxide(s-CO₂) Power Cycle for Waste Heat Recovery: A Review from Thermodynamic Perspective

Round 1

Reviewer 1 Report

The aim of the paper is to provide a critical review of engineering background, technical challenges, and current advances of the sCO2 cycle for waste heat recovery. The authors efforts are really appreciable, especially in the "Further perspectives" section, where the focus on open challenges is firmly related to the real technology barriers. However, the authors review is clearly focused on thermodynamic analysis and do not cover many other aspects of the technology related to specific components and sub-systems.

The authors are kindly invited to review the declared scope of the paper mentioning only a review on scientific literature with respect to thermodynamic analysis of sCO2 cycles.

The authors are kindly invited to make a further effort explaining why, despite the great enthusiasm of the recent years, the sCO2 cycles struggle to gain a market appreciation and a wide exploitation.

The authors are kindly invited to accurately review the terminology used in the paper and to clearly explain the difference with reference to the terms "regenerative cycle" and "recuperative cycle”. It seems the terms are used interchangeably, while the thermodynamic sense is different.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The current work is well organized and has a sound base. It gives a good review of the s-CO2 power cycle use for waste heat recovery, as it summarizes the research conducted up to date on this field. There are only a few points I would like to stress out, shown below;

1. Line 147: you mention that other power conversion choices (such as electrochemical systems etc.) are still not ready for large scale and commercial applications, however, nor are the technologies chosen to be investigated in this study as your work concludes.. Therefore, I would add more reasons for which you have extracted these choices from the investgation.
2. Line 174: since you have been using a lot the term "bottoming cycle" throughout the document, it would be wise to clarify what it refers to, the first time you mention it in your text.
3. Line 269: maybe the reference to Sharma et al. concerns a gas turbine and should be better included in the next section? Or it refers to an ICE?
4. Line 464: "moreover, great... heat source". Please elaborate.
5. It is surprising that there is so little experimental data on s-CO2 cycles since the research shows profound benefits from their use. You have already given some reasons for that (i.e. technical barriers etc.), however, hasn't there been any research on the commercial units you mention in the last paragraph of section 5? Any data on efficiency that could help a direct comparison to other experimental cycles?
6. The use of English language in the document is extraordinary, well-done. There are only a few points that require spell check, which I hereby mention:
   • Line 108, point (2), remove the verb (Impersonal syntax) since you don't use verbs in points 1 and 3. 
   • Line 124: "water as the working fluid"--> "water as working fluid"
   • Line 164: "...landfills has been also carried out"
   • Line 259: I would replace the verb "done" by "conducted"
   • Line 318: "..., which was more than..."
   • Line 391: "...be found obviously"--> Needs clarification
   • Line 404: "...should be taken seriously"

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

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Comments for author File: Comments.pdf

Author Response

Thank you very much for your comments. We have carefully modified the manuscript according to the iThenticate report.

Round 2

Reviewer 3 Report

Low Novelty and lack of Scientific perspective.

 

There are already many review papers on waste heat recovery of the S-CO2 system, and the technical details covered in this paper are insufficient. For example, even the suggested cycle layouts are not drawn.

There is no discussion as to why S-CO2 is considered as WHR.

Also, even though it is a review paper, information from the past is presented as a representative. It is difficult to see data from China in 2016 or data from 2012 as newly updated.

Considering these reasons, the paper seems to be insufficient for publication in High-impact journals.

Author Response

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Author Response File: Author Response.docx

Round 3

Reviewer 3 Report

The point pointed out was the comment on the part of the representative data (for example, Fig 1 or Fig 4) citing the old data. It still cites data from 8 and 4 years ago, respectively, which is not suitable for the latest review articles.

 

 

Author Response

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Author Response File: Author Response.docx

Round 4

Reviewer 3 Report

There are no additional comments.