Development of Pilot-Scale CO₂ Methanation Using Pellet-Type Catalysts for CO₂ Recycling in Sewage Treatment Plants and Its Validation through Computational Fluid Dynamics (CFD) Modeling

Round 1

Reviewer 1 Report

The submitted manuscript described a pilot-scale CO2 methanation using the pellet-type catalysts. The authors showed many informative research results on the pilot-scale reactor design and its validation. The manuscript is well-organized and highly scientific for publication in this journal. As the current status, the manuscript is sufficiently in a good condition for publication. Only one minor issue can be improved for acceptance. The authors prepared pellet-type catalyst for the CO2 methanation, but its characterization is not provided. The photo of the pellet-type catalyst can be included. In addition, if the authors can include various characterization data for providing the physicochemical properties of the pellet-type catalyst, it should become more qualified for publication.

Author Response

Dear Editor and Reviewer,

We would like to thank you for your insightful comments and valuable suggestions on our manuscript. We have responded to the decision letter in the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

1.In the "Figure 1. Process diagram of carbon resource integration.", the Sewage treatment may be "Anaeroxic-Anoxic-Oxic" process, which usually called "A2O" process.

2. The catalyst preparation and description process needs to be improved (2.2.1Preparation of pellet catalysts).

3. Will the composition of the gas not correspond to the actual? Usually, the exhaust gas may be composed of H2, CO2，CO， CH4 and H2O. However, in this paper the exhaust gas is composed of 16.34% H2, 4.31% CO2, 26.45% CH4, and 52.9% H2O.

4. There was CO in the figure 14, but the author did not disrcbe in the main text.

5. There are few references in this paper and english writing needs to be improved.

 

Author Response

Dear Editor and Reviewer,

We would like to thank you for your insightful comments and valuable suggestions on our manuscript. We have responded to the decision letter in the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

Review comment for the communication article “Development of pilot-scale CO2 methanation using pellet-type catalysts for CO2 recycling in sewage treatment plants and its validation through CFD modeling”

 

The authors discussed the size of the reactor for CO2 methanation using CFD simulations, created an actual pilot plant, and evaluated its performance. Attempts to convert CO2 into useful substances using electric power have been pointed out as globally important from the viewpoint of SDGs, and the usefulness of this research is considered to be high. However, their presentations are not good and the manuscripts are not logical. The introduction can be regarded to have optimized the pilot plant by CFD, but as far as the text is read, it is not "optimized". They considered only two reactors, and could only argue which of these was better. Although the simulation results are explained in chapters cold-flow, reacting-flow, and hot-flow, the definitions of these three conditions are not found in the method section, which confuses the reader. It is not possible to judge whether the conditions in the experiment shown in Table 1 are optimized by CFD simulation. It also does not state how the shape of the catalyst used or the shape of the reactor (not the size) was decided. The calculation of the energy balance excludes the power required for electrochemical H2 production, which will be very misleading to the reader. It is not necessary to perform LCA (life cycle assessment), but at least the total amount of power used to generate H2 (or the amount of power per day) should be shown. In addition, there are some minor revised points.

Minor points:

1. In line 64, there is a typo for equation numbering.
2. The resolutions of the figures are low, and some characters in the figures cannot be read on the printed paper (e.g., Fig. 1).
3. The label of the vertical axis in Figure 5 is incorrect.
4. Figure 8 is not a figure but is a scheme.
5. The use of abbreviations (CFD) in titles should be avoided.
6. For “This study selected a Ni-0.2Ce-0.1Zr catalyst with excellent CO2 methanation performance as a powder catalyst” in line 143, references are needed, and if possible, the author should show the performance at laboratory level.

 

Author Response

Dear Editor and Reviewer,

We would like to thank you for your insightful comments and valuable suggestions on our manuscript. We have responded to the decision letter in the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The “℃” in lines 158 and 159 may be note consistent with the following. The author needs careful examination.

Author Response

Dear Editor and Reviewer,

We would like to thank you for your insightful comments and valuable suggestions on our manuscript. We have responded to the decision letter in the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

Please make revisions based on the responses for C8 and C10. The authors made reponses to the comments, but they did not make any revisions for the comments requesting major revisions.

Author Response

Dear Editor and Reviewer,

We would like to thank you for your insightful comments and valuable suggestions on our manuscript. We have responded to the decision letter in the attachment.

Author Response File: Author Response.docx

Round 3

Reviewer 3 Report

The manuscript has been revised carefully by the authors. The paper is well presented. I recommend the acceptance of this paper.