Hydrogen Purification by Pressure Swing Adsorption: High-Pressure PSA Performance in Recovery from Seasonal Storage

Round 1

Reviewer 1 Report

The paper deals with an interesting problem for hydrogen and its purification. The findings and results of the paper have the potential to contribute to the related fields of science and literature. However, the document needs improvement in some topics, as outlined below:

1. In the introduction of the article, please avoid grouped quotations. Present a synthesis of past work highlighting key insights and current gaps in the study of these systems. Provide more information about the conclusions of these studies, showing what is new, instead of just repeating what has previously been found. 

2. What is the contribution of Figure 1 used in the introduction of the article?

3. The paper needs a more comprehensive drawing of the experimental setup than the one given in Figure 5. To improve the quality of the paper, pay attention to the drawings.

4. What is MFC? There are some similar abbreviations, but no explanation. The article needs an abbreviation index.

5. The "Results and Discussion" sections are in the form of reports. An appropriate comparative analysis of the article with previous articles should be appropriately discussed.

Although the subject of the paper is original, there are some errors and deficiencies in its presentation.

 

Author Response

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Reviewer 2 Report

1.       In Figure 1, a and b are not labelled. Figure 1 a is not legible.

2.       In line 48 and 49, Hydrogen could provide up 48 to 24 % of total energy demand in the EU by 2050. How did you calculate this exact %?

3.       In line 77, what does “unsaturated forces” mean?

4.       In line 80, i.e. the adsorbed species can be recovered and the adsorbent is regenerated by pressure. I think “is” missing.

5.       The adsorption pressure range is chosen from 25 to 60 bar. Is there any reason for this specific range. In table 2, the spelling “Bara” is to be corrected.

6.       What do the horizontal numbers and the vertical numbers represent for in figures 7, 10, 12, and 14?

7.       Can at least one of them be compared with 100% pure one?

8.       References are needed for the equations.

9.       What do the vertical numbers represent in figure 8?

1.   References style is not consistent. E.g. reference 26, 30 the journals are not abbreviated.

1.   I have not seen DOI in references in journals. Is Journal’s policy or just for the help for the reviewers?

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

The subject of this study is very interesting and significant from a practical point of view. Indeed, the authors have clearly demonstrated the capability of hydrogen purification by pressure swing adsorption using a pilot plant they developed themselves.

The research in this manuscript is new and original.

The research was extensive, well planned and executed, and the explanations in the text were understandable and logical.

With all praise for the authors, I would like to add a few small suggestions:

-        Enlarge Figure 1 (the text on it should be legible), present it in the text (in the introductory part) and add the labels "a" and "b",

-        Present Figure 3 also in the introductory part,

-        Present figure 8, and briefly describe it as a summary picture (under number 14) at the end of all stages of the cleaning process. Change the order of the other pictures accordingly.

-        At the end of the manuscript you have to present the basic conclusions of this work (form a new chapter "Conclusion").

Author Response

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Reviewer 4 Report

This work shows very practical experimental results for the development and operation of the PSA system, especially for the large scale underground storage of hydrogen. Four stages of scenario for the PSA operation was proposed and investigated using a lab scale equipment. However, manuscript structures, figures, discussion, and English language should be improved further. I think that it can be published with major revision.

 

1.     English should be improved.

2.     Various PSA applications were provided as literature on the page 4. However, there is no literature survey on the PSA application especially for the underground storage (UGS). Please add more literature and explain the originality of the work.

3.     You should explain the reasons why you assumed the 4 stages to simulate the seasonal recovery. Do you think it is an enough number of stage to investigate the scenario of the seasonal recovery? In addition, I think there should some limitations caused by the assumption of the 4 stages. Please explain it on the manuscript.

4.     Please add explanation how to select the adsorption pressure and mole fraction ratio of the Table 2. There is no sufficient explanation about the values (e.g. 25-60 bar, 98:2 to 65:35 ratio).

5.     As listed in Table 3, total 16 experiments were conducted. However, you only selected run#1, 7, 13, 16. You should explain why you chose these cases and why they were better than others. In addition, I think you don’t need to list them according to the order of your real experiment, but you can reorder and rename them to be more easily understood by the readers.

6.     For Figure 6, 7, 9-14, it’s better to indicate what action occurred at each time. (e.g. in case of figure 6, 830 sec first pressure equalization, 1160 sec blow down, etc.). Please give the detailed information about the step and corresponding time on the figures. It was very difficult to follow all the steps from your figures.

7.     Recovery and standard deviation in Figure 8 should be explained in the separate session, for example, by adding new session 3.5. Figure 8 includes all the results for the stages 1-4, but it is in the session 3.1. Also, I think that you should improve the comparison of the stages 1-4 in the separate session. I can understand each stage separately, but I think comprehensive discussion comparing them is insufficient.

8.     Followings are minor revisions
- Figure 1 is too small to read. It should be enlarged and the resolution should be maintained high.
- At lines 158-160, reference should be added.

Author Response

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Round 2

Reviewer 4 Report

The manuscript has been revised according to the comments, so I think it can be accepted in the present form.