Hydrogen-Enriched Compressed Natural Gas Network Simulation for Consuming Green Hydrogen Considering the Hydrogen Diffusion Process
Round 1
Reviewer 1 Report
The authors present some results about the concentration of hydrogen in gas pipeline by considering the dynamics of the production processes. The manuscript is well written and organized and the topic has a huge scientific soundness at the moment. The results are well described and reported as well as the conclusions.
However, I would like to see a section about hydrogen storage. After production, hydrogen can be stored with different methods (compressed gas, liquid or with solids) at different scales and then transported. In my opinion, it would be very interesting to include also the effect of H2 storage in underground caverns. Specifically, as maybe the authors know, due to the bacteria and rocks action, hydrogen can undergo to chemical modifications and can be converted into hydrogen sulphide and methane itself. In this case, the dynamics does not depend on the hydrogen production process but on the metabolism of bacteria and the interaction with rocks as a function of time.
To this aim, you can use this work published the last year:
https://doi.org/10.3390/en14102856 (Figure 1 and tables)
I recommend the publication of the manuscript after this modifications (minor revision). Good work to the authors.
Author Response
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Reviewer 2 Report
Review Qiu et al.
The authors carried out a study on hydrogen in gas networks. While the topic of the paper is of general interest as it is very timely, the paper is relatively poorly written. The language is in parts hard. There are also many technical flaws that permit a rigorous assessment of the work reported by the authors, e.g. in most plots, the color scale is not defined. Also, the authors repeatably use the term ‘volume friction’. I do not understand Fig. 1 at all. Actually, essentially all figures remain somewhat erratic; the figure captions do not provide the required information to understand the meaning of the figures. There are several problems with the mathematical formulas and nomenclature, e.g. they seem to carelessly typeset parts of formulas in italic (which of course affects the mathematics.. Italic is restricted to variables, including indices). These are only examples of technical flaws that are in the paper, but there are many more.
There are also several problems with the story: the authors dive into a great detail depth in parts that are not necessary for the main story. But these ‘side-stories’ make the paper lengthy. An example is the extensive discussion on how energy is obtained from solar radiation.
Author Response
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Reviewer 3 Report
Main question addressed by the research: The work addresses hydrogen enriched compressed natural gas network simulation for consuming green hydrogen considering diffusion process.
Originality and relevance of the topic: The topic is relevant to the field and it considers a suitable model (research gap).
Added value of the paper: The manuscript takes into account the study of green hydrogen network, however the main purpose of it is not clearly stated. The paper should include what aspects are critical for these assessments and clearly explain why they are analysing those and why they are needed at the end of the Introduction.
Quality of figures: Very good and easy to follow.
Specific improvements for the paper to be considered:
- I think they have covered all the aspects required for the results, however the validation of the results is not clearly explained and this is essential in order to justify the reliability of the results.
- Abstract is too short and general. It should summarize the main findings and applications of the paper.
- Section 1.4 is not needed as it follows the typical structure of the paper.
- Glossary of all the terms is needed.
- The conclusions are poor and they would need more elaboration so they clearly match the results.
Author Response
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Reviewer 4 Report
This paper investigates the effects of the intermittent and fluctuating green hydrogen produced by hydropower, wind and PV on the dynamic distribution of hydrogen concentration after it is blended into natural gas pipelines. This topic is interesting, the paper is well structured with useful insights. However, I have some concerns as follows.
Major concern:
1. Hydro power, wind farm and PV station are not likely to be deployed at the same place, so the assumptions of the case studies have to be justified. For electrolysis-based H2 generation, particularly by consuming wind and PV, storage is a must. Therefore, the fluctuation and intermittency of renewables are not likely to impact the blend of H2 as shown in the case studies. The practicality of this study should be further justified.
Minor concern:
2. Avoid using the values of parameters in equations, use a symbol instead. E.g., Eq 9, 10.
3. Typos of “Mass frictions” in the y axis in Figure 6 and all similar figures.
4. Figure 5 does not make sense. Since the nodes and pipes are not connected one by one, these dots should not be connected. It will make more sense to use figures like Fig 4 which depicts the topology and indicate the flow rate in each pipe and pressure of each node.
5. The output of wind and PV is complementary which is not general. What if wind and PV is not complementary, say there is a lot of wind and no PV?
Author Response
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Round 2
Reviewer 2 Report
the authors did not respond to the comments of the authors. A meaningful re-evaluation is therefore not feasible.
Author Response
For detailed responses, please refer to the attached response letter.
Author Response File: Author Response.docx
Reviewer 3 Report
Paper has significantly improved, it should be published.
Author Response
Many thanks for this concluding comment and we’re honored to be recognized by the reviewer.
Author Response File: Author Response.docx
