Techno-Economic Analysis of Onsite Sustainable Hydrogen Production via Ammonia Decomposition with Heat Recovery System

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1 All techno-economic indicators in the manuscript are derived from Aspen Plus simulations, yet the underlying model has not been properly validated. The authors claim to have calibrated the SGT-400 turbine for 100 % H₂ operation, but in fact they rely solely on the power output reported in Reference 22 for a cursory comparison. Reference 22 is cited without a complete bibliographic entry and does not appear in any reputable peer-reviewed journal or conference. Its title, The Effects of Intrinsic Parameters on the Performance of Industrial Gas Turbines (2018), strongly suggests that the data come from an earlier natural-gas test, not from hydrogen firing. To establish the credibility of the hydrogen-fired turbine model, validation should use experimental data from actual hydrogen turbines rather than legacy natural-gas data. Several publicly available pure-hydrogen or high-hydrogen-blend turbine tests could be used for cross-validation.

2 The first fifteen lines of Section 2 are still template instructions and not part of the research content; they should be removed entirely.

3 There are multiple mass balance and energy balance errors throughout the paper; all balances need to be recalculated.

4 In Section 2.1.1 the authors assume “hydrogen mass flow rate = natural-gas mass flow rate,” which disregards the actual operating constraints of the equipment.

5 The stated ammonia feed of 480 kg s⁻¹ is far beyond what a 12.8 MW turbine would require; both units and orders of magnitude must be checked.

6 Figures and tables are very rough—adequate for a student assignment perhaps, but they need substantial graphical improvement before publication.

Author Response

attached

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

General Comments:

  This analysis focuses on the technological analysis of onsite hydrogen production through ammonia decomposition utilizing the heat from exhaust gas generated through a hydrogen-fueled gas turbine, which is considered economically viable. The background and discussion are relatively stable. The authors should improve the aim, export the significant findings and schematic representation for hydrogen production via ammonia decomposition by convective heat transfer with technological and economic analysis, and revise accordingly.

Authors Comments:

Consequently, this article is publishable if the authors provide improvement as the following directions:

1. The title of this article, ‘A facile analysis of onsite hydrogen production via ammonia decomposition by convective heat transfer,’ should be revised to increase its significance and readability! In addition, the abstract should be written in the present tense. The author should add a graphical abstract for better readability. Furthermore, the authors should provide a scheme with technological and economic analysis of hydrogen production via ammonia decomposition by convective heat transfer, and revise accordingly.
2. The introduction section is relatively large. Please revise the significant information to enhance the readability!
3. The materials and methods section has errors and typos regarding lines (165 to 179). Please revise it.
4. Authors should improve the overall construction of the manuscript. The author should add a clear flowchart and a scheme to enhance significance and readability. In addition, please remove a few figures and tables from the main text and add supporting information.
5. Tables 2-6 should be revised with a standard, significant, and clear format.
6. On page 9 (line 315), the authors state, ' Error! Reference source not found. and Error! Reference source not found.’ Please revise it.
7. On page 9 (lines 318 - 319), the authors state, ' The OPEX estimation is shown in Error! Reference source not found. and Error! Reference source not found.’ Please revise it.
8. Please provide significant information regarding the novelty of this article in the conclusion section that you have achieved.
9. Please consider more recent research articles cited. For example, references 23 (1983) and 28 (1968) should be revised with more recent articles.

Comments on the Quality of English Language

This article contains typos and grammar mistakes. The author must carefully revise it with a professional English writer.

Author Response

attached

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

In this paper, the authors conduct a techno-economic analysis of onsite hydrogen production via ammonia decomposition, utilizing heat from the exhaust gas of a hydrogen-fueled gas turbine, and compare the results with the conventional furnace-based method. The levelized cost of hydrogen (LCOH) is estimated at $5.64/kg, with the price of ammonia identified as the most significant and sensitive contributor to the LCOH. Several comments and clarifications must be addressed before the paper can be accepted for publication.

1. Page 1, Subsection 1.1: I assume the authors intended to write 'storage and transport of hydrogen' rather than 'storage of transport of hydrogen'.
2. In Section 1.3, the authors list several previous studies on the LCOH using different methods. However, the connection between these past studies and the current work is not very clear. It would strengthen the introduction if the authors could clarify what is still missing in the existing literature and how this study addresses those gaps. For instance, have any previous studies specifically looked at using waste heat to lower heat supply costs?
3. It would be helpful to present the results from Tables 3 to 5 using figures. Additionally, Figure 6 should be revised, as the current version makes it difficult to see the other categories.
4. Some important data have not been clearly described. For example, the thermal efficiency from both waste heat and combustion heat to the reactor is not specified. Additionally, information such as equipment prices, catalyst prices, and material degradation used in TEA analysis is missing.
5. Figure 9 needs a clearer explanation. Does the lower LCOS at higher reactor temperatures result from more efficient ammonia conversion, thereby reducing raw material usage?
6. While LCOH is an important metric discussed in this paper, it would be helpful if the authors could explicitly show the reduction in heat energy consumption when using waste heat compared to traditional methods.
7. The paper has some minor grammatical issues, particularly involving long sentences that are missing commas. For example, on page 1: "To achieve net zero carbon emission when using hydrogen fuel, it is necessary to transit into using green hydrogen however, cost would be a barrier for transition of grey hydrogen to green hydrogen as the cost of green hydrogen is about 3 times the cost of grey hydrogen", a comma is needed before “however”, and it would be clearer to rephrase this as: ‘the cost of transitioning from grey to green hydrogen would be a barrier, as green hydrogen is approximately three time more expensive’. On page 2: "Hydrogen is a low-density gas by volume making it difficult to store in large quantities without high pressure or low temperatures, hence making the storage and transportation of hydrogen fuel expensive." A comma is needed before the first 'making’. Similar issues appear in several parts of the paper. While these are not major problems, careful proofreading and revision would improve the clarity and readability of the manuscript.

 

Author Response

attached

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

Overall, the topic is interesting but the quality of the text dos not meet quality standards of scientific articles. Signifficant improvements are needed. Specific comments.

1/ English must be improved.

2/ At the end of the introduction section the motivation and novelty should be better elaborated.

 

3/ Lines 164 to 179 is the text that remains from instructions for authors. It should be removed, and replaced with the authors’ contribution.

4/ line 190: ‘…is assumed to be the same natural gas fuel flow rate.’ What rete do you mean, mass, molar or volumetric? How this assumption is justified. Usually, fuel replacement limits result from the TIT (Turbine Inlet Temperature).

5/ Turbine simulation results should be presented in a consolidated way in a table. Ther should be presented and compared key parameters such as: air mass flow rate, fuel mass flow rate, exhaust gas mass flow rate, TIT, TOT (Turbine Outlet Temperature). At the moment the quality of the model cannot be assessed.

6/ What is Q in eq. (3). The description of symbols should be more precise. For example in what temperature range Dh is considered for reactants and products?

7/ Quality of Fig.4 is low. The figure should present key parameters or symbols of components mentioned in the text below. Why there are 4 reactors and NH3 absorbers?  

 

8/ There is no difference between Fig. 4. And 5. The hot gas flow is not presented.

 

9/Key simulation results should be presented in a table. At the moment the results are nor being revealed.

 

10/ The assumptions for economic analysis should be presented. For example, it is not known how many hours per year the system is in operation. Service and maintenance costs and requirements are not justified. How do you treat the income from electricity? Is the entire amount of hydrogen consumed in the turbine or you produce some hydrogen for the market? Overall, some equations presenting Cash Flows would help. Hydrogen balance is also interesting.

 

11/Sources of information for key data presented in tables 3 and 4 are not revealed. How did you get this numbers (e.g. FCI) ? Overall, reliability of financial information should be improved.

Comments on the Quality of English Language

 

 1/ English should be improved. For example ‘Storage of Transport of Hydrogen’ neither does read well nor is fully understandable. Another example, line 49:

,… with high energy consumption which will result in high production cost of hydrogen.’

Suggestion: ,… with high energy consumption, which results in a high hydrogen production cost.’

Another, line 53: ‘…as hydrogen can be stored in physical based and material based.” This sentence is grammatically incorrect and difficult to understand.

Please cross check the entire article.

Author Response

uploaded

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Agree

Reviewer 4 Report

Comments and Suggestions for Authors

In my opinion the revised version of the paper is considerably better thet the original text. Overall, the article presentes an interesting pre-fesiability study that contributes to the global discussion on the future hydrogen economy. In particular, the text, although academic, provides interesting insights on technical and financial feasibility of using ammonia as a hydrogen carrier. In my opinion the text can be considered for publication.

One suggestion is to thorougly review the text and correct spellilng mistakes before the pubication. For example: "Siemen" should be replaced with "Siemens" :-)