Review Reports - Biomass-to-Green Hydrogen: A Review of Techno-Economic-Enviro Assessment of Various Production Methods

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article is well-structured, with a clear division of sections that discuss the different hydrogen production methods, their evaluation from an economic point of view, and their technological feasibility, but I believe it is necessary to explain the technical terms for readers less versed in the subject. The preliminary review is sufficiently broad; however, I believe it is necessary to include more examples where the indicated technologies have been applied to have reference scenarios. The review covers classical thermochemical, biological, and electrochemical processes but does not consider the state of the art in terms of emerging technologies. I suggest briefly including a section on the environmental impacts of each method, but allowing consideration of the possible effects of each case, considering that precisely one of the factors driving green hydrogen is its low impact.

Production costs require delving into the current market conditions and projecting their evolution according to the public policies that exist today in most countries to encourage their insertion. No consideration is given to the integration of hydrogen into existing processes or industries and how this affects production costs or the technological challenges this would require. The economic assessment could be improved by further analysis of long-term operating costs and potential changes in input price,

I suggest a more detailed analysis of LRTs by considering tariff barriers and other factors that could affect them. I believe that the comparative analysis should be improved, given a more detailed comparison, including pros and cons, scalability, and long-term projections. Although socioeconomic factors are very complex to analyze, there is no analysis of their effects on unemployment rates or others. I suggest taking a case example (Australia, another OECD country, and other countries with different economic scenarios) with economies of different sizes to analyze its impacts. Similarly, geopolitical aspects that could affect the scenario and the results of the application of this technology were not considered. Although this review identifies areas in need of improvement, it can be strengthened by providing specific recommendations for future research to identify gaps in the current knowledge.

Finally, I suggest reviewing some format aspects such as the equations and quality of the pictures, among other visual aspects.

Author Response

The authors understand that it is their responsibility to thank the distinguished referee for his insightful comments. Without a doubt, these comments improve the article's quality. An attempt has been made to give an appropriate response to the opinions of the esteemed referee.

Reviewer #1:

Response to Comment 1:

Based on the reviewer's advice, the acronyms table was added to the article's text to help readers who are not as familiar with the subject matter understand the technical words. The third part of this article provides a thorough overview of the several processes such as thermochemical, biological, and electrochemical ones that may be used to produce hydrogen from biomass. It also addresses the benefits and drawbacks of each process in terms of technology. The economics of these techniques were then investigated. The current analysis condensed a portion (Section 4.3) on the bio-environmental effects (carbon dioxide emissions) of each approach, in accordance with the proposed reviewer (The manuscript is highlighted by a yellow color).

Response to Comment 2:

I want to start by saying thank you for the insightful review. The Section 4.2 and Table 3 were included in the current investigation (The manuscript is highlighted by a yellow color). On the one hand, a detailed description of each method's technological hurdles may be found in Tables 5 and 6. An additional economic value study based on long-term operational expenses and prospective price fluctuations has to take into account a variable factor like inflation that differs across national boundaries.

Response to Comment 3:

We want to start by saying thank you for the reviewer's outstanding advice. The proportion of economic indicators, such as the tariff, that differ between countries depending on their respective political, economic, and social situations is outside the purview of this article due to its special timing and complexity. One potential topic for a recurring post on the topic of hydrogen generation from biomass is an analysis and evaluation of the item on hydrogen production costs. Tables 5 and 6 list the benefits, drawbacks, and scalability of each biomass-based hydrogen generation technique. Due to the analysis and examination of time as well as the particular complexity of the breadth and diversity of social indicators, social variables were removed from the article's title. As a result, the authors of this paper will definitely note the need to examine social indicators like the unemployment rate, even though they are not included in the study but are an appealing idea in other demonstrations. As was indicated in a few lines above, each country's economic circumstances are unique and are ascribed to a distinct age depending on the political and social circumstances that govern it as well as its geographic location. The purpose of adding the fifth section to the article's text was to give a precise evaluation for further investigation (The manuscript is highlighted by a yellow color). According to the opinion of the honorable referee, the title of the article was changed as follows:

Biomass-to-Green Hydrogen: A Review of Techno-Economic-Enviro Assessment of Various Production Methods

Finally, I suggest reviewing some format aspects such as the equations and quality of the pictures, among other visual aspects.

Response to Comment 4:

The equations were verified, and the examination's visual components' clarity and picture quality improved.

Reviewer 2 Report

Comments and Suggestions for Authors

The study is devoted to the comparative analysis of technical and economic characteristics of the main modern technologies of hydrogen production from biomass. This is an interesting and as yet incompletely explored area in which technology is actively developing. However, the environmental and social parameters (as indicated in the title) of each of the technologies are practically outside the focus of the paper.

In addition, the study has significant methodological flaws.

When assessing the economic aspects of different hydrogen production technologies, the authors nowhere use discounting, although all production projects have a long life cycle. Such estimates of economic viability are very crude.

When comparing capital costs and H2 production costs (Table 1), the authors rely on only one source for each method. This is incorrect because capital and production costs vary significantly from project to project, and therefore average data from meta-analysis should be used.

In addition to the to the above-mentioned shortcomings, there are also significant comments on the structure of the article.

The abstract does not describe the research methods. I also recommend that the results be included so that the reader can get an idea of the study from the abstract.

The introduction is too short. It is not clear what exactly the authors are going to research, what is the gap in existing knowledge, how exactly they are going to fill it.

The methodology section does not describe the research methodology itself, as well as the information sources on which this research is based.

There is not always a description of the acronyms used. For example, in line 174, the abbreviation SRNG appears for the first time in the text, but is not explained.

Comments on the Quality of English Language

The English language is fine, although there is too much use of the passive voice in some sentences.

Author Response

Reviewer #2:

First and foremost, the esteemed referee is thanked for his insightful comments. We hope that the answers provided will persuade the impartial referee. The following are the answers:

Response to Comment 1:

The third part of this article provides a thorough overview of the several processes such as thermochemical, biological, and electrochemical ones that may be used to produce hydrogen from biomass. It also addresses the benefits and drawbacks of each process in terms of technology. The economics of these techniques were then investigated. The present study detailed Section 4.3 on the biological and environmental effects of each approach, as recommended by the reviewer (The manuscript is highlighted by a yellow color). Furthermore, there is no need to look at social factors like the unemployment rate in the study because the social parameter that was mentioned in the article's title has been removed due to the analysis and review of time as well as its unique complexity in terms of the breadth and diversity of social indicators.

In addition, the study has significant methodological flaws.

When assessing the economic aspects of different hydrogen production technologies, the authors nowhere use discounting, although all production projects have a long life cycle Such estimates of economic viability are very crude.

Response to Comment 2:

We would first like to express our gratitude to the esteemed reviewer. As you are aware, each nation has distinct economic circumstances that vary depending on its political and social framework as well as its geographic location. As a result, the indicative rate also known as the rate of discounting varies throughout countries. Because of this, the study evaluated the various techniques of producing hydrogen from biomass in terms of their economic sustainability over an extended life cycle using metrics like IRR and payback period (Table 2).

Response to Comment 3:

The reviewer's suggestion is quite intriguing. The Section 4.2 and Table 3 (The manuscript is highlighted by a yellow color) were included in the study's text at the reviewer's request.

In addition to the to the above-mentioned shortcomings, there are also significant comments on the structure of the article.

The abstract does not describe the research methods. I also recommend that the results be included so that the reader can get an idea of the study from the abstract.

Response to Comment 4:

The abstract of the paper was revised, and research methodologies were incorporated in response to the Honorable reviewer's ruling (The manuscript is highlighted by a yellow color). It is important to note that the study's results have been evaluated in the final few sentences.

The introduction is too short. It is not clear what exactly the authors are going to research what is the gap in existing knowledge, how exactly they are going to fill it.

Response to Comment 5:

The reviewer's insightful comment is much appreciated by the writers. The preliminary part was included at the reviewer's suggestion. The objective of this research and its phases were also outlined, along with the gap in our current understanding (The manuscript is highlighted by a yellow color).

The methodology section does not describe the research methodology itself, as well as the information sources on which this research is based.

Response to Comment 6:

The reviewer felt that the investigation's methodology was altered in the second section (The manuscript is highlighted by a yellow color).

There is not always a description of the acronyms used. For example, in line 174 the abbreviation SRNG appears for the first time in the text, but is not explained.

Response to Comment 7:

Based on the reviewer's advice, the acronyms table was added to the article's text to help readers who are not as familiar with the subject matter understand the technical words.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The inclusion of original experimental data still needs to be reviewed. Without such information it is difficult to validate the results shown. These data could be presented in a summary table or similar format to facilitate interpretation. Improvements are noted in some parts, for example, the inclusion of original experimental data in Section 4.2 and Table 3. In addition, Section 4.2 provides a comparison of the scalability and technological readiness of various methods which addresses my second point made above. Based on this, I believe that my first observation has not been fully remedied and requires revision.

Beyond these brief substantive observations, I believe that a thorough revision of the format of the paper presented is required. For example, the biography is not in the form that MDPI uses, the equations are still poorly formatted, the tables look cluttered and cluttered, the chemical formulas and other form aspects are not well presented. In terms of visual presentation, the work leaves something to be desired. Strongly suggest that this part be revised before acceptance is considered.

Author Response

Reviewer #1:

Response to comments:

According to the referee, for better interpretation as well as easier comparison of the results, the subpoena from the following Section 3 of the study, which deal with the costs of producing hydrogen using different processes derived from biomass, was moved to Section 4 (4.1.). The results were taken and put in Table 1 (this table was revised in relation to the previous state). A brief interpretation of the results was also provided. These new modifications are highlighted by a yellow color in the text.

Additionally, the referee's decisions state that the following modifications were provided:

The article format was modified in order to match the Hydrogen Journal's style.
The reactions and equations matched the Journal's format.
Every table has been updated to match the Journal's format (MDPI uses).
Every image's resolution and quality were enhanced.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have significantly improved the article and responded to all comments. I believe that in the current version the article can be published. I recommend moving the table with abbreviations to the beginning.

Author Response

Reviewer #2:

I recommend moving the table with abbreviations to the beginning.

Response to Comment:

The referee recommended moving the abbreviation table to the beginning of the article.