Thermo-Mechanical Numerical Analysis of Stress and Damage Distribution within the Surrounding Rock of Underground Coal Gasification Panels

Round 1

Reviewer 1 Report

 

1. Abstract should be simplified according to the word limit for publishment.

2.Background should be divided into several secondary chapters to clarify its structure.

 

3. an update in the references list is welcome. Some interesting fundamental references, even a bit old, can also be added, e.g.:

Cutting energy characteristics for brittleness evaluation of rock using digital drilling method. Engineering Geology, 2023, 319, 107099.

Determination of the constant m(i) in the Hoek-Brown criterion of rock based on drilling parameters. International Journal of Mining Science and Technology, 2022; 25: 615–621.

4. In the conclusion part, the content should be simplified to emphasize the advancement of this research, taking example of dividing the conclusion into several pieces and adding quantitative results.

This study aims to investigate the thermo-mechan-ical behavior and integrity of the surrounding rock in the gasification vicinity to ensure safe and efficient UCG processes.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

General opinion

This paper investigates the behavior of the rocks surrounding an underground coal gasification (UCG) site. UCG is a method of extracting gas from coal seams in the ground. The study conducts experiments to test the properties of the rocks at different temperatures, as these properties can change with temperature. Using a model that combines thermal and mechanical factors, the study analyzes the stress and damage distribution near the gasification area. The research also explores the causes of rock failure in UCG, considering factors like panel orientation, gasification chamber width, temperature, and pressure. The findings of this study can be used to improve the design and safety of UCG processes, making coal gasification operations more efficient. Future research can build upon these findings by investigating additional factors and refining the models for a better understanding of the UCG process.

Also the findings of the study have practical implications for the design and assessment of underground coal gasification (UCG) processes. By investigating the thermo-mechanical behavior and integrity of the surrounding rock, the study can contribute to the safety and efficiency of UCG operations. This can help in optimizing the design of UCG sites and ensuring the safe extraction of synthesis gas from coal seams.

The manuscript has both practical applications and provides important theoretical insights for future studies. Overall, the manuscript combines practical implications for UCG design and operation with important theoretical insights that can guide future research in this field.

 

Introduction

The introduction of this paper can be enhanced to effectively captivate and educate the reader about the subject matter.

The literature review is presented quite well, but in very short form and includes mainly the experience of authors from China. I strongly recommend that you consider the works of other authors. Enhance this part with more current studies. Here I would like to bring your attention to the paper

Saik, P.; Berdnyk, M. Mathematical model and methods for solving heat-transfer problem during underground coal gasification. Min. Miner. Depos. 2022, 16, 87-94. https://doi.org/10.33271/mining16.02.087

Gao, W.; Zagorščak, R.; Thomas, H.R. Insights into ground response during underground coal gasification through thermos-mechanical modeling. Int J Numer Anal Methods Geomech, 2022, 46, 3-22.

Please consider it and add more relevant information.

 

Section 2

In the section 2 authors describe Experimental Study of Rock Properties with Temperature Dependency but the methodology of mentioned research is not described. Why?

 

Methodology

- Can you provide more details about the thermo-mechanical coupling model that was developed? How was it used to analyze the stress and damage distribution near the gasification chamber?

- How were the failure mechanisms in the gasification surrounding rocks identified and characterized? Were there any observable patterns or trends in the failure modes?

 

- How were factors such as panel orientation, gasification chamber width, temperature maintaining duration, operating temperature, and reactor operating pressure incorporated into the analysis of failure mechanisms in the gasification surrounding rocks?

- Were there any specific limitations or assumptions made in the methodology that should be taken into consideration when interpreting the results of the study?

 

Results

Lines 413-429.

- In comparison to thermal stresses, how significant is the impact of mechanical and thermal properties of the roof and floor strata on the overall extent of damage?

- Despite the decreasing temperatures of the roof and floor strata, why does the extent of the damage zone continue to enlarge during this stage?

 

Conclusions

In the conclusions section of the paper, it is crucial to highlight the novelty and importance of the research. This will provide readers with a clear understanding of the unique contributions of the study and the potential implications for future research and practical applications. Therefore, it is necessary to concisely and explicitly express the innovative elements of the research in the concluding part of the paper.

 

 

With revisions addressing the suggestions provided, this paper holds potential for publication and contributes valuable insights to the field.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Authors in their work investigate the thermo-mechanical behavior of rocks in underground coal gasification (UCG). Through rock property tests under varying temperatures and developing a thermo-mechanical coupling model, stress and damage near the gasification chamber are analyzed. Influential factors on the stress state and failure risks during UCG, including temperature dependency, panel orientation, gasification chamber width, and operating pressure, are evaluated.

The methodology is sound and the results and discussion are relevant.

I believe that the article is interesting to readers of Processes.

Following are my comments to the authors.

> The experiments and results presented in the study offer insightful data, but they don't provide a clear understanding of the long-term implications. It remains uncertain how the findings apply to the sustained integrity of the rocks surrounding the gasification chamber in the long run during the underground coal gasification process. Could authors clearer this point in their manuscript?

> The overall quality of the figures in the paper could be improved. Some appear repetitive.

> Figure 16 is hard to read and confusing.

> Figures 25 and 27 display strikingly similar behaviors, which may lead to confusion or redundancy. It may be beneficial for the authors to use a different approach to illustrate the damage zone, or at the very least, highlight specific points where differences occur. This could provide clearer distinctions and enhance the understanding of these figures.

> Authors need to include the limitations of their works and insights for future works.

No comments.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

The authors reported the thermo-mechanical numerical analysis of stress and damage distribution within the surrounding rock of underground coal gasification panels. Besides some additional statements that need to be included (e.g., introduction part should include the gabs that the present report will expected to fill), the novelty of the report is very low and there are plenty of reports that are almost exactly same investigation. For example, International Journal of Coal Geology, 2014, 134-135, 1-16; https://doi.org/10.1177/01445987198889; etc. Therefor, the paper is not suitable for publication.

I think English is fine.

Author Response

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Reviewer 5 Report

The authors presented an interesting paper. The Paper is well-written and can be useful for practice. The research design, questions, hypotheses, and methods are clearly stated. The paper is suitable for the journal Processes.
Minor review:
1. Please ensure the abstract is short but reflects the approach, results, and conclusions correctly and concisely.
2. Please check the keywords to ensure they are appropriate and complete.
3. All variables used in the equations should be clearly explained in the text. Similarly, formatting symbols in equations should be straightforward in the text. Please check SI units for all physical quantities.
4. The references and the citation don't work the way the authors just added to the text. (Reference source not found 237, 244...).
5. Please remove bunch citing, like [18,25,40–42] or [9,41,43–45]. If the pieces of literature are important, please separately explain their results and output.
6. The Limitations of the proposed study need to be discussed before conclusion.
7. In discussion, authors should discuss the results and how they can be interpreted from the perspective of previous studies and the working hypotheses. Future research directions may also be highlighted.
8. Conclusions are not written properly. Major findings need to be mentioned in this.

I suggest accepting the paper, but my comments should be resolved.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Dear authors, I am more than satisfied with the corrections provided by you. Congratulations to the authors.

Reviewer 4 Report

The authors considers my previous concerns on the manuscript. I think it can be considered for publication.

The language is fine.