Simulation of Underground Coal-Gasification Process Using Aspen Plus

Round 1

Reviewer 1 Report

The article contains interesting analyzes of the results of the underground coal gasification process by differentiating gases in specific flow zones. Important distinctions are the obtained dependencies of mole fraction on oxidation, reduction and methanation zones, which are scientifically interesting: Below are some comments and suggestions:

1. In the introduction, it should be mentioned that the underground gasification process requires determining the stability of the gasification channel due to the significant impact of high temperature on the surrounding rocks (doi:10.3390/en14206464); this is particularly important in the case of direct surroundings with claystones;

2. In the second chapter, it is worth adding temperature ranges in which individual stages of coal gasification take place: oxidation, reduction, methanation reaction; dry distillation and drying – this will allow for better specification of the research issue;

3. In chapter three, it should be written what geological and mining conditions are reflected in the modeling; please describe the depth and thickness of the coal seam;

4. In the fourth chapter regarding the discussion of the results, reference should be made to several literature items in which the influence of selected geometric parameters of mining equipment was examined: diameter and length of the pipeline on the change in temperature and pressure, as well as the influence of different gas content on the gasification process - so that the results were a form of discussion and comparison of results;

5. In the conclusions, one statement should be added regarding the choice of gasification agent for future research.

Author Response

Dear reviewer：

We thank you for the opportunity to revise the “Simulation of underground coal gasification process by Aspen Plus” for publication in energies. We thank the reviewers for their feedback on our manuscript (energies-2922475). The review comments have been of significant help in the revision and improvement of this paper. The authors have carefully analyzed the problems of the paper according to the review comments and revised the manuscript in response to some of the experts' revisions. At the same time, it should be noted that the modification will not affect the overall content and thinking logic of this paper. Once again, I sincerely thank the editors and reviewers for their hard work.

Thank you for your comments and suggestions on this paper, the authors have carefully analyzed the problems of the paper according to the review comments and have revised the manuscript, the specific revision instructions are as follows:

1、“ In the introduction, it should be mentioned that the underground gasification process requires determining the stability of the gasification channel due to the significant impact of high temperature on the surrounding rocks (doi:10.3390/en14206464); this is particularly important in the case of direct surroundings with claystones”

Modification Instructions：The articles recommended by the reviewers have been referenced and cited in the introductory section, as suggested by the reviewers (Ref. [13]). Other relevant literature has also been consulted to provide a brief analysis of the effect of temperature on the stability of the rock around the gasification channel.

2、“In the second chapter, it is worth adding temperature ranges in which individual stages of coal gasification take place: oxidation, reduction, methanation reaction; dry distillation and drying – this will allow for better specification of the research issue”

Modification Instructions：Temperature ranges have been added at the beginning of Chapter 2 for the oxidation, reduction, methanation and drying zones of the coal gasification process.

3、“In chapter three, it should be written what geological and mining conditions are reflected in the modeling; please describe the depth and thickness of the coal seam”

Modification Instructions：It has been added in the beginning part of Chapter 3 that the target coal seam for simulating the underground gasification process of coal in this paper is to take the depth of 800-900m and the thickness of the coal seam is 8-10m as the target coal seam.

4、“In the fourth chapter regarding the discussion of the results, reference should be made to several literature items in which the influence of selected geometric parameters of mining equipment was examined: diameter and length of the pipeline on the change in temperature and pressure, as well as the influence of different gas content on the gasification process - so that the results were a form of discussion and comparison of results”

Modification Instructions：Relevant references have been added to the discussion of results section in Chapter 4, describing the effect of pipeline results on temperature and pressure, as well as the effect of different gasifier contents on syngas fractions

5、In the conclusions, one statement should be added regarding the choice of gasification agent for future research.

Modification Instructions: Conclusion 6 has been added to the conclusions, which illustrates that when CO₂/H₂O is used as the gasification agent, depending on the target orientation of the synthesis gas (H₂ or CH₄), this can be achieved by referring to the gasification agent ratios in this paper.

Kind regards,

Shuxia Yuan

Author Response File: Author Response.docx

Reviewer 2 Report

The writers of this paper model the complex procedure of underground coal gasification using Aspen Plus. They explore the subtle effects of pressure and temperature variations on gasification water, spray water, syngas, oxygen, and other pipeline components. In addition, the study covers the impact of different pipe sizes on the performance of pipeline conveying. The effects of critical factors, including the oxygen-water ratio, processing capacity, and spray water volume, on syngas composition and component development within different reaction zones are analyzed. Optimal injection pressures, liquid water injection techniques, and the complex impacts of different oxygen-water ratios on syngas composition are all uncovered in this manuscript's exhaustive analysis of underground coal gasification processes. I recommend that the following comments be considered to make this article more publishable:

1.      The length of the abstract is quite long. It's important to keep abstracts brief and focused on the most critical aspects of the study to maintain reader interest and clarity.

2.      The abstract jumps into technical details without providing sufficient background information on the importance or relevance of studying underground coal gasification using Aspen Plus simulation.

3.      The introduction does not clearly state the specific problem or research gap the study aims to address.

4.      The introduction must include some previous studies on the same topic.

5.      The manuscript does not clearly outline the assumptions made during the model-building process, which raises questions about the accuracy and validity of the simulation results.

Author Response

Dear reviewer：

We thank you for the opportunity to revise the “Simulation of underground coal gasification process by Aspen Plus” for publication in energies. We thank the reviewers for their feedback on our manuscript (energies-2922475). The review comments have been of significant help in the revision and improvement of this paper. The authors have carefully analyzed the problems of the paper according to the review comments and revised the manuscript in response to some of the experts' revisions. At the same time, it should be noted that the modification will not affect the overall content and thinking logic of this paper. Once again, I sincerely thank the editors and reviewers for their hard work.

Thank you for your comments and suggestions on this paper, the authors have carefully analyzed the problems of the paper according to the review comments and have revised the manuscript, the specific revision instructions are as follows:

1、The length of the abstract is quite long. It's important to keep abstracts brief and focused on the most critical aspects of the study to maintain reader interest and clarity.

Modification Instructions：Appropriate deletions have been made to the abstract section and the research focus of the paper has been highlighted

2、The abstract jumps into technical details without providing sufficient background information on the importance or relevance of studying underground coal gasification using Aspen Plus simulation.

Modification Instructions：The importance and relevance of using Aspen Plus to simulate underground coal gasification processes has been added to the abstract.

3、The introduction does not clearly state the specific problem or research gap the study aims to address.

Modification Instructions：Gaps in the study of fixed-bed gasification in the study of underground gasification of coal have been added to the introduction, gaps in the study of temperature and pressure variations of the gasifier in the pipeline and of the syngas in the output process have been filled, and the study of the effect of different pipe diameters on the gasifier in the delivery process has been added.

4、“The introduction must include some previous studies on the same topic.”

Modification Instructions：A large number of references have been referred to in the introduction section to analyze the previous analysis of the effects of gasification agent, temperature, coal type, etc. on syngas components in the coal underground gasification process, the effects of gasification temperature on the stability of gasification channels, and the previous analysis of the simulation of the coal underground gasification process using Aspen Plus software.

5、“The manuscript does not clearly outline the assumptions made during the model-building process, which raises questions about the accuracy and validity of the simulation results.”

Modification Instructions：The simulation conditions have been assumed in the second section of the text, which has been bolded in red, assuming the conditions: (1) the model is a steady-state model; (2) the model includes the following reaction processes: coal combustion, coal gasification (reduction reaction, methanation reaction), and coal pyrolysis. (3) The subsurface gasification characteristics are taken in-to account and the pressure variations in the furnace are ignored; (4) The gasifier and coal are completely mixed in the three reactors; (5) No heat transfer occurs in the fluid in the pipe, it is an adiabatic process.

Kind regards,

Shuxia Yuan

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The authors have incorporated all previous suggestions, and I have no additional recommendations. The manuscript is now prepared for online publication.