Mitigating Coal Spontaneous Combustion Risk within Goaf of Gob-Side Entry Retaining by Roof Cutting: Investigation of Air Leakage Characteristics and Effective Plugging Techniques
Sergey Frolov
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript presents the results of computational and experimental studies of the ventilation air leakage to the gob area in the coal mine aimed at estimating the risk of spontaneous combustion of remaining coal. The manuscript fits the scope of Fire and provides some interesting technical solutions for decreasing air leakage to the gob area. Unfortunately, it must be rejected in the current form as (i) the computational results are not substantiated by the mesh sensitivity and validation studies, and (ii) the experimental studies are not substantiated by the error analysis and important details of measurements. Both points are mandatory. I believe, the thoroughly revised manuscript could be reconsidered after rejection. My detailed comments are given below.
(1) The manuscript is very difficult to read. The authors must make the sentences shorter and be careful with grammar and spelling. Some examples: line 37 ("Mine fires are one of..."); line 75 ("The resulting in the gas..."); lines 99-101 ("Guo et al. [42] through on-site measurement and theoretical analysis, the air leakage and gas concentration of the working face with W-type and U-type ventilation methods respectively were studied, and..."); Figure 4, Table 1, Figure 10 ("Air inttel tunnel, Air outtel tunnel"); lines 156-158 ("point was set at the spacing of 55 m inside the wall of the section of the 17202 working face gob-side entry retaining. 17202 working face, which is located in the wall of the gob-side entry retaining section at a spacing of 55 m."); etc.
(2) Figure 1: The legends on the dashed background are not readable.
(3) Line 95: Before this line the authors talk only about Y - and U-shaped ventilation systems and suddenly mention the "U+L" system, which must be explained for the reader.
(4) Line 158: What is the depth of the monitoring point inside the gob?
(5) Figure 3: The figure caption is confusing.
(6) Lines 173-180: All the definitions are applicable to a steady-state flow. Do the authors guarantee that SF6 admixture spreading in the roadways attains the steady state for the time intervals under consideration? The authors must provide a clear ground to this.
(7) Lines 184-185: The authors use different SF6 release points in calculations (point #1 of 8) and in measurements (point #2 of 8), which is illogical, as the results could be directly compared otherwise. Please, explain the reason.
(8) Line 185: The authors must provide solid grounds to the adopted value of the "error coefficient K" equal to 5 (500%?).
(9) Figure 4: Please show the locations of the monitoring points ##1 to 8 in this figure.
(10) Line 210: What is the value of air temperature adopted in the model?
(11) My main concern with this manuscript is the absence of Sections on numerical implementation (discretization, solution, code); mesh sensitivity; and example of code validation against a well-established test case. These sections are absolutely necessary for the computational study. Otherwise, the authors are strongly recommended to remove all the computational results from the manuscript.
(12) Line 217: "Figure 6" must be replaced by "Figure 5." Also, the caption to this figure must indicate that the results are related to calculations rather than measurements, like "Predicted time histories of SF6 in each sampling point."
(13) The same ("predicted") must be added to the captions of Figures 6 to 9, 11 and 12.
(14) Line 229: The sentence "The change trend and the tracer gas measurement results are the same" is inappropriate here, as the reader is still not aware of the measurements. This sentence must be placed, e.g., in the Conclusion.
(15) Line 236: The authors must provide the detailed procedure of gas sampling, which is very important for this study. Please provide the sequence of actions, timing, volumes of sampling bags, etc., as well as the types and errors of measuring equipment.
(16) Table 2: is the accuracy of 2 decimal numbers appropriate for the SF6 concentration in PPM?
(17) Line 274: The authors must introduce here the concept of "oxygen concentration index." Despite this concept is long known, the authors neither provide a reference, nor explanation. This is not acceptable.
(18) Line 341: The reference to Figure 15 must be moved here.
(18) The conclusions look not well substantiated in terms of the computational results by the reason indicated in item (10). The results of measurements do not contain the error analysis, which is mandatory for the experimental study.
Comments on the Quality of English LanguageModerate editing of English language required
Author Response
Thank you very much for your review of our paper, we are very grateful to you for taking the time to provide valuable feedback and suggestions for our paper. We think that your suggestions for our paper are very insightful. According to your suggestions, our reply is attached. Thank you again for your evaluation and thank you for your support for our work. If you have other ideas or more suggestions for our paper, please feel free to contact us, we are very welcome to continue to communicate with you.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors studied the air leakage law of the gob area under the 110 mining method through field testing combined with numerical simulation and proposed targeted sealing measures. The theme of the paper is very instructive for the safe production of coal mines, but there are still some problems to be solved.
1. In section 3.1.2, the air leakage measurement in the gob-side entry retaining is based on the SF6 tracer gas method, in which the SF6 tracer gas enters the goaf, leading to a gradual decrease in the SF6 detection concentration, which is then used to calculate the air leakage rate. The air leakage route in section 3.1.1 shows that the airflow partly enters the gob area and then leaks into the gob-side entry retaining. The two airflow routes are opposite. Whether the airflow was regulated in the two inlet lanes of the working face during the test, if so, should be explained.
2. In section 4.1.1, the tracer gas release flow rate is 109.49 L/min, and the maximum value of SF6 concentration measured at 1# measuring point is about 70ppm: in section 4.1.2, the release volume of SF6 tracer gas is set to 1200mL/min, and the concentration of SF6 in the gob-side entry retaining is about 60ppm, so why is there a huge difference in the release flow rate of the SF6 tracer gas but not much difference in the concentration of the SF6 tracer gas?
3. In section 4.3.1, please check that the expression "along the top of the cut on the side of the open stay lane" is correct?
4. In section 5.1, the maximum reaction temperature of the spraying material used is 94.7 °C. Whether to meet the rules of mine fire prevention and extinguishing ?
5. In line 343 of the text " (2) Working protection. Use equipment such as gas masks and protective clothing to protect construction workers from injury" a complete statement? If so, please describe in detail.
6. Please refer to Table 3 to check whether the title of Table 7 is reasonable? It's best to make a distinction.
Comments on the Quality of English LanguageThe overall English is good, but pay attention to some grammatical expressions.
Author Response
Thank you very much for your review of our paper, we are very grateful to you for taking the time to provide valuable feedback and suggestions for our paper. We think that your suggestions for our paper are very insightful. According to your suggestions, our reply is attached. Thank you again for your evaluation and thank you for your support for our work. If you have other ideas or more suggestions for our paper, please feel free to contact us, we are very welcome to continue to communicate with you.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for Authors(1) The author conducted an in-depth study on the "air leakage law and plugging technology in the goaf of the gob-side entry retaining by roof cutting ", and mastered the air leakage law of the goaf under the ventilation mode of "two in and one out" of the working face the gob-side entry retaining by roof cutting through the combination of numerical simulation with the SF6 tracer gas. At the same time, the author also successfully solved the common air leakage problem in the goaf of the gob-side entry retaining by roof cutting through plugging simulation and field application, which greatly reduced the possibility of coal spontaneous combustion in the goaf. This study provides reliable guidance for similar mine production practices
(2) The research idea of the paper is relatively clear, starting from the actual problems existing in mine production, effectively grasping the air leakage law of the gob area under the new process, and putting forward targeted solutions. There is no doubt that scholars in this field and mine workers are very interested in the research topic of this article.
(3) In addition, there are some deficiencies in the language and format of the article, which the authors are advised to check carefully. For example, in line 41 of the text, "Figure 1 (a)" is used, while in line 49, "Figure 1 (b)" is used, and a similar problem exists in line 309 of the text. Figure"; in line 139 of the text, "v min" should be rewritten as "vmin"; in line 154, "the cut- top along the air stay lane" should be adopted. The expression "the cut- top along the air stay lane" in line 154 is not in line with the field of expertise, and it is suggested to amend it to "gob-side entry retaining by roof cutting". In line 256, replace "The" with "the" in " As depicted in Figure 8, The airflow leaks into the goaf from the working face and then flows to the upper area ".
(4) The overall graphing quality of the paper is high, but the font sizes in Figures 12 and 13 are not consistent with those in the other figures, and it is recommended that the authors standardise the text sizes in the figures for the overall aesthetics of the article.
(5) For better reading and understanding of this paper, it is suggested that the author should amend line 154 from " the cut- top along the air stay lane " to " gob-side entry retaining by roof cutting ".
(6) On the whole this is a good article and I recommend it for publication on condition that the authors rectify the necessary errors pointed out.
Comments on the Quality of English LanguageThe quality of English language is not bad.
Author Response
Thank you very much for your review of our paper, we are very grateful to you for taking the time to provide valuable feedback and suggestions for our paper. We think that your suggestions for our paper are very insightful. According to your suggestions, our reply is attached. Thank you again for your evaluation and thank you for your support for our work. If you have other ideas or more suggestions for our paper, please feel free to contact us, we are very welcome to continue to communicate with you.
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsTitle may be modified to "Investigation of air leakage characteristics of gob-side entry in longwall goaf areas and the impact of spray plugging on retaining wall of the gob-side entry" or similar.
It would be easy to read / understand if 'gob-side entry' is used in the paper - instead of 'gob-side entry retaining'.
In some places, 'retaining wall of gob-side entry' -OR- 'gob-side entry retaining wall' may be used depending on the context.
Comments on the Quality of English Language
Good paper, but takes time to read/ understand.
Editing by an English language expert would give more value to this important paper.
Author Response
Thank you very much for your review of our paper, we are very grateful to you for taking the time to provide valuable feedback and suggestions for our paper. We think that your suggestions for our paper are very insightful. According to your suggestions, our reply is attached. Thank you again for your evaluation and thank you for your support for our work. If you have other ideas or more suggestions for our paper, please feel free to contact us, we are very welcome to continue to communicate with you.
Author Response File: Author Response.pdf
Reviewer 5 Report
Comments and Suggestions for Authors1. Some inscriptions on the diagram are not visible (Fig. 1).
2. Very small font size on the diagram (Fig. 2).
3. I would like to receive more information about the Oxygen consumption rate (UDF) (Table 1). What gas fills the gob if the oxygen concentration is below 21% vol. (Figure 9)? Does the model take into account the transport equations of components (O2, N2, ...)?
4. Does the model take into account the energy equation? It is known that thermal processes play a large role in the process of spontaneous combustion of coal. The intensity of spontaneous combustion is influenced by such parameters as density, heat capacity, thermal conductivity of coal, temperature, heat transfer.
Author Response
Thank you very much for your review of our paper, we are very grateful to you for taking the time to provide valuable feedback and suggestions for our paper. We think that your suggestions for our paper are very insightful. According to your suggestions, our reply is attached. Thank you again for your evaluation and thank you for your support for our work. If you have other ideas or more suggestions for our paper, please feel free to contact us, we are very welcome to continue to communicate with you.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors have addressed all my comments. The manuscript could be now accepted as it is.
Author Response
We thank you very much for taking the time to review our papers and accept our contributions. Your professional opinions and suggestions have played an important guiding role in our research, and we are deeply honored to be recognized by you.
Author Response File: Author Response.pdf
Reviewer 5 Report
Comments and Suggestions for Authors1. Table 1 has confused values of activation energy and gas constant.
2. It is probably worth to specify in the article that the energy equation is not taken into account when modeling gob area. So that there would be no confusion.
Author Response
Thank you for your valuable suggestions when reviewing our manuscripts. Your professional insights and suggestions are of great significance to us and we are confident that these feedbacks will greatly enhance the quality of our research and the readability of our papers. According to your suggestions, we have made a comprehensive revision and improvement of the manuscript, as shown in the attachment materials. Your comments and suggestions make us re-examine our research, and we have benefited a lot from it. Thank you again for your careful reading and valuable suggestions. If you have any further suggestions or comments on the changes or other aspects we have made, we will be very grateful and happy to listen. We look forward to more opportunities to continue working with you in the future.
Author Response File: Author Response.pdf
