Prediction of Gas Emissions in the Working Face Based on the Desorption Effects of Granular Coal: A Case Study

Round 1

Reviewer 1 Report

This paper studies the prediction of gas emission in working face based on the desorption effects of granular coal, which has good research value. The following modification suggestions are made for the whole paper:

1、Please give a detailed introduction to the gas emission situation of the working face during normal production. Such as the working face production state and gas emission amount during the abnormal gas emission.

2、The coal particle size recognition method in this paper belongs to Sampling Statistics. How to ensure the reliability of the results?

3、When physical experiments are used to test the gas desorption law of coal with different particle sizes, is it necessary for each group of experiments to verify and analyze for many times?

4、In addition to coal particle size, should other key factors such as temperature and moisture be considered comprehensively?

5、The maximum error of the model is 15.3%, which is difficult to effectively provide support for field production. It is suggested to define the application scope of the model in the conclusion.

6、Please check the format of references.

Author Response

Dear reviewers,

Thank you very much for your valuable comments. we have responded to the comments one by one and revised the article accordingly. Please review it again. If there are any imperfections, please make further suggestions, and we will make full efforts to modify them, thank you very much!

Responds to the reviewer’s comments:

1、Please give a detailed introduction to the gas emission situation of the working face during normal production. Such as the working face production state and gas emission amount during the abnormal gas emission.

Answer：The introduction of the 12302 working face has been revised in the article. The production state and the value of gas emission during the abnormal gas emission of working face are added, and the reason for the abnormal gas emission is simply explained.

2、The coal particle size recognition method in this paper belongs to Sampling Statistics. How to ensure the reliability of the results?

Answer：Thanks for your valuable work. At present, there is no mature method for coal particle size distribution recognition. In this study, the method of calculating average grain size by random sampling at different times and places is adopted, which can reflect the general distribution of coal particle size to a certain extent. However, the mine site conditions are complex, and the number of samples and randomness will have a certain impact on the recognition results. A more accurate and efficient method of coal particle size identification needs to be further explored in the future.

3、When physical experiments are used to test the gas desorption law of coal with different particle sizes, is it necessary for each group of experiments to verify and analyze for many times?

Answer：When the physical experiment is used to test the gas desorption law of coal with different particle sizes, it is not only a single experiment but multiple adsorptions and desorption experiments on coal with different particle sizes and comprehensive analysis of the experimental data.

4、In addition to coal particle size, should other key factors such as temperature and moisture be considered comprehensively?

Answer: Thanks for your valuable comment. Other factors such as environmental temperature and water content also have a great influence on coal gas desorption. However, in the designated mine environment, the external factors are basically stable, and the key factors of coal gas desorption are the differences in coal size. Therefore, the coal particle size is considered the key factor in this study.

5、The maximum error of the model is 15.3%, which is difficult to effectively provide support for field production. It is suggested to define the application scope of the model in the conclusion.

Answer：The conclusion (3) has been revised. It has been modified to: “The prediction models of coal cutting, coal caving, coal wall, and goaf residual coal gas emission were separately established according to the gas source of the working face and the desorption characteristics of the coal with different particle sizes. And the correlation coefficient between the predicted value and the actual value was 0.97. In addition, the minimum and maximum errors of the established prediction model were 0.37% and 15.3 %, respectively (the overall average error is 5.29 %). When the daily mining speed of a working face is below 9m/d, the average error of gas emission prediction model is 5.08%. Therefore, if the daily mining speed of a working face is below 9m/d, the prediction results of the present study can evidently provide effective support for on-site production.”

6、Please check the format of references.

Answer：All references were rechecked and the format was uniformly updated.

Author Response File: Author Response.pdf

Reviewer 2 Report

In this paper, the influence of coal particle size distribution on gas emission in coal mining face is studied, and the prediction model of gas emission in coal mining face is obtained. The validity of the prediction model is verified by taking a fully mechanized top coal caving face in a coal mine as an example. However, only one coal sample is studied, and the results are not universally representative. There is no analysis on the coal type, industrial composition, physical and mechanical properties of coal and gas adsorption or desorption constant on coal. These factors have an impact on coal gas emission and should be considered. The parts with problems have been highlighted and the problems pointed out in the manuscript. The problems are as follow:  
1.Taking No. 2 coal seam of Wangjialing coal mine in Shanxi Province as the research object, the influence of coal particle size on gas desorption was studied. Only one coal sample was studied, and the results were not representative. The title of the article should be changed as ”Prediction of gas emission in the 12,302 working face in Wangjialing Coal Mine based on the desorption effects of granular coal”.
2.In the abstract, there is a sentence "the current study aimed to establish a multi-field coupled seepage destruction experimental system to predict gas emission in the working face." The research in this paper does not involve the multi field coupled seepage theory. Why do you write this sentence?
3.The Keywords do not meet the requirements, the words with broad meanings are not suitable as keywords.
4.The coal type, industrial composition adsorption or desorption constant of gas on coal, and physical and mechanical properties of the studied coal samples were not analyzed. These factors have an impact on coal gas emission and should be considered.
5.In Section 3, the experiment system, experiment steps and experiment process are not described in detail.
6.In Section 3, the basis for selecting particle size distribution of experimental coal samples is not stated.
7.The influence of coal particle size on gas emission is not fully summarized in the conclusions.
8.References [1] - [7] are not important for the study in this paper, and there is no need to cite them.
9.English writing needs to be improved. English expression does not conform to English expression habits, and there are errors in grammar and morphology. There are misused words and miswritten words in the text. Some sentences fail to express the meaning and the terms are inconsistent.
10.The symbols used in some formulas are incorrectly written.
11.The title of Fig. 3 is not clear.
12.The coordinate axis names in Figure 4 and figure 5 are wrong.
13.The coordinate axis names and units are missing in Figure 6.
14.In the part of acknowledgment, the authors affirm that this research is supported by two national natural science funds, which is unreasonable. Please select one fund project that is closely related to this research and truly supports this research for acknowledgment.

Comments for author File: Comments.pdf

Author Response

Dear reviewers,

Thank you for your letter and for the reviewers’ comments concerning our manuscript entitled “Prediction of gas emission in working face based on the desorption effects of granular coal” (ID:1886646). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our research. We have studied the comments carefully and have made a correction which we hope meets with approval. Revised portions are marked in red on the paper. The main corrections in the paper and the responses to the reviewer’s comments are as follows:

Responds to the reviewer’s comments:

1.Taking No. 2 coal seam of Wangjialing coal mine in Shanxi Province as the research object, the influence of coal particle size on gas desorption was studied. Only one coal sample was studied, and the results were not representative. The title of the article should be changed as ”Prediction of gas emission in the 12,302 working face in Wangjialing Coal Mine based on the desorption effects of granular coal”.

Answer：Thank you for your valuable comments. In this article, a method of gas emission prediction based on the desorption characteristics of coal with different grain sizes is proposed and verified in the Wangjialing coal mine. Therefore, As a result, the title of the article has been changed to: “Prediction of gas emission in working face based on the desorption effects of granular coal: a case study”.

2.In the abstract, there is a sentence "the current study aimed to establish a multi-field coupled seepage destruction experimental system to predict gas emission in the working face." The research in this paper does not involve the multi field coupled seepage theory. Why do you write this sentence?

Answer：The name of the experimental system independently developed and designed is: “multi-field coupling desorption experimental system.” However, in this study, only some functions of the experimental system are used. Related modifications have been made in the article to remove the related descriptions of seepage and multi-field coupling. The name of the experimental system was changed from "Multi-field Coupled Seepage Desorption Experimental System" to "Coal Desorption Experimental System".

3.The Keywords do not meet the requirements, the words with broad meanings are not suitable as keywords.

Answer：This article has modified the keywords. The final key words are the following: “Coal particle size; Physical experiment; Desorption intensity; Gas emission attenuation; Prediction model.”

4.The coal type, industrial composition adsorption or desorption constant of gas on coal, and physical and mechanical properties of the studied coal samples were not analyzed. These factors have an impact on coal gas emission and should be considered.

Answer：Thanks for your valuable comment. Other factors such as the type of coal, industrial components, and adsorption constant also have a great influence on coal gas desorption. However, in the designated mine environment, the external factors are basically stable. In addition, because the established model is a statistical model of gas desorption, the influence of these factors on gas desorption in the experiment has been reflected in the variation law of gas desorption. When the experimental site is changed, it is necessary to re-conduct the coal desorption experimental test and revise the model. Therefore, the coal particle size is considered the key factor in this study.

5.In Section 3, the experiment system, experiment steps and experiment process are not described in detail.

Answer：In Section 3, a detailed description of the experiment system and experiment steps is added.

6.In Section 3, the basis for selecting particle size distribution of experimental coal samples is not stated.

Answer：Through preliminary basic experimental tests, it is found that coal gas desorption is greatly affected by particle size. A small change in particle size will greatly affect the gas desorption law when the particle size is small. However, when the particle size becomes large, the influence of the change in particle size on gas desorption gradually decreases. When the particle size increases to a certain extent, the particle size is no longer the main reason affecting gas desorption. Therefore, when determining the experimental coal particle size distribution, in order to reduce the number of experiments, according to the principle of "the larger the coal particle size, the larger the selected distribution interval". The final experimental coal particle size is determined at below 0.5mm, 0.5-1mm, 1-2mm, 2-5mm, 5-10mm, 10-20mm six intervals.

7.The influence of coal particle size on gas emission is not fully summarized in the conclusions.

Answer：The content of conclusion 1 is modified. Conclusion 1 is modified as follows: Coal particle size directly affects the gas desorption capacity. Increased coal particle size reduces the initial desorption intensity and attenuation coefficient of gas emission. When the coal particle size is < 1 mm, the gas desorption occupies a large proportion of the first 20 min. When the particle size increases to more than 1 mm, more than 70 % of the gas could then be desorbed in the coal in the first 10 min. However, when the coal particle size increases to a certain level, especially when the coal particle size is greater than 10mm , the initial desorption intensity and attenuation coefficient of gas emission gradually maintain a constant value. This shows that the gas desorption capacity of coal stabilizes with increases in coal particle size.

8.References [1] - [7] are not important for the study in this paper, and there is no need to cite them.

Answer：Thanks for your comment. References 1-7 have been removed from this article.

9.English writing needs to be improved. English expression does not conform to English expression habits, and there are errors in grammar and morphology. There are misused words and miswritten words in the text. Some sentences fail to express the meaning and the terms are inconsistent.

Answer：This article has been re-checked for accuracy in English writing; the grammatical and lexical errors have been corrected, and the descriptions of relevant professional terms have been re-determined.

10.The symbols used in some formulas are incorrectly written.

Answer：We are sorry for our mistakes. The formula of the prediction model was carefully checked, and the error symbol and related description were modified.

11.The title of Fig. 3 is not clear.

Answer：We are sorry for our mistakes. The title of Figure 3 has been changed.

12.The coordinate axis names in Figure 4 and figure 5 are wrong.

Answer：We are sorry for our mistakes. The coordinate axes in Figure 4 and Figure 5 have been checked and redrawn, and the names of the coordinate axes have been modified.

13.The coordinate axis names and units are missing in Figure 6.

Answer：Figure 6 has been redrawn. Add the names and units of the axes in Figure 6.

14.In the part of acknowledgment, the authors affirm that this research is supported by two national natural science funds, which is unreasonable. Please select one fund project that is closely related to this research and truly supports this research for acknowledgment.

Answer：The acknowledgements were revised to clarify the National Natural Science Foundation of China (NSFC) funding project for this study.

Author Response File: Author Response.pdf

Reviewer 3 Report

As for the article, I want to note the following. Relevance disclosed fully, the introduction provides sufficient background information and includes relevant links. The obvious advantage of this article is that the authors carried out an extensive set of experimental studies. A gas emission model has been developed. Dependences of the strength of granulated coal over time have been established.

However, there are also some controversial statements.

1) The authors state that “…the minimum and maximum errors of the established prediction model were 0.37 and 15.3%, respectively…”. The minimum error of the developed model is doubtful due to the fact that the spread of physical and mechanical properties of coal and rocks (including strength) in mines is 10...30%, and can reach large values. Therefore, the model error of 0.37% looks doubtful.

2) The authors showed that the models were developed separately “The prediction models of coal cutting, coal caving, coal wall, and goaf residual  coal gas emission were separately established …”, but then the relationships between these models should be established. The text of the article does not specify the parameters linking the models.

In my opinion, in the context of this article, instead of the term “Prediction”, it is more correct to use the term “Forecast”.

Scientific results have implications for practical engineering analysis of mining operations.  The content of the article is presented in a technically understandable language.

In general, the article makes a good impression, I recommend it for publication.

Author Response

Dear reviewers,

First, the authors would like to express their grateful thanks to the reviewers very much for their helpful suggestions and comments. We have modified the manuscript accordingly, and the detailed corrections are listed as below point by point. All the revisions are highlighted in red in the revised manuscript.

(1) The authors state that “…the minimum and maximum errors of the established prediction model were 0.37 and 15.3%, respectively…”. The minimum error of the developed model is doubtful due to the fact that the spread of physical and mechanical properties of coal and rocks (including strength) in mines is 10...30%, and can reach large values. Therefore, the model error of 0.37% looks doubtful.

Answer：Thank you for your comments. The strength and structure of coal greatly influence the prediction of gas emission, so the prediction of gas emission will usually have a great error due to the influence of the coal structure itself. However, the model developed in this study is equivalent to a statistical prediction model because it is based on the study of coal desorption law and is established through statistical analysis to reduce the influence of the environment, coal structure, and other factors on gas emission prediction.

(2) The authors showed that the models were developed separately “The prediction models of coal cutting, coal caving, coal wall, and goaf residual  coal gas emission were separately established …”, but then the relationships between these models should be established. The text of the article does not specify the parameters linking the models.

Answer：Thanks for your valuable work. In this article, the prediction model of gas emission is established, which is mainly tested by the desorption characteristics of coal with different particle sizes, and the characteristic equation of desorption change is obtained by analyzing the test results. Although some parameters are common, such as gas emission intensity and residence time, each model is independent of each other, and the total gas emission quantity of working face is the sum of the gas emission values of each sub-source.

Author Response File: Author Response.pdf

Reviewer 4 Report

The paper studied the gas emission from the working face of coal mines. The desorption strength for different coal particle sizes was estimated and discussed and compared with real data. This is an important topic, but the following comment should be addressed.

-          A new section entitled “research methodology” should be created to present all research steps including the sampling procedure, preparing the samples, data collecting, and analysis.

-          There is no information about the mine area, extraction method, and mechanical properties of the coal.

-          What is the meaning of “mining rate”? is that extraction speed?

-          Regarding Figure 8, the prediction errors are categorized into three groups; small, medium, and big. What criterion was used for this? Explain.

-          In Figure 6, the title of the axles is missed.

-          In section 5.2, it is important to present the correlation coefficient between the measured and predicted gas emissions.

-          The relationship between mining speed and particle size should be mentioned.

Author Response

Dear reviewers,

Thank you very much for your valuable comments. we have responded to the comments one by one and revised the article accordingly. Please review it again. If there is any imperfections, please make further suggestions, and we will make full efforts to modify, thank you very much!

1. A new section entitled “research methodology” should be created to present all research steps including the sampling procedure, preparing the samples, data collecting, and analysis.

Answer：Thanks for your valuable work. In the article, we added subsection 3.2: Introduction of experimental steps and scheme., in which the experimental steps are introduced in detail, including the sampling procedure, preparing the samples, data collection, and other related content.

2.There is no information about the mine area, extraction method, and mechanical properties of the coal.””

Answer：Thanks for your comment. The test mine is located in the Wangjialing Coal Mine in Xiangning County, Shanxi Province, China. Currently, the coal seam No. 2 is the main mining seam. The longwall backward mining method and comprehensive mechanized top caving technology are used for this mine. And the characteristics of coal seam No. 2 are mainly characterized by low permeability and low gas content. And the relevant content has been modified in the paper.

3.What is the meaning of “mining rate”? is that extraction speed?

Answer：We are sorry for our mistakes. "Mining rate" is a typo; it actually refers to the percentage of ore mined and ore designed, The correct spelling is “recovery ratio.” which has been corrected in the text.

4.Regarding Figure 8, the prediction errors are categorized into three groups; small, medium, and big. What criterion was used for this? Explain.

Answer：In the actual production process of the mine, the mining speed is basically maintained at 4.5-7m/d during normal mining. When the conditions of the coal seam are better, and the production and efficiency can be increased, the mining speed will increase to 7-9m/d. However, if the management in the construction process is not standardized, the mining speed will exceed 9m/d. Therefore, dividing the error group is mainly according to the production situation of the site.

5.In Figure 6, the title of the axles is missed.

Answer：We are sorry for our mistakes. Figure 6 has been redrawn. Add the names and units of the axes in Figure 6.

6.In section 5.2, it is important to present the correlation coefficient between the measured and predicted gas emissions.

Answer：Thanks for your comment. In order to judge the accuracy of the predicted value, it is necessary to conduct a correlation analysis between the predicted value and the measured value. Therefore, the relevant content of the correlation analysis is added, and the correlation coefficient between the predicted value of gas emission and the actual value of 12302 working face was finally determined to be 0.97, which indicates the reliability of the predicted value.

7.The relationship between mining speed and particle size should be mentioned.

Answer：Thanks for your valuable work. Coal mining speed directly affects the size of coal particles. The sampling test method adopted in this study made it difficult to accurately determine the relationship between coal cutting speed and particle size. Therefore, the next step of work will focus on image recognition technology and develop equipment that can accurately determine coal particle size during production. The relationship between coal particle size and coal mining speed is obtained accurately, and the coal cutting speed is taken as one of the main controlling factors in the prediction model of gas emission.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The paper has been revised according to the comments of the reviewer, but the following problems still exist:

1.The modified keywords do not meet the requirements. The suggested keywords are: mine gas control; gas emission prediction; emission prediction model; gas emission law; coal granularity influence.

2.Line 116-117, the term “comprehensive mechanized top caving” is wrong, it should be “fully mechanized mining with top coal caving”.

3.Line 398, the term “ fully mechanized top-coal caving” is wrong, it should be “fully mechanized mining with top coal caving”.

4.Some sentences don't express the meaning accurately. There are grammatical and lexical problems, verb tenses, verb singular and plural forms, misuse of prepositions, misuse of punctuation, lack of punctuation, etc. .

5.The axis name and unit problems in Figure 6 have been indicated by the reviewer on the figure. Please revise the figure.

6.In Table 2, the item names in the header column are incorrect, and the variable unit annotation format is not acceptable. The problems have been marked by the reviewer in Table 2. Please revise the table.

7.Parts of the conclusions are not expressed accurately, and the reviewer has revised them. The author is requested to review and confirm the revised contents.

8.The reviewer has identified some problems in the paper, and has revised and marked them in the manuscript. Similar problems may exist elsewhere in the paper. Please check and revise the paper carefully.

Comments for author File: Comments.pdf

Author Response

Response to Reviewer 2

Dear reviewers,

Thank you very much for your valuable comments. we have responded to the comments one by one and revised the manuscript accordingly. Please review it again. If there are any imperfections, please make further suggestions, and we will make full efforts to modify them, thank you very much! The main corrections in the paper and the responses to the reviewer’s comments are as follows:

Responds to the reviewer’s comments:

1.The modified keywords do not meet the requirements. The suggested keywords are: mine gas control; gas emission prediction; emission prediction model; gas emission law; coal granularity influence.

Answer：Thanks for your valuable comment. The keywords have been revised according to your comments.

2.Line 116-117, the term “comprehensive mechanized top caving” is wrong, it should be “fully mechanized mining with top coal caving”；Line 398, the term “ fully mechanized top-coal caving” is wrong, it should be “fully mechanized mining with top coal caving”.

Answer：We are sorry for our mistakes. In Lines 116-117 and 398, the terms “fully mechanized mining with top coal caving” are misused. Therefore, all have been corrected for this technical term.

3.Some sentences don't express the meaning accurately. There are grammatical and lexical problems, verb tenses, verb singular and plural forms, misuse of prepositions, misuse of punctuation, lack of punctuation, etc. .

Answer：Thank you very much for your work on this article. In view of these problem that some sentences don't accurately express the meaning. This article has been checked and revised according to your suggestions.

4.The axis name and unit problems in Figure 6 have been indicated by the reviewer on the figure. Please revise the figure.

Answer：Regarding the problem in Figure 6, we have redrawn it according to your suggestion. The axis name and unit problems in Figure 6 have been modified.

5.In Table 2, the item names in the header column are incorrect, and the variable unit annotation format is not acceptable. The problems have been marked by the reviewer in Table 2. Please revise the table.

Answer：Table 2 has been modified based on your comments. The item names and variable unit annotation format have been corrected.

6.Parts of the conclusions are not expressed accurately, and the reviewer has revised them. The author is requested to review and confirm the revised contents.

Answer：For the expression in the conclusion, it has been revised according to your suggestion.

7.The reviewer has identified some problems in the paper, and has revised and marked them in the manuscript. Similar problems may exist elsewhere in the paper. Please check and revise the paper carefully.

Answer：Extraordinary work that thanks you for everything. You have made me fully aware of my own shortcomings. We have once again reviewed and revised the manuscrip in response to all the questions you raised. We are grateful for the reviewer’s insights on the accuracy of academic English writing.

Author Response File: Author Response.doc

Reviewer 4 Report

there is no comments

Author Response

Response to Reviewer 4 

Dear reviewers,

We would like to thank the efforts and time of your and the reviewers. We have carefully checked and improved the English writing in the revised manuscript. And the references were checked and modified. Please review it again. If there are any imperfections, please make further suggestions, and we will make full efforts to modify them.

Author Response File: Author Response.doc