Effect of Coal Particle Breakage on Gas Desorption Rate during Coal and Gas Outburst

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The issues addressed in the manuscript are highly topical. In underground coal mining, the explosion hazard is an important factor to be taken into account during mining.
Comments:
The objectives of the study are clearly defined.
In section 3 Experiment, I would have welcomed a more detailed description of the samples in terms of their relevant parameters
 Were samples collected from multiple sites? It would be useful to include the locations and their basic description.
Were there any incidents of accidents with elevated methane concentrations at the sites/operations?
The authors could conclude by stating if the study contributes to practical applications.

Author Response

 

Dear Editor and Reviewer

 

Thanks very much for your email and the reviewers’ comments, regarding our submission of the manuscript “Effect of coal particle breakage on gas desorption rate during coal and gas outburst” (Manuscript ID: applsci-2777436).

 

The manuscript is now revised according to the suggestions of the reviewers and editor. Main changes in the text are in red in the revised manuscript.

 

Our responses to the comments by the reviewers are on separate pages.

 

With best regards.

 

Yours sincerely,

 

Gun Huang

Qiang Cheng

Corresponding author:

Name: Gun Huang

Institution: Chongqing University, Chongqing 400030, China

E-mail: [email protected]; [email protected]

 

Detailed responses to the reviewers’ comments (Manuscript ID: applsci-2777436)

 

We appreciate the reviewers for their careful reading of our manuscript (Manuscript ID: applsci-2777436) and useful suggestions on how to improve our presentation. The following are our responses and explanations to the issues raised by the reviewers, where line numbers, page numbers, table numbers, and figure numbers are those in the revised manuscript. The revised portions are highlighted in red and the line numbers and page numbers were in bold.

Reviewer #1: The issues addressed in the manuscript are highly topical. In underground coal mining, the explosion hazard is an important factor to be taken into account during mining. The objectives of the study are clearly defined.

Point 1: In section 3 Experiment, I would have welcomed a more detailed description of the samples in terms of their relevant parameters. Were samples collected from multiple sites? It would be useful to include the locations and their basic description.

Response: Thanks for your valuable comments! To describe the coal samples in more detail, the coal type and location of the coal samples used in the experiment are supplemented. The following are the relevant revisions：

Line 285 on Page 8:‘Yang conducted diffusion experiments on anthracite coal with different particle sizes from the No. 1 Mine in Yangquan, Shanxi. Guo conducted similar experiments using an-thracite coal samples from the No. 7 coal seam of the Haizi Coal Mine in the Huaibei Coalfield, China. Wang used coking coal from No. 10 Mines in Pingdingshan, Henan.’

Line 293 on Page 8:‘Cai performed crushing tests using samples of bituminous coal obtained from the Nangtiao Tower Mine in Shenmu, Shanxi, as well as samples of coking coal sourced from the No. 10 Mine in Pingdingshan, Henan..’

The cited literature is marked and will not be repeated in the text as it has already been discussed in detail in existing literature.

Point 2: Were there any incidents of accidents with elevated methane concentrations at the sites/operations? The authors could conclude by stating if the study contributes to practical applications.

Response: Thanks for your comments! The huge amounts gas, contained in coal seams, are released into the mine atmosphere during the exploitation process, causing a very high threat to work safety [1]. Coal mining involves breaking coal into smaller pieces, which releases trapped gas within the coal. This can lead to dangerous situations, such as coal gas outbursts, where a large amount of gas is suddenly released, causing a rapid increase in gas concentration. Under equal adsorption equilibrium pressure, smaller particles in coal lead to faster gas desorption. Under the same adsorption equilibrium pressure, the reduction of coal particle size will accelerate the desorption rate of adsorbed gas in coal. This study has conducted a precise analysis that precisely measures the impact of coal crushing on the volume and rate at which gas is released from the coal. It also identified general analytical relationships that can be used to understand and predict this desorption process.

Reference

1. Palka, D.; Brodny, J.; Tutak, M.; Nitoi, D., The role, importance and impact of the methane hazard on the safety and efficiency of mining production. Production Engineering Archives 2022, 28, (4), 390-397.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

General

The manuscript elaborates on a specific topic of applied research concerning analyzing the influence of coal crushing on gas desorption volume and the rate of this desorption. Of course, the authors arrived at the well-known fact that these parameters increase with decreasing coal particle size after crushing. This simply follows from the significant increase in the effective diffusion coefficient with reducing particle size (D_e=D/(R²). However, the authors have developed an exact analysis that quantifies the effect of coal crushing on gas desorption volume and rate of this desorption and provides general analytical relationships that allow its investigation over time and for different initial conditions. This can be seen as a contribution of the work. However, there are several inaccuracies in the text that should be corrected. 

 

In particular

For all equations that represent integrals in the manuscript, italics should not be used for the "d" in the differential factor (e.g., dR).

Line 120 - equation (1) - first, the label R₀ is used, obviously meaning boundary (one cannot define a boundary other than R₀ for a homogeneous spherical object), and then r₀ is used (for C₀) - this should be unified.

Line 139 - equation (3) makes no sense. dR is, by definition, an infinitesimal step. Multiplying a finite number by an infinitesimal number again represents an infinitesimal number, which V(R) clearly is not (integration is probably forgotten).

Line 153 - equation (5). For clarity, it would be useful to put M_inf before the integral, similar to (7)

Line 163 - the theorem practically says that fi(R) is the size distribution before breakage and psi(R) after breakage, which is the opposite of the statement in line 196 - R₁ before and R₂ after breakage, which determines equations (16), (17), etc. (which thus contradict (8), (9), etc.). That is, the theorem on line 163 must be corrected to a clear statement corresponding to the following equations.

Line 192 - in equation (14) (and also (29)), the expression for the product 6*second root is not happy. There should be some space or a period sign, or an exponent of 1/2 should be used for the square root (as in (11)). The way the relation (14) is now written evokes the sixth root to some extent.

Line 220 - the citation of the 2022 study is inappropriate to justify relation (19). The proof of its validity is at the level of primary school homework, and it is extremely unlikely that relation (19) would have been discovered until 2022.

Line 256 - equation (25) - in the context of the preceding, it should not be beta(r) but beta(R). Likewise, for (27) - all Rs should be capital letters.

Line 300 - Table 1 - "Correlation Coefficient R²" - this is completely confusing (R² is the Coefficient of determination and equals the square of the Pearson correlation coefficient). The numbers in the table appear to be correlation coefficients - then R² should be deleted (if only for consistency with the R used for particle size).

 

Author Response

 

Dear Editor and Reviewer

 

Thanks very much for your email and the reviewers’ comments, regarding our submission of the manuscript “Effect of coal particle breakage on gas desorption rate during coal and gas outburst” (Manuscript ID: applsci-2777436).

 

The manuscript is now revised according to the suggestions of the reviewers and editor. Main changes in the text are in red in the revised manuscript.

 

Our responses to the comments by the reviewers are on separate pages.

 

With best regards.

 

Yours sincerely,

 

Gun Huang

Qiang Cheng

Corresponding author:

Name: Gun Huang

Institution: Chongqing University, Chongqing 400030, China

E-mail: [email protected]; [email protected]

 

Detailed responses to the reviewers’ comments (Manuscript ID: applsci-2777436)

 

We appreciate the reviewers for their careful reading of our manuscript (Manuscript ID: applsci-2777436) and useful suggestions on how to improve our presentation. The following are our responses and explanations to the issues raised by the reviewers, where line numbers, page numbers, table numbers, and figure numbers are those in the revised manuscript. The revised portions are highlighted in red and the line numbers and page numbers were in bold.

Reviewer #2: The manuscript elaborates on a specific topic of applied research concerning analyzing the influence of coal crushing on gas desorption volume and the rate of this desorption. Of course, the authors arrived at the well-known fact that these parameters increase with decreasing coal particle size after crushing. This simply follows from the significant increase in the effective diffusion coefficient with reducing particle size (De=D/(R²). However, the authors have developed an exact analysis that quantifies the effect of coal crushing on gas desorption volume and rate of this desorption and provides general analytical relationships that allow its investigation over time and for different initial conditions. This can be seen as a contribution of the work. However, there are several inaccuracies in the text that should be corrected.

Point 1: For all equations that represent integrals in the manuscript, italics should not be used for the "d" in the differential factor (e.g., dR).

Response: Thanks for your valuable suggestion! We replace the integration factors in equations (3), (5), (6), (7), (8), (9), (24), (26), (27) from italic 'd' to regular font 'd'.

Point 2: Line 120 - equation (1) - first, the label R₀ is used, obviously meaning boundary (one cannot define a boundary other than R₀ for a homogeneous spherical object), and then r₀ is used (for C0) - this should be unified.

Response: Thanks for your suggestion! Line 187 on Page 3: The boundary conditions in equation (1) are unified to R₀. We Unify the boundary condition in equation (1) to R₀.

Point 3: Line 139 - equation (3) makes no sense. dR is, by definition, an infinitesimal step. Multiplying a finite number by an infinitesimal number again represents an infinitesimal number, which V(R) clearly is not (integration is probably forgotten).

Response: Thanks for your suggestion! Line 156 on Page 4: We change equation (3) to dV(R)= φ(R)V₀dR .

Point 4: Line 153 - equation (5). For clarity, it would be useful to put Minf before the integral, similar to (7)

Response: Thanks for your suggestion! Line 170 on Page 4: We put M_inf before the integral, similar to equation (7). 

Point 5: Line 163 - the theorem practically says that fi(R) is the size distribution before breakage and psi(R) after breakage, which is the opposite of the statement in line 196 - R1 before and R2 after breakage, which determines equations (16), (17), etc. (which thus contradict (8), (9), etc.). That is, the theorem on line 163 must be corrected to a clear statement corresponding to the following equations.

Response: Thanks for your suggestion! Line 184 on Page 5: We explicitly state what is meant in terms of ψ and φ, Where ψ(R)  is the function of coal grain size distribution before coal breakage; φ(R) represents the function of coal grain size distribution after coal breakage.

Line 216 on Page 6: We change φ₁ and φ₂ in equation (15) to ψ and φ respectively to make the paper consistent.

Point 6: Line 192 - in equation (14) (and also (29)), the expression for the product 6*second root is not happy. There should be some space or a period sign, or an exponent of 1/2 should be used for the square root (as in (11)). The way the relation (14) is now written evokes the sixth root to some extent.

Response: Thanks for your comments! Considering the reviewer’s suggestion, we change equations (11), (14), (26), (28) and (31) to make equations clearer.

Point 7: Line 220 - the citation of the 2022 study is inappropriate to justify relation (19). The proof of its validity is at the level of primary school homework, and it is extremely unlikely that relation (19) would have been discovered until 2022.

Response: Thanks for your comments! On Page 6: According to the reviewer's comments, the less meaningful equation S₂/S₁=R₁/R₂ has been deleted.

Point 8: Line 256 - equation (25) - in the context of the preceding, it should not be beta(r) but beta(R). Likewise, for (27) - all R should be capital letters.

Response: Thanks for your comments! Line 265 on Page 7: Considering the reviewer’s suggestion, we change β(r) in equation (24) to β(R) and change R to be capital letters in equation (26).

Point 9: Line 300 - Table 1 - "Correlation Coefficient R²" - this is completely confusing (R² is the Coefficient of determination and equals the square of the Pearson correlation coefficient). The numbers in the table appear to be correlation coefficients - then R² should be deleted (if only for consistency with the R used for particle size).

Response: Thanks for your comments! Line 316 on Page 9: Considering the reviewer’s suggestion, we change "Correlation Coefficient R²" to coefficient of determination.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

As a reviewer of the article entitled "Effect of coal particle breakage on gas desorption rate during coal and gas outburst“, I would like to present/supplement the issue discussed in the above article in general terms, and at the same time point out a few issues that the authors can supplement/correct.

The coal-gas/methane system in hard coal mining around the world is determined by two basic physical parameters: methane carrying capacity and methane desorption intensity.

The intensity of methane desorption is perceived as a quick method of estimating the methane carrying capacity.

From a physical point of view, methane emissions from coal grains are governed by diffusion processes (indicated quite extensively by the authors of this article).

Therefore, the value of the desorption intensity index is a certain resultant of the methane content in coal and the value of the methane diffusion index on coal.

The uncertainty in estimating the methane carrying capacity, taking into account the intensity of desorption, lies precisely in the failure to take into account the value of the diffusion index - as noted by the authors of the periodical.

Methane carrying capacity is one of the most important parameters determining the outburst hazard in all countries in the world where this energy resource is exploited. Examples of criteria values for selected countries: Australia 9m³/tonne; China 10m³/ton or Hungary 8m³/ton.

This parameter is extremely important when designing ventilation systems in mines!

Desorption intensity index - is a value characterizing the amount of mathane released from an experimental coal sample (as presented by their authors in the research methodology). This indicator is used in various versions in individual countries around the world. It is noted that individual countries have equivalents of both national methane carrying capacity and desorption intensity ("D", "De").

Chinese mining regulations assume the use of the gas desorption index - its value refers to the gas pressure in hard coal and the degree of destruction of the original structure of the coal. It is measured using MD-1 desorbent developed by China Coal Research Institute (CCRI) Fushan (on the basis - Coal Mine Safety, People Republic of China: Part 1: Preliminary Analisys - National consultans 2008).

It seems to me that the article is missing (in relation to determining the methane carrying capacity and the dependent "indicator" of desorption intensity) - information on how the above is influenced by the depth of exploitation and the content of volatile parts in the tested samples - note for possible supplementation.

The emission/desorption of gas/methane from coal is often associated with three phenomena: specific desorption from the coal surface, gas diffusion within the grains and gas filtration through a system of fractures in the coal bed. The authors should address this issue in their publication.

Generally, gas emission from coal is caused by a decrease in the pressure/concentration of the surrounding gas. In mine conditions (in-situ), the above phenomenon is related to the exploitation (exposure of the cracked coal rock).

In the article, the authors quoted/referred to several known empirical diffusion equations used for unipore models. It is worth the authors mentioning a few words about the remaining most frequently encountered and practiced ones, e.g. the Crank and Timofijew equation. There are also a number of variables that are not present in the model used in the article. A short analysis can be made.

The current empirical knowledge about the physical properties of coals in terms of their stroke rate determines the criterion indicators of this process. These include: resistance toc ompression and tightness.

The above parameters and many others also have a huge impact on the phenomenon of gas release/output from coal.

It is worth mentioning why this issue was not discussed in the article, i.e. the relationship between the rate of gas desorption from coal, taking into account, for example, the following parameters: compactness, compressive strength, bulk density, cohesion or internal friction angle.

To sum up, I believe that the reviewed article meets the requirements in terms of science and research.

It touches on an important aspect of work safety in the event of natural hazards (also in the aspect of associated hazards).

The topic discussed by the authors is a known issue, although in many aspects it has not yet been fully discovered (for example the phenomenon of gas desorption from coal beds).

My review (due to the very broad aspect of the discussed issue) is only a conclusion with possible recommendations to the authors.

Comments for author File: Comments.pdf

Author Response

 

Dear Editor and Reviewer

 

Thanks very much for your email and the reviewers’ comments, regarding our submission of the manuscript “Effect of coal particle breakage on gas desorption rate during coal and gas outburst” (Manuscript ID: applsci-2777436).

 

The manuscript is now revised according to the suggestions of the reviewers and editor. Main changes in the text are in red in the revised manuscript.

 

Our responses to the comments by the reviewers are on separate pages.

 

With best regards.

 

Yours sincerely,

 

Gun Huang

Qiang Cheng

Corresponding author:

Name: Gun Huang

Institution: Chongqing University, Chongqing 400030, China

E-mail: [email protected]; [email protected]

 

Detailed responses to the reviewers’ comments (Manuscript ID: applsci-2777436)

 

We appreciate the reviewers for their careful reading of our manuscript (Manuscript ID: applsci-2777436) and useful suggestions on how to improve our presentation. The following are our responses and explanations to the issues raised by the reviewers, where line numbers, page numbers, table numbers, and figure numbers are those in the revised manuscript. The revised portions are highlighted in red and the line numbers and page numbers were in bold.

Reviewer #3: As a reviewer of the article entitled "Effect of coal particle breakage on gas desorption rate during coal and gas outburst“, I would like to present/supplement the issue discussed in the above article in general terms, and at the same time point out a few issues that the authors can supplement/correct.

Point 1: For all equations that represent integrals in the manuscript, italics should not be used for the "d" in the differential factor (e.g., dR). The coal-gas/methane system in hard coal mining around the world is determined by two basic physical parameters: methane carrying capacity and methane desorption intensity……. It seems to me that the article is missing (in relation to determining the methane carrying capacity and the dependent "indicator" of desorption intensity) - information on how the above is influenced by the depth of exploitation and the content of volatile parts in the tested samples - note for possible supplementation.

Response: Thanks for your valuable comments! As suggested, we clarify the effect of burial depth on gas contend. Gas content gradually increased with the increase of coal seam buried depth. The field test results show that the gas content takes an upward trend with the increase of burial depth of coal seam below the gas weathered zone. However, with the increase of coal burial depth, gas content increase speed is decreasing, and gas content reaches a certain value when burial depth closes to a fixed value. It can be drawn from the seam buried depth within a certain range, a positive correlation is presented between the gas content and coal seam buried depth. The coefficient in proportion would gradually reduce with the burial depth, then the gas content remained unchanged [1]. Therefore, we illustrate the influence by the depth of exploitation on desorption in Lines 40-45 on Page 1:“With the increase of burial depth, the outburst intensity increases remarkably. This is mainly due to changes in geological structure and coal seam thickness, which affect gas pressure and ground stress. As a result, the failure mode changes from tensile to shear failure, with higher unloading rates making tensile failure more likely. Additionally, under a higher gas desorption rate, the scope of the non-failure zone becomes smaller [2].”

We clarify the influence by the content of volatile parts in the tested samples on methane carrying capacity in Lines 47-53 on Page 2: “The impact of volatiles on the porous structure of coal samples and the resulting changes in methane adsorption capacity[3]. Volatile-related deformations in the coal's porous structure influenced methane adsorption behavior. Microstructural characterizations revealed that volatiles could be found trapped in the pores or cross-linked in the network, with each state affecting different aspects of coal-coal interactions and the overall structure of coal.”

Point 2: The emission/desorption of gas/methane from coal is often associated with three phenomena: specific desorption from the coal surface, gas diffusion within the grains and gas filtration through a system of fractures in the coal bed. The authors should address this issue in their publication.

Response: Thanks for your valuable comments! As suggested, we address this issue in Lines 53-59 on Page 2:“Coal consists of fracture networks and coal matrix blocks that are interlocked and distributed without overlapping relationships [4, 5]. Matrix blocks in coal contain numerous pores that serve as storage sites for gas and facilitate its flow. Gas is primarily extracted through fractures and pore channels within the coal [6]. The emission of gas from coal is often associated with three phenomena: specific desorption from the coal surface, gas diffusion within the grains and gas filtration through a system of fractures in the coal bed [7, 8].”

Point 3: Generally, gas emission from coal is caused by a decrease in the pressure/concentration of the surrounding gas. In mine conditions (in-situ), the above phenomenon is related to the exploitation (exposure of the cracked coal rock). In the article, the authors quoted/referred to several known empirical diffusion equations used for unipore models. It is worth the authors mentioning a few words about the remaining most frequently encountered and practiced ones, e.g. the Crank and Timofijew equation. There are also a number of variables that are not present in the model used in the article. A short analysis can be made.

Response: Thanks for your valuable comments! We make a short analysis. The same phenomenon can be described both empirically and theoretically. For example, in the Determination method of gas desorption index by drill cuttings commonly used in coal mines, the desorption amount has a linear relationship with the root square of time. This relationship can also be derived by solving the diffusion equation using the Laplace transform method. Experience and theory are consistent.

Point 4: The current empirical knowledge about the physical properties of coals in terms of their stroke rate determines the criterion indicators of this process. These include: resistance toc ompression and tightness. The above parameters and many others also have a huge impact on the phenomenon of gas release/output from coal. It is worth mentioning why this issue was not discussed in the article, i.e. the relationship between the rate of gas desorption from coal, taking into account, for example, the following parameters: compactness, compressive strength, bulk density, cohesion or internal friction angle.

Response: Thanks for your valuable comments! Adsorbed gas is the main part of gas in coal, so the change in desorption rate of adsorbed gas before and after coal crushing is taken in account in this paper, but the change in free gas in coal before and after coal crushing is not considered. Parameters such as compressive strength, cohesion, internal friction angle, etc. mainly affect the ease of coal crushing, so this article has not yet considered the impact of these parameters on the desorption rate.

Reference

1. Yang, Y. G., Jinlong, Quantitative Relationship Between Gas Content and Burial Depth of Coal Seam. Safety in Coal Mines 2014, (1), 1-4.
2. Liu, T.; Li, M. Y.; Zou, Q. L.; Li, J. F.; Lin, M. H.; Lin, B. Q., Crack instability in deep coal seam induced by the coupling of mining unloading and gas driving and transformation of failure mode. International Journal of Rock Mechanics and Mining Sciences 2023, 170.
3. Sun, W.; Wang, N.; Chu, W.; Jiang, C., The role of volatiles and coal structural variation in coal methane adsorption. Science Bulletin 2015, 60, (5), 532-540.
4. Liu, P.; Qin, Y.; Liu, S.; Hao, Y., Numerical Modeling of Gas Flow in Coal Using a Modified Dual-Porosity Model: A Multi-Mechanistic Approach and Finite Difference Method. Rock Mechanics and Rock Engineering 2018, 51, (9), 2863-2880.
5. Xu, H.; Qin, Y.; Wu, F.; Zhang, F.; Liu, W.; Liu, J.; Guo, M., Numerical modeling of gas extraction from coal seam combined with a dual-porosity model: Finite difference solution and multi-factor analysis. Fuel 2022, 313.
6. Sun, L.; Wang, H.; Zhang, C.; Zhang, S.; Liu, N.; He, Z., Evolution of methane ad-/desorption and diffusion in coal under in the presence of oxygen and nitrogen after heat treatment. Journal of Natural Gas Science and Engineering 2021, 95.
7. Busch, A.; Gensterblum, Y., CBM and CO2-ECBM related sorption processes in coal: A review. International Journal of Coal Geology 2011, 87, (2), 49-71.
8. Zang, J.; Wang, K., A numerical model for simulating single-phase gas flow in anisotropic coal. Journal of Natural Gas Science and Engineering 2016, 28, 153-172.

 

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

Dear authors,

I think that you have very well presented the model that defines the investigated parameters in the desorption process of coal gas containing gas. The rate of desorption and the effective diffusion coefficient are in a certain functional dependence, as you have shown.

Further, as you state, When the coal is of the same size before and after crushing, the gas desorption rate ratio of the coal containing the gas is the square root of the reciprocal of the effective diffusion coefficient. It is clear that the granulation changes during the process.

I think the following should be stated:

- In a few sentences in the manuscript discussion, clarify the impact of your assumptions on the model.

- The assumption was made that the diffusion coefficient is constant and that the coal particles are of the same shape. How does this assumption affect your model?

- How does the moisture content in the material affect the diffusion coefficient?

- Take into account the possibility of different problems that can occur at different temperatures. The diffusion process itself can be disturbed by this parameter.

Best Regards

Author Response

 

Dear Editor and Reviewer

 

Thanks very much for your email and the reviewers’ comments, regarding our submission of the manuscript “Effect of coal particle breakage on gas desorption rate during coal and gas outburst” (Manuscript ID: applsci-2777436).

 

The manuscript is now revised according to the suggestions of the reviewers and editor. Main changes in the text are in red in the revised manuscript.

 

Our responses to the comments by the reviewers are on separate pages.

 

With best regards.

 

Yours sincerely,

 

Gun Huang

Qiang Cheng

Corresponding author:

Name: Gun Huang

Institution: Chongqing University, Chongqing 400030, China

E-mail: [email protected]; [email protected]

 

Detailed responses to the reviewers’ comments (Manuscript ID: applsci-2777436)

 

We appreciate the reviewers for their careful reading of our manuscript (Manuscript ID: applsci-2777436) and useful suggestions on how to improve our presentation. The following are our responses and explanations to the issues raised by the reviewers, where line numbers, page numbers, table numbers, and figure numbers are those in the revised manuscript. The revised portions are highlighted in red and the line numbers and page numbers were in bold.

Reviewer #4: I think that you have very well presented the model that defines the investigated parameters in the desorption process of coal gas containing gas. The rate of desorption and the effective diffusion coefficient are in a certain functional dependence, as you have shown.

Further, as you state, When the coal is of the same size before and after crushing, the gas desorption rate ratio of the coal containing the gas is the square root of the reciprocal of the effective diffusion coefficient. It is clear that the granulation changes during the process.

Point 1: In a few sentences in the manuscript discussion, clarify the impact of your assumptions on the model. The assumption was made that the diffusion coefficient is constant and that the coal particles are of the same shape. How does this assumption affect your model?

Response: Thanks for your valuable comments! As suggested, we clarify the impact of the assumptions on the model in Lines 489-496 on Page 16-17: “The accuracy of the desorption model for broken coal depends the diffusion model and particle size distribution of the coal particles. In these diffusion models, coal particles are typically assumed to be spherical. The effective diffusion coefficient decreases as diffusion time increases. At the same time, in a short time period like 30 seconds, the effective diffusion coefficient changes little and the outburst is short-lived. Therefore, when estimating the amount of desorbed gas during outburst, it is assumed that the effective diffusion coefficient remains constant.”

Point 2: How does the moisture content in the material affect the diffusion coefficient? Take into account the possibility of different problems that can occur at different temperatures. The diffusion process itself can be disturbed by this parameter.

Response: Thanks for your valuable comments! As suggested, We interpret the effects of moisture and temperature on the diffusion coefficient separately. Moisture in coal affects its pore structure and gas adsorption capacity. Higher moisture leads to shorter adsorption time and lower pressure drop. The gas adsorption capacity of coal decreases gradually with increasing moisture, indicating that moisture occupies pore space and reduces adsorption sites. Different diffusion models can be used to calculate diffusion coefficients based on coal rank. Moisture also affects gas migration and diffusion channels, reducing adsorption time, desorption rate, and diffusion rate of coal seam [1]. Increasing moisture content in low-rank coal (LRC) leads a decrease in desorption volume and initial desorption rate. The initial diffusion coefficient (D₀) and moisture content (M) have a negative linear relationship, expressed as D₀ = λM + D_dry, where λ and D_dry are material constants and D₀ is the diffusion coefficient of the dry coal sample. Additionally, as moisture content increases, the time-varying diffusion coefficient (D_t) and its decay rate decrease noticeably. This indicates that moisture can greatly hinder the diffusion capacity of LRC. The competitive adsorption between moisture and methane molecules is a significant factor influencing the diffusion properties of LRC. It's important to note that there is a critical moisture content threshold, beyond which further increases have no significant impact on reducing desorption and diffusion capacity [2].

 

The coal diffusion coefficient and particle size greatly impact temperature variation and the release of adsorbed gas [3]. The desorption process is a heat absorption and cooling process, which is mainly influenced by the equilibrium pressure and the particle size of the coal samples. The amount of desorption and the absolute desorption temperature variation increases with increasing equilibrium pressure and increases with decreasing particle size of the coal sample [4].

 

Reference

1. Wang, L.; Chen, E.-t.; Liu, S.; Cheng, Y.-p.; Cheng, L.-b.; Chen, M.-y.; Guo, H.-j., Experimental study on the effect of inherent moisture on hard coal adsorption-desorption characteristics. Adsorption-Journal of the International Adsorption Society 2017, 23, (5), 723-742.
2. Jiang, J.; Peng, H.; Cheng, Y.; Wang, L.; Wang, C.; Ju, S., Effect of Moisture on Time-Varying Diffusion Properties of Methane in Low-Rank Coal. Transport in Porous Media 2023, 146, (3), 617-638.
3. Wei, C.; Liu, S., Determination of diffusion coefficient and convective heat transfer coefficient for non-isothermal desorption-diffusion of gas from coal particles. Fuel 2023, 352.
4. Ye, Q.; Li, C.; Yang, T.; Wang, Y.; Li, Z.; Yin, Y., Relationship between desorption amount and temperature variation in the process of coal gas desorption. Fuel 2023, 332.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I thank the authors for their detailed responses to my review and completion of the manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

The corrections made are appropriate