Coal and Gangue Active Identification Method Using Microwave Irradiation-Infrared Detection
Round 1
Reviewer 1 Report
1) Authors have mentioned that there were more than 30 methods for coal and gangue identification, but all of them had unsatisfactory experimental results due to the harsh environment of the underground longwall top coal caving (LTCC) working face. In my opinion, you should present the specific traits of longwall top coal caving for comprehensive understanding of the problem of coal dilution, because you have mentioned LTCC a lot. It was also essential to consider the physical properties of coal and gangue and their mixtures (coarseness, ash content, moisture content etc.), that can have a significant impact on results of using the proposed method in LTCC face conditions.
2) In my view, the test results of specific heat capacity of coal and gangue at different temperatures presented in Figure 9 are wrong. The specific heat capacity of coal cannot change so substantially within a small temperature range. It's obvious to me the specific heat capacity of coal at temperatures 35 and 45 0C are wrong (especially for the case of 35 0C). In my opinion, there is no reason to believe that such results for coal are correct.
3) Authors conclude that “Based on the above data analysis, it can be concluded that under the same coal and gangue particle size and microwave irradiation time conditions, in the order of particle size from small to large, the temperature increase of the sample coal particles after microwave irradiation is 1.3 times, 1.7 times, 2.0 times and 2.3 times that of gangue.”, but in real conditions coal and gangue particle size are different. In addition, the size of the particles used in the experiment is tens or even hundreds of times smaller than the size of the particles under real conditions. It is not clear how the results of the experiment will be used for real-world applications.
4) It is not clear how the authors propose to apply the active identification method in real conditions of LTCC face, taking into account the continuous conveying of coal and gangue, an uneven distribution of the gangue along a longwall face length and most importantly near-permanent coal dilution.
Author Response
Please see attached reply to Reviewer 1.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This paper focuses on coal and gangue material identification to help improve the efficiency of the mining method. The paper is meaningful and valuable. However, minor revisions are needed and a significant improvement of the manuscript is required in order to be recommended for publication.
(1) The latest research achievements should be cited in references.
(2) The moisture content in coal and gangue also has a great influence on the test results, and the influence of this factor is not considered in this paper.
(3) The microwave emission frequency used in the experiment in this paper is 2.45ghz. Is it verified that the experimental effect is the best under this emission frequency?
(4) The field application effect of the microwave irradiation-infrared detection coal gangue identification method is not mentioned in the paper.
(5) This coal-gangue identification method does not consider the influence of dust during underground application.
Comments for author File: Comments.pdf
Author Response
Please see attached reply to Reviewer 2.
Author Response File: Author Response.pdf
