Review Reports - Quality Assessment of <i>Quercus scytophylla</i> Liebm Charcoal Produced in a Metal Kiln in the Cordón Grande Ejido, Guerrero, Mexico

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

-2. CEVAG...it's 1st mentioned here, better use full name

-13-14, R2 value is quite too low to get this conclusion

-abstract. should be written in just one paragraph

-keywords, authors should revise to select the significant terms, not regular term like ash, volatile

-70, introduction. authors should add more literature studies why sapwood and hardwood were compared in this work? what's the major assumption for authors that want to be tested.

-90.air intake is controlled by chimneys located in the lower section of the furnace......how to control air intake? is there any flow controller?

-fig 2, authors should revise all labels to English

-table1. for granulometry, what is the conventional sizing ? why authors selected these sizing for testing in this study

-171. The initial weight of the green wood averaged 3600 kg....did authors measure moisture content? it's important for interprete the data and repeatibility

-table2, please explain more criteria about how authors separate lower, middle and upper from each other

-table 4, please discuss why granulometry affects different parts on calory values

-245-247, when the fixed carbon content of this study is below the international standards, so how authors concluded that the results in this work is acceptable?

-303 linear relationship...why authors did not try to fit the corelation with other fitting, than just linear. The R2 value is quite too low here

Author Response

Comments 1: 2. CEVAG...it's 1st mentioned here, better use full name

Response 1: Thank you for pointing this out. We agree with this comment. Therefore, the full name of CEVAG was written. Page 1, lines 2-3; pag 3., lines 90-92.

Comments 2: 13-14, R2 value is quite too low to get this conclusion

Response 2: Thank you for pointing this out. We agree with this comment. A linear model has been adjusted because it is the highest value available for the coefficient of determination. In fact, this value does not increase with the transformation of the variables involved in the model or by using a polynomial regression. Therefore, the regression model is reported with the scope that it allows. See page 1, lines 13-15.

Comments 3: abstract. should be written in just one paragraph

Response 3: Thank you for pointing this out. We agree with this comment. The summary was written in a single paragraph. Page 1, lines 1-20.

Comments 4: keywords, authors should revise to select the significant terms, not regular term like ash, volatile

Response 4: Thank you for pointing this out. We agree with this comment. The keywords were corrected, page 1, lines 21-22.

Comments 5: 70, introduction. authors should add more literature studies why sapwood and hardwood were compared in this work? What’s the major assumption for authors that want to be tested.

Response 5: Thank you for pointing this out. We agree with this comment. The questions are answered in lines 71-74, page 2.

Comments 6: 90.air intake is controlled by chimneys located in the lower section of the furnace......how to control air intake? is there any flow controller?

Response 6: Thank you for pointing this out. We agree with this comment. The answers to the questions are given in lines 100-101, page 3.

Comments 7: fig 2, authors should revise all labels to English

Response 7: Thank you for pointing this out. We agree with this comment. The labels in Figure 2 have been corrected. Page.4

Comments 8: table1. for granulometry, what is the conventional sizing ? why authors selected these sizing for testing in this study

Response 8: Thank you for pointing this out. We agree with this comment. The answers to these questions are given in line 141-142, page 5.

Comments 9: 171. The initial weight of the green wood averaged 3600 kg....did authors measure moisture content? it's important for interprete the data and repeatability

Response 9: Thank you for pointing this out. We agree with this commentThe moisture content was measured and added in lines 112-114, page 4.

Comments 10: table2, please explain more criteria about how authors separate lower, middle and upper from each other

Response 10: Thank you for pointing this out. We agree with this comment. The answers to the questions are given in lines 120-122, page 4.

Comments 11: table 4, please discuss why granulometry affects different parts on calory values

Response 11: Thank you for pointing this out. However, Table 4 evaluates the amount of carbon recovered per kilogram in the screens used in the study. These results do not indicate caloric values.

Comments 12: 245-247, when the fixed carbon content of this study is below the international standards, so how authors concluded that the results in this work is acceptable?

Response 12: Thank you for pointing this out. We agree with this comment. The answer is justified by the wording found in lines 262-264, page 10.

Comments 13: 303 linear relationship...why authors did not try to fit the corelation with other fitting, than just linear. The R2 value is quite too low here

Reviewer 2 Report

Comments and Suggestions for Authors

This paper conducted carbonization of the sapwood and heartwood of Quercus scytophylla in a CEVAG-type metal kiln, and systematically evaluated the effects of different furnace layer positions on the physical and chemical properties of the charcoal (such as calorific value, density, volatile matter, ash content, fixed carbon, etc.). The quality of the paper can be improved by making the following revisions:
The unit of density in Table 3 is incorrect; an extra letter "r" has been added.
2. The carbonization process described in the text lacks crucial temperature and time data. The text only describes the structure of the furnace and the method of vacuum extraction, but there is no information about the carbonization temperature curve, the heating rate or the final temperature. It is suggested to add the initial drying stage temperature range, the upper limit of the carbonization temperature, the duration of the process, and the moment when the intake valve is closed. The carbonization process and temperature conditions directly determine the results of fixed carbon, volatile matter, and ash content; otherwise, the experiment cannot be replicated.
3. In the text, "upper part best quality" is mentioned. However, when we compared the data, we found that the highest calorific value was in the lower layer, while the highest density was in the upper layer. It is suggested to elaborate separately. Otherwise, there will be a phenomenon of logical confusion.
4. The article states that the fixed carbon content is 73.7–74.1%, which is slightly lower than the international standard of 75%. There is no significant difference between sapwood and heartwood. It is suggested that a detailed discussion be held on the fixed carbon results. For example, the difference in extractive content between sapwood and heartwood and its impact on fixed carbon, as well as the difference in moisture content between sapwood and heartwood and its influence on fixed carbon, etc.
5. The introduction section is somewhat lacking. The description and summary regarding the performance improvement of charcoal need to be enhanced.

Author Response

Comments 1: The unit of density in Table 3 is incorrect; an extra letter "r" has been added.

Response 1: Thank you for pointing this out. We agree with this comment. The errors have been corrected.

Comments 2. The carbonization process described in the text lacks crucial temperature and time data. The text only describes the structure of the furnace and the method of vacuum extraction, but there is no information about the carbonization temperature curve, the heating rate or the final temperature. It is suggested to add the initial drying stage temperature range, the upper limit of the carbonization temperature, the duration of the process, and the moment when the intake valve is closed. The carbonization process and temperature conditions directly determine the results of fixed carbon, volatile matter, and ash content; otherwise, the experiment cannot be replicated.

Response 2: Thank you for pointing this out. Temperature data were not measured during the carbonization process. On the other hand, lines 112-114 (page 4) refer to the moisture conditions of the wood, and lines 116-119 (page 4) indicate the composition of the samples. The carbonization process was carried out in accordance with the Jáquez y Guzmán Manual (line 99, page 3).

Jáquez, A.; Guzman, F.; México. Secretaría de Agricultura, Ganadería y Desarrollo Rural and Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias (México).; Centro de Investigación Regional del Norte Centro.; Campo Experimental Valle del Guadiana and Fundación Produce Durango. Manual para elaborar carbón vegetal en horno metálico tipo "CEVAG"; Folleto para productores.

Comments 3. In the text, "upper part best quality" is mentioned. However, when we compared the data, we found that the highest calorific value was in the lower layer, while the highest density was in the upper layer. It is suggested to elaborate separately. Otherwise, there will be a phenomenon of logical confusion.

Response 3: Thank you for pointing this out. The results in Table 2 (calorific value) and Table 3 (basic density) cannot be separated, because the calorific value analysis was performed for wood and coal, and the same applies to basic density.

Comments 4. The article states that the fixed carbon content is 73.7–74.1%, which is slightly lower than the international standard of 75%. There is no significant difference between sapwood and heartwood. It is suggested that a detailed discussion be held on the fixed carbon results. For example, the difference in extractive content between sapwood and heartwood and its impact on fixed carbon, as well as the difference in moisture content between sapwood and heartwood and its influence on fixed carbon, etc.

Response 4: Thank you for pointing this out. We agree with this comment. The response to this comment is given in lines 262-264, page 10; and lines 345-346, pag. 11.

Comments 5. The introduction section is somewhat lacking. The description and summary regarding the performance improvement of charcoal need to be enhanced.

Response 5: Thank you for pointing this out. We agree with this comment. The answer to this comment is given in lines 68-74, page 2.

Reviewer 3 Report

Comments and Suggestions for Authors

Quality Assessment of Quercus scytophylla Liebm Charcoal Produced in a Metal Kiln

Abstract: The aim of the study was to assess the quality of charcoal produced from Quercus scytophylla Liebm. in Guerrero, Mexico. The test conditions using a CEVAG metal kiln were described. A factorial design was used to analyze the effect of wood heterogeneity (sapwood vs. heartwood) and kiln position (low, medium, high) on the yield and physicochemical properties of the charcoal.

The obtained results were presented.

The methods for assessing calorific value and charcoal fraction were not described.

Introduction: The demand for wood charcoal in Mexico was presented and compared to global demand.

The growing interest in this form of solid fuel for individual public needs was indicated.

The specific aim of the study was to assess the quality of charcoal produced from both sapwood and heartwood of Quercus scytophylla Liebm. in portable metal kilns installed at logging sites in Mexico.
The research question is not well-defined – for example, determining the difference in the calorific value and quality of charcoal from sapwood and heartwood of Quercus scytophylla Liebm.

Materials and Methods
The study area and habitat are well described, and the choice of oak species for the study is justified.
Unfortunately, the principles for selecting the kiln (retort) for the study are not provided. The rationale for selecting charcoal from specific heights is not provided, nor is the justification for selecting only three heights for charcoal sampling for evaluation.

The principles for assessing charcoal quality are described. The study location and standards used for assessing wood quality are provided.
The parameters of the raw material for testing and the principles for selecting samples for testing are not assessed.
The choice of kiln was also insufficiently justified.

Results.

The results indicate no significant differences in the calorific value of sapwood and heartwood. This is supported by the density of the raw material.
Methodological studies of the granulation of individual layers of the harvested charcoal are indicated. Friability, moisture content, and ash content were assessed.

Discussion
The impact of kiln (retort) selection on charcoal production was described. The effect of temperature gradients on changes in the structure of the produced charcoal was well interpreted.
The results were supported by a literature review of various kiln models and a comparison of wood species in Mexico. Literature data providing a comparison for the authors' own results were well referenced.

Conclusions
The villages correspond to the research factors and simultaneously provide all the main answers regarding the validity of using Quercus scytophylla Liebm wood for charcoal production and kiln (retort) selection for the highest quality and efficiency production.

The charcoal production index value for the input wood was not provided.

References
The literature was appropriately selected with a broad review considering the publication dates of the cited works.

Author Response

Comments and Suggestions for Authors

Comments 1, Introduction: The methods for assessing calorific value and charcoal fraction were not described.

Response 1: Thank you for pointing this out. We agree with this comment. The comment is addressed in lines 68-70, page 2.

Comments 2, Introduction: The research question is not well-defined – for example, determining the difference in the calorific value and quality of charcoal from sapwood and heartwood of Quercus scytophylla Liebm.

Response 2: Thank you for pointing this out. We agree with this comment. The comment is answered in lines 71-74, page 2.

Comments 3, Materials and Methods:Unfortunately, the principles for selecting the kiln (retort) for the study are not provided. Response 3.1: Thank you for pointing this out. We agree with this comment, The comment is answered in lines 95-99, page 3.

The rationale for selecting charcoal from specific heights is not provided, nor is the justification for selecting only three heights for charcoal sampling for evaluation Response 3.2 : Thank you for pointing this out. We agree with this comment. The answer to this comment is given in lines 116-117, page 4.

Comments 4, Materials and Methods: The parameters of the raw material for testing and the principles for selecting samples for testing are not assessed.

Response 4: Thank you for pointing this out. We agree with this comment. The answer to this comment is given in lines 116-117, page 4.

Comments 5, Materials and Methods: The choice of kiln was also insufficiently justified.

Response 5: Thank you for pointing this out. We agree with this comment. The answer to this comment can be found on lines 95-99, page 3.

Comments 6, Conclusions: The charcoal production index value for the input wood was not provided.

Response 6: Thank you for pointing this out. We agree with this comment. The answer to this comment can be found on lines 345-346, page 11.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Author Response

Editor comments: The revised manuscript and your reply indicate that temperature/time (thermal profile) data were not measured during the carbonization. Please add an explicit statement in Methods (and a short paragraph in Discussion) acknowledging this, explaining that the process followed the CEVAG manual and operator control, and discuss how absence of measured temperature profiles limits mechanistic interpretation and repeatability. If possible, suggest this as a concrete recommendation for future work.

Response: Thank you for pointing this out. We agree with this comment. The section on methods was added in lines 103-105 (page 3); the section on discussion was added in lines 264-268 (page 10); and finally, the section on suggestions for future research can be found in lines 359-360 (page 11).

Reviewer 2 Report

Comments and Suggestions for Authors

The author has made detailed revisions based on the suggestions provided and they can now be accepted and published.

Author Response