Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The titled paper presents a compelling investigation into an innovative approach to reducing carbon emissions within the metallurgical industry. The study explores the integration of biochar into coking coal blends to produce bio-coke, providing a sustainable alternative to traditional coke. The research is timely and highly relevant, particularly in the context of transitioning coal regions and the irreversible reduction of coking coal production in Europe.

The work is distinguished by its high application potential. The thorough experimentation and analysis conducted by the authors demonstrate that bio-coke, produced with up to 20% biochar, holds promising characteristics for use in carbothermal reduction processes, particularly in the smelting of ferroalloys. The increase in CO₂ reactivity index (CRI) and the maintained durability suggest that bio-coke could effectively replace conventional coke, contributing significantly to emission reductions in the metallurgical process.

The scientific value of the paper is noteworthy due to its originality in experimental design and meticulous analysis of results. The authors have employed a systematic approach to assess the impact of biochar on various properties of bio-coke, such as bulk density, porosity, and reactivity. The findings on structural and textural changes are particularly valuable for understanding the potential industrial applications of bio-coke.

The state-of-the-art review is comprehensive, incorporating insights from 66 publications, which underscores the robust foundation of the study. The clarity of figures and the logic presented in their sequence significantly enhance the reader's understanding of the experiments and outcomes.

In conclusion, this study not only provides critical insights into sustainable metallurgical processes but also paves the way for further studies and industrial-scale applications of bio-coke. The integration of biochar not only aligns with environmental goals but also offers a feasible pathway for the metallurgical industry to meet its sustainability objectives. The authors should be commended for their clear presentation and the substantial contribution this paper makes to both scientific research and practical applications in metallurgical engineering.

Author Response

The authors would like to express their gratitude to the Reviewer for his contribution to the preparation of the review and for the positive reception of the prepared manuscript. A positive reception is always an incentive for further work.

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript entitled “A Study on Bio-Coke Production - The Influence of Biochar Addition to the Coking Blend on Bio-Coke Quality Parameters” is well-written. The research related to bio-coke, its properties, and the study of its application for non-blast furnace metallurgical processes is interesting and important. During the review process, some questions and comments arose that the authors are recommended to consider.

 

Line 38: It would be much better if the authors here clarified that this is about the blast furnace. Moreover, keeping the burden structure, along with sustaining skeleton permeability and drainage efficiency, is a unique ability of coke since other carbon materials cannot perform this function. As a result, coke is an indispensable carbon material for the blast furnace.

Lines 47-49, would be better to rewrite the sentence without using “thanks”.

Line 72, I would suggest changing “manifested” to “proved” or “evidenced.”

The authors' excellent and comprehensive literature review is well worth reading. However, the introduction of the research-type paper is too long. It would be recommended that this part be shortened slightly.

On line 254, it would be helpful if the authors could provide the composition of the coal blend and the proximate and ultimate analysis of the coals used to obtain biocoke.

It is also recommended that the authors provide a proximate and ultimate analysis of the obtained biocokes.

In Table 1, the TiO₂ index should be specified using subscript. Further, authors are advised to check the entire text, as some indexes are specified without using subscripts.

Also, in Table 1, fixed carbon is listed after the sulfur. Fixed carbon is related to proximate analysis and should be listed after the volatile matters.

In Table 1, it is noticeable that the alkalinity index for charcoal is much higher than that of coal. I would like to see the values ​​of the alkalinity index for biocokes as well. It can only be assumed that these values ​​will be lower for biocokes than charcoal.

In Figure 2, the authors recommend that the legends be unified. “Gravity-charged” or “gravity charged”. One of them should be selected.

It is interesting to see that charcoal in these studies was characterized by lower volatiles compared to the coal blend. If stamping is not used, the biocoke yield is reduced due to the addition of biochar/charcoal to the coal blend, which is characterized by higher volatiles.

Lines 457, 459, please take care about subscript.

Lines 594: at the moment, coke for blast furnaces has a CRI of app. 22-25 wt.% and a CSR of app. 60 wt.%. From this point of view, biocoke is absolutely unacceptable for blast furnaces.

Author Response

Comment 1: The manuscript entitled “A Study on Bio-Coke Production - The Influence of Biochar Addition to the Coking Blend on Bio-Coke Quality Parameters” is well-written. The research related to bio-coke, its properties, and the study of its application for non-blast furnace metallurgical processes is interesting and important. During the review process, some questions and comments arose that the authors are recommended to consider

Response 1: The authors would like to express their gratitude for the contribution made in the review and positive reception and evaluation of the manuscript. Taking into account the reviewer's comments will help to improve the quality of the manuscript, which will be beneficial to the potential reader.

Comment 2: Line 38: It would be much better if the authors here clarified that this is about the blast furnace. Moreover, keeping the burden structure, along with sustaining skeleton permeability and drainage efficiency, is a unique ability of coke since other carbon materials cannot perform this function. As a result, coke is an indispensable carbon material for the blast furnace.

Response 2: As per comment, clarification regarding blast furnace application has been added.

Comment 3: Lines 47-49, would be better to rewrite the sentence without using “thanks”.

Response 3: As per comment, the sentence was rewrited.

Comment 4: Line 72, I would suggest changing “manifested” to “proved” or “evidenced.

Response 4: As per comment, the sentence was rewrited.

Comment 5: The authors' excellent and comprehensive literature review is well worth reading. However, the introduction of the research-type paper is too long. It would be recommended that this part be shortened slightly.

Response 5: Thank you for the positive assessment of the work put into preparing the review for the introduction section. Due to the fact that this is the first article on the quality parameters of bio-coke authored by us, we wanted to provide potential readers with as much basic information as possible, so that when reading they would not have to often look for other articles related to the subject. Our intention was to include as much information as possible in one place, while maintaining a certain conciseness. Therefore, I hope that it will not be a problem if we keep the current shape of the introduction.

Comment 6: On line 254, it would be helpful if the authors could provide the composition of the coal blend and the proximate and ultimate analysis of the coals used to obtain biocoke.

Response 6: Unfortunately, because the blend formula was selected with an industrial partner, we cannot provide detailed data on blend composition and individual coal quality due to confidentiality issues. We hope it is not a problem.

Comment 7: It is also recommended that the authors provide a proximate and ultimate analysis of the obtained biocokes.

Response 7: As suggested by Reviewer, we have provided approximate and ultimate analysis values ​​in Appendix 1 - Table A1.

Comment 8: In Table 1, the TiO₂ index should be specified using subscript. Further, authors are advised to check the entire text, as some indexes are specified without using subscripts.

Response 8: According to the comment, manuscript was revised in order to correct subscripts.

Comment 9: Also, in Table 1, fixed carbon is listed after the sulfur. Fixed carbon is related to proximate analysis and should be listed after the volatile matters.

Response 9: According to the comment, the Table 1 content was corrected.

Comment 10: In Table 1, it is noticeable that the alkalinity index for charcoal is much higher than that of coal. I would like to see the values ​​of the alkalinity index for biocokes as well. It can only be assumed that these values ​​will be lower for biocokes than charcoal.

Response 10: We agree with the comment that the alkalinity index for bio-cokes should be lower than for charcoal alone. The higher the charcoal content, the lower it should be - more similar to the value for coke produced without the addition of charcoal. However, we did not determine the detailed ash composition for all the bio-cokes tested, which is necessary to determine the alkalinity index. We assumed that this is a roughly additive value and can be estimated with quite good accuracy knowing the approximate analysis values ​​and ash chemical composition of blend and charcoal.

Comment 11: In Figure 2, the authors recommend that the legends be unified. “Gravity-charged” or “gravity charged”. One of them should be selected.

Response 11: According to the comment, the legend was corrected.

Comment 12: It is interesting to see that charcoal in these studies was characterized by lower volatiles compared to the coal blend. If stamping is not used, the biocoke yield is reduced due to the addition of biochar/charcoal to the coal blend, which is characterized by higher volatiles.

Response 12: As the Reviewer rightly noted, in the examined case the content of volatiles in the added charcoal was lower than in the coal blend, which resulted in a percentage increase in the coke/bio-coke yield. Thanks to the lower content of volatiles, the amount of renewable carbon is higher than that resulting directly from the value of the 20% addition and amounts to approx. 24%. This was also verified in the C14 analysis carried out by indsutrial partner. From the point of view of increasing the yield and increasing the renewable carbon content, biochars with an even lower content of volatiles, which are already offered on the market - produced at temperatures above 800oC, can be used.

Comment 13: Lines 457, 459, please take care about subscript

Response 13: According to the comment, subscripts were corrected.

Comment 14: Lines 594: at the moment, coke for blast furnaces has a CRI of app. 22-25 wt.% and a CSR of app. 60 wt.%. From this point of view, biocoke is absolutely unacceptable for blast furnaces.

Response 14: As the Reviewer rightly noted, in modern blast furnaces the requirements for CRI/CSR are very strict. The values ​​given in line 594 refer to the minimum values ​​for the average size of blast furnaces currently used. Of course, as the Reviewer noted, the CRI/CSR values ​​obtained for our bio-coke do not meet the requirements for blast furnace coke. Whether they meet the assumptions for ferroalloys in SEAF must be verified on an industrial scale. Due to the lower height and the associated lower load, there is a chance that they will. In the case of blast furnaces, it seems to us that there is a certain possibility, but with the use of much smaller amounts of added biochar and an appropriately optimized coking blend.

Reviewer 3 Report

Comments and Suggestions for Authors

The article is fully discussed and the result analysis is more detailed and accurate. It is recommended to be employed.

Author Response

The authors would like to express their gratitude for the contributions made during the preparation of this review and for the positive reception of the manuscript.