Formation of Improved Metallurgical Properties and Carbon Structure of Coke by Optimizing the Composition of Petrographically Heterogeneous Interbasin Coal Batches

Round 1

Reviewer 1 Report (Previous Reviewer 2)

The revisions have successfully addressed the issues raised in my review. I consider the manuscript suitable for publication in its current form.

The revisions have successfully addressed the issues raised in my review. I consider the manuscript suitable for publication in its current form.

Author Response

Comments 1: The revisions have successfully addressed the issues raised in my review. I consider the manuscript suitable for publication in its current form.

Response 1: Thank you very much for your review.

Reviewer 2 Report (Previous Reviewer 1)

This paper investigates how to improve the quality of metallurgical coke by optimizing coal batch composition from different coal basins. The authors use petrographic analysis, thermodynamic modeling, and pilot coking tests to demonstrate that adjusting maceral content and selecting compatible coals improves coke strength and structure. The authors may want to consider the following suggestions.

L85–L92: The aim of the study should be articulated more clearly. Consider ending the introduction with a paragraph that outlines the specific research questions and hypotheses.

L372–L420: Please specify the number of replicates for each experimental coking test (e.g., n = 3) and provide statistical error ranges or standard deviations where appropriate.

L530–L590: Ensure temperature units (°C) are consistent and clearly labeled in Table 6. It would also help to specify the instruments or models used (e.g., Gieseler plastometer, dilatometer).

L900–L950: Although ΔGf,i values are cited from literature [48], a brief table or supplementary file with these values and their justification would improve reproducibility.

L1010–L1050: The discussion of resistivity as a proxy could be more concise and could explicitly connect to industrial-scale monitoring potential.

Pls check the above.

Author Response

This paper investigates how to improve the quality of metallurgical coke by optimizing coal batch composition from different coal basins. The authors use petrographic analysis, thermodynamic modeling, and pilot coking tests to demonstrate that adjusting maceral content and selecting compatible coals improves coke strength and structure. The authors may want to consider the following suggestions.

Comments 1: L85–L92: The aim of the study should be articulated more clearly. Consider ending the introduction with a paragraph that outlines the specific research questions and hypotheses.

Response 1: Thank you for clarifying, we have made changes to the text of the article. An addition has been made to text: «…When blending coal to obtain coke of a certain strength, including the maximum possible strength, the only criterion for the technological properties of the blend that meets these requirements should be not the rank (quality), but rather the criterion of optimality, based on the calculation of specific values of the properties of the charge according to the properties of its components. Such a unique indicator could be the value of the Gibbs free energy of formation (ΔG_f,total).The uniqueness and practical value of introducing the thermodynamic index (ΔG_f,total) lies in the fact that it takes into account not only the content of vitrinite and inertinite, but also the reflection coefficients for all maceral types. This approach allows the overall thermodynamic stability of the coal mixture to be assessed using a single integral value».

Comments 2: L372–L420: Please specify the number of replicates for each experimental coking test (e.g., n = 3) and provide statistical error ranges or standard deviations where appropriate.

Response 2: All tests were performed twice (n = 2). Discrepancies in the results of parallel determinations performed in the same laboratory, by the same laboratory technician, on the same instrument for two representative portions taken from the same analytical sample did not exceed the permissible values. The table shows the permissible deviations of the relevant indicators.

Comments 3: L530–L590: Ensure temperature units (°C) are consistent and clearly labeled in Table 6. It would also help to specify the instruments or models used (e.g., Gieseler plastometer, dilatometer).

Response 3: We made some changes to Table 6 and added the units of measurement for temperature. The research was done using standardized methods that clearly define the steps and equipment specs. You can find the list of standardized methods in the references.

Comments 4: L900–L950: Although ΔGf,i values are cited from literature [48], a brief table or supplementary file with these values and their justification would improve reproducibility.

Response 4: We added a dedicated figure (Fig. 8) where the Gibbs free energy of coal macerals is plotted as a function of the mean reflection coefficient. We believe this graphical presentation plotted using data from [50]) better illustrates the correlation between coal rank and maceral thermodynamic properties.

Comments 5: L1010–L1050: The discussion of resistivity as a proxy could be more concise and could explicitly connect to industrial-scale monitoring potential.

Response 5: In our opinion, the above discussion describes the mechanism of transformation of the physical properties of coal (dielectric) as a result of its carbonization, which causes the cleavage of functional groups, increased aromatization, and ordering of the structure during the formation of coke (a conductor of the first kind). Therefore, in our opinion, it is relevant. The text also states that monitoring the quality of coke and its readiness based on the specific resistivity indicator does not require much time, additional reagents, or costs, and is therefore an efficient and reliable method.

 

Author Response File: Author Response.pdf

Reviewer 3 Report (Previous Reviewer 3)

I still suggest the addition of the content of carbon surface chemistry and citations as suggested in the former comment to make the paper more convincing.  I don't understand why the authors didn't consider this at all. 

No comment

Author Response

Comments 1: I still suggest the addition of the content of carbon surface chemistry and citations as suggested in the former comment to make the paper more convincing.  I don't understand why the authors didn't consider this at all.

Response 1: Thank you for clarifying, we have made changes to the text of the article. An addition has been made to text: It should also be noted that the organic carbon matrix consists not only of carbon atoms, but also of other heteroatoms, such as hydrogen, oxygen, nitrogen, halogen, sulfur, phosphorus, etc. These atoms are bonded on the carbon edges, and determine the chemical properties of the coal surface. The presence of oxygen functional groups (phenols, quinones, carboxyl groups) on the surface significantly affects the reactivity, dispersibility, and electrical properties of these materials [Dang, Y., Liu, Y., Xiang, P., Tan, Z., Tian, Z., Greiner, М., Heumann, S., Ding, Y., Qiao, Z.-An. Carbon Surface Chemistry: Benchmark for the Analysis of Oxygen Functionalities on Carbon Materials. Adv. Mater., 2025, 37(11), 2418239.], surface chemistry affects the chemical behaviors of carbon in some specific chemical reactions [Ding, Y., Qiao, Z.-An. Carbon Surface Chemistry: New Insight into the Old Story. Adv. Mater., 2022, 34(42), 2206025].

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report (Previous Reviewer 1)

I checked the revised manuscript. It has been successfully revised according to my suggestions. Now, it can be accepted as is.

None.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

This manuscript addresses the issue of multi-basin coal blending in the coking industry by optimizing the lithological composition of coal batches, resulting in significant improvements in the quality of metallurgical coke. The innovation lies in introducing the Gibbs free energy of formation to predict the carbon structural order of coke, which is further validated through industrial coke oven tests. However, the thermodynamic mechanism underlying the use of Gibbs free energy of formation requires a more in-depth explanation to justify its applicability. The methodology section should be streamlined for clarity, and the sources of key parameters should be provided to enhance the reproducibility of the experiments and the generalizability of the model.

Question 1: The novelty of the research appears somewhat limited. The overall research methodology closely resembles existing studies on coal blending optimization. It is recommended to highlight how this study differs from previous work and clearly articulate its innovative contributions, particularly the uniqueness and practical value of introducing the thermodynamic index (ΔGf,total).

Question 2: The article introduces ΔGf,total as an indicator for assessing the structural orderliness of coal mixtures, which is a novel approach, but it lacks an in-depth discussion of the actual physical significance and reliability of this index. It is recommended to include an explanation of its reproducibility.

Question 3: The number of figures and tables is relatively high, with some information being repetitive. The data in Table 1 appears somewhat disorganized, making it difficult to identify corresponding relationships. In Tables 2 through 6, certain plots present overlapping variables (e.g., both CSR and CRI are shown as functions of FC and Vt). It is recommended to consolidate some of these figures to enhance readability.

Question 4: The experimental method section is overly lengthy and should be consolidated. It is recommended to integrate some of this content into tables and focus on the key experimental design and core parameters directly relevant to this study.

Question 5: Some English sentences contain awkward or repetitive expressions (e.g., "the coke cake with boxes was delivered according to the usual technology"). It is recommended to revise the language for improved scientific clarity and readability.

Question 6: Inconsistent use of terminology: for instance, English terms for 'ash content', ' poorly caking ', and ' plastic–viscous properties' are used inconsistently in the manuscript, sometimes mixing "ash content" and "ash yield", or using "caking power", etc. It is recommended to standardize the terminology to enhance professionalism.

Question 7: “During thermal destruction, it forms a significant amount of non-volatile, slow-moving products…” — this description of the pyrolysis products of U.S. coal appears somewhat subjective. It is recommended to cite existing literature regarding the yields of tar, gases, and other products to provide stronger data support and enhance scientific rigor.

Question 8: The list of ISO and national standards(e.g., page 4, materials and methods, paragraph 2) is extensive and redundant. Consider presenting these methods in a compact summary table with columns for standard number, test name, and property measured. This will greatly enhance readability and allow readers to quickly identify relevant methods.

Question 9: On Page 7, Table 6 (last two rows), the distinction between “actual” and “calculated” total batch data is not clearly explained. This should clarify how the "calculated" values were derived, and what assumptions or estimations were involved in contrast to the “actual” values. This explanation should be included in the table caption or adjacent paragraph.

Question 10: The reference formatting is inconsistent and should be revised to strictly adhere to the journal’s required style.

Reviewer 2 Report

Please address the following major comments:

 

Would the authors also clarify the mechanism regarding how this optimization method increases the carbon orderliness in coke, especially if compared with cokes produced using classical coking process.

 

With the large imported coal resource being highly diverse, how do the authors think that their optimal approach would work over time with variable coal quality from various basins?

 

Given that there are differences between domestic and foreign methods of classification for the properties of coals: what have the authors done to ensure consistency and replicability of the results, particularly when trying to make alignment toward regulatory or industry specific schemes?

 

how much the mutual contamination and the non-uniform rank assignment at enrichment plants influence the coal batch formulation accuracy, and whether the authors have taken any quantitative measures to monitor or reduce something like these influences?

 

Would it be possible for the authors to give us more insights into the limitations that exist in the mathematical models available in literature until now to predict coke quality, given what they observed experimentally, i.e., how their experimental findings could help in bridging the existing gap, or better still, assist in developing a general predictive framework?

 

When following the national standards recommended order of operations, what were efforts made to control or reduce potential sources of variability or error, and how should this be accounted for in the interpretation of the data?

 

Due to the far-reaching application of international standards for plastometric and dilatometric investigation, have the authors encountered any cross-standard biases or disagreements, particularly during foreign vs. domestic coal sample comparisons? If yes, how were they considered in interpretation of the data?

 

Can the authors clarify, why a crushing degree of best batches was chosen as optimal and could authors also discuss potential trade-offs between increasing crushing (fines content) and it´s effect on resulting physical/mechanical properties of the coke.

 

Were there any production related scale up (scale down) challenges reported in the lab-to-industry work & if so, what was done to address them and were the methods for mitigation successful?

 

Can the authors discuss more about different structure properties of both American and Ukrainian bituminous coals at similar level of metamorphism and how these structural differences effect on coke making, quality and strength?

 

How can the intra-batch variation in vitrinite reflectance be quantitatively associated with important coke performance parameters such as mechanical strength, reactivity and to what extent these relationships can be formalised into a predictive model?

 

The fine carash fraction is reported to be (48,8 % of the dust-like and the high-ash fraction in some of the sies; how does this gradometric distribution influence not only be coke quality but that this plays in the production process as eg.affect the quality of the smoke according to the emission figure, the by-product recovery and the efficiency of the plant?

 

For th edition, while choosing or using some varieties of coal, what are the scientific reasons, of including or excluding the same and what are the limits of their generality in application to other coking plants having different raw material bases?

 

Where do the performance values of coke quality parameters such as M25, M10, CRI and CSR differ from ranges and norms for the metallurgical coke required for BF operation with outputs for coke production?

 

The authors need to provide a more critical discussion on the usability and limitations of weighted Gibbs free energy (ΔGf,total) as predictive parameter for coke quality especially on charges with significant difference in petrographic compositions?

 

The regression models and correlations are strong but could the authors state the stability of these relationships under different operational or compositional conditions, and any statistical caveats that should be taken into account?

 

What key technical/logistical challenges are foreseen in the adoption of optimal batch strategies into an industrial setting, particularly where routine access to high-end analysis may be limited?

 

Would the authors be able to suggest some forms of research or pilot scale studies that could also help to further confirm and enhance the practical value of their work in using their recommendations to optimize for multi-basin coal blends on a coke production facility?

Manuscripts don't have line numbers; please refer to my above comments.

Reviewer 3 Report

In this manuscript, the authors attempted to address the complex coal sourcing for Ukrainian coking plants, an optimized method combining petrographic analysis and thermodynamic modeling was proposed. The optimized coke significantly improves blast furnace efficiency. The manuscript is acceptable after addressing some cautious considerations and revisions:

1. Optimization relies on specific coals (e.g., U.S. coal, Coal G), with unverified applicability to other types; can the sample scope be expanded?

2.Conclusion recommends "adding 10% OS coal," yet only "Coal G" appears in the main text (Table 8); Is there some parts missed?

3.Optimizing the composition affects the carbon structure and metallurgical properties. The complexity of carbon structure and surface chemistry should be discussed. Some related works can be referred to in the revised manuscript (Carbon 37, 1999, 1379; Carbon 77, 2014, 175; Adv. Mater. 2022, 2206025; Adv. Mater. 2025, 2418239).

 

4.The accuracy of the resistivity method was not contrasted with established methods (e.g., microstructure analysis).

5.The box coking test (Fig. 1) lacks description of temperature uniformity control measures, potentially affecting coke quality consistency.

6.Microstructural properties like coke pore structure were not analyzed, providing no direct evidence for the conclusion on "ordering of the carbon structure".