Circular Economy in Charcoal Production: Valorization of Residues for Increased Efficiency and Sustainability

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors,

The abstract is too vague. It should be more specific to the focus of the manuscript.

There is an unexplained presentation on the type of gases used in the study? It could be the indirect heat of combustion or the more complex carbonization gases. If the gases was used as a heat source, this should be explicitly stated in the manuscript. If the latter was the case, what gases were detected and what measures were employed to prevent contamination of the wood load?

Using carbonization gases or indirect heat for pre-drying wood is not a novel idea. There is no information on the knowledge gap that necessitated this study.

Author(s) should state the recommended values for high-quality charcoal according to the referenced NBR standard?.

Did author(s) consider other key tests including bulk density, hardness and reactivity of the charcoal?

Since there was no critical limit reached in the study, what could be the optimum process parameters for maximum yield? 150 C for 30 mins could just be at the lower end of high-quality charcoal production.

Line 237: There is no equation 5.

Lines 286-289: It is not possible to read the results from Fig. 5.

Lines 357-359: Invalid conclusion because there is no wood cell wall compositional analysis conducted in the study. 

Line 362: Author(s) should be consistent with the unit for calorific value (HHV).

Moisture content values, if available should be added to Table 2.

Table 2: High VM may lead to sparking and unwanted emission levels in industrial application. What can author(s) do to ameliorate this?

Although statistical analysis was mentioned, no proof of its use in the results and no comparison was made.

Author Response

All changes suggested by reviewer 1 are highlighted in red.

The abstract is too vague. It should be more specific to the focus of the manuscript.

“This study explores using combustion gases from charcoal production to enhance efficiency and quality in the Brazilian steel industry, where charcoal competes with coal. The research focuses on pre-drying Eucalyptus sp. wood with these gases before carbonization. An innovative system channels combustion gases from the carbonizing furnace to a separate drying furnace. Wood samples were dried at 120°C and 150°C for 15, 22.5, and 30 hours before carbonization. The study assessed the gravimetric yield of charcoal, semi-carbonized wood, and fines, and analyzed key charcoal properties. Results showed that drying with combustion gases at 150°C increased charcoal yield by 7%, regardless of drying time. This pre-drying method also improved charcoal quality, raising fixed carbon content from 74.68% to over 81% and reducing volatile matter from 24.40% to below 18%. These findings indicate that using combustion gases for wood drying significantly enhances charcoal production efficiency and quality, while also reducing greenhouse gas emissions, promoting a more sustainable and environmentally friendly alternative to conventional methods.”

 

There is an unexplained presentation on the type of gases used in the study? It could be the indirect heat of combustion or the more complex carbonization gases. If the gases was used as a heat source, this should be explicitly stated in the manuscript. If the latter was the case, what gases were detected and what measures were employed to prevent contamination of the wood load?

The study did not analyze the composition of the gases; however, their composition does not affect the quality of the wood. The sole function of the gases was to provide heat for the wood drying process.

 

Using carbonization gases or indirect heat for pre-drying wood is not a novel idea. There is no information on the knowledge gap that necessitated this study.

While using carbonization gases or indirect heat for pre-drying wood is indeed not a novel concept, this study addresses specific gaps in the existing research. Previous studies have often focused on the general principles and benefits of these methods. However, this research provides detailed experimental data on the effects of pre-drying Eucalyptus sp. wood at different temperatures and durations using combustion gases. It quantifies the improvements in charcoal yield and quality, offering precise metrics that were previously underexplored.

Additionally, the study introduces an innovative system for channeling combustion gases, which could be more efficient and practical for industrial applications. This specific approach and its documented benefits contribute valuable insights to the field, supporting the development of more sustainable and efficient charcoal production methods.

Author(s) should state the recommended values for high-quality charcoal according to the referenced NBR standard?.

The standard does not recommend an optimal value for the quality of charcoal, only describing the methodologies for the tests.

 

Did author(s) consider other key tests including bulk density, hardness and reactivity of the charcoal?

These tests could have been carried out, however, we opted for tests that are closer to those required by charcoal producers. Leaving the information closer to their reality.

 

Since there was no critical limit reached in the study, what could be the optimum process parameters for maximum yield? 150 C for 30 mins could just be at the lower end of high-quality charcoal production.

 

Line 237: There is no equation 5.

The friability test was described in the paragraph, so it is not necessary to include the equation. Therefore, the reference to "equation 5" was removed.

 

Lines 286-289: It is not possible to read the results from Fig. 5.

We have increased the size of figures 5 and 6.

 

Lines 357-359: Invalid conclusion because there is no wood cell wall compositional analysis conducted in the study. 

The sentence with this statement has been removed.

 

Line 362: Author(s) should be consistent with the unit for calorific value (HHV).

Moisture content values, if available should be added to Table 2.

we corrected the error of the calorific value unit

 

Table 2: High VM may lead to sparking and unwanted emission levels in industrial application. What can author(s) do to ameliorate this?

When using charcoal, the material's combustion process is controlled so that there is no unnecessary loss of energy. Furthermore, the values ​​found do not present this problem.

Reviewer 2 Report

Comments and Suggestions for Authors

Manuscript ID: sustainability-3478825

Title: How the furnace system improves charcoal production by utilizing process residues, a circular economy approach

Authors: Angélica de Cássia Oliveira Carneiro et al.

 

Line 49. Change reference [4] for 2023 or 2024 year.

Line 41. Avoid more than 3 references for a fact in one sentence. A maximum of 3 in a sentence is allowed for Sustainability. Describe this information in detail.

Introduction. The authors have not provided detailed values for the processes of charcoal production described. It is necessary to add more values: technological parameters, temperatures, duration, etc.

Section 2. Why didn’t authors use the TG/DSC analyses for the carbonization of the wood samples?

Section 3. Figure 5c and Figure 6b. Why is there such a big temperature extremum in the second stage of carbonation?

Table 1. Why the semi-carbonized wood yield for 120 °C and 15 h was higher compare to the 22.5 and 30 h?

Section 3.4. What is the best parameters for charcoal production according authors opinion?

 

Technical errors:

Line 25. Change “hours” to “h” in all article text.

Line 137. Change “meters” to “m” in all article text.

Lines 213, 216, 219. Change “equations 1” to (1), etc.

Author Response

All changes suggested by reviewer 2 are highlighted in green.

 

Line 49. Change reference [4] for 2023 or 2024 year.

The article with this reference was published in 2020, so the authors did not change the date

 

Line 41. Avoid more than 3 references for a fact in one sentence. A maximum of 3 in a sentence is allowed for Sustainability. Describe this information in detail.

The error was fixed, we only put three references

 

Section 2. Why didn’t authors use the TG/DSC analyses for the carbonization of the wood samples?

Thermogravimetric analysis helps to understand wood during the carbonization process

 

Section 3.4. What is the best parameters for charcoal production according authors opinion?

Gravimetric yield is the best quantitative parameter, while fixed carbon content is the best qualitative parameter.

 

Technical errors:

Line 25. Change “hours” to “h” in all article text.

The suggestion was accepted

 

Line 137. Change “meters” to “m” in all article text.

The suggestion was accepted

 

Lines 213, 216, 219. Change “equations 1” to (1), etc

The suggestion was accepted

Reviewer 3 Report

Comments and Suggestions for Authors

After reading your article, I can say that it is worthy of publication in the journal. But you can improve the quality of the article according to my comments: 1. Clearly articulate the unique contributions of the proposed kiln system compared to existing designs. 2. Include more detailed comparisons with previous studies to strengthen the discussion. 3. Justify the choice of 120°C and 150°C as the selected drying temperatures. 4. Provide additional details to ensure that the methodology is fully reproducible. 5. Elaborate on why Eucalyptus sp. was chosen as the primary raw material for the study. 6. Refine the description of the statistical methods to improve their clarity. 7. Consider adding a cost-benefit analysis of the proposed approach for practical relevance. 8. Strengthen the link between the research findings and broader sustainability objectives. 9. Ensure consistency in the use of units and terminology across the manuscript. 10. Improve the quality of the figures by enhancing labels and legends for better interpretation. 11. Address potential limitations and risks associated with the system’s implementation. 12. Discuss the environmental impact of combustion gas emissions in greater detail. 13. Assess whether the proposed technology is scalable for industrial use. 14. Provide more specifics on the tools and methods used for temperature monitoring.

Author Response

All changes suggested by reviewer 3 are highlighted in gray.

 

Clearly articulate the unique contributions of the proposed kiln system compared to existing designs. 

The penultimate paragraph of the introduction has been rewritten

Justify the choice of 120°C and 150°C as the selected drying temperatures. 

This temperature was selected to facilitate the drying of the wood while minimizing structural damage.

 

Elaborate on why Eucalyptus sp. was chosen as the primary raw material for the study. 

Eucalyptus is the main species used in the production of charcoal in Brazil

this information has been added to the manuscript

 

Consider adding a cost-benefit analysis of the proposed approach for practical relevance. 

This stage of the project focused on creating the methodology, ensuring its efficiency, there is the possibility of other researchers analyzing the costs

 

Strengthen the link between the research findings and broader sustainability objectives. 

Ensure consistency in the use of units and terminology across the manuscript. 

The units were standardized in the manuscript

 

Improve the quality of the figures by enhancing labels and legends for better interpretation. 

The size of the figures has been changed

 

Address potential limitations and risks associated with the system’s implementation. 

Discuss the environmental impact of combustion gas emissions in greater detail. 

Assess whether the proposed technology is scalable for industrial use. 

Limitations and Potential Risks

 

Although the furnace system has shown promising results, it is important to recognize the potential limitations and risks associated with its implementation:

 

Initial Investment: Constructing a furnace system with additional components for wood drying may require a higher initial investment compared to traditional carbonization furnaces. Operational Complexity: The modified furnace system introduces additional operational complexities, such as gas flow control and temperature monitoring, which may require specialized training for operators. Maintenance: Regular maintenance of gas ducts, fans, and other components is crucial to ensure optimal performance and prevent potential leaks or malfunctions. Safety: Handling combustion gases and high temperatures requires strict safety measures to protect workers from potential hazards.

 

Environmental Impact of Combustion Gas Emissions

 

Using combustion gases for wood drying offers significant environmental benefits, such as reducing greenhouse gas emissions by utilizing a byproduct of the carbonization process. However, it is essential to consider the environmental impact of combustion gas emissions in greater detail:

 

Composition of Combustion Gases: The composition of combustion gases can vary depending on the type of wood used and carbonization conditions. Analyzing the composition of the gases can help identify potential pollutants and optimize the combustion process to minimize harmful emissions. Filtration and Cleaning Systems: Implementing filtration and cleaning systems for combustion gases can further reduce pollutant emissions, such as particulate matter and volatile organic compounds (VOCs). Carbon Dioxide (CO2) Emissions: Although using biomass for charcoal production is considered carbon-neutral, it is important to monitor and account for CO2 emissions from the combustion process to assess the overall environmental impact.

 

Scalability for Industrial Use

 

The proposed technology demonstrates significant potential for scalability for industrial use:

 

Modular Design: The modular design of the furnace system allows for easy expansion and replication on an industrial scale. Flexibility: The system can be adapted for different types of wood and production capacities, making it suitable for various industrial applications. Automation: Automating processes such as gas flow control and temperature monitoring can improve efficiency and reduce operational costs on an industrial scale. Integration with Other Processes: The system can be integrated with other industrial processes, such as energy generation and chemical production, to optimize resource utilization and reduce environmental impact.

 

 

Provide more specifics on the tools and methods used for temperature monitoring.

Temperature control was carried out using thermocouples installed in various locations within the carbonization furnace, drying oven, and pipelines.

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Author(s),

I have no further comments. 

Reviewer 2 Report

Comments and Suggestions for Authors

The authors made changes according to the recommendations of the reviewers. In this form, the article can be accepted.

Reviewer 3 Report

Comments and Suggestions for Authors

I think that article can be published in this form.