Solid Biofuel from the Amazon: A Circular Economy Approach to Briquette Production from Wood Waste

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

-The introduction section should be developed especially about torrefaction studies and the importance of the study should be emphasized.

-If possible, ICP-OES analyses should be undertaken to determine the chemical changes in the briquettes on torrefaction used in the study, as well as FT-IR for the change of bond groups and mineral elements present in them.

-The method of referencing in the study should be reduced to a single one. please check the section 4.1. 

-Some of the findings contradict the sentence in the introduction: "This results in a material with higher calorific value and low hygroscopicity, enhancing its potential for energy generation". The reason for this should be explained in detail in the discussion.

-In the conclusion part, a precise and clear result is given for each tree type. For example, the most suitable torrefaction for peroba mica species should be 14 MPa for briquette production at 220 C.

Author Response

Changes suggested by the reviewer are marked in Yellow in the manuscript

-The introduction section should be developed especially about torrefaction studies and the importance of the study should be emphasized.

Information about the torrefaction process has been added, changes are marked in yellow

 

“Torrefaction is a thermal process that involves heating biomass to temperatures up to 300°C in an oxygen-free environment. This process removes moisture and volatile com-pounds, resulting in a dry, energy-dense, and hydrophobic material that is easier to store, transport, and grind compared to untreated biomass. Torrefied biomass has a higher cal-orific value and improved combustion properties, making it an attractive alternative to coal in power generation [15,16]. Additionally, it reduces the challenges associated with biomass variability and enhances the efficiency and reliability of biomass energy systems [17], by converting raw biomass into a more uniform and stable form, torrefaction contrib-utes to the optimization of biomass as a renewable energy source, facilitating its integra-tion into existing energy infrastructures Torrefaction for 1.2 h at 260 °C increased the the higher calorific value in 20% of Oak wood [15], for spruce wood, grass and rice husk, Tor-refaction at 300 °C increased the calorific value by 22.35 and 13% , respectively [17].”

 

-If possible, ICP-OES analyses should be undertaken to determine the chemical changes in the briquettes on torrefaction used in the study, as well as FT-IR for the change of bond groups and mineral elements present in them.

Sorry. but we are unable to carry out these tests

 

-The method of referencing in the study should be reduced to a single one. please check the section 4.1. 

We have corrected the error, the changes are marked in yellow.

 

-Some of the findings contradict the sentence in the introduction: "This results in a material with higher calorific value and low hygroscopicity, enhancing its potential for energy generation". The reason for this should be explained in detail in the discussion.

The torrefaction process primarily degrades the hemicellulose and cellulose molecules in the biomass. These molecules are rich in oxygen and hydroxyl groups; therefore, their removal increases the calorific value and decreases the hygroscopicity of the material. The information from the introduction and the results was reorganized for coherence. Therefore, the penultimate paragraph of the introduction was rewritten

 

-In the conclusion part, a precise and clear result is given for each tree type. For example, the most suitable torrefaction for peroba mica species should be 14 MPa for briquette production at 220 C.

Information has been added

“Based on the density and strength of the briquettes, we recommend producing briquettes with 14 MPa pressure and torrefaction at 200°C for Aspidosperma populifolium (Peroba Mi-ca) and Dipteryx odorata (Cumaru). For Mimosa scabrella (Bragatinga), we recommend us-ing the material without torrefaction and pressing it at 14 Mpa”

Reviewer 2 Report

Comments and Suggestions for Authors

Reviewer Comments

Dear author(s):

The study aimed to measurement evaluate the physical, chemical, and energetic properties of wood residues by torrified and their use in the briquettes production. The manuscript demonstrates novelty and is consistent with the journal's scope. However, substantial improvements in presentation are necessary.

abstract:

In my opinion, in this section, it is recommended to state the important findings in this study include the values ​​of the properties of quality briquettes.

Introduction:

1.     According to my interpretation, the author states on page 2, line 52, that torrefaction takes place within the temperature range of 225 to 300°C in an environment devoid of oxygen. However, the author conducted the process at temperatures lower than 225 °C. Is it accurate to refer to this process as torrefaction? or still carbonization step? Kindly provide a clarification to prevent any misinterpretations.

2.     The state of the art seems lacking, and it is necessary to carry out additional gap analysis with previous research related to torrefaction using biomass/other wood waste raw materials.

Materials and methods:

1.     In this section, the dimensions of the wood waste are specified as 60 cm in length, 7.5 cm in width, and 2 cm in thickness. However, the graphical abstract clearly indicates the utilization of sawdust. Which sample is appropriate for use sawdust or wood waste with big dimension?

2.     What was the number of repetitions performed in this study?

3.     What experimental design and statistical analysis did you employ to assess your data using the Tukey test with a 5% confidence level in Table 1? Provide a detailed explanation in the methodologies section.

Result and discussion:

1.     In the 4.1 (Biomass characterization), page 7, line 164 and 166, please see instructions for authors, how to compose an accurate references https://www.mdpi.com/journal/forests/instructions

2.     For every instance in which the author applies repetition, each datum must be accompanied by its associated standard deviation. (please complete standard deviation in Table 1, Figure 1 A, B, C. D, E, F, and H).

3.     Include a discussion of the research findings in accordance with the statistical analysis that was employed.

Author Response

Changes suggested by the reviewer are marked in red in the manuscript

abstract:

In my opinion, in this section, it is recommended to state the important findings in this study include the values ​​of the properties of quality briquettes.

Density and compressive strength values ​​have been added to the abstract

“Briquettes showed optimal characteristics at compression pressures of 10 and 14 MPa, resulting in increased density (between 1.06 and 1,15 g.cm^-3) and compression strength (between 6.48 and 21.02 MPa).”

Introduction:

1. According to my interpretation, the author states on page 2, line 52, that torrefaction takes place within the temperature range of 225 to 300°C in an environment devoid of oxygen. However, the author conducted the process at temperatures lower than 225 °C. Is it accurate to refer to this process as torrefaction? or still carbonization step? Kindly provide a clarification to prevent any misinterpretations.

Torrefaction goes up to a temperature of 300°C, where the thermal decomposition reaction is in the endothermic phase, the minimum torrefaction temperature varies depending on the author, so we changed the sentence, saying only that torrefaction occurs up to 300 degrees celcius

“Torrefaction occurs at temperatures up to 300°C in an oxygen-free atmosphere”

2. The state of the art seems lacking, and it is necessary to carry out additional gap analysis with previous research related to torrefaction using biomass/other wood waste raw materials.

We have added the results of biomass torrefaction in other scientific works.

“Torrefaction occurs at temperatures up to 300°C in an oxygen-free atmosphere. Dur-ing this process, cellulose and hemicellulose are degraded more than lignin, increasing the carbon content [15,16]. This results in a material with higher calorific value and low hygroscopicity, enhancing its potential for energy generation [17]. Torrefaction for 1.2 h at 260 °C increased the the higher calorific value in 20% of Oak wood [15], for spruce wood, grass and rice husk, Torrefaction at 300 °C increased the calorific value by 22.35 and 13%, respectively [17].”

Materials and methods:

1. In this section, the dimensions of the wood waste are specified as 60 cm in length, 7.5 cm in width, and 2 cm in thickness. However, the graphical abstract clearly indicates the utilization of sawdust. Which sample is appropriate for use sawdust or wood waste with big dimension?

The samples measuring 60 cm in length, 7.5 cm in width, and 2 cm in thickness were crushed and the sawdust was used in the production of briquetes. The information has been added to the manuscript

“The samples measuring 60 cm in length, 7.5 cm in width, and 2 cm in thickness were torrefied, then air-conditioned to determine the equilibrium moisture content of the wood. Finally, the samples were crushed and the sawdust was used in the production of briquettes.”

2. What was the number of repetitions performed in this study?

Ten briquettes were produced per treatment. The number of repetitions was added to the manuscript

“Briquettes with 32.5 mm diameter and 17.08 mm length were produced with 17 g of wood particles in a laboratory equipment (Lippel, Model LB-32) at 120 °C for 7 minutes pressing time and 6 minutes cooling time. Three pressures were tested: 7, 10 and 14 MPa (based on preliminary studies). These pressure and cooling time conditions were defined from preliminary tests to avoid briquettes with cracks or fissures. Ten briquettes were produced per treatment. Briquetting mass loss was calculated gravimetrically.”

3. What experimental design and statistical analysis did you employ to assess your data using the Tukey test with a 5% confidence level in Table 1? Provide a detailed explanation in the methodologies section.

The information has been added to the manuscript

“Statistical analysis

The experimental design used was completely randomized (DIC). The data were submitted to tests for homogeneity of variances (Bartlett test, 5% of significance) and nor-mality (Shapiro-Wilk test, 5% of significance) prior to variance analysis. The contrast be-tween the means of the parameters evaluated was determined by the tukey test at 5% sig-nificance level.”

Result and discussion:

1. In the 4.1 (Biomass characterization), page 7, line 164 and 166, please see instructions for authors, how to compose an accurate references

https://www.mdpi.com/journal/forests/instructions

The text was corrected in accordance with the Sustainability.

2. For every instance in which the author applies repetition, each datum must be accompanied by its associated standard deviation. (please complete standard deviation in Table 1, Figure 1 A, B, C. D, E, F, and H).

The authors decided to put the coefficient of variation, the values ​​are in superscript. We also transformed figure 1 into a table to place the statistical test and the coefficient of variation

3. Include a discussion of the research findings in accordance with the statistical analysis that was employed.

The discussion has been reformulated, the changes are marked in red

 

Reviewer 3 Report

Comments and Suggestions for Authors

The topic of the research work and manuscript is really interesting and provides new information. However, there are several issues to be addressed towards its quality improvement before publication. Could the conditions chosen to be applied and described in the manuscript (180 to 220°C for sixty minutes under a nitrogen atmosphere) be considered a torrefaction process of biomass? Since, the authors also refer that "Torrefaction occurs between 225 and 300°C in an oxygen-free atmosphere". Under the proposed conditions 180-220 oC, we usually treat thermally the sawnwood, towards the enhancement of the material's properties as a solid structural material. Why would you use the gross heating value instead of net one? In line 22, probably the word "test/testing" would be appropriate to be added. In line 23, before and after torrefaction? Leave space between the value and celsius symbol. In line 24, is it "densifity"? What about the ash content of these materials, which contributes one of the most restricting factor towards biomass / wood wastes utilization in biofuels production?Since your provided values of ash in the results, make a brief reference to this parameter in the abstract and introduction. Add more keywords, probably biofuels, heating value etc. In line 38, please add the relevant work of  https://doi.org/10.1002/bbb.2235 as a reference. The term hemicellulose is better to be used in plural form due to the nature of this chemical constituent. An in-depth state-of-the-art analysis including literature review is missing from the introduction chapter. This would definitely highlight as well the potential knowledge and research gap on this field. In line 52, what about the changes in extractives during the process? In lines 52-53, you rather avoid providing part of your results. What do you mean by "wood residues"?also brances, folliage or bark material are included in this material? In line 56, torrefied and non-torrefied as well as a reference? Provide details for the climatic chamber. Since you intend to work with residues, why did you treat the material in dimensions of 60 cm × 7.5 cm × 2 cm? Which were the conditions in the chamber for the moisture content decrease? In line 92, non-treated as well? ISO 11093-9 should be provided in the references list as well. Did you apply any statistical analysis on the results of this work? Provide details on the measurement of fixed carbon, volatile material, and ash content, standards used etc. Could you provide the standard deviation values on the bars of charts? Are there any relevant studies in the literature concerning the utilization of these species? Try to use the same format in the different charts (times new roman) and also in the references provided in the text, you presented both [] and parenthesis with surname-year of publication. . How would you explain the inrease of EMC in densified material of higher pressure applied? In 259-260 lines, what do you mean by "considering the briquette's final use"? 

 

 

Comments on the Quality of English Language

I would propose to the authors to use "higher" instead of "greater: in the text. In line 54, probably instead of energetic, you could use "combustion characteristics". In biomass's, please remove the 's.

Author Response

Changes suggested by the reviewer are marked in purple in the manuscript

The topic of the research work and manuscript is really interesting and provides new information. However, there are several issues to be addressed towards its quality improvement before publication.

Could the conditions chosen to be applied and described in the manuscript (180 to 220°C for sixty minutes under a nitrogen atmosphere) be considered a torrefaction process of biomass?

The torrefaction process involves subjecting the biomass to a temperature of up to 300 degrees in an oxygen-free atmosphere. This condition was met, and furthermore, the quality of the raw material was altered, so the working conditions were adequate.

Since, the authors also refer that "Torrefaction occurs between 225 and 300°C in an oxygen-free atmosphere". Under the proposed conditions 180-220 oC, we usually treat thermally the sawnwood, towards the enhancement of the material's properties as a solid structural material.

The minimum torrefaction temperature varies according to different authors; however, there is a consensus that the maximum temperature is 300°C. Therefore, the sentence has been revised.

Why would you use the gross heating value instead of net one?

The net heating value depends on the hydrogen content, a parameter we are unable to evaluate; therefore, we used the gross heating value.

In line 22, probably the word "test/testing" would be appropriate to be added.

The suggestion was accepted.

In line 23, before and after torrefaction?

The suggestion was accepted.

In line 24, is it "densifity"?

The correct term is energy density, the error has been corrected

What about the ash content of these materials, which contributes one of the most restricting factor towards biomass / wood wastes utilization in biofuels production?

Since your provided values of ash in the results, make a brief reference to this parameter in the abstract and introduction. Add more keywords, probably biofuels, heating value etc.

The suggestion was accepted.

The term hemicellulose is better to be used in plural form due to the nature of this chemical constituent.

The suggestion was accepted

An in-depth state-of-the-art analysis including literature review is missing from the introduction chapter. This would definitely highlight as well the potential knowledge and research gap on this field.

The introduction has been reworked

In line 52, what about the changes in extractives during the process?

The authors focused on cellulose, hemicellulose, and lignin because they are the most important constituents in wood, and their alterations have the greatest impact on the final quality of the product.

In lines 52-53, you rather avoid providing part of your results.

The paragraph was reformulated to meet the request

What do you mean by "wood residues"?also brances, folliage or bark material are included in this material?

The residues are parts of wood that remained from the wood sawing process, not including branches and leaves. This information was added to the manuscript.

In line 56, torrefied and as well as a reference?

The non-torrefied one was considered a reference

Try to use the same format in the different charts (times new roman) and also in the references provided in the text, you presented both [] and parenthesis with surname-year of publication.

The suggestion was accepted

How would you explain the inrease of EMC in densified material of higher pressure applied?

The use of the graph and the scale led to this type of interpretation. To correct the error, we created a table and conducted a statistical test. In this way, it was found that the increase in pressure did not alter the equilibrium moisture content of the samples.

In 259-260 lines, what do you mean by "considering the briquette's final use"?

Briquettes can be used for a variety of purposes, such as residential heating or food preparation, so the end use must be considered.

Reviewer 4 Report

Comments and Suggestions for Authors

The research results presented in the manuscript "Solid Biofuel from the Amazon: A Circular Economy Approach to Briquette Production from Wood Waste" are valuable.

This is an interesting research topic.

The reviewer thinks it would be interesting to compare the performance of burning briquettes with direct biomass burning with regard to energy consumption for briquette preparation.

My comments and recommendations:

Comment 1: The whole paper needs English editing.

Comment 2: The title, abstract and keywords correspond to the aims and objectives of the manuscript. The reviewer thinks that it would be appropriate to add to the keywords: “Wood Waste Management” and remove “Waste Management”.

Comment 3: The abstract is informative and contains the main findings of the article. The Introduction could be expanded with the knowledge of other authors who dealt with the properties of wood waste from the other wood species with regard to its use for energy purposes.

Comment 4: The Materials and Methods:

2.1 Wood torrefaction: The reviewer recommends stating the density of the wood species used, as the effect of the treatment and the quality of the briquettes largely depends on it. State how the moisture content of the wood residues was determined.

Line 59: I suggest: Untreated wooden residues dimensions …

Specify the pressure value (Line 70).

2.2 Biomass characterization: Line 81: … not eq. 1 but …(1).

2.4 Briquettes properties: Line 105: …. MA-835/450UR)... close the parenthesis.

Why was the density of briquettes determined by immersion in mercury? It is dangerous for health! It is also possible to use other, safe liquids.

Describe a method of determining density and give an equation. It was about the buoyancy method?

Line 115: not eq. 2  but …(2).

Line 125: I think that five measurement repetitions are not enough.

Comment 5: The Results

3.2. Briquette properties: Figure 1 a) and Line 166: In a scientific article, it is not standard to use multiples and parts of the original unit. The reviewer suggests writing the density unit in kg.m^-3.

Comment 6: The Discussion

4.1. Biomass characterization: Lines 176 and 178: References should be numbered indicated by a numeral or numerals in square brackets.

4.2. Briquette properties: Lines 214 and 215: I think the expression ...the material's energy density" ... is not correct. I assume the authors meant ... "energy efficiency".

Line 237: Reference should be numbered indicated by a numeral or numerals in square brackets.

Comment 7: The Conclusions reflect the main findings of the manuscript.

Comment 8. The References cited in this manuscript are appropriate and relevant to presented area of research.

 

Best regards,

Comments on the Quality of English Language

Moderate editing of English is required

Author Response

Changes suggested by the reviewer are marked in gray in the manuscript

My comments and recommendations:

Comment 1: The whole paper needs English editing.

The manuscript has undergone an English revision.

Comment 2: The title, abstract and keywords correspond to the aims and objectives of the manuscript. The reviewer thinks that it would be appropriate to add to the keywords: “Wood Waste Management” and remove “Waste Management”.

The suggestion was accepted

Comment 3: The abstract is informative and contains the main findings of the article. The Introduction could be expanded with the knowledge of other authors who dealt with the properties of wood waste from the other wood species with regard to its use for energy purposes.

The suggestion was accepted

“ However, the low energy density of the residues generated in wood processing limit their transport and utilization for bioenergy [10–12]. To overcome these issues, it is possi-ble to torrefy and compact the biomass. The briquette production process involves press-ing the biomass at 120°C and 80 kgf.cm-2, forming blocks of defined volume with greater particle size homogeneity, lower moisture content, and higher density compared to the raw material [13,14]. Torrefaction for briquette production shows potential for widely used species in Brazil in large plantations, such as sugarcane, coffe husk ans eucalyptus [11-13], However, studies on the use of residues from species derived from native forest management plans have not kept up with the demand.”

Comment 4: The Materials and Methods:

2.1 Wood torrefaction: The reviewer recommends stating the density of the wood species used, as the effect of the treatment and the quality of the briquettes largely depends on it. State how the moisture content of the wood residues was determined.

Line 59: I suggest: Untreated wooden residues dimensions …

The suggestion was accepted

Specify the pressure value (Line 70).

The pressure was reduced close to zero. The suggestion was accepted.

2.2 Biomass characterization: Line 81: … not eq. 1 but …(1).

The suggestion was accepted.

2.4 Briquettes properties: Line 105: …. MA-835/450UR)... close the parenthesis.

The suggestion was accepted.

Why was the density of briquettes determined by immersion in mercury? It is dangerous for health! It is also possible to use other, safe liquids.

It is possible to use other liquids for the immersion test, however, mercury shows good results because, due to its high density, it does not penetrate the test specimen. We can ensure that all safety procedures were carried out during the test.

Describe a method of determining density and give an equation. It was about the buoyancy method?

The equation has been added

Line 115: not eq. 2  but …(2).

The suggestion was accepted

Line 125: I think that five measurement repetitions are not enough.

We made a mess, in fact, ten repetitions were performed per treatment. the error has been corrected

Comment 5: The Results

3.2. Briquette properties: Figure 1 a) and Line 166: In a scientific article, it is not standard to use multiples and parts of the original unit. The reviewer suggests writing the density unit in kg.m^-3.

The suggestion was accepted

Comment 6: The Discussion

4.1. Biomass characterization: Lines 176 and 178: References should be numbered indicated by a numeral or numerals in square brackets.

The suggestion was accepted. Ajeitar hoje a tarde

4.2. Briquette properties: Lines 214 and 215: I think the expression ...the material's energy density" ... is not correct. I assume the authors meant ... "energy efficiency".

The suggestion was accepted

Line 237: Reference should be numbered indicated by a numeral or numerals in square brackets.

The suggestion was accepted. Ajeitar hoje a tarde

Comment 7: The Conclusions reflect the main findings of the manuscript.

Thanks

Comment 8. The References cited in this manuscript are appropriate and relevant to presented area of research.

Thanks

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Thank you for considering my suggestions.

Author Response

The experiment produced briquettes from different wood species. For each species, briquettes were produced without torrefaction and torrefied at three distinct temperatures, in addition to using three different compaction pressures. Therefore, considering the torrefaction temperature, the treatment without torrefaction can be considered as the control, which can also be applied to the biomass characterization. Considering the compaction pressure in briquette production, it is impossible to produce them without pressure, hence there is no treatment with zero pressure. In this context, the authors believe that all possible measures to have a control treatment in the experiment were taken.

Reviewer 3 Report

Comments and Suggestions for Authors

Almost all the changes were followed by the authors, though in a rather rough not a thorough and detailed way. It could be considered for publication in this journal. 

Comments on the Quality of English Language

Acceptable

Author Response

The experiment produced briquettes from different wood species. For each species, briquettes were produced without torrefaction and torrefied at three distinct temperatures, in addition to using three different compaction pressures. Therefore, considering the torrefaction temperature, the treatment without torrefaction can be considered as the control, which can also be applied to the biomass characterization. Considering the compaction pressure in briquette production, it is impossible to produce them without pressure, hence there is no treatment with zero pressure. In this context, the authors believe that all possible measures to have a control treatment in the experiment were taken.