Evaluation of the Physical, Mechanical, and Calorific Properties of Briquettes with or without a Hollow Made of Wheat (Triticum aestivum L.) Straw Waste

Round 1

Reviewer 1 Report

In this paper, the physical-mechanical and thermal properties of two wheatgrass type briquette are investigated and compared with beech. Some useful results will be useful for practice. They may be considered for publication with the following revisions：

1.Materials and Methods section part: the proximate analysis and element analysis of raw materials should be given.

2. Section 3.1 " Moreover, the very large standard deviation of the inner diameter of the lighter can be explained by the irregular radial expansion of the lighter toward their hollow." Please explain the meaning of this sentence.

3. Section 3.2 Please explain the effect of density size and what kind of results you want to get.

4.The label of the chart is wrong, such as there are two figures 1 and two figures 2, the first table is table 2, please double check.

5.Unify figure and figure, change the table into a three-line table, and center the chart.

6.Section 3.6, line 456 draws on some elements of linear geometry, please explain further, and what Table V is fitted by.

7.Formatting issues, there are two 3.6 chapters, and the 3.5 after 3.6 chapters is wrong.

8.Fig 7: I do not understand the meaning of Fig 7 here, and it does not seem to help readers understand this paper.

9.The conclusion states that its properties and uses are comparable to those of type briquette obtained from beech wood chips or fire wood. The paper states that the ash content of straw is 10 times higher than that of beech wood chips and that ash content also has a significant effect on properties, please explain how it will affect the white briquette utilization.

10.Some references is suggested to cited:

Review on biomass metallurgy: Pretreatment technology, metallurgical mechanism and process design, Int. J. Miner. Metall. Mater., 29(2022), No. 6, pp. 1133-1149.

Author Response

The authors hereby thank the reviewer for his work in evaluating the paper and assure him that we have read the observations and proposals very carefully, and have favorably resolved each of these requirements.

1.Materials and Methods section part: the proximate analysis and element analysis of raw materials should be given.

Author response: At point 2.7 it has added "proximate and elemental analysis". Other explanatory elements were also added in this chapter, which sustain the new problems. “The proximate analysis usually contains moisture content, volatile matter, fixed carbon and ash content determination. When the moisture content is zero, the sum of the other 3 matter must be 100%. The elemental analysis contain evaluates the main chemical elements as carbon, hydrogen, oxygen, ash, etc”.

2. Section 3.1 " Moreover, the very large standard deviation of the inner diameter of the lighter can be explained by the irregular radial expansion of the lighter toward their hollow." Please explain the meaning of this sentence.

Author response: In this subchapter of paper, in the area of the mentioned expression, some additions were made, for a better understanding. The explanation of these irregularities was given by the fact that the same return stresses of the material after pressing act on the inside on a smaller surface producing larger and irregular deformations. Adding: “Normally, the stresses on the outside and inside of the briquette should be equal, but due to the smaller surface of application of these stresses on the inside (a surface 2.6 times smaller), their influence will be greater. The effect is also amplified by the fact that the direction of these efforts is radial, appearing more prominent areas and less prominent areas.”

3. Section 3.2 Please explain the effect of density size and what kind of results you want to get.

Author response: Some adds were made in this section “The densities of the 3 types of briquettes were different, for the same reasons. Regarding the two types of briquettes without voids T1 and T2, the thinner briquettes had a higher density, because the same pressure of the piston acts on a smaller surface. For the same reason, the density of T3 hollowed briquettes was slightly higher than the one T2 without voids, even though the outer diameter was almost the same.”

4.The label of the chart is wrong, such as there are two figures 1 and two figures 2, the first table is table 2, please double check.

Author response: All table and figures numbers were checked and revised. Anyway, this was needed as the first two figures were deleted.

5.Unify figure and figure, change the table into a three-line table, and center the chart.

Author response: The necessary changes were made. All tables and figures were put in concordance with the requirements of journal.

6.Section 3.6, line 456 draws on some elements of linear geometry, please explain further, and what Table V is fitted by.

Author response: Some explanations were inserted: “By substituting the percentage values of the carbon, hydrogen and oxygen content in relation (15), the predicted value of the calorific value will be obtained, value placed in the last column of table 2. Based on these values (of the carbon content and the calorific value) the graph from Fig. 6 was obtained”.

7.Formatting issues, there are two 3.6 chapters, and the 3.5 after 3.6 chapters is wrong.

Author response: The necessary formatting aspects were made in the new version of paper.

8.Fig 7: I do not understand the meaning of Fig 7 here, and it does not seem to help readers understand this paper.

Author response: For a better understanding the next paragraph was added: “Fig 7 is a statistical diagram, which reveals the average value, standard deviation, number of tests, p-value and Anderson-Darling's coefficient. Based on these values, the statistical analysis of the values was made and the range of variation of the values was found for a confidence interval of 95%.”

9.The conclusion states that its properties and uses are comparable to those of type briquette obtained from beech wood chips or fire wood. The paper states that the ash content of straw is 10 times higher than that of beech wood chips and that ash content also has a significant effect on properties, please explain how it will affect the white briquette utilization.

Author response: In the conclusions part, some additions were made, in order to observe the similarities and differences between the briquettes made of wheat straw and those made of beech. The first 4 conclusions were improved, emphasizing the use of beech remains and, above all, the differences between wheat straw and beech wood, from a calorific and ash content point of views. In this way, the 3-rd and 4-th conclusions underwent the following additions: "The calorific value of 17.69 MJ/kg of wheat straw was almost similar to that of beech remains, with a decrease of only 3.7%" and “Ash collection will be done at shorter intervals, and larger and covered storage spaces must be taken into consideration”.

10.Some references is suggested to cited:

Review on biomass metallurgy: Pretreatment technology, metallurgical mechanism and process design, Int. J. Miner. Metall. Mater., 29(2022), No. 6, pp. 1133-1149.

Author response: This suggested reference was added at position 58. Also, this reference was cited in the text.

Authors

Reviewer 2 Report

The language use proficiency needs significant improvement and it currently hinders the proper reviewing of this manuscript. There are a few major revisions required as follows:

1) Introduction is too long and contains unrelated information. For example, why mention the yield of Miscanthus or willow when this study is about wheat straw! Basic details like energy conversion coefficients is included, which is unnecessary. Please provide only the most important and the most recent info, and cut the introduction short by at least 2 paragraphs.

2) Please remove Figure 1 - the carbon cycle. It is too general and not even cited in the text.

3) The figure numbers are in wrong order - please correct. Also, please make sure that the figure numbers are cited in the text.

4) The materials and methods are too long. If you are citing a different work, there is no need to provide detailed information. Please move some of the unnecessary information to the supplementary data.

5) The figure captions and legends must be self sufficient. What does 71 si 26 mm mean? Or what about CDF? Please provide the full forms, either in the caption or in the legend. If different treatment names are included, please provide their information too.

6) Why call the treatments as T1, T2, T3 in Figure 3 but not in Figure 2? Since you have already defined the parameters for T1, T2 and T3, in the beginning of Results, please stick to these terminology.

7) I strongly disagree with the fact that you have extrapolated the ash and calorific value to the area of crop cultivation, i.e., kg/ha and MJ/ha. This is an unrelatable quantity and restricts comparison to other reports. Please only use the MJ/kg and % values for calorific value and ash content, respectively.

Author Response

Reviewer 2

The authors hereby thank the reviewer for his work in evaluating the paper and assure him that we have read the observations and proposals very carefully, and have favourably resolved each of these requirements.

The language use proficiency needs significant improvement and it currently hinders the proper reviewing of this manuscript.

Authors answer: The paper has been revised from the point of view of the English language by a teacher specialized in technical translations.

1) There are a few major revisions required as follows: Introduction is too long and contains unrelated information. For example, why mention the yield of Miscanthus or willow when this study is about wheat straw! Basic details like energy conversion coefficients is included, which is unnecessary. Please provide only the most important and the most recent info, and cut the introduction short by at least 2 paragraphs.

Authors answer: The introduction part was substantially shortened, from about 100 lines to 60 lines (just a little over a page). Substantial changes were necessary to restore the content of this introduction. Also, the calorific transformation coefficients were eliminated. as was the figure with the carbon circuit in nature. Only 2 paragraphs were finally obtained.

2) Please remove Figure 1 - the carbon cycle. It is too general and not even cited in the text.

Authors answer: The figure 1 with the carbon circuit in nature was erased.

3) The figure numbers are in wrong order - please correct. Also, please make sure that the figure numbers are cited in the text.

Authors answer: The figure number was fixed, especially due to the fact that two of them were eliminated. Also, all figures were cited in the paper.

4) The materials and methods are too long. If you are citing a different work, there is no need to provide detailed information. Please move some of the unnecessary information to the supplementary data.

Authors answer: Some of method elements were shorted or eliminated (about 16 rows). Also, the briquetting press with crank mechanism has been removed, including the explanations about it. Only the elements necessary for a good reproduction of the research approach have remained.

5) The figure captions and legends must be self sufficient. What does 71 si 26 mm mean? Or what about CDF? Please provide the full forms, either in the caption or in the legend. If different treatment names are included, please provide their information too.

Authors answer: The data that were required were added for each figure (especially Fig 2, Fig 3 and Fig 4).

6) Why call the treatments as T1, T2, T3 in Figure 3 but not in Figure 2? Since you have already defined the parameters for T1, T2 and T3, in the beginning of Results, please stick to these terminology.

Authors answer: Fig 2 was improved, specifying density for T1, T2 and T3 samples.

7) I strongly disagree with the fact that you have extrapolated the ash and calorific value to the area of crop cultivation, i.e., kg/ha and MJ/ha. This is an unrelatable quantity and restricts comparison to other reports. Please only use the MJ/kg and % values for calorific value and ash content, respectively.

Authors answer: In fact, the work extrapolated the calorific value and ash content per surface unit of the wheat plants. The motivation was that in agriculture, both the amount of grain and that of straw is related to the hectare. Therefore, for readers with knowledge and interests in the agricultural field, these data are welcome, and help them in their agricultural activities. Consequently, please allow us to keep these ways of expression, which will help the reader specialized in the agricultural field to understand this issue.

Authors

Reviewer 3 Report

This manuscript evaluates physical, mechanical and calorific properties of briquettes prepared from wheat straw.  This group has previously published a paper on the same topic (Physical and calorific properties of wheat straw briquettes and pellets by Cosmin Spirchez, Aurel Lunguleasa , Constantin Ionescu, and Catalin Croitoru, MATEC Web of Conferences 290, 2019). In the present paper, the briquettes are prepared is various forms.  In addition to physical and calorific properties, mechanical properties are included.  Further, this paper makes no reference to this previous study.  The present paper expands on their previous work and it is important to consider such work for publication.  On the other hand, this paper is so poorly written, it is difficult recommend for publication in the present form.  Therefore, I suggest, authors seriously consider having it edited by a native English speaker.

There are 2 figures with the same number Figure 1.

“Figure 1. The CO2 cycle in nature during the production and combustion of wheat straw” – unnecessary.

“Figure 1. Briquetting machine” is also unnecessary.

All figures should be redone professionally and presented clearly– remove title on top of the figure, properly label the x and the y-axis – e.g., y axis on figures 2 and 3 are Percent- what is it percent of??

Some figures legends written as Figure 1, Figure 2 etc. but some are written as Fig. 4, Fig. 5 etc. – please be consistent.

Figure 5 – has 2 data points in a straight-line? As expected the line as to be straight? What kind of linearity testing are you doing here?

Author Response

Reviewer 3

The authors hereby thank to the reviewer for his work in evaluating the paper and assure him that we have read the observations and proposals very carefully, and have favourably resolved each of these requirements.

1.This manuscript evaluates physical, mechanical and calorific properties of briquettes prepared from wheat straw.  This group has previously published a paper on the same topic (Physical and calorific properties of wheat straw briquettes and pellets by Cosmin Spirchez, Aurel Lunguleasa, Constantin Ionescu, and Catalin Croitoru, MATEC Web of Conferences 290, 2019). In the present paper, the briquettes are prepared is various forms.  In addition to physical and calorific properties, mechanical properties are included.  Further, this paper makes no reference to this previous study.  The present paper expands on their previous work and it is important to consider such work for publication.  On the other hand, this paper is so poorly written, it is difficult recommend for publication in the present form.  Therefore, I suggest, authors seriously consider having it edited by a native English speaker.

Author response:

 -The paper that is mentioned took into consideration some preliminary and experimentally unvalidated research, at a low level, as of a paper usually written for a conference. Other type of briquettes was used. Besides, if you put the two works in the mirror, you can see that there are few similarities, less than 3%.

 -This paper was referenced in the present research.

 -The English grammar constructions were improved by an English teacher specialized in technical translations.     

2.There are 2 figures with the same number Figure 1.

“Figure 1. The CO2 cycle in nature during the production and combustion of wheat straw” – unnecessary.

“Figure 1. Briquetting machine” is also unnecessary.

Author response: The two figures were erased definitively, and the next ones were recounted.  

3.All figures should be redone professionally and presented clearly– remove title on top of the figure, properly label the x and the y-axis – e.g., y axis on figures 2 and 3 are Percent- what is it percent of??

Some figures legends written as Figure 1, Figure 2 etc. but some are written as Fig. 4, Fig. 5 etc. – please be consistent.

Author response:

-The title from the top of Fig 2, Fig 3 and Fig 4 was extracted.

-The abscise and vertical axis of the above 3 figures were unified and clearly presented. E.g., the Oy axis were completed as: Percent of value participation, %. This name is usually used in statistics.

-The writing in the legend of the figures has been unified, according to the requirements of the journal, as Figure 1, Figure 2, etc. Only the abbreviated version was used in the text, Fig. 1, Fig. 2, etc.

4.Figure 5 – has 2 data points in a straight-line? As expected the line as to be straight? What kind of linearity testing are you doing here?

Author response:

• Figures like figure 5 are the most important ones for observing the combustion yield of a lignocellulosic material depending on moisture content. Each woody species or type of fuel has a different diagram. The upper line represents the high calorific value and the lower one represents the lower calorific value. The distances on the horizontal axis, of the intersection of the two lines HCV and LCV, are different from one species to another.
• For a better understanding, I changed the horizontal division unit to 20%. In this way we will easily find for a moisture content of 20% values of HCV around 16 MJ/kg and of LCV of 14 MJ/kg, and in this way for any other value of moisture content. In this way, the combustion efficiency can be evaluated quickly, especially when we have fuel with a high moisture content.

Authors,

Round 2

Reviewer 2 Report

The authors' have adequately addressed this reviewer's concerns. Only minor spell-check is required throughout the manuscript. E.g.:

1) Check the spelling for species 

2) Check the spelling for splitting in Figure 4 caption.

Author Response

Reviewer 2

• Check the spelling for  Authors put “specie”.

Authors: Word “specie” was changed with “material” in Table 2, and with “biomass” in the text.

• Check the spelling for splittingin Figure 4 caption. In Fig 4 caption author put “Splitting”.

Authors: Inside of Fig 4, we change the word “spliting” with correct form “splitting”.

Authors,

Reviewer 3 Report

I have re-reviewed this manuscript and I am very disappointed to report-back my observations (see below).  I am simply reluctant to recommend this paper for publication unless the authors consider the suggestions seriously and make thorough changes.

11.   The recommendation was for major review previously – changes made are minor.  The paper still lacks cohesiveness.  In spite of claiming that that it has been reviewed by native English speaker, the grammatical errors are in plenty that need to be corrected.

22.   While I fully understand the authors may not be native English speakers, it is important to present their work meaningfully. In this regard, in the revised version, English is marginally improved for certain sentences, but still the readability of the manuscript, overall, is extremely poor.  For example, as guidance, here is the abstract re-written form the original with about the same number of words.  Therefore, I suggest the authors simplify the complicated, run-on sentences to improve readability.

Rewritten Abstract:

Large amounts lignocellulosic biomass in the form of straw is leftover after wheat harvesting that could be utilized for beneficial purposes. The latter has led to the emergence of new technologies to make use of this resource.  One such technology currently in use turns the wheat straw into briquettes. The present study, we have prepared and evaluated physical, mechanical and calorific properties of two types of briquettes made of wheat straw.  The two types briquettes prepared were (i) hollow briquettes and (ii) solid briquettes. The densities of these briquettes obtained on a mechanical device with a crank mechanism was 1.169 kg/m3, irrespective of whether the briquettes were hollow or solid. The briquettes densities are consistent with European standards. The calorific value of wheat straw was 17.69 MJ/kg. Although the calorific value was somewhat lower than the beech wood briquettes (18.38 MJ/kg), it is adequate for their combustion in both stoves and thermal power plants. The ash content of wheat straw was 9.1% (~10-fold higher than that of beech wood). The briquettes showed a compressive mechanical strength of 1.15-2.17 N/mm2 and splitting mechanical strength of 0.17-0.39 N/mm2 suggesting that the straw briquettes were well compacted and can be stable during transport and/or other manipulations. In conclusion, wheat straw briquettes have similar physical, mechanical and calorific properties to those prepared from beech wood biomass and a viable solution to replace beech wood briquettes with similar efficiency.

33. The changes suggested for figures previously – they be prepared professionally. it is still not done correctly.  They deleted two figures made some small changes to X and Y axis.  But ignored the rest.  For example;

a.       Why do you need the title “Normal” on top of Figures 2, 3 and 4?

b.       Why do you need the background grid in Figure 5, 6, 7 and 8?

c.       Why do you need the title “Probability plot of ash content   Normal - 95% Cl.  In this figure are you measuring Chlorine (Cl) or what is Cl.  Describe such thing the figure legend after the title.

d.       In figure 8 - Why do you need the line commenting the histograms?

e.       Some of the figure legends are incomplete, e.g., “Figure 9. Content of ash, volatile and fix carbon”   of what?  What is this Fix Carbon?

f.        There are many more things like this that needs fixing in the figures, Tables as well as the text.

44.  Table 2. Modelling the calorific value of wheat straw according to chemical compounds – You are really not modelling anything in this table, you are simply reporting percent composition of “C”, “H”, “O”, “Ash” and calorific values of wheat straw and comparing them to Beech wood and charcoal.  Plus, there are no chemical compounds of any kind analyzed or reported in this table.  So the title makes no sense.  In the previous version – I suggested to have native English speaker rewrite this manuscript for these kinds of reasons.

5. Table 2 and other places you use the word “Specie”.  It should be “Biomass” or something else.  Further, In Table 2 – how is charcoal a Specie or a species? The same word “Specie” is loosely used elsewhere in the text as well.

Author Response

Reviewer 3

11. The recommendation was for major review previously – changes made are minor.  The paper still lacks cohesiveness.  In spite of claiming that that it has been reviewed by native English speaker, the grammatical errors are in plenty that need to be corrected.

Authors response: The work was corrected from the point of view of English grammar and topic by a native English, by involving the proofreading system of a professional editor (as you can see in the revised paper) from the MDPI group of journals.

22.  While I fully understand the authors may not be native English speakers, it is important to present their work meaningfully. In this regard, in the revised version, English is marginally improved for certain sentences, but still the readability of the manuscript, overall, is extremely poor.  For example, as guidance, here is the abstract re-written form the original with about the same number of words.  Therefore, I suggest the authors simplify the complicated, run-on sentences to improve readability.

Rewritten Abstract:

Large amounts lignocellulosic biomass in the form of straw is leftover after wheat harvesting that could be utilized for beneficial purposes. The latter has led to the emergence of new technologies to make use of this resource.  One such technology currently in use turns the wheat straw into briquettes. The present study, we have prepared and evaluated physical, mechanical and calorific properties of two types of briquettes made of wheat straw.  The two types briquettes prepared were (i) hollow briquettes and (ii) solid briquettes. The densities of these briquettes obtained on a mechanical device with a crank mechanism was 1.169 kg/m3, irrespective of whether the briquettes were hollow or solid. The briquettes densities are consistent with European standards. The calorific value of wheat straw was 17.69 MJ/kg. Although the calorific value was somewhat lower than the beech wood briquettes (18.38 MJ/kg), it is adequate for their combustion in both stoves and thermal power plants. The ash content of wheat straw was 9.1% (~10-fold higher than that of beech wood). The briquettes showed a compressive mechanical strength of 1.15-2.17 N/mm2 and splitting mechanical strength of 0.17-0.39 N/mm2 suggesting that the straw briquettes were well compacted and can be stable during transport and/or other manipulations. In conclusion, wheat straw briquettes have similar physical, mechanical and calorific properties to those prepared from beech wood biomass and a viable solution to replace beech wood briquettes with similar efficiency.

Authors response: This form of abstract was put in the new revised paper, replacing even the new abstract given by MDPI English editor.     

33. The changes suggested for figures previously – they be prepared professionally. it is still not done correctly.  They deleted two figures made some small changes to X and Y axis.  But ignored the rest.  For example;
34. Why do you need the title “Normal” on top of Figures 2, 3 and 4?

Author response: The word “Normal” from Fig 2, 3, and 4 was erased. In statistics, this word shows that all values have a normal distribution.

1. Why do you need the background grid in Figure 5, 6, 7 and 8?

Authors response: A grid graph highlights other points on the graph that are not directly visible. For example, in figure 5 it can be seen that if we have briquettes with a moisture content of 60%, the approximate calorific value will have the values LCV=7500 kJ/kg and HCV=12000 kJ/kg. For any other moisture content we have, it can be observed directly, without doing additional tests, which are the calorific value. The same statements can be made in the case of the other gridded figures. Therefore, please accept that these figures to remain gridded.

1. Why do you need the title “Probability plot of ash content   Normal - 95% Cl.  In this figure are you measuring Chlorine (Cl) or what is Cl.  Describe such thing the figure legend after the title.

Authors response: Keeping the model of the other figures in the paper, the title of the figure was deleted, including the words in question. Of course, the abbreviation "CI" is not related to the chemical abbreviation, but to the statistical one, that is, "Confidence Interval".

1. In figure 8 - Why do you need the line commenting the histograms?

Authors response: It can be seen from the text that there are some interpretations of the results obtained and visible on the histogram. Since a figure must be cited in the text, other discussions and interpretations can be introduced in these lines.

9. Some of the figure legends are incomplete, e.g., “Figure 9. Content of ash, volatile and fix carbon” of what?  What is this Fix Carbon?

Authors response: The necessary addition was made; the expression "of wheat straw" was added. Also, “Fix carbon” became “Fixed carbon”.

1. There are many more things like this that needs fixing in the figures, Tables as well as the text.

Authors response: The authors examined each figure and table from the points of view expressed by the reviewer and made the necessary corrections where needed.

44. Table 2. Modelling the calorific value of wheat straw according to chemical compounds – You are really not modelling anything in this table, you are simply reporting percent composition of “C”, “H”, “O”, “Ash” and calorific values of wheat straw and comparing them to Beech wood and charcoal.  Plus, there are no chemical compounds of any kind analyzed or reported in this table.  So the title makes no sense.  In the previous version – I suggested to have native English speaker rewrite this manuscript for these kinds of reasons.

Authors response: - I think the problem was solved by changing the expression "chemical compounds" with another one "chemical elements". Authors added in the text: "According to the methodology from point 2.2, the problem that Table 2 solves is that the calorific value of any plant material is dependent on the percentages of the component chemical elements and the calorific value of each one". In this sense, see also the dependency relationship (15). It is good to know a priori the calorific value of each material, by knowing the component chemical elements, in this way there is no need for sophisticated tests and statistical validation of the results.

 -Native speaker of journal was used to revise paper.

5. Table 2 and other places you use the word “Specie”.  It should be “Biomass” or something else.  Further, In Table 2 – how is charcoal a Specie or a species? The same word “Specie” is loosely used elsewhere in the text as well.

Authors response: -The word "species" in table 2 has been changed to "material". The word "biomass" was not used because charcoal is not "biomass".

-In the text of paper, the word “specie” was replaced by “biomass”.

Authors,