Review Reports

Round 1

Reviewer 1 Report

The paper shows some interesting study on advanced assessment of biomass materials degradation in pneumatic conveying systems. There are a few concerns and some suggestions. 

1. In the manuscript, it does not mention how accurate of the Moisture Content is achieved. How is the Moisture Content calculated, dried or wet based? 

2. How the Settled Bulk Density was determined?

3. For coffee beans there is no value of Mechanical Durability in Table 1, does this mean that the value is 100% if it does not disintegrate. Can you put 100% instead of "-" if this sample was not measured?

4. If Ligno durability Tester was not used in mechanical durability measurements, describing it is not necessary.

5. It is not clear to me why only one experiment was conducted for coffee beans. Is it not possible to obtain pneumatic flow for other process conditions? Could you please explain this?

6. If you have photos of the materials after the experiment, attaching them would help in evaluating the material after the experiment.  Especially if they are partially degraded in the process.

7. The paper determined the moisture content of the material before the process, in relation to the fact that it can also affect the mechanical properties it would also be helpful to determine the moisture content after the experiment, if this is still possible.

8. In Figure 5, the description of the gray line (Slip Velocity) is missing.

9. In figure 4b there are 5 lines, and 4 descriptions, description of Blend 4 is missing.

10. In Table 1, Table 3, and Table 7, the unit  "kg" should be lowercase.

11. When using "%" units, do not use spaces after the numerical value, as in lines 223, 253, 254, 258, 272.

Author Response

The paper shows some interesting study on advanced assessment of biomass materials degradation in pneumatic conveying systems. There are a few concerns and some suggestions.

1. In the manuscript, it does not mention how accurate of the Moisture Content is achieved. How is the Moisture Content calculated, dried or wet based?

Responses: The measurement methods and accuracy are added in the manuscript.

2. How the Settled Bulk Density was determined?

Responses: The measurement method used is added in the manuscript by using a standard volume container.

3. For coffee beans there is no value of Mechanical Durability in Table 1, does this mean that the value is 100% if it does not disintegrate. Can you put 100% instead of "-" if this sample was not measured?

Responses: The durability was measured using the tumbling box method. In the table, the data for coffee beans is added.

4. If Ligno durability Tester was not used in mechanical durability measurements, describing it is not necessary.

Responses: The sentence is removed.

5. It is not clear to me why only one experiment was conducted for coffee beans. Is it not possible to obtain pneumatic flow for other process conditions? Could you please explain this?

Responses: This is because we were struggling to get the representative materials secured. The quantity of test materials was not enough to support all test conditions to be conducted. Also, the coffee bean was so sensitive to degradation and the conveying conditions. So as an indicator, one test condition was properly conducted and presented. 

6. If you have photos of the materials after the experiment, attaching them would help in evaluating the material after the experiment. Especially if they are partially degraded in the process.

Responses: Photos of degraded materials (aged wood pellets and roasted coffee beans) are added in Figure 1. The coffee beans have more degradation than the wood pellets. The photos added here are just indicators. The evaluation of degradation was achieved by doing size analysis.

7. The paper determined the moisture content of the material before the process, in relation to the fact that it can also affect the mechanical properties it would also be helpful to determine the moisture content after the experiment, if this is still possible.

Responses: It is not necessary because the moisture content of the materials have not been changing too much during the tests. It will change only if the materials are stored for a long period of time.

8. In Figure 5, the description of the gray line (Slip Velocity) is missing.

Responses: The description of the grey line was given in the lines of 199-200.

9. In figure 4b there are 5 lines, and 4 descriptions, description of Blend 4 is missing.

Responses: The description of the lines is added in the caption.

10. In Table 1, Table 3, and Table 7, the unit "kg" should be lowercase.

Responses: These have been corrected.

11. When using "%" units, do not use spaces after the numerical value, as in lines 223, 253, 254, 258, 272.

Responses: These have been corrected accordingly.

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors have presented an interesting topic that is worth exploring. In my opinion, it would be worth enriching the manuscript with a better quality diagram and photographs of the materials not only before but also after the tests.

Author Response

The authors have presented an interesting topic that is worth exploring. In my opinion, it would be worth enriching the manuscript with a better quality diagram and photographs of the materials not only before but also after the tests.

Responses: Photos of degraded materials (aged wood pellets and roasted coffee beans) are added to the Figure 1. Figure 2 is improved for a better quality.

Reviewer 3 Report

General Comments      
This paper presents a methodology to measure the degradation of bulk biomass materials (wood pellets and dry roasted coffee beans) in the pneumatic control of pipeline transportation. Particle velocity has been used as a variable to study. Degradation increases with increasing particle velocity and it decreases by increasing solid feed rate, due to increased air mass flow rate. An interesting laboratory set up shown in this study could be assesses the degradation of biomass pellets of different strengths and feedstock material by designing pipeline as per industrial practice along with designated number and type of bends in pipeline.

Nevertheless, the bibliographical references must be updated, there are none from 2022. Figures and tables are appropriate and show the data, but they are not easy to interpret and understand. A discussion of the measurement has been omitted. However, the authors present some important conclusions, and it is not easy to find the evidence and arguments presented, so a review of the discussion must be carried out so that it can be considered to recommend the manuscript to be accepted.  

Comments        
- How were the properties of the materials determined? (Table 1)

- Pneumatic conveying system  (Figure 2) must be enhanced: The figure is clear but the text does not have the right format.          

- Characteristics  of electrostatic sensors must be included.

- Space between the number and an abbreviated unit of measurement must be review.

- Why Ligno durability Tester is not employed in this work?

- Figures 3 and 4 must be improve to a better and easy interpretation of them, for example, there are two Blue lines.

- Discussion of Figures 3, 4 and 5 is omitted.

- Table 3 and 7 are related and an important information could be found if they compare and discuss deeply the results. The same occur with the Tables 4, 5 and 6 with Tables  8, 9 and 10.

Author Response

MDPI- Reviewers’ comments

This paper presents a methodology to measure the degradation of bulk biomass materials (wood pellets and dry roasted coffee beans) in the pneumatic control of pipeline transportation. Particle velocity has been used as a variable to study. Degradation increases with increasing particle velocity and it decreases by increasing solid feed rate, due to increased air mass flow rate. An interesting laboratory set up shown in this study could be assesses the degradation of biomass pellets of different strengths and feedstock material by designing pipeline as per industrial practice along with designated number and type of bends in pipeline.

Nevertheless, the bibliographical references must be updated, there are none from 2022. Figures and tables are appropriate and show the data, but they are not easy to interpret and understand. A discussion of the measurement has been omitted. However, the authors present some important conclusions, and it is not easy to find the evidence and arguments presented, so a review of the discussion must be carried out so that it can be considered to recommend the manuscript to be accepted. 

Responses: A discussion of the measurements and a review of the result discussion are added to the discussion part. This emphasises the novelty of the study and provides the evidence for the conclusions. The references have been updated and a new reference is added. However, there is a limited work being done in the last year (2022). It is believed that the references can covered the topic.

Comments       

- How were the properties of the materials determined? (Table 1)

Responses: The methodology for the material properties is added in the manuscript.

- Pneumatic conveying system  (Figure 2) must be enhanced: The figure is clear but the text does not have the right format.  

Responses: Figure 2 is amended so a clearer figure is presented.       

- Characteristics  of electrostatic sensors must be included.

Responses: The electrostatic sensors have been studied in detail and shown in the reference [31]. The work has been published. In this manuscript, characteristics of the electrostatic sensors is included.

- Space between the number and an abbreviated unit of measurement must be review.

Responses:  These have been corrected.       

- Why Ligno durability Tester is not employed in this work?

Responses: The description of Ligno has been removed.    

- Figures 3 and 4 must be improve to a better and easy interpretation of them, for example, there are two Blue lines.

Responses: The quality of the figures have been improved so the lines can be better to interpreted.          

- Discussion of Figures 3, 4 and 5 is omitted.

Responses: Discussion of Figures 3, 4 and 5 is added in the section of discussion.         

- Table 3 and 7 are related and an important information could be found if they compare and discuss deeply the results. The same occur with the Tables 4, 5 and 6 with Tables  8, 9 and 10.

Responses: Table 3 and 7 are Not directly correlated but comparative. Table 3 is the velocity measurements for fresh wood pellets, and Table 7 is the  velocity measurements for aged wood pellets. They are compared (line 232-237) and discussed (line 288-394). The degradation in the Tables 4, 5 and 6 with Tables  8, 9 and 10 are also discussed. A new discussion is added to emphasise the explanation.      

Author Response File: Author Response.pdf

Reviewer 4 Report

Abstract

L10-17 these lines can be shorted. Many information about the problem. So, the abstract can be shorted.

L25-27 these lines can be descripted more specifically.  Which materials?

L27-28 the conclusion must be written more appropriately.

 Introduction

This section was written appropriately and it was focused according to objective. Some observation can be considered:

 L36-39 This sentence can be referenced with following reference:  https://doi.org/10.1007/s12649-015-9420-1

L89-82 This line can be written. This can be removed or relocated after the objective.

L101 Kg/m³ change for kg/m³, K is for kelvin.

 Material and methods

L116 the resolution of figure 2 must be improved. The line must be drawn in black color.

L191 Any information about statistical analysis was presented.

L180-181 this lines can be removed-

 Results and discussion

L187 Change Kg for kg in “y” axis. The title is twice. The number must be written with 1 or 2 decimals.

L192-215 Although, the results are presented in table or figure, the description is null. It is impossible to reader to follow the article.

L200 Idem

L214 This line can be written. This can be removed or relocated after the objective.

L201 Kg/m³ change for kg/m³, K is for kelvin.

L249-251 this tables can be grouped. There are many tables and figures in the article.

L256-259 Which table or figure can be observed this results?

  Conclusions

Conclusion is not summary of results, then this part can be shorted.

L296-301 The lines can be removed.

L308-312 this conclusion is not derived from this study.

L317-319 Idem

Author Response

MDPI- Reviewers’ comments

Abstract

L10-17 these lines can be shorted. Many information about the problem. So, the abstract can be shorted.

Responses: It has been shortened.

L25-27 these lines can be descripted more specifically.  Which materials?

Responses: The sentence means the material is comprehensive. Any material which is degradable will have the same problem in pneumatic conveyors.

L27-28 the conclusion must be written more appropriately.

Responses: it has been rewritten.

Introduction

This section was written appropriately and it was focused according to objective. Some observation can be considered:

L36-39 This sentence can be referenced with following reference:  https://doi.org/10.1007/s12649-015-9420-1

Responses: This reference is added as recommended.

L89-82 This line can be written. This can be removed or relocated after the objective.

Responses: The sentences have been rewritten and make the description clearer.

L101 Kg/m3 change for kg/m3, K is for kelvin.

Responses: it has been changed.

Material and methods

L116 the resolution of figure 2 must be improved. The line must be drawn in black color.

Responses: Figure 2 is improved with a higher quality.

L191 Any information about statistical analysis was presented.

Responses: Statistical analysis is presented in Figure 3(b) as standard deviation. However, it has been discussed in detail. It shows the variations of the measurements.

L180-181 this lines can be removed-

Responses: The description of the Lingo tester is removed. However, the name of the durability tests is kept as it shows the recommended methods.

Results and discussion

L187 Change Kg for kg in “y” axis. The title is twice. The number must be written with 1 or 2 decimals.

Responses: The figure is corrected.

L192-215 Although, the results are presented in table or figure, the description is null. It is impossible to reader to follow the article.

L200 Idem

Responses: Section 3.1 shows an example of particle velocity measurements and corresponding air velocities. The degradation results are shown in sections of 3.2, 3.3 and 3.4. The discussion of the results is presented in section 4. To emphasise the discussion and a better interpretation of the results, a new section of discussion is added.

L214 This line can be written. This can be removed or relocated after the objective.

Responses: It has been corrected.

L201 Kg/m3 change for kg/m3, K is for kelvin.

Responses: This is corrected accordingly.

L249-251 this tables can be grouped. There are many tables and figures in the article.

Responses: The results in tables were designed according to impact conditions so the degradation can be compared in terms of different operation conditions. If it takes the fines contents as presented, it can be easily interpretated. 

L256-259 Which table or figure can be observed this results?

Responses: This is a direct comparison between the aged wood pellets and the fresh wood pellets. If looking at the particle velocities for the two types of wood pellets, it will be noticed which results were referred to.

Conclusions

Conclusion is not summary of results, then this part can be shorted.

Responses: Conclusion is rewritten and more summarised.

L296-301 The lines can be removed.

Responses: The sentence is revised so a better description is presented.

L308-312 this conclusion is not derived from this study.

L317-319 Idem

Responses: The conclusion is rewritten and improved.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The authors improve the manuscript, and I accept in the present form.