Determination of the Angle of Repose and Coefficient of Rolling Friction for Wood Pellets

Round 1

Reviewer 1 Report

This paper calibrates the relevant contact parameters of the biomass pellets, such as the coefficient of static friction and the coefficient of rolling friction by DEM. The results of the study can provide some reference for the development and process optimization of biomass pellets transportation and production machinery.

1、It is suggested to divide 2.3 into two subsections, 2.3 Contact model 2.4 Simulation model

2、Are the various length particles generated in the simulation generated by volume distribution or radius distribution? Additional clarification is needed in this paper.

3、Which are the coefficients of friction mentioned in section 3.2? the coefficient of static friction or the coefficient of rolling friction?

4、The repose angle formed by different contact parameters between biomass pellets and contact material also varies, and the surface roughness of contact material also affects the size of the formed stacking angle, which is recommended to be added.

5、Some variables are not uniform, such as µs and Ct in line 143.

Author Response

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Reviewer 2 Report

Review of the manuscript ID: agronomy-1584644

 

Determination of the angle of repose and coefficient of rolling friction for wood pellets

 

The manuscript presented for review concerns the technologically important physical parameters of wood biomass pellets, i.e. the angle of repose and the coefficient of rolling friction.  The Authors have determined experimentally and by simulation the variations of the angle of repose with the drop height. Furthermore, an optimal procedure for its determination was established, which was then used for the calibration of the coefficient of rolling friction.

The research carried out by the Authors, the methods used and their description do not raise any major objections. However, some issues require supplementation or correction, namely:

 

1. In my opinion, the beginning of the Introduction - lines 21-29 - is too laconic. At this point, the importance of the physical properties of bulk materials should be defined more precisely. After all, the knowledge of angles of repose and slippery angles of repose, poured bulk density and tapped bulk density, etc., is indispensable and taken into account while transporting (e.g. by belt conveyors) materials crumbled into various forms and shapes, designing storage places and places of technological processing as well as designing specialist containers and dispensers. This issue is important both for granular materials and for raw materials of more irregular shape and size. Examples are, e.g. rock material in mining, wood particles used in the production of particleboard, or cereal grains and flours in agriculture and the food industry.
2. The sentence in line 25 page 1 - "Biomass for burning is commonly transformed into pellets, a particular kind of granular material" also seems too vague. I would suggest supplementing the content on the use of different types of biomass. The Authors did not provide any literature on this topic.
3. In Table 1, page 2 - instead of "Humidity", "Moisture content" should be used. Humidity is a technical term to indicate the amount of water vapor that is present in the air.
4. For the potential reader, it is not entirely clear why the Authors performed the simulation for a drop height of 105 mm, when the standard they used requires 75 mm, and the base was metal plate, not pellets. On page 7 and 8, Fig. 6 and in the text below (line 236-238) it is stated that only for the pellet base, the AoR below 100 mm cannot be investigated. Please clarify.
5. The sentence on page 8, line 243-244 should be in the appropriate place in subsection 2.3.
6. Please unify the notation of height units: cm or mm. In the paper, the Authors use both notations.

Author Response

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Reviewer 3 Report

This study is of interest, but the relation to pellet research and storage of pellets should be increased. The most important, the paper are missing a purpose and aim. 

Determination of the angle of repose and coefficient of rolling friction for wood pellets

In general, this study can be of importance and can be linked to problems associated with handling of pellets, however, the connection to pellet industry and pellet research is week, can and should be increased.

Abstract

Has to be rewritten, I missing the background, purpose and aim with the study, why pellets, and the conclusion, related to purpose

Introduction

I´m missing introduction related to why study angle of response, from an industrial perspective.

Other studies that have study pellet storage are missing

There is no purpose and aim behind the study, why it is done and what hypothesis it has

Method

Row 81 what data is related to manufacture and have the authors measured the rest?

Table 1

The pellets that was used, I´m missing inlet durability test related to standards for durability

 Is humidity the same as moisture content in the pellets, if so is it based on wet or dry base?

Density under compaction, what does that mean in your study

Volume (mm3) 513,54 is that right?

Row 110-116 How many times? Is sextuplet the right word? The tests are sextupleted, 12 drops and then replaced and 60 times? It is unclear what is the right amount of test, can be clarified.

In general, a good method and an interesting study

Discussion

I missing the discussion where relation and connection to industrial handling of pellets where the fall can be up to 5m and the substrate varies from concrete to layers of pellets. What do the results mean? How can these be used, what does it mean from a larger perspective. Ones again the purpose are missing with the paper

I missing the connection to pellet quality, how does AoR linked to durability, maybe out of scope?

I lack a comparison with spherical data, what do the results say compared to other studies.

Can the pellet be compared with other well-defined materials?

Author Response

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Author Response File: Author Response.docx

Reviewer 4 Report

The determination of the angle of repose for granular materials is needed to obtain the necessary parameters to perform DEM simulations. 
This is an extensive research, with a lot of experimental and numerical analysis. 
Thematically the work is interesting for the researchers and professionals and the proposed manuscript is relevant to the scope of the journal.

I found it appropriate after some modifications and clarification from the Authors.

The overall organization and structure of the manuscript are appropriate. The paper is well written and the topic is appropriate for the journal.
The aim of the paper is well described and the discussion was well approached, its results and discussion are correlated to the cited literature data.
In the introductory part, the authors give elaboration of the overall context stating the motivation and the objectives of the work, literature review of the research pathways .
The literature review is comprehensive and properly done.

The significance of the Work: Given the large number of analyzed data, this is an interesting study with a possible significant impact in this area.
Statistical interpretation of the analytical data must be more properly presented.

The verification of the model should be performed. 

Other Specific Comments: The work is properly presented in terms of the language. The work presented here is very interesting and well done, it is presented in a compact manner.
In general, there are no doubtful or controversial arguments in the manuscript. The methodology applied in the research is presented in clear manner, so that it is repeatable by other authors.

The main drawback of the paper i s the extent of novelty, or the main novelty in the present work, compared to the works of other researchers? In my opinion, the authors should put additional effort to demonstrate that the present work gives a substantial contribution in the research area.

Author Response

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Round 2

Reviewer 2 Report

Dear Authors,

All comments made in the review have been taken into account and necessary corrections have been made to the manuscript. After revision, the manuscript does not cause my objections and I now recommend it for publication.

Comments for author File: Comments.pdf