Carbon-Efficient Production Scheduling of a Bioethanol Plant Considering Diversified Feedstock Pelletization Density: A Case Study

Round 1

Reviewer 1 Report

Global Appreciation

The authors propose an interesting contribution to the Production Scheduling for Bioethanol Plant considering the evaluation of both the profit and Carbon efficiency while testing diversified feedstock density.

The proposed approach was tested for a case study in a bioethanol Production Company in China.

Globally, the paper is well organized, the written style in English requires minor spell check to result scientifically clear. Besides that, the appropriate paper size is presented.

Concerning the abstract, the proposal, and paper achievements should be placed clearer. Also, the sentences related to the model, and with the membership weighted method could be improved.

The introduction and literature review are paper sections strongly positive. The authors presented a deep overview of different contributions and perspectives. These allow the reader to capture the core scientific achievements and ongoing developments. Nevertheless, in the paper content some mathematical concepts, entities, and results are poorly presented, these should be reworked to improve readability.

Moreover, the case study and the results are generically presented while shortly discussed. Finally, conclusions are sounding with the core achievements but interesting developments could be also proposed concerning future contributions.

Based on the former observations I consider that the paper can be Accept after minor revision (corrections to minor methodological errors and text editing)

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Detailed Comments to Authors.

A brief synthesis of the detailed comments/suggestions is also presented below.

Abstract

Sentences related to the mathematical model should be reworked to clarify the developed approach and the methodology used to solve the scheduling optimization problem.

1. Introduction and 2. Literature Review

All placed references were checked for consistency. All were properly placed and cited.

3. Problem Description

The problem description focused essentially on the Bioethanol production process. Some modeling and solving assumptions are introduced at the end of this section. Nevertheless, no explicit assumption is presented about price dependency or either about the scheduling period (e.g. time horizon, discretization procedure, period duration, etc.).

These are major formulation entities that deserve a future explanation. All effective assumptions should be listed and detailed in terms of their description.

4. Problem Formulation

This section requires some improvements that will benefit paper content in terms of scientific consistency and readability. Particularly, some mathematical entities and figures should be reworked.

A former question is related to the set of planned periods, t∈ T.

Authors argue about strategic and tactical approaches brought by previous contributions, although no explicit definition of the planned periods is presented for the scheduling proposal. 

This is a major issue because, namely, price variability over time as well as cost parameters dependency on time should be fairly discussed.

Formulation

The a priori assumptions to the formulation should be made clear.

Moreover:

• A dual-objective model is used in the case-study but no previous statement was presented in the formulation section.
• Also, the criteria on the economical and the carbon emission objectives should be clarified in accordance.
  How did these influence the evaluations and measures?

Besides that,

• The objective functions were used to define a membership function having weighting factors, denoting the importance of economic and environmental objectives.
• Due to the different dimensions of the two objectives, a normalization procedure is adopted to facilitate the comparison.

So, the procedures used to achieve the max and min values of both objective functions should be explained.

5. Case-Study

An interesting case is presented and some analyses of the experiments are developed. Just some few questions:

Figure 3 - “Curves of normalized F1 and F2 varying with W1.” Should be reworked.

Concerning graphic illustration, W1 axis should be placed in the scale 0-1, otherwise the figure seems to have an incomplete analysis of W1 values. The graphic should present a more detailed scale.

Also, at least, F1 and F2 values for W1=0 and W1=1 should be detailed to clarify the meaning of the membership function.

An equivalent situation is presented in Figure 7 for the “Total profit and carbon emission under different W₁”. This figure should be also reworked.

Besides that:

• How the sensitivity analysis over the model parameters were conducted? Noticing the impact of binary variables M_j in the mathematical formulation, some explanation should be introduced.
• The solution statistics are not explicitly discussed for the scenarios presented.

6. Conclusions

The presented study is a concrete and motivating research area.

As previously mentioned, the conclusions are sounding with the core achievements, and interesting ideas are proposed concerning future contributions.

Besides that, no time assumptions are presented, but a large number of model entities depends on the time horizon and on the duration of time periods. So, the contribution brought by the proposed formulation could be summarized more clearly.

Also, different issues related to the trade-off between costs, capacities, and raw-materials available can introduce further interesting analysis.

These should be observed and carefully analyzed.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

Dear authors,

I have enjoyed reading the paper but I wonder why you have chosen Processes as the journal to publish your paper.

Whether you will publish here or somewhere else, there are some general remarks to your paper. While the dual-objective optimisation scheduling and MILP are well described, the context where you place the research needs enforcement, both in Introduction, Literature Review and Conclusions. Suggestions are recorded in the enclosed file. 

What I find very interesting is that you record profit in your model with a 2G bioethanol plant (80 t/year capacity) and mere 44% of biomass procurement costs in the overall costs. I went through your problem formulation, but I can’t revive it. I suggest that you verify the items in your calculations, convert the values in the US and compare the results with the similar results in the literature and practice for bioethanol biorefineries, regardless if it is dual-objective optimisation problem or not. 

Some general remarks would be:

• define an abbreviation at the first mentioning and then continue with the abbreviation from then on (e.g. mixed  integer linear programming - MILP etc.)
• use USD as a currency used in international studies which will help the reader in comparison of values;
• round the values when that is suitable (e.g. Tables 8-10)
• be uniform with expressions such as "dual" or "bi",
• is "carbon" assuming "GHG emissions"? Either yes/no, please describe in the text.
• References must be adjusted to the standard of the journal.

Good luck with the next level.

Best regards,

Comments for author File: Comments.pdf

Author Response

Please see the attachment

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Dear Authors,

thank you for the effort invested in improving the paper. It was an excellent approach with a weak narrative. Now it is ok to publish the paper.

Best of luck in citations,

B. Kulisic