Upgrading Carthamus by HTC: Improvement of Combustion Properties

Round 1

Reviewer 1 Report

This manuscript deals with the experimental study of carthamus pomace potential as a fuel and its hydrochar combustion behavior. The manuscript fits well the scope of Fire and could be considered for publication after major revision. My detailed comments are given below.

(1) Line 181: Eq. (3) must be replaced by Eq. (1)

(2) The text related to Figure 3 and the figure itself look irrelevant to the study, at least in the present form. It is not clear what types of experimental series are plotted on the graph, what units are used for the microcolumn dimensions, what color fields are presented in the snapshot, etc. If the authors intend to have this material in the text, they must provide all necessary information on the statement of the problem in COMSOL Multiphysics software, so that the interested reader could be able to reproduce their results. Also, once the authors mention the account for various heat transfer resistances, including conductive, convective, and radiation mechanisms under dynamic conditions, they must indicate the comparative effect of all these mechanisms on the obtained results. Also, a validation example must be provided.

(3) The experimental study must include the error analysis, which is absent for all measurements reported in the manuscript. It could happen that some differences in Figs. 2, 4, and 5 could be within the measurement error.

(4) It would be instructive if the authors provide some grounds on their choice of a heating rate of 20°C/min in the thermal degradation studies of feedstock samples. 

(5) In Lines 185-187, the authors describe the procedure of determining the activation energy and pre-exponential factors entering Eq. (1). In view of it, it would be instructive to have an example of the corresponding Arrhenius plot showing the expected linear dependence, as well as the claimed values of the activation energy plotted in Figure 10. How about the value of the pre-exponential factor entering Eq. (1)?

(6) English gramma must be checked, e.g., in Lines 240, 368, etc.

Minor editing of English language is required

Author Response

We really thank the reviewer for his/her suggestions that will help us improve our manuscript. Bellow we explain how we have addressed the different comments, as well as the modifications we have made in the revised version of the manuscript.

Reviewer 2 Report

Dear Authors,

In my opinion the paper is well written and concise. The topic of the paper is not of the highest interest but the experimental data obtained could be important to specific audience. Therefore I would recommend it for publication after some minor changes.

Comments:

In the text it is repeatedly used the term „fumes“. In combustion, it is customary to use the term „flue gases“.

Line 181 – It is eq(1) that is rearanged and integrated to give eq(3).

Line 374 – The expression should be reformulated to express the LHV in SI units (kJ/kg).

Line 393 – In eq(7) mass flow = volume flow x density!

Line 520 – unit of mass flow should be per time (kg/s)

Line 521 – same as previous.

Author Response

We really thank the reviewer for his/her suggestions. According to your suggestions, some changes have been made; in this letter we answer each of the points that have been raised, and describe how we have addressed them all in the new version of the manuscript.

Author Response File: Author Response.pdf

Reviewer 3 Report

The document presents a detailed study on hydrothermal carbonization (HTC) of Carthamus cake for solid biofuel production. It examines how HTC process parameters affect the properties of resulting hydrochars (HCs) and evaluates their combustion behavior and economic viability. Overall, the document contributes valuable insights to HTC and biomass valorization, impacting the development of sustainable energy sources. Some of the suggestions to further improve the quality of the manuscript:

1. The manuscript does not provide enough specific details about the COMSOL model used to produce Figure 3, making it difficult to fully evaluate its accuracy and limitations.

2. The TGA data provided in Figure 6-9 shows the variance of combustion characteristic with the change in temperature. I request the authors to discuss and support the observed results.

3. Expand discussion of findings' implications. Relate the current study's findings to previous research in the field of HTC and biomass valorization.

Author Response

We are very grateful to reviewer 3 for the time and effort he/she has devoted to improve our manuscript. Thank you very much; your suggestions have definitely moved us to put effort to make it better. We have followed the different points raised by the reviewer, that have been addressed in the new version, as we explain below.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have properly addressed all my comments. The manuscript could be now considered for publication in the present form.

Author Response

Dear reviewer, thank you so much for your help that has been very important for us to improve our manuscript.