Review Reports - Characterization of Pyrolysis Products of Forest Residues and Refuse-Derived Fuel and Evaluation of Their Suitability as Bioenergy Sources

Round 1

Reviewer 1 Report

This work deals with analyzing the solid, liquid and gas products of a pyrolysis process from forest residues (FOR), pine cones (PCO) and refused derived fuel (RDF). Since the authors stated that there is a lack of information concerning this technology regarding the mentioned raw materials, this is a novelty brought up to the scientific community. The overall structure of the manuscript is sound, the topic is clear and concise and the results are presented well. However, before publication I would like for a few points to be addressed:

(1) How were the yields in Figure 2 obtained /calculated? There is no mention of it in the Materials and Methods section only that a mass balance has been performed.

(2) The sentence beginning in line 246 needs to be checked in terms of grammar.

(3) Why are there no gas evolution profiles for RDF and FOR?

Author Response

Hania, 22/12/2022

MANUSCRIPT applsci-2099643

POINT-BY-POINT REPLY TO REVIEWERS COMMENTS

First of all, the authors would like to thank the reviewers for their kind and useful comments, which helped to improve the article.

-Reviewer 1
Solid and liquid products of pyrolysis were weighed and gaseous products were calculated by difference. An explanation is given in page 4, first paragraph.

Grammar was checked.
An example was given, because some journals allow a certain number of figures. We hope that the editor will accept these extra figures. Therefore, the gas evolution profiles for FOR and RDF were added, Figures 5 and 6.

Reviewer 2 Report

Please find the attachment.

Comments for author File: Comments.pdf

Author Response

Hania, 22/12/2022

MANUSCRIPT applsci-2099643

POINT-BY-POINT REPLY TO REVIEWERS COMMENTS

First of all, the authors would like to thank the reviewers for their kind and useful comments, which helped to improve the article.

-Reviewer 2
Major comments

The abstract was improved.
Literature review was extended, because the editor requested to increase word count due to journal restrictions. Nevertheless, past investigations relevant to current on forest residues and RDF were reported, nr. 12, 17,18,22,23,24,30 and 21, respectively. Past studies on RDF could not be compared with present work, because they were referred to microwave catalyzed pyrolysis (P. Yang et al. Fuel Processing Technology, 227, 2022), gasification of modeling coposites at 800˚C by TGA (S. Aluri et al. Fuel Processing Technology, 179, 2018), co-pyrolysis (fast) of RDF with high density polyethylene (J.A.M. Chavando et al. Int.J. of Hydrogen Energy, 47, 2022) and pyrolysis of RDF with high content of plastics (COVID 19 wastes) at 900˚C for gas analysis (M. Zajemska et al. Fuel, 320, 2022). The novelty of work was stressed in the last two paragraphs of the introduction section.
The title was made more specific.
The variations in C and O contents with temperature in Table 2 are explained in section 3.2, first paragraph.
In section 2.2 it was reported that the condensate was centrifuged to collect bio-oil, which was then analyzed as discussed in section 3.3.
(a) and (b) are shown in Figures 4-6. In page 5, section 2.3 it was explained how the gaseous products were quantitatively characterized by online TG-MS experiments. Cumulative gas analysis was performed up to 350, 450 and 550˚C and the higher heating value was calculated.
More explanations about evolution of gases are given in section 3.4.
Conclusions was improved in a single paragraph.

Minor Comments.

1. The capacity of the reactor was included in section 2.2 and the type of flow meter in Figure 1.
2. Temperature was included in section 2.2. First bath was at ~15˚C, second bath at ~10˚C.
3. The composition of RDF is included in section 2.1.
4. 1 These are results, section 2 refers to methods only.
5. S content was included in Table 2 for comparison reasons with other tables and for indicating that it was below detection limits.
6. Reference 31 is included , 4^th and 5^th lines of section 3.3 also. Cannot remove S, because heavy oil contains S.

Reviewer 3 Report

1)The introduction is too long and not concrete. It needs to be more direct and condensed. Also, it is necessary to emphasize the motivation for this work, as well as the novelties it brings.

2) In Fig.4, why there are totally different trend for CO and CO2 with the increase of temperature. The explanations are not convicincing.

3) The English should be further polished. For example, Page 2, Line 78,

Very few investigations analyzed the physicochemical features of bio-oils from....

Author Response

Hania, 22/12/2022

MANUSCRIPT applsci-2099643

POINT-BY-POINT REPLY TO REVIEWERS COMMENTS

First of all, the authors would like to thank the reviewers for their kind and useful comments, which helped to improve the article.

-Reviewer 3

The editor asked to extend the text, because the journal has restrictions on word count. Nevertheless, we have tried to improve this section and stress the novelty of work in the last two paragraphs.
Explanations are given for the gases in page 9, section 3.4.
English was revised as much as possible.

Round 2

Reviewer 2 Report

Please find the attachment.

Comments for author File: Comments.pdf

Author Response

-Reviewer 3 (second round)

Major comments

1) I copied here the text, which clearly explains why in this case oxygen increased. As previously mentioned, oxygen is on a dry ash free basis. “On the other hand, Table 2 shows that when the temperature was ≥450°C the carbon content of FOR and RDF chars was reduced, suggesting its bounding in volatile species. The decrease in carbon content was reflected in the rise of oxygen concentration of biochars. Thus, the higher heating value of these biochars dropped significantly and it was lower than that corresponding to raw biomass fuels (15.2 MJ/kg against 17.3 MJ/kg for FOR and 11.1 MJ/kg against 26.3 MJ/kg for RDF).”

2) In section 2.2 it was reported that the condensate was centrifuged to collect bio-oil, which was then analyzed as discussed in section 3.3.

3) We corrected x-axis to include only gases and not any moisture from the sample. As explained, these graphs are from the online TG-MS system. Please refer again to first answer Nr 6) above.

Minor Comments.

1) Heavy hydrocarbons or other organics could be condensed at this temperature and comprised condensate (Bio-oil and water). Gases below C4 were emitted and analyzed as described.

2) S was removed

Reviewer 3 Report

The authors basically answered the reviewer's comments, it can be accepted after minor revision. For example, the digits (CO2, H2, CH4, etc) in Figure 3,4,5 should be subscript .

Author Response

-Reviewer 2(second round)

Subscripts were introduced in the figures