Sorghum Biomass as an Alternative Source for Bioenergy

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

After a detailed reading of the presented research and an overall literature review, the reviewer's recommendation is that the manuscript should be rejected in its present form, and authors should be encouraged to resubmit their work after resolving the following issues: 

1. From a reviewer's point of view, the assessment of the considered samples should involve some additional experimental data for the analysed sorghum biomass. The FQI solely focuses on energy characteristics, but the use of this renewable energy source must also take into account environmental concerns. In that sense, one of the biggest challenges related to the application of biomass in the form of pellets and briquetes is PM emissions from direct combustion, and that's why the ash analysis should also be included in the overall assessment of the considered fuels. For example, the higher amounts of Na and K oxides in biomass ash enhanced PM emissions. Furthermore, the data of ultimate analysis (i.e., elemental composition) as well as the analysis of LHV of the selected samples are commonly present in this kind of research. 

2. The presentation of the results of the analysis should be further improved. For example, it will be very interesting to show how the density of the sample changes with the addition of biooil to wood and sorghum samples. That analysis will confirm the decision to use 3% bio-oil as a reference for the integral sample (wood and sorghum). 

3. The conclusion should be rewritten in order to further highlight the novelty of the presented research and to point out the viability of the utilisation of sorghum biomass as a potential renewable energy source in the future.

Comments on the Quality of English Language

The English language is OK. Minor editing is required to correct typos.

Author Response

1. From a reviewer's point of view, the assessment of the considered samples should involve some additional experimental data for the analysed sorghum biomass. The FQI solely focuses on energy characteristics, but the use of this renewable energy source must also take into account environmental concerns. In that sense, one of the biggest challenges related to the application of biomass in the form of pellets and briquetes is PM emissions from direct combustion, and that's why the ash analysis should also be included in the overall assessment of the considered fuels. For example, the higher amounts of Na and K oxides in biomass ash enhanced PM emissions. Furthermore, the data of ultimate analysis (i.e., elemental composition) as well as the analysis of LHV of the selected samples are commonly present in this kind of research. 

We agree with you about the environmental concerns by renewable energy biomass and it will be the second step of our project, considering 3 types of burn process, once it influence directly the emissions, as well the ashes detailed analyses. Right now we do not have budget to do that, but this analysis does not compromise our results once it are complementary.  In this first step is focus to show an alternative biomass for energy generation and how to use it in a better way.

We see a necessity to show this result fast, to indicate for industry a better way to burn this type of biomass considering the scenario of biomass scarcity in some parts of Brazil.

2. The presentation of the results of the analysis should be further improved. For example, it will be very interesting to show how the density of the sample changes with the addition of biooil to wood and sorghum samples. That analysis will confirm the decision to use 3% bio-oil as a reference for the integral sample (wood and sorghum). 

We added density information. But as expected, it not changed density on compression process. The decision to use 3% of bio-oil is bases on increase HHV.

3. The conclusion should be rewritten in order to further highlight the novelty of the presented research and to point out the viability of the utilisation of sorghum biomass as a potential renewable energy source in the future.

Thank you for all suggestions, especially for this one. We rewrote the conclusion in a much better way.

Reviewer 2 Report

Comments and Suggestions for Authors

The present work  tested  different mixtures of SB, eucalyptus wood (W), and eucalyptus bio-oil (Bo) as briquettes for HHV  

and least ash. some issues should be adressed:

 

(1) the title of this paper, namely "Sorghum Biomass as an Alternative Source for Bioenergy"，The title isn't a little too broad；

(2) Why did the author compare the biomass compression materials prepared by "sorghum straw" and "eucalyptus" separately? What is the basis of material selection？

(3) The quality of figure 2-4 must be improved;

(4) Line 279-281,"It is important to note that both SB and W types of biomass with or without the addition of Bo could be used for industrial purposes such as heating and generating electricity.", What does the author want to say, not quite understand.

(5)In addition to the photos shown in Figure 1, whether the author can provide other characterization results of biomass solid fuel, such as FTIR,SEM, etc.

Author Response

(1) the title of this paper, namely "Sorghum Biomass as an Alternative Source for Bioenergy"，The title isn't a little too broad；

Maybe, "Sorghum Biomass for Bioenergy purpose"? This title is shorter, but we feel that is not clear to the reader that sorghum biomass is an alternative biomass.

(2) Why did the author compare the biomass compression materials prepared by "sorghum straw" and "eucalyptus" separately? What is the basis of material selection？

We compared and alternative biomass (sorghum biomass) with a traditional biomass (wood), and the mixtures of both to show a better way to use the alternative biomass. We clarified it in the material/methods and results section.

(3) The quality of figure 2-4 must be improved;

We improved the quality of these figures. Thank you!

(4) Line 279-281,"It is important to note that both SB and W types of biomass with or without the addition of Bo could be used for industrial purposes such as heating and generating electricity.", What does the author want to say, not quite understand.

We have clarified this on page 7.

(5)In addition to the photos shown in Figure 1, whether the author can provide other characterization results of biomass solid fuel, such as FTIR,SEM, etc.

We are not able to do this in this stage of our project once we do not have budget at this moment, but going to include for second stage. Your suggestion arrived just in time, thank you for that. It will complement our future results.

Reviewer 3 Report

Comments and Suggestions for Authors

The article is good, with interesting highlights.

I would like if the authors made the following suggestions:

1 - in the results when they talk about the component properties (Table 2) they don't talk and calculate the FIxed carbon. This significant property helps explain the talk about the "long-lasting embers". So I recommend they put this calculus.

2 - The authors made a discussion with graphics, which is very important, but if they put a table with results it would help to clarify the discussion of the results.

3 - The authors made a lot of mixed materials, and in line 320, they talk about the better mix. If they write the results of all of the mixtures in a table it will clarify the discussion, and the readers can understand better, why they show that specific mix will be better. So I suggest that they do this.

Author Response

1 - in the results when they talk about the component properties (Table 2) they don't talk and calculate the FIxed carbon. This significant property helps explain the talk about the "long-lasting embers". So I recommend they put this calculus.

We added this information. Thank you for this suggestion.

2 - The authors made a discussion with graphics, which is very important, but if they put a table with results it would help to clarify the discussion of the results.

We chose graphics presenting the confidence interval of the mean (pTukey < 0.05) to provide the results that shows each mixture effect and we have clarified the meaning of symbols, data points, and error bars used.

3 - The authors made a lot of mixed materials, and in line 320, they talk about the better mix. If they write the results of all of the mixtures in a table it will clarify the discussion, and the readers can understand better, why they show that specific mix will be better. So I suggest that they do this.

We indicate the better mixture based on HHV increment plus the lower ash content. It was calculated by equation provide by the model including all mixtures and these two variables. It would be less accurate if the better mixture was indicated based only in one variable, using ANOVA for each variable.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Despite making significant improvements to the revised version of the manuscript by addressing the reviewers' comments, further improvement is necessary.

 

From the reviewer's point of view, the authors should further prove the statements about the energy benefits by utilising of compresed mixtures of considered biomass samples. For example, if authors would like to clearly present that issue, it will be very useful to analyse how the low heating value of samples will change with lowering the moisture content, as can be seen in the values in Table 2. This will allow for the quantification of the energy benefits. The HHV does not good represent the energy content of the fuel for biomass utilisation in commercial combustion devices, due to different moisture contents.

Author Response

Reviewer 1: From the reviewer's point of view, the authors should further prove the statements about the energy benefits by utilising of compresed mixtures of considered biomass samples. For example, if authors would like to clearly present that issue, it will be very useful to analyse how the low heating value of samples will change with lowering the moisture content, as can be seen in the values in Table 2. This will allow for the quantification of the energy benefits. The HHV does not good represent the energy content of the fuel for biomass utilisation in commercial combustion devices, due to different moisture contents.

This suggestion was really pertinent and enriched our "product", the densified biomass at low moisture content.  We add at table 2 the net caloric value concept for each biomass and explain how moisture decreases HHV and real energy generation at industry. We appreciate that.