Co-Combustion of Waste Tires and Plastic-Rubber Wastes with Biomass Technical and Environmental Analysis

Round 1

Reviewer 1 Report

General comments

This manuscript is aimed at the study of co-combustion or co-gasification of biomass with scrap tires as well as with polymeric waste materials. Experiments were carried out in two types of equipment; pyrolysis of the chosen feed in pellet combustion boiler at the preset temperature of 500 ºC while the feed gasification in a common downdraft reactor with the input streams preheating using temperature of 800 ºC. Both processes were focused on utilization of waste materials (tires, plastics, rubber) for energy recovery. In case of combustion, the amount of heat produced was investigated with respect to the feed composition (tire or waste polymeric material percentage). Regarding the waste material gasification, the principal parameter was the lower heating value of the produced gas and its variation with the feed composition. In my view, presented results are preliminary data only. Although the authors intent to present some general trends, larger set of experiments should be carried out to support these conclusions. Grammar and wording of this manuscript have to be substantially improved.

 

Introduction

Some parts of the text are repeated, see paragraph limited by rows 61-65, page 2. There is large to excessive number of cited sources, e.g. the source [4] does not seem to be essential for this manuscript. Many of these sources are used as lumped reference, see e.g. row 94 on page 2, thus losing their distinction. Consequently, for the reader it is hard to find the source information.

 

Materials and methods

What does the following phrase mean (row 132, page 3): In co-combustion the tests were performed to observe the gaseous emissions at different thermal powers (66 and 157 kW) and temperatures (380 and 526 °C) [26]. Are these experimental results? If so, why are they presented here? If these are results of Glushkov et al., this information should form a part of Introduction section. Are all the equipment specifications important (e.g. power supply, dimension and weight)? See Tables 1, 2, etc. Lumped references, row 190, page 5. “Power” calculation is not fully described. According to equations 1 and 2 (rows 218 and 225, respectively, page 5) always the same value of power is obtained as cooling water mass flow and temperature is constant in all experiments. The authors should introduce enthalpy balance of the whole equipment (at the steady state conditions) including heat content of input streams and flue gases. Moreover, one should deduce from equation 2 that the feed water temperature is 23 ºC; this information is missing in the text. Substitute word “qualify” with “quantify”: row 231, page 6. Precision and accuracy of analytical equipment (Madur Photon II gas analyzer) is not provided. In Fig. 3 (page 8), position of thermocouples measuring Toxi and Tred (see Tables 7 and 8) should be given. It is expected that this information is included in the text together with specification of different reactor zones. Paragraphs, rows 266-270, page 7 and rows 298-302, page 8, contain essentially the same information. One of these paragraphs should be omitted.

 

Results and discussion

In combustion test results, the information on the amount of air used for combustion is missing. This is an important parameter influencing both conditions inside the equipment as well as composition of flue gases. Further, also temperature of input streams was not supplied (Table 5, pages 9-10; Table 6, page 11). Did you use a constant air flow in all experiments? Did you check the ashes composition, e.g. their carbon content? Do you have any explanation for the boiler temperature variation with the feed composition (Tables 5 and 6)? According to Table 6, feed mass flow varied with the feed composition. In my view, results given in this table and the respective figures were obtained at conditions that do not allow their direct comparison. In this set of experiments more than one parameter (feed composition) was changed. Also in co-gasification experiments the reaction conditions are not fully defined. Again, the amount of air used in oxidation part of gasification is not detailed. Again, as in case of co-combustion, feed mass flow varied within the experiments. Consequently, it is hard to draw clear conclusions regarding the effect of feed composition on the gasifier performance. The authors comment the effect of equivalence ratio on the flue gas composition (e.g. row 430, page 13); however, the information on the applied air mass/volumetric flow is missing. Tars and char amount should be estimated at least after each experiment, i.e. prior to the feed composition change.

 

Conclusions

I agree with the authors that interesting new data are shown in this study. On the other hand, the authors try to interpret incomparable results.

Author Response

Response to Reviewer 1:

 

Thank you very much for your comments.

We sincerely appreciate your comments and hope that the changes made to the document will be appreciated by the reviewer.

Then we will try to answer the questions made by the reviewer one by one. In addition we will introduce in the original manuscript the changes in red color

We take this opportunity to thank the reviewer for his interesting comments that we have included in the text.

General comments

This manuscript is aimed at the study of co-combustion or co-gasification of biomass with scrap tires as well as with polymeric waste materials. Experiments were carried out in two types of equipment; pyrolysis of the chosen feed in pellet combustion boiler at the preset temperature of 500 ºC while the feed gasification in a common downdraft reactor with the input streams preheating using temperature of 800 ºC. Both processes were focused on utilization of waste materials (tires, plastics, rubber) for energy recovery. In case of combustion, the amount of heat produced was investigated with respect to the feed composition (tire or waste polymeric material percentage). Regarding the waste material gasification, the principal parameter was the lower heating value of the produced gas and its variation with the feed composition.

Thank you very much for your interesting comments. We agree with the issues raised by the reviewer. Indeed, our work is part of a larger Project where we try to energetically value industrial waste of urban origin, basically plastics and rubber to treat them mixed with biomass of forest and / or agricultural origin. Analyzing its energy potential in different proportions comparing combustion and gasification processes from an energy and environmental point of view.

In my view, presented results are preliminary data only. Although the authors intent to present some general trends, larger set of experiments should be carried out to support these conclusions. Grammar and wording of this manuscript have to be substantially improved.

we try to better substantiate the results obtained and improve the the grammar and wording of the manuscript

 

Introduction

Some parts of the text are repeated, see paragraph limited by rows 61-65, page 2.

Thank you . We have proceeded to modify the manuscript. The paragraph was changed, there really was a repetition of ideas. Row 59-61, page 2.

 There is large to excessive number of cited sources, e.g. the source [4] does not seem to be essential for this manuscript. Many of these sources are used as lumped reference, see e.g. row 94 on page 2, thus losing their distinction. Consequently, for the reader it is hard to find the source information.

We had many references to the same paragraphs, we reduced references not only to the suggested paragraphs, but to the entire manuscript.

 

 

Materials and methods

What does the following phrase mean (row 132, page 3): In co-combustion the tests were performed to observe the gaseous emissions at different thermal powers (66 and 157 kW) and temperatures (380 and 526 °C) [26]. Are these experimental results? If so, why are they presented here? If these are results of Glushkov et al., this information should form a part of Introduction section.

The paragraph has been omitted and placed in the introduction, and this point has been further explored, comparing the results achieved with other studies performed.

Are all the equipment specifications important (e.g. power supply, dimension and weight)?

In fact they are not. we remove less relevant information from the tables

See Tables 1, 2, etc. Lumped references, row 190, page 5. “Power” calculation is not fully described. According to equations 1 and 2 (rows 218 and 225, respectively, page 5) always the same value of power is obtained as cooling water mass flow and temperature is constant in all experiments. The authors should introduce enthalpy balance of the whole equipment (at the steady state conditions) including heat content of input streams and flue gases. Moreover, one should deduce from equation 2 that the feed water temperature is 23 ºC; this information is missing in the text.

Equation two was merely an example. But blame our, we do not refer. We decided to remove equation two and explain the experiment a little better.

Substitute word “qualify” with “quantify”: row 231, page 6.

Thanks. It is replaced.

Precision and accuracy of analytical equipment (Madur Photon II gas analyzer) is not provided.

The specifications of the gas analysis equipment were submitted, as well as the calorimeter.(Calorimeter - row 253-254, page 7) (Gas analyser  - row 284-285, page 7-8)

In Fig. 3 (page 8), position of thermocouples measuring Toxi and Tred (see Tables 7 and 8) should be given. It is expected that this information is included in the text together with specification of different reactor zones.

In the image we insert arrows indicating the location of the thermocouples as well as the pressure probes. And we try to explain your location better (row 325-329, page 9).

Paragraphs, rows 266-270, page 7 and rows 298-302, page 8, contain essentially the same information. One of these paragraphs should be omitted.

The second paragraph is omitted.

 

Results and discussion

 

In combustion test results, the information on the amount of air used for combustion is missing. This is an important parameter influencing both conditions inside the equipment as well as composition of flue gases. Further, also temperature of input streams was not supplied (Table 5, pages 9-10; Table 6, page 11). Did you use a constant air flow in all experiments?

The amount of air used for combustion test was all the same (72,97 m3/h) and the temperature were placed in the table 7, pages 11, and table 8, page 12, and tried to better explain the controlled parameters in row 366-370, page 11.

 

Did you check the ashes composition, e.g. their carbon content?

We analyzed all the ashes of the tests, but we thought the manuscript would get a little lengthy with them. Now we put the ash analysis on row 419-442, page 14.

Do you have any explanation for the boiler temperature variation with the feed composition (Tables 5 and 6)?

Can find the justification in row 366-370, page 11. We have problems to feed the equipment with hight quantity of reside in the mixtures and with the excess of air.

 

According to Table 6, feed mass flow varied with the feed composition. In my view, results given in this table and the respective figures were obtained at conditions that do not allow their direct comparison. In this set of experiments more than one parameter (feed composition) was changed.

You're right when you repair that tests are not comparable, it's a fact. We actually had a lot of problems with the boiler feeding, because either the excess waste or the characteristics of waste (notably the density), did not allow an equal feed in both tests.

 

Also in co-gasification experiments the reaction conditions are not fully defined. Again, the amount of air used in oxidation part of gasification is not detailed. Again, as in case of co-combustion, feed mass flow varied within the experiments. Consequently, it is hard to draw clear conclusions regarding the effect of feed composition on the gasifier performance. The authors comment the effect of equivalence ratio on the flue gas composition (e.g. row 430, page 13); however, the information on the applied air mass/volumetric flow is missing.

In gasification tests the feeding difficulty was even greater than in combustion tests. However, we have already entered the values of the inlet air in the reactor, as well as the ER. We have also corrected paragraph 472-473, pages 15-16.

 

 Tars and char amount should be estimated at least after each experiment, i.e. prior to the feed composition change.

 We carried out the gasification and combustion tests followed to find out how much mixing capacity the equipment could handle. It is true that we could have done the tests separately, and the analysis of the products from both processes would be correctly analysed, but also for reasons of fuel limitation, we took the option to perform the tests followed.

 

Conclusions

I agree with the authors that interesting new data are shown in this study. On the other hand, the authors try to interpret incomparable results.

The aim of the present study was not to make a direct comparison of the two technologies, but to demonstrate that gasification is an energy efficient and more environmentally sustainable alternative to combustion as a future option for energy recovery. This same statement we put it in the conclusion.

We take this opportunity to thank the reviewer for his interesting comments that we have included in the text.

Author Response File: Author Response.pdf

Reviewer 2 Report

In this paper the authors analyze the technology of co-combustion of waste tires and plastic-rubber wastes with biomass. The technical and environmental analysis are performed. The present work studies the possibility of energy recovery by thermal conversion of combustible residual materials, namely tires and rubber-plastic.

In general, this is an interesting study providing new insights in the most important field of improving efficiency. The results of this work are interesting and useful for researchers and engineers. Overall, the paper is well-structured. I would recommend this manuscript for publication in the Sustainability journal. However, a number of issues mentioned below should be addressed to make the manuscript suitable for publication in Sustainability:

The possibility of heat recuperation by organic fuel conversion is not new. The thermochemical recuperation technology can be considered as energy recovery technology by thermal conversion of combustible materials. Therefore, in the Introduction the thermochemical recuperation as an energy recovery technology by thermal conversion of combustible materials should be discussed. I recommend to use following references: "Thermodynamic equilibrium analysis of combined dry and steam reforming of propane for thermochemical waste-heat recuperation." International Journal of Hydrogen Energy 42.22 (2017): 14926-14935.; "Thermochemical recuperation by ethanol steam reforming: Thermodynamic analysis and heat balance." International Journal of Hydrogen Energy 44.59 (2019): 30865-30875.；"Thermochemical waste‐heat recuperation by steam methane reforming with flue gas addition." International Journal of Energy Research 43.6 (2019): 2216-2226.

Author Response

Reviewer 2 –                    

                                                

Comments and Suggestions for Authors

In this paper the authors analyze the technology of co-combustion of waste tires and plastic-rubber wastes with biomass. The technical and environmental analysis are performed. The present work studies the possibility of energy recovery by thermal conversion of combustible residual materials, namely tires and rubber-plastic.

In general, this is an interesting study providing new insights in the most important field of improving efficiency. The results of this work are interesting and useful for researchers and engineers. Overall, the paper is well-structured. I would recommend this manuscript for publication in the Sustainability journal. However, a number of issues mentioned below should be addressed to make the manuscript suitable for publication in Sustainability:

Thank you very much for your interesting and constructive comments. Then we will include your suggestion in the text in red. Thank you very much again.

The possibility of heat recuperation by organic fuel conversion is not new. The thermochemical recuperation technology can be considered as energy recovery technology by thermal conversion of combustible materials. Therefore, in the Introduction the thermochemical recuperation as an energy recovery technology by thermal conversion of combustible materials should be discussed. I recommend to use following references: "Thermodynamic equilibrium analysis of combined dry and steam reforming of propane for thermochemical waste-heat recuperation." International Journal of Hydrogen Energy 42.22 (2017): 14926-14935.; "Thermochemical recuperation by ethanol steam reforming: Thermodynamic analysis and heat balance." International Journal of Hydrogen Energy 44.59 (2019): 30865-30875.；"Thermochemical waste‐heat recuperation by steam methane reforming with flue gas addition." International Journal of Energy Research 43.6 (2019): 2216-2226.

Thank you very much for your recommendations. We have incorporated in the Introduction the three references to the recommended studies.

“The thermochemical recuperation as an energy recovery technology by thermal conversion of combustible materials was discussed in diffents studies”   [1]

“Some scientific works considers the scheme of fuel-consuming equipment with a thermochemical heat recuperation system by using ethanol steam reforming. The main concept of thermochemical recuperation (TCR) is the transformation of exhaust gases heat into chemical energy of a new synthetic fuel that has higher calorimetric properties such as low-heating value. Thermochemical recuperation can be considered as an on-board hydrogen production technology.” [2]

“There are studies that suggest the process flow schematic of fuel-consuming equipment with thermochemical waste-heat recuperation by steam methane reforming with an addition of flue gas to the reaction mixture” [3]

[1]Pashchenko,D.Thermodynamic equilibrium analysis of combined dry and steam reforming of propane for thermochemical waste-heat recuperation. International Journal of Hydrogen Energy. 2017, 42 (22) ,14926-14935. (DOI: 10.1016/j.ijhydene.2017.04.284).

[2]Pashchenko,D.Thermochemical recuperation by ethanol steam reforming: Thermodynamic analysis and heat balance. International Journal of Hydrogen Energy. 2019, 44 (59), 30865-30875. (DOI: 10.1016/j.ijhydene.2019.10.009).

[3]Pashchenko,D. Thermochemical waste-heat recuperation by steam methane reforming with flue gas addition. International Journal of Hydrogen Energy. 2019, 43 (6) , 2216-2226. (DOI: 10.1002/er.4436).

 

We take this opportunity to thank the reviewer for his interesting comments that we have included in the text.

 

Author Response File: Author Response.pdf

Reviewer 3 Report

The paper is interesting, it presents a study about the energy recovery of tires and rubber-plastic mixed with biomass through combustion and gasification. The study presents two different experiments (one for combustion and another for gasification).

The paper can be published taking into account the following considerations:

The chapter numbering must to be corrected Line 190 has to be checked, the sentence is not correct. Line 194 has to be checked, the format is not correct. Figure 3 is not numbered. Line 477, where “2.26 MJ/Nm³ ” should be 2.6 MJ/Nm³ Title 3 is missing (Must appear “3. Results”) Line 377, where authors write “biomass consumption” should be “fuel feeding”

 

Table 6:

Has the percentage of oxygen been obtained by difference? (%O = 100 - %N- %C - %H - %S -%Ashes)

The used tires and the plastics and rubbers are both mixtures. The values of their components are average values. Is the variance associated with each high value?

Table 7:

Are the total emissions produced known? It would be interesting to know the ratio of amount of pollutant per power generated.

Table 9:

To know the composition of the four ash streams would be very interesting.

Tabla 10:

What do the “T oxi” and “T red” parameters mean?

ER values should be commented in the text.

Tables 7 and 10:

If the ashes, tars and chars had been counted in each test, the results would have been more complete. Will these three streams vary depending on the mixtures?

4. Conclusions:

Conclusions should be based on the results obtained and commented in the work.

The first paragraph is not correct, it doesn’t come from the work.

References that have not been commented in the paper appear in the second and third paragraphs.

The conclusions must be rewritten.

Author Response

Thank you for your comments.

We sincerely appreciate your comments and hope that the changes made to the document will be appreciated by the reviewer.

Then we will try to answer the questions asked by the reviewer one by one. The changes made are written on a background of a different color (    )

We take this opportunity to thank the reviewer for his interesting comments that we have included in the text.

General comments

The chapter numbering must to be corrected

Thank you very much for your interesting comments. We have carried out a complete revision of the text and proceeded to correctly number the different sections and subsections. Thanks for the correction.

 Line 190 has to be checked, the sentence is not correct.

We have modified this sentence (Line 200)

Line 194 has to be checked, the format is not correct.

Thank you. We have proceeded to modify this error

Figure 3 is not numbered.

Thank you. We have proceeded to number this figure

 Line 477, where “2.26 MJ/Nm3 ” should be 2.6 MJ/Nm3

Thank you. We apologize for this error. We have corrected it.

Title 3 is missing (Must appear “3. Results”)

Thank you very much again. We had effectively omitted the title 3 Results because the picture omitted the title. Now we have already corrected it.

 Line 377, where authors write “biomass consumption” should be “fuel feeding”

Thank you. We have proceeded to modify according to the reviewer's correct comment

 

Table 6:

 

Has the percentage of oxygen been obtained by difference? (%O = 100 - %N- %C - %H - %S -%Ashes)

Exactly. Our equipment, Thermo Scientific ™ FLASH 2000 CHNS / O Analyzers, analyzes oxygen in a separate column and with different drag gases than those used in the analysis of Carbon, Nitrogen, Hydrogen, and Sulfur. For a question of saving resources and time, we make the difference as the reviewer suggests in the question.

 

The used tires and the plastics and rubbers are both mixtures. The values of their components are average values. Is the variance associated with each high value?

Regarding the question, we performed three repetitions for each analysis and take into account the average value. Standard deviation between each analysis was not significant (> 0.5%)

Table 7:

Are the total emissions produced known? It would be interesting to know the ratio of amount of pollutant per power generated.

In this question, what we did was, increase the residue as the test went on. For each increase in waste (20, 40 and 60%) we made an average of every 10 minutes, the pollutants it was releasing and the power. We don’t know the total emissions produced.

 

Table 9:

To know the composition of the four ash streams would be very interesting.

Yes, the reviewer is absolutely right. However, we chose to carry out the teste without stop the equipment, with the sole purpose of knowing what the maximum residue capacity is that the equipment could support and which emissions of each mixture.

 

Tabla 10:

What do the “T oxi” and “T red” parameters mean?

The parameters Toxi and Tred refer to oxidation temperatures and reduction temperatures. The oxidation temperature is located next to the air inlet in the gasifier, where there is a combustion zone to supply energy to the gasification or reduction (endothermic) zone. The reduction temperature is further below the oxidation zone, where the coals will suffer the thermal cracking and form gas. The oxidation zone is an exothermic zone, where combustion reactions prevail that will provide the necessary energy for gasification (reduction zone). Figure 3 shows the two zones.

 

ER values should be commented on in the text.

Thank you. We have proceeded to modify according to the reviewer's correct comment. Line 497-503.

 

 

 

Tables 7 and 10:

If the ashes, tars and chars had been counted in each test, the results would have been more complete. Will these three streams vary depending on the mixtures?

The reviewer is absolutely right, the results would have been more complete. Yes, these two streams vary during the addition of polymers to the fuel. That is, the more polymers we add to the mixture, the more volatile we will find in the mixture when subjected to a thermochemical process, this volatiles will release and form more hydrocarbons, forming more tar. The formation of charcoal is also less As the mixture increases, due to the low content of fixed carbon present in the polymers, and the theme gets worse for plastics and rubbers.

 

Conclusions:

Conclusions should be based on the results obtained and commented in the work.

Thank you very much for your comment. We have carried out a review of the Final Conclusions according to the work and the results obtained

The first paragraph is not correct, it doesn’t come from the work.

Thanks for the correction. We proceeded as requested by the reviewer.

References that have not been commented in the paper appear in the second and third paragraphs.

Thank you very much for your comment. We have proceeded to comment previously in the manuscript this reference

The conclusions must be rewritten.

Thank you very much for your comment. We have rewritten the conclusions again to make them clearer and more interesting.

 

We take this opportunity to thank the reviewer for his interesting comments that we have included in the text.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Less important of my previous recommendations were reflected in the corrected version of this manuscript, although I did not expect that Introduction would be "inflated" to such extent. Still, the need of experiments carried out at comparable conditions is evident.

There is a misunderstanding, the authors claim that the conditions at co-combustion experiments cannot be the same as at co-gasification. They are definitely right. My comment, however, was that conditions during co-combustion were not the same for all four experiments using plastics and rubber as fuel component. Thus, data presented in Fig. 5 contain incomparable data.

The same is valid for co-gasification experiments and data presented in Fig. 6 (four experiments) and also in Fig. 7 (three experiments). Consequently, comments and conclusions deduced from these figures are not justified.

I recommend to omit these three figures (Figs. 5, 6 and 7) as misleading, and also to correct the respective comments. Data presented in Tables 8, 10 and 11 should be commented as separate experiments, e.g. the results of four experiments on co-combustion of biomass with the addition of plastics and rubber (Table 8) are data obtained at four different experimental conditions. I would not recommend deducing any trends from these four (independent) experiments (see e.g. rows 411-414, page 13).

Similar criticism can be written assuming data comparison presented in Fig. 6 and that in Fig. 7.

Regarding the newly introduced Table 10 and the respective text, I am confused with the use of terms "ash" and "coal". I also would expect much lower content of combustibles in "ash" produced by co-combustion than the values presented in this Table.

There is some problem with the chapters numbering at the page 5.

New paragraph introduced into Conclusions section can be omitted.

English grammar and wording has to be improved substantially. It is recommended to ask a help of native-speaking person.

Author Response

Thank you for your comments.

We sincerely appreciate your comments and hope that the changes made to the document will be appreciated by the reviewer.

Then we will try to answer the questions asked by the reviewer one by one. The changes made are written on a background of a different color (yellow) in the manuscript, to differentiate them from the 1 round of revision

We take this opportunity to thank the reviewer for his interesting comments that we have included in the text.

 

 

General comments

Less important of my previous recommendations were reflected in the corrected version of this manuscript, although I did not expect that Introduction would be "inflated" to such extent. Still, the need of experiments carried out at comparable conditions is evident.

Thank you very much for your interesting comments. Thanks for the correction. Studies about thermal gasification with commercial downdraft reactors, with this type of fuels, are recent studies, which reduces the number of articles available for an extensive review of the literature. Another problem we encounter is related to the type of gasifier, we use a commercial fixed bed gasifier and most of the studies available are related to fluidized bed gasifiers. Another study was added that carries out thermal gasification and combustion tests for waste tires.

There is a misunderstanding, the authors claim that the conditions at co-combustion experiments cannot be the same as at co-gasification. They are definitely right. My comment, however, was that conditions during co-combustion were not the same for all four experiments using plastics and rubber as fuel component. Thus, data presented in Fig. 5 contain incomparable data..

We agree, the tests are not comparable, so we decided to follow the reviewer's guidelines table 5 was removed.

The same is valid for co-gasification experiments and data presented in Fig. 6 (four experiments) and also in Fig. 7 (three experiments). Consequently, comments and conclusions deduced from these figures are not justified..

Thank you. We decided to omit the tables that the reviewer proposed to us and justify the tests in a more isolated way.

I recommend to omit these three figures (Figs. 5, 6 and 7) as misleading, and also to correct the respective comments. Data presented in Tables 8, 10 and 11 should be commented as separate experiments, e.g. the results of four experiments on co-combustion of biomass with the addition of plastics and rubber (Table 8) are data obtained at four different experimental conditions. I would not recommend deducing any trends from these four (independent) experiments (see e.g. rows 411-414, page 13)..

The figures and comments regarding the data presented in the manuscript were removed, following the guidelines of the reviewer.

Similar criticism can be written assuming data comparison presented in Fig. 6 and that in Fig. 7..

Figures 6 and 7 were removed, following the reviewer's guidelines.

Regarding the newly introduced Table 10 and the respective text, I am confused with the use of terms "ash" and "coal". I also would expect much lower content of combustibles in "ash" produced by co-combustion than the values presented in this Table.

Evidently we were wrong to write "ashes" in the table related to the co-gasification tests, thank you very much for clarification. They are, in fact, coals, since we have always been gasifying, as the er's prove.

Regarding the energy content of the ashes from co-combustion, we also found it strange, but everything indicates that there was incomplete combustion due to the various feeding problems we had during the tests.

 

 

There is some problem with the chapters numbering at the page 5..

There was a pointing problem in the introduction and the number of chapters changed. Thanks for watching it.

New paragraph introduced into Conclusions section can be omitted.

Thanks for the correction. We proceeded as requested by the reviewer.

English grammar and wording has to be improved substantially. It is recommended to ask a help of native-speaking person.

English was revised by a native.

We take this opportunity to thank the reviewer for his interesting comments that we have included in the text.

Author Response File: Author Response.docx

Reviewer 2 Report

The authors have addressed my comments and I recommend publication.

Author Response

Revisor 2 –2 ronda                    

                                                

Comentarios y sugerencias para autores

Los autores han abordado mis comentarios y recomiendo su publicación.

Muchas gracias por confiar en nuestro trabajo. Aprovechamos esta oportunidad para agradecer el trabajo realizado por el revisor.

Author Response File: Author Response.docx

Reviewer 3 Report

OK

Round 3

Reviewer 1 Report

Majority of my comments were addressed in this revised version of the manuscript. In my view, still some minor improvement can be achieved especially regarding the grammar and wording. Otherwise, the manuscript is now in acceptable shape for publication.

Author Response

Thank you for your comments.

Thank you very much for your comment. We have proceeded to revise the text completely regarding especialy the grammar and wording. by an expert reviewer in English editions. Thank you very much.

We take this opportunity to thank the reviewer for his interesting comments that we have included in the text.

Author Response File: Author Response.docx