Natural Gas Conversion and Liquid/Solid Organic Waste Gasification by Ultra-Superheated Steam

Round 1

Reviewer 1 Report

Review of a manuscript titled " Methane Conversion and Liquid/Solid Organic Waste Gasification by Ultra-Superheated Steam" by Frolov et al.

The authors have demonstrated the gasification of organic waste experimentally with ultra-superheated steam using a pulsed denotation gun.  Even though the work is quite novel, but several important details are missing.

1. In general literature review of the authors is very selective. Even though the authors claim that first-time experimental demonstration of biomass gasification using pulsed detonation is done. But, to my knowledge, the authors have missed the work given below  (i) Pierce, T. H. (1987). Detonation‐induced coal gasification. International journal of energy research, 11(2), 203-231.  (ii) Hunter, L. G. (1998). Pulse detonation device for coal gasification. In Fuel and Energy Abstracts (Vol. 1, No. 39, p. 69). (iii) Pierce, T. H., Afify, E. M., & Zickefoose, R. T. (1979). Detonation-induced coal gasification. Final report (No. DOE/ET/10451-T1). North Carolina State Univ., Raleigh (USA). Dept. of Mechanical and Aerospace Engineering. (iv) Mei, D., Zhou, J., Biney, P. O., & Huque, Z. (1998). Slag Characterization and Removal Using Pulse Detonation Technology During Coal Gasification (No. DE-FG22-95MT95010-10). Federal Energy Technology Center (FETC), Morgantown, WV, and Pittsburgh, PA.
2. Figure 1 which was described in section 3 is a little confusing, it would be better to clearly mark the 3 sections of the tube. 
3. In line 188-189, the author states the steady-state thermal mode will take about 5 mins (300 sec), then why the experiments for varying phi from 0.8 to 1.3 was performed over a span of 50 sec as shown in figure 6?
4. There is a significant discrepancy in results shown in Figures 6 and 7. for example, CO2 vol fraction for phi =1 in figure 6 is 55% and in figure 7 is 80%. why?
5. It is understood the gasification is not complete with f = 1 Hz, why rise the f = 5 hz. what would happen if f = 3 hz. will that be sufficient.
6. Also, it would be better if the authors comment on what will the gasification if one would increase rate of injection of liquid or biomass in the reactor?

Author Response

We are grateful to the reviewer for valuable comments. We made our best to follow all the comments. All changes in the revised manuscript are marked in yellow.

Review of a manuscript titled " Methane Conversion and Liquid/Solid Organic Waste Gasification by Ultra-Superheated Steam" by Frolov et al.

The authors have demonstrated the gasification of organic waste experimentally with ultra-superheated steam using a pulsed denotation gun.  Even though the work is quite novel, but several important details are missing.

1. In general literature review of the authors is very selective. Even though the authors claim that first-time experimental demonstration of biomass gasification using pulsed detonation is done. But, to my knowledge, the authors have missed the work given below  (i) Pierce, T. H. (1987). Detonation‐induced coal gasification. International journal of energy research, 11(2), 203-231.  (ii) Hunter, L. G. (1998). Pulse detonation device for coal gasification. In Fuel and Energy Abstracts (Vol. 1, No. 39, p. 69). (iii) Pierce, T. H., Afify, E. M., & Zickefoose, R. T. (1979). Detonation-induced coal gasification. Final report (No. DOE/ET/10451-T1). North Carolina State Univ., Raleigh (USA). Dept. of Mechanical and Aerospace Engineering. (iv) Mei, D., Zhou, J., Biney, P. O., & Huque, Z. (1998). Slag Characterization and Removal Using Pulse Detonation Technology During Coal Gasification (No. DE-FG22-95MT95010-10). Federal Energy Technology Center (FETC), Morgantown, WV, and Pittsburgh, PA.

To follow this comment, we have supplemented Introduction with several sentences and references.

As for the detonation technologies, they provide similar gasification temperatures (above 2200 K) without gas–plasma transition but do not need special structural materials and/or refractory linings for gasifier walls. First mentioning of detonation technologies go back to [13, 14], where pulverized coal gasification was studied in a single-pulse detonation-induced flow with the coal particle residence time in the detonation products ranging from 1 to 15 ms. Despite too few tests were performed for conclusive statements, combined yields of CO and CH₄ attained 40% of the total initial carbon content in the coal samples. The author of [15] filed a patent on a pulse detonation device for autothermal coal gasification. The pulse detonation device was intended for discharging high pressure steam, oxygen, and other exhaust products into the bed of coal in a gasifier. It was implied that the high temperature, high pressure exhaust pulses might enhance the gasification process, keeping the coal bed from excessive slagging. It was also implied in [15] that the purge air between detonation cycles was discharged into the coal bed to support coal combustion. Consequently, a part of the available carbon was consumed by combustion. The remaining carbon was consumed in gasification reactions with carbon dioxide, steam, and hydrogen creating product gases. The product gases were subsequently burned in a combustion chamber for powering a gas turbine. The authors of [16] showed the potential of using pulsed detonations for mechanical removal of slag and fouling deposits from heat transfer surfaces in coal-firing power plants.

2. Figure 1 which was described in section 3 is a little confusing, it would be better to clearly mark the 3 sections of the tube. 

We replotted the former Fig. 1 (now Fig. 2) by explicitly indicating three sections of the detonation gun.

3. In line 188-189, the author states the steady-state thermal mode will take about 5 mins (300 sec), then why the experiments for varying phi from 0.8 to 1.3 was performed over a span of 50 sec as shown in figure 6?

Thank you! The time in the former Fig. 6 (now Fig. 7) must be in minutes rather than seconds. Also, experiments with stepwise variation of phi were conducted after the gun attained the steady-state thermal mode (it is indicated in the original text). To avoid misunderstanding, we have added a sentence: “Changes in phi affected the gun wall temperature insignificantly.”

4. There is a significant discrepancy in results shown in Figures 6 and 7. for example, CO2 vol fraction for phi =1 in figure 6 is 55% and in figure 7 is 80%. why?

Sorry, by mistake the numbers in former Fig. 6 (now Fig. 7) were incorrect (in the original text it was written that Φ changes from 0.91 to 1.4). We have put true numbers, thank you! It should be noted that the new Fig.7 shows only one experimental run as an example, while Fig. 8 shows the results of 10 runs. To avoid misunderstanding, this fact is outlined additionally in the text.

5. It is understood the gasification is not complete with f = 1 Hz, why rise the f = 5 hz. what would happen if f = 3 hz. will that be sufficient.

We have taken 5 Hz as an extreme condition to ensure very high time-averaged mean temperature. As a matter of fact, we are going to increase pulse frequency step-by-step (2, 3, 4, and 5 Hz) to observe changes in the syngas composition. To follow this comment, we have added a sentence: “The value of 5 Hz is taken as an extreme condition just to see a difference.”

6. Also, it would be better if the authors comment on what will the gasification if one would increase rate of injection of liquid or biomass in the reactor?

If we increase the mass flow rate of liquid waste above 3 g/s (see new Fig. 11), we observe oil residue in the exhaust system. This means that a frequency of 1 Hz and a median residence time of 2 s do not provide complete gasification. When we replaced the 100-liter gasifier by a 40-liter gasifier, other conditions being equal, incomplete gasification was observed when the mass flow rate of liquid waste was above 15 g/s. Interestingly, the contents of H2, CO, CH4 and CO2 were in average the same as in Fig. 11, thus indicating the primary importance of the gasification temperature. As for the solid waste (sawdust), we did not see much difference in the plateau syngas composition when loading 2 or 3 kg of feedstock in the gasifier. These details we are planning to publish in the next paper.

Author Response File: Author Response.pdf

Reviewer 2 Report

Manuscript ID energies-1697778 entitled “Methane Conversion and Liquid/Solid Organic Waste Gasification by Ultra-Superheated Steam” presents an valuable topic that may be of interest to readers. However, in its current form, the manuscript does not meet the standards of scientific work. In my opinion, it can be accepted after deep corrections. My remarks below:

1. Graphical abstract will be very useful for readers to understand Authors intentions.
2. Introduction needs to be corrected and expanded. The authors provided only commonly known information. The authors must underline the major findings of their work and explain novelty of this study comparatively with their published papers or other similar studies. The technology presented in the manuscript should be presented against the background of other methods used for the gasification of organic waste, including biological methods based, among others, on fermentation: https://doi.org/10.3390/fermentation7010012, https://doi.org/10.3390/en15030911,  https://doi.org/10.3390/en14071831.
3. Please indicate the strengths and weaknesses of this technology, as well as the technological and economic efficiency of the process compared to other solutions aimed at the energetic use of organic waste. In Discussion or in Introduction section.
4. Please take into account the research hypotheses that were formulated and that were verified. What was the inspiration and basis for undertaking the presented research? Technological, economic factor? What hypotheses did the authors put forward and what did they want to achieve, what to prove?
5. Chapters 2 Pulsed detonation gun technology and 3 Gasifier should be included in the methodology section.
6. Please add the Methods and materials section and enter Chapters 2 and 3 there as Method Characteristics and Test Stand Characteristics.
7. The methodology (4 Experimental procedures ) is unclear. There is no clear division of experiments into stages, variants and series. The analytical procedures are very briefly described. There is no exact physical and chemical characteristics of the organic wastes used. Needs to be completed.
8. An organizational chart of the research conducted would be very helpful in understanding the Authors' intentions.
9. There is no indication of the type of devices, analytical equipment, models, producers and countries of origin used. It needs to be completed.
10. The greatest weakness of the manuscript is the lack of a properly conducted statistical analysis of the research results. Without a comparative analysis, the results and conclusions are unreliable, with no scientific value. What statistical tests were used to assess the significance of differences between the variables, what level of probability or significance was used, what post-hoc tests were used. This has to be completed and the results of the static analysis are given in the tables.
11. There is no clearly defined Results chapter.
12. The Authors do not even provide standard deviations, and the results are based on averages, which gives no information about the scatter of the results. This also needs to be completed.
13. Lack of information on the number of replicates of the study.
14. The data was presented in a too simple way in the text. Depth discussion is necessary. The discussion of the results is very poor, it can be said that it does not exist at all. This has to be extended significantly. Please compare the obtained results with the works of other authors.
15. Economic analysis of the process and perform energy balance is absolutely necessary.
16. The Conclusion must be revised. The main results must be presented in this section.
17. The paper was written in standard, but correction English is necessary. The size of the article is to short to the contents.
18. The manuscript adheres to the journal's standards after major revision.

Author Response

We are grateful to the reviewer for valuable comments. We made our best to follow all the comments. All changes in the revised manuscript are marked in green.

Manuscript ID energies-1697778 entitled “Methane Conversion and Liquid/Solid Organic Waste Gasification by Ultra-Superheated Steam” presents an valuable topic that may be of interest to readers. However, in its current form, the manuscript does not meet the standards of scientific work. In my opinion, it can be accepted after deep corrections. My remarks below:

1. Graphical abstract will be very useful for readers to understand Authors intentions.

Actually, we have uploaded the graphical abstract together with manuscript during submission procedure. By some reason the graphical abstract is absent in the system. We will upload it again.

2. Introduction needs to be corrected and expanded. The authors provided only commonly known information. The authors must underline the major findings of their work and explain novelty of this study comparatively with their published papers or other similar studies. The technology presented in the manuscript should be presented against the background of other methods used for the gasification of organic waste, including biological methods based, among others, on fermentation: https://doi.org/10.3390/fermentation7010012, https://doi.org/10.3390/en15030911,  https://doi.org/10.3390/en14071831.

We have added some more references on the topic, including one of those mentioned by the reviewer.

3. Please indicate the strengths and weaknesses of this technology, as well as the technological and economic efficiency of the process compared to other solutions aimed at the energetic use of organic waste. In Discussion or in Introduction section.

We have added a paragraph at the end of Section 4 Discussion on this issue.

4. Please take into account the research hypotheses that were formulated and that were verified. What was the inspiration and basis for undertaking the presented research? Technological, economic factor? What hypotheses did the authors put forward and what did they want to achieve, what to prove?

We wanted to demonstrate the new technology. It is written at the end of Introduction. Also, we have added a new section 5 Mass and Energy Balances to demonstrate attractive economic features of the technology.

5. Chapters 2 Pulsed detonation gun technology and 3 Gasifier should be included in the methodology section.

6. Please add the Methods and materials section and enter Chapters 2 and 3 there as Method Characteristics and Test Stand Characteristics.

We have completely restructured the manuscript in terms of sections: Introduction is now followed by Methods and Materials, Results, Discussion, Mass and Energy Balances, and Conclusions sections with appropriate subsections.

7. The methodology (4 Experimental procedures ) is unclear. There is no clear division of experiments into stages, variants and series. The analytical procedures are very briefly described. There is no exact physical and chemical characteristics of the organic wastes used. Needs to be completed.

In the new section 2 Methods and Materials, we have added a subsection 2.3 Materials. In this subsection, we have described the experimental series, placed tables with natural gas composition, as well as with proximate and ultimate analyses of liquid and solid wastes under study. Because we used natural gas rather than pure methane, we have replaced “methane” by “natural gas” all throughout the manuscript where applicable, including the manuscript title.

8. An organizational chart of the research conducted would be very helpful in understanding the Authors' intentions.

In the new subsection 2.3, we have indicated the sequence of our studies and materials used.

9. There is no indication of the type of devices, analytical equipment, models, producers and countries of origin used. It needs to be completed.

We have added the missing information where applicable.

10. The greatest weakness of the manuscript is the lack of a properly conducted statistical analysis of the research results. Without a comparative analysis, the results and conclusions are unreliable, with no scientific value. What statistical tests were used to assess the significance of differences between the variables, what level of probability or significance was used, what post-hoc tests were used. This has to be completed and the results of the static analysis are given in the tables.

In the new subsection 2.3, we have added a sentence: “Each experimental run was repeated at least 3 times to collect the data on the reproducibility of results in terms of the average value and the run-to-run scatter of this value.” Also, we have added a sentence to subsections 3.1, 3.2.1 and 3.2.2: “The maximum run-to-run scatter in the measured values of volume fractions of H2 and CO is ±4%,” “The maximum run-to-run scatter in the measured values of volume fractions of H2 and CO is ±5%,” and “The maximum run-to-run scatter in the measured values of volume fractions of H2 and CO is ±5%.

11. There is no clearly defined Results chapter.

To follow this comment, we have combined all results in one Section: Results.

12. The Authors do not even provide standard deviations, and the results are based on averages, which gives no information about the scatter of the results. This also needs to be completed.

In our original figures 5, 7, and 10, the scatter of the results is indicated by error bars, which is written in figure captions (see Figs 7). Nevertheless, to follow the comment, we have duplicated this information in the manuscript by adding the value of scatter to some sentences and figure captions.

13. Lack of information on the number of replicates of the study.

To follow this comment, we have added a sentence to the manuscript: “Each experimental run was repeated at least 3 times to collect the data on the reproducibility of results in terms of the average value and the run-to-run scatter of this value.”

14. The data was presented in a too simple way in the text. Depth discussion is necessary. The discussion of the results is very poor, it can be said that it does not exist at all. This has to be extended significantly. Please compare the obtained results with the works of other authors.

To follow this comment, we have compared our results with those obtained by other authors in section 4 Discussion, and extended the list of references, correspondingly.

14. Economic analysis of the process and perform energy balance is absolutely necessary.

To follow this comment, we have added a new section to the manuscript, 5 Mass and Energy Balances.”

15. The Conclusion must be revised. The main results must be presented in this section.

Following this comment, we have reformulated conclusions.

16. The paper was written in standard, but correction English is necessary. The size of the article is to short to the contents.

A native English-speaking colleague has checked our English and made some corrections.

16. The manuscript adheres to the journal's standards after major revision.

Thank you very much for valuable and useful comments!

Author Response File: Author Response.pdf

Reviewer 3 Report

In my opinion, the manuscript describes a case study rather than scientific  research. The introduction section is poor because the authors did not wider describe the state-of the-art. Also, any novel aspect of the study has not been defined. The practical part of  the manuscript is mainly directed to the description of the technology and installation used in the study, but much lower has been desired on the experiments performed.  Experimental part is very limited to only a few results obtained with almost no discussion provided. Hence, I cannot recommend the manuscript to be published in the journal of Energies.

Author Response

We are grateful to the reviewer for valuable comments. We made our best to follow all the comments. 

In my opinion, the manuscript describes a case study rather than scientific  research. The introduction section is poor because the authors did not wider describe the state-of the-art. Also, any novel aspect of the study has not been defined. The practical part of  the manuscript is mainly directed to the description of the technology and installation used in the study, but much lower has been desired on the experiments performed.  Experimental part is very limited to only a few results obtained with almost no discussion provided. Hence, I cannot recommend the manuscript to be published in the journal of Energies.

Following these comments, we have added some more references to the Introduction section to indicate the state-of-the-art in the field. As for the novel aspect of this study, we have defined it at the end of Introduction and at the end of Discussion sections. We rearranged the manuscript structure and included all results into Results section, which contains the data of over 100 experiments, over 60 thermodynamic calculations, and over 20 3D gas-dynamic calculations. As for Discussion, we have compared our findings with those obtained by other researchers with an alternative plasma-arc gasification technology, provided some economic details, and formulated pros and contras of our technology.

Author Response File: Author Response.pdf

Reviewer 4 Report

The authors have used the experimental technology of a pulsed detonation gun for the gasification of organic wastes with ultra-superheated steam. The results are interesting and the manuscript can be accepted after addressing the following comments:

1. The introduction section must include the latest studies performed on the gasification of organic waste treatment or mention briefly about the techniques available for waste treatment systems.
2. Steam gasification also yields oil, slag, and unconverted waste. The authors should also include the details on the yield of these components.
3. The authors should briefly discuss the limitations of the current work and how it can be implemented on an industrial scale to minimize organic waste.
4. The authors may also highlight the potential applications of the current methodology to the other waste material including (waste plastics and municipal waste.)

Author Response

We are grateful to the reviewer for valuable comments. We made our best to follow all the comments. All changes in the revised manuscript are marked in grey.

The authors have used the experimental technology of a pulsed detonation gun for the gasification of organic wastes with ultra-superheated steam. The results are interesting and the manuscript can be accepted after addressing the following comments:

1. The introduction section must include the latest studies performed on the gasification of organic waste treatment or mention briefly about the techniques available for waste treatment systems.

We have extended the Introduction section by adding some new references on the known gasification technologies.

2. Steam gasification also yields oil, slag, and unconverted waste. The authors should also include the details on the yield of these components.

To follow this comment, we have added a paragraph to the Discussion section.

It is worth noting that no condensed-phase by-products like tar and char were detected in the gasification experiments under discussion. Also, there were no mineral residues. On the one hand, it is explained by the feedstocks used (natural gas, waste machine oil, and wood sawdust) containing nearly no ash. On the other hand, it is explained by high gasification temperature (well above 1200 K) and relatively long residence time (up to 15 s) of feedstocks in the gasifier.

3. The authors should briefly discuss the limitations of the current work and how it can be implemented on an industrial scale to minimize organic waste.

We have addressed this issue at the end of Discussion section.

4. The authors may also highlight the potential applications of the current methodology to the other waste material including (waste plastics and municipal waste.)

We have addressed this issue at the end of Discussion section.

Author Response File: Author Response.pdf

Reviewer 5 Report

Dear Authors,

The article is interesting. The work has an original, author character. The authors presented an innovative technology - the technology of a pulsed detonation gun for gasification of organic waste with ultrasuperheated steam.

It is necessary to introduce additions and explanations.

Chapter  1 Introduction

Verse 31

Quote: „………gasification product is syngas containing, on the one hand, H₂ and CO, and, on the other hand…”

Comment: CH₄ is also a product of gasification, which the authors did not mention.

Verses 40, 41

Quote: „Low-temperature gasification technologies are characterized by relatively low quality of syngas………………………..and the low efficiency of the proces.”

Comment: What do the Authors understand under „relatively low quality of syngas”? It is too vague, it should be clearly stated in the text.

Analogical remark regarding the wording „the low efficiency of the proces”.

Verses 45, 46

Quote: ”High-temperature gasification provides high quality syngas, ……….and high process efficiency.”

Comment: Analogical remarks as to verses 40,41.

Chapter  2 Pulsed detonation gun technology

Verses 86-89

Quote: „A change in the temperature of the reactor wall from 450 to 800 K leads only to a slight increase in the time-averaged mean USS temperature: from 2200 to 2300 K. This means that the walls of the flow reactor can be cooled, and it is not necessary to use expensive heat-resistant materials for their manufacture.”

Comment: How do the authors implement the wall cooling process? Will cooling not cause cracks, material damage (with such ΔT the walls may crack)?

Chapter  3 Gasifier

The authors described the installation, but it would be necessary to provide a schematic diagram with the indication of all existing mass flows, the direction of the flow of the reactants.

Chapter  6 Gasification of liquid and solid organic wastes

1. The fuel characterization of liquid (waste machine oil) and solid organic wastes (wood sawdust) must be provided: moisture, ash content, HHV or LHV, elemental composition of a combustible substance - C, H, N, S, Cl, O. The authors only reported that the initial moisture content of sawdust was 25–30% wt.
2. The proposed gasification process is quite complicated. Taking into account the originality of the process, it would be good to present the energy balance of the process.

Chapter   6.1 Liquid waste

Fig.10

The simultaneous decrease in CO and CO₂ is incomprehensible. It seems that as CO falls, so does CO₂. What part of the CO₂ share comes from the conversion of coal in the charge, and what from the gasifying agent (it is 80% vol H₂O and up to 20% vol CO₂). This requires a comment.

Chapter   8 Conclusions

Verses 403-406

Quote: „Comparison of all experiments on methane conversion as well as experiments  on gasification of liquid and solid organic wastes under the same conditions (f = 1 Hz, P ≈ 1 atm) showed that the composition of the product syngas in terms of H₂ and CO almost  did not depend on the type of organic feedstock.”

Comment: This requires a deep scientific explanation and, above all, a reference to the specific content of the carbon element in the charge and the degree of its conversion. Please refer to the kinetics of the process.

Reviewer

 

Author Response

We are grateful to the reviewer for valuable comments. We made our best to follow all the comments. All changes in the revised manuscript are marked in magenta.

The article is interesting. The work has an original, author character. The authors presented an innovative technology - the technology of a pulsed detonation gun for gasification of organic waste with ultrasuperheated steam.

It is necessary to introduce additions and explanations.

Chapter  1 Introduction

Verse 31

Quote: „………gasification product is syngas containing, on the one hand, H₂ and CO, and, on the other hand…”

Comment: CH₄ is also a product of gasification, which the authors did not mention.

Following this comment, we have made proper changes in the text.

Verses 40, 41

Quote: „Low-temperature gasification technologies are characterized by relatively low quality of syngas………………………..and the low efficiency of the proces.”

Comment: What do the Authors understand under „relatively low quality of syngas”? It is too vague, it should be clearly stated in the text.

Analogical remark regarding the wording „the low efficiency of the proces”.

Following this comment, we have made proper changes in the text.

Verses 45, 46

Quote: ”High-temperature gasification provides high quality syngas, ……….and high process efficiency.”

Comment: Analogical remarks as to verses 40,41.

Following this comment, we have made proper changes in the text.

Chapter  2 Pulsed detonation gun technology

Verses 86-89

Quote: „A change in the temperature of the reactor wall from 450 to 800 K leads only to a slight increase in the time-averaged mean USS temperature: from 2200 to 2300 K. This means that the walls of the flow reactor can be cooled, and it is not necessary to use expensive heat-resistant materials for their manufacture.”

Comment: How do the authors implement the wall cooling process? Will cooling not cause cracks, material damage (with such ΔT the walls may crack)?

The thermal state of reactor walls is very similar to that of a piston engine, e. g., Diesel. The maximum operation temperature is above 2700 K, whereas the wall temperature is about 450 K. The water-cooling jacket protects the wall, while the near wall temperature in the reactor experiences large gradients. This implication is included in the last paragraph of the Discussion section.

Chapter  3 Gasifier

The authors described the installation, but it would be necessary to provide a schematic diagram with the indication of all existing mass flows, the direction of the flow of the reactants.

To follow this comment, we have added a new figure (now Fig. 1) and the corresponding text to the manuscript (see section 2).

Chapter  6 Gasification of liquid and solid organic wastes

1. The fuel characterization of liquid (waste machine oil) and solid organic wastes (wood sawdust) must be provided: moisture, ash content, HHV or LHV, elemental composition of a combustible substance - C, H, N, S, Cl, O. The authors only reported that the initial moisture content of sawdust was 25–30% wt.
2. The proposed gasification process is quite complicated. Taking into account the originality of the process, it would be good to present the energy balance of the process.

To follow these comments, we have added tables with feedstock properties and an additional section entitled “Mass and energy balances.” Also, we have added the related sentences to the Abstract and Conclusions.

Chapter   6.1 Liquid waste

Fig.10

The simultaneous decrease in CO and CO₂ is incomprehensible. It seems that as CO falls, so does CO₂. What part of the CO₂ share comes from the conversion of coal in the charge, and what from the gasifying agent (it is 80% vol H₂O and up to 20% vol CO₂). This requires a comment.

As a matter of fact, the former Fig. 10 (now Fig. 11) shows some irregular behavior of CO and CO2 vs. G. We would say that both CO and CO2 tend to attain constant values (in average) with G. To avoid misunderstanding, we have reformulated a sentence related to former Fig. 10 as:

“The volume fractions of H2, CO, and CH4 increased from 10, 20, and 0%vol d.b. at G = 0 to 30–35, 30–40, and 6–10%vol d.b., at G > 0, respectively, while the volume fraction of CO2 decreased from 70 to 20–30%vol d.b.”

Chapter   8 Conclusions

Verses 403-406

Quote: „Comparison of all experiments on methane conversion as well as experiments  on gasification of liquid and solid organic wastes under the same conditions (f = 1 Hz, P ≈ 1 atm) showed that the composition of the product syngas in terms of H₂ and CO almost  did not depend on the type of organic feedstock.”

Comment: This requires a deep scientific explanation and, above all, a reference to the specific content of the carbon element in the charge and the degree of its conversion. Please refer to the kinetics of the process.

To follow this comment, we have added a paragraph in Discussion section:

It is well known from the equilibrium calculations of organic waste gasification [25] that at temperatures ~900 K, carbon, and oxygen exist as CO₂, tar and char, i.e., tar and char conversion is low; at temperatures above ~1200 K, in presence of carbon, CO₂ breaks down to CO and available oxygen mostly reacts with carbon to form CO and CO₂ rather than with H₂ to form water; and at temperatures above ~1800 K tar and char are completely transformed to syngas composed mainly of H₂ and CO. According to Tables 1 and 2 natural gas and waste oil contain comparable amounts of carbon (~95 and ~85%wt, respectively) in their composition, whereas wood sawdust contains only ~49%wt carbon and ~45%wt oxygen. Therefore, it is not that surprising that syngas compositions for natural gas and waste oil in Fig. 13 are close to each other in terms of H₂ and CO contents. As for wood sawdust, at high temperatures (above ~1200 K) the bound oxygen available in wood mostly reacts with carbon to form CO. In view of it, the amount of CO in the gasification products of sawdust is as high, as that in the gasification products of natural gas and waste oil.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have answered all the queries well. The manuscript can accepted in current form. 

Reviewer 2 Report

Thanks a lot for improving manuscript. The Authors took into account all my sugestions and remarks. In my opinion manuscript can be publish in current form.

Reviewer 3 Report

I appreciate the authors effort in revising the manuscript, but I sustain my decision that the material described is a case study report with poor scientific value, hence, I cannot recommend it for publication in a scientific paper.