Efficiency of Using Heat Pumps in a Hydrogen Production Unit at Steam-Powered Thermal Power Plants

Round 1

Reviewer 1 Report

The analysis of municipal solid waste (MSW) utilization to produce hydrogen from MSW with the integration of thermal power plants (TPPs) is novel. The authors are appreciated for such a work. Having said that the authors have to bring modifications to the paper befitting to the journal. 

Q1. Motivation in the abstract is fine. The abstract is incomplete without the qualitative analysis. The efficiency of using heat pumps has to be indicated qualitatively, in terms of % change.

Q2. The introduction is well-written. In Figure 1, the Y-axis is wrongly represented. How do you explain it as a waste of income?

Q3. Are Table 1 and Figure 1 comparable, if so, then there are discrepancies/mismatches in the values.

Q4. In Table 1 it is mentioned waste burial and in Figure 1 MSW disposal is mentioned. Are they the same or different? Better to use the sam,e terminology and hence modify accordingly.

Q5. The flow chart in the methodology is good. Equation 1 relates the mass flow rate of synthesis gas produced in the gasifier. Also, give another equation where synthesis gas is related to the consumption of RDF and the mass content of ash.

Q6. Appreciate the authors for considering three possible directions (Figure 3) for using heat from HP. Contributions by each direction have to be indicated in terms of % of change.

Q7. How do you relate the Listed parameters in lines 264 to 305 to the directions given in figure 3. Relating the parameters with the directions will be interesting to the readers.

Q8. Figure 5 doesn't indicate the performance. This only represents H2 and CO extraction. Correct the figure accordingly. There is a flaw in representing the data.

Q9. Correct and re-write the sentence, "Fig. 5 shows that the influence of the morphological composition of waste on the performance range of this unity increases as the consumption of processed MSW increases", line 321 and 322.

Q10.  There is a flaw in the figure 6 in representing the data. The inference given in line 359 362 does not relate to the figure. Correct the inference and the figure accordingly.

Q11. Figure 7 is a good contribution to the paper. How this water consumption is compensated by the generated power, If possible in terms of % change.

Q12. Figures 8 and 9 are also good contributions by the authors. Since you mentioned marginal advantage for this unit, could you explain the cumulative advantage of this system?

Q13. The discussion and conclusion are listed well. Indicate the main efficiency/performance parameters in terms of % change. That would attract the readers.

There are grammatical errors. A few of them are suggested in the comments. The authors need to read carefully before they resubmit the paper.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The article addresses a topic of great interest linked to the valorization of waste with thermochemical processes for the production of hydrogen, specifically integrated by the innovative idea of using the waste energy of the process to power a heat pump. The topic of waste valorisation for decarbonisation and hydrogen production is also consider as a topic of priority  by the European Community which, in the framework of the programme PCEI, has financed few pilot projects amounting to hundreds of millions of euros.

The article is well structured and addresses aspects of thermodynamic modeling and economic analysis in great detail.

However, it is based on the hypothesis of gasification of  waste, without analyzing the problems of this process for the treatment of waste, characterized by variability in both size and chemical composition and also seasonal variability. In particular, although it indicates that gasification takes place at 850 °C, but the it lacks information both on the type of gasifier on which the proposal is based and  type of gasifying agent (air, oxygen and steam etc.). Furthermore, no information on the purification system for the reduction of tar and dust etc. is specified in the text. Also, it is requested to provide more details on the synthesis reactor (temperature, catalysts etc.).

In view of all cited above, an update of the article integrating the state of the art on the types of commercial gasifiers that treat waste suitable for the production of syngas with a high hydrogen content, is required,

In the above context, needless to say that the most promising technologies for this application are the gasifiers, which operate at temperatures above 1600 °C with oxygen and steam as gasifying agent that provide for the fusion of the ashes which are rapidly cooled to be vitrified, thus significantly reducing environmental impact problems

It is obvious/evident that without the specific and precise information on the different technical aspects mentioned above which influence the feasibility and reliability of the system, the article loses its meaning and detailed in-depth analysis that has been done and presented nicely in the article, becomes meaningless.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Congratulate the authors for their credible work. All the best

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Thank you so much for addressing to the the questions  sent to you from reviewers  during revision phase of the paper. I am happy to inform you that I  satisfied by the answer given to all the questions. I have notice that even the questions raised by other evaluators are duly addressed, as well. I am happy to state that the paper, in its present revised version with integration of information/explanation provided by you, certainly appears to be much improved.

Author Response

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Author Response File: Author Response.docx