Optimization of Heat Recovery Networks for Energy Savings in Industrial Processes
Round 1
Reviewer 1 Report
In this paper, the authors conducted a numerical study for the optimization of heat exchanger networks. After reviewing the paper, I have the following main observations.
1. It is a topic of interest to the researchers in the related areas and the knowledge in this paper can contribute the heat recovery applications of the industrial processes.
2. The subject is explained clearly, discussed properly with enough credit given to the contributions of the authors in this field. References are well-chosen with related subject in a time range as well as a recent decade.
3. The present form of the paper is well organized, theoretical approach and the calculation method is presented.
4. But, during the heat exchange stages, the constrains of heat exchanger efficiencies, pressure drops and other losses were not considered
5. In addition to that the numerical uncertanities must be considered and presented.
6. A validation of the proposed model should be provided.
7. In the cost analysis, the initial and/or retrofit costs must be considered.
8. To generalize the results, savings can be given as percentage rather than a specific value of application.
With the view of the above observations, I concluded that this paper must be revised according to the comments given above for further consideration.
Author Response
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Author Response File: 
Author Response.docx
Reviewer 2 Report
Several issues must be clarified in this contribution. It is not sufficient to say that the model handles phase change since it only considers energy balances. In heat recovery networks, apart from the energy balance, the thermal and hydraulic performance is required as well as the exchanger geometry. None of these are considered. See more points of criticism below:
1.- The paper deals with retrofit of existing heat recovery networks, authors assume that the performance of existing heat exchangers is not important and only energy balances are analysed in the paper.
2.- Authors are strongly recommended to use international systems units. Instead of Mcal/h, use MW.
3.- Further explanation is needed about the minimum temperature approaches reported in Table 4. For instance, why match H1-C2 takes a minimum approach of 3.2 °C?
4.- No data on heat exchanger surface area is provided
5.- Minimum temperature approach of exchanger H1-C1 is modified arbitrarily between 32°C to 13.3 °C, then it is changed from 10°C to 29°C. on what basis? This is not clear.
6.- Line 352: “So far, both solutions in Figures 6 and S1 have been taken as alternatives being evaluated for their technical and economic feasibility.” Neither the paper nor the supplementary material provides technical or economic analysis.
7.- Line 214: “Tables 1 and 2 show the stream data extracted from the EG process flowsheet, 214 which is complicated and is not shown for confidentiality reasons.” This is confusing. The stream data has been provided in the tables.
Author Response
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Author Response File: Author Response.docx
Reviewer 3 Report
This manuscript presents results regarding the optimization of heat recovery networks for energy savings. The content of the paper is related to the scope of the journal but the authors should consider the below comments to improve their paper.
1. As far as I understand I do not see the reason to limit the application of the model to the chemical industry as it can be understood from the title. According to the mathematical model and the obtained results the optimization steps can be similarly applied to any other type of industrial process which involves streams with different temperatures and requires heat integration. Clearly it was applied for an existing chemical industrial plant but that does not mean that it cannot be used for other type of processes. The author should reformulate the title according to this observation.
2. Please use in the whole manuscript the units in accordance with the international system of units (SI) to facilitate the comparison with other studies. For instance, instead of Mcal/h use W or kW/MW/GW..etc.
3. Please insert some citations for the description and data (tables 1,2) at the beginning of section 4.
4. Regarding the applicability of the approach I think that it is far from being ready to be deployed for industrial use. Yes, it can identify an optimal heat recovery network for energy saving and determine the amount of energy that can be recovered. But in what type of heat exchangers? What is the cost of the system, the trade-off between energy and capital? There are no data on how much capital, maintenance cost would such a system require in comparison to energy costs…In my opinion without an economic assessment that clearly states the benefits it does not matter if we save 1 Mcal/h ore 1 Gcal/h. The authors need to include an economical assessment as well..
5. Another fact is that there is no comparison with the existent alternatives presented in the literature for heat recovery networks. In the results and discussion section there should be some discussion why is the alternative presented by the authors better to the existing models from the literature.
Author Response
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Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The revised paper is acceptable in the present form.
Author Response
Many thanks for your approval.
Reviewer 2 Report
Authors have answered and clarified all issues raised in previous review.
Author Response
Many thanks for your approval.
Reviewer 3 Report
The authors had improved the manuscript but I have to reiterate some of my previous comments.
1. The type of heat exchanger is a key component in any optimization approach. We will not get the same technical and economic performances on different types of heat exchangers. The type of heat exchanger needs to be specified and technically described in details (dimensions, number of tubes, etc.). If it is a tubular, plate or extended surface heat exchanger?
2. Again, in my opinion without an economic assessment that clearly states the benefits it does not matter if we save 1 Mcal/h ore 1 Gcal/h. The authors need to include an economic assessment as well. Based on heat exchanger type and dimensions (especially heat exchanger active surface area) how much capital, maintenance cost would such a system require in comparison to energy costs. Besides energy balance, heat exchanger design (selection of heat transfer equipment and the calculation of heat transfer area and exchanger cost) needs to be considered.
3. The affirmations regarding the economic aspects need to be more detailed. What algorithm and assumptions were used?
Author Response
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Author Response File: Author Response.docx
Round 3
Reviewer 3 Report
