Dynamic Modelling and Simulation of a Multistage Flash Desalination System

Round 1

Reviewer 1 Report

Manuscript ID: processes-1092058

Manuscript Title: Dynamic modelling and simulation of MSF desalination system

This paper proposes the mathematical model of multi-stage flash desalination system.

The authors should compare the previous studies to highlight their research. Just an example, what are the main differences between this manuscript and the following studies:

• MSF process modelling, simulation and optimisation : impact of non-condensable gases and fouling factor on design and operation. Optimal design and operation of MSF desalination process with noncondensable gases and calcium carbonate fouling, flexible design operation and scheduling under variable demand and seawater temperature using gPROMS.
• Mode-Based Analysis and Optimal Operation of MSF Desalination System

The expressions inside the parentheses should be aligned with the text (Tsea, Tsteam, etc. )

In my opinion, since this is a dynamic modelling and simulation study, the authors should provide more details about the simulation and their application. They say that they use MATLAB software, they should include coding, algorithm, interface screenshots, etc. at the Appendix section for the other researchers to re-apply to test the results, and apply/improve for their own problems.  

In general, the authors answer the questions in the paper that might arise. There exist critical discussions. The study is well structured.

I recommend this study can be accepted after the above-mentioned minor revisions.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

This paper presented a mathematical model of multi-stage flash system based on first principle to obtain the transient performance change. The effect of physical parameters with the change of brine concentration and temperature, non-ideal difference and heat loss of demister on the system performance, and the phenomenon of unequal temperature drop in each flash stage was studied. This paper should be rejected due to the low quality of this paper. The detailed review comments are in the following:

1. In the paper title, please avoid using the abbreviation of MSF.
2. In terms of the novelty of this paper, please highlight your novelty in the paper. There are several papers published in this field (e.g., Dynamic Modeling and Simulation of MSF Desalination Plants, Dynamic modelling of Heat Exchanger fouling in multistage flash (MSF) desalination, Modelling, simulation, optimization and control of multistage flashing (MSF) desalination plants Part I: Modelling and simulation, etc.). The process or modeling is more novel compared with the previous results reported in the literature?
3. In Introduction, please introduce the differences among these treatment technologies.
4. Besides the dynamic modeling of MSF desalination, what is the status of experimental studies on this topic?
5. Please add more previous results from the literature regarding the physical parameters effect.
6. Figure 1 needs to be revised. It is hard to distinguish these routes in the system. Any novel parts in this system compared with other works?
7. In Section 2.2, please give some references for these equations used in this model.
8. In Section 3, for the validation of the simulation results, what is the accuracy of this simulation? What is the error? How is the consistency with the results of Gao Hanhan et al.? There is no comparison. So in Section 4, how could we evaluate the accuracy of these data reported in this section? Even in this section, all the results are presented with any detailed analysis. The authors just simply showed the results in these 20 figures. More detailed analysis should be added in the current version.
9. In Conclusions, there are too many abbreviations. Please list the key findings from this work which are different from the literature. What are the implications and future applications of this simulation?
10. A proof reading by a native English speaker should be conducted to improve both language and organization quality.  

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript presents a dynamic mathematical model of a MSF desalination process and the dynamic response of the system to changes in the main operational variables are investigated.

The topic of the work is very interesting, although there are a number of mathematical models for the MSF process already published in the literature, therefore proper justification must be provided. The work fits well in the scope of the journal. I think that the English writing should be significantly improved and double-checked. The structure and organization of the manuscript seems fine to me. The description of the mathematical model needs to be enhanced, providing more information when possible. The writing should be also enhanced; repetition occurs a lot, variables are not always described. The validation must be improved, showing comparison with real data and errors. The analyses performed could be improved, for example justifying the selection of the variables to be changed. Finally, conclusions need revision to be more appealing, shortened when possible, and providing meaningful conclusions.

Comments:

Title
- Maybe it is better not to use the acronym MSF and put multistage flash.

Abstract
TBT, BBT should be described. Also it could be considered not to write the symbols of feed seawater temperature, concentration, etc. within the abstract.

“can be obtained” do not has sense here, rewrite as “is obtained” or similar. Please check the English writing. The abstract should include briefly the main results of the work.

1. Introduction

• “and is not perfect” in line 56, this comment is strange, please rewrite as “it has drawbacks” or similar.
• “a comparatively perfect” line 64, please correct.
• “mechanism modeling and simulation” line 70. What does it mean?
• The literature review is fine, but the novelty of the paper with respect is already published should be further explained.

2. Flowsheet and Model of Multi-Stage Flash (MSF) Process

• The title of the section should be checked, “flowsheet” maybe is not correct here. In 2,1 “Process description” or similar could fit better.
• “Numbered lists can be added as follows: The complete dynamic”. What does it mean? Please rewrite and check English.
• Please describe every variable just below where it is presented for the first time. Eg. C_B0.
• Please justify why it is assumed that the brine holdup in the condenser is constant. Also, why the energy balance of the heating steam is done in steady-state conditions?
• Consider to include “the evaporation of fresh water is ignored” in the list of assumptions (lines 126-129), as well as other assumptions made to simplify the model.
• Equation 19 is correct? Please verify it.
• Subsection 2.2.3. Please describe briefly the equations presented. Putting only the equations does not help the readers to understand what is being written.
• Correlations in 2.2.4 are valid for whatever value of the variables? Please, if they can be used only within a range, indicate it.
• Where is it presented the dynamic relationship between the pressure and mass flow rate between stages?
• The level (m) of distillate in the stages is not modelled?

3. Model analysis and validation

• Table 3, Length of condenser in kg/h??
• What does it mean “under constant working conditions”, line 248?
• Please, put the figures just below they are mentioned for the first time in the text, never before.
• The validation of the dynamic model is done against steady-state values. Why? Is it because the lack of real dynamic data from industrial plant?
• With respect the validation, a comparison between the real/experimental data and simulation results should be presented. Instead, only simulation results are shown. Please indicate the %error between real and simulated results for the variables selected.

4. Dynamic simulation and analysis

• The effect of the feedwater temperature increase is very small in the brine temperatures. Can you give an explanation for that?
• The subsection 4.1.2 is equal to 4.1.1 in terms of results, with inverse behaviour. Maybe both analyses could be mixed putting similar analyses in one figure, and therefore shorten text and figures.
• For the feedwater concentration analysis, the effect on the TBT, BBT, and brine temperatures is so small (order of 0.1-0.2C) that it could be concluded that it does not affect to those variables at all. Such lower temperature differences could be attributed also to error in the experimental measurements. How do you explain this?
• Please, do not repeat the name of a variable with its symbol once it has been described. I mean, for example “distillate flowrate ( )” and so on. Please use only or distillate flowrate, but not both at the same time.
• When presenting figures and explaining the results, please try not to repeat what it is shown in the figure but to explain why that occurs, if it is known.
• The effect of the steam mass flow rate is not analysed, why?

5. Conclusion

• Conclusions are long and not attractive to read. Results have been presented before, here, among the main results obtained, please try to give a general overview of the main conclusions of the work, in terms for example of why this model has been useful when analysing the transient response of the system against variations in the operational variables. Are there any combination of the variables change that make the system to be operated with more stability? The distillate flow rate decreases with the increase of the feedwater concentration but increases with the steam temperature, therefore, it could be reasonable to think that increasing the steam temperature when the feedwater concentration increases is a kind of control strategy to maintain the levels of distillate in the plant. This analysis maybe is not in the scope of the work but is an example of how more interesting results could be extracted using this simulation tool.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Since the authors did not improve the paper according to the comments. The novelty of this paper is not good enough to be published in Processes. There is no validation in the paper even this issue has been raised in the first round review. What is validation? Not just using the input data from other works, any results validated? The English writing is also poor. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

1. TBT, BBT should be described in the abstract.
2. The novelty of the paper with respect is already published should be further explained. Still not corrected, the use of Runge-Kutta algorithm is not a novelty, it is habitually used in solving dynamic equations.
3. Please describe every variable just below where it is presented for the first time. For example variables in Eq. 1. Or in line 158, h is the specific enthalpy of ..., in kJ/kg.
4. The list of assumptions is still not complete. There are a lot of simplifications not included in the assumptions.
5. In fig. 9, the brine temperature during the dynamic process... do you mean the steady-state value? Because the temperature should vary with time. You must compare steady-state values or dynamic values, but not mixed.
6. The captions of the figures must be more descriptive.
7. Conclusions must include specific findings of the work.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

The present form is ok. Only minor checks should be done.