Investigation on Gas Hydrates Formation and Dissociation in Multiphase Gas Dominant Transmission Pipelines

Round 1

Reviewer 1 Report

This article exhibited a study of gas hydrate formation and dissociation study. The authors used Gasoline+CO2+Water and Crude oil+CO2+Water system in the pressure range of 2.5–3.5MPa with fixed water cut as 15% using gas hydrate rocking cell equipment.

I have insignificant remarks:

1. In line 26, The authors should avoid abbreviations (HLVE Data)
   in Keywords. However, if that abbreviation is in the keyword list, corrections are not be needed.
2. in line 112 and Figure 1 there are unexplained abbreviations such as "PLC controller" and VP, GP, PG that should be explained.
3. In line 122, P - constant (isobaric) thermodynamic cycle was named by authors as "T-cycle". Is it correct?
   

Author Response

REVIEWER - 1
COMMENTS	CORRECTION MADE
In line 26, The authors should avoid abbreviations (HLVE Data) in Keywords. However, if that abbreviation is in the keyword list, corrections are not be needed.	HLVE is abbreviated as Hydrate Liquid Vapour Equilibrium. It is presented in Line 16 of the manuscript under the abstract.
In line 112 and Figure 1 there are unexplained abbreviations such as "PLC controller" and VP, GP, PG that should be explained.	The Figure 1 is edited accordingly with nomenclature table presented to understand the Abbreviations.
In line 122, P - constant (isobaric) thermodynamic cycle was named by authors as "T-cycle". Is it correct?	It’s an Isochoric method. Since the Volume of the sample is fixed and no further changes will occur in the sample volume. Line 122-124. Citation provided.

Author Response File: Author Response.pdf

Reviewer 2 Report

Review of the article «Investigation on Gas Hydrates Formation and Dissociation in Multiphase Gas Dominant Transmission Pipelines» by S. Jai Krishna Sahith, Srinivasa Rao Pedapati and Bhajan Lal

This research is relevant and will be interest the wide class of readers.
However, despite the advantages of this scientific research, I have the following remarks:

1. There are a lot of thermodynamic data in the article, so I will recommend the Authors to collect the most important data as table. It will be quite conveniently for readers;

2. The axis label of figures should be writing more readable and visual quality of the figures should be improved. Figures had been improved (see Figures 5, 6);

3.I found a few typos in the text. All typos should be corrected by Authors.

I recommend to the Editor-in-Chief to accept this article for publication after the minor revision.

 

Comments for author File: Comments.pdf

Author Response

REVIEWER - 2
COMMENTS	CORRECTION MADE
There are a lot of thermodynamic data in the article, so I will recommend the Authors to collect the most important data as table. It will be quite conveniently for readers.	Adjusted and Presented in Table – 1.
The axis label of figures should be writing more readable and visual quality of the figures should be improved. Figures had been improved (see Figures 5, 6)	Adjusted and Edited for Clear Understanding.
I found a few typos in the text. All typos should be corrected by Authors.	Clearly Edited Using Grammarly Language Reviewer Tool.

Author Response File: Author Response.pdf

Reviewer 3 Report

That is a really interesting study. In this work gas hydrate, formation and dissociation of two multiphase systems are studied. The paper is well structured and the results presented well. 

There are some points which need to b clarified.

• In the experimental part, the device is explained to work in isobaric condition if that is the case, how they have followed the pressure drop during the hydrate formation? 
• The volume change due to hydrate formation is not considered in equation (2). 

After providing a reasonable explanation for the above-mentioned comments, this paper is qualified for publication in Applied Sciences journal.

 

Author Response

REVIEWER - 3
COMMENTS	CORRECTION MADE
In the experimental part, the device is explained to work in isobaric condition if that is the case, how they have followed the pressure drop during the hydrate formation?	It’s an Isochoric method. It was a typo error from my end. Since the Volume of the sample is fixed and no further changes will occur in the sample volume. Line 122-124. Citation provided.
The volume change due to hydrate formation is not considered in equation (2).	Line 247 - 250. An assumption is made that there is no change in the Volume of Water during the Gas hydrate Formation. This is because of the closed system in the experimental setup, and the volume change due to the temperature effect is minimal on the volume of the water. Citation provided.

Author Response File: Author Response.pdf

Reviewer 4 Report

This work presents a rather interesting study on the phase diagram and formation of clathrate in the CO₂-water-gasoline/crude oil systems. The experimental design is sound and the reported results are of interest to the petroleum industry, which make it suitable for publication in Applied Sciences. However, the English presentation can be much improved. I've outlined a few of those below, along with some technical comments.

• In general, the most important conclusion of this work, to me, is the discrepancy between the effect of gasoline vs crude oil on the stability and formation kinetics of CO₂ hydrate. This is a key result, and the underlying physical rationale should be much better explained than what is laid out in the text. For example, I do not fully understand what the authors meant by "the availability of more top carbon chains" in the crude oil system (line 191). Do they mean "longer carbon chains"? Even so, I don't see how that would necessarily promote hydrate formation. "The highly reactive nature" of impurities (line 193) is a very hand-waving way of explaining things and not satisfactory. Which impurities specifically are highly reactive? How do they chemically interact with water and/or CO₂? The authors later apply this same reasoning to explain the 50-fold increase in reaction rate vs pure water (Figure 9). Without sufficient justification, I do not find this to be a credible interpretation.
• The same thing goes for the gasoline system. What does "anti-hydrating inhibitors" (line 252) mean? How does their presence make the processed fuel "more stable towards fluctuations in temperature and pressure" (line 187)? And what does that have to do with inhibiting hydrate formation and decreasing the reaction rate? Again, I'm looking for a much more thorough chemical/physical discussion of these phenomena.
• For those familiar with gas hydrates but not necessarily in the petroleum field, definition of "water cuts" might be helpful. From the context, I assume it refers to the weight fraction of water in the sample, but this needs to be clearly defined.
• Materials section 2.1: the source of CO₂ and water are specified on lines 101-102, but there's no mention of where the crude oil and gasoline samples come from.
• Figure 1: the abbreviations need to be defined in the caption. I guess PG stands for pressure gauge, and GV for gas valve, but don't know what VP and A/D are. Also, why is the gas cylinder labeled "air" when it's CO₂ in the experiments?
• Line 131: what is the heating rate? How do you know it's sufficient for thermodynamic equilibrium to be reached?
• Figure 4: docosane is repeated twice in the plot.
• Figure 7: legend is missing. What does the orange curve represent?
• English corrections (not exhaustive, there are many more):
  • Line 18: should be "studies were performed"
  • Line 38: "enclathrate" small gas molecules
  • Lines 54-58: this paragraph needs citations
  • Line 75: CFD needs to be defined
  • Line 81: delete "formations" after "gas hydrate"
  • Line 88: need "the" before "trend"
  • Line 90: should be "studies"
  • Line 123: washed with distilled water and dried.
  • Figure 2: sulpher should be "sulfur"

Author Response

REVIEWER - 4
COMMENTS	CORRECTION MADE
Line 191,193 – How does the impurities and longer carbon chains effects the Gas hydrates formation?	Line 196, citation provided for the justification of Claim.
How does their presence make the processed fuel "more stable towards fluctuations in temperature and pressure	Line 260, citation provided for the justification of Claim.
For those familiar with gas hydrates but not necessarily in the petroleum field, definition of "water cuts" might be helpful. From the context, I assume it refers to the weight fraction of water in the sample, but this needs to be clearly defined.	Line 77. The definition of water cut is added. Line 92. Corrected to for clear understanding of water cuts
Materials section 2.1: the source of CO2 and water are specified on lines 101-102, but there's no mention of where the crude oil and gasoline samples come from.	Line 104-105. The details of the sample collection locations are added.
Figure 1: the abbreviations need to be defined in the caption. I guess PG stands for pressure gauge, and GV for gas valve, but don't know what VP and A/D are. Also, why is the gas cylinder labelled "air" when it's CO2 in the experiments?	The Nomenclature is added in the Figure for Understanding the Abbreviations. The Gas cylinder naming is changed according to the comment.
What is the heating rate? How do you know it's sufficient for thermodynamic equilibrium to be reached?	Line 135: Heating rate is 0.5 C and is modified in the manuscript
Figure 4: docosane is repeated twice in the plot.	Corrected
Figure 7: legend is missing. What does the orange curve represent?	Legend is Modified to represent both curves
Language and Grammatical Mistakes	Clearly Edited Using Grammarly Language Reviewer Tool.

Author Response File: Author Response.pdf

Round 2

Reviewer 4 Report

The authors have improved the manuscript and addressed most of my minor comments. However, the main criticisms in my original review still have not been adequately answered. For instance, no explanation was given for my previous inquiry on why longer hydrocarbon chains promote hydrate formation (line 196). The authors cited 2 references for the claim on line 199 that impurities in crude oil promote clathrate formation because of their highly reactive nature. I do not have access to one of those references, so couldn't really assess it any further. Why don't the authors just spell out the reason explicitly and then cite them, to help alleviate the work on the readers? I wasn't exactly looking for a reference to justify the claim; rather, I was more interested in the  physical/chemical rationale of the process. I do believe that the work is worth publishing; however, I sincerely hope that the authors will consider putting forth some explanations to increase the intrinsic scientific value of the paper before the final version is published.

• Figure 1: suggest changing "nomenclature" to "abbreviations". Pressure gauge is misspelled.
• Line 136: heating rate of 0.5 C per what? Minute or hour?
• Line 78: delete the second "Water Cut is"
• Line 94: 15% by weight or by volume
• Line 115: attached "to", not "by"
• Line 116: equipped "with", not "to"
• Line 128: "no change in the sample volume"
• Line 268: "affects" not "effects"

Author Response

Firstly, Thanks a lot for the valuable comments given to improve the quality of my paper.

I highly appreciate it.

Please find the table below with details about the corrections made according to the comments given.

REVIEWER - 4
COMMENTS	CORRECTION MADE
For instance, no explanation was given for my previous inquiry on why longer hydrocarbon chains promote hydrate formation (line 196). The authors cited 2 references for the claim on line 199 that impurities in crude oil promote clathrate formation because of their highly reactive nature. I do not have access to one of those references, so I could not really assess it any further. Why don't the authors just spell out the reason explicitly and then cite them, to help alleviate the work on the readers? I was not exactly looking for a reference to justify the claim; rather, I was more interested in the physical/chemical rationale of the process.	Line 199 – 203. The explanation is provided for a Clear understanding of the claim along with Citation.
Figure 1: suggest changing "nomenclature" to "abbreviations". The pressure gauge is misspelled	Edited according to the comments
Line 136: heating rate of 0.5 C per what? Minute or hour?	Line 136. The Heating rate is per hour. Modified accordingly.
Line 78: delete the second "Water Cut is"	Line 78. Adjusted the definition properly without the repetition
Line 94: 15% by weight or by volume	Line 93. 15% by volume. Clarification is Provided.
Line 115: attached "to", not "by"	Line 115: Corrected
Line 116: equipped "with", not "to"	Line 116: Corrected
Line 128: "no change in the sample volume"	Line 128: Corrected
Line 268: "affects" not "effects"	Line 268: Corrected

Author Response File: Author Response.docx