Controlled Production of Natural Gas Hydrates in an Experimental Device with an Internal Circulation Circuit
, Pavol Mičko 1, Nikola Čajová Kantová 1, Zuzana Kolková 1, Peter Hrabovský 1 and Pavol Belány 1Round 1
Reviewer 1 Report
The equations stop at number 10 and jump directly to 13.
The equations and the parameters are identical to those used in reference 34.
There should be an extensive comparison between the determined results and simulations, and also between the current paper and paper 34.
Author Response
- Yes the equation numbers are corrected.
- Yes for the mathematical analysis, the model described in more detail in paper 34 was used. The experimental setup was changed in order to reduce the energy demand of the formation and to speed up the time of hydrate formation. The mathematical model is used to determine the optimum boundary conditions for hydrate formation and the time of hydrate formation during the experiment in the new experimental setup. We also use the model to determine the approximate amount of hydrate that will be produced. The paper is mainly focused on the experimental measurement and description of the principle of operation of the device. The mathematical model is analyzed in great detail in papers [29, 30,31,32,33,34,35, 36].
Author Response File: 
Author Response.docx
Reviewer 2 Report
The paper faces an interesting concept of energy storage, i.e. gas-hydrates as energy storage. Therefore, it is attractive for publication in Energies.
My comments are below:
"development of energy efficient recovery of hydrate generation is currently incomplete and still in progress" - please rephrase the sentence, as "currently incomplete" is not the best formulation
"development of energy efficient recovery of hydrate generation is currently incomplete and still in progress" - word "considered" sounds inappropriate.
in sentence "Atomized water moves at a relatively high velocity in a volume of gas compressed to a very high pressure" delete word "very" as very high pressure definition depends on the context.
Something is wrong grammatically in this part of the text: "The pressure waveform was sensed by a piezoresistive pressure transducer with a measurement range of 0 ... 400 bar accuracy ±0.25% at temperature range 0...+70℃. Type B uncertainty."
"We will use a frequency converter..." - it has already been used.
In chapter 3 (3. Determination of the hydrate formation model) t is not car how the natural gas as a mixture can be interpreted mathematically (mixing rules). It would be very interesting if the analysis was compared with real natural gas composition (with impurities). It is not clear how the fugacity is determined to calculate oversaturation. It is not defined what "quantization" does mean.
In figure 5, y-axis range could be changed to 60 - 80 bar, to allow better examination of nonlinearity.
Similar can be applied for figure 6
Overall, the mathematical analysis of hydrate forming is too simple, and not explained in detail. That leads to recommendation to improve the literature review and references. The results are evaluated qualitatively in the conclusion and there is also room for an improvement.
Author Response
- Sentence changed to: "However, the technology of forming methane hydrates in an energy-efficient manner is a current challenge for the future.“
- Delete word "very“.
- Sentence changed to: „The pressure was measured by a piezoresistive sensor with an accuracy of 0 ... 400 bar ± 0.25% at a temperature range of 0...+70℃. Type B uncertainty.“
- Correct future tense for the past tense – "used“ .
- The fugacity was removed from equation number 1 because I misinterpreted the equation from reference [29] (in equation (19)). That was my mistake. By approximating the fugacity coefficient, the equation was derived in its present form. A more detailed formulation and specification is given in reference [29]. "Quantization" is a mistake was meant and the word calculation was used.
- In graph numbers 5 and 6, the range of the y-axis has been changed to make the change in the curve more visible.
- Yes a simple model was used for the mathematical analysis. The aim was to estimate the boundary conditions of hydrate formation and the time of hydrate formation during the experiment. Also the model will find the approximate amount of hydrate that will be produced. The paper is mainly focused on the experimental measurement and description of the principle of the device function. The mathematical model is analyzed in great detail in papers [29, 30,31,32,33,34,35, 36].
Author Response File: Author Response.docx
