Dissociation and Combustion of a Layer of Methane Hydrate Powder: Ways to Increase the Efficiency of Combustion and Degassing

Questions and remarks

Answers and corrections

1

 The text has numerous usage and grammar problems; professional proofreading is required.

English corrected.

2

2.    Line 68. Replace “negative temperatures” for below 0 deg C or below 273 K for consistency with the next sentence.

Thank you for the remark. The text has been corrected.

3

Line 76. I don’t think “implementation” is the right word here. Revise usage here.

“implementation of self-preservation” corrected to “occurrence of self-preservation”

4

Lines 114-115. Use the same units for consistency. Do the authors mean uncertainty instead of accuracy?

The temperature values are given everywhere in K. The specified sentence has been deleted because it was incorrect. Temperature was maintened with a smaller interval of readings (+ 0.25 K)

5

Line 129. Is this a confidence interval? If so, at what level?

The sentence has been deleted. «… to a range of values of 0.1-0.4 mm.» corrected to “… to a range of values from 0.2 to 0.3 mm.”

6

Line 144. The main text says: “forced laminar air flow”, but the profile shown in figure 1b is for turbulent flow.

The figure contains only schematic information. Since the thickness of the velocity profile is much smaller than the transverse size of the figure, the it has been renewed: the velocity profile has been removed.

7

Instrumental and experimental uncertainties need to be reported. Refer to the Guide to Expression of Uncertainty.

A description of the errors has been added to the text.

8

Please report gas and water purities.

The gas and water purities have been added.

9

A nomenclature section should be added.

The nomenclature has been added.

10

Lines 173 to 180 and the rest of the main. Greek letters, variables, subscripts and superscripts tend to not match the numbered equations.

Notation and indexes are now given in the same style.

The nomenclature was added. In Eq. 2 P and r corrected to P_f and r_f.

11

Figure 3. Do the circles and yellow diamonds represent experimental data? Please add them to the legend.

Thank you for having found the inaccuracy in the figure. Figure 3 has been corrected.

12

Line 291. Typographical error.

Corrected.

13

Across the text. Please be consistent when showing the decimal period. Sometimes the comma is used, sometimes the period. E.g. Figure 5: in caption 0.003 and in the figure itself 2,5

Fig. 5 corrected.

The figures have been corrected.

14

Figure 8 caption. 1-h = 3 mm is confusing. Maybe blue circles, 3 mm ; red squares, 7 mm ; etc?

The colors have been added to the caption.

15

How reproducible were the results shown in Figure 8? How many replicates were performed for each condition (add this information to main text?

Sentences with data on repeated experiments and discrepancies of curves have been added to the text.

Questions and remarks

Answers and corrections

1

 Introduction: please Update the information in this section using section 5 of

the following comprehensive review article on gas hydrates: doi.org/10.1039/C8CS00989A

you can also find more recent works about hydrate formation/dissociation kinetics in section 3 of this article.

The review with specified works has been added to the Introduction.

2

·        Experimental methods: please provide the error number in measuring the pressure.

The pressure error has been added to the experimental methods.

3

·         Dissociation of gas hydrates at negative temperatures: please provide references for all the equations provided in this article. here it is important to give credit to the people who developed other modelling approaches and properly discuss the differences of your model with previous ones.

The fundamental differences of the presented model from the existing ones have been added to the text of the article.

4

·        For the modelling section did you use any available software or open-source code, or you developed a piece of code? Please clearly discuss this in the article.

The text of the article has been added with: "For solving the system of equations, a special computational code has been developed to find the characteristic parameters of the dissociation of gas hydrates, as well as the parameters of combustion under quasi-stationary modes. "

5

·        Line 179: the authors used ideal gas approximation, could you discuss the limitations of using an ideal gas approximation in your model.

The experimental conditions that allow using the ideal gas approximation have been added to the text of the article. Of course, in the general case, it is necessary to take into account the compressibility of the gas.

6

·        Please calculate and discuss the errors of the modelling study as it has not been mentioned in the article.

Data on the calculation scheme, the difference grid, errors, as well as data on discrepancies with the experiments have been added to the text of the article.

7

·        Please do another proofreading.

English has been corrected.

Questions and remarks

Answers and corrections

1

list of symbols is required, to better follow the analytic explanation

The nomenclature was added.

2

some further detail present in ref 24 and 42 should be added to the text.

The additional information has been added.

3

Why did you use 1 °C and 5 - 5.6 MPa to form hydrates?these thermodynamic conditions are above the common equilibrium conditions for methane hydrates, thus they do not correspond to the real reservoirs' configuration. See for example data present in (Fluid Phase Equilibria, 536 (2021) 112958) about methane hydrates. I ask you to explain in detail why you opted for these values, by comparing them with data already produced in literature.

Thank you very much for this question.

The procedure that we used for the sysntesis of the methane gas hydrates was developed long time ago (Ogienko, A. G., Kurnosov, A. V., Manakov, A. Y., Larionov, E. G., Ancharov, A. I., Sheromov, M. A., & Nesterov, A. N. (2006). Gas Hydrates of Argon and Methane Synthesized at High Pressures: Composition, Thermal Expansion, and Self-Preservation. The Journal of Physical Chemistry B, 110(6), 2840–2846. doi:10.1021/jp053915e) to provide fast syntesis of the gas hydrate with good reliability.

First fine particles of crashed ice (crushing was performed at 77K to provide brittleness of ice) were loaded to the cell at the in was pressurized with methane. After it the cell was put to the frigde at 1^oC and kept there for several days to form hydrate.

After this the hydrate was quenched at 77K, grinded, put back to the cell and pressurized again to form hydrate from the residual unconverted water which might be left due to mass transfer limitations.

The step 2 was repeated.

The temperature 1^oC was choosen to be close to the melting temperature of ice but slightly above it, because solid state reactions are slow, but melting ice may provide nucleation centers for hydrate growth.

The pressure was choosen due to the following reasons:

1. Synthesis of hydrate was performed at isochoric conditions, so we needed to pressurize the cell considering that the pressure is supposed to decrease due to the hydrate formation process.

To form gas hydrates, thermodynamic driving force is required and commonly, if there is not kinetic limitations, the higher the driving force — the faster the formation process. And to form hydrate typically one needs to provide either lower temperature or higher pressures than the equilibrium values. Forming the hydrate for the further studies, we did not aim to simulate the reservoir conditions (we did not form hydrate in porous media for these studies either), we made pure methane hydrate to study its burning characteristics, so the main requirement for the procedure was to reliably form pure gas hydrate with good conversion rate in amount required for studies in relatively short period of time.

A decrease in the gas pressure would lead (with a high ice load into the reactor) to an increased concentration of ice in the resulting methane hydrate.

4

Temperature is expressed in "°C", while the accuracy of measurements in "K"; please adjust it;

It is corrected.

5

The same request of point 4 is request at line 140 – 141.

It is corrected.

6

Subscripts must be inserted where necessary in Lines 170 - 177, to make the description of Eq. 1 more understandable.

Subscripts were added. The nomenclature was added. Eq. 1 is written in a general form. In Eq. 2 P and r corrected to P_f and r_f.