Study on temperature characteristics of hydrate slurry during

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Study on temperature characteristics of hydrate slurry during cyclopentane-methane hydrate formation Jing Cai, Ya-Fei Hu, Yu Zhang, Chun-Gang Xu, Zhao-Yang Chen, Qiunan Lv, and Xiao-Sen Li Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b03655 • Publication Date (Web): 11 Jan 2018 Downloaded from http://pubs.acs.org on January 11, 2018

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Study on temperature characteristics of hydrate slurry during cyclopentane-methane hydrate formation Jing Cai,a,b,c,d,e Ya-Fei Hu,f Yu Zhang,a,b,c,d Chun-Gang Xu,a,b,c,d Zhao-Yang Chen,a,b,c,d Qiu-Nan Lv, a,b,c,d Xiao-Sen Lia,b,c,d,∗ a

Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, China

b

CAS Key Laboratory of Gas Hydrate, Guangzhou 510640, China

c

Guangdong Provincial Key Laboratory of New and Renewable Energy Research and Development, Guangzhou

510640, China d

Guangzhou Center of Gas Hydrate Research, Chinese Academy of Science, Guangzhou 510640, China

e

University of Chinese Academy of Sciences, Beijing 100049, China

f

Hisense Kelon Electrical Holdings Company Limited, Foshan, China

Abstract In this work, the temperature characteristics of hydrate slurry related to transition heat in the cyclopentane (CP)/methane (CH4) hydrate formation process were systematically investigated. A crystallizer with a special heat-insulating layer of aerogel was designed to hold the transition heat, and the hydrate slurry could be heated in the crystallizer. Temperatures were measured in the process of the hydrate formation under the conditions of different operating pressures, volumes of solution, ways of gas injection and volume ratios of CP to water. The highest temperature of hydrate slurry (Th) and the maximum temperature difference (∆Tmax) relative to the initial temperature were adopted to evaluate the influence of different conditions. The experimental results indicated that the hydrate formation interface and thermal interface obviously move from the initial gas/CP interface and CP/water interface

∗

Corresponding author. Tel: +86-20-87057037; fax: +86-20-87034664.

E-mail address: [email protected]. (X.-S. Li)

ACS Paragon Plus Environment

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towards the bulk solution. Both the increase of operating pressure and the decrease of solution volume have positive effect on enhancing the hydrate slurry temperature. In addition, the volume ratio of CP to water also significantly affects the fluctuation of the hydrate slurry temperature. The hydrate slurry could be heated up to 294.45 K and the ∆Tmax of 16.30 K could be obtained, and such high heat could be effectively collected and used elsewhere. Keywords: hydrate slurry; temperature characteristic; transition heat; cyclopentane

1. Introduction Natural gas hydrates (NGHs) are ice-like non-stoichiometric inclusion compounds formed by water molecules and guest molecules under the conditions of low temperature and/or high pressure. For the NGHs, the typical guest molecules include methane (CH4), ethane (C2H6) and propane (C3H8). These guest molecules are enclosed into the host cavities through van der waals force, forming the gas hydrate with stable structures. The framework of the host cavities are constructed by water molecules through hydrogen bonds. Generally, the hydrate structures include three different types, such as structure I (sI), structure II (sII) and structure H (sH), depending on the pressure, temperature, guest molecules, etc.1 In the nature, the sI NGHs have been detected in the permafrost and the deep marine sediments where the NGHs stably exist due to the conditions of ample gas supply, suitable temperature and high pressure. Since the 1960s, the NGHs have attracted the world’s attention for two reasons: (1) a cubic NGHs can contain approximately 170 cubic natural gas under the conditions of standard temperature and pressure (STP), (2) the amount of carbon resource in the NGHs reservoirs over the world is estimated as twice as that in the proved fossil fuels on the earth.2 Therefore, the NGHs are regarded as an alternative energy resource for future.1 It is crucial to develop reasonable technologies to produce natural gas from the NGHs. In general, producing natural gas from the NGHs deposition is different in comparison with that from the natural gas field. For the NGHs exploitation technique, it involves changing the thermal state of the NGHs reservoir, decomposing the gas hydrates in NGHs reservoir and collecting the natural gas from the NGHs reservoir. Presently, some exploitation techniques have been proposed and investigated for several decades. These techniques can be classified into four basic schemes: (1) depressurization,3,

4

(2) thermal stimulation,5,


6

(3) chemical

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stimulation7,

8

and (4) replacement of CH4 by carbon dioxide (CO2).9,

10

Besides some

combination technologies have also been developed. Hot brine injection is the one that combines thermal stimulation with chemical stimulation. For such combination technology, not only the heat is supplied to decompose the NGHs, but also the salinity is adopted to break the original stable NGHs phase equilibrium condition. Based on the double effect of the hot brine injection on the NGHs decomposition, therefore, the combination technology is a relatively energy-efficiency technology.6 Hydrate formation is an exothermic process, with the effective and fast hydrate formation rate, a large amount of transition heat can be accumulated in the hydrate formation system. According to this exothermal characteristic of hydrate formation, we proposed a novel technique to prepare the warm brine in-situ seafloor via hydrate formation process for the NGHs exploitation in marine sediment based on the injection of hot brine.11, 12 By the method, the heat loss along the material transmit pipelines can be reduced significantly and the energy efficiency can be enhanced remarkably. As shown in Fig. 1, the conceptual scheme of the warm brine in-situ seafloor and its dual horizontal well systems are detailed.11 A continuous crystallizer is divided into six parts: warm brine zone, hydrate formation zone, hydrate uplifting and brine descending zone, hydrate decomposition zone, brackish water zone and hydrate former zone. As reported by Chen et al.11 and Zang et al.13, the process of generating hot warm brine in-situ seafloor via hydrate formation can be performed as follows. Firstly, the hydrate promoter is injected into the apparatus, which is installed in the seafloor, and the multi-hydrates rapidly form under the submarine conditions of high pressure and low temperature. As expected, the residual seawater can be heated owing to the exothermic effect of hydrate formation, and the salinity of residual seawater can be continuously enhanced due to the desalination effect of hydrate formation. As a result, the warm residual seawater with high salinity can be produced. Subsequently, such warm seawater can be injected into the NGHs reservoir to decompose the NGHs and produce natural gas from the NGHs reservoir. Theoretically, this method is helpful to reduce the heat loss and enhance the energy efficiency for the NGHs exploitation. However, for this novel exploitation technique, three obstacles need to get through, including the determination of the appropriate hydrate promoter for enhancing the amount of transition heat related to hydrate formation, optimization of the


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operating condition for accelerating the hydrate formation rate and elimination of the hydrate agglomeration for ensuring the hydrate slurry mobility in the crystallizer. For the appropriate thermodynamic hydrate promoter, water-insolubility compounds, such as cyclepentane (CP), neopentane, cyclohexane, methyl-cylopentane, tetrahydrothiophene (THT), trim-methylene sulfide (TMS), have been vastly investigated.15, 16 Especially, CP has been systematically investigated because it has significant advantages on moderating the hydrate formation equilibrium conditions, shortening the hydrate formation induction time, accelerating the hydrate formation rate and releasing a large amount of transition heat. Based on the prediction of vapor-hydrate equilibrium ratio (Kvs values) correlations, Tohidi et al.15 reported that CP was the best heavy hydrate promoter in both binary and ternary hydrate formation system. Lv et al.14, 16-19 carried out a series of thermodynamic studies on CH4 hydrate formation in water and brine aqueous systems by adding CP, TMS, THT and the mixture of CP and TMS. Lv et al.17 also investigated the kinetic process of the CP/CH4 hydrate formation in the sodium chloride aqueous solution. It proved that the induction time was dramatically shortened by adding CP into the hydrate formation system. Moreover, the higher ratio of CP to water leaded to the faster the CP/CH4 hydrate formation rate. In addition, CP was also adopted as a type of hydrate promoter to moderate the thermal condition and enhance the hydrate formation rate in the hydrate-based CH4 separation process.20, 21 Similarly, CP was added into the hydrate formation system to recover CO2 from fuel and flue gas mixture.22, 23 All these reports testified that CP has a positive effect on moderating hydrate formation condition, shortening the gas hydrate induction time, and enhancing the hydrate formation rate. Besides, the hydrate formation enthalpy of CP/CH4 hydrate is 130.25 kJ/mol at 285 K.16 It means that a large amount of transition heat can be released in the process of the CP/CH4 hydrate formation. Therefore, in this work, the water-insolubility of CP is determined as a great thermodynamic promoter, and the systems containing CP and CH4 are adopted to produce the warm brine for the NGHs exploitation in marine sediment. In order to generate the available warm brine for producing natural gas from the NGHs deposition, four stages need to be achieved before its application. In our previous works, three elemental stages have been completed. Firstly, Chen et al.11 proposed the blueprint of the warm brine in-situ seafloor via the hydrate formation process for the NGHs exploitation and


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testified the flexibility of the hydrate-based warm brine prepared process for marine gas hydrate thermal stimulation using the TOUGH+HYDRATE. According to the results of calculation, the warm brine injection was evaluated as a useful NGHs exploitation method for its heating coefficient of 3.0, comparing with the other conventional hot brine injection.11 Secondly, in order to determine the suitable hydrate promoters, Lv et al.14, 16, 19 performed a series of experimental research on the formation equilibrium data of the binary hydrates containing the promoter and CH4, furthermore, systematically evaluated their formation enthalpies in the pure water system and brine water system. When the water-insoluble compound (CP) and help gas (CH4) were determined as the suitable hydrate formation materials, the formation kinetics of the CP/CH4 binary hydrate were investigated in the sodium chloride aqueous solution under the certain conditions of temperature and pressure, stimulating the conditions at various depths of ocean water.13, 17 It was found that the driven force played an important role on the hydrate formation, and the hydrate formation rate was sharply enhanced due to the addition of CP. Next, the finally stage is to figure out temperature characteristics of the hydrate slurry and the residual aqueous solution in pure water system and brine aqueous solution system in the process of the CP/CH4 binary hydrate formation, and to produce hot water and warm brine in the scale-up equipment. For holding the transition heat, a special crystallizer with heat insulation layer was designed to investigate temperature characteristics of the hydrate slurry and the residual solution resulted from the transition heat, which is related to the formation enthalpies in the process of the hydrate formation. CP and CH4 were adopted as the hydrate promoter and help gas, respectively, and all experiments were carried out at temperature of 278.15 K. The temperatures near the interfaces (including gas/CP interface and CP/water interface), in the hydrate slurry and in the bulk solution were monitored and measured, recording as T1, T2 and T3, respectively. Especially, the highest temperature (Th) is the highest value of the hydrate slurry temperature related to the transition heat in the process of the hydrate formation, and the temperate difference (∆Tmax) is the maximum value between the highest temperature (Th) and the initial temperature of 278.15 K. The influence of different operating pressures, the solution volumes, gas injection ways and volume ratios of CP to water on the hydrate slurry temperature were investigated.


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2. Experimental section 2.1 Materials Cyclopentane (CP) with the purity of 99.00 % was supplied by Chengdu Best Reagent Co., Ltd. Methane (CH4) with the purity of 99.99 % was supplied by Foshan Huate Special Gas Co., Ltd. The deionized water was prepared by an ultrapure water equipment GREEN-10T with a resistivity of 18.25 MΩ/cm, which supplied by Nanjing ultrapure water Co., Ltd. 2.2 Apparatus The schematic diagram of the experimental apparatus is shown in Fig. 2. The setup mainly consists of a crystallizer, a gas supply unit, a liquid inlet unit, a low temperature chamber and a data acquisition unit. The crystallizer with an inner volume of 125 mL is made of 316 stainless steel. The gas inlet is located at the bottom of the crystallizer and the gas is introduced into the crystallizer trough the bubble plate distributor. The crystallizer can be pressurized up to 15.0 MPa in the temperature range of (273.15 – 323.15) K. For purpose of holding the transition heat related to the formation enthalpies during the hydrate formation, the crystallizer is insulated by the insulation layer of aerogel with the heat conductivity coefficient less than 0.02 W/ (m•K). As shown in Fig. 2, three temperature couples are located at inner wall of the crystallizer to monitor and measure the hydrate slurry and the residual solution temperature during the hydrate formation. From the top to the bottom, the temperature couples of T1, T2 and T3 are located near the gas/liquid CP and liquid CP/water interface (place a), in the hydrate slurry (place b) and in the bulk solution (place c), respectively. Especially, the pressure of the crystallizer is measured by the pressure transducer (model trafag8251, TRAFAG) with the uncertainty of 0.04 MPa. A gas supply unit is applied to maintain the crystallizer pressure constant. The gas supply vessel is made of 316 stainless steel with the maximum operation pressure of 40.0 MPa. The pressure in the gas supply vessel is measured by the pressure transducer (model setra 5310, Setra Systems, Inc.) with the uncertainty of ±0.02 MPa. The vacuum pump (2XZ-0.5) is used to make the crystallizer air-free and suck the solution into the crystallizer before the experiments. All above mentioned equipment and materials are placed in the low temperature chamber refrigerated by the cooled-air circulation refrigeration machine (BSTP-Z500S). The operating temperature of the chamber, recorded as Te, is in the range of (275.15 - 298.15) K, which is adopted to


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stimulate the seafloor temperature at seawater depth of around 1800 m.11 The temperature of the crystallizer, gas supply vessel and the chamber is measured by the Pt1000 thermal couple (JM6081, Hefei Ding Li Co., Ltd.) with the uncertainly of ±0.05 K. The data of pressures and temperatures are acquired by a data acquisition system (Agilent 34970), connecting with a computer. 2.3 Procedure During the experiments, the temperature of the low temperature chamber was set to the given value, and the actual chamber temperature was minored as Te. All equipment and materials (CH4 gas cylinder, CP and water) were placed in the chamber, and precooled to 278.15 K. Before the experiment, the deionized water was sucked into the crystallizer using the vacuum pump, and the crystallizer was thoroughly washed three times. After the crystallizer was dried and vacuumed, the desired volume of CP and water were charged into it. Five minutes later, the CH4 gas was introduced into the crystallizer and pressurized up to the operating pressure. When the gas was introduced through the bubble plate located at the bottom of the crystallizer, the gas bubbles with a certain size were generated in the bulk solution. Then, the gas bubbles rose from the bottom to the gas/liquid CP interface through the CP/water interface. In the process of gas bubble rising, gas bubbles led to the strong disturbance to supply gas and liquid contact area, and the gas bubbles might be shelled by the pure CP hydrate or the CP/CH4 binary hydrate, which form around the gas bubble boundary. Due to the density of the pure CP hydrate or the CP/CH4 binary hydrate lower than that of water, the hydrates ascended spontaneously and accumulated in the CP/water interface. Accordingly, T1, T2 and T3 increased due to the transition heat related to the hydrate formation enthalpies. The experiment was considered to be completed when T1, T2 and T3 began to significantly decrease. Then, the crystallizer was decompressed to the atmospheric pressure for hydrate decomposition. After the hydrate decomposition completely, the gas released from the hydrate was collected in the crystallizer, and its volume was measured by displacing water into the cylinder. Then, based on such volume, the amount of CH4 enclosed in the hydrates was calculated according to the gas state equation. During the experiments, the time was recorded as t0 when the liquid solutions were charged into the crystallizer, and the data of pressure and temperature were recorded by the computer.


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3. Results and discussions In order to understand the temperature characteristics of the hydrate slurry resulted from the transition heat during the hydrate formation, total 12 runs of experiments are carried out with different operating pressures (runs 4, 9 and 10), the solution volumes (runs 6, 4, 7 and 8), the ways of the gas injection (runs 4, 11 and 12) and the volume ratios of CP to water (runs 1, 2, 3, 4 and 5). The change of the hydrate slurry temperature and gas consumption are summarized in Table 1. T1, T2 and T3 are temperatures at the different places of the inside crystallizer, as shown in Fig. 2. In addition, Th expresses the highest temperature of the hydrate slurry resulted from the transition heat, and ∆Tmax is the temperature difference between Th and T0 in the crystallizer. Especially, (Th-1, Th-2, Th-3) and (∆Tmax-1, ∆Tmax-2, ∆Tmax-3) are the highest temperature and the highest temperature difference for T1, T2 and T3, respectively. 3.1 Temperature characteristics of hydrate slurry For the solution with the volume ratio of CP to water (30/40) under the conditions of 278.15 K and 8.50 MPa, the changes of T1, T2 and T3 with time in the system with injecting CH4 and without injecting CH4 are shown in Fig. 3. From Fig. 3(a), it can be seen that the change trends of T1, T2 and T3 are similar in the system with injecting CH4. Firstly, in the initial period of 0 - 400 s, T1, T2 and T3 are stable, and no obvious temperature perturbations can be observed. It means that the precooling effect is feasible in the low temperature chamber. Then, due to the transition heat resulted from the hydrate formation, T1, T2 and T3 promptly increase when the gas is introduced into the crystallizer at time of 400 s. The temperature change reflects the hydrate formation rate and the difference between the amount of transition heat and the amount of the heat loss transferring from the crystallizer to ambient. When the hydrate formation rate is fast, the amount of transition heat is more than that of the heat loss, resulting in the increase of the hydrate slurry temperature. When the hydrate formation rate is slow, the amount of transition heat is as same as that of the heat loss, resulting in the stable hydrate slurry temperature. Otherwise, when the hydrate formation is completed, no transition heat can be released, resulting in decreasing of the hydrate slurry temperature. Therefore, the hydrate formation can be divided into three stages: stage of temperature increasing (stage A) with fast hydrate formation rate, stage of temperature being stable (stage B) with limited hydrate formation rate and stage of temperature decreasing


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(stage C) with no hydrate formation, in terms of the temperature change in the process of the hydrate formation. From Fig. 3(b), all of T1, T2 and T3 show no obvious change in the system without injecting CH4, comparing with those in the system with injecting CH4. Especially, both T1 and T3 keep stable all long, and T2 show a little increase during the hydrate formation. It is resulted from that T2 locates near the liquid CP/water interface, as shown in Fig. 2 Besides, based on the volume of the residual solution drained from the crystallizer, it is found that only a little transition heat is released owing to the limited hydrate formation rate during the pure CP hydrate formation. Therefore, the effect of the transition heat related to the pure CP hydrates on the hydrate slurry temperature can be ignored while a great amount of the CP/CH4 binary hydrates are forming. Moreover, it also illustrates that the hydrates containing CP initially form in the liquid CP/water interface. As shown in Fig. 3(a), in stage A (400 - 5400 s), T1, T2 and T3 steeply increase. It means that CP/CH4 binary hydrates form with a fast rate when the CH4 gas is introduced into the bulk solution with bubbling. Especially, the hydrate can continuously form due to the enough disturbance and sufficient contact area between gas bubbles and the bulk solution with the gas bubbles continuously rising from the bottom, resulting in the sharp increase of the hydrate slurry temperatures (T1, T2 and T3). However, with hydrate formation, T1, T2 and T3 start to present the obvious temperature difference at the same time. Take the temperature at the 1500 s as an example, T1, T2 and T3 are 285.66 K, 283.83 K and 280.44 K, respectively. The temperature difference between T1 and T2, T1 and T3, and T2 and T3 are 1.73 K, 5.22 K and 2.93 K, respectively. All of temperature difference among T1, T2 and T3 are higher than their initial temperature differences before the gas injection in period of 0 – 400 s. As shown in Fig. 2, it can be seen that the place a and the place b are around the initial gas/liquid CP interface and liquid CP/water interface, respectively, while the place c is immersed into the bulk solution. The difference of T1 and T3 is the highest, and T1 increase prior to T2 and T3 accordingly. It illustrates that the CP/CH4 binary hydrate form around the gas bubble boundary during the gas bubbles raise and accumulate in the gas/liquid CP interface. Moreover, the hydrate formation in the initial liquid CP/water interface is more intense than that in the bulk solution, and more transition heat is accumulated in the hydrate slurry around


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the liquid CP/water interface rather that in the bulk solution. Both T2 and T3 are lower than T1, and T2 is higher than T3. It may be ascribed to four aspects. First of all, the amount of the hydrate formed around the gas boundary as the shell is limited, accordingly, the transition heat resulted from the hydrate formation is limited. It results in that the heat could be conductive from the hydrate shells towards their surrounding solution is limited as well. Secondly, the thermal couples of T2 and T3 are located in the stagnant layer with quiet low heat transfer velocity, and it results in that the heat conduction capability of the bulk solution is limited on the horizontal direction. Thirdly, there is the convection flow on the vertical direction due to the gas bubble raise from the bottom towards gas/liquid CP interface, and such convection can be strengthened based on the disturbance resulted from collision and breakage among bubbles. Therefore, the hydrate shells and the transition heat resulted from the hydrate formation are carried from the bottom of the solution towards the gas/liquid CP interface with heat transferring on horizontal direction, eventually, the gas bubbles with the hydrate shells and the heat are accumulated in the gas/liquid CP interface. As a result, T2 is higher than T3 at the same time. Finally, around the gas/liquid CP interface, the transition heat resulted from the hydrate formation around the gas bubbles is converged together. Moreover, more transition heat can be accumulated by virtue of the second generation of the hydrate formation related to the gas bubble breakage and the enough gas/liquid contact around the interfaces, including gas/liquid CP interface and liquid CP/water interface. Consequently, T1 is highest temperature during the hydrate formation. Moreover, T1 will stay the highest value during the whole experiment because the tight hydrate layer benefits for holding the heat. And the hydrate forms incessantly between gas and the interstitial water in the hydrate layer is also helpful to accumulate more transition heat. In the later stage of stage A, take the temperature at 4000 s as an example, T1, T2 and T3 are 292.78 K, 292.52 K and 291.34 K, respectively. The temperature difference between T1 and T2, T1 and T3, and T2 and T3 are 0.26 K, 1.44 K and 1.18 K, respectively. Although the temperature difference between T1 and T3 is still the highest, all these temperature difference are lower than those obtained at 1500 s. It may be resulted from three aspects. Firstly, the transition heat accumulated in the hydrate layer around the initial gas/liquid CP interface transfers constantly on horizontal and vertical direction. Secondly, the hydrate formation interface moves from the gas/liquid CP interface,


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through the liquid CP/water interface and towards the bulk solution owing to the gas bubble disturbance. Moreover, the hydrate formation rate continuously reduces due to the decrease of driving force related to the thermal condition change, which is resulted from the increase of the system temperature under the constant pressure. In sum, such temperature difference in stage A illustrates that the hydrate formation interface and the heat conduction around the initial interfaces, including gas/liquid CP interface and liquid CP/water interface, constantly move towards the bulk solution during the hydrate formation, and their transferring have a significant effect on the temperature characteristic of the hydrate slurry. The similar phenomenon was ever reported by V. A. Kamath.24 Besides, the change of thermal status in the system, resulting from the temperature increase, limits the hydrate formation rate in the later stage of stage A. For stage A, the amount of the heat loss corresponding to the heat transferring from the crystallizer towards ambient can be ignored due to the fast hydrate formation rate. For stage B (5400 - 7800 s), T1, T2 and T3 reach their individual plateaus and keep stable. It illustrates that the transition heat resulted from the hydrate formation is equal to the heat loss with transferring from the crystallizer towards ambient because of the decrease of the hydrate formation rate. In addition, it also illustrates that the transition heat could conduct more evenly in the hydrate slurry and the residual solution as the hydrate formation time is prolonged. For stage C (after 7800 s), T1, T2 and T3 gradually decrease. It means that transition heat resulted from the hydrate formation is less than the heat loss with transferring from the crystallizer to ambient because the hydrate formation is completed. Moreover, the obvious and stable temperature difference among T1, T2 and T3 can be found in stage B and C, rooted in the systematical temperature difference as shown in the period of 0 – 400s in Fig 3(a) and Fig. 3(b). Due to the similar trends of T1, T2 and T3, T2 is mainly adopted as following to illustrate the temperature change of hydrate slurry in the process of the hydrate formation under the different conditions. 3.2 Effect of operating pressure Experiments of run 4, 9 and 10 were carried out with the solution volume of 70 mL at 278.15 K, consisting of 30 mL CP and 40 mL water, under conditions of different operating pressure of 2.50, 5.50 and 8.50 MPa, respectively. Fig. 4 shows the changes of T2 at different operating


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pressures. It can be found that T2 has the similar trend with that shown in Fig. 3. Under different pressure of 2.50, 5.50 and 8.50 MPa, the value of T2 gradually increases in stage A when the gas is introduced into the crystallizer. In addition, the highest value of Th-2 is obtained at the end of stage A under the conditions of 2.50, 5.50 and 8.50 MPa. Their value is 293.25 K, 287.67 K and 279.27 K, respectively, as detailed in Table 1. At 2.50 MPa, Th-2 is quite small due to the limitation of transition heat resulted from the limited hydrate formation. By the contrast, under the conditions of 5.50 MPa and 8.50 MPa, more transition heat can be accumulated in comparison with 2.50 MPa because the hydrate formation is more intense at 5.50 MPa and 8.50 MPa than 2.50 MPa. Consequently, the highest Th-2 can be obtained, and the maximum temperature difference (∆Tmax-2) is up to15.1 K at 8.50 MPa. It indicates that the hydrate slurry can be heated with 15.1 K at 8.50 MPa, and the temperature of the hydrate slurry increase with increase of the operation pressure. Because the higher pressure is helpful to accelerate the hydrate formation, consequently, the value of Th-2 can be enhanced effectively. Therefore, the operating pressure of 8.50 MPa is adopted in following experiments. In addition, the changes of T2 in stage B and stage C are similar with that shown in Fig. 3, as mentioned in Section 3.1. 3.3 Effect of solution volume Experiments of run 6, 4, 7, 8 were carried out with different solution volume of 49, 70, 84, 105 mL at 278.15 K and 8.50 MPa. Fig. 5 shows the changes of T2 with different solution volume. It can be found that T2 gradually decreases with the increase of the solution volume. The highest Th-2 is obtained in the solution with the volume of 49 mL, while the lowest Th-2 is obtained in the solution with the volume of 105 mL. The values of Th-2 are similar in the solution with the volume of 70 mL and 84 mL. It means that the change of solution volume has a significant effect on the hydrate slurry temperature. In other words, in the crystallizer with fixed volume, the excess amount of gas is helpful to form the hydrates. As detailed in Table 1, Th-1 and Th-3 also decrease with increase of the solution volume. With the solution volume in range from 49 mL to 105 mL, Th-2 decreases from 293.66 K to 287.96 K. It is resulted from two reasons, including the amount of the CP/CH4 binary hydrates and the residual volume of the solution during the hydrate formation. On the one hand, compared with the solution volume of 105 mL, the less volume of the solution means that the larger


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amount of gas can be introduced, resulting in the excess gas for the hydrate formation process. Accordingly, the gas and liquid contact areas with small volume solution are sufficient in comparison with that with large volume solution. As a result, the amount of the CP/CH4 binary hydrate can be increased and the amount of the transition heat resulted from hydrate formation can be enhanced with small volume solution rather than these with large volume solution. On the other hand, under the same conditions of the temperature and operating pressure, the less solution volume also means the less volume of the residual solution remained after the hydrate formation. As shown in Fig. 6, the amount of the gas consumption has little change with solution volume ranging from 49 mL to 105 mL. It illustrates that the amount of the transition heat resulted from hydrate formation fail to be changed significantly. Consequently, for the similar amount of the transition heat resulted from hydrate formation, 1 mL residual solution can adsorb more transition heat with less residual solution volume than that with more residual solution volume. As a result, Th-2 decreases with the increase of the solution volume. The ∆Tmax-2 decreases with increase of the solution volume. The highest ∆Tmax-2 is also obtained with the solution volume of 49 mL. According to Table 1, the values of Th-3 obtained in 49 mL and 105 ml are lower than those obtained in 70 mL and 84 mL. It also illustrates both the amount of the transition heat and the amount of the residual solution affect the hydrate slurry temperature for T3 is immersed in the bulk solution, as shown in Fig. 2. Therefore, taking Th, ∆Tmax, and the volume of the residual solution, the solution volume of 70 mL is adopted to produce the warm water in this work. 3.5 Way of gas injection For experiments of run 4, 11 and 12, three different ways of the gas injection, W1, W2 and W3, were adopted. W1 was the continuous gas injection way, in which the gas was pressurized up to the desired value of 8.50 MPa continuously. W2 was the multi-step gas injection way, in which the gas was pressurized from 0 to 2, 4, 6 and 8.50 MPa with the internal time of 10 minutes. W3 was the same multi-step gas injection way of W2, in which the internal time was 30 minutes. All experiments were carried out in the solution with the solution volume of 70 mL at 278.15 K, 8.50 MPa. Fig. 7 shows the change of T2 with the different gas injection ways of W1, W2 and W3. In the process of gas introduction by the means of the multi-step gas injection (W2 and W3), several stable temperature platforms can be observed. In addition, the


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

gas injection time with W2 and W3 is approximately 3950 s and 10750 s, respectively. Regardless of different gas injection ways, when the operating pressure is pressurized up to the desired value of 8.50 MPa, T2 with different gas injection ways of W1, W2 and W3 significantly increases and reaches to the individual highest value of Th-2. As shown in Table 1, the values of Th-2 with W1, W2 and W3 are 293.27 K and 293.70 K, respectively. Although the gas bubble can supply the gas and the solution enough, the degree of turbulence depends on the bubble size and bubble generation frequency.24 In this work, for the gas injection way of W1, W2 and W3, both bubble size and bubble generation frequency are identical. Therefore, the bubble turbulence resulted from multi-step gas injection of W2 and W3 has no significant effect on accelerating the hydrate formation rate and enhancing the value of Th-2 and ∆Tmax-2. Thus, the continuous gas injection way is adopted to shorten the hydrate formation time. 3.6 Effect of CP/water volume ratio Fig. 8 shows the comparison of T2 obtained with different volume ratios of CP to water at 278.15 K and 8.50 MPa. From Fig. 8, it can be seen that T2 shows similar trend as detailed in Fig. 3(a). In stage A, T2 sharply increases with the CP/water volume ratio of 15/55, 25/45 and 30/40, while T2 slightly increases with the CP/water volume ratio of 5/65 and 45/25. In addition, the CH4 consumption and the temperature difference are shown in Fig. 9. It can be found that the temperature difference increase with the increase of CP volume from 5 mL to 25 mL, but decrease with the CP volume from 25 mL of 45 mL. For instance, Th-2 is 283.78 K, 291.99 K, 294.45 K, 293.25 K and 281.76 K under the ratios of 5/65, 15/55, 25/45, 30/40 and 45/25. On the contrary, the CH4 consumption deceases with the increase of CP volume from 5 mL to 25 mL, but increase with the CP volume from 25 mL to 45 mL. It indicates that the temperature change relates to the proportion of the CH4 hydrate, CP hydrate and CP/CH4 binary hydrate. According to the ideal molecular formula of CP/CH4 binary hydrate ( 8CP・ 16CH4・136H2O), the optimal volumes of CP and water are 16.5 mL and 53.5 mL for the solution volume of 70 mL, respectively. The temperature change and the CH4 consumption are affected by the optimal CP volume of 16.5 mL, resulting in different hydrates proportion with changing the volume ratio of CP to water. With the ratio of 5/65, the largest amount of CH4 consumption is 0.361 mol. It illustrates that main hydrate is the CH4 hydrate due to the


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Energy & Fuels

limitation of CP volume. Therefore, Th-2 is fairly low (283.78 K) for the formation enthalpies of CH4 hydrate is only around 54 kJ/mol.25 With the volume ratio from 15/55 to 25/45, the CH4 consumption decreases and the temperature difference increases. It illustrates that the CP/CH4 binary hydrate becomes dominant with the increase of the CP volume. However, with the volume ratio from 25/45 to 30/40, the CP hydrate becomes dominant rather than CP/CH4 binary hydrate, and such proportion of the CP hydrate increases with increase of the CP volume is not helpful to enhance the hydrate slurry temperature. Although both the formation enthalpies of CP hydrate and CP/CH4 binary hydrate are more than 121 kJ/mol,16 the amount of CP/CH4 binary hydrate has more significant effect on improving the temperature of the hydrate slurry relative to the pure CP hydrate. Similar phenomenon can be found in Fig. 3(b), the pure CP hydrate forms with the limited formation rate, and the temperature only has a little increase near the liquid CP/water interface. As a result, the temperatures decrease accordingly from the volume ratio of 25/45 to 30/40, and the maximum ∆Tmax-2 (16.30 K) is obtained under the condition of 278.15 K and 8.50 MPa with the volume ratio of 25/45, as shown in Table 1. Such decrease of Th-2 and ∆Tmax-2 and increase of the CH4 consumption may relate to that the accumulation of the CP hydrate prevents CH4 molecules from contacting the liquid phase of CP and water to form the hydrates. In addition, the different structures of CP hydrate and CP/CH4 binary hydrate affects the CH4 consumption. For the sI CH4 pure hydrate, CH4 molecules are encaged into the small and lager cavities of the sI hydrates, resulting in the large CH4 consumption. For the sII CP/CH4 binary hydrate, the CH4 molecules only encage into the small cavities. Hence, the CH4 consumption is decreased. These trends of CH4 consumption also indirectly testifies that the proportion of the CH4 hydrate, CP hydrate and CP/CH4 binary hydrate is changed with the increase of CP volume from the volume ratio of 5/65 to the volume ratio of 30/40. With the volume ratio of 45/25, the decrease of ∆Tmax-2 and the increase of CH4 consumption may refer to the CH4 dissolution towards liquid CP. Therefore, it leads to the lowest temperature of 281.76 K and the largest CH4 consumption of 0.298 mol. In addition, Th-3 shows the similar trend as Th-2, and the maximum value of Th-3 is 294.06 K, which is obtained in the system with the ratio of 25/45. Therefore, the volume ratio of 25/45 is a better volume ratio of CP to water on enhancing the highest hydrate slurry temperature (Th).


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

4. Conclusion In this work, the temperature characteristics of hydrate slurry related to the transition heat resulted from hydrate formation were systematically investigated with the different conditions of operating pressure, solution volume, way of gas injection and volume ratio of CP to water by measuring the hydrate slurry temperature. Especially, the highest hydrate slurry temperature (Th) and the maximum temperature difference (∆Tmax) were adopted to evaluate the influence of the different conditions. The experimental results show that the hydrate formation and thermal interfaces constantly move from the initial gas/liquid CP interface, through liquid CP/water interface and towards the bulk solution in the process of hydrate formation, and the thermal status continues to change with the increase of the hydrate slurry temperate. In addition, the hydrate slurry temperature can be enhanced by increasing the operating pressure and decreasing the solution volume, while it shows little change with adoption of the multiple gas injection. The volume ratio of CP to water has a significant influence on the values of Th and ∆Tmax. The highest Th-2 of 294.45 K and the maximum ∆Tmax-2 of 16.3 K are obtained in the 70 mL solution with the CP/water volume ratio of 25/45 at 278.15 K and 8.50 MPa in conjunction with the continuous gas injection. The total amount of transition heat is not calculated because of the uncertain proportion and the volume of CH4 hydrate, CP hydrate and CP/CH4 binary hydrate, and it will be carried out in the future. Acknowledgments This work was supported by National Science Fund for International S&T Cooperation Program of China (No.2015DFA61790), National Key Research and Development Plan of China (No. 2016YFC0304002) and Key Laboratory Fund of Gas Hydrate (Y607j91001), which are gratefully acknowledged.

References 1.

Sloan, E. D. K., C. A., Clathrate Hydrates of Natural Gases. 3nd Ed ed.; CRC Press, Taylor & Francis

Group: Boca Raton, 2008. 2.

Englezos, P., Clathrate Hydrates. Industrial & Engineering Chemistry Research 1993, 32, (7),

1251-1274. 3.

Zhou, Y.; Castaldi, M. J.; Yegulalp, T. M., Experimental Investigation of Methane Gas Production

from Methane Hydrate. Industrial & Engineering Chemistry Research 2009, 48, (6), 3142-3149. 4.

Oyama, H.; Konno, Y.; Masuda, Y.; Narita, H., Dependence of Depressurization-Induced


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Dissociation of Methane Hydrate Bearing Laboratory Cores on Heat Transfer. Energy & Fuels 2009, 23, 4995-5002. 5.

Wang, Y.; Feng, J. C.; Li, X. S.; Zhang, Y.; Chen, Z. Y., Large Scale Experimental Investigation on

Influences of Reservoir Temperature and Production Pressure on Gas Production from Methane Hydrate in Sandy Sediment. Energy & Fuels 2016, 30, (4), 2760-2770. 6.

Kamath, V. A.; Godbole, S. P., Evaluation of Hot-Brine Stimulation Technique for Gas-Production

from Natural-Gas Hydrates. Journal of Petroleum Technology 1987, 39, (11), 1379-1388. 7.

Elgibaly, A.; Elkamel, A., Optimal hydrate inhibition policies with the aid of neural networks.

Energy & Fuels 1999, 13, (1), 105-113. 8.

Dong, F. H.; Zang, X. Y.; Li, D. L.; Fan, S. A. S.; Liang, D. Q., Experimental Investigation on Propane

Hydrate Dissociation by High Concentration Methanol and Ethylene Glycol Solution Injection. Energy & Fuels 2009, 23, 1563-1567. 9.

Xu, C. G.; Cai, J.; Lin, F. H.; Chen, Z. Y.; Li, X. S., Raman analysis on methane production from

natural gas hydrate by carbon dioxide-methane replacement. Energy 2015, 79, 111-116. 10. Zhang, Y.; Xiong, L. J.; Li, X. S.; Chen, Z. Y.; Xu, C. G., Replacement of CH4 in Hydrate in Porous Sediments with Liquid CO2 Injection. Chemical Engineering & Technology 2014, 37, (12), 2022-2029. 11. Chen, Z. Y.; Feng, J. C.; Li, X. S.; Zhang, Y.; Li, B.; Lv, Q. N., Preparation of Warm Brine in Situ Seafloor Based on the Hydrate Process for Marine Gas Hydrate Thermal Stimulation. Industrial & Engineering Chemistry Research 2014, 53, (36), 14142-14157. 12. Li, X. S.; Xu, C. G.; Zhang, Y.; Ruan, X. K.; Li, G.; Wang, Y., Investigation into gas production from natural gas hydrate: A review. Applied Energy 2016, 172, 286-322. 13. Zang, X. R.; Lv, Q. N.; Li, X. S.; Li, G., Experimental Investigation on Cyclopentane-Methane Hydrate Formation Kinetics in Brine. Energy & Fuels 2017, 31, (1), 824-830. 14. Lv, Q. N.; Li, L.; Li, X. S.; Chen, Z. Y., Clathrate hydrate dissociation conditions and structure of the methane plus cyclopentane plus trimethylene sulfide hydrate in NaCl aqueous solution. Fluid Phase Equilibria 2016, 425, 305-311. 15. Tohidi, B.; Danesh, A.; Tabatabaei, A. R.; Todd, A. C., Vapor-hydrate equilibrium ratio charts for heavy hydrocarbon compounds .1. Structure-II hydrates: Benzene, cyclopentane, cyclohexane, and neopentane. Industrial & Engineering Chemistry Research 1997, 36, (7), 2871-2874. 16. Lv, Q. N.; Li, X. S.; Chen, Z. Y.; Feng, J. C., Phase Equilibrium and Dissociation Enthalpies for Hydrates of Various Water-Insoluble Organic Promoters with Methane. Journal of Chemical and Engineering Data 2013, 58, (11), 3249-3253. 17. Lv, Q. N.; Song, Y. C.; Li, X. S., Kinetic Study on the Process of Cyclopentane plus Methane Hydrate Formation in NaCl Solution. Energy & Fuels 2016, 30, (2), 1310-1316. 18. Lv, Q. N.; Li, L.; Li, X. S.; Chen, Z. Y., Formation Kinetics of Cyclopentane plus Methane Hydrates in Brine Water Systems and Raman Spectroscopic Analysis. Energy & Fuels 2015, 29, (9), 6104-6110. 19. Li, L.; Lv, Q. N.; Li, X. S.; Feng, J. C.; Chen, Z. Y., Phase Equilibrium and Dissociation Enthalpies of Trimethylene Sulfide plus Methane Hydrates in Brine Water Systems. Journal of Chemical and Engineering Data 2014, 59, (11), 3717-3722. 20. Zhong, D.-L.; Daraboina, N.; Englezos, P., Recovery of CH4 from coal mine model gas mixture (CH4/N2) by hydrate crystallization in the presence of cyclopentane. Fuel 2013, 106, (0), 425-430. 21. Zhong, D.-L.; Ding, K.; Yan, J.; Yang, C.; Sun, D.-J., Influence of Cyclopentane and SDS on Methane Separation from Coal Mine Gas by Hydrate Crystallization. Energy & Fuels 2013, 27, (12), 7252-7258. 22. Li, X. S.; Xu, C. G.; Chen, Z. Y.; Wu, H. J., Hydrate-based pre-combustion carbon dioxide capture


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process in the system with tetra-n-butyl ammonium bromide solution in the presence of cyclopentane. Energy 2011, 36, (3), 1394-1403. 23. Li, X. S.; Xu, C. G.; Chen, Z. Y.; Cai, J., Synergic effect of cyclopentane and tetra-n-butyl ammonium bromide on hydrate-based carbon dioxide separation from fuel gas mixture by measurements of gas uptake and X-ray diffraction patterns. International Journal of Hydrogen Energy 2012, 37, (1), 720-727. 24. Kamath, V. A.; Holder, G. D., Dissociation Heat-Transfer Characteristics of Methane Hydrates. Aiche Journal 1987, 33, (2), 347-350. 25. Lee, S. P., S.; Lee, Y.; Seo, Y., Measurements of Dissociation Enthalpy for Simple Gas Hydrates Using High Pressure Differential Scanning Calorimetry. Korean Chemical Engineering Research 2012, 50, (4), 666-671.


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Energy & Fuels

Table Caption Table 1. Data of Th, ∆Tmax and gas consumption under different conditions. Figure Caption Fig. 1 Conceptual depiction of the warm brine in situ gas production in the marine sediment. Fig. 2 Schematic of the experimental apparatus. Fig. 3 Temperature changes of pressure and temperatures in the crystallizer in the solution with the volume ratio of CP/water (30/40) at 278.15 K and 8.50 MPa, (a) with injecting CH4, (b) without injecting CH4. Fig. 4 Comparison of T2 in the solution with the volume ratio of CP/water (30/40) under the different condition of operating pressure at 278.15 K. Fig. 5 Comparison of T2 in the different volume solution with the volume ratio of CP/water (30/40) at 278.15 K and 8.50 MPa. Fig. 6 Values of ∆Tmax-2 and the amount of gas consumption obtained in the different volume solution with the volume ratio of CP/water (30/40) at 278.15 K and 8.50 MPa. Fig. 7 Comparison of T2 in 70 mL solution with the volume ratio of CP/water (30/40) under the condition of different gas injection ways at 278.15 K and 8.50 MPa. Fig. 8 Comparison of T2 in 70 mL solution with different volume ratio of CP/water at 278.15 K and 8.50 MPa. Fig. 9 Values of ∆Tmax-2 and the amount of gas consumption obtained in the different volume ratio of CP/water at 278.15 K and 8.50 MPa.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 1 Conceptual depiction of the warm brine in situ gas production in the marine sediment.11, 12


Page 20 of 26

Page 21 of 26

Low Temperature Chamber Gas Outlet Valve

T Data Acquisition

P T P Insulation Layer

T

Crystallizer

PC

Methane

Supply Vessel

CP a

T1

b Solution

T2

c

T3

Vacuum Pump

Refrigeration

Fig. 2 Schematic of the experimental apparatus.

300

(a)

296

A

294

C

B

T2

Te

T3

P

20 18 16 14

t=4000 s

292

T1

12

290 288

10

t=1500 s

286

8

284

6

282

4

280 2

278

0

276 0

2000 4000 6000 8000 10000 12000 14000 16000 18000 Time (s)


Pressure (MPa)

298

Temperature (K)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Energy & Fuels

280.0

(b)

279.5

T1 T2

279.0

T3

Temperature /K

278.5 278.0 277.5 277.0 276.5 276.0 275.5 275.0 0

10000

20000

30000

40000

50000

60000

70000

80000

Time (s)

Fig. 3 Temperature changes of pressure and temperatures in the crystallizer in the solution with the volume ratio of CP/water (30/40) at 278.15 K and 8.50 MPa, (a) with injecting CH4, (b) without injecting CH4.

296 294 292

Temperature (K)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 26

290 288 286

2.50 MPa 5.50 MPa 8.50 MPa

284 282 280 278 276 0

2000

4000

6000

8000

10000

12000

14000

Time (s)

Fig. 4 Comparison of T2 in the solution with the volume ratio of CP/water (30/40) under the different condition of operating pressure at 278.15 K.


Page 23 of 26

296 294 292

Temperature (K)

290 288 286

49 mL 70 mL 84 mL 105 mL

284 282 280 278 276 0

1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

Time (s)

Fig. 5 Comparison of T2 in the different volume solution with the volume ratio of CP/water (30/40) at 278.15 K and 8.50 MPa.

18

0.60 ∆Tmax-2

0.55

gas consumption

16

0.50

15

0.45

14

0.40

13

0.35

12

0.30

11

0.25

10

0.20

9

0.15

8

0.10

7

0.05

6

Gas consumption (mol)

17

Temperature difference (K)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

0.00 49

70

84

105

Volume of the solution (mL)

Fig. 6 Values of ∆Tmax-2 and the amount of gas consumption obtained in the different volume solution with the volume ratio of CP/water (30/40) at 278.15 K and 8.50 MPa.


Energy & Fuels

296 294

Temperature (K)

292 290 288 286

0 10 min 30 min

284 282 280 278 0

5000

10000

15000

20000

25000

30000

Time (s)

Fig. 7 Comparison of T2 in 70 mL solution with the volume ratio of CP/water (30/40) under the condition of different gas injection ways at 278.15 K and 8.50 MPa.

296 294 292 Temperature (K)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 26

290 288

5/65 15/45 25/45 30/40 45/25

286 284 282 280 278 0

4000

8000

12000

Time (s)

Fig. 8 Comparison of T2 in 70 mL solution with different volume ratio of CP/water at 278.15 K and 8.50 MPa.


Page 25 of 26

0.60

20 18

∆Tmax-2

0.55

gas consumption

0.50

16

0.45 14

0.40

12

0.35

10

0.30

8

0.25 0.20

6

0.15 4

0.10

2

Gas consumption (mol)

Temperature difference (K)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

0.05 0.00

0 5/15

15/55

25/45

30/40

45/25

Ratio of CP/Water

Fig. 9 Values of ∆Tmax-2 and the amount of gas consumption obtained in the different volume ratio of CP/water at 278.15 K and 8.50 MPa.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Table 1 Data of Th, ∆Tmax and gas consumption obtained under different conditions. Th /K

T0

P

CP

Water

/K

/MPa

/mL

/mL

Th-1

Th-2

Th-3

1

278.15

8.50

5

65

284.70

283.75

2

278.15

8.50

15

55

291.03

3

278.15

8.50

25

45

4

278.15

8.50

30

5

278.15

8.50

6

278.15

7

∆Tmax-2

Gas consumption

/K

/mol

282.98

5.63

0.361

291.99

291.75

13.84

0.275

297.67

294.45

294.06

16.30

0.113

40

293.54

293.25

292.63

15.10

0.158

45

25

282.06

281.76

281.49

3.61

0.298

8.50

21

28

293.91

293.66

279.19

15.51

0.174

278.15

8.50

36

48

292.46

292.48

292.43

14.33

0.170

8

278.15

8.50

45

60

288.06

287.96

287.90

9.81

0.143

9

278.15

5.50

30

40

287.94

287.67

287.18

9.52

0.121

10

278.15

2.50

30

40

279.36

279.27

279.08

1.21

0.013

11

278.15

8.50

30

40

294.50

293.27

292.65

15.12

0.233

12

278.15

8.50

30

40

293.71

293.70

291.10

15.57

0.217

Runs


Study on temperature characteristics of hydrate slurry during

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