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Study on the temperature characteristics in the process of cyclopentane-methane binary hydrate formation with a set of large-scale equipment
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Energy Procedia 158 Energy Procedia 00(2019) (2017)5888–5894 000–000 www.elsevier.com/locate/procedia
10th International Conference on Applied Energy (ICAE2018), 22-25 August 2018, Hong Kong, 10th International Conference on Applied Energy China(ICAE2018), 22-25 August 2018, Hong Kong, China
Study on the temperature characteristics in the process of StudyThe on 15th theInternational temperature characteristics in the Symposium on formation District Heating andprocess Cooling cyclopentane-methane binary hydrate with a set ofoflargecyclopentane-methane binary hydrate formation with a set of largescale equipment scaleofequipment Assessing the feasibility using the heat demand-outdoor Jing Cai,a,b,c,d,e Jin-Ming Zhang,a,b,c,d,e Ya-fei Hu,f Zhao-Yang Chen,a,b,c,d Xiao-Sen Lia,b,c,d,* a,b,c,d,e Jing Cai,a,b,c,d,e Jin-Ming Zhang, Ya-fei Hu,f Zhao-Yang Xiao-Senforecast Lia,b,c,d,* temperature function for a long-term districtChen, heata,b,c,d demand Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou, 510640, China a
b a CAS Key Laboratory of Gas Hydrate, Guangzhou, 510640, China Guangzhou of Energy Conversion, China a,b,c Institute a aChinese Academy of bSciences, Guangzhou, 510640, c c b Guangdong Provincial Key Laboratory New and Renewable Energy Research and Development, CAS Key of Laboratory of Gas Hydrate, Guangzhou, 510640, China Guangzhou, 510640, China d c Center of Gas Hydrate Chinese Academy of Science, Guangzhou, Guangzhou, 610640, China GuangdongGuangzhou Provincial Key Laboratory of New Research, and Renewable Energy Research and Development, 510640, China a e IN+ Center fordGuangzhou Innovation, Center Technology and Policy Research -Chinese Instituto Superior Av. Rovisco 1, 1049-001 University of Chinese Academy of Sciences, Beijing, 100049, China Pais of Gas Hydrate Research, Academy ofTécnico, Science, Guangzhou, 610640, China Lisbon, Portugal b f e Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France Veolia Hisense Kelon Electrical Holdings Company Beijing, Limited,100049, Foshan,China China University of Chinese Academy of Sciences, c Département Systèmesf Hisense Énergétiques Environnement - IMT Atlantique, 4 rue AlfredChina Kastler, 44300 Nantes, France KelonetElectrical Holdings Company Limited, Foshan, c
I. Andrić
*, A. Pina , P. Ferrão , J. Fournier ., B. Lacarrière , O. Le Corre
Abstract Abstract Abstract In this work, the temperature characteristics of hydrate slurry related to transition heat in the cyclopentane (CP)/methane (CH4) In this formation work, the temperature of crystallizer hydrate slurry to transition heat inlayer the cyclopentane (CP)/methane (CH4) hydrate process werecharacteristics investigated. A withrelated a special heat-insulating of aerogel and vacuum insulating District heating are transition commonly addressed thewith literature as the oneresidual of the most effective for decreasing the hydrate formation process investigated. Aand crystallizer a special heat-insulating layer of aerogel andTemperatures vacuum insulating layer was designednetworks to holdwere the heat, the in hydrate slurry and water could be solutions heated. were greenhouse gas process emissions from the building investments which returned through thewere heat layer was designed to hold heat,sector. andunder theThese hydrate slurryrequire and residual beare heated. Temperatures measured in the of the the transition hydrate formation the systems conditions of the 4 high ℃and 8.5water MPa.could The highest temperature of hydrate sales.(TDue to the the changed climate and building renovation demand in theadopted future could measured the process of thetemperature hydrateconditions formation under the 4 policies, ℃and 8.5heat MPa. The highest temperature of decrease, hydrate slurry and maximum difference (∆T between Tof the initial temperature were to evaluate the h)in max)conditions h and prolonging the investment return period. slurry (Th)of anddifferent the maximum temperature (∆Tcharacteristics temperature were adopted to evaluate the influence conditions on the difference temperature theinitial hydrate formation. The experimental results max) between Tduring h and the The mainthat thisconditions paper is toon assess feasibility of interface using the obviously heat demand –hydrate outdoor temperature function for heattowards demand influence ofscope different the the temperature characteristics during the experimental results indicated the of hydrate formation interface and thermal moving fromformation. the initial The gas/CP interface forecast. interface. Thethe district Alvalade, located in Lisbon was asmax a of case study. The district isinterface consisted ofhigh 665 indicated that hydrate formation and thermal moving from thecould initial towards CP/water The of hydrate slurryinterface could be heated up(Portugal), tointerface 23.47 ℃obviously andused the ∆T 19.47 ℃ begas/CP obtained, and such buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district CP/water The hydrate slurry be heated up to 23.47 ℃ and the ∆Tmax of 19.47 ℃ could be obtained, and such high heat couldinterface. be effectively collected and could used elsewhere. renovation were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were heat could bescenarios effectively collected and used elsewhere. compared with results from a dynamic heat demand Copyright © 2018 Elsevier Ltd. All rights reserved. model, previously developed and validated by the authors. ©The 2019 The Authors. Published by Elsevier Ltd. th International results that when only weather change is considered, the marginofof the error10could be acceptable for someon applications Copyright © showed 2018 Elsevier Ltd. Allresponsibility rights reserved. Selection and peer-review under of the scientific committee Conference Applied This iserror an open accessdemand article under the CCthan BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) th International (the in annual was lower 20% for all weather scenarios considered). However, after introducing renovation Selection and peer-review under responsibility of the scientific committee of the 10 Conference on Applied Energy (ICAE2018). Peer-review under responsibility of theupscientific committee of ICAE2018 – Theand 10threnovation International Conference on Applied Energy. scenarios, the error value increased to 59.5% (depending on the weather scenarios combination considered). Energy (ICAE2018). The value of slope coefficient on average the range of 3.8% up to 8% per decade, that corresponds to the Keywords: hydrate slurry; temperatureincreased characteristic; transition within heat; cyclopentane decrease hydrate in the slurry; number of heating hours of 22-139h the heating season (depending on the combination of weather and Keywords: temperature characteristic; transitionduring heat; cyclopentane renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and 1.coupled Introduction the accuracy of heat demand estimations. 1.improve Introduction © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. * Corresponding author. Tel: +86-20-87057037; fax: +86-20-87034664.
address:author. [email protected]. (X.-S. Li)fax: +86-20-87034664. * E-mail Corresponding Tel: +86-20-87057037; Keywords: Heat demand; Forecast; Climate change E-mail address: [email protected]. (X.-S. Li) 1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility the scientific 1876-6102 Copyright © 2018 Elsevier Ltd. All of rights reserved. committee of the 10th International Conference on Applied Energy (ICAE2018). Selection and peer-review under responsibility of the scientific committee of the 10th International Conference on Applied Energy (ICAE2018). 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of ICAE2018 – The 10th International Conference on Applied Energy. 10.1016/j.egypro.2019.01.536
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Jing Cai et al. / Energy Procedia 158 (2019) 5888–5894 Author name / Energy Procedia 00 (2018) 000–000
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Hydrates are types of ice-like nonstoichiometric inclusion compounds, which are formed by water molecules (host) and guest molecules, such as light hydrocarbon molecules (guest) and additives molecules, under the conditions of low temperature and/or high pressure. These guest molecules are encaged into the host cavities trough van deer Waals force, forming NGHs with stable structures. The framework of the host cavities are constructed by water molecules trough hydrogen bonds, and it is difficult to keep stable without encaging guest molecules. For the natural gas hydrate (NGHs) as energy resources, the guest molecules are mainly the light hydrocardon, including methane (CH4), ethane (C2H6), and propane (C3H8). For other multi-hydrates formed in the hydrate-based process, the guest molecules usually include hydrate promoters and small size gas molecules, such as carbon dioxide (CO2), hydrogen (H2). Generally, the hydrate structures include three different types, structure I (sI), structure II (sII), and structure H (sH), depending on the pressure, temperature, guest molecules, etc.[1] In nature, most of sI NGHs have been detected in permafrost and deep marine sediments where the NGHs stably exist owing 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) one 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 proven fossil fuels on Earth.[2] Thus, NGHs are regarded as an alternative energy resource for the future. Various NGHs exploitation technologies have been widely investigated. For instance, depressurization,[3,4] thermal simulation,[5] CO2-CH4 replacement [6,7] and chemical inhibitor.[8] Especially, the NGHs testing exploitations have been adopted in the NGHs reservoirs at Mallik2L-38 of Canada (2008), the eastern of Nankai Trough of Japan (2013, 2017) and the Shenhu sea area of China (2017). Hydrate formation is an exothermic process, a large amount of transition heat release during the hydrate formation especially when the hydrates form with an effective and fast formation rate. On the one hand, such transition heat can be utilized as a kind of energy resource, enhancing the energy efficiency of the hydrate-based techniques; On the other hand, it oppositely affects the hydrate formation rate and limits the hydrate-based technology industrial application. For the transition heat utilized as the energy resource, a novel technique was proposed 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.[7,8] The conceptual scheme of the warm brine in situ seafloor and its dual horizontal well systems were detailed in our previous report.[7] As reported, the heat loss along the material transmit pipelines can be reduced significantly and the energy efficiency can be enhanced remarkably. By the method, the hot warm brine can be generated in situ seafloor via hydrate formation process as following steps. Step 1, add the hydrate promoter into the crystallizer located in the seafloor to form the multi-hydrates rapidly under the submarine conditions of high pressure and low temperature, producing the warm brine water on basis of the exothermic effect and the desalination effect in the process of the multi-hydrates formation. Step 2, inject such warm brine water into the NGHs reservoir for producing natural gas from the NGHs reservoir. Step 3, decompose the multi-hydrates floating up to the top of the crystallizer and recycle the hydrate formation promoter after the multihydrate dissociation. Theoretically, this novel method is beneficial for reducing the heat loss and enhancing the energy efficiency in the NGHs exploitation process. For the realization of this exploitation technique its , several obstacles need to be got through, including the determination of the appropriate hydrate promoter for enhancing the amount of transition heat related to hydrate formation, optimization of the operating condition for accelerating the hydrate formation rate, understanding the temperature characteristics in the process of the hydrate formation, and elimination of the hydrate agglomeration for ensuring the hydrate slurry mobility in the crystallizer. For the appropriate hydrate promoter, cyclopentane (CP) has been testified as the excellent one in our previous works.[9] For the optimal operating condition and the temperature characteristics, the testing experiments was carried out in the mini-crystallizer with the inner volume of 123 mL.[10] The temperature characteristic of the hydrate slurry and residual solution has been initial investigated during the hydrate formation. According to the experimental results, the hydrate slurry can be heated up to 21.3 ℃ from approximately 4 ℃. Moreover, the highest temperature of the hydrate slurry could be enhanced by changing the pressure. Therefore, in order to produce a large amount of hot water or warm brine water, it needs to figure out the transition heat related to the hydrates formation and its conduction during the hydrate formation in the large 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 resulting from the transition heat. Such
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transition heat is related to the formation enthalpies in the process of the hydrate formation. In this work, CP and CH4 were adopted as the hydrate formation promoter and help gas, respectively. All experiments were carried out at the temperature of 4 ℃and the pressure of 8.5 MPa, simulating the submarine conditions as reported in reference, [7] and the hydrate slurry temperature in the large-scale equipment were investigated in detail. 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, recorded as T i (i representing the number from 1 to 22). Especially, the highest temperature (Th) is the highest temperature of the hydrate slurry heated up by the transition heat in the process of the hydrate formation, and the maximum temperate difference (ΔTmax) is the maximum value between the highest temperature (Th) and the initial temperature of 4 ℃. 1. Experimental section 2.1 Apparatus The materials were detailed in our previous work.[10] The schematic diagram of the experimental apparatus is shown in Fig. 1. 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 10 L is made of 316 stainless steel, and it can be rotated with around 60 degrees from the vertical position to horizontal trough a fixed trestle. 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 35 MPa in the temperature range of (0 – 50) ℃. 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). Especially, the vacuum insulating layer is also adopted between the insulation layer of aerogel and the outside wall of the crystallizer. As shown in Fig. 1, 22 temperature couples are installed at inner wall of the crystallizer to monitor and measure the temperatures of the hydrate slurry and the residual solution during the hydrate formation. Especially, T15 is adopted to measure the temperature of the crystallizer outside wall. With the solution volume of 5.60 L adopted in this work, T10, T11 and T16 to T20, are located between the gas/liquid CP and liquid CP/water interface, T1 to T9 are immersed into the bulk water, and T12 to T14 are situated in gaseous phase. 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 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 admission line air-free. All above mentioned equipment and materials are placed in the low temperature chamber refrigerated by the cooled-air circulation refrigeration machine (BSTPZ500S). The operating temperature of the chamber, recorded as T e, is in the range of (0-25) ℃, which is adopted to stimulate the seafloor temperature at seawater depth of around 1800 m.[7] 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. 2.2 Procedure During the experiments, the temperature of the low temperature chamber was set to the given value of 4 ℃, and the actual chamber temperature was minored as T e. All equipment and materials (CH4 gas cylinder, CP and water) were placed in the chamber, and precooled to 4 ℃. Prior to the experiment, the deionized water was poured into the crystallizer from the top of the crystallizer, and the washing water was poured out by rotating the crystallizer though the fixed trestle. After the crystallizer was thoroughly washed three times, and vacuumed, the desired volume of CP and water were injected into it. Thirty 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 installed at the bottom of the crystallizer, the gas bubbles with a certain size were generated in the bulk water, and then, 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
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accumulated in the CP/water interface. Accordingly, the temperature near the interfaces increased due to the transition heat related to the hydrate formation enthalpies. The experiment was considered to be completed when the temperatures began to significantly decrease. During the experiments, the time was recorded as t 0 when the liquid solutions were injected into the crystallizer, and the data of pressure and temperature were recorded by the computer. In addition, it was proven that the enthalpies of the hydrate formation without gas injecting is limited.[10]
Fig.1. Schematic of the experimental apparatus.
2. Results and discussion 2.1. Temperature change during the hydrate formation In order to understand the temperature characteristics of the hydrate slurry resulted from the transition heat during the hydrate formation in the large-scale equipment, the experiments were carried out in the special crystallizer with inner volume of 10 L under the conditions of 4 ℃ (recorded as T0) and 8.50 MPa with the CP to water volume ratio of 0.30. The volume of 5.6 L solution including CP and water were conducted into the crystallizer with the gas to solution volume ratio of 0.308. All experiments were performed in the low temperature chamber to stimulate the seafloor temperature at seawater depth of around 1800 m. Total 22 temperature couples were used to measure the temperature changes at different position during the hydrate formation, and they were recorded as T i (i=1, 2...., 22). Moreover, Th expresses the highest temperature of the hydrate slurry resulted from the transition heat, and ∆T max is the temperature difference between T h and T0 in the crystallizer. Especially, Th-i and ∆Tmax-i are the highest temperature and the highest temperature difference for each Ti. Fig. 2 shows the temperature change at different time during the hydrate formation.
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Fig. 2. Temperature change in the process of the hydrate formation. a, 0; b, 50 min; c, 210 min; d, 760 min; e, 1360 min.
According to the temperature changing properties, the hydrate formation is divided into four stages. As shown in Fig. 2, stage 1 (a to b) is from 0 to 50 min, representing the precooling process before the gas injection; stage 2 (b to c) is from 50 min to 210 min, representing the strong hydrate formation process; stage 3 (c to d) is from 210 min to 760 min, representing the weak hydrate formation process; and stage 4 (d to e) is from 760 min to 1360 min, representing the hydrate formation completed. From Fig. 2(a) and (b), it can be found that the temperature of CP and water are less than 6 ℃. Because the materials are precooled in the low temperature chamber, and the chamber works stable. From Fig. 2(c), the obvious temperature change can be observed between the gas/liquid CP interface and liquid CP/water interface, which can be found in detail from Fig. 1. It means that the hydrates firstly form in the liquid CP layer, and the transition heat related to the hydrate formation are moving towards the gas/liquid interface and liquid CP/water interface with different heat transferring rate. From Fig. 2(d), the temperate significantly decrease and the weak temperature difference in the bulk water can be found. It shows that the hydrate formation is limited and the heat is continuously transferring from the hydrate formation interface towards into bulk water. From Fig. 2(e), the temperature in the crystallizer continues to decrease, and no temperature difference is observed at the end of the experiment. It means the hydrate formation is completed and the transition heat could be hold to some extent in the crystallizer. 2.2. Temperature characteristics in the hydrate formation process Table 1 details the different values of Th and ∆Tmax. Fig. 3 shows the temperature change between the gas/liquid CP interface and the liquid CP/water interface, and Fig. 4 shows the temperature change in bulk water From Fig. 3, it can be found that the temperature among T16 to T22 increase sharply. It means that CP/CH4 binary hydrates form with a fast rate when the CH4 gas is injected at around 60 min. The hydrates can continuously form due to the enough disturbance and sufficient contact area among gas bubbles, liquid CP and water with the gas bubbles continuously rising, resulting in the sharp temperature increase in the liquid CP phase. Especially, T18 with the most significant temperature change proves the firstly hydrate formation interface. And the transition heat transfers towards the liquid CP/water interface in the process of the hydrate formation. Same phenomenon can be observed in Fig 2 as well. From Fig.1 and Table 1, the Th-13 is smaller than Th-19, meaning that not only the transition heat are transferring towards the liquid CP/water interface, but also the hydrate formation interface are moving along with the same trend. The movement of the heat interface and the hydrate formation interface are proceeding with the strong hydrate forming. It is consistent with the results as shown in Fig. 2 (c). And the highest Th-18 of 23.47 ℃ and the maximum ∆Tmax-18 of 19.47 ℃ are obtained. As shown in Fig. 3, it can be found the transition heat could be hold to some extent in the crystallizer, and the transition heat are transferring from the liquid/CP interface towards the bulk water during the hydrate formation. As a result, the bulk water can be warmed, and the hot water can be produced by controlling the conditions.
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Table 1. Data of Th and ∆Tmax obtained at different position. Ti
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
Th-i (℃)
7.18
7.80
8.60
9.53
10.77
11.90
12.90
13.25
13.62
15.51
13.84
∆Tmax (℃)
3.18
3.80
4.60
5.53
6.77
7.90
8.90
9.25
9.96
11.51
9.84
Ti
T12
T13
T14
T15
T16
T17
T18
T19
T20
T21
T22
Th-i (℃)
9.84
10.19
10.41
8.80
11.89
14.02
23.47
19.96
18.09
15.63
15.19
∆Tmax (℃)
5.84
6.19
6.41
4.80
7.89
10.02
19.47
15.96
14.09
11.63
15.19
Fig. 3. Temperature change in the liquid CP phase in the process of the hydrate formation.
Fig. 4. Temperature change in the residual water phase in the process of the hydrate formation
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3. Conclusion In this work, the temperature characteristics related to the transition heat were systematically investigated at the different conditions of 8.5 MPa and 4 ℃ by measuring the hydrate slurry temperature. Especially, T h and ∆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. The highest T h-18 of 23.47 ℃ and the maximum ∆Tmax-18 of 19.47 ℃ are obtained. 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. Moreover, the effect of the different conditions, such as operating pressure, solution volume, size of the gas bubbles and volume ratio of CP to water etc., on the temperature characteristics will be carried out in the future. The temperature can be further enhanced by changing the conditions, and such high heat could be effectively collected and used elsewhere. Acknowledgements We are grateful for the support of the Key Program of National Natural Science Foundation of China (51736009), National Key R&D Program of China (2016YFC0304002, 2017YFC0307306), the National Natural Science Fund (51476174), International S&T Cooperation Program of China (2015DFA61790). References [1] Englezos, P., Clathrate Hydrates. Industrial & Engineering Chemistry Research 1993, 32, (7), 1251-1274. [2] Sloan, E. D. K., C. A., Clathrate Hydrates of Natural Gases. 3nd Ed ed.; CRC Press, Taylor & Francis Group: Boca Raton, 2008. [3] Konno, Y.; Masuda, Y.; Hariguchi, Y.; Kurihara, M.; Ouchi, H., Key Factors for Depressurization-Induced Gas Production from Oceanic Methane Hydrates. Energy & Fuels 2010, 24, (3), 1736-1744. [4] Konno, Y.; Oyama, H.; Nagao, J.; Masuda, Y.; Kurihara, M., Numerical Analysis of the Dissociation Experiment of Naturally Occurring Gas Hydrate in Sediment Cores Obtained at the Eastern Nankai Trough, Japan. Energy & Fuels 2010, 24, (12), 6353-6358. [5] Li, G.; Moridis, G. J.; Zhang, K.; Li, X. S., The use of huff and puff method in a single horizontal well in gas production from marine gas hydrate deposits in the Shenhu Area of South China Sea. Journal of Petroleum Science and Engineering 2011, 77, (1), 49-68. [6] Goel, N., In situ methane hydrate dissociation with carbon dioxide sequestration: Current knowledge and issues. Journal of Petroleum Science and Engineering 2006, 51, (3-4), 169-184. [7] 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. [8] 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. [9] Lv QN, Li XS, Chen ZY. Formation of cyclopentane - methane hydrates in brine systems and characteristics of dissolved ions. Applied Energy. 2016;184:482-90. [10] Cai, J.; Hu, Y. F.; Zhang, Y.; Xu, C. G.; Chen, Z. Y.; Lv, Q. N.; Li, X. S., Study on Temperature Characteristics of Hydrate Slurry during Cyclopentane–Methane Hydrate Formation. Energy & Fuels 2018.
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Energy Procedia 158 Energy Procedia 00(2019) (2017)5888–5894 000–000 www.elsevier.com/locate/procedia
10th International Conference on Applied Energy (ICAE2018), 22-25 August 2018, Hong Kong, 10th International Conference on Applied Energy China(ICAE2018), 22-25 August 2018, Hong Kong, China
Study on the temperature characteristics in the process of StudyThe on 15th theInternational temperature characteristics in the Symposium on formation District Heating andprocess Cooling cyclopentane-methane binary hydrate with a set ofoflargecyclopentane-methane binary hydrate formation with a set of largescale equipment scaleofequipment Assessing the feasibility using the heat demand-outdoor Jing Cai,a,b,c,d,e Jin-Ming Zhang,a,b,c,d,e Ya-fei Hu,f Zhao-Yang Chen,a,b,c,d Xiao-Sen Lia,b,c,d,* a,b,c,d,e Jing Cai,a,b,c,d,e Jin-Ming Zhang, Ya-fei Hu,f Zhao-Yang Xiao-Senforecast Lia,b,c,d,* temperature function for a long-term districtChen, heata,b,c,d demand Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou, 510640, China a
b a CAS Key Laboratory of Gas Hydrate, Guangzhou, 510640, China Guangzhou of Energy Conversion, China a,b,c Institute a aChinese Academy of bSciences, Guangzhou, 510640, c c b Guangdong Provincial Key Laboratory New and Renewable Energy Research and Development, CAS Key of Laboratory of Gas Hydrate, Guangzhou, 510640, China Guangzhou, 510640, China d c Center of Gas Hydrate Chinese Academy of Science, Guangzhou, Guangzhou, 610640, China GuangdongGuangzhou Provincial Key Laboratory of New Research, and Renewable Energy Research and Development, 510640, China a e IN+ Center fordGuangzhou Innovation, Center Technology and Policy Research -Chinese Instituto Superior Av. Rovisco 1, 1049-001 University of Chinese Academy of Sciences, Beijing, 100049, China Pais of Gas Hydrate Research, Academy ofTécnico, Science, Guangzhou, 610640, China Lisbon, Portugal b f e Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France Veolia Hisense Kelon Electrical Holdings Company Beijing, Limited,100049, Foshan,China China University of Chinese Academy of Sciences, c Département Systèmesf Hisense Énergétiques Environnement - IMT Atlantique, 4 rue AlfredChina Kastler, 44300 Nantes, France KelonetElectrical Holdings Company Limited, Foshan, c
I. Andrić
*, A. Pina , P. Ferrão , J. Fournier ., B. Lacarrière , O. Le Corre
Abstract Abstract Abstract In this work, the temperature characteristics of hydrate slurry related to transition heat in the cyclopentane (CP)/methane (CH4) In this formation work, the temperature of crystallizer hydrate slurry to transition heat inlayer the cyclopentane (CP)/methane (CH4) hydrate process werecharacteristics investigated. A withrelated a special heat-insulating of aerogel and vacuum insulating District heating are transition commonly addressed thewith literature as the oneresidual of the most effective for decreasing the hydrate formation process investigated. Aand crystallizer a special heat-insulating layer of aerogel andTemperatures vacuum insulating layer was designednetworks to holdwere the heat, the in hydrate slurry and water could be solutions heated. were greenhouse gas process emissions from the building investments which returned through thewere heat layer was designed to hold heat,sector. andunder theThese hydrate slurryrequire and residual beare heated. Temperatures measured in the of the the transition hydrate formation the systems conditions of the 4 high ℃and 8.5water MPa.could The highest temperature of hydrate sales.(TDue to the the changed climate and building renovation demand in theadopted future could measured the process of thetemperature hydrateconditions formation under the 4 policies, ℃and 8.5heat MPa. The highest temperature of decrease, hydrate slurry and maximum difference (∆T between Tof the initial temperature were to evaluate the h)in max)conditions h and prolonging the investment return period. slurry (Th)of anddifferent the maximum temperature (∆Tcharacteristics temperature were adopted to evaluate the influence conditions on the difference temperature theinitial hydrate formation. The experimental results max) between Tduring h and the The mainthat thisconditions paper is toon assess feasibility of interface using the obviously heat demand –hydrate outdoor temperature function for heattowards demand influence ofscope different the the temperature characteristics during the experimental results indicated the of hydrate formation interface and thermal moving fromformation. the initial The gas/CP interface forecast. interface. Thethe district Alvalade, located in Lisbon was asmax a of case study. The district isinterface consisted ofhigh 665 indicated that hydrate formation and thermal moving from thecould initial towards CP/water The of hydrate slurryinterface could be heated up(Portugal), tointerface 23.47 ℃obviously andused the ∆T 19.47 ℃ begas/CP obtained, and such buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district CP/water The hydrate slurry be heated up to 23.47 ℃ and the ∆Tmax of 19.47 ℃ could be obtained, and such high heat couldinterface. be effectively collected and could used elsewhere. renovation were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were heat could bescenarios effectively collected and used elsewhere. compared with results from a dynamic heat demand Copyright © 2018 Elsevier Ltd. All rights reserved. model, previously developed and validated by the authors. ©The 2019 The Authors. Published by Elsevier Ltd. th International results that when only weather change is considered, the marginofof the error10could be acceptable for someon applications Copyright © showed 2018 Elsevier Ltd. Allresponsibility rights reserved. Selection and peer-review under of the scientific committee Conference Applied This iserror an open accessdemand article under the CCthan BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) th International (the in annual was lower 20% for all weather scenarios considered). However, after introducing renovation Selection and peer-review under responsibility of the scientific committee of the 10 Conference on Applied Energy (ICAE2018). Peer-review under responsibility of theupscientific committee of ICAE2018 – Theand 10threnovation International Conference on Applied Energy. scenarios, the error value increased to 59.5% (depending on the weather scenarios combination considered). Energy (ICAE2018). The value of slope coefficient on average the range of 3.8% up to 8% per decade, that corresponds to the Keywords: hydrate slurry; temperatureincreased characteristic; transition within heat; cyclopentane decrease hydrate in the slurry; number of heating hours of 22-139h the heating season (depending on the combination of weather and Keywords: temperature characteristic; transitionduring heat; cyclopentane renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and 1.coupled Introduction the accuracy of heat demand estimations. 1.improve Introduction © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. * Corresponding author. Tel: +86-20-87057037; fax: +86-20-87034664.
address:author. [email protected]. (X.-S. Li)fax: +86-20-87034664. * E-mail Corresponding Tel: +86-20-87057037; Keywords: Heat demand; Forecast; Climate change E-mail address: [email protected]. (X.-S. Li) 1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility the scientific 1876-6102 Copyright © 2018 Elsevier Ltd. All of rights reserved. committee of the 10th International Conference on Applied Energy (ICAE2018). Selection and peer-review under responsibility of the scientific committee of the 10th International Conference on Applied Energy (ICAE2018). 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of ICAE2018 – The 10th International Conference on Applied Energy. 10.1016/j.egypro.2019.01.536
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Hydrates are types of ice-like nonstoichiometric inclusion compounds, which are formed by water molecules (host) and guest molecules, such as light hydrocarbon molecules (guest) and additives molecules, under the conditions of low temperature and/or high pressure. These guest molecules are encaged into the host cavities trough van deer Waals force, forming NGHs with stable structures. The framework of the host cavities are constructed by water molecules trough hydrogen bonds, and it is difficult to keep stable without encaging guest molecules. For the natural gas hydrate (NGHs) as energy resources, the guest molecules are mainly the light hydrocardon, including methane (CH4), ethane (C2H6), and propane (C3H8). For other multi-hydrates formed in the hydrate-based process, the guest molecules usually include hydrate promoters and small size gas molecules, such as carbon dioxide (CO2), hydrogen (H2). Generally, the hydrate structures include three different types, structure I (sI), structure II (sII), and structure H (sH), depending on the pressure, temperature, guest molecules, etc.[1] In nature, most of sI NGHs have been detected in permafrost and deep marine sediments where the NGHs stably exist owing 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) one 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 proven fossil fuels on Earth.[2] Thus, NGHs are regarded as an alternative energy resource for the future. Various NGHs exploitation technologies have been widely investigated. For instance, depressurization,[3,4] thermal simulation,[5] CO2-CH4 replacement [6,7] and chemical inhibitor.[8] Especially, the NGHs testing exploitations have been adopted in the NGHs reservoirs at Mallik2L-38 of Canada (2008), the eastern of Nankai Trough of Japan (2013, 2017) and the Shenhu sea area of China (2017). Hydrate formation is an exothermic process, a large amount of transition heat release during the hydrate formation especially when the hydrates form with an effective and fast formation rate. On the one hand, such transition heat can be utilized as a kind of energy resource, enhancing the energy efficiency of the hydrate-based techniques; On the other hand, it oppositely affects the hydrate formation rate and limits the hydrate-based technology industrial application. For the transition heat utilized as the energy resource, a novel technique was proposed 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.[7,8] The conceptual scheme of the warm brine in situ seafloor and its dual horizontal well systems were detailed in our previous report.[7] As reported, the heat loss along the material transmit pipelines can be reduced significantly and the energy efficiency can be enhanced remarkably. By the method, the hot warm brine can be generated in situ seafloor via hydrate formation process as following steps. Step 1, add the hydrate promoter into the crystallizer located in the seafloor to form the multi-hydrates rapidly under the submarine conditions of high pressure and low temperature, producing the warm brine water on basis of the exothermic effect and the desalination effect in the process of the multi-hydrates formation. Step 2, inject such warm brine water into the NGHs reservoir for producing natural gas from the NGHs reservoir. Step 3, decompose the multi-hydrates floating up to the top of the crystallizer and recycle the hydrate formation promoter after the multihydrate dissociation. Theoretically, this novel method is beneficial for reducing the heat loss and enhancing the energy efficiency in the NGHs exploitation process. For the realization of this exploitation technique its , several obstacles need to be got through, including the determination of the appropriate hydrate promoter for enhancing the amount of transition heat related to hydrate formation, optimization of the operating condition for accelerating the hydrate formation rate, understanding the temperature characteristics in the process of the hydrate formation, and elimination of the hydrate agglomeration for ensuring the hydrate slurry mobility in the crystallizer. For the appropriate hydrate promoter, cyclopentane (CP) has been testified as the excellent one in our previous works.[9] For the optimal operating condition and the temperature characteristics, the testing experiments was carried out in the mini-crystallizer with the inner volume of 123 mL.[10] The temperature characteristic of the hydrate slurry and residual solution has been initial investigated during the hydrate formation. According to the experimental results, the hydrate slurry can be heated up to 21.3 ℃ from approximately 4 ℃. Moreover, the highest temperature of the hydrate slurry could be enhanced by changing the pressure. Therefore, in order to produce a large amount of hot water or warm brine water, it needs to figure out the transition heat related to the hydrates formation and its conduction during the hydrate formation in the large 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 resulting from the transition heat. Such
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transition heat is related to the formation enthalpies in the process of the hydrate formation. In this work, CP and CH4 were adopted as the hydrate formation promoter and help gas, respectively. All experiments were carried out at the temperature of 4 ℃and the pressure of 8.5 MPa, simulating the submarine conditions as reported in reference, [7] and the hydrate slurry temperature in the large-scale equipment were investigated in detail. 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, recorded as T i (i representing the number from 1 to 22). Especially, the highest temperature (Th) is the highest temperature of the hydrate slurry heated up by the transition heat in the process of the hydrate formation, and the maximum temperate difference (ΔTmax) is the maximum value between the highest temperature (Th) and the initial temperature of 4 ℃. 1. Experimental section 2.1 Apparatus The materials were detailed in our previous work.[10] The schematic diagram of the experimental apparatus is shown in Fig. 1. 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 10 L is made of 316 stainless steel, and it can be rotated with around 60 degrees from the vertical position to horizontal trough a fixed trestle. 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 35 MPa in the temperature range of (0 – 50) ℃. 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). Especially, the vacuum insulating layer is also adopted between the insulation layer of aerogel and the outside wall of the crystallizer. As shown in Fig. 1, 22 temperature couples are installed at inner wall of the crystallizer to monitor and measure the temperatures of the hydrate slurry and the residual solution during the hydrate formation. Especially, T15 is adopted to measure the temperature of the crystallizer outside wall. With the solution volume of 5.60 L adopted in this work, T10, T11 and T16 to T20, are located between the gas/liquid CP and liquid CP/water interface, T1 to T9 are immersed into the bulk water, and T12 to T14 are situated in gaseous phase. 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 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 admission line air-free. All above mentioned equipment and materials are placed in the low temperature chamber refrigerated by the cooled-air circulation refrigeration machine (BSTPZ500S). The operating temperature of the chamber, recorded as T e, is in the range of (0-25) ℃, which is adopted to stimulate the seafloor temperature at seawater depth of around 1800 m.[7] 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. 2.2 Procedure During the experiments, the temperature of the low temperature chamber was set to the given value of 4 ℃, and the actual chamber temperature was minored as T e. All equipment and materials (CH4 gas cylinder, CP and water) were placed in the chamber, and precooled to 4 ℃. Prior to the experiment, the deionized water was poured into the crystallizer from the top of the crystallizer, and the washing water was poured out by rotating the crystallizer though the fixed trestle. After the crystallizer was thoroughly washed three times, and vacuumed, the desired volume of CP and water were injected into it. Thirty 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 installed at the bottom of the crystallizer, the gas bubbles with a certain size were generated in the bulk water, and then, 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
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accumulated in the CP/water interface. Accordingly, the temperature near the interfaces increased due to the transition heat related to the hydrate formation enthalpies. The experiment was considered to be completed when the temperatures began to significantly decrease. During the experiments, the time was recorded as t 0 when the liquid solutions were injected into the crystallizer, and the data of pressure and temperature were recorded by the computer. In addition, it was proven that the enthalpies of the hydrate formation without gas injecting is limited.[10]
Fig.1. Schematic of the experimental apparatus.
2. Results and discussion 2.1. Temperature change during the hydrate formation In order to understand the temperature characteristics of the hydrate slurry resulted from the transition heat during the hydrate formation in the large-scale equipment, the experiments were carried out in the special crystallizer with inner volume of 10 L under the conditions of 4 ℃ (recorded as T0) and 8.50 MPa with the CP to water volume ratio of 0.30. The volume of 5.6 L solution including CP and water were conducted into the crystallizer with the gas to solution volume ratio of 0.308. All experiments were performed in the low temperature chamber to stimulate the seafloor temperature at seawater depth of around 1800 m. Total 22 temperature couples were used to measure the temperature changes at different position during the hydrate formation, and they were recorded as T i (i=1, 2...., 22). Moreover, Th expresses the highest temperature of the hydrate slurry resulted from the transition heat, and ∆T max is the temperature difference between T h and T0 in the crystallizer. Especially, Th-i and ∆Tmax-i are the highest temperature and the highest temperature difference for each Ti. Fig. 2 shows the temperature change at different time during the hydrate formation.
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Fig. 2. Temperature change in the process of the hydrate formation. a, 0; b, 50 min; c, 210 min; d, 760 min; e, 1360 min.
According to the temperature changing properties, the hydrate formation is divided into four stages. As shown in Fig. 2, stage 1 (a to b) is from 0 to 50 min, representing the precooling process before the gas injection; stage 2 (b to c) is from 50 min to 210 min, representing the strong hydrate formation process; stage 3 (c to d) is from 210 min to 760 min, representing the weak hydrate formation process; and stage 4 (d to e) is from 760 min to 1360 min, representing the hydrate formation completed. From Fig. 2(a) and (b), it can be found that the temperature of CP and water are less than 6 ℃. Because the materials are precooled in the low temperature chamber, and the chamber works stable. From Fig. 2(c), the obvious temperature change can be observed between the gas/liquid CP interface and liquid CP/water interface, which can be found in detail from Fig. 1. It means that the hydrates firstly form in the liquid CP layer, and the transition heat related to the hydrate formation are moving towards the gas/liquid interface and liquid CP/water interface with different heat transferring rate. From Fig. 2(d), the temperate significantly decrease and the weak temperature difference in the bulk water can be found. It shows that the hydrate formation is limited and the heat is continuously transferring from the hydrate formation interface towards into bulk water. From Fig. 2(e), the temperature in the crystallizer continues to decrease, and no temperature difference is observed at the end of the experiment. It means the hydrate formation is completed and the transition heat could be hold to some extent in the crystallizer. 2.2. Temperature characteristics in the hydrate formation process Table 1 details the different values of Th and ∆Tmax. Fig. 3 shows the temperature change between the gas/liquid CP interface and the liquid CP/water interface, and Fig. 4 shows the temperature change in bulk water From Fig. 3, it can be found that the temperature among T16 to T22 increase sharply. It means that CP/CH4 binary hydrates form with a fast rate when the CH4 gas is injected at around 60 min. The hydrates can continuously form due to the enough disturbance and sufficient contact area among gas bubbles, liquid CP and water with the gas bubbles continuously rising, resulting in the sharp temperature increase in the liquid CP phase. Especially, T18 with the most significant temperature change proves the firstly hydrate formation interface. And the transition heat transfers towards the liquid CP/water interface in the process of the hydrate formation. Same phenomenon can be observed in Fig 2 as well. From Fig.1 and Table 1, the Th-13 is smaller than Th-19, meaning that not only the transition heat are transferring towards the liquid CP/water interface, but also the hydrate formation interface are moving along with the same trend. The movement of the heat interface and the hydrate formation interface are proceeding with the strong hydrate forming. It is consistent with the results as shown in Fig. 2 (c). And the highest Th-18 of 23.47 ℃ and the maximum ∆Tmax-18 of 19.47 ℃ are obtained. As shown in Fig. 3, it can be found the transition heat could be hold to some extent in the crystallizer, and the transition heat are transferring from the liquid/CP interface towards the bulk water during the hydrate formation. As a result, the bulk water can be warmed, and the hot water can be produced by controlling the conditions.
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Table 1. Data of Th and ∆Tmax obtained at different position. Ti
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
Th-i (℃)
7.18
7.80
8.60
9.53
10.77
11.90
12.90
13.25
13.62
15.51
13.84
∆Tmax (℃)
3.18
3.80
4.60
5.53
6.77
7.90
8.90
9.25
9.96
11.51
9.84
Ti
T12
T13
T14
T15
T16
T17
T18
T19
T20
T21
T22
Th-i (℃)
9.84
10.19
10.41
8.80
11.89
14.02
23.47
19.96
18.09
15.63
15.19
∆Tmax (℃)
5.84
6.19
6.41
4.80
7.89
10.02
19.47
15.96
14.09
11.63
15.19
Fig. 3. Temperature change in the liquid CP phase in the process of the hydrate formation.
Fig. 4. Temperature change in the residual water phase in the process of the hydrate formation
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3. Conclusion In this work, the temperature characteristics related to the transition heat were systematically investigated at the different conditions of 8.5 MPa and 4 ℃ by measuring the hydrate slurry temperature. Especially, T h and ∆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. The highest T h-18 of 23.47 ℃ and the maximum ∆Tmax-18 of 19.47 ℃ are obtained. 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. Moreover, the effect of the different conditions, such as operating pressure, solution volume, size of the gas bubbles and volume ratio of CP to water etc., on the temperature characteristics will be carried out in the future. The temperature can be further enhanced by changing the conditions, and such high heat could be effectively collected and used elsewhere. Acknowledgements We are grateful for the support of the Key Program of National Natural Science Foundation of China (51736009), National Key R&D Program of China (2016YFC0304002, 2017YFC0307306), the National Natural Science Fund (51476174), International S&T Cooperation Program of China (2015DFA61790). References [1] Englezos, P., Clathrate Hydrates. Industrial & Engineering Chemistry Research 1993, 32, (7), 1251-1274. [2] Sloan, E. D. K., C. A., Clathrate Hydrates of Natural Gases. 3nd Ed ed.; CRC Press, Taylor & Francis Group: Boca Raton, 2008. [3] Konno, Y.; Masuda, Y.; Hariguchi, Y.; Kurihara, M.; Ouchi, H., Key Factors for Depressurization-Induced Gas Production from Oceanic Methane Hydrates. Energy & Fuels 2010, 24, (3), 1736-1744. [4] Konno, Y.; Oyama, H.; Nagao, J.; Masuda, Y.; Kurihara, M., Numerical Analysis of the Dissociation Experiment of Naturally Occurring Gas Hydrate in Sediment Cores Obtained at the Eastern Nankai Trough, Japan. Energy & Fuels 2010, 24, (12), 6353-6358. [5] Li, G.; Moridis, G. J.; Zhang, K.; Li, X. S., The use of huff and puff method in a single horizontal well in gas production from marine gas hydrate deposits in the Shenhu Area of South China Sea. Journal of Petroleum Science and Engineering 2011, 77, (1), 49-68. [6] Goel, N., In situ methane hydrate dissociation with carbon dioxide sequestration: Current knowledge and issues. Journal of Petroleum Science and Engineering 2006, 51, (3-4), 169-184. [7] 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. [8] 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. [9] Lv QN, Li XS, Chen ZY. Formation of cyclopentane - methane hydrates in brine systems and characteristics of dissolved ions. Applied Energy. 2016;184:482-90. [10] Cai, J.; Hu, Y. F.; Zhang, Y.; Xu, C. G.; Chen, Z. Y.; Lv, Q. N.; Li, X. S., Study on Temperature Characteristics of Hydrate Slurry during Cyclopentane–Methane Hydrate Formation. Energy & Fuels 2018.