Energy efficiency analysis of natural gas hydrates production method

doi:10.11949/0438-1157.20200360

Abstract

Abstract:

The decomposition of natural gas hydrates is a phase change process, which involves the consumption and conversion of various forms of energy, such as electrical energy, chemical energy, and thermal energy. In order to evaluate the economy capacity of natural gas hydrates exploitation, an exergy model was established to calculate the energy efficiency ratio (EER) of hydrate production method. The CO₂ replacement method is taken as a case study to introduce the calculation equation and flow chart of energy efficiency ratio in any production period. The amount of CO₂ injection, gas production and mole fraction of methane in produced gas are three key parameters in the process of CO₂ replacement. The ratio between the amount of gas production and CO₂ injection is defined as production injection ratio to eliminate the influence of deposit size. This work studied the influence of production injection ratio and the mole fraction of methane in produced gas on EER. The results show that the EER of gas hydrates production by CO₂ replacement is between 0.31 and 6.4 under the set conditions, and it increases with the increase of production injection ratio. In addition, increasing the mole fraction of methane in produced gas can reduce the energy consumption for gas separation and increase EER. Therefore, there are two effective ways to increase EER of CO₂ replacement through controlling the amount of gas production and the mole fraction of methane in produced gas. The EER model is established to provide guidance for the optimization of gas hydrate mining process.

Key words: hydrate, production, energy efficiency, exergy, model, CO₂ replacement

摘要：

天然气水合物分解是一个相变过程，开采时涉及各种形式能量的消耗和转化，如电能、化学能、热能等。为了科学地评价天然气水合物开采技术的经济性，建立了以有效能（）为核心的能源效率计算方程，并以CO₂置换法开采天然气水合物为例，介绍任意生产周期内能源效率的计算方法和流程框图。在CO₂置换开采天然气水合物的工艺过程中，注气量、产气量和产气中甲烷含量是三个关键参数，将产气量与注气量之比定义为采注比，分析采注比及产气中甲烷含量对能源效率的影响。结果表明：在设定条件下CO₂置换开采天然气水合物的整体能源效率介于0.31～6.4之间；增大采注比，有利于提高能源效率；产气中甲烷的摩尔分率越高，气体分离的能耗越低，能源效率也可显著提高。因此，调控产气量和产气中甲烷摩尔分率是提高CO₂置换法能源效率的主要途径。通过所建立的能效计算方程为天然气水合物开采工艺的优化提供指导。

关键词: 水合物, 生产, 能源效率, 模型, CO₂置换

CLC Number:

TE 53

WANG Xiaohui,XU Qiang,ZHENG Huaxing,SUN Changyu,CHEN Guangjin. Energy efficiency analysis of natural gas hydrates production method[J]. CIESC Journal, 2020, 71(12): 5754-5762.

王晓辉,许强,郑华星,孙长宇,陈光进. 天然气水合物置换开采的能源效率研究[J]. 化工学报, 2020, 71(12): 5754-5762.

Figures/Tables 10

Table 1 The standard compositions of air

组分	组成/%
N₂	75.60
O₂	20.34
H₂O	3.12
CO₂	0.03
Ar	0.91
Ne	0.0018
He	0.00052

Fig.1 The schematic diagram of natural gas hydrates exploitation by CO2 replacement (revised from Teng et al.[27])

Fig.2 Relationship between shipping cost of CO2 and distance

Fig.3 The relationship between the energy consumed for gas separation and CH4 mole fraction

Fig.4 The flow chart of energy efficiency ratio for the production of natural gas hydrates by CO2 replacement

Table 2 The enthalpy and entropy of CO2 under different conditions

条件	焓，H/(kJ/mol)	熵, S/(J/(mol·K))
基态(0℃, 0.1 MPa)	8.8	44
运输条件(-20℃, 2 MPa)	6.797	36.653
注入条件(20℃, 15 MPa)	10.406	47.64
回注条件(20℃, 0.1 MPa)	22.076	119.93

Fig.5 The relationship between energy efficiency ratio and production injection ratio for the production of natural gas hydrates by CO2 replacement

Fig.6 The relationship between energy consumption and production injection ratio for the production of natural gas hydrates by CO2 replacement

Fig.7 The relationship between energy efficiency ratio and CH4 mole fraction in produced gas for the production of natural gas hydrates by CO2 replacement

Fig.8 The relationship between energy consumption and CH4 mole fraction in produced gas for the production of natural gas hydrates by CO2 replacement

References 31

1	陈光进, 孙长宇, 马庆兰. 气体水合物科学与技术[M]. 北京: 化学工业出版社, 2008.
	Chen G J, Sun C Y, Ma Q L. Gas Hydrate Science and Technology [M]. Beijing: Chemical Industry Press, 2008.
2	Chong Z R, Yang S H B, Babu P, et al. Review of natural gas hydrates as an energy resource: prospects and challenges [J]. Applied Energy, 2016, 162: 1633-1652.
3	Boswell R, Collett T S. Current perspectives on gas hydrate resources[J]. Energy & Environmental Science, 2010, 4(4): 1206-1215.
4	周守为, 陈伟, 李清平, 等. 深水浅层非成岩天然气水合物固态流化试采技术研究及进展[J].中国海上油气, 2017, 29(4): 1-8.
	Zhou S W, Chen W, Li Q P, et al. Research on the solid fluidization well testing and production for shallow non-diagenetic natural gas hydrate in deep water area[J]. China Offshore Oil Gas, 2017, 29(4): 1-8.
5	赵金洲, 李海涛, 张烈辉, 等. 海洋天然气水合物固态流化开采大型物理模拟实验[J]. 天然气工业, 2018, 38(10): 76-83.
	Zhao J Z, Li H T, Zhang L H, et al. Large-scale physical simulation experiment of solid fluidization exploitation of marine gas hydrate[J]. Natural Gas Industry, 2018, 38(10): 76-83.
6	Sun J, Ning F, Liu T, et al. Gas production from a silty hydrate reservoir in the South China Sea using hydraulic fracturing: a numerical simulation[J]. Energy Science and Engineering, 2019, 7: 1106-1122.
7	Wang B, Dong H S, Fan Z, et al. Numerical analysis of microwave stimulation for enhancing energy recovery from depressurized methane hydrate sediments[J]. Applied Energy, 2020, 262: 114559.
8	Sun Y F, Wang Y F, Zhong J R, et al. Gas hydrate exploitation using CO2/H2 mixture gas by semi-continuous injection-production mode[J]. Applied Energy, 2019, 240: 215-225.
9	Yang X, Sun C Y, Su K H, et al. A three-dimensional study on the formation and dissociation of methane hydrate in porous sediment by depressurization[J]. Energy Conversion & Management, 2012, 56(2): 1-7.
10	李佳, 梁贞菊, 王照亮, 等. 不同分子模型对甲烷水合物分解微观特性表征[J]. 化工学报, 2020, 71(3): 955-964.
	Li J, Liang Z J, Wang Z L, et al. Characterization of microscopic nature of methane hydrate decomposition by different molecular models[J]. CIESC Journal, 2020, 71(3): 955-964.
11	李淑霞, 李杰, 靳玉蓉. 不同饱和度的天然气水合物降压分解实验[J]. 化工学报, 2014, 65(4): 1411-1415.
	Li S X, Li J, Jin Y R. Depressurizing dissociation of natural gas hydrate with different saturation[J]. CIESC Journal, 2014, 65(4): 1411-1415.
12	Sun X, Luo T T, Wang L, et al. Numerical simulation of gas recovery from a low-permeability hydrate reservoir by depressurization[J]. Applied Energy, 2019, 250: 7-18.
13	周雪冰, 刘婵娟, 罗金琼, 等. 甲烷水合物分解过程的微尺度测量[J]. 化工学报, 2019, 70(3): 1042-1047.
	Zhou X B, Liu C J, Luo J Q, et al. Microscopic measurements on methane hydrate dissociation[J]. CIESC Journal, 2019, 70(3): 1042-1047.
14	Grover T, Holditch S A, Moridis G. Analysis of reservoir performance of messoyakha gas hydrate field[C]//Proceedings of the International Offshore and Polar Engineering Conference. 2008.
15	Falser S, Uchida S, Palmer A C, et al. Increased gas production from hydrates by combining depressurization with heating of the wellbore[J]. Energy & Fuels, 2012, 26(10): 6259-6267.
16	阮徐可, 李小森, 徐纯刚, 等. 天然气水合物降压联合井壁加热开采的数值模拟[J]. 化工学报, 2015, 66(4): 1544-1550.
	Ruan X K, Li X S, Xu C G, et al. Numerical simulation of gas production from hydrate by depressurization combined with well-wall heating[J]. CIESC Journal, 2015, 66(4): 1544-1550.
17	Li S X, Zheng R Y, Xu X H, et al. Energy efficiency analysis of hydrate dissociation by thermal stimulation[J]. Journal of Natural Gas Science & Engineering, 2016, 30: 148-155.
18	Yuan Q, Sun C Y, Wang X H, et al. Experimental study of gas production from hydrate dissociation with continuous injection mode using a three-dimensional quiescent reactor[J]. Fuel, 2013, 106(4): 417-424.
19	Feng J C, Wang Y, Li X S, et al. Production performance of gas hydrate accumulation at the GMGS2-Site 16 of the Pearl River Mouth Basin in the South China Sea[J]. Journal of Natural Gas Science & Engineering, 2015, 27: 306-320.
20	Feng J C, Wang Y, Li X S, et al. Investigation into optimization condition of thermal stimulation for hydrate dissociation in the sandy reservoir[J]. Applied Energy, 2015, 154: 995-1003.
21	Feng J C, Wang Y, Li X S. Energy and entropy analyses of hydrate dissociation in different scales of hydrate simulator[J]. Energy, 2016, 102: 176-186.
22	Li S, Zheng R, Xu X, et al. Energy efficiency analysis of hydrate dissociation by thermal stimulation[J]. Journal of Natural Gas Science and Engineering, 2016, 30: 148-155.
23	Sun Y F, Zhong J R, Li W Z, et al. Methane recovery from hydrate-bearing sediments by the combination of ethylene glycol injection and depressurization[J]. Energy & Fuels, 2018, 32(7): 7585-7594.
24	Zhao J F, Xu K, Song Y C, et al. A review on replacement of CH4 in natural gas hydrates by use of CO2[J]. Energies, 2012, 5(2): 399-419.
25	Wang M, Wang X, Deng C, et al. Process modeling and energy efficiency analysis of natural gas hydrate production by CH4-CO2/H2 replacement coupling steam methane reforming[J]. Computer Aided Chemical Engineering, 2019, 47: 131-136.
26	王晓辉. 注气开采天然气水合物实验模拟与能效分析[D]. 北京: 中国石油大学, 2017.
	Wang X H. Experimental simulation and energy efficiency analysis of gas hydrates production by gas injection method[D]. Beijing: China University of Petroleum (Beijing), 2017.
27	Teng Y F, Zhang D X. Long-term viability of carbon sequestration in deep-sea sediments[J]. Science Advances, 2018, 4: eaao6588.
28	刘玉亮. LNG公路槽车运输经济性研究评价[J]. 时代金融, 2013, 27: 293.
	Liu Y L. Study on the economy of LNG transportation by tank car[J]. Times Finance, 2013, 27: 293.
29	Mallon W, Buit L, Wingerden J V, et al. Costs of CO2 transportation infrastructures [J]. Energy Procedia, 2013, 37: 2969-2980.
30	Yuan Q, Sun C Y, Yang X, et al. Recovery of methane from hydrate reservoir with gaseous carbon dioxide using a three-dimensional middle-size reactor[J]. Energy, 2012, 40(1): 47-58.
31	Yuan Q, Sun C Y, Liu B, et al. Methane recovery from natural gas hydrate in porous sediment using pressurized liquid CO2[J]. Energy Conversion and Management, 2013, 67: 257-264.

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