沼气超临界压力低温脱碳-液化耦合流程研究

doi:10.11949/0438-1157.20241279

摘要/Abstract

摘要：

大力发展沼气是缓解我国天然气供应紧张的重要途径，但是沼气中CO₂含量高达20%以上，严重影响热值和储运。沼气脱碳后制LNG可显著提高热值和储运便捷性。本研究提出一种沼气超临界压力低温脱碳-液化耦合流程，以解决现有沼气低温脱碳技术中精馏易冻堵、低压凝华能耗高的难题。采用HYSYS软件和遗传算法对所提出的流程进行了建模和优化，结果表明，沼气在8.5 MPa下冷却到-131℃时可将CO₂脱除至0.5%。当CO₂含量在10%~30%时，系统比功耗为0.5295~0.6149 kWh/kg LNG，系统㶲效率为57.5%~62.1%。与基于双塔精馏、化学吸收、低压凝华等的工艺相比，在LNG密度仅降低11.9%时，可实现比功耗降低60%以上。

关键词: 脱碳, 二氧化碳, 甲烷, 液化, 优化

Abstract:

Biogas is an important renewable energy source, produced from organic matter, which has no net carbon emissions from a life cycle perspective. The development of biogas is an important way to alleviate China's natural gas supply shortage. However, the CO₂ content in biogas is generally higher than 20%, which poses negatively impacts on the calorific value, storage and transportation of biogas. Biogas liquefaction after CO₂ removal to produce LNG can significantly improve the calorific value of biogas and facilitate its storage and transportation. This study proposes an integrated process of cryogenic CO₂ removal under supercritical pressure and liquefaction for biogas to address the challenges in existing cryogenic CO₂ removal technology: the risk of freeze blockage in distillation and the high energy consumption associated with low-pressure de-sublimation. The de-sublimation of biogas under critical pressure not only facilitates the effective separation of CO₂ and CH₄, but also reduces the energy consumption of the subsequent methane liquefaction process. The proposed process is modeled in HYSYS and optimized by genetic algorithm coded in MATLAB. The results show that when biogas is cooled to -131℃ at 8.5 MPa, CO₂ can be removed to 0.5% by supercritical de-sublimation. As the CO₂ content increases, the specific power consumption and exergy efficiency of the system increases gradually. When the CO₂ content is between 10% and 30%, the specific power consumption of the system is 0.5295—0.6149 kWh/kg LNG, with the exergy efficiency reaching 57.5%—62.1%. Compared with CO₂ removal processes based on dual-pressure distillation, chemical absorption, low-pressure de-sublimation, the specific power consumption is reduced by over 60% with only 11.9% reduction in LNG density. The considerable reduction in power consumption implies that this study presents a novel approach for high-efficient LNG production from biogas, which holds significant implications for promoting economically viable biogas-to-LNG conversion.

Key words: CO₂ removal, carbon dioxide, methane, liquefaction, optimization

中图分类号:

TQ 025.4

何婷, 张开, 林文胜, 陈利琼, 陈家富. 沼气超临界压力低温脱碳-液化耦合流程研究[J]. 化工学报, 2025, 76(S1): 418-425.

Ting HE, Kai ZHANG, Wensheng LIN, Liqiong CHEN, Jiafu CHEN. Research on integrated process of cryogenic CO₂ removal under supercritical pressure and liquefaction for biogas[J]. CIESC Journal, 2025, 76(S1): 418-425.

图/表 13

图1 CH4-CO2二元系P-T相图[29]

Fig.1 P-T phase diagram of CH4-CO2 binary system[29]

图2 沼气超临界压力低温脱碳-液化耦合系统示意图

Fig.2 Schematic diagram of integrated cryogenic CO2 removal under supercritical pressure and liquefaction process for biogas

图3 沼气超临界压力低温脱碳-液化耦合流程图C—压缩机;HE—换热器;Q—热量;S-L—液固分离器;V—阀;W—功;WC—水冷器

Fig.3 Integrated cryogenic CO2 removal under supercritical pressure and liquefaction process for biogasC—compressor;HE—heat exchanger;Q—heat flow;S-L—solid-liquid separator;V—valve;W—work;WC—water-cooler

表1 优化参数设置

Table 1 Parameter settings for process optimization

参数		数值
假设条件	水冷器出口温度	35℃
	设备压降	0
	最小换热温差	3℃
	压缩机绝热效率	85%
遗传算法参数	种群规模	100×变量数
	最大代数	200
	交叉概率	0.6
	变异	0.05

表2 优化参数的上下限

Table 2 Upper and lower bounds of parameters to be optimized

优化变量	下限	上限
N₂₀₁-C₁ /(kmol/h)	0	600
N₂₀₁-C₂ /(kmol/h)	0	600
N₂₀₁-C₃ /(kmol/h)	0	600
N₂₀₁-C₄ /(kmol/h)	0	600
P₂₀₄/kPa	1800	3500
P₂₀₈/kPa	110	250
T₂₀₆/℃	-50	-10
T₂₀₈/℃	-135	-100

图4 热力系统的㶲分类

Fig.4 Exergy classification of thermodynamic systems

表3 流程关键节点参数

Table 3 Key process parameters

物流		温度/℃	压力/kPa	摩尔流量/(kmol/h)	CO₂ 含量/%	CH₄ 含量/%
原料气侧	101	35	101	1000	30	70
	107	35	8500	1000	30	70
	108	-40	8500	1000	30	70
	109	-131	8500	703.5	0.05	99.95
	110	-130	1000	703.5	0.05	99.95
	301	-131	8500	296.5	100	0
	304	30	8500	296.5	100	0
混合制冷剂	201	32	130	1064
	205	35	2560	1064
	206	-30	2560	1064
	208	-130	2560	1064
	209	-135.9	130	1064
	211	-43.2	130	1064

表4 本研究和其他研究的对比

Table 4 Comparison between this study and other studies

流程	比功耗/(kWh/kg LNG)	比功耗降低幅度/%
本研究	0.6149	—
双塔精馏^[25]	2.07	70.3
化学吸收^[25]	1.54	60.1
低压凝华^[27]	1.574	60.9

表5 不同CO2含量下制冷循环的参数

Table 5 Parameters of the refrigeration cycle under different CO2 contents

CO₂含量/%	混合制冷剂流量/(kmol/h)	制冷剂组分含量
CO₂含量/%	混合制冷剂流量/(kmol/h)	甲烷	乙烷	丙烷	正丁烷
10	1340	0.220149	0.35597	0.10597	0.31791
15	1279	0.248632	0.308835	0.111024	0.331509
20	1210	0.247934	0.293388	0.123967	0.334711
25	1140	0.245614	0.280702	0.131579	0.342105
30	1064	0.23496241	0.28195489	0.13345865	0.34962406

图5 不同CO2含量下的理论液化功和理论分离功

Fig.5 Theoretical liquefaction work and theoretical separation work under different CO2 contents

图6 不同CO2含量下的理论功耗和实际功耗

Fig.6 Theoretical and actual power consumption under different CO2 contents

图7 不同CO2含量下系统的比功耗和㶲效率

Fig.7 Specific power consumption and exergy efficiency of the system under different CO2 contents

图8 不同CO2含量下的CO2捕集率

Fig.8 CO2 capture rates under different CO2 contents

参考文献 31

13	Baccioli A, Antonelli M, Frigo S, et al. Small scale bio-LNG plant: comparison of different biogas upgrading techniques[J]. Applied Energy, 2018, 217: 328-335.
14	Ryan J M, Schaffert F W. CO₂ recovery by the Ryan/Holmes process[J]. Chemical Engineering Progress, 1984, 80(10): 53-56.
15	Berstad D, Anantharaman R, Nekså P. Low-temperature CO₂ capture technologies — applications and potential[J]. International Journal of Refrigeration, 2013, 36(5): 1403-1416.
16	Roussanaly S, Anantharaman R, Lindqvist K. Multi-criteria analyses of two solvent and one low-temperature concepts for acid gas removal from natural gas[J]. Journal of Natural Gas Science and Engineering, 2014, 20: 38-49.
17	Pellegrini L A. Process for the removal of CO2 from acid gas: EP13774252.4[P]. 2015-09-16.
18	Valencia J A, Denton R D. Method and apparatus for separating carbon dioxide and other acid gases from methane by the use of distillation and a controlled freezing zone: US04533372A[P]. 1985-08-06.
19	Thomas E R, Denton R D. Conceptual studies for CO₂/natural gas separation using the controlled freeze zone (CFZ) process[J]. Gas Separation & Purification, 1988, 2(2): 84-89.
20	Northrop P S, Valencia J A. The CFZ^TM process: a cryogenic method for handling high-CO₂ and H₂S gas reserves and facilitating geosequestration of CO₂ and acid gases[J]. Energy Procedia, 2009, 1(1): 171-177.
21	Hart A, Gnanendran N. Cryogenic CO₂ capture in natural gas[J]. Energy Procedia, 2009, 1(1): 697-706.
22	Babar M, Bustam M A, Maulud A S, et al. Enhanced cryogenic packed bed with optimal CO₂ removal from natural gas; a joint computational and experimental approach[J]. Cryogenics, 2020, 105: 103010.
23	Baccanelli M, Langé S, Rocco M V, et al. Low temperature techniques for natural gas purification and LNG production: an energy and exergy analysis[J]. Applied Energy, 2016, 180: 546-559.
24	Naquash A, Qyyum M A, Haider J, et al. Renewable LNG production: biogas upgrading through CO₂ solidification integrated with single-loop mixed refrigerant biomethane liquefaction process[J]. Energy Conversion Management, 2021, 243: 114363.
1	曾金繁. 醇胺和膜分离结合的沼气脱碳工艺流程模拟研究[D]. 上海: 上海交通大学, 2021.
	Zeng J F. Process simulation and parameter optimization of CO₂ removal by alkanolamine and membrane for biogas purification[D]. Shanghai: Shanghai Jiao Tong University, 2021.
2	中国沼气学会. 中国沼气行业“双碳”发展报告[R]. 北京: 中国沼气协会, 2021.
	China Biogas Society. Report on the “double carbon” development of China's biogas industry[R]. Beijing: China Biogas Society, 2021.
3	尹龙天. 基于MEA-乙醇吸收的旋转床用于沼气中CO₂脱除性能与模拟研究[D]. 北京: 北京化工大学, 2021.
	Yin L T. Study on the performance and simulation of CO₂ removal from biogas by a rotating bed based on MEA-ethanol absorption[D]. Beijing: Beijing University of Chemical Technology, 2021.
4	曾金繁, 巨永林. 采用醇胺法的沼气脱碳工艺流程模拟及优化[J]. 现代化工, 2021, 41(8): 224-229.
	Zeng J F, Ju Y L. Process simulation and parameter optimization of alkanolamine route for removing CO₂ from biogas[J]. Modern Chemical Industry, 2021, 41(8): 224-229.
5	周淑霞. 沼气液化制取生物质LNG关键技术研究[D]. 济南: 山东大学, 2012.
	Zhou S X. Research on key technologies on liquefied production of biomass LNG from biogas[D]. Jinan: Shandong University, 2013.
6	He T, Si B, Gundersen T, et al. Integrated ethane recovery and cryogenic carbon capture in a dual mixed refrigerant natural gas liquefaction process [J]. Energy, 2024, 290: 130125.
7	洪宗平, 叶楚梅, 吴洪, 等. 天然气脱碳技术研究进展[J]. 化工学报, 2021, 72(12): 6030-6048.
	Hong Z P, Ye C M, Wu H, et al. Research progress in CO₂ removal technology of natural gas[J]. CIESC Journal, 2021, 72(12): 6030-6048.
8	He T, Liu Z, Son H, et al. Comparative analysis of cryogenic distillation and chemical absorption for carbon capture in integrated natural gas liquefaction processes[J]. Journal of Cleaner Production, 2024, 383: 135264.
9	何婷, 林文胜. 基于余热利用的活化MDEA法脱除CO₂的天然气液化系统[J]. 化工学报, 2021, 72(S1): 453-460.
	He T, Lin W S. Natural gas liquefaction system with activated MDEA method for CO₂ removal based on waste heat utilization[J]. CIESC Journal, 2021, 72(S1): 453-460.
10	Baena-Moreno F M, Saché E, Pastor-Pérez L, et al. Membrane-based technologies for biogas upgrading: a review[J]. Environmental Chemistry Letters, 2020, 18(5): 1649-1658.
11	Yusuf N, Almomani F. Recent advances in biogas purifying technologies: process design and economic considerations[J]. Energy, 2023, 265: 126163.
12	Bi Y J, Ju Y L. Review on cryogenic technologies for CO₂ removal from natural gas[J]. Frontiers in Energy, 2022, 16(5): 793-811.
25	Hashemi S E, Sarker S, Lien K M, et al. Cryogenic vs. absorption biogas upgrading in liquefied biomethane production — an energy efficiency analysis[J]. Fuel, 2019, 245: 294-304.
26	Pellegrini L A, De Guido G, Langé S. Biogas to liquefied biomethane via cryogenic upgrading technologies[J]. Renewable Energy, 2018, 124: 75-83.
27	Spitoni M, Pierantozzi M, Comodi G, et al. Theoretical evaluation and optimization of a cryogenic technology for carbon dioxide separation and methane liquefaction from biogas[J]. Journal of Natural Gas Science and Engineering, 2019, 62: 132-143.
28	Xiong X J, Lin W S, Gu A Z. Integration of CO₂ cryogenic removal with a natural gas pressurized liquefaction process using gas expansion refrigeration[J]. Energy, 2015, 93: 1-9.
29	Babar M, Bustam M A, Ali A, et al. Thermodynamic data for cryogenic carbon dioxide capture from natural gas: a review[J]. Cryogenics, 2019, 102: 85-104.
30	Peng D Y, Robinson D B. A new two-constant equation of state[J]. Industrial & Engineering Chemistry Fundamentals, 1976, 15: 59-64.
31	Smith J M, Ness H, Abbott M M. Introduction to Chemical Engineering Thermodynamics[M]. New York: McGraw-Hill, 1975.

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