Process comparison of seawater desalination with LNG cold energy utilization

doi:10.11949/j.issn.0438-1157.20151088

Abstract

Abstract:

The freezing desalination method is not being used widely,since it needs refrigeration system that consumes much electricity power.On the other hand,liquefied natural gas(LNG)will release a lot of cold energy during its vaporization process.Thus,combining the two processes of LNG vaporization and seawater freezing will produce freshwater while gasifying LNG.In this paper,two kinds of seawater freezing desalination methods are compared,which are the secondary refrigerant/seawater direct-contact method and the secondary refrigerant/seawater indirect-contact method.The indirect-contacting method is then chosen for further study because it is simple and easy to be applied.Two processes are presented with different refrigerant conditions.In the non-phase-change process,the secondary refrigerant remains as subcooled liquid in the whole cycle.In the phase-change process,the secondary refrigerant is vaporized when freezing the seawater,and is condensed when gasifying the LNG.Performances of the two systems at different refrigerating temperatures are analyzed.The study shows that the phase-change process has smaller refrigerant mass flow rate and power consumption.The results show that it is practical to achieve seawater desalination by recovery of LNG cold energy.

Key words: desalination, natural gas, vaporization, recovery, cold energy, process

摘要：

冷冻法海水淡化方法的制冷系统耗电量大,因而应用得并不广泛。另一方面,液化天然气(LNG)在其汽化过程中会释放出大量冷能。因此,将LNG蒸发和海水冻结两个过程结合起来可以在汽化LNG的过程中同时制取淡水。本文比较了两种冷冻法海水淡化的方案,即二次冷媒/海水直接接触法和二次冷媒/海水间接接触法。鉴于其简单和便于应用,选择间接接触法开展进一步研究。按照冷媒的不同工作状态提出了两种流程。在无相变流程中,二次冷媒在整个循环中保持在过冷液体状态。而在相变流程中,二次冷媒在冷冻海水时蒸发,并在汽化LNG时冷凝。在不同制冷温度下对两个流程的性能进行了分析。研究表明,相变流程制冷剂流量和功耗均较小。同时,研究结果说明利用LNG冷能进行海水淡化是可行的。

关键词: 淡化, 天然气, 汽化, 回收, 冷能, 流程

CLC Number:

TQ083⁺.4

LIN Wensheng, HUANG Meibin, GU Anzhong. Process comparison of seawater desalination with LNG cold energy utilization[J]. CIESC Journal, 2015, 66(S2): 318-324.

林文胜, 黄美斌, 顾安忠. 利用LNG冷能的海水淡化流程比较[J]. 化工学报, 2015, 66(S2): 318-324.

References 20

[1]	Kim T S,Ro S T.Power augmentation of combined cycle power plants using cold energy of liquefied natural gas[J].Energy,2000,25:841-856.
[2]	Lin Wensheng,Huang Meibin,He Hongming,Gu Anzhong.A transcritical CO2 Rankine cycle with LNG cold energy utilization and liquefaction of CO2 in gas turbine exhaust[J]. Journal of Energy Resources Technology-Transactions of the ASME,2009,131(4):042201.
[3]	Wang Tao,Lin Wensheng,Gu Anzhong.Analysis of working fluid and variable working conditions of organic Rankine cycle utilizing LNG cold energy[J]. CIESC Journal(化工学报),2010,61(S2):107-111.
[4]	Takashi N,Naohiko Y.Air separating method using external cold source[P]:US,5220798.1993-06-22.
[5]	Rakesh A.Liquefied natural gas refrigeration transfer to a cryogenics air separation unit using high nitrogen stream[P]:US,5137558.1992-08-11.
[6]	Gao Ting,Lin Wensheng,Gu Anzhong.Improved processes of light hydrocarbon separation from LNG with its cryogenic energy utilized[J].Energy Conversion and Management,2011,52(6):2401-2404.
[7]	Gao Ting(高婷),Lin Wensheng(林文胜),Gu Anzhong(顾安忠).Light hydrocarbons separation at high pressure from liquefied natural gas with its cryogenic energy utilized[J].CIESC Journal(化工学报),2009,60(S1):73-76.
[8]	Cravalho E G,McGrath J J,Toscano W M.Thermo-dynamic analysis of the regasification of LNG for the desalination of sea water[J].Cryogenics,1977,17(3):135-139.
[9]	Antonelli A.Desalinated water production at LNG-terminals[J].Desalination,1983,45(2):383-390.
[10]	Chen Ping,Chen Xiaodong,Free K W.An experimental study on the spatial uniformity of solute inclusion in ice formed from falling film flows on a sub-cooled surface[J].Journal of Food Engineering,1999,39(1):101-105.
[11]	Chen Ping,Chen Xiaodong,Free K W.Solute inclusion in ice formed from sucrose solutions on a sub-cooled surface-an experimental study[J].Journal of Food Engineering,1998,38(1):1-13.
[12]	Chen Xiaodong,Chen Ping,Free K W.A note on the two models of ice growth velocity in aqueous solutions derived from an irreversible thermodynamics analysis and the conventional heat and mass transfer theory[J].Journal of Food Engineering,1997,37(3):395-402.
[13]	Qin F G F,Chen Xiaodong,Farid M M.Growth kinetics of ice films spreading on a subcooled solid surface[J].Separation and Purification Technology,2004,39(1/2):109-121.
[14]	Song M,Steiff A,Weinspach P-M.Parametric analysis of direct contact evaporation process in a bubble column[J].International Journal of Heat and Mass Transfer,1998,41(12):1749-1758.
[15]	Song M,Steiff A,Weinspach P-M.Direct-contact heat transfer with change of phase:a population balance model[J].Chemical Engineering Science,1999,54(17):3861-3871.
[16]	Song M,Steiff A,Weinspach P-M.The analytical solution for a model of direct contact evaporation in spray columns[J].International Communications in Heat and Mass Transfer,1996,23(2):263-272.
[17]	Song M,Steiff A,Weinspach P-M.A very effective new method to solve the population balance equation with particle-size growth[J].Chemical Engineering Science,1997,52(20):3493-3498.
[18]	Wang Peng,Chung T S.A conceptual demonstration of freeze desalination-membrane distillation(FD-MD)hybrid desalination process utilizing liquefied natural gas(LNG)cold energy[J].Water Research,2012,46(13):4037-4052.
[19]	Xia Guanghui,Sun Qingxuan,Cao Xu,Wang Jiangfeng,Yu Yizhao,Wang Laisheng.Thermodynamic analysis and optimization of a solar-powered transcritical CO2(carbon dioxide)power cycle for reverse osmosis desalination based on the recovery of cryogenic energy of LNG(liquefied natural gas)[J].Energy,2014,66:643-653.
[20]	Huang Meibin(黄美斌),Lin Wensheng(林文胜),Gu Anzhong(顾安忠),Huang Jianmin(黄建民).Refrigerant direct-contact seawater desalination utilizing LNG cold energy[J].Journal of Chemical Industry and Engineering(China)(化工学报),2008,59(S2):204-209.