Comprehensive Applied Research on LNG Cold Energy

LI Jin-wei

【Abstract】As the use of liquefied natural gas increases，the comprehensive use of liquefied natural gas cold can save a lot of resources.For reasonable and comprehensive use of this cold energy，research situation of LNG cold energy use at home and abroad will be examined.I will explain the current situation and disadvantages of the existing research and propose optimization research on LNG integrated thermal utilization process.

【Key words】LNG；Cold energy；Comprehensive application

中圖分類號： TE09 文獻標識碼： A 文章編號： 2095-2457（2018）24-0193-003

DOI：10.19694/j.cnki.issn2095-2457.2018.24.093

0 Preface

China is the world's largest developing country，the energy crisis in China is particularly prominent，and it is necessary to change the way of development of energy."China's energy and electricity development prospects" is based on the fact that energy efficiency improvement of conventional energy utilization technology gradually slows down，electrification level rises，natural gas consumption rapidly increases，coal consumption decreases，oil consumption Indicating that the amount is relatively stable.Coal consumption fell below 58%，coal consumption rate in coal consumption increased to 55%，natural gas consumption rate increased to about 10%.As new energy development matures， natural gas is undoubtedly the emerging energy with the best，most practical，most promising，efficient and clean advantages.[1]

Low temperature technology is an indispensable and indispensable technology for China 's defense modernization and national economic construction，and usually requires gas such as oxygen，nitrogen，hydrogen，helium，etc.to obtain low temperature by compression expansion and squeezing effect. Currently，low temperature technology is widely used for industrial gas liquefaction and separation，food freezing， superconducting applications，material processing，aerospace technology，energy and medicine.

1 Research status at home and abroad

1.1 Research Status of Comprehensive Application of LNG Cold Energy at Home and Abroad

Liquefied natural gas is a multicomponent mixed gas， its main component is methane，it is colorless，odorless， non-toxic，non-corrosive，the main products after combustion are CO2，H2O，there is little air pollution，It emits a lot of heat.It is recognized as the cleanest energy on the planet.

After withdrawing natural gas from the gas field， treat it by dehydration，desulfurization etc，then liquefy it into a low temperature and high pressure liquid at -162℃，store in a low temperature storage tank at -161.5℃，0.1MPa using a special ship or oil.Tanker transport.Generally，the power consumption and utility consumption per LNG ton are about 850kWh.According to the first law of thermodynamics，it is known that LNG releases a large amount of low temperature cold energy and its value is about 830kJ/kg，that is 230 to 240 kwh.In 2014，the amount of LNG imports in China is 1989.07 million tons， of which about 4.59 billion kWh may be converted into electricity.[2～5]

Currently，LNG thermal utilization is diverse and can be roughly divided into direct use and indirect use.Direct use mainly includes air separation，power generation，light hydrocarbon separation，dry ice manufacture，refrigeration， seawater desalination，etc.Indirect use mainly includes low temperature grinding，frozen foods，and pollutant treatment.

Japan is one of the earliest countries to develop LNG cold heat mainly in air separation，power generation，low temperature crushing，dry ice，refrigerator，and it is used in many countries of the world.In countries such as Australia and France，LNG cold heat is mainly used for air separation and light hydrocarbon separation，and researches on LNG cooling utilization are also being conducted in countries，regions such as the United States，Russia and the European Union.

China has imported many LNG since 2005 and now there are 24 LNG receiving base projects nationwide. Three of them are followed by LNG project，Shenzhen Dapeng Bay LNG，Fujian Putian LNG，Shanghai Xiaoyangshan LNG.China's current LNG imports are rapidly increasing，but China's LNG cold energy use is still in the early stages.Since the late 1990's，China began research on LNG cold energy utilization technology.Many domestic universities and research institutions have made many new advances about the reasonable use of LNG cold.LNG cold utilization later，[7]and a cold new air separation process can be done to improve the system，the program with LNG flow，the concept of the early introduction of nitrogen circulation，for the use of LNG Professor Zhejiang University Professor Power Chang[6]Japanese research group Using cold capacity，eliminating Freon as a hollow cooling cycle，reducing the number of nitrogen compressors operating at low temperature.Tongji University[8]explored the principle and method of using cold heat in the latter half of the 1990s.Shanghai Jiao Tong University[9-11]Professor Anz Anzhong's research team has created a series of achievements that systematically studied the use of LNG cold heat in the field of LNG cold utilization. Shanghai Maritime University[12]conducted basic research on application of LNG cold energy to refrigerator and utilization of LNG cold-heat cascade.Depending on China's first LNG terminal，China South University University professor Hua Ben set up gas research research center，led the research team， cold in low temperature cereal storage，hydrocarbon separation of light，research and other aspects It is integrated to optimize the use of domestic LNG cold heat utilization technology research plays an important role. Xi'an Jiaotong University[13]Professor Li Yanzhong's research group conducted technical research and development of LNG cold energy mainly in automotive technology.[14] Engineering Thermal Science Chinese Academy of Engineering implemented a new air using integrated LNG cold heat utilizing LNG cold class supercritical CO2 Brayton cycle and a new cycle of Rankine cycle power generation，CO2 separation technology system，LNG cold heat Sub process and other research. Northern China Municipal Engineering Design and Research Institute，Thermal Engineering Xi'an Institute，Petrochemical Industry Planning Institute，CNOOC Base Group，Open Air Separation Group Co.，Ltd.Design and laboratory also actively using LNG cold-heat research and technology Development of other large research units involved.[15]

1.2 Optimization based on the research status of LNG cold energy comprehensive application at home and abroad

With the development of refrigeration technology， humans are becoming more and more perfect in pursuit and understanding of low temperature，cryogenic devices are becoming increasingly widespread.Currently，the process medium used for cryogenic processing generally has two types of gaseous media and a liquid medium.The use of endothermic phase change（vaporization）to obtain a low temperature environment is the most common way to obtain ultra low temperature.The method of cryogenically treating liquid nitrogen with refrigerant freezing is broadly divided into（1）liquid nitrogen immersion frozen，（2）vapor latent heat of liquid nitrogen or low temperature nitrogen freezing.Thus， refrigeration can be divided into three types：（a）a system based on radiant heat transfer，（b）a system based on convective heat transfer，（c）a combination of radiant heat transfer and convective heat transfer.system.

According to the method（C），LN 2 can be replaced by LNG，the inner tank is a low temperature treatment tank，the inside of the tank is piped with a serpentine tube type heat exchanger，the liquid nitrogen vaporizes in the serpentine pipe，convection heat Transmission and radiation exchange of cold nitrogen are used.The method of cryogenically treating the sample in a hot way has advantages of good heat exchange effect，uniform temperature distribution and small temperature variation.

Research and practical application of LNG cold energy utilization has progressed，and scholars both in Japan and abroad are engaged in many related studies.Yellow Meibin will be cooled by heat exchanging with intermediate refrigerant LNG via intermediate refrigerant piping Cryogenic heat exchangers are cooled by terminal equipment freezing mounting or refrigeration cooled down to cold.The cold LNG cold source is a coolable way，as well as substantial energy savings and economy，the operating mode of the U.INS set design and flow system is used and verified for cold storage of cold LNG I can.Based on a compression refrigeration process like the conventional electric Liuzong bin ammonia，the result is to increase the LNG refrigeration cycle，the process of cold utilization rate of 87.8%，the process of exergy efficiency of 26.8%. Messineo and colleagues set an intermediate refrigerant transmission system between the receiving station and the cold district and use the carbon dioxide selected as the intermediate refrigerant to effectively reduce transmission energy consumption.Using HYSYS simulation in the energy efficiency cold exergy cooling comparison Xiao Electric ammonia compression refrigeration process using the LNG satellite station，the results of the exergy efficiency showed to do both 12.1% and 26.6% respectively I will.Tang Xianwen and colleagues calculated the exergy efficiency of LNG cold energy for cold storage by the exergy analysis method， and as a result，the maximum exergy efficiency was 30%. LNG cold heat has many uses in cold storage，but dissemination of LNG cold is a low efficiency global fire protection system irrationality，fire is not a detailed analysis of reasons for low efficiency，improved Wanfang data The fire efficiency of the system has not increased in an effective way to do.Furthermore，some studies have performed simple analysis of the exergy efficiency of a single stage refrigeration system，but no clear definition and calculation formulas for the COP and exergy efficiency of the system are given.[16～23]

2 Conclusion

Based on the research on the comprehensive use of LNG cold energy，many scholars from domestic and overseas have done a lot of research and have achieved certain results.

（1）Different physical and chemical properties of different LNGs present mature applications in different application fields.

（2）LNG and other liquefied gas low temperature that provides the theoretical basis for irreversible loss distribution，the cause and size of the energy system， rational use of LNG and other liquefied gas cold heat， and optimizes the application of liquefied gas cold energy Explain the correct exergy analysis of energy.The storage device and its heat exchanger provide a theoretical basis.

（3）Due to the vigorous development of natural gas in the country，LNG cold energy utilization technology is also mature.LNG cold can be roughly divided into direct use and indirect use.For direct use，air separation，power generation，light hydrocarbon separation，dry ice manufacturing，refrigeration， desalination of seawater，etc.are mainly used. Process， indirect use mainly includes low temperature crushing， frozen foods， pollutant treatment.

（4）Simulation study on low temperature storage equipment and heat exchanger utilizing liquefied gas cold heat，and heat loss in heat exchanger of low temperature storage facility accounted for 78.9% of fire damage of whole system.

Summary：LNG cold can be used for the production of cold thermal power generation，air separation，low temperature grinding，seawater desalination，liquid carbon dioxide and refrigerated warehouse.LNG cold can be used at various temperatures，but with LNG cold-heat one-time use technology，cold energy can not be fully utilized and fire loss of the process far from LNG cold heat overall use is large.It is determined that integrated optimization greatly improves the recovery of LNG cooling capacity and that the LNG thermal regeneration industry can select the corresponding low temperature energy interval due to the gradient utilization characteristics of LNG cold heat recovery.Therefore，an effective and reasonable organization for forming industrial eco industrial parks can effectively maintain production stability and maximize profits.

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