Utilizing Liquefied Natural Gas Cold Energy Research Articles

Optimum design and exergy analysis of a novel cryogenic air separation process with LNG (liquefied natural gas) cold energy utilization

A novel cryogenic air separation process with LNG (liquefied natural gas) cold energy utilization that produces liquid nitrogen and oxygen is proposed and analyzed. Air separation process problems such as process configuration complexity, extreme operating conditions and high operating costs are covered. In this process heat from the top vapor stream of the column is recovered and exchanged with heat in the bottom liquid and feed streams. It is noted that column operating pressure can be decreased compared with the high pressure portion of the air separation systems. In fact, the high and low pressure columns are combined here to exchange nitrogen latent heat with oxygen latent heat. This significantly reduces the energy input to the main compressor located before the column. Also, to completely utilize the cold energy of the LNG and to offset some of the consumed power, a power generation cycle is integrated with the process. This cycle utilizes pure oxygen from the air separation unit. The cryogenic air separation process is simulated and the main parameters are analyzed. It is shown that the energy consumption for the proposed air separation process with LNG cold recovery is about 38.5% lower compared for a convectional cryogenic air separation process. The energy and exergy efficiencies increase by 59.4% and 67.1%, respectively.

Analysis for Cascade Recycling of LNG Cold Energy

Considerable cold energy embodied in liquefied natural gas (LNG) can be recycled in LNG regasification, which can not only save energy but also avoid cold pollution within the low-temperature fluid emission. Review on both domestic and overseas is conducted on the recycling of LNG cold energy in different applications. Against the single purpose utilization of LNG cold energy with a large amount of energy loss, the cascade recycling strategy is proposed for highly-efficient utilization of LNG cold energy. Based on the defined cold exergy efficiency, the exergy analysis is performed for some different recycling applications of LNG cold energy. The system exergy rate method is used to compare the superiority of modes in which the LNG is converted into NG under normal temperature. The results show that the exergy efficiency of a LNG cold energy cascade recycling system is higher than that of a single utilization system. Apart from the improved efficiency, the cascade recycling strategy can expand the applicable temperature range of LNG cold energy compared with the single utilization. Finally, the entropy and entransy for evaluating the LNG cold energy transport process are compared and discussed, from which it is indicated that entransy is more appropriate for the heat transfer process with low-temperature or large temperature difference, as is the case for LNG cold energy recycling.

Theoretical approach of freeze seawater desalination on flake ice maker utilizing LNG cold energy

In this work, a novel concept in freeze desalination (FD) was introduced. Nowadays the total liquefied natural gas (LNG) production capacity has reached 290Mt/year. Its enormous cold energy released from re-gasification can be used in the freeze desalination process to minimize the overall energy consumption. A process of FD on flake ice maker utilizing LNG cold energy was designed and simulated by HYSYS software. An ice bucket on flake ice maker was chosen as seawater crystallizer mainly due to its continuous ice making and removing ice without heat source. A dynamic model of the freezing section has been developed and simulated through gPROMS software. The results show that the consumption of 1kg equivalent LNG cold energy can obtain about 2kg of ice melt water. In addition, it is shown that the power consumption of this LNG/FD hybrid process is negligible.

Integration of light hydrocarbons cryogenic separation process in refinery based on LNG cold energy utilization

China depends on naphtha (derived from oil) as the main feedstock for ethylene plants, resulting in margins that are negatively co-related with the price of oil. Clearly, light hydrocarbons provide cost advantages over the conventional naphtha feedstock. Consequently, the recovery of light hydrocarbons from refinery gas has been gathering more and more significance. Nonetheless, the cryogenic separation needs low process temperatures, substantially increasing the refrigeration load requirements and, attendantly, the compression requirements associated with the refrigeration system. In this paper, the cold energy of liquefied natural gas (LNG) is applied to light hydrocarbons cryogenic separation process to replace the compression refrigeration system on the basis of one China refinery. The results show that LNG can provide 14,373kW cold energy for the separation process, resulting in a direct compression power saving of 7973kW and making the utilization rate of LNG cold energy as high as 71.9%.

The Project Design for Cold Energy Recovery of LNG Vehicle Air-Conditioning System

A kind of potential fuel for vehicles is Liquefied Natural Gas (LNG) whose cryogenic energy can be recovered for vehicles air-conditioning system. In this paper, LNG city bus air-conditioning system utilizing LNG cold energy is concerned to be subject investigated. The design requirements of cold energy recovering for LNG city bus air-conditioning system are introduced and the project design is presented.

A conceptual demonstration of freeze desalination–membrane distillation (FD–MD) hybrid desalination process utilizing liquefied natural gas (LNG) cold energy

The severe global water scarcity and record-high fossil oil price have greatly stimulated the research interests on new desalination technologies which can be driven by renewable energy or waste energy. In this study, a hybrid desalination process comprising freeze desalination and membrane distillation (FD–MD) processes was developed and explored in an attempt to utilize the waste cold energy released from re-gasification of liquefied natural gas (LNG). The concept of this technology was demonstrated using indirect-contact freeze desalination (ICFD) and direct-contact membrane distillation (DCMD) configurations. By optimizing the ICFD operation parameters, namely, the usage of nucleate seeds, operation duration and feed concentration, high quality drinkable water with a low salinity ∼0.144 g/L was produced in the ICFD process. At the same time, using the optimized hollow fiber module length and packing density in the DCMD process, ultra pure water with a low salinity of 0.062 g/L was attained at a condition of high energy efficiency (EE). Overall, by combining FD and MD processes and adopting the optimized operation parameters, the hybrid FD–MD system has been successfully demonstrated. A high total water recovery of 71.5% was achieved, and the water quality obtained met the standard for drinkable water. In addition, with results from specific energy calculation, it was proven that the hybrid process is an energy-saving process and utilization of LNG cold energy could greatly reduce the total energy consumption.

A simplified model of direct-contact heat transfer in desalination system utilizing LNG cold energy

With the increasingly extensive utilization of liquefied natural gas (LNG) in China today, sustainable and effective using of LNG cold energy is becoming increasingly important. In this paper, the utilization of LNG cold energy in seawater desalination system is proposed and analyzed. In this system, the cold energy of the LNG is first transferred to a kind of refrigerant, i.e., butane, which is immiscible with water. The cold refrigerant is then directly injected into the seawater. As a result, the refrigerant droplet is continuously heated and vaporized, and in consequence some of the seawater is simultaneously frozen. The formed ice crystal contains much less salt than that in the original seawater. A simplified model of the direct-contact heat transfer in this desalination system is proposed and theoretical analyses are conducted, taking into account both energy balance and population balance. The number density distribution of two-phase bubbles, the heat transfer between the two immiscible fluids, and the temperature variation are then deduced. The influences of initial size of dispersed phase droplets, the initial temperature of continuous phase, and the volumetric heat transfer coefficient are also clarified. The calculated results are in reasonable agreement with the available experimental data of the R114/water system.

Development status of liquefied natural gas industry in China

With the significant economic growth in China, energy related environmental issues become more and more serious. Most of air pollutants are produced by burning coal. In order to achieve a sustainable balance between economic growth and environmental protection, China has been taking measures to expand the role played by natural gas, especially since the beginning of the 21st century. As the liquid form of natural gas, liquefied natural gas (LNG) has also been paid more attention in the country. This paper explores main motives for the fast development of China’s LNG industry. An overview of the industry is also described, covering LNG receiving terminals, plants and transportation. Despite a relatively short development history of LNG industry in China, there are many remarkable successes. City-gas supply by LNG is widely applied in many small to medium cities, and LNG vehicles and cold energy utilization are growing rapidly with governmental supports. At the end, the developmental trends of China’s LNG industry are introduced. All the discussions show that LNG is strategically important in China’s future energy infrastructure.

Performance enhancement of conventional combined cycle power plant by inlet air cooling, inter-cooling and LNG cold energy utilization

This paper has proposed an integrated advanced thermal power system to improve the performance of the conventional combined cycle power plant. Both inlet air cooling and inter-cooling are utilized within the proposed system to limit the decrease of the air mass flow contained in the given volume flow as well as reduce the compression power required. The latent heat of spent steam from a steam turbine and the heat extracted from the air during the compression process are used to heat liquefied natural gas (LNG) and generate electrical energy. The conventional combined cycle and the proposed power system are simulated using the commercial process simulation package IPSEpro. A parametric analysis has been performed for the proposed power system to evaluate the effects of several key factors on the performance. The results show that the net electrical efficiency and the overall work output of the proposed combined cycle can be increased by 2.8% and 76.8 MW above those of the conventional combined cycle while delivering 75.8 kg s−1 of natural gas and saving 0.9 MW of electrical power by removing the need for sea water pumps used hitherto. Compared with the conventional combined cycle, the proposed power system performance has little sensitivity to ambient temperature changes and shows good off-design performance.

A Transcritical CO2 Rankine Cycle With LNG Cold Energy Utilization and Liquefaction of CO2 in Gas Turbine Exhaust

A novel transcritical Rankine cycle is presented in this paper. This cycle adopts CO2 as its working fluid with exhaust from a gas turbine as its heat source and liquefied natural gas (LNG) as its cold sink. With CO2 working transcritically, large temperature difference for the Rankine cycle is realized. Moreover, the CO2 in the gas turbine exhaust is further cooled and liquefied by LNG after transferring heat to the Rankine cycle. In this way, not only is the cold energy utilized but also a large part of the CO2 is recovered from burning of the vaporized LNG. In this paper, the system performance of this transcritical cycle is calculated. The influences of the highest cycle temperature and pressure to system specific work, exergy efficiency, and liquefied CO2 mass flow rate are analyzed. The exergy loss in each of the heat exchangers is also discussed. It turns out that this kind of CO2 cycle is energy-conservative and environment-friendly.

LNG (liquefied natural gas): A necessary part in China's future energy infrastructure

Abstract This paper presents an overview of the LNG industry in China, covering LNG plants, receiving terminals, transportation, and applications. Small and medium scale LNG plants with different liquefaction processes have already been built or are being built. China's first two LNG receiving terminals have been put into operation in Guangdong and Fujian, another one is being built in Shanghai, and more are being planned. China is now able to manufacture LNG road tanks and containers. The construction of the first two LNG carriers has been completed. LNG satellite stations have been built, and LNG vehicles have been manufactured. LNG related regulations and standards are being established. The prospects of LNG in China are also discussed in this paper. Interesting topics such as small-scale liquefiers, LNG cold energy utilization, coal bed methane liquefaction, LNG plant on board (FPSO – floating production, storage, and off-loading), and LNG price are introduced and analyzed. To meet the increasing demand for natural gas, China needs to build about 10 large LNG receiving terminals, and to import LNG at the level of more than 20 bcm (billion cubic metre) per year by 2020.

Thermodynamic analysis of extraction processes for the utilization of LNG cold energy

Thermodynamic analysis of the extraction processes from a constant pressure LNG (liquefied natural gas) vessel was performed in this study. LNG was assumed to be a binary mixture of 90% methane and 10% ethane by mole fraction (83:17 by mass fraction). The changes in the thermodynamic properties and the amount of utilizable cold energy were predicted during the extraction processes. Both vapour and liquid extraction processes were investigated using a computer model. During vapour extraction, the temperature of the LNG in the vessel increases dramatically, and the extracted vapour composition of methane decreases rapidly near the end of the extraction process. Utilizable cold energy has a maximum at a residual mass ratio of about 0.2. It was found that the temperature gradient due to the vapour composition change had a major effect on the behaviour of the cold energy during the vapour extraction process at a constant pressure. During the liquid extraction process, the changes in the thermodynamic properties and utilizable cold energy are negligible. When the pressure of the vessel increases, the total cold energy which can be utilized from LNG decreases.