Design and Optimization of a Full-Generation System for Marine LNG Cold Energy Cascade Utilization

This paper took a 100,000 DWT LNG fuel powered ship as the research object.Based on the idea of"temperature matching,cascade utilization"and combined with the application conditions of the ship,a horizontal three-level nested Rankine cycle full-generation system which combined the high-temperature waste heat of the main engine flue gas with the low-temperature cold energy of LNG was proposed in this paper.Furthermore,based on the analysis and selection of the parameters which had high sensitivity to the system performance,the parameters of the proposed system were optimized by using the genetic algorithm.After optimization,the exergy efficiency of the marine LNG gasification cold energy cascade utilization power generation system can reach 48.06%,and the thermal efficiency can reach 35.56%.In addition,this paper took LNG net power generation as the performance index,and compared it with the typical LNG cold energy utilization power generation system in this field.The results showed that the unit mass flow LNG power generation of the system proposed in this paper was the largest,reaching 457.41 k W.

Construction and Optimization of Liquefied Natural Gas Regasification Cold Energy Comprehensive Utilization System on Floating Storage Regasification Unit

In this paper, the efficient utilization of liquefied natural gas(LNG) vaporization cold energy in offshore liquefied natural gas floating storage regasification unit(FSRU) is studied. On the basis of considering different boil-off gas(BOG) practical treatment processes, a cascade comprehensive utilization scheme of cold energy of LNG based on the longitudinal three-stage organic Rankine cycle power generation and the low-grade cold energy used to frozen seawater desalination was proposed. Through the comparative analysis of the effects of the pure working fluid and eight mixed working fluids on the performance of the new system, the combination scheme of system mixed working fluid with the highest exergy efficiency of the system was determined. Then, the genetic algorithm was used to optimize the parameters of the new system. After optimization, the net output power of the LNG cold energy comprehensive utilization system proposed in this paper was 5186 kW, and the exergy efficiency is 30.6%. Considering the power generation and freshwater revenue, the annual economic benefit of the system operating is 18.71 million CNY.

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.