LNG Receiving Terminal Cold Energy Utilization Technology Studies

In recent years,under the support and promotion of clean energy policy,the trade of liquefied natural gas(LNG)increased year by year in China.But LNG should be gasificated before supplied to consumers.During the gasification process,LNG can release a lot of cold energy,approximately 240kWh/t.Recycling and using the cold energy of LNG fully,it could not only save energy,but also reduce the environmental impacts of LNG gasification.The gasification characteristics of LNG under different pressure were studied in this paper.The results showed that the effect of pressure on LNG cold energy utilization should be considered fully.Simple model of heat transfer between LNG and propane was established,and the expressions of exergy loss and exergy efficiency during the gasification process were deduced.The analysis showed that the medium and conditions which exchange heat with LNG should be choosed reasonably for reducing exergy loss and improving exergy efficiency.In this paper,some models of LNG cold energy utilization such as power generation,air separation,cold warehouse,CO2 liquefaction,cryogenic comminution and desalination were established with HYSYS software,the results of exergy efficiency and saved power of using unit LNG cold energy in these process were calculated and analyzed.The results showed that both of exergy efficiency and saved power of unit LNG cold energy used in power generation and desalination were lower than other process.And the effect of energy saving in Air separation was the most significant,but exergy efficiency of cryogenic comminution was the highest.Due to LNG cold energy could not be used efficiently by a single process,a new integrated utilization model was introduced in this paper.The research results showed that the saved power by using cold energy of one ton in the integrated system was about 2.7 times as that in a single process.The exergy loss of integrated system was only 14.69% of that using LNG cold energy in a single process and the exergy efficiency of integrated system has increased by 49.85%.In order to overcome the problem that the supply and demand of LNG cold energy are not synchronized in time and space,a propane circulatory system was introduced for recycling and storing LNG cold energy in this paper.This system could transport LNG cold energy to the outside of the receiving terminals for integrated utilization.This system was set in parallel with the by-pass pipes,the original gasification process and the mechanical refrigeration systems of LNG cold energy utilization devices to ensure the security and reliability of supplying gas and cold in the receiving terminals.But the exergy efficiency of this system was lower than the integrated system with using LNG cold energy directly.In Qingdao LNG receiving terminal,LNG has more C2+ light hydrocarbon.For this situation,the existing light hydrocarbon separation process was improved in this paper.The simulation results showed that the recovery rate of C2+ light hydrocarbon was higher and the energy consumption was lower,but the exergy efficiency was also very low for using LNG cold energy.Combined with the industrial environment nearby Qingdao receiving terminal,the lean LNG cold energy was used in cryogenic comminution system integrated with the light hydrocarbon separation process.And the exergy efficiency was greatly improved and has reached 72.65%,higher than that of direct gasification.So this system could avoid to wasting a lot of cold energy.