Research On Cold Energy Utilization System In The Gasification Process Of LCNG Fueling Stations

Nowadays the world energy structure is in great transition and natural gas has become the most attractive clean energy to the world.Natural gas vehicle industry is booming.Especially in China.LCNG fueling station which uses LNG as raw material for CNG vehicles has a huge development foreground in our country.In the process of the working condition,LNG gasification will produce about 870 kJ/kg cold energy that directly releases into the air.This paper will focus on it and design a set of cold energy recovery and comprehensive utilization in the LCNG fueling stations.First of all,through the literature research,common LNG cold energy recovery and utilization technology are analyzed.According to the features of LCNG fueling stations,this paper puts forward 4 kinds of cold energy recovery processes and finally chooses the single-stage cycle ice storage system from aspects of economy,practicality and the overall efficiency.And50%ethylene glycol aqueous solution has been selected to the cold energy recovery system with the consideration of freezing point and security.Secondly,HYSYS software is used to simulate the design process.According to the simulation parameters and laboratory conditions,a set of cold energy recovery equipment is built which simulates working condition of LCNG fueling station.Through the design and field research,spiral tube heat exchanger,cryogenic piston pump and external melting-typed ice storage tank are selected and produced with help of manufacturers.In order to ensure safety,reducing valve and exhaust pipe and electrical heater are designed to decrease nitrogen pressure and to prevent the ethylene glycol solution frozen blocking respectively.Thirdly,taking advantage of the built experiment apparatus,four sets of experiments simulating the actual working condition of the ice filling,ice melting and ice fill-melting condition are completed.By the analysis of experimental data,spiral tube heat exchanger efficiency is from 75%to 85%.And the main factor affecting the efficiency is the environmental temperature.Surplus area design should be fully considered to ensure the heat exchange effect.Thermal efficiency of ice storage tank varies according to different condition.Ice filling condition is 47%,ice melting is over 95%and ice fill-melting condition is 52%.It indicates that melting efficiency is much higher than ice filling in the ice storage tank,and thermal efficiency increases obviously when disturbance exists.Cold energy recovery efficiency of the overall system varies from 22%to 26%,slightly lower than the HYSYS simulation value 32%.Except for the reason of the heat exchanger and ice storage tank analyzed,additional one is the refrigerant reservoir absorbs a part of cold energy.Finally,on the basis of experimental data,a 20000 Nm~3 daily sale LCNG fueling station is analyzed with static economic evaluation method to evaluate the economy of the whole system.Cold energy recovery efficiency is set at 25%,then new investment cost of cold energy recovery system is?58000,saving cost on the operating for the whole year is?14400,and the investment capital recovery period is calculated to be 4.03 years,which seems to be economic feasible of this system.Combined with its own significance background of comprehensive utilizing resources,cold energy recovery and utilization system at LCNG fueling station is worth promoting.