Research On Hydrogen Production Technology By Power Generation From Cold Energy In LNG Receiving Terminal

A large amount of cold energy will be released during LNG regasification.At present,the total annual receiving capacity of 22 LNG receiving terminals in service is94.42 million tons in China.According to the estimation of full load state,the total amount of cold energy that these stations can provide 22.66 billion k Wh each year.Trying to use cold energy is of great significance for energy conservation,emission reduction and realizing the double carbon goal.In order to calculate the cold energy utilization potential of LNG and seek a reasonable cold energy utilization scheme,this thesis reveals the relationship between the amount of LNG cold energy and cold exergy released under different gasification pressure and temperature through HYSYS software simulation,and obtains the T-s diagram of LNG gasification process.Based on a LNG receiving station in China,this thesis designs the process flow of the LNG cold energy utilization system that combines Rankine cycle power generation with propane as the working fluid and proton exchange membrane(PEM)electrolysis of water for hydrogen production.The performance of the cold energy power generation system is analyzed with the specific work as the evaluation index.The results show that the most influential factor on this index is the LNG temperature after heat exchange with propane,followed by the evaporation pressure and condensation temperature of propane,and the evaporation temperature of propane has the least influence.The exergy loss and exergy efficiency of each equipment in the cold energy power generation system are calculated by using HYSYS software.The result shows that the sum of the exergy losses of the three heat exchangers accounted for 88% of the total exergy loss.Further,the image exergy analysis method is used to analyze the change law of exergy loss from the inlet to the outlet of the heat exchanger,and it is found that the energy grade of the hot and cold fluids at the inlet of the heat exchanger is quite different,and it is also the main part of the exergy loss.These exergy loss distribution rules point out the direction for improving the performance of cold energy power generation system and improving its energy utilization rate.This thesis analyzes the hydrogen production processes of alkaline water electrolysis and PEM water electrolysis from the aspects of applicability and safety,and recommends the PEM water electrolytic process with stronger adaptability to unstable power supply.Considering the fluctuation of natural gas export flow,the change of gas source composition and seawater temperature,this thesis calculates the power generation and hydrogen production of a LNG terminal from 2018 to 2019.The equipment selection and cost estimation are carried out for the cold energy power generation system and PEM water electrolytic hydrogen production system of the LNG receiving terminal.According to the actual operation in 2018,the power generation cost is 0.36 yuan / k Wh and the hydrogen production cost is 29.79 yuan / kg.For some special LNG receiving terminal,the improvement plans for cold energy power generation process and equipment are respectively given.If the receiving terminal transports to natural gas power plants,direct expansion cycle for power generation process can be added.If the intermediate medium heat exchanger is used in the receiving terminal,the investment in fixed assets can be reduced by modifying the heat exchanger.Among them,the process improvement has the most obvious effect on reducing costs.At this time,the cost of power generation and hydrogen production are reduced to 0.19 yuan/k Wh and 18.62 yuan/kg respectively.