Study Of SOFC Distributed Energy Systems Integration Of Utilizing LNG Satellite Station Cold Energy

Most liquefied natural gas（LNG）satellite stations in China currently fail to utilize cold energy in actual operation and the cold energy is taken away by air or water,which may result in the waste of cold energy.It has become a development trend in energy industry to utilize LNG cold energy by adopting a clean and efficient new energy system.However,the current research on the utilization of LNG cold energy using an integrated system of solid oxide fuel cell（SOFC）is still insufficient.In addition,the high-temperature exhaust gas of SOFC has a high waste heat utilization value,and humidified gas turbines such as humid air turbines（HAT）and steam-injected gas turbines（STIG）need a stable heat source.Hence,the paper proposed and studied the SOFC-STIG distributed energy system and SOFC-HAT distributed energy system utilizing LNG cold energy.The main work is as follows:The direct calculation model of tubular SOFC was established and the accuracy of the model was verified through comparison with the experimental data.Compared with other direct calculation models,this model improved the accuracy of the calculation results.Moreover,the main parameters affecting its thermal performance were simulated and analyzed on the basis of tubular SOFC system’s performance evaluation criteria.The influence of the main parameters on the main thermal performance indexes including current density,voltage,output electric power,equipment’s exergy loss,electrical efficiency and exergy efficiency of SOFC was studied.The research demonstrated that the increase of operating pressure and temperature would enhance the performance of SOFC system as well as the main performance indexes like electrical efficiency and exergy efficiency,while the increase of fuel flow would undermine the performance of SOFC system and the main performance indexes.It was found that SOFC system performs best when the fuel utilization ratio reaches 0.85,which laid the foundation for the research of SOFC integrated system using LNG cold energy.From the perspective of energy grade,the mechanism of cascade utilization of fuel chemical energy in tubular SOFC power generation was studied.Firstly,the chemical energy of high-grade fuel gas was converted into that of lower-grade syngas by reforming reaction,and the grade of reforming reaction heat was improved by reducing the grade of fuel chemical energy,so that it could be upgraded to the grade of syngas,and the primary utilization of its chemical energy was completed.Then the chemical energy of syngas was directly converted into battery energy by the electrochemical reaction inside SOFC,and the secondary utilization of its chemical energy was completed.Hence,the grade balance formula of SOFC power generation system and the income formula of chemical energy cascade utilization in power generation process were given,and the income source and cause of effective utilization of chemical energy in power generation process were obtained.With the analysis above,the principle of energy utilization in system integration was proposed,that was,"systems with different function should be integrated reasonably according to energy grades",which provided a theoretical basis for further research of the integrated system.Based on the grade analysis method and the mechanism of integrated cascade utilization of fuel chemical and physical energy,the SOFC-STIG distributed energy system and SOFC-HAT distributed energy system utilizing LNG cold energy were proposed.A mathematical model of key equipment like humidifier was established and the accuracy of the model was verified,shedding light upon the critical parameters’influence on humidifier’s performance.Moreover,the energy and exergy analysis were conducted based on the SOFC-STIG integrated system and SOFC-HAT integrated system thermal performance criteria to find out the main parameters’influence.The research showed that the exergy loss of SOFC accounted for the highest proportion of the total exergy loss of the system,the percentage of SOFC-HAT integrated system was up to 37.08%.Besides,the thermal performance of the system was degraded with the increase of fuel’s flow rate.As steam injection ratio increased,their performance first enhanced and then was degraded.Both of the two systems performed best when the fuel utilization ratio reached 0.85.The two systems used LNG cold energy in stages,which not only reduced the power consumption of air compressor by about 10%,but also effectively recovered CO₂in exhaust gas,and its recovery rate and purity were over98%.In addition,the system also had a certain peak shaving function,which provided a new way for LNG cold energy utilization in China and had theoretical guiding significance.A performance analyzing model aimed at SOFC-STIG distributed energy system and SOFC-HAT distributed energy system utilizing LNG cold energy was established.A comparative study of thermal performance,environmental performance and economic performance focusing on two new integrated systems and a cold energy utilizing system in certain LNG receiving station in Southeastern costal region was conducted.The results showed that the comprehensive performance indexes such as generating power,generating efficiency,thermal efficiency and CO₂ emission of the two new integrated systems were obviously superior to the existing cold energy utilization system.The two new integrated systems in LNG satellite stations had different performance advantages:SOFC-HAT distributed energy integrated system using LNG cold energy performed better in terms of thermal performance and LNG gasification capacity while SOFC-STIG distributed energy integrated system using LNG cold energy performed better in terms of environmental performance and economic performance.Therefore,the research of the SOFC-STIG distributed energy system and SOFC-HAT distributed energy system provides a reasonable calculation model and it is of theoretical guiding significance for the practical application.