Research On Power System Of Diesel Reforming Solid Oxide Fuel Cell

At present,in China’s islands,offshore platforms,large ships and other special areas or facilities,most of the diesel generating units are still used for power generation,but diesel generating units have low efficiency,high noise and high emission problems.Due to the existence of complete diesel storage equipment in these special areas or industries,diesel has become the preferred fuel for reasons such as renovation costs,and the innovation of diesel energy systems in islands and other places has become one of the important trends in future development.As an emerging power generation technology,SOFC has higher power efficiency than traditional diesel units.However,SOFC in the traditional diesel reforming mode is still plagued by carbon deposition and CO₂ emissions,and the traditional CO₂ separation technology consumes high energy.CLHG can produce high-purity H₂ and avoid SOFC carbon deposition.In addition,its inherent CO₂separation function can achieve zero-energy-consuming separation of CO₂.In addition SOFC high quality waste heat has high utilization value.Based on this,SOFC-GT-ORC and SOFC-STIG new energy supply systems using CLHG to treat diesel are proposed.The main work is presented as follows:The mathematical model of diesel reforming and SOFC are established,and the accuracy of the model is verified by experimental data,which lays a foundation for the subsequent system integration.Afterwards,the differences in the thermal performance of SOFC under diesel autothermal reforming,steam reforming and CLHG modes were studied.The study showed that diesel steam reforming has the highest synthesis gas yield.However,due to its endothermic reaction,diesel autothermal reforming SOFC exhibits the best performance.However,after considering CO₂ separation,SOFC using CLHG to treat diesel has more obvious advantages in terms of power output and avoiding carbon deposition.Based on the performance evaluation standard of diesel-fuel CLHG-SOFC,the in-fluence of main parameters on the thermodynamic study performance of CLHG and SOFC is studied and obtained,which provides a basis for parameter setting in the subsequent system integration process.Then,on the basis of study on the thermodynamic performance of CLHG diesel treated SOFC monomer,the chemical energy cascade utilization theory and energy grade viewpoint,the chemical energy utilization mechanism and revenue source of the fuel treatment and power generation process in the CLHG-SOFC system were revealed:First,the high chemical energy grade of diesel is reduced to the lower chemical energy grade of hydrogen through CLHG,realizing the first utilization of fuel chemical energy;then in the SOFC system,the chemical energy grade of hydrogen is reduced to the electrical energy grade,realizing the second utilization of fuel chemical energy.Compared with direct fuel combustion,CLHG and SOFC use two chemical energy utilization processes to reduce the diesel chemical energy grade that should be directly reduced to the thermal energy grade to the hydrogen chemical energy grade and the electrical energy grade in turn,which reduces the irreversible loss in the process of chemical energy utilization and realizes the effective cascade utilization of chemical energy.On the basis of analysis approach of energy grade and the principle of cascade utilization of chemical energy and physical energy,new energy supply systems of SOFC-GT-ORC and SOFC-STIG for CLHG diesel treatment were proposed and studied.The selection of organic working medium,the method of system scale enlargement and the maximum pressure are studied.The influence of the main parameters on the performance of the integrated system is studied.In addition,exergy analysis,energy grade analysis and exergoeconomic analysis were combined to comprehensively evaluate the system.The results show that isopentane is the most suitable working medium for the final exhaust temperature and heat of the integrated system.The results show that isopentane is the most suitable working fluid for the final exhaust gas temperature and heat of the integrated system;simply increasing the fuel flow to increase the power output and expanding the SOFC effective surface area to increase the SOFC power capacity are both unfavorable to the scale expansion and performance enhancement of the hybrid system.The capacity enlargement process of the integrated system is relatively stable when they are expanded at the same time;The maximum pressure of the CLHG diesel processing SOFC-STIG integrated system is 13 bar;when the steam injection ratio is 0.054,the thermodynamic study performed best;both systems have the best performance when the fuel utilization rate is 0.9;both systems avoid SOFC carbon deposition and achieve zero-energy-consumption separation of CO₂ with a separation purity of 97.3%.Besides,it was found that the energy grade difference at the cold end of heat exchanger such as air preheater in the integrated system is large,indicating that the exergy loss was only reflected in the numerical value.And the larger exergoeconomic factor also indicates that the smaller exergy loss is very large relative to the cost.The combination of these three methods can comprehensively reveal the causes of the irreversible loss in the chemical energy utilization process and the relativity of its exergy loss values.Also,the limitation of the traditional exergy balance method that cannot deeply analyze the essence of irreversible loss can be overcome.Moreover,the theoretical basis for the subsequent research on the integration and optimization of SOFC systems using CLHG to treat diesel is provided.The performance of CLHG diesel processing SOFC-GT-ORC and SOFC-STIG integrated systems are compared,and the typical systems are selected for economic analysis.This study indicates that the diesel-fueled CLHG-SOFC-STIG system has more obvious advantages in terms of thermal efficiency,cost,electricity price and complexity.At the same time,the dynamic investment payback period of the integrated system is 5.99years,and the reduction rate of the investment recovery period is significantly higher than that of SOFC cost reduction,which proves the feasibility of the new integrated system in future engineering applications.In summary,this dissertation proposes and studies the SOFC-STIG and SOFC-GT-ORC integrated systems for CLHG diesel treatment,and conducts in-depth research on the chemical energy cascade utilization mechanism,performance characteristics and optimization methods of the integrated system.providing a reasonable design model and theoretical support for subsequent system integration and engineering applications.