Modeling And Performance Analysis Of Solid Oxide Fuel Cell System With Hydrocarbon Fuels

In recent years,China’s economy has developed rapidly,and the demand for energy is also increasing;The energy issue is related to the national economy and people’s livelihood,and people’s research on energy development and utilization technology has never been interrupted.Since ancient times,the mode of energy use has been constantly changing,and fossil fuels have been dominant since modern times.However,fossil energy reserves are limited,and due to violations and excessive exploitation,a large number of safety accidents have occurred.Additionally,due to geological damage,natural disasters also occur frequently.Traditional energy conversion equipment has drawbacks such as low efficiency and high carbon emissions,leading to potential climate change crises such as the greenhouse effect.Therefore,it is urgent to find renewable and clean new alternative energy sources or develop efficient energy conversion technologies to reduce the global carbon emission.Carbon based fuels include many energy sources such as coal,natural gas,coal derived gas,and biomass.They have the characteristics of large reserves,diverse types,and high energy density.In order to solve the problems of high carbon emission and low energy conversion efficiency,it is necessary to study efficient energy conversion devices.Ssolid oxide fuel cell（SOFC）is an electrochemical device,not being limited by Carnot cycle efficiency,it can achieve a power generation efficiency of more than60%,and the efficiency of cogeneration is close to 90%.And the cell also has advantages such as wide fuel adaptability,effective utilization of waste heat,and near zero CO₂ emission,making it a highly potential energy conversion device.The combination of carbon based fuel with SOFC for the design and research of cogeneration system can maximize the clean and efficient use of carbon based fuel.In this thesis,based on the chemical process simulation software Aspen Plus platform,according to the heat and mass transfer balance,and using Fortran language in the software,the electrochemical reaction model occurred inside the cell was established.The design,efficiency analysis and sensitivity analysis of key parameters of the carbon based SOFC cogeneration system using gasified gas,natural gas and biogas as fuel were carried out.Using the above analysis methods,the research results obtained in this project are mainly as follows:（1）A centralized gasification fuel cell cogeneration（IGFC-CHP）system using gasification gas as fuel was designed and analyzed.Under the proposed operating conditions,the net power generation efficiency of SOFC can reach 37.54%,the hot water efficiency is 35.11%,and the overall energy utilization rate of the system can reach 78.58%.The main factor affecting the efficiency of IGFC power generation is the activation polarization loss caused by electrochemical reactions of hydrogen and oxygen ions overcoming their activation energy.By developing new high-efficiency catalysts or reusing anode exhaust gas,the fuel utilization rate of the fuel cell can be significantly improved.After sensitivity analysis,it was found that using appropriate fuel utilization rate and fuel flow rate can effectively reduce the operating cost of the system,and the air excess ratio should be increased as much as possible within the selectable range.（2）The SOFC-CHP system using methane as fuel is designed and analyzed:the calculation results of heat and mass transfer are obtained.After optimization,the ideal system with the power generation efficiency of 51%,the hot water efficiency of 22%,the steam efficiency of 20%,the total energy utilization rate of 93%,and the CO₂emission concentration of 70%is obtained.The system sets boundary conditions in combination with the actual situation,which can provide reference for the design of the SOFC cogeneration system.（3）A SOFC-GT combined system using biogas as fuel was designed and analyzed,with a power generation efficiency of 49.8%,a net power generation efficiency of63.18%,and a comprehensive energy utilization rate of 78.34%.The sensitivity analysis results indicate that the increase in fuel flow rate has the greatest impact on the system output power,but it is negatively correlated with the power output efficiency and has no significant impact on the bottom heat recovery subsystem.Although blindly increasing fuel flow can improve power output,it has a negative impact on efficiency and also increases the cost of system feeding.Therefore,it is not recommended to use the method of increasing fuel flow to increase system output power.Although the increase in S/C ratio is unfavorable for the net output power and energy utilization rate of the system,the overall impact is not significant,so the S/C ratio can be as large as possible within the specified range.The higher the S/C ratio,the lower the possibility of carbon deposition in SOFC and reformer.When the fuel utilization rate is 0.825,the system output power is the highest,and at 0.9,the SOFC power generation efficiency is the highest.The GT power generation efficiency steadily increases,while the ORC steadily decreases.There is an optimal value of 0.9 for the fuel utilization rate,which can maximize the energy utilization efficiency of the system.