Thermal Performance Study Of The MR-SOFC Integrated System

The clean,pollution-free and high efficiency of energy utilization is the trend of power generation system and energy industry,and is also one of the research directions of thermodynamics.Based on the principle of cascade utilization of energy,an integrated system of solid oxide fuel cell（SOFC）with methanol reforming as fuel was established in this paper.The low-grade heat（such as solar energy）is used to produce hydrogen from methanol reforming.With the improvement of solar energy grade,the chemical energy of fuel is also increased,and the the chemical energy of reforming products can be directly converted into electric energy in the battery,thus increasing the potential of energy comprehensive utilization.The purpose of this paper is to recover high-temperature waste heat from SOFC by the atmospheric pressure gas turbine（APGC）,gas-steam combined cycle（GT-ST）and the humid air turbine cycle（HAT）.By modeling and simulating calculation,the thermodynamic characteristics of the system scheme are analyzed and studied.The main work accomplished of this thesis is as follows:First,a thermodynamic model is developed for the solid oxide fuel cell system,which uses solar energy to convert methanol to hydrogen as the fuel.The methanol thermal decomposition reaction is driven by solar energy at medium and low temperature,and the solar energy is converted into chemical energy of hydrogen-rich fuel（H₂,CO）,which is used to drive SOFC fuel cells to generate electricity,the utility model realizes the high-efficiency power generation utilization of solar energy and methanol fuel.The effects of fuel flow rate,cell operating pressure and cell operating temperature on the system performance are studied in detail by modeling and simulating the fuel reforming,cell current density and cell voltage,and the variation law of solar energy utilization efficiency is analyzed.It is found that the power of the battery increases with the increase of the operating pressure and temperature,while the power efficiency of the system decreases with the increase of the operating pressure and increases with the increase of the operating temperature.Then,based on the characteristics of low cost,low difficulty and easy application of the SOFC at atmospheric pressure,in order to realize the recovery and utilization of the high-temperature exhaust gas from the SOFC at atmospheric pressure,the APGC is used as the bottom cycle under ambient pressure,the power generation efficiency of the system is improved.By combining fuel cell with traditional power cycle,the chemical,electrochemical,and thermodynamic hybrid system is characterized by clean energy conversion process and high conversion efficiency.The utility model realizes the double benefits of the efficient utilization of solar energy and the recovery of the residual heat of the battery.Under the design condition,the total generating power of the system is increased by 91.96k W and the corresponding generating efficiency is increased by24.85%.Furthermore,based on the better system performance of the SOFC under pressurized operation,the high efficiency GT-ST is adopted to recover the residual heat and unreacted fuel,thus realizing the high efficient cascade utilization of the residual heat of the power,further improving the efficiency and efficient energy use of the system.At the same time,the HAT is used to recover the residual heat from the high temperature exhaust gas of the SOFC,and the power of the gas turbine is increased without increasing the steam turbine.The performance of three high efficiency MR-SOFC（Methanol reforming-SOFC）integrated systems was compared.Compared with the traditional power generation system,the total power generation efficiency of SOFC integrated system has been greatly improved.Under the designed conditions,the total power generation efficiency of integrated system of SOFC-APGC,SOFC-GT-ST and SOFC-HAT are 58.15%,63.44%and 59.74%respectively.Finally,an SOFC experimental system fueled by hydrogen from methanol reforming has been designed and tested.The test results of methanol reforming products in the experiment are in good agreement with the theoretical results of the software simulation.The feasibility of the methanol reforming SOFC equipment in practical production is verified in principle,and the variation law of the system power generation performance with fuel utilization ratio is obtained.For a 15-cell SOFC system,the SOFC efficiency can reach the optimal value of 46.24%when the fuel efficiency reaches 0.802.