| Solid oxide fuel cell（SOFC）has attracted wide attention in recent years due to its advantages of high efficiency and environmental protection.Nickel-based anode and high temperature operation make it possible to use hydrocarbons as fuel for direct internal reforming.Electrochemical performance,fuel utilization rate,power generation efficiency and carbon deposition are the critical problems of DIR-SOFC.The solutions mainly include operating conditions,structure optimization and electrode material manufacturing.In this paper,the DIR-SOFC fueled by CH4-H2O is studied by experimental test and numerical simulation.（1）A planar DIR-SOFC experimental equipment was established.The effects of operating temperature,steam-carbon ratio（S/C）,fuel flow rate and intake methods on the electrochemical performance,fuel utilization and power generation efficiency of DIR-SOFC fueled with CH4-H2O were studied.（2）Based on the Maxwell-Stefan-Knudsen model,the diffusion behavior of H2 in porous anodes for electrochemical reaction after methane steam reforming was studied.The limiting current density and the composition of anode outlet gas of DIR-SOFC fueled with CH4-H2O at different operating temperatures were measured experimentally,and the effective diffusion coefficient of H2 in porous anodes was calculated,and the tortuosity of SOFC porous anode was about 2.78.Research shows that the effective diffusion coefficient of fuel gas in porous anode increases with the increase of temperature,and the micro-structure parameters of the anode restrict the diffusion behavior of fuel gas,which affects the electrochemical performance of SOFC.（3）Using COMSOL Multiphysics 5.3,a multi-channel three-dimensional numerical model was established based on the cell material,microscopic parameters by experiments and self-designed geometric structure of the connector.The validity of the model was verified by experiments.The functions of mass,momentum,energy,charge conservation equation and the reaction kinetics of CH4-H2O reforming were coupled in this model,the mass transfer in porous electrodes is modeled by Maxwell-Stefan-Knudsen model,and the effective diffusion coefficient of fuel gas in porous anode was modified by using porosity and tortuosity factor.The temperature distribution,concentration distribution and reaction rate distribution of DIR-SOFC fueled with CH4-H2O were simulated.And the effects of operating temperature,S/C and current density on the reforming reaction and thermodynamic carbon deposition of DIR-SOFC were investigated.The results show that the reaction rate distribution of methane steam reforming（MSR）is consistent with that of CH4 concentration,and the MSR reaction rate at the inlet is the highest and decreases gradually along the length of the cell,the size of gas channel and rib plate affects the mass transfer and reforming reaction,and thermodynamic carbon deposition is most likely to occur at the fuel inlet.Carbon deposition can be inhibited by increasing operating temperature,S/C and current density appropriately.When the current density is 0.6 A/cm2,the operating temperature is higher than 750℃and S/C is greater than2.5,thermodynamic carbon deposition does not occur in the anode. |
PDF Full Text Request