Simulation And Analyzed Of The High-temperature Solid Oxide Electrolysis Cell

Tantalum-based molten salt reactors（TSMR）coupled with high-temperature electrolysis systems（HTE）can be used to produce hydrogen by electrolysis and to produce carbon monoxide by electrolysis of carbon dioxide,and can achieve very high hydrogen and carbon monoxide production efficiency,efficient utilization of nuclear energy,and reduction of CO₂ emissions.The high-temperature solid oxide electrolytic cell（SOEC）in the high-temperature electrolysis system is a new type of energy utilization method,which can convert electrical energy and thermal energy into chemical energy,and has the advantages of high efficiency and cleanliness.The main methods for studying SOEC are experimental and simulation.Since the existing SOEC experiments can not observe the gas distribution,current density distribution and temperature distribution inside the SOEC,the gas distribution,current density distribution and temperature distribution are directly related to the stability and durability of the electrolytic cel.However,simulation studies have many advantages that are not available in experiments,such as good economics,short time-consuming,and ability to analyze the internal conditions of the electrolytic cel;and numerical simulation methods have shown important value in monitoring,equipment development,optimization,and effect prediction.Based on the experimental data of hydrogen production from high temperature electrolyzed water vapor,this dissertation uses the UDF of ANSYS FLUENT software to write a three-dimensional CFD model of high temperature solid oxide electrolytic cell（SOEC）,and extends the model to high temperature electrolytic carbon dioxide and CO₂/H₂O co-electrolysis.The effects of oxygen partial pressure and the structure and size of cell on the performance of the electrolytic cel,the problem of carbon deposition for electrolytic carbon dioxide,the effect of the reverse water gas shift reaction on the co-electrolysis and the effects of connection rib width on co-electrolysis performance and carbon deposition stu6died by the SOEC three-dimensional CFD model.The research contents and conclusions are as follows:（1）The effect of the sweep gas with different oxygen partial pressures on the performance of the electrolytic cell was studied.The oxygen partial pressure range studied in the paper was 1.01×10³–1.0×10⁵ Pa.The results show that the reversible open circuit voltage increases with increasing oxygen partial pressure,whereas the polarization voltage caused by the combination of activation polarization,ohmic polarization and concentration polarization decreases with increasing oxygen partial pressure.The lower the oxygen partial pressure at a lower current density,the better the performance of the solid oxide electrolytic cel,and the higher the oxygen partial pressure at higher current densities,the better the performance of the solid oxide electrolytic cel.Therefore,the use of low oxygen partial pressure sweep gas at low current density is beneficial to reduce the power consumption of the electrolysis process.At high current density,the use of oxygen as the sweep gas is beneficial to reduce the electric energy consumption of the electrolyzed water and to obtain oxygen as a vice products to increase economic value.（2）Based on computational fluid dynamics software,a three-dimensional model of solid oxide electrolysis cell was established to study the effect of cell size and structure on the performance of the electrolytic cel.The cell size used in this paper is4×4 cm²,8×8 cm² and 16×16 cm²,the flow channel structure used is co-flow type,counter-flow type and cross-flow type.The results show that under the same boundary conditions,the cross-flow type electrolytic cell has higher electrolysis performance than the counter-flow type and co-flow type electrolytic cel.Counter-flow current electrolytic cel s have lower current density and temperature gradients than the parallel-flow and cross-flow electrolytic cel s.When the working voltage is lower than the thermal neutral voltage,the size of the electrolytic cell has little effect on the electrolysis performance.When the working voltage is higher than the thermal neutral voltage,the electrolytic current density is larger when the electrolytic cell size is larger;however,the uniformity of the temperature and current density distribution in the electrolytic cell also becomes worse as the cell size increases.Through calculation and analysis,it can be seen that for an electrolytic cell with an effective area of 16×16 cm²,when the overall reaction ratio is 70%,the electrolytic current density can reach 8033A/m² under the electrolysis voltage of 1.35 V,and the uniformity of temperature and current density distribution in the electrolytic cell is improved.（3）Through the high-temperature electrolysis carbon dioxide 3D-CFD model,the C-H-O three-phase diagram and the distribution of the carbon element mole fraction in the cathode of the electrolytic cell are used to analyze the positions of carbon in the electrolytic cel,and the effect of the temperature,gas reaction rate,porosity and the gas composition on the carbon deposition.The results show that carbon deposits are likely to occur at cathode-electrolyte interface and the carbon deposition is mainly concentrated at below the connecting rib.When the temperature is 1123K,the electrolytic cell has almost no place for being easy to carbon deposition.The higher the gas reaction rate,the more the area is easy to deposition carbon.High current density,lower operating temperature,high gas conversion rate and smal er electrode porosity tend to promote the carbon deposition problem in electrolytic cell carbon dioxide,so choose the appropriate temperature and gas transfer rate and increase the cell porosity can control the occurrence of carbon deposit problems.（4）Simulation of co-electrolysis reactions in electrolytic cel s of different size interconnects by H₂O/CO₂ co-electrolysis model,and the influence of the size of the connector on the co-electrolysis performance and carbon deposition was analyzed.The results show that the performance of the electrolytic cell is best when the connection rib size is 0.8 mm,but the smaller the connection rib size,the more uniform the current density distribution in the electrolytic cel.The ribs size affects the gas diffusion in the electrode.The larger the connection rib size,the more unfavorable the gas diffusion is,so the more easily the carbon deposition is formed at the cathode-electrolyte interface.Therefore,the use of 0.6-0.8mm ribs for the electrolytic cell can effectively balance the various factors to obtain the best performance.