Research On Calculation Method Of Phase Diagram Of High Temperature Molten Salt Heat Storage Materials

In the backdrop of the global energy crisis,environmental pollution,looking for the sustainable development of alternative energy sources is around the corner,around the world to carry out the solar wind and biomass energy and other renewable energy development and utilization of the solar thermal power generation is one of the important way to solve the problem of the current energy and environment,but the unstable nature of discontinuous restricted its large-scale application.As a result,the heat storage system is very important for the research on the development of solar energy heat utilization.But the heat storage material cost is high,the poor performance has always been difficult to solve the problem.Heat storage material,the author of this paper the key link to carry out the exploration,will adopt a molten chlorides as the research object,by seeking to screen the best performance of chlorine salt heat storage material,decrease the cost of regenerative heat system goals are met.Taking the price and performance of chloride as the screening conditions,NaCl,KCl,MgCl2 and CaCl2 quaternary molten salt systems with wide sources,low cost and good thermal properties were selected for in-depth study.Based on the existing binary phase diagram,the modified quasi-chemical solution model was used to calculate and complete the phase diagram drawing.The low eutectic point component and temperature were predicted according to the calculation results,and the accuracy of the method was verified by comparing with the data in the literature.In the phase diagram optimization calculation of binary chloride molten salt system,the phase diagrams of NaCl-KCl,NaCl-MgCl2,NaCl-CaCl2,KCl-MgCl2,KCl-CaCl2 and MgCl2-CaCl2 were obtained and compared with the experimental data in the literature.For NaCl-KCl binary system,the calculated eutectic temperature is 929.34K,and the eutectic composition is 50.02mol%KCl.For the NaCl-CaCl2 binary system,the calculated eutectic temperature is 776.66K,and the eutectic composition is 52.14mol%CaCl2.For KCl-MgCl2 binary system,the calculated eutectic temperature is 695.85K,and the eutectic composition is 30.12mol%MgCl2.For KCl-CaCl2 binary system,the calculated eutectic temperature is 873.33K,and the eutectic composition is 24.97mol%CaCl2.For the MgCl2-CaCl2 binary system,the calculated eutectic temperature is 890.56K,and the eutectic composition is 47.37mol%CaCl2.For NaCl-MgCl2 binary system,the calculated eutectic temperature is 723.3K,and the eutectic composition is 42.97mol%MgCl2.The error between the above conclusions and the experimental values is less than 3%.The calculation results show that the calculated values of liquidus are in good agreement with the experimental data,and the optimal ratio of molten salt is determined,and a set of reliable and detailed thermodynamic model parameters are obtained,which lays a partial foundation for the construction of chloride phase diagram database.In the calculation of ternary chloride molten salt system phase diagram,the ternary phase diagram of NaCl-MgCl2-CaCl2,NaCl-KCl-MgCl2,CaCl2-KCl-NaCl and KCl-MgCl2-CaCl2 were obtained by optimization calculation,For ternary system of NaCl-MgCl2-CaCl2,the calculated eutectic temperature is 421.45,and the eutectic composition is 50.99mol%NaCl,22.78mol%MgCl2 and 26.23mol%CaCl2.For the ternary system of NaCl-KCl-MgCl2,the calculated eutectic temperature is 387,and the eutectic composition is 21.09mol%NaCl,52.57mol%KCl and 26.34mol%MgCl2.For CaCl2-KCl-NaCl ternary system,the calculated eutectic temperature is 476.88,and the eutectic composition is 50.95mol%CaCl2,8.38mol%KCl and 40.67mol%NaCl.For the ternary system of KCl-MgCl2-CaCl2,the calculated eutectic temperature is 415.72,and the eutectic composition is 69.37mol%KCl,27.74mol%MgCl2 and 2.89mol%CaCl2.Results show that the model based on modified quasi chemical solutions,using the method of asymmetric Toop model,calculate the phase diagram of the liquidus coincide well with the experimental data,further verify the correction of model applied in the liquid phase chemical solutions,according to the binary and ternary subsystem optimization parameters,can accurately predict more groups of the thermodynamic properties of the liquid solution.The chloride has low melting point,boiling point above 800,low component cost and good thermal property,which is expected to be the main high temperature heat storage and heat transfer material in solar thermal power generation system.