Calculation And Application Of Phase Equilibrium Of Electrolyte Aqueous Solution Systems

Electrolyte aqueous solutions existed in petrochemical,coal chemical,hydrometallurgy and environmental chemistry fields.For example,acid water stripping,amine liquid absorption and regeneration,brine crystallization and other industrial processes.When the chemical process simulation software was used to simulate the industrial process containing electrolytes,it's necessary to consider the particularity of electrolyte components,where both chemical equilibrium and phase equilibrium occured in solution.Therefore,it's very important to calculate the phase equilibrium of the electrolyte system.Based on the self-developed process simulation software,the electrolyte related physical properties database was expanded,the interaction parameter library of electrolyte activity coefficient model was established,the electrolyte activity coefficient models were optimized and the electrolyte phase equilibrium calculation algorithm was improved,and verified the accuracy and reliability of the model through the actual industrial process.Firstly,both physical parameters and interaction parameters of the electrolyte activity coefficient models were collected.The interaction parameter library required by the Pitzer and ENRTL was established using the SQLite database,and the electrolyte physical properties database was expanded,including ionic properties database,solid property database,reaction equation and equilibrium constant database.Secondly,the electrolyte activity coefficient models were optimized and the interaction parameters database was invoked.Through testing and analysis,the activity coefficients calculated by the optimised Pitzer,ENRTL and the extended model showed a relative deviation of less than 1%from those calculated by current mainstream chemical process simulation software,which verified the accuracy of the electrolyte activity coefficient models.Then,the calculation algorithm of phase equilibrium module of electrolyte aqueous solution system was improved.The phase equilibrium of H₂O-NH₃-CO₂ system and H₂O-MDEA-H₂S-CO₂ system was calculated by constant temperature and constant pressure flash evaporation.The results showed that,except for trace ions,the relative deviation between the flash results of other components and those calculated by the mainstream chemical process simulation software was about 1%,which verified the feasibility of the new improved phase equilibrium algorithm.Finally,the self-developed simulation software was used to simulate the circulating hydrogen desulfurization tower and acid gas desulfurization tower of diesel hydrogenation unit and the circulating hydrogen desulfurization tower of residue hydrogenation unit in a factory,and the simulation results of each tower were compared with the actual results.The results showed that the optimized electrolyte phase equilibrium calculation module can simulate the actual process flow,and the deviation between the calculation results and the actual was within the allowable error range of the industry,which verified the availability of the self-developed electrolyte calculation system.To sum up,it's of great theoretical significance and industrial application value to study the phase equilibrium calculation of electrolyte aqueous solution system and develop a general electrolyte phase equilibrium module,which promotes the development of process simulation software in China.