Stream-and-Unit Based Thermodynamic Modeling And Calculation Method

Thermodynamic property calculation is the foundation of chemical process simulation and optimization, which exerts an important influence on the convergence properties and results of the simulation. Chemical mechanism models usually involve physical property data in streams or operating units, such as phase equilibrium constant, density, enthalpy, entropy. Before simulating calculation, accurate thermodynamic property calculation methods should be confirmed. Due to the complexity of the actual physical system, properties calculation may cause difficulties: ① when modeling with equation-oriented (EO) approach, difficulties such as coping with if-else statements or sequential iterations causing by the chosen thermodynamic property models itself may break the effect of EO approach; ② solvers can’t obtain the gradient at iteration points from surrogate model; ③ numbers of thermodynamic property models must be set up in large-scale models, which costs much in modeling. To solve these problems, the main research contents and contributions of the paper are shown as follows:1. Thermodynamic property surrogate model method is proposed based on Kriging surrogate model and LHS sampling method. The characteristic between input and output variables in property models is considered when choosing the accurate regression model and parameters. High accuracy surrogate models can be made aim at different property systems.2. Gradient model is proposed to make thermodynamic property surrogate model have better convergence properties. The gradient information can be sent to modeling platform solver by rewriting the analytical derivatives of regression equations, which maintains the good convergence properties of the equation-oriented models.3. Surrogate modeling method base on stream and unit is proposed, which can deal with different chemical process full of streams and operating units. Thermodynamic property surrogate model can be quickly built on the basis of the operating condition and component with high reusability and independence and low costs.4. A set of automated programs and external equation model are developed for the high efficiency in property surrogate modeling. Customers can generate the surrogate models and obtain the related parameters files by operating the program according to their demands. Writing the external equation statements with related parameters files can easily realize the surrogate models.5. Surrogate property models are used in air separation unit and ethylene slurry polymerization simulations, replacing the original property calculation methods, overcoming the difficulties mentioned above.