Rigorous simulation optimization

Select the optimal sequence. Use rigorous simulation for the final assessment... 

Column process design proceeds stepwise. The shortcut step eliminates the least-desirable options and provides a starting point for the rigorous step. The rigorous step fine-tunes the design and completes the column optimization. This chapter addresses the shortcut step. Graphical shortcut techniques were covered in the previous chapter. Rigorous simulation is addressed in detail in the next chapter. 

Developing such as model is a preliminary and necessary stage in achieving real time plant optimization which involves treating data reconciliation and rigorous simulation simultaneously by means of optimization techniques, whose objective is to maximize process profitability (Perunicic et.al.,2007). 

Rigorous Flowsheet Optimization Using Process Simulators and Surrogate Models... 

As reference we consider the direct separation scheme. The design of columns was done in Aspen Plus by means of shortcut methods followed by rigorous simulation. The energetic consumption depends on the reflux ratio. We assume that the optimal R/Rmi is 1.3, and column pressures of 2 and 1 bar with 0.2 bar pressure drop. Table 11.2 presents the results. Note that the initial feed temperature is 298 K, and therefore the reboiler duty of the first column includes feed preheating. 

MINLP was repeated with a more detailed statistical separation model and separation cost based on rigorous simulation. The solution without IS of allyl chloride yielded a profit of 19.109 M /a gained in one PFR. When the solution was analysed in the EAR all IS alternatives was found to be unattractive (Fig 3a). The only possible improvement could be achieved on the final separation. Six final separation alternatives (FS) were analysed in the EAR (Fig. 3b) to suggest new superstructure. The new superstructure comprised one PFR, no IS and the best four final separation alternatives. The optimal MINLP solution yielded a profit of 20.079 M /a and the alternative with the least expensive condensation of propene was selected for the final superstmcture. 

A rigorous simulation and optimization of reactive distillation processes usually is based on nonlinear fimctions for a realistic description of the reaction kinetics and the vapor-liquid-equilibrium. Within GAMS models, this description leads to very complex models that often face convergence problems. By using the new so-called external functions, the situation can be improved by transferring calculation procedures to an external module. 

The optimal eontrol profiles identified by the solution of the non-linear programme were used to simulate the network through rigorous distributed parameter models on SPEEDUP to obtain a detailed deseription of its... 

Simulation Sciences, Inc. Documentation for ROMEO (Rigorous On-line Modeling with Equation-based Optimization. Brea, CA (1999). 

The bottom-up approach, which develops detailed plant simulation and optimization models, optimizes them, and translates the results from the simulations and optimization into practical operating heuristics. This approach often leads to large models with many variables and equations that are difficult to solve quickly using rigorous optimization algorithms. 

---