Aspen Custom Modeler

Aspen Technology, Inc. Aspen Plus, Aspen Custom Modeler, Dynaplus, Split, Advent, Adsim. Cambridge, MA (1998). 

Aspen Engineering Suite (e.g. Aspen Custom Modeler ) (Aspen Technology, Inc., USA) http / /www.aspentech.com... 

Batchfrac batch distillation Ratefrac distillation and absorber column distillation Aspen Plus Optimizer equation oriented optimization Aspen Custom Modeler new model builder Aspen OnLine online connection with knowledge capture... 

Aspen Custom Modeller modelling environment for user add-on units and programming in dynamic simulation. 

ASPEN Custom Modeler [Weierstrafi 1999] Prosys Technology Ltd. 

Nowadays, several process simulators such as Aspen Plus and Aspen HYSYS are commercially available for simulating complete chemical processes. Common process units and a property database for numerous chemicals are available in such simulators. However, models for less common and/or new process units (for example, membrane separation) are not readily available in the simulators, but they may be available in the literature or can be developed from first principles. Mathematical model for a new process unit can be implemented in Aspen Custom Modeler (ACM), and then it can be exported to (included in) Aspen Plus or Aspen HYSYS for simulating processes having a new process unit besides common process units such as heat exchangers, compressors, reactors and columns. Process simulators for simulation and ACM for implementing models of new process units are... 

The membrane module used for the simulation of the HMD process in Aspen HYSYS is developed using Aspen Custom Modeler (ACM) v8.4, and then compiled using Microsoft Visual Studio 2010. 

The steady-state rate-based model used in this case study was similar to the model from Section 10.4.2, with the pseudohomogeneous mode for the reaction kinetics and the Maxwell-Stefan diffusion description. The model was implemented into ASPEN Custom Modeler together with another, simpler rate-based model, with effective diffusivities. The latter allows starting values for the Maxwell-Stefan-based model to be generated, thus enhancing convergence. 

Effective diffusivities were used for the calculation of the mass-transfer coefficients. In contrast to the binary Maxwell-Stefan diffusivities, the effective diffusivities were calculated via available procedures in ASPEN Custom Modeler , whereas the Wilke-Chang model was used for the liquid phase and Chapman-Enskog-Wilke-Lee model for the vapor phase [94]. In the full model, computationally intensive matrix operations for the Maxwell-Stefan equations are necessary. The model has been further extended to consider the presence of liquid-liquid separation [110, 111]. 

Solution of the coupled partial differential and integral equations is performed using a finite difference scheme on an Aspen Custom Modeler platform. Discretization meshes along r and z directions are, respectively, 0.2 mm and 4 mm. To ensure convergence of the numerical scheme, both the fast Newton method for nonlinear solver with convergence criterion on residuals, and a MA48 linear solver are used. Typical simulation duration is 30min on a 3 GHz CPU and 1.5 Go RAM computer with a 10" for the absolute equation tolerance. 

Others have taken different approaches for greater accuracy or the use of industrial data. Custom molecules can be created in Aspen Properties, along with corresponding physical property parameters and models, and custom electrolyte reactions can be entered in the Chemistry section and all of the associated equilibrium constant models. For more information on this approach, see Mudhasakul et al. [10], who developed an Aspen Properties package for this system. Alternative strategies include developing custom models in Aspen Custom Modeller for the different units of operation using simplified forms of the piperazine interaction equations [26]. 

The relevant models for the reactive distillation column and peripherals have been developed and implemented into the simulation environment ASPEN Custom Modeler . Simulations of the heterogeneously catalysed synthesis of TAME have included 11 components. The species and the boiling points at the operating pressure of 4 bar are listed in Table 1. The key components of the inert fractions of the feed have been used to represent the hydrocarbon fractions (see Table 1). VLE is described by UNIQUAC model, with the Redlich-Kwong equation of state. In simulations, four reactions are considered the main reactions (l)-(3) and the formation of dimethyl ether (7). 

Figure 3 Hybrid process in simulation environment Aspen Custom Modeler ...

Four examples are presented on which a Newton solver fails to find the solution while it converges when the new initial point produced by the algorithm is used. The Aspen Custom Modeler commercial simulator is used to pose the examples. 

The commercial simulator Aspen Custom Modeler (ACM) has been used to pose various examples for testing the proposed algorithm. The examples are chosen because they are difficult to solve from their initial points. In all the examples, the standard Newton solver available in the simulator fails to find the solution, while it converges with the new initial point found by the algorithm. 

This chapter has studied the control of a column-pervaporation process for producing high-purity ethanol to overcome the azeotropic limitation encountered in distillation. A conventional control structure is developed that provides effective dismrbance rejection for both production rate and feed composition changes. A simple pervaporation model is developed in Aspen Custom Modeler that captures the important dynamic features of the process. The model uses pervaporation characteristic performance curves to determine diffusivities. Component fluxes depend upon composition driving forces between the retentate and permeate sides of the membrane. The dynamics of the pervaporation cells are assumed to be dominated by composition and energy capacitance of the liquid retentate. 

To meet this challenge, we developed a multiple-component optimization methodology that fully accounts for the behaviour of individual components within the process reactors, separators and the recycle gas loop. While in the binary pinch approach the composition and flows of reactor feed and separator gas are fixed, our multiple-component approach allows these compositions to float, so long as constraints such as minimum hydrogen partial pressure and minimiun gas-to-oil ratio are met. Simulation models for reactors, high-pressure and low-pressure separators are used to correctly model overall process behaviour. We also developed a network simulation tool based on AspenTech s Aspen Custom Modeler (ACM) software. 

Examples of equation-oriented simulators include ACSL, gPROMS, and Aspen Custom Modeler (Luyben, 2002). 

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