Process simulation—steady state ASPEN PLUS

Process simulators, steady state, dynamic, and batch, are used throughout the textbook (ASPEN PLUS, HYSYS.Plant, CHEMCAD, PRO/II, BATCH PLUS, and SUPERPRO DESIGNER). This permits access to large physical property, equipment, and cost databases... 

It is important to note that all of these methods use only steady-state information, so steady-state process simulators such as Aspen Plus can be easily used to perform the calculations. The methods all require that various variables are held constant, while other variables change. For example, two product compositions can be held constant, or a tray temperature and reflux flow rate may be held constant. The Design Spec/Vary feature in Aspen Plus is used to achieve the fixing of the desired independent variables and the calculation of all the remaining dependent variables. 

The stream conditions shown in Figure 14.1 are from the dynamic simulation of the process at steady-state conditions with the recycle of solvent loop closed. This loop did not converge in the steady-state Aspen Plus simulation. Other simulation issues are discussed in the next section. 

In this chapter, the methods for shortcut C R analysis, using the results of steady-state simulations, have been described. The methods require the use of software for the solution of material and energy balances in process flowsheets (e.g., ASPEN PLUS, HYSYS.Plant) and for controllability and resiliency analysis (i.e., MATLAB). The reader is now prepared to tackle small- to medium-scale problems, and in particular should... 

The material in this chapter is based on articles by Subawalla and Fair, AlArfaj and Luyben, and Luyben. Rigorous steady-state simulation of the process is performed using Aspen Plus. All columns use rigorous RadFrac models. Details of how to use Aspen Plus for simulating conventional as well as reactive distillation columns are provided in work by Luyben. ... 

Aspen Plus Steady-state process simulation www.aspentec.com... 

To study different operating conditions in the pilot plant, a steady-state process simulator was used. Process simulators solve material- and energy-balance, but they do not generally integrate the equations of motion. The commercially-available program, Aspen Plus Tm, was used in this example. Other steady-state process simulators could be used as well. To describe the C02-solvent system, the predictive PSRK model [11,12], which was found suitable to treat this mixture, was applied. To obtain more reliable information, a model with parameters regressed from experimental data is required. 

S 2] With the steady-state process simulator Aspen Plus , thermodynamic models for the sulfur-iodine cycle given in [132] are combined with chemistry models which describe the dissociation and precipitation reactions. 

Throughout this book, we have seen that when more than one species is involved in a process or when energy balances are required, several balance equations must be derived and solved simultaneously. For steady-state systems the equations are algebraic, but when the systems are transient, simultaneous differential equations must be solved. For the simplest systems, analytical solutions may be obtained by hand, but more commonly numerical solutions are required. Software packages that solve general systems of ordinary differential equations— such as Mathematica , Maple , Matlab , TK-Solver , Polymath , and EZ-Solve —are readily obtained for most computers. Other software packages have been designed specifically to simulate transient chemical processes. Some of these dynamic process simulators run in conjunction with the steady-state flowsheet simulators mentioned in Chapter 10 (e.g.. SPEEDUP, which runs with Aspen Plus, and a dynamic component of HYSYS ) and so have access to physical property databases and thermodynamic correlations. 

In this chapter, the principles behind the use of several widely used flowsheet simulators are introduced. For processes in the steady state, these include ASPEN PLUS, HYSYS.Plant, CHEMCAD, and PRO/n. For batch processes, these include BATCH PLUS and SUPER-PRO DESIGNER. 

Have completed several exercises involving steady-state simulation using one of the four simulators, ASPEN PLUS, HYSYS.Plant, CHEMCAD, and PRO/II, and involv-ing batch process simulation using one of the two simulators, BATCH PLUS and SUPERPRO DESIGNER. 

Be able to optimize a process using ASPEN PLUS and HYSYS.Plant beginning with the results of a steady-state simulation. 

The steady-state RadFrac model in Aspen Plus consisted of four-column sections one stripper, two parallel absorbers, and a rectifier. In reality, there is only one column, but these four fictitious vessels are used in the simulation to model the real physical equipment Before exporting the file into Aspen Dynamics, a number of important changes had to be made in order to obtain a pressure-driven dynamic simulation. Figure 12.21a gives the Aspen Dynamics process flow diagram with aU the real and fictitious elements shown. The lower part of Figure 12.21b shows the controller faceplates. Note that the two controllers with remote set points (RCl and RC2) are on cascade. 

In this example the steady-state simulation of two bioethanol processes is conducted by modifying the model developed by McAloon et al. using Aspen Plus and Microsoft Excel, where the non-random two Hquid thermodynamic model is used [41,43,44]. The plant capacity is considered to be 100 milhon gal per year (378.5 km per year) for both cases. The simulation results shown in Tables 6.2—6.4 provide information on the overall input and output material, component balance, and utihty consumption for both cases. 

The previous chapter discussed the methods and techniques for using Aspen Plus simulation software to develop and optimize steady-state designs for azeotropic distillation systems. Once the steady-state design is complete, the dynamic controllability of the process should be explored. Only looking at the steady state does not tell you whether the process is operable. Dynamic simulations and the development of an effective control stmcture are vital parts of process development. 

We use a simple process as a numerical example to illustrate moving from a steady-state simulation in Aspen Plus to a dynamic simulation in Aspen Dynamics. Figure 4.15 shows the flowsheet and the control stmcture. The flash drum is the same as the one sized in Section 4.1.2. It is a vertical vessel 2 ft in diameter and 4 ft in height. Figure 4.16 shows the Aspen Plus process flow diagram. 

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