Aspen Plus blocks

Figure 4.2 Simulation flowsheet (a) ASPEN PLUS blocks (b) ASPEN PLUS icons (c) HYSYS.PIai icons (d) CHEMCAD icons (e) PRO/II icons.

The tubular reactor in Aspen Plus is called RPLUG and is installed on the flowsheet as shown in Figure 5.21. Two different tubular reactors with their feed and product streams are shown. The five possible types of reactors are listed on the Specifications page tab when Setup under the reactor block is clicked. 

In order to focus on the main issues of process integration, we disregard the distillation column for heavies, as well as the transalkylation section. A preliminary simulated flowsheet in Aspen Plus [9] is shown in Figure 6.8, with values of temperatures, pressures and heat duties. The fresh feed of propylene is llOkmol/h. Note that design specifications are used for the fine tuning of the simulation blocks. The fresh benzene is added in the recycle loop as makeup stream so as to keep the recycle flow rate constant. This approach makes the convergence easier. 

For more sophisticated spreadsheet models, Aspen Plus allows the user to link a spreadsheet to a simulation via a user model known as a USER block. The designer can create a new spreadsheet or customize an existing spreadsheet to interact with an Aspen Plus simulation. The USER block is much easier to manipulate when handling large amounts of input and output data, such as streams with many components or unit operations that involve multiple streams. The procedure for setting up a USER MS Excel model is more complex than using a calculator block but avoids having to... 

As in Example 4, the EXTRACT block in the Aspen Plus process simulation program (version 12.1) is used to model this problem, but any of a number of process simulation programs such as mentioned earlier may be used for this purpose. The first task is to obtain an accurate fit of the liquid-liquid equilibrium (LLE) data with an appropriate model, realizing that liquid-liquid extraction simulations are very sensitive to the quality of the LLE data fit. The NRTL liquid activity-coefficient model [Eq. (15-27)] is utilized for this purpose since it can represent a wide range of LLE systems accurately. The regression of the NRTL binary interaction parameters is performed with the Aspen Plus Data Regression System (DRS) to ensure that the resulting parameters are consistent with the form of the NRTL model equations used within Aspen Plus. 

The following stream comes out of a distillation tower (described in detail in Chapter 6). It is at 138 psia and 197.5°F. If the pressure is reduced (adiabatically) to 51 psia, what will be the vapor fraction and temperature (Hint In Aspen Plus, put a valve before the Flash2 unit, and reduce the pressure with the valve block.)... 

You can use Aspen Plus to solve this problem using the DSTWU block, which stands for DiSTillation-Winn-Underwood. 

The next simulation is for the same column, but using the RadFrac block in Aspen Plus. The feed is the same, the pressure is 138 psia, and the Refinery/Chao-Seader property method is used. This example uses 26 stages, and you run Aspen Plus to see what the split is. (Notice that you cannot easily set the split and find the number of stages or reflux ratio needed to achieve it.) Set the reflux ratio to 3.44 and enter the feed on the thirteenth stage. 

The next step is to tell the computer which blocks are going to use utilities. Select block B3 (the heater before the reactor) and click on the input button, then the Utility tab. Select Gas, as shown in Figure 7.14. Do the same thing for block B5 (the cooler after the reactor), and select Water, and then blocks BI and B9 and select Electricity (at 5 cents/kW h). Now the utilities have been specified to Aspen Plus. 

Unfortunately, the relationships between both results are not always straightforward. To use a simulator such as Aspen Plus, the simulation model has to be composed from pre-defined blocks. Therefore, the composition of the simulation model is specific to the respective simulator and may deviate structurally from the PFD. 

The integrator tool is used to derive a. simulation model for Aspen Plus from the initial PFD. Here, the user has to perform two decisions. While the heating step can be mapped structurally 1 1 into the simulation model, the user has to select the most appropriate block for the simulation to be performed. Second, there are multiple alternatives to map the PFR. Since the most straightforward 1 1 mapping is not considered to be sufficient, the... 

As a second step, ModKit- - is used to define the flowsheet model of the -caprolactam process, using the imported models from Aspen Plus, gPROMS, and MOREX as building blocks. The flowsheet topology is defined according to Fig. 5.20. The next step concerns the specification of a simulation experiment to be executed by the CHEOPS simulation framework. ModKit-f supports this step by generating a template of an input file for CHEOPS, which contains the necessary information except for the actual values of the feed streams and the parameters of the simulation. These have to be filled in by the user before he finally launches the simulation in CHEOPS. 

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