Selecting A Fluids Package

Let us show step by step how to simulate the utility system. The first step is common to all the process simulators and consists of selecting the components and thermodynamics. After selecting a New case in HYSYS, a window appears in which the user must select the Fluid Package and select the thermodynamics and the components associated to that Fluid Package. Figure 8.49 shows the initial window. 

Under the Components tab, select water. The user input under the Property tab is probably the most critical input required to run a successful simulation. This key input is the Base Method found under the Specifications option. The Base Method is the thermodynamic basis for all the simulation calculations. Since the fluid is water, select steam fluid package. Aspen has a tool in the toolbar that will automatically take the user through the required data input in a stepwise fashion. The button that does this is the blue N with the arrow next to it in the toolbar, an alternative method is to double click on the material stream and specify the feed stream conditions, and then double click on the pipe segment and specify pipe conditions as shown in Figure 2.13. 

Select a new case in Hysys, add the components involved, and then select PRSV as a fluid package. Enter the simulation environment, select material stream, and specify feed conditions, that is, temperature, pressure, and flow rates. In the composition page specify the mole fraction of feed components or specify feed components molar flow rates by clicking on Basis (Figure 5.28). Specify the reaction stoichiometric coefficients after selecting the kinetic reaction type. In the reaction basis, specify reaction basis unit, rate units, and reaction phase. 

The next step is the selection of a Fluid Package for this model. The Fluid Package refers the thermodynamic system associated with the chosen list of components. We move to the Fluid Pkgs tab in the Simulation Basis Manager and add click Add (Figure 4.45) Aspen FfYSYS will automatically choose the component list and present options for a Property Package for these components. 

Because of the mathematical and numerical difficulties involved in the development of a CFD package this activity has been undertaken mainly by specialists where the user is kept away from the details of the solution procedures. Nowadays there exist many user-friendly CFD packages which allow the engineer to set up and solve complex fluid flow problems with relative ease. First we would like to make a few comments on the selection of commercially available CFD packages and the aspects which should be kept in mind in this connection ... 

From the list of fluid packages, select the desired thermodynamic package. The list of available packages can be narrowed by selecting a filter to the left of the list (such as EOSs, activity models etc.). 

The components associated to a given fluid package can be selected by clicking on the view button under Component List Selection. The components can be selected directly from the list (by clicking on the Add Pure button), removed from the list. 

In a new case in Hysys, add all components involved in the mixture, select Anto/ne as the fluid package, and then enter the simulation environment. Click on stream in the object pallet, then click on any place in the PFD, double click on the stream and enter molar compositions of each component. In the conditions page set the vapor/phase fraction = 0 the calculated temperature (which is the boiling point temperature at the given pressure 1.5 atm) is 105.5°C as shown in Figure 1.1. 

In a new case in Pro/ll, add all components involved, for the fluid package select the Peng-Robinson EOS, click on stream in the object pallet, and then click and drag in the PFD area. Double click on the stream and specify pressure as 1.5 atm, as a second specification, select Dew Point from the pull-down menu (Figure 1.6). Double click on flow rate and specify the molar composition of all streams. For total flow rate you can enter any value, for example, 1 kgmol/h (Figure 1.7). 

In a new case in Hysys, add the components ethane and water, and select the appropriate fluid package (NRTL). Enter the simulation environment and mix the two streams as shown in Figure 1.39. The Workbook is used to display the stream summary table below the process flow sheet. Click on Workbook in the toolbar once the workbook appears, click on Setup in the Workbook menu, and then click on Add to add the required variables from the list of variables. Once all information required is added to the workbook, right click anywhere in the PFD area and select Add Workbook Table. 

In a new case in Provision, add the components ethane, nitrogen, and water, and select NRTL as the appropriate fluid package. Connect two feed streams to a mixer and the outlet stream to a flash unit The result is shown in Figure 1.40. 

In a new case in Hysys, add benzene and toluene components and select the appropriate fluid package. Peng-Robinson EOS is a proper fluid package for hydrocarbons. The process flow sheet is shown in Figure 1.42. 

Open a new case in PRO/ll, click on the component selection icon (the benzene ring in the toolbar), select water, and then select the stream fluid package. Click on the pipe segment in the object palette and then click anywhere in the PFD area to place the pipe. Click on Stream in the object palette then generate the inlet stream (SI) and the exit stream (S2). Double click on stream SI and specify inlet temperature and pressure feed stream (Figure 2.8). 

Select a new case in Hysys. For components, select water and for fluid package, select ASME steam. Enter the simulation environment. Select the pipe segment from the object palette. Specify the feed stream conditions, stream composition, and product stream temperature. 

Open a new case in Hysys, select water as the pure component, ASME steam for the fluid package, and then enter the simulation environment. Select the pipe segment from the object palette, double click on the pipe and fill in the connection page. Click on the Worksheet tab set the feed and product stream temperatures to 20°C (isothermal condition) and the feed pressure to 20 atm. Click on the Rating tab then click on Append segment and specify the parameters of the pipe as shown in Figure 2.29. 

Open a new case in Hysys, select water for component, ASME Steam as fluid package, and then enter simulation environment. Build pipe flow sheet. Double click on feed stream and specify feed stream conditions. Double click on the pipe segment on the object palette, switch to the Rating page, and click on the Append Segment, and then add pipes and fitting as shown in Figures 2.46 and 2.47. 

Open a new case in Hysys. Add water as the pure component, and select ASME steam for the fluid package. Construct the pipe process flow sheet and specify the feed stream conditions. Double click on Pipe Segment on the process flow sheet, click on the Rating tab, and then click on Append Segment to add the pipe specification (length, nominal size, elevation, and fittings) as shown in Figures 2.58 and 2.59. 

Select a new case in Hysys. For Components, select ethanol and water for Fluid Package, select Non-Random Two Liquid (activity coefficient model), NRTL, and then enter the simulation environment. From the object palette, select Mixer and place it in the PFD area. Create two in let streams and connect one exit stream. Click on stream 1 and enter 25°C for temperature, 5 atm for pressure, and 100 kmol/h for molar flow rate. In the composition page enter the value 0.2 for ethanol and 0.8 for water. Click on stream S2 and enter 25°C for temperature and 5 atm for pressure to ensure that both the ethanol and water are in the liquid phase, and 100 kmol/h for molar flow rate. In the composition page, enter 0.4 for ethanol and 0.6 mole fraction for water. To display the result below the process flow sheet, right click on each stream and select the show table, double click on each table and click on Add Variable, select the component mole fraction and click on Add Variable for both ethanol and water. Remove units and label for stream 2 and remove labels for stream 3. Results should appear like that shown in Figure 3.2. 

Open a new case in PRO/II and select the conversion reactor from the object palette then, connect inlet and exit streams. Click on the Component tab (benzene ring in the toolbar) and select the components, NHj, Oj, NO, and H2O. From the thermodynamic data, select the most commonly used fluid package, the Peng Robinson EOS. Double click on the inlet stream (SI) and the Stream Data screen should appear. Click on Flowrate and Composition, then Individual... 

In a Hysys new case, all the components involved in the problem is selected for this case, it is water. For fluid package, ASME Stream is selected, then Enter Simulation Environment. 

According to manual calculation, the cold water outlet temperature was 45°C. The results obtained match with the values obtained from Hysys, PRO/II, Aspen Plus, and SuperPro software. Selection of a suitable fluid package is very important to obtain the correct results. Also, providing the sofware with correct values of temperature, pressure, flow rate, and composition will lead to obtain the right solution. 

Select a suitable fluid package by clicking on Fluid Pkgs tab in this case, the Non-Random Two-Liquid, NRTL is the most suitable fluid package. Close the fluid package window. 

Under Properties, Specifications, select the base property method. Since these components are liquids, NRTL thermodynamic package is the most convenient fluid package. Install CSTR reactor under Reactors in the model library, and connect inlet and exit streams. Specify the feed stream conditions and composition. Input the reactor specifications double click on the reactor block. The reactor Data Browser opens. Specify an adiabatic reactor and the reactor volume to 4433 liters the value obtained from hand calculations (Figure 5.11). Add the reactions to complete the specifications of the CSTR. Choose the Reactions block in the browser window and then click on Reactions. Click New on the window that appears. A new dialog box opens enter a reaction ID and specify the reaction as Power Law. Then click on Ok. The kinetic data are very important to make Aspen converge. Mainly specifying accurate units for pre-exponential factor A, is very important (see the k value in Figure 5.12). The value MUST be in SI units. 

The first step in the flow sheet simulation is to define process flow sheet connectivity by placing unit operations (blocks) and their connected streams. To define a process flow sheet block, select a model from the Model Library (Column and then DSTWU) and insert it in the workspace. To define a process stream, select Streams from the Model Library and click to establish each end of the steam connection on the available inlet and outlet locations of the existing blocks. Building process flow sheet using shortcut distillation form the model library, for fluid package, Peng Robinson EOS is used. Date needed for simulation. 

Start a new case in Hysys, Select Acetone, Water, and MIBK for the components. Use the NRTL Fluid Package. 

Start a new case in Hysys, Select Acetone, Water, and MIBK for the components. Use the UNIQUAQ Fluid Package. Check the binary coefficients simply click the Binary Coeffs tab. To specify the undefined values in LLE processes, select UNIFAC LLE, and click on Unknowns Only (Figure 8.29). 

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