Flow Aspen HYSYS

As shown in Figure 4.C.2, Aspen HYSYS simulation file is opened first. In VBA, Dim statement is used for declaration of variables, whereas Set statement is used for creating new objects. Then, values of feed flow rate, length and diameter of each reactor, and temperatures of inlet streams of both separators are transferred from cells C3 to Cll in Excel worksheet named DV to Aspen HYSYS , to Aspen HYSYS. To reduce computational time, remember to deactivate HYSYS solver before this transfer, and then activate it after transferring values of all decision variables to proceed with the calculations... 

After the convergence of the simulation, values of product flow rate and duties of both coolers are transferred from the simulator to cells C2 to C4 in Excel worksheet named Data from Aspen HYSYS . VBA code for these variables and/or data transfer is given in Eigure 4.C.2 include this code in the new macro... 

Feed Flow Rate.MolarFlow = Sheets("DV to Aspen Hysys").Ran e("C3") Reaetorl.TubeLength = sheets("DV to Aspen Hysys").Ran9e("C4")... 

Here, F, Zf and h are, respectively, the molar flow rate, mole fraction of component of i and total enthalpy, all in cell k their subscripts, ret and perm, refer to retentate and permeate streams. Equations (10.4) and (10.5) are mass balances and mass-transfer equations for each of the components present in the membrane feed. The cross-flow model [Equations (10.3)-(10.7)] was implemented in ACM v8.4 and validated against the experimental data in Pan (1986) and the predicted values of Davis (2002). The Joule-Thompson effect was validated by simulating adiabatic throttling of permeate gas through a valve in Aspen Hysys. Both these validations are described in detail in Appendix lOA. 

CO2 is absorbed into propylene carbonate in a packed column. The inlet gas stream is 20 mol% CO2 and 80 mol% methane. The gas stream flows at a rate of 2 m /s and the column operates at 60°C and 60.1 atm. The inlet solvent flow is 2000 kmol/h. Use Aspen HYSYS to determine the eoncentration of CO2 (mole%) in the exit gas stream, the column height (m) and the column diameter (m). 

The information flow in the mathematical model coincides with the material flow in the process (the process simulator Aspen HYSYS is a ranarkable exception). This assumption allows us to gather the variables associated with the streams entering the unit and define the functions that calculate the variables for the output streams. 

Sequential modular approach has some clear advantages for process flowsheeting that explain why it still dominates the technology of steady-state simulation over the simultaneous or equation-oriented approach. Table 8.2 shows a list of pros and cons about sequential modular process simulators. In order to cope with the disadvantages, a few process simulators have improved the flow of information and avoid redundant computations. As an example, Aspen HYSYS has implemented the bidirectional transmission of information technology. 

We have included two example sections. The first one is dedicated to the modular process simulator CHEMCAD. In the second one, we will show an example using Aspen HYSYS. CHEMCAD follows a classical input-output structure that is the most common approach in modular simulator. HYSYS, however, calculates a unit as soon as all its degrees of freedom are satisfied. In other words, it is able to calculate inputs in terms of outputs in most of the unit operations, which gives the user more flexibility specifying the problem, but at the same time the responsibility of correctly placing the recycles to avoid inconsistencies in the information flow. We leave gPROMS for Chapter 9 due to the differences we presented in the introduction. 

Here, we must ranark that with the following information Aspen HYSYS is capable of calculating the steam flow rate (or water flow rate). Classical modular process simulators cannot perform this calculation because we are calculating an input in terms of outputs. 

Figure 3.13 shows the process flowsheet ofthe simplified VDU model built by Aspen HYSYS. Since the first absorber (flash and striping sechon) is an absorber without any side draw and side pumparound and the condihons of atmospheric residue and steam are fixed, there is no addihonal specificahon required to run the first column. It is unlikely to change any process variables such as flash zone temperature and VR yield. However, we can add a heat flow to the feed stage to ensure that the flash-zone temperature matches the plant measurement (Figure 3.14). 

Aspen HYSYS uses a custom correlation based on fully-developed flow (away from the catalyst particle acceleration zone) that accounts for various angles of riser inclination. We present a similar correlation from Bolkan-Kenny et al. [47] in Eq. (4.1) using dimensionless Froude numbers, Eqs. (4.2)-(4.3). This correlation is essentially a function of riser diameter, D gravitational constant, g superficial gas velocity, u and Up terminal settling velocity of the catalyst particle. 

We click Add in the Case Studies Tab to create new case study Case Study 1 as shown in Figure 4.97. Once we create the case study, we must select the variables that we will change in the course of the case study (Independent variables) and variables we want to observe (Dependent variables). In general, it is not possible to set product yields as independent variables. Aspen HYSYS issues an error if we cannot set a particular variable s type as independent For the first case study, the only independent variable is the Feed Flow rate. 

Next we specify the flow rates, yields and composition of all the key streams from the reformer. A compositional analysis is necessary to make sure that we model key reaction paths accurately. We recommend that users enter all compositional information for gas streams in mol% and aU compositional information for liquid streams in vol.% or wt.%. Given the data available, we can enter the flow rates of each steam on a gas flow or mass flow basis. We note that internally. Aspen HYSYS will convert all measurements into a mol% to ensure overall material balance in the model results. 

Figure 6.4 Built-in process flow diagram of Aspen HYSYS Petroleum Refining HCR.

In the HYSYS.Plant simulator, this is accomplished by the Adjust operation, in CHEM-CAD by the CONT subroutine, and in PRO/II by the CONTROLLER subroutine. In ASPEN PLUS, the equivalent is accomplished with so-called design specifications. The latter terminology is intended to draw a distinction between simulation calculations, where the equipment parameters and feed stream variables are specified, and design calculations, where the desired properties of the product stream (e.g., temperature, composition, flow rate) are specified and the equipment parameters (area, reflux ratio, etc.) and feed stream variables are calculated. In HYSYS.Plant, the Adjust operation is used to adjust the equipment parameters and some feed stream variables to meet the specifications of the stream variables. Furthermore, the Set object is used to adjust the value of an attribute of a stream in proportion to that of another stream. 

The conditions for this simulation are shown in Figure 4.21 and sununarized in Exercise 4.2. As mentioned before, representative values are assumed for the flow rates of the species in the gas and toluene recycle streams. Also, typical values are provided for the heat transfer coefficients in both heat exchangers, taking into consideration the phases of the streams involved in heat transfer, as discussed in Section 13.3. Subroutines and models for the heat exchangers and reactor are described in the ASPEN and HYSYS modules on Heat Exchangers and Chemical Reactors on the multimedia CD-ROM that accompanies this text. In ASPEN PLUS and HYSYS.Plant, there are no models for furnaces, and hence it is recommended that you calculate the heat required using the HEATER subroutine and the Heater model, respectively. For estimation of the thermophysical properties, it is recommended that the Soave-Redlich-Kwong equation of state be used. 

As shown on the CD-ROM that accompanies this book (following the links HYSYS — Chemical Reactors Setting Up Reactors —> CSTR or ASPEN —> Chemical Reactors Kinetic Reactors — CSTRs RCSTR), analysis of this process shows the possibility of multiple steady states. For example, at a water flow rate of 400 kmol/hr, the following steady states are obtained (1) conversion of 83% with an effluent temperature of 62°C, (2) conversion of 45% with an effluent temperature of 44°C, and (3) conversion of 3% with an effluent temperature of 25°C. The intermediate steady state at 45% conversion is unstable, while the other two steady states are stable. Furthermore, a controllability and resiliency (C R) analysis on this process is carried out in Case Study 21.1, where a design involving a single CSTR is compared with one utilizing two CSTRs in series. ... 

Fuel cell system models have been developed to help understand the interactions between various unit operations within a fuel cell system. Most fuel cell system models are based on thermodynamic process flow simulators used by the process industry (power industry, petroleum industry, or chemical industry) such as Aspen Plus, HYSIS, and ChemCAD. Most of these codes are commercially distributed, and over the past years they have offered specific unit operations to assist modeling fuel cell stacks (or at least a guide for putting together existing unit operations to represent a fuel cell stack) and reformers. Others (16) have developed more sophisticated 2-D... 

Water is flowing in a 10-m horizontal smooth pipe at 4 m/s and 25°C. The density of water is 1000 kg/m and the viscosity of water is 0.001 kg/m s. The pipe is Schedule 40, 1 in. nominal diameter (2.66 cm ID). Water inlet pressure is 2 atm. Calculate pressure drop in the pipe using hand calculations and compare the results with those obtained using Hysys, PRO/ii, and Aspen software. 

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. 

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