HYSYS.Plant

If the pressure is fixed, there are 5 degrees of freedom. A mass balance allows specily the flow of distillate (D) (benzene) and intermediate product (P) (toluene) to a narrow interval. Therefore, although the kriging metamodel depends on 5 variables two of them can be almost fixed a priori, which increase the robustness of the model. The simulator (Hysys.Plant) forced us to specify the liquid (L) and vapor (V) streams that are withdraw from second column and returned to the first one. As remaining specification we chose the reflux ratio (RR). Initial values for these last three degrees of freedom, a reasonable interval of values as well as the number of trays of each column the feed and products tray positions, can be estimated using a shortcut method [6]... 

Hysys.Plant steady state and dynamic simulation to evaluate designs of existing plants, and analyse safety and control problems. 

Hysys.Operator Training start-up, shutdown or emergency conditions, consisting of an instructor station with DCS interface, and combined with Hysys.Plant as calculation engine. 

Aspen Engineering Suite 11.1 (includes ASPEN PLUS, ASPEN DYNAMICS, ASPEN PINCH, ASPEN SPLIT, BATCH PLUS, etc.) and HYSYS.Plant... 

Six major process simulators are widely used in the chemical process industries today. These are ASPEN PLUS, BATCH PLUS and HYSYS.Plant (Aspen Technology, Inc.), PRO/n (Simulation Sciences, Inc.), CHEMCAD (ChemStations, Inc.), and SUPERPRO DESIGNER (Intelligen, Inc.). In this book and the associated multimedia CD-ROM, coverage is provided of ASPEN PLUS and HYSYS.Plant, which are the two most widely used process simulators. It should be mentioned that once the principles of process simulation are understood, it is a relatively easy matter to switch from one simulator to another. 

In recent years, property information systems have become widely available in computer packages. Some are available on a stand-alone basis, such as PPDS2 (1997), while others are available within the chemical process simulators, such as ASPEN PLUS, HYSYS.Plant, PRO/n, CHEMCAD, BATCH PLUS, and SUPERPRO DESIGNER. Commonly, constants and parameters are stored for a few thousand chemical species, with programs provided to estimate the property values of mixtures, and determine the constants and parameters for species that are not in the data bank using estimation methods or the regression of experimental data. Virtually all of the property systems estimate the properties of mixtures of organic chemicals in the vapor and liquid phases. Methods are also provided for electrolytes and some solids, but these are less predictive and less accurate. 

Understand degrees of freedom in modeling process imits and flowsheets, and be able to make design specifications and follow the iterations implemented to satisfy them. When using HYSYS-Plant, the reader will learn that its implementation of bidirectional information flows is very efficient in satisfying many specifications. 

Learn the step-by-step procedures for using ASPEN PLUS and HYSYS.Plant. The CD-ROM covers many of these steps. Additional assistance is available by consulting the extensive user manuals distributed with the software. 

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. 

The multimedia CD-ROM that accompanies this book also explains how to use the dynamic simulators. Emphasis is placed on HYSYS.Plant. Using HYSYS.Plant, the design... 

A degrees-of-freedom analysis (Smith, 1963 Rudd and Watson, 1968 Myers and Seider, 1976) is incorporated in the development of each subroutine (or block, or model) that simulates a process unit. These subroutines solve sets of AEquaiions involving Nvanabies. where A Equations < A variabies- Thus, there are Nd = A, ariabies Equations degrees of freedom, or input (decision) variables. Most subroutines are written for known values of the input stream variables, although HYSYS.Plant permits specification of a blend of input and output stream variables, or output stream variables entirely. 

In HYSYS-Plant, the models are programmed to reverse the information flow when appropriate, that is, to accept values for the variables of the product streams and to compute the variables of the feed streams. HYSYS.Plant implements the so-called bidirectional information flow, as described next. 

In nearly all of the flowsheet simulators, the material and energy balances for the process units are solved given specifications for the inlet streams and the equipment parameters, along with selected variables of the outlet streams (e.g., temperatures and pressures). The unknown variables to be computed are usually those of the outlet streams (typically, the flow rates and compositions). The HYSYS.Plant simulator is a notable exception in that most combinations of specifications are permitted for each simulation model. With this flexibility, HYSYS.Plant can implement a reverse information flow, in which specifications are provided for the product streams and the unknown variables of the inlet streams are computed. More commonly, HYSYS.Plant implements a bidirectional information flow, involving the calculation of the unknown variables associated with the inlet and outlet streams. Whenever a stream variable is altered, the adjacent process units are recomputed. This causes the information to flow in parallel to the material streams, when a unit downstream is recomputed, or opposite to the material streams when a unit upstream is recomputed. 

In the HYSYS.Plant simulator, bidirectional information flow is utilized to compute the vapor fraction of the feed stream, other process simulators, where, instead, an iteration loop is created in which a guess is provided for d>i and iterations are carried out until the specified value of 4>2 is obtained, as discussed in the next subsection. Note that for the heater or cooler model in most simulators, the vapor fraction can be specified for both streams and the heat duty computed. ... 

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. 

For assistance in the use of the Adjust and Set objects, the reader is referred to the module HYSYS -> Principles of Flowsheet Simulation Getting Started in HYSYS -> Convergence of Simulation on the multimedia CD-ROM that accompanies this text. As was discussed in the subsection on bidirectional information flow, for all of its subroutines, HYSYS.Plant provides a bidirectional information flow, that is, when product stream variables are specified, the subroutines calculate most of the unknown inlet-stream variables. In CHEMCAD, a control unit, with one inlet stream and one outlet stream (which may be identical to the inlet stream), is placed into the simulation flowsheet using the CONT subroutine. The parameters of the control unit are specified so as to achieve the desired value of a stream variable (or an expression involving stream variables) or an equipment parameter (or an expression involving equipment parameters) by manipulating an equipment parameter or a stream variable. This is the feed-backward mode, which requires that the control unit be placed downstream of the units being simulated. The CONT subroutine also has afeed-forward mode. 

For the benzene-toluene mixer, Figure 4.8b shows the HYSYS.Plant simulation flowsheet in which the Adjust operation manipulates the flow rate of stream S2 to achieve the desired temperature. ... 

Figure 4.8 Feedback control—design specifications for the benzene-toluene mixer (a) ASPEN PLUS blocks (b) HYSYS.Plant icons.

When using ASPEN PLUS, the details of the convergence forms and the CONVERGENCE paragraph generated can be found in Chapter 17, Volume 2, of the ASPEN PLUS User Guide. See also the modules in ASPEN — Principles of Flowsheet Simulation —> Recycle on the multimedia CD-ROM that accompanies this book. For HYSYS.Plant, the user can consult the modules under HYSYS Principles of Flowsheet Simulation —> Getting Started... 

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. 

In HYSYS.Plant, the Shortcut Column model is used, which is described in the modules under HYSYS Separations —> Distillation —> Shortcut Distillation Column on the CD-ROM. 

In this section, several subroutines have been recommended for usage with ASPEN PLUS and HYSYS.Plant. These recommendations can be extended readily to permit the Simula tions to be carried out with CHEMCAD or PRO/II. 

Aspen IPE is also used to calculate equipment sizes and estimate capital costs for the MCB separation process in Section 16.7. Then, a profitability analysis is performed in Section 17.8. In Section 21.5, process controllers are added and their responses to various disturbances are computed using HYSYS.Plant in dynamic mode. Hence, for the MCB separation process, the process simulators have been used throughout the design process, although most design teams use a variety of computational tools to carry out these calculations. 

Be able to prepare a steady-state simulation using ASPEN PLUS and HYSYS.Plant and be familiar with the capabilities of CHEMCAD and PRO/II. 

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. 

This problem is easily modified if you are working HYSYS.Plant, CHEMCAD, or PRO/II. 

The problem can be modified for the usage of HYSYS.Plant, CHEMCAD, orPRO/II. 

To see how an adiabatic PFR is designed to provide a 75% conversion of toluene, see the CD-ROM that accompanies this book. Follow the link HYSYS — Chemical Reactors Setting Up Reactors -> PFR for a solution obtained with HYSYS.Plant, astA ASPENChemical Reactors Kinetic Reactors... 

PFTRs —> RPLUG for a solution with ASPEN PLUS. Note that the results provided by these simulators are almost identical the HYSYS.Plant result calls for a reactor volume of 3,690 ft D = 9.2 ft, L = 55.3 ft), while ASPEN PLUS gives a volume of 3,774 ft (D = 9.3 ft, L = 55.8 ft). The main reason for the slight discrepancy is due to the neglected pressure drop in the HYSYS.Plant simulation (the ASPEN PLUS calculation assumes a pressure drop of 5 psia). ... 

The CD-ROM that accompanies this book provides more complete coverage of the modeling of reactions and reactors using the process simulators. For ASPEN PLUS, follow the link ASPEN —> Chemical Reactors Overview. For HYSYS.Plant, see HYSYS-> Chemical Reactors Overview. 

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