Aspen flowsheet

Data Acquisi Data Plottin Flowsheeting Data Acquii Database M Dynamics Distillatio Flush Dru Labelling ASPEN AutoCAD CDRAFT ... 

This is the fun (and frustration) of chemical reaction engineering. While thermodynamics, mass and heat transfer, and separations can be said to be finished subjects for many engineering apphcations, we have to reexamine every new reaction system from first principles. You can find data and construct process flowsheets for separation units using sophisticated computer programs such as ASPEN, but for the chemical reactors in a process these programs are not much help unless you give the program the kinetics or assume equihhrium yields. 

Many aspects of a process can be evaluated with a chemical process flowsheet program such as Aspen. These programs handle mass balances and heat loads on each component with great accuracy. Separation components can also be handled accurately as long as they are rather straightforward. Cost databases also exist on these programs that allow rapid costing of many components. 

Several companies (D.B.R. Oilphase/Schlumberger, Infochem Computer Services, Ltd., Calsep) have commercially available computer programs (DBR hydrate, Multiflash, PVTSim) for the prediction of hydrate properties, and such methods are incorporated into process flowsheeting programs such as ASPEN , HYPERCHEM , and SIMCI . Researchers in the CSM laboratory (Sloan and Parrish, 1983 Sloan et al., 1987 Mehta and Sloan, 1996) generated new parameters for the prediction of si, sll, and sH hydrates, which were incorporated into the program, CSMHyd. 

We click on Start and select Programs, Aspen Tech, Aspen Engineering Suite, Aspen Plus 2004, and Aspen Plus User Interface. The window shown in Figure 2.26 opens. A Blank Simulation is selected, and clicking OK opens a blank flowsheet shown in Figure 2.27. 

Figure 2.27 Aspen Plus window with flowsheet.

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. 

Figure 6.34 shows the Aspen Plus flowsheet with these two adiabatic reactors installed. The empty reactor is 10 m in length. The catalyst-filled reactor is 20 m in length. The reactor effluents for the two cases are identical. Control valves are installed on the gas feedline and the gas reactor effluent line. Figure 6.35 shows the Catalyst page tab window under Setup for the reactor with catalyst. The catalyst properties are specified. 

Figure 6.37 Aspen dynamics flowsheet with default controllers.

Aspen Dynamics has the capability of using flowsheet equations for specifying a desired relationship. We illustrate this by setting up an equation that defines the PV signal to a temperature controller as T(6). The reactor block is COOLANT, so the T(6) temperature is BLOCKS( COOLANT ).T(6). 

The control structure shown in Figure 6.57 is installed on the flowsheet. The feed is flow-controlled. The outlet temperature is controlled by manipulating the coolant flowrate. Note that the OP signal is sent to both of the control valves on the coolant stream, opening and closing them simultaneously. The setup works in the simulations, but it is not what would be used in a real physical system. A pressure-driven simulation in Aspen Plus requires that valves be placed on both the inlet and outlet coolant streams. In a real system, the cooling water would be drawn from a supply header, which operates a fixed pressure. A single control valve would be used, either on the inlet or on the outlet, to manipulate the flowrate of coolant. 

Preparing for Export to Aspen Dynamics The dynamic units in the flowsheet are... 

The file is pressure checked and exported into Aspen Dynamics. A flow controller is installed on the feed. A pressure controller is installed that holds reactor pressure by adjusting valve V24 in the process discharge line. Figure 7.30 shows the flowsheet with these controllers installed. 

A major limitation in many flowsheeting systems is the inability to handle electrolytes. New work in this area is now being reported ( 1, 42) and two commercial systems are available (43, 44TT The ASPEN system ( ) has incorporated a solids handling capability to overcome another common deficiency. 

A major development effort has been underway at M.I.T. from 1976 to 1979 to develop a next-generation process simulator and economic evaluation system named ASPEN (Advanced System for Process ENgineering). The 150,000-line computer program will simulate the flowsheet of a proposed or operating plant. In addition to calculating detailed heat and material balances,... 

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. 

Figure 6.15 presents a compact flowsheet based on catalytic distillation, as simulated with Aspen Plus [9], Benzene and propylene are fed in countercurrent in... 

For the purpose of conceptual design of the bioethanol plant, Aspen Plus will be used as the flowsheet simulator. However, most of the key components involved in the process are not defined in the standard Aspen Plus property databases, and therefore their physical property data are not available. The National Renewable Energy Laboratory (NREL) has developed a database that includes a complete set of properties for the currently identifiable compounds in the ethanol process [28]. 

The SR method can be applied to distillation columns, but the equations of the algorithm do not allow the solution of the condenser and the reboiler with the other stages in the column. Because only the energy balances are used as independent functions, reboiler and condenser duties, reflux ratio, and the boilup ratio have to be specified. This overspecifies the column and the solution cannot be found. The condenser and the reboiler can be solved as separate unit operations in a flowsheet as demonstrated by Fonyo et al. (39). The SR method is used in the ABSBR step of FLOWTRAN of Monsanto, St. Louis, Missouri, and also in both the public release version of ASPEN and in ASPENPlus of AspenTech, Cambridge, Massachusetts. 

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. 

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