ASPEN unit operations models

A library of generalized models is supplied in ASPEN to allow the user to simulate coal conversion processes as well as chemical and petroleum processes. A listing of ASPEN s unit operations models is given in Table I. Space does not permit descriptions of the models here, however, the ASPEN project reports (2) discuss their capabilities. 

The development and the design of new processes are today extensively based on mathematical modelling and simulation. The entire process is modelled through combining individual unit operation models. Several flowsheeting programs (Aspen+ , HySim , ChemCAD Pro II etc.) have already found their place in engineering... 

Unit Operations Models for Process Analysis using ASPEN... 

Another example is the systematic analysis undertaken by Palsson et al. on combined SOFC and gas turbine cycles [36]. In combination with a robust and accurate 2-D SOFC model, the system-level model attempts to provide an unbiased evaluation of performance prospects and operational behaviours of such systems. The 2-D SOFC model was integrated into a process simulation tool. Aspen Plus , as a user-defined model, whereas other components constituting the system are modelled as standard unit operation models. Parametric studies can be carried out to gain knowledge of stack and system behaviour such as the influence of fuel and air flow rate on the stack performance and the mean temperature and the effects of cell voltage and compressor pressure on the system efficiency. The pressure ratio is shown to have a large impact on performance and electrical efficiencies of higher than 65% are possible at low-pressure ratios. 

To generate ternary plots and to use them for design. Aspen Split is used. This software is imbedded in Aspen Plus and can be accessed by going to the toolbar and clicking Library and References. The window shown in Figure 8.11 opens in which the Aspen Split box should be checked. A new page tab will appear at the bottom of the process flow diagram next to those of the standard unit operation models, which is shown in... 

In 2006, GA participated in a study conducted by the Savannah River National Laboratory (Summers, 2006). The S-I process was coupled to a VHTR with a required helium return temperature near 600°C. To efficiently match temperature requirements with available heat, a design was developed to supply HI decomposition section energy with recovered heat from the sulphuric acid decomposition section. For the purposes of comparison and analysis in this paper, the GA flow sheets will refer to this design, and CEA flow sheets will refer to a design in which helium supplies heat to both acid decomposition sections. CEA uses ProSimPlus for flow sheet analysis, and GA uses Aspen Plus . A previous study (Buckingham, 2008) showed that the two process simulators give similar calculated results when the same unit operations and stream compositions are modelled, although different thermodynamic models are used for the calculations. 

This paper describes the advanced engineering capabilities of ASPEN and demonstrates their use by means of an example problem. The advanced capabilities include the ability to model unit operations involving solids, the ability to compute the properties of coal and coal-derived materials, and great flexibility for the user to add specialized models or other computations. 

Unit Operation Aspen Plus Models UniSim Design Models... 

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... 

First, the chapter lists the possible unit operations in the Aspen Plus Model Library, because the process is a connected set of the units. Then an example process is illustrated that makes ammonia from nitrogen and hydrogen. You will be able to get both the mass balances and the energy balances for the process. With this information you can determine the size of most of the equipment needed, and hence its cost. You can also determine the operating cost for heating, cooling, compression, and other tasks. The process involves a... 

The ability to model Selexol-based unit operations in Aspen Plus or Aspen HYSYS was recently made possible by the inclusion of the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) physical property model. As in Aspen HYSYS (see Section 6.1.1), a single chemical DEPG be used as a proxy for the mixture. Simple example files for using PC-SAFT with Selexol for one- or two-unit operations are included with the Aspen Plus distributiOTi, and an example for using PC-SAFT in Aspen HYSYS is available for download to subscribers of the Aspen Technology support website. 

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... 

Start the Aspen program, select Aspen Plus User Interface, and when the Connect to Engine window appears, use the default Server Type Local PC. Select Pipe under the Pressure Changes tab from the Equipment Model Library and then click on the flow sheet window where you would like the piece of equipment to appear. In order to add material streams to the simulation, select the material stream from the Stream Library. When the material stream option is selected, a number of arrows will appear on each of the unit operations. Red arrows indicate a required stream and blue arrows indicate an optional stream. 

The initial flowsheet presents a blank interface where we can place different objects from the Object palette shown in Figure 4.48. The initial tool palette only shows typical unit operations anddoesnot show the advanced Aspen HYSYS Petroleum Refining objects. We will use both toolbars to build the complete FCC model. We can bring up the advanced palette by pressing F6. 

Figure 4.72 shows the converged FCC unit operation window after Aspen HYSYS has successfully solved the model. We connect an effluent stream by bringing up the Connections section of the Design Tab and typing in Effluent for the Reactor Effluent stream. A stream titled Effluent will appear on the FED and we can use this stream to build further downstream fractionation units. 

As a consequence, corporations operating PUREX plants have been using sophisticated process simulation codes, including the PAREX code in France (45-47), SpeedUp (Aspen Plus) in the UK (48), and SIMPSEX code in India (49-51). Argonne Model for Universal Solvent Extraction (AMUSE) code in the United States was contrived not only for PUREX, but for UREX+ processes (52), which will be mentioned later. In Japan, similar efforts have also been made (53-55). 

In addition to handling the conventional vapor/liquid process operations, the ASPEN library of process models includes solids handling and separation units, a set of generalized reactors, improved flash and distillation unit models and process models from the FLOWTRAN simulator. The user can also include his or her own model or key elements of a model, such as the reaction kinetics, in FORTRAN code. 

This unit can simulate any type of separation processes, as distillation, absorption, stripping, or extraction columns, modelled as cascade of counter-current equilibrium stages. The model Radfrac in Aspen Plus is particular powerful. It is first built on the inside-out algorithm that increased dramatically the robustness in simulating distillation-based operations (Boston, 1980). Columns with multiple feeds, side streams products, stage heaters or coolers, can be treated, as illustrated in Fig. 3.13. The following capabilities are generally available ... 

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