An Interactive Approach to Teaching Steady-State Simulation of Chemical Processes


Department of Chemical Engineering, University of Pennsylvania, Philadelphia, PA 19104/6393

Key Words: Process design, simulation, multimedia, CD-ROM

February, 1996


A multimedia module for instruction in the Process Design course has been developed and tested by seniors in chemical engineering. One hundred and twenty pages of text were merged with animation, voice and video, providing the benefits described herein.


The use of multimedia modules in education is a rapidly growing trend. Instead of purchasing bulkpacks of extra readings, sample problems and old exams, students can now go to their university's computer rooms and get the information in a more entertaining and more easily remembered format. Or even simpler, they can buy a CD-ROM disk along with their text book, and get the information from their computer at home (if it is equipped with a CD-ROM drive and a sound card). We have recently completed the first multimedia module to be used by the chemical engineering students at the University of Pennsylvania. The focus of the module is on steady-state simulation of chemical processes and is intended primarily for chemical engineering seniors taking Process Design. We created the module principally during the summers of 1994 and 1995, and released it for use by the students in November 1995.

Multimedia modules have many advantages over the more conventional text-book and lecture-based approach to education. While it is not our intention to compare and contrast multimedia modules with lectures and standard texts, we hope to show how we have incorporated voice, video, animation, hypertext links and other interactive features into our module to create an effective and entertaining educational experience.

Content of Module

Before we demonstrate how the module conveys the principles of chemical process simulation, a brief history leading to the development of the module and its role in the Process Design course is appropriate. Over the past forty years, a two-course sequence in Process Design has been offered at the University of Pennsylvania. With the advent of formal methods of process synthesis and computer simulation, the Fall lecture course has evolved to concentrate on these aspects, and the Spring project course enables the students to make increasing usage of the latest design tools and strategies in carrying out more and more sophisticated designs. For a more complete discussion of the two courses, see the recent article by Seider and Kivnick [1].

In the lecture course, after typical societal needs are presented and the steps in creating a process design are outlined, process synthesis is introduced based on the strategy recommended by Rudd et al. [2]. To accomplish this, a case study is used which involves the synthesis of a vinyl chloride process, to show by example how to use heuristics to: (1) synthesize the reaction paths, (2) distribute the chemicals, (3) synthesize the separation trains, (4) synthesize the network of heat exchangers, (5) insert power-related units (pumps, compressors, and turbines), and (6) carry out task integration.

Before a formal discussion of the heuristics for process synthesis, using the approach advanced by Douglas [3], the steady-state simulation of process flowsheets is introduced. Here, the students learn to synthesize the reaction section of a plant, followed by the separation section, by means of the interactive analysis approach made possible by process simulators such as ASPEN PLUS, PRO/II, HYSIM, and CHEMCAD. As the students simulate processes in the steady state, they learn several important heuristics; for example: (1) quench hot gases before separation, (2) consider distillation to separate the chemical species in a liquid stream, (3) consider removing the light species first (direct sequence) or the heavy species first (indirect sequence), (4) pump liquids, if possible, and (5) try to avoid compression and refrigeration. More importantly, the students become comfortable in the use of the process simulators and aware of the calculations the simulators perform routinely. Then, after the introduction of the simulators, the course turns to a formal discussion of the heuristics for process synthesis, as mentioned above, using the Douglas approach. This leads to formal methods for: (1) the design of separation trains, (2) the elimination of lost work, (3) heat and power integration, and (4) the design of heat exchangers, before the methods of cost estimation and profitability analysis are covered.

To improve instruction in the basics of steady-state simulation, teaching materials have been needed. Although most schools use one or more of the simulators in their design course(s), for the most part the teaching materials are not well developed and are not sufficiently complete to be shared by faculty at different schools. The challenge for us in preparing courseware has been to find the proper blend of the modern computational approaches and the simple heuristic approaches. This, in our opinions, is the basis for an increasing number of process designs in industry. Our challenge is to find a way to incorporate these techniques into the curriculum.

In the initial preparation of the courseware for steady-state simulation, we undertook to revise FLOWTRAN Simulation - An Introduction [4] to cover steady-state simulation using the latest process simulators. A draft of the text was completed and used to teach with ASPEN PLUS, Release 8.5. As seen from the Contents in Figure 1, the coverage is similar, but expanded considerably to introduce the subroutines used to model the process units. The models are reviewed briefly with emphasis on the specifications necessary and the computed results. The preparation of text was accompanied by the generation of the multimedia module, as described below. The challenge, in this regard, was to find a vehicle for improving instruction through the usage of animation, voice, and video.

Use of Interactivity

Since this was our first attempt at multimedia authoring, we lacked familiarity with the latest authoring packages. On the advice of a multimedia expert in the Computing and Educational Technology Department of the University of Pennsylvania School of Engineering and Applied Science, we chose the Macromedia DIRECTOR 4.0.4 for WINDOWS software package. We found this package to be extremely powerful and easy to learn. Many of the basic skills could be learned directly from sample files and step-by-step tutorials, and the reference manuals provided quick access to the more sophisticated skills such as the use of LINGO (a scripting language) to control one's movie.

The module was prepared largely over the summers of 1994 and 1995 by two seniors in chemical engineering. The work during the first summer included reformatting the text and figures and creating animation. During the second summer, much of the module was updated to include the features of ASPEN PLUS Release 9 and its Graphical User Interface (GUI), a major departure from the previous paragraph-structured input language. We added instruction on completing the ASPEN PLUS Forms to: (1) simulate process units, (2) specify the sequence in recycle calculations, (3) implement design specifications, and (4) utilize FORTRAN inserts. In addition, we added animation and interactivity to make the module more user friendly and enjoyable to use. Following is a tour of our module which highlights its key interactive aspects, to show how we convey the principles of steady-state simulation.

Ease of Use

Figure 2 shows the opening frame of the module. As the student watches a man walking across the grounds of a chemical plant, he or she may choose to enable the sound and to set the volume level, if desired. A narrated introduction provides highlights and brief instructions as the student observes the chemical plant and, subsequently, the Table of Contents in Figure 1. Within the module, most frames have at least three buttons: "continue", "previous" and "main menu". From the questionnaire responses we received from the Process Design class, all of the students found the module easy to use.

Hypertext Links

The hypertext links provide major interactive capabilities for the module. These links allow users to navigate through the module by pointing to and clicking on highlighted text. The main menu in Figure 1 provides an example of this. Instead of flipping through pages of text (the text version of the module is 120 pages long) to find a particular section, the student can point to and click on any section title, and rapidly access that section.

Often the figures in traditional texts are positioned apart from the sections of the text that refer to them. An advantage of hypertext links is that they provide a direct connection to figures for quick reference. For example, a simulation of a separation process with recycle, as shown in Figure 3, is presented early in the module to illustrate the kinds of calculations and results provided by the process simulators. The printout of the results computed by ASPEN PLUS is voluminous and difficult to follow for a beginner; without a drawing of the flowsheet, it is difficult to keep track of the process units and streams whose results may be ten pages apart. In contrast, the module allows the student to step through the results unit-by-unit. Each frame shows a diagram of the process unit and the computed equipment parameters. Pointing to and clicking on any stream in the diagram causes the equipment parameters to be replaced by the computed stream variables, while the diagram remains on the screen. The results are easier to follow, and inter-related information may be readily associated.

Another section of the module describes the simulation of a simple, two-phase flash vessel as an introduction to steady-state simulation by ASPEN PLUS. It is important for beginners to understand the different ways this flash vessel can be represented by: (1) a sketch, (2) a simulation diagram, and (3) an ASPEN PLUS flowsheet. The module permits the student to click on highlighted text to see each of these representations one at a time. The text describing each remains on the screen, for ready reference.

Hypertext links also provide quick reference to material that has been introduced previously. For example, in the section on FORTRAN statements in ASPEN PLUS, a sample problem is introduced. Steam and methane are fed to a reactor in a 1:1 ratio. Two feed streams are mixed with a recycle stream and sent to the reactor; thus a FORTRAN statement is necessary to adjust the flow rate of the methane feed to maintain the 1:1 feed ratio as the composition of the recycle stream changes during convergence of the recycle loop. Four FORTRAN variables are defined for the sampled and manipulated variables on the ASPEN PLUS FORTRAN form in Figure 4. If the student loses track of the streams, he or she can click on the text that reads "click here to see the flowsheet" to refresh his or her memory. The advantage of hypertext links over conventional text is comparable to the ease of searching a compact disk as compared to a conventional audio tape.


The module contains one digital video of a laboratory distillation column in operation. The two minute segment of the glass column was filmed and converted to a QUICKTIME digital video. The column contains eight bubble-cap trays, a reboiler section, and a total condenser. The video brings the student sufficiently close to the trays to see the frothing of vapor from the bubble caps and the liquid falling through the downcomers. While the operation of a distillation column can be taught in the classroom, the module shows the intimate contact of vapor and liquid in ways that can only be appreciated in the laboratory. The video is narrated to draw attention to the important features of the column and its condenser and reboiler. Note that the two-minute segment of video accounts for nearly one-third of the disk space required by the module. Thus, while extremely helpful, digital video can quickly deplete the memory of a CD-ROM disk.


Probably the most powerful interactive capability of this module is the use of voice for narration and instruction. Its presence is felt throughout the module (unless your PC does not have a sound card). It is like having your professor looking over your shoulder as you read to point out things like "make sure you realize that that ASPEN PLUS flowsheet does not show the convergence unit" or "notice that the energy balance involving the inlet and outlet streams isn't satisfied because some of the energy is lost through heat transfer from the flash vessel." We developed the module first without voice, and then examined it frame-by-frame to determine where voice should be added, before modifying the text and the timing of the frames to allow for narration. We used WAVE STUDIO by Creative Labs to record the sound files, which worked very well for the simple voice tracks.

The use of voice is especially effective in providing instructions for completion of the ASPEN PLUS forms. The voice tutorial enlivens the Getting Started guide by Aspen Tech. on building and running a process model. Through the use of HIJAAK by Inset Systems, Inc., the ASPEN PLUS interface was converted to bitmapped pictures which are the basis of the tutorial. Voice enables us to "talk" a beginner through a simple simulation from start to finish. The flash-vessel example described above enables us to introduce the student to every ASPEN PLUS window and form he or she will encounter in the example simulation, while narration explains how to create the ASPEN PLUS flowsheet in Figure 5, input the data on the forms, run the simulation, and view the results. Voice instructions also guide the user through examples involving design specifications and FORTRAN inserts. In addition, methods for changing the stream and block names and for overriding the calculation sequences determined by ASPEN PLUS are explained through narrated examples. With this instruction, students should be able to simulate most steady-state processes encountered as an undergraduate.

Narration is also helpful in presenting the introductory process design for the separation of HCl, benzene and monochlorobenzene, as discussed above and shown in Figure 4. To understand this separation process, more explanation is required than can be derived from the flowsheet alone. As the process flow diagram is presented, unit-by-unit, narration makes it easier for the student to comprehend and retain the specifics of the process (i.e., HCl, benzene and MCB are sent to a preheater, the HCl is concentrated in an adiabatic flash, the HCl stream is sent to an absorber to remove benzene, the benzene/MCB stream is sent to a treater to remove trace quantities of HCl, the treated stream is then sent to a distillation column where benzene is recovered in the distillate and MCB is recovered in the bottoms). In multimedia format, this separation process, which is rather complex for beginning students in Process Design, is rather easy to follow.

Narration accompanies most of the frames that contain figures or animation. For example, the introductory screens to the sections on Pumps and Compressors and on Heat Exchangers show photographs of industrial pumps and heat exchangers. The narration briefly explains aspects of the equipment and its operation normally not covered in lectures that concentrate on theory.

Like video, voice files require a lot of memory. Our module requires nearly 100 megabytes of disk space to provide approximately four hours of instruction. It includes 20 megabytes of digital video (for only one video segment) and 25 megabytes of digital voice (for approximately 25 minutes of narration). Consequently, memory space for voice on a 650 megabyte CD-ROM is not an issue.


The two objectives in providing animation are: (1) to present information more clearly, and (2) to make the module more enjoyable and entertaining. The module contains several thousand frames which require at least four hours to digest from beginning to end. Consequently, students find it difficult to retain the abundance of information being displayed on a computer screen. Animation helps to keep the student's attention and to reinforce the basic principles.

In the section on recycle, animation is particularly effective in helping students trace the sequence through the process units in iterative recycle calculations. Especially when multiple recycle streams are present, animation helps to clarify the alternative sequences. For example, when studying nested recycle loops, a yellow marker moves from unit-to-unit as the inner recycle loop is converged. Then, the marker passes through the outer loop before returning to the inner loop, and the process is repeated, as illustrated for the simulation flowsheet shown in Figure 6. Through this and similar animation, students can understand complex calculation sequences more easily.

Another animation shows two tanks, one operating in the steady state and the other operating dynamically in response to disturbances in the feed flow rate. The tank at steady state has a constant holdup. The holdup of the second tank is varying and a liquid-level controller is working to keep it steady by adjusting the flow rate of the product stream. Yet other animation includes a highlighted trace of an ASPEN PLUS history file which helps students to better appreciate the utility of the history file for tracing the iteration sequence when convergence problems are encountered.

Student Response

After three weeks in which the module was used optionally by seniors in Process Design at Penn, most of the students indicated, in their responses to a questionnaire, that the module was very helpful in some aspects (e.g., in providing instruction for completing the ASPEN PLUS forms, in the solution of example problems, and in recycle analysis), but repetitive of the text in others. This is probably because the first version of the module did not differ markedly from the text, which the students received together with other notes for the Process Design course. During the summer of 1995, much interaction was added; yet the bulk of the text was retained. For the authors, it has been difficult to decide whether text should be retained when audio is added. On the basis of student response, we will experiment by removing more of the text in the future.

Future Releases

In future releases, we are anxious to enable the student to work problems with ASPEN PLUS in one window while operating the module in another. It is anticipated that operating systems such as WINDOWS '95 will accommodate this mode of interaction. Then, after receiving instructions in the module, the student can test his or her understanding by solving problems with ASPEN PLUS. This will be more convenient than the current practice of aborting the module, starting ASPEN PLUS, aborting ASPEN PLUS, and restarting the module. Furthermore, the student will be encouraged to carry out parametric and optimization studies using ASPEN PLUS.


Having devoted over 1000 student hours to the preparation of this multimedia module, we have concluded that the time was well spent. The animation, voice, video and hypertext links enrich the text and provide a powerful didactic tool. The module teaches more than a lecturer accompanied by text alone. It provides, on a CD-ROM, experiences that would otherwise be achieved through a combination of text books, lectures, video presentations, classes in a computer room, and class trips to a chemical plant. Ironically, these conclusions, and the previous discussion, are presented in written text. In the future, when journal articles become available on-line, they, too, can be expected to be in multimedia formats that clarify the benefits we have described. Perhaps, multimedia formats will be so commonplace that articles such as this will no longer be necessary.


The advice and assistance of Andy Perch, Paul Shaffer and Helen Anderson are appreciated. Financial support provided by Dean Gregory Farrington facilitated the work on this module. His enthusiastic support is acknowledged with gratitude. The assistance of Charles McMahon in providing a CD-ROM writer is appreciated. Thanks are extended to Arnold Kivnick for his helpful comments. Finally, several colleagues at Aspen Technology, Inc., especially Jila Mahalec, encouraged us to prepare this courseware. Their encouragement is also appreciated. Partial support was provided by the NSF Research and Curriculum Development Program under grant number EEC95-27441.


W.D. Seider, and A. Kivnick, "Process Design Curriculum at Penn: Adapting for the 1990s," Chemical Engineering Education, Spring, 1994, pp. 92-97.

D.F. Rudd, G.J. Powers, and J.J. Siirola, Process Synthesis. Prentice Hall, 1973.

J.M. Douglas, The Conceptual Design of Chemical Processes. McGraw-Hill, 1988.

J.D. Seader, W.D. Seider, and A.C. Pauls, FLOWTRAN Simulation - An Introduction. Third Edition, CACHE, Austin, Texas, 1987.

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