Coupling of modeFRONTIER v4 with Aspen Plus 2006 in a WIN32 OS environment

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Introduction
Aspen Plus 2006 is a process simulation software commonly used for process engineering and chemical engineering tasks. In order to solve optimization problems such as sensitivity analysis’ in Aspen Plus 2006, a coupling of modeFRONTIER v4 optimization software with Aspen Plus 2006 on a WIN32 operating system will be carried out and documented in this paper. A simple process is chosen to explain the necessary steps of work.

Description of a simple Aspen Plus 2006 simulation task
Two input streams of H2O (H2O1 and H2O2) with different temperatures are fed into a static mixer (MIXER) and result in one output stream (H2OMIX) as shown in Figure 1.

Figure 1: Aspen Plus 2006 User Interface Process Flowsheet window

The stream input specifications are shown in Table 1.

Table 1: Input stream specifications

This simple example is run and will converge without errors (IDEAL property method).

Optimization goal and modeFRONTIER v4 workflowsheet
Aim of the sensitivity analysis, carried out by modeFRONTIER v4, is the maximization
of the output stream mass flow while keeping the output stream temperature at as close to 62 °C (335 K) as possible. The modeFRONTIER v4 workflowsheet of this simple multi objective optimization problem is shown in Figure 2.
Table 2 will explain the workflow nodes used in Figure 2.

Figure 2: modeFRONTIER v4 workflowsheet

 

Table 2: Description of workflow nodes

Process flow in modeFRONTIER v4
4 input variables (as shown in Table 2) are set for this optimization problem. Their range of values is shown in Table 3.

Table 3: Range of input variable values

The input file window in modeFRONTIER v4 will look like Figure 3. Note that the input format is set to #0 so it will fit the format of the simu1.inp input file.

Figure 3: Input Variable Properties window in modeFRONTIER v4

The simu1_inp node is an exported file of the Aspen Plus 2006 simulation explained in chapter 2 with the extension “.inp”. The complete log is shown below.

This file is modified by modeFRONTIER v4 for each single optimization computation.
Therefore it has been edited so modeFRONTIER v4 is able to locate the needed input information within the simu1.inp (see below).

The simu1_out node is a Aspen Plus 2006 report file retrieved when running the simulation with the Aspen Plus 2006 Simulation Engine instead within the Aspen Plus 2006 User Interface environment. To start the Aspen Plus 2006 Simulation Engine from the Windows DOS-Console the following path has to be entered but may differ from machine to machine:

Then the folder must be switched to the folder, where the simu1.inp is located. In this case it is stored in

Now the simulation can be run with the following command:

This command will start a simulation with the input information of the simu1.inp file.
The optional indentifier /getridof will purge all unnecessary output files but also create a single simu1.out output file. The log of the operation is shown below.

The modeFRONTIER v4 file output node simu1_out with the simu1.out file as input will look like below but is not shown completely because of its size. Note that the output units are different from the input units (for example °C input and K output). However this will not effect the correct computation of the optimization. The simu1.out will inherit the unit settings of the initial run of the simulation and in this way the units may be applied as requested.

Note, that the output variables chosen for modeFRONTIER v4 are marked relative (red = variable, green = reference string) since the output file might change slightly and an absolute positioning could cause errors. The selected reference string should be unique throughout the file.

The two output variables temp_out and flow_out are each connected to specific optimization goal nodes. The absolute value of the difference of 335 minus the outlet temperature in Kelvin shall be minimized. In other words the temperature should be as close to 62 °C (335 K) as possible. This is implemented in modeFRONTIER v4 as shown in Figure 4.

Figure 4: Design Objective Properties window in modeFRONTIER v4

The second optimization objective is a simple maximization of output mass flow.

Logic flow and DOS Batch script node in modeFRONTIER v4
The optimization wizard of modeFRONTIER v4 recommends a Multi Objective Generic Algorithm (MOGA II) with at least 8 generations (time for one simulation = 0,33 min; time for overall simulation = 0,2 h).

Figure 5: Scheduler window in modeFRONTIER v4

The Design of Experiments (DOE) should be set to v4.

Figure 6: Design of Experiments window in modeFRONTIER v4

The DOSBatch4 script node should be configured as shown in Figure 7. To enter the correct execution path the script window (red circle) has to be opened.
The path is stated in “ ” so it is interpreted as a string (actual path may very from machine to machine). This allows advanced characters like spaces which otherwise may be interpreted incorrect.

Figure 7: DOS-Batch Properties window in modeFRONTIER v4

Figure 8: DOS-Batch Script window in modeFRONTIER v4

However the identifiers at the end have to be stated outside the “ ”. With simu1 the simu1.inp input file will be used for the simulation and /getridof will purge all unnecessary report files and will create just one simu1.out output file. In this way also a lot of disc space will be saved when multiple simulations will be computed by modeFRONTIER v4. The Logic End node is implemented to terminate the optimization correctly.

Run and analysis of the optimization
The modeFRONTIER v4 project is saved under the file name simu1.prj in the directory

The simulation is carried out, no error designs are created and a total of 31 design cases have been computed. The resulting Designs Table is shown in Figure 9.

Figure 9: Designs Table of the simu1.prj

Figure 10: Parallel Coordinates chart in modeFRONTIER v4

The optimal designs are marked with a green hook in column 3. The Parallel Coordinates chart (Figure 10) identifies two groups of designs: On group with maximum output of mass flow (design 3, 7, 10, 16, 18 27) and another group of minimal temperature difference to 335 K (design 1, 11, 22, 23 28).
However the variety of answers is yet not satisfying so the optimization is run again, this time with a DOE of 10 designs and a MOGA II of 10 generations. The optimization completes with a total of 100 designs. A derived table of all important designs is shown in Figure 11. Duplicates have not been discarded.

Figure 11: Optimal designs of second optimization run.

In a 4D bubble chart the designs can be evaluated by the user as shown in Figure 12.

Figure 12: 4D bubble chart of a derived designs table

The user has to decide whether a trade-off solution is reasonable or if an extreme solution is desirable.

Summary
A coupling of Aspen Plus 2006 and modeFRONTIER v4 on a WIN32 operating system has been shown in this document. A simple simulation problem has been computed and was later evaluated in a sensitivity analysis.

 

 

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