Flowsheet Control with Python Scripts

Introduction

Let us study the effect of the pressure on the temperature profile of the Acetone Column created on the previous tutorial. We will use the IronPython Scripting, Spreadsheet and Charts features available in DWSIM to generate, organize and analyze the results.

DWSIM Model (Classic UI)

1. Save the previous simulation with a different file name and remove everything from the flowsheet except the objects depicted on the following picture:

Process Flowsheet Diagram

1. Go to the Script Manager, click New on its toolbar to create a script (leave its interpreter at IronPython) and enter the following script:

   # Get Acetone Column object reference from the Flowsheet
   column = Flowsheet.GetFlowsheetSimulationObject("Acetone Column")
   
   # define the list of column pressures in bar
   Plevels = [8, 9, 10, 11, 12]
   
   # setup spreadsheet table headers
   Spreadsheet.Worksheets[0].Cells["A1"].Data = "Stage"
   Spreadsheet.Worksheets[0].Cells["B1"].Data = "P = 8 bar"
   Spreadsheet.Worksheets[0].Cells["C1"].Data = "P = 9 bar"
   Spreadsheet.Worksheets[0].Cells["D1"].Data = "P = 10 bar"
   Spreadsheet.Worksheets[0].Cells["E1"].Data = "P = 11 bar"
   Spreadsheet.Worksheets[0].Cells["F1"].Data = "P = 12 bar"
   
   # add column of stage numbers
   j = 1
   for stage in column.Stages:
       Spreadsheet.Worksheets[0].Cells[j, 0].Data = j
       j += 1
   
   # loop through the pressure values, set them and run the simulation, collecting the results
   i = 1
   for Pnew in Plevels:
       for stage in column.Stages:
           stage.P = Pnew * 100000 # set new stage pressures in Pa
       Flowsheet.SolveFlowsheet2() # request a flowsheet calculation
       j = 1
       for t in column.Tf: # column.Tf is the vector of final stage temperatures in K
           Spreadsheet.Worksheets[0].Cells[j, i].Data = t # write the temperature values in the corresponding column
           j += 1
       i += 1
   

2. Run the script asynchronously with the Run Script (Async) button, or F5 (this keeps DWSIM responsive while the column is solved at the five pressures, which takes a few minutes; the script writes each temperature column to the Spreadsheet as soon as that solve ends):

Run Python Script (Async)

1. Go to the Spreadsheet, select the data range A1:F62 (the stage numbers and the five temperature columns, with their headers), click with the right mouse button and select Create 2D XY Chart from Selection.

Create new chart from selected spreadsheet data range

1. Open the new chart on the Charts tab and, in its property grid, set Title (3. Plot) to Acetone Column Pressure Sensitivity and Y Axis Title (6. Y Axis) to Temperature (K). The X axis title (Stage) and the series names come from the spreadsheet headers. The chart should look like the following picture:

Pressure-Temperature dependence of the Acetone Column

1. Analyze the results obtained and discuss them with your colleagues.

The temperatures are in K. At 8 bar the profile runs from about 397 K at the top (Stage 1, the condenser) to 404 K at the reboiler (Stage 61), and every bar more raises the whole profile by 4 to 6 K, up to 414 K and 425 K at 12 bar. Above the feed stage the profile is almost flat, since the upper section holds the high-pressure azeotrope; below it the temperature rises quickly towards the boiling point of pure acetone at the column pressure.