1. Evolving a Control System - supplement to “Process Monitoring and Control”
3rd year Design Module

2. Elements of a “Control Loop”
Measure, Control, Manipulate
Control FC
Measure
Manipulate

3. Common Control SchemesFC PC PC
Flow Control
Downstream
Pressure Control
Upstream
Pressure Control LC TC LC
Temperature Control
Level Control (inlet)
Level Control (outlet)

4. First - The Overall Process
Look at the overall process mass balance Control first
Every process needs something that ‘controls’ the flow rate through it
Every process needs something to ‘control’ the inventory in it
Inventory is Pressure for gasses, Liquid Level for liquids FC

5. Overall Process
Method 1: Control it’s flow in & “hold” it back with pressure or level
Mass Balance FC PC
Separation 2
Reactors
Separation PC
Things to consider: - Notice recycles don’t change inventory!
A rearrangement of these is possible/desirable (depends on feed stream)
This is a ‘”degree of freedom” analysis
Regneration

6. Look at the individual equipment
Heat exchangers need something to control temperature TC
Temperature Control

7. Look at the individual equipment
Separators need something to control Liquid Level and possibly pressure LC LC
Level Control (inlet)
Level Control (outlet)
Choose based on whether feed into the tank is being ‘controlled’ by an upstream process or not.

8. Look at the individual equipment
Separators need something to control Liquid Level and possibly pressure PC LC

9. The Controllers Duel for control over the Flow
Degrees of Freedom
Aka Dueling Control
You can only control the flow once in a system that requires/implies conservation of mass
This Doesn’t work !!
The Controllers Duel for control over the Flow FC FC

10. This Doesn’t work PC PC
This works ! PC PC

11. SAMPLE FC TC LC

12. What to submit An electronic PFD
Setup to print your PFD to the PDF Creator on the cluster computers – File, Printer Setup, Graphic Printer, Choose the PDF Creator
Print the Process Flow Diagram (to the PDF Creator)
Use Acrobat “snapshot tool” (camera icon) to copy and paste the PFD into Powerpoint
Drag and drop the symbols from this file onto you powerpoint slide

13. Symbols to use