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Evolving a Control System - supplement to “Process Monitoring and Control”

This article explores the elements of a control loop in a process, including measurement, control, and manipulation. It discusses various control schemes such as flow control, downstream pressure control, upstream pressure control, temperature control, and level control.

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Evolving a Control System - supplement to “Process Monitoring and Control”

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  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 Schemes FC 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 PC PC Method 1: Control it’s flow in & “hold” it back with pressure or level Mass Balance FC Separation 2 Reactors Separation • 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 PC • Separators need something to control Liquid Level and possibly pressure LC

  9. 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. PC PC PC PC • This Doesn’t work This works !

  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

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