Plant-wide Control Example: Vinyl Chloride Production

Report
Ref.: Sieder et al, Product and Process Design Principles, 2nd
Edition, Wiley, 2004.
Plant-wide Control
Example: Vinyl Chloride Production
First Reaction: Chlorination of Ethylene
C2 H 4  Cl2  C2 H 4Cl2
At 90oC , 1.5 atm and about 100% conversion
Second Reaction: Thermal cracking of Dichloroethane
C2 H 4Cl2  C2 H3Cl  HCl
At 500oC , 26 atm and about 60% conversion of DCE
Products specifications:
Main product: VC (Liquid) with more than 99% purity
By product: HCl (Gas) with more that 99% purity
After preliminary design, the PFD and Mass & Energy balance Table are as follows
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Plant-wide Control
Example: Vinyl Chloride Production
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Plant-wide Control
Example: Vinyl Chloride Production
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Plant-wide Control
Example: Vinyl Chloride Production
Step 1: Design a control system to produced 100,000 lb/hr VCM with more than 99% purity
Step 2: Twenty control valves have been positioned in the PFD (DOF determination)
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Plant-wide Control
Example: Vinyl Chloride Production
Step 3: Establish the energy-management system: V-3, V-6, V-5, V-7, V-8, V-20
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Plant-wide Control
Example: Vinyl Chloride Production
Step 4: Set the production rate: V-1
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Plant-wide Control
Example: Vinyl Chloride Production
Step 5: Control product quality (V-11, V-16, V-13, V-18), and safety, environmental, and
operational constraints
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Plant-wide Control
Example: Vinyl Chloride Production
Step 6: Fix recycle flow rates (V-4) and vapor and liquid inventories (R-100, V-19, V-10,
V-12, V-14, V17, V-15.
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Plant-wide Control
Example: Vinyl Chloride Production
Steps 7 & 8: Check component balances and control individual units (V-2)
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Plant-wide Control
Example: Vinyl Chloride Production
Steps 9: Optimize economics and improve dynamic controllability: The setpoint of recycle
flow controller is set in proportional to the feed flow rate.
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