Method: Vary heat flux.
Process: Net vapor rate zero or positive.
Advantages: Simple, fast response. Constant condensate drum pressure.
Disadvantages: Control valve is bigger than for other options. Open to atmosphere.
Application: Pressure towers with excess gas vented to atmosphere.
Configuration notes: Rarely used today due to emission controls.
Operation: Direct control of overhead pressure. Inert gas (air) drawn in and out as required to maintain condenser pressure. Control of exchanger heat transfer by inert blanketing.
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