Method: Vary net vapor rate, no make-up gas.
Process: Must always have vapor product
Advantages: Simple and rapid control.
Disadvantages: Compressor may be oversized to add required control margin. Oversize applies to both capacity and compression ratio.
Application: Vapor going to higher pressure equipment.
Variants: Vapor may return to upstream of condenser, to condensate drum, or to compressor suction.
Configuration notes: A bypass relief of gas to low pressure (flare, fuel) often added to allow operation when compressor is down.
Operation: Material is recycled to move the compressor operation to maintain constant suction pressure.
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