Method: Vary blanketing vapor above drum.
Process: Net vapor rate positive or zero.
Advantages: Simple, fast response.
Disadvantages: Net consumption of pressurizing gas. Two
control valves. May have tuning problems.
Application: Pressure towers.
Variants: Adding make-up gas upstream of the condenser
may reduce gas rate required due to partial vapor blanketing of
the condenser. However, response time will be slightly slower.
Configuration notes: Pressurizing gas must be compatible
with the process. Some pressurizing gas may enter distillate product
and reflux. Equalizing line not required.
Operation: When pressure drops below desired set point,
vapor added to receiver. When pressure rises above desired set
point, vapor product line opened.
Warnings:
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