Method: Vary condensing area.
Process: Net vapor rate zero. Condensate drum runs at a
lower pressure than tower pressure.
Advantages: Condenser may be mounted below condensate drum.
Disadvantages: Two control valves required. Condenser requires
subcooling area.
Application: Often used with very large and heavy condensers
or with equipment requiring recurring cleaning or maintenance
(exchangers at grade). Preferred system to use with cooling boxes
as condensers. Cooling boxes have too high an internal heat capacitance
on the cooling water side to allow for rapid changes in cooling
water level.
Variants:
Configuration notes: A liquid level must be maintained
in the exchanger at all times.
Operation: To maintain pressure on the tower overhead,
the control valve in the condenser line DP varies. As control
valve DP changes, pressure balance between the bypass and the
condenser flows varies the liquid level in the condenser. This
changes the allocation of condensing versus subcooling surface
available. To maintain drum pressure, the control valve in the
bypass line varies flow through the bypass.
Warnings: Mounting condenser below drum requires sub-cooling
in condenser for stable operation
Return to Table of Methods
Return to consolidated paper list