Method: Vary heat flux. Varies cooling medium rate.
Process: Net vapor rate zero.
Advantages: Simple.
Disadvantages: Coolant return temperature may be high.
Application: No longer commonly called for in the design
of new plants. Often added to existing units when original control
schemes prove inadequate. Often used in older plants. Commonly,
a 'manual' form of this control scheme is used. Block valves on
the cooling water are pinched to reduce cooling water flow on
a seasonal basis or at reduced rates. Then a more conventional
pressure control scheme handles day-to-day control to set point.
Variants:
Configuration notes: Cooling water fouls more rapidly with
increasing temperature and decreasing velocity. A minimum rate
and/or return temperature over-ride with a secondary pressure
control system may be required.
Operation: Varying coolant rate causes LMTD to change.
This modifies total heat flux.
Warnings: Low velocity and high temperature cooling water
increases probability and severity of condenser fouling.
Return to Table of Methods
Return to consolidated paper list