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Flooded condensers are the prime tower pressure-control methods tor total condensers that generate only liquid products, and although these control methods can be troublesome, a good understanding of their principles will help achieve improved, trouble-free operations
Pressure is the most important variable for controlling distillation columns (Figure 1) because pressure affects every aspect of a distillation system: vaporization, condensation, temperature, volatility and so on. An unsteady pressure typically results in an unsteady column.
There are several ways to control tower pressure, depending on how the tower is configured. If a tower has an overhead vapor product, manipulating the vapor flowrate usually controls pressure. If the tower has no vapor product (it has a total condenser and produces only liquid), tower pressure can be controlled by partially flooding the condenser and manipulating the liquid level in the condenser. Another alternative for either vapor or liquid products is to manipulate the coolant flowrate (or temperature) to control the tower pressure. Coolant manipulation is popular in refrigerated towers, but is usually avoided in cooling-water condensers, as it can cause accelerated fouling and corrosion.
Flooded condenser control is by far the preferred pressure-control method used with water-cooled total condensers (those generating liquid products only). It is also common with air-cooled total condensers. In this control method, the condenser area is partially flooded by condensate. The flooded tubes do not contact the vapor and perform little condensation. The column pressure Is controlled by manipulating the flooded area. Raising the liquid level in the condenser floods additional tubes, which reduces condensation area, thereby raising tower pressure. Conversely, lowering the liquid level in the condenser exposes more tubes, which increases the condensation area, and subsequently lowers the column pressure.
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The principles of flooded condenser controls were described in literature more than 60 years ago. Chin's classic paper on distillation pressure-control describes many of the principles and good practices [7]. Yet, these methods continue to be among the most troublesome distillation controls. A good understanding of the principles, as well as learnings from past experiences, are key for avoiding many of the potential problems [2] , This article provides an updated and detailed description of the principles of flooded condenser control, and applies them to address many...