Figure 310

Overhead system for vacuum or pressure column—large amount of inerts as we can tell, they are equally valid for pressure and vacuum columns as for atmospheric columns. If cooling water is adjusted manually, the flow is either insufficient or excessive.

So-called "water savers" are cooling-water exit-temperature controls. They have the advantage of minimizing cooling-water flow rate for any given heat load. Their use also minimizes subcooling—and there are instances where this is desirable—but at the expense of variable condensate temperature. This can cause variable internal reflux unless it is compensated for (see Chapter 11, Section 2). This kind of control is often implemented as shown in Figure 3.7; pressure is controlled by manipulation of makeup and vent valves.

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