Venting reflux splitter

A reflux splitter can be installed with an external gravity-reflux system (Fig. 19.56), an internal condenser system (Fig. 19.5c), and a pumped reflux system (Fig. 19.5ci). Venting near the top of the reflux splitter is important if vacuum creation is undesirable (130) or when noncondensables may be present. Figure 19.5a shows a vented reflux splitter construction (130). 

Problem A knockback condenser mounted on a C3 splitter reflux drum exhibited liquid carryover (as evidenced by the vent line icing-up). This indicated product loss from liquid caixying over rather than dripping back into the reflux drum. Also the vent line metallurgy would not withstand the cold temperatures produced. 

Some troublesome experiences with liquid carryover fi om these condensers have been reported (381). The author had an experience with liquid carryover from a vent condenser mounted on top of a Cg splitter reflux drum (similar to Fig. 15.14c). Carryover occurred whenever the vent control valve opened excessively, and was recognized by "watering or icing up of the line downstream of the valve (due to liquid flashing). The author is familiar with other similar experiences. Installing a valve limiter was sufficient to prevent carryover in the above case. 

First, the reflux drum liquid level dropped as the uncondensed vapors accumulated in the drum. Next, the operators reduced the reflux rate to prevent the reflux pump from running dry. Then, the splitter pressure rose rapidly, and the relief valve popped. This effectively vented the lighter hydrocarbons from the tower and allowed the operators to regain control. 

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