Reflux splitter

The more volatile isobutylene product component flows upward through the upper distillation section 10 to a reflux splitter, 13, and then to a reflux condenser, 14, where it is cooled by room temperature water and withdrawn via line 14. Reflux is recirculated within the splitter 13 by a reflux line. 

The plant shown in Fig. 18.7 is often simplified for small installations. In place of the reboiler, a heating coil may be placed in the bottom of the column and generate vapor from the pool of liquid there. The condenser is sometimes placed above the top of the column and the reflux pump and accumulator are omitted. Reflux then returns to the top plate by gravity. A special valve, called a reflux splitter, may be used to control the rate of reflux return. The remainder of the condensate forms the overhead product. 

Decomposition in elementary simulation blocks. Example an azeotropic distillation column may be decomposed in reboiled stripping column, heat exchanger, three-phase flash separator and reflux splitter. 

Sutro weir dividers. A device often used for separating gravity reflux and distillate in continuous distillation systems is a Sutro weir divider. There are several variations, two of which (68) are shown in Fig. 19.4. It is suitable for small-scale systems and can eliminate the need for flow metering. Unlike the reflux splitter (below), it decouples... 

Reflux splitters. A reflux splitter (Fig. 19.5a) is an on/off solenoid-operated device actuated by a timer. The timer setting corresponds to a fixed reflux-distillate flow ratio. This setting is manipulated manually. The solenoid operates a slide gate that diverts all the liquid either to the column or to the product route. The solenoid operates at a high frequency so that neither reflux nor distillate flow is interrupted. 

Reflux splitters are extensively used in batch distillation (44, 106), but they have also been used in small continuous distillation columns. They have a distinct cost advantage in small columns. Even more important, flow measurement in small reflux lines is difficult (106) because of the small orifice bore required. The problem is most acute in corrosive and fouling applications, where the orifice bore may change during service. Reflux splitters offer a low-cost alternative for controlling small columns. 

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). 

A reflux splitter is difficult to incorporate in continuous distillation MB control schemes because it couples variations of the material balance stream (i.e., the distillate) with reflux rate changes. This is especially troublesome when reflux ratio is high, and a rise in distillate rate will effect a severalfold increase in reflux rate. The author experienced one case of poor continuous distillation control which was attributed to the above shortcoming. The author recommends restricting application of reflux splitters to batch distillation, where they work well. In continuous distillation, Sutro weir dividers are far more suitable. 

Galluzzo, J. F., "Installing a Reflux Splitter under Positive Pump Pressure, Chem. Eng., Feb. 13, 1967, p. 180. 

These different types of internal reflux splitters have to be chosen depending on the specific retrofit case, based on their features listed in Table 9.1. 

Figure 9.7 Various internal reflux splitters (a) moving-bucket type, (b) manual type and (c) in-the-column type.

Retrofit of Side Stream Columns to Dividing Wall Columns 265 Table 9.1 Comparisons of several reflux-splitter systems (Shin et a I2013). 

One important device in a DWC is an internal reflux splitter to manipulate the split of the liquid coming from the coluum overhead into the dividing wall section. A moving-bucket-type splitter was designed and fabricated to provide a precise split adjustment. Because of the potential risks from restless movement of its mechanical parts, it was replaced with a manual-type reflux splitter in the next turnaround period. 

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