Side Reboilers and Intercoolers

Side or outrigger reboilers are sometimes used to supplement the capacity of the bottom s reboiler. Intercoolers or side slip-stream coolers are sometimes used to supplement the capacity of the overhead condenser. 

Side reboilers and intercoolers also function as super-fractionation separation stages. They are just a subcase of once-through thermosyphon reboilers and partial overhead condensers. 

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Distillation columns and other multistage columns generally require heat addition and/or removal, which normally take place at the reboiler and/or condenser. For a variety of reasons, it may be desirable in certain types of columns to add or remove heat at intermediate trays aside from the condenser and reboiler. Examples of such columns include demethanizers that utilize a side reboiler alongside the bottom reboiler, multi-product columns where intermediate condensers are associated with some of the side products, and absorber intercoolers used for partial removal of the heat of absorption. The method most commonly employed for exchanging heat between a column tray and a heat source or sink is the pumparound, where a fluid is drawn from the tray, sent to a heat exchanger, then pumped back to the column. The following sections pertain to the various applications of side heaters and coolers and the different types of pumparounds. 

Each equipment symbol shown in Table 1.1 corresponds to the simplest configuration for the represented operation. More complex versions are possible and frequently desirable. For example, a more complex version of the reboiled absorber, item (5) in Table 1.1, is shown in Fig. 1.7. This reboiled absorber has two feeds, an intercooler, a side stream, and both an interreboiler and a bottoms reboiler. Acceptable design procedures must handle such complex situations. 

Heat can be transferred at a rate Qj from (-H) or to (-) stage j to simulate stage intercoolers, interheaters, condensers, or reboilers as shown in Fig. 1.7. The model in Fig. 15.1 does not allow for pumparounds of the type shown in Fig. 15.2. Such pumparounds are often used in columns having side streams in order to conserve energy and balance column vapor loads. 

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