Reboiler design kettle reboilers

The column inventory also can be reducdd by the use of low-holdup column internals, including the holdup in the column base. As the design progresses, other features can be included to reduce the inventory. Thermosyphon reboilers have a lower inventory than kettle reboilers. Peripheral equipment such as reboilers can be located inside the column. ... 

The kettle reboiler is shown in Fig. ll-3.5ishell-side, this common design provides adequate dome space for separation of vapor and hquid above the tube bundle and surge capacity beyond the weir near the shell cover. 

Figure 10-96B. Horizontal thermosiphon reboiler on distillation column shell and tube design, not kettle. Boiling in shell.

The horizontal natural circulation systems do not use a kettle design exchanger, but rather a 1-2 (1 shell side, 2 tube-side passes) unit, with the vaporized liquid plus liquid not vaporized circulating back to a distillation column bottoms vapor space or, for example, to a separate drum where the vapor separates and flows back to the process system and where liquid recirculates back along with make-up feed to the inlet of the horizontal shell and tube reboiler. See Figures 10-96A-C. 

The kettle unit used in the reboiling service usually has an internal weir to maintain a fixed liquid level and tube coverage. The bottoms draw-off is from the weir section. The reboiling handled in horizontal thermosiphon units omits the disengaging space because the liquid-vapor mixture should enter the distillation tower where disengaging takes place. The chiller often keeps the kettle design but does not use the weir because no liquid bottoms draw off when a refrigerant is vaporized. 

The article of Fair and Klip presents a detailed analysis of the necessary design features and equations for horizontal kettle reboilers, horizontal thermosiphon reboilers, and vertical thermosiphon reboilers. Other useful references on reboilers are 185,186,188,190,192,194,195,196,197, and 201. 

Product column reboiler kettle type, heat transfer area 4 m2, design pressure 2 bar, materials stainless steel. 

Kettle reboilers, and other submerged bundle equipment, are essentially pool boiling devices, and their design is based on data for nucleate boiling. 

In a tube bundle the vapour rising from the lower rows of tubes passes over the upper rows. This has two opposing effects there will be a tendency for the rising vapour to blanket the upper tubes, particularly if the tube spacing is close, which will reduce the heat-transfer rate but this is offset by the increased turbulence caused by the rising vapour bubbles. Palen and Small (1964) give a detailed procedure for kettle reboiler design in... 

PALEN, J. W. and Taborek, J. J. Chem. Eng. Prog. 58, No. 7 (July 1962) 37-46. Refinery kettle reboilers proposed method for design and optimization. 

Example 8.12 summarizes the results of such calculations made on the basis of data in Heat Exchanger Design Handbook (1983). Procedures for the design of kettle, thermosiphon and forced circulation reboilers also are outlined by Polley (in Chisholm, 1980, Chap. 3). 

Reboilers need to be located next to the tower they serve, except for the pump-through types, which can be located elsewhere. Fired heater reboilers are always located away from the associated tower and use a pump to circulate the bottoms. Kettle-type reboilers are preferred from an operational and hydraulic standpoint because they can be designed without the worry of having to ensure sufficient head for circulation required by thermosyphon reboilers. However, kettle reboilers require a larger-diameter shell that is more cosdy, and the reboiler must be supported at a sufficient elevation to get the product to the bottoms pump with adequate NPSH. 

Palen and Small suggest that a factor of safety of 0.7 be applied to the maximum flux estimated from equation 12.74. This will still give values that are well above those which have traditionally been used for the design of commercial kettle reboilers such as that of 37,900 W/m (12,000 Btu/ft h) recommended by Kern (1950). This has had important implications in the application of submerged bundle reboilers, as the high heat flux allows a smaller bundle to be used, which can then often be installed in the base of the column saving the cost of shell and piping. 

---