Reboiler design thermosiphon reboilers

Hughmark, G. A. (1961) Chem. Eng. Prog. 57 (July) 43. Designing thermosiphon reboilers. 

Fair, J. R. (1960) Pet Ref. 39 (February) 105. What you need to design thermosiphon reboilers. 

Figure 8, from Design Data for Thermosiphon Reboilers, by D. C. Lee, J. W. Dorsey, G. Z. Moore F. Drew Mayfield, Chemical Engineering Progress, Vol. 52, No. 4, pp. 160-164 (1956). Reproduced by permission of the American Institute of Chemical Engineers. 1956 AIChE. ... 

Collins, Gerald K., Horizontal-Thermosiphon Reboiler Design, Chemical Engineering, July 19, 1976. 

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

Kem deserves a lot of credit for developing design methods for many heat transfer situations and in particular the natural circulation phenomena as used for thermosiphon reboilers and shown in part in Figures 10-96A-D. 

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 vertical thermosiphon reboiler is a popular unit for heating distillation column bottoms. However, it is indeed surprising how so many units have been installed with so little data available. This indicates that a lot of guessing, usually on the very conservative side, has created many uneconomical units. No well-defined understanding of the performance of these units exists. Kern s recommended procedure has been found to be quite conservative on plant scale units yet it has undoubtedly been the basis for more designs than any other single approach. For some systems at and below atmospheric pressure operation, Kern s procedure gives inconsistent results. The problem is in the evaluation of the two-phase gas-liquid pressure drop under these conditions. 

This method for vertical thermosiphon reboilers is based on semi-empirical correlations of experimental data and is stated to predict heat transfer coefficients 30 percent, which is about the same range of accuracy for most boiling coefficient data. The advantage of this method is that it has had significant design experience in the industry to support it. It is also adaptable to other types of reboilers used in the industry. See Figures 10-110 and 10-111. 

A thermosiphon reboiler is to be designed for a fractionator that separates propane as the bottoms product. The conditions below the bottom tray are 401 psia and 164°F. A total of 17,600 Ib/hr vapor is to be produced. 

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. 

Design Select a thermosiphon reboiler as the preferred operation, if design is acceptable. 

General Guides for Vertical Thermosiphon Reboilers Design... 

The mechanical design of thermosiphon reboiler piping must be carefully examined for (a) system pressures and (b) elevadon reladonship between the liquid level in the disdl-ladon column and the verdcal or horizontal reboiler. Kem provides an excellent presentadon on this topic, including the important hydraulics. AbboT also presents a computer program for this topic. 

Chapter 10, Heat Transfer, has been updated and now includes several important design techniques for difficult condensing situations and for the application of thermosiphon reboilers. 

COLLINS, G. K. (1976) Chem. Eng., NY 83 (July 19th) 149. Horizontal-thermosiphon reboiler design. 

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