Thermosiphon reboilers

At the bottom of the column, a liquid sump of constant and perfectly mixed molar liquid holdup Mg is provided. A portion of the hq-uid flowing from this sump passes to a thermosiphon reboiler, with the... 

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. 

In axial flow, a large flow area affords a low pressure drop and ean be of espeeial advantage when eondensing under vaeuum or when used as a thermosiphon reboiler. 

Figures 10-96A-E illustrate horizontal and vertical thermosiphon reboiler flow arrangements.

Figure 10-96A. Horizontal thermosiphon reboiler, a. Recirculating feed system, b. Once-through feed system. Both are natural circulation. (Used by permission Yilmaz, S. B. Chemical Engineering Progress, V. 83, No. 11, 1987. American Institute of Chemical Engineers. All rights reserved.)...

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

Yilmaz recommends that the maximum velocity in the exit from the horizontal thermosiphon reboiler be the work ofCollinsd ... 

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. 

Figure 10-105. Nozzle connections for vertical thermosiphon reboilers.

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. 

Physical properties at expected operating temperatures. See Figure 10-112 for temperature-pressure effects in vertical thermosiphon reboilers. 

Figure 10-110. Typical vertical tube-side thermosiphon reboiler. (Used by permission Fair, J. R. Petroleum Refiner, Feb. 1960, p. 105. Gulf Publishing Company. All rights reserved.)...

The thermosiphon reboiler has inherent instabilities. A valve or other flow restriction in the inlet line helps overcome these instabilities. Adjustment possibilities of a valve also compensate for variations in reboiler duty as imposed by changes in operation of the fractionator. 

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. 

Equivalent Feet of Inlet and Outlet Piping Vertical Thermosiphon Reboiler... 

Vertical Thermosiphon Reboiler Comparison Effect of Pressure Drop and Pipe Size on Selection... 

Figure 10-121. Hajek correlation thermosiphon reboilers overall coefficients at maximum flux. (Used by permission Hajek, J. D. Private communication. Deceased.)...

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. 

Johnson, A. 1., Circulation Rates and Over-All Temperature Driving Forces in a Vertical Thermosiphon Reboiler, presented at AlChE Heat Transfer Sym., Louisville, KY, Mar. 20 (1955). 

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