Thermal design of reboilers is now done largely by computer programs that make possible the stepwise calculations necessary to account accurately for the effects of the changing vapor fraction through the reboiler. Many programs are available for sale or through membership in proprietary organizations. Any computer program should be carefully reviewed with respect to internal methods used and amount of data support before trusting for final designs. This is especially true in boiling, because many empirical relationships are still necessary even in a computer-based reboiler design method. Even if detailed computer calculations are used, it is helpful to have available shortcut manual methods that can be used for preliminary estimates of reboiler size or to verify the general range of the computer-calculated heat transfer coefficients. This section gives stepwise instructions for applying the equations in Section 278 to obtain a shortcut initial estimate of the required reboiler heat transfer area.

A. Example problem

Vaporize a medium-wide-boiling-range hydrocarbon mixture at moderate pressure using available steam. Roughly size kettle, horizontal thermosiphon, and vertical thermosiphon reboilers for this service.

(a) General data

Duty required: 14.6 MW
Operating pressure: 1,000 kPa