7/30/2019 Reboilers Selection

1/4

The GPSA Engineering Data Book1 has an excellent

section on reboilers. The most common types are the

following:

Forced circulation (Figure 1)Natural circulation (Figure 2)

Once-through

Recirculating

Vertical thermosyphon (Figure 3) Horizontal thermosyphon (Figure 4) Flooded bundle (Kettle) (Figure 5) RecirculatingBaffled bottom (Figure 6)

For thermosyphon reboilers, the hydraulic aspects are

as important as the heat transfer aspects. The design of

thermosyphon reboiler piping is too broad a subject forthis handbook. Some good articles on the subject can be

found in References 214. Reference 3 is particularly

good for horizontal thermosyphon reboilers. Table 1 has

typical vertical thermosyphon design standards.

Figure 7 provides an overview of reboiler selection

choices. The accompanying notes provide information for

a quick or first cut estimate of the appropriate type for

a given application. Tables 212

and 313

provide additional,more detailed, selection data. Table 2 gives advantages

and disadvantages for all the major reboiler types. Table

3 is limited to thermosyphon types.

For reboilers, especially thermosyphon types, the

devil is in the details. The information presented herein

is intended for preliminary work. Final design is per-

formed by experienced engineers using detailed design

techniques.

General notes for thermosyphon reboilers:

1. Never use inclined piping for two-phase flow in a

process plant. This is particularly true for reboilerreturn piping. Use only horizontal or vertical runs.

2. If the reboiler heating medium is condensing steam,

provide a desuperheater if the superheat is more than

4060F.

(text continued on page 88)

Figure 1. Forced-circulation reboiler arrangement.

Figure 2. Natural-circulation reboiler arrangements.

Figure 3. Vertical thermosyphon reboiler connected to

tower.

7/30/2019 Reboilers Selection

2/4

Table 1

Typical Thermosiphon Reboiler Design Standards*

Figure 4. Horizontal thermosyphon reboiler.

Figure 5. Kettle reboiler arrangement.

Figure 6. RecirculatingBaffled bottom.13 (Reproduced

with permission of the American Institute of Chemical

Engineers, copyright 1997 AIChE, all rights reserved.)

*By permission, D. C. Lee, J. W. Dorsey, G. Z. Moore and F. D. Mayfield, Chem. Eng. Prog., Vol. 52, No. 4., p. 160 (1956).

**Cross Section area of vapor nozzle off to channel must be minimum of 1.25 times total flow area of all tubes.

7/30/2019 Reboilers Selection

3/4

Figure 7. Quick Selection Guide.

1Preferable to recirculating where acceptable vaporization rates can be maintained (less than 2530%). This type is

chosen when there is a need to minimize exposure of degradable and/or fouling substances to high temperatures.2Used for large duties, dirty process, and frequent cleaning required. The process is usually in the shell side. This type

is used in 95% of oil refinery thermosyphon applications.3Used for small duties, clean process, and only infrequent cleaning required. Vaporization is usually less than 30%,

but less than 15% if the fractionator pressure is below 50 psig. The viscosity of the reboiler feed should be less than

0.5cp. Put a butterfly valve in the reboiler inlet piping. This type is used in nearly 100% of chemical plant thermosyphon

applications (70% of petrochemical).4Greater stability than unbaffled.5Usually used where piping pressure drop is high and therefore natural circulation is impractical.6Very stable and easy to control. Has no two-phase flow. Allows low tower skirt height. This type is expensive, however.

Table 2

Reboiler Comparison12

(table continued on next page)

7/30/2019 Reboilers Selection

4/4

Table 2 (continued)

Reboiler Comparison12

Reproduced with permission from Hydrocarbon Processing, Oct. 1992, copyright Gulf Publishing Co., Houston, Texas, all rights reserved.

Table 3

Thermosyphon Selection Criteria13

Reproduced with permission of the American Institute of Chemical Engineers, copyright 1997 AIChE, all rights reserved.