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Quotes - Engineering - SalesBKU Kettle Type U-Tube Exchangers
Boiling Duty and Vapor Disengagement
In a K shell the bundle sits in the lower portion of an enlarged shell, submerged in boiling liquid. Vapor rises into the free space above, where velocity drops far enough that entrained droplets fall back rather than leaving with the vapor. A weir at the far end maintains the liquid level over the bundle.
Why U-tubes. The heating medium is usually steam or hot oil at a temperature well above the boiling liquid, so the differential is large and the startup transient is abrupt. A U-bundle absorbs both. It also lifts out, which matters because the boiling side fouls as dissolved solids concentrate.
Sizing the vapor space. This is where kettles are most often got wrong. Too little disengagement height and liquid carries over into the column or the downstream equipment. The vapor space is sized on vapor loading, not on convenience.
Blowdown. Whatever does not vaporize concentrates. A kettle needs a blowdown connection at the bottom and a policy for using it, or the boiling side scales and the heat flux collapses.
Typical Construction
- Shell: K - kettle, enlarged for vapor disengagement
- Front head: B - bonnet (A channel also used)
- Rear head: U - U-tube bundle
- Typical duty: Reboiler, vaporizer, steam generator
- Liquid level: Maintained by an internal weir over the bundle
- Vapor space: Sized on vapor loading and allowable entrainment
- Heating medium: Steam, hot oil or hot process fluid in the tubes
- Blowdown: Bottom connection required for concentrating service
- Bundle: Removable for boiling-side cleaning
- Codes: ASME Section VIII, TEMA R, B or C
BKU Kettle Type U-Tube Exchangers
CONFIGURATION • TEMA
BEU Heat Exchangers
BEU U-tube heat exchangers: bonnet front head, single-pass E shell, U-tube bundle. The least expensive removable-bundle exchanger and the most common
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CONFIGURATION • TEMA
AEU Heat Exchangers
AEU U-tube heat exchangers with a channel and removable cover, so the tube side opens for inspection without breaking the process piping.
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CONFIGURATION • TEMA
DEU High-Pressure
DEU U-tube heat exchangers with a D-type high-pressure front head closure, for tube-side pressures beyond bolted bonnet and channel construction.
+ Learn MoreBKU Kettle Type U-Tube Exchangers
Reboiler Versus Vaporizer
The hardware is the same; the service is not. A reboiler returns vapor to a distillation column and its duty is set by the column's heat balance, so it has to be stable across turndown and controllable. A vaporizer converts a liquid feed to a vapor product and is usually a simpler, steadier duty.
The design consequence is mostly in the control arrangement and the turndown range rather than the exchanger geometry, but it changes how the unit is rated.
Where the Heat Flux Limit Bites
Boiling heat transfer improves with temperature difference up to a point, beyond which the surface goes into film boiling and the coefficient collapses. Designing close to that limit produces an exchanger that works on the test sheet and misbehaves in service.
This is why kettle reboilers are rated conservatively on flux, and why a large temperature difference is not automatically a good thing on boiling duty.
