Forced Draught Air Cooled Heat Exchanger API 661 For Petroleum Industry
Forced Draught Air Cooled Heat Exchanger with API 661, Petroleum Industry
Selection of Induced Draught or Forced Draught
The air-cooled heat exchanger shall be either a forced-draught exchanger or an induced-draught exchanger and shall include the components shown in Figure 1 and any auxiliaries such as ladders, walkways and platforms. Forced-draught fans should be used, except that induced-draught fans should be considered for the following situations:
- If temperature control of the process is critical and sudden downpour of rain (i.e. excessive cooling) can cause operating problems
- To minimize the risk of hot-air recirculation
- On sites where air-side fouling is a significant problem, however forced draft can be used if screens are specified
- To improve thermal performance in the event of a fan failure (due to the stack effect)
- In hot climates, where the fan plenum chamber shields the bundle from the sun
- For services that have a temperature approach of 11 °C (20 °F) or less
Figure 1: Forced Draught vs Induced Draught Configurations
| A) Forced Draught |
B) Induced Draught |
| 1 - Tube Bundle |
6 - Fan |
| 2 - Header |
7 - Fan Ring |
| 3 - Nozzle |
8 - Fan Deck |
| 4 - Supporting Column |
9 - Drive Assembly |
| 5 - Plenum |
10 - Fan Guard |
Construction of Tube Bundle
Tube bundles shall be rigid, self-contained, and designed for handling as a complete assembly.
A) Removable cover-plate header
B) Removable bonnet header
| Typical Construction of Tube Bundles |
| 1 |
Tubesheet |
| 2 |
Removable cover plate |
| 3 |
Removable bonnet |
| 4 |
Top and bottom plates |
| 5 |
Tube |
| 6 |
Pass partition |
| 7 |
Gasket |
| 8 |
Nozzle |
| 9 |
Side frame |
| 10 |
Tube spacer |
| 11 |
Tube support cross-member |
| 12 |
Tube keeper |
| 13 |
Vent |
| 14 |
Drain |
| 15 |
Instrument connection |
Tubes and Finning
Maximum Fin Selection Temperature for Fin Bonding Types:
| Fin Bonding Type |
Maximum Process Temperature °C (°F) |
| Embedded fins |
400 (750) |
| Externally bonded (hot-dip galvanized steel fins) |
360 (680) |
| Extruded fins |
300 (570) |
| Footed fins (single L) & overlap footed fins (double L) |
130 (270) |
| Knurled footed fin, either single L or double L |
200 (390) |
| Externally Bonded (welded or brazed fins) |
> 400 (750) (maximum should be negotiated) |
Tubes and Finning Construction