The fans pull air up through the bundle and throw it out of a fan stack at high velocity, away from the cooler. Designed and built in Stafford by Spiro-Gills Thermal Products, supplied and supported in the GCC by Petromarsh.
Tap a part to see what it does. The red line is the hot process fluid in the tubes, the blue lines are the air drawn up through the bundle by the fans.
Fan stack. A tall fan ring with a rounded inlet. It guides the air into the fan and sends it out upward at high velocity, well clear of the cooler inlet.
Fans. Axial fans above the plenum. They work in the warm exhaust air, so blade, bearing and belt temperature limits must be checked.
Motor and drive. Here the motor and belt sit on a bridge under the fan. Some designs put the motor below the bundle with a long shaft. Either way, reaching it needs a platform.
Plenum. The hood between bundle and fan. It evens out the air flow and covers the bundle, shading it from sun and protecting it from rain and hail.
Finned tube bundle. The same finned tube bundle as a forced-draft cooler. Air reaches it evenly from the open space below.
Headers. Plug, cover-plate or manifold headers at each end, chosen for pressure and fouling, as on a forced-draft cooler.
Process nozzles. Inlet and outlet connections, flanged to your piping class.
Structure. Legs and beams that carry the bundle, plenum and fans. The fans load the plenum structure rather than the ground.
An induced-draft cooler uses the same bundle, headers and fans as a forced-draft one. The difference is where the fan sits, and that changes air distribution, recirculation, maintenance and the temperature the fan sees.
Suction spreads air more evenly across the bundle face than a fan blowing into it. Better distribution means the bundle works more uniformly.
Air leaves the fan stack at about two and a half times the velocity of a forced-draft cooler. Less hot air falls back to the inlet, so the cooler sees true ambient.
The fan, belts and bearings sit in the exhaust air. If the process inlet is very hot, a fan failure can expose them to high temperatures, so the design limits exhaust air temperature, typically to around 100°C.
Both types use the same bundles and fans. Tap each one to compare how they behave on a hot, sunny GCC site.
Fans in fan stacks above a closed plenum. Even air flow, high exit velocity, bundle shaded. Fans and drives sit in warm exhaust air.
Common where outlet temperature must stay close to a high design ambient.
Fans below the bundle push cool air up. Drives are easy to reach and see only ambient air, but the bundle is open to the sky.
The default for hot process inlets and most refinery services.
A forced-draft fan moves cooler, denser air and needs slightly less power for the same mass flow. An induced-draft fan moves warmer air but avoids recirculation losses.
On induced draft, fan and drive work is done from a top platform, and the fans and plenum must be moved to lift a bundle out. On forced draft, the bundle lifts straight up.
If fans stop, hot process fluid can heat the still air around fan blades and belts. API 661 asks the designer to check fan and drive temperature limits, which often sends very hot services to forced draft.
Tubes, fins and headers are chosen exactly as for a forced-draft cooler. The plenum and fan stacks are galvanised steel, and fan blades are aluminium or FRP.
| Part | Carbon steel | Stainless and duplex | Other options |
|---|---|---|---|
| Header boxes | Plate, forgings and pipeSA-516 Gr 70 · SA-105 · SA-106 Gr B | 304L, 316L, duplex 2205SA-240 · SA-182 · SA-312 | Low-temperature carbon steel, impact testedSA-516 with SA-20 · SA-333 · SA-350 LF2 |
| Tubes | Seamless or weldedSA-179 · SA-214 · SA-334 | 304L, 316L, duplexSA-213 · SA-249 · SA-789 | Admiralty brass, copper-nickelSB-111 |
| Fins | Aluminium, the usual choice1000-series aluminium strip | Stainless steel welded finsfor hot or corrosive air | Copper fins, or galvanised carbon steel welded finshot-dip galvanised |
| Plenum and fan stack | Galvanised carbon steel sheet and sections, or stainless steel for corrosive coastal airhot-dip galvanised to ISO 1461 | ||
Induced-draft coolers follow the same codes as forced-draft ones. The fan and drive checks in API 661 matter more, because they run in warm air.
Requirements for air-cooled heat exchangers in petroleum, petrochemical and natural gas plants: headers, tubes, fins, fans, drives and structure.
Pressure design of the header boxes, plugs and nozzles, with the U stamp where it is required.
CE marking for Europe. UKCA under the Pressure Equipment (Safety) Regulations 2016 for the UK.
Rating software from Heat Transfer Research, Inc. Not a code, but the industry reference for air-cooler thermal design.
Sound power found from sound pressure (3744) or sound intensity (9614) measurements. Used to check the noise guarantee.
Hot-dip galvanised coatings on structure, plenum and fan stacks.
Material specifications, and qualified welding procedures and welders for headers and tube-to-tubesheet joints.
Non-destructive testing methods, and certified mill certificates for every pressure part.
Company specifications for air coolers from Saudi Aramco, ADNOC or Shell, applied on top of API 661.
Your engineers red-line our drawings, you approve the design twice before production starts, and you can witness the tests. Tap a step to see what happens and which documents you receive.
Spiro-Gills Thermal Products has designed and built bespoke air-cooled heat exchangers and finned tube in Stafford since 1946, and has supplied them to more than 100 countries. Thermal design is done in HTRI, welding is to ASTM code, and the company holds ISO 9001:2015. Petromarsh is their exclusive representative in the GCC.
Send the duty and the site conditions. The HTRI design will compare forced and induced draft and tell you which one fits.
