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Most ACC OEM’s has their fans under slung from a parallel helical shaft gearbox, with motor supported of the gearbox as well. The fan bridge is above the fans, with access lane to ACC gearbox and motor from above between the inclined A-frames. The latest CTi standards draft for gearbox is also based on the same arrangement. Lately, for our project, one of the vendor is proposing a right angle gearbox,and drive arrangement mounted below the fans, supported of separate steel structure from ground. The arrangement is like those in induced draft cooling towers,I.e fan motor mounted independently connected to a right angle bevel gearbox through a drive shaft.we have no experience with this arrangement for ACC drive. The fan in this case is a 32ft frp design. Members thoughts and recommendations on advantage or disadvantages of these drive arrangements will be helpful in our decision.
Regards
Shameer -
Shameer
Excellent question. As you say, the induced draft arrangement is very common in cooling towers with large fans and small fans. Normally in this arrangement, the motor is outside the fan stack in the cooler air. You do not mention how the fans and gearboxes will be accessed in this new arrangement. It is not obvious.
In the normal cooling tower, the structural beams are narrow and the steel support is either a round pipe or narrow steel I beams. In concrete framed towers the fan blades are some times too close to the wider beams that are in a concrete tower and cause a pulsation/vibration due to aerodynamics of the airflow passing these beams. The large beams in a motor bridge could cause this same issue.
Also, the air temperature that would be flowing over the gear reducer and motor may be too warm to properly cool the gear and fan.
The benefits of this arrangement may be very interesting. The exit velocity from the fan stacks will be much higher than a normal A Frame ACC and I would assume there is no real perimeter walls. Thus, recirculation should be reduced. Air flow into the fans should be less effected by wind, thus the flow will be more uniform and will likely reduce blade stress.
Hope this helps; Gary Mirsky -
Shameer,
please send me a private message at desmond-dot-dehaan@howden.com -
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