(3d) Evaluating Centrifugal Fan Retrofit

The reactions to produce ethylene via Steam Cracking are highly endothermic and require large heat absorbed at high temperatures to form olefins. This heat is provided by combustion of fuel in cracking furnaces that are the effective reactor, generating large quantities of flue gas. An ethylene cracking furnace can be debottlenecked to handle more feed, but the Induced Draft fan handling the flue gas will see higher volume and power demands. A total fan replacement is an option, but this would require a relatively large capital financial investment and may require the affected furnace to be offline for potential ducting changes. There are many options to consider which may allow a more economical retrofit of the existing fan.

Potential retrofit options may include new wheels, change in the type of wheel, diameter or width of the wheel, or the speed at which the wheel rotates. The fan laws can be used to evaluate the potential capacity and/or head increase that may be possible, and to determine the resulting impact on the motor and power consumption.

This paper discusses the benefits and methodology used in evaluating changes to the hardware and resulting performance of the centrifugal fan. We also explain how the retrofit operation would impact secondary centrifugal fan components such as dampers, motors, couplings or bearings. Finally, we present examples of how centrifugal fans were modified and the benefits of retrofitting the fan versus a total fan replacement.