(81b) Evaluating Centrifugal Fan Retrofit

Brad Smith, P.Eng.

Sales Manager

Twin City Clarage, LLP

Mike Lowe

Senior Sales Application Engineer

Twin City Clarage, LLP

Abstract:

The reaction to produce ethylene via Steam Cracking is highly endothermic and it requires a large amount of heat to be absorbed at high temperatures to form olefins from paraffins. This heat is provided by combustion of fuel in cracking furnaces that are the effective reactor that generates 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 stack removal and ducting changes that are associated with a complete fan change. There are many options to consider that may allow a more economical retrofit of the existing fan.

Potential retrofit options may include new impellers, change in the impeller type, the impeller diameter or width, or the speed at which the impeller rotates. The fan laws can be used to evaluate the potential capacity and/or pressure 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 to evaluate 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 compared to a total fan replacement.