(123c) Benefits of Direct Drive Motors in Cooling Towers

Steam Cracking of hydrocarbons to produce olefins produces low temperature waste heat flows; the largest are associated with condensers, pre-coolers, and compressor intercoolers, as well as surface condensers for turbine drivers. The waste heat is typically rejected to cooling water, and the efficiency and reliability of the cooling towers is critical to maximizing throughput and maintaining ethylene plant production capacity in summer. As plants age, cooling tower maintenance costs consume an increasing but essential part of the maintenance budget in the ethylene industry.

The most prevalent cause of cooling tower downtime is failure of the right angle gearbox or associated mechanical components, such as the driveshaft or disc couplings, which are needed to link the slow speed fans to high speed motors. Further, the elimination of these components reduces the losses in the drive system and offers the possibility for improved overall system efficiency. This paper details a motor topology which allows for the replacement of the high-speed motor, driveshaft, couplings, and gearbox with a slow speed permanent magnet (PM) motor, directly coupled to the fan shaft, and driven with a variable speed drive.

A case study is presented with maintenance and efficiency improvement data provided. Data on the existing installed base of this motor design is provided to establish the technology has been field tested and proven.