Rexnord® Omega™ Couplings Simplify Powerplant’s Fan Drive Adjustments
CASE STUDY
At a major eastern U.S. powerplant, Rexnord Omega couplings are simplifying adjustments on large fan drives, accommodating misalignment, and reducing maintenance requirements.
The plant’s turbine floor, nearly as large as three football fields, contains five steam turbine generating units and 20 gas turbines for peak loads, with a total electrical capacity of more than 1400 megawatts. Eight 1200 hp forced draft (FD) fans operate at 1200 rpm to force air through the steam boilers and make them burn hotter and more efficiently. Eight 200 hp induced draft (ID) fans operate in 200º F temperatures at 890 rpm to recirculate gas from the boiler outlet into the boiler inlet.
All fans are connected to large electrical drive motors by a shaft coupling that permits the motor mounting to be adjusted and the drive system to be aligned properly. Every component of the fan system must operate continuously for up to several years without shutdown for repair or maintenance.
This E140 Rexnord Omega coupling is installed
on a forced draft fan drive. Green rings at right
are shrink disc mounting that makes it easy to
adjust the axial position of the hubs on the
shaft without heating
The original lubricated gear couplings tended to wear and develop backlash that sometimes caused vibration. To install the couplings, they generally had to be heated and shrink-fitted to the shaft. This took several hours, and adjustment was difficult. When thermal growth made it necessary to readjust a motor’s axial shaft alignment, the interference-fit hubs had to be heated to move them and then rechecked for alignment after they cooled, often repeating the procedure several times.
The utility’s maintenance staff replaced the couplings with Rexnord Omega couplings. These split-in-half flexible polyurethane couplings consist of only two hubs and two half-elements. They are non-lubricated, material-flexing couplings that incorporate torsionally soft flex elements to protect the connected equipment by cushioning shock loads, reducing torsional vibration, and absorbing unavoidable misalignment.
On the FD fans, fan shaft diameter is 6", and motor shaft is 5". A Rexnord Omega E140 coupling connects the two components. The couplings on the FD fans are joined to the shafts using a Rexnord keyless shrink disc option. The shrink discs are external locking devices that are installed over the hub projections. They incorporate several axial locking screws that, when tightened, cause the locking collars to exert radial forces on a tapered inner ring and the hub. The resulting radial clamping pressure between the shaft and hub establishes a solid connection. The shrink disc mounting combines the convenience of a slip fit with a “permanent-type” shaft connection equal to an interference fit.
Easily maintained radically split Omega
coupling on a
200 hp fan drive
Now, adjustment takes a matter of minutes instead of hours. Lubrication is unnecessary, and the new couplings accommodate normal misalignment without excessive wear. The utility has realized significant annual savings because of reduced labor for installation and adjustment, elimination of coupling lubrication, and potentially longer coupling life. As a result, the utility has put similar couplings in service at several of its other power plants.
4-154-106CS/9-30-03
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