Dresser-Rand has developed a new seal design for Datum centrifugal compressors. The damper seals improve rotor-dynamic stability at high pressures and reduce section-to-section leakage in straight-through and back-to-back compressor configurations by as much as 50%, the company says. The seals reduce recycled flow, lower energy consumption, and require fewer compressor bodies for each application, the company says.
In the past, high-pressure centrifugal compressors suffered from rotor-dynamic instability because high-pressure process gas produces considerable excitation and reaction forces on the rotor.
The damper seals improve rotor-dynamic stability at high pressures and reduce section-to-section leakage in straight-through and back-to-back compressor configurations by as much as 50%, the company says.
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"Traditionally, as the discharge pressure of a centrifugal compressor increases, the destabilizing forces increase, while damping from the bearings remains constant," says J. Jeffrey Moore, manager for development engineering at Dresser-Rand in Olean, New York. "The resulting excitation and vibration problem can lead to mechanical damage to the compressor. When forward-driving forces exceed the resisting dissipation forces, self-excitation occurs in the first whirling mode of the rotor. The result can be significant sub-synchronous vibration that is limited only by contact between the rotor and stator parts. This instability is not encountered until late in the project cycle."
Consequences can include costly downtime and hardware changes.
As a result, D-R engineers developed swirl brakes and hole pattern damper seals to reduce excitation and improve damping, greatly reducing the likelihood of rotor-dynamic instability, the company says. The damper seal replaces traditional honeycomb seals and is machined from solid, high-grade aluminum. The honeycomb seal is fabricated from a very hard "super-alloy" material. In the case of the hole pattern seal, the damper seal can be made with clearances similar to those of a standard labyrinth to eliminate any negative impact on compressor performance. As pressures, power, and temperature increase, the seals can be manufactured from other materials, as appropriate.
