Thrust balancing device for cryogenic fluid machinery

Abstract

An improvement for a turbine generator or pump having main bearings separated by a span of shaft and a thrust equalizing mechanism adjacent one of said main bearings, the improvement comprising a stationary length compensator interposed between the thrust equalizing mechanism and its adjacent main bearing to reduce the span between said main bearings. Preferably the length compensator is composed of material that shrinks less than the shaft of the generator, and the height of the length compensator, i.e., the compensating dimension, is selected according to desired thrust equalizing mechanism operating parameters over a temperature range.

Description

[0001]Applicant claims the benefit of U.S. Provisional Application No. 60 / 446,460, filed Feb. 10, 2003.BACKGROUND OF THE INVENTION[0002]This invention relates in general to means and methods for balancing the thrust felt by pumps and turbine generators operating in a cryogenic environment, and in particular to a novel improvement in a thrust balancing configuration to enhance the rotordynamic behavior of vertical cryogenic pumps and turbine generators.[0003]The LNG (liquid nitrogen gas) production plants currently in the design stages are utilizing economy of scale to increase production with lower capital costs, which has the effect of increasing the power ratings of the critical rotating equipment being supplied.[0004]As the power requirements increase with the demand for the next generation of liquefaction plants, the generator size must increase physically. As the generator is the dominant component in terms of rotordynamic stability, the increased size has negative ramification...

AI Technical Summary

Benefits of technology

[0007]An object of this invention is to provide a way for the lower bearing to be disposed closer to the upper bearing, thereby reducing the gap therebetween, without interfering with the functioning of a thrust balancing mechanism.

[0008]A further object of this invention is to provide an improvement for reducing the span between main bearings to offset the reduction in critical speed resulting from increased machinery size.

Problems solved by technology

As the generator is the dominant component in terms of rotordynamic stability, the increased size has negative ramifications to the machine reliability.

For example, higher power ratings of variable speed hydraulic turbine generators implicitly require larger physical sizes, but the possible loss of generator load demands critical speed separation below continuous speed and above maximum “breakaway” speed.

Furthermore, in the design of cryogenic turbine generators and pumps, there limitations on bearing size, shaft diameter and overall diameter of machines of this type.

However this is not readily accomplished in machines having ball bearings which are cooled and lubricated by the product fluid.

The TEMs (Thrust Equalizing Mechanism) mechanisms incorporated in machinery designed by Ebara International Corporation, Sparks, Nev., are good examples of such thrust balancing mechanisms which employ a combination of fixed and variable orifices, but there are limitations with regards to location, length and resultant variable orifice gap size.

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