Rotary kinetic fluid motors or pumps – Axially opposed working fluid paths to or from runner – Plural – separate – parallel – simultaneous flow paths
Reexamination Certificate
2002-10-15
2004-06-22
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Axially opposed working fluid paths to or from runner
Plural, separate, parallel, simultaneous flow paths
C415S100000, C415S912000, C029S888021
Reexamination Certificate
active
06752589
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to apparatus and methods for retrofitting steam turbines and retrofitted steam turbines. Particularly, the present invention relates to methods for replacing a large-diameter steam path, for example, of a substantially reaction stage design, with a smaller diameter steam path, for example, a substantially impulse stage design, while retaining certain component parts, including the outer shell of the original turbine in the retrofitted turbine.
In steam turbine technology, two distinct steam path designs are prevalent. In reaction stage turbine designs, a portion, for example, about 50% of the stage pressure drop, takes place across the rotating blades, increasing the velocity of the steam and imparting energy to the blades by reaction, as well as momentum exchange. In impulse stage turbine designs, theoretically the entire stage pressure drop is converted into velocity in the nozzles. No pressure drop occurs across the rotating buckets, which change the direction of the steam and absorb energy by momentum exchange.
Wheel and diaphragm-type mechanical constructions are typical in impulse stage design steam paths, whereas a drum-type construction characterizes reaction stage design steam paths. It will be appreciated, however, that an impulse stage design may employ either wheel and diaphragm or drum-type construction. Significantly, improvements in the design and efficiency of steam turbines have resulted in an increase in the root reaction of the impulse stage design without significantly increasing the stage reaction. That is, improved efficiency of the steam turbine has occurred with increased reaction in the impulse stage design but with a reaction level substantially less than a reaction stage design. There are substantial dimensional and design differences in the steam path of this improved impulse stage design, in comparison with the steam path of the reaction stage design. For example, the improved impulse stage design results in a combination of root diameter and length of the bucket less than the corresponding dimensions using a reaction stage design, on the order of about 50% less. Thus, the improved impulse stage design steam path has an inner shell much smaller in diameter than the corresponding diameter of the inner shell of a reaction stage design steam path. The impulse stage design steam path typically has a smaller diameter outer shell as well. Notwithstanding these dimensional and design differences, it is desirable to retrofit steam turbines having existing reaction stage type steam paths with the improved impulse stage design steam path to provide a retrofitted turbine with greater efficiency.
BRIEF DESCRIPTION OF THE INVENTION
In accordance with a preferred embodiment of the present invention, there are provided methods for retrofitting a large diameter steam path, for example, those typified by reaction stage design steam paths with a smaller diameter steam path, for example, those characterized by an improved and more efficient impulse stage steam path design. While it will be appreciated that a smaller diameter rotor and inner shell, characteristic of the improved impulse stage steam path design, replaces corresponding internal parts of the reaction stage steam path design, there has remained the desirability of utilizing the outer shell of the existing turbine with the steam path of the improved impulse design stage as well as other components. That is, to simply replace the steam path of the reaction stage design with the steam path of the improved impulse stage design would undesirably require an inner shell design with long, thick supporting extensions to accommodate the larger outer shell of the extant turbine. The thick extensions would be difficult to cast and might result in excessive thermal stresses during warm-up and cool-down of the retrofitted steam path. Accordingly, the present invention provides an interface between the replacement steam path of the improved impulse stage design and the outer shell of the turbine formerly housing the steam path of the reaction stage design. The interface also allows axial, vertical and radial positioning to be maintained while maintaining inner shell thickness to a minimum to avoid thermal stresses during transient operations.
In order to retrofit a steam path of the reaction stage design with a steam path of an impulse stage design according to a preferred embodiment of the present invention, the inner shell and rotor of the reaction stage design are removed and replaced by an inner shell and rotor of the improved impulse stage design. Because of the gap between the outer shell of the original turbine and the inner shell of the substituted steam path of the impulse stage design, an interface or bridging member is provided between the new inner shell and the old outer shell. Particularly, carrier section or ring halves are interposed between the new inner shell and the original outer shell and enable the reduced diameter steam path for incorporation into the outer shell of the turbine previously having the larger diameter steam path.
In a preferred embodiment according to the present invention, there is provided a method of retrofitting a first steam turbine having an outer shell including a pair of upper and lower outer shell halves and a first steam path of a first diameter in part defined by a first inner shell and a first rotor, to provide a retrofitted second steam turbine, comprising the steps of (a) removing the upper outer shell half, the first inner shell and the first rotor from the lower outer shell half of the first turbine, (b) inserting a lower carrier section into the lower outer shell half, (c) providing a second rotor and a second inner shell in part defining a second steam path of a second diameter smaller than the first diameter of the first steam path, (d) disposing a lower inner shell half of the second inner shell within the lower carrier section, (e) disposing the second rotor into the lower inner shell half of the second inner shell, (f) disposing an upper inner shell half of the second inner shell about the second rotor, (g) disposing an upper carrier section about the upper inner shell half of the second inner shell and (h) securing the upper outer shell half to the lower outer shell half of the first turbine thereby providing a retrofitted second steam turbine having a reduced diameter second steam path.
In a further preferred embodiment according to the present invention, there is provided a method of retrofitting a first steam turbine having a first steam path of a substantially reaction stage design to provide a second turbine having a second steam path of a substantially impulse stage design comprising the steps of (a) removing a first inner shell and a first rotor forming part of the first steam path of the substantially reaction stage first turbine from an outer shell of the first turbine design and (b) placing in the outer shell of the first turbine a steam path having the impulse stage design of the second turbine including a second inner shell and a second rotor, said carrier section being located between the second inner shell and the outer shell of the first turbine to bridge a gap therebetween.
In a further preferred embodiment according to the present invention, there is provided a retrofitted turbine comprising an inner shell surrounding a rotor and defining a steam path, an outer shell surrounding the inner shell and the rotor and a structural bridging member between the inner and outer shells bridging a gap between the shells.
REFERENCES:
patent: 3592557 (1971-07-01), Haas
patent: 3754833 (1973-08-01), Remberg
patent: 4326832 (1982-04-01), Ikeda et al.
patent: 4362464 (1982-12-01), Stock
patent: 4431371 (1984-02-01), Thomson
patent: 5388960 (1995-02-01), Suzuki et al.
patent: 6305901 (2001-10-01), Bell et al.
Caruso David Alan
Vogan James Harvey
General Electric Company
Look Edward K.
McAleenan J. M.
Nixon & Vanderhye
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