Patent Publication Number: US-8123462-B2

Title: Pressurized sealed chamber between multiple pressurized casings of machine and related method

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to steam turbines, gas compressors, or any device with a rotating shaft that penetrates multiple pressurized casings and has a bearing between those casings. More particularly, the invention relates to increasing the pressure in the vicinity of the bearing between multiple casings to reduce the leakage from the casings around the shaft. 
     Current turbo-machines such as steam turbines often employ multiple casings with bearings residing in stationary standards between the casings. In current practice, the bearings operate in an environment of atmospheric air. Operating the bearing at atmospheric pressure requires the higher pressure gas or steam within the casing to be sealed against a pressure difference equal to the gauge pressure present at the end of the casing. To contain the gas or steam within the casing, each casing includes a series of non-contacting gland seals, referred to as an end packing. Each end packing includes a number of non-contacting seals such as leaf seals, brush seals, labyrinth seals, etc., that partially seal against the rotating shaft of the steam turbine. Due to the finite clearance in these seals there is an inevitable leakage of gas or steam that results in lost potential to produce rotating shaft work in a turbine or increased shaft work required in a compressor. The rate of leakage is dependent upon the seal geometry, clearance, and pressure difference between the gas or steam inside the casing and the air outside the casing. 
     BRIEF DESCRIPTION OF THE INVENTION 
     A first aspect of the disclosure provides a machine comprising: a rotating shaft; a plurality of casings, each casing including: a part operably coupled to the rotating shaft and operable at a pressure greater than atmospheric pressure, and an end packing for partially sealing the respective casing to the rotating shaft; a sealed chamber fluidly coupling the first end packing and the second end packing, the sealed chamber having a third pressure greater than atmospheric pressure; and a bearing positioned within the sealed chamber between the first casing and the second casing for supporting the rotating shaft. 
     A second aspect of the disclosure provides a method comprising: providing a machine including a rotating shaft and a plurality of casings, each casing including: a part operably coupled to the rotating shaft and operable at a pressure greater than atmospheric pressure, and an end packing for partially sealing the respective casing with the rotating shaft; providing a standard positioned between two casings, the standard supporting a bearing for the rotating shaft; and sealing the standard in a sealed chamber fluidly coupling the two casings, the sealed chamber having a pressure greater than atmospheric pressure. 
     A third aspect of the disclosure provides a standard for supporting a bearing for a rotating shaft extending between a plurality of casings, each casing having a different pressure greater than atmospheric pressure, the standard comprising: a sealed chamber for fluidly coupling to an end packing of a first casing and a second casing, the sealed chamber having a pressure greater than atmospheric pressure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic diagram of a multiple casing steam turbine including a standard according to the disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a machine  100  including a standard  102  according to embodiments of the disclosure. Machine  100  includes a plurality of casings  104 ,  124 , each casing including a part  124 ,  126  operably coupled to a rotating shaft  108  and operable at a pressure greater than atmospheric pressure. In one embodiment, machine  100  takes the form of a steam turbine including a first casing  104  including a first turbine  106  operably coupled to a rotating shaft  108  and operable at a pressure greater than atmospheric pressure, i.e., about 14.7 pounds per square inch absolute (psia). In one example, first turbine  106  is a high pressure (HP) turbine that may operate, for example, at a first pressure P 1  ranging from about 1000 psia and about 3500 psia. First casing  104  also includes an end packing  110  for partially sealing the casing with rotating shaft  108 . Machine  100  may also include a second casing  124  including a second turbine  126  operably coupled to rotating shaft  108 . Second turbine  126  is operable at a second pressure greater than atmospheric pressure. In one example, second turbine  126  is an intermediate pressure (IP) turbine that may operate, for example, at a second pressure P 2  ranging from about 200 psia to about 600 psia. Consequently, the first pressure P 1  in first casing  104  is greater than the second pressure P 2  in second casing  124 . Second casing  124  also includes an end packing  130  for partially sealing the casing with rotating shaft  108 . As understood, other turbine(s) in more casings such as a low pressure (LP) turbine, not shown, may also be provided. 
     Each end packing  110 ,  130  includes a number of non-contacting seals such as leaf seals, brush seals, labyrinth seals, etc., that partially seal against rotating shaft  108  of steam turbine  100 . As understood, second end packings  110 ,  130 , however, do not completely seal casings  104 ,  124  with rotating shaft  108 . Conventionally, an area between end packings of a multiple casing steam turbine and the structure therein such as a standard for a bearing for supporting the rotating shaft are provided at atmospheric pressure. 
     In order to reduce leakage from casings  104 ,  124 , embodiments of the disclosure provide a sealed chamber  140  fluidly coupling first end packing  110  and second end packing  130 . Sealed chamber  140  may be provided in a number of ways such as a cover sealingly coupled to each end packing  110 ,  130  as part of standard  102 . Sealed chamber  140  is pressurized to a third pressure P SC  greater than atmospheric pressure. In one embodiment, the pressure within sealed chamber  140  ranges from about 300 psia to about 350 psia, e.g., 325 psia. Pressure within sealed chamber  140  may be slightly higher than that of second, lower pressure casing  124 , e.g., 20-100 psia greater. However, this is not necessary as the first and second pressures P 1  and P 2  may both be greater than the third pressure P SC . Standard  102  supports a bearing  142  for rotating shaft  108 . The gas within sealed chamber  140  may be different than that in casings  104 ,  124  (or the surrounding atmosphere) and may include, for example, air, an inert gas or a combination thereof. 
     Although particular pressures have been disclosed relative to casings  104 ,  124  and sealed chamber  140 , it is understood that the teachings of the disclosure are not to be limited to those particular pressures. The teachings of the disclosure can be applied to any steam turbine, compressor or other device having multiple casings penetrated by a rotating shaft having differences in pressure between casings. As understood, the structure of a compressor is very similar to that of a steam turbine as described herein. In the case of a compressor, a first compressor  106  (formerly first turbine) may operate at a first pressure P 1 , and a second compressor  126  (formerly second turbine) may operate at a second pressure P 2  greater than atmospheric pressure. In any event, the first pressure P 1  in first casing  104  is greater than the second pressure P 2  in second casing  124 . 
     Embodiments of the disclosure also provide a method including providing a machine  100  and a standard  102  and sealing the standard in sealed chamber  140  fluidly coupling the two casings, the sealed chamber having a pressure greater than atmospheric pressure. Embodiments of the disclosure also include standard  102  for supporting bearing  142  for rotating shaft  108  of machine  100 . In this case, standard  102  includes sealed chamber  140  for fluidly coupling to an end packing  110 ,  130  of first casing  104  and second casing  124  of the machine. Again, sealed chamber  140  has a pressure P SC  greater than atmospheric pressure. 
     The above described embodiments of the present disclosure increase the power output and efficiency of a machine such as steam turbine or gas compressor with split casings (e.g., high pressure and intermediate pressure). Increased output and efficiency results in greater performance of machine  100 . 
     It is emphasized that while the disclosure has been described relative to a steam turbine, that the teachings of the disclosure are applicable to any device with a rotating shaft that penetrates multiple pressurized casings and has a bearing between those casings, e.g., a gas compressor. 
     The terms “first,” “second,” and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another, and the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context, (e.g., includes the degree of error associated with measurement of the particular quantity). The suffix “(s)” as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term (e.g., the metal(s) includes one or more metals). Ranges disclosed herein are inclusive and independently combinable (e.g., ranges of “up to about 25 wt %, or, more specifically, about 5 wt % to about 20 wt %”, is inclusive of the endpoints and all intermediate values of the ranges of “about 5 wt % to about 25 wt %,” etc). 
     While various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made by those skilled in the art, and are within the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.