Patent Application
20080001363
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
As discussed in detail below, embodiments of the present invention provide a rotary machine (for example, an electric generator, a gas turbine, or the like) in which a brush sealing system is disposed between a stationary component and a rotary component. The sealing system includes a holding device coupled to the stationary component. The exemplary sealing system includes a plurality of carbon fibers or bristles coupled to the holding device and configured to contact the rotary component. In accordance with aspects of the present invention, the parameters (such as friction coefficient, thermal conductivity, temperature capability, or the like) of the carbon fibers are chosen so as to maintain minimal clearances between the rotary component and the surrounding stationary component resulting in reduced fluid leakage and increased efficiency of the rotary machine. The bristle material also facilitates minimizing interface temperature between the sealing system and the rotary component during operation of the machine. Specific embodiments of the present invention are discussed below referring generally to
Referring to
In the illustrated embodiment, the rotary machine 10 includes a stator 16, and a rotor 18 coaxially aligned with the stator 16. The rotor 18 is radially spaced apart from the stator 16 to define a gap 20 between the stator 16 and the rotor 18. Although in the illustrated embodiment, the stator 16 circumferentially surrounds the rotor 18, certain other applications require the rotor to circumferentially surround the stator as known to those skilled in the art. A fluid 21 is disposed in the gap 20 in such a way that the fluid 21 has a pressure drop generally transverse to the gap 20. The pressure drop is generated during operation of the machine 10. The brush seal 12 in accordance with aspects of the present invention includes a plurality of graphite or carbon bristles 22 configured to contact the rotor 18 to reduce leakage of fluid and also reduce temperature at a seal-rotor interface. The brush seal 12 is explained in greater detail with respect to subsequent figures below.
Referring to
Referring to
Typically, the conventional brush sealing system is configured to contact the rotor 18 thereby generating frictional heat at the seal-rotor interface during operation of the machine. The heat generated at the seal-rotor interface may be dissipated by convection, conduction through the brush seal, conduction through the rotor, or the like. When conventional brush seals are used, temperature at the seal-rotor interface increases, resulting in expansion of the rotor 18. The rotor expansion leads to higher interference between the brush seal and the rotor 18 causing brush seal wear and increased leakage of fluid between the rotor 18 and the stator. This reduces efficiency of the rotary machine.
The carbon bristles 22 in accordance with aspects of the present invention facilitates minimizing seal wear and maintaining temperature at the seal-rotor interface minimum. In certain exemplary embodiments, the brush seal 12 has the following parameters in order maintain a minimum temperature at seal-rotor interface. One effective bristle material of the brush seal has a friction coefficient less than 0.25, thermal conductivity greater than 8 watts per meter-kelvin (W/mK), and a temperature capability greater than 700 degrees fahrenheit. It should be noted that the values of the above mentioned parameters are exemplary values and should not be construed as limiting values. The combination of friction coefficient and thermal conductivity parameter of the bristle material of the brush seal 12 facilitates minimizing rotor expansion and ensuring adequate heat dissipation via conduction through the seal 12. The temperature capability parameter of the bristle material of the brush seal 12 facilitates minimizing seal wear resulting from higher temperature at the rotor-seal interface. In certain exemplary embodiments, the bristle material includes carbon or graphite. In certain other exemplary embodiments, the seal material may include other non-metallic material. In accordance with aspects of the present invention, the diameter of each bristle is maintained in the range of 0.1 to 1 mils so that a clearance of 0.1 mils may be maintained between the brush seal 12 and the rotor 18.
Referring to
An exemplary brush seal 64 is provided in the packing ring segment 52. The brush seal 64 in accordance with aspects of the invention includes a plurality of circumferentially extending array of carbon bristles 66 provided between a pair of side plates 68, 70. The side plate 68 extends short of the rotary component surface whereas the other side plate 70 forms a tapered tooth 69 similar to the tapered tooth 60 of the labyrinth seal. The tapered tooth 60 forms part of the labyrinth seal and also forms a backing plate at a low pressure side of the bristles 66. The tips of the bristles 66 are configured to contact the rotary component 58 forming a brush seal therewith. The brush seal 64 is provided in a groove, which extends circumferentially in the packing ring segment 52. In accordance with aspects of the present invention, each carbon bristle 66 has a diameter in the range of 0.1 to 1 mils. The carbon bristles 66 facilitate to minimize seal wear and maintain temperature at the seal-rotary component interface minimum. In certain exemplary embodiments, the carbon bristles have the following properties: strength-900 Ksi (kilopounds per inch squared), fiber modulus-19 Msi (Megapounds per inch squared), elongation-2%, service temperature-930 degrees fahrenheit, thermal conductivity-11.8 W/mK (watts per meter-kelvin). Smaller diameter of carbon bristles results in lower effective clearance at the seal-rotary component interface, and also lower stiffness resulting in lower heat generation. Greater strength of the carbon bristles results in greater stress capability. Higher thermal conductivity of the carbon bristles results in lower temperature at the seal-rotary component interface.
In certain exemplary embodiments, a plurality of springs may be provided between axially opposite flanges 51 of the packing ring segment 52 and the hook flanges 56 of the groove 46. The springs are configured to displace the packing ring segment radially outwards. Pressurized fluid may be introduced into the groove 46 via a passage 63 provided in the stationary component 48 for displacing the packing ring segment 52 radially inwards, for example, during steady state operating conditions of the rotary component 58 to effectively seal between high and low pressure regions 65, 67 respectively of the machine. In certain exemplary embodiments, the bristles 66 may be provided side-by-side along both circumferential and axial directions thereby providing a tortuous path between the bristles 66 for fluid flow between high and low pressure regions 65, 67 respectively of the machine.
Referring now to
As discussed previously, in certain exemplary embodiments, bristle material of the brush seal 64 has a friction coefficient less than 0.25, thermal conductivity greater than 8 watts per meter-kelvin (W/mK), and a temperature capability greater than 700 degrees fahrenheit. The combination of friction coefficient and thermal conductivity parameter of the bristle material of the brush seal 64 facilitates minimizing rotor expansion and ensuring adequate heat dissipation via conduction through the seal 64. The temperature capability parameter of the bristle material of the brush seal 64 facilitates minimizing seal wear resulting from higher temperature at the rotary component-seal interface.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
