Abstract:
A method is provided for cooling a seal located in a wall of a chamber and through which a movable shaft passes, the seal being heated by hot pressurized vapor that leaks through the seal into the chamber and internal friction. The method comprises the steps of: providing a chamber in which the seal is located and into which the hot pressurized vapor leaks; injecting cool liquid into the chamber in which the seal is located; and cooling and condensing the hot pressurized vapor in the chamber thus cooling the seal.

Description:
TECHNICAL FIELD 
     This invention relates to a method of and apparatus for cooling a seal for machinery including rotating machinery, and more particularly, for cooling the seal of a turbine shaft. 
     BACKGROUND OF INVENTION 
     Rotating machinery, such as turbine in which wheels mounted on a shaft, require rotary seals in the region where the shaft passes through the pressure chamber that contains the turbine wheels. Such seals inhibit leakage of working fluid from the pressure chamber into the seal operating environment and then into the atmosphere. In addition, seals are also required in other machinery. 
     Seals for rotating machinery usually comprise a labyrinth seal followed by a mechanical seal. Labyrinth seals serve to restrict the rate of flow of working fluid and reduce its pressure toward atmospheric pressure, but not to prevent or contain the flow. Typically, labyrinth seals have many compartments positioned very close to the surface of the shaft for presenting to the working fluid in the pressure chamber a torturous path that serves to reduce pressure and inhibit, but not halt leakage. A mechanical seal, on the other hand, serves to contain the working fluid. The extent to which containment is achieved depends on the design of the seal and the nature of the working fluid involved. 
     When the working fluid is steam, some escape of the working fluid can be tolerated. Nevertheless, a shaft seal for the steam turbine is a critical item. It is even more critical when the working fluid is a hydrocarbon, such as pentane or isopentane, and the turbine operates as part of an organic Rankine cycle power plant. In such case, the mechanical seals must preclude to as great an extent possible the loss of working fluid to the atmosphere. Reliable operation of the mechanical seals for turbines, as well as for other types of equipment where the temperature of the mechanical seal is elevated, requires the seals to operate under optimum working conditions of pressure, temperature, vibration, etc. These working conditions have a significant impact on seal leakage rates and seal life expectancy, for example. By extending seal life, turbine life and hence reliability is extended. 
     Seal life is adversely affected by high operating pressure and temperature that tends to distort seal faces. High operating pressure also increases wear rate, heat generated at the seal faces which further distorts seal faces and results in increased leakage. In addition, the high pressure increases power consumption for the turbine sealing system. 
     In a related system, described in U.S. Pat. No. 5,743,094, the disclosure of which is incorporated by reference, a method of and apparatus for cooling a seal for machinery is disclosed. In the system and apparatus disclosed in the &#39;094 patent, a cooled surroundings is produced in the seal operating environment in which a mixture of cooled liquid droplets and vapor is present. This mixture is supplied to the condenser of the power plant unit for condensing the vapor present in the mixture. Such a system, thus requires a condenser for condensing the cooled mixture present in the seal-operating environment, 
     High operating temperatures of the seal components adversely affect seal life. High seal component temperatures increase wear on the seal faces, and also increase the likelihood that the barrier fluid when used will boil. It is therefore an object of the present invention to provide a new and improved method of and apparatus for cooling the seals for equipment. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In accordance with the present invention, a method is provided for cooling a seal located in a wall of a chamber and through which a movable shaft passes, the seal being heated by hot pressurized vapor that leaks through the seal into the chamber and internal friction. The method comprises the steps of: (a) providing a chamber in which the seal is located and into which the hot pressurized vapor leaks; (b) injecting cool liquid into the chamber in which the seal is located; and (c) cooling and condensing the hot vapor in the chamber thus cooling and reducing the pressure in the chamber surrounding the seal. Preferably, the method includes the step of providing a pressure chamber for containing the hot pressurized vapor within which a turbine wheel is mounted on the shaft, and vapor leaks past a labyrinth mounted on the shaft between the turbine wheel and the seal. Also, preferably, the method additionally comprises the step of adding the liquid to the chamber in which the seal is located by injecting the liquid into the chamber near a disc mounted in the chamber, the disc being mounted on, and rotatable with, the shaft. Furthermore, the method, preferably, in addition can be used in a power plant that includes a vaporizer for vaporizing a working fluid, a turbine mounted on the shaft for expanding the working fluid, a condenser for condensing expanded working fluid, and a cycle pump for returning condensate from the condenser to the vaporizer, and comprises the step of supplying the liquid exiting the chamber to a line exiting the condenser and connected to the cycle pump. Moreover, the method furthermore, preferably includes comprising the step of adding the liquid to the chamber in which the seal is located from the output of the cycle pump. 
     Furthermore, according to the present invention, apparatus is also provided for cooling a seal located in a wall of a chamber and through which a movable shaft passes, the seal being heated by hot pressurized vapor that leaks through the seal into the chamber in which the seal is located and internal friction. The apparatus comprises a chamber in which the seal is located and into which leaks the hot pressurized vapor and means for injecting liquid into the chamber such that the hot pressurized vapor is cooled and condenses in the chamber, thus cooling and reducing the pressure in the chamber surrounding the seal. Preferably, the apparatus also includes a turbine wheel mounted on the shaft in the pressure chamber containing hot pressurized, vaporized working fluid, wherein the shaft passes through a labyrinth seal mounted on the shaft. Also, preferably, the apparatus additionally comprises means for adding the liquid to the chamber in which the seal is located near a disc in the chamber mounted on the shaft and rotatable therewith. Furthermore, the apparatus, preferably, in addition can be used in a power plant that includes a vaporizer for vaporizing a working fluid, a turbine mounted on the shaft for expanding the working fluid, a condenser for condensing expanded working fluid, a cycle pump for returning condensate from the condenser to the vaporizer and means for supplying the liquid exiting the chamber to a line exiting the condenser and connected to the cycle pump. Moreover, the apparatus further preferably includes a supply means for supplying the liquid from the output of the cycle pump is the means or injecting liquid into the chamber in which the seal is located. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention are described by way of example with reference to the accompanying drawings wherein: 
         FIG. 1  is a black diagram of a power plant into which the present invention is incorporated; 
         FIG. 2  is a pressure enthalpy diagram showing the sources of fluid that contribute to heating and cooling the seal; 
         FIG. 3  is a side view, partially in section, showing one embodiment of the present invention; 
         FIG. 4  is a side view of a modification of the embodiment shown in  FIG. 3 ; 
         FIG. 5  is a side view of a further modification of the embodiment shown in  FIG. 3 ; and 
         FIG. 6  is a block diagram of an embodiment of the present invention and also shows another power plant into which the present invention is incorporated. 
     
    
    
     Like reference numerals and designations in the various drawings refer to like elements. 
     DETAILED DESCRIPTION 
     Referring now to the drawings, reference numeral  10  of  FIG. 1  designates a power plant into which the present invention is incorporated. Power plant  10  includes vaporizer  12  for vaporizing a working fluid, such as water, or a heat transfer working fluid (e.g., Dowtherm J, or Therminol LT, etc.), and producing vaporized working fluid that is supplied to turbine  14 . Usually, turbine  14  will be a multistage turbine, but the principle of the invention is applicable to a single stage turbine as well. 
     Vaporized working fluid supplied to turbine  14  expands in the turbine and produces work that is converted into electricity by a generator (not shown). The cooled, expanded working fluid is exhausted into indirect condenser  16  wherein the vaporized working fluid is condensed by the extraction of heat in the coolant supplied to the condenser. The condensate, at a relatively low pressure and temperature, as compared to the conditions at the outlet of the vaporizer, is pressurized by cycle pump  18  and returned to the vaporizer, completing the working fluid cycle. 
     Seal  20 , which is the seal between the atmosphere and the pressure chamber (not shown) containing the stages of the turbine, is contained in a seal chamber that is isolated from the pressure chamber by a labyrinth seal (not shown) and from the atmosphere by the mechanical seal (not shown). This mechanical seal has to be cooled. As shown, cool liquid working fluid is supplied to the seal chamber by cycle pump  18  through valve  22  in connection  19 , and the chamber is connected to vessel  21  by connection  17 . Furthermore, seal chamber  20  is connected via line  24  and a restricting orifice to a low-pressure region, e.g. the turbine exhaust limiting the seal chamber pressure and for venting non-condensable gases (NCG&#39;s) from the seal chamber in case NCG&#39;s accumulate in the seal chamber. 
     When power plant  10  is an organic Rankine cycle power plant, operating with a heat transfer working fluid like Therminol LT, for example, as the working fluid, the conditions in the condenser typically will be about 350° F. at about 15 psia, and the conditions at the outlet of the cycle pump typically will be about 350° F. at about 200 psia. 
     The actual conditions in the seal chamber can be controlled by valve  22  by regulating the flow of cool liquid working fluid to the seal chamber. Typically, working fluid vapor leaking through the labyrinth seal into the seal is at about 40 psia and about 550° F. Under these conditions, the cooler liquid, which is supplied via valve  22 , will interact with the leakage vapor thus cooling and condensing the same by directly transferring heat to the liquid in the seal chamber thus preventing the heating of the seal chamber and reducing the pressure therein. This has the beneficial effect of reducing the temperature of the seal itself without directly cooling the seal with the liquid working fluid. In addition, NCG venting/pressure limiting line  24  vents NCG&#39;s (if present) from seal chamber  20  and controls their accumulation therein. By connecting line  24  to a low-pressure region e.g. the turbine exhaust, the pressure in seal chamber  20  can be limited. 
     The operation described above is illustrated by FIG.  2 . As indicated, leakage of vapors from the pressure chamber of the turbine whose conditions are indicated by point  22  to the seal chamber whose conditions are indicated by point  24  result in a pressure reduction inside the seal chamber which is held at the conditions of vessel  21  indicated by point  26 . The condition of liquid working fluid furnished by cycle pump  18  to the seal chamber, indicated by point  28 , changes from point  28  to point  26 . Condensate produced in the seal chamber is supplied to vessel  21  and pump  23  supplies the condensate from vessel  21  to the exit of condenser  16  indicated by point  29 . Based on this schematic showing, the heat balance is as follows:
     (1) m liq ×h liq +m vapor ×h vapor =m cond ×h cond      where m liq =cold liquid flow rate   h liq =enthalpy of cold liquid   m vapor =vapor leakage flow rate   h vapor =vapor enthalpy   m cond =m liq +m vapor      h cond =enthalpy of condensate at vessel pressure and required condensate temperature.   

     Specific details of one embodiment of the invention is shown in  FIG. 3  to which reference is now made where reference numeral  30  designates apparatus according to the present invention incorporated into turbine  14 A. Apparatus  30  includes seal chamber  20 A in the form of seal chamber  32 , defined by housing  34  rigidly attached to stationary mounting  36  containing bearing  38  on which shaft  40  of turbine wheel  41  is mounted by a suitable key arrangement. A housing that defines a high-pressure housing or chamber  43  containing hot pressurized working fluid vapors contains wheel  41 . 
     Labyrinth seal  42  mounted in face  44  of housing  34  provides the initial resistance to leakage of the hot vaporized working fluid in chamber  43  into seal chamber  32 . Such leakage is indicated by chain arrows A and B. Normally, this leakage would heat mechanical seal  46  having sealing faces carried by, and rotating with, shaft  40 . This face is in contact with a stationary sealing face carried by hub  48  rigidly attached to housing  36 . Normally, both stationary and rotating or dynamic seal faces are cooled by a barrier fluid, e.g., pressurized mineral oil pressurized to about 15 psi above the maximum seal chamber pressure (e.g., about 30 to 40 psia in the present embodiment). 
     Seal chamber  32  is connected by connection  50  to vessel  21 . This chamber is also connected via connection  52  to the output of cycle pump  18  as shown in FIG.  1 . Pressurized liquid working fluid at the temperature substantially of the condenser is supplied via connection  52  to spray head nozzles  54  that open to the interior of seal chamber  32 , and relatively cold liquid working fluid is sprayed onto cylindrical shield  56  further converting the liquid into fine droplets inside seal chamber  32 . The fine droplets interact with hot vapor leakage B thereby cooling this hot vapor by means of direct contact heat transfer of heat in the vapor to liquid contained in the droplets and condensation of the hot vapor takes place thus producing a liquid including the working fluid condensate that is vented and drained by connection  17  into vessel  21 . As a result, the temperature of mechanical seal  46  can be maintained at a desired temperature by regulating the amount of liquid supplied to connection  52 . Shield  56  shields mechanical seal  46  from direct contact with cool liquid from the condenser and thus projects the seal against thermal shock. 
     The preferred embodiment of the present invention is described with reference to  FIG. 4 , considered at present the best mode for carrying out the present invention, and is designated by reference numeral  60 . This embodiment includes turbine wheel  41 A rigidly attached to shaft  40 A that passes though housing  34 A, and mechanical seal  46 A inside seal chamber  32 A. Instead of labyrinth seal  42  engaging shaft  40  directly, as in the embodiment of  FIG. 3 , seal  42 A engages hub  62  rigidly attached to the shaft. However, the labyrinth seal may engage the shaft if preferred. Hub  62  includes flange  64  that lies inside seal chamber  32 A close to face  44 A of housing  34 A and thus rotates together with shaft  40 A. Conduit  52 A in face  44 A carries liquid working fluid from the cycle pump to nozzle  54 A opening to seal chamber  32 A and facing flange  64 . 
     Pressurized cold working fluid liquid from the cycle pump is sprayed into contact with flange  64  producing a spray of fine droplets which are carried by centrifugal force into seal chamber  32 A by reason of the rotational speed of the flange. In addition, leakage of vaporized working fluid A through seal  42 A encounters the spray of cold liquid as soon as the vaporized working fluid passes through seal  42 A so that most of leakage B is cooled before entering seal chamber  32 A. This embodiment provides rapid engagement of the hot vapor leaking into seal chamber  32 A with cold working fluid, and the rotational movement of flange  64  ensures intimate mixing of the spray of cold liquid with leakage vapors so that the hot vapor is cooled and condensed in seal chamber  32 A. Consequently, a liquid containing condensate is produced that drains to vessel  21  and pump  23  supplies this liquid to the exit of condenser  16 . 
     A further embodiment is described with reference to FIG.  5  and numeral  65  designates apparatus For cooling a seal. This embodiment is similar in many respects to the embodiment described with reference to  FIG. 4  wherein, in this embodiment, cooled working fluid is injected into chamber  32 B via conduit  52 B in face  44 B carrying liquid working fluid from the cycle pump so that it also impinges on flange or disc  64 . However, in this embodiment, cooled working fluid liquid is injected via labyrinth seal  42 B into seal chamber  32 B at spray  54 B as well as delivered in the opposite direction via labyrinth seal  42 B to spray  53 B so that the leakage of hot, high pressure working via this labyrinth seal is eliminated or at least reduced. Also in this embodiment, liquid containing condensate is produced in seal chamber  32 B that drains to vessel  21  and pump  23  supplies this liquid to the exit of condenser  16 . 
     Reference numeral  10 E of  FIG. 6  designates a further power plant into which the present invention is incorporated, power plant  10 E comprising intermediate fluid turbine  14 E and organic working fluid turbine  74 E. In this arrangement, vapor from heat recovery vapor generator  40 E is supplied to the inlet of turbine  14 E via line  13 E and the exhaust therefrom is supplied to recuperator  15 E with the vapors exiting recuperator  21 E being supplied to condenser/vaporizer  16 E. A more complete description of the operation of this arrangement can be found in U.S. patent application Ser. No. 09/902,802, filed Jul. 12, 2001, the disclosure of which is hereby incorporated by reference. High-pressure seal chamber  20 E, associated with intermediate fluid turbine  14 E, is supplied with cool condensate from condenser/vaporizer  16 E by pump  18 E via flow conditioning apparatus  19 E. Apparatus  19 E serves to properly regulate the flow of condensate liquid working fluid to seal chamber  20 E, to isolate the flow of cool condensate to the seal chamber of intermediate turbine  14 E, and to allow maintenance to the apparatus without interrupting the operation of the turbines. 
     In this embodiment, the preferred working fluid used in the intermediate fluid turbine  14 E is Therminol LT or Dowtherm J. The working fluid used in organic working fluid turbine  74 E and its associated working fluid cycle can be pentane, i.e. n-pentane or iso-pentane, or other suitable hydrocarbons. 
     Apparatus  19 E includes manually operated, variable, flow control valve  22 E, a fixed orifice device (not shown), a filter (not shown), and an on/off, or shut-off valve (not shown) serially connected together, and temperature indicator  27 E. The size of the fixed orifice, together with the setting of valve  22 E, determines the flow rate of cool condensate or liquid working fluid to seal chamber  20 E. The filter serves to filter from the condensate supplied to the seal chamber any contaminants whose presence would adversely affect the operation of the seal chamber. The on/off, or shut-off valve is preferably a manually operated ball-valves that can be selectively operated to disconnect the seal chamber from pump  18 E when filter replacement or other maintenance operations are necessary allowing the turbine to run for a short time without cooling of the seal chamber and until these maintenance operations are completed. Furthermore, maintenance operations performed when the turbine or power plant is shut down or stopped are simplified by this aspect of the present invention. Finally, the temperature indicators provide an indication of the temperature of the fluid exhausted from seal chamber  20 E. 
     Valve  22 E is manually operated, preferably in accordance with the temperature of the fluid in line  17 E. That is to say, the amount of cooling condensate applied to seal chamber  20 E can be adjusted by an operator by changing the setting of valve  22 E in response to the temperature indicated by the temperature indicator. Optionally, temperature sensors or transducers that produce control signals in accordance with the temperature of the cooling liquid leaving the seal chamber can replace the temperature indicators. In such case, valve  22 E could be replaced with a valve that is responsive to such control signals for maintaining the proper flow rate of cooling liquid to seal chamber  20 E. 
     While the embodiments described above refer to a chamber as a form of the operating seal environment, any suitable enclosure may be used. 
     Furthermore, while the above description refers to the working fluid as a organic working fluid, the present invention can also be used with connection to steam such as in a steam turbine system using for example a gland condenser. For example, cool steam condensate can be pumped from the cycle pump to the seal of the steam turbine chamber via a conduit or line in order to cool and condense by directly contacting the high-pressure steam leaking across the seal. According to the present invention, a further conduit or line can be provided for collecting the liquid water from the seal and supply it to an accumulation vessel and thereafter to the cycle pump. 
     In addition, when an organic working fluid is used as the working fluid in the Rankine cycle power plant such as the one described with reference to  FIGS. 1 and 6  in the intermediate fluid turbine  14 E and its associated working fluid cycle (as well as the working fluids used in the embodiments described with reference to  FIGS. 2 ,  3 ,  4  and  5 ) the working fluid is preferably chosen from the group bicyclic aromatic hydrocarbons, substituted bicyclic aromatic hydrocarbons, heterocyclic aromatic hydrocarbons, substituted heterocyclic aromatic hydrocarbons, bicyclic or heterobicyclic compounds where one ring is aromatic and the other condensed ring is non-aromatic, and Their mixtures such as napthalene, 1-methyl-napthalene, 1-methyl-napthalene, tetralin, quinolene, benzothiophene; an organic, alkylated heat transfer fluid or a synthetic alkylated aromatic heat transfer fluid, e.g. thermal oils such as Therminol LT fluid (an alkyl substituted aromatic fluid), Dowtherm J (a mixture of isomers of an alkylated aromatic fluid), isomers of diethyl benzene and mixtures of the isomers and butyl benzene; and nonane, n-nonane, iso-nonane, or other isomers and their mixtures. The most preferred working fluid used is an organic, alkylated heat transfer fluid or a synthetic alkylated aromatic heat transfer fluid, e.g. thermal oils such as Therminol LT fluid (an alkyl substituted aromatic fluid), Dowtherm J (a mixture of isomers of an alkylated aromatic fluid), isomers of diethyl benzene and mixtures of the isomers and butyl benzene. 
     The advantages and improved results furnished by the method and apparatus of the present invention are apparent from the foregoing description of the preferred embodiment of the invention. Various changes and modifications may be made without departing from the spirit and scope of the invention as described in the appended claims.