Abstract:
In a steam turbine plant having a vacuum pumping configuration which has a jet pump and a liquid ring pump disposed in series one after the other, steam collecting in the plant, preferably mixed with air, is used as a motive fluid for the jet pump. As a result, the downstream liquid ring pump can be dimensioned so as to be comparatively small. The vacuum pumping configuration is preferably configured as a central vacuum pumping system for the steam turbine plant and serves to deaerate a multiplicity of plant components.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application is a continuation of copending International Application No. PCT/DE01/03673, filed Sep. 24, 2001, which designated the United States and was not published in English. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    Field of the Invention  
           [0003]    The invention relates to a steam turbine plant having a vacuum pumping configuration that has a jet pump and a liquid ring pump disposed in series one after the other. The invention also relates to a method of operating a steam turbine plant, in which a plant component is deaerated by use of a vacuum pumping configuration which has a jet pump and a liquid ring pump disposed in series one after the other.  
           [0004]    In a steam turbine plant, for example in the field of power generation, a main turbine plant having a plurality of turbine stages is provided as a rule in order to utilize as effectively as possible the energy content of the steam provided. As a rule, high-capacity steam turbine plants have a high-pressure stage, an intermediate-pressure stage and a low-pressure stage, steam heated in a boiler is fed to the high-pressure stage and expands in the direction of the low-pressure stage. At the end, the low-pressure stage has a vacuum in the order of magnitude of between 18 mbar and 80 mbar. The steam discharging from the low-pressure stage is fed to a condenser and is condensed there.  
           [0005]    The gas quantity collecting during the condensing in the condenser must be drawn off from the latter. Provided for this purpose is a vacuum pumping configuration, which, on account of the low final pressure at the low-pressure stage, must reach a vacuum of, for example, ≦18 mbar on the suction side. On account of the steam quantity which collects in the steam turbine plant and which is large as a rule, the vacuum pumping configuration must be configured for drawing off a large gas quantity of a delivery gas from the condenser in order to deaerate the latter.  
           [0006]    Furthermore, in a steam turbine plant for a large power plant, an auxiliary turbine for a feed water supply to the boiler is normally provided, the auxiliary turbine having, for example, an output of 20 MW, compared with an output of the main turbine plant of about 1 GW. A condenser, which must be deaerated, is likewise assigned to the auxiliary turbine.  
           [0007]    As a rule, the respective condenser contains a tube system, to which the steam to be condensed is admitted from the turbine. The steam is cooled by water, which is fed to the condenser via a “water chamber”. In order to maintain the operability of the condenser, the water chamber must also be deaerated. On account of the different requirements for the deaerating capacity with regard to the condenser for the low-pressure stage, for the auxiliary turbine, and with regard to the water chamber of the condenser, a separate vacuum pumping configuration is currently provided for each of the three subsystems.  
           [0008]    For deaerating a condenser of a steam turbine, British Patent GB 1 542 483 discloses a vacuum pumping configuration in which a jet pump and a liquid ring pump are provided in series one after the other. The motive fluid provided for the jet pump is air. The vacuum to be achieved is improved by connecting the jet pump upstream of the liquid ring pump. A vacuum of about 50 mbar can typically be achieved with a liquid ring pump. A vacuum of up to &lt;15 mbar can be achieved with the entire system by connecting a jet pump upstream.  
           [0009]    In the system formed of the jet pump and the liquid ring pump there is generally the problem that the liquid ring pump has to be configured for both the quantity of the actual delivery gas to be drawn off plus the quantity of the motive fluid for the jet pump. In this case, the requisite quantity of motive air for an air-operated jet pump is many times higher than the quantity of delivery gas to be drawn off from the condenser. For example, in order to compress a delivery-gas mass flow from a condenser, formed of a mixture of about 15 kg/h of air and 35 kg/h of steam, from about 40 mbar to 125 mbar by the jet pump, a working-air mass flow of about 200 kg/h is required. On account of this high air proportion, the liquid ring pump is to be configured for dry air as the delivery gas. This reduces the capacity of the liquid ring pump, compared with moist air as the delivery gas.  
           [0010]    A liquid ring pump and its operating principle can be seen, for example, from the Siemens brochure titled “ELMO-L2BL1-luftgekühlt, õlfrei: die neue Generation von Vakuumpumpen” [ELMO-L2BL1—Air-Cooled, Oil-Free: The New Generation Of Vacuum Pumps], Siemens Aktiengesellschaft Germany, 12/98, Order No.: E20001-P782-A208, or from the Internet at http:\\www.ad.siemens.de/elmo (status August 2000). The liquid ring pump described has an impeller sitting eccentrically in a housing. By the impeller rotation, an operating medium, as a rule water, forms a water ring revolving with the impeller in the housing. On account of the eccentric configuration of the impeller, sectional spaces of different size form between the impeller hub and the water ring revolving with the impeller, and the medium to be pumped is compressed in the sectional spaces.  
           [0011]    Furthermore, the combination of a jet pump with a downstream liquid ring pump has been disclosed, for example, by Published, European Patent Application EP 0 088 226 A2, U.S. Pat. No. 4,484,457 A and Published, Non-Prosecuted German Patent Application DE 29 13 960 A1. According to EP 0 088 226 A2, the liquid ring pump is operated with oil as the operating medium, which is heated up to a temperature of about 130° C. In order to utilize the energy stored in the oil, provision is made to evaporate water via a heat exchanger and to feed the steam as the motive fluid to the jet pump. A separate supply of motive fluid is therefore not necessary in the system. However, the system is restricted to oil-operated liquid ring pumps, in which the oil can be heated to temperatures above 100° C. As a rule, the liquid ring pumps are operated with water, which is normally heated up to about 35° C. at most, as can be seen from the above-mentioned Siemens brochure.  
           [0012]    The interaction of a liquid ring pump with a turbine has also been disclosed by U.S. Pat. No. 4,484,457, which claims the same priority as EP 0 088 226 A2.  
           [0013]    According to Published, Non-Prosecuted German Patent Application DE 29 13 960 A1, air is fed as motive fluid to the jet pump from a separator assigned to the liquid ring pump. In this case, the air extracted from the separator is dehydrated so that air that is as dry as possible is fed to the jet pump.  
           [0014]    A jet pump to which steam is fed as the motive fluid has been disclosed, for example, by U.S. Pat. No. 3,481,529. A liquid ring pump is connected directly downstream of the jet pump.  
         SUMMARY OF THE INVENTION  
         [0015]    It is accordingly an object of the invention to provide a steam turbine plant, and a method of operating the steam turbine plant that overcome the above-mentioned disadvantages of the prior art devices and methods of this general type, which permits a cost-effective operation of a steam turbine plant in a simple installation.  
           [0016]    With the foregoing and other objects in view there is provided, in accordance with the invention, a steam turbine plant. The plant contains a vacuum pumping configuration having a jet pump and a liquid ring pump disposed in series one after another, a sealing steam circuit for a turbine seal, and a steam line connected to the sealing-steam circuit and provided for feeding steam, collecting in the steam turbine plant, as a motive fluid for the jet pump. The steam line connected to the jet pump.  
           [0017]    The object is achieved according to the invention by a steam turbine plant having a vacuum pumping configuration which has a jet pump and a liquid ring pump disposed in series one after the other, a steam line for feeding steam, collecting in the plant, as the motive fluid for the jet pump being connected to the jet pump.  
           [0018]    The steam used in this case is in particular excess steam in order not to impair the efficiency of the steam turbine plant. The use of steam as the motive fluid has the decisive advantage that, as a result, the quantity of noncondensable motive fluid required is markedly reduced compared with the motive air normally used. As a result, it is possible to configure the liquid ring pump disposed downstream of the jet pump for markedly smaller mass flows, so that considerable cost savings can thereby be achieved. This is because, through the use of steam or of steam/air mixture under atmospheric pressure as the motive fluid, the power requirement with regard to the mass flow to be delivered by the liquid ring pump decreases by about 40-50%, since the vaporous mass proportion in the liquid ring pump condenses and does not have to be compressed to atmospheric pressure.  
           [0019]    The steam line via which steam is fed as the motive fluid to the jet pump is expediently connected to a sealing-steam circuit for a turbine-shaft sealing system.  
           [0020]    To seal the rotating turbine shaft, a labyrinth seal, through which “sealing steam” is directed, is provided as a rule. After leaving the turbine seal, the sealing steam is also referred to as low-tension steam. The low-tension steam is a “waste product” collecting in the steam turbine plant and is therefore especially suitable for use as motive fluid under atmospheric pressure without impairing the efficiency of the steam turbine plant.  
           [0021]    In addition, the feeding of the low-tension steam to the vacuum pumping configuration also has the decisive advantage that the low-tension steam—due to the principle of the liquid ring pump—condenses. The condensing system, normally provided in a steam turbine plant, for the low-tension steam is therefore not necessary. As a result, investment costs can be saved, and in addition the requisite installation requirement is reduced compared with conventional steam turbine plants.  
           [0022]    A gas line for admixing air for forming a steam/air mixture as motive fluid for the jet pump is expediently connected to the steam line. This results in especially efficient operation for the jet pump. In particular, an approximately uniform mass flow distribution between air and steam is set for the mixture. In addition, the admixing of air has the advantage that the requisite quantity of motive fluid can be set in a simple manner, in particular when the quantity of low-tension steam is limited, so that the steam quantity alone is not sufficient as the motive fluid.  
           [0023]    In this case, the gas line, with its further end, is expediently connected on the pressure side to the liquid ring pump and in particular to a separator assigned to the liquid ring pump. The air compressed to atmospheric pressure by the liquid ring pump is therefore also used as the motive fluid. This has the advantage that a separate compressor for feeding the jet pump is not required.  
           [0024]    According to an expedient configuration, the vacuum pumping configuration is connected to a condenser via a first deaerating line for deaerating the condenser, which is provided for condensing process steam discharging from a steam turbine, in particular from a low-pressure part of a steam turbine.  
           [0025]    The vacuum pumping configuration is at the same time preferably connected via a second deaerating line to a second condenser, which is assigned to an auxiliary turbine. Thus preferably both the condenser of the main turbine and that of the auxiliary turbine are deaerated via the same vacuum pumping configuration. A plurality of vacuum pumping configurations assigned to the individual condensers are therefore not necessary.  
           [0026]    As a rule, the condenser, for a cooling liquid, has a water chamber, which, in order to deaerate it, is preferably connected to the vacuum pumping configuration via a third deaerating line.  
           [0027]    A uniform, central vacuum pumping system in the form of the vacuum pumping configuration is therefore provided, and the vacuum pumping system provides a vacuum for a multiplicity of components in the steam turbine plant. As a result, the installation cost and also the maintenance cost with regard to the vacuum pumping system are markedly reduced compared with a multiplicity of decentral vacuum pumping systems.  
           [0028]    To deaerate the water chamber, the third deaerating line is preferably connected to an additional port of the liquid ring pump. Via the additional port, saturated water-chamber air being emitted from the cooling water is drawn off from the water chamber. This has the essential advantage that the quantity of saturated air drawn off from the water chamber is fed separately to the liquid ring pump and is not added to the delivery-gas quantity drawn off from the two condensers.  
           [0029]    In this case, the additional port is expediently disposed between a suction connection and a pressure connection of the liquid ring pump and is connected to a working or compression space forming during operation. The third deaerating line therefore feeds the saturated air from the water chamber to the liquid ring pump in an intermediate region between the suction connection and the pressure connection. In this region, a sufficient vacuum for deaerating the water chamber is still provided by the liquid ring pump. At the same time, however, the feeding at this point does not lead to an increase, or only leads to an imperceptible increase, in the power requirement of the liquid ring pump. Delivery capacity is provided by the liquid ring pump via the cavitation protection port virtually “for nothing”. When the third deaerating line is disposed at the additional port, the liquid ring pump therefore does not need to be of larger dimensions.  
           [0030]    The use of such an additional port as an additional suction connection is a basic principle here and is generally suitable for all liquid ring pumps and is not restricted to application in a steam turbine plant. A liquid ring pump having such an additional port is also suitable, for example, for deaerating a screen part on papermaking machines in the paper industry.  
           [0031]    In general, such a liquid ring pump is suitable for use in the field of papermaking. By suitable placing of the additional port between the suction connection and the pressure connection, and by the selection of the diameter of the additional port, the suction capacity can at the same time be varied within certain limits both with regard to the volumetric quantity and with regard to the vacuum to be achieved.  
           [0032]    Furthermore, the object is achieved according to the invention by a method of operating a steam turbine plant, in which a plant component is deaerated by a vacuum pumping configuration which has a jet pump and a liquid ring pump disposed in series one after the other, steam collecting in the steam turbine plant, in particular excess steam, being fed as motive fluid to the jet pump.  
           [0033]    The advantages and preferred configurations recited with regard to the steam turbine plant can accordingly be applied to the method.  
           [0034]    Other features which are considered as characteristic for the invention are set forth in the appended claims.  
           [0035]    Although the invention is illustrated and described herein as embodied in a steam turbine plant, and a method of operating a steam turbine plant, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.  
           [0036]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0037]    [0037]FIG. 1 is an illustration of a steam turbine plant according to the invention; and  
         [0038]    [0038]FIG. 2 is a diagrammatic, sectional view through a liquid ring pump. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0039]    Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown a steam turbine plant  2  that has a steam turbine  4  which in particular is a low-pressure stage of a, for example, 3-stage main turbine plant. Such a multistage main turbine plant is used, for example, in power plants for the generation of power with an output within the gigawatt range. On an output side, the steam turbine  4  has a vacuum, which in a low-pressure stage is typically within a range of between 18 mbar and 80 mbar. Process steam P fed to the steam turbine  4  leaves the latter via output lines  6  and is fed to a first condenser  8 . The process steam P is condensed in the condenser  8 , the condensate being discharged via a discharge line  10  and fed again as feed water to a boiler (not shown in any more detail).  
         [0040]    During the condensing, a gas/steam mixture designated as delivery gas F collects in the first condenser  8  and is drawn off via a first deaerating line  12  by a vacuum pumping configuration  14 .  
         [0041]    Furthermore, the steam turbine plant  2  has an auxiliary turbine  16  that is configured in a similar manner to the steam turbine  4  but for a markedly lower output. The auxiliary turbine  16  is used in particular for driving a feed water pump and typically has an output of about 20 MW. In a similar manner to the steam turbine  4 , a second condenser  18  is assigned to the auxiliary turbine  16 , the process steam P fed to the auxiliary turbine  16  being condensed in the second condenser  18 . In a similar manner to the first condenser  8 , the condensate is discharged via a discharge line  10 . To deaerate the second condenser  18 , a second deaerating line  20  is provided, which is likewise connected to the vacuum pumping configuration  14 . Via the second deaerating line  20 , a gas/steam mixture is likewise pumped out of the second condenser  18  as the delivery gas F. In this case, the first deaerating line  12  opens into the second deaerating line  20 .  
         [0042]    The two condensers  8 ,  18  preferably have water as a cooling medium, which is stored in a water chamber  22  of the respective condenser  8 ,  18 . During operation of the condensers  8 ,  18 , an air cushion forms in the respective water chamber  22 . To deaerate at least the water chamber  22  of the first condenser  8 , a third deaerating line  24  is provided, which likewise leads to the vacuum pumping configuration  14 . In this case, the saturated air being emitted from the cooling water is drawn off from the water chamber  22  and is designated as water-chamber air WL.  
         [0043]    The vacuum pumping configuration  14  contains a jet pump  26  and a liquid ring pump  28  disposed downstream of the jet pump  26  in the direction of flow. To this end, the second deaerating line  20  is connected to a suction region  27  of the jet pump  26 , and the latter is connected on the output side to a suction connection  30  of the liquid ring pump  28 . The delivery gas F from the two condensers  8 ,  18  is thus first of all precompressed by the jet pump  26 . To this end, the jet pump  26  is operated with a motive fluid T that is fed externally and mixes with the delivery gas F. The pressure in the first condenser  8  and in the second condenser  18  is typically within a range which corresponds approximately to the output pressure of the steam turbine  4  and of the auxiliary turbine  16 , respectively. There is therefore a vacuum within a range of between 18 and 80 mbar in both condensers  8 ,  18 . Consequently the delivery gas F likewise has this vacuum. It is compressed approximately by the factor  3  in the jet pump  26  and then further up to ambient pressure in the liquid ring pump and is expelled via a pressure connection  34 .  
         [0044]    Furthermore, the liquid ring pump  28 , between the suction connection  30  and the pressure connection  34 , has an additional port  35 , to which the third deaerating line  24  is connected. In this case, the additional port  35  is disposed between an intake slot  70  and a pressure slot  72  (see FIG. 2) in non-illustrated “control disks” of the liquid ring pump  28 . Due to the operating principle of the liquid ring pump  28 , the pump mixture of the delivery gas F and the motive fluid T fed via the suction connection  30  mixes with the operating medium of the liquid ring pump  28 . In this case, the operating medium is water W. The latter together with condensate possibly collecting from the pump mixture is separated from air L in a separator  38 . The water W is fed again to the liquid ring pump  28  via a heat exchanger  40 . The air L is fed as the motive fluid T to the jet pump  26  via a gas line  42 , in which a valve  44  is connected. Excess air L is given off to the environment from the vacuum pumping configuration  14  via an exhaust-air line  46 .  
         [0045]    It is essential that, in addition to the air L, steam D is also fed as the motive fluid T to the jet pump  26  via a steam line  48 . A further valve  44  is connected in the steam line  48 . In this case, the steam line  48  is connected to a sealing-steam circuit  50  in which sealing steam S is directed through a number of turbine seals  52 . The turbine seals  52  in this case are assigned to the steam turbine  4  and to the auxiliary turbine  16  and are configured as labyrinth seals in order to seal off a rotating shaft of the turbines  4 ,  16  from the environment. After flowing through the turbine seals  52 , the sealing steam is also referred to as low-tension steam. The steam D is fed as the motive fluid T to the jet pump  26 . The motive fluid T is therefore a steam/air mixture, it being possible for the respective proportions of the steam D and of the air L to be set via the two valves  44 . An equal distribution between steam D and air L is preferably set. If an adequate steam quantity is available, steam D may also be used exclusively as the motive fluid T. Since the low-tension steam is excess steam collecting in the steam turbine plant  2 , the overall efficiency of the steam turbine plant  2  is not impaired by use of the low-tension steam as the motive fluid T. In addition to the use of the low-tension steam, other types of steam collecting in the steam turbine plant are also suitable. For example, the steam collecting in the sealing-steam system for control purposes and normally discarded in one of the condensers  8 ,  18  is suitable.  
         [0046]    The operating principle of the liquid ring pump  28 , which has an impeller  64  mounted eccentrically in the housing  62  of the liquid ring pump  28 , can be seen with reference to the schematic representation of a cross section through the liquid ring pump  28  according to FIG. 2. During operation, the water W forms a liquid ring  66  which revolves with the impeller  64 , so that sectional spaces  68  of different volume form between the individual spokes of the impeller  64  and the liquid ring  66 . An intake slot via which the medium to be drawn in is drawn in via the suction connection  30  is provided in the housing  62  at the end face at the position identified by reference numeral  70 . Due to the eccentric configuration, the medium to be pumped is compressed in the course of the revolution of the impeller  64  and is expelled via a pressure slot to the pressure connection  34  at the position identified by reference numeral  72 .  
         [0047]    The additional port  35  is disposed between the intake slot  70  and the pressure slot  72  in the housing  62  and is connected to the working space, which is formed by the individual sectional spaces  68 . Depending on the position of the additional port  35 , the suction capacity, prevailing at this position, of the liquid ring pump  28  varies with regard to both the prevailing vacuum and the delivery quantity. In addition, the suction capacity can be varied by selection of the diameter of the additional port  35 .  
         [0048]    Although the vacuum at the additional port  35  is above the vacuum applied at the suction connection  30 , it is sufficiently low in order to permit deaeration of the water chamber  22 . The volumetric suction capacity for deaerating the water chamber  22  is also sufficiently high. Since the third deaerating line  24  is not connected to the suction connection  30 , the liquid ring pump  28  is not additionally loaded by the additionally fed gas mixture G or is only barely subjected to additional loading by the latter. Slightly greater dimensioning, possibly necessary due to the connection of the third deaerating line  24 , of the liquid ring pump  28  is in any case more favorable compared with a separate pumping system for the deaeration of the water chamber  22 .  
         [0049]    A steam turbine plant of such a configuration with a uniform, central vacuum pumping configuration  14  has essentially the following advantages:  
         [0050]    a. On account of the use of steam D and air L as the motive fluid T for the jet pump  26 —compared with the use exclusively of air L as the motive fluid T—the liquid ring pump  28  can be configured to be markedly smaller, since the steam D condenses in the liquid ring pump, and only the air proportion has to be compressed to atmospheric pressure.  
         [0051]    b. The low-tension steam collecting in the sealing-steam circuit  50  is preferably completely directed via the vacuum pumping configuration  14 . In this case, it is not absolutely necessary for the entire quantity of the low-tension steam to be used as the motive fluid T for the jet pump  26 . By the feeding of the low-tension steam to the liquid ring pump  28  having the associated separator  38 , the low-tension steam is condensed, so that a separate condensing system is not required for the low-tension steam.  
         [0052]    c. For all the plant components that have to be connected to a vacuum system, the vacuum pumping configuration  14  is provided as a central vacuum system. This makes possible a simple and cost-effective installation. In particular, it is not necessary to install a plurality of decentral vacuum pumping systems.  
         [0053]    d. Due to the connection of the third deaerating line  24  to the additional port  35 , a suction capacity provided virtually “for nothing” by the liquid ring pump  28  is utilized without the liquid ring pump  28  having to be of larger dimensions due to the connection of this third deaerating line  24 .