Abstract:
Described is a device ( 1 ) for sealing a power station pump. The device ( 1 ) includes a pump housing ( 10 ) with first and second ducts ( 15, 16 ) for passage of a fluid, and a shaft ( 20 ) including a first passage ( 51 ) for the fluid, a mechanical packing ( 70 ) mounted between the shaft ( 20 ) and the pump housing ( 10 ) and friction elements for rubbing-together a rotating part ( 71 ) and a stationary part ( 72 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application claims benefit under 35 U.S.C. §119(a) of co-pending FR Patent Application Number 1255283 entitled “PUMP SEALING DEVICE” filed Jun. 6, 2012, the substantially identical disclosure of which is incorporated by reference herein in its entirety. 
       TECHNICAL FIELD 
       [0002]    This relates to a pump sealing device. More specifically, it relates to a device for sealing a pump of a nuclear power station. It may also relate to a fossil fuel power station, notably one producing electricity by burning coal, oil or natural gas. In the case of a nuclear power station, it is a pump the function of which is to send water to heaters situated before the inlet to the reactor. 
       BACKGROUND 
       [0003]    The thermal barrier function and function of cooling the friction elements of mechanical packing are performed by tappings (ducts with (an) inlet(s) and (an) outlet(s) that feed certain zones are defined as tappings) arranged in the pump housing, the mechanical packing and in the fluid header if there is one. Existing techniques make maintenance difficult because piping has first of all to be removed. Moreover, having numerous tappings in standard components increases costs, notably because of the need to make the holes and weld on the supply piping. Furthermore, the cooling water comes from two different circuits, namely an auxiliary cooling circuit used for the thermal barrier function and another circuit for cooling the friction elements of the mechanical packing using water from the pump and an external heat exchanger. 
         [0004]    Such devices make sealing-device maintenance difficult in so far as the tappings are made in the mechanical packing and in the pump housing. 
         [0005]    That being the case, the problem set here is that of producing a pump sealing device of the abovementioned type, which is of simple construction and facilitates maintenance of said device and improves the life of the device. The present invention also seeks to combine two functions into one and the same single sealing device where there is just one cooling circuit the purpose of which is to cool the friction elements of the mechanical packing and to form a thermal barrier that protects the mechanical packing from heat, so as to lengthen the life of the device. The mechanical packing provides sealing at the end of a shaft and on the outside of the pump housing. The temperature of the mechanical packing and of the water flowing near the mechanical packing must not exceed a threshold temperature, conventionally 100° C. Now, typically, the water circulating through the pump is at a temperature of around 200° C. Bearing in mind the mechanical properties of the packing and notably of the stationary and rotating face rings (the stationary and rotating friction elements of the mechanical packing are defined as the stationary and rotating face rings) and how they are arranged in the sealing device, it is important to protect them from excessive heat in order to protect them from degradation. What happens is that an exchange of heat by conduction between the pump housing and the mechanical packing may impair correct operation of the seal and notably may impair sealing at the point between the stationary face ring and the rotating face ring. Moreover, friction between the rotating part of the mechanical packing defined by the rotating face ring of the packing on the one hand, and the stationary part defined by the stationary face ring of the packing on the other hand, dissipates energy in the form of heat, leading to a rise in temperature and to premature wear of the stationary and rotating face rings. Thus, in order to lengthen the life of the mechanical packing, provision is made for the mechanical packing to be cooled at the places where the friction occurs, namely at that point in the mechanical packing and, more specifically, at the point where there is relative motion between the rotating face ring and the stationary face ring. 
         [0006]    Furthermore, the present invention seeks notably to optimize the maintenance of the sealing device and to lengthen the life of the sealing device. Another object of the present invention is to reduce the number of components that make up the sealing device and at the same time to reduce the costs of manufacturing a pump sealing device. 
         [0007]    The solution proposed by the present invention is that the device for sealing a pump comprises:
       a pump housing comprising first and second ducts for the passage of a fluid;   a shaft comprising, near the pump housing, a first passage for the fluid;   a mechanical packing mounted between the shaft and the pump housing and comprising friction elements for the rubbing-together of a rotating part and of a stationary part,
           said device having two states, a shut down first state in which no fluid circulates through said device and an operating second state in which the fluid flows in a flow circuit passing via:   
           the first passage to supply the circuit with fluid,   a second passage comprised between the pump housing and the packing and communicating with said friction elements, the second passage then forming a means of cooling the friction elements and a thermal barrier,   the first duct to supply the second passage with cooled fluid,   the second duct to remove the hot fluid from the second passage.       
 
         [0016]    Such an arrangement advantageously allows maintenance to be made easier and allows the life of the sealing device to be lengthened while at the same time reducing the number of components that make up the device and the cost of manufacturing such a component. The pump housing, the shaft and the mechanical packing together incorporate a means of cooling the friction elements and a thermal barrier, which therefore need to be supplied with fluid. The present invention proposes using a single circuit to supply both the means for cooling the friction elements and the thermal barrier via the second passage. Some of the fluid circulating through the second passage has the function of cooling the mechanical packing adjacent to this second passage, so as to lower the temperature of the friction elements therefore allowing pump usage with no risk of leakage; this then prevents pump water from coming into contact with the external surroundings. Another proportion of the fluid circulating through the second passage has the function of forming a thermal barrier so as to protect the packing, notably the friction elements thereof, from the heat dissipated by the pump housing and caused by the hot water circulating through said pump. 
         [0017]    The flow circuit followed by the fluid advantageously makes it possible to reduce the number of components of which the device is made. More specifically, all the arrangements of pump housing, shaft and packing, correlated with the fluid circuit offers the benefit of a reduced number of components while at the same time offering optimized means of protecting the packing and the friction elements thereof. 
         [0018]    In one embodiment, a first chamber extends radially between the packing and the pump housing and axially between the cover and a fourth passage. 
         [0019]    In one embodiment, the device might comprise a second chamber comprised between the pump housing on the one hand and the packing on the other and might define, in the operating state, a second thermal barrier. 
         [0020]    In another embodiment, the above-mentioned second chamber is bounded:
       radially, by the shaft and a bore formed in the pump housing,   axially, by the packing and the pump housing.       
 
         [0023]    In another embodiment, a gap runs longitudinally between the shaft and the pump housing, said gap running circumferentially and defining, in the operating state, a third thermal barrier. 
         [0024]    In yet another embodiment, the pump housing might comprise a third passage providing communication between said second and third thermal barriers. 
         [0025]    In another embodiment of the invention, the third passage immediately faces, in the axial direction, the lateral part of the stationary face ring. 
         [0026]    In another embodiment, a first passage between the shaft and the pump housing is intended for circulating the fluids from the pump toward the gap. 
         [0027]    In one embodiment, the second passage might comprise said first and second chambers, the fourth passage, a third passage providing communication between the second chamber and the gap, and the gap. 
         [0028]    In yet another embodiment, the second operating state is triggered by the shaft beginning to rotate. 
         [0029]    In another embodiment of the invention, the sealing device further comprises a fluid-cooling device connected to first and second ducts. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURE 
         [0030]    Other features and advantages will become further apparent from the description given hereinafter, by way of entirely nonlimiting indication, with reference to the attached drawing in which: 
           [0031]      FIG. 1  shows half of a cross section through one example of a sealing device according to the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    Two sealing devices  1  are provided to prevent pressurized hot water from getting out into the external atmosphere while at the same time not impeding the rotation of a shaft  20 . Each of the two sealing devices  1  is positioned at each exit of the shaft  20 .  FIG. 1  depicts just one device  1 . 
         [0033]    Each of the devices  1  comprises:
       a pump housing  10  which contains pressurized hot water and energy recuperation components;   a rotary shaft  20  supporting the impellor the vanes of which impart motor power to this hot water, said shaft  20  emerging from the housing  10  on each side to rest on bearings; one of its ends is coupled to a drive system, not depicted; the exits of the shaft  20  are sealed by sealing devices  1 ;   a cover  40  fixing a mechanical packing  70  to the pump, and more specifically to the inside of the pump housing  10 ; it is fixed to the pump housing  10  by fixing means;   a mechanical packing  70  comprising a rotating face ring  71  and a stationary face ring  72  defining friction elements which respectively constitute a rotating part  71  and a stationary part  72 ;   the rotating face ring  71  rotating with the shaft  20  and in surface-to-surface contact with the stationary face ring  72 ; sealing occurring at the interface between these two face rings;   the stationary face ring  72 , kept pressed against the rotating face ring  71 , may have the ability to move only translationally;   a rotating face ring carrier, holding the rotating face ring  71 ;   a non-rotating face ring carrier, holding the stationary face ring  72  and allowing the face ring  72  to move in a translational movement;   a mechanical packing liner, connected to the shaft  20 ; this constitutes a wall of the mechanical packing  70  in contact with the shaft  20  while protecting it.       
 
         [0043]    The sealing device  1  is intended to be positioned between the rotary shaft  20  and the pump housing  10 . More specifically, the device  1  is arranged at the exit of the shaft  20 , outside the pump housing  10 , so as to prevent pressurized hot water circulating in the pump housing  10  from flowing out of said housing  10 . Furthermore, the sealing device  1 , the rotary shaft  20  and the pump housing  10  are arranged together in such a way as not to impede the rotation of the shaft  20  with respect to the pump housing  10 . The shaft  20  rotates about an axis  20   a.    
         [0044]    The mechanical packing  70 , defining a sealing means, is fitted to the sealing device  1 . The mechanical packing  70  comprises said stationary sealing face ring  72  connected in a fluidtight manner to the pump housing  10  and said rotating sealing face ring  71  connected in a fluidtight manner to the rotary shaft  20 . When the shaft  20  rotates about its axis  20   a , the rotating face ring  71  rubs against the stationary face ring  72  over an annular friction surface. The stationary face ring  72  and the rotating face ring  71  each respectively has: radially outer surfaces and radially inner surfaces. At least a portion of the radially outer surfaces communicate with a first chamber  120  defining an exchange zone. The first chamber  120 , defining an exchange zone, is comprised between that part of the packing  70  that is oriented radially toward the outside and the pump housing  10 ; this first chamber  120  is adjacent to the friction elements formed by the stationary face ring  72  and rotating face ring  71 . In the operating state, the first chamber  120  contains a fluid for cooling the friction elements. When the circuit is in the operating state and when the first chamber  120  contains a cooled fluid, then a first thermal barrier  31  runs between the packing  70  and the housing  10 , said first thermal barrier being formed by the first chamber  120  filled with a fluid. Preferably, the first chamber  120  runs radially between the packing  70  and the pump housing  10  and axially between the cover  40  and a fourth passage  14   b.    
         [0045]    The device  1  may comprise face ring pressing means to press the stationary face ring  72  and the rotating face ring  71  axially against one another. The purpose of these means is to maintain contact between the stationary face ring  72  and the rotating face ring  71 . 
         [0046]    In one embodiment of the invention, the cover  40  defines a cap. According to this embodiment, the cover  40  is arranged between the pump housing  10  and the mechanical packing  70 —straddling the pump housing  10  and the packing  70 . Its purpose is to incorporate the mechanical packing  70  within the pump housing  10  and then hold it fixedly in position. 
         [0047]    The arrangements of ducts, passages and tappings in the pump housing  10 , and between the pump housing  10  and the shaft  20 , notably in the region of the packing  70 , have two main functions
       to form a thermal barrier  30  between the pump housing  10  and the mechanical packing  70 ;   to cool the mechanical packing  70  and more specifically the stationary face ring  72  and the rotating face ring  71 .       
 
         [0050]    Thus, the circulation of a fluid through the aforementioned ducts is aimed essentially at protecting the mechanical packing  70  from external harm, notably the harmful effects of heat, and to lengthen its life. 
         [0051]    Preferably, the thermal barrier  30  is made up of the first thermal barrier  31 , of the second thermal barrier  32  and of the third thermal barrier  33 . 
         [0052]    The pump housing  10  comprises first and second tappings  12 ,  13  communicating respectively with first and second ducts  15 ,  16 . The first tapping  12  and the first duct together supply the thermal barrier  31  and the friction elements  71 ,  72  with cooled fluid, while the second tapping  13  and the second duct  16  together remove the hot fluid contained in the third thermal barrier  33 . 
         [0053]    According to an embodiment that has not been depicted, by means of a suitable arrangement of the cover  40  with the pump housing  10 , the first duct  15  communicates with a third duct arranged in the cover  40 . This third duct communicates with the first chamber  120 . Arranged in this way, the first duct  15  and the third duct supply the first chamber  120  with fluid, and this causes the stationary face ring  72  and the rotating face ring  71  to be immersed in a fluid for cooling purposes. 
         [0054]    The first chamber  120  defines a radial space between the packing  70  and an internal wall of the housing  10 . The second chamber  130  defines an axial space between the housing and the packing  70 . As shown in  FIG. 1 , the second chamber  130  is radially bounded by the shaft  20  and a bore formed in the pump housing  10 ; it is bounded axially, over a portion of a first side of said second chamber, by the mechanical packing and possibly by a wall of the pump housing and, over a portion of a second side of said second chamber, by the pump housing  10 . This second chamber  130  comprises, on its first side, a fourth passage  14   b  forming a communication between the first chamber  120  and the second chamber  130 , and on its second side a third passage  14   a  forming a communication between the second chamber  130  and the gap  140 . 
         [0055]    In the operating state, the fluid contained in the first chamber  120  will therefore flow into the fourth passage  14   b  before completely or partially filling the second thermal barrier  32  defined by the aforementioned second chamber. 
         [0056]      FIG. 1  shows us that the thermal barriers  31 ,  32  are substantially annular in shape. 
         [0057]    The second thermal barrier  32  communicates with a third thermal barrier  33  via a third passage  14   a  arranged in the pump housing  10 . The third passage  14   a  immediately, in the axial direction, faces the lateral part of the stationary face ring  72 ; further, the third passage  14   a  and the lateral part of the stationary face ring  72  are separated from the second thermal barrier  32 . 
         [0058]    The third passage  14   a  communicates with a gap  140  running circumferentially along the shaft  20 . As depicted in  FIG. 1 , the gap  140  runs between the pump housing  10  and the rotary shaft  20 . In the operating state, the fluid contained in the second thermal barrier  32  will therefore circulate toward the gap  140  via the third passage  14   a  in order to ensure continuity with the second thermal barrier  32  and prevent heat from being transferred from the pump housing  10  to the shaft  20 . When filled with fluid, the gap  140  defines a third thermal barrier  33 . 
         [0059]    The second tapping  13  is arranged in the pump housing  10 . It runs between the gap  140  and an exterior surface of the pump and allows hot fluid to be removed to outside the mechanical assembly formed by the pump housing  10 , the packing  70  and the shaft  20  and possibly the cover  40 . Preferably, the hot fluid is discharged to a fluid cooling device, of the heat exchanger type. 
         [0060]    In one embodiment, in order to supply the cooling circuit with fluid, use is made of a first passage  51  between the rotary shaft  20  and the bore of the pump housing  10 . More specifically, fluid from the pump can flow to the gap  140 , said gap  140  and said first passage communicating with one another. In this embodiment, the cooling circuit is supplied via the fluid removed from the pump. Thus, the device  1  has two states: a shut down first state in which no fluid circulates through the device  1 , and an operating second state in which the fluid follows a flow circuit passing via:
       the first passage  51  in order to supply the circuit with fluid,   a second passage comprised between the pump housing  10 , the packing  70  and the shaft  20 , and communicating with the friction elements, the second passage then forming a means for cooling the friction elements and a thermal barrier  30 ,   the first tapping  12  to supply the second passage with cooled fluid,   the second tapping  13  to remove the hot fluid from the second passage.       
 
         [0065]    In the shut down first state, the water from the pump is in all the gaps  120 ,  130 ,  140 ,  14   a ,  14   b . In the operating second state, rotation of the shaft  20  allows the circuit supplying the packing  70  and the thermal barriers  31 ,  32 ,  33  to begin to circulate. 
         [0066]    Furthermore, it should be emphasized that fluid from the pump flows, in an unwanted manner, between the shaft  20  and the pump housing  10  at the passage  51 . Provision is therefore made to put this fluid to good use by making it flow through the circuit. The leakage between the pump housing  10  and the shaft  20  then becomes advantageous. 
         [0067]    Preferably, the second passage comprises the first chamber  120 , the fourth passage  14   b , the second chamber  130 , the third passage  14   a  and the gap  140 . 
         [0068]    In one embodiment, the second passage might, and this list is not exhaustive, comprise: the first chamber  120  cooling the friction elements in a fluid and defining the first thermal barrier  31 , the second chamber  130  defining the second thermal barrier  32 , and the gap  140  defining the third thermal barrier  33 . The fourth passage  14   b  provides communication between the first and second chambers  120 ,  130 . The fourth passage  14   b  provides communication between the first thermal barrier  31  and the second thermal barrier  32 . The third passage  14   a  provides communication between the second thermal barrier  32  defined by the second chamber  130  and the third thermal barrier  33  defined by the gap  140 .