Abstract:
An integrated bleed regulator system adapted to be fitted to a steam turbine, the system including a fixed part resembling a diaphragm and has a downstream part including distributor blades between an inner ring and an outer ring. A moving part is provided upstream of the fixed part and constitutes a regulator disk having distributor blades between an inner ring and an outer ring. The disk, according to its annular position, totally or partially obstructs a steam passage in the upstream to downstream direction or does not obstruct it at all and the surface of the regulator disk downstream of the inner and outer rings is at an upstream pressure (P 1 ). A passage is also provided so that at least part of an upstream surface of the assembly formed by the inner and outer rings communicates with a space downstream of an upstream part of the distributor blades at a pressure (P 2 ).

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to the field of steam turbines. 
     To be more precise, the invention relates to a system intended to be fitted to steam turbines of the type referred to as controlled extraction steam turbines, commonly called controlled bleed steam turbines. 
     Turbines of the type referred to are encountered in many industrial processes combining generation of electrical power and regulation of the pressure in a steam network. A steam network is fed by bleeding steam from the expansion stage of the turbine. To this end, a bleed control unit controls the extraction pressure, which can be measured, in order to regulate it, either in the vicinity of the control unit or at a relatively distant point in the network. 
     In the prior art, the bleed control units are of different types to suit the type of turbine and in particular can consist of a control valve or a gate valve. 
     The control valve is external to the steam flow and operates like a standard control valve. Although in theory it does not have any limitation restricting the extraction pressure, it nevertheless has the drawback of requiring a space for installing it which is of considerable length in the axial direction, generating non-negligible head losses. 
     The gate valve has a fixed part and a rotary part. It is inserted between two successive stages of the turbine. Referring to FIG. 1, which shows a gate valve, the rotary part (regulator disk)  2   a  is made up of two concentric rings, namely an inner ring  21   a  and an outer ring  20   a , with the upstream part of the distributor blades  22   a  between them. The fixed part resembles a diaphragm but carries only the downstream part  12  of the distributor blades, between an outer ring  121  and an inner ring  122 . When fully open, the gate valve resembles a standard diaphragm. This configuration is shown in the developed sections of the gate valve distributor blades represented in FIG. 2 (fully open), FIG. 3 (partly open) and FIG. 4 (fully closed). The arrow  f  shows the direction of the steam. 
     If P 1  is the upstream pressure (see FIG. 1) and P 2  the downstream pressure in the steam flow behind the regulator disk  2   a , only the downstream (rear) face of the blades  22   a  is exposed to the downstream pressure P 2  and all the rest of the rear face and the front face (upstream face) of the regulator disk  2   a  are exposed to the upstream pressure P 1 . 
     When the disk  2   a  is fully open, as shown in FIG. 2, the upstream and downstream pressures are the same and it is to this pressure that the downstream face of the blades  22   a  is exposed, even though it is in contact with the fixed blades  12 . However, if the steam flow is slightly obstructed (FIG. 3) head losses are produced and the downstream pressure P 2  is lower than the upstream pressure P 1 , which presses the regulator disk against the fixed part of the gate valve. This is particularly important in the fully closed situation (FIG. 4) in which the downstream pressure P 2  is the condenser pressure, for example. 
     Accordingly, a bleed regulation system of the above kind has the major drawback of being limited to an extraction pressure of approximately 10 to 12 bars. This is because, in the current configuration shown in FIG. 1, the pressure forces acting on the regulator disk  2   a  are absorbed by the rubbing surfaces between it and the fixed part, rotation inducing unacceptable specific pressures therein if the extraction pressure becomes too high. 
     SUMMARY OF THE INVENTION 
     An intention of the present invention is to alleviate some of the drawbacks of the prior art. 
     The invention accordingly provides an integrated bleed regulator system adapted to be fitted to a steam turbine, the system including a fixed part resembling a diaphragm and including a downstream part of distributor blades between an inner ring and an outer ring and a moving part upstream of said fixed part and constituting a regulator disk comprising an upstream part of said distributor blades between an inner ring and an outer ring, in which system said disk, according to its angular position, totally or partially obstructs the steam passage in the upstream to downstream direction or does not obstruct it at all and the surface of said regulator disk downstream of said inner and outer rings is at the upstream pressure, which system is characterized in that means are provided so that at least part of an upstream surface of the assembly formed by the inner and outer rings of the regulator disk communicates with a space downstream of an upstream part of the distributor blades where the pressure is the downstream pressure. 
     In one embodiment of the invention said means include at least one part forming a counter-abutment with at least a part of the upstream surface of the assembly formed by the inner and outer rings of said regulator disk with a small operating clearance, said regulator disk includes at least one annular groove open on the side facing said counter-abutment part, and at least one passage connects said groove to the space downstream of said upstream part of said distributor blades of the regulator disk where the pressure is the downstream pressure. 
     According to another feature of the invention said passage opens into a downstream well on the downstream side of said upstream part of the distributor blades of the regulator disk. 
     Thus, in the invention, it is possible to increase the maximum pressure up to which the steam bleed regulator system can operate correctly. 
     What is more, the invention involves only a slight increase in overall size compared to a standard gate valve. 
     In a first embodiment of the invention said counter-abutment part is at the periphery of said fixed part. 
     In a second embodiment of the invention said counter-abutment part is at the level of the internal bore of said fixed part. 
     In a third embodiment of the invention said system includes two counter-abutment parts, one of which is at the periphery of said fixed part and the other of which is at the level of the central area thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the invention will become apparent on reading the following description of three preferred embodiments of the invention, which description is given by way of illustrative and non-limiting example only and with reference to the accompanying drawings, in which: 
     FIGS. 1-4 represent a gate valve configuration according to the prior art; 
     FIG. 5 is a simplified diagrammatic side view of a first embodiment of a steam bleed regulator system of the invention; 
     FIG. 6 is a simplified diagrammatic perspective view of one embodiment of a moving part of the system shown in FIG. 5; 
     FIG. 7 is a simplified diagrammatic side view of a second embodiment of a system of the invention; 
     FIG. 8 is a simplified diagrammatic perspective view of one embodiment of a moving part of the system shown in FIG. 7; 
     FIG. 9 is a simplified diagrammatic side view of a third embodiment of a system according to the invention; and 
     FIG. 10 is a simplified diagrammatic perspective view of one embodiment of a moving part of the system shown in FIG.  9 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A first embodiment  10  of a bleed regulator system according to the invention will now be described with reference to the simplified diagrams of FIGS. 5 and 6. 
     As a general rule, in the remainder of this description, it is assumed that fluid enters the steam bleed regulator system from the left and leaves it to the right. In other words, the upstream face of the system is the left-hand face of the system and its downstream face is its right-hand face. 
     In the standard manner, a system  10  for regulating the bleeding off of steam (flowing in the direction indicated by that of the arrow f) has a fixed part  11  which resembles a diaphragm. The fixed part  11  includes only the downstream part  12  of the distributor blades. A diaphragm has a ring structure comprising an outer ring  121  and an inner ring  122 . 
     The downstream part  12  of the distributor blades is fastened to the outer and inner rings  121 ,  122 . The bore of the inner ring  122  is equipped with seals  13  to limit downstream leakage of steam. The periphery of the ring  121  has an exterior shoulder  14  for locating the integral regulator system  10  within the turbine. The system  10  also has a moving part consisting of a regulator disk  15 . 
     The regulator disk  15 , part of which is shown in isolation and in perspective in FIG. 6, comprises two concentric rings, namely an inner ring  22  and an outer ring  23 , with the upstream part  21  of the distributor blades  12 ,  21  between them. 
     The system  10  consisting of the fixed part  11  and the regulator disk  15  constitutes a rotary closure system. 
     The regulator disk  15  turns about the axis of the machine and is supported by a guide  17  of the fixed part  11 . Pressure forces acting in the upstream to downstream direction press the regulator disk  15  onto the fixed part  11 , against inner and outer annular rubbing bearing surfaces  18 ,  19  of the fixed part  11 . 
     Because of pressure balancing holes  16 , the pressure acting on the rear face of the inner ring  22  of the regulator disk  15  is the upstream pressure P 1 . 
     In accordance with the invention, the pressure acting on at least part of the upstream surface of the combination of the inner and outer rings  22  and  23  of the regulator disk  15  is the pressure P 2  of the steam flow downstream of the upstream part  21  of the distributor blades  12 ,  21 , and this partly or totally compensates, or even overcompensates, the force applied to the regulator disk  15  in the upstream to downstream direction because of the pressure difference P 1 -P 2  between the upstream and downstream faces of the upstream part  21  of the distributor blades. The compensation depends on the area over which the downstream pressure P 2  acts. 
     To this end, an annular groove  114  on the upstream face of the outer ring  23  of the regulator disk  15  is connected by a passage  115  to the portion of the steam flow downstream of the upstream part  21  of the distributor blades, where the pressure is the pressure P 2  (see FIG.  5 ). The downstream face of the upstream part  21  of the distributor blades advantageously includes a downstream well  113  and the passage  115  terminates in the well  113 . The annular groove  114 , which is open on the side towards the outside of the outer ring  23 , is closed by a part counter-abutment  110  joined to the fixed part  11  and covering part of the upstream face of the outer disk  23 , with a small operating clearance  116 . 
     Because of one or more passages  112  in the part  110 , the pressure acting on the rear face of the outer ring  23  is the upstream pressure P 1 . The part  110  is fixed to the fixed part  11  by screws  111 . The counter-abutment part  110  “closing” the groove  114  covers the upstream face of the outer ring  23 , with the small clearance  116 , along outer and inner annular surfaces  117  and  118  with the groove  114  between them. 
     Accordingly, by virtue of the invention, the pressure in the groove  114  is the downstream pressure P 2  and the area of the groove  114  can be calculated so that it is less than, equal to or greater than the downstream area of the upstream part  21  of the distributor blades, where the pressure is the downstream pressure P 2 , which is maximum in the totally closed configuration shown in FIG.  4 . 
     It is therefore possible to compensate partly, or even to overcompensate, the force acting on the disk in the upstream to downstream direction and thereby to relieve the pressure applied by the disk  15  to the bearing surfaces  18 ,  19 . This enables the bleed pressure to be increased. 
     The small operating clearance  116 , which is obviously necessary, generates a permanent fluid leak which is drained via the passages  115 . This permanent leak has the advantage of guaranteeing a flow of fluid preventing heating of the stages of the turbine further downstream, independently of the degree of closure of the regulator disk  15 . 
     A second embodiment  30  of a system according to the invention will now be described with reference to the simplified diagrams of FIGS. 7 and 8. 
     Components already described with reference to FIG. 5 retain the same reference number. Only aspects thereof specific to this second embodiment are described here. 
     In this embodiment of the invention, the counter-abutment part  310  is at the level of the guide  17  of the fixed part  11 , i.e. at the height of the bore of the moving regulator disk  31 . The periphery of the regulator disk  31  is therefore free. In some cases, and in particular when the overall size in the center is small, a maneuvering arm necessary for rotating the regulator disk  31  can even be provided here, for example. The upstream annular groove  311  is therefore located in the central area of the moving regulator disk  31 , i.e. on the inner ring  22 , and between the outer and inner central annular upstream surfaces  313 ,  314 . 
     The balancing passages  312  through the counter-abutment part  310  are at substantially the same height as the balancing holes  16  in the inner ring  22  of the regulator disk  31 , thereby facilitating exchange of fluid between the upstream side of the counter-abutment part  310  and the downstream side of the inner ring  22 . 
     The clearance  316  is provided between the counter-abutment part  310  and the regulator disk  31  at the height of the outer and inner bottom annular upstream surfaces  313 ,  314 . 
     The fixed part  11  and the counter-abutment part  310  constitute a single component. Thus no fixing means are needed for fixing these two parts together. The system  30  is quicker to install because this eliminates the step of fixing together the two parts (i.e. the counter-abutment part  310  and the fixed part  11 ). 
     Because of the passages  310  through the regulator disk  31  the pressure in the annular groove  311  is the same downstream pressure P 2  as the pressure in the downstream wells  113 . 
     The annular groove  311  is on the upstream face of the inner ring  22  of the regulator disk  31 . 
     A third embodiment  50  of a system according to the invention will now be described with reference to the simplified diagrams of FIGS. 9 and 10. 
     Components already described with reference to FIG. 5 retain the same reference number. Only their aspects specific to the third embodiment of the invention are described here. 
     This third embodiment of the invention is a combination of the first and second embodiments of the invention described above. 
     To be more precise, the bleed regulator system  50  comprises two counter-abutment parts  52 ,  53 . The first counter-abutment part  52 , located at the height of the bore of the regulator disk  51 , and the part  11  constitute a single component. The second counter-abutment part  53  is fixed to the periphery of the fixed part  11 , for example by means of a screw  54 . The system  50  can be installed, even if the available space is small, provided that there is the same amount of room at the level of the periphery of the regulator disk  51  and at the level of the bore in the regulator disk. 
     A bleed regulator system of the above kind has the advantage of enabling substantially equal distribution of pressure forces in the upstream to downstream direction on the inner and outer rings  22  and  23  of the regulator disk  51 . Also, the two counter-abutment parts  52 ,  53  also distribute pressure forces in the downstream to upstream direction on their active faces (i.e. the faces that face toward the regulator disk  51 ) substantially equally. 
     A clearance  55  is provided between the two counter-abutment parts  52 ,  53  and the moving regulator disk  51  at the height of the respective outer and inner annular upstream surfaces  56 ,  57 ,  58 ,  59 . 
     Each counter-abutment part  52 ,  53  has one or more respective balancing passages  510   b ,  510   a  through it. 
     The outer ring  23  of the regulator disk  51  has on its upstream face an outer annular groove  511  and the inner ring  22  has on its upstream face an inner annular groove  512 . The grooves are “closed” by the counter-abutment parts  53 ,  52 , with the essential operating clearance  55 . Each of the outer and inner upstream annular grooves  511 ,  512  communicates with at least one downstream well  113  via at least one centripetal first passage  513  and at least one centrifugal second passage  514 . 
     Accordingly, as in the previous embodiments, the downstream pressure P 2  in the downstream wells  113  and on the downstream face of the blade parts  21  of the regulator disk  51  is present in the grooves  511  and  512  and therefore over a portion of the upstream surface of the regulator disk  51 .