FR2607874A1 - Output shaft device for a water pump under high pressure and temperature, particularly for a feed pump of a steam-powered electric power station - Google Patents

Abstract

A mechanical sealing gasket includes a revolving bead 8 bearing against a non-revolving bead 9. It is cooled by a circuit of pressurised water including an exchanger EB, PS, EH fed through an inlet 22 by the low-pressure water of a general cooling circuit outside the pump. This exchanger is integrated into a water box which also includes a thermal barrier which is located between this gasket and the pump body 1 and which includes two walls 30, 40 cooled in series by the low-pressure water leaving this exchanger. Application to steam-powered thermal electric power stations.

Description

Shaft outlet device for high pressure and temperature water pump, in particular for a 9 steam power station food pump
The present invention relates to a shaft output device for a water pump under high pressure and temperature, in particular for a food pump of a steam power plant.

 At the hot water drive shaft outputs for power plants, there is usually a two-part device.

- A first, the seal, is used to seal the pressurized water of the pump from the ambient environment in which the shaft end comes out. In the current state of technology (graphite grain on carbide grain with ethylene / propylene seals), this mechanical seal is refrigerated because it can only accept a moderate temperature (around 800 Celsius).

- A second, the thermal barrier, is used to thermally isolate the shaft outlet containing the packing from the rest of the pump whose water is around 16O at 1800 Celsius.

 These two devices are connected, outside the pump, to general refrigeration circuits existing in the power plant. However, with regard to the mechanical seal, this circuit must pass through an intermediate exchanger so as not to mix the water of the pump whose pressure is approximately 40 bars with the water of the general circuits whose pressure is approximately 7 bars. This exchanger of classic design is outside the pump.

 This arrangement is shown in Figures 1 and 2.

 Figure 1 is a very schematic view showing cooling circuits and Figure 2 is an axial sectional view of a known output device performing these circuits.

 A rotary pump shaft 102 rotates about its axis A in the body 101 of this pump, under the action of an external turbine, not shown, to drive blades inside this body and not shown. The pressurized hot water which is inside this body is prevented from passing outside by a mechanical seal comprising a rotating grain 108 (see fig. 2) secured to the shaft 102 and rubbing against a fixed grain, where more exactly not rotar.t 109 pushed axially by this grain rotating by a spring 113. The radially inner faces of these grains are at atmospheric pressure. Their radially outer faces are cooled by a lining cooling circuit, the water of which enters through an inlet 122 and exits through an outlet 124. The water is entrained in this circuit by a WPR screw rotating with the shaft 102 opposite 'a fixed WPS surface. This circuit is under high pressure because it communicates with the interior space of the body 101 by a parasitic passage formed by the necessary radial clearance between the rotating shaft 102 and a fixed thermal barrier wall 130.

 This latter wall is cooled by a low pressure water circuit comprising an inlet 123 and an outlet 125 through which it communicates with a supply line DGA and discharge CGE of a general low pressure cooling circuit of the power station (see f; g.1). The lining cooling circuit passes through an intermediate exchanger EA external to the device to cool its water. This exchanger is supplied from the CGA and CE pipes of the general low-pressure cooling circuit.

 This known device has various drawbacks of excessive consumption of water from the general cooling circuit, size, and assembly complexity.

 The object of the present invention is in particular to obtain a significant reduction in the flow rate of the cooling water of the general circuit while having low pressure drops, and to reduce the size and complexity of the shaft output device.

 And it relates to a shaft output device for high pressure and temperature water pump, in particular for food pump of a steam power plant / - this device being intended to be placed between the shaft (2) of a rotary pump and the fixed hollow body (1) of this pump at the outlet of this shaft out of this body to prevent hot pressurized water circulating in this pump body from escaping into the external space and so as not to thus hampering the rotation of this shaft, this shaft having an axis (A) around which it rotates, - this device comprising a mechanical sealing gasket itself comprising a non-rotating sealing grain (9) tightly connected to the said pump body (1), - a rotating etanenity grain (8) tightly connected to said shaft (2) and rubbing against this fixed grain on a friction surface in the form of a crown coaxial with this shaft, each of these two grains being in contact on the one hand, by a radial surface outer cement, with a space under high pressure (VH) which colnrauniqu with the interior of this body and on the other hand, by a radially inner surface, with a space under low pressure (VB) whose pressure is close to that of the atmosphere, - and grain support means (13) for axially pressing these two grains; ns against one another so as to maintain on this friction surface a contact ensuring the seal between said volumes under high and low pressure, - this device further comprising a fixed water box disposed between said pump body (1) and said seal, surrounding the latter, this box forming a circuit for cooling the seal under high pressure suitable for discharging on the one hand the heat reaching this lining and coming from said high temperature water circulating in said pump body (1), and on the other hand the heat generated by the friction of said grains l ' one on the other, so that may keep this seal at a suitable operating temperature, this circuit passing through said high pressure volume (VH) in contact with said sealing grains, - water circulation means (VPR, VPS) inside this box and driven by said shaft (2) for circulating water in the circuit, - a low pressure cooling water circuit, - and a lining cooling heat exchanger for transferring heat from said lining cooling circuit to this low pressure cooling circuit while resisting the difference in water pressures in these two circuits, - this device being characterized by the fact that said packing cooling exchanger (EG) is formed by said water box t3, 5, 6), inside thereof, said lining cooling circuit being completely inside this box, this box having an inlet (22) and an outlet (24) to allow the water in said circuit to refr oidification at low pressure to circulate between a part of this last circuit which is outside the device and a part of this circuit which is inside this box and which passes through this lining cooling exchanger.

 Preferably, according to a known arrangement, a fixed thermal barrier is formed around said pump shaft (2), in the vicinity thereof, between said pump body (1) and said seal. (7, 8, 9, 10, 13) for removing heat in its path from this pump body to this lining, this thermal barrier internally comprising a barrier cooling water circuit connected to said cooling circuit The device according to the present invention is further characterized by the fact that said thermal barrier (30, 32, 34, 36, 38, 40) is formed by a part of said water box (3, 5, 6) said barrier cooling circuit being connected, inside said water box, in series downstream from the part (EB) of said low pressure circuit which is in said lining cooling exchanger (EG), so as to facilitate the realization of this water box and this barr and effectively cool said seal with a moderate water flow in this low pressure circuit.

 An important characteristic of the present invention is therefore to integrate the intermediate exchanger for cooling the lining with the thermal barrier in a unlike water box which is fixed in the pump body at the level of the outlet of the shaft, around of it which runs right through it.

 Sufficient space is left around the shaft to slide the cartridge of the mechanical seal with its pumping ring comprising a CVPS screw).

 There is only one external circuit left to plug into the box: an inlet and a return of cooling water from the general circuit of the power plant.

 We thus obtain all the functions in two cartridges let us go up successively in the body - cooling of the packing - thermal protection - sealing - passage of the rotating shaft.

 A suitable construction of the lining cooling exchanger will be described below and allows, all having low pressure drops, a significant reduction in the cooling flow rate by using the same water for the thermal barrier and for refrigerating the lining.

 This simplifies assembly and takes up more space, thanks to a reduction in the number of hydraulic connections and auxiliary components, and this results in better reliability.

 With the aid of the attached schematic figures, a description will be given more particularly below, by way of nonlimiting example, how the present invention can be implemented in the context of the description which was given below. above. When the same element is represented in several figures, it is designated therein by the same reference sign.

 When one of these reference signs was used above it was to allow reference to these same figures and, in particular if it was in parentheses, by way of nonlimiting example. The mode of implementation described includes the provisions mentioned above as advantageous according to the present invention. It should be understood that the elements mentioned may be replaced by other elements ensuring the same technical functions.

 Figures 1 and 2 show a known device and have already been described.

 FIG. 3 represents a partial view in axial section of a food pump of a steam power plant using two identical shaft outlet devices according to the present invention.

 FIG. 4 represents a schematic view of the cooling circuits of one of these devices.

 Figure 5 shows an axial sectional view of this device.

 FIG. 6 represents an enlarged view of a detail VI of FIG. 5.

 In accordance with FIG. 3, a food pump of a nuclear steam power station with a nuclear boiler has an axis A and comprises a water inlet conduit 200 through which the water arrives in a radial direction not shown. An inner body 201 separates this water into two guided streams. by blades 203, represented by arrows 202 and symmetrical with respect to a plane of symmetry of pump 204 perpendicular to itaxis A.

 The water of each of these streams is distributed all around the shaft 2 by the pump body 1 and the internal body 201 of which only the parts located, in the figure, above this tree are shown, and it is directed according to arrows 208, with the help of guide lanes 2.05 towards radial blades of the central wheel 206 entered, born in rotation by the shaft 2.

 The water driven in rotation by these vanes is taken up by fixed diffuser vanes 210 which are oblique to the plane of the figure and direct the water towards an outlet volute 212 which has, in section not represented by the plane of symmetry 204, a spiral shape well known to specialists. Bearings of the shaft 2 are not shown, nor an external turbine which drives this shaft.

 Two symmetrical shaft outlet devices 214 and 216 are provided to prevent hot pressurized water from escaping into the external atmosphere while not interfering with the rotation of the shaft 2.

 The device 214 is represented in FIGS. 4, 5 and 5 which show the following elements 1 / Pump body: it contains a hot pressurized strip as well as the energy recovery members (diffuser, volute).

2 / Rotating shaft: it supports the wheel whose vanes 206 give the driving energy to this hot water. It comes out on each side of the body 1 to rest on the oil bearings. One of its ends is coupled to a drive turbine, not shown. The outlets are sealed by mechanical seals.

3 / External body of the water box: it is fixed to the pump body by 3 'screws. This boot contains cooling water. It has two functions: thermal screen and refrigeration which will be specified later.

4 / Insulating sleeve: it protects the shaft 2 from thermal shock and distributes the thermal gradient in the event of a stop.

4A / Key for fixing this socket.

5 / Fixing cover: it fixes the mechanical seal cartridge to the pump and closes the axially outer face of the water box.

6 / Packing box: it is part of the water box, contains the mechanical packing and constitutes the radially inner wall of the packing cooling exchanger EG. It contains the VPS stator part of a pumping ring which also includes a rotary screw VPB for entraining water in the packing cooling circuit.

7 / Rotating grain holder: it keeps the grain rotating and has on its peripheral part the VPR screw pumping the water to circulate it between the mechanical seal and the EG exchanger.

8 / Rotating grain: it is a ring of silicon carbide which rotates with the shaft 2 and which is in plan contact on rotating plane with the non-rotating grain 9. The sealing is done at the interface between these two grains .

9 / Non-rotating grain: it is a carbon ring impregnated with antimony which is kept under pressure on the grain 8. it is only mobile in translation.

10 / Non-rotating grain carrier: it maintains the grain 9 and allows significant axial displacements thereof.

11 / Shirt if it is linked to the shaft 2. It constitutes a wall of the mechanical seal in contact with this tree while protecting the latter. It constitutes an almost closed and removable assembly (cartridge) with the housing 6 and the cover 5.

 1 Key for fixing this shirt.

12 / Guard ring: in the event of major leaks, this ring stops the pressurized water jet which could damage the environment.

13 / Springs: although the mechanical seal is compensated (balance of pressures on the various faces), part of the bearing force of the grains is applied by these springs especially in the event of a pressure drop.

14 / Deflector it forces the circulation of water to lick the interface of the grains and improves their refrigeration.

15 / Inserts if they are retractable and during assembly or disassembly, they oblige the shirt 11 to follow the movement in translation of the cover 5 thanks to their engagement in a sort 16 of this shirt, so that the entire cartridge moves simultaneously nement.

 Preferably and in accordance with the figures, said packing cooling exchanger (EG) has an internal wall (6 ′ forming an internal lateral surface (EI) of this exchanger, this surface being coaxial with said pump shaft (2), - a wall external (26) forming an external lateral surface (3E) of this exchanger coaxial with the previous one, leaving between it a radial interval to form an annular space, - and a separating wall of exchanger (PS) arranged in this annular space for separating, on the one hand, a high pressure exchanger space (EH) which is radially interior and which communicates with said high pressure space (VH) in contact with the grains by two passages extending radially and located one (IH) at an axially inner end, the other (XH) at an axially outer end of this exchanger space to constitute a part of said packing cooling circuit and to separate on the other hand an exchanger space with b radially outer pressure seal (EB).

- Water circulation means (VPR, VPS) inside this box and driven by said shaft (2) to circulate water in the circuit.

- A low pressure cooling water circuit, - and a lining cooling heat exchanger for transferring heat from said lining cooling circuit to this low pressure cooling circuit while resisting the difference in pressure. water in these two circuits.

- This device being characterized by the fact that said packing cooling exchanger (EG) is formed by said water box (3, 5, 6), inside of it, said packing cooling circuit being completely inside this box, this box has an inlet (22) and an outlet (24) to allow the water from said low pressure cooling circuit to circulate between a part of this latter circuit which is outside the device and a part of this circuit which is inside this box and which passes through this lining cooling exchanger.

 Preferably, more particularly, and again in accordance with the figures, said separating wall (PS) consists of two walls which are substantially helical, which have different inclinations on the axis (A) of said pump shaft (2) and which join on two helical lines which have the same pitch and which are an outer helix formed on said outer lateral surface (Et) and an inner helix formed on said inner lateral surface (EI), so that this wall has substantially the shape of the surface of the threads of a screw, and that this wall has both a large heat exchange surface, and a high rigidity to resist said pressure difference despite a small thickness to facilitate heat exchange.

 Preferably, more particularly still, and still in accordance with the figures, said inner (rI) and outer (EE) lateral surfaces are cylindrical of revolution around said axis (A) of the pump shaft (2) so as to facilitate the production of said exchanger (6, 26, PS).

 Preferably and in accordance with the figures, said thermal barrier comprises a cooling wall with parasitic passage (30) which constitutes a wall of said water box and which surrounds said pump shaft (2) over a certain length with a small radial interval to avoid any contact between this fixed wall and this rotating shaft, this radial interval constituting a parasitic passage (30A) which allows the hot water inside the pump body (1) to communicate with said packing cooling circuit (VH, IH, EH, XH), - a thermal barrier core (32) inside this barrier, radially outside relative to said cooling wall of parasitic passage, and delimiting with this wall a water conduit in the general form of a coaxial sheet to allow the water of said low pressure circuit to cool the radially outer face of this wall so that the radially inner face of this wall cools the water standing in the said parasitic passage (30A) between the pump body and the packing cooling circuit., - a barrier water inlet pipe (34) for bringing the water leaving said exchanger space at low pressure (FB ) until this conduit delimited by the radially outer face of the parasitic passage cooling wall, - and a barrier water outlet conduit (36) for the exit of this water after it has cooled this wall.

 And we also adopt the preferred arrangements below, in accordance with the figures - Said barrier water inlet duct (34) has the general shape of a coaxial sheet and is delimited between said barrier core (32) and an axially outer barrier wall (38) which extends radially or obliquely from an axially inner end of said exchanger (EG) up to said parasitic passage cooling wall (30), - said outlet duct d barrier water (36) having the general shape of a coaxial sheet and being delimited between this same barrier core and an axially inner barrier wall (40) which constitutes an outer wall of said water box, so that these barrier water inlet and outlet conduits evacuate the heat transmitted by conduction from said pump body (1) to said water box.

- Said axially inner barrier wall (40) leaves a gap in the general shape of a coaxial sheet between it and the wall of said pump body (1) to form a sheet of thermally insulating stagnant water (42) and reduce heat transfer by conduction of said body towards said lining.

- The water in said packing cooling circuit (Vu, I; i, ES, id) flows in a general axial direction towards the inside of the pump in said packing cooling exchanger (C-) and in a general direction axial towards the outside of the pump in said high pressure space (EH) in contact with the grains, so that this exchanger operates against the current.

- The passage section of said barring water outlet conduit (36) is chosen to be sufficient for the speed of the water in this conduit to be substantially lower than in the passage between said barrier core (32) and said wall parasitic passage cooling (30), so that this duct also constitutes a thermally insulating gap between said pump body (1) and said seal (7, 8, 9, 10, 13).

- The radially outer face of said parasitic passage cooling wall (30) carries cooling fins (4Ji arranged in baffles.

 It appears from the above that we thus realize a water box which has three distinct heat exchange zones traversed in series - a first zone, in double helical form (the EG exchanger), separates the water under pressure circulating in the seal under 4C bars of cooling water at around 7 bars and used to evacuate the energy dissipated by the mechanical seal which is around 30 K9. The double helix shape allows high flow rates with little pressure drop, speeds sufficient for good thermal convection, and a large exchange surface.

- A second zone, cylir.drique with baffles (wall 30) is located near the shaft and cools a possible entry of hot water at high pressure due either to a leak in the mechanical seal, or to recirculation of water around the tree.

- A third and final zone (the conduit 36 and the wall 40) envelops the two preceding ones and brings the cooling water towards the outlet by making a thermal screen thanks to a low flow speed.

 More precisely, concerning this third zone (see FIG. 6) the water is at 1800C inside the body 1, the wall of this body locally has a thickness of 25 mm, the standing water sheet 42 has a thickness of 5 mm which allows the temperature to go from 165 C to 55 C, the wall 40 has a thickness of 7., and the water circulates in the conduit 36 at a temperature close to 50 C.

Claims (10)

REVLiDICATI0NS 1 / Shaft outlet device for high pressure and temperature water pump, in particular for food pump of a steam power plant. - This device being intended to be placed between the shaft (2) of a rotary pump and the fixed hollow body (1) of this pump at the outlet of this shaft outside this body to prevent hot water under circulating pressure in this pump body to escape into the outside space and so as not to hinder the rotation of this shaft, this shaft having an axis (A) around which it rotates, - this device comprising a mechanical seal itself comprising a non-rotating sealing grain (9) tightly connected to said pump body (1), - a rotating sealing grain (8) tightly connected to said shaft (2) and rubbing against it grain fixed on a friction surface in the form of a crown coaxial with this shaft, each of these two grains being in contact on the one hand, by a radially external surface, with a space under high pressure (VH) which communicates with the interior of this body and on the other hand, by a radially inner surface, with a space under low pressure (VB), the pressure of which is close to that of the atmosphere, - and grain support means (13) for axially pressing these two grains against each other so as to maintain on this surface a contact ensuring sealing between said volumes under high and low pressure, - this device further comprising a fixed water box disposed between said pump body (1) and said seal by surrounding it, this box forming a circuit for cooling water of high pressure packing suitable for removing on the one hand the heat reaching this packing and coming from said high temperature water circulating in said pump body (1), and on the other hand the heat generated by the friction of said grains one on the other, so as to maintain this lining at a suitable operating temperature, this circuit passing through said volume under high pressure (VH) in contact with said sealing grains, - of the means water circulation ens (VPR, WPS) inside this ball and driven by said shaft (2) to circulate water in the circuit, - a low pressure cooling water circuit, - and an exchanger lining cooling heat for transferring heat from said lining cooling circuit to this low pressure cooling circuit while resisting the difference in water pressures in these two circuits, - this device being characterized in that said packing cooling exchanger (EG) is formed by said water box (3, 5, 6), inside thereof, said packing cooling circuit being completely inside this box, this box containing an inlet (22) and an outlet (24) for allowing the water from said low pressure cooling circuit to circulate between a part of this latter circuit which is outside the device and a part of this circuit which is inside this gearbox and which passes through this lining cooling exchanger. 2 / Device according to claim 1, characterized in that said packing cooling exchanger (EG) has an internal wall (6) forming an inner lateral surface (EI) of this exchanger, this surface being coaxial with said pump shaft ( 2), - an external wall (26) forming an external lateral surface (EE) of this exchanger coaxial with the previous one, leaving between it a radial interval to form an annular space, - and a separating wall of exchanger (PS) disposed in this annular space to separate, on the one hand, a high pressure exchanger space (EH) which is radially interior and which communicates with said high pressure space (VH) in contact with the grains by two passages extending radially and located one (1H) at an axially inner end, the other (XH) at an axially outer end of this exchanger space to constitute a part of said packing cooling circuit and to separate on the other hand a radially external low pressure exchanger space (5B) forming part of said low pressure cooling circuit, this separating wall extending axially over the entire length of and annular space and radially through all of said gap between said interior lateral surfaces and exterior, going alternately from one to the other of these two surfaces several times along the length of this annular space. 3 / Device according to claim 2, characterized in that said separating wall (PS) consists of two walls which are substantially helical, which have different inclinations on the axis (A) of said pump shaft (2) and which join on two helical lines which have the same pitch and which are an external helix formed on said external lateral surface (EE) and an internal helix formed on said internal lateral surface (and), so that this wall has substantially the shape of the surface of the threads of a screw, and that this wall has both a large heat exchange surface, and a high rigidity to resist said pressure difference despite a small thickness to facilitate heat exchange. 4 / Device according to claim 3, characterized in that said inner side surfaces (EI) and outer (EE) are cylindrical of revolution around said axis (A) of the pump shaft (2) so as to facilitate the realization of said exchanger (6, 23, PS). 5 / Device according to claim 1, wherein, according to an arrangement in itself known, a fixed thermal barrier is formed around said pump shaft (2), in the vicinity thereof, between said pump body (1) and said seal (7, 8, 9, 10, 13) for discharging heat in its path from this pump body to this seal, this thermal barrier internally comprising a barrier cooling water circuit connected to said low pressure cooling circuit, - this device being characterized in that said thermal barrier (30, 32, 34, 36, 38, 40) is constituted by a part of said water box (3, 5, 6) , said barrier cooling circuit being connected, inside said water box, in series downstream of the part (EB) of said low pressure circuit which is in said packing cooling exchanger (EG), so as to facilitate the realization of this water box and this barrier e and effectively cooling said seal with a moderate water flow in this low pressure circuit. 6 / Device according to claim 5, characterized. by the fact that said thermal barrier comprises a parasitic passage cooling wall (30) which constitutes a wall of said water box and which surrounds said pump shaft (2) over a certain length with a small radial interval to avoid any contact between this fixed wall and this rotating shaft, this radial interval constituting a parasitic passage (30A) which allows the hot water inside the pump body (1) to communicate with said cooling circuit by flow (VH, IH, EH , XH), - a thermal barrier core (32) internal to this barrier, radially external with respect to said wall with cooling parasitic passage, and delimiting with this wall a water conduit in the general shape of a coaxial sheet to allow the said circulating water at low pressure to cool the radially outer face of this wall so that the radially inner face of this wall cools the water standing in said parasitic passage (30A ) between the pump body and the packing cooling circuit, - a barrier water inlet pipe (34) for bringing the water leaving said low pressure exchanger space (FB) to this pipe delimited by the radially outer face of the parasitic passage cooling wall, - and a barrier water outlet duct (36) for the outlet of this water after it has cooled this wall. 7 / Device according to claim 6, characterized in that said barrier water inlet conduit (34) has the general shape of a coaxial sheet and is delimited between said barrier core (32) and a axially outer barrier wall (38) which extends radially or obliquely from an axially inner end of said exchanger (EG) to said parasitic passage cooling wall (30), - said water outlet conduit barrier (36) having the general shape of a coaxial ply and being delimited between this same barrier core and an axially inner barrier wall (40) which constitutes an outer wall of said water box, so that these conduits the inlet and outlet of barrier water dissipate the transmitted heat. by conduction of said pump body (t) towards said water box. 8 / Device according to claim 7, characterized in that said axially inner barrier wall (40) leaves an interval in the general form of coaxial ply. between it and the wall of said pump body (1) to form a sheet of thermally insulating stagnant water (423 and reduce the heat transfer by conduotion from said Body to said packing. 9 / Device according to claim 7, characterized in that the water of said lining cooling circuit (VR, IM, EH, XH) flows in a central axial direction towards the inside of the pump in said cooling exchanger of packing (EG) and in a general axial direction towards the exterior of the pump in said space at high pressure (EH) in contact with the grains, so that this exchanger operates against the current 10 / Device according to claim 7, characterized by the fact that the passage section of said quarry water outlet duct (36) is chosen to be sufficient for the speed of the water in this cone to be substantially lower than in the passage between said barrier core (32) and said parasitic passage cooling wall (30), so that this duct also constitutes a thermally insulating gap between said pump body (i) and said seal (7, 8, 9, 10, 13). 11 / Device according to claim 6, characterized in that the radially outer face of said cooling wall of parasitic passage (30) carries cooling fins (44) dis  posed in baffles.