Coupling of a turbopump for molten salts

Abstract

The invention relates to a device comprising at least one vertical pump (3) and at least one associated turbine (4) for transporting, over a level difference, a heat-transfer fluid brought to a high temperature, wherein the device further comprises a device for mechanically coupling the turbine (4) with the pump (3), comprising a gearbox (21) with a gimbal coupling (41) located on the turbine (4) side, allowing the mechanical energy produced by the turbine (4) to be reused to actuate the pump (3).

Claims

1. A device comprising at least one centrifugal vertical axis pump (3) and at least one associated centrifugal vertical axis turbine (4) for transporting, over a level difference, a heat-transfer fluid brought to a high temperature, the pump (3) ensuring an upward movement of said fluid in a first section of a pipe (17) from a first cold storage reservoir (2) and the turbine (4) being actuated by said fluid during the downward return movement of said fluid in a second section of the pipe (17) toward a second hot storage reservoir (5), wherein the device further comprises a mechanical device for coupling the turbine (4) with the pump (3), said mechanical coupling device comprising a gearbox (21) with a gimbal coupling (41) located on the turbine (4) side, allowing the mechanical energy produced by the turbine (4) to be reused to actuate the pump (3), and wherein the centrifugal turbine (4) is a device substantially identical to the centrifugal pump (3) and has a vertical axis parallel to and of the same orientation as the centrifugal pump (3), but operated for having fluid flowing in the opposite direction.

2. The device according to claim 1, wherein the pump (3) or the turbine (4) is mono- or multi-staged, uni- or multi-cellular and has wheels with closed or semi-open radial vanes.

3. The device according to claim 1, wherein the pump (3) and the turbine (4) are designed to operate with a mixture of molten salts selected from the group consisting of sodium nitrate, potassium nitrate and lithium nitrate.

4. The device according to claim 1, wherein the pump (3) and the turbine (4) are designed to operate with a mixture of molten salts having pressures up to 60 bar.

5. The device according to claim 1, wherein the pump (3) and the turbine (4) are designed to operate with a mixture of molten salts whereof the temperature is comprised between 100 and 600° C.

6. A concentrated solar power plant comprising: a plurality of heliostats positioned on the ground around a central concentration tower (1), said tower comprising at its apex at least one thermo-solar exchanger (20); a first circuit (17) for transporting molten salts from the first cold storage reservoir (2) to said exchanger (20) and returning the molten salts brought to high temperature to second storage reservoir (5), said exchanger (20) being located at the apex of the tower (1), a height that is greater than that of the reservoirs (2, 5); a second circuit (18) for generating steam by means of heat exchange with the first circuit (17) of molten salts and producing electricity by means of a turbine/generator system (7, 8, 9); wherein the power plant further comprises the device comprising at least one vertical axis pump (3) and at least one associated vertical axis turbine (4) according to claim 1.

7. The device according to claim 1, wherein the centrifugal vertical axis turbine (4) is a reverse pump of the same design as the at least one centrifugal vertical axis pump (3) but with different vane wheels.

Description

SHORT DESCRIPTION OF THE DRAWINGS

(1) Embodiments according to the state of the art and to the invention are described below with more detail using the appended figures.

(2) FIG. 1, already mentioned, diagrammatically shows a concentrated solar power plant CSP of the type having a central tower, with molten-salt circulation and coupling to a conventional electricity-production system.

(3) FIG. 2 shows a diagrammatic view of the mechanical coupling system according to the invention, between the pump for conveying the heat-transfer fluid to the central tower and the power-recovery turbine upon the return of the heat-transfer fluid to the storage reservoir.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

(4) According to one preferred embodiment of the present invention, the pumps 3 and the power-recovery turbines 4 are mechanically coupled to each other in order to recover energy with the best possible yield.

(5) A specific type of pump is necessary for the molten-salt application according to the invention. Such pumps will for example have the following features: vertical shaft; (multi)cellular, mono- or multi-staged construction with closed (or semi-open) wheels; installation above the salt reservoir, preferably with an immersed body, in order to simplify drainage; construction with a cantilevered shaft possible if the immersion depth of the pump, i.e., the distance between the bedplate and the suction tubing, is small enough; failing this, intermediate bearings necessary on the shaft line; shaft tightness with the bearing plate achieved by a labyrinth seal, with gravitational return of the leaks toward the reservoir; variable-frequency electric motor; use of appropriate materials and construction to withstand the high temperatures of the molten salts, etc. The materials used will for example withstand corrosion and abrasion.

(6) Such pumps have already been used in the field of ground, parabolic solar collectors, but with relatively low fluid pressures.

(7) The sizing of the pump must take into account the following three parameters: its length (for example, approximately 15 m), its variable speed and the high power required.

(8) Advantageously, according to the invention, the power-recovery turbines will have the same design, optionally with specific vane wheels. In principle, operating the centrifugal pumps in the opposite direction suffices to achieve turbine mode. The pump-turbine mechanical coupling is ensured by a gearbox 21, with a gimbal coupler 41 on the turbine side in order to allow the differential expansions between the pump 3 and the turbine 4.

(9) In the state of the art, only in-line coupling systems between horizontal pump and turbine, with clutch, are known.

(10) Of course, the turbines 4 cannot recover the whole power consumed by the pumps, given the yields of the pumps and turbines, working in opposite directions.

(11) Still according to the invention, the power difference will be compensated for by electric pumps of the same type (not shown), that are necessary to overcome pressure losses and to start the system anyway.

KEY

(12) 1 solar concentration tower 2 cold salt reservoir 3 supply pump to the tower 4 recovery turbine 5 hot salt reservoir 6 flow pump toward the steam generator 7 steam generator 8 turbine(s) 9 electricity generator 10 condenser 11 deaerator 12 economizer 13 kettle boiler 14 superheater 15 repeater 16 mixing pump 17 molten-salt circuit 18 water/steam circuit 20 solar receivers and exchangers 21 gear box 41 cardan shaft

(13) TABLE-US-00001 TABLE 1 TURBINE CYCLE TOWER Rated Duration hours 6 24 17.9 Storage Therm MWh 2553 Elec MWh 894 894 Absorbed power MW 425 Turbine 37.3 50 Salt flow rate kg/s 970 To the exchangers 242 325 Temp. of the cold reservoir ° C. 260 Condenser T ° C. 45.8 Hot reservoir temperature ° C. 550 Condenser P bar 0.10 Salt weight tons 20952 Deaerator T ° C. 105 Volume m.sup.3 12040 Diameter m 31 Height m 16 Steam flow rate kg/s 30.8 41.2 Steam pressure bar 120 120 Steam temperature ° C. 530 530 Reheating pressure bar 20 20 Reheating temperature ° C. 530 530