Method and turbine for expanding an organic operating fluid in a rankine cycle

Abstract

A method and a turbine for expanding an organic operating fluid in a Rankine cycle includes the step of feeding the operating fluid to a turbine provided with a plurality of arrays of stator blades alternating with a plurality of arrays of rotor blades, to define corresponding turbine stages, constrained to a shaft which rotates on the respective rotation axis. The method also includes: a) causing a first expansion of the operating fluid in one or more radial stages of the turbine, b) diverting the operating fluid exiting from the radial stages in a direction axial and tangential with respect to the rotation axis, and c) causing a second fluid expansion in one or more axial stages of the turbine. Step b) corresponds to an enthalpy change of the operating fluid equal to at least 50% of the average enthalpy change provided for completing the fluid expansion in the turbine.

Claims

1. A method for expanding an organic operating fluid in a Rankine cycle, comprising: feeding the organic operating fluid to a turbine provided with a plurality of stages, each defined by an array of stator blades alternating with an array of rotor blades constrained to a shaft which rotates on a respective rotation axis, and further comprising the following steps: a) causing a first expansion of the organic operating fluid through one or more radial stages, and b) diverting the organic operating fluid in a blade array, named angular blades, from a substantially radial expansion direction to an expansion direction substantially axial and tangential with respect to an observer integral with said angular blades, and c) inducing a second fluid expansion of the organic operating fluid through one or more axial stages, wherein said step b) corresponds to an enthalpy change of the organic operating fluid equal to at least 50% of the average enthalpy change provided for completing the fluid expansion in the turbine.

2. The method according to claim 1, wherein the step a) is carried out by leading the organic operating fluid through at least one array of stator blades and a corresponding array of rotor blades disposed alternated one another in a radial direction, the step c) is carried out by leading the organic operating fluid through at least one array of stator blades and a corresponding array of rotor blades disposed alternated one another in an axial direction, and the step b) is carried out by leading the organic operating fluid through an array of stator or rotor angular blades.

3. The method according to claim 1, wherein the angular blades are rotor blades and wherein between steps b) and c) the following step is carried out: d) inverting a way of fluid expansion direction downstream of the array of angular blades.

4. The method according to claim 1, wherein at least 10% of an enthalpy change caused by the expansion of the operating fluid in said step b) is transformed to kinetic energy of the organic operating fluid exiting from the array of angular blades.

5. A turbine for an expansion of an organic operating fluid of a Rankine cycle, comprising arrays of stator blades and arrays of rotor blades, alternated to the former, and a shaft for supporting the rotor blades which is rotating on a respective rotation axis, wherein in a first section of the turbine the arrays of stator blades and the arrays of rotor blades alternate in a substantially radial direction, in a second section of the turbine the arrays of stator blades and the arrays of rotor blades alternate in a substantially axial direction, and between the first and the second sections of the turbine there is at least one array of stator or rotor blades, named angular blades, arranged to divert the organic operating fluid from a substantially radial expansion direction to a substantially axial and/or tangential expansion direction, wherein an enthalpy change of the organic operating fluid expanded through the angular blades is equal to at least 50% of an average enthalpy change provided for completing the expansion of the organic operating fluid in the turbine.

6. The turbine according to claim 5, wherein a leading edge of the angular blades extends in a substantially axial direction and a respective trailing edge extends in a substantially radial direction.

7. The turbine according to claim 5, wherein the angular blades extend in a substantially curved radial and axial direction.

8. The turbine according to claim 5, wherein said angular blades extend at least partially in a tangential direction to increase a tangential component of a fluid speed vector at least in a relative motion observed by an observer integral with the angular blades.

9. The turbine according to claim 5, further comprising an axial intake manifold of the organic operating fluid arranged aligned with the shaft, and wherein said shaft is cantileverly supported by bearings provided from an opposite side with respect to said intake manifold and wherein said angular blades are stator or rotor blades.

10. The turbine according to claim 5, further comprising a volute, wherein said angular blades are rotor blades and between them and the array of immediately downstream stator blades, the volute defines a curve of about 180° in which the axial direction of fluid expansion is inverted.

11. The turbine according to claim 10, wherein a passage section between the angular blades and said curve is at least partially increasing to obtain a slowdown of the organic operating fluid before the respective expansion direction is inverted.

12. The turbine according to claim 10, wherein downstream of said curve the volute is provided with at least one inflow/extraction port of the organic operating fluid.

13. The turbine according to claim 10, further comprising an intake manifold of the organic operating fluid radially arranged with respect to the shaft, in a substantially intermediate position between respective supporting bearings.

14. The turbine according to claim 5, wherein at least one array of rotor blades is assembled on supporting disks coupled to corresponding flanges of the shaft with a Hirth toothing.

15. The turbine according to claim 14, wherein upstream and downstream of a first supporting disk, with respect to the rotation axis, at least one chamber is provided and defined by a corresponding inner volume of the turbine, and wherein chambers, which are arranged on a same side of the first supporting disk are substantially isolated one from another, and wherein the first supporting disk is provided with at least one through hole for equalizing a pressure inside two chambers, which are separated by the first supporting disk itself, or for equalizing a pressure of a chamber downstream of the first supporting disk with a pressure inside the first section of the turbine.

16. The turbine according to claim 15, further comprising a second supporting disk, wherein the second supporting disk is placed downstream of the first supporting disk and it is provided with at least one through hole for equalizing a pressure inside the chamber immediately upstream of the second disk itself with exhaust pressure of the turbine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further details of the invention will be evident anyway from the following description course made with reference to the attached drawings, in which:

(2) FIG. 1 is a partial section view of a first embodiment of the turbine according to the present invention;

(3) FIG. 2 is a partial section view of a second embodiment of the turbine according to the present invention;

(4) FIG. 3 is a partial section view of a third embodiment of the turbine according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(5) FIG. 1 is a partial view, in an axially symmetrical section, of a turbine 1 according to the present invention for the expansion of an organic operating fluid.

(6) Preferably the operating fluid belongs to hydrocarbon class, more preferably to cyclic hydrocarbons. For example, the operating fluid is cyclopentane.

(7) The turbine comprises a shaft 2 extending in the axial direction X, an outer case 3, or volute, and a plurality of arrays of stator blades S.sub.1-S.sub.n and rotor blades R.sub.1-R.sub.n alternated one another, that is according to the scheme S.sub.1-R.sub.1; S.sub.2-R.sub.2; S.sub.n-R.sub.n, etc.

(8) In particular the turbine 1 is conceptually divided in a first section A and in a subsequent section B according to the expansion direction of the operating fluid vapor. In the first section A, named high-pressure section, a first expansion of the operating fluid is provided in a substantially radial direction, that is orthogonal to the X axis; in the second section B, named low-pressure section, a second expansion of the operating fluid is provided in a substantially axial direction, that is parallel to X axis.

(9) Between the two A and B sections of the turbine at least one array of angular stator blades AR is provided, which have the function of diverting the operating fluid flow from the initial radial direction of expansion to the axial, or even tangential, direction (direction orthogonal to the paper sheet while observing FIG. 1).

(10) In particular the turbine 1 shown in FIG. 1 comprises three stages radially arranged S.sub.1-R.sub.1; S.sub.2-R.sub.2; S.sub.3-R.sub.3 upstream the array of angular blades AR and one or more stages axially disposed R.sub.4-S.sub.4; R.sub.5-S.sub.5 (not shown), downstream the array of angular blades AR. Generally the number of stages upstream and downstream the angular blades AR can be different.

(11) The angular stator blades AR are constrained to the volute 3 and, as shown in figure, they extend according to a curved path (seen in axial section). The leading edge AR.sub.i of the blades AR extends preferably in the axial direction and the trailing edge AR.sub.o extends preferably in the radial direction; therefore each blade AR extends along a curved path with such a course of the fluid dynamic duct to decrease or eliminate (with respect to values upstream of the blades themselves) the average radial component of the operating fluid flow and to generate the axial and tangential components.

(12) Preferably the stator blades AR extend, when observed by an observer placed on the rotation axis X, with a first substantially radial length between a base and a peripheral portion next which the blades curve circumferentially or tangentially, and after they have an inter-blade duct that is gradually diverted in the axial and tangential direction.

(13) Some rotor blades R.sub.n and preferably all of them, are supported by supporting disks 8 constrained to the shaft 2 of the turbine 1 by means of a Hirth toothing identified by numeral reference 10 (in partial section). In particular, the supporting disks 8 are coupled to a flange 9 of the shaft, as shown in figure. The Hirth toothing allows the disks 8 to “float” in the radial direction, self-centering with respect to X axis.

(14) Steel stay rods (not shown) push the supporting disks 8 axially against the corresponding coupling flange of the shaft 2.

(15) The shaft 2 is supported by bearings (shown along with a fluidic sealing) at the respective ends, or else it is preferably cantileverly supported, with the bearings arranged at the same side of the supporting disks 8.

(16) The volute 3 is provided with one or more inflow manifolds 7 of the operating fluid vapor to be expanded.

(17) The path the vapor made during the relative expansion is shown by the arrows.

(18) FIG. 2 shows an alternative embodiment of the turbine 1, in which the angular blades AR are rotor blades, supported by a disk 8. Reference numerals equal to those indicated in FIG. 1 identify identical or equivalent elements.

(19) Differently from the preceding solution, the vapor flow of the operating fluid is diverted from the array of angular blades AR in the axial direction, but counterflow with respect to the axial extension of the turbine 1, that is diverted towards the part where the fluid intake in turbine 1 is provided. For this reason the volute 3 defines a toroidal duct 4 that curves like a U to invert the feeding flow direction, so that to direct the flow towards the low-pressure stages B.

(20) Preferably, downstream the array of rotor angular blades AR, the section of the duct 4 increases to cause the flow slowdown before the inversion of its feeding direction. Between the blade array AR and the low-pressure section B, one or more inflow or extraction ports 5 can be present.

(21) Also in this second embodiment the angular blades AR increase preferably the tangential component of speed vector of the vapor flow with respect to the value downstream the angular blades AR themselves.

(22) FIG. 3 shows a third embodiment of the turbine 1. The angular blades AR are stator blades and they are supported by the volute 3. Differently from the first embodiment, the shaft 3 is cantileverly supported on corresponding bearings provided in the same side of the volute 3, and in particular at the same side of the exhaust volute of the volute 3.

(23) In this embodiment the inflow of the vapor to be expanded is realized directly in the front direction, as shown in figure, by means of an axial manifold 6 assembled aligned and coaxial with respect to the shaft 2. Also in the first embodiment with the shaft 2 cantileverly assembled, the axial manifold 6 can be adopted.

(24) Also in the second and third embodiment the number of stator and rotor stages can be different from what shown in figures.

(25) Referring to FIGS. 1-3, the turbine 1 comprises the chambers C1, C2, C3, C4, each delimiting a volume inside the turbine characterized by a relative pressure value. Chambers C1, C2, C3, C4 are arranged to obtain a compensation of axial thrusts acting on supporting disks 8 by virtue of pressure differences between the different sections A-B of the turbine 1.

(26) Particularly referring to FIG. 1, labyrinth L keeps chamber C3 substantially separated from high-pressure section A. To avoid the pressure of operating fluid passing through the high-pressure section from pushing the first supporting disk 8 towards the chamber C1 (rightwards viewing FIG. 1), the latter is communicating with high-pressure section A by means of one or more through holes which open between the arrays S.sub.1 e R.sub.1 crossing the first disk 8, or else in other position in the section A itself.

(27) Similarly, chambers C2 and C4 are communicating one to another and to the exhaust section of the turbine through a duct extending through the second supporting disk 8; between the chamber C1 and C2 a separating labyrinth is provided.

(28) With the described arrangement, the pressure of chamber C1 is equal or near to the fluid pressure in the selected point of high-pressure section A and the pressure in chambers C2, C3 and C4 is equalized to the exhaust pressure of turbine 1.

(29) The turbine 1 shown in any one of FIG. 1-3 allows to carry out the method according to the present invention, as described above.

(30) Advantageously the turbine 1 allows to obtain a high enthalpy change and a high expansion ratio in a Rankine cycle with organic fluid.