DESCRIPTION The present invention relates to a set of channel nozzles for a centripetal turboexpander of an organic rankine cycle power generation unit, comprising a disk like plate with a number of vans, which are radially arranged on the plate. Further the invention relates to the use of the set of channel nozzles and a turbine. Modern waste heat utilization technologies represented by organic rankine cycle (ORC) power generation units require very compact, reliable and economically efficient turbomachinery solutions. A conventional approach in centripetal turbine design, as known from US 7,948,105 B2, allows developing turboexpanders with pressure ratios of up to 10. For perspective ORC systems with new heat transfer fluids like Novec 649 ^® and other, very often higher pressure ratios up to 25 are required. Implementation of conventional turboexpander design for pressure ratios above 10 will require multistage solutions leading to higher costs and reducing reliability. Multistage solutions may also require implementation of gearboxes leading to additional losses and requiring additional auxiliary systems for cooling and lubrication. To reduce costs and increase the efficiency it is desirable to be able to provide single stage centripetal turboexpander technology for perspective ORC systems with high pressure ratios at different scales.

Natural ORC fluids like Pentane are used in state of the art systems, which physical properties lead to relatively low pressure ratios below 10, suitable for implementation of conventional centripetal turboexpanders. A disadvantage of Pentane is its high fiammability, what leads to safety problems.

An alternative to the use of Pentane as ORC fluid is the use of Cyclopentane in two stage turboexpanders. The use of Cyclopentane with overheating, leads to relatively high pressure ratios. Disadvantage of Cyclopentane is that it is also a flammable fluid. A further disadvantage arises from the use of two stage turboexpanders. Two stage turboexpanders lead to increased costs compared to single stage turboexpanders and to a higher complexity of the system.

For small scale ORC systems with 100 to 500kW it is known to use refrigerants like HFC-245fa and HFC- 134a. These fluids require pressure ratios below 10 but are not environmental safe due to their impact on the global warming and their long lifetime within the atmosphere of more than 5 days. These fluids have to be replaced by new generation fluids like Novec 649 and others.

Novec 649° has very good environmental safety characteristics and heat transfer properties, allowing waste heat utilization in a wide temperature range. A problem using it in ORC systems is that it leads to relatively high pressure ratios of up to 20 and higher. In conventional turboexpander technology single turboexpander stages are used for cost effectiveness and reliability. High pressure ratios higher than 10 can not be used in conventional turboexpanders due to the fact, that those higher pressure ratios can not be released in conventional single stage turboexpanders.

The object of the present invention is to overcome the problems described above. Especially an object of the present invention is to specify a system with a single stage turboexpander able to be used with new heat transfer fluids, particularly environmental safe fluids with good thermal properties for heat transfer like Novec 649 . A further object of the present invention is to describe a set of channel nozzles for a centripetal turboexpander of an organic rankine cycle power generation unit and its use as well a turbine with this set of channel nozzles, able to overcome the problems described above, especially with reduced costs and complexity. The set of channel nozzles, which can also be described as nozzle block, should make it possible to use new heat transfer fluids like Novec 649 ^® in single stage turbines with high pressure ratios above 10.

The above objects are achieved by a set of channel nozzles for a centripetal turboexpander of an organic rankine cycle power generation unit according to claim 1 and the use of the before described set of channel nozzles according to claim 7 as well as a turbine with the before described set of channel nozzles according to claim 14. The set of channel nozzles for a centripetal turboexpander of an organic rankine cycle power generation unit according to the present invention comprises a disk like plate with a number of vans, which are radially arranged on the plate, with a number of vanes in the range of 4 to 8. Set of nozzles known from the state of the art have a high number of vans, for example described in US 7,948,105 B2 with 17 vans. With described channel nozzle vans of the kind known from the state of the art, high pressure ratios higher than 10 with new heat transfer fluids like Novec 649 in single stage turbines are not possible. The new design of the set of channel nozzles according to the present invention allows high pressure ratios higher than 10 with new heat transfer fluids like Novec 649 in just a single stage turbine. This reduces costs and complexity, makes it possible to use environmentally safe heat transfer fluids at high pressure ratios and lead so to high efficiency of a single stage turbine. In the set of channel nozzles according to the present invention channels can be formed between neighboring vanes on the plate, with an angle a in the range of 5 to 9 grad formed between the main direction of a respective channel at the inner circumference of the plate and a tangent to the interception of the inner circumference of the plate and the main direction of a respective channel. With channels of angle a in the range of 5 to 9 grad high pressure rations higher than 10, particularly higher than 20 can be reached even with new fluids like Novec 649° in centripetal turboexpanders of an organic rankine cycle power generation unit.

The vans can have a form of a droplet cross section, particularly with a backside of the droplet bent towards the inner circumference of the plate. This leads to a good channeling of the heat transfer fluid in the direction central part of the turboexpander. Particularly the set of channel nozzles can have the form of a brim of a hat, giving a favorable fluid flow. The disk like plate can comprise two radial parts, an outer flat annular part and an inner annular part, which is in the form of a raised disk like plate, particularly with a chamfer outer edge of the plate, and on top radially arranged vans. This as well leads to a favorable fluid flow.

The set of channel nozzles can have a fixed geometry, without flexible vanes movable relative to the main body of the set of channel nozzles. This reduces complexity, simplifies production of it, and gives a fixed angle of the fluid flow to get the desired flow within the centripetal turboexpander and to be able to reach high pressure ratios.

The use of a set of channel nozzles according to the present invention can comprise the use in a turbine, particularly in a centripetal turboexpander of an organic rankine cycle power generation unit.

The use can comprise a pressure ratio of turbine inlet pressure to the turbine outlet pressure greater than 10, particularly in the range of 10 to 25. A good pressure ratio of turbine inlet pressure to the turbine outlet pressure to be used can be in the range of 25. This makes it possible to use a turbine with high effectiveness.

Further the set of channel nozzles according to the present invention can be used in an organic rankine cycle, particularly with a medium as fluid whit good thermal dynamic properties, particularly a low evaporation temperature and / or high evaporation pressure, and / or with an environmental safe medium as fluid, particularly without global warming effect and / or low lifetime within the atmosphere of less than 5 days.

As a heat transfer fluid Fluoroketone can be used, particularly Novec 649°. This newly used fluid in turbines as heat exchange fluid gives the before mentioned advantages. It is environmentally safe, has good thermal dynamic properties, particularly a low evaporation temperature and a high evaporation pressure, and can be used in a single stage turbine with pressure ratios greater than 10.

The set of channel nozzles can be used in an organic rankine cycle with a velocity of the fluid within the channels higher than Mach 1, particularly with a velocity in the range of Mach 1.5 to 2.5, preferably in the range of Mach 1.8. With the described velocities it is possible to use a pressure ratio greater than 10 in a single stage turbine. The set of channel nozzles according to the invention can be used in combination with a turbine expander wheel in a turbine stage.

A turbine according to the present invention can comprise exactly one stage, which is a single stage with exactly one turbine expander and exactly one set of channel nozzles as described before.

The advantages in connection with the described method to use and described turbine according to the present invention are similar to the previously, in connection with the set of channel nozzles described advantages.

The present invention is further described hereinafter with reference to illustrated embodiments shown in the accompanying drawings, in which:

FIG. 1 illustrates an embodiment of a set of channel nozzles 1 according to the present invention in front view with a number of vanes 2 in the range of 4 to 8, particularly 7, and

FIG. 2 illustrates in front view the set of channel nozzles 1 of Fig. 1 with a turbine wheel 3 fitting in its middle opening 4, and

FIG. 3 the set of channel nozzles 1 and turbine wheel 3 of Fig. 2 in cross sectional view.

In FIG. 1 is shown an embodiment of a set of channel nozzles 1 according to the present invention in front view. It has the form of a brim of a hat, i.e. is disk like with a circular opening 4 in the middle. It comprises two flat radial parts, an inner part 5 and an outer part 6 of the disk. The, in radial direction inner part 5 of the disk is thicker than the outer part 6, with an edge 7 between both radial flat parts of the disk, which is slanted in the direction away from the middle of the disk.

On top respectively on the surface of the inner part 5 vans 2 are arranged. In the embodiment of FIG. 1 seven vans 2 are shown. According to the present invention the number of vans 2 should be in the range between 4 and 8.

The vans 2 have a form of a droplet cross section, with the same orientation of all droplets along the circumference of the inner part 5 of the disk and arranged on a circle with the same center point as the circular disk 1. The backside of the droplet form is tapered to the end and bent towards the inner circumference of the plate 1. The front side is rounded pointing in the direction of the circumference of the edge 7. Between neighboring vanes 2 on top of the disk like plate 1 channels are formed. Between the main direction of a respective channel 9 at the inner circumference of the plate and a tangent 8 to the interception of the inner circumference of the plate and the main direction of a respective channel an angle a in the range of 5 to 9 grad is formed. In the embodiment shown in FIG. 1 the angle a is 9 grad.

The vans 2 can be affixed to the inner disk like part 5 for example by screws, pins, clamps or other means. Drilled holes 10 can be comprised by the set of channel nozzles 1 to affix it in a turbine. As shown in FIG. 2 a turbine wheel 3 can be arranged within the circular opening 4 of the set of channel nozzles 1. This arrangement can be part of a centripetal turboexpander of an organic rankine cycle power generation unit, not shown in the figures for simplicity reasons. A stream of fluid, for example a Fluoroketone as heat transfer fluid, particularly Novec 649 ^® is directed by vans 2 through the channels of static set of channel nozzles 1 and through its circular opening 4 with the turbine wheel 3, and from there trough the turbine, particularly an one stage turbine. With the described set of channel nozzles 1 according to the present invention pressure rations higher than 10, particularly in the range of 25 can be released even with new, environmentally safe fluids like Novec 649 in just a single stage turbine. This leads to a high efficiency of the turbine, simple and cost effective design and environmentally safe components of the turbine. In FIG. 3 the set of channel nozzles 1 and turbine wheel 3 of Fig. 2 are shown in a cross sectional view. The vanes 2 in FIG. 3 are oriented in direction bottom of the picture. It is good visible in FIG. 3, how the turbine wheel 3 is arrange within the central circular opening 4 of the set of channel nozzles 1.

The set of channel nozzles 1 is usually made of a metal like stainless steel. But also other mechanically stable, chemically and heat resistant materials, for example aluminum alloys, plastics or ceramic can be used. The above described embodiments of the present invention can be used also in combination and combined with embodiments known from the state of the art. For example other cross sectional forms of the set of channel nozzles 1 are possible. The disk like form of the set of channel nozzles 1 can be instead of being flat also being inwardly or to the outside rounded. The part between the inner part 5 and the outer part 6 of the disk can be in form of a step, with a chamfer outer edge or without, or with a rounded edge. Different forms and arrangements are possible for the set of channel nozzles 1 according to the present invention.

One of the main advantages of the present invention is the high efficiency possible at high pressure rates greater than 10, with use of new environmentally friendly fluids like Novec 649° as heat transfer medium in just a single stage turbine.