DESCRIPTION

TECHN ICAL FIELD

The present invention relates to a turbomachine assembly, particularly an integral turbocompressor-turboexpander assembly.

BACKGROUND ART

Turboexpanders are widely used for industrial refrigeration, oil and gas processing and in low temperature processes. In some known applications turboexpanders are used in organic Rankine cycles (ORC). When an organic Rankine cycles is used in a mechanical drive appl ication, a turboexpander is normally connected to a turbocompressor which is used to compress a process gas. The connection requires the operative gas in the Rankine cycle to be separated from the process gas circulating in the turbocompressor. In addition the turboexpander and the turbocompressor normally operate at different speeds. For these reasons, the turbocompressor requires a high speed shaft which is connected to the turboexpander shaft by means of a gearbox or of a hydraulic coupling able to vary the speed ratio. The two separated shafts permit the two gasses to be kept separated, the gearbox (or hydraul ic coupling) permits the speed of the turbocompressor to be varied from the speed of the turboexpander.

The main drawback of this solution is the fact that two shaft mountings and the connection between them normally imply a large number of bearings, seals, complex components (for example gear wheels) and auxiliaries, thus increasing losses and cost.

The gearbox configuration is also limited in power due to gearbox inevitable l imitations of power and size. It is therefore desirable to modify known turbocompressor- turboexpander assemblies in order to achieve lower losses and costs, by reducing the overall assembly complexity, in particular in terms of the total number of components, without dimin ishing the assembly overall performance.

SUMMARY

According to a first embodiment, the present invention accomplishes such an object by providing a turbomachine assembly comprising :

- a shaft, - a radial gas expander supported on the shaft between at least one first bearing and at least a second bearing,

- a compressor supported on the shaft in overhung position adjacent to one or the other of said first and second bearings,

- said compressor including a plurality of movable inlet nozzles and said radial gas expander including a plurality of movable guide vanes.

Movable nozzles and vanes are used to regulate overall process and maximize the efficiency of the machine in all operating conditions. This can be done independently for the expander and the compressor, thus allowing the compressor and expander to be operated at the same speed, and therefore overcoming the need for a gearbox or hydraulic coupling between them.

Further advantages of the present invention are achieved with a turbomachine assembly obtained in accordance with the dependent claims. For example, the insertion of a seal on the shaft between the expander and compressor impellers allows two different gasses to be operated by them .

BRIEF DESCRIPTION OF TH E DRAWINGS Other object feature and advantages of the present invention will become evident from the following description of the embodiments of the invention taken in conjunction with the following drawings, wherein :

- Figures 1 is a sectional lateral view of a turbomachine assembly according to the present invention;

- Figure 2 is a schematic view of the turbomachine of Figure 1 ;

- Figure 3 is a schematic view of a possible variant, in accordance with the present invention, of the turbomachine of Figure 1 .

DETAILED DESCRIPTION OF SOME PREFERRED EMBODIMENTS OF THE INVENTION

With reference to the attached figures, a turbomachine assembly 1 comprises:

- a shaft 1 0 having a rotation axis Y,

- a radial gas expander 2 supported on the shaft 1 0 between a first group of bearings 1 1 and a second group of bearings 1 2,

- a centrifugal compressor 3 supported on the shaft 1 0 in overhung position .

In a typical embodiment of the present invention the radial gas expander 2 is included in an organic Rankine cycle operating a suitable organic gas, for example cyclopentane. However the present invention is not limited to organic Rankine cycle or to a specific gas operated by the radial gas expander 2.

The turboexpander 2 comprises a first, high pressure stage 2a and a second, low pressure stage 2b. The working fluid enters the first, high pressure stage 2a of the turboexpander 2, exits the first turboexpander stage 2a to be del ivered through an interstage path 1 6 to the inlet of the second, low pressure stage 2b of the turboexpander 2. The path 1 6 includes a plurality of struts 1 7 for guiding the gas flow from the first stage 2a to the second stage 2b in order to optimize the efficiency.

With reference to figures 1 and 2, the operative gas enters the high pressure stage 2a radially, flows through a first set of movable inlet guide vanes 5a and then through the impeller of the high pressure stage 2a. The operative gas exits the high pressure stage 2a axially and it is guided by the interstage path 1 6 to enter the low pressure stage 2b radially after flowing through a second of movable inlet guide vanes 5b. The operative gas exits the low pressure stage 2b axially and is directed outside the turboexpander 2 by an axial outlet 8.

As an alternative (fig . 3) the operative gas exits the low pressure stage 2b axially and is directed outside the turboexpander 2 by a radial outlet 9. According to different embodiments of the present invention (not shown) the turboexpander 2 is a single stage turboexpander or a multistage turboexpander having three or more stages.

According to different embodiments of the present invention (not shown) the turboexpander 2 is a multistage turboexpander where some of the stages comprise movable inlet guide vanes and the other stages comprise fixed inlet guide vanes.

In all possible embodiments of the present invention, at least one of the turboexpander stages comprises a movable set of inlet guide vanes.

The radial gas expander 2 is supported on the shaft 1 0 between a first group of bearings 1 1 , adjacent to the high pressure stage 2a, and a second group of bearings 1 2, adjacent to the low pressure stage 2b. The groups of bearings 1 1 , 12 are conventional and known in the art and each of them can comprise one or more bearings of the magnetic, gas or lubricated type or a combination thereof.

With reference to figures 1 and 2, the centrifugal compressor 3 is supported on the shaft 1 0 in overhung position, adjacent to the first group of bearings 1 1 . As an alternative (fig . 3), the centrifugal compressor 3 is supported on the shaft 1 0 in overhung position, adjacent to the second group of bearings 1 2.

In both the embodiments of figure 2 and 3, a process gas enters the turbocompressor 3 axially, flows through a plurality of movable inlet nozzles 20, then through an impeller and finally exits the turbocompressor 3 radially.

In general, according to the present invention, the plurality of movable inlet nozzles 20 is optional and there are possible embodiments which do not include them . The present invention is however not limited to a particular type of turbocompressor, for example a double flow compressor may be used instead of a single flow compressor.

The centrifugal compressor 3 processes, for example, a refrigerant fluid in an LNG system or a gas to be forwarded in a pipel ine. As a further alternative embodiment (not shown) the turbomachine assembly 1 , when the turboexpander 2 produces more power than needed by a single turbocompressor, comprises two overhung turbocompressors respectively adjacent to the first and second group of bearings 1 1 , 1 2. As a variant of the last embodiment, turbomachine assembly 1 comprises one overhung turbocompressor and one overhung electric generator respectively adjacent to the first and second group of bearings 1 1 , 1 2. In all the embodiments, the compressors, being mounted on the same shaft 1 0 of the turboexpander 2, are operated at the same speed n of the turboexpander 2. The value of speed n can be constant or variable.

The embodiments of figures 2 and 3 can be operated at constant speed . In such embodiments, the inlet gu ide vanes 5a, 5b and the inlet nozzles 20 permit to vary the operating point of the turboexpander 2 and the turbocompressor 3, respectively, in order to vary, for example, the inlet/outlet pressures or mass flow rate of each gas in the turboexpander 2 and in the turbocompressor 3. The operating points of the turboexpander 2 and the turbocompressor 3 are therefore varied independently from one another without needing to differentiate the relevant speeds, thus allowing a single shaft to be used for both the turboexpander 2 and the turbocompressor 3.

In other embodiments (not shown), where the movable inlet nozzles 20 are not present, the operating point of the turbocompressor can be varied by changing the rotating speed n of the shaft 1 0, while the operating point of the turboexpander 2 is varied by operating the inlet guide vanes 5a, 5b accordingly. The operating points of the turboexpander 2 and the turbocompressor 3 are therefore varied independently also in these embodiments.

Between the rad ial gas turboexpander 2 and the turbocompressor 3, the turbomachine assembly 1 comprises two seals 1 5, provided on the shaft 1 0 in respective position adjacent to the impellers of the turbocompressor of the turboexpander stage which is closer to the turbocompressor (high pressure stage in the embodiment of figure 2, low pressure stage in the embodiment of figure 3). Seals 1 5, which are conventional and known in the art, permit to separate from one another the two gasses respectively flowing in the turboexpander 2 and in the turbocompressor 3, thus allowing different gasses to be used in the turboexpander 2 and in the turbocompressor 3. With reference to figures 2 and 3, at an axial end of the shaft 10 opposite to the turbocompressor 3, the turbomachine assembly 1 further comprises a balance drum 1 9 to compensate the sum of axial thrusts generated in operation by the turboexpander 2 and the turbocompressor 3.

While the disclosed embodiments of the subject matter described herein have been shown in the drawings and fully described above with particularity and detail in connection with several exemplary embodiments, it will be apparent to those of ord inary skill in the art that many modifications, changes, and omissions are possible without materially departing from the novel teachings, the principles and concepts set forth herein, and advantages of the subject matter recited in the appended claims. Hence, the proper scope of the disclosed innovations should be determined only by the broadest interpretation of the appended claims so as to encompass all such modifications, changes, and omissions.