MULTIPLIER

DESCRIPTION

Field of the invention

The present invention relates to a turbomachine, for example a turbine or a compressor, provided with an integrated speed reducer/multiplier. In the first case, the turbine is suitable for thermodynamic steam cycles and is particularly suitable for an organic Rankine cycle (hereinafter also ORC cycle). In the second case, the compressor may belong to a heat pump system. The speed reducer/multiplier is used to reduce the turbine output speed or to increase the compressor input speed so that the solution is suitable for coupling with a generator or with an industrial electric motor, preferably with 4 poles.

Background art

As is known, a thermodynamic cycle is defined as a finite succession of thermodynamic transformations (for example isotherms, isochores, isobars or adiabatic) at the end of which the system returns to its initial state.

This cycle can be direct, for example a direct Rankine cycle, in which a thermal source is used for the production of mechanical/electrical energy and heat at a lower temperature than that of the thermal source. The thermodynamic cycle can also be of the inverse type, for example a heat pump cycle, in which a mechanical/electrical energy source is used together with a thermal source to produce heat at a higher temperature than that of the thermal source.

In particular, an ideal Rankine cycle in its simplest version is a thermodynamic cycle composed of two adiabatic transformations and two isobaric transformations, characterized by the fact that the working fluid undergoes changes of state, from liquid to gaseous and vice versa. In the case of a direct cycle, its purpose is to transform heat into work. This cycle is generally adopted above all in thermoelectric plants for the production of electricity and uses water as the driving fluid, both in liquid form and in the form of steam, with the so-called steam turbine.

More specifically, organic Rankine cycles (ORC) have been hypothesized and implemented using high molecular mass organic fluids for the most diverse applications, in particular also for the exploitation of low- medium enthalpy thermal sources. As in other steam cycles, the plant for an ORC cycle includes one or more pumps to feed the organic working fluid, one or more heat exchangers to carry out the preheating, vaporization and possible superheating or heating phases in supercritical conditions of the same working fluid, a vapor turbine for the expansion of the fluid, mechanically connected to an electric generator, a condenser which returns the organic working fluid to the liquid state and a possible regenerator to recover the heat downstream of the turbine and upstream of the condenser. A speed reducer is normally placed between the turbine and the electric generator in order to reduce the speed of the turbine shaft to values suitable for operating the electric generator. A heat pump cycle, on the other hand, envisages a compressor which, by absorbing energy from an electric motor, raises the pressure of the working fluid; a condenser in which the working fluid condenses and transfers heat to the user, a throttling valve (or in any case an expander) in which the working fluid in the liquid phase expands to a lower pressure and an evaporator in which the working fluid vaporizes by absorbing heat from the low-temperature heat source. A speed multiplier is normally placed between the electric generator and the compressor in order to increase the speed of the electric motor to values suitable for operating the compressor.

The critical component in the turbomachine-reducer/multiplier coupling is the rotary seal on the turbomachine shaft which must prevent the working fluid from escaping from inside the turbomachine itself. Furthermore, high rotation speeds of the turbomachine and high process temperatures make the proper functioning of this seal particularly critical.

Some known solutions foresee to use:

- a double mechanical seal with oil placed between the two as a barrier fluid. This solution has a limitation linked to applications in which the product of pressure and rotation speed exceeds a predetermined value. Furthermore, it cannot avoid that there is a small leakage of barrier oil towards the side of the turbomachine shaft where the working organic fluid is present, leakage which can become significant in the event of premature failure of the seal;

- in medium-small machines, up to a few hundred kW of the compressor, and operating at relatively low temperatures (< 100°C) it is often used a solution accepting that the lubricating oil, of a type that is not miscible with the working fluid, enters the heat pump circuit and is then separated from the working fluid and recovered;

- a double gas seal fed with inert gas (for example nitrogen). In addition to being expensive and axially very bulky, gas seals often have intolerable defects, such as the continuous entry of barrier gas towards the side of the shaft of the turbomachine where the working organic fluid is present (absolutely deleterious to performance of closed cycle systems such as ORC or heat pumps since the barrier fluid is a non-condensable gas). For this reason, this solution provides for the presence of further chambers and labyrinths, one of these fed by the vapor of the working fluid so as to collect in a special chamber, kept at a slightly lower pressure, the flow of working fluid and inert gas for a subsequent treatment in a special separator. In addition to being particularly expensive, this solution is complex and delicate to manage, even for example in the management of prolonged stops and start-ups;

- a double gas seal fed with the working fluid itself. If the working fluid itself (i.e., its vapor) is used, the operation of the seal itself may not be acceptable, as it is designed to work with a very clean dry gas compared to a vapor which can leave deposits, such as carbon deposits, in presence of high temperatures. If on the one hand, the use of the working fluid vapor does not create problems for the system in the case of leakage towards the side of the turbomachine shaft where the organic working fluid is present, on the other hand the leakage towards the other side of the double seal then needs to manage this leakage of process fluid, with a solution similar to what was previously described;

- for small or medium sized machines (up to a few hundred kW of mechanical power) a 'sealed' solution can also be used, i.e., in which there is in fact no outward rotating seal, since the support bearings of the shaft and the generator/electric motor, connected directly to the turbomachine, are immersed in the working fluid itself and the shaft itself rotates at a high rotation speed which does not allow the use of traditional industrial electric generators (for example, 2 or 4 poles) but high frequency generators, with special and expensive solutions to be adopted for the bearings themselves and for the coupling between the electrical network and the high frequency generator. In fact, this solution is not feasible especially for large turbomachine.

Therefore, there is a need for a design solution for the turbomachine that solves or at least mitigates the above-mentioned drawbacks.

Summary of the invention

The solution of the technical problems referred to in the previous paragraph is obtained, according to the present invention, with a turbomachine provided with a speed reducer/multiplier integrated in the turbomachine itself.

The proposed solution (which will preferably be applicable to turbomachine with a power higher than 100 kW) allows to overcome the limits and defects of what is currently available, providing for the use of a rotating seal towards the external environment of the traditional type, such as a so- called mechanical, installed on the slow shaft of a turbomachine. Therefore, this seal will operate under absolutely quiet speed and temperature conditions. Furthermore, the seal is easily replaceable because it is in fact external to the turbomachine itself.

It will be acceptable to have the lubricating oil, the turbine bearings and the reducer/multiplier itself 'contaminated' by small quantities of working fluid, as better explained below.

According to one aspect of the present invention, therefore, a turbomachine is described provided with an integrated speed reducer/ multiplier and a seal downstream of the speed reducer/ multiplier, having the characteristics stated in the independent product claim annexed to the present description.

Further embodiments of the aforementioned plant, preferred and/or particularly advantageous, are described according to the characteristics set forth in the attached dependent claims.

Brief description of the drawings

The invention will now be described with reference to the attached drawing (figure 1), which illustrates a non-limiting embodiment of a turbine equipped with a speed reducer. What will be said below with reference to the turbine can also be applied in the case of a compressor, where, as mentioned, the reducer will be replaced by a speed multiplier which in fact performs the same function as the reducer but with an inverted power flow mechanics that pass through it.

Detailed description

Referring to Figure 1, the integrated turbine/reducer system 20 comprises an expansion turbine 1 connected to a speed reducer 2. The speed reducer 2 reduces the rotation speed of the shaft 3 of the turbine to a value suitable for driving a preferably synchronous 4-pole electric generator 18 (of known type) connected to the electric net. For example, in the case of a 50Hz electric net, a 4-pole generator will rotate at 1500rpm (1800rpm on a 60Hz net) whereas the turbine typically requires a much higher rotational speed, such as 6000rpm (a compressor even higher speeds).

Advantageously, the turbine 1 operates in an organic Rankine cycle (ORC) plant.

Preferably, the turbine 1 is an axial turbine and even more preferably it is a multistage axial turbine with the rotor discs mounted cantilevered on the shaft 3 of the turbine 1.

Preferably, the speed reducer 2 is preferably an epicyclic speed reducer in order to keep the input and output shafts of the gear reducer also co-axial.

The shaft 3 of the turbine 1 is physically separated from an input shaft 2' of the reducer 2 and is supported by oil-lubricated rolling bearings 4 installed inside the casing 5 of the turbine shaft. The rolling bearings 4 of the shaft 3 of the turbine 1 provide both radial and axial support to the shaft itself. In order to isolate the process area of the organic working fluid of the turbine 1, i.e., the area in which the organic working fluid is expanded, from the outlet area of the turbine shaft 3, where the bearings are installed, preferably rolling bearings, a sealing device 6 is provided, such as for example a labyrinth seal, or in any case a device which does not have a perfect seal, preferably non-contacting seals. This type of seal does not provide a completely hermetic separation of the shaft 3 from the process zone but is suitable for operating at much higher speeds and temperatures than a rotary contact seal. Since inside the turbine there is a slightly higher pressure than that present in the casing 5 (or rather the pressure in the casing 5 is maintained at a slightly lower level than that of the turbine), the environment inside of the casing 5 of the shaft 3 receives a small flow rate of working fluid which mixes with the lubricating oil.

In order to avoid passage of oil from the environment of the speed reducer 2 to the environment of the turbine 1 it is possible to adopt an insulation ring (of a known type, as described in the Applicant's patent EP 2 591 211 Bl, and therefore not shown in figure) to completely seal the internal environment of the turbomachine from the environment of the casing 5. The shaft 3 of the turbine 1 is connected to the input shaft 2' of the speed reducer 2 via a coupling device 7.

The speed reducer 2 is designed to be pressure-tight and is connected to the casing 5 of the shaft 3 via a sealed connection pipe 7', preferably a bellows pipe, so that the pressure inside the speed reducer is equal to the pressure acting on the shaft 3 and there is no communication with the external environment.

The speed reducer 2 is also connected to the discharge side of the turbine (or to the suction side in the case of the compressor) via a pressure balancing line 8 in which a compressor 14 is installed, so that it is ensured that the pressure in the inside of the speed reducer 2 is slightly lower than that of the turbine discharge to achieve what was previously said, in order to avoid the entry of lubricating oil into the process area of the turbine 1. In this way lubricating oil infiltrations are avoided inside the process area, while, as already mentioned, there will be small infiltrations of organic working fluid inside the casing 5 of the shaft 3 and the speed reducer 2. As an alternative to connecting the balancing line 8 to the discharge side of the turbine, it may be convenient to connect this line to a suitable point in the system (ORC cycle or heat pump) where the pressure is in any case lower than the turbine discharge pressure, to avoid the need for the compressor 14. It is also possible to maintain the pressure value inside the turbine 1 slightly higher than in the reducer 2 through suitable design measures in the turbine, for example with a suitable arrangement of the labyrinths inside the turbine 1 itself.

The output shaft 2" of the speed reducer 2 is provided with a double mechanical seal 9, which thus guarantees complete sealing against the external environment. This double mechanical seal 9 works with rotation speeds and with temperatures which are much lower than those inside the turbomachine, thus resulting in a reliable and frequently used component in the industry, for example of rotary pumps, and will preferably be of the type with barrier fluid (typically the same lubricating oil as for bearings and gearbox). Furthermore, this double mechanical seal 9 is in such a position that it is not necessary to disassemble the shaft 3 of the turbine 1 in cases where the seal itself has to be repaired or replaced. Incidentally, it should be noted that in order to replace the seal it is also possible to operate the previously described insulating ring (of a known type, as described in the Applicant's patent EP 2 591 211 Bl, and therefore not shown in the figure) and the shut-off valve 19 to keep all the turbomachine and reducer environment separate from the ORC (or heat pump) cycle. The gears 10 and the rolling bearings 11 of the speed reducer are lubricated by forced circulation of the oil in a lubrication circuit 17. The oil is recovered in a tank 12 which can be integral with the speed reducer 2 or external to it, depending on the quantity of lubricating oil required. From the tank 12, the lubricating oil, by means of a suitable pump 16, is pumped into a cooler 13 and then into the lubrication circuit, having the function of both lubrication and cooling for the components of the speed reducer (gears, rolling bearings) and for the shaft 3 (and related rolling bearings 4) of the turbine 1. During operation, the lubricating oil will be contaminated by the organic working fluid which emerges from the sealing device 6 of the turbine 1 on the basis of the mixing properties of the two fluids. Therefore, a separator 15 can advantageously be installed to separate the organic working fluid from the lubricating oil, thus allowing the lubricating properties of the oil to be kept under control.

Preferably, in the event that the heat generated by the speed reducer 2 itself is not sufficient to provide a correct separation by evaporation of the working fluid contained in the lubricating oil, the separator 15 can be heated to a controlled temperature by means of the coil 21 to improve the separation process. The separated working fluid will be conveniently returned to the ORC (or heat pump) cycle circuit, for example by connecting it to balancing line 8 as in Fig. 1.

In addition to the embodiments of the invention, as described above, it should be understood that there are numerous further variants. It must also be understood that said embodiments are only exemplary and do not limit the object of the invention, nor its applications, nor its possible configurations. On the contrary, although the description given above makes it possible for the professional man to implement the present invention at least according to an exemplary configuration thereof, it must be understood that numerous variations of the components described are conceivable, without thereby departing from the object of the description invention, as defined in the appended claims.