Patent Description:
The present disclosure also concerns thermodynamic systems including turbomachines and generators for waste heat recovery.

Several industrial processes produce a large amount of waste heat. Typical examples of waste heat generating processes are industrial processes for steel, glass and cement production. Other examples are thermodynamic processes for the generation of mechanical or electric power by conversion of thermal power generated by fuel combustion. Typically, power generation processes using fuel convert less than <NUM>% of the thermal power generated by combustion into useful electric or mechanical power. The temperatures of the exhaust combustion gas range typically between <NUM> and <NUM> and the exhaust thermal power can be worth multi MW (megawatt). The heat contained in the exhaust combustion gas is discharged in the environment and wasted. This has a severe environmental impact.

Systems already exist, which allow capturing part of the waste heat and convert it into useful power, or use it as such, for instance for heating of buildings. However, existing systems for converting part of the waste heat in useful electrical or mechanical power are complex and expensive, require large footprint and are demanding in terms of operational costs. They may also underperform in off design conditions. <CIT> discloses an integrated expander-motor compressor.

A need therefore exists for machines and systems, which overcome or alleviate one or more of the drawbacks of the systems of the current art mentioned above.

Disclosed herein is an integrated hermetically sealed turboexpander-generator, comprising a hermetically sealed casing arrangement, wherein a turboexpander, a fluid pressurizing turbomachine and an electric generator are arranged. The turboexpander, the electric generator and the fluid pressurizing turbomachine are mounted along the same shaft line, such that they rotate at the same speed. The electric generator is arranged at one end of the shaft line, so that thermal load thereon is minimized.

As used herein, a fluid pressurizing turbomachine is a turbomachine adapted to pressurize the working fluid flowing through the integrated machine. If the fluid is in a liquid state, the fluid pressurizing turbomachine includes a pump. If the fluid is in the gaseous state, the fluid pressurizing turbomachine includes a compressor. The nature of the fluid pressurizing turbomachine used depends mainly on the kind of thermodynamic cycle in which the integrated hermetically sealed turboexpander-generator is used. Usually, the fluid pressurizing turbomachine comprises a compressor, as Brayton cycles or other cycles not involving a change of phase of the working fluid are preferably involved in waste heat recovery. However, the possibility is not excluded of using a Rankine cycle or other cycles involving a phase change in the working fluid. In such case usually the fluid pressurizing turbomachine includes a pump.

As used herein, a hermetically sealed casing arrangement may include a single casing, which houses the three rotary machines mentioned above, with a common shaft extending therethrough. Rotary seals can be provided along the shaft, to prevent leakages from one rotary machine to the other, for example to separate the cooling gas of the electric generator from the working fluid processed through the turboexpander and the fluid pressurizing turbomachine. No rotary parts of the machine are however exposed outside the casing arrangement, such that leakages towards the environment are prevented.

The hermetically sealed casing arrangement may, however, also include two or more casings, each of which is hermetically sealed and houses one or two of the rotary machines mentioned above, i.e. the turboexpander, the fluid pressurizing turbomachine and the electric generator. In such case, torque is transmitted from one casing to the other through a magnetic joint, such that also in this case no rotating mechanical part is exposed towards the exterior of the casing arrangement, which remains hermetically sealed as a whole.

As used herein, a common shaft line can consist of a single shaft or of shaft line portions, i.e. separate shafts, which are coupled to one another physically by a joint, such as a flexible joint, or magnetically, through a magnetic joint, such that the whole shaft line rotates at the same rotary speed, except as far as the oscillations permitted by the joint are concerned. No gears or speed manipulating devices are required between rotary machines.

The common shaft line of the turboexpander, electric generator and fluid pressurizing turbomachine is supported by active magnetic bearings, thus avoiding the use of rolling bearings, as well as hydrostatic or hydrodynamic bearings. A lubricant or load bearing fluid circuit is thus not required, making the integrated and hermetically sealed machine simpler, less expensive and less critical as far as potential lubricant leakages are concerned.

In embodiments, the same working fluid is used also for cooling the active magnetic bearings of the integrated, hermetically sealed turboexpander-generator and for further cooling the electric generator.

The integrated, hermetically sealed turboexpander-generator is thus connected to the outside world only through the following:.

If required, additional flanges can be provided for circulating a cooling medium through or around the active magnetic bearings and the electric generator. As mentioned, the same working fluid can be used as cooling medium for the active magnetic bearings and/or for the electric generator. Suitable heat exchangers can be provided to keep the working fluid circulating in the active magnetic bearings and electric generator at suitable temperature, removing heat form the active magnetic bearings and from the electric generator.

No rotary mechanical component projects from the hermetically sealed casing arrangement towards the environment.

Each of the turboexpander and the fluid pressurizing turbomachine is arranged between respective bearings, i. e in an in-between bearings configuration. The electric generator is usually arranged between radial bearings.

In currently preferred embodiments, both the turboexpander and the fluid pressurizing turbomachine are multi section turbomachines, in which each section comprises at least one stage. The multi-stage/multi-section configuration allows reaching high pressure and temperature ratios, adapted to achieve high thermodynamic cycle efficiencies.

A compact combined, hermetically sealed machine is thus provided, which has limited dimensions and reduced cost.

Thus, the three machines (turboexpander, fluid pressurizing turbomachine and electric generator) required to convert waste heat into useful electric power are merged in a single, integrated, hermetically sealed machine. The hermetical seal avoids gas leakages in any operating conditions, thereby avoiding the need for any working fluid reintegration and also avoiding environmental pollution.

The use of active magnetic bearing avoids the need for any lubrication and possible contamination of the working fluid by the lubricant.

The single shaft line is driven by the turboexpander (turbine) that drives both driven machines, namely the electric generator and the fluid pressurizing turbomachine (compressor or pump). This simple layout allows large flexibility in the assembly, as it is possible to include turboexpander reheating and/or compressor intercooling without modifying the machine.

Embodiments and features of the integrated hermetically sealed turboexpander-generator are outlined below, reference being made to the attached drawings, and are set forth in the appended claims, the content whereof form an integral part of the present description.

Disclosed herein is also a thermodynamic system including a waste heat source, adapted to directly or indirectly transfer heat to a working fluid processed through an integrated, hermetically sealed turboexpander-generator as outlined above, to convert part of the waste heat into electrical power.

Embodiments of the thermodynamic system are described below with reference to the attached drawings.

To provide a more compact and less expensive thermodynamic system for recovering waste heat, a hermetically sealed integrated turboexpander-generator is disclosed herein, which includes a hermetically sealed casing arrangement, which houses a turboexpander and a fluid pressurizing turbomachine, in combination with the electric generator, which converts mechanical power generated by the turboexpander into electric power. The integrated, hermetically sealed combined machine avoids leakages along rotary shafts towards the outside environment, and avoids the need to connect separate rotary machines by shafts extending through the respective casings. A compact and leakage-free combination of rotary machines is thus obtained. A common shaft line, including the rotor of the electric generator, the rotary parts of the turboexpander and the rotary parts of the fluid pressurizing turbomachine, is supported by active magnetic bearings, such that lubrication circuits can be dispensed with. To reduce heat load on the electric generator, this latter is arranged at one end of the shaft line. Several useful arrangements of the various rotary machines will be described in detail here below.

The integrated turboexpander-generator can be used in a closed Brayton cycle using a suitable working fluid such as CO<NUM> in a supercritical cycle. The fluid pressuring turbomachine will in such case include a compressor. The use of a Rankine cycle for waste heat recovery is, however, not excluded. In such case the fluid pressurizing turbomachine includes a pump.

In the following description reference will be made to a system using waste heat from the exhaust combustion gas from a gas turbine engine. Those skilled in the art will nevertheless understand that the integrated turboexpander-generator and the relevant thermodynamic cycle disclosed herein can be used for recovering waste heat from other sources, such as any industrial process which produces waste heat at a suitable temperature as a by-product of the process. Different working fluids can be used in the thermodynamic cycle depending, inter alia, upon the temperature level of the waste heat. Specifically, supercritical carbon dioxide cycles can be used, but the use of other working fluids, e.g. other organic fluids such as pentane and cyclo-pentane, is not excluded.

Referring now to <FIG>, a simplified thermodynamic system <NUM> includes a source of waste heat <NUM> and a waste heat recovery circuit <NUM>. In the embodiment of <FIG> the waste heat source includes a gas turbine engine <NUM>, which is configured for power generation, i.e. for generating electric power through an electric generator <NUM>, electrically coupled to an electric power distribution grid <NUM>.

In other embodiments, the gas turbine engine <NUM> can be configured for mechanical drive, i.e. the mechanical power generated by the gas turbine engine <NUM> can be used as such, rather than being converted into electric power. Mechanical power can be exploited to drive a compressor or a compressor train, for instance in a natural gas liquefaction system or in a gas pipeline.

In the exemplary embodiment of <FIG> the gas turbine engine <NUM> is a two-shaft gas turbine engine, including an air compressor <NUM>, a combustion chamber <NUM> and a turbine section <NUM>. The turbine section <NUM> comprises a high-pressure turbine <NUM> and a low-pressure turbine <NUM>. In a manner known per se, the high-pressure turbine <NUM> is mechanically coupled to the air compressor <NUM> and the low-pressure turbine <NUM> is mechanically coupled to the electric generator <NUM>. Compressed air from the air compressor <NUM> is mixed with fuel and the mixture is ignited, to generate compressed, high-temperature combustion gas in combustion chamber <NUM>. The compressed, high-temperature combustion gas is expanded sequentially in the high-pressure turbine <NUM> to generate power to drive the air compressor <NUM>, and in the low-pressure turbine <NUM> to generate power to drive the electric generator <NUM>.

While in <FIG> a two-shaft gas turbine engine is illustrated, in other embodiments the gas turbine engine <NUM> may be a one-shaft gas turbine engine, or a three-shaft gas turbine engine, or any kind of gas turbine engine adapted to generate mechanical power for mechanical drive or electric generation purposes, as the case may be. The gas turbine engine <NUM> can be a heavy-duty gas turbine engine, or an aero-derivative gas turbine engine.

The exhaust combustion gas is discharged from the gas turbine engine <NUM> through a stack <NUM>. The exhaust combustion gas contains thermal energy at a temperature which may be as high as <NUM>. The waste heat recovery circuit <NUM> is used to convert part of said waste heat into further useful power, specifically in the form of electric power.

In the embodiment of <FIG>, waste heat is transferred from the gas turbine engine <NUM> to the waste heat recovery circuit <NUM> through an intermediate heat transfer loop <NUM>, for safety reasons. In this way, a working fluid processed in the waste heat recovery circuit <NUM> does not circulate around the gas turbine engine <NUM>. This is particularly useful if the working fluid used in the waste heat recovery circuit is a flammable or explosive fluid, e.g. an organic fluid such as cyclo-pentane.

A pump <NUM> circulates a heat transfer fluid (arrow F) in the closed intermediate heat transfer loop <NUM> through a first heat exchanger <NUM> and through a second heat exchanger <NUM>. The first heat exchanger <NUM> is arranged upstream of the stack <NUM>. In the first heat exchanger <NUM> the heat transfer fluid is in heat exchange relationship with the exhaust combustion gas discharged by the gas turbine engine <NUM> towards the stack <NUM>. Heat is transferred from the exhaust combustion gas to the heat transfer fluid. In the second heat exchanger <NUM> the heat transfer fluid is in heat exchange relationship with the working fluid processed through the waste heat recovery circuit <NUM>, for instance supercritical CO<NUM>, or another organic fluid and heat is transferred from the heat transfer fluid to the working fluid.

In other embodiments, not shown, the intermediate heat transfer loop <NUM> can be dispensed with. This is particularly the case if the working fluid is not flammable or explosive, for instance, if CO<NUM> is used. If no intermediate heat transfer loop <NUM> is used, a heat exchanger is provided between the gas turbine engine <NUM> and the stack <NUM>, through which heat is directly exchanged between the exhaust combustion gas and the working fluid circulating in the waste heat recovery circuit <NUM>.

The waste heat recovery circuit <NUM> includes an integrated turboexpander-generator <NUM>, wherein the rotary machinery required to convert waste heat into electric power is housed in a hermetically sealed casing <NUM>. As used herein, a "hermetically sealed casing" is a casing, which has inlet and outlet flanges for the circulation of the working fluid, but does not have a rotary shaft protruding therefrom or facing the environment, such that no rotary seals are required and fluid leakages along rotary shafts are avoided.

A hermetically sealed casing can be formed by one or more casing sections, coupled to one another such that the rotary components of the turboexpander-generator are entirely and sealingly housed in the casing, while torque is transmitted from one casing section to the other through a magnetic joint, without the need for a mechanical transmission.

While several embodiments of the turboexpander-generator will be described in detail with reference to the following <FIG>, in <FIG> the turboexpander-generator <NUM> is illustrated only schematically as broadly including a turboexpander <NUM>, a fluid pressurizing turbomachine <NUM> and an electric generator <NUM>, mounted along a common shaft line <NUM>. In the following description of several embodiments, the fluid pressurizing turbomachine <NUM> includes a compressor, as in preferred embodiments the working fluid circulating in the waste heat recovery circuit <NUM> performs a closed Brayton cycle, with no changes of phase of the working fluid. The use of a Rankine cycle is however not excluded. In such case the working fluid undergoes cyclic change of phase. In this case the fluid pressurizing turbomachine will include a turbopump.

High-pressure and high-temperature working fluid from the second heat exchanger <NUM> of the heat transfer loop <NUM> is expanded in the turboexpander <NUM> and heat contained in the working fluid is partly converted into mechanical power available on shaft line <NUM>. The mechanical power is partly used to drive the compressor <NUM> and the exceeding mechanical power is converted into electric power by the electric generator <NUM>. The electric power is delivered to the electric power distribution grid <NUM>, possibly through a variable frequency drive (VFD) <NUM>.

The expanded working fluid from the turboexpander <NUM> is chilled in a heat exchanger or heat sink <NUM>, and delivered to the compressor <NUM>. The compressed working fluid is delivered by the compressor <NUM> back to the heat exchanger <NUM>.

The embodiment of <FIG> further comprises a heat recuperator <NUM> upstream of the heat sink <NUM>. The heat recuperator <NUM> includes a heat exchanger that transfers heat from the expanded working fluid to the compressed working fluid, between the delivery side of compressor <NUM> and the second heat exchanger <NUM>.

The waste heat recovery circuit <NUM> of <FIG> is a simplified circuit. A more complex waste heat recovery circuit <NUM> is illustrated in the embodiment of <FIG>, where the same reference numbers indicate identical or equivalent parts as those shown in <FIG> and described above.

In <FIG> the integrated turboexpander-generator <NUM> includes a two-section turboexpander <NUM> and a two-section compressor <NUM>.

The first and second turboexpander sections are labeled <NUM> and <NUM>, respectively and are arranged in series, i.e. in sequence. The compressed and heated working fluid from the second heat exchanger <NUM> is partly expanded in the first turboexpander section <NUM> and further expanded to the final low pressure in the second turboexpander section <NUM>.

In the embodiment of <FIG> the turboexpander <NUM> is a reheated turboexpander. The partly expanded working fluid discharged from the first turboexpander section <NUM> is reheated in the second heat exchanger <NUM> prior to be subject to final expansion in the second turboexpander section <NUM>.

The first and second compressor sections are labeled <NUM> and <NUM> and are arranged in series. The expanded working fluid from the turboexpander <NUM> is partly compressed in the first compressor section <NUM> and further compressed to the final high-pressure in the second compressor section <NUM>.

In the embodiment of <FIG> the compressor <NUM> is an intercooled compressor. The partly compressed working fluid delivered by the first compressor section <NUM> is cooled in an intercooler heat exchanger <NUM> before being processed through the second compressor section <NUM>.

Moreover, the waste heat recovery cycle <NUM> of <FIG> further comprises a heat recuperator <NUM>. The heat recuperator <NUM> is aimed at exchanging heat between the expanded working fluid discharged by the second turboexpander section <NUM> and the compressed working fluid delivered by the second compressor section <NUM>. Since the expanded working fluid discharged by the second turboexpander section <NUM> is at a higher temperature than the compressed working fluid delivered by the second compressor section <NUM>, the recuperator <NUM> allows recovery of low-temperature heat from the exhaust working fluid, thus increasing the overall efficiency of the cycle.

While in <FIG> reheating, intercooling and heat recuperation are provided in combination, it shall be understood that in other embodiments, not shown, one or two of these efficiency-enhancing arrangements may be foreseen. For example, an intercooled compressor can be used in a cycle with heat recuperation but without reheating, or else with reheating and without heat recuperation. Similarly, heat recuperation can be used alone, without compressor intercooling and without reheating, or with an intercooled compressor without reheating, or else with reheating but without compressor intercooling.

In all embodiments, the rotary machines required to convert heat into electric power, namely turboexpander, compressor and electric generator, are all housed in the same hermetically sealed casing <NUM>, with the rotary components of the machinery on the same shaft line.

As will become apparent from the following description of various embodiments of the integrated turboexpander-generator <NUM>, the sequence in which the rotary machines are arranged in the casing <NUM> can be different from what is schematically shown in <FIG> and <FIG>.

With continuing reference to <FIG> and <FIG>, the following <FIG> schematically illustrate different arrangements of the machinery forming the integrated turboexpander-generator and compressor <NUM>. <FIG> show only schematically the rotary components of the integrated turboexpander-generator <NUM> and the mutual relationship therebetween. The outer hermetically sealed casing is omitted.

In all embodiments a single shaft line is provided, which is supported for rotation by a plurality of active magnetic bearings. As will be described in more detail below, the shaft line can include a single shaft, or a plurality of shafts, i.e. shaft line portions, for instance two shafts, drivingly coupled to one another by respective joints, to form a single shaft line where all shafts or shaft portions rotate at the same rotary speed, except the difference due to angular oscillations allowed by a flexible joint, if any, provided along the shaft line.

Referring now to <FIG>, in one embodiment the integrated turboexpander-generator <NUM> includes the shaft line <NUM> formed by a single shaft supported by a plurality of radial active magnetic bearings <NUM>, <NUM>, <NUM>, <NUM> and by one axial active magnetic bearing <NUM>. The position of this latter may be different from the one shown in <FIG>. The rotary machines are arranged in the following sequence, from left to right in the figure: electric generator <NUM> arranged between bearings <NUM> and <NUM>; turboexpander <NUM>, arranged between bearings <NUM> and <NUM>; compressor <NUM> arranged between bearing <NUM> and <NUM>. In the exemplary embodiment of <FIG> there is neither reheating nor intercooling. A single inlet flange and a single outlet flange are provided for the turboexpander <NUM> and a single inlet flange and a single outlet flange are provided for the compressor <NUM>.

In the embodiment of <FIG>, as well as in other embodiments disclosed later on, the turboexpander <NUM> can be a radial turboexpander, e.g. a centripetal turboexpander, or an axial turboexpander, or a hybrid axial-radial turboexpander. Similarly, the compressor <NUM> can be a radial compressor, i.e. a centrifugal compressor, an axial compressor, or a hybrid axial-radial compressor.

In the embodiment of <FIG>, as well as in other embodiments disclosed later on, the turboexpander <NUM> can be a single-section turboexpander. In preferred embodiments, however, the turboexpander <NUM> is a multi-section turboexpander. Similarly, the compressor <NUM> can be a single-section, or preferably a multi-section compressor.

The sequence in which the rotary machines are arranged can be different from the one illustrated in <FIG>.

According to the present invention, however, the turboexpander <NUM> is arranged in a central position, between the electric generator <NUM> and the compressor <NUM>. Since these latter are driven machines, by arranging the turboexpander <NUM> therebetween, the transmission of mechanical power along the shaft line <NUM> is optimized.

Moreover, the orientation of the turbomachines may be selected in various ways, as far as the inlet and outlet are concerned. In preferred embodiments, however, the turboexpander <NUM> is arranged with the discharge side oriented towards the electric generator, as shown in <FIG>, such that less thermal load is applied to the electric generator <NUM>.

<FIG> illustrates the same arrangement as in <FIG> and the same reference numbers designate the same parts as in <FIG>. In <FIG>, however, the compressor <NUM> is an intercooled multi-section compressor, as schematically illustrated at IC. The compressor <NUM> thus comprises two inlet flanges and two outlet flanges. Partly compressed gas from a first compressor section is cooled in an intercooler (see intercooler <NUM>, <FIG>) and delivered to the second compressor section for further compression.

<FIG> illustrates the same arrangement as in <FIG> and the same reference numbers designate the same parts as in <FIG>. In <FIG>, however, the turboexpander <NUM> is a reheated multi-section turboexpander, as schematically illustrated at RH. The turboexpander <NUM> has two inlet flanges and two outlet flanges. Working fluid partly expanded in the high-pressure turboexpander section is reheated prior to be delivered to the inlet of the second turboexpander section, as schematically shown in <FIG>.

<FIG> illustrates the same arrangement as in <FIG>, but using an intercooled, multi-section compressor <NUM> (see IC) and a multi-section reheated turboexpander <NUM> (see RH).

While in the embodiments of <FIG> the shaft line <NUM> is formed as a single shaft, in other embodiments the shaft line <NUM> may include two or more shaft line sections, i.e. two or more shafts coupled to one another by respective joints.

The embodiments of <FIG> are similar to the embodiments of <FIG>, but the shaft line <NUM> is formed by two shaft line portions, i.e. two shafts, labeled <NUM> and <NUM>, coupled to one another by a joint <NUM>.

The joint <NUM> can be a mechanical joint, such as a flexible joint or a rigid joint, such as a Hirth joint. In other embodiments, a magnetic joint can be used instead. If a magnetic joint is used, the casing <NUM> can be in actual fact a casing arrangement formed by two separate casings, each hermetically sealed, i.e. without any mechanical rotary part protruding outside the casing or casing portion. The torque along the shaft line is transmitted magnetically through adjacent casings.

In the embodiment of <FIG> the joint <NUM> is advantageously arranged between the electric generator <NUM> and the turboexpander <NUM>. If a magnetic joint <NUM> is used, the generator casing is physically isolated from the turboexpander and compressor casing. This allows isolating the generator cooling gas system from the working fluid circuit and controlling generator windage losses.

As mentioned above in connection with <FIG>, the mutual position of the electric generator <NUM>, turboexpander <NUM> and compressor <NUM>, as well as the position of the thrust bearing <NUM> can be different than the one illustrated.

The use of joints <NUM>, in particular flexible or magnetic joints, along the shaft line <NUM> reduces radial coupling of the shafts or shaft line portions at both sides of the joint and mitigates rotor dynamic risks.

In the embodiments of <FIG> a larger number of radial active magnetic bearings <NUM> is required, since a radial bearing is required at each side of the joint <NUM>.

While in the embodiments described above the hermetically sealed casing arrangement includes a single casing, if one or more magnetic joints are provided along the shaft line <NUM>, the casing arrangement can be formed by two or more separate casings or casing portions. One possible embodiment using a magnetic joint and two casings joined to one another to form a hermetically sealed casing arrangement is shown in <FIG>. The integrated turboexpander-generator is again labeled <NUM> and the various components thereof are labeled with the same reference numbers used in <FIG>.

The integrated turboexpander-generator <NUM> includes a hermetically sealed casing arrangement <NUM>, which comprises a first casing or casing portion <NUM> and a second casing or casing portion <NUM> arranged in sequence and mechanically coupled to one another.

The turboexpander <NUM> comprises a first turboexpander section <NUM> and a second turboexpander section <NUM> and is provided with reheating (RH). The compressor <NUM> is an intercooled compressor (IC) and comprises a first compressor section <NUM> and a second compressor section <NUM>. The turboexpander <NUM> and the compressor <NUM> are housed in casing portion <NUM> and are supported on shaft line portion <NUM>. This latter is supported by radial bearings <NUM>, <NUM>, <NUM> and by thrust bearing <NUM>.

The electric generator <NUM> is housed in the casing portion <NUM> and is supported therein for rotation on shaft line portion <NUM>, by means of two radial bearings <NUM> and <NUM>.

A magnetic joint <NUM> connects the shaft line portion <NUM> and the shaft line portion <NUM> and transmits torque generated by the turboexpander <NUM> from the shaft line portion <NUM> to the shaft line portion <NUM>, to drive the electric generator <NUM>.

The magnetic joint <NUM> comprises a first magnetic joint portion <NUM> housed in casing portion <NUM> and a second magnetic joint portion <NUM> housed in casing portion <NUM>. The two portions of the magnetic joint are coupled magnetically but not mechanically, such that they can be separated from one another by solid walls of adjoining first and second casing portions <NUM> and <NUM>. Power is transmitted through the facing walls of the casing portions through the magnetic field of the magnetic joint <NUM>.

When a casing arrangement comprising two separate casing portions <NUM> and <NUM> is used, a complete separation is obtained between the interior of the two casing portions. In the exemplary embodiment of <FIG> the electric generator <NUM> is thus hermetically isolated from the turbomachines and no rotary seals are required along the shaft line <NUM>, between the electric generator <NUM> and the two turbomachines, namely the turboexpander <NUM> and the compressor <NUM>.

As mentioned above, the active magnetic bearings <NUM>, <NUM> and the electric generator <NUM> can be provided with a cooling circuit using the working fluid processed by the integrated turboexpander-generator as a cooling medium. <FIG> show schematics of an active magnetic bearing <NUM> and of the electric generator <NUM> with relevant schematically represented cooling circuit.

A cooling circuit <NUM> for the active magnetic bearings <NUM>, <NUM> is shown in <FIG> and includes a circulating pump or fan <NUM> and a heat exchanger <NUM>, through which the cooling medium is circulated to discharge heat removed from the active bearings <NUM>, <NUM>. Reference numbers <NUM>, <NUM> indicate cavities and ducts for the circulation of the cooling medium through the active magnetic bearings. <NUM>, <NUM>.

A cooling circuit <NUM> for the electric generator <NUM> is schematically shown in <FIG>. The electric generator <NUM> is represented as including a rotor <NUM> rotationally mounted on shaft <NUM> and a stator <NUM> stationarily housed in the casing <NUM>. A pump or fan <NUM> circulates the cooling medium thorough a heat exchanger <NUM> to remove heat therefrom. Cavities <NUM> and ducts <NUM> are disposed inside the casing <NUM> for circulating the cooling medium through the stator <NUM> of the electric generator <NUM>.

The cooling circuits <NUM> and <NUM> may be combined in a single cooling circuit.

By using the same working fluid as a cooling medium, the system consisting of the integrated turboexpander-generator <NUM> and relevant cooling circuit(s) can be hermetically sealed, thus avoiding leakages of working fluid towards the environment surrounding the casing <NUM>.

Claim 1:
An integrated hermetically sealed turboexpander-generator (<NUM>), comprising:
a hermetically sealed casing arrangement (<NUM>; <NUM>, <NUM>);
a turboexpander (<NUM>; <NUM>, <NUM>) arranged in the hermetically sealed casing arrangement;
a fluid pressurizing turbomachine (<NUM>; <NUM>, <NUM>), arranged in the hermetically sealed casing arrangement (<NUM>; <NUM>, <NUM>); and
an electric generator (<NUM>), arranged in the hermetically sealed casing arrangement (<NUM>; <NUM>, <NUM>);
wherein:
the turboexpander (<NUM>; <NUM>, <NUM>), the fluid pressurizing turbomachine (<NUM>; <NUM>, <NUM>) and the electric generator (<NUM>) are arranged on a common shaft line (<NUM>; <NUM>, <NUM>), comprising at least one shaft rotatingly supported by active magnetic bearings (<NUM>, <NUM>-<NUM>) in the hermetically sealed casing arrangement (<NUM>; <NUM>, <NUM>); and
at least one of the turboexpander (<NUM>; <NUM>, <NUM>) and the fluid pressurizing turbomachine (<NUM>; <NUM>, <NUM>) is arranged between bearings of the active magnetic bearings;
characterized in that the electric generator (<NUM>) is arranged between bearings of the active magnetic bearings (<NUM>, <NUM>) at one end of the common shaft line (<NUM>; <NUM>, <NUM>);
wherein the turboexpander (<NUM>; <NUM>, <NUM>) is arranged in a central position between the electric generator (<NUM>) and the fluid pressurizing turbomachine (<NUM>; <NUM>, <NUM>); and
wherein each of the turboexpander (<NUM>; <NUM>, <NUM>) and the fluid pressurizing turbomachine (<NUM>; <NUM>, <NUM>) is arranged between respective bearings of the active magnetic bearings (<NUM>, <NUM>-<NUM>).