ROTARY PISTON MACHINE AND ITS USE

Description

[0001] The invention relates to a rotary piston engine, and in particular to a Roots engine. Furthermore, the invention relates to a device for reducing the pressure of a pressurized gas, and in particular to a device for expanding the pressure of a pressurized gas by reducing the pressure while maintaining the volume of the gas to generate mechanical energy using a rotary piston engine, in particular a Roots engine. Furthermore, the invention relates to systems comprising such a device, and in particular to systems in which the pressurized gas can be steam.

[0002] Pressurized gases are used in a variety of industrial processes. One example is a steam cycle with a steam generator, pressure reduction station, and the steam processing unit.

[0003] If the pressure reduction station is to process large pressure references, turbomachinery is typically used, which provides steam at different pressures at different outlets. However, for only small pressure differences, turbomachinery is too complex.

[0004] For ecological and economic reasons, it is desirable to also use lower gas pressure reductions, for example to generate mechanical energy (and possibly electricity).

[0005] It is known to use rotary piston engines to expand a pressurized gas to generate mechanical energy. Such a machine is described in DE 10 2013 112024 A1, which discloses the preamble of claim 1. However, such rotary piston engines are also used to compress gases.

[0006] The use of machines with movable parts can be problematic when the gases reach high temperatures, such as 150 °C. In this case, the bearings for the movable parts of such machines must be protected from heat. However, this is not always easy to achieve, thus increasing the cost of manufacturing such machines and limiting their range of applications.

[0007] The object of the invention is to create a rotary piston machine which can be used both for the compression and expansion of gases at high temperatures, as is the case with water vapor, for example.

[0008] To achieve this object, the invention proposes a rotary piston machine which is provided with a housing having a rotor chamber with a gas inlet opening and a gas outlet opening, at least two rotors, each of which has a rotor shaft with two opposite axial ends and with at least two radially projecting rotor arms, wherein the rotor arms are arranged uniformly distributed over the circumference of the rotor shaft and the rotor arms of the rotors engage with each other and lie against each other in a gas-tight manner, wherein the housing has two housing end walls with bearings for the axial ends of the rotor shafts and, between these, a housing peripheral wall surrounding the rotors, in which the inlet opening and the outlet opening are arranged, wherein the inside of the housing peripheral wall is cylindrical between the inlet opening and the outlet opening and on both sides of the inlet opening and the outlet opening, and wherein the rotor arms move along the inside of the housing peripheral wall in a gas-tight manner when the rotors rotate,a synchronous gear arranged outside the rotor chamber for the synchronous rotation of intermeshing rotors in opposite directions, two fluid-cooled heat shields protecting the bearings of the rotor shafts in the housing end walls from the heat of the gas, which are arranged inside the rotor chamber on the inside of the housing end walls.

[0009] The rotary piston machine according to the invention has at least two intermeshing rotors arranged within a rotor chamber of the machine housing. A rotary piston machine constructed in this way is also referred to as a Roots-type machine, which is typically used as a compressor, but can also be used to expand gases in which, due to the process, small pressure differences occur, which can advantageously be used to generate mechanical energy using the rotary piston machine according to the invention.

[0010] The rotors, which are rotatably arranged in the rotor chamber of the housing, each have a rotor shaft with two or three or even more radially projecting rotor arms. The rotor chamber of the housing, in which the at least two rotors are accommodated, has cylindrical inner walls along which the rotors pass in a gas-tight manner as they rotate. The rotors are arranged between an inlet opening and an outlet opening of the housing. The bearings for the rotor shafts are located on two housing end walls, while the cylindrical inner wall is formed on the inside of a housing peripheral wall between the two housing end walls.

[0011] According to the invention, two heat shields are arranged in the rotor chamber of the housing, which rest against the housing end walls from the inside. These heat shields protect the bearings arranged in the housing end walls from excessive heating caused by hot gases used by the device to generate mechanical energy. Such hot gases are present, for example, in steam cycles, where the temperature of the steam can reach 200°C and more. Equipping the device without heat shields would run the risk of thermal damage to the bearings.

[0012] At least one of the two heat shields also protects the synchronous gear, which is typically located outside the rotor chamber, from heat exposure. This synchronous gear ensures equal, opposing rotation of adjacent, meshing rotors.

[0013] According to the invention, the heat shield is fluid-cooled, with the condensate from a steam circuit, for example, being used as the cooling fluid. This is particularly advantageous when the condensate is used as a barrier fluid and thus, in a sense, as a heat shield for cooling the rotor shaft seals. Such shaft seals are known in the art; examples include labyrinth seals, cooling ring seals, mechanical seals, floating ring seals, or stuffing box seals.

[0014] In a further advantageous embodiment of the invention, each heat shield has cooling channels passing through it, which extend between an inlet-side collecting channel and an outlet-side collecting channel and whose shape leads to identical hydraulic pressure conditions among each other.

[0015] The heat shields have through-holes through which the axial ends of the rotor shafts extend. Advantageously, the through-holes surround the shaft seals of the rotor shafts. The cooling channels surround the through-holes on two opposite sides and extend between the inlet-side collecting channel and the outlet-side collecting channel. Appropriate cooling channel routing ensures that all cooling channels have the same length or the same hydraulic pressure conditions.

[0016] The advantage of the invention lies in the relatively simple and trouble-free design of the rotary piston machine, which is considerably simpler in construction than, for example, a turbomachine. The rotary piston machine according to the invention achieves relatively good efficiencies at low pressure ratios, which is not usually the case with a turbomachine. The speed of the rotors is significantly lower than the speed of the bladed rotor of a turbomachine, which, moreover, is extremely complex in design due to its large number of different stator and rotor blades. The heat shields allow, for example, standard components to be used when selecting the rotary bearings for the rotors, as the heat shields protect these bearings from the high gas inlet temperatures. This eliminates the need for cooling the bearings and eliminates the need for more costly, temperature-resistant materials.The heat shields protect not only the bearings and the synchronous gear for the rotors but also the shaft seal areas. This represents a further advantage of the rotary piston engine according to the invention, especially when the processed medium (in the case of a steam cycle, water) can be used as the cooling fluid.

[0017] The Roots engine according to the invention (e.g., rotary piston engine and, in particular, Roots engine) operates isochorically. The engine utilizes small pressure differences to generate mechanical energy. On the other hand, the pressure of a medium can be increased by small pressure differences by applying mechanical energy. In both cases, thermal energy is not used to generate mechanical energy during expansion or to realize the pressure difference during compression.

[0018] A possible application of the rotary piston machine according to the invention can be seen in a device for relaxing a pressurized gas, in particular a water vapor, by reducing the pressure while maintaining the volume of the gas for generating mechanical energy, wherein the device is provided with a housing having a rotor chamber with a gas inlet opening for the inflow of pressurised gas and a gas outlet opening for the outflow of gas which has been reduced in terms of its volume and pressure and thus expanded, at least two rotors, each of which has a rotor shaft with two opposite axial ends and at least two radially projecting rotor arms, wherein the rotor arms are arranged uniformly distributed over the circumference of the rotor shaft and the rotor arms of the rotors engage with each other and lie against each other in a gas-tight manner, wherein the housing has two housing end walls with bearings for the axial ends of the rotor shafts and between these a housing peripheral wall surrounding the rotors, in which the gas inlet opening and the gas outlet opening are arranged,wherein the inside of the housing peripheral wall between the gas inlet opening and the gas outlet opening and on both sides of the gas inlet opening and the gas outlet opening is cylindrical, and wherein the rotor arms move gas-tight along the inside of the housing peripheral wall when the rotors rotate, wherein each rotor encloses a gas volume between each two of its arms that follow one another in the direction of rotation and the inside of the housing peripheral wall, and this gas volume can thus be transferred from the gas inlet opening to the gas outlet opening, two fluid-cooled heat shields that protect the bearings of the rotor shafts in the housing end walls from the heat of the gas, which heat shields are arranged inside the rotor chamber on the inside of the housing end walls, wherein the rotational energy of at least one of the rotor shafts is the mechanical energy resulting from the expansion of the gas.

[0019] The rotational energy available at the rotor shaft of at least one of the rotors can be used to operate a generator to generate electricity or to operate a mechanical system.

[0020] Alternatively, the rotary piston machine according to the invention can be used for the compression of hot gases by driving the rotor shaft of one of the rotors in rotation by a machine, in particular an electric machine.

[0021] In an advantageous embodiment of the invention, the device can be used in a steam generating and steam-operated or steam-processing plant, which is provided with a steam generator for generating steam at a pressure higher than the pressure of the steam for operating the plant or the steam to be processed, a unit to be operated with steam or a steam processing unit and a pressure reduction station between the steam generator and the unit to be operated with steam or the steam processing unit, wherein the aforementioned device according to the invention forms the pressure reduction station or is connected in parallel to it.

[0022] When the device according to the invention is connected in parallel to the pressure reduction station of the system, a shut-off valve can be provided that can be quickly closed if the steam pressure cannot or must not be reduced by releasing it in the device according to the invention, for example, because the safety and reliable operation of the system requires it. A control valve can also be provided in the parallel connection to the pressure reduction station, whereby another such control valve can also be part of the pressure reduction station.

[0023] But in general terms, the device according to the invention can be part of a pressurised gas plant provided with a unit which is to be operated with the pressurised gas or which processes it, and a pressure reduction station upstream of the unit for reducing the pressurised gas to a value suitable for the operation of or for processing in the unit, wherein the aforementioned device according to the invention forms the pressure reduction station or is connected in parallel to it.

[0024] Such a system can advantageously be a compressor that provides compressed gas, for example, for the operation of a blast furnace. Typically, turbocompressors are used as compressors, which are also commonly operated with surge limit control. If such a surge limit control is too slow, there is a risk that the compressor will exceed its surge limit, which leads to the generation of mechanical shocks and pulses not only within the compressor but also in the downstream system components. This, in turn, can cause system damage.

[0025] Therefore, when retrofitting such systems, it is advisable, for example, to further reduce the inlet pressure of the gas entering the compressor. This is sometimes done by "blowing off" the gas for safety reasons. It is now economically and ecologically sensible to use the device according to the invention instead of this "blowing off."

[0026] The advantage of the device according to the invention lies in the relatively simple and trouble-free design of the rotary piston machine, which is considerably simpler in construction than, for example, a turbomachine. The device according to the invention achieves relatively good efficiencies at low pressure ratios, which is not usually the case with a turbomachine. The speed of the rotors is significantly lower than the speed of the bladed rotor of a turbomachine, which, moreover, is extremely complex in design due to its large number of different stator and rotor blades. The heat shields allow, for example, standard components to be used when selecting the rotary bearings for the rotors, as the heat shields protect these bearings from the high gas inlet temperatures. This eliminates the need for cooling the bearings and eliminates the need for more costly, temperature-resistant materials.The heat shields protect not only the bearings and the synchronous gear for the rotors but also the shaft seal areas. This represents a further advantage of the device according to the invention, particularly when the processed medium (in the case of a steam cycle, water) can be used as the cooling fluid.

[0027] The invention is explained in more detail below using an exemplary embodiment and with reference to the drawing. In detail: According to the invention, a rotary piston machine is used to relax the pressurized gas by reducing the pressure and maintaining the volume of the gas. The rotary piston machine has at least two intermeshing rotors which are rotatably mounted in a housing. The two rotors each have a rotor shaft with two or three or even more radially projecting rotor arms. The rotor chamber of the housing, in which the at least two rotors are accommodated, has cylindrical inner walls along which the rotors pass in a gas-tight manner as they rotate. The rotors are arranged between an inlet opening and an outlet opening of the housing.The bearings for the rotor shafts are located on two housing end walls, while the cylindrical wall inner side is formed on the inside of a housing peripheral wall between the two housing end walls.

[0028] Such a rotary piston engine is also called a Roots engine, which is typically used as a compressor. The device according to the invention is an isochoric engine, i.e., a machine that reduces the pressure of the gas while leaving its volume unchanged.

[0029] According to the invention, two heat shields are arranged in the housing, which rest against the housing end walls from the inside. These heat shields protect the bearings arranged in the housing end walls from excessive heating caused by hot gases used by the device to generate mechanical energy. Such hot gases are present, for example, in steam cycles, where the temperature of the steam can reach 200°C and more. Equipping the device without heat shields would run the risk of thermal damage to the bearings.

[0030] At least one of the two heat shields also protects the synchronous gear, which is typically located outside the rotor chamber, from heat exposure. This synchronous gear ensures equal, opposing rotation of adjacent, meshing rotors.

[0031] According to the invention, the heat shield is fluid-cooled, with the condensate from a steam cycle, for example, being used as the cooling fluid. This is particularly advantageous when the condensate is used as a barrier fluid and thus, in a sense, as a heat shield for cooling the shaft seals of the rotors. Such shaft seals are known in the art; a labyrinth seal is one example.

[0032] The rotational energy available at the rotor shaft of at least one of the rotors can be conveniently used to operate a generator to generate electricity.

[0033] In a further advantageous embodiment of the invention, each heat shield has cooling channels passing through it, which extend between an inlet-side collecting channel and an outlet-side collecting channel and whose shape leads to identical hydraulic pressure conditions among each other.

[0034] The heat shields have through-holes through which the axial ends of the rotor shafts extend. Advantageously, the through-holes surround the shaft seals of the rotor shafts. The cooling channels surround the through-holes on two opposite sides and extend between the inlet-side collecting channel and the outlet-side collecting channel. Appropriate cooling channel routing ensures that all cooling channels have the same length or the same hydraulic pressure conditions.

[0035] In an advantageous embodiment of the invention, the device can be used in a steam generating and steam-operated or steam-processing plant, which is provided with a steam generator for generating steam at a pressure higher than the pressure of the steam for operating the plant or the steam to be processed, a unit to be operated with steam or a steam processing unit and a pressure reduction station between the steam generator and the unit to be operated with steam or the steam processing unit, wherein the aforementioned device according to the invention forms the pressure reduction station or is connected in parallel to it.

[0036] When the device according to the invention is connected in parallel to the pressure reduction station of the system, a shut-off valve can be provided that can be quickly closed if the steam pressure cannot or must not be reduced by releasing it in the device according to the invention, for example, because the safety and reliable operation of the system requires it. A control valve can also be provided in the parallel connection to the pressure reduction station, whereby another such control valve can also be part of the pressure reduction station.

[0037] But in general terms, the device according to the invention can be part of a pressurised gas plant provided with a unit which is to be operated with the pressurised gas or which processes it, and a pressure reduction station upstream of the unit for reducing the pressurised gas to a value suitable for the operation of or for processing in the unit, wherein the aforementioned device according to the invention forms the pressure reduction station or is connected in parallel to it.

[0038] Such a system can advantageously be a compressor that provides compressed gas, for example, for the operation of a blast furnace. Typically, turbocompressors are used as compressors, which are also commonly operated with surge limit control. If such a surge limit control is too slow, there is a risk that the compressor will exceed its surge limit, which leads to the generation of mechanical shocks and pulses not only within the compressor but also in the downstream system components. This, in turn, can cause system damage.

[0039] Therefore, when retrofitting such systems, it is advisable, for example, to further reduce the inlet pressure of the gas entering the compressor. For safety reasons, this is sometimes achieved by "blowing off" the gas. It is now economically and ecologically sensible to use the device according to the invention instead of this "blowing off."

[0040] The invention is explained in more detail below using an exemplary embodiment and with reference to the drawings. In detail: Fig. 1 is a perspective view of an embodiment of the rotary piston machine, Fig. 2 is a section through the rotary piston machine to illustrate the arrangement and intermeshing of two rotors of the rotary piston machine, Fig. 3 is a further sectional view through the rotary piston machine to illustrate the bearings and their heat protection by the heat shields, Fig. 4 is a plan view of one of the heat shields with the cooling channel guide and Fig. 5 is an example of an application of the rotary piston machine according to the invention in which mechanical energy can be generated by expanding a pressurised gas, which is water vapor, and thus by reducing the pressure of the gas.

[0041] Fig. 1 shows schematically a rotary piston engine 10 as a Roots engine, which has a housing 12 with a gas inlet opening 14 and a gas outlet opening 16. Between the two openings there is a rotor chamber 18 (see Fig. 2). The housing 12 has a peripheral wall 20 provided with the two openings and two housing end walls 22. Flanged to one of the two housing end walls 22 is a cover 24 for a synchronous transmission 26.

[0042] A first cross-sectional view through the housing 12 shows Fig. 2In this exemplary embodiment, two rotors 28 are located in the rotor chamber 18 of the housing 12, each having three rotor arms 30, which in turn protrude radially and evenly distributed over the circumference from a rotor shaft 32. The inner side 34 of the housing peripheral wall 20 is cylindrical. As is generally known with Roots machines, the intermeshing rotors form a gas-tight seal between them, which is also the case with the inner side 34 of the housing peripheral wall 20. Minimal clearances are typically provided here, so that the rotors 30 do not directly contact the inner side 34 of the housing peripheral wall 20, but rather move along it at a minimal distance.

[0043] In the second cross-sectional view according to Fig. 3 Among other things, the synchronous gear 26 can be seen. The shafts 32 of the two rotors 28 are rotatably mounted on the housing end walls 22, which Fig. 3shown at 36. Between the rotor chamber 18 and the rotary bearings 36 there is a shaft seal 38, which can be designed, for example, as a labyrinth seal.

[0044] Two heat shields 40, located within the rotor chamber 18 on the inside of the housing end walls 22, protect the pivot bearings 36 and the synchronous gear 26 from thermal influences caused by hot gases flowing through the rotary piston engine 10. The two heat shields 40 have through-openings 42 for the shafts 32 of the rotors 28. These heat shields 40 are cooled by a fluid and protect the pivot bearings 36 and the synchronous gear 26 from heat influences. The shaft seals 38 are located in the through-openings 42 (or behind them as viewed from the rotor chamber 18).

[0045] A plan view of the cooling channel side 44 of a heat shield 40 facing the housing end walls 22 and lying against the inside thereof in the installed state shows Fig. 4 The cooling channel side 44 has two coolant collection channels 46, 48, between which are located several cooling channels 50 that connect the two collection channels 46, 48. The collection channels 46, 48 and the cooling channels 50 are machined as grooves into the cooling channel side 44 of the heat shield 40. A circumferential seal 51 seals the cooling channel side 44 from the inside of the housing end wall 22. The design of the cooling channels 50 is selected such that the hydraulic conditions in all cooling channels 50 are essentially identical.

[0046] An application example of the rotary piston machine 10 according to the invention for generating electrical energy by utilizing low differential pressures of gases, in particular of water vapor, is shown in Fig. 5This figure shows a steam circuit 52 in which steam is generated at pressure P1 in a steam generator 54. This steam flows via a pressure control valve 56 to a steam processing unit 58, where the steam expands and condenses. The condensate flows via condensate line 60 to a boiler feed pump 64, which brings the condensate to pressure P1 and feeds it to the steam generator 54.

[0047] Connected in parallel to the pressure control valve 56, which, more generally, is a pressure reduction station, is the rotary piston engine 10 according to the invention, which may be preceded by a further pressure control valve 66 and / or may also be connected in parallel to a pressure control valve 68. Furthermore, a shut-off valve 70 is provided, which is closed when the pressure reduction of the steam required for the operation of the rotary piston engine 10 is not available due to process conditions. The rotary piston engine 10 drives a generator 72 to convert the pressure difference of the steam into electrical energy.

[0048] As in Fig. 5As shown, the condensate is used to cool the rotary piston machine 10 or the heat shields 40 of the rotary piston machine 10. Typically, the shaft seals 38 are also cooled or supplied with a sealing medium. The condensate can also be used for this purpose. For this purpose, the condensate is branched off downstream of the boiler feed pump 64 via a branch line 62 and fed to the two cooling plates of the rotary piston machine 10, before then entering the condensate line 60. Pressure control valves 74, 76 can be located in the branch line 62 both upstream and downstream of the heat shields 40. LIST OF REFERENCE SYMBOLS

[0049] 10 Rotary piston machine 12 Casing 14 Gas inlet opening 16 Gas outlet opening 18 Rotor chamber 20 Casing peripheral wall 22 Casing end wall 24 Cover 26 Synchronous gear 28 Rotor 30 Rotor arms 32 Rotor shaft 34 Inside of the casing peripheral wall 36 Pivot bearing 38 Shaft seal 40 Heat shield 42 Through opening 44 Cooling channel side 46 Collecting channel 48 Collecting channel 50 Cooling channel 51 Seal 52 Steam circuit 54 Steam generator 56 Control valve 58 Steam processing unit 60 Condensate line 62 Branch line 64 Boiler feed pump 66 Pressure control valve 68 Pressure control valve 70 Butterfly valve 72 Generator 74 Pressure control valve 76 Pressure control valve

Claims

1. A rotating piston engine comprising - a housing (12) having a rotor chamber (18) with a gas inlet opening (14) and a gas outlet opening (16), - at least two rotors (28), each of which has a rotor shaft (32) with two opposite axial ends and with at least two radially protruding rotor arms (30), wherein the rotor arms (30) are arranged to be evenly distributed across the circumference of the rotor shaft (32), and the rotor arms (30) of the rotors (28) engage with each other and in doing so rest against each other in a gas-tight manner, - wherein the housing (12) comprises two housing end walls (22) with bearings (36) for the axial ends of the rotor shaft (32) and a housing circumferential wall (20) therebetween surrounding the rotors (28), in which the gas inlet opening (14) and the gas outlet opening (16) are arranged, wherein the inside (34) of the housing circumferential wall (20) is cylindrically formed between the gas inlet opening (14) and the gas outlet opening (16) and on both sides of the gas inlet opening (14) and the gas outlet opening (16), and wherein the rotor arms (30) move along the inside (34) of the housing circumferential wall (22) in a gas-tight manner when the rotors (28) are rotating, - a synchromesh gear (26) arranged outside the rotor chamber (18) for synchronous rotation of intermeshing rotors (28) in opposite directions, - characterized by two fluid-cooled heat shields (40) protecting the bearings (36) of the rotor shafts (32) in the housing end walls (22) from heat of the gas, and arranged within the rotor chamber (18) inside on the housing end walls (22).

2. The rotating piston engine according to claim 1, characterized in that each heat shield (40) comprises cooling channels (50) passing therethrough, which extend between an input side related collecting channel (46) and an output side related collecting channel (48) and whose design leads to the same hydraulic pressure ratios between them.

3. The rotating piston engine according to claim 2, characterized in that each head shield (40) comprises one passage opening (42) per rotor (28) for an axial end of the rotor shaft (32) of the respective rotor (28), that the input side related collecting channel (46) and the output side related collecting channel (48) are each arranged on opposite sides of the passage opening (42), and that the cooling channels (50) extend around the passage openings (42).

4. The device according to any one of claims 1 to 3, characterized in that the bearings (36) for the axial ends of the rotor shafts (32) of the rotors (28) are provided with labyrinth seals, or cooling ring seals, or mechanical seals, or floating seals, or stuffing box seals (38).

5. Use of a rotating piston engine according to any one of claims 1 to 4 for compensation of a gas by driving the rotor shaft (32) of one of the rotors (28) by a machine, in particular by an electric machine, in a rotating manner.

6. Use of a rotating piston engine according to any one of claims 1 to 4 for generating mechanical energy by expanding a pressurized gas, in particular pressurized water vapor, by the gas entering the rotor chamber (18) through the gas inlet opening (14) and each rotor (28) enclosing a gas volume between respectively two of its consecutive rotor arms (30) in the direction of rotation and the inside (34) of the housing circumferential wall (20), and the gas volume is thus transferred from the gas inlet opening (14) to the gas outlet opening (16), wherein the rotation energy of at least one rotor shaft (32) is the mechanical energy resulting from the expansion of the gas.

7. Use of a rotating piston engine according to claim 6, characterized by a generator (72) for generating electricity from mechanical energy, wherein the generator (72) is in operative connection with at least one of the rotor shafts.

8. An installation generating water vapor and operated by water vapor or processing water vapor, comprising - a water vapor generator (54) for generating water vapor with a pressure higher than the pressure of the water vapor for operating the installation or the water vapor to be processed, - a unit (58) to be operated with water vapor or a unit (58) processing water vapor, - a pressure reduction station (56) between the water vapor generator (54) and the unit (58) to be operated with water vapor or processing water vapor, and - a rotating piston engine according to any one of claims 1 to 4, which forms the pressure reduction station or is connected in parallel to the pressure reduction station (56).

9. An installation to be operated with pressurized gas, comprising - a unit (58) to be operated with the pressurized gas or processing the pressurized gas, - a pressure reduction station (56) upstream the unit (58) for reducing the pressurized gas to a value suitable for operating the or for processing in the unit (58), and - a rotating piston engine according to any one of claims 1 to 4, which forms the pressure reduction station or is connected in parallel to the pressure reduction station (56).

10. The installation according to claim 9, characterized in that the unit (58) to be operated with gas or processing the gas comprises a compressor.

11. The installation according to claim 10, characterized in that the unit (58) to be operated with gas or processing gas comprises a furnace adapted to be supplied with gas compressed by the compressor.