UNIT AND METHOD

TECHNICAL FIELD

[0001] The disclosure concerns improvement in gas compressors. Specifically, em- bodiments disclosed herein concern integrally geared compressors.

BACKGROUND ART

[0002] Integrally geared compressors are often use to process air, carbon dioxide or steam. One advantage of integrally geared compressors is the possibility of multiple intercooling between compressor stages, as well as the possibility of driving sequen- tially arranged compressor stages at different rotational speeds.

[0003] GB 1048966 discloses a compressor arrangement including an electric motor which drives a main gear meshing with a first pinion at a first end of a first compressor shaft and with a second pinion at a first end of a second compressor shaft. A first compressor is drivingly coupled to the second end of the first compressor shaft and a second compressor is drivingly coupled to the second end of the second compressor shaft.

[0004] US2016/0230771 discloses a bull gear compressor including a bull gear driven into rotation by a steam turbine. The steam turbine is drivingly coupled to a driving shaft coupled to the bull gear through a pinion keyed on the driving shaft. A main compressor is directly driven by the driving shaft. Further compressor units are drivingly coupled to the bull gear through driven shafts arranged peripherally around the bull gear.

[0005] Integrally geared compressors of the current art still suffer from some limita tions. In particular, the inlet volumetric flow rate is limited. In order to improve the inlet flow rate, larger impellers have been developed, but this calls for a reduction of the rotational speed. As an alternative, double flow machines have been envisaged, wherein the first compression stage is split into two separate impellers, which operate in parallel, such that a larger volumetric inlet flow can be processed by the same ma chine. Double flow integrally geared compressors are cumbersome and, specifically, have a large footprint.

[0006] A need therefore exists for improvements in the design of integrally geared compressors, in order to preserve the advantages of these machines, but removing or alleviating their limitations.

SUMMARY

[0007] According to one aspect, disclosed herein is a novel structure of an integrally geared compressor including a bull gear supported for rotation in a gear casing, and a plurality of pinion shafts, supported for rotation in the gear casing. Each pinion shaft includes a respective pinion, which meshes with the bull gear.

[0008] According to the novel arrangement disclosed herein, a first pinion shaft has a first end drivingly coupled to a first axial compressor unit comprising a gas inlet, a gas outlet and an axial compression wheel, which is supported in an overhung fashion at the first end of the first pinion shaft. A second compressor unit is supported in an overhung fashion at a second end of the first pinion shaft. The gas outlet of the first axial compressor unit is fluidly coupled to a gas inlet of the second compressor unit. A second pinion shaft is drivingly coupled to a compressor arrangement comprising a further compressor unit supported in an overhung fashion at a first end of the second pinion shaft. The further compressor unit is a centrifugal compressor unit.

[0009] In some embodiments, the compressor can include more than one axial com pressor unit, for instance two axial compressor units arranged at opposite ends of the first pinion shaft.

[0010] Further embodiments and advantageous features of the integrally geared com pressor are outlined below and set out in the enclosed claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Reference is now made briefly to the accompanying drawings, in which:

[0012] Fig. l is a sectional view of an integrally geared compressor according to the present disclosure; and [0013] Fig.2 is a flowchart summarizing the method of operating an integrally geared compressor according to the disclosure.

DETAILED DESCRIPTION

[0014] A novel compressor is disclosed, to improve the inlet flowrate of an integrally geared compressor without increasing the overall footprint of the machine. The com pressor comprises a bull gear, which drives into rotation two or more pinion shafts peripherally arranged around the bull gear. Each pinion shaft includes a pinion mesh ing with the bull gear. The pinions may have different diameters and different number of teeth, so that the pinion shafts revolve at different rotational speeds. A compressor driver is drivingly coupled to a central shaft, which rotates the bull gear. The rotary motion is transmitted, with different transmission ratios, from the bull gear to the pin ions meshing therewith. Compressor stages are drivingly coupled to the pinion shafts. The most upstream compressor stage is an axial compressor stage drivingly coupled to a first one of said pinion shafts. The second and subsequent compressor stages can be centrifugal compressor stages, arranged in sequence for further compression of the gas flow delivered by the axial compressor stage. Intercoolers can be provided between one or more pairs of sequentially arranged compressor stages, to remove heat from the partly compressed process gas and improve the overall efficiency of the multistage, integrally geared compressor.

[0015] The most upstream axial compressor stage is adapted to process larger inlet flowrates than usual centrifugal compressor stages. A compact machine is thus ob tained, adapted to process large amounts of inlet gas.

[0016] Turning now to the drawings, Fig.1 shows a top view of an integrally geared compressor 1 with a compressor casing 3 sectioned according to a horizontal plane to show the components housed in the casing 3

[0017] A bull gear 5 is supported for rotation in the casing 3 The bull gear 5 is driv ingly coupled to an input shaft 7, which can be driven into rotation by a drive unit 9, for instance an electric motor, or any other suitable drive unit. The bull gear 5 is sup ported by means of bearings 11 13 for rotation in the casing 3 around a main rotation axis A-A. [0018] The bull gear 5 can rotate at the speed of the drive unit 9, or at a different speed, e.g., if a speed manipulation device, such as a gearbox 8, is arranged along the shaft line between the drive unit 9 and the input shaft 7

[0019] The compressor 1 further includes a plurality of pinion shafts. In Fig.1 two pinion shafts are shown. Nevertheless, it shall be understood that a larger number of pinion shafts can be provided in the same compressor 1.

[0020] A first pinion shaft 15 is supported for rotation around a rotation axis B-B by means of bearings 17, 19. A first pinion 21 is keyed on, or integrally formed with the first pinion shaft 15. The first pinion 21 meshes with the bull gear 5. The first pinion shaft 15 is therefore driven into rotation by drive unit 9 at a rotational speed which is determined by the transmission ratio between the bull gear 5 and the first pinion 21.

[0021] A second pinion shaft 23 is supported for rotation around a rotation axis C-C by means of bearings 25, 27. A second pinion 29 is keyed on, or integrally formed with the second pinion shaft 23. The second pinion 29 meshes with the bull gear 5. The second pinion shaft 23 therefore rotates at a rotational speed which is given by the transmission ratio between the bull gear 5 and the second pinion 29. In some embodi ments, the rotation speed of the second pinion shaft 23 can be higher than the rotation speed of the first pinion shaft 15.

[0022] In general, the integrally geared compressor 1 includes a first, most upstream axial compressor unit driven by the first pinion shaft 15 at a first rotational speed, and a centrifugal compressor arrangement driven by the second pinion shaft at a second rotational speed. The first rotational speed and the second rotational speed are higher than the rotational speed of the bull gear 5.

[0023] The centrifugal compressor arrangement may include one or more centrifugal compressor units. As mentioned, in some embodiments, not shown, a third or further pinion shafts may be provided to drive additional centrifugal compressor units belong ing to the centrifugal compressor arrangement. As will be described in detail below, in the embodiment of Fig.1 a centrifugal compressor unit is also provided on the first pinion shaft 15, opposite the axial compressor unit 31, for rotation at the same rota tional speed of this latter. [0024] More specifically, in the embodiment of Fig.1, the compressor 1 has four compressor units. As already mentioned, the first, most upstream compressor unit 31 is arranged at a first end of the first pinion shaft 15. A second compressor unit 33 is arranged at a second end of the first pinion shaft 15. Additional third and fourth com pressor units 35, 37, forming part of the centrifugal compressor arrangement, are driven by the second pinion shaft 23. More specifically, a third compressor unit 35 is arranged at a first end of the second pinion shaft 23 and a fourth compressor unit 37 is arranged at a second end of the second pinion shaft 23.

[0025] The first, second, third and fourth compressor units are arranged in sequence, starting from the most upstream compressor unit 31 to the most downstream compres sor unit 37, such that process gas is firstly compressed in the axial compressor unit 31, which has a higher volumetric flow rate, and subsequently stepwise compressed in sequence in the remaining centrifugal compressor units 33, 35 and 37.

[0026] An intercooler can be provided along the connection line connecting each pair of sequentially arranged compressor units 31-37. By way of example, an intercooler 39 is shown in Fig. 1 along a connection line 41 fluidly coupling the first compressor unit 31 to the second compressor unit 33.

[0027] The first compressor unit 31 includes a gas inlet 43, a gas outlet 45 and an axial compression wheel 47 therebetween. In the embodiment of Fig.1, the axial com pressor unit 31 comprises two axial compression stages, each including a circular ar rangement of rotary blades 49 keyed on the axial compression wheel 47 and a respec tive set of stationary blades or vanes 51, mounted on a casing 52 of the axial compres sor unit 31 . The number of axial compression stages shown is by way of example only and it should be understood that the axial compressor unit 31 can include a different number of axial compression stages, for example three or more. In some embodiments, the stationary blades 51 may have a variable inclination. The angular position of the stationary blades 51 can be adapted to operating conditions of the compressor 1 by means of a suitable control device schematically shown at 53. The control device 53 is adapted to pivot each stationary blade 51 around a radial axis, i.e., an axis orthogonal to the rotation axis B-B of the axial compressor unit 31 .

[0028] In the embodiment of Fig.1, the axial compression wheel 47 is mounted in an overhung fashion on the first end of the first pinion shaft 15.

[0029] In the embodiment of Fig 1, the gas inlet 43 is an axial inlet and the gas outlet 45 is a radial outlet. The flow of partially compressed gas from the axial wheel is radially diverted towards the radial outlet. A scroll 55 collects the partially compressed gas from the axial compression wheel 47 and directs the flow of partially compressed gas through a diffuser 57 towards the gas outlet 45. In some embodiments, as shown in Fig.l, the diffuser 57 is a vaned diffuser 57, to improve the efficiency of the first compressor unit 31 .

[0030] Each compressor unit 33, 35 and 37 includes one or more centrifugal com pressor stages. In the embodiment of Fig.l, each centrifugal compressor unit 33, 35, 37 includes a single centrifugal compressor stage with a single centrifugal compressor impeller. The possibility of having multiple centrifugal compressor stages in one, some or all the compressor units 33, 35, 37 is not ruled out.

[0031] In the embodiment of Fig.1, the second, third and fourth compressor units 33, 35, 37 are similar to one another. Specifically, the second compressor unit 33 is a cen trifugal compressor unit comprising a single centrifugal impeller 61 mounted in an overhung fashion on the second end of the first pinion shaft 15 and rotatingly arranged in a casing 63, having a gas inlet 65 and a gas outlet 67. A vaned diffuser 69 can be arranged between the centrifugal impeller 61 and the gas outlet 67. In other embodi ments, the diffuser 69 can be a non-vaned diffuser.

[0032] Similarly, the third compressor unit 35 is a centrifugal compressor unit com prising a centrifugal impeller 61 mounted in an overhung fashion on the first end of the second pinion shaft 23 and rotatingly arranged in a casing 73, having a gas inlet 75 and a gas outlet 77. A vaned or non-vaned diffuser 79 can be arranged between the centrifugal impeller 61 and the gas outlet 77. The gas inlet 75 is fluidly coupled with the gas outlet 67 of the second compressor unit 33 through a connection line, not shown, along which an intercooler can be provided, similarly to intercooler 39 along line 41.

[0033] The fourth compressor unit 37 is a centrifugal compressor unit comprising a centrifugal impeller 81 mounted in an overhung fashion on the second end of the second pinion shaft 23 and rotatingly arranged in a casing 83, having a gas inlet 85 and a gas outlet 87. A vaned or non-vaned diffuser 89 can be arranged between the centrifugal impeller 81 and the gas outlet 87. The gas inlet 85 is fluidly coupled with the gas outlet 77 of the third compressor unit 35. An intercooler can be provided along a connection line, not shown, between the third compressor unit 35 and the fourth compressor unit 37.

[0034] The compressor 1 is therefore configured to process a gas flow entering the first axial compressor unit 31 first, and subsequently further compressed in the second, third and fourth centrifugal compressor units 33, 35 and 37 in sequence. The axial compression wheel 47 and the centrifugal compressor impeller 61 of the compressor unit 33 rotate at the same rotational speed. The impellers 71 and 81 of the third and fourth compressor units 35 and 37 rotate at the same rotational speed, which is prefer ably different from the rotational speed of the axial compression wheel 47 and of the centrifugal impeller 61.

[0035] In some embodiments, the rotational speed of the second pinion shaft 23, the centrifugal impeller 71 and the centrifugal impeller 81 is higher than the rotational speed of the first pinion shaft 15 and of the axial wheel 47 and centrifugal impeller 61 keyed thereon. The ratio between the rotational speeds of the first and second pinion shafts 15, 23 is given by the ratio between the number of teeth of the pinions 21 and 29. By designing the bull gear 5 and the pinions 21, 29 with the proper number of teeth, the optimum rotational speed ratios for a given application of the compressor 1 can be set.

[0036] Fig.2 summarizes the method of operation of the compressor 1. The inlet gas flow (step 100) is firstly compressed in the axial compressor unit 31 (step 101) and subsequently further compressed in the second, centrifugal compressor unit 33 (step 103). An intercooling step is also shown at 102. Partially compressed gas from the second, centrifugal compressor unit 33 is delivered to the third, centrifugal compressor unit 35 for further compression (step 105) and finally to the fourth centrifugal com pressor unit 37 for final compression (steps 107) to the delivery pressure. An inter cooling step 104 and an intercooling step 106 can be foreseen between the compression step in centrifugal compressor unit 33 and the compression step in centrifugal compressor unit 35 and/or between the compression step in centrifugal compressor unit 35 and the compression step in the centrifugal compressor unit 37.

[0037] The axial compressor stage 31 can include a high Mach axial wheel to in crease the maximum flowrate in the first compression unit, without making recourse to a double flow architecture and to excessively large impeller sizes. A compact com pressor with reduced footprint and high efficiency is thus obtained.

[0038] The embodiment disclosed so far is by way of example. In other embodi ments, not shown, the integrally geared compressor can include more than one axial compressor unit. For instance, a first pinion shaft may be drivingly coupled to an axial compressor unit at both the first end and second end thereof.

[0039] Exemplary embodiments have been disclosed above and illustrated in the ac companying drawings. It will be understood by those skilled in the art that various changes, omissions and additions may be made to that which is specifically disclosed herein without departing from the scope of the invention as defined in the following claims.