Screw machine with backpressure recovery system

Abstract

Screw machine comprising a male rotor (3) and a female rotor (2), enclosed in a case (4) or body, inside which they rotate in counter-rotation. Said body (4) comprises opposite shaped openings (41) and (42) into which the rotors are inserted, and is closed on one delivery side, by a delivery group (5), and on the other suction side by a suction group (6), in correspondence with the aforementioned openings. A gas (or air) passes from the suction group through a suction duct created between the two rotors; the rotation of the rotors closes said suction duct, and the compressed gas is pushed towards the delivery side. Between the delivery group, the case, and between the suction group and the case, there are respective flanged connections of suction (7) and delivery (8), appropriately shaped to accommodate the rotor shafts and to couple with the openings of the machine body and suction or delivery groups. The closing area of the compressor body on the delivery side is carried out by means of said delivery body (8), which meets the edge (43) of the opening of said machine body (4). In said closing area, between the delivery body (8) and said edge (43) of the opening of the machine body, a perimeter channel (9) is obtained, externally to an impression (I) of the barrels, whose path follows said impression.

Description

[0001] SCREW MACHINE WITH BACKPRESSURE RECOVERY SYSTEM

[0002] The present invention relates to a screw machine, such as for example a compressor or an expander.

[0003] The screw compressor is a rotary volumetric compressor consisting of two parallel rotors externally provided with multiple helical profiles (screws) such that they can mesh with each other. The two rotors are housed in a stator composed of two cylinders that intersect longitudinally, inside which the rotors rotate with a clearance that cannot be reduced beyond a certain limit.

[0004] The rotor shafts are supported by bearings, and generally one rotor drives the other through the meshing of the same helical profiles (oil-injected compressors). Sometimes both can be commanded by a pair of external gears to avoid their contact and friction otherwise present (dry compressors). During rotation, the profiles of the screws uncover a suction port, placed at one end of the stator, through which air or gas enters to fill the volume between the profiles themselves until its maximum extension.

[0005] On the opposite side, the profiles interpenetrate, reducing the volume and compressing the gas enclosed therein until uncovering the delivery port. The operation of the screw compressor is based on the counter-rotation action of two helical rotors that compress the gas or air taken from the suction duct and carry it towards the delivery side. During this path, the space is reduced and, consequently, the pressure increases.

[0006] The screw compressor is widely diffused due to the diffusion of its construction technology. Many producers and assemblers offer this product in various variants: single-stage, two-stage for high pressure, with or without oil for "oil-free" applications. The rotation speed of the motor can differ from that of the driving rotor, being connected not only directly but also by multiplying / reducing gears or by the pulley ratio when a belt is present.

[0007] These types of industrial compressors provide compressed gas or air continuously, are highly controllable, extremely efficient, and quiet (in terms of workplace safety, environmental protection, and noise emissions). The screw expander, similarly to the compressor, comprises two counter-rotating rotors (male and female screws) connected to the corresponding shafts that transmit motion to an electric generator. The fluid expands by rotating the rotors and proceeds in an axial direction in the volume that is generated between the lobes of the screws. The gas fills the volume between the screws, is isolated and then discharged to the delivery area at low pressure.

[0008] The expander, similarly to the compressor, is composed of a stator case housing the rotors, where the expansion of the working fluid occurs. It has inlet and outlet ports (or flanges) for connection to the plant. The component is usually obtained from a cast iron blank, made of either grey or ductile iron, but it can also be made of other materials.

[0009] In these machines (expanders or compressors), gaskets are also used, whose main function is to make the sealing to the outside of the working fluid inside the case, and to confine the lubricating oil, if present, inside the machine or in well-defined areas thereof, for example between the support bearings and the compression chamber, avoiding any type of contamination. A lubrication system supplies oil to the bearings and other mechanical members where contact is expected, in order to decrease internal friction and reduce local temperatures.

[0010] In said machines, the interface area between the rotors and the stationary bodies is a particularly critical area, the imperfect sealing between the compartments created by the meshing of the helical profiles of the screws (rotors) and the respective stator parts (compressor body and delivery body), and the unavoidable presence of clearances required for proper mechanical operation of the compressor, cause flow rate leakages by the effect of the pressure difference between the low-pressure area (suction) and the high-pressure area (delivery). The back-flow rates represent an energy inefficiency for the compressor, since it performs work to compress a certain amount of air or gas, which, however, is not available at delivery because it recirculates towards the suction. Reducing and / or recovering said losses makes it possible to process and have available at delivery a greater flow rate, closer to the theoretical one, with a consequent increase in efficiency. The present conceptual invention solves the above-mentioned problems by making a backpressure recovery system obtained through a channel between the delivery body and the compressor body, with any appropriate shape and dimension and adapted to receive, convey, and discharge the leakages related to backpressure. The channel, comparable to a conveyance ring, constitutes a preferential path for collecting the leakages that occur through the axial and radial clearances between rotors and stators (for the mechanisms described above), and conveys them again towards the delivery port, due to the centrifugal effect caused by the rotation of the rotors.

[0011] An aspect of the present invention relates to a screw machine, such as for example a screw compressor or screw expander, having the features of attached claim 1.

[0012] Further features of the present invention are contained in the dependent claims.

[0013] The features and advantages of the present invention will become more apparent from the following description of a possible embodiment of the invention, provided by way of example and not limitation, referred to the attached schematic drawings, in which:

[0014] • Figure 1 illustrates a screw compressor in an exploded perspective view, according to the present invention;

[0015] • Figure 2 illustrates a compressor body and a delivery body in an exploded perspective view, according to the present invention;

[0016] • Figure 3 illustrates a side view of the screws and the delivery body of the compressor of Figure 1;

[0017] • Figure 4 illustrates a front view of the compressor body of Figure 1 with the screws therein;

[0018] • Figures 5a and 5b illustrate a first embodiment of the invention made on the delivery body of Figure 3;

[0019] • Figures 6a and 6b illustrate a second embodiment of the invention made on the delivery body of Figure 3;

[0020] • Figure 7 illustrates an enlarged detail of the connection area between the delivery body and the compressor body according to the present invention; • Figure 8 illustrates the delivery body highlighting a scheme of conveyance towards the delivery, by the effect of the rotors through a channel, according to the present invention.

[0021] With reference to the above-mentioned figures, the screw machine of the present invention (in the example case, it is a compressor) comprises two helical rotors or screws, respectively male rotor 3 and female rotor 2, enclosed in a case or compressor body 4 inside which they rotate in counter-rotation.

[0022] Said body comprises opposite shaped openings 41 and 42 into which the rotors are inserted.

[0023] The machine body is closed on one side (delivery side) by a delivery group 5 comprising a delivery body 8 in correspondence with the aforementioned openings 41 and 42, and on the other side (suction side) by a suction group 6.

[0024] A gas (or air) passes from the suction group through a suction duct created between the two rotors; the rotation closes said suction duct, and the compressed gas is pushed towards the delivery side. In the case where the machine is an expander, the compressed gas is introduced into the machine and expanded therein, causing rotation of the two rotors and following the natural expansion process (thus from a lower- volume duct to a higher-volume one).

[0025] Each rotor comprises a rotation shaft 21 and 31 that rotates in the case or body 4 by means of suitable bearings, consisting of a central helical profile area 22 and 32 made in such a way as to progressively reduce the space between rotors and stator.

[0026] The two rotors are usually designed with different profiles. The male rotor is typically provided with convex lobes, whereas the female rotor usually has concave cavities. It is due to these features that they mesh with each other.

[0027] A dedicated motor supplies the compressor with the required power. The motor is used to impart rotation, usually to the male rotor, which in turn operates the female rotor. In the case where the machine is an expander, one of the two shafts 21 or 31 can be associated with an electric generator. At the ends of both rotors, dedicated bearings are positioned to maintain the rotors in the correct position. They are located into the stationary bodies, typically on the suction and delivery sides (groups 5 and 6).

[0028] Normally, between the delivery group, the case and between the suction group and the case, there are respective flanged connections of suction 7 and delivery 8, provided with gaskets that ensure the sealing of the parts inside the machine.

[0029] Said flanged connections, in the internal areas, are appropriately shaped to accommodate the rotor shafts and the bearings, and to couple with the openings of the case and suction or delivery groups.

[0030] The closing area of the compressor body on the delivery side is carried out by means of said delivery body 8, which meets the edge 43 of the opening of said machine body 4, and is the area where internal fluid is at high pressure. Therefore, said area is particularly prone to leakages and losses that impair the performance and yield of the machine.

[0031] According to the present invention, in said area between the delivery body 8 and said edge 43 of the opening of the compressor body, a perimeter channel 9 is obtained, externally to an impression I of the barrels in which the rotors are housed (which is the seat of the rotors in the machine body 4), whose path follows said impression.

[0032] The channel can extend in depth (thus in a direction perpendicular to the delivery plane), or in width (with radial extension with respect to the impression of the barrels), or still in a suitable combination of the two.

[0033] Said channel is preferably made on the surface 81 of the delivery body 8 which meets the edge 43 of the compressor body, or alternatively on the edge 43 of the opening of the compressor body. In a further alternative, both the edge 43 of the compressor body and the surface 81 of the delivery body 8 are shaped so that, when they are joined together, they form said channel 9.

[0034] Said channel, comparable to a conveyance ring, constitutes a preferential path for the leakages that would occur through the axial and radial clearances between rotors and stators (for the mechanisms described above), collecting them and conveying them again toward the delivery port, due to the dynamic effect produced by the rotation of the rotors.

[0035] In Figures 5a and 5b, a first embodiment of the invention is illustrated, wherein the channel 9 is made on the surface 81 of the delivery body that faces the compressor body 4, and is shaped as a perimeter recess 9, externally to the impression I of the barrels.

[0036] In Figures 6a and 6b, a second embodiment of the invention is illustrated, wherein the channel 9 is made on the surface 81 of the delivery body that faces the compressor body 4, and is shaped as a lowered area with respect to the surface 81 that includes the impression area I of the barrels.

[0037] In Figure 7, a detail of the perimeter channel 9 made on the delivery body 8 is illustrated, wherein the clearances G between the rotating parts (helices 2 and 3) and fixed parts (compressor body 4 and delivery body 8) are clearly visible, while the arrows C indicate how the leakages are conveyed into the channel 9, improving the sealing of the machine. Similarly, in Figure 8, where the entire delivery plane is substantially visible, the conveyances C of the possible leakages between said clearances G are visible.

Claims

CLAIMS1. Screw machine comprising a male rotor (3) and a female rotor (2) enclosed in a case (4) or body, inside which they rotate in counter-rotation, said body (4) comprises opposite shaped openings (41) and (42) into which the rotors are inserted and is closed on one delivery side by a delivery group (5) and on the other suction side by a suction group (6) in correspondence with the aforementioned openings, a gas (or air) passes from the suction group through a suction duct created between the two rotors; the rotation of the rotors closes said suction duct and the compressed gas is pushed towards the delivery side, between the delivery group, the casing and between the suction group and the casing there are respective flanged connections of suction (7) and delivery (8), appropriately shaped to accommodate the rotor shafts and to couple with the openings of the machine body and suction or delivery groups, the closing area of the compressor body on the delivery side is carried out by means of said delivery body (8) which meets the edge (43) of the opening of the machine body (4), characterized in that in said closing area between the delivery body (8) and this edge (43) of the opening of the machine body a perimeter channel (9) is obtained externally to a impression area (I) of the barrels in which the rotors are housed whose path follows said impression.

2. Screw machine according to claim 1, in which said channel (9) develops in a direction perpendicular to the delivery plane.

3. Screw machine according to claim 1, wherein said channel (9) extends in width with respect to the delivery plane.

4. Screw machine according to claim 1, wherein said channel (9) extends both in a perpendicular direction and in width with respect to the delivery plane.

5. Screw machine according to claim 1, wherein said channel is made on the surface (81) of the delivery body (8) which meets the edge (43) of the compressor body.

6. Screw machine according to claim 1, wherein said channel is made on the edge (43) of the opening of the compressor body.

7. Screw machine according to claim 1, wherein both the edge (43) of the compressor body and the surface (81) of the delivery body (8) are shaped so that when they are joined together they form said channel (9).

8. Screw machine according to claim 5, wherein the channel (9) is made on the surface (81) of the delivery body that faces the compressor body (4) and is shaped as a perimeter recess externally to the impression (I) of the barrels.

9. Screw machine according to claim 5, wherein the channel (9) is made on the surface (81) of the delivery body that faces the compressor body (4) and is shaped as a lowered area with respect to the surface (81) that includes the impression area (I) of the barrels.

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