SCREW COMPRESSOR WITH A SHUNT-ENHANCED COMPRESSION AND PULSATION TRAP (SECAPT)
A shunt-enhanced compression and pulsation trap (SECAPT) for a screw compressor assists internal compression (IC), reduces gas pulsation and NVH, and improves off-design efficiency, without using a slide valve and/or a serial pulsation dampener. The SECAPT includes an inner casing (e.g., an integral part of the compressor chamber) and an outer casing (e.g., surrounding part of the inner casing near the compressor discharge port) forming at least one diffusing chamber with a nozzle and a feedback region that provides a feedback flow loop between the compressor chamber and the compressor discharge port. The SECAPT automatically compensates cavity pressure to meet different outlet pressures (hence eliminating under-compression and/or over-compression when the discharge port opens), partially recovers potential energy associated with the under-compression (UC), and traps and attenuates gas pulsations and noise before the discharge port opens.
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The present invention relates generally to the field of rotary gas compressors, and more particularly relates to rotary screw compressors having twin meshing helical-shaped multi-lobe rotors.
BACKGROUNDA rotary screw compressor uses two helical screws, known as rotors, to compress the gas. In a dry running rotary screw compressor, a pair of timing gears ensures that the male and female rotors each maintain precise positions and clearances. In an oil-flooded rotary screw compressor, injected lubricating oil film fills the space between the rotors, both providing a hydraulic seal and transferring mechanical energy between the driving and driven rotor. Gas enters at the suction port of the compressor and gets trapped between moving threads and compressor casing forming a series of moving cavities as the screws rotate. Then the volumes of the moving cavities decrease and the gas is compressed. The gas exits at the end of the screw compressor through a discharge port normally connected to a discharge dampener to finish the cycle. It is essentially a positive displacement mechanism but using rotary screws instead of reciprocating motion so that displacement speed can be much higher. The result is a more continuous stream of flow with a more compact size when comparing with the traditional reciprocating types.
However, it has long been observed that screw compressors inherently generate gas pulsations with pocket passing frequency at discharge, and the pulsation amplitudes are especially significant when operating under high pressure and/or at off-design conditions of either an under-compression (UC) or an over-compression (OC). An under-compression, as shown in
To address the after-effects of the mismatch problem, a large pulsation dampener known in the trade as reactive and/or absorptive type as shown in
To overcome the mismatch problem at source, a concept called slide valve has been explored widely since 1960s as demonstrated in
In an effort to achieve the same goal of the slide valve variable Vi idea but without its complexity and limitation of applications, a shunt pulsation trap (SPT) technology as shown in
Accordingly, it is always desirable to provide a new design and construction of a screw compressor that is capable of achieving high gas pulsation and NVH reduction at source and improving compressor off-design efficiency without externally connected silencer at discharge or using a slide valve while being kept compact in size and suitable for operating reliably for high efficiency, variable pressure ratio applications at the same time.
SUMMARYGenerally described, the present invention relates to a shunt enhanced compression and pulsation trap (SECAPT) for screw compressor having a compression chamber with a suction port and a discharge port, and a pair of multi-helical-lobe rotors housed in the compression chamber forming a series of moving cavities for trapping, compressing and propelling the trapped gas in the cavities from the suction port to discharge port. The SECAPT comprises an inner casing as an integral part of the compression chamber, and an outer casing surrounding part of the inner casing near the discharge port forming at least one diffusing chamber, therein housed at least one feedback flow loop through at least one flow nozzle (located at one of the moving cavities at least one male lobe span away or totally isolated from the suction port) to communicate between the propelled moving cavities and the discharge port. In this way, the SECAPT automatically compensates cavity pressure, in a similar way as inflating or deflating a basketball by adding or subtracting gas to the cavity, to meet different outlet pressures (hence eliminating the under-compression and/or over-compression when the discharge port opens), partially recovers the potential energy associated with the under-compression (UC), and traps and attenuates gas pulsations and noise before the discharge port opens.
These and other aspects, features, and advantages of the invention will be understood with reference to the drawing figures and detailed description herein, and will be realized by means of the various elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing summary and the following brief description of the drawings and detailed description of the example embodiments are explanatory of example embodiments of the invention, and are not restrictive of the invention, as claimed.
Although specific embodiments of the present invention will now be described with reference to the drawings, it should be understood that such embodiments are examples only and merely illustrative of but a small number of the many possible specific embodiments which can represent applications of the principles of the present invention. Various changes and modifications obvious to one skilled in the art to which the present invention pertains are deemed to be within the spirit, scope and contemplation of the present invention as further defined in the appended claims.
It should also be pointed out that though drawing illustrations and description are devoted to a dual rotor screw compressor for enhancing gas compression and attenuating gas pulsations in the present invention, the principle can be applied to screw vacuum pump and/or other rotor combinations such as a single rotor screw or a tri-rotor screw. The principle can also be applied to other media such as gas-liquid two phase flow as widely used oil-injected screws for refrigeration. In addition, screw expanders are another variation except being used to generate shaft power from a media pressure drop.
To illustrate the principles of the present invention,
Referring to
As a novel and unique feature of the present invention, a SECAPT apparatus 50 is comprised of at least one flow nozzle (trap inlet) 51 branching off from the compression chamber 32 into at least one diffusing chamber 55 and a feedback region (trap outlet) 58 communicating with the compressor outlet 37. As shown in
When a screw compressor 10 is equipped with the SECAPT apparatus 50 of the present invention, there exist both a reduction in the gas pulsation and induced noises transmitted from screw compressor outlet to downstream flow as well as an improvement in internal flow field (hence its adiabatic off-design efficiency) for under-compression and/or over-compression operations. The theory of operation underlying the SECAPT apparatus 50 of the present invention can be described as follows. As illustrated in
There are several advantages provided by the SECAPT when compared to a screw compressor with serially connected traditional dampener. First of all, the required mass is more efficiently transported using a nozzle 51 into the “starved” or under-compressed cavity 39 to minimize fill-in time and pulsation generation at discharge. It can be seen that the required mass flow 53 is first “borrowed” from the outlet area 37 and then “returned” to the outlet area 37 by a shunt feedback flow loop as shown in
On the other hand, the theory of operation underlying the SECAPT apparatus 50 for an over-compression mode is different. As illustrated in
To facilitate and optimize the feedback flow 53 or 54 at the flow nozzle 51 in either direction between the cavity 39 and diffusing chamber 55, more than one nozzle can be used to feed both male and female sides of the cavity 39, and/or the nozzle/s can optionally be in the form of circular hole (3-dimensional nozzle) or slot (2-dimensional nozzle) arranged in parallel with the lobe seal line of the cavity 39 (for illustration purposes, both are shown in
If the range of the pressure ratio variation or the extent of OC and UC is small, a one-stage SECAPT is enough to cover the compounded compression phase when the distance between the nozzle 51 opening to discharge port 37 opening is smaller than one lobe span or screw pitch t as shown in
Referring to
In addition to a two-port configuration for a screw compressor application discussed above for the first and second example embodiments, a three-port configuration can be used for a screw vacuum pump application for pulling deep vacuum. In a vacuum pump embodiment, the suction port of the compressor is connected to a process or a vessel where a deep vacuum is to be created while the outlet port of the compressor is connected through a silencer to atmosphere. In addition, a third port is added that is also open to atmosphere and allows cool atmospheric air into the compressor cavity through the SECAPT to extend the pressure ratio range, e.g., from about 4/1 to about 20/1 or more.
Referring to
As such, various embodiments of the invention provide advantages over the prior art. For example, a screw compressor with a shunt enhanced compression and pulsation trap (SECAPT) in parallel with the compressor internal compression helps eliminate the under-compression and/or over-compression (sources of discharge gas pulsations and energy losses) when discharge port opens. A screw compressor with a shunt enhanced compression and pulsation trap (SECAPT) can be as effective as a slide valve variable Vi design but without mechanical moving parts and limitation to oil-injected applications. A screw compressor with a shunt enhanced compression and pulsation trap (SECAPT) can be an integral part of the compressor casing so that it is compact in size by eliminating the serially connected pulsation dampener at discharge. A screw compressor with a shunt enhanced compression and pulsation trap (SECAPT) can be capable of achieving energy savings over a wide range of pressure ratios. A screw compressor with a shunt enhanced compression and pulsation trap (SECAPT) can be capable of achieving reduced gas pulsations and NVH over a wide range of pressure ratios. A screw compressor with a shunt enhanced compression and pulsation trap (SECAPT) can be capable of achieving energy savings and higher gas pulsation attenuation over a wide range of speed and cavity passing frequency. And a screw compressor with a shunt enhanced compression and pulsation trap (SECAPT) can be capable of achieving the same level of adiabatic off-design efficiency as a slide valve over a wide range of pressure and speed.
It is to be understood that this invention is not limited to the specific devices, methods, conditions, or parameters of the example embodiments described and/or shown herein, and that the terminology used herein is for the purpose of describing particular embodiments by way of example only. Thus, the terminology is intended to be broadly construed and is not intended to be unnecessarily limiting of the claimed invention. For example, as used in the specification including the appended claims, the singular forms “a,” “an,” and “the” include the plural, the term “or” means “and/or,” and reference to a particular numerical value includes at least that particular value, unless the context clearly dictates otherwise. In addition, any methods described herein are not intended to be limited to the sequence of steps described but can be carried out in other sequences, unless expressly stated otherwise herein.
While the claimed invention has been shown and described in example forms, it will be apparent to those skilled in the art that many modifications, additions, and deletions can be made therein without departing from the spirit and scope of the invention as defined by the following claims.
Claims
1. A screw compressor, comprising:
- a compression chamber and a pair of meshing multi-helical-lobe rotors housed within the compression chamber, wherein the compression chamber has a flow suction port and a flow discharge port, wherein the rotors rotate to cooperatively form a series of moving cavities within the compression chamber for trapping and compressing fluid and propelling the trapped fluid from the suction port to the discharge port; and
- a shunt-enhanced compression and pulsation trap (SECAPT) apparatus including a diffusing chamber having a first flow nozzle providing fluid communication between the moving cavities inside the compression chamber and the diffusing chamber and having a feedback region providing fluid communication between the diffusing chamber and the discharge port, wherein the SECAPT defines a first stage of a feedback flow loop,
- wherein in operation the SECAPT achieves high gas pulsation and NVH reduction and improved compressor off-design efficiency without using a serial pulsation dampener or a slide valve.
2. The screw compressor as claimed in claim 1, wherein the first flow nozzle is positioned at a distance at least one lobe span away, or is totally sealed or isolated, from the suction port, but is positioned before the discharge port.
3. The screw compressor as claimed in claim 2, further comprising a second flow nozzle that is positioned at a distance at least one lobe span away, or totally sealed or isolated, from the first flow nozzle, but is positioned before the discharge port, and defining a second stage of the feedback flow loop.
4. The screw compressor as claimed in claim 1, further comprising a third flow nozzle that is positioned at a distance at least one lobe span away, or totally sealed or isolated, from the second flow nozzle, but is positioned before the discharge port, and defining a third stage of the feedback flow loop.
5. The screw compressor as claimed in claim 1, wherein the first flow nozzle has a circular cross-sectional shape with a converging or a converging-diverging cross-sectional area transitioning along an axis of the nozzle.
6. The screw compressor as claimed in claim 1, wherein the first flow nozzle has a rectangular cross-sectional shape with a converging cross-sectional area transitioning along an axis of the nozzle.
7. The screw compressor as claimed in claim 5, wherein the converging cross-sectional area has a continuous transition from a circular cross-sectional shape at a throat of the nozzle to a generally rectangular slot shape at the compression chamber, with a longer side of the rectangular slot shaped nozzle at the compression chamber oriented generally along a longer side of the moving cavity.
8. The screw compressor as claimed in claim 5, wherein the converging-diverging cross-sectional area has a continuous transition from a circular cross-sectional shape at a throat of the nozzle to a generally rectangular slot shape at the compression chamber, with a longer side of the rectangular slot shaped nozzle at the compression chamber oriented generally along a longer side of the moving cavity.
9. The screw compressor as claimed in claim 1, wherein the first flow nozzle is positioned a distance away from the rotor axis and aimed in generally the same direction as an angular rotation of one of the rotors.
10. The screw compressor as claimed in claim 1, wherein the pair of meshing multi-helical-lobe rotors includes a male rotor and a female rotor, and wherein two of the first flow nozzles are provided with one first flow nozzle positioned at the male rotor and with the other first flow nozzle positioned at the female rotor, and wherein the two nozzles are open simultaneously to moving male and female cavities in the compression chamber.
11. A screw compressor, comprising:
- a compression chamber and a pair of meshing multi-helical-lobe rotors housed within the compression chamber, wherein the compression chamber as a flow suction port and a flow discharge port, wherein the rotors rotate to cooperatively form a series of moving compression cavities within the compression chamber for trapping and compressing fluid and propelling the trapped fluid from the suction port to the discharge port; and
- a shunt-enhanced compression and pulsation trap (SECAPT) apparatus including a diffusing chamber having a first flow nozzle providing fluid communication between the moving cavities inside the compression chamber and the diffusing chamber and the diffusing chamber and having an access port providing fluid communication between the diffusing chamber and ambient atmosphere, wherein the SECAPT defines a first stage of a feedback flow loop,
- wherein in operation the SECAPT achieves deep vacuum with high gas pulsation and NVH reduction and improved compressor off-design efficiency without using a slide valve.
12. The screw compressor as claimed in claim 11, wherein the first flow nozzle is positioned at a distance at least one lobe span away, or is totally sealed or isolated, from the suction port, but is positioned before the discharge port.
13. The screw compressor as claimed in claim 11, further comprising a second flow nozzle that is positioned at a distance at least one male lobe span away, or totally sealed or isolated, from the first flow nozzle, but is positioned before the discharge port, and defining a second stage of the feedback flow loop.
14. The screw compressor as claimed in claim 11, further comprising a third flow nozzle that is positioned at a distance at least one male lobe span away, or totally sealed or isolated, from the second flow nozzle, but is positioned before the discharge port, and defining a third stage of the feedback flow loop.
15. The screw compressor as claimed in claim 12, wherein the first flow nozzle has a circular cross-sectional shape with a converging or a converging-diverging cross-sectional area transitioning along an axis of the nozzle.
16. The screw compressor as claimed in claim 12, wherein the first flow nozzle has a rectangular cross-sectional shape with a converging cross-sectional area transitioning along an axis of the nozzle.
17. The screw compressor as claimed in claim 15, wherein the converging cross-sectional area has a continuous transition from a circular cross-sectional shape at a throat of the nozzle to a generally rectangular slot shape at the compression chamber, with a longer side of the rectangular slot shaped nozzle at the compression chamber oriented generally along a longer side of the moving cavity.
18. The screw compressor as claimed in claim 15, wherein the converging-diverging cross-sectional area has a continuous transition from a circular cross-sectional shape at a throat of the nozzle to a generally rectangular slot shape at the compression chamber, with a longer side of the rectangular slot shaped nozzle at the compression chamber oriented generally along a longer side of the moving cavity.
19. The screw compressor as claimed in claim 11, wherein the first flow nozzle is positioned a distance away from the rotor axis and aimed in generally the same direction as an angular rotation of one of the rotors.
20. The screw compressor as claimed in claim 11, wherein the pair of meshing multi-helical-lobe rotors includes a male rotor and a female rotor, and wherein two of the first flow nozzles are provided with one first flow nozzle positioned at the male rotor and with the other first flow nozzle positioned at the female rotor, and wherein the two nozzles are open simultaneously to moving male and female cavities in the compression chamber.
Type: Application
Filed: Sep 8, 2020
Publication Date: Mar 10, 2022
Applicant: HI-BAR BLOWERS, INC. (Fayetteville, GA)
Inventors: Paul Xiubao HUANG (Fayetteville, GA), Sean William YONKERS (Peachtree City, GA)
Application Number: 17/014,357