A PUMP AND A METHOD OF PUMPING A GAS

Abstract

A pump includes a pump housing element and a further element; one of the pump housing and the further element comprising a helical protrusion extending towards the other element, the other element comprising at least one liquid opening. The helical protrusion, pump housing and further element form a path from a gas inlet to a gas outlet. The helical protrusion has an axial cross section that is wider at its attached end than it is at its free end. The pump housing and further element are mounted rotatably with respect to each other; and the at least one liquid opening is configured such that liquid output from the at least one liquid opening forms a liquid blade, the liquid blade being operable to drive gas along the path from the gas inlet to the gas outlet on rotation of one of the elements.

Claims

1. A pump for pumping a gas, said pump comprising: a pump housing element and a further element; one of said pump housing and said further element comprising a protrusion extending towards the other element, said other element comprising at least one liquid opening; said protrusion, pump housing and further element forming a path from a gas inlet to a gas outlet; wherein said further element is concentrically mounted within a bore of said pump housing and said pump housing and further element are mounted rotatably with respect to each other; and said protrusion comprises a helix, a cross section through an axial plane of said helix varying such that said helix is narrower at a point towards said other element and wider at an intersection of said protrusion with said one of said pump housing and said further element from which said protrusion extends; said at least one liquid opening is configured such that liquid output from said at least one liquid opening forms a liquid blade, said liquid blade being operable to drive gas along said path from said gas inlet to said gas outlet on rotation of one of said elements.

2. The pump according to claim 1, wherein said protrusion is at least twice as wide at a point 10% along the protrusion from the element from which it extends as it is at a point 95% along the protrusion and preferably more than four times as wide.

3. The pump according to claim 1, wherein an upper surface of said at least one protrusion has a substantially parabolic form.

4. The pump according to claim 1, wherein said at least one protrusion extends from said pump housing element and has a cross section through a radial plane such that said protrusion does not mask said pump housing element from one or both of: (i) a water blade extending tangentially out from said further element; and (ii) a water blade extending at right angles from said further element.

5. (canceled)

6. The pump according to claim 1, wherein a lower surface of said at least one protrusion is flat.

7. The pump according to claim 1, wherein a trailing edge with respect to the direction of rotation of said cross section of said protrusion in said radial plane is at an acute angle with respect to a tangent to said pump housing wall that is between a maximum angle where said trailing edge is parallel to said tangent of said further element and up to 15% less than said maximum angle wherein said trailing edge of said protrusion in said radial plane is optionally angled such that said surface is substantially parallel to a tangent of said further element.

8. (canceled)

9. The pump according to claim 1, wherein a leading edge with respect to the direction of rotation of said cross section of said protrusion in said radial plane lies between a curved line curved in the direction of rotation and with a radius of curvature equal to half a distance between said pump housing element and said further element and a line extending away from said trailing edge and parallel to a tangent of said further element wherein a leading edge with respect to the direction of rotation of said cross section of said protrusion in said radial plane optionally comprises a surface substantially perpendicular to a tangent to said further element.

10-11. (canceled)

12. The pump according to claim 1, wherein an axial cross section of said protrusion has a substantially parabolic form.

13. The pump according to claim 1, wherein said protrusion has a cross section through a radial plane comprising a segment of a circular cross section of said pump housing element wherein said pump housing is optionally mounted to be stationary and said further element is mounted to rotate.

14. (canceled)

15. The pump according to claim 1, wherein said at least one liquid opening is formed on a surface of said element that is mounted to rotate.

16. The pump according to claim 1, wherein a cross section of said path formed by said protrusion, pump housing and further element decreases from said gas inlet to said gas outlet.

17. The pump according to claim 1, wherein said at least one liquid opening comprises at least one liquid opening extending along at least a portion of a length of one of said pump housing or further element wherein said at least one liquid opening is optionally arranged along a longitudinal direction running substantially parallel to an axis of said elements.

18. (canceled)

19. The pump according to claim 1, wherein said at least one liquid opening is arranged in the form of a helix extending around a surface of said pump housing or further element.

20. The pump according to claim 1, wherein an angle of said helix changes from said gas inlet towards said gas outlet such that a pitch of said helix reduces towards said gas outlet.

21. The pump according to claim 1, further comprising a liquid reservoir, said further element being rotatably mounted and comprising a hollow body having an opening at a lower end extending into said liquid reservoir, an internal diameter of said hollow rotor increasing from said lower end.

22. The pump according to claim 1 comprising a plurality of liquid openings wherein said plurality of liquid openings optionally provide a plurality of streams of liquid which form a plurality of liquid blades between said pump housing element and said further element.

23. (canceled)

24. The pump according to claim 22, wherein at least one set of said plurality of liquid outlets are arranged adjacent to each other and streams output from said at least one set of said plurality of liquid outlets form a single liquid blade.

25. The pump according to claim 1 wherein said pump comprises a vacuum pump.

26. The wet scrubber for reducing pollutants pumped from an abatement system, said wet scrubber comprising a pump according claim 1.

27. A method of pumping a gas, said method comprising: outputting liquid from at least one liquid opening on one of a pump housing element or a further element, the other of said pump housing and said further element comprising a protrusion, said protrusion, pump housing and further element forming a path from a gas inlet to a gas outlet; wherein said protrusion comprises a helix, a cross section through an axial plane of said helix varying such that said helix is narrower at a point towards said other element and wider at an intersection of said protrusion with said one of said pump housing and said further element from which said protrusion extends; rotating one of said pump housing element or said further element such that liquid output from said at least one liquid opening forms a liquid blade and drives gas along said path from said gas inlet to said gas outlet on rotation of one of said elements.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

[0071] FIG. 1 shows a screw pump type embodiments with a helical protrusion on the stator bore and liquid openings on the rotor;

[0072] FIG. 2 shows a cross section through a radial plane, of a thread not according to an embodiment;

[0073] FIG. 3 schematically shows the directions of the liquid blades at different operating pressures;

[0074] FIG. 4 shows a helical thread of a pump according to an embodiment;

[0075] FIG. 5 shows a helical thread of a pump according to another embodiment;

[0076] FIG. 6 shows a cross section in the radial plane of the thread of FIG. 5;

[0077] FIG. 7 shows a helical thread of a pump according to a further embodiment;

[0078] FIG. 8 shows liquid openings on an inner component for forming longitudinal liquid blades according to embodiments;

[0079] FIG. 9 shows liquid openings on an inner component for forming a helical liquid blade according to an embodiment; and

[0080] FIG. 10 show a hollow shaft in a reservoir with liquid blades formed by liquid expelled from liquid openings during rotation of the shaft.

DETAILED DESCRIPTION

[0081] Before discussing the embodiments in any more detail, first an overview will be provided.

[0082] Embodiments provide a pump comprising liquid blades that are high velocity surfaces formed of liquid, which surfaces emulate some of the solid mechanical surfaces which are found in conventional vacuum pumps and which are used as the physical boundaries to isolate and move pockets of gas. The liquid may be water, other liquids may be used for example to change characteristics of the pump such as vapour pressure or process compatibility.

[0083] The size and shape of the liquid surfaces will adapt to the relative position of the other pump elements unlike a rigid solid surface found in conventional pumps and will also provide a good seal with other surfaces provided they are suitably shaped without either causing appreciable wear on these surfaces or relying on tight tolerances or being sensitive to particulates in any gas or fluid flow being pumped.

[0084] The liquid “blades” are formed from a continuous stream of liquid originating from holes or slots. In some embodiments they are in a rotating element that forms the rotor of the pump. The streams of liquid travel at high velocity towards the other pump housing element. The pressure required to drive the liquid from one element to the other under high velocity can be achieved through centrifugal action of the rotating element, through a pressurised liquid source, or through a combination of the two.

[0085] Protrusions formed between the elements define a helical path that liquid blade(s) can drive gas along on rotation of one of the pumping house elements. The protrusions form a path from an inlet at one longitudinal end of the pump to an outlet at the opposing longitudinal end.

[0086] FIG. 1 shows an embodiment where the further element 10 is mounted within the pump housing element 20. In this embodiment, the protrusion 25 is a thread extending from the inner surface of pump housing element 20. This internal thread 25 is in the form of a helix. This can be used in conjunction with the inner components of FIG. 8 having longitudinal slots or that of FIG. 96 having helical slots.

[0087] In this embodiment the inner component 10 is rotatably mounted with the lower end in a liquid reservoir 30. On rotation of the inner component or rotor 10, liquid rises up the hollow shaft and is output through liquid openings to form longitudinal liquid blades 40 which sweep gas along a helical path defined by thread 25, stator bore 20 and rotor 10 from gas inlet 50 to gas outlet 52. In effect the liquid surfaces 40 create trapped ‘pockets’ along the thread form and as the liquid surfaces rotate the pockets move from the gas inlet towards the gas outlet. The shape of the thread may be adapted to the curvature of the liquid surface to provide appropriate sealing across the channel.

[0088] Although in this embodiment the thread is on the stator and the rotor rotates, where the helical path is formed by a mechanical thread or protrusion on the surface of one of the components, it is only relative motion between the two components that is required and as such, the thread could be on the rotor and the stator could have the liquid outlets. In this regard the stator is the fixed part and the rotor the rotating part, the rotor may be the inner component or it may be the outer component. In the latter case, the stator is a cylinder within the rotating outer component. In this embodiment, the stator and rotor may be concentrically mounted. It should be noted that where the liquid openings are on the static component then a different way of driving the liquid from the liquid openings will be required, such as by connection to a pressurised liquid source.

[0089] Although in this embodiment the liquid outlets are shown as slots extending vertically, they may be a plurality of adjacent liquid outlets following this formations, or they may have a different formation, albeit they will extend along the longitudinal axis of the component between the gas inlet 50 and gas outlet 52.

[0090] An advantage of having a mechanical thread 25 is that there may be an increased tolerance to back migration of the liquid when it hits the opposing surface, driving the liquid towards the outlet and achieving higher pressure ratios across the pump.

[0091] One potential problem with such an arrangement is illustrated with respect to FIG. 2. FIG. 2 schematically shows a cross section through the pump of FIG. 1. In this case with a simple non-tapered screw thread the water blade 40 may be blocked by the surface profile of the thread 25 before reaching the wall.

[0092] FIG. 2 schematically shows how water expelled from an outlet by a rotating body will continue to move in the direction of travel of the rotating body such that it will form a blade which if other forces are discounted, is in a direction tangential to the rotor as shown by line 40. As the blade rotates from point 1 to point 2, a conventional thread 25 with a substantially uniform narrow rectangular radial cross section will block the blade 40 from reaching the stator wall at certain positions of the blade, and this will cause an area 60 which does not seal. This area will follow the path of the screw helix from top to bottom and may cause a leakage path between the top and bottom of the stator.

[0093] Embodiments seek to address this by matching the surface profile of the protrusion or thread 25 to the extremes of the blade profile to allow the water blade to reach the outer wall under the different pressure conditions that the pump may operate under.

[0094] FIG. 3 schematically shows how the profile of the blade may vary with differing pressure differences (PD) between the blades, the possible blade profiles 40a and 40b being shown. Blade edge 40a schematically represents the case with no pressure difference between the blades, that is the condition at startup for example. Blade edge 40b schematically represents the case of a higher maximum pressure difference across the blades. It should be noted that these representations are schematic and do not take into account other factors that affect the shape of the blade such as the rotational movement of the rotor. In reality the shape of blade 40b may be more of a tear drop or semi-circular shape the curve extending in the direction of rotation of the rotor.

[0095] Bearing the different potential geometries of the blade in mind, the channel design should be such as to create a seal even with DP=0. Were this not the case then generating the initial pressure difference would be difficult. Blade edge 40a assumes one extreme case to create a seal DP=0 mbar, while line 40b represents the other extreme case to create a seal e.g. DP=maximum. The location of the blade at other pressure differences will lie between the two extremes.

[0096] FIG. 4 shows different views of a helical thread according to an embodiment where the cross section (and the initial portion) of the thread is/are adapted to avoid or at least inhibit the potential leakage path formed by the blades being blocked by the thread profile from reaching the opposing wall.

[0097] FIG. 4a shows an isometric view of the thread.

[0098] FIG. 4b shows in the lower figure a cross section through the lines B-B of the upper figure. As can be seen when taking a horizontal or radial cross section through this inclined thread, the portion of the thread closer to the stator wall is thicker and thus, a section through the thread shows this section extending further than the section towards the centre. Thus, in the horizontal or radial plane, the cross section of the inclined thread forms a shape of a circle segment, which shape that does not block the blade from reaching the wall. This is in contrast to the cross section of the inclined substantially linear thread of FIG. 2, that leads to a “shadow” where no water reaches the wall, the shape does not form a shadow for the water blade

[0099] FIG. 4C shows the tapered profile of the screw thread in the axial or vertical plane. As can be seen the profile is symmetrical about a mid line and has a substantially parabolic profile. The mid line is perpendicular to the wall of the stator. This profile provides a surface which a vertical water blade will pass over without pulling away from the thread surface and reach the edge wall and thereby inhibit any leakage of gas.

[0100] FIG. 5 shows a further example which illustrates the minimum permissible cross sectional profile of screw thread so that it matches the two extremes of the transmission path of a particle ejected from the nozzle. The trailing edge with respect to the direction of rotation which is clockwise in this example, has an edge that is parallel to a tangent of the inner rotating element. This corresponds to the water blade path where there is no pressure difference so particle travels along the tangent. This cross section defines the predominately parabolic vertical profile of the upper surface of the thread shown in detail C. At the other extreme of maximum pressure difference the particle travels with a radius of curvature equal to half the gap, this defines the profile of the lower surface.

[0101] FIG. 6 shows in more detail a radial cross section of the protrusion of minimum area, whereby the trailing edge (second edge encountered when rotating clockwise) follows the line of a water blade at zero pressure difference and the leading edge (first edge of protrusion encountered by blade) follows the form of the water blade at maximum pressure difference.

[0102] The protrusion shown in FIGS. 5 and 6 provide an example of a thread, with the leading and trailing edges being defined by the path of the blades at the extreme ends of operation of the pump and the horizontal or radial cross section of the protrusion being at a minimum or lower value. The area of the protrusion can be extended by making the angle of the trailing edge more acute at the apex with the outer wall and by making the leading edge extend further in a counter clockwise direction.

[0103] It may for example be advantageous to make the leading edge perpendicular to the tangent of the inner element, as this corresponds to a flat lower surface of the protrusion which may make it easier to machine. This is shown in FIG. 7. Alternatively a symmetrical protrusion may have advantages, the blade tending to adhere to rounded surfaces, and in this case the cross section will have the shape of a circle segment form of FIG. 4, while the axial cross section of the protrusion will have an outer parabolic form.

[0104] In some embodiments the liquid openings on the inner component 10 may have a longitudinal form as shown in FIG. 9 to provide axial blades that drive the gas along the helical path formed by the thread 25. In other embodiments the inner component 10 may have liquid openings in a helical form to provide a helical blade.

[0105] Where the liquid openings have a helical form to form helical blades, then the helical form of the thread and blades progress in opposite directions, such that if the helical thread descends in a clockwise direction, the helical blades descend in an anti-clockwise direction.

[0106] FIGS. 8 and 9 show different arrangements of liquid openings 15 on the inner components of pumps of embodiments. In FIG. 8 the openings 15 are arranged longitudinally in an axial direction along the inner component 10 and in operation provide longitudinal blades for sweeping gas along a path defined by protrusions on the outer component. Each blade may be formed by one longitudinal slot or by a plurality of liquid openings arranged along a length of the inner component. A plurality of blades may be provided at different circumferential positions of the inner component.

[0107] FIG. 9 shows an alternative embodiment where the liquid opening is a helix and provides in operation a helical blade. In the embodiment shown the helix is formed from one helical slot, while in other embodiments, it may be formed from a plurality of openings arranged along a helical path.

[0108] The liquid blades are formed by driving liquid through the openings. This may be done in a number of ways, by for example using a pressurised liquid source. However, in some embodiments where the liquid openings are on the rotor of the pump, the force for driving the liquid is provided by the driving mechanism used to rotate the rotor.

[0109] FIG. 10 shows how on rotation of a hollow rotor 10 within a liquid reservoir 30, liquid is driven through liquid openings to form liquid blades. FIG. 10 shows a cross section through a substantially circular hollow shaft 10 which is configured to rotate in a substantially circular stator bore 20. The shaft forms the rotor 10 of the pump and has an outside diameter that is smaller than the stator bore 20 inside diameter. The axes of the shaft and stator are orientated vertically and the base of the hollow open ended shaft is submerged in a liquid reservoir 30.

[0110] FIG. 10 shows the liquid 32 from liquid reservoir 30 rising up the shaft 10 on rotation of the rotor. The hollow bore of the shaft 10 has an internal increase in diameter 12 positioned below the liquid reservoir level which serves when the shaft rotates to accelerate the liquid through centrifugal force and pump it up the inside of the shaft then out of holes or elongated slots (not shown) in the shaft to form a contiguous liquid surface 40 between the shaft or rotor 10 and the stator inner bore 20. The liquid flows back down the inner wall of the stator bore 20 into the reservoir 30. This is on a continuous cycle basis, such that the liquid, in some embodiments water, that contacts the stator inner bore 20 travels down the bore under gravity and replenishes the reservoir. Note that the arrows depict the direction of flow of the liquid to create a single surface or blade 40.

[0111] The liquid inside the shaft is forced through the holes/slots under centrifugal force and travels towards the stator bore to form the plurality of liquid surfaces 40, these form blades that drive the gas through the pump as the rotor 10 rotates.

[0112] Although in many of the embodiments described above the liquid circulation providing the liquid surface is generated by a rotating rotor providing a centrifugal force on the liquid, in some embodiments an alternative way of generating the liquid circulation is used, namely that of a high pressure liquid source.

[0113] Such a high pressure liquid supply or pump could be used separately or in conjunction with regulated shaft rotation—enabling independent variability of both fluid velocity and shaft frequency according to pumping performance requirements allowing controllable efficiency and pump tuning.

[0114] In some embodiments, the pump may be used in a wet scrubbing environment so that the pumping function may be integrated into the wet scrubbing, the liquid blades being an advantage in such an embodiment. In this regard, by placing one of the liquid blade pumps in line with process gas flow the pump may be used for wet scrubbing in addition to vacuum generation—for example on the outlet (or inlet) of an abatement system.

[0115] Where a means to drive the shaft is required such as a motor and frequency inverter or belt drive, such a drive system may preferentially be positioned at the top of the shaft to reduce risk of liquid leaking into the drive means.

[0116] In summary, embodiments function effectively where a circulation of liquid that meets or exceeds the emission from the liquid outlets can be achieved. This helps sustain the blades as a continuous surface. It should be noted that many parameters such as the size of the liquid outlets, the type of liquid used, the liquid velocity, the distance between elements and the length of blade and the speed of rotation all affect the formation and maintenance of the liquid surfaces. Thus, these features should be selected depending on the properties required of a particular pump, such as power consumption, pumping capacity and compression.

[0117] Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

[0118] Although elements have been shown or described as separate embodiments above, portions of each embodiment may be combined with all or part of other embodiments described above.

[0119] Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are described as example forms of implementing the claims.