CN113396271B

CN113396271B - Pump and method for pumping gas

Info

Publication number: CN113396271B
Application number: CN202080014275.4A
Authority: CN
Inventors: I·D·斯通斯
Original assignee: Edwards Ltd
Current assignee: Edwards Ltd
Priority date: 2019-02-15
Filing date: 2020-02-13
Publication date: 2023-10-03
Anticipated expiration: 2040-02-13
Also published as: GB2581382B; KR20210126599A; GB201902106D0; JP2022520444A; WO2020165592A9; CN113396271A; WO2020165592A1; GB2581382A; US20220213892A1; EP3924604A1

Abstract

A pump and a method for pumping a gas are disclosed. The pump includes: pump casing elements and further elements; one of the pump casing and the further element comprises a helical projection extending towards the other element, the other element comprising at least one liquid opening. The helical projection, the pump housing and the further element form a path from the gas inlet to the gas outlet. The helical protrusion has a wider axial cross-section at its attachment end than at its free end. The pump housing and the further element are rotatably mounted relative 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 operable to drive gas along the path from the gas inlet to the gas outlet upon rotation of one of the elements.

Description

Pump and method for pumping gas

Technical Field

The field of the invention relates to pumps and methods of pumping gases.

Background

Different types of pumps for pumping gases are known. These pumps include: a trap pump, wherein the gas is trapped on a surface within the pump before being removed; a power or momentum transfer pump, such as a turbo molecular pump, in which gas molecules are accelerated from an inlet side towards an outlet or exhaust side; and a positive displacement pump, wherein gas is captured and moves from an inlet to an outlet of the pump.

Positive displacement pumps provide a moving pumping chamber that is typically formed between one or more rotors and a stator, the movement of the rotors moving the effective pumping chamber. The gas received at the inlet enters and is trapped in the pumping chamber and moves to the outlet. In some cases, the volume of the air bag is reduced during movement to improve efficiency. Such pumps include Roots pumps and rotary vane pumps. The chamber typically expands in order to draw gas into the chamber, and the chamber volume typically contracts in order to expel gas from the chamber. Such a change in volume may be achieved, for example, in a rotary vane pump by vanes that extend into and out of the pump chamber using means such as springs that themselves are subject to wear, or by moving a gas pocket (a pocket of gas) and creating a change in volume between the inlet and outlet using two synchronized rotors and stators in conjunction with each other in a Roots pump or a screw pump. Additional rotors require additional shafts, bearings, and timing methods such as gears to synchronize rotor movement.

Furthermore, in order to minimize or at least reduce leakage and to efficiently move the gas when it is trapped, the moving parts need to form a tight seal with each other and with the static parts forming the trapped gas volume. Some pumps use liquids such as oil to seal between surfaces of trapped volumes, while others rely on tight non-contact clearances, which can result in increased manufacturing costs and can also result in the pump being sensitive to lock-up or capture if particles or impurities are present in the fluid that these parts contact or pump.

It would be desirable to provide a pump that is resistant to wear, provides a low power consumption, relatively small pumping mechanism, and is relatively inexpensive to manufacture and operate.

Disclosure of Invention

A first aspect of the present invention provides a pump for pumping gas, the pump comprising: pump casing elements and further elements; one of the pump casing and the further element comprises a projection extending towards the other element, the other element comprising at least one liquid opening; the projection, pump housing and the further element form a path from a gas inlet to a gas outlet; wherein the further element is mounted concentrically within the bore of the pump casing and the further element are rotatably mounted relative to each other; and the projection comprises a spiral, the cross-section through the axial plane of the spiral varying such that the spiral is narrower at a point towards the other element and wider at the intersection of the projection and the one of the pump housing and the other element from which the projection extends; and the at least one liquid opening is configured such that liquid output from the at least one liquid opening forms a liquid blade operable to drive gas along the path from the gas inlet to the gas outlet upon rotation of one of the elements.

The inventors of the present invention have appreciated that if the elements of the pump are configured with liquid openings such that the liquid output through the openings forms a surface or vane between the elements of the pump, the liquid vane may be used to drive gas through the pump as one of the elements rotates relative to the other. Furthermore, if the elements of the pump are configured such that the helical protrusions extending therebetween form a path from the gas inlet to the gas outlet, such a path may direct gas from the inlet to the outlet, driven by liquid vanes extending between the elements and spanning the path. This will potentially provide a simple, compact, low power, low cost arrangement and will avoid or at least reduce the problems due to friction and wear between the contact surfaces and the costs involved in manufacturing tolerances of tight clearances.

Such vanes may be formed by driving liquid through one or more liquid openings. The placement of liquid openings on one of the elements allows the liquid flow to create a liquid surface or vane between the elements. Such liquid blades are deformable by their nature, are low cost, and are capable of providing a good seal between surfaces of a trapped volume without requiring strict manufacturing tolerances. Furthermore, such a blade itself is not subject to wear and provides very little wear on the surfaces it contacts.

The vanes are formed from flowing liquid such that the liquid forming the vanes is continuously replenished. The surface of the vane acts with the surface of the element and the protrusions to confine, capture, isolate or encapsulate the gas to be pumped. Rotation of one of the elements causes the trapped gas to move from the gas inlet to the gas outlet along a path defined by the protrusion. The gas to be pumped is located on either side of the blade.

One or the other of the elements may be mounted for rotation, or both may be mounted for rotation in opposite directions. In this respect, it is not important which is the rotating element, which requires relative movement between the elements. In some embodiments, the pump casing elements are mounted stationary and the other elements are mounted for rotation.

However, one potential problem with this design is that without careful design of the shape of the helical protrusion, portions of the protrusion may shield the outer wall from the blade and leakage paths along the shielded area may occur. To address this potential problem, the helical protrusion is configured such that it has a tapered axial profile such that it is wider at the wall to which it is attached than at its free end. A helical thread having a non-tapered axial profile provides a substantially rectangular radial profile and such a shape may originate from the portion of the liquid blade shroud wall from which it extends. Such shielding is detrimental to pump performance, providing a leakage path along the spiral from the gas outlet to the gas inlet. The wider thread at the wall edge provides a horizontal cross section that is also wider towards the wall, limiting the masking effect of the profile on the liquid blade.

Although in some embodiments the variation in width of the protrusion may have a plurality of values, the protrusion is at least twice as wide at a point along 10% of the protrusion of the element from which it extends, and in some embodiments more than four times as wide at a point along 95% of the protrusion.

In some embodiments, the upper surface of the at least one protrusion has a form corresponding to a semiparabolic curve.

It may be advantageous if the protrusions have a curved form such that the liquid is not thrown off the surface but tends to adhere to it. The substantially parabolic form of the upper surface provides a radial profile of the form: it may have a trailing edge (the trailing or last edge that the blade encounters when rotating) that is substantially straight and extends at an angle from the wall to which it is attached. It should be noted that the axial section or plane is a section or plane parallel to and passing through the axis of the pump about which the rotary element rotates, and the radial section or plane is a section or plane perpendicular to the axis, which is substantially horizontal in operation of most embodiments of the pump.

In some embodiments, the at least one projection extends from the pump casing element and has a cross-section through a radial plane such that the projection does not obscure the pump casing element from water vanes extending tangentially from the further element.

The inventors of the present invention have appreciated that in order for the pump to pump effectively, the shape of the protrusions should be such that the protrusions do not obscure the liquid vanes from reaching the outer wall at some point, as this may provide a leakage path along the entire length of the spiral. When determining how such leakage paths can be avoided or at least suppressed, the inventors have realized that the direction of the liquid blade will vary depending on the operating conditions, and intermediate conditions should also be covered if the protrusions can be designed to be effective for extreme conditions. Thus, the protrusions are configured such that the pump housing wall is not obscured by the protrusions from the tangential vanes, which is relevant to conditions where there is no pressure differential across the vanes.

In some embodiments, the at least one projection extends from the pump casing element and has a cross-section through a radial plane such that the projection does not obscure the pump casing element from water vanes extending at right angles from the further element.

At higher pressure differences, the vane may extend substantially perpendicular to the further elements of the interior, and in this case the projection may be designed taking this into account.

In some embodiments, the lower surface of the at least one projection is flat, such a configuration providing a projection that does not obscure the outer wall from the vertical liquid blade.

In other embodiments, the protrusion has a substantially parabolic cross-section in the axial plane.

It may be convenient to form the protrusions as symmetrical protrusions having upper and lower surfaces of the same parabolic form. Such a projection forms an effective seal with the liquid blade along the length of the spiral.

In some embodiments, a trailing edge relative to a direction of rotation of the cross-section of the projection in the radial plane is at an acute angle relative to a tangent to the pump casing wall, the acute angle being between a maximum angle at which the trailing edge is parallel to the tangent of the further element and up to 15% less than the maximum angle.

As previously mentioned, the angle of the trailing edge should be selected to prevent the radial profile of the protrusion from obscuring the outer wall from the blade. Even under extreme conditions, the trailing edge parallel to the tangent of the inner rotating element provides acceptable performance, however, the protrusions may be formed with a slightly larger area and a slightly smaller acute angle.

In some embodiments, the leading edge relative to the direction of rotation of the cross-section of the projection in the radial plane is located between a curve curved in the direction of rotation and having a radius of curvature equal to half the distance between the pump casing element and the further element and a line extending away from the trailing edge and parallel to a tangent of the further element.

For the purposes of this patent application, the leading edge of a helical thread is considered to be the portion of the thread in this radial plane that the blade first contacts when rotating, and the trailing edge is the portion that it contacts when moving past this portion of the thread.

The desired shape of the leading edge may be configured to avoid shadowing of the wall by the protrusions depending on higher operating pressure conditions. The limit corresponding to operating at maximum pressure conditions corresponds to the blade having a curved surface with a radius of half the gap between the elements. Even under extreme conditions, a protrusion with a correspondingly shaped leading edge will be acceptable. This form involves a minimum profile that provides an acceptable seal and can be expanded by: the leading edge is extended away from the direction of rotation until it is parallel to the tangent of the inner element.

In fact, a profile that matches the radial or horizontal profile of the protrusion with the trajectory of the droplets of the vane under extreme conditions will provide a protrusion that does not obscure the outer wall from the vane and provides acceptable pumping. Although the inclined leading edge should be maintained, the profile can be enlarged.

In the case of a radial profile having both a leading edge and a trailing edge parallel to the tangent of the inner element, then the radial profile forms a circular arc segment in the annular gap between the two elements.

In some embodiments, the lower surface of the at least one protrusion is flat and this provides a leading edge with respect to the direction of rotation of the radial profile, which leading edge is substantially perpendicular to the tangent of the further element.

Such an arrangement is easy to machine and provides a protrusion with acceptable performance in the case that the upper surface is curved and wider at its intersecting end than at its free end.

In some embodiments, the at least one liquid opening is formed on a surface of the element mounted for rotation.

The element mounted for rotation is often referred to as a rotor and may be advantageous if this is an element with liquid openings, as the rotational movement may assist in draining liquid from the liquid openings to form the blades.

In some embodiments, the profile of the path formed by the protrusion, pump housing and further element decreases from the gas inlet to the gas outlet.

In some cases, the profile of the path may decrease continuously or along a portion of the path between the inlet and the outlet. The resulting volume reduction results in volumetric compression of the gas as it is pumped, which not only assists in venting the gas from the chamber, but also reduces the power required to pump a given volume of gas.

In some embodiments, the inner member is mounted eccentrically within the bore of the outer member, while in other embodiments, the inner member is mounted concentrically within the bore of the outer member.

Eccentrically mounting the internal components means that when there is relative rotation, the air pocket formed by the pump casing element and the liquid vanes will change volume around the perimeter of the element. Such eccentric mounting requires that the blades change size as the element rotates, but this will occur naturally. No mechanical or sliding parts, such as springs and solid blades, are required to create the varying blade dimensions.

The liquid outlets may be arranged in a variety of ways. There may be multiple liquid outlets arranged adjacent to each other or there may be a single outlet in the form of a channel. In some embodiments, the slot or outlets have a longitudinal form extending substantially parallel to the axis of the element. Such an arrangement provides vanes that are substantially perpendicular to the radius of the pumping chamber.

In other embodiments, the slots or adjacent outlets may be angled relative to the axis of the element and in some cases may form a spiral such that spiral liquid vanes are formed between the stator and the rotor.

Pumps configured to produce such vanes may be used in combination with helical protrusions on the surface of other components. The helical protrusion provides a pump that functions in a manner similar to a screw pump. Such protrusions may be used in combination with axial liquid blades or helical blades.

In some embodiments, the angle of the spiral varies from the gas inlet toward the gas outlet such that the pitch of the spiral decreases toward the gas outlet.

The reduction in the helical pitch towards the gas outlet provides volumetric compression of the gas as it is pumped, which not only assists in expelling the gas from the chamber, but also reduces the power required to pump a given volume of gas.

In some embodiments, at least one of the pump housing and the further element is tapered such that a distance between the stator and the rotor decreases towards the gas outlet.

One way to provide a pumping chamber that reduces the size between the inlet and the outlet is to provide a taper such that the distance between the elements decreases towards the gas outlet. In some embodiments, the non-rotating element or stator is tapered, while in other embodiments, the rotating element or rotor is tapered. Tapering the non-rotating stator is typically the simplest way to create a reduction in the size of the pumping chamber towards the gas outlet.

In some embodiments, the at least one of the pump casing and the further element that is tapered is non-axisymmetric tapered.

While the generally conical shape will be axisymmetric, in some embodiments the bore of the outer member tapers non-axisymmetrically toward the gas outlet, while in other embodiments the inner member may have an increased diameter.

In some embodiments, the plurality of liquid outlets provides a plurality of liquid flows that form a plurality of liquid vanes between the pump housing element and the further element.

Although in some embodiments the pump may include a single liquid opening to form a single liquid vane, it includes multiple liquid openings. The liquid from the plurality of openings may form a single vane, or the openings may be arranged such that the liquid discharged from them forms a plurality of vanes.

In some embodiments, at least one set of the plurality of liquid openings is disposed adjacent to one another, and the streams output from the at least one set of the plurality of liquid openings combine to form a single liquid vane.

In some cases, there may be multiple openings and a group of these openings may form a single vane. In case there is only one blade, the group may comprise all liquid openings, while in other embodiments there may be a plurality of groups, each arranged to form their own blade. Although the liquid vanes may be formed from a single liquid outlet in the form of a trough, in some embodiments they may be formed from a plurality of adjacent openings that are close enough together to cause the liquid flow through each to polymerize and form a single vane. Having multiple openings rather than a single slot may improve the structural integrity of the elements on which they are disposed and thereby improve the mechanical integrity of the pump.

For the purposes of this patent application, where the term "rotor" is used, this refers to the rotating pump housing or another element, and where the term "stator" is used, this refers to the element with respect to which the rotor rotates. Furthermore, the gas to be pumped may be a vapor or a mixture of gas and vapor or a gas with particles entrained therein.

In some embodiments, the rotor is rotatably mounted within the bore of the stator, and the liquid flow forming the liquid vanes between the rotor and the stator bore is operable to drive gas through the pump as the rotor rotates within the stator bore.

Rotation of the rotor provides relative movement between the surfaces surrounding the gas pocket such that, in some embodiments, the liquid surface drives the gas along a pumping path from the gas inlet to the gas outlet. In some embodiments, such relative movement may be provided in conjunction with a change in the volume of the air bag without any appreciable wear on the surfaces that limit the air bag, as at least one is formed by a liquid vane, and due to its deformable nature, its surface shape and size will adapt to the distance between the rotor and stator during rotation.

In some embodiments, the pump comprises a drive mechanism for applying a driving force to a liquid to drive the liquid from the liquid source through the at least one liquid opening.

Although the driving force exerted on the liquid may come from a source external to the pump, the pump may be connected to an external source of pressurized liquid, for example, in some embodiments the pump itself comprises a driving mechanism for exerting such driving force on the liquid.

Although the liquid openings may be formed on the surface of the rotatable inner member, in some embodiments they are formed on the surface of the stationary outer member. This may have the advantage that: enabling a simpler way of supplying pressurized liquid to the pump.

In some embodiments, the pump further comprises a liquid reservoir, the inner member being rotatably mounted and comprising a hollow body having an opening at a lower end, the opening extending into the liquid reservoir, the inner diameter of the hollow rotor increasing from the lower end.

One way to provide a driving force to the liquid with the liquid outlet on the rotating inner member is to use a hollow member and rotate the hollow member. In such embodiments, rotation of the hollow rotor will cause the liquid within the hollow rotor body to be centrifugally urged against the outer periphery of the hollow rotor body and out through the one or more liquid outlets, thereby forming a liquid flow. With the liquid outlets properly arranged, the liquid flow will form liquid vanes extending to the stator bore.

In the case of the hollow rotor having an opening at the lower end extending into the liquid reservoir, the increased inner diameter of the hollow rotor from said lower end will assist the liquid rising inside the rotor and being expelled through the liquid outlet when the rotor rotates. In this way, there is a smaller diameter at the lower end immersed in the liquid reservoir and the diameter increases upwards with the hollow body. This causes the liquid urged against the inner surface of the hollow body by centrifugal force to rise along an increasing inner diameter towards the top of the rotor body. The increase in diameter may be an oblique increase, or it may be a stepwise increase, or it may be a combination of both. It may also be supplemented by vanes on the inner surface of the rotor to support the acceleration of the liquid towards larger diameters. The liquid is thrown towards the inner surface of the hollow body and rises under the acceleration and pressure of the subsequent liquid. The rotational speed will influence the height at which the liquid is pushed up the hollow body and will influence other parameters, such as the density of the liquid. The appropriate rotor speed and size may be selected according to the desired flow rate of liquid to be pumped through the outlet to form the blade or vane. It should be noted that sufficient liquid should be supplied from the reservoir into the hollow rotor body to maintain an uninterrupted flow of liquid between the rotor and stator for efficient pumping of gas. This in turn will depend on parameters such as the rotational speed of the rotor and the size and number of outlets, as well as the height of the rotor.

In some embodiments, the pump includes at least one hydrodynamic bearing to support at least one end of the rotating element.

The rotor of the pump is supported on bearings, and typically these are roller bearings or ball bearings, which can be expensive parts, require lubrication and are subject to wear. Hydrodynamic bearings that utilize a liquid film between the cylindrical shaft and the bore may be suitable for this type of pump. In some cases, the hydrodynamic bearing is filled with liquid from the same liquid source as the pump blades, thereby efficiently utilizing the liquid supply and mechanical features already used in the pump and avoiding the use of additional components or different lubricant liquids.

While the pump may be a variety of things, such as a compressor, in some embodiments it comprises a vacuum pump. The pump according to the embodiments constitutes a particularly efficient vacuum pump, allowing for an efficient way of transporting the gas with low wear and low initial costs.

A second aspect of the invention provides a wet scrubber for reducing contaminants pumped from an emission abatement system, the wet scrubber comprising a pump according to the first aspect of the invention.

The abatement system is typically used in conjunction with a wet scrubber that provides a liquid stream to react with the gas or remove particulates from the gas pumped from the abatement system. The pump that uses the liquid surface to move the gas may be used in combination with an additional liquid scrubbing source or alone, providing both the liquid source and the pumping required to move the gas and remove particles therefrom.

A third aspect of the invention provides a method of pumping a gas, the method comprising: outputting liquid from at least one liquid opening on one of the pump casing element or the further element, the other of the pump casing and the further element comprising a projection, the pump casing and the further element forming a path from a gas inlet to a gas outlet; wherein the projection comprises a spiral, the cross-section through the axial plane of the spiral varying such that the spiral is narrower at a point towards the other element and wider at the intersection of the projection and the one of the pump housing and the other element from which the projection extends; and rotating one of the pump housing element or the further element such that liquid output from the at least one liquid opening forms a liquid vane and drives gas along the path from the gas inlet to the gas outlet upon rotation of one of the elements.

Further specific and preferred aspects are set out in the attached independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate and may be combined differently than those explicitly set out in the claims.

Where a device feature is described as being operable to provide a function, it will be understood that this includes the device feature providing that function or being adapted or configured to provide that function.

Drawings

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

FIG. 1 shows a screw pump embodiment with screw protrusions on the stator bore and liquid openings on the rotor;

FIG. 2 shows a cross-sectional view of a radial plane of a thread, not according to an embodiment;

fig. 3 schematically shows the direction of a liquid blade at different operating pressures;

FIG. 4 illustrates a helical thread of a pump according to one embodiment;

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

FIG. 6 shows a cross-section in the radial plane of the thread of FIG. 5;

FIG. 7 shows a helical thread of a pump according to another embodiment;

FIG. 8 illustrates liquid openings on an inner member for forming a longitudinal liquid blade according to an embodiment;

FIG. 9 illustrates liquid openings on an inner member for forming a spiral liquid blade according to one embodiment; and

fig. 10 shows a hollow shaft in a reservoir with liquid blades formed by liquid discharged from a liquid opening during rotation of the shaft.

Detailed Description

Before discussing embodiments in more detail, an overview will first be provided.

Embodiments provide a pump that includes liquid blades that are high-speed surfaces formed from liquid that simulate certain solid mechanical surfaces found in conventional vacuum pumps and that act as physical boundaries to isolate and move air pockets. The liquid may be water, for example, other liquids may be used to alter pump characteristics such as vapor pressure or process compatibility.

The size and shape of the liquid surface will accommodate the relative positions of other pump elements, unlike rigid solid surfaces found in conventional pumps, and will also provide a good seal with other surfaces, provided they are properly shaped without causing appreciable wear on these surfaces, or relying on tight tolerances or sensitivity to particles in any gas or fluid stream being pumped.

The liquid "vanes" are formed by a continuous flow of liquid from holes or slots. In some embodiments, they are in a rotating element that forms the rotor of the pump. The liquid flow is directed at a high velocity to the other pump casing element. The pressure required to drive the liquid from one element to another element at high speed may be achieved by centrifugation of the rotating element, a source of pressurized liquid, or a combination of both.

The protrusions formed between the elements define a helical path along which the liquid vane can drive gas as one of the pumping housing elements rotates. The protrusions form a path from an inlet at one longitudinal end of the pump to an outlet at the opposite longitudinal end.

FIG. 1 shows an embodiment in which a further element 10 is mounted within a pump casing element 20. In this embodiment, the protrusion 25 is a thread extending from the inner surface of the pump casing element 20. The internal thread 25 is in the form of a screw. This can be used in combination with the inner member with longitudinal grooves of fig. 8 or the inner member with spiral grooves of fig. 9.

In this embodiment, the inner member 10 is rotatably mounted with its lower end in the liquid reservoir 30. As the inner member or rotor 10 rotates, liquid rises along the hollow shaft and is output through the liquid openings to form longitudinal liquid blades 40, which liquid blades 40 sweep gas along a helical path defined by the threads 25, stator bore 20 and rotor 10 from gas inlet 50 to gas outlet 52. In effect, the liquid surface 40 creates trapped "pockets" along the thread form, and as the liquid surface rotates, the pockets move from the gas inlet to the gas outlet. The shape of the threads may be adapted to the curvature of the liquid surface to provide a proper seal across the channel.

Although in this embodiment the screw thread is on the stator and the rotor rotates, wherein the helical path is formed by a mechanical screw thread or protrusion on the surface of one of the parts, only a relative movement between the two parts is required and thus the screw thread may be on the rotor and the stator may have a liquid outlet. In this regard, the stator is a stationary part and the rotor is a rotating part, the rotor may be an inner part, or it may be an outer part. In the latter case, the stator is a cylinder within the rotating outer member. In this embodiment, the stator and rotor may be mounted concentrically. It should be noted that in case the liquid opening is on a stationary part, then a different way of driving the liquid from the liquid opening would be required, for example by being connected to a pressurized liquid source.

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

One advantage of having mechanical threads 25 is that when the liquid impinges on the opposing surface, there may be an increased resistance to reverse migration of the liquid, thereby driving the liquid toward the outlet and achieving a higher pressure ratio across the pump.

One potential problem with such an arrangement is illustrated with respect to fig. 2. Fig. 2 schematically shows a cross-section of the pump of fig. 1. In this case, where a simple non-tapered thread is used, the water blade 40 may be blocked by the surface profile of the thread 25 before reaching the wall.

Fig. 2 schematically shows how water discharged from the outlet through the rotating body will continue to move in the direction of travel of the rotating body, so that it will form a blade that, if other forces are not considered, is in a direction tangential to the rotor, as indicated by line 40. As the blade rotates from point 1 to point 2, the conventional thread 25, having a substantially uniform narrow rectangular radial profile, will block the blade 40 from reaching the stator wall at certain locations of the blade, and this will result in an unsealed area 60. This region will follow the path of the thread helix from top to bottom and may result in a leakage path between the top and bottom of the stator.

Embodiments seek to solve this problem by: the surface profile of the protrusions or threads 25 is extremely matched to the profile of the vane to allow the water vane to reach the outer wall under different pressure conditions under which the pump may operate.

Fig. 3 schematically shows how the profile of the blade may vary with different Pressure Differences (PD) between the blades, showing possible blade profiles 40a and 40b. The blade edge 40a schematically represents a situation where there is no pressure difference between the blades, i.e. for example at start-up. Blade edge 40b schematically represents a situation where the maximum pressure differential across the blade is high. It should be noted that these representations are schematic and that other factors affecting the shape of the blade, such as rotational movement of the rotor, are not considered. In practice, the shape of the blades 40b may be more teardrop-like or semicircular, with the curve extending in the direction of rotation of the rotor.

The channel design should be such that a seal is formed even with dp=0, taking into account the different possible geometries of the blades. If this is not the case, it will be difficult to create an initial pressure differential. The blade edge 40a assumes one extreme of forming a seal dp=0 mbar, while the line 40b represents the other extreme of forming a seal, e.g. dp=maximum. The position of the blade at other pressure differences will be between these two extremes.

Fig. 4 shows a different view of a helical thread according to an embodiment, wherein the profile (and initial portion) of the thread is adapted to avoid or at least inhibit potential leakage paths formed by the blades being blocked by the thread profile to the opposite wall.

Figure 4a shows an isometric view of the thread.

Fig. 4B shows a section through line B-B of the upper drawing in the lower drawing. As can be seen when a horizontal or radial section through the inclined thread is taken, the part of the thread closer to the stator wall is thicker and, therefore, the section through the thread shows that the section extends further than the section towards the centre. Thus, in a horizontal or radial plane, the cross-section of the inclined thread forms the shape of an arc segment, which does not block the blade from reaching the wall. This is in contrast to the inclined substantially linear thread profile of fig. 2, which results in no "shadow" of water reaching the wall, the shape not forming a shadow of the water blade.

Fig. 4C shows the tapered profile of the thread in the axial or vertical plane. As can be seen, the profile is symmetrical about a midline and has a substantially parabolic profile. The midline is perpendicular to the wall of the stator. The profile provides a surface over which the vertical water vanes will pass without disengaging from the threaded surface and reaching the edge wall and thereby preventing any gas leakage.

Fig. 5 shows another example illustrating a minimum allowable cross-sectional profile of a thread such that it matches both extremes of the transport path of particles ejected from the nozzle. The trailing edge relative to the clockwise direction of rotation in this example has an edge parallel to the tangent of the inner rotating element. This corresponds to a water blade path without a pressure differential, so the particles travel tangentially. This section defines the predominantly parabolic vertical profile of the upper surface of the thread shown in detail C. At the other extreme of the maximum pressure difference, the particles travel with a radius of curvature equal to half the gap, which defines the contour of the lower surface.

Fig. 6 shows in more detail the radial profile of the minimum area protrusion, whereby the trailing edge (the second edge encountered when rotating clockwise) follows the line of the water blade at zero differential pressure, while the leading edge (the first edge of the protrusion encountered by the blade) follows the form of the water blade at maximum differential pressure.

The protrusion shown in fig. 5 and 6 provides one example of a thread in which the leading and trailing edges are defined by the vane path at the extreme end of pump operation and the horizontal or radial profile of the protrusion is at a minimum or lower value. By making the angle of the trailing edge sharper at the apex with the outer wall, and by extending the leading edge further in a counter-clockwise direction, the area of the protrusion can be enlarged.

For example, it may be advantageous to have 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 be advantageous, the blade tending to adhere to a circular surface, and in this case the profile would have the shape of the circular arc segment form of fig. 4, while the axial profile of the protrusion would have an external parabolic form.

In some embodiments, the liquid openings on the inner member 10 may have a longitudinal form as shown in fig. 9 to provide axial vanes that drive the gas along a helical path formed by the threads 25. In other embodiments, the inner member 10 may have a liquid opening in the form of a spiral to provide a helical blade.

In the case of a liquid opening having a helical form to form a helical blade, the helical form of the thread and the blade proceeds in opposite directions, such that if the helical thread descends in a clockwise direction, the helical blade descends in a counter-clockwise direction.

Fig. 8 and 9 show different arrangements of the liquid openings 15 on the inner part of the pump of the embodiment. In fig. 8, the openings 15 are arranged longitudinally along the inner part 10 in the axial direction and in operation longitudinal vanes are provided for sweeping the gas along the path defined by the protrusions on the outer part. Each vane may be formed by one longitudinal slot or by a plurality of liquid openings arranged along the length of the inner part. The plurality of vanes may be disposed at different circumferential positions of the inner member.

Fig. 9 shows an alternative embodiment in which the liquid opening is helical and in operation a helical blade is provided. In the illustrated embodiment, the spiral is formed by one spiral groove, while in other embodiments it may be formed by a plurality of openings arranged along a spiral path.

The liquid blades are formed by driving liquid through these openings. This may be accomplished in a variety of ways, such as by using a pressurized liquid source. However, in some embodiments where the liquid opening is on the rotor of the pump, the force for driving the liquid is provided by a drive mechanism for rotating the rotor.

Fig. 10 shows how liquid is driven through the liquid openings to form liquid vanes as the hollow rotor 10 rotates within the liquid reservoir 30. Fig. 10 shows a cross section of a substantially circular hollow shaft 10, the shaft 10 being configured to rotate in a substantially circular stator bore 20. The shaft forms the rotor 10 of the pump and has an outer diameter smaller than the inner diameter of the stator bore 20. The axes of the shaft and stator are vertically oriented and the base of the hollow open-ended shaft is submerged in the liquid reservoir 30.

Fig. 10 shows liquid 32 from liquid reservoir 30 rising along shaft 10 as the rotor rotates. The hollow bore of the shaft 10 has an internal diameter increase 12 below the liquid reservoir level which serves to accelerate the liquid by centrifugal force as the shaft rotates and pump it upwardly within the interior of the shaft and then outwardly from the bore or elongate slot (not shown) in the shaft to form a continuous liquid surface 40 between the shaft or rotor 10 and the stator bore 20. The liquid flows back down the inner wall of the stator bore 20 into the reservoir 30. This is on a continuous circulation basis so that liquid, in some embodiments water, contacting the stator bore 20 travels down the bore under gravity and supplements the reservoir. Note that the arrows depict the direction of flow of the liquid to form a single surface or vane 40.

The liquid within the shaft is forced through the holes/slots and toward the stator bores by centrifugal force to form the plurality of liquid surfaces 40, which form vanes that drive the gas through the pump as the rotor 10 rotates.

While in many of the embodiments described above, the liquid circulation providing the liquid surface is created by rotating the rotor to provide centrifugal force to the liquid, in some embodiments an alternative way of creating the liquid circulation, namely a high pressure liquid source, is used.

Such a high pressure liquid supply or pump may be used alone or in combination with a regulated shaft rotation, enabling independent variability of fluid speed and shaft frequency depending on pumping performance requirements, allowing for controllable efficiency and pump adjustment.

In some embodiments, the pump may be used in a wet scrubbing environment such that the pumping function may be integrated into the wet scrubbing, with liquid vanes being an advantage in such embodiments. In this regard, by aligning one of the liquid vane pumps with the process gas flow, the pump may be used for wet scrubbing in addition to creating a vacuum, for example at the outlet (or inlet) of the abatement system.

In case a device for driving a shaft, such as a motor and a frequency converter or a belt drive, is required, such a driving system may preferably be positioned at the top of the shaft to reduce the risk of liquid leaking into the driving device.

In summary, embodiments function effectively where liquid circulation meeting or exceeding the discharge from the liquid outlet can be achieved. This helps to maintain the blade as a continuous surface. It should be noted that many parameters such as the size of the liquid outlet, the type of liquid used, the liquid velocity, the distance between the elements and the length of the blades and the rotational speed all affect the formation and maintenance of the liquid surface. Therefore, these characteristics should be selected according to the characteristics required for a particular pump, such as power consumption, pumping capacity and compression rate.

Although illustrative embodiments of the invention have been disclosed in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to the precise embodiments, 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.

Reference numerals

10. Rotary element

15. Liquid opening

20. Pump housing element

25. Protrusions

30. Liquid storage device

32. Liquid from a reservoir

40. 40a, 40b liquid blade

50. Gas inlet

52. Gas outlet

60. A gas leakage path.

Claims

1. A pump for pumping gas, the pump comprising:

pump casing elements and further elements;

one of the pump housing element and the further element comprises a projection extending towards the other element, the other element comprising at least one liquid opening;

the projection, the pump housing element and the further element form a path from a gas inlet to a gas outlet; wherein the method comprises the steps of

The further element is mounted concentrically within the bore of the pump casing element, and the pump casing element and the further element are rotatably mounted relative to each other; and

The projection comprises a spiral, the cross-section through the axial plane of the spiral varying such that the spiral is narrower at a point towards the other element and wider at the intersection of the projection with the one of the pump casing element and the other element from which the projection extends;

the at least one liquid opening is configured such that liquid output from the at least one liquid opening forms a liquid vane operable to drive gas along the path from the gas inlet to the gas outlet upon rotation of one of the pump housing element and the further element.

2. The pump of claim 1 wherein the projection is at least twice as wide at a point along 10% of the projection at a point along 95% of the projection at an element from which it extends.

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

4. A pump according to any of claims 1 to 3, wherein the at least one projection extends from the pump casing element and has a cross-section through a radial plane such that the projection does not obscure the pump casing element from water vanes extending tangentially from the further element.

5. A pump according to any of claims 1 to 3, wherein the at least one projection extends from the pump casing element and has a cross-section through a radial plane such that the projection does not obscure the pump casing element from water vanes extending at right angles from the further element.

6. A pump according to any one of claims 1 to 3, wherein the lower surface of the at least one projection is planar.

7. The pump of claim 4 wherein a trailing edge relative to a direction of rotation of the cross-section of the projection in the radial plane is at an acute angle relative to a tangent to a wall of the pump housing element, the acute angle being between a maximum angle of the trailing edge parallel to the tangent of the further element and 85% of the maximum angle.

8. The pump of claim 7, wherein the trailing edge of the protrusion in the radial plane is angled such that the trailing edge is substantially parallel to a tangent of the further element.

9. The pump of claim 7 wherein a leading edge of a direction of rotation of the section in the radial plane relative to the projection is located between a curve curved in the direction of rotation and having a radius of curvature equal to half of a distance between the pump housing element and the further element and a line extending away from the trailing edge and parallel to a tangent of the further element.

10. Pump according to claim 9, wherein the leading edge of the rotation direction of the section plane in the radial plane with respect to the projection comprises a surface substantially perpendicular to a tangent of the further element.

11. The pump of claim 10, wherein a lower surface of the at least one protrusion is flat.

12. A pump according to any one of claims 1 to 3, wherein the axial profile of the projection has a substantially parabolic form.

13. A pump according to any one of claims 1 to 3, wherein the projection has a cross-section through a radial plane, the cross-section comprising a section of a circular cross-section of the pump housing element.

14. A pump according to claim 13, wherein the pump casing element is mounted stationary and the further element is mounted for rotation.

15. A pump according to any one of claims 1 to 3, wherein the at least one liquid opening is formed on a surface of the further element mounted for rotation.

16. A pump according to any one of claims 1 to 3, wherein the cross-section of the path formed by the projection, the pump housing element and the further element decreases from the gas inlet to the gas outlet.

17. A pump according to any of claims 1 to 3, wherein the at least one liquid opening comprises at least one liquid opening extending along at least a portion of the length of one of the pump housing element or the further element.

18. The pump of claim 17, wherein the at least one liquid opening is arranged in a longitudinal direction extending substantially parallel to the axes of the pump casing element and the further element.

19. A pump according to any of claims 1 to 3, wherein the at least one liquid opening is arranged in the form of a spiral extending around a surface of the pump casing element or the further element.

20. A pump according to any one of claims 1 to 3, wherein the angle of the helix varies from the gas inlet towards the gas outlet such that the pitch of the helix decreases towards the gas outlet.

21. A pump according to any one of claims 1 to 3, further comprising a liquid reservoir, the further element being rotatably mounted and comprising a hollow body having an opening at a lower end extending into the liquid reservoir, the further element having an inner diameter that increases from the lower end.

22. A pump according to any one of claims 1 to 3, comprising a plurality of liquid openings.

23. The pump of claim 22, wherein the plurality of liquid openings provide a plurality of liquid flows that form a plurality of liquid vanes between the pump housing element and the further element.

24. The pump of claim 22, wherein at least one set of the plurality of liquid openings are disposed adjacent to one another and the streams output from the at least one set of the plurality of liquid openings form a single liquid vane.

25. A pump according to any one of claims 1 to 3, wherein the pump comprises a vacuum pump.

26. A wet scrubber for reducing contaminants pumped from an emission abatement system, the wet scrubber comprising a pump according to any one of claims 1 to 25.

27. A method of pumping a gas, the method comprising:

outputting liquid from at least one liquid opening on one of the pump casing element or the further element, the other of the pump casing element and the further element comprising a projection, the pump casing element and the further element forming a path from a gas inlet to a gas outlet; wherein the method comprises the steps of

rotating one of the pump housing element or the further element such that liquid output from the at least one liquid opening forms a liquid vane and driving gas along the path from the gas inlet to the gas outlet upon rotation of one of the pump housing element and the further element.