WO2019034876A1

WO2019034876A1 - Momentum transfer pump and wet scrubber

Info

Publication number: WO2019034876A1
Application number: PCT/GB2018/052321
Authority: WO
Inventors: Ian David Stones
Original assignee: Edwards Limited
Priority date: 2017-08-17
Filing date: 2018-08-16
Publication date: 2019-02-21
Also published as: GB201713185D0; GB2565577A; GB2565577B

Abstract

A pump for pumping a gas from a gas inlet towards a gas outlet is disclosed. The pump comprises: a pumping chamber comprising an inner component mounted within and being surrounded by a stator bore; at least one of the inner component and the stator bore comprising in a side wall between the gas inlet and the gas outlet a plurality of liquid outlets, the plurality of liquid outlets being configured such that a stream of liquid output from each of the plurality of liquid outlets is directed towards the gas outlet such that gas molecules within the pumping chamber are driven by the streams of liquid towards the gas outlet. At least some of the plurality of liquid outlets are located at different circumferential positions around a circumference of the stator bore or the inner component; and at least some of the plurality of liquid outlets are located at different axial positions along a length of the pumping chamber.

Description

MOMENTUM TRANSFER PUMP AND WET SCRUBBER

FIELD OF THE INVENTION

The field of the invention relates to pumps.

BACKGROUND

Different types of pumps for pumping gases are known. These include entrapment type pumps, where a gas is captured on a surface inside the pump prior to being removed; kinetic or momentum transfer pumps such as

turbomolecular pumps where the molecules of the gas are accelerated from the inlet side towards the outlet or exhaust side, and positive displacement pumps, where gas is trapped and moved from the inlet towards the outlet of the pump.

Many types of pumps have moving parts with small clearances which require high manufacturing tolerances and are subject to wear.

One type of momentum transfer pump that does not have moving parts is an ejector pump. This type of pump relies on a jet of water that is squirted from an outlet into a venturi. The water flow imparts momentum to gas molecules and generates a flow of gas through the venturi. Such pumps are cheap to

manufacture and are robust. However, they are relatively inefficient, require a lot of water and do not generate a high pressure differential.

An alternative type of momentum transfer pump that also does not have moving parts is a diffusion pump. Here a hollow post with downward slanting outlets is placed in a heated oil bath. The heated oil bath causes the oil to boil and produce oil vapour which rises up the shaft and out of the downward slanting outlets. The vapour then travels in a downward direction towards the stator bore wall where it condenses and flows into the oil bath. Gas molecules are entrained in the vapour and travel down the pumping chamber to a gas outlet.

Disadvantages of this pump are that it consumes a lot of power and only operates effectively at low pressures, requiring an additional pump when creating a vacuum from atmospheric pressure.

It would be desirable to provide an alternative pump that is resistant to wear and relatively inexpensive to manufacture and operate.

SUMMARY

A first aspect of the present invention provides a pump for pumping a gas from a gas inlet towards a gas outlet; said pump comprising: a pumping chamber comprising an inner component mounted within and being surrounded by a stator bore; at least one of said inner component and said stator bore comprising in a side wall between said gas inlet and said gas outlet a plurality of liquid outlets, said plurality of liquid outlets being configured such that a stream of liquid output from each of said plurality of liquid outlets is directed towards said gas outlet such that gas molecules within said pumping chamber are driven by said streams of liquid towards said gas outlet; wherein at least some of said plurality of liquid outlets are located at different circumferential positions around a circumference of said stator bore or said inner component; and at least some of said plurality of liquid outlets are located at different axial positions along a length of said pumping chamber.

The present invention provides a momentum transfer pump that uses streams of liquid output from outlets at different circumferential positions along an axis of a pumping chamber to drive the gas through the pump. The outlets are arranged such that the streams of liquid that are output have a directional component towards the gas outlet such that where they collide with gas molecules they transfer momentum to the gas molecules in the direction of the outlet. By providing the liquid outlets at different axial and circumferential positions an efficient means of impacting a large number of gas molecules and diverting them towards the gas outlet is provided. A simple yet effective way of driving gas molecules from a gas inlet towards a gas outlet is provided that is relatively inexpensive, may not have moving parts and yet provides effective pumping. Furthermore, as the driving force is supplied by liquid streams rather than solid surfaces, the need for high manufacturing tolerances with the associated high costs are mitigated.

In some embodiments, at least some of said plurality of liquid outlets at said plurality of different axial positions are offset with respect to each other such that at least adjacent liquid outlets in an axial direction are located at different circumferential positions.

It may be advantageous if liquid outlets that are adjacent in the axial direction are offset with respect to each other. This reduces the possibility of gas molecules being driven towards the gas outlet by one stream of liquid and then being impeded by impact with a stream from a liquid outlet located closer to the gas outlet. In some embodiments all liquid outlets are offset with respect to each other axially, while in others it may be only immediate neighbours that are offset. The way the outlets are arranged will depend on the length of the pumping chamber and the pressure differentials required. It may be advantageous if all outlets are offset circumferentially with respect to each other or it may be that it is better if the offset pattern repeats such that after say 5 outlets the outlets are aligned again and the pattern repeated.

In some embodiments, said plurality of liquid outlets are arranged such that streams of liquid output from said plurality of liquid outlets obstruct a direct straight path from said gas inlet to said gas outlet. It may be advantageous if the offset of the liquid outlets is arranged so that there is no direct line of sight from the gas inlet to the gas outlet. This helps prevent or at least impede backflow of gas from the outlet to the inlet and helps improve the efficiency of the pump. In some embodiments the offset is provided by the plurality of liquid outlets being arranged in the form of a helix on at least one of said inner component's outer surface and said stator bore's inner surface. A helix provides liquid outlets that are offset axially with respect to each other and cover the whole circumference of the pumping chamber several times along the axial length.

In some embodiments, said plurality of liquid outlets are angled towards said gas outlet.

The directional requirement of the liquid stream towards the gas outlet may be provided liquid outlets that are angled in this direction.

Although the pumping chamber may have a number of forms, in some

embodiments the pumping chamber has an annular cross section. An annular cross section has the advantages of no corners for particle deposition and eddies to form. It also provides two surfaces on which liquid outlets can be arranged.

In some embodiments, a cross section of said pumping chamber reduces in size downstream of at least one of said plurality of liquid outlets.

It may be advantageous if the pumping chamber reduces in size downstream of at least one of the plurality of liquid outlets. Reducing the size of the pumping chamber towards the gas outlet provides built-in volumetric compression of the gas as it is pumped. This reduction in size may be provided by tapering one or both of the inner component and stator bore. In some embodiments, the reduction in pumping chamber size may be formed by at least a portion of said stator bore having a tapered diameter, such that said diameter is larger upstream of at least one of said plurality of liquid outlets than said diameter is downstream of said at least one of said plurality of liquid outlets. In other embodiments, changes in diameter of at least one of said stator bore and said inner component provides a cross section of said pumping chamber that decreases and then increases towards said gas outlet providing a venturi effect to said gas flow.

Passing the gas through a venturi-shaped pumping chamber provides

acceleration of the gas and then a reduction in pressure, which latter may help entrain the gas within the flow of liquid and pull it towards the gas outlet.

In some embodiments, at least some of said plurality of liquid outlets are located on said inner component.

The liquid outlets may be located on the inner component or they may be located on the outer component or they may be mounted on both the inner and the outer component. In some embodiments, the inner component is rotatably mounted within the stator bore and in such an embodiment at least some the liquid outlets are located on the inner component such that as it rotates the circumferential position of the outlets move and the streams of liquid output sweep in an arc around the cross section of the pumping chamber.

In some embodiments, the pump comprises a motor for rotation of the inner component.

In some embodiments, the inner component has a cylindrical tubular form.

In some embodiments, said streams of liquid are operable to drive said gas through said pump on rotation of said inner component within said stator bore.

In some embodiments, the pump comprises a liquid reservoir in which the inner component is partially immersed. In such embodiments rotation of the rotor may cause the liquid to be output through the outlets by a centrifugal force to form the streams of liquids for driving the gas through the pump. In some embodiments, said inner component has an opening at a lower end extending into said liquid reservoir, an internal diameter of said inner component increasing from said lower end.

By providing the inner component with a decreasing internal diameter and standing it in the liquid reservoir then on rotation centrifugal forces drive the liquid up the internal surface of the inner component and out through the liquid outlets to form the streams of liquid.

In other embodiments, the pump comprises a liquid inlet for connection to a pressurised liquid source and it is the pressurised liquid source that provides the force for pushing the liquid out through the outlets to form the streams of liquids that pump the gas.

In some embodiments, the stator bore is rotatable, this may be as an alternative to the inner component rotating or it may be that they both rotate in opposite directions. In some embodiments the pump comprises a vacuum pump.

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

Abatement systems are often used in conjunction with wet scrubbers which provide a stream of liquid to remove particulates from the gases that are pumped from the abatement system. A pump that uses a liquid stream to move the gas may be used either in conjunction with an additional liquid scrubbing source or on its own. Using liquid to provide the pumping force for the gas has the advantage in a wet scrubbing environment of the liquid providing both the pumping and some particulate removal. Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.

Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 illustrates the inner component of a pump according to an embodiment; Figure 2A and 2B show further illustrations of outlets on the inner component of a pump according to an embodiment; and

Figure 3 schematically shows a pump according to an embodiment.

DESCRIPTION OF THE EMBODIMENTS

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

A momentum transfer type pump is disclosed which uses streams of liquid output through multiple liquid outlets and directed towards a gas outlet to drive a gas from a gas inlet to gas outlet. The pumping chamber has an annular type cross section with an inner and outer component, the liquid outlets being formed on either one or both of the inner and outer components and the gas inlet and outlet being towards opposing ends of the pumping chamber. In some embodiments, the inner and/or outer components rotate such that the streams of liquid sweep around the pumping chamber. The inner and outer components may be mounted coaxially with respect to each other. Figure 1 shows the inner component in the form of hollow shaft 10 of a pump according to an embodiment. This inner component 10 is surrounded by an outer component or stator bore (not shown) such that an annular shaped pumping chamber is defined between the two components. In this embodiment, liquid outlets 15 are formed at an angle a with respect to the axis of the shaft 10 such that a liquid stream output through the liquid outlet 15 has a downward directional component towards the gas outlet at the lower end of the Figure. Liquid output through each of the outlets forms a stream of liquid 40 downwards towards the gas outlet and outwards towards the stator wall. On impacting the stator wall the liquid flows down the wall to be collected at the base of the stator bore.

As can be seen the outlets are offset from each other, such that neighbouring outlets in an axial direction have an offset compared to those in an adjacent row. In some embodiments, liquid outlets are offset with respect to all other outlets such that no two outlets are at the same circumferential position. In other embodiments, the pattern of outlets may be offset for one or more rows and then the pattern may repeat, such that every four rows for example the outlets will be aligned. The circumferential offset arrangement eliminates the line of sight between the outlet and inlet.

Figure 2A shows a further example of the arrangement of the liquid outlets where the axial offset is provided by the outlets being arranged in a helical formation. In this arrangement liquid streams from the different outlets provide streams that cover the cross section of the pumping chamber the streams being repeated at different axial positions. Although not shown these outlets will be angled as in Figure 1 , such that liquid is output both outwards and downwards.

Figure 2B shows a further diagram schematically illustrating the slope of the liquid outlets that provides the direction of the liquid streams 40 towards the gas outlet. In this embodiment as in Figure 1 the outlets are arranged in rows around a circumference of the inner component of the pump. Each row is at a different axial position and although not shown in this figure each outlet is offset with respect to outlets in neighbouring rows. In this embodiment the inner component 10 is within a tapered stator bore 20. The tapering of the stator bore provides smooth volumetric compression of the gas as it is driven from the gas inlet at the upper end towards the gas outlet at the lower end of the figure. In other embodiments the taper of the bore may be such that it reduces the area of cross section and then increases it such that a venturi is formed, the gas being accelerated as it enters the narrowing portion of the venturi. There is then a reduction in pressure in the gas flow as it enters the wider portion of the venturi helping to sweep the gas molecules towards the gas outlet.

Figure 3 shows a further example of a pump where an inner component or rotor 10 is rotationally mounted in a fluid reservoir. The rotor 10, may be a rotor as shown in any of Figures 1 , 2A or 2B. As the rotor 10 rotates liquid from liquid reservoir 30 rises up the shaft of rotor 10. The hollow bore of the rotor 10 has an internal increase in diameter 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 the liquid outlets 15 in the shaft to form several liquid streams 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 drains back to the reservoir to replenish It. Note that the arrows depict the direction of flow of the liquid. The rotation of the shaft accelerates the liquid to create a pumping action, liquid inside the shaft is forced through the holes 15 under centrifugal force and travels towards the stator bore 20 to form a plurality of liquid streams 40, that drive the gas through the pump as the rotor 10 rotates. 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.

REFERENCE SIGNS 10 Rotor

15 liquid outlet 20 stator bore 30 liquid reservoir 40 liquid stream

Claims

1 . A pump for pumping a gas from a gas inlet towards a gas outlet; said

pump comprising:

a pumping chamber comprising an inner component mounted within and being surrounded by a stator bore;

at least one of said inner component and said stator bore comprising in a side wall between said gas inlet and said gas outlet a plurality of liquid outlets, said plurality of liquid outlets being configured such that a stream of liquid output from each of said plurality of liquid outlets is directed towards said gas outlet such that gas molecules within said pumping chamber are driven by said streams of liquid towards said gas outlet; wherein

at least some of said plurality of liquid outlets are located at different circumferential positions around a circumference of said stator bore or said inner component; and

at least some of said plurality of liquid outlets are located at different axial positions along a length of said pumping chamber.

2. A pump according to claim 1 , wherein at least some of said plurality of liquid outlets at said plurality of different axial positions are offset with respect to each other such that at least adjacent liquid outlets in an axial direction are located at different circumferential positions.

3. A pump according to claim 2, wherein said plurality of liquid outlets are arranged such that streams of liquid output from said plurality of liquid outlets obstruct a direct straight path from said gas inlet to said gas outlet.

4. A pump according to claim 2 or 3, wherein said plurality of liquid outlets are arranged in the form of a helix on at least one of said inner

component's outer surface and said stator bore's inner surface.

5. A pump according to any preceding claim, wherein said plurality of liquid outlets are angled towards said gas outlet.

6. A pump according to any preceding claim, wherein said pumping chamber has an annular cross section.

7. A pump according to any preceding claim, wherein a cross section of said pumping chamber reduces in size downstream of at least one of said plurality of liquid outlets.

8. A pump according to claim 7, wherein at least portion of said stator bore has a tapered diameter, such that said diameter decreases from said gas inlet to said gas outlet. 9. A pump according to claim 7, wherein changes in diameter of at least one of said stator bore and said inner component provides a cross section of said pumping chamber that decreases and then increases towards said gas outlet providing a venturi effect to said gas flow. 10. A pump according to any preceding claim, wherein at least some of said plurality of liquid outlets are located on said stator bore.

1 1 . A pump according to any preceding claim, wherein at least some of said plurality of liquid outlets are located on said inner component.

A pump according to claim 1 1 , wherein said inner component is rotatably mounted within said stator bore.

13. A pump according to claim 12, said pump further comprising a motor for rotating said inner component.

14. A pump according to any preceding claim, wherein said inner component has a cylindrical tubular form.

15. A pump according to claim 14 when dependent on claim 13, wherein said streams of liquid are operable to drive said gas through said pump on rotation of said inner component within said stator bore.

16. A pump according to claim 15, said pump further comprising a liquid

reservoir in which said inner component is partially immersed.

17. A pump according to claim 16, wherein said inner component has an

opening at a lower end extending into said liquid reservoir, an internal diameter of said inner component increasing from said lower end. 18. A pump according to any one of claims 1 to 15, said pump comprising a liquid inlet for connection to a pressurised liquid source.

19. A pump according to any preceding claim wherein said pump is a vacuum pump.

20. A wet scrubber for reducing pollutants pumped from an abatement system, said wet scrubber comprising a pump according to any preceding claim.