GB2179099A - Vacuum aerator feed nozzle - Google Patents

Abstract

A feed nozzle for bulk solids handling apparatus comprising a tube 1 having an inlet suction end 3 and an outlet end 5 and a sleeve 31 surrounding it. At the inlet end there is an end cap 40 which directs pressurised fluid, e.g. compressed air, introduced at high pressure into the annular area between the tube and sleeve, through an annular orifice 47 into the inlet end of the tube. The orifice directs the air along the tube towards the outlet end so as to create a suction at the inlet end, for sucking up material. There is a convergent/divergent restrictor 49 fitted inside the tube downstream of the annular orifice so that the pressurised fluid, after passing through a throat of the restrictor, expands into the outlet of the tube. The sleeve 31 is adjustable so as to vary the size of the orifice 47. The end cap 40 and the restrictor 49 are replaceable. <IMAGE>

Description

SPECIFICATION Vacuum aerator feed nozzle This invention relates to bulk solids handling apparatus for picking up any form of powder or granular material (or even liquid material) from fine powders below 20 microns to granular products up to about 5mm particle size, including fibrous products and bulk solids varying in bulk density from about 30kg/m3 to 3000kg/m3. More especially, the invention relates to a vacuum aerator feed nozzle for picking up the material, and then conveying it along a pneumatic feed line.

Many industries have a requirement for powdered or granular material, such as fly ash, cement, sugar or grain, or sludge, such as sewage, or very lightweight material, such as perlite to be removed from one location and then transferred to a further location.

More often than not, the only practical way to remove the material from the first location is to suck it out using a vacuum or suction hose, but there are limits to how far the material can be moved using this method, firstly because the maximum negative pressure that can be obtained is very limited, and secondly because this negative pressure soon becomes lost, at pipe joints, valves and the like. Accordingly, the material has to be double handled, and after being sucked out from the first location, it is normally stockpiled, or deposited in an intermediate hopper or buffer storage, and then conveyed by another conveyor system to the further location. This therefore only provides a discontinuous or batch material handling system.Also, the vacuum distance is usually relatively long and, with the limited pressure drop available in a vacuum system, the quantity of product conveyed is also limited in these types of application.

In normal pneumatic conveying systems which combine vacuum and positive pressure conveying lines, the necessary cyclical sequencing can only be achieved by the opening and closing of valves. In these combined systems, valve reliability is a real problem due to the nature of the material being handled penetrating valve parts, and eroding valve seats.

Also of course, the continuous substantial fluctuations from negative to positive pressure, over considerable ranges, soon causes valves to wear out.

Ejectors have been known for a great many years and successfully handle large quantities of air. They can also be used for other similar applications. With air or gas as the motive fluid, ejectors only perform well when they pump a gas against a very low differential pressure, for example, air movers discharging to atmosphere. An efficient type of air-mover uses the Coanda principle in which a high velocity layer of air adheres to a special inlet profile and as a result turns through 90". This high velocity layer causes a pressure drop in a throat region of the ejector which induces a flow of ambient air into the device at an inlet.

The successful operation of ejectors based upon this principle is dependent upon the accurate profile or "Coanda Surface" being maintained. Thus it is imperative that this profile is not damaged. Even a thin oxide film can destroy the profile and hence the ejector's performance. It is clear that if an attempt was made to use the ejector for moving solids in particle form, the abrasiveness of many solids material would quickly ruin the Coanda profile (by the rapid wear caused by high velocity solid particles impinging on the surface).

We have now devised a bulk solids handling apparatus and more specifically a vacuum aer- ator feed nozzle which overcomes the above mentioned disadvantages. A particular feature of the nozzle is that with the application of compressed air to the nozzle, it can pick up product by using vacuum over a very short distance, typically 50mm, and then can convey this product under positive pressure to the desired location. This process of collection and delivery is achieved on a continuous basis. Furthermore, the nozzle has no valves or other moving parts to be damaged by high velocity solid particles or suction.

According to the present invention, we provide a vacuum aerator feed nozzle comprising a tube having a suction inlet end and an opposite outlet end, a sleeve surrounding the inlet end and sealingly engaged with the tube at a location spaced from the inlet end of the tube and having at or adjacent the inlet end an annular end cap which directs pressurised fluid introduced at high pressure into the annular area between the tube and sleeve through an annular orifice into the inlet end of the tube which is internally fitted with a convergent/divergent restrictor so that the pressurised fluid, after passing through a throat of the restrictor, will expand into the outlet end of the tube, thus creating a suction to draw material, in which the inlet end of the tube is located through the end cap and inlet end of the tube for subsequent ejection at the outlet end.

If desired, the annular sleeve may have small apertures therein to provide material fluidising jets so that when the sleeve fitted to the inlet end of the tube is inserted into a material to be conveyed, the material is aerated and fluidised.

Preferably, the restrictor is removably located within the inlet end of the tube. Preferably, the restrictor has on its outer cylindrical surface a step for locating with the end face of the tube. Preferably, the convergent internal face of the restrictor defines part of the annular orifice.

Preferably, the end cap is removably located within one end of the sleeve and has an external wall with a step on its outer face for location against an end face of the sleeve, the outer wall being connected to an inner wall defining one wall of the annular orifice, the inner face of this inner wall defining an inlet opening to the nozzle.

At its end remote from the end cap, the sleeve is preferably fitted with an end fitting, there being an inlet aperture in the end fitting which is preferably tapped to receive a pressure fitting for a fluid inlet line, the end fitting terminating in an inwardly directed annular flange having an annular seal associated therewith for sealing engagement with the outer wall of the tube.

Preferably, the sleeve together with its end fitting and end cap are slidably supported on the tube for longitudinal movement relative thereto so as to adjust the size of the annular orifice, the end of the sleeve adjacent the end cap being supported by a plurality of pegs projecting radially outwards from the tube.

Preferably, the pegs are also used to lock the restrictor in position within the tube. Preferably, the sleeve is supported at its other end by the end fitting and seal associated therewith and the longitudinal position of the sleeve with its end cap and end fitting is adjusted by means of one or more bolts or the like extending between the end fitting and a flange secured to the tube at a location spaced from its inlet end.

A vacuum aerated feed nozzle in accordance with the invention is now described by way of example with reference to the accompanying drawing which is a longitudinal section through the nozzle.

Referring to the drawing, the nozzle comprises a tube 1 having a suction inlet end 3 and an opposite outlet end 5. A sleeve 31 surrounds the inlet end 3 of the tube 1 and is held in concentric spaced relationship with the tube 1 by a plurality, e.g. three, pegs 7 equally spaced around the periphery of the tube 1 at one end, and by an end fitting 9 at the other end. The end fitting is detachably secured to the sleeve 31 by screws 11 and at its end has an internal flange 13, the inner face of which is slidably supported on the outer wall of the tube 1. A pressure seal 39 is located in a suitable groove in this face. At its opposite end the sleeve 31 is fitted with a removable end cap 40. The end cap is of annular configuration with the annulus having a generally U-shaped cross-section so as to define an outer wall 41 and an inner wall 42 connected together by an annular end wall 59.

The outer wall 41 is stepped at 44 so that a portion of reduced diameter fits snugly within the inlet end of the sleeve 31 and is locked in position by means of a plurality of screws 46.

At its inlet end 3, the tube 1 is provided with a restrictor 49 forming a snug fit within the tube 1, the outer wall of the restrictor 49 being stepped as shown at 48 to enable the restrictor to be positively located on the end face of the tube 1. The restrictor is of course therefore removable and is held in position within the tube 1 by threaded end portions 15 of the studs 7 passing through apertures in the tube 1 and engaging in threaded apertures in the thickest part of the restrictor 49 which part has a generally cylindrical internal wall 53.

The cylindrical wall 53 merges at one end with a gradually diverging wall portion 55 leading towards the outlet end 5 of the tube 1 and at its other end with a steeply converging wall portion 51.

The outer face of the inner wall 42 of the end cap 40 is of frusto-conical configuration having the same cone angle as the converging wall portion 51 of the restrictor 49 and these two conical walls define an annular orifice 47 for fluid, e.g. air introduced under pressure into the annular space 19 between the tube 1 and sleeve 31. The pressurised fluid is introduced through a high pressure line into the space 17 through an inlet aperture 43 which is threaded to receive an end fitting on the air line. This pressurised fluid will then move in the direction of the arrows 19 towards the inlet end 3 of the tube 1 where it will change direction as indicated by the arrows 45 after hitting the curved internal surface of the end wall 59.The high pressure fluid is therefore ejected through the annular orifice 47 into the reduced diameter throat or cylindrical wall portion 53 of the restrictor 49 and then expands as it passes through the diverging portion 55 in the direction of the arrow 21.

The sleeve 31 is adjustably located on the tube 1 and can be moved longitudinally of the sleeve so as to adjust the dimensions of the orifice 47 by means of any suitable adjustment mechanism. As shown, this comprises a plurality of threaded studs 33 secured to the flange 13 and passing through a threaded aperture in a fixed flange 35 on the tube 1. It will thus be appreciated that by rotating the studs 33 a small adjustment of the longitudinal position of the sleeve 31 and hence of the location of the wall 42 can be achieved. The sleeve 31 can then be locked in position by means of a lock nuts 37.

The effect of fluid at high pressure, e.g.

compressed air, being ejected through the narrow orifice 47 is to create a suction at the inlet 57 of the end cap 40 so that when the end cap 40 together with the inlet end of the sleeve 31 and the inlet end 3 of the tube 1 are inserted into a mass of powdered or granular material or the like, the material will be sucked into the pipe 1 and then conveyed under pressure through the outlet end of the pipe 1 which would normally be connected to a conveying line.

Certain bulk solids have characteristics such as cohesiveness which restrict or even prevent air from passing through the mass of material which of course means that when the nozzle is inserted into the mass of material it will not flow into the inlet 57. Accordingly, for certain bulk solids to be conveyed, it is necessary to fit a sleeve 31 which has a series of small apertures, for example of about 1mm diameter, formed in the wall of the sleeve.

These apertures (not shown) would be located around the periphery of the sleeve in different horizontal planes, their precise location depending upon the material to be conveyed.

Accordingly, when the nozzle is inserted into the mass of bulk solids to be conveyed a proportion of the high pressure air in the annular space 17 is directed through the apertures into the bulk solid material so as to aerate or fluidise the material in the immediate vicinity of the inlet 57 of the nozzle thus reducing the resistance of the material to the flow of surrounding air through the material and into the nozzle. The fluidising air also encourages the bulk material to flow more freely towards the inlet 57 and the aerating air also contributes to the total volume at the inlet 57 so as to provide the necessary pick-up velocity.

The vacuum aerated feed nozzle can provide an essential part of a bulk solids handling apparatus the other essential parts of which would be a compressor for supplying fluid under pressure, e.g. compressed air, to the annular space 17 and a pipeline for delivering the material to be conveyed from the outlet end 5 of the nozzle to a required location.

Accordingly, the apparatus may be portable.

For example, the nozzle and pipeline together with a compressor and drive unit could be mounted on a trailer or lorry or it may be a free-standing unit. However, the nozzle has been specifically designed for hand-held operation to give flexibility of use in extracting bulk solids from inaccessible areas and for conveying the solids to remote locations.

The nozzle has been designed to avoid potential wear at the most critical location which is at the annular orifice 47. However, it will be noticed that both the end cap 40 and the convergent/divergent restrictor 49 are both replaceable units. The material of these units can be chosen to match the particular application, for example stainless steel might be used for picking up and conveying food products, but for products such as sand or coal dust a nickel-hard steel or ceramic coated steel might be used.

The suction which is created at the inlet 57 by the expansion of the high pressure fluid just downstream of the inlet 57 must obviously be sufficient to start material flowing through the nozzle. Accordingly, the volume of the air which is induced to flow through the inlet 57 must be sufficient to give a pick-up velocity of somewhere between about 20 and 60m/sec. In order to achieve this flow rate the dimensions of the annular space 17, the width of the orifice 47 and the angle it forms with the longitudinal axis of the tube 1 are critical.

Accordingly, the volume of the space 17 is chosen to enable the quantity of fluid, e.g. air supplied by the compressor through the inlet aperture 43 to flow towards the annular orifice 47 without excessive energy losses; thus, the intention is to control the velocity of air flow in the direction of arrows 19. However, the width of this space 17 influences the overall size of the nozzle and should be kept to a minimum, consistent with the minimal energy loss aspect. Preferably, the width of the annular space 17 should be in the range of 10 to 20mm depending upon the overall size of the nozzle.

Also improtant is the shape of the interior of the annular end cap 40 and the angle of the internal wall defining the inlet 57, as well as the angles made with the longitudinal axis of the tube 1 by the converging and diverging surfaces of the restrictor 49. It is also important to have the correct throat diameter, i.e.

the diameter of the cylindrical portion 53 in relation to the diameter of the inlet 57 and the air flow rate through the orifice 47 relative to the pressure of air in the space 17 are also critical and will of course depend upon the nature of the bulk solids to be conveyed.

Accordingly, the diameter of the orifice 47, the angle which it forms with the longitudinal axis of the tube 1 and the diameter of the cylindrical portion 53 of the restrictor 49 should be such that for a particular bulk solid and compressed air supply these inter-relating parts of the nozzle create an induced air flow at the inlet 57 which generates a pick-up velocity sufficient to entrain and convey the solid particles. In order to minimise the energy losses in this region, the air flowing through the gap at orifice 47 must be less than about 340 m/s and the direction of this air flow should avoid excessive separation of the air from the solid annular surface of the restrictor 49. Thus, preferably the angle which the face of the orifice 47 makes with the longitudinal axis of the tube 1 should be less than 20 .

Additionally, the ratio of the diameter of the orifice 47 to the diameter of the cylindrical portion 53 preferably should be greater than 1 and less than 1.5.

Furthermore, to avoid separation of the air at the boundary of the restrictor 49 with the divergent wall portion 55, the angle of the face of 55 with the longitudinal axis of the tube 1 preferably should be less than 8 .

Another critical dimension is the axial distance between the end wall 59 of the end cap 40 and the outlet end of the orifice 47. It has been found, for example, that unless the geometry of the restrictor 49 is correct it is impossible to avoid extensive pressure loss immediately downstream of the restrictor towards the outlet end of the tube 1 due to shock and similar occurrences. In this respect, immediately downstream of the throat area or cylindrical wall area 53 of the restrictor, the solid particles being conveyed should have achieved a velocity of at least 15-20 m/sec.

and it is then necessary to convert most of the velocity head of the air to pressure so as both to minimise energy losses and to provide a positive pressure which is required to overcome the resistance to flow through a pipeline immediately downstream of the outlet end 5 of the tube 1. Even the diameter of the pipeline can be critical for successful operation of the apparatus.

For efficient performance of the invention, the axial spacing between the two annular walls defining the orifice 47 should preferably vary from about lmm up to about 8mm. The actual distance for a particular nozzle unit will depend upon the volume of compressed air supplied, the nature of the bulk solid to be conveyed and the overall size of the unit. It has been found that the annular gap in the orifice 47, i.e. the shortest distance between the walls defining the gap, can be adjusted from say about 2mm to 1.4mm to give the same momentum flux at the throat portion 53 for different air supply rates ranging from say about 6 to about 4cu/m per minute. In this respect it is vital to ensure that an equivalent volume of air is induced into the throat to create sufficient air velocity so as to create a suction in the inlet 57 to pick up the product.

For example, if the rate of air supply is less than expected then the flow rate through the orifice will be less. It may be possible to increase this flow rate by decreasing the width of the orifice but alternatively it may be possible to achieve adequate performance by changing the restrictor 49 and providing one with a different geometry and by changing the diameter of the pipeline connected to the outlet end 5 of the tube 1.

Due to it being largely independent of the characteristics of the bulk solid, and due to the simplicity of its application, there is an extensive range of bulk solids handling operations for which the nozzle of the present invention is suitable. Some examples of applications include the transport of perlite (a product having a very low bulk density) stored in a containter at ground level, through a vertical height of about 40 metres into a silo at a rate of over 2 tonnes per hour; the transfer of asbestos waste (a material containing ingredients such as various types of asbestos, hardfacing cements, glass fibres, cladding materials, bitumatics, shredded bonding wire, etc.) from a sealed skip (due to environmental hazards) through a largely vertical distance, less than about 10 metres, at rates of about 1 tonne per hour into a processing furnace; the conveying of gypsum plaster from a ground level bag-splitting machine (a very dusty area) through about 10 metres vertically and then about 10 metres horizontally into product mixing equipment at rates of around 4 or 5 tonnes per hour; final clean-up operations after bulk ship unloading; transfer of ingredients from open drums into process machinery; and similar applications.

It will of course be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope and spirit of the invention.

Claims (15)

1. A feed nozzle for bulk solids handling apparatus comprising a tube having a suction inlet end and an opposite outlet end, a sleeve surrounding the inlet end and sealingly engaged with he tube at a loction spaced from the inlet end of the tube and having at or adjacent the inlet end an annular end cap which directs pressurised fluids, introduced at high pressure into the annular area between the tube and sleeve, through an annular orifice into the inlet end of the tube, thus creating a section to draw material, in which the inlet end of the tube is located, through the end cap and inlet end of the tube, the tube being internally fitted with a convergent/divergent restrictor so that the pressurised fluid, after passing through a throat of the restrictor, will expand into the outlet end of the tube, for subsequent ejection at the outlet end.

2. A nozzle according to claim 1 wherein the annular sleeve has small apertures therein to provide material fluidising jets so that when the sleeve fitted to the inlet end of the tube is inserted into a material to be conveyed, the material is aerated and fluidised.

3. A nozzle according to either of claims 1 and 2 wherein the annular orifice has face on the side thereof adjacent the inlet end of the tube, angled with respect to the longitudinal axis of the tube, for directing air ino the tube towards the oulet end, the angle between the face and the said longitudinal axis being less than 20 .

4. A nozzle according to any one of claims 1, 2 and 3 wherein the restrictor is removably located within the inlet end of the tube.

5. A nozzle according to any one of claims 1 to 3 wherein the restrictor has on its outer cylindrical surface a step for locating with the end face of the tube.

6. A nozzle according to any one of claim 1 to 4 wherein the convergent internal face of the restrictor defines part of the annular orifice.

7. A nozzle according to any one of claims 1 to 5 wherein the end cap is removably located within one end of the sleeve and has an external wall with a step on its outer face for location against an end face of the sleeve, the outer wall being connected to an inner wall defining one wall of the annular orifice, the inner face of this inner wall definig an inlet opening to the nozzle.

8. A nozzle according to any one of claims 1 to 7 wherein the sleeve is fitted with an end fitting at its end remote from the end cap, there being an inlet aperture in the end fitting which is preferably tapped to receive a pressure fitting for a fluid inlet line, the end fitting terminating in an inwardly directed annular flange having an annular seal associated therewith for sealing engagement with the outer wall of the tube.

9. A nozzle according to claim 8 wherein the sleeve together with its end fitting and end cap are slidably supported on the tube for longitudinal movement relative thereto so as to adjust the size of the annular orifice, the end of the sleeve adjacent the end cap being supported by a pluraity of pegs projecting radially outwards from the tube.

10. A nozzle according to claim 9 wherein the axial spacing between the two annular wals defining the orifice is variable from about 1mm to about 8mm.

11. A nozzle according to claims 9 or 10 wherein the pegs are also used to lock the restrictor in position within the tube.

12. A nozzle according to any one of claims 9, 10 and 11 wherein the sleeve is supported at its other end by the end fitting and seal associated therewith and the longitudinal position of the sleeve with its end cap and end fitting is adjusted by means of one or more bolts or the like extending between the end fitting and a flange secured to the tube at a locatin spaced from its inlet end.

13. A nozzle according to any one of the previous claims wherein the angle between the divergent wall surface of the restrictor and the longitudinal axis for the tube immediately downstream of the throat is 8" or less.

14. A nozzle according to any one of the previous claims wherein the annular separation of the tube and the sleeve is between lOmm and 20mm.

15. A feed nozzle for bulk solids handling substantially as hereinbefore described and as shown in the accompanying drawing.