GB2031748A

GB2031748A - Continuous mixing

Info

Publication number: GB2031748A
Application number: GB7932241A
Authority: GB
Original assignee: BRITISH RES AGRICULT ENG
Current assignee: BRITISH RES AGRICULT ENG
Priority date: 1978-10-09
Filing date: 1979-09-18
Publication date: 1980-04-30
Also published as: GB2031748B; FR2438497B1; FR2438497A1; DK419079A

Abstract

ln the continuous mixing of materials such as particulate solids and a liquid, a mixer 10 is provided in the form of an open-topped chamber 12 having an inlet 26 for the solids, a tangential inlet 19 for the liquid and a circular discharge outlet 30 for the resulting mixed materials. The mixing is effected by a vortex created in the material by the tangential introduction of the liquid component through inlet 19. A further inlet may be provided for recycling the mixture to the chamber 12. The chamber may have alternative configurations such as cylindrical, conical or combinations thereof. Means may also be provided to control the flows of material to obtain desired mixture concentrations. <IMAGE>

Description

SPECIFICATION Improvements in and relating to mixers The present invention relates to mixers.

Liquid feeds for livestock are normally prepared by mixing a dry meal with a liquid, the latter usually being water but quite frequently whey, skim milk or some other nutritious liquid having similar flow properties to water.

The main constituent of pig meal is usually a ground cereal or cereals (usually barley under U.K. conditions) to which are added other ground cereals, miller's offals, minerals, vitamins, etc. in proportions that ensure a balanced diet for the type of livestock concerned.

The particle sizes of such meals usually fall within the range 250 ym to 1000 ym.

Where water is one of the main constituents of a liquid feed for pigs, it is usual to adjust the ratio of water to meal so that the dietary requirements of the animal are met, no other source of water being provided. The optimum ratio of water to meal required varies with age, young pigs requiring a food with a water/meal ratio of about 2:1, whereas more mature animals normally require feeds with ratios between 2.5:1 and 3.5:1.

The mechanical mixers currently in use on farms can be divided into two types, namely large batch mixers, and small semi-continuous mixers.

The large batch mixers are similar to those in use in a wide range of industries, and have a minimum capacity of about one cubic metre, but in practice are more usually of about 5 cubic metres capacity or more, so that a single batch of meal sufficient to feed all the pigs can be prepared before each feeding period. Thus they are large and expensive components, and, as with most batch operations, automation of the filling and mixing cycles requires a more complicated control and monitoring system than is the case with continuous or semi-continuous systems.

The small semi-continuous mixers are mechanically similar to certain types of large batch mixer but have a capacity of about 200 litres or less. These run continuously during the feeding operation, being automatically topped-up to a pre-set level whenever liquid feed is drawn from them. They are normally replenished with meal by means of an auger or similar conveyor of known volumetric output and by means of a water supply that has been pre-set to give the correct flow to provide the required water/meal ratio. The principal weakness of this system is that the mixer and its electric control circuit are once again relatively complicated and expensive to manufacture.

It is an object of the invention to improve the equipment currently available for mixing dry meal with a liquid to provide a liquid feed for any farm livestock but in the first instance for the pig, which is the class of livestock most commonly fed with liquids.

According to the present invention, a mixer for the continuous mixing together of a flow of first material and a flow of second material comprises a chamber adapted to operate at atmospheric pressure, first inlet means for the continuous introduction of the first material into the chamber, second inlet means for the continuous introduction of the second material into the chamber, the first inlet means being arranged to direct the first material into the chamber either tangentially to the inner wall of the chamber or with a significant component of its motion tangential to the inner wall of the chamber thereby to create in the chamber a vortex of at least the first material, and discharge means for the continuous discharge of the two materials from the chamber after mixing without significant disturbance of the vortex.A third inlet means similar to the first can be added whenever recycling of the mixture to the mixing chamber is desirable or convenient.

Because the mixer of the present invention is a relatively simple device with no moving parts, it has the advantage over the prior art devices of lower manufacturing costs and higher reliability.

In one mode of operation, the first material will be a liquid or a solid in suspension in a liquid and the second a solid in particulate form but the reverse situation is also possible e.g. where the first material is a gaseous suspension of solids and the second material is a liquid or a solid in suspension in a liquid sprayed into the chamber from the second inlet means.

Conveniently the chamber is cylindrical, or partly cylindrical, or conical, or part conical, or bowl-shaped or part bowl-shaped.

In one embodiment, the second inlet means presents the chamber with an inlet aperture spaced from the vortex and of significantly smaller diameter than the diameter of at least that part of the chamber surrounding the inlet aperture.

The discharge means is preferably centred about the axis of the vortex.

Although it is not inconceivable that the mixer should be disposed to produce a vortex having a horizontal or inclined axis, in practice it will normally be easier and more satisfactory to have the mixer disposed to produce a vortex with an axis that is vertical or not significantly different from vertical e.g. within 5" of the vertical.

Conveniently the chamber is open-topped and preferably also high enough to prevent splash-over of materials from the chamber.

Although a mixer according to-the present invention may take very many alternative shapes and sizes, present results indicate certain design parameters as being linked to improved performance of the mixer in certain cases, in particular where the first material is water or a liquid with flow properties substantially similar to those of water.

Thus according to preferred features, where the chamber is cylindrical and closed at its lower end by an end wall lying perpendicular to the longitudinal axis of the chamber, and having a central discharge aperture and the height of the cylinder is from four to six times its internal diameter, then the ratio of the diameter of the inlet aperture presented by the first inlet means to the internal diameter of the cylinder is preferably from 0.03 to 0. 15, the ratio of the height of the first inlet from the end wall of the cylinder to the internal diameter of the cylinder is preferably from 0.4 to 1.5, and the discharge aperture is preferably circular with a diameter of from 20% to 50% the internal diameter of the cylinder. These features are not mutually exclusive and two or more of them may be present in the same design.

The invention also includes an assembly comprising a vortex mixer according to the present invention and a control system for controlling the flows of materials into the mixer.

In the previous control systems used with the mechanical batch mixers and semi-continuous mixers of the prior art, the meal is meterered volumetrically and the system is therefore sensitive to changes in the bulk density of the meal. It is known that the bulk density of such meals can vary considerably, depending on such factors as the fineness of grinding and other characteristics of the constituents of the meal. Variations in bulk density of + 10% have been recorded under farm conditions, and therefore frequent calibration of volumetric metering devices is essential if pigs are to be fed to an accuracy of + 5% of the desired weight of feed per pig (the generally-accepted target). Such calibrations are in practice rarely carried out efficiently under farm conditions.

The relatively low manufacturing cost of mixers of the present invention makes it possible to introduce more accurate but more expensive metering and dispensing equipment without exceeding the cost of conventional systems based on a mechanical mixer and according to a preferred embodiment, the assembly of the present invention includes a weighing device for the second material linked to a flow control for the first material thereby to maintain the materials in the mixer substantially in a preselected mass ratio. In one such embodiment for example, the assembly includes the use of a weighing device for dry meal linked to an automatic valve controlling the water flow to the mixer thereby substantially to maintain a pre-set water/meal ratio by weight irrespective of meal bulk density.

The invention further includes a pipeline feeding system for pigs or other animals in which the first material is a liquid, for example water, and the second material is meal or a like material, the system comprising a vortex mixer according to the present invention, supply means for supplying the second material to the mixer substantially at a preselected rate, further supply means for supplying liquid to the mixer substantially in a preselected proportion to the amount of second material supplied, output control means for controlling the output from the mixer so that it may either be recirculated, dumped or directed through pipes to one or more feeding stations for the pigs or other animals and one or more dispensing devices at the or each feeding station and adapted to dispense the wet pigfood or other food mixed in the mixer.

Although meal and water have been specifically referred to above, it is expected that other powdered or granular solids of similar particle size to meal but different densities can also be satisfactorily mixed with liquid, conveyed, and dispensed, and the term "like material" is to be correspondingly interpreted.

Moreover no problems are anticipated when the meal (or other solids) are mixed with liquids other than water often containing a proportion of suspended solids but with substantially similar flow properties e.g. a nutritious liquid such as whey, skim milk, or recycled mixtures of meal and liquid.

In a preferred embodiment the dispensing device comprises a dispensing chamber operatively connected with an aperture in the wall of one pipe of the pipeline, the device including a plug member movable between a first position in which it closes the connection to the dispensing chamber but allows material to continue along the bore of the pipe and a second position in which it closes, or partially closes, the bore of the pipe downstream of the pipe wall aperture but allows material in the pipe upstream of the aperture to pass through said connection into the dispensing device, the chamber of which is vented to atmosphere.

Conveniently the dispensing device meters the wet pig food or other food before dispensing it and in one such embodiment the dispenser includes dispenser control means operative to cause or allow the plug means to move from the second position to the first position in response to the detection of a preselected weight of material in the dispensing chamber. Metering by weight rather than; volume is preferred because variations in mixture density can occur.

According to another aspect of the invention, the invention comprises a method of mixing particulate solids material with a lic !id e.g. to provide animal feeds having a liquid/ solid ratio of as low as 1.7:1 by weight, the method comprising the steps of forming a vortex of the liquid at atmospheric pressure and introducing the particulate solids material into the vortex (e.g. at the eye of the vortex).

In particular, but not exclusively, the invention includes such a method of preparing pig food or other food by mixing a particulate form of the food with water to provide a freeflowing slurry. The invention further includes pig or other food prepared by this method.

According to a further aspect of the invention, the invention comprises a method of mixing solids material with a liquid comprising the steps of forming a vortex of a gaseous suspension of solids and introducing a liquid or solid in suspension in a liquid into the vortex.

Conveniently, the liquid or solid in suspension in a liquid is sprayed into the vortex at the eye of the vortex.

Embodiments of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a side elevation of a mixer according to the present invention; Figure 2 is a plan view of the same mixer; Figure 3 is a vertical section taken on the line A-A in Fig. 2; Figure 4 is a simplified and somewhat diagrammatic vertical section of the mixer; Figure 5 is a plan view of a first alternative design of mixer; Figure 6 is a vertical section taken along the line B-B in Fig. 5; Figure 7 is a plan view of a second alternative; Figure 8 is a vertical section taken along the line C-C in Fig. 7; Figure 9 is a plan view of a third alternative; Figure 10 is a vertical section taken along the line D-D in Fig. 9;; Figure ii is a largely schematic view of a pipeline feeding system for pigs incorporating a mixer according to the present invention; and Figure 12 is a perspective view of a feed dispenser from the system of Fig. 11.

Thus referring first to Figs. 1 to 4, a mixer 10 according to the present invention comprises a vessel 1 2 defining a cylindrical chamber 14. Typically the vessel 1 2 would be a length of plastic pipe of smooth interior finish of approximately 1 50 mm internal diameter.

A first inlet 1 6 to the chamber is provided by a nozzle member which comprises a nozzle 1 9 mounted in a cylindrical housing 20 which enters the chamber through a wall aperture 21 to which it is secured and sealed. The nozzle housing 20 is joined to an inlet pipe 22 by a pipe union 24.

A second inlet 26 to the chamber is provided either by the open top of the vessel 1 2 (Figs. 1 to 3) or by a second inlet pipe 27 (Fig. 4) of approximately 60 mm diameter (to reduce the amount of dust flying about).

It will be seen from Fig. 2 that the discharge end of nozzle 1 9 is substantially tangential to the inner wall of the vessel 1 2.

A circular discharge aperture 30 is provided in the flat base plate 32 of the vessel for the discharge of materials from the chamber into the inlet 34 of a pump (not shown in Figs. 1 to 4).

The base plate 32 is bolted to the inlet flange 36 by four bolts 38 which are countersunk to ensure a flat smooth base to chamber 14 and to the bottom flange 40 of vessel 1 2 by a ring of bolts 42. Typically base plate 32 would be a 6 mm steel plate drilled to match the mounting holes on the two flanges 36, 40.

Although mixers according to the present invention, and in particular the mixer of Figs.

1 to 4, are useful for mixing a large range of materials, the invention was arrived at principally in an attempt to provide a mixer which would combine dry meal with a liquid to produce homogeneous mixtures of wet animal feed. By "meal" in this context is meant milled grains of cereal such as barley, wheat or maize, together with any additives required to produce a balanced diet for the class of animal concerned and the term "liquid" in this context refers to liquid materials such as water, skimmed milk, whey or other liquids fed to this class of animal.

In operation of the assembly for this purpose, the vortex 44 (Fig. 4) is established by the swirling effect of a jet of liquid from nozzle 1 9 as it enters the chamber tangentially. This effect is augmented by the suction created by the pump at discharge aperture 30 as liquid leaves the chamber.

Once this vortex is established with the liquid along, the dry meal is fed by gravity through inlet 26 into the eye of the vortex, i.e. there is no reliance upon the suction of the pump to move the dry material into the chamber.

When the meal comes into contact with the rapidly circulating liquid of the vortex, it is carried deeper into the chamber by the motion of the liquid and mixing is achieved before the wet feed leaves the chamber through discharge aperture 30 in its way to the pump.

Under normal operating conditions the volumetric rate of supply of meal and liquid to the mixer 10 is less than the displacement rate of the pump, and since the top of the mixing chamber is open to the atmosphere a continuous draught of air is drawn down into the vessel carrying with it many of the smaller meal particles that can form airborne dust.

These small particles are brought into contact with the moving liquid and like the heavier particles are eventually carried with it into the pump.

As already indicated above in general terms, certain parameters have been established as being responsible for the optimum operation of a mixer having the general characteristics of the embodiment described and illustrated with reference to Figs. 1 to 4.

These parameters are for water or for liquids having physical properties similar to those of water and may not be applicable to liquids with physical properties substantially different to those of water.

Accordingly the relevant dimensions have been indicated for this embodiment in Figs. 1 to 3, where Zis the nozzle-input height (Fig.

3), Dthe internal diameter of the chamber (Fig. 2), dthe diameter of the discharge aperture 30 (Fig. 2), athe internal diameter of the input nozzle (Fig. 1), tthe nozzle offset (Fig. 2) and Hthe height of the chamber (Fig.

3).

Using this nomenclature, the important ratios are: Z Nozzle input height D Chamber internal diameter t Nozzle offset D Chamber internal diameter d Outlet diameter D Chamber internal diameter H Chamber height D Chamber internal diameter and a Input nozzle internal diameter D Chamber internal diameter Values of these ratios were obtained from tests using different flow rates, nozzles and mixing chambers. These were related to observed performance and upper and lower limits were identified for each group as being somehow linked with satisfactory operation of the mixer. The preliminary conclusions are discussed below.

Ratio (1) Z/D (Nozzle height/chamber internal diameter) Tests showed that, in general terms, positioning the inlet nozzle too low reduced the turbulence at the top of the vortex and also impeded the downward movement of liquid.

Consequently, meal was not drawn into the pump very effectively but formed a 'solid' rotating lump at the top of the vortex.

Conversely, introducing liquid into the chamber too far above the base reduced the speed and therefore stability of the vortex sometimes resulting in blockages because the weaker vortex was unable to remove meal quickly enough to stop bridging. In addition, the lack of turbulence in the bottom of the chamber was found to create a centrifugal separation effect that caused larger, heavier meal particles to remain in suspension without entering the pump.

From these preliminary findings it seems that provided Z/D is between 0.4 and 1.5 then performance should be satisfactory.

Ratio (2) t/D (Nozzle offset/Chamber internal diameter) It has been established that a range of t/D values of between 0.05 and 0.22 is satisfactory and it is thought that values larger than this are unlikely to be more effective because they will probably increase the chances of reverse flow and vortex collapse.

Ratio (3) d/D (Outlet diameter/Chamber diameter) As the base of the vortex chamber is preferably mounted directly on the pump inlet to reduce the risk of blockages, the diameter of the discharge aperture 30 is largely governed by the size of the pump. The conclusion is that the optimum ratio is likely to be between 0.2 and 0.5.

Ratio (4) H/D (Chamber height/Chamber diameter) Tests show that for a given chamber diameter, reducing the size of the nozzle diameter increases the required height H. This may be explained in terms of the kinetic energy of the jet which is proportional to (average jet velocity)2, hence reducing the nozzle size and maintaining a constant volumetric throughput raises velocity and so increases the kinetic energy input to the mixer, consequently raising the liquid level in the chamber.

A further point to be borne in mind is that the mixer must be tall enough to accommodate the maximum likely flow. Although as explained above the sizes of input nozzle used will vary this maximum level, the indication so far is that an H/D ratio of between 4 and 6 should prove satisfactory in most cases.

Ratio (5) a/D (Nozzle diameter/Chamber diameter) The above ratios apply to input nozzles which are substantially circular in cross-section. There is no doubt that nozzles having different cross-sections (e.g. rectangular, semicircular or oval) could be used, but the appropriate ratios for such nozzles have not been determined.

Selection of the input nozzle diameter depends largely upon the adequacy of the liquid supply. Whilst it is desirable from the mixing point of view to establish a fast and hence strong vortex by using small diameter nozzles these may not be capable of giving the desired volumetric throughput in any particular case and so a larger nozzle may be needed.

There is a limit to the largest nozzle size that can be consistent with satisfactory mixing and this appears to be approximately 15% of the chamber diameter. Similarly, the smallest size practicable seems to be about 3% of chamber diameter. It may in fact be necessary to make provision for substituting different sizes of nozzles since a given nozzle is unable to produce efficient mixing over a wide range of flow rates and according to a preferred feature of the invention, two or three different nozzles are fitted in the chamber for use sequentially as the flow rate changes. The nozzles could also be used together if desired e.g. to assist in debridging meal especially with thick mixtures.Multiple nozzles also allow the mixer to be used with a recirculatory pipeline system, the additional nozzle or nozzles being used to reintroduce the mixture to the vessel 1 2 tangentially or partly tangentially.

In addition to those critical dimensions discussed above, it should be pointed out that three other parameters are needed to define the performance of the mixer. These are the meal throughput M (Kg/minute), the liquid flow rate Q (litres/minute) and the average liquid input velocity V (metres/second), the theoretical relationship between these parameters being given by the expression 1000 Q V= 1 5 na2 where a is measured in millimetres.

As already indicated, the mixer 10 need not necessarily be exactly as illustrated in Figs. 1 to 4. Figs. 5 and 6 indicate, by way of example, a modification of the first design in which the first inlet means (for the liquid component) comprises an L-shaped pipe 46 bolted to the inner wall of vessel 1 2 by U-bolt clamps 48, 49. Typically pipe 46 would be 1 3 mm outside diameter copper tube, the horizontal lower section 50 serving as a nozzle for the introduction of a tangential jet of liquid into chamber 14.

Although the embodiment of Figs. 3 and 4 has the disadvantage that the pipe 46 will at least to some extent render the establishment of a stable vortex more difficult within chamber 14, it has the compensating advantage that the height of the inlet aperture (51) that it presents to the chamber can readily be varied to suit different mix concentrations.

Figs. 7 and 8 show how the basic design of Figs. 1 to 4 can be modified to have an inverted cone-shaped base section 54 of approximately 100" included angle (a). Although the particular model tested was too short to tolerate liquid flows of greater than 10 litres/ minute (H/D ratio = 1), for lesser flows it was used successfully to mix small quantities of meal and water without causing a centrifugal separation of heavier meal particles. It would seem likely therefore that using a conical-base chamber does not impede mixing and under certain circumstances could prove beneficial.

The significant dimensions and ratios stated earlier for flat-base embodiments may not necessarily apply to a conical-base mixer as the vortex characteristics are different. Whatever the shape of the chamber base, however, it is important that it is smooth and that there are no projections such as bolt heads or holes on its surface as these tend to cause eddies which can spoil the vortex in the chamber.

Figs. 9 and 10 show a further modification in which the vessel 1 2 has an upwardly tapering portion 56 terminating in a solids inlet port 26 of reduced diameter (though not so small as to result in sub-atmospheric pressures being induced in the mixer). As in the embodiment of Figs. 5 and 6, the inlet for the liquid component is provided by a 1 3 mm outside diameter copper pipe, although in the present embodiment the pipe is not vertically adjustable but passes through an appropriate aperture in the walls of vessel 1 2 to which it is secured by welding.

Despite any 'bath-plug' effect which might encourage free spiral vortices to rotate in a particular direction, the direction of the jet discharge will be the deciding factor in all the embodiments above described since these are designed to operate with the jet forces sustaining the vortex many times greater than the Coriolis forces responsible for the natural effects.

As regards the possibility of inclining the nozzle or indeed the whole mixer, it has been found by experiment that inclining the axis of the nozzle either up or down from the horizontal (and keeping chamber 1 2 vertical) reduces the strength of the vortex and also the mixing performance. No work has been done to establish the effect of inclining the chamber but this does not appear to offer any advantage over a vertical arrangement.

As has already been indicated above, the present invention extends not just to a mixer but also to an assembly including a control system for the supply of materials to the mixer and further to a pipeline feeding system incorporating both the mixer and the control system.

One such feeding system is shown in Fig.

11 which illustrates an automated pig-feeding system 60.

Thus referring now to Fig. 11, it will be seen that system 60 includes a vortex mixer 10 according to the present invention and that this is associated with the usual liquid inlet pipe 22 and a solids inlet 26.

The inlet liquid for the mixer comes from a liquid supply header tank 62 (continuously topped up during operation of the feed system) via a down pipe 64. The liquid input flow rate is under the control of unit 66 which may either be a valve or a pump. In an alternative version (not illustrated) the liquid inlet comes instead from a pressurized pipeline, for example, a water main or a pump.

The continuous flow of solids (68) for inlet 26 is provided by a conveyor 70 which is mounted on bearings or knife edges so that it is free to pivot in a vertical plane. The conveyor receives meal from a hopper 72 (continuously topped up from the main bulk hopper 74 by gravity or by mechanical means e.g. a feed auger 76). The weight of conveyor 70 is counter balanced by having the drive unit 78 offset.

The loaded hopper 72 is supported at a small distance above the belt and no part of its weight rests on the belt. The volumetric rate of supply of meal to the belt may be varied by means of an adjustable sliding gate at the outlet from hopper 72.

The weight of material on the conveyor 70 is supported on the plunger 80 of a pneumatic load cell 82 which operates on a low pressure (10 to 30 p.s.i.) clean air supply line 84 to continuously adjust the control unit 66 in proportion to the weight of meal on the belt in such a way as to maintain the liquid/meal input to the mixer at a preselected desired ratio or within a preselected range of ratios.

In the illustrated embodiment of Fig. 11, the pump 86 (referred to earlier in the discussion of Figs. 1 to 10) is an eccentric rotor pump driven by a pump motor 88. If other designs of pump are to be used for this purpose, it is desirable for thick pig meal and liquid mixtures (e.g. 2:1 liquid: meal) with their correspondingly high viscosities, that these should be positive displacement pumps.

However, in situations where significantly lower solids concentrations are required and therefore the viscosities are less, there seems to be no reason why other types of pump should not work equally well although to reduce risk of blockage it is always desirable that the pump inlet be vertical and attached to the chamber base as closely as possible.

Whatever the type of pump used, its action is to cause further mixing of liquid and solid within the pump and once having passed through the pump, the mixed materials are more ready to be distributed through the following pipeline system.

This system comprises a main feed pipe 89 and a number of side pipes (of which only two 90, 91 are shown) each leading to a series of dispensers. For simplicity only one such series is shown and this only in part, only the first two dispensers 93, 94 in the series being illustrated.

In addition, the pipeline includes a main diverter valve 96 with associated drain pipe 98 and a number of circuit diverter valves (e.g. 100, 101) for the different side pipes.

These latter valves may for example be operated in sequence so that the first series of feed dispensers is fully loaded before the mixture is passed on through pipe 89 to the next series and so on. The dispensers are located one above each pig pen.

Fig. 1 2 shows one of the dispensers (container 93) in more detail. In essence it comprises a container 103 of about 40 litres capacity which may be formed by joining two truncated cones 104, 105 as shown or may be of any other convenient size, shape or design. It is vented to atmosphere by any convenient means (e.g. a hole near the top).

The container is suspended by four small springs 107 from a plate 109 attached by any convenient means, e.g. a bracket, chain or wire, to any suitable support which is usually a component of the building housing the animals (not shown). A valve unit at the top of the container is connected to the side pipe 90 by screwed or welded joints (not shown) and contains a hinged, plug member 111.

In the raised position (shown in Fig. 1 2) the plug member partially or completely blocks off that part of pipe 90 downstream of the container and deflects all or part of the wet feed downwards into the container 103 usually through an anti-splash tube which is suspended beneath the plug member 111 and terminates just above a conical "door" 114 at the base of the container. The plug member is held in the raised position by a latch 11 2 which automatically engages with an adjustable stop. A calibrated adjusting screw 11 3 lever or quadrant or any other conventional adjusting device is used to control the effective length of this stop.This in turn controls the amount that the container 103 can move downwards (as the load increases) before the latch is freed and the plug member drops to the "container-closed" position to stop further loading. Normally the plug member 111 is spring-loaded to ensure rapid closure.

In other words, the setting of calibrator screw 11 3 decides the amount of material to be accepted by the dispenser 93 before the plug member 111 closes and the material in pipe 90 bypasses the dispenser and continues down the pipe 90 to the next dispenser 94 in the series. When all the containers in the series have been filled in this way, the diverter valve 100 is switched to isolate side pipe 90 and the material is now ready to be dispensed.

At the bottom end of the container, the discharge aperture is shown closed off by the conical "door" 114 attached to the lower end of the piston rod 11 5 of a double-acting, double-ended pneumatic cylinder 116. Thus referring still to Fig. 12, to empty the container 103 air is admitted to the lower half of the cylinder 116, thus drawing the conical door 114 up through the material present in the container at the time.

At its top end, piston rod 115 carries a rubber buffer 1 24 and as rod 115 moves upwardly to open aperture 122, this buffer will engage plug member 111 and push it into the raised position where it is held, in readiness for the next filling operation, by the latch 11 5. Before refilling begins, however, cylinder 11 6 will have been operated e.g.

automatically, once the container is empty to close door 114 again and return the dispenser to the situation illustrated in Fig. 1 2.

As previously indicated above, the maximum meal content that may be satisfactorily achieved is probably that associated with a meal to liquid mass ratio of about 1:1.7 but the mixer will produce mixtures at solids concentrations below this level. Its performance in mixing solids other than meal with liquid or in mixing meal with liquids other than water, however, has not yet been assessed in detail.

In a modification of the system above described, the dispensers 93, 94 etc. are replaced by manually-controlled or remotelycontrolled valves so that mixture not required at any of the pens can be recirculated through the system. Obviously in this case the inputs to the mixer will have to be switched on and off intermittently (or the mixer would overflow), but this is easily done automatically by means of high-level and low-level control probes within the vessel 1 2.

Minor modifications of the system described and illustrated in Fig. 11 will be obvious to those skilled in the art. For example the control unit 66 could be mechanically or electrically linked to the weighing means 70 rather than pneumatically. Basically, however, it is envisaged that any such system should preferably include the vortex mixer together with means for supplying and weighing dry meal, means for controlling the quantity of liquid entering the mixer in proportion to the weight of meal supplied, means for controlling the output from the mixer so that it may either be recirculated, dumped or diverted through pipes to pigs and a device to weigh and dispense wet pig-food to a number of pigs housed in one pen with the possibility of arranging several devices in series along a pipeline to feed more pigs.

The good performance of the pipeline system relies principally on the performance of the mixer. As already indicated above, important aspects of the invention are seen as including among other things: (1) a cylindrical mixing chamber with a flat base where the height of the chamber is between 4 and 6 times its diameter; (2) a method of producing a jet of fluid that induces a vortex in the mixer, currently by using a nozzle of circular cross-section in which the ratio of the nozzle diameter used to the chamber diameter is greater than .03 but less than .15 and the height of this nozzle above the point of intersection of the base and the wall of the chamber is between 0.4 and 1.5 times the chamber diameter;; (3) an outlet from the chamber in the form of a circular hole in the base concentric with the chamber to discharge the mixture, the diameter of this hole being greater than 20% but less than 50% of the chamber diameter; (4) a mixing chamber to perform a function similar to that described in paragraph (1) above but with a conical base; (5) a method of preparing pig food or other food having preset and controlled liquid/meal ratios by using the vortex mixer in conjunction with an automatic meal weighing and liquid control system; and (6) a method of mixing granular or powdered material with a liquid in which the liquid content of the resulting mixture is sufficiently low to give a mixture ratio of down to 1.7:1 (liquid/solids by weight) using a cylindrical mixing chamber open to atmospheric pressure, mixing being effected by inducing vortex motion by means of a horizontal jet offset from the central axis of the mixer and tangential to the chamber wall, and a circular outlet in the base concentric with the walls of the chamber.

Claims

1. A mixer for the continuous mixing together of a flow of first material and a flow of second material comprising a chamber adapted to operate at atmospheric pressure, first inlet means for the continuous introduction of the first material into the chamber, second inlet means for the continuous introduction of the second material into the chamber, the first inlet means being arranged to direct the first material into the chamber either tangentially to the inner wall of the chamber or with a significant component of its motion tangential to the inner wall of the chamber thereby to create in the chamber a vortex of at least the first material, and discharge means for the continuous discharge of the two materials from the chamber after mixing without significant disturbance of the vortex.

2. A mixer as claimed in Claim 1 including a third inlet means similar to the first added for recycling of the mixture to the mixing chamber.

3. A mixer as claimed in Claim 1 or Claim 2 in which the chamber is cylindrical, or partly cylindrical, or conical, or part conical, or bowl-shaped or part bowl-shaped.

4. A mixer as claimed in any preceding claim in which the second inlet means presents the chamber with an inlet aperture spaced from the vortex and of significantly smaller diameter than the diameter of at least that part of the chamber surrounding the inlet aperture.

5. A mixer as claimed in any preceding claim in which the discharge means is centred about the axis of the vortex.

6. A mixer as claimed in any preceding claim with a vortex axis that is within 5" of the vertical.

7. A mixer as claimed in Claim 6 in which the vortex axis is vertical.

8. A mixer as claimed in any preceding claim in which the chamber is open-topped.

9. A mixer as claimed in Claim 8 in which the chamber is high enough to prevent splashover of materials from the chamber.

10. A mixer as claimed in any preceding claim in which the chamber is cylindrical and closed at its lower end by an end wall lying perpendicular to the longitudinal axis of the chamber and having a central discharge aperture, the height of the cylinder being from four to six times its internal diameter.

11. A mixer as claimed in Claim 10 in which the ratio of the diameter of the inlet aperture presented by the first inlet means to the internal diameter of the cylinder is from 0.03 to 0.15.

1 2. A mixer as claimed in Claim 10 or Claim 11 in which the ratio of the height of the first inlet means from the end wall of the cylinder to the internal diameter of the cylinder is from 0.4 to 1.5.

1 3. A mixer as claimed in any of Claims 10 to 1 2 in which the discharge aperture is circular with a diameter of from 20% to 50% the internal diameter of the cylinder.

14. A mixer as claimed in any preceding claim in which the first inlet means comprises two or more nozzles fitted in the chamber for sequential use to suit changes in flow rate of the first material.

1 5. A mixer substantially as hereinbefore described with reference to and as illustrated in Figs. 1 to 4 or Figs. 5 to 8 in the accompanying drawings.

1 6. A mixer substantially as hereinbefore described with reference to and as illustrated in Fig. 9 and 10 of the accompanying drawings.

1 7. An assembly comprising a mixer as claimed in any preceding claim and a control system for controlling the flows of materials into the mixer.

1 8. An assembly as claimed in Claim 1 7 including a weighing device for the second material linked to a flow control for the first material thereby to maintain the materials in the mixer substantially in a preselected mass ratio.

1 9. An assembly as claimed in Claim 1 8 including a weighing device for dry meal linked to an automatic valve controlling a water flow to the mixer thereby substantially to maintain a pre-set water/meal ratio by weight irrespective of meal bulk density.

20. An assembly as claimed in Claim 1 7 and substantially as hereinbefore described with reference to and as illustrated in Fig. 11 of the accompanying drawings.

21. A pipeline feeding system for pigs or other animals in which the first material is a liquid and the second material is meal or a like material, the system comprising a mixer as claimed in any of Claims 1 to 1 6 or an assembly as claimed in any of Claims 1 7 to 20, supply means for supplying the second material to the mixer substantially at a preselected rate, further supply means for supplying liquid to the mixer substantially in a preselected proportion to the amount of second material supplied, output control means for controlling the output from the mixer so that it may either be recirculated, dumped, or directed through pipes to one or more feeding stations for the pigs or other animals and one or more dispensing devices at the or each feeding station and adapted to dispense the wet pig-food or other food mixed in the mixer.

22. A pipeline feeding system as claimed in Claim 21 in which the dispensing device comprises a dispensing chamber operatively connected with an aperture in the wall of one pipe of the pipeline, the device including a plug member movable between a first position in which it closes the connection to the dispensing chamber but allows material to continue along the bore of the pipe and a second position in which it closes, or partially closes, the bore of the pipe downstream of the pipe wall aperture but allows material in the pipe upstream of the aperture to pass through said connection into the dispensing device, the chamber of which is vented to atmosphere.

23. A pipeline feeding system as claimed in Claim 21 or Claim 22 in which, in operation, the dispensing device meters the wet pig food or other food before dispensing it.

24. A pipeline feeding system as claimed in Claim 23 in which the dispenser includes dispenser control means operative to cause or allow the plug means to move from the second position to the first position in response to the detection of a preselected weight of material in the dispensing chamber.

25. A pipeline feeding system as claimed in Claim 23 or Claim 24 wherein the metering is by weight rather than by volume.

26. A pipeline feeding system substantially as hereinbefore described with reference to and as illustrated in Fig. 11 of the accompanying drawings.

27. A pipeline feeding system as claimed in any of Claims 21 to 26 including a dispensing device substantially as hereinbefore described with reference to and as illustrated in Fig. 1 2 of the accompanying drawings.

28. A method of mixing particulate solids material with a liquid comprising the steps of forming a vortex of the liquid at atmospheric pressure and introducing the particulate solids material into the vortex.

29. A method as claimed in Claim 28 tor mixing animal feeds having a liquid/solid ratio of as low as 1.7:1 by weight.

30. A method as claimed in Claim 28 or Claim 29 in which the solids material is introduced into the vortex at the eye of the vortex.

31. A method as claimed in any of Claims 28 to 30 for preparing pig food or other food by mixing a particulate form of the food with water to provide a free-flowing slurry.

32. Pig or other food prepared by the method of Claim 31.

33. A method of mixing particulate solids material with a liquid comprising the steps of forming a vortex of a gaseous suspension of solids and introducing a liquid or a solid in suspension in a liquid into the vortex.

34. A method as claimed in Claim 33 in which the liquid or solid in suspension in a liquid is sprayed into the vortex at the eye of the vortex.

35. A method as claimed in Claim 28 or Claim 33 substantially as hereinbefore described with reference to the accompanying drawings.