While not limited in this respect, we envisage particular applicability of the present concepts for the conditioning of powder food ingredients, such as flour or powdered fat.

BACKGROUND Powders used in industrial processes raise special issues of storage, handling and transport. Particular issues associated with the particulate nature of the material include - temperature control; - moisture absorption; - aggregation ; - settlement ; - separation of mixed components or different particle sizes; - chemical degradation and others. Difficulties in any one or more of these respects can raise serious problems in downstream processing of a material, in terms of the processing as such and/or in terms of the quality of the resulting product.

An example of a powder material presenting processing problems is flour, used in the baking of dough/pastry products e. g. bread loaves. For a given dough/pastry preparation, there is usually an optimum temperature for the flour e. g.

18C° when charged to a dough mixture. Above the optimum temperature, yeast in the dough is prematurely activated and moisture is driven off from the dough mix. This tends to make the finished loaf underweight, so the charging temperature is important.

However flour is typically delivered from the mill retaining, to varying degrees, heat from the milling process.

It is transferred from bulk storage to a batch weigh hopper (positioned above a dough mixer), usually by pneumatic transfer. The transfer temperature depends on ambient conditions and may be as high as 30°C ; in any event it is hard to control. As a result the ideal charging temperature (18C°) cannot be achieved reliably.

Similar issues arise with other powders, e. g. freeze- dried oils and the like, where in-process temperature control can be crucial.

SUMMARY OF INVENTION It would be desirable to have a means for processing powder, for example flour, that enables all or some of these difficulties to be addressed. A preferred aim is to be able to deliver a powder, e. g. food ingredient such as flour, to a mixing or other downstream process at a predetermined charging temperature.

What we propose is to charge the powder into a conditioning chamber having a gas-permeable base and subject the charge of powder to an up-flow of gas through the base.

The gas flow rate differs in different regions over the base, causing powder in one or more higher-flow regions to rise and spill over to one or more lower-flow regions, bringing about progressive mixing and agitation of the powder in a ventilated state, and preferably in a fluidised state. This characteristic movement of the powder in the chamber lends itself to conditioning the powder rapidly in various ways, because the entire batch of powder can progressively and rapidly be exposed to predetermined conditions. The conditions can be determined by controlling the nature and state of the gas which is blown, and/or the conditions in the chamber.

Thus, gas may be blown into the chamber at a regulated temperature and/or moisture content. The chamber wall may be temperature-controlled, e. g. by means of a heating or cooling jacket.

The chemical nature of the gas may be selected according to the powder being processed. Preferably it is substantially inert to the powder under the conditions in the chamber. For flour, air is preferred.

The powder material is usually charged to the conditioning chamber batchwise.

The mode of discharge of the conditioned powder material from the chamber is not strictly limited, but we particularly prefer to discharge the material through a discharge port having a discharge valve whose valve element seats against a valve seat of a port leading from the interior of the chamber.

Preferably the valve element and/or the discharge port includes one or more regions subject to a clearing flow of gas. Such a flow can serve to keep the closing/sealing surfaces of the valve element and seat clear of powder as they meet, and/or facilitate the flow of powder out through the port. Such a flow may be provided by surfaces at or adjacent the port and/or valve element having one or more gas flow openings in communication with a pressurised gas supply conduit.

The discharge port is preferably through the centre of the chamber base.

Another aspect of the invention is apparatus for conditioning powder, e. g. flour conditioning apparatus, or apparatus itself comprised in a food processing line, comprising a conditioning chamber e. g. in the form of an upright column; a gas-permeable base of said chamber, e. g. a mesh, sinter or porous plate, with gas permeation holes small enough for the base to retain the powder to be processed; a gas distribution system for introducing a flow of pressurised gas into the chamber interior through the gas- permeable base, the gas distribution system including means for providing a higher gas flow pressure at one or more higher-flow regions of the gas-permeable base than at one or more other lower-flow regions thereof.

In a preferred embodiment the gas distribution system includes means such as dividing walls or discrete sub-chambers for enabling flows of gas at different pressures to different respective regions of the gas-permeable base. For example a distribution chamber mounted beneath the base of the conditioning chamber may be divided into sub-chambers.

Usually there are more than two distinct regions to which distinct gas supply rates or pressures apply, e. g. sub- chambers. For example there might be four e. g. as two high- flow regions as quarter sectors with two low-flow regions as quarter sectors between them. The sub-chambers may have discrete gas supplies for full independence of control. Or, pressure differential between chambers may be created by restricted flow communications between sub-chambers.

The gas-permeable base may be held in place between peripheral walls of the conditioning chamber and gas distribution chamber.

The conditioning chamber may be provided with any one or more of temperature control means, e. g. a heating/cooling jacket, sensing means for measuring conditions (e. g. temperature pressure) inside the chamber or at its wall and weighing means for weighing the charge in the chamber.

A discharge port may be provided through the base of the chamber as discussed previously. Because a discharge channel of the port may extend down through or adjacent a gas distribution chamber as described above, the gas distribution system may easily communicate with this channel via one or more ports, jets or permeable walls to provide a clearing gas flow as mentioned previously. The valve element of a discharge valve may have a convex leading surface shaped to seat against an annular valve seat of the discharge port. A drive for the valve element may have a drive member extending to an opposite extreme, e. g. the top, of the conditioning chamber where is it operatively connected to a drive. The valve element may have one or more internal gas flow channels leading to its surface, to clear powder from the surface in use as mentioned previously. A gas supply for this purpose may be fed along a drive member on which the valve element is mounted.

Preferably the chamber base inclines down towards the discharge port, to assist discharge of material. It may have a conical form, for example.

The apparatus may be programmed so that operation of the discharge valve can be made dependent on the readings of one or more sensors as mentioned above.

A further aspect of the invention is a method of making a flour-based product in which flour is fed from storage to a mixing stage by way of a method or apparatus as specified herein. More generally, a method in which a powder is conditioned by a method or apparatus as described herein and then passed to a downstream process stage, e. g. physical and/or chemical, e. g. mixing or reacting or treating.

A preferred embodiment of the invention will now be described by way of example, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig 1. is a partly schematic sectional view of a conditioning tower; Fig. 2 is a similar but fragmentary view showing details of the base of the tower ; Fig. 3 discusses details of the upper part of the tower in section; Fig. 4 is a separate side view of a discharge valve and its actuating system; Fig. 5 shows the discharge valve element in section and insitue, and Fig. 6 shows the use of load cells.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS With reference firstly to Fig. 1, the principal elements of the assembly are a conditioning column 2 defining a cylindrical internal space, a base construction 1 with a gas distribution chamber arrangement, and a discharge valve 3.

This particular embodiment is designed for use with flour used in a baking process, but similar constructions are effective with a variety of powder materials.

With reference additionally to Fig. 2, the base of the column is a discrete component securable by an upper flange 4 to a flange on the lower edge of the column 2 above. The base has an outer wall 5, a base wall 6, a central column 7 which together form a closed containment or distribution space. A set of radially-extending internal dividing plates 8, e. g. from 2 to 10 plates, preferably at least 3, subdivides the containment into discrete chambers. The top edges of the divider plates 8 incline downwards towards the centre, defining a generally conical form of the upper opening of the base onto which a gas-permeable membrane 9 is secured. The edges of the membrane are clamped at the securing flange 4 by a locking mechanism 14. At the centre, a removable tubular valve seat component 10 extends down through the centre of the central column 7. This valve seat component 10 has a top formation which clamps the inner periphery of the membrane 9 down in position. The seat component 10 is held in place by a locking fastener 11 at its lower end. The tube of the valve seat component 10 also incorporates a gas-permeable membrane, surrounding it in tubular form, whose function is described later.

Above the membrane, elongate ridged clamping ribs or spines 12 are provided, extending along in alignment with the upper edges of the divider plates 8 below-four, in this example-to help support the main span of the membrane 9.

The clamping spines 12 are circumferentially narrow, deriving stiffness from their axial height and being upwardly convergent to minimise the turbulence caused in up flowing gas. The inner ends of the spines 12 have guide surfaces converging towards the column axis.

The angle between the conical primary membrane 9 and a radial plane is an important factor in achieving good powder movement and may need to be varied according to the powder e. g. flour being processed and the other processing parameters. Preferably therefore components such as the divider plates 8 are changeable or adjustable to enable the angle to be changed. This angle is also significant in discharging powder from the central port.

A gas supply to the subdivided gas distribution reservoir is adapted so that preconditioned gas (in particular, preconditioned preferably as to temperature and/or moisture content) can be fed with varying flow parameters from the different sub-chambers thereof. The gas supplies are not shown but suitable pressurised sources in themselves are readily available. The skilled person can adopt any suitable mode of connecting the supply into the column base to achieve the required variations. For example different supplies at different rates/pressures may be fed independently to different ones of the sub-chambers. Or, a single supply can be fed to the entire base unit and fed to different sub- chambers through different rate-control formations, such as orifices, incorporated in the base construction to achieve the desired variation. Additionally or alternatively the variation may include or be a temporal variation e. g. so that a region of relatively high flow moves from one part of the base area to another e. g. rotationally, as processing proceeds. In any event, the result is gas flows of predetermined and controlled flow velocities, up through the permeable membrane 9 into the column and also inwardly via the inner column construction 7 and through the secondary membrane 13 the discharge conduit.

By having preconditioned gas flowing from different chambers of the base reservoir at different pressures and transfer velocities, powder e. g. flour in the column above the respective chambers migrates upwardly and downwardly on pressure waves inside the column at different velocities according to its region. Suitable flow rates and flow rate differences may be determined with reference to the bulk density and specific gravity of the material.

Powder situated above a high pressure/velocity chamber rises more quickly than powder above a lower pressure/velocity chamber. These differing rates of movement cause powder moving faster to shear off from upper regions of the notional column that it forms, generally by virtue of an unsustainable angle of repose at the top of the overall column of flour, and move laterally on to an area that is moving at a slower rate.

This lateral movement of powder from one region to another applies load and back pressure onto the lower velocity region, causing powder from that low pressure column to migrate laterally-generally from a region near the base of the column-into the path of an adjacent column with a different pressure/velocity, typically a higher pressure/velocity.

It will be appreciated that these differential movements of powder can give rise to a circulation of material from one region of the column to another, leading to efficient exposure of the entire batch of powder to the predetermined conditions associated with the flowing gas. Thus, the batch of powder can quickly be brought to a homogeneous state. Different grades of flour give different flow behaviours, and the variations are adjusted to achieve satisfactory and full conditioning.

Figure 3 designates further features associated particularly with the column part of the apparatus. It designates the lower flange 15 that clamps releasably onto the upper flange 14 of the base unit, a cylindrical inner column wall 16 defining the interior space, a closed column top 17 which may optionally be detachable, an intermediate jacket wall 18 and an outer insulation wall 19.

The jacket arrangement provides supplementary means for controlling conditions in the column interior, i. e. in addition to preconditioning the gas fed in through the base.

In particular when jacketed and insulated as shown in Fig. 3, the jacket can be supplied with hot, cold or chilled water, or with steam, or with any other cooling or temperature-raising medium. Or, other forms of temperature control may be used, such as electric heating elements or the like. An electrical heat trace system may be applied to the external surface of the column as a means of controlling internal temperature.

Fig. 3 also shows one of a plurality of sensor pods or sockets 20 exposed to the column's interior for sensors to detect conditions there, for example temperature or moisture levels.

In certain industrial processes it may be desirable to supplement control of the conditions inside the column by some direct interior conditioning device, such as a lance, probe, ball or other element extending or projecting permanently or temporarily into the column interior. The same access facility may be provided for one or more sensors.

With certain processes it may be desirable or necessary to add materials, e. g. additive materials such as essences or flavourings, to the powder material (e. g. flour) during its conditioning in the tower. Means may be provided for injecting additive materials, e. g. through injector openings, lances, internally-projecting elements, spray balls or the like.

Preferably the entire column including the upper part and the gas distribution arrangement at the base is subject to monitoring/control sensors. In addition to monitoring conditions in the column as mentioned above, relevant conditions in the gas supply such as pressure, flow, temperature, moisture are also preferably monitored at relevant control points. These monitored values may be compared automatically against process set points or profiles for the apparatus and process in question. Where parameters need to be varied this variation may be done automatically under the control of a programmed PLC (Programmable Logic Controller) or other suitable processor by feedback e. g. to controls for any one or more of powder discharge rate, temperature control, moisture control, gas flow rate, gas moisture and gas temperature.

It is important to be able to remove material readily from the column without losing the applied conditioning, and taking into account the prevailing difficulties of handling powdering materials. Figs. 4 and 5 indicate features for operating one preferred form of valved discharged port for the column. In the preferred embodiment the port for discharge of conditioned powder material from the column interior is a central port through the base; defined by the cylindrical conduit 30 through the seat component 10 in the present embodiment. This component 10 is a seat in the sense that its upper mouth has an annular face forming a seat for engagement with the head 21 of a linearly-actuated valve operated from above, i. e. through the column interior. Operating the valve from within avoids the conditioned powder leaving the column being obstructed by valve operating mechanism. The illustrated valve is operated by a linear actuator 25 via a main shaft 23 extending down through a fixed shaft housing 24 through the centre of the column to a mounting 22 carrying an inter-changeable valve head 21. This valve head has a convex bulbous form, its convex downward sealing face being shaped to be guided to the centre by complementary inclined guide faces of the clamping spines 12 and to seal onto the mouth of the valve seat tube 10 with a minimum of sliding and crushing. To promote a good seal without trapping or damaging powder particles, this embodiment is enhanced by provision of a set of internal channels in the valve head, emerging at strategically placed ports 221 adjacent to the sealing location. These internal gas channels are supplied with pressurized gas through the actuating shaft 23 which is hollow. By blowing jets of gas from these ports as the valve head 21 approaches'docking'with the valve seat 10, powder residues are blown away from the sealing faces to facilitate a good seal.

Also, with the valve open i. e. the head 21 lifted from its seat 10, the same gas jets promote a free and distributed flow of powder out through the discharge conduit 30. A feature of this construction is that by using a linear actuator with a proportional control, the spacing of the valve head 21 above its seat is precisely determined and can be used to meter or regulate the discharge flow rate.

The embodiment contemplates fluidising flows of gas at several zones of the process, and these have roles in discharging the powder (flour) from the column. They are as follows.

Firstly there is of course the flow of gas from the primary membrane 9, already described with reference to its conditioning function. It should be noted that the preconditioned gas from the membrane 9 also assures a fluidised state of powder (flour) adjacent the base of the column that allows it to flow freely and in particular to be easily discharged from the port 30.

Also relevant in discharge is the secondary membrane 13 mentioned previously, located between the column structure 7 of the base and its removable valve seat 10. Gas, preferably preconditioned gas, is fed to this secondary membrane 13 either directly from a communication with the general gas distribution system in the base (Fig. 2) or from an independent gas source. The inward gas flow through the permeable wall 13 promotes free flow of powder escaping through the column to the discharge port 30.

Also, in relation to the discharge conduit 30, the removable valve seat component 10 may comprise flow openings for gas to be fed to its sealing face, for example, an array of through-holes on its sealing face. Gas, preferably preconditioned gas, can be fed to such opening (s) either as a distribution from the general distribution space in the base (Fig. 2) or indirectly from an independent gas source.

A further gas flow/fluidising feature is'in relation to the clamping ribs or spines 12. These may be provided with arrays, e. g. multiple rows, of through-holes on their surfaces or flanks (not shown). Gas, e. g. preconditioned gas, can be fed through suitable communications either from the gas distribution reservoir (Fig. 2) or from an independent gas source. Gas flow from the flanks of the spines 12 further promotes a free flow of powder towards the discharge outlet.

Finally, as mentioned there is the possibility of providing multiple through-holes from the surface of the valve head 21-which may be interchangeable so as to change the gas flow properties-through which a gas flow, preferably of preconditioned gas, may be passed.

With reference to all of the gas flow locations mentioned above, it is particularly preferred if the gas flow from them can be adjusted independently of other gas flows in the apparatus. This facility enables the overall behaviour of the apparatus to be optimised to a given powder e. g. flour to promote efficient discharge from the conditioning space.

Finally, Fig. 6 indicates how the conditioning tower may be provided with a weighing facility e. g. by being supported on load cells 26. These may have various functions. For example on loading of the tower, the load cells 26 may indicate when a predetermined set added weight is reached whereupon the feed is automatically interrupted.

Another function of the weight control is to control the weight of discharge or dosing of conditioned powder from the tower, by controlling the degree of opening of the discharge valve in accordance with the actual rate of discharge determined by weight change and a target value.

For example data from the load cell system may be continuously monitored and compared automatically with a programmed procedure parameter incorporated in the logic controller mentioned above. Feedback systems which a skilled person can readily provide can be used to modulate the discharge valve opening to increase or decrease the flow rate or dosing rate of flour to match the prescribed rate.

We have found that by using the apparatus and methods described herein, one can obtain a homogeneously conditioned batch of flour or other powder that can rapidly be brought to a predetermined condition e. g. of temperature and easily held at that condition, and discharged entirely or partially or at a controlled rate while maintaining the predetermined condition.

The skilled reader will appreciate that numerous variations are possible from the described embodiment on the basis of the general teachings herein.