EP0855941B1

EP0855941B1 - A device and apparatus for classification and separation of particles in cereal milling process

Info

Publication number: EP0855941B1
Application number: EP96934686A
Authority: EP
Inventors: P. Siegismund Schneider
Original assignee: Ocrim SpA
Current assignee: Ocrim SpA
Priority date: 1995-10-19
Filing date: 1996-10-15
Publication date: 2000-01-19
Anticipated expiration: 2016-10-15
Also published as: EP0855941A1; WO1997014513A1

Description

The invention relates to a device and apparatus for classification and separation of particles in cereal milling process. Particularly the separation of particles is separation of bran and germ particles from endosperm particles, which are obtained milling wheat. The final product is for example flour and/or semolina.

Conventionally, wheat is ground on roller mills which simultaneously remove outer bran layers and germ from the wheat berry. The ground stock leaving the roller mills is typically sifted to remove flour, as well as sorted to specific granulation ranges for either further processing on subsequent roller mills, or classification of endosperm particles with simultaneous removal of bran and germ particles. The latter classification and separation is commonly referred to as "purification", employing an apparatus called "purifier".

A known purifier apparatus comprises vibration means, a screen deck, for sieving the particles, and a plurality of second vacuum chambers arranged above the screen deck to achieve a laminar air flow and to permit operation with selective air velocities between individual vacuum chamber sections. So the particles are divided into three parts: one part passing through the screen deck, a second part lifted by the laminar upward directed air flow and a third part, made of the heavier and larger particles which cannot pass through the screen deck and cannot be lifted.

Actual classification and terminal velocity separation begins with the entry of the product bed into the vacuum chamber, leaving the solid bottom feeding channel and moving onto the screen deck of sieve housing. The upward directed air flow, generated by the vacuum chamber passes through the screen deck and starts to fluidize the product bed, thereby sharply reducing the angle of internal friction, permitting particles of lower density to gradually migrate to the surface of the product bed. Once the low density particles are on the surface of the product bed, they can be lifted off the surface and carried up through the vacuum chambers into the air manifold, when set air velocities are exceeding their terminal velocity. Those low density particles, which are more or less imbedded within the product bed when entering the screen deck area, will have to travel horizontally until the described effect of fluidization and deck oscillation has permitted these particles to migrate to the surface for exposure to terminal velocity separation. So these known apparatuses have the problem of being less effective in separating bran and germ particles in the front section of the screen deck. Without binding to theories, a reason may in fact be the fact that in that area the particles are not correctly stratified according to density, or at least are not stratified as well as occurs in the terminal area of the screen deck. So, the common screen deck length has been established reflecting the less effective separation and classification in the front section of the known apparatus.

This is a significant disadvantage when many of these machines are in use. A solution of this problem is not easy because many variables are working. For example, simultaneaously with the horizontal travel of the particles, other movements occur: contemporaneously with the upward migration of low density particles within the screen bed, high density particles are migrating to the bottom of the screen deck and pass through the screen when exposed to a mesh opening larger than their own size. Also product stratification is augmented by externally induced oscillation, which promotes the screening action and product conveyance on the deck.

DE-U-93 07 072 describes a screening device according to the preamble of claim 1, in which the majority of a bulk material stream passes through a screen deck, leaving only foreign materials, such as metal parts or material lumps, as residuals. The objective is to reduce the required screening surface for separation purposes of latter parts. This device is not compatible to the aims of the present invention.

EP-A-0 081 087 describes a ground raw coal separator for the separation of a bulk material consisting of a fine and coarse particle first component of lower specific gravity and at least one other component of higher specific gravity. This device is not compatible to the aims of the present invention.

Particularly the above two documents comprise a fluidized bed, followed by a screen deck, but do not have an independent vacuum air source and a plurality of vacuum chambers, and necessary means of air flow adjustments, to facilitate separation of low density bran and germ particles.

EP-A-0 427 679 describes a concentrator for whole grains, that has suction air flow for fluidization of whole grains and drop-through screening. Under the drop-through zone there is arranged an improved screen deck, provided with a secondary diffuser deck. This device is not compatible to the aims of the present invention and does not have a compressed air source to facilitate separation of low density bran and germ particles.

An aim of this invention is therefore that of solving the above disadvantages with a device for the classification and separation of particles in cereal milling process comprising: connecting means to connect said device to a screen deck of a purifier, which screen deck can accomplish separation by sifting, a fluidizing bed to support said particles, a pressure chamber arranged under said fluidizing bed, a compressed gas source, a gas inlet port in said chamber for connecting said compressed gas source with said chamber; so that in said pressure chamber a pressure higher than atmospheric pressure is achieved; said fluidizing bed being gas permeable so that a gas passing through said gas inlet port and through said fluidizing bed can accomplish a stratification of said particles, according to density, characterised in that a first vacuum chamber is connected with an upper side of said fluidizing bed.

The above device can be used together with old existing purifier apparatuses, or can be assembled with new ones. So the invention also relates to an apparatus comprising the above described device and a screen deck, arranged after said device, for sieving the particles, and a plurality of second vacuum chambers arranged above said screen deck.

The invention relates also to a process for the classification and separation of particles in cereal milling comprising a first stage in which particles are stratified on a fluidizing bed operating between a compressed gas source and a vacuum and a second stage in which said stratified particles are separated by sifting. Preferably the stratification is achieved by means of terminal velocity separation. Preferably the stratification comprises bran and germ particles floating on the surface of a product bed, prior to the entry of said product bed onto a sifting step.

Preferably the fluidizing bed entails a gas flow of from 3 to 48, preferably 6 to 24 cubic meters per square meter of fluidizing bed surface and per minute.

The features of the invention will result more clearly from the following description, referred to the enclosed drawings in which:

figure 1 is a front section view of a prior art arrangement, and

figure 2 is a front section enlarged view of the arrangement according to the invention.

With reference to figures 1 and 2 the inlet port 1 of the purifier receives a product mixture consisting of endosperm, bran and germ particles of a specific granulation range. The feeder section 2 spreads the incoming product uniformly across the width of the feeding channel and conveys the so formed product bed into the processing section. Product spreading and conveying is accomplished via oscillation of the entire sieve housing 3, of which the feeder section 2 is an integral part. The oscillating means 13 are made with means per se known.

The sieve housing 3 includes preferably one to three superimposed screen decks 4. Furthermore, the sieve housing includes single or multiple collecting troughs for the screen "throughs", multiple selector valves to achieve finely divided product classifications, dedicated to specific "throughs" outlets 10. Each screen deck preferably includes four sieve frames in length, each one allocated to a specific screen mesh size.

A plurality of second vacuum chambers 5 is arranged above the screen deck 4 for lifting lower density bran and germ particles off the fluidized product bed traveling on the screen deck 4. The second vacuum chambers 5 are separated by partitions 6 to achieve a laminar air flow above the product bed and to permit operation with selective air velocities between individual second vacuum chambers sections. A second air regulating valve 7 is provided for each of said second vacuum chambers to control air quantities in individual second vacuum chamber sections.

The second valves 7 are connected with a vacuum source via an air manifold 8. Preferably a filter dust collector separates the "purifier liftings" from the air serving the purifier. The outlet 12 of air manifold 8 collects lower density bran and germ particles.

The outlet 9 collects the tail-over products 11 which have neither passed through the screens, nor have been lifted out by terminal velocity separation.

The connecting means 20 connect the feeder section 2 to the screen deck 4. The connecting means 20 are represented by a welding, but other means can be used. A fluidizing bed 15 supports the particles. The fluidizing bed 15 is gas permeable and solid impermeable. In other words, air can pass, upwards, through the fluidizing bed 15 and particles cannot pass downwards. The fluidizing bed 15 can be made for example with a mat.

A pressure chamber 16 is arranged under the fluidizing bed 15. A compressed gas source 18 is connected with the pressure chamber 16 via a gas inlet port 23. Particularly the gas source 18 is connected with the pressure chamber 16 by means of a valve 17, preferably a flow control valve. So that in said pressure chamber 16 a pressure higher than atmospheric pressure is achieved, and so that a gas passing through said gas inlet port 23 and through said fluidizing bed 15 can accomplish a stratification of said particles, according to density. Particularly valve 17 allows a precise air volume adjustment to a preset fluidization level of the particles, where density stratification is achieved without expelling particles above the product bed.

A first vacuum chamber 24 is connected with an upper side of the fluidizing bed 15. The first vacuum chamber 24 is connected with an air manifold 8 via a flow control valve 25.

The invention achieves at least the following advantages:

The classification and terminal velocity separation process is improved and/or shortened by eliminating the horizontal travel of un-stratified high density endosperm particles and entrained low density bran and germ particles within the second vacuum chambers 5. The device according to the invention presents a fully stratified product bed at the entry point of the second vacuum chambers 5.

The air volume of the purifier, for the purpose of terminal velocity separation can be reduced, by reducing the length of the second vacuum chambers 5.

The required floor space of the purifier can be reduced by reducing the overall length of the purifier.

Claims

A device for the classification and separation of particles in cereal milling process comprising: connecting means (20) to connect said device to a screen deck (4) of a purifier, which screen deck can accomplish separation by sifting, a fluidizing bed (15) to support said particles, a pressure chamber (16) arranged under said fluidizing bed, a compressed gas source (18), a gas inlet port (23) in said chamber for connecting said compressed gas source with said chamber; so that in said pressure chamber a pressure higher than atmospheric pressure is achieved; said fluidizing bed (15) being gas permeable so that a gas passing through said gas inlet port (23) and through said fluidizing bed (15) can accomplish a stratification of said particles, according to density, characterised in that a first vacuum chamber (24) is connected with an upper side of said fluidizing bed.
A device according to claim 1 in which said gas source (18) is connected with said pressure chamber by means of a valve (17).
A device according to claim 2 in which said valve (17) is a flow control valve.
A device according to at least one of the preceding claims in which said fluidizing bed (15) is solid impermeable.
A device according to at least one of the preceding claims in which said fluidizing bed (15) entails a gas flow of from 3 to 48, preferably 6 to 24 cubic meters per square meter of fluidizing bed surface and per minute.
An apparatus comprising: a device according to at least one of the preceding claims, a screen deck (4), arranged after said device, for sieving said particles, and a plurality of second vacuum chambers (5) arranged above said screen deck (4) to achieve a laminar air flow and to permit operation with selective air velocities between individual second vacuum chamber sections (5).
An apparatus according to claim 6 comprising a second valve (7) for each of said second vacuum chambers (5).
An apparatus according to claim 7 in which said second valves (7) are connected with an air manifold (8) and a vacuum source.
A process for the classification and separation of particles in cereal milling comprising a first stage in which particles are stratified on a fluidizing bed operating between a compressed gas source and a vacuum and a second stage in which said stratified particles are separated by sifting.
A process according to claim 9 in which said stratification is achieved by means of terminal velocity separation, particularly for the low density particles of the surface layer.
A process according to at least one of claims 9 or 10 in which said stratification comprises bran and germ particles floating on the surface of a product bed, prior to the entry of said product bed onto a sifting step.
A process according to at least one of the preceding claims in which said fluidizing bed entails a gas flow of from 3 to 48, preferably 6 to 24, cubic meters per square meter of fluidizing bed surface and per minute.