Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS FOR CLEANING AND DESTONING PARTICULATE FOODS
MELD OF THE INVENTION
This invention relates to the cleaning of particulate materials that are
slightly
heavier than water, with a specific gravity (20/20°C) range of 1.01 to
2.01 and
thus readily sink in water, by the removal of foreign particulate objects that
are: 1. lighter than water and thus float, 2. are of such size and shape as to
sink very slowly albeit being heavier than water, and 3. are much heavier than
water and sink rapidly in water. The applications of this invention are in the
fields of cleaning dry or water soaked beans, peas, grain or other foods by
the
removal of stones and other heavy foreign objects such as metal pieces, glass
pieces, etc., and also, by the removal of light debris such as plant leaves
and
stems. bean pods, soil, grain dust, etc.
DESCRIPTION OF PRIOR ART
Processes for the cleaning of granular materials are numerous and well known.
In the food industry, dry beans are processed through ~destoners', where water
flowing over a pan with V-shape corrugations, carries the beans over the peaks
of the V's, while the stones are caught and remain in the valleys of the V's.
Another version of the common destoners is the 'Riffle Board' with inclined
baffles on a flat surface, where flowing water carries the beans over the
baffles,
while the stones are trapped between the baffles. Yet another variation for
destoning with water consists of a shallow cyclone of water in which the beans
are introduced in the vortex, the stones travel down to the bottom with the
centrifugal force, while the beans are carried upward and out by overflowing
water. Such devices have high energy consumption because of the many
obstructions provided for the water to flow, and have a very limited capacity
for
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stones, and often misperform if the water velocity is not well controlled and
maintained uniform across the width of the pan. Periodic discrarge of the
collected stones is necessary and some loss of beans occurs with the stones
discharged. The aforementioned devices are not capable of removing light
debris that floats or settles very slowly, e.g., plant leaves and stems, bean
pods,
soil, grain dust, dead insects etc., from the desired product. Such light
debris
often constitutes a major portion of the impurities in food particulates such
as
beans and peas.
US Patent 4,913,803 describes a process for the separation of similarly sized
particles having different terminal velocities. A sieving step is carried out
first,
to remove smaller and/or larger particles to produce a mixture of 'similarly
sized' particles. Except for the mixtures of anion and cation exchange resins,
which are nearly perfect spheres of nearly the same size, as cited, the
principles of US Patent 4,913,803 can not be readily applied to natural
granular materials such as peas and beans, which have a wide range of particle
shapes and sizes. Furthermore, there is no provision to remove particles that
have no 'terminal velocity', i.e., that do not sink in water.
US Patent 4,784,757 describes an apparatus for the separation of mineral ores
of different specific gravities. Water is used to separate materials that have
a
lower settling velocity from those that have higher settling velocities, thus,
dividing the starting material into two or more fractions heavier than water.
No
provision is made to separate materials that have very low, or no settling
velocity.
US Patent 3,097,159 describes an apparatus using water, for the cleaning of
granular materials, such as wheat, where the particulates are well mixed with
water with agitation, then separated into fractions of different densities via
froth flotation in a centrifuge. US patent 4,466,542 uses fluidization of
grains
and cereals with air to separate those into light, medium and heavy grain
fractions.
z
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It would be quite advantageous to have a food cleaning apparatus that is
simple to construct and easy to operate and maintain, can operate with low
energy and water consumption, and has high reliability in separating the light
particulates, e.g., plant leaves and stems, dead insects, grain dust etc. and
heavy particulates, e.g., metal and glass pieces, stones etc., from the
desired
medium density range food particulates.
SUMMARY OF TIDE INVENTI
Particulate material, such as dry peas or beans, herein referred to as feed',
is
introduced into a column with stagnant water, or water flowing upwardly at a
very small velocity, so that materials that float or sink very slowly in
water, are
carried up to the surface of the water in that column, and accumulate there in
case of stagnant water or, are removed from the column via a small flow of
water taken over a weir or stand pipe which carries such floating material out
of the column. The heavier particles flow downward and enter a second column
where water is flowing upwardly at a velocity sufficiently high to carry the
desired particulates, such as peas and beans upward, while the heavier
particulates such as stones, glass and metal fall to the bottom of the second
column. Air may be introduced as small bubbles, in the first column to assist
in the upward movement of the light particulates, based on the well known
principles of froth floatation. Discharge of water from the apparatus occurs
through weirs, dams, stand pipe etc., which maintain the overflow from a water
level at atmospheric pressure.
DESCRIPTION OF SHE DRAWING
Figure 1 is a schematic illustration of apparatus embodying one form of the
invention. Figure 2 is a schematic illustration of apparatus embodying a
second form of the invention.
DETAILED DESCRIPTION
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Refernng to Figure 1, the apparatus consists of two nearly vertical columns 1
and 2. Column 1 is connected to column 2 through an entry port 3 which is
below the top of column 2 and at least 6 inches above the bottom end 4 of
column 2, such that particles falling through column 1 will enter column 2 at
some point between the top and bottom of column 2. Water inlets 5 and 6,
allow water flow to be introduced into column 2 at points between port 3 and
bottom end 4. Water may be introduced through just one or a multitude of inlet
points. The bottom of column 2 has provisions that allow for the removal of
heavy particles collecting there, either on a continuous basis via mechanical
means, such as a bucket elevator or an auger, or intermittently, via a clean
out
plug or a discharge valve 14, as shown.
Heights of the water levels 8 and 9 in the two columns are such that when
water flow is initiated, most or all of the incoming flow goes out through
weir
7, as shown, at the top of column 2. Effective height of water level 9 in
column
1 is somewhat greater than that of the water level 8 in column 2, so that
water
flows out either mostly or entirely through the top of column 2, while a stand
pipe 11 as shown, or a weir of adjustable height allows a small flow or no
flow
of water through the top of column 1. It will be noted that flow of water out
of
the apparatus occurs from water surfaces that are at atmospheric pressure,
avoiding energy losses that occur when control devices such as valves are
used,
and reducing the cost of the apparatus.
Water is introduced through lines 5 and 6 at a rate such that the desired
particles viz., beans, peas etc. are carried upward with the flow of water,
while
the undesired heavier particles such as stones and metal pieces continue to
fall
and collect at the bottom 4 of column 2. The average water velocity through
the
cross section of column 2 will preferably be in the range of 5 to 200 cm/ sec
while that through column 1 will preferably be in the range of 0 to 20 cm/sec.
A more preferable average velocity range is 6 to 50 cm/ sec through column 2
and 0 to 10 cm/ sec through column 1. The average water velocity through
column 2 must always be higher than that through column 1. The suitable
water velocity through each column is dependent upon the size, shape and
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density of the desired particulates as well as those for the impurities being
removed, and is also somewhat dependent upon the density of the water being
used. The diameter of each column can be as large as necessary to obtain the
desired production rate, but it should preferably be at least 1 cm for each
column and more preferably, at least eight times the average projected
diameter of the desirable particulates. It is also preferable that either the
entire
columns 1 and 2, or at least parts thereof, be made of transparent material
for
visibility through the column. It is to be understood that the columns may
have
cross sectional forms other than circular, e.g., rectangular or oval.
To start the cleaning process, a flow of water is established through lines 5
and
6, at the desired rate, thereby establishing a water level 8 in column 2 and 9
in column 1. Most or all of the in-flowing water flows out of column 2 via
outlet
10, as shown. Height of the weir or stand pipe I 1 in column 1 is adjusted so
as to get the desired overflow of water out of column 1. Water level 9 in
column
1 will be slightly higher than level 8 in column 2, because most or all of the
flow will be through column 2.
Feed is introduced into column 1 via line 12. Column 1 may have an enlarged
hopper like open end, as shown, which will facilitate introduction of the feed
particles, as well as provide lower linear water velocity, so as not to carry
upward, particles that are expected to sink. It is preferable that line 12 dip
below the surface of water 9 as a dip leg, to minimize disturbances on the
surface of water in column 1. Particles that float or sink very slowly, float
up
to the surface of water in column 1, whence, a small discharge of water,
carries
those materials out. In case of no water being removed from column 1, such
light particles will accumulate at the surface of water there. In operations
where the amount of light particles to be removed per batch is small, it may
be
desirable to let those particles accumulate at the surface, to be removed at
the
end of the run. In extended runs, or in case the feed contains significant
amount of light particles, continuous removal of the light particles will be
necessary, as otherwise, those particles will build-up in the feed
introduction
area, and may even plug up the lines, or will be purged from the apparatus
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along with the desirable particles in the second fraction, thus re-
contaminating
the desired food particulates.
Depending upon the nature of the material to be cleaned, for example, in
cleaning wheat where there is much dust, it would be desirable to introduce a
small flow of air in column 1, via line 13 and below the water level 9, to aid
in
the upward movement of the fines, based on the principles of froth floatation.
The upward-traveling air bubbles resulting from air flow help carry the light
fraction upwardly to the water surface.
Particles that sink through column 1, enter the upward flowing water stream
in column 2, where depending upon the water velocity, a separation of lighter
and heavier particles occurs, with the lighter particles flowing upward and
exiting the apparatus with the overflowing water, while the heavier particles
settle to the bottom 4. Water velocity is adjusted so as to allow for most of
the
desired particles to be carried up and out by the flowing water. Because of a
significant difference in the settling velocities of the desired particles,
viz.
beans, peas etc. and those for the undesired foreign matter, e.g., stones,
metal
and glass particles etc., it is not particularly difficult to adjust the water
flow
as to obtain the desired separation. Water velocity required to effect the
desired
separation is different for different species of beans, peas, etc. because of
the
differences in the projected cross-sectional areas and densities of the
different
species, which in turn cause differences in settling velocities. It would be
preferable to operate at water velocity such that some of the desired
particles
sink a short distance after entering column 2, before those are picked up and
carried back-up by the flow of water.
Particles that are carried out with the flowing water are separated from the
water, which may be recycled or purged. Conventional de-watering devices
such as vibrating screens are used to separate the desired particles from
water,
producing clean particles free from foreign objects.
Heavy particles that settle to the bottom 4 in column 2 are either
continuously
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or periodically removed from the apparatus by suitable means, such as pointed
out hereinabove.
In a second embodiment of the invention, schematically shown in Figure 2,
column 1 is located within column 2, providing an annular space between the
two columns, with the feed particles dropping through the inner column 1 into
the upward flowing water stream in column 2, which flows upward through the
annular passage surrounding column 1. While this arrangement is workable,
the embodiment of
Figure 1 which includes the laterally spaced columns is preferred because
there is no velocity change caused by the change in cross-sectional area
available for the flow of water when the two columns are separate, as would
happen with the two concentric columns, where the flow of water is through
the entire column 2 until it reaches the annulus, which is of smaller cross-
sectional area, thus increasing the water velocity through the annulus. In
Figure 2, the opening 3 at the lower end of column 1 is considered to be the
entr-~~ port to column 2, which port is located between the upper and lower
ends
of column 2.
While I have shown and described particular embodiments of my invention, it
will be obvious to those skilled in the art that various changes and
modifications may be made without departing from my invention in its broader
aspects; and I, therefore, intend herein to cover all such changes and
modifications as fall within the true spirit and scope of my invention.
