Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to apparatus for heating
granular materials such as, for example, mustard seeds,
peanuts, cacao beans, coffee beans, and soybeans.
Particularly in the food industry the heating of
granular materials is frequently required. Conventional heating
methods have been used and, more recently, the use o micro-
wave heating has been proposed.
It is an object of the present invention to provide
an improved apparatus for heating granular materials effic-
iently and more uniformly than previous microwave heatingmethods.
Accordingly the present invention provides an
apparatus ~or heating granular materials including an in-
clined cylindrical metal heating chamber provided with an
upper inlet and a lower outlet for said granular material,
means for rotating the heating chamber about its longitudin-
al axis, means for supplying microwave energy to the heating
chamber, a tubular portion connected to said upper inlet for
supplying said granular material to said heating chamber,
means for supplying hot gas to said heating chamber through
said tubular portion, means for supplying said granular mat-
erial to said tubular portion whereby the granular material
acts as an air lock to ensure that substantially all said
hot gas is fed to said heating chamber, the dimensions of
said tubular portion being such that the radius of the
tubular portion is less than A/3.412 to substantially reduce
the escape of microwave energy, where ~ is the freespace
wavelength of the microwave energy used.
One embodiment of theinvention will now be des-
cribed, by way of example, with reference to the singlefigure of the accompanying drawing which is a diagrammatic
representation of a microwave system for heating granular
materials.
~ Referring to the figure a cylindrical metal heating
chamber 2 is;provided and is inclined at an angle of 15-20
to the horizontal plane. An upper inlet 4 and a lower outlet
6 is provided for the heating chamber.
As shown, the lower outlet 6 is actually one of
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several discharge tubes circumferentially spaced around the
lower end of the heating chamber 2 and, in practice, feeding
into an enclosed outlet conduit 8 for collection of the
treated granular material through a discharge chute 9.
A tubular portion in the form of tube 10 is con-
nected to the inlet 4 whilst rotation o~ the heatiny chamber
about its axis is achieved by way of a drum motor, chain
drive and support bearing arrangement 12. Hot gas or air
is supplied to the free end of tube 10 from an air/gas source
14 and the dimensions of tube 10 are so designed that the
radius of the tubular portion 10 is less than ~/3.412 to
substantially reduce the escape of microwave energy where
is the freespace wavelength of the microwave energy.
The granular material is fed into tube 10 from a
hopper 16 by way of a substantially vertical feed tube 18.
A feed motor 20 controls rotation of a paddle mechanism 22
to ensure feeding of the granular material 24 to the chamber
2 at a controlled rate. ~s will ~e evident, the granular ma-
terial itself acts as an air lock to ensure that substantially
all the hot gas is fed to the heating chamber 2. After heat-
ing, the granular material is discharged through the plurality
of radial discharge tubes 5. The material may become airborne
within the drum, to produce better drying of the material.
The cylindrical metal heating chamber 2 is provided
with thermal insulation 26 to reduce heat loss to the surround-
ings and also with an internal structure arrangement 28, made
of Teflon*, ceramic or metal, to control the flow of granular
material through the apparatus. The internal structure ar-
rangement provides better mixing and consists basical]y of a
plurality of concentric rings and longitudinal strips to
form pockets or compartments. The preferred material for the
structure is Teflon* but in caseswhere extremely high temper-
atures are anticipated metal may be used if care is taken to
avoid sharp edges which could result in electrical breakdown.
Thus, there is provided a cascading rotary processor consisting
of an inclined rotating cylinder with an internal structure
to control the tumbling action and product movement through
the drum. Product residence time is primarily a function of
* Trademark
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the rate of rotation of the drum for a given incline and
internal structure. Feed rate is controlled separatelv.
As shown, microwave energy from a source 30 is
supplied through an axially located tube 32 and teflon
window 34 to the interior of the chamber 2~ A rotating
joint and choke arrangement 36 is provided at the junction
of tube 32 and chamber 2 to prevent microwave leakage.
The drum forms a multi-mode cavity and hence its dimensions
are not critical. The dimensions of the discharge tubes 6
and the loading tube 10 are such that microwave energy
cannot escape. The principle of "waveguide beyond cut-off"
is utilized to prevent leakage, resulting also
in a simpler mechanical arrangement.
In use, the granular material is fed into the
hopper 16 and thence through tube 10 to the interior of
revolving drum 2. After suitable heating and treatment by
the microwave energy, the material exits through the lower
outlets 6. The continuous tumbling of the material results
in more uniform heating thereof.
It will be seen that the above-described embodiment
provides a cascading rotary drier configuration in combination
with microwave power. The provision of an internal structure
forming "compartments" facilitates control of the flow of
material through the processor whilst the use of the product
to form an "air lock" ensures that substantially all the
process air or gas is fed to the processing drum. One unit
operated successfully with microwave energy at 2450 MHz and
at power levels up to 12 Kw but it will be' understood that
these values are in no way restrictive. The processor was
useful in dealing with, for example, the inactivation of
myrosinase enzyme in mustard seed, destruction of nematospora
in mustard seed, destruction of tripsin inhibitor in soybeans,
and the destruction of aflatoxins in peanuts.
The compartmental structure used resulted in a
well-controlled flow rate which is particularly advantageous
and has been difficult to achieve with other apparatus~
The apparatus could conveniently, without much modi-
fication, be used in a variety of different applications
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such as drying, roasting, enzyme inactivation, pasteuriza-
tion or sterilization.
In use it was found that a processor utilizing a
drum 1 ft in diameter, 36 in. in length, rotating at about
1 RPM and operating at a power level of 5.5 Kw at a frequency
of 2450 MHz was capable of processing mustard seed for the
purpose of inactivating the myrosinase enzyme at a rate of
60 kg per hour.
It will be readily apparent to a person skilled
in the art that a number of variations and modifications
can be made without departing from the true spirit of the
invention which will now be pointed out in the appended
claims.
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