Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates primarily to food
processing equipment, and, more particularly, to a continuous
flow system for controlling the moisture content and sulphur
dioxide concentration of food products and more specifically
fruits and vegetable products. The invention may also be
utilized in processing other products where the control of
moisture is required and the process may further be adapted
to adding other ingredients within the same equipment wherein
the moisture equalization is achieved.
Description of the Prior Art
Existing processes for controlling and equalizing
the moisture content and/or sulphur dioxide concentration of
dehydrated apple products are "batch" processes in which
discrete quantities of product such as apples, are sequentially
processed as a unit. A batch of product in range from 2,000
to 12,000 pounds is initially dried to a moisture content
that is lower than the accepted market level which is
greater than 14 to 16% but usually about 23%. This overdrying
is necessary since fluxuations in moisture content cannot be
allowed to exceed the accepted market level or target value
` since there are no provisions in conventional equalization
processes for accurately reducing the moisture content to a
specific value. At the same time, the concentration of sulphur
dioxide in the product is reduced below the target value. After
drying, the batch of product is stored in stationary piles or
large revolving drums, and the batches are allowed to sit with
or without agitation for a period of time usually between 8
and 48 hours. This storage period allows moisture within the
batch to migrate from high to low levels until an overall
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equilibrium is reached. It is this rnigration process that
is conventionally referred to as "equalizing". After the
moisture content and sulphur dioxide concentration of the
batch has been equalized, the moisture content of the batch
is raised to the target value by the addition of water. This
is accomplished by spraying water onto stationary piles of
product. An additional equalizing step is sometimes used
after the moisture content of the product has been raised.
Either shortly before or directly after the moisture content
of the product has been adjusted to the target value, the
sulphur dioxide concentration is also adjusted in a batch
process. This is usually accomplished by the injection of
gaseous sulphur dioxide, with or without tumbling, or by
placing the product in a chamber in the presence of burning
rock sulphur. The product may then be allowed to further
equalize for a period of time before being packaged for
shipment. In summary, conventional processing techniques
first batch dry the product below the target value, and then
batch moisturize the product to the target value.
The principal disadvantages of a batch type process
are its long process time and high cost. Batch processing
` systems do not lend themselves to automation so that product
measurements and subsequent manipulation must generally be manually
accomplished. Furthermore, the processing times for such batch
~; type processes frequently run to as long as 40 hours.
Consequently, the capital costs for processing high volumes
of products is exceedingly large. Additionally, batch type
re-drying processes require high unit costs and they are
often detrimental to product quality.
SUMMARY OF THE INVENTION
-- It is an object of the invention to provide a system
for equalizing the moisture and when required the sulphur
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dioxide content of moisture absorbing products which can be
readily automated with relative ease thereby reducing the cost
of processing the product.
It is another object of the invention to provide a system
for equalizing the moisture and sulphur dioxide content of
moisture absorbing products which requires a relatively short
processing time thereby increasing the throughput of such
systems.
It is still another object of the invention to provide a
system for controlling and equalizing the moisture and sulphur
dioxide content of food products which consistently produces
products of uniformly high quality.
These and other objects of the invention are accomplished
by initially increasing the moisture content and sulphur dioxide
concentration, if required, in raw food products above a pre-
determined target value. For this purpose, food product in chip,
diced, extruded or comminuted form are directed into a rotating
steaming reel containing a high humidity and sulphur dioxide
environment. The humidified product is then transferred to a
drying reel either directly or subsequent to a short mixing stage,
in which the moisture content of the product is reduced to a
predètermined target value. The processed product is then
packaged either directly or subsequent to a short mixing stage.
It is important to note that the product flows continuously
through the processing system, and the rate of travel as well as
the operating parameters of the system are adjusted as a
function of continuous measurements performed throughout the
system. The process is especially adapted to processing fruit
products such as apples, but may be adapted to process various
fruit and vegetable products. The same inventive concept and
equipment is readily useable and adapted for controlling
moisture in products such as wood fibers, straw and other
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moisture absorbing products wherein control of moisture
content is required.
BRIEF DESCRIPTION OF THE EIGURES OF THE DRAWINGS
Fig. 1 is an isometric view of the equalizing system
showing the steaming and drying reels.
Fig. 2 is a side elevational view, partially cutout,
of the steaming reel.
Fig. 3 is an end elevational view of the steaming reel
taken from the infeed end.
Fig. 4 is an end elevational view of the steaming reel
taken from the discharge end.
Fig. 5 is a transverse cross-sectional view of the
drying reel.
Fig. 6 is a detailed view of the steaming and drying
reel structure.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The equalizing system, as illustrated in Fig. 1,
includes a steaming unit 10 and a drying unit 12 which are
substantially similar in structure to each other. The product
to be treated in the desired form is loaded into the steaming
unit 10 by an infeed conveyor 14, and the humidified product
is transported from the steaming unit 10 to the drying unit
12 by an intermediate conveyor 16. The moisture content of
the product carried by the intermediate conveyor 16 is
continuously measured by a conventional infrared moisture
sensor 18 in order to automatically and continuously adjust
the operating parameters of the steaming unit 10. Finally,
product having a predetermined moisture content and sulphur
dioxide concentration is carried from the discharge end of
the drying unit 12 by a discharge conveyor 20. The moisture
content of the product carried by the discharge conveyor 20
is also measured by an infrared moisture sensor 22.
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The steaming or moisture increasing unit 10 includes
a steaming drum 24 rotatably mounted in a frame 26 and driven
by an electric motor 2~ through a transfer box 30 and a sheave 32
mounted on a support axle 34 ~or the reel 24. An exhaust hood
36 overlies the steamillg unit lO to prevent sulphur dioxide
and steam from building up inside the building tnot shown)
housing the steaming unit 10 and drying unit 12. A tubular
exhaust conduit 38 vents the exhaust hood 26, and a pair of
vent pipes 40 extend between the steaming reel 2~ and the
exhaust hood 36.
The product entering the steaming unit 10 will generally
have a moisture content below the predetermined target value
which, for apples, is about 23%. However, under certain
circumstances the moisture content of the product may exceed
the target value. In either case the moisture content and
sulphur dioxide concentration of the product is raised above
the target value by injècting steam and sulphur dioxide carried
by the steam into the reel 24 as illustrated in greater detail
below. For example, for apples having a moisture target value
of 23~, the moisture content of the product leaving the steaming
unit 10 will generally have a moisture content of about 25~.
This "overshooting" is desirable since it allows the moisture
content to be reduced to the target value by subse~uent drying.
The high sugar content of apples and other fruit products causes
the product to become quite sticky when moisture is added. This
results in adherence to equipment surfaces and very poor
transfer qualities. By increasing the moisture content of
the product above the target value, the subsequent drying
removes surface moisture and tends to seal the surface of the
product so that the final product is less sticky. The increased
moisture content also allows better penetration of the sulphur
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;~ dioxide into the product. Thus moisture is added to the
product even where the moisture content of the product entering
the steaming unit 10 is at or above the target value. In addi-
tion to sealing the surface of the product by steaming and
then drying, the steam must be used to adjust the sulphur
dioxide concentration of the product even when moisture content
is at or above the target value. Since the sulphur dioxide
is carried by the steam, it would not be possible to adjust
the sulphur dioxide concentration upwardly without also increasing
the moisture content of the product. As the steaming reel 24
continuously rotates the product contained therein is continuously
mixed thereby causing the moisture content and sulphur dioxide
concentration of the product to equalize so that the product
leaving the steaming unit 10 is relatively uniform in moisture
content and sulphur dioxide concentration. The rotational
speed of the drying reel 24 as well as the temperature, moisture
content and flow rate of the steam entering the unit 10 is
adjusted either manually or automatically under the control of
the moisture sensor 18 in order to provide the desired operating
characteristics. In general, steam flow may be altered by
valve adjustment, and sulphur dioxide flow may be adjusted
by flow meter adjustment. The required sulphur dioxide
- concentration is determined by testing the end product in
the laboratory and increased or decreased as required.
Product discharged from the steaming unit 10 is carried
to an infeed chute 42 of the drying unit 12 by the intermediate
conveyor 16. The drying unit 12 is substantially identical
to the steaming unit 10. The differences between the units 10,
12 are that the exhaust hood 56 of the drying unit 12 is mounted
directly on the frame 26 over the reel 24 whereas the exhaust
hood 36 of the steaming unit has a closed bottom and is connected
to the closed top of the frame 26 through pipes 40. Also,
the drying unit 12 includes an air inle~ duct system as explained
hereinafter, and this duct system is not found in the steaming
unit 10. Consequently, identical reference numerals are used
in the two units 10, 12 to designate identical structures. I-Iot
air is injected into the drying unit 12 through a duct system
including an inlet duct 44 connected to a transition piece 46
by a flexible boot 48. Air is drawn into the ducting by a
conventional roof mounted fam 50 and is heated by a conventional
hurner 52, preferably fired by natural gas, and conducted to
the transition piece 46 through a cylindrical conduit 54. The
product entering the drying unit 12 will have a fairly uniform
moisture content considerably in excess of the target value.
The hot air flowing through the continuously mixing product
reduces the moisture content to the target value as measured
by the moisture sensor 22. The residence time of the product
in the drying is a function of the rotational velocity of
the drum 24, the angle of inclination of the drum 24 and the
size of the exit port which is adjustable. The moisture sensor
22 can be used to automate the operating characteristics of
the drying unit 12 to automatically achieve a desired quantity
and uniform moisture content in the product. The hot,
humidified air leaving the drying unit 12 is collected by
an exhaust vent 56 integrally formed with the housing 26 and
conveyed to the atmosphere outside the building through a
tubular vent pipe 58.
The structure of the steaming and drying units 10, 12,
respectively, is illustrated in greater detail in Figs. 2 and 3.
The housing 26 is supported by upstream and downstream legs
60, 62, respectively. The downstream legs 62 are pivotally
secured to the frame 26 thereby allowing the height of the
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upstream legs 60 to be adjusted in order to alter the inclination
of the reel 24. Initial tests performed during the installation
`~ of the unit lO, 12 are used to determine the optimum angle of
inclination of the reel 24 in order to achieve the optimum resi-
dence time of the product in the reel 24. The height of the
legs 60 is then fixed by sultable means. As best seen in
Fig. 1, the exhaust pipes 40 of the steaming unit 10 are flexible
thereby allowing the lonyitudinal and vertical position of the
frame 26 to vary slightly during this adjustment. The product
conveyed by the inlet conveyor 14 (Fig. l) is loaded into an
inlet hopper 42 which directs it into the reel 24. Inspection
access to the reel 24 is provided through doors 64 in the housing
; 26, and cleaning access is provided through side panels 66
pivotally secured to the housing 26 at 68 and secured at 70.
The reel 24 is fabricated, as best illustrated in Figs. 5 and
6, from a screen 72 connected to the axle 34 through rigid
spokes 74. The screen 72 is pivotally secured at 76 to the
spokes 74 at one side thereof, and removably clamped to the
spokes 74 by releasable clamp 78 at the other end thereof.
Thus access to the inside of the reels 24 may be obtained by
opening the panels 66 and pivoting the screen 72 outwardly.
An elongated plate 80 projecting slightly beyond the outer
periphery of the reel 24 prevents the flow of steam or hot
air around the periphery of the reel 24 thereby causing the
steam or hot air to flow through the interior of the reel.
` The discharge structure for the steaming unit lO and
drying unit 12 is best illustrated in Fig. 4. The ends of
the reels 24 are closed by a top panel 82 and a pair of
discharge doors 84 for adjusting the size of the discharge
opening 86. The doors 84 contain annular arcurate slots 88
having a fixedly mounted stud 90 extended therethrough
so that the doors 84 may be rotated about the shaft 34. The
position of the doors 8~ depends upon specific operating
characteristics of the steaming and drying units, 10, 12,
respectively including the temperclture of the steam or hot
air entering the unit, the characteristics of the product
and the rotational speed of the drum. Product passiny through
the discharge opening 86 is directed to a conveyor 16 in the
case of the steaming unit 10 or 20 in the case of the drying
unit 12 by a discharge chute 92.
A steam inlet 94 is positioned near the bottom of the
housing 26 of the steaming unit 10, but the inlet 94 is
not included in the drying unit 12. As best illustrated in
Fig. 4, but also shown in Fig. 3, the shaft 34 is rotatably
mounted on the frame 25 by a bearing 96 which is secured to a
frame cross member 25 by bolts 98.
The improved moisture control and equalizing system
is thus capable of quickly and inexpensively processing moisture
absorbing products which require a uniform and consistent
moisture content and if required, the sulphur dioxide content
may be simultaneously regulated by utilizing a continuous
process instead of the conventional batch process, and by
first increasing the moisture content and sulphur dioxide
content of the product beyond the final or target value
and then reducing the moisture content and sulphur dioxide
concentration to the target value. As previously stated the
same basic equipment and mode of operation may be used on
various products wherein it is required to equalize and
control the moisture content of the end product. The equipment
employed and the overall system are also adaptable for use
in adding solids, preservatives, nutrients and other substances
during moisture equalization treatment.
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