Note: Descriptions are shown in the official language in which they were submitted.
~219878
E~ERGY EFFICIE~T CONTINUOIJS
RENDERING SYSTEM -
WILLIAM F. SCHOTTELKOTTE
This invention relates to the dry rendering of
S animal, fish and poultry hy-products, and has to do more
particularly with a continuous rendering system wherein
the raw materials are continuously processed as opposed to
being processed on a batch or step-by-step basis.
BACKGROUND OF THE INVENTION
The present invention is based on the type of
continuous rendering system taught in U.S. Patents Nos.
3,506,407 and 3,673,227 which teach a simplified
continuous rendering system wherein the raw materials,
upon being initially hogged, are subjected to a single
cooking and blending operation. While systems in
accordance with the subject patents are in widespread use
and have been highly successful, their overall efficiency
has decreased due to the ever increasing cost of the
energy required to operate them. Consequently, anything
which can be done to decrease energy consumption will
result in substantial savings in the operation of the
system.
In addition to the use of cookers to release the fats
from the ma~erials being processed, various types of
evaporators have been used for such purpose, either alone
or in series, with the materials moving from one
evaporator to another as the rendering operation proceeds.
While evaporators are energy efficient, they nonetheless
require much finer grinding of the raw materials than does
a cooker, and consequently their overall energy efficiency
is diminished, particularly where the nature of the raw
materials is such that a substantial amount of energy must
be expended to initially process the raw materials for
introduction into the evaporators.
The present invention contemplates the utilization of
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both a cooker and an evaporator, together with an initial separa-
tion of the raw materials in a manner which requires substantially
less energy than would be required utilizing either cookers or
evaporators alone.
SUMMARY OF THE INVENTION
The invention provides in combination in a system for
the dry rendering of raw materials in the form of animal, poultry
and fish by-products to produce fat and tankage:
a. hogger means for initially reducing the raw materials to
chunks and pieces,
b. heating means for heating the chunks and pieces from
the hogger to form a slurry,
c. press means for dividing the heated slurry into two
fractions, the first fraction comprising free-run fluids and soft
moisture bearing material, and the second fraction comprising the
oversize,
d. evaporator means for receiving the first fraction from
said press means and for partially dehydrating the first fraction,
e. a cooking vessel having an inlet end and an outlet end,
f. means for collecting moisture vapor generated in said
cooker and introducing the collected moisture vapor into said
evaporator to serve as a heat source for said evaporator,
g. means for delivering both the partially dehydrated first
fraction from said evaporator and the second fraction from the
press means into the inlet end of said cooking vessel, and
h. separating means for receiving cooked materials discharg-
ed from the outlet end of said cooking vessel, said separating
12198~78
- 2a -
means acting to separate the fat from the cooked material.
From another aspect, the invention provides a process
for the dry rendering of raw materials in the form of animal,
poultry and fish by-products to produce fat and tankage, comprising
the steps of:
a. initially reducing the raw materials to chunks and pieces,
b. heating the chunks and pieces to form a heated slurry,
c. pressing the heated slurry to separate it into a first
fraction comprising free-run fluids and soft moisture bearing
material, and a second fraction comprising the oversize,
d. partially dehydrating the first fraction in an evaporator,
e. introducing the partially dehydrated first fraction and
the second fraction into a cooking vessel and admixing and cooking
the fractions in the cooking vessel, including the steps of
collecting moisture vapor generated in the cooker and utilizing
the collected moisture vapor as a heat source for the evaporator,
and
f. removing the cooked material from the cooking vessel
and separating the fat from the cooked materials.
The raw materials are preferably heated to a temperature
in the range of 130-205F to form the slurry.
The second fraction from the screw press, i.e., the
"oversize", is conveyed directly to a cooker, preferably of the
type disclosed in the aforementioned United States Patent Nos.
3,506,407 and 3,673,227. A significant feature of the invention
resides on the fact that the first fraction, after being partially
12~9i~7~3
- 2b -
dehydrated in the evaporator, is also conveyed to the cooker
wherein it is admixed and blended with the second fraction and
the blended fractions maintained for a residual time sufficient
to break down the protein cells and free the fats therefrom,
which is
1219~78
accompanied by the release of moisture from the blended r
fractions. The released moisture is collected and
introduced into the evaporator where it serves as t~e heat
source to effect the initial dehydration of the first
Sfraction. Thus a primary saving in energy is effected by
utilizing the moisture generated during the cooking
operation to operate the evaporator, the evaporator being
operated under vacuum to thereby lower the boiling point
of the moisture in the first fraction. Efficiencies are
10also realized in the operation of the cooker in that
cooking time is a function of the amount of moisture which
must be rem~ved from the materials being cooked. Since r
the materials introduced into the cooker will have a p
reduced moisture content due in part to the initial
15pressing of the slurry which removes some of the moisutre
from the second fraction and in part to the partial
dehydration of the first fraction in the evaporator, the
reduced moisture content of the materials being cooked
will require less cooking time and hence less energy in
20the form of heat required to complete the cooking cycle.
A secondary, yet important, savings in energy results
from the use of a screw press to effect separation of the
raw materials, as opposed to the use of additional hoggers
or other types of mills to reduce the materials to a
25condition in which they can be fed to the evaporator. For
example, a press of a size suitable to form the required
fractions at a throughput rate of about 24,000 pounds per
hour requires a 50-75 horsepower motor, whereas comparable
hoggers or mills require a 300-600 horsepower motor.
Upon the heating of the mixture in the cooker to the
desired end point temperature, the mixture is discharged
into a draining device where the free-run fat may be
separated from the solids by means of gravity drainage.
Since the drained fat will contain residual solids, a
sediment tank is provided in which the heavier solids are
~Z19~7~
removed, the partially clarified fat being pumped to a
decanting type centrifuge where remaining residual solids
are removed. The residual solids discharged from th~
draining device, together with the solids recovered from
the sediment tank and from the centrifuge, are conveyed to
a finishing press wherein the solids are compacted into a
cake. Any residual fats recovered during the final r
pre~sing operation are returned to the sediment tank for
further clarification.
DESCRIPTION OF THE DRAWING
FIGURE 1 is a schematic view of a dry rendering
system in accordance with the invention.
FIGURE 2 is a fragmentary schemat~c view of a portion
of the system illustrating a modification in the manner in
which the initially hogged material is heated to form a
slurry.
FIGURE 3 is a fragmentary schematic view of another
modification in the manner in which the initially hogged
material is heated.
DESCRIPTION OF THE PREFERRED EMBODIME~T
An important feature of the present invention resides
in the utilization of essentially conventional rendering
equipment, and to this end the system of the present
invention is particularly adapted for the retrofitting of
existing systems utilizing continuous cookers and/or
evaporators to achieve material savings in energy
consumption, both steam and electrical. The principles of
the invention also may be applied to systems utilizing
batch cookers, an essential consideration being to
effectively increase the throughput of the system per unit
of time, thereby decreasing the amount of energy required
to process a given volume of materials.
The raw materials to be processed are initially
collected in a raw material bin 1 having screw conveyors 2
which convey the raw materials to an inclined screw
~'19~7B
conveyor 3 which delivers the raw materials to an
electromagnet and chute assembly 4 for the separation of
tramp metal, the raw materials falling directly fro~ the
chute assembly 4 into a hogger 5 which acts to reduce the
raw materials to the desired mean particle size.
Preferably, the hogger will reduce the material particle ,~
size to chunks and pieces approximating 1/2 to 3/4" cubes
with no pieces larger than about a 3" cube.
In the embodiment illustrated in FIGURE 1, the sized
raw materials from the hogger S are transported to a
slurry tank 6 wherein a sufficient amount of hot recycled
fat is admixed with the sized raw materials to provide a
pumpable slurry. In this connection, it will be
understood that the addition of the hot fat, which is
recycled from the fat recovered from the raw materials
being processed, acts to initially heat the raw materials
and in itself will effect the release of a portion of the
fats contained in the raw materials. Optionally, the
hogged raw material may be heated by other means, such as
by providing a steam jacket on the slurry tank 6 to which
steam is supplied through a steam conduit 7, or by using
separate raw material preheaters as will be discussed
hereinafter. The essential consideration is the provision
of a heated slurry which, in the embodiment of FIGURE 1,
ic pumped from the slurry tank 6 by feed pump 8 directly
to the screw press 9 which is preferably of the flow
through type having one or more screws of diminishing
pitch and/or increasing root diameter of the screw shafts,
the screw or ~crews being surrounded by perforated screen
or barrel bars, the arrangement being such that as the raw
materials are compacted by the screw or screws, the
perforated screen or barrel bars will permit free-run
fluids to drain from the press. As the raw materials are
compacted, the press will separate soft moisture bearing
materials from the residual solids. To this end, a
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retarding choke may be used at the discharge end of the
press.
The utilization of a screw press at this stage~ s an
important feature of the invention in that there is a
considerable savings in electrical energy due to the fact
that the screw press requires substantially less horse- -
power than other types of equipment, such as the mills
heretofore utilized to hydraulically grind the raw
materials in their own liquid, i.e., fat and moisture.
Thus, instead of utilizing the power necessary to finely
comminute the raw materials to the size necessary for
passage through an evaporator, the screw press is utilized
to obtain a first fraction composed of the free-run fluids
and soft moisture bearing materials which can be
discharged directly into an evaporator feed tank 10. The
second fraction, or "oversize" from the screw press, is
conveyed by screw conveyors 11 to the inlet end of the
cooker 12, the function and operation of which will be
discussed hereinafter.
The first fraction of raw material contained in
evaporator feed tank 10 is pumped by evaporator feed pump
13 into the tube side of the evaporator 14, which is of
conventional construction, wherein the first fraction of
free-run fluids and soft materials is heated by means of
atmospheric steam generated in the cooker 12 and conveyed
to the shell side of the evaporator by means of an
entrainment trap 15 and conduit 16. Preferably, the tube
side of the evaporator will be operated under a 26" Hg.
vacuum to lower the boiling point of the water contained
in the first fraction, and in accordance with conventional
practice, the heated fraction i~ circulated from the
evaporator 14 to the separator 17 and back through the
evaporator several times either by natural circulation or
by forced circulation. The water vapor evaporated from
the first fraction in the separator is discharged through
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121987~
conduit 18 to a condenser 19, the condensate being
discharged through conduit 20 to a sewer. Non-
condensibles from the shell of the evaporator 14 wi~ be
discharged through conduit 21 and combined with the
non-condensibles from the condenser 19 for discharge
through a conduit 22. The discharge conduit 22 may be
connected to a scrubber (not shown) to remove obnoxious
odors prior to release into the atmosphere. A vacuum pump
23 is used to draw a vacuum on the evaporator 14,
separator 17, and condenser 19. ,
After circulation through the evaporator system
several time~ the partially dehydrated first fraction is
pumped from the separator 17 by discharge pump 24 and
conduit 25, the partially dehydrated fraction being fed
through conduit 26 to the entrance end of cooker 12 where
it is introduced into the cooker along with the "oversize"
fraction from screw press 9.
In the cooker 12 the "oversize" from the screw
preCs 9 and the partially dehydrated fraction from the
evaporator 14 are admixed and heated under essentially
atmospheric pressure. PreEerably, the cooker will
comprise an elongated vessel surrounded by a steam jacket,
the vessel having a steam shaft and steam tubes rotatably r
mounted within the vessel together with agitating means to
thoroughly admix the blended fractions as they are heated
in the cooker. Alternatively, disc type or batch type
cookers may be used. When the mixture is heated to the
desired end point temperature, which is preferably about
275~F, it is discharged from the cooker by a suitable L
discharge control device, such as a variable speed bucket
elevator (not shown), onto a screw type conveyor 27 which
delivers the mixture to a drainage type screw conveyor 28 r
wherein the free-run fat is separated from the residual
solids by means of gravity drainage through a suitable
screen. The drained fat, which contains some residual
'7~3 ~
8 ~.
solids, falls into a sediment tank 29 provided with a
screw conveyor 30 arranged to remove solids collec ~d by
gravity separation. The partially clarified fat in the
sediment tank 29 is pumped to a decanter-type continuous
centrifuge 31 which acts to remove residual solids from
the fat, the fat being discharged through conduit 32 to a
fat surge tank 33. From this tank the fat may be either
recycled to the slurry tank 6 through conduit 34 or
dishcarged through conduit 35 to a fat storage tank (not
shown), or portions of the fat may be simultaneously fed
in both directions.
Residual solids from the centrifuge 31 are conveyed
by a screw conveyor 36 to the outlet side of the drainage F
screw 28 where they are combined with the residual solids
lS discharged from the drainage screw, the combined solids
beinq conveyed by a screw conveyor 37 for final pressing
in a finishing press of known construction (not shown)
which may embody an hydraulic sleeve type choke having
automatic compensating characteristics to accommodate
variations in the composition of the residual material.
Normally the final pressing operation will be conducted
under high pressure to remove residual fat which is
returned to the sediment tank 29. The solids from the
final pressing operation are compacted into a cake and
discharged from the system.
In an e~emplary embodiment of the invention utilizing
a continuous cooker having a heat transfer area of 900
square feet and operating at a steam pressure of 150 psi,
with the heated raw materials fed to the press at a
temperature of 165F. and using a vertical evaporator
having one-hundred and fifty-three tubes each with a l.78"
inside diameter and a length of 20', the system is capable
of a raw material throughput of approximately 24,360
pounds per hour utilizing raw material having a water
content of approximately 60~ and a fat content of
12~9~7~3 ~
g ~.
approximately 21%. With the cooker operating at an
endpoint temperature of about 275F, approximately ~940
pounds of water will be evaporated per hour, the moisture
vapor from the cooker being collected and utilized to heat
the raw materi~l introduced into the evaporator to a
temperature of approximately 138F under a 26" Hg vacuum,
the evaporator acting to evaporate approximately 7460
pounds of water per hour. The system output is
approximately 4580 pounds per hour of finished fat and
5380 pounds per hour of pressed cake or crax having a
water content of approximately 4%. The thermal efficiency
(pounds per steam per pound of water evaporated) of the -
system when so operated is .83. r
A material savings in energy is achieved by utilizing
a screw press to initially separate the free-run fluids
and the soft moisture bearing material from the residual
solids in that a screw press of a size sufficient to
handle the throughput of the system may be operated
utilizing a motor which requires only a fraction of the
horsepower required to operate the equipment normally
utilized to grind the raw material to a size suitable for
dehydrating in an evaporator. An even greater savings in
energy is realized in utilizing the moisture-vapor
generated in the cooker to heat the evaporator. In this
connection, at least 50~ of the moisture in the raw
materials should be sent to the evaporator for the system
to operate at maximum efficiency and fully utilize all of
the moisture-vapor from the cooker. It is only when
exceedingly dry raw materials are encountered that the
first fraction will contain less than 50~ of the moisture
in the raw materials. With the normal selection and mix
of raw materials, first fraction will contain 60~80% of
the moisture in the raw materials and optimum efficiency
will attained. When exceedingly dry raw materials are
encountered, as noted above, the system will operate
1219878
satisfactorily but optimum efficiency may not be attained.
Modifications may be made in the invention with~out
departing from its spirit and purpose. One such
modification is shown in FIGURE 2 wherein a surge bin 38
is interposed between the hogger 5 and the slurry tank 6,
the surge bin having a variable speed screw conveyor 39
for delivering the raw materials to the slurry tank, the
surge bin being provided with load cells 40 to control the
feeding speed of the conveyor 3 which delivers raw
materials to the hogger. The provision of the surge bin
facilitates the continuous operation of the system by L
controlling raw material input and ensuring the necessary
residence time in the slurry tank to effect the desired
heating of raw materials prior to their delivery to the
press.
FIGURE 3 illustrates another embodiment of the
invention wherein the raw materials from the hogger 5 are
deposited on a screw conveyor 41 which conveys the raw
materials through a preheater 42, which may be heated by
steam from steam conduit 7a, the heated raw materials
being fed from the preheater directly to the press 9. If
desired, provision can be made to introduce recycled hot
fat into the raw materials through conduit 34a in advance
of passage of the raw materials through the preheater 42,
the recycled fat serving to supplement the heating action
of the preheater. It is also within the spirit of the
invention to utilize a surge bin, as shown in FIGURE 2,
with the preheater of FIGURE 3 to provide additional
control over the operation of the system.
r
