TANK HOUSE DEPARTMENT.
TANK HOUSE DESIGN -- ISOLATION AND VENTILATION -- SEPARATION OF PRESS
ROOM -- DIGESTERS -- RENDERING TANK -- SURFACE BOX -- PRESS AND PUMP
-- COOKING KILLING STOCK -- OPERATING TANK BLOW OFF -- PRESSING
TANKAGE -- TREATMENT OF LARD AND TALLOW -- TITER IN TALLOW AND LARD
-- STEAM FOR COOKING -- COOKING TESTS -- OPERATING ODORLESS -- TESTS
-- CATCH BASIN.
=Introductory.=--When slaughtering was done promiscuously throughout
the country, sufficient product was not available at any one point to
necessitate a tank house, consequently open kettles were used either
with fire under them, or jacketed for steam, the best of the fat was
thus rendered, and the balance was thrown away. It being impossible to
render offal to advantage under these conditions, the “digester” as it
is called by many, was evolved. It consists of a closed tank in which
cooking is done at forty pounds steam pressure, giving a temperature
of nominally 287° F., this high temperature thoroughly disintegrating
all products in the tank, liberating all the grease. The residue from
cooking in this manner, after being pressed, is dried and sold as
fertilizer. The effectiveness of this process is shown, for instance,
by the fact that if a hundred cattle heads are put into a tank, after
cooking, the bones are entirely disintegrated, except the teeth.
=Tank House Design.=--Almost any arrangement of tank, surface box and
press can be made to serve the purpose of rendering. The method and
arrangement shown herein are those practiced by one of the revisors of
this work and embodies principles as described.
The requisite apparatus for a rendering or tank house consists of but
few articles, viz: the rendering tank or digester, the surface or
skimming box, and a press, but the design and operation is of such
consequence that the same will be described in detail.
=Isolation and Ventilation.=--The rendering building from its character
should be isolated and arranged for ventilation on at least three
sides. The United States sanitary requirements compel the complete
separation of the edible from the inedible section by the use of
separate buildings or a parting wall.
[Illustration: FIG. 65.--SECTION THROUGH TANK HOUSE.]
=Separation of Press Room.=--If the business is large the owner is
fully justified in extending the parting wall through and dividing the
press room. This arrangement requires the double investment in presses,
cloths and all equipment, but gives the advantage that the pressings
can be collected from edible tankage and used for edible purposes,
provided always that the equipment is kept in proper shape. Whereas, if
the parting wall is not extended through the press room, the oils are
considered contaminated and are usable only for inedible purposes.
[Illustration: FIG. 66.--LITTLE NECK RENDERING TANK.]
The section shown indicates that type of house where the press room is
single, and the house above the press floor is divided.
[Illustration: FIG. 67.--TANK HOUSE, SHOWING NESTING OF TANKS.]
=Tank House Hazards.=--The tank house, from the nature of the business
being hazardous, is best to be of fire-proof construction. Tanks
constructed as shown in Fig. 66, with the little neck head can be
nested four in a bay and be made fully accessible on all floors.
The nesting of tanks six feet in diameter in a sixteen-foot square bay
provides sufficient strength to make it possible to suspend the tanks
from the floor beams above, suitably arranged, it further avoids the
necessity of supports near to the tanks, which greatly facilitate
cleanliness.
=Situation of Surface Boxes.=--The grease content in the fertilizer
is a matter of dollars and cents. When the oil is withdrawn from the
tanks it cannot be seen and no matter how closely watched considerable
oil will pass through to the surface box where it can be collected.
Consequently the second story of the tank house is a high story with
the surface boxes placed convenient to the second floor so as to be
readily worked. Further reference to this is made later.
=Press Room.=--The press room is arranged so that the press can be
built directly beneath the surface boxes, from whence the car is passed
to the press for pressing out the moisture.
=Digesters.=--The “digester” indicated, together with its method of
suspension and nesting has been successfully used and was the practice
followed by a well known designer for a number of years. The diameter
and height of the digester ordinarily used is 6 × 16 feet on the tank
body. The writer invariably has specified half-inch thick tank steel
for the reason that the increased thickness is of so little additional
weight, and the labor being such a considerable factor, that it was
thought well to provide this additional thickness to take care of
corrosion and acid attack.
=Little Neck Rendering Tank.=--Lugs can be placed in any position
desirable for support. The little neck for filling needs no comment. It
is provided with a six-point security and by the use of ring-bolts with
male and female flanged closing and gasket, can readily be made steam
tight.
=Tank Gate Valve.=--Tank department foremen are divided in ideas as to
using sliding steam gate valves, in which the gate is operated by lever
for quick opening or the screw type valve. The latter should be the
rising stem type.
=Surface Box.=--The surface box shown is a jacketed type used for
plants where tank water is collected for evaporation. The cost of this
is justified as against being annoyed with coils in the tank.
=Press and Pump.=--Practically all presses now in use are hydraulic.
These are overhead or under types, the latter being mostly used.
[Illustration: FIG. 68.--SECTION OF RENDERING TANK.]
[Illustration: FIG. 69.--DESIGN OF STEAM JACKETED SURFACE BOX.]
The style of pump used is a question of importance. The writer
specifies steam operated hydraulic pumps in preference to power
driven pumps, since the former can be operated from a governor that
automatically keeps full pressure on the pump. With the power pump,
when the motive power is stopped, a leak, the size of a pin point, in a
valve, will cause a leakage that releases the pressure and makes poor
pressing. Be aware of the fact that there is no method of extracting
water from the fertilizer so cheap as pressing and the only limit
should be the strength of the cloths. Fig. 70 shows how a hydraulic
press and pump should be connected.
[Illustration: FIG. 70.--DIAGRAM OF HYDRAULIC PRESS WITH PIPING AND
PUMP.]
=Cooking Killing Stock.=--The tank should be clean; draw in about two
hogsheads of water for a 6 × 16 foot tank, or a proportionate amount
for tanks of other sizes; turn on the steam to boil the water, and then
begin filling the tank. Allow sufficient steam to enter to keep the
tank boiling slowly. When the tank is two-thirds full, shut off the
steam, draw off the water and refill with water; turn on the steam,
bringing the contents to a boil the second time. Do not fill the
tank to exceed three-fourths full, as the cooking is better done if
sufficient room is left. After cooking for a half hour, draw off the
water a second time. It will be found, especially in cooking product
from the killing department, that the water drawn off is dark colored,
from the blood and dirt that has accumulated on the tissue. If this
is not withdrawn it has the effect of darkening the lard or tallow
materially.
After the water has been drawn the second time, put on the tank head
and turn on the steam, the condensation from the steam is sufficient
to cook the material; no more water is needed. See that the blow-off
and escape pipes are shut and the pet-cock is open. Continue cooking in
this manner until a moderate pressure is built up, then admit steam to
full pressure of forty-five pounds, open the escape valve just enough
so that you may know the gas is escaping. At the completion of this
operation the cooking begins. A tank of tallow should cook thoroughly
in from nine to ten hours with forty pounds pressure.
_Cold Spots._--Oftentimes freshly killed material will lie closely
together and a “cold spot” will occur--a spot where the material has
become partially solidified and the steam has not penetrated. In such
case, shut off the steam, draw off the water, and then turn on the
steam, the cold spots will disappear. “Cold spot” has the effect of
souring lard and tallow; in other words before the heat has penetrated
into the solid mass, the heat surrounding it will have caused it to
sour. This point should be watched closely, especially in cooking lard.
Tankmen should try the pet-cock on the tank each half hour to find out
if the tank is “flush.” If the tank is “flush” or foaming, the foam
will come out instead of steam. In this case, shut off the tank ten
minutes, then draw off the water, but see that no grease is drawn off
with it. The cause of the flushing, or foaming, is that the tank is
too full, or that there is too much water in it, consequently it is
necessary that the tankman should try his pet-cock very often during
the operation of cooking to see that the contents are being properly
cooked.
=Cutting Tanks.=--Cuttings and cold products of like character are
usually carried in cold water while filling, and are not parboiled as
described for “killing” tanks.
=Releasing Pressure.=--When the tank is cooked, shut off the steam
and open the pet-cock for about ten minutes, then the escape valve,
being careful not to give it too much escape at first, or the tank will
“roll.” By this is meant that the original heat in the oil contents
will generate steam in the contents beneath which, when the pressure
is relieved, will cause the contents to boil violently, but if the
pressure is reduced slowly, this condition will not arise. When a tank
has “rolled” it takes a great deal more time to settle it, the grease
being thoroughly mixed up with the residue of the tank. As the pressure
decreases the operator can increase the rapidity of release.
[Illustration: FIG. 71.--DETAIL OF PIPING CONNECTIONS. TOP OF RENDERING
TANK.]
The pressure being relieved from the tank, take out the head, use
about a water-pail full of fine salt to settle the tank. This salt is
scattered over the contents in the tank and has the effect of settling
sediment and tissue which may be held in suspension. The tank should
stand about two hours to thoroughly settle before drawing the oil. Draw
the oil from the side valves of the tank into coolers. It is often
necessary, in doing this, to raise the contents of the tank, as there
may be considerable tallow or lard below the lowest draw-off valve.
Such being the case run water into the bottom of the tank sufficient to
raise its contents so that all the rendered oil can be drawn through
the lowest valve.
[Illustration: FIG. 72.--DETAIL OF PIPING CONNECTIONS, BOTTOM OF
RENDERING TANK]
=Operating Tank Blow-Off.=--Descriptive of the connections for
operating rendering tank connections is the following subject matter.
The exhaust connections are illustrated in drawings, Figs. 71 and 72,
and essentially consist of, beginning at tank neck:
(1) Spring pop safety valve set at 45 pound pressure to automatically
release in case of excessive pressure arising and failure of weighted
pop valve to relieve.
(2) Pressure gauge on each riser to indicate pressure on the individual
tank to insure its being under pressure and under heat. The siphon bend
between gauge and pipe is preferably filled with glycerine.
(3) Try cock on bottom of drip line to open occasionally as test for
“gas.”
(4) Globe valve, ³⁄₈ inch, operated slightly open to allow gas to
release from tank and create very small circulation.
(5) Globe valve, 1¹⁄₂ inch; blow down valve to be used when releasing
all pressure from tanks.
(6) Angle type pop safety valve to relieve into the discharge line.
(7) Check valve attached to the line to prevent any foaming or steam
from an adjacent tank discharging into this unit via the exhaust system.
(8) Exhaust header used in conjunction with the system to collect all
gases and steam discharged from the battery of tanks.
(9) Cooking connections: It is preferable to drill the inlet nozzle at
bottom of tank at the lowest point possible and to admit steam on two
sides of nozzle not opposite but on an angle as shown in plan. This
prevents “dancing” tanks.
_Check Valves._--Check valves are placed in the admission valve to
prevent floaters or foreign materials entering lines and stopping the
control valves and steam and water.
_Inlet Header._--For usual purposes steam and water are admitted into
the tank at one point and steam at one, see _Nos. 12-a_ and _12-b_ on
diagram. If tank water is being collected and evaporated, line _12-c_
is introduced and used as follows:
Ordinarily the use of _12-b_ is for admitting water into bottom of
tank in case the oil line after tank contents are cooked and settled
are below the draw cocks.
In the event tank water is being saved to avoid weakening tank water
by introduction of cold clean water, this result is accomplished by
pumping tank water into the tank via the connection _12-c_. If tank
water is not being evaporated, _12-c_ line and connection is omitted.
_Draw Down Pipe._--If the oil is high and water appears at the
draw-cocks _14_ and _15_, then the content is lowered by opening cock
_No. 13_ and lowering the body as much as required.
_Oil Draw Cocks, 14 and 15._--When the tank is cooked, oil settled and
the tank raised or lowered by use of _No. 12_ connections or _No. 13_
cock, the oil belt should be such that the bottom of it is about on a
line with cock _14_, and the main body of oil is drawn through cock
_No. 15_.
=Surface Box Treatment.=--After the oil is drawn out of the tank, the
residue is dumped into the surface box. Anything that has not been
thoroughly cooked will float on top in the vat. These floaters should
all be skimmed off and put back into the tank to be re-cooked. The
contents should be thoroughly agitated with a pole or rake, cooked
fifteen minutes, allowed to settle and the oil carefully skimmed off.
This should be done two or three times on each vat so as to free all
the oil possible.
If tank water is being collected the boiling is done by steam jacket on
the box; if not, by direct application of free live steam. In either
case stir contents freely.
=Pressing Tankage.=--As soon as the operation of the skimming of the
vat has been thoroughly accomplished the contents are in the proper
condition to be pressed and should be handled while still hot. The
water is mostly drained off. In building the cakes, a portable car is
run under the surface box. By the use of a quick opening lever gate the
contents are dropped in quantity desired upon a press cloth; between
each cheese is placed a rack--the process being thus, a rack made of 1
× ¹⁄₄ inch material, usually elm, thoroughly nailed together, is first
laid on the press head; next a frame of the size and depth required to
handle the product is used. This frame should not exceed two inches in
depth. The press cloth is then spread over them and the material drawn
onto the press. Well spread out, the cloth is carefully folded over the
top of it. The form is then lifted off the press, another press rack is
put on top of the cheese already made, and the process repeated. Ten or
twelve plates are usually used to a press.
After the car is filled it is placed in the hydraulic press and
pressure applied. This should be done slowly at first, giving the water
ample time to run out of the press. If the pressure is applied too
rapidly the tendency is for the material to slide out on one side or
the other, but if the water is pressed out slowly the material adheres
better or gets a good “bond,” so that it will not slip.
After the press has run until the cakes are about one-half of their
original thickness spray with hot water, thoroughly washing off the
sides of the press, turn on more pressure until this reaches about
300 tons on a 5 × 5 foot plate. It will be found that it is the last
pressing which brings out the grease.
Where tankage is properly handled it should run from six to eight per
cent of residual grease on a dry basis. Where improperly handled it
will oftentimes run from eighteen to twenty per cent, the excess being
lard or tallow which should have been saved, but worthless if left in
tankage.
=Treatment of Lard and Tallow.=--As the oils are being withdrawn from
the rendering tanks the same should be passed through a small over-flow
type of catch tank arranged so that the oils pass through a straining
system to remove fibre or floaters. From the above basin the oils
should be passed to the receivers or coolers preparatory to settling.
In the judgment of the writer these tanks should preferably be in
a department or room separated from the rendering department, to
avoid possibility of contact and absorbing odors. The receivers or
reservoirs should be circular in form with a coil of heating pipe
arranged, supported from the sides of the kettles. The pipe should be
sufficiently spread to allow perfect cleaning.
The cones on the bottom should be at an angle of 45° so as to collect
the sediment, water or scrap that may deposit in small volume. The
scrap should be settled out and removed daily. Tallow and lard should
be allowed to cool to a tiercing temperature and kept in as large
volume as conditions permit, so as to obtain uniformity in cooler.
In case of lard, killing and cutting lard should be intimately mixed in
equal proportions if possible.
=Titer in Tallow and Lard.=--Titer in tallow, frequently referred to,
is a relative test of hardness. The test was originally devised for
the use of candle makers who wanted an oil containing the largest
percentage of stearic acid. Stearic acid has a hardness of about 55°
Centigrade. The hardness of other substances is relative to this as
follows: commercial oleo stearine, about 50.5° C.; tallow, 41° to 43°
C.; No. 2 tallow or grease, 39° to 43° C.; P. S. lard, 35.5° to 37° C.
Every trimming in the animal has a different hardness; the thinner the
cattle, the harder the tallow. Bone fat or marrow is very soft. Animals
of different feeding show varying hardness, so there is no method of
manufacture that will vary the hardness content of product other than
selection. In a general way, cattle ruffle, caul, or that used usually
in oleo melting is relatively hard. For example, oleo stock will
analyze as hard as 46° C., while the tallow from the same house will
analyze 43° C.
This hardness is determined in the chemical laboratory as follows: The
fat is melted and 25 cubic centimeters are drawn and mixed with 20 C.
C. wood alcohol, 10 C. C. of 50° Baume caustic soda solution and the
contents boiled until completely saponified. The alcohol is evaporated
by drying. The residue is ground and boiled with an excess of diluted
sulphuric acid until all the soap has been changed to fatty acid and
the clear oil floats. The water in the vessel is drawn from below the
fat, and the fatty acids collected in a glass vessel, which are allowed
to stand on steam coils until the oily stratum is clearly defined.
The fatty acids are placed in an observation room and the point of
solidification observed. The result is the titer, which is the degree
Centigrade at which the fatty acid from an oil or stearine solidifies
after being melted.
The other item of consequence in tallow analysis is the rancidity,
known as the free fatty acid. This should be kept low and is usually
variable with the care given the product. No. 1 tallow, for example,
should show under two per cent of low grade greases, and will run as
high as twenty per cent.
=Steam for Cooking.=--A question frequently asked is the quantity of
steam required to cook a tank. An accurate test conducted on a mixed
tank of pork products, killing and cutting stock, under standard
conditions showed thus:
Weight of Raw Stock 12,266
Water filled in Tank 9,634
------
21,900
After Cooking:--
Lard 6,040
Skimmings 479
Water Tankage 19,360
25,879
--------------
Accumulation-Steam Condensed 3,979
Steam per 1,000 pounds, Raw Stock 324 lbs.
=Cooking Test and Expense.=--The following test on the cost for cooking
was made on killing and cutting lard--very large digesters--and from
it valuable deductions can be made. Expert opinion has pronounced test
_No. 1_ and test _No. 3_ as producing comparatively the best results in
manufacture.
KILLING AND CUTTING STOCK
_Product_ No. 1 No. 2 No. 3 No. 4
Weight raw product 41,572 lbs. 41,236 lbs. 48,491 lbs. 41,322 lbs.
Under pressure 12¹⁄₄ hrs. 11 hrs. 11 hrs. 11 hrs.
Yield P. S. lard 32,665 lbs. 32,880 lbs. 24,525 lbs. 21,920 lbs.
_Boilers_
Water evaporation
while cooking 35,460 lbs. 24,420 lbs. 36,800 lbs. 23,990 lbs.
Reduced to coal on
6 to 1 evap. 5,910 lbs. 4,070 lbs. 6,134 lbs. 3,986 lbs.
Boiler pressure
average 57.6 lbs. 62.8 lbs. 51.6 lbs. 50 lbs.
Tank pressure
average 40.2 lbs. 40.5 lbs. 34.5 lbs. 32.5 lbs.
_Results_
Cost fuel at $1.36
per ton $4.02 $2.77 $4.17 $2.71
Steam, per 1,000
lbs. raw product 853 lbs. 593 lbs. 759 lbs. 579 lbs.
Fuel, per 1,000
lbs. raw product 142 lbs. 99 lbs. 126 lbs. 98.5 lbs.
Cost fuel, 1,000
lbs. raw product $.097 $.067 $.086 $.065
Clear Snowy Clear Clear
Temperature 32 to 34 34 to 35 22 to 38 13 to 18
_Remarks on Cooking:_
No. 1 Test Cooked with three waters, boiled two hours before heading.
No. 2 Test Cooked with one water, tank filled before heading.
No. 3 Test Cooked with two waters, boiled two hours before heading.
No. 4 Test Cooked with one water, tank filled before heading.
=Tests.=--Innumerable tank house tests are made. The following few are
submitted for quick reference, giving an idea as to yields of various
kinds of products:
TEST ON CONDEMNED HOGS--YIELD OF GREASE.
Condemned hogs to tank 954 lbs.
Yield of white grease 467 lbs. 48.95%
Yield pressed tankage 173 lbs. 18.13%
Yield dry tankage 86 lbs. 9.01%
On the above the leaf lard was left in and heads off.
COMPARATIVE TEST OF SHEEP HEADS AND JAWS TO TANK AND BONE HOUSE.
325 sheep heads and jaws (cheeks
off) to tank 765 lbs.
Yield to tallow 73 lbs. @ $ 0.06 per lb. $4.38
Yield dried tankage 150 lbs. @ 19.00 per ton 1.42
Total value $5.80
Value, per head, $0.0178; tallow, 9.54%; dried tankage, 19.47%.
325 sheep heads and jaws (cheeks
off) to bone house 765 lbs.
Yield to tallow 51 lbs. @ $ 0.07 per lb. $3.57
Yield dried bones 177 lbs. @ 18.00 per ton 1.59
Total value $5.16
Value, per head, $0.0159; tallow, 6.66%; dried bones, 23.14%.
TEST ON TRIPE TRIMMINGS.
Green weight to tank 1,206 lbs.
Yield prime tallow 356 lbs. 29.52%
Yield tankage 53 lbs. 4.39%
TEST ON CONDEMNED LIVERS.
Green weight to tank 1,010 lbs.
Yield No. 2 tallow 42 lbs. 4.16%
Yield pressed tankage 206 lbs. 20.38%
Yield dry tankage 103 lbs. 10.19%
TEST ON CATTLE PECKS TO TANK.
Green weight to tank 1,306 lbs.
Yield No. 2 tallow 16 lbs. 1.22%
Yield tankage 95 lbs. 7.27%
TEST ON CATTLE PAUNCHES TO TANK.
Green weight to tank 1,056 lbs.
Yield prime tallow 94 lbs. 8.90%
Yield pressed tankage 106 lbs. 10.04%
Yield finished tankage 53 lbs. 5.02%
TEST ON HOG STOMACHS TO TANK, UNTRIMMED.
Killed, 240 pigs and 836 hogs, a total of 1,076.
Green weight to tank 2,845 lbs.
Yield prime steam lard 1,275 lbs. 44.81%
Yield finished tankage 188 lbs. 6.60%
TEST ON WINDPIPES TO TANK.
Green weight to tank 880 lbs.
Yield No. 1 tallow 141 lbs. 16.00%
Yield tankage 33 lbs. 3.75%
TEST ON SHEEP PAUNCHES AND PLUCKS TO TANK.
(Trimmings from sheep house.)
Green weight to tank 1,150 lbs.
Yield No. 1 tallow 105 lbs. 9.13%
Yield pressed tankage 89 lbs. 7.73%
Yield dry tankage 45 lbs. 3.86%
TEST ON SHEEP (OFFAL).
Green weight to tanks 28,680 lbs.
Yield tallow No. 1 4,538 lbs. 2.28 lbs. per head
Yield tallow No. 2 730 lbs. .37 lbs. per head
Yield tankage 2,893 lbs. 1.46 lbs. per head
TEST ON NECK TRIMMINGS FROM KILLING FLOOR.
Green weight to tanks 880 lbs.
Yield No. 1 tallow 397 lbs. 45.11%
Yield dry tankage 49 lbs. 5.56%
TEST ON SHEEP FEET TO TANK.
Green weight to tank 1,170 lbs.
Yield No. 2 tallow 40 lbs. 3.42%
Yield dry tankage 148 lbs. 12.65%
=Operating Odorless.=--The question is frequently asked if rendering
departments can be operated odorless. They can be operated so as not to
become a nuisance. To do this requires:
(1) Ample tanks with no neglect about promptly rendering all products
and reducing them to lard, tallow or dry fertilizer.
(2) Collecting and evaporating all tank waters.
(3) Drying of tankage done under vacuum or otherwise controlling odors.
(4) Catch basins under cover, skimmed frequently and contents cooked
promptly.
(5) The rendering department kept tightly closed and department
operated with forced draft, all discharged air passed through large
water-wash, and the introduction into the air of gas boiled from tar
oil.
(6) All tank exhaust and vapors connected to a piping system, the steam
condensed by water spray, and the vapor collected and passed under
furnaces of boilers.
(7) Keep everything hot, allow nothing to lay around and sour.
=Catch Basin.=--Every packing house needs an adequate catch basin
system. Local basins established in departments near to points where
products are handled, serve to collect many fats and oils that, by
clean handling, are edible products, and can be used as such.
Where melted fats are produced cold water sprays should be introduced
to coagulate the oils. Wiers for over and under-flow should be put in
to retard flow and submerge particles so they may harden and float. A
large general basin should be introduced so that all outflowing sewers
can be passed to them, to the end that all water flows slowly through
the basin to catch any and all particles of floating fats or meats.
The basins should be placed under the care and jurisdiction of one
person, who should see that they are kept clean and frequently skimmed.
It is to good purpose to place them under roof so they will have
attention at all times.