CHAPTER XIV.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.

—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.

—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.

—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.

FIG. 65.—SECTION THROUGH TANK HOUSE.

—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.

FIG. 66.—LITTLE NECK RENDERING TANK.

Thesectionshown indicates that type of house where the press room is single, and the house above the press floor is divided.

FIG. 67.—TANK HOUSE, SHOWING NESTING OF TANKS.

—The tank house, from the nature of the business being hazardous, is best to be of fire-proof construction. Tanks constructed as shown inFig. 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, suitablyarranged, it further avoids the necessity of supports near to the tanks, which greatly facilitate cleanliness.

—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.

—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.

—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.

—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 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.

—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.

—Practically all presses now in use are hydraulic. These are overhead or under types, the latter being mostly used.

FIG. 68.—SECTION OF RENDERING TANK.

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. 70shows how a hydraulic press and pump should be connected.

FIG. 70.—DIAGRAM OF HYDRAULIC PRESS WITH PIPING AND PUMP.

—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 incooking 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.

—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.

—Cuttings and cold products of like character are usually carried in cold water while filling, and are not parboiled as described for “killing” tanks.

—When the tank is cooked, shut off the steam and open the pet-cock for about ten minutes, thenthe 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.

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.

FIG. 72.—DETAIL OF PIPING CONNECTIONS, BOTTOM OF RENDERING TANK

—Descriptive of the connections for operating rendering tank connections is the following subject matter. The exhaust connections are illustrated in drawings,Figs. 71and72, 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 are placed in the admission valve to prevent floaters or foreign materials entering lines and stopping the control valves and steam and water.

—For usual purposes steam and water are admitted into the tank at one point and steam at one, seeNos. 12-aand12-bon diagram. If tank water is being collected and evaporated, line12-cis introduced and used as follows:

Ordinarily the use of12-bis for admitting water into bottomof 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 connection12-c. If tank water is not being evaporated,12-cline and connection is omitted.

—If the oil is high and water appears at the draw-cocks14and15, then the content is lowered by opening cockNo. 13and lowering the body as much as required.

—When the tank is cooked, oil settled and the tank raised or lowered by use ofNo. 12connections orNo. 13cock, the oil belt should be such that the bottom of it is about on a line with cock14, and the main body of oil is drawn through cockNo. 15.

—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.

—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 clothis 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.

—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 tiercingtemperature 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, 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.

—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:

—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 testNo. 1and testNo. 3as producing comparatively the best results in manufacture.

KILLING AND CUTTING STOCKProductNo. 1No. 2No. 3No. 4Weight raw product41,572lbs.41,236lbs.48,491lbs.41,322lbs.Under pressure12¹⁄₄hrs.11hrs.11hrs.11hrs.Yield P. S. lard32,665lbs.32,880lbs.24,525lbs.21,920lbs.BoilersWater evaporation while cooking35,460lbs.24,420lbs.36,800lbs.23,990lbs.Reduced to coal on 6 to 1 evap.5,910lbs.4,070lbs.6,134lbs.3,986lbs.Boiler pressure average57.6lbs.62.8lbs.51.6lbs.50lbs.Tank pressure average40.2lbs.40.5lbs.34.5lbs.32.5lbs.ResultsCost fuel at $1.36 per ton$4.02$2.77$4.17$2.71Steam, per 1,000 lbs. raw product853lbs.593lbs.759lbs.579lbs.Fuel, per 1,000 lbs. raw product142lbs.99lbs.126lbs.98.5lbs.Cost fuel, 1,000 lbs. raw product$.097$.067$.086$.065ClearSnowyClearClearTemperature32 to 3434 to 3522 to 3813 to 18Remarks 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.

KILLING AND CUTTING STOCK

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.

—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.

On the above the leaf lard was left in and heads off.

COMPARATIVE TEST OF SHEEP HEADS AND JAWS TO TANK AND BONE HOUSE.

Value, per head, $0.0178; tallow, 9.54%; dried tankage, 19.47%.

Value, per head, $0.0159; tallow, 6.66%; dried bones, 23.14%.

TEST ON TRIPE TRIMMINGS.

TEST ON CONDEMNED LIVERS.

TEST ON CATTLE PECKS TO TANK.

TEST ON CATTLE PAUNCHES TO TANK.

TEST ON HOG STOMACHS TO TANK, UNTRIMMED.Killed, 240 pigs and 836 hogs, a total of 1,076.

TEST ON WINDPIPES TO TANK.

TEST ON SHEEP PAUNCHES AND PLUCKS TO TANK.(Trimmings from sheep house.)

TEST ON SHEEP (OFFAL).

TEST ON NECK TRIMMINGS FROM KILLING FLOOR.

TEST ON SHEEP FEET TO TANK.

—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.

—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.

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