CHAPTER XV.TANK WATER.

Soil Fertility — Animal Feeding — Tank Water — Separation of Solids — Collecting Grease — Testing Tank Water — Evaporating Tank Water — Description of Apparatus — Cleaning Evaporators — Table of Boiling Points — Testing Stick — Copperas in Water to Evaporate — Solids in Water — Drying Stick — Value of Tankage — Quantity of Tank Water — Cost of Evaporating.

—The constant drain on the soil by raising of grain; feeding animals and sending them away for slaughter, and the non-return of the nitrogen element has made great inroads on the productivity of soil. Through volume after volume and in every manner possible, economic writers are impressing this upon the agricultural interests and advocating the making up of such deficit by rotating crops, turning under legume and plants that might extract nitrogen from the air by the processes of nature which daily are becoming more familiar to every one. Value and demand for the nitrogenous elements for this purpose has caused the packer to exercise all possible care to produce and conserve for sale any and all nitrogenous products.

—Experiment has also shown that nitrogenous products have a very high value as a nutritive food for growing and fattening animals, so much so in fact, that in many agricultural districts the entire output of tankage from local packing houses is now sold in the immediate neighborhood for stock foods. Under various names evaporated tank water is an ingredient of these.

—Invisible but in considerable quantity,nitrogenous solids were formerly lost in the various waters from cooking, but they are now collected and reduced to a semi-solid, or solid form. These are classified under the one broad name of tank water, but they include almost any water in which animal matter is cooked unless the water be of such character that it can be used for edible purposes. The chief sources of supply are rendering tank water, blood water, bone house cooking water, ham and tripe boiling water, etc. It is estimated that any water showing density of ¹⁄₂° Beaume scale is worthy of concentration.

—Evidently the more dilute the water, the more water it is necessary to evaporate, and hence more costly to concentrate. In raising the tanks so as to flow the oil from the tank cocks, it is necessary at times to admit fresh water. To avoid this the water from one tank is usually transferred to another of the same character by use of a pump.

—After the tankage has been dumped into the skimming box and all grease skimmed off, the tank water should be drawn into a separate vat. The “press water,” which is the water from the pressing of the tankage, should also be collected. The floor drainage except from the tank filling floor, and practically all water produced in the tank house, should be collected; in fact, some operators go to the extreme of not connecting the tank house sewer system to the city sewer so as to intentionally preclude the wasting of water.

—The tank water is collected in large vats for processing. The solids or sludge is undesirable to handle, consequently in draining the tank water from the surface vats into the storage, it is necessary to have the holes of the screens in the surface vats reduced to about one-quarter of an inch in size in order that all of the solids will be retained in the surface vats and not be permitted to go into the tank water catch basins.

The tank water storage vats should be equal to a day’s capacity and should be filled in rotation in order that agitation will be going on only in the vat being filled or the vat being emptied, and that the water in the balance of the storage vats will be permitted to be held under a settling process in the meantime, which is as follows: Heat the water to a temperatureof 180° to 185° F., and then allow it to drop down to 170° F., carrying it at this temperature from eight to twenty-four hours, according to the length of time it is possible to carry the water for settling purposes, up to 36 hours is an advantage.

—In the surface boxes spoken of in preceding chapter, it is very essential to agitate the tankage in the surface vats and keep it under steam long enough for some of the grease to rise to the top of the surface boxes and be skimmed off before the tank water is run into the storage vats. Skim the grease very carefully from the top of the water in any vat that is to be used for evaporation; then pump the water to the evaporator supply tank. After the water is pumped out of the basin, it will be necessary to remove the bottom of settlings each time after the tank is emptied.

—Pump the bottoms from the holding tanks into a surface box from which these settings are passed on to the press cheeses with pressed tankage, so that the fibrous material will collect the sludge. It is absolutely necessary that these settlings be taken out of the storage vats each time the vats are emptied in order to keep them sweet and to prevent the tank water from souring as it certainly will, unless cleaned at least twice a week. It is much better to clean them every time.

—Tank water is tested with a standard hydrometer for liquids heavier than water, and as stated previously, any water indicating ¹⁄₂° on the Beaume scale, is collected.

A sample of the tank water is cooled to 150° F. Drop a hydrometer into the water and take reading at a point on a level with the water; a hydrometer reading from 1 to 20, is used for this purpose. If hydrometer reads 2.00, the amount of the solids in the water is estimated at 3.83 per cent as shown on thetablefor figuring tank water. If the hydrometer should read 2.50, the estimated solids is one-half of the difference between solids shown on table at 2° Beaume and 3° Beaume added to solids at 2° Beaume which is 4.80 per cent.

—The evaporating of tank water, it is proposed to do in the most economical mannerpossible, and advantage is taken of the fact that as the pressure is lowered the boiling point is reduced. For example, water at atmospheric pressure and sea level boils at 212° F., and water under a twenty-eight inch vacuum boils at 100° F. Advantage is taken of these physical facts in the evaporating of tank water.

There are a number of types of evaporators using the same principle, although we show one only, that which is most extensively used, the well-known Swenson machine. This apparatus consists of one, two or three cells, dependent upon the economy it is wanted to attain.

FIG. 73.—SWENSON EVAPORATOR.

—The cells are numbered1,2and3, beginning at the left. The rectangular box at the bottom of each cell consists of a cast iron false head or chamber at either end, in which copper flues are expanded. Steam is introduced into the chamber ofNo. 1, and the tubes surrounded with tank water. The steam in the coils causes the water to boil and the steam boiled off is passed to the steam chamber of the second cell. The tank water in cellNo. 1by this boiling is condensed and is passed to cellNo. 2, where a further boiling takes place, and the concentrated liquid is passed to cellNo. 3for its last boiling.

The auxiliary pumps shown are for transfer purposes from cell to cell, and for pumping the condensate from the steam chambers.

—The large pump at the right hand is the vacuum pump. The vapor withdrawn from cellNo. 3by the withdrawal action of the pump is condensed by the introduction of cold water in the conical enlargement shown. This condensation produces a partial vacuum, the customary gauge measurement showing 23 to 27 inches, dependent upon the quantity and temperature of the water. This vacuum continues in a lesser degree to the second cell, thence to the first and where the vacuum usually maintained is six inches. By reference to the table of boiling points the comparative temperature in each cell is ascertainable.

—Evaporators to be effective must be clean, on the same principle as cleaning boilers produce best results. At regular intervals, say, fortnightly, they should be boiled out with a solution of 75 lbs. caustic soda in 1500 gallons of water. This will clean the flues and maintain the machine output.

TABLE OF BOILING POINTS.

—The residue from the evaporators or the “Stick” as it is now called, should be pumped into a receptaclefitted with closed steam coils. The tank water vats are similarly fitted.

—Stick is tested the same as tank water, excepting a hydrometer graduated from 20° to 40° is used. It is usual to evaporate to a density of 29° Beaume, which is 64.61 per cent dry solid. To calculate the quantity of concentrated or dry stick containing 4 per cent moisture produced from 29° Beaume stick, multiply the number of gallons of stick by 10.27 lbs. to get weight of 29° Beaume stick; then take 64.61 per cent of this weight, which is weight of dry solids, then add 4 per cent moisture to this amount by dividing the weight of dry solids by .96; the result is weight of concentrated tankage containing 4 per cent moisture.

—This is usually “sulphate of iron” of commerce, although some institutions make their supply thus: Using a lead-lined vat holding about 200 gallons; into this put about 160 gallons of 60-degree sulphuric acid, adding water enough to make the solution about 12° Beaume. Into this solution place scrap iron of any description and allow it to stand until the solution will dissolve no more iron. Pump the solution into a shallow lead-lined vat with lead coils, and evaporate to about 40° degrees Beaume. It is next drawn off into barrels of fifty gallons each and to each barrel add forty pounds of black oxide of manganese and thoroughly mix.

—An early practice and one which had the merit of fixing free ammonia before it passes off in a gaseous form was the introduction of copperas in tank water, while settling, and before evaporation. The vats of tank water are tested with a Beaume hydrometer and for every 2,000 gallons of tank water at indicated degree, Beaume, ordinary commercial copperas should be added as follows:

These varying amounts of copperas are put into a barrel of hot water and thoroughly stirred until dissolved. The solution is then poured into a vat of tank water, the mass allowedto stand six or eight hours, and then skimmed off before being pumped to the evaporating machine.

—The percentage of solids and liquids, as well as the respective weights in tank water at different degrees Beaume, are shown in the following table:

TABLE FOR TANK WATER.

—This is done in two ways, by the use of drying rolls and by mixing with drying tankage in a rotary dryer. When drying stick over the rolls, evaporate it in the evaporators to 26° Beaume and mix with this 26° Beaume stick, about 17 per cent of copperas before putting the mixture over the rolls. This has a tendency to prevent theconcentrated tankage from absorbing moisture when in storage. Many operators dry stick without the use of copperas, but the copperas prevents in a measure the stick absorbing moisture from the air.

—Fig. 74shows a standard twin stick roll. This equipment is made of two cast iron rolls built when new to sustain 50 lbs. pressure. The stick is deposited in a pan beneath and the revolving roll collects a film of substance which is dried as the roll revolves and is sliced from the surface of the roll by a close fitting scraper, being removed in a powdered form.

FIG. 74.—STANDARD TWIN STICK ROLL.

—The practice now generally adopted is the mixing of the stick with tankage and drying in the standard fertilizer dryer, using a fifteen foot dryer with stationary shell and revolving shaft, with arms cylindrical type, usually known as the “Smith” dryer. The usual charge is 4,000 lbs. pressed tankage and 1,200 lbs. stick, agitating while the stick is being admitted so as to assist in equal mixing. The stick should be at a temperature of 190° F., or near thereto when used. The heated substance seems to produce less tailings, or small balls requiring milling.

—To appreciate the value of the substances to be collected in this manner, we refer to copy of test, made by an expert, on a plant handling about 5,000 cattle and 5,000 hogs per week, as follows:

ESTIMATE OF THE PRODUCTION AND VALUE OF TANKAGE MADE BY EVAPORATING TANK WATER.

TEST FOR AMOUNT OF WATER DRAINED OFF VATS BEFORE PULLING TANKAGE.

TOTAL NUMBER OF TIMES TANKS FILLED AND COOKED.

BASIS FOR ESTIMATE OF PRODUCTION.

Total units of ammonia per tank, 5,652. Average units of ammonia per tank, 16.73. 8 per cent of moisture, dry basis.

This production at $1.66 per unit would be worth $27.77 per ton, or the yearly production would bring $24,396.32.

Figuring the production of tankage to be 66,000 pounds per week and that with this could be mixed through the dryer 600 pounds or 107.3 gallons of stick, 25° Beaume with each ton of dry tankage—then 33 × 600 pounds, or 19,800 pounds, would be the limit of production from the tank water.

The regular tankage runs on an average of 10 per cent ammonia and 16.4 bone phosphate, and as shown above the production from the tank water with 8 per cent moisture would run 16.73 per cent ammonia. The product would therefore consist of the following:

Analysis, ammonia 11.55%, bone phosphate 12.62%Value per ton $19.93, or for the yearly production, $44,459.84.

Should there be added worthless material sufficient to reduce the percentage of ammonia to 10, the following formula would apply:

Analysis, ammonia 10%; bone phosphate 10.92%.Value per ton $17.25¹⁄₂, or for yearly production $44,468.32

RECAPITULATION.

—This is variable, depending upon closeness of saving and density; also quantity of solid substance measured, and other items, but generally speaking from cattle slaughtered—ten gallons per head, and from pigs two and one-half gallons per head are collected.

—The following test shows the cost of producing stick through evaporators. The cost at the present time would be 100% higher owing to coal costs:

COST OF EVAPORATING TANK WATER.

NOTE: The equivalent gallons concentrated from 10% to 70% solids are calculated from a table and not from analysis of the tank water and stick; therefore, are only approximately correct.The steam cost at $0.132 per 1,000 pounds is far below present average conditions.

—The quantity of stick it is possible to produce is indicated in the following table:

ANNUAL PRODUCTION TANK WATER AND STICK.

The relative quantity of Stick to dried fertilizer produced is about 40%, but the stick is more valuable due to its higher ammonia content and the mixture of the stick with the standard fertilizer increases the value per ton of the fertilizer.

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