4. Dehydrating by Indirect Heat. In cases where the emul sion is not too refractory, the oil may be pumped into the bottom of a tank 8 by 20 ft. through a spider with from 78 to holes. About 500 ft. of 2-in. pipe for a steam coil should be used, and the tank should contain at least 10 ft. of water, which should be heated and maintained at a temperature of from 150 to 200° F. As oil and water have different coefficients of expansion, they will separate upon going through the heated water, the oil rising to the top while the water mingles with that below. The latter can- be drawn off whenever necessary, to keep a level of about 10 feet. These methods are all continuous, and can be installed in units large enough to dehydrate 500 to 20,000 barrels of oil a day.
Handling Oil. In pumping-wells, or wells flowing at a moderate rate, the oil can be pumped to storage without appreciable loss if the proper precautions are taken. All pipe lines of the gather ing-system should be laid in trenches and buried sufficiently deep for protection from heat or cold. As it is usually the custom to gauge each well separately for its production, tanks are installed at each well and the oil measured there before being pumped to storage. These tanks are usually from 25 to 100 barrels capacity, one or more being placed at each well, depending upon the amount of production. If the well is making sand, a box with baffle boards is placed upon a scaffold so that it discharges into the tank and the lead-line from the pump runs into it. The sand can be shoveled out of the box, to prevent it from entering the tank. If the well makes water, it can be partially drained at this point. By the use of tanks and sand boxes, the running of oil into earthen sumps can be avoided and a great deal of oil saved from loss by seepage and evaporation. Tanks should have close-fitting covers made of boards and roofing paper to prevent loss of the more volatile con stituents. The use of tail pumps is to be recommended where the oil cannot be gravitated from the well. They are made of worn out working-barrels with a standing valve below and a leather cup-valve above and are bolted to the main sill in line with the outside end of the walking-beam. A polished rod extends to the beam, as in the case of the oil-well pump ; the tail pump has a 3-in. suction running to the well tank and discharges into the gathering-system, a check-valve having been placed in the latter to eliminate back-pressure. Instead of removing the tail pump when the tank has been emptied, a by-pass may be installed so that by closing the discharge gate and opening the by-pass gate the remaining oil circulates with each stroke of the beam and keeps the pump from becoming dry. The tail pump can be used only
upon wells making a production up to 350 barrels. A steam pump becomes necessary on a larger production.
Some operators use a water-covered storage-tank with the sides protected by a wooden cover to prevent evaporation in light gravity oils, while others paint the outside of the tanks white to reduce the intensity of the sun's rays. The large shipping tanks in any case should be well protected and the oil discharged from the gathering system into the tank through an overshot which should run within a few feet of the bottom. For a production of 1000 barrels per day two 2000-barrel tanks are sufficient for storage, while for a produc tion of from 5000 to 6000 barrels 5000 to 10,000-barrel tanks are used. In cases where it becomes necessary to store oil or where a gusher may be expected, 55,000-barrel tanks are built, but where the oil is kept moving daily in small shipments, they are hardly necessary.. All shipping tanks are equipped with three or more sampling cocks placed at proper intervals on the side, and the suction line to the pump is usually 16 in. or more from bottom to prevent the sludge and water from being delivered to the pur chaser. A swing-pipe is generally used on the inside end of the suction so that oil can be drawn from any level. The area of the heater-coil and all dead-wood is subtracted from the tank at the time that it is measured or 'strapped.' The latter is done by taking the mean of three measurements of the outside diameter and a corresponding number of the height, and reducing the result to barrels of 42 gallons. This is the basis upon which the purchaser buys the oil ; a gauge sheet is made for every /-in. and a copy given to the seller.
Upon obtaining a full tank of oil, the gauger of the purchasing company `thiefs' or samples it at three or four levels, the samples be ing placed in different receptacles. The 'thief' is a specially made bucket which can be lowered to a certain point and a sample of oil taken from that particular level. Samples are usually obtained at the bottom of the discharge, at the top of the oil and two inter mediate samples at equal distances. These are taken to the test house, where, after. shaking, 50 cc. of oil from each is poured into a 100-cc. burette and 50 cc. of gasoline added. After being thor oughly mixed by shaking, the burettes are placed in a 'centrifuge' capable of making 1000 to 3000 revolutions per minute and re volved for 20 minutes. The centrifugal motion throws the base sediment and moisture to the outside or bottom point of the burette; the readings are taken and multiplied by two, there being 50 cc.