LOSSES IN STORAGE In the storage of petroleum there are large losses. Long exposure of petroleum to the air means an escape of the lighter hydrocarbons. This wastage or loss is the main problem to be met and solved in any storage plan. Losses in storage are clue to: (a) Seepage.
(b) Losses of evaporation.
(c) Increase in specific gravity.
Seepage losses are found particularly in unlined earthen reservoirs.
In California, losses of 7 to 10 per cent with oil of 12 to16°B e. can be attributed to seepage losses. In areas like the Mid Continent oil field the loss by seepage of the light oils is so great as to preclude any idea of using anything but steel or wooden storage.
With good concrete-lined reservoirs seepage losses showed from 1 to 2 per cent per year.
Evaporation Losses.—The greatest loss in storage is due to the escape of the light volatiles from the crude oil and the increase in the specific gravity of the oil. Unroofed reservoirs show large losses.
The losses of light volatiles from open sump holes under a blaz ing sun are high. Were such oil allowed to stand long there would be only a tarry residue remaining.
It has been found that losses from wooden and steel covered tanks vary greatly. Losses as high as 25 per cent a year have been obtained from wood-roof tanks. Steel-tank storage of light oils in Oklahoma;shows losses ranging from 0.5 to 2.5 per cent per year.
In California, wooden-covered steel tanks showed losses of 0.1 per cent to 2.5 per cent per month.
Loss in Specific Gravity.—It has been found that oils lose very little in gravity in the &nine scale under good storage conditions. Cushing crude stored 2 years and 5 months showed a change from 40° to 3813e. or a loss of 2°. Some Glenn pool crude showed a change after 7 years and 3 months of 32.9 to 32.7 or 0.2°, a remarkable showing. A loss in specific gravity of 0.5° per year would be a high average for good steel storage.
Tank Farms.—The large pipe-line companies group their storage tanks together into "tank farms." One may count 40 or 50 large 55,000-bbl. tanks assembled on one tract of ground. Such tanks are usually spaced 200 to 300 ft. apart. Each tank
is surrounded by an earthen reservoir. In case of fire and the bursting of an oil tank the burning oil is confined to the reservoir or sump.
Oil-Tank Fires.—Oil tank fires (see Fig. 69) result largely from ignition of the gases from the tank during electrical storms. The escaping vapors are ignited by the lightning. Such storms are rare in California. In Oklahoma and Kansas the loss has been as high as twenty 55,000-bbl. tanks in a year or over 1,000,000 bbl. of oil. In Oklahoma and Kansas oil tank fires are numerous. Occasionally, careless handling of matches or smoking causes fires, but such cases are rare.
Cunningham Protector.—There are several methods of fire fighting. Prevention is, of course, most desirable. Along the line of prevention from electrical storms there is the Cunningham Fire Protector. (See Fig. 70, page 164.) This consists of a de vice through which the gases and vapors from the stored oil must pass. The roof of the tank is sealed tight by a treated can vas cover. Then the trap, or device for escaping gases, is placed at the highest point on the roof.
The gases are carried to a point beyond the dyke or fire bank around the reservoir, and are there allowed to escape through a screened hood. The claims made for this system are that the sealing of all the vents in the tank prevents the fires and also prevents large evaporation losses. Fire fighting and preventive measures also reduce insurance rates.
Foamite-firefoam System.—This system is purely an exting uishing one after a fire has started.
Figure 71 shows the system working. Alum is in A, the acid tank, and licorice in the B tank, each holding 18,000 gal.
In case of fire, these solutions are pumped to the mixing chamber on the storage tanks. As soon as mixed, chemical action commences and a thick foam is formed. This foam flows from the mixing chamber over the surface of the burning oil. The chemicals generate carbonic acid gas which chokes the fire and at the same time the foam excludes the air. In a few minutes the fire is extinguished.