Class 1. Asphaltic base crudes, residuums, or other oils which require heating facilities to reduce the viscosity in order that the oil may be handled by the storage and burning equipment.

Class 2. Oils of a sufficiently low viscosity to make heating equipment unnecessary.

In general, an oil of Class 1 should not have a viscosity above 2000° Engler at 60°F. Oils of a higher viscosity than this can be used at plants provided with special equipment. It is imperative that oils of this class be heated to a temperature at which they have a viscosity of 12° Engler or lower before they reach the burner, in order to obtain proper atomization. It is desirable that this viscosity be obtained at a temperature below the flash point of the oil, in order to minimize fire hazards and to insure uniform feed to the burner.

For an oil of Class 2, 12° Engler at 60°F. is the approximate maximum viscosity permissible.

Method of determination: Viscosity should be determined with a standard Engler instrument according to the recognized method of manipulating this viscosimeter. Other standard viscosimeters may be used in special cases and their readings converted to Engler degrees by means of recognized tables or formulas.

7. Flash Point.—In general it is desirable that the flash point of Class 1 oils should not be below 140°F., and that of Class 2 oils not below 120°F. It should be noted that for Class 1 oils, specifications for flash point are contingent upon viscosity requirements as well as upon general considerations for safety requirements and evaporation losses.

Method of determination: Pensky-Martens closed-cut tester manipulated according to standard procedure.

8. Specific Gravity. Specifications for specific gravity are superfluous. In case oil is purchased by weight and measured by volume an accurate determination of its specific gravity is essential.

Method of determination: By specific gravity balance, pycnometer, or hydrometer. If conversion of Baume readings to specific gravity is necessary it is essential that the Baume hydrometer be accurate and that the proper modulus for this instrument be used. Specific gravities should be reported at 60°F. compared to water at 60°F. If they are determined at other temperatures the temperature corrections given in Bureau of Standards Circular 57 should be used.

9. Impurities. The oil should not contain more than 2 per cent. by volume of moisture and sediment. Proper deductions should be made from all oil deliveries for the impurities contained therein so that the oil purchased shall be pure oil.

Method of determination: A definite volume of the oil sample should be thoroughly shaken or "cut" with an equal volume of gasoline of a specific gravity not greater than 0.74, and centrifuged. An appropriate tube that goes with a special machine is commonly used for this purpose. Centrifuging should be continued until there is a clear line of demarcation between the water and sediment and oil in the bottom of the tube, and until a constant reading of water and sediment is obtained. From this reading the percentage by volume of water and sediment is computed. If the oil under consideration has a specific gravity greater than 0.96, one volume of oil to three volumes of gasoline should be used rather than equal volumes. When there is a question that the gasoline used for thinning the oil in making this determination renders insoluble certain of its fuel constituents, then mixtures of gasoline and carbon disulphide, or of gasoline and benzol may be used for "cutting," providing the specific gravity of such mixtures is not greater than 0.74. If, after continued centrifuging, a clear line of demarcation between the impurities and the oil is not obtainable, the uppermost line should be read. If this procedure proves unsatisfactory, 100 cc. of the sample may be distilled with an excess of hydrocarbons saturated with water and having boiling points slightly above and below that of water. Distillation is continued until a volume equal to the volume of hydrocarbons added has been distilled over into a graduated tube. The water in the oil is thus distilled over and readily collects at the bottom of this tube, where the percentage may be read off. The percentage of sediment in the oil may then be determined on the sample remaining in the distilling flask by "cutting" it with gasoline and centrifuging. The percentage of water obtained in the tube added to the percentage of sediment gives a total percentage to be deducted for moisture and impurities.

10. Sulphur Content.-Appreciable sulphur content in a fuel oil is objectionable. However, a content of 4 per cent. or less is not sufficiently objectionable to cause the rejection of a fuel oil for general purposes. (In general, experiments in burning fuel oils of various sulphur content have shown that the corrosive

effects on the boiler tubes or heating surfaces are negligible. However, with steel stacks and low stack-gas temperatures, considerable corrosion in the stack has been noted. In handling these oils, prior to burning, the corrosive action of the sulphur on steel storage tanks, piping, etc., is quite apparent and should be considered. If the oil is to be used for special metallurgical or other purposes where sulphur fumes are decidedly objectionable, it is necessary to specify a limiting figure for the sulphur content of the oil.)

Method of determination: Complete combustion in a bomb by means of oxygen or sodium peroxide, the sulphur being weighed as barium sulphate.

11. Calorific Value.-A standard of 18,500 B.t.u. to the pound of pure fuel oil is a good figure to be taken as the basis, if the fuel oil is to be purchased on calorific determinations. A bonus may be paid for calorific value in excess of this figure and deductions made if the heating value of the fuel is below 18,500 B.t.u. per pound.

Method of determination: Any bomb calorimeter of recognized accuracy.

12. Methods of Sampling. The accuracy of these different tests depends upon the care with which an average representative sample of the fuel oil delivery has been taken, and the importance of obtaining such a sample can not be overestimated. Top, middle, and bottom samples should be taken with a standard "car thief" and these samples should be combined and thoroughly mixed to form one sample for car deliveries. Where oil is received in tanks or reservoirs the swing pipe should first be locked at a position well above the level of the water and sediment usually found in the bottom of such tanks. Tanks should be sampled every foot for the first 5 feet above the bottom of the swing pipe, and at 5-ft. intervals from there to the surface of the oil. This sampling should be done with a standard tank thief, the samples "cut" individually, and deductions for impurities made on the separate volumes which these samples represent. If the tank is a large one, it should be sampled through at least two hatches. In receiving large deliveries of the more viscous oils it is necessary to take many samples in order to insure fair and average impurity (M. and B. S.) deductions. This is because water and sediment do not readily settle out of such oils.

13. General Specifications can not be Drawn to Advantage for Fuel Oils. Individual conditions and requirements at the points of consumption influence to a large degree the specifications for viscosity, flash point, and sulphur content. Definite specifications can be drawn for a fuel oil which will meet practically all requirements, but it can readily be seen that such specifications will exclude much of the fuel oil now available, and for most purposes the requirements need not be severe. Hence, it is advised that in purchasing fuel oil the individual requirements be studied and that as lenient specifications as possible be written which will insure an oil that will be satisfactory for the conditions for which it is intended.

CHAPTER XVII

FUEL OIL PRICES AND OIL PRODUCTION

By October 1920, as this Second Edition of "Fuel Oil and Steam Engineering" is about to go to press, the authors have come to the realization of the fact that the price of California fuel oil has more than doubled since the first edition of this book appeared just two years ago. Since, then, the constantly depleting storage of oil by the large production companies is making marked inroads into the possible supply of fuel oil in the near future, a discussion of this is of vital interest to the subject matter of this

FIG. 75.-Water softening plant at the Sierra and San Francisco Power Company's 27,000 kw. oil burning station. The use of pure water free from scale forming matter is the first requisite toward keeping boilers clean.

book in that economy production in the power plant depends directly upon the prices of this commodity prevailing in the open market and the ability of the operator to obtain fuel supply.

For the following able discussion of this matter we are indebted to J. E. Woodbridge, formerly chief engineer of the Sierra and San Francisco Power Company.