Domestic Fuel Oil - Advances in Chemistry (ACS Publications)

Domestic Fuel Oil J. BENNETT HILL

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 2, 2015 | http://pubs.acs.org Publication Date: January 1, 1951 | doi: 10.1021/ba-1951-0005.ch021

Sun Oil Co., Marcus Hook, Pa.

During the past 25 years the use of distillate fuel oil for residential heating has increased more than 23fold. Whereas in 1926 domestic fuel oil represented only 1.1% of the crude oil refined, in 1950 it represented 11% and has become a major petroleum product to be reckoned with. Today about 1 6 % of the fuel oil supplied for homes with central heating plants is fuel oil No. 1, a straight-run product similar to kerosene. The other 84% is supplied as fuel oil No. 2 or heavier to homes equipped with burners which can satisfactorily burn a heavier and higher B.t.u. product. This latter fuel now incorporates large percentages of stocks from catalytic cracking and has a higher heat content than straight-run fuel. The only real problem in using catalytic or other cracked stocks has been in sludge-forming tendency, and this has been satisfactorily solved by refinery treatments or the use of additives.

Twenty-five years ago the domestic fuel oil business was no more than a healthy infant; in fact, if we go back another five years, we are hardly aware of its existence. B u t i n 1926 the 200,000 domestic oil burners i n this country consumed 9,715,000 barrels of fuel oil, or about 1.1% of the crude petroleum run to stills. The oil burner was recognized as here to stay, and the oil industry was giving quite a bit of thought to its future. T h a t thought was justified. A s of the end of last year (1950) there were 5,146,354 domestic oil burners, and they consumed during the year 228,000,000 barrels of fuel oil, or 1 1 % of the crude petroleum run. The infant has really grown up (Figure 1). The three principal fuels for domestic central heating systems are coal, fuel ου, and gas. The growth of fuel oil has been mostly at the expense of the hand-fired coal furnace. One of the main attractions of fuel oil was automatic heat, and the automatic coal stoker was for a time a lively competitor. Lately its popularity has very much declined. W i t h in recent years the extension of natural gas lines has resulted i n increased popularity for gas heating, and i n 1950 the sales of gas burners actually surpassed the sales of oil burners, as shown b y the following percentage figures on sales of automatic heating equipment: gas burners, 5 6 . 3 % ; oil burners, 42.6%; and automatic stokers, 1.1%. The estimated 1950 figures for fuel consumed, on a B . t . u . percentage basis, compared with the immediately postwar year of 1946, are as follows: Coal, % Fuel oil, % Gas, %

1046

1Θ50

65.7 19.9 14.4

49 28 23

The rapid growth of the new fuel oil industry to its present size has not, of course, been unaccompanied b y problems, both to the burner industry and to petroleum refiners. 246

In PROGRESS IN PETROLEUM TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1951.

HÎLl—DOMESTIC FUR OIL

247


Fortunately, the two industries have listened to each other and have been able to work together. A n y discussion of the development of fuel oil requires a preliminary discussion of the types of burners which have been developed and which are i n use. The burner and the fuel must be adapted to each other just as the automobile engine and its gasoline must be adapted. There are, however, very much wider differences i n types of burners than i n types of automobile engines. While this paper is primarily concerned with fuels and burners for domestic central heating systems, it must not be forgotten that there are about 7,000,000 oil-burning, spaceheating units i n use that consume a large volume of fuel, not included i n the graphs i n Figure 1. These units vary a l l the way from the portable, unpiped, wick kerosene stove to the larger piped heating stoves i n common use.

GROW"ΓΗ OF DOM EST C 0 L HEAT

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1155 16th St.,TECHNOLOGY; N.W. In PROGRESS IN PETROLEUM Advances in Chemistry; American ChemicalDC Society: Washington, DC, 1951. Washington, 20036

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ADVANCES IN CHEMISTRY SERIES

248

Oil burners are usually classified into the following groups and subgroups: I II


III

Vaporizing burners (pot-type) Natural draft Forced draft Atomizing burners (gun-type) Low pressure H i g h pressure Vertical rotary burners W a l l flame Suspended flame

The vaporizing-type burner vaporizes the fuel on a hot surface, or by radiant heat, and burns it as a gas. The simplest type uses natural draft and requires a fairly volatile, clean-vaporizing, and clean-burning fuel. While the trend has been away from the natural draft burner, large numbers of them were installed i n low cost housing under the construction program following W o r l d W a r I I . M o s t vaporizing burners are equipped with mechanical draft, which not only improves their functioning but somewhat widens their tolerance to heavier fuels. The common atomizing burners are of the gun type. The oil is atomized either b y a high pressure (40 to 200 pounds) solid injection nozzle spraying the oil into the air stream, or b y mixing the oil with air at low pressure and obtaining air atomization at the nozzle. H i g h pressure burners are the more prevalent, although the low pressure burners are increasing i n popularity, particularly i n the smaller sizes. Atomizing burners are much more tolerant of heavier and lower volatility fuels than are the vaporizing type. The wall flame rotary burner is actually a vaporizing burner i n which fuel is thrown from a distributing head, rotating at moderate speed, as a coarse spray. This fuel strikes a vaporizing ring located along the walls of the combustion chamber where it is vaporized, ignited, and burned. Combustion takes place upward from the vaporizing ring along the walls of the combustion chamber. The suspended flame rotary burner produces atomization of the oil b y throwing it off as a spray from a cone, cup, or disk, rapidly revolving about a vertical axis. The spray is supported by the air stream and burns i n a flat, circular flame. I n 1950 the comparative sales of burners of the various types were as follows : vaporizing, 5 . 1 % ; high pressure atomizing, 70.9%; low pressure atomizing, 13.4%; and vertical rotary, 10.6%. Domestic fuel oil originally was almost exclusively a straight-run or virgin fraction from petroleum, with a boiling range like kerosene or somewhat higher. I t was sold under such names as "distillate," "straw distillate," or even as kerosene. The variations, however, i n the burning qualities of the fuel supplied, and the different quality demands of different types of burners, early led to a classification of fuels b y the American O i l Burner Association into three classes, and these were adopted i n 1929 as a commercial standard of the U . S. Department of Commerce. Although there have been numerous modifications of burner units between 1929 and the present, the revisions i n fuel oil N o . 1 and N o . 2 specifications have been relatively minor, as shown i n Table I . This table presents a comparison of the 1929 and most recent, or 1948, specifications. T h e N o . 3 fuel o i l classification, which had never been generally accepted, has been dropped. Table I.

Comparison of Commercial Standards Specifications of 1929 and 1948 No. 1 1929

Flash, ° F . Water and sediment, max. Pour point, max., ° F . Carbon residue (10% res.), max. Distillation, ° F . 10% max. 90% max. E n d point Viscosity/100° F . , centistokes Saybolt Universal, max. Gravity, ° A P I , min.

No. 2 1948

1929

1948 100 0.10 20 0.35

100-165 0.05 15

100 Trace 0 0.15

125-190 0.05 15

420

420

600

625 1.4-2.2

440 620

35

675 40' 26


No. 3 1929 150-200 0.1 15 460 675 55'


HILL—DOMESTIC FUEL OIL

249

Under the 1948 commercial standard C S 12-48, fuel oil N o . 1 is defined as "intended for vaporizing pot-type burners and other burners requiring this grade," whereas N o . 2 is defined as "for general purpose domestic heating for use in burners not requiring N o . 1." The N o . 1 fuel is therefore specified to have a low 1 0 % point in the A S T M distillation to ensure quick starting, and a low end point and low carbon residue to ensure clean vaporization. Since the N o . 2 fuel is burned as an atomized spray, these qualities are given much wider latitude. The viscosity specifications on both grades are to ensure proper mechanical functioning of the burner. The gravity specifications are an indirect measure of the carbon to hydrogen ratio and of the chemical composition. This property is i m portant since i t is related to burning quality. The low A P I gravity fuel contains a greater proportion of the nonparaffin hydrocarbons—olefins, naphthenes, and particularly aromatics. It has a higher B.t.u. content per gallon but burns more slowly with a longer flame and requires more air for combustion. It is therefore less suitable for the pot-type burner than is the high gravity fuel. In accordance with these specifications fuel oil N o . 1 has continued to be a straightrun fuel approaching kerosene in its properties. As a matter of fact, on the East Coast, where there has been a much more complete shift of fuel oil customers from N o . 1 to N o . 2 than i n other sections of the country, N o . 1 is substantially kerosene. I n sections where the utilization of N o . 1 is greater, more advantage is taken of the greater specification tolerance over kerosene. I n refining, the fuel is usually sweetened and sometimes sodaor acid-treated, or even solvent-refined. Where it is sold as "range o i l " for space heaters, especially pipeless, it is important that it be free from objectionable odors, both i n the fuel itself and in its combustion products, and more drastic refining is required. Fuel oil N o . 1 is also a high grade Diesel fuel and has to compete with its use for that purpose. Furthermore, it is also an excellent cracking stock and therefore competes with gasoline. The question of how popular i t will remain is consequently entirely one of economics, and certainly the burner that can handle a l l qualities of N o . 2 has a distinct economic advantage over that requiring N o . 1. I n 1950, fuel oil N o . 1 represented 16% of the total domestic fuel oil business. I n the case of fuel oil N o . 2, refiners early recognized the competition of straight-run oil with its use as a cracking stock, and started to incorporate cracked stocks into this product. This trend has become increasingly pronounced, particularly since the advent of catalytic cracking, which produces a fuel well suited to modern burners. While actual figures are not available, it is probably safe to say that cracked stocks make up at least 7 0 % of the N o . 2 oil sold today. The cracked oils are of lower A P I gravity and, as a result, the customer is getting more B.t.u.'s for his money, but the burner manufacturer has to design for slower burning and longer flame. The use of cracked stocks i n N o . 2 has meant additional problems for the refiner. Besides having to refine for odor and color, he is also faced with a stability problem. While catalytic cracking as a rule produces a more stable oil than does thermal cracking, there are still compounds present which on aging will form insoluble sludge. This sludge, if permitted to form, clogs burner screens, and eventually results in trouble. Little has so far appeared in the scientific literature on the chemistry of sludge formation in these oils. The work of Thompson, Druge, and Chenicek (8,9) shows that sludges are much richer i n sulfur and nitrogen than are the oils from which they are precipitated and that some of the typical compounds of these elements increase the amount of sludge formed in a given time. There is other evidence that oxygen compounds present i n the oil may play a part. Unpublished work of the D u Pont Co. (2) shows that the sludges have molecular weights of about 300 to 400; this indicates that condensation or polymerization does not play a conspicuous part i n the chemistry of sludge formation. M a n y laboratories are working on this chemistry, and the next few years will doubtless see other important contributions to its literature. The steps which are being taken by refiners to ensure against any sludge trouble are varied. Since many cracked stocks do not show the tendency to form sludge, those that do can sometimes be sorted out and eliminated from the blend. I n most cases chemical


250

ADVANCES IN CHEMISTRY SERIES

treatment, such as with caustic soda or sulfuric acid, is resorted to. The proper treatment to effect adequate stability improvement depends on the particular stock and must be determined b y the individual refiner. The most interesting recent development to avoid sludge troubles is the use of addi tives. F o r this purpose the common antioxidants are usually comparatively ineffective. The patent literature indicates that the attack on the sludge problem is along two lines. The first of these is to inhibit the reaction which forms sludge b y means of a stabilizing additive. Prominent among these additives are amino compounds of various degrees of complexity (8,4,6 7). The second is to peptize the sludge i n such a way that i t does not plate out on the screens and eventually plug them. M e t a l soaps are prominent i n this class (1,5). A n y prediction of the future growth of domestic fuel oil requires a better crystal ball than any of us have. O i l has won its present popularity b y its greater convenience over the hand-fired coal furnace. W i t h the rapid rise i n our standard of living, the American householder has become thoroughly allergic to stoking a furnace, particularly when i t gets h i m out of bed earlier i n the morning. Other competitors, natural gas and liquefied petroleum gas, which also give automatic heat, are increasing i n popularity. C o a l might even stage a comeback b y the development of a fully satisfactory automatic system for burning i t . The interest of the oil-heat industry is to be sure that the technology of oil burning is made as simple and convenient for the householder as possible. Continuance of the existing cooperation between the equipment manufacturers and petroleum refiners should ensure this.


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Acknowledgment Figures are compiled from data published b y Bureau of the Census, Bureau of Mines, and American Petroleum Institute, to which acknowledgment is made.

Literature Cited (1) Caron, J. B. R., Wies, Calmy, and Glendenning, Ε. B . (to Shell Development Co.), U. S. Patent 2,527,987 (Oct. 31, 1950). (2) D u Pont de Nemours & Co., Inc., Ε. I., private communication from Petroleum Chemicals Division. (3) Mikeska, L . Α., Kittleson, A . R., and Smith, W . M . (to Standard Oil Development Co.), U . S. Patent 2,453,850 (Nov. 16, 1948). (4) Pedersen, C. J., and Bender, R. O. (to Ε. I. du Pont de Nemours & Co., Inc.), Ibid., 2,401,957 (June 11, 1946). (5) Proell, Wayne A . (to Standard Oil Co. [Indiana]), Ibid., 2,422,566 (June 17, 1947). (6) Sargent, E. L., and Aberright, E. A. (to Socony-Vacuum Oil Co.), Ibid., 2,353,192 (July 11, 1944). (7) Scafe, Ε. T . (to Socony-Vacuum Oil Co.), Ibid., 2,261,003 (Oct. 28, 1942). (8) Thompson, R. B., Chenicek, J . Α., Druge, L . W., and Symon, Ted, Division of Petroleum Chemistry, Preprints (General Papers), p. 103, 18th Meeting, A M . C H E M . S O C , Chicago, September 1950. (9) Thompson, R. B., Druge, L . W., and Chenicek, J . Α., Ind. Eng. Chem., 41, 2715-21 (1949). RECEIVED April 19, 1951.


Domestic Fuel Oil - Advances in Chemistry (ACS Publications)

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