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I N D USTRIAL A N D ENGINEERING CHi7MIXTR Y
Refinery Problems Affecting MotorFuel Supplies By F. A. Howard and N. E. Loomis DEVELOPMENT DEPARTMENT, STANDARD OIL COMPANY OF NEW YORK, N. Y.
NSW
JERSEY,
N PRESENTING this paper it is not the intention of
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the authors to describe any new equipment or to present original data, but rather to summarize facts which are well known to petroleum technologists but which are too often neglected in refinery operation. Further, since this paper deals solely with present refinery problems, the many interesting technical questions involved in the possible use of shale oil, alcohol, benzene, etc., will not be discussed. As was pointed out by one of the authors in a paper presented before the American Petroleum Institute in 1921,l the most important single problem affecting motor fuel supplies a t the present time is that of the production and conservation of a maximum quantity of the highly volatile fractions of gasoline. Gasoline specifications require a certain ratio of light to middle to heavy fractions, and no matter how much the quantity of middle or heavy fractions may be increased, the supply of motor fuel will be limited by the supply of light fractions, unless a sacrifice of volatility is permitted. The problem of supplying these light fractions becomes of increasing importance from year to year. As far as the refiner is concerned, cracking offers the only means of directly increasing the production of these light fractions, and that its important function in this connection is well recognized is proved by the widespread interest which now exists in regard to such processes. Less attention has been paid, however, to the equally important phase of conserving these highly volatile fractions. The very nature of these fractions results in the losses incident to refinery operations being largely a t their expense. Their conservation may be considered from these angles-( 1) proper processing equipment and methods, ( 2 ) recovery of volatile liquid hydrocarbons from refinery gases, and ( 3 ) protection against evaporation losses in storage. P R O P E R PROCESSIKG
EQUIPMEXT -4ND
METHODS
The use of ample condenser surface and proper arrangements to provide countercurrent flow between the cooling water and the oil is essential on all distillation equipment with low-boiling stocks, The amount of gasoline carried off by the gas from such stills increases rapidly with increase in temperature, and to prevent this loss and subsequent loss from the running pans the lowest possible temperature o n the naphtha streams should be maintained. This point is frequently lost sight of in the desire of the refiner to run his stills to capacity, and it is no uncommon occurrence in summer to find such streams running a t temperatures above 100” F. The most rudimentary knowledge of the general form of the vapor-pressure curves on hydrocarbons of the gasoline range should be sufficient to convince the refinery management that a t temperatures approaching the initial boiling point so closely each degree Fahrenheit is like the proverbial inch on the nose, as far as its effect on losses is concerned. Kevertheless, it is sometimes difficult for the refinery chemist or engineer to make the full importance of this clear, and as a result preventable losses of light gasoline a r e still more common than they should be. The “look-boxes” of the stillhouse should be gas-tight and should be connected into the refinery gas system. A Howard, “Qualitative Limitations in Refining a n d Marketing of Gasoline.”
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gas exhauster on the gas-collecting system should maintain as nearly as possible a balanced pressure on these boxes. Care should be taken not to draw air into the gas lines, for this greatly reduces the efficiency of any gasoline-recovery system. The “running pans” into which the distillate streams flow provide another common source of loss. I n these pans the naphtha is being continually agitated by the constant inflow and intermittent pumping. When the pans are equipped with loose hatches, a stream of gasoline vapors frequently can be observed pouring out. The naphtha pans should be equipped with tight roofs and connected into the gas-. collecting system. Further loss from the pans is frequently caused by carelessness in drawing water off the bottoms, allowing some of the oil to run to the sewers. From the pans the subsequent handling of the naphtha should be in gas-tight equipment. The use of open agitators for treating and sweetening, which permit the escape of vapors, is unnecessary and wasteful.
RECOVERY OF VOLATILE LIQUID HYDROCARBONS FROM REFIKERY GASES I n the preceding discussions it has been assumed that the refinery is equipped with a gas-collecting system. Many refiners still neglect this, and even insist that the amount of gas produced in ordinary distillation is negligible. This may be true in rare instances, but in general the value of the gas and the gasoline that can be recovered from the gas makes a proper collecting and gasoline recovery system a good investment. The amount of the gas which must be handled may be materially reduced by attention to the points already made-exclusion of air and maintenance of low temperature on the naphtha streams. There are many modifications of gasoline-recovery systems. It is difficult to decide to just what extent recovery is justified. By using a high-pressure process, gross recoveries can be materially increased over what is possible a t atmospheric pressure, but this increased recovery is chiefly in the least stable fractions. The decision in regard to the type of system to be used must be based upon a comparison of costs with amount of gasoline that can be put into the purchasers’ hands, and this item is dependent upon such factors as amount of blending stock available, time spent in storage before marketing, weather conditions, etc. It is a fact, however, that any system is so much better than no system a t all that consideration of relative merits of different processes should not be permitted to delay action very long.
PROTECTION AGAINST EVAPORATION LOSSESIN STORAGE Probably the greatest single source of loss of gasoline a t refineries is evaporation from storage tanks. On finished products this loss is especially serious, in that not only the material, but the cost of refining it is lost. Here again the loss is predominantly a t the expense of the most volatile fractions. Tests carried out a t various refineries have shown that the average gasoline in standard. steel tankage mill lose about 6 per cent per year, equivalent to over $30,000 for each 55,000-bbl. tank. The magnitude of these evaporation losses has caused much work t o be done on means for decreasing them. The common suggestions made in the past may be grouped as: 1-Me,ans for keeping the contents of the tanks cool-such as spraying, insulation or jacketing of sides and roof, special paints, etc. 2-Means for preventing diffusion and drafts-such as special breather valves, protection of eaves from leaks, etc.
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I N D U S T R I A L A N D ENGINEERING CHEMISTRY
3-Means for eliminating breathing losses and recovering gases delivered from tanks-such as tight-roof tanks connected to gasometers and gasoline-recovery systems.
There are merits to most of these suggestions, and most of them will repay their use under favorable conditions; but none of them has appeared to be a generally adaptable solution of the problem, either because it affected only one cause of the loss or because of undue expense. For this reason the Development Department of the Standard Oil Company (N. J.) began work about three years ago to find a universally satisfactory solution of the evaporation problem. The basis of this work was the idea that the surest preventive was to float upon the surface of the oil some fluid which of itself had a negligible vapor pressure. TJnfortunately, Nature has so ordered things that all light liquids have high vapor pressures. The problem, therefore, resolved itself into the production of a liquid of low vapor pressure and insoluble in gasoline, with which could then be incorporated other material sufficiently light to float the mixture. To make a long story short, this eventually led to the development of the product known by the trade name of “Sealite,” which is essentially a mixture of glucose, cornstarch, glycerol, glue, and calcium chloride, so proportioned that it is insoluble in oil, incombustible, nondrying, does not absorb moisture, and does not ferment. The original solution can be readily pumped and handled in tank cars. It weighs, however, about 11 lbs. per gal., and in this form will, of course, not float upon oil. The finished “Sealite” is made by beating the “Sealite” solution with air to produce an emulsion or foam. This beating must be carefully controlled to give a product weighing about 4.75 lbs. per gal. The inclusion of too little air will not make it light enough to float on gasoline, and the inclusion of too much air makes it so stiff that it will not flow properly upon the surface of the oil. Microscopic examination indicates that the air bubbles are 0.0005 in. in diameter. This foam is handled in barrels and applied to the surface of the oil in the storage tanks. Tests have shown that a 1-in. layer of it will last a t least a year, and in that time will reduce the storage loss to a t least one-fifth of normal loss. I n fact, the prevention of evaporation is practically complete and the observed losses are probably mainly due to leakage and escape of permanent gas. The material is entirely soluble in water, and, although this is an advantage in the cleaning of tanks, it necessitates weather-tight tank roofs. In addition to minimizing evaporation, “Sealite” is an effective fire-prevention agent. Tests carried out on small tanks have shown that when the layer of “Sealite” is broken and the oil ignited, the foam will quickly flow together again and extinguish the blaze. This occurs even if the “Sealite” and oil are first subjected to violent disturbance. In these tests the “Sealite” has not been destroyed, but is only charred on the surface, and the fire test can be repeated several times with the same lot of foam. We believe that in the case of large tanks covered with “Sealite,” even if the break in the protective blanket is so extensive as to prevent its closing entirely, the fire will be localized to a small portion of the surface and will, therefore, be much easier of control. “Sealite” passed out of the experimental stage last year, and is now being used by several large companies on both gasoline and crude storage. Up to the present time a total of over 14,000,000 bbls. of gasoline and light crude oil have been protected in this manner. The effectiveness of the protection afforded leads us to believe that “Sealite” constitutes a definite advance in efforts to conserve the light fractions of petroleum and thereby increase the quantity and better the quality of our available supplies of motor fuel.
Alcohol as a Motor-Fuel Constituent‘ By Henry A. Gardner FORTHE BUREAUOF -kERONAUTICS,NAVY DEPARTMENT, WASHINGTON, D. c .
ASOLINE, even of the highest grade aviation type, is not entirely satisfactory as a motor fuel, at least for aircraft. Impurities present have caused corrosion difficulties. Detonation troubles have been serious. It has not been economical because it cannot be used effectively a t high compressions, as such compressions-say 7: 1 -are obtainable from a practical standpoint only when detonation can be prevented. Benzene-gasoline mixtures have been used for a considerable period of time to prevent detonation, and in this respect have probably been satisfactory. Ordinary motor benzene, however, may be rich in gum-forming agents and of high sulfur content, so that considerable corrosion difficulties are possible. A very high-grade benzene, free from such products, is apparently difficult to obtain in large quantities, on account of the already existing market for the ordinary grades for use in making automobile-gasoline blends. Moreover, the production of benzene is not unlimited, and the requirements in war time for explosive purposes might be so great as to cause interference with its use as a fuel. Furthermore, it has a tendency to cloud a t low temperatures, and partial solidification within fuel lines might be caused at very high altitudes. The percentages of benzene necessary with compression ratios greater than 6:1, for instance, would be dangerous, from this standpoint, a t high altitudes. Other “antiknocks” have been proposed for use with gasoline, and various metallic ethyl compounds have been experimented with in this direction, excellent work having been accomplished by certain research workers in this field. It has been stated, however, that the effect upon spark plugs in high-compression engines would make its use for aeronautics inadvisable a t present. Alcohol has been experimented with for a considerable period of time, being mixed with gasoline in various proportions, usually 95 per cent alcohol being used. Ether, benzene, and other materials have been added to the mixtures to effect miscibility and prevent separation. Corrosion troubles due to the water present, the impurities in the benzene or gasoline used, separation of constituents, and the bad odor of the ether, have sometimes been observed with such mixtures, and they have not therefore been found generally satisfactory. Absolute alcohol has recently been made in large commercial quantities, and offers considerable possibilities as a constituent of motor fuels, being miscible a t all temperatures and in all proportions with gasoline.
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REQUIREMESTS FOR AIRCRAFT FUEL It might be well to outline in general the requirements for a satisfactory fuel for aviation purposes: Such a fuel must be made in large commercial amounts and be available in practically unlimited quantities. It should be low in cost. It should be practically free from gum-forming constituents or corrosive agents, so that it will not attack or plug up valves or affect the interiors of combustion chambers. 1 The Bureau of Aeronautics of the U. S. PL’avy has been experimenting for a considerable period of time on blended fuels for aircraft. Some preliminary observations made available to the writer through his association with the bureau in this work have been summarized in a general way. No final conclusions are being drawn from the work conducted to date-which is, of course, of a preliminary nature-this presentation being merely descriptive of the type of experiments now being carried on by the bureau.
