Oil burners, oil furnaces, and methods of installation, have been the subject of many articles, but information concerning oil-burning systems, based upon scientific principles, is still in great demand, especially in the manufacturing districts of our country.
Fuel oil, as it is termed (this being the residuum from oil refineries), has for many years been of great service to our manufacturers, and has justified its popularity not only by producing a superior manufactured product, but by turning out approximately 50 per cent, more product than can be made with coal fuel under like conditions. To install a system requiring only an oil-storage tank, a small pump, and an oil-supply main with numerous laterals leading to the various burners, furnaces, boilers, etc., is a comparatively simple matter; and, because fuel oil is very volatile, it is not necessary to heat it, even during the winter months in a very cold climate. Furthermore, only a small amount of power is required to atomize fuel oil, this often being done by a positive pressure blower, or by a mechanical burner. An analysis of fuel oil, together with that of various other liquid fuels, is given in Table I.
In the middle and eastern sections of the United States, four systems for burning fuel oil have been successfully employed: namely, gravity feed; column gravity feed; the pneumatic system; and oil-pump feed.
Gravity Feed— In the gravity-feed system, the oil is supplied to the burner from a supply tank located approximately 8 ft. higher than the burners. This is the cheapest and most simple system to install and operate, but is not approved by the National Board of Fire Underwriters.
Column Gravity Feed.—By column gravity feed, the oil is pumped from the storage tank through the supply pipes to the burners. The excess oil is then forced into a column, consisting of a pipe 2 in. in diameter and approximately 20 ft. in height, provided at the top with a vent and an overflow pipe, which carries the excess oil which overflows back to the oil-storage tank. It is obvious that by this method, the pressure maintained at any burner depends upon the difference in level between the burner and the top of the oil column. When this difference in level is 16 ft., the corresponding pressure would be approximately 7½ lb.
The Pneumatic System.—In the pneumatic system, the compressed- air line of the factory is connected to the top of the oil-storage tank, thus putting the oil under a pressure, which may be regulated and controlled by means of an adjustable set-screw on the pressure-reducing valve on the compressed-air line. The pipe which supplies oil to the shop is coupled at or near the bottom of the oil-storage tank.
Oil-Pump Feed.—The pumping system is now most commonly used. Here a pump is employed to force the fuel from the storage tank and deliver it through a main supply pipe and laterals leading from it to the different burners. A pressure-relief valve, located at or near the pump, maintains the required oil pressure, as well as allowing the excess oil to return through an overflow pipe to the storage tank. In this system, the oil-storage tank is provided with a filling pipe, usually 3 in. in diameter; a man-hole; and a vent for the escape of gas. The regulations of the National Board of Fire Underwriters in the central and eastern parts of this country, require the tank, or tanks, to be located at least 30 ft. from any building, and to be covered with 2 ft. of earth. The type of oil pump is sometimes reciprocating, operated either by compressed air or by steam, and sometimes rotary or triplex, driven either by motor or by belt.
The Use of Oils Heavier than Fuel Oils.—The advent and popularity of automobiles and oil engines has created such a demand for by-products of fuel oil that it has now become too valuable to be used as fuel, notwithstanding its excellent quality. The manufacturing world must, therefore, install in future some system by which heavier oils can be used, and especially petroleums from the Mexican and Southern California fields, which are particularly available as fuel, because they contain so small a proportion of volatile oil, gasoline, kerosene, etc. Analyses of Californian and Mexican crude oils are given in Table I. The completion of the Panama Canal will, no doubt, result in vast quantities of this fuel being delivered to the southern and Atlantic ports of the United States.
Efforts have been made in the eastern parts of the United States during the past year and a half, to burn the heavy petroleum from the Mexican fields, which has an average gravity of 14° Baume. Through ignorance, when attempting to use this oil, no means were provided for heating the fuel in the storage tank; the oil pump which had been used for ordinary fuel was not changed to adapt it for a heavier fuel; the oil pipe lines were not laid so that the fuel would be constantly in circulation; and the pressure valve was not located appropriately for the heavier oil. The result was that the fuel system had to be shut down until the oil had been removed from the tanks by buckets.
I have often been amused by the efforts of persons who were accustomed to burn fuel oil, but who were not familiar with the use of heavy crude oils. For, notwithstanding that the heavy crude oil, when appropriately handled, is a better fuel than ordinary so-called fuel oil, because it has a higher calorific value per gallon, nevertheless, these efforts have often resulted in crude oil being condemned.
Oil-Burning Systems.—The system shown in Fig. 1, by the use of which any petroleum from 12° to 46° Baume can be scientifically used as a fuel, comprises: an oil-storage tank provided with a 5-in. filling pipe, a ¾-in. steam coil, a man-hole, a vent pipe, an overflow pipe, a suction-pipe flange, etc., as required by the National Board of Fire Underwriters; an oil pump of adequate proportions operated by steam or compressed air, or, if it be a triplex pump, driven by a belt or motor; and an oil-supply pipe so located that it follows the line of furnaces, boilers, kilns or other equipment, without the use of laterals, and with riser pipes from oil-supply pipe to burners, each of which must not exceed 3 ft. in length. The system must also include an appropriately located pressure-relief valve, and, adjacent to it, a by-pass valve to drain the oil- supply pipes when the system is not in service. An overflow pipe is connected with the relief valve and also with the by-pass valve, so that the excess oil will be led back to the storage tank. This system insures a constant, perfect circulation of the oil to each burner, and eliminates all dead ends on the supply lines.
Coating the oil-pipe threads with a paste consisting of litharge and glycerine before assembling, will prevent leakage. The unions should be ground joint. Gum or rubber should never be used, and lead gaskets should be used in flanges. I deem it always advisable to use malleable-iron beaded fittings on all oil-pipe lines.
Heating the Oil.—The object of heating the crude oil is to reduce its viscosity, and it should be heated in the storage tank to a temperature
that will allow it to be pumped easily. The oil is also heated in the supply and overflow pipes by running a steam pipe alongside of them, and inclosing both in an 8-in. square box which, when the pipes have been tested, is filled with dry sand. By regulating the amount of steam passing through the heater pipe, the oil is supplied to the burners at a temperature just below its vaporizing point. When the pipes are inclosed in the manner described only a small quantity of steam is needed, and, by laying the steam pipe below the oil pipe in the box, it is accessible at all times. Some persons prefer to heat the oil by passing a 3/8-in. steam pipe through the oil-supply pipe. The first cost of this is cheaper, but, if the steam pipe should leak, it is difficult to make the necessary repairs.
Accurate Temperature Required.—The economic advantage of accurately heating the oil to the desired temperature is shown by some tests in which a saving of 20 per cent, of Mexican crude oil required was made by heating it to 160° F. (which is 10° below its vaporizing point) instead of 120° F. The control of temperature is so important that thermometers should be used in direct contact with the fuel as it passes to the burner (see Fig. 2). Two or three such thermometers, well located, will save much oil and increase the output of the furnaces. The overheating of the oil is an example of carelessness which should be severely condemned, and which may readily be detected by the puffing of the burner, due to escaping vapor.
Liability to Fire through the Use of Oil.—There is less liability of fire from liquid fuel, employed by means of a modern fuel-supply system, than there is from the use of coal or coke, yet there are many different rules prevailing in different parts of the country for the location of oil-storage tanks. In the eastern and middle sections of our country, the law of the National Board of Fire Underwriters require all storage tanks to be placed 30 ft. from any building and covered by 2 ft. of earth, while in San Francisco they are placed in the space formerly used for coal, immediately under the sidewalk, and are filled by oil-tank wagons or oil-tank cars from the street. I have at hand evidence which proves that, of the hundreds of oil-storage tanks located in the city of San Francisco at the time of the late earthquake and disastrous fire, not one exploded or increased the conflagration or was the direct cause of financial loss. It is impossible for many manufacturers to place oil-storage tanks 30 ft. from any building, because their buildings cover their entire ground, and the Fire Underwriters’ law quoted forbids them to be placed under the
sidewalks. This places some manufacturers at an unfair disadvantage in competition with others, because it prohibits them from the use of crude fuel for such purposes as the heat treatment of metals, drop forging, welding, etc.
All manufacturers are to-day looking for quantity as well as quality of output, and, as oil can be safely stored under the street sidewalk in one section of the country, then, why can it not in another section? In other words, why should we not have uniform laws? If crude oil were as volatile as gasoline, there might be some grounds for fear, but it is not. As far as the danger from dripping oil is concerned, it may be obviated by sprinkling over the floor of the pump house, and around the storage tank, a mixture of 8 lb. of sodium carbide with 1 bushel of sawdust.
Tar as a Fuel.—The present rapid increase in the use of by-product coke ovens makes available an excellent fuel in the tar which is obtained as a by-product, to the extent of about 10 gal. per ton of coal coked. Many steel works have found it to their advantage to burn this tar, which is usually conveyed to the burners by gravity, the storage tank, as shown in Fig. 3, being placed 3 or 4 ft. above the burners, being provided with a heater coil and with heater pipes running alongside the supply pipes, substantially as described above. Steel plants are seldom insured, and any plant which does not carry insurance can burn heavy oil successfully in the same manner.
“Water-gas tar” is a residuum from gas works using the water-gas system, and is an excellent fuel, which has a calorific value of 16,970
B.t.u. per pound, equivalent to 161,200 B.t.u. per gallon, there being 9½ lb. of this tar per gallon. It is ordinarily supplied as fuel under the boilers of the plant by the gravity-feed system just described.
Burners.—Burners should be constructed so as to atomize liquid fuel of any specific gravity purchasable in the open market without changing any of the parts and without carbonization. One form of burner is shown in Fig. 4. Burners should be simple to operate, and as few as possible should be used in each equipment. The flames should fill the fire box, or charging space, of the furnaces, completely, in order that the heat may be evenly distributed. If mechanical burners are used, the oil pressure should be sufficient to insure complete atomization, and the construction of the burner should be such as to provide either a round or a flat flame, as required. If atomizing burners are used, the pressure of oil and air or steam must be constant, because any fluctuation in the pressure of either the oil or the medium used for atomizing will give a variation in the kind of flame and in the temperature. For example, we may have alternatively a flame that is oxidizing, reducing, or smoky, whereas the combustion system should give complete control of the kind of flame whenever necessary. A smoky flame should always be avoided, because it causes loss of fuel and decrease in temperature. Technically speaking, carbon dioxide indicates perfect combustion, while carbon monoxide shows imperfect combustion.
Kinds of Service for which Liquid Fuel is Suitable.—The burning of liquid fuel is a science, and only by burning it scientifically can successful results be obtained. To condemn oil fuel is simply an exhibition of ignorance, for it has been thoroughly tested throughout the eastern and middle States, and the heavy California oil has been successfully burned in every form of service on the Pacific coast for the past 25 years. Petroleum of low specific gravity is the fuel of the twentieth century, and the demand for it will increase every year from every manufacturing nation which endeavors to keep pace with modern progress. No fuel has, however, been so wastefully used as petroleum. For example, many open-
hearth furnaces require 61 gal. of oil to produce a ton of steel; whereas, 32 gal. should be sufficient, and I could mention 20 other instances showing equally great variations. A continuous billet-heating furnace, 66 by 10 ft., is shown in Fig. 5.
Petroleum should be used only in those classes of work in which it is more economical than coal, coke, or gas. I regret to say that in many instances it has been employed where it could not possibly compete in price with other fuels produced in the immediate vicinity. Comparisons may be readily made by the following figures: Assuming that the petroleum has the calorific value given in Table I, and assuming that good bituminous coals have calorific values of 14,000 B.t.u. per pound, then, in good drop-forge practice, 60 gal. of oil would be equivalent to 1 long ton of coal; in boiler practice, under like conditions, 147 gal. of oil would be equivalent in evaporating power to 1 long ton of coal; in welding locomotive flues, 58 gal. of oil are equal to a ton of coal, and in locomotive service on an average division, one can ordinarily estimate that 180 gal. of oil are equivalent to a ton of coal. In locomotive service, the use of oil eliminates the smoke nuisance and the loss caused by the burning of ties, grain fields, forests, or buildings. In large forging plants 82 gal. of oil will do the work of a ton of coal. The use of oil has, of course, the advantage in the matter of there being no ashes to handle, and, in a large plant, one man can fire and water-tend a battery of 12 oil-fired boilers with perfect ease.
During the past five years, oil has been much in demand to increase the efficiency of boilers by supplementing the coal fire during the peak of the load, and has also proven so valuable for emergency boilers in water-power plants, etc., that the actual cost is not considered in this service.
Three barrels of oil (42 gal. per barrel) are equivalent to 4,615 lb. of hickory; 4,200 lb. of white oak; 4,400 lb. of yellow pine. Six gallons of Texas crude oil are equivalent to 1,000 cu. ft. of natural gas.
The calorific value of petroleum produced in all sections of the world is about the same, while the calorific value of coal varies greatly. For example, the calorific value of Pocahontas coal is 15,391 B.t.u per pound, while that of Illinois coal is only 10,000 B.t.u. per pound.
I give these data simply to show that it requires actual operating tests in different classes of service to obtain a definite comparison between the relative value of oil, coal, wood, and gas, as fuel. To attempt to make such a comparison by calculating with the calorific values of the various fuels is only misleading, because heat is required to liberate the gases of coal, and in welding, for example, you must first coke your fire when using bituminous coal, and therefore there is a two-fold waste of fuel; namely, the heat required to liberate the gases and the waste of heat while coking the fire, because it is impossible to weld with a green fire. In flue-welding locomotive flues, commonly termed in railway shops “safe-ending,” one can attain and maintain a welding temperature by using modern oil furnaces, and 60 flues can be welded per hour; using coal instead, it is good practice when 14 to 16 flues are welded per hour with the same number of men. Thus the use of coal in this service involves a waste of both time and fuel.
In California, where petroleum is cheap and coke is costly, oil-fired air furnaces should be used, instead of coke-fired cupolas, for making gray iron castings, because oil produces a better quality of metal with a higher tensile strength and the furnace up-keep is less. Fig. 6 is a sectional view of a 12-ton air furnace. California petroleum is low in sulphur, while Mexican oil is high in sulphur, but all consequent difficulty can be obviated if a combustion chamber is used on the furnace and the proper amount of air is admitted under the flame at the correct time and place. If some inventor, having the audacity of genius, would invent an oil-fired cupola of modern construction, it would be a great blessing to those in the foundry practice who are situated where oil can compete in cost with coke in present cupola practice, and, as such a process would
occupy but one-fourth of the shop space of a corresponding air furnace, it would be in great demand.
The value of certain steels depends upon their heat treatment, and because of the perfect distribution of the heat and the absolute control over the temperature, oil is an incomparable fuel for this purpose.
In the types of service mentioned below, the use of oil has been thoroughly tested, and it has been found to be an ideal fuel, but, of course, the economic effect will depend upon the relative price of oil and coal in the locality where the industry is carried on: For annealing, for asphaltum mixers. Babbitt heating, bolt making, brass melting, brazing, bread ovens, etc., brick and art-tile kilns, case hardening, cast-iron melting, rotary cement kilns, channel-iron heating, chocolate-bean roasting, continuous heating, copper-plate heating, copper refining, core drying, crematories, crucible brass melting, crucible steel melting, drop forging, enameling, flue welding, glass lehrs, glass melting, incinerators, indirect-fired furnaces, japanning ovens, ladle heating, locomotive steam raising, locomotive-tire heating, malleable-iron and gray-iron air furnaces, mold drying, ore smelting, plate heating, pipe bending, pipe-flange welding, portable torches, rivet making, rolling-mill work, rotary kilns, shaft and billet heating, sand drying, sheet-steel heating, steel melting, steel mixers, tar stills, tempering, welding scrap iron, wire annealing, wire making, as well as stationary, marine, and locomotive boilers of all types and capacities.
In conclusion, I refer to an exhaustive report compiled in 1904 by the Liquid Fuel Board of the United States Navy. The test was under the direction of the late Rear Admiral George W. Melville, but the work was done by the President of the Liquid Fuel Board, one of our honored members, Rear Admiral John R. Edwards. This report stands to-day as the highest authority in marine boiler practice. The fuels used were procured from various sections of the United States, and these tests brought liquid fuel to the attention of the world, with the result that all the leading nations are installing it on their battle ships, and some authorities believe that the liquid-fuel question is one which may determine the relative naval strength of the nations. It should, therefore, be our aim as loyal Americans to obtain as wide a knowledge of this fuel as possible, and we believe that the American Institute of Mining Engineers was not only serving the best interests of the manufacturing world, but those of our nation, when it established the Committee on Petroleum and Gas, to promote research on this important fuel, the supply of which we believe to be fully equal to the demand, as has been the case with coal, natural gas, and other fuels.
