US2100049A - Method of burning fuel - Google Patents

Description

Nov. 23, 1937. K" 2,100,049

METHOD OF BURNING FUEL Filed NOV. 8, 1934 Patented Nov. 23, 1937 UNITED STATES PATENT OFFICE Oil Burner Corporation poration of Wisconsin Madison, Wis., a corpplication November 8, 1934, Serial No. 752,035 60laims. (Cl. 158-1175) This invention relates to processes of combustion and to processes or methods of burning fuel,

particularly in the vaporizing type of oil burners and in perforated wall type burners.

The fuels used in burners of the type to-which the invention refers are petroleum products which are commonly referred to as hydrocarbons. These hydrocarbons are found in a gaseous state, a liquid state, and a solid state. For example, if a crude oil is subjected to heat and distillation is eifected, hydrocarbons known as methane (CH4), ethane (C2Ha), propane (C3Ha), butane (C4H10), etc., are derived. These latter are all gaseous hydrocarbons and follow the formula CnH2n ,1... 2, and While. these might conceivably be iised in burners of the typeembodying the invention, it is not commonly done and operation is usually with liquid hydrocarbons.

Liquid hydrocarbons generally start with pentane (C5H12), hexane j(CoH14), heptane (C'zHm), etc., according to the formula CnHZn plus 2 until the solid group is reached, such as paraffin (CaoI-Isz).

Combustion, or the burning of fuel oil, consists essentially in heating the liquid to a sufliciently high temperature and adding suflicient oxygen to break down the hydrocarbon into carbon dioxide and water with the consequent liberation of heat.

There are two distinct processes by which this can be done, and in either case, the hydrocarbon is subjected to a sufficiently high temperature and sufl'icient oxygen must be present. The two methods of burning a hydrocarbon, such as fuel oil (CzoHez), are separate and. distinct and produce different chemical reactions, although in either case complete combustion may be secured provided sufficiently high temperatures are employed and sufficient oxygen-is present.

The first method, or the method commonly used in connection with pot type burners, is characterized by the absence of flame-in the lower portion of the bowl. Here the. fuel is admitted, vaporized at a relatively low temperature and mixed with air as it rises upwardly. The amount of air' admitted and the temperature at which this mixture of air and gases is maintained, is insufficient tocause effective combustion. As this mixture nears the top or outlet of the pot, it is struck by a comparatively large amount of air, causing combustion or burning to take place. The type of pots or bowls used are provided with openings in the side wall. These openings are few and widely scattered, starting relatively high from the bottom of the pot. Near the top of the pot are larger holes and a comparatively larger number of them which admit a large amount of' air at this point. In some instances, a slot or gap around the outlet is used to obtain the same effect. This commonly used method uses a limited oxygen supply, that is, insufficient oxygen is present to cause complete combustion when the vaporized fuel combines chemically with the oxygen present. Thereafter a large amount of oxygen is added, at which time complete combustion will occur. Before combustion occurs, the hydrocarbon, in combining with the oxygen present, undergoes three chemical changes. The first of these is known as the formation of alcohols and is represented by the formula:

2C20H42 plus Oi ZCzcHuOH 2C20H41OH plus O2=2C19H39CHO plus ZHzO Continuing this process, these aldehydes form acids in accordance with the following formula;

- 2C19H39CHO plus O2=2C19H39COOH Upon addition of the final large air supply, these acids burn, or break down, to form carbonv dioxide and water as'follows:

2C19H39COOH plus 5902=40CO2 plus 40H2O These changes represented show the formation of H10 and CO2 from C20H4z as the hydrocarbon passes through the alcohol, aldehyde and acid stages previous to burning.

The second known method of burning a hydrocarbon in a pot type burner consists in adding all the oxygen necessary for complete combustion at one time. This method causes rapid combustion, and great noises and extremely high temperatures occur in the pot. These high temperatures cause the pot to deteriorate rapidly, and due to the serious drawbacks of the method and the construction used in connection therewith, apparatus using thissecond method has practically disappeared from the market. The entire'reaction of adding a large initial amount of air to the hydrocarbon to cause immediate combustion as is inherent in this second method r can be shown by a single formula, inasmuch as the hydrocarbon starts burning immediately.

This shows the formation of H20 and CO: from CzoHn as'tlie hydrocarbon passes directly through V ment of the parts.

construction of the burner equipment, and the type of flames produced are apparent even to the most uninitiated.

The present invention utilizes certain preferred elements and characteristics relating to the burner construction as set forth in the first method, but employs certain principles of the method of burning as related in the second method. In other words, the second method of burning fuel oil with certain modifications, is used in connection with certain preferred modifications of perforated wall pot-type of burner as set forth in the first method.

An important object of the present invention is to provide a burner which utilizes advantages of the methods and apparatus used in the two aforesaid methods, and which eliminates the disadvantages inherent to those methods.

Another object of the invention is to provide an oil burner of the pot type which is provided with openings in the wall thereof, said openings being of a sufllcient size to permit entry of sumcient air to allow partial combustion of the fuel to occur at the bottom of the pot, the burner having additional openings in the wall to admit air suflicient to complete the processof combustion; and which is constructed and arranged so that the temperature in the bottom of the pot, during normal operation of the burner, is higher than the endpoint of any of the fuels used.

Another object of the invention is to provide a burner of practically noiseless operation and which, during operation, permits a flame to burn upwardly from the bottom of the pot.

A further object of the invention is to provide a process of burning relatively heavy fuel 0i1s without the formation of excess residual carbon and coking, and which is not limited to the lighter fuels, such as kerosene, range oil and distillate as recommended in conventional methods.

Still another object of the invention is to provide a. process for maintaining a normal operating temperature in the pot which is beyond that required to vaporize the heaviest hydrocarbon present, adding sufficient air so that combustion occurs immediately as the hydrocarbon is vaporized, and then adding additional air so that complete combustion of all the fractions of the hydrocarbons will occur at the rate at which fuel is being supplied to the combustion bowl.

The process consists generally in introducing hydrocarbon fuel into a vaporizing zone, maintaining said zone during -normal operation at such a temperature that vaporization of lighter hydrocarbons and heavier hydrocarbons occurs simultaneously, mixing the hydrocarbons with a sufl'icient amount of atmospheric oxygen at the point of vaporization to maintain such a temperature, and supplying additional oxygen progressively to complete the process of burning whereby excess carbon and coke formations will be practically eliminated.

Numerous other objects and advantages will be apparent throughout the progress of the following specification.

The accompanying drawing illustrates a selected embodiment of the invention and the views therein are as follows:

Fig. 1 is a detail vertical sectional view through one form of burner embodying the invention.

Fig. 2 is a similar View of a similar type of burner including slight vmodifications in arrange- In the present construction aperforated wall type of pot is used. The openings start relatively close to the bottom and are of such size as to admit only suflicient air to cause active combustion to occur in the bottom of the pot, or, in other words, at the point of vaporization. Additional holes are provided along the side walls of the pot above the lower openings, and these additional holes are of such size and in such numbers as to add air progressively to the burning mixture so that sumcient air for complete combustion has been added when the top or upper row of holes is reached. The lower holes directly adjacent to the bottom of the pot are of greatest importance and the amount of air which they admit determines the temperature in the vaporizing area. The greater the amount of air admitted at this point, the more complete will be the combustion at the bottom of the pot and consequently the higher will be the temperatures at this point. If these holes are relatively large, the temperatures will rise higher than is necessary. Also if these holes are made excessively large the noise of combustion will become noticeable. It is, therefore, important that these holes be of proper size so that only sufilcient air is allowed to enter to cause active combustion to start. Air is then added progressively through the remaining holes in the side walls of the pot as the burning mixture rises upwardly so as to complete the process of burning. Tests show that by-varying the lower row of holes any desired temperature in the vaporizing area can be 4 secured. For practical purposes it has been determined that approximately 1100 F. is ample to completely vaporize any of the fuels commonly used for domestic heating purposes and yet prevent disturbing noises from occurring.

Typical burner designsembodying the above principles, and which have been found very satisfactory in commercial use comprise a suitable outer casing or jacket 5 mounted on a suitable supporting base 6. A burner bowl or pot I having an exteriorly positioned annular flange 8 is supported by the outer surrounding side walls of the jacket 5. The surrounding walls 9 of the bowl or pot 'l are spaced a predetermined distance from the surrounding jacket or casing 5 to provide a space, or air passage Ill, which may completely surround the bowl 1. Air is supplied to the passage 10 through the duct I l, and a fuel inlet l2 supplies the liquid hydrocarbon to the interior or combustion chamber of tlie'bowl 1.

A refractory ring", preferably made of ceramic material, is arranged above the burner and overhangs the bowl I at its upper end as clearly shown in the drawing. A plurality of relatively large holes- I4 are made inthe walls of the bowl I, and these openings I4 may be larger and greater 'in number than the conventional arrangement now in use. The holes I4 may be carried down the side of the bowl to a point just-above the bottom of the bowl. openings blows directly across the top of the liquid hydrocarbon and causes initiation of combustion to occur at that point. As the flame in the bowl rises, additional air is supplied progressively in sufficient quantity-to complete the process of burning. In Fig. 2 the holes in the uppermost row are shown larger, as indicated at l5, whereby it is possible to shorten the height of the bowl.

The characteristic flame of a burner'having Air entering the lower holes or temperature in excess of 660 F. be maintained a the type of bowl in accordance with the present invention is long and narrow as indicated at I i.-

The flame starts from the bottom of the bowl and is spaced from the side walls thereof, passing up through the center opening'to a maximum height of probably several times the depth of the bowl. The amount of oil capable of being burned in a given size bowl is several times as great as in conventional burners, depending of invention has a capacity of eight quarts of oil per hour. The average rate of vaporization in the conventional low temperature types of burners as set forth in the two known methods is approximately th of a quart per hour per square inch of vaporizing surface as compared to approximately %th of a quart per hour in the present new high temperature type of burner.

'The exact temperature at which the bottom of the flre bowl or pot should be maintained is important, and, of course, this temperature will depend on the fuel to be burned. In any event the temperature in the vaporizing area must be kept higher, during normal operation, than the end point of the fuel used because such temperature is essential if continuous operation is to behad without the formation of residue. Fuel oil #2, American Oil Burner Association speciflca-' tion, sets forth the minimum flash point as being 125 F.; the maximum flash point 190 F.; and the 10% point 440 F.; the 90% point 620 F.. and the end point as 660 F. In order to completely burn this fuel, it is essential that in the vaporizing area during continued normal operation.

If the temperature in the vaporizing area is kept below 660 F., a portion of the fuel will remain unvaporized, and if operation is continued indefinitely under these conditions, unvaporized fuel will accumulate and as the heavier ends become heated in an insuiiicient amount of air for complete combustion, residual carbon or coke will be formed. In a similar manner if a burner is operated under forced conditions, that is, for long periods of time at a high percentage of its maximum burning capacity, the reflected heat of the flame causes the temperatures within the bowl to increase substantially. vaporization would then occur at a rapid rate and without increase in the amount of oxygenbeing supplied to theJower portion of the bowl, leaving it without suflicient oxygen to cause burning. Under these latter conditions temperatures in the vapor- .izing area will become suflicient to break down the hydrocarbon, with the formation of coke.

Therefore, in order to have continuous normal operation without the accumulation of residual formations in the vaporizing area of the bowl, it is essential to have temperatures in this area in excess of the end point of the fuel being burned,

' so that-the fuel will become completely vaporized,

and suflicient oxygen must be present at the initiation of vaporization to cause active combustion to occur at the point of vaporization, and at any rate of vaporization within. the capacity of the bowl. When such is the case and the flame rises in the bowl, further oxygen may be added by all times higher than the end point of the fuel' being burned with suflicient oxygen at the point of initiation of vaporization to cause immediate burning without the formation of the various gaseous compounds whichare formed in the successive intermediate steps previously described in connection with the conventional process. In other words, this is a direct process of burning, whereas the conventional might be termed indirect. This relatively higher vaporizing temperature is determined by the holes I t in the burner side walls, the location of the holes, and the number'thereof. By increasing the size of the holes I4 and placing them closer together, as well as keeping them close to the bottom of the bowl.

'the vaporizing temperature can be increased. it

is well known that any petroleum product or byproduct will completely burn if vaporized at a sufllciently high temperature and given enough oxygen, with the exception of the mineral deposits found present. Actual tests made with crude oil, hard carbon (or coke) formations, and tar, show these materials capable of burning completely, except for a few flne minerals which form mineral ash and which are usually so light that the air currents cause them to be blown away.

As previously set forth, the present invention is not'limited to the lighter fuels, such as kerosene, range oil, and distillate, but includesthe heavier fuels. ,If the principles of the present invention are adhered to, and a burneris designed for the particular fuel intended, in accordance with the present invention. the heavier fuel will become completely burned.

tain vaporizing temperatures as high as 1600 F.,

but these very high temperatures cause rapid deterioration of the bowl and in some cases crack the walls of the bowls, therefore necessitating replacement. Also, if the size of the openings is too greatly increased, the noise of combustion would likewise greatly increase. However, for practical purposes it has been found that a vaporizing temperature of 1100" F. will burn #1, #2 or #3 oils of the American Oil Burner Association specification with entire satisfaction without in any way causing deterioration of the bowl or increasing the noise of combuston. Tests have proven that the life of the burner bowl is indefinite when the vaporizing temperature of the bowl is approximately 1100 F. This temperature is sumciently beyond the end point of these fuels to give complete vaporization and yet prevent excess noise of combustion. Deterioration and shortening of the life of the bowl is prevented if this temperature is not exceeded.

A practical illustration, to further explain the invention, was made with a combustion bowl five erating at aproximately its maximum output of 1100 F. at various points in the vaporizing area, and that it is capable of successfully burning oil of extremely low gravity and high end point. The actual combustion occurs slowly and is extremely quiet. It is impossible to form carbon under any reasonable adjustment inasmuch as suiflcient air is admitted in the lower row of holes 'to cause initiation of combustion at thispoint,

avoiding the possibility of decomposing the fuel in an insufficient supply of oxygen with the resultant formation of carbon.

It is apparent that this construction can be altered and still cause combustion to occur as above described. For example, instead of the lower row of openings consisting of a row of holes of .136 inch in diameter, two rows of holes forming the same total opening might be employed and give practically identical results. Likewise, the remaining holes could be changed without necessarily changing the results.

Bowls of larger or smaller diameters, depending upon the amount of fuel to be burned per hour, may have the sizes of the holes, spacing and arrangement thereof proportioned accordpoint of the fuel being burned. Therefore, some carbon is likely to accumulate at this point. If

the fuel inlet to the burner is at the bottom floor of-the bowl asindicated at I! in Fig. 1, carbon will eventually cover over the opening and clog the fuel inlet. If the oil inlet to the bowl is placed in the side wall of the bowl below the lowermost row of holes M, a slight improvement is obtained as the carbon must first build up over the entire opening before it will be completely clogged. The arrangement of a rod within the feed line to dislodge the carbon would be of some assistance, but eventually the carbon would form over the path of the rod and completely envelop it and therefore render it ineffective.

By bringing the oil feed line into the side walls of the bowl as indicated at [8 in Fig. 2, the

carbon area is confined to a point directly overthe oil inlet and. immediately surrounding it, leaving the bottom of the bowl free and clear of any accumulation. By localizing this carbonizing effect, the carbon may be dislodged by means of a rod l9, Fig. 2, inserted in the feed line. The dislodged carbon formation, which will only occur directly over the end of the feed line, will drop to the bottom of the bowl where it will be struck by the incoming jets of air in the lowermost row of holes and be subjected to the heat of combustion causing it to be burned. By this arrangement the entire vaporizing area in the bottom of the bowl is maintained at a uniformly high temperature. The location of the feed line in the side wall of the bowl with the air* openings completely surrounding it, causes the carbon formation to localize, leaving the vaporizing area free and clear.

The present invention provides for normal opcrating temperatures higher than the end point of the fuel supplied, and inasmuch as the fuel is vaporized as rapidly as it is being admitted, no residual fuel will remain in the bowl. fractions of the fuel will be distilled at the same time and this condition exists as long as fuel is being supplied in amountswithin the vaporizing capacity --f the particular bowl used. In other words, distillation of the lighter ends followed by the heavier ends is not occurring, but all fractions of the fuels are being volatilized at once. Thepresent process, therefore, may be distinguished from others by the fact that all the fractions of the hydrocarbons are burned coincidentally. Y

By a temperature above the "end point" is meant to define such a temperature in the firepot and particularly in the zone where the oil is added as would cause the continuous vaporization of substantially all the fractions of the oil as they are added.

Also, all Y Many of the so-called fuel oils now being supplied are blends or mixtures of a relatively light volatile fuel and heavier fuel so as to produce a resultant fuel of the gravity desired. The mixing or blending of the various oils causes certain difficulties in the conventional types of burners because of the heavy hydrocarbons present. These mixtures or blends are, however, readily burned in an apparatus constructed in accordance with the present invention as proven.

changes as fairly fall within the scope of the following claims.

The invention is hereby claimed as follows:

1. The process of combustion which consists in introducing a liquid fuel into the combustion zone of a burner adjacent the bottom thereof, maintaining the bottom of the combustion zone at a temperature higher than the end point of the liquid fuel introduced during normal operation of the burner, supplyingsufllcient air at the bottom of the zone to cause the liquid fuel to burn at such rate at the bottom of the zone as to maintain said temperature thereof, and finally adding additional air progressively toward the top of the zone to allow complete combustion.

2. The process of combustion which consists in vaporizing liquid hydrocarbon fuel at a temperature higher-than the end point of the hydrocarbon, mixing suflicient air at the point of vaporization with the hydrocarbon fuel vapor to cause initiation of combustion and to cause such temperature to be maintained, and admitting air progressively to the burning hydrocarbon fuel vapor after initiation of combustion to complete the combustion of the fuel vapor.

3. The method of burning a liquid hydrocarbon fuel which comprises introducing the liquid hydrocarbon fuel into the bottom of a combustion space and supplying air to the bottom of said space in amount sufllciently restricted to cause a portion only of the hydrocarbon fuel to burn substantially at the bottom of the space, main-- taining the temperature at the bottom of said combustion space at a point sufllciently above the end point of the hydrocarbon fuel to cause continuous vaporization of substantially all the fractions of the hydrocarbon fuel, and maintaining said temperature by the combustion of said fuel.

4. The process of combustion which consists in introducing a liquid hydrocarbon fuel into an upstanding combustion space of a burner at the bottom of said space, maintaining the bottom of said combustion space at a temperature higher than the end point of the hydrocarbon fuel whereby to vaporize all fractions of the fuel, supplying sufficient air only at the bottom of the space to cause the hydrocarbon fuel to burn substantially at the bottom of said space, the air being in a quantity restricted sufiiciently to permit burning of only a portion of the fuel vapor.

5. The process of combustion which consists in vaporizing a liquid hydrocarbon fuel at a temperature sufficiently higher than the end point to cause substantially simultaneous vaporization of all of the fractions of the hydrocarbon fuel, mixing a restricted quantity of air suflicient to support combustion of only a portion of the fuel vapors therewith at the time of vaporization to permit immediate initiation of combustion, al=- lowing the residual vapors to move away from the point of vaporization, and admitting additional air progressively to the burning hydrocarbon fuel vapor as it moves to complete combustion, and maintaining said temperature by combustion of the, fuel.

6. The process of combustion which consists in introducing a liquid hydrocarbon fuel into one end of a combustion space, introducing into said space adjacent the place oij fuel introduction sufflcient air to vaporize said fuel at a temperature higher than its end point by combustion of a portion of the fuel vapor suflicient to cause said temperature to be maintained, and afterward introducing additional air progressively into said combustion space to complete combustion of the fuel vapor.

OSCAR L. BOCK.

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