US2661054A - Apparatus for vaporization and combustion of hydrocarbon distillates - Google Patents

Description

Dec. 1, 1953 E c. HYATT ETAL 7 2,661,054

APPARATUS FOR VAPORIZATION AND COMBUSTION 0F HYDROCARBON DISTILLATES Filed June 26, 1948 Patented Dec. 1, 1953 UNITED STATES 'i'NT QFFICE APPARATUS FOR VAPORIZATHON AND COM- BUSTION 0F HYDROCARBON DISTIL- LATES Edwin C. Hyatt, Luther L. Lyon, Jr., and Willis R. Swanson, Wichita, Kane, assignors to The Coleman Company, Inc, Wichita, Kane, a corporation of Kansas Application June 26, 1948, Serial N 0. 35,318

7 1 Claim. 1

This invention relates to combustion apparatus which is particularly adapted for the vaporization and combustion of hydrocarbon distillates. The invention is effective in the vaporization and combustion of straight run hydrocarbon distillates, but is particularly useful in the vaporization and combustion of cracked fuels such as catalytically cracked and thermally cracked or reformed hydrocarbon distillates, or any combination thereof.

The present application is a continuation-inpart of our copending application, Serial No. 20,644, filed April 13, 1948, for vaporization and Combustion Process for Hydrocarbon Distillates.

Distillate fuel oils are classified generally, for commercial purposes, in two groups: straight run fuels, by which we mean fuels that are produced essentially by distillation processes alone; and cracked fuels, by which we mean fuels produced by thermal, catalytic or reforming processes.

The general problem is that of utilizing hydrocarbon distillate fuels in a combustion apparatus without producing excess formations of carbon, asphaltic or tarry-like residues, soot' or smoke. The widespread use of cracking processes for the production of high octane gasolines has resulted in greater supplies of the by-product distillate fuels originating from these cracking processes. Many difficulties have been experienced because these cracked fuels form much greater quantities of undesirable residues during vaporization and combustion than do straight run fuels.

To cite a specific example of difficulties encountered, excessive vaporization and combustion residues were produced when a cracked fuel was used in a common pot-type vaporizing oil burner. Less vaporization and combustion residues were produced when a straight run fuel was used in this burner.

Similar difiiculties are experienced with other types of oil burners, diesel engines, and other oil-burning devices. The greatly increased use of oil-burning devices has caused fuel shortages, particularly of straight run fuels. By blending straight run and cracked fuels, a mixture is available that performs somewhat more satisfactorily than the original cracked fuels; however, the fundamental difficulties still remain, although modified in degree. A process that could be employed for the use of cracked fuels would make possible efficient utilization of all available fuel oils.

The conventional method of introducing fuel oil to most burners is by conveying the oil through a pipe or channel where the oil is in wetting contact with the pipe. In pot-type burners, the oil is allowed to flow from the pipe onto the bottom, with the oilwetting the bottom of the burner. If the temperature of the pipe or bottom is such that some vaporization of the oil is accomplished, then tarry residues may deposit upon the bottom and upon the pipe, and eventually may impede the flow of oil through the pipe. The collection of tarry residues in the burner limits the efficient life of the burner. Further, in existing types of oil burners, the mixing of fuel oil vapor with air is usually accomplished in a space Where combustion of the vapor and air is takingplace. This condition tends to prevent the adequate mixing of the vapor and air before combustion is initiated, and usually results in the formation of soot and smoky or yellow colored flames. Cracked fuel oils particularly, which contain more aromatic and olefin hydrocarbons, either alone or in admixture with straight run fuels, cannot satisfactorily be hanled in such equipment.

An object of the present invention is to provide apparatus for the vaporization and combustion of hydrocarbon distillates which will result in a minimum production of such residues that would tend to interfere with the operation of the apparatus. Another object is to provide means whereby cracked fuels, in addition to straight run fuels, may be vaporized, mixed with air, and subjected to combustion process while maintaining the apparatus therefor in clean and efficient use over long periods of time. A still further object is to provide apparatus for utilizing hydrocarbon distillate fuels by employing non-wetting vaporization on a hot surface under conditions which result in a minimum production of residues which if formed would interfere with the operation of the apparatus. Yet another object is to provide apparatus in which an adequate mixing of fuel oil vapor and combustion oxygen is obtained before combustion of the mixture is allowed to take place, means being provided for preventing the flame from being propagated back into the vaporization and mix ing zones. A further object is to provide ameans of introducing the oil to be vaporized with respect to the vaporizing surface, whereby the feeding means for the liquid fuel is maintained at a relatively low or cool temperature so that residues do'not form thereon, etc. Another object'is to provide combustion apparatus in which the flame of the burner is utilized for heating the'surface on which the oil is vaporized to a non-wetting temperature. A still further object is to provide apparatus in which air is mixed with vapors evolved from a surface maintained at non-wetting temperatures, a conduit being provided for leading the vapors to a point where combustion occurs near and heats said surface while at the sametime means are provided for effectively mixing the oil vapors with the air in the conduit, Otherspecific objects and advantages will appear as the specification proceeds.

The current trend of opinion among those 3 skilled in the art has followed mainly;tworpa.t terns. One view is that temperatures in the vaporization zone should be kept low in order'to prevent cracking and the accumulationofcarbon deposits. Another view isthat the burning of cracked oil fuels which contain more aromatic and olefin hydrocarbonsshould be avoided be"- cause of their tendency to.build.up tarry and coke deposits. Cauley and Linden' (Oil and Gas Journal, Aug. 10, 1946), state: Burner manufacturers have previously found that: high temperatures in the bottom of pot-type burners were.

conducive to good operation with straight run fuels, whereas present studies have shown the reverse to be beneficial in combustion of aromatic fuels. A reorientation of ideas upon combustion in such burners is'therefore indicated.

Griswold in Fuels; Combustion and Furnaces (1946), described on page 276, the art and difficulties as follows: vaporizing burnersrequire light fuelswhich vaporize at temperatures below that at which appreciable thermal decomposition or cracking occurs. Nevertheless, carbon accumulates slowly, even withfuels as light as kerosene, necessitating periodical cleaning of the wick or pot.

Cauley and Linden (Oil and Gas Journal, Aug. 10, 1946), believe that radiant heat would speed up'cracking of aromatics in the liquid state to such an extent that many molecules are likely to crackand join togetherbefore they vaporize. They designed a pot-typeburner with a radiation shield near the bottom in an attempt to-prevent this from occurring. They summarized their combustion studies of cracked'fueloils by stating, Combustion studies pointed to the desirability of a progressive type of oxidation of aromatics, if such couldbe achieved, and suggested lower temperatures during mixing of air and oil vapors.

Moyer in Oil, Fuels and Burners (1937), page 84, states'that, vaporizing burners are not well suited to burn the heavier oil fuels for the reason that they are likely to contain hydrocarbons which will not resist cracking before they reach the vaporizing temperature. When a'large drop, or even a film, of" oil comes into contact with the hot metal of the pot, the cracking-is likely to occur in that part of the'drop of oil which is nearest the highly heated surface; and in that case the rest of the oilin the drop forms a blanket between the solid products that result from cracking and the air, so' that solid carbon is deposited inan unburned'condition on the surface'of the pot."

i-leiple and Sullivan in their'paper Mechanisms of Combustion andTheir Relation to Oil Burner Design, presented at the annual meeting of American Society of Mechanical Engineers, December 1-5, 1947, made the following statement regarding this subject: Accordingly, the presence of olefins in fuel-oil distillatesmay give; rise to tarry, and coke-like deposits ifthe temperature to which unburned fuel is exposed should become excessively high;

We have discovered that liquid oil, including the cracked fuel oil distillates, may be efficiently vaporized by feeding the oilonto a very hot surface, the temperature of the surface being so high as to prevent the liquid oil fromwetting the surface when applied thereto. Inone embodiment of our invention, oil is dropped or fed onto a hot surface maintained at a temperature at which the oil will not wet the surface and on which the oil forms in a dropor droplets,

' are": probably vaporizing surface--gaseous f with each drop essentially surrounded on all sides by its own vapor. Under these conditions, where liquid fuel oil as such is probably never in. contact with the hot surface, very little, if any, carbon, asphalt or scotis formed due to the vaporization of the fuel oil.

We use the term wetting in its usual meaning-todescribe the conditions existing when lit:- uid fuel oil'is inintimate contact with the v a porizing' surface, forming an oil-surface interface-:- Similarly, non-wetting is used to scribe. the conditions existing when f el oil is not in intimate contact with the vapoi ing surface, and where the interfaces formal oilgand'gaseous fuel cit-liquid fuel oil. Wh liquid fuel oil does not wet a surface, it c the-'actionof'water on a very hot iron surface.

We have'found that when fuel oil is in wet ting contact with a steel. surface whose temperature is such that an appreciable vaporization of the oil occurs, tarry residues are formed. However, if the fuel oil is in non-wetting contact with a steel surface whose temperature is such that vaporization of the oil occurs, very little, if any, tarry residue is deposited on the steel surface.

The new apparatus employs a conduit leading from'a blower or from any other source of air currents, etc. The conduit passes over a hot surface which is maintained at a non-wetting temperature and the conduit is bent back upon itself'so'as to discharge products of combustion adjacent to the hot surface for heating the same. Oilis fed by any suitable means but preferably through the conduit so to drop the oil or otherwise discharge it upon the surface itself. The apparatus contemplated may take a norm ber: of'forms; One form of the apparatus is iT.- lustrated' in the drawings, in which Fig. 1 is a broken side view in elevation and partlyinvertical section of apparatus embodying our invention; and Fig. 2, a broken perspectivei view ofthe" discharge end portion of the fuel mixture'conduit.

Inthe illustration. given, Hi designates a supply tank from which a pipe 5! leads downwardly'to-a metering device or valve 12. li'l themetering device i2, the pipe 13 leads thron a fuel' mixture conduit Hi and is provided with a downwardly extending discharge end it.

The conduit M communicates at its rear end withithe discharge'end of a blower casing 16 equipped with a blower or impeller Ii.

Communicating with the lower portion of conduit. l kisa' casingiB providing a vaporizing-chamber. The bottom of the casing 18 con stitutes a vaporizing plate 19 against which flame may be impinged to raise the tempera-- ture of: the. plate preferably to a non-wetting temperature; We prefer to" equip the plate IL with depending web members 2% for increasing, the concentration of 'heat upon the plate. The discharge point of the fuel pipe is is aligned with the'outlet from the vaporizing chamber.

The conduit I4 is turned upon itself to form a substantially U-shaped structure with an outlet just below the plate i9. In the structure illustrated, the outlet 25 of the conduit i i COl'Ilmunicates with a cylindrical grid 22 provided with perforations 23. The entire circumference of the cylinder 22 is perforated with openings 23, as shown in Fig. 2, through which the flame may. be propagated. Single or multiple grids may be used and by the term'fgridf We mean such single or multiple structures; f A pilot tube 24 is preferably located adjacent to the grid 22 so as to ignite the combustion gases therein and is also so located as to direct heat against the plate It to bring it to a nonwetting temperature. It will be understood that any suitable type of auxiliary heating meansmay be employed. I

Proper mixing of the air with the fuel vapors within the conduit [4 is important and weprefer to equip the conduit internally with vanes or other devices for effectively. blending the vapors with the air or other oxygen-containing gases. In the specific illustration given, we provide vanes 25 supported upon a rod 26'so that the current of air and vapors are caused to rotate and become mixed with each other prior to their admission into the grid 22.

The flame emanating from the grid may burn in the air or it may be combined in a chamber formed by the burner casing 2! and the casing 21 may be provided with the usual stack 28. 3

We prefer to equip the fan casing I6 with an extension providing an overflow chamber 29 having a partition wall 39.! therein. Upon a pivot pin 3'! is mounted a rod 32 supporting the float 33 at one end and a mercury switch 34 at'the other end. Should fuel oil overflow into the chamber containing the float 33, the float will rise and tilt the switch 34 so as to break the circuit of the blower motor, and also to operate electrically-operated means for stopping the flow of oil, the flow of gas to the pilot, etc. "Since such structure is well known, a detailed descrip- 2 tion is herein believed to be unnecessary.

In the specific form of apparatus illustrated in Figs. 1 and 2, the air or other oxygen-containing gas is delivered by the blower through conduit M where it picks up the vapors from the hot surface i9. The surface 19 preferably is heated to a non-wetting temperature so that the drops of fuel oil discharged from the pipe is will form substantially no residue within the chamber of casing 13. The vapors rise from the vaporization chamber, pass into the conduit 14, and are carried with the current of air upwardly and around the U-bend and into engagement with the mixing vanes 25. The vanes 25 may be placed at various points along the conduit as needed to produce effective mixing. The combustion mixture containing air and fuel oil vapors is discharged into the cylindrical grid 22 and combustion occurs within and outside of the grid, as indicated in Fig. 1. The flames from Fuel Oil Property (Mobilheat) Initial Boiling Point, F .L

% Boiling Point, F 50% Boiling Point, F...

95% Boiling Point, F..- 578 End Boiling Point, F 624 A. P. I. Gravity 33.3 Aniline Number, F 135.0 Carbon Hydrogen Ratio 6.

Diesel Index with gun-type burners.

' EXAMPLE 1 a A domestic type of forced draft oil burner, of the general design shown in the drawing, was constructed having a capacity of 55,000 B. t. u. perhour. The flame was arranged so that it provided the heat for the surface that vaporized the oil. This burner consumed 100 gallons of.catalytically cracked (Mobilheat) No. 2 fuel oil at the rate of 3.7 lbs. per hour. The ternperature of the vaporizing surface was 1000 F., and the drops of oil did not wet the vaporizing surface. The vaporization residue averaged 0.03 gm. per gallon of fuel consumed. This is in. contrast to approximately 4.0 gm. per gallon ofresidue produced in conventional vaporizing burners under the same condition. The performance of the burner was also superior to the conventional oil burners in other respects. The measured carbon dioxide was 14.7% and less than 0.05% carbon monoxide, with an indicated combustion efficiency of approximately 82%. The smoke measurement was 100% clear as measured by the ICHAM tests.

Because this burner operates properly with lower air velocities than are necessary with guntype oil burners, quieter operation was possible with blower motors of significantly lower horsepower. A simple gravity fuel supply system with an oil flow safety cutoff float mechanism was employed instead of the more complex and expensive pumps and safety controls necessary I These simplifications made possible an oil burner weighing only a small fraction of the weight of a conventional gun-type oil burner.

' EXAMPLE 2 A natural draft type of burner was oonstructed for intorducing the oil and vaporizing the oil under non-wetting conditions. This burner operated at a rate of 35,000 E. t. u. per hour time produces 14.7% carbon dioxide was believed to. be the result of vaporizing in the manner already described and the mixing of the vavpors with air before the mixture was ignited.

In additional operations, we have further increased the ratio of fuel oil vapor to combustionoxygen such that the resulting flue gases analyzed 11% 'to 12% carbon. dioxide, 4% to 6% carbon monoxide, and 0-l% oxygen. The flames in such work were completely blue. From this work, we believe that adequate mixing of fuel oil vapor and combustion oxygen is r a primary factor in eliminating the formation of soot or smoke.

Some of the foregoing operations were performed with a metallic grid separating the combustion chamber from the mixing chamber. In other experiments, we dispensed with the use of the grid by increasing the velocity of the cornbustible mixture in the mixing chamber which prevented the combustion taking place until the velocity was decreased by expansion ofthe mixture into the combustion chamber. This again resulted in completely blue flames and no detectable formation of soot or smoke' The walls of the mixing chambers were maintained at a high temperature in order to prevent condensation of the fuel oil vapor on the wall.

In the practice ofthe invention with different types of oils, it is found that the wetting temperatures and non-wetting temperatures vary with the difierent oils. It is therefore not possible to set out a specific temperature which may be designated as the initial non-wetting tempera" ture for all. the oils. Generally, we that with commercially available fuel oils whose 96% boiling point under 708" 3?. (similar to the oil in Example 1), the initial non-wetting temperature on a steel su lies above 766 F. 671th heavier fuel oils, he initial nonavetting temperature may be as high as 1569 Where substantial quantities of oxygen are present v e prefer'to maintain the temperatures below 1200 However, ignition of the vaporiz d oil within the vaporizing chamber provided by casing 18 is substantially controlled in our method of operation by causing the vaporized oil to meet the stream of air considerably above the vaporizing surface 19; that is, within conduit Thus, a high concentration of vaporr'ed fuel oil is maintained Within the vaporizing chamber, which th by effectively envelope shields the vaporn9; surface as W911 as the hotter side walls of casing i8. Furthermore, it will be understood that the EX? ignition temperature for any given fuel-air mixture depends not only on the conc ntration of fuel in the mixture, but also on the time of 6X- pcsure to this temperature. In tests to determine the temperatures required Within the vaporizing chamber to cause actual combustion, it was found. that an ignition temperature of around 2699" F. was required. The lowest temperature at h such combustion was obtained with any 0 the oils mentioned herein was 1860" F. The initial non-wetting temperature for any fuel oil is easily determined in a moment by dropping the oil upon a hot plate whose temperature is being raised between about 766 F. and 1569 F. and observing when the oil ceases to wet the surface and begins to dance upon the surface. For commercial pur poses, the temperature of the surface should be held substantially above the initial non-wetting temperature.

A No. 1 oil was found to have an initial nonwetting temperature of 725 lhe (Mobilheat) No. 2 oil was found to have an initial non-wetting temperature of 760 F. An A. S. '1. M. reference oil had initial non-wetting temperature of 825 F. Heavier oils were found to have substantially higher initial non-wetting temperatures.

While in the practice of the invention, we pre fer to employ a non-wetting temperature for the oil, it will be understood that there are tempera tures which are substantially non-wetting temperatures or so close thereto that an appreciable accumulation of carbon which would interfere with the operation does not occur, and such conditions are contemplated as being a part of the invention herewith.

While in the foregoing specification, we have set out a specific embodiment of the invention in great detail for the purpose of illustrating the invention, it will be understood that such details of structure may be varied widely by those skilled in the art without departing from the spirit of our invention.

We claim:

In an apparatusfor burning acombustiblemixture containing air and fuel oil vapor, the combination comprisinga conduit having an air inlet at one end and a combustible mixture outlet at the other end, said conduit having a generally horizontal portion adjoining said air inlet and a gooseneck portion between said horizontal portioniand-said combustible mixture outlet, blower means for supplying said air to said conduit inlet under'pressure, an oil burner secured to the outlet end of said conduit at a spaced distance beneath said horizontal conduit portion, a casing providing a vaporizing chamber located between said horizontal conduit portion and said burner, said casing having-a bottom portion adapted. to be heated by said burner and providing on its inside a vaporizing surface in the bottom of said chamber, said chamber communicating with the bottom of said horizontal conduit portion, a pipe for feeding liquid'fuel oil onto said vaporizing surface, said pipe extending downwardly into said horizontal conduitportion at a point spaced from said vaporizing chamber in the direction of said blower means, sloping downwardly within said conduit in the path of the air discharge from said blower means to a point adjacent said vaporizing chamber, and terminating in a downwardly-extending discharge end above said vaporizing surface, and a casing providing an overflow chamber communicating with the bottom of said horizontal conduit portion at a point spaced from said vaporizing chamber in the direction of said blower means, the bottom of the upper portion of said conduit gooseneck being elevated above the bottom of said horizontal conduit portion so that oil overflowing from said vaporizing chamber will flow in the direction of said blower means and into said overflow chamber.

EDW-I N C. HYATT. LUTHER L. LYON, JR. WILLIS B. SWANSON.

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