US3323574A - Liquid-fuel burner - Google Patents

Description

June 1967 o. H SCHADE, JR 3,323,574

LIQUID-FUEL BURNER Filed April 15, 1965 2 Sheets-Sheet .2

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United States Patent 3,323,574 LIQUID-FUEL BURNER Otto H. Schade, J12, North Caldweil, NJ assignor to Radio Corporation of America, a corporation of Delaware Filed Apr. 15, 1965, Ser. No. 448,533 Claims. (Cl. 158-54) ABSTRACT OF THE DISCLOSURE the lighter vapors. The superheated vapors are then directed to a burner where the vapors are burned.

This invention relate to liquid-fuel burners, and particularly to an improved and novel means for utilizing, in an efficient and trouble-free manner, liquid fuels, such as leaded gasoline, with such burners.

In certain applications in which liquid-fuel burners are used, such as in the provision of heat for thermoelectric generators used in remote and out-ofthe-way places, it is desirable that the burners operate unattended in an efiicient, safe, and trouble-free manner for long periods of time. For reasons of practicality and efficiency, it is also desired that the burners be fireable with a Widely used and inexpensive fuel, such as leaded gasoline, andthat the burners be operable without powenconsuming auxiliary devices, such as combustion-air blowers, and the like.

For avoiding the use of auxiliary combustion-air blowers, a vaporizing burner which aspirates its own combus- .tion air is preferable in these appliactions. One problem with known vaporizing liquid-fuel burners is the difliculty of obtaining complete combustion of the fuel entering the combustion zone. Gasoline and related petroleum fuels comprise constituents having boiling points which vary over a relatively wide range, and it frequently occurs that the liquid fuel is incompletely vaporized prior to its introduction into the burner combustion zone. The unvaporized constituents do not completely burn thereby producing soot which accumulates on the various burner members and upon the element or load heated by the burner. The soot deposits interfere with eflicient combustion of the fuel and with eflicient and uniform transfer of heat to the burner load.

A further problem with the use of liquid-fuels, and especially leaded gasoline, is that various substances from the fuel are deposited onto the walls of the various passageways leading to and Within the burner which constrict and eventially clog these passageways. Also, certain of these deposits are combustible thereby creating a fire hazard. Frequent cleaning of these passageways is thus required.

It is an object of this invention to provide a novel and improved liquid-fuel vaporizing burner operable safely and efliciently for long periods of unattended time, and usable with liquid fuels such as leaded gasoline.

Another object is to provide a novel and improved means for converting liquid fuels such as leaded gasoline into a vapor suitable for efficient and trouble-free use wit-h burners.

For achieving these objects, a vaporizer is provided to which the liquid fuel is fed under pressure. Within the vaporizer, and in the path of the liquid fuel, is a first region in which the liquid fuel is heated to a preselected temperature for vaporizing a preselected portion of the lower boiling point constituents of the fuel. The heated fuel is then passed into a separating chamber wherein the non-vaporized constituents are separated from the vaporized constituents. Within the separating chamber, the nonvaporized constituents may be further heated for vaporizing any of the lower boiling point constituents entrained therewith. The vaporized fuel flows from the separating chamber into a second region where the vapor is superheated and wherein any liquid droplets traveling with the vapor are vaporized. The superheated vapors, virtually devoid of liquid droplets, then pass into a burner wherein the vapors are burned.

The burner may comprise a presently known burner. However, preferably the burner is designed to provide a controlled flame-front, wherein the deposition onto portions of the burner of certain salts normally formed in the combustion zone of the burner is avoided.

This and other features of the vaporizer and burner are described in greater detail hereinafter in connection with a description of embodiments illustrated in the drawings, wherein:

FIG. 1 is a side elevation in section of one embodiment of a vaporizer,

FIG. 2 is a side elevation in section of another embodiment of a vaporizer, and

FIG. 3 is a side elevation, partly broken away and partly in section, of a liquid'fuel vaporizing burner and a thermoelectric converter load heated by the burner.

The vaporizer it} shown in FIG. 1 comprises a body casing 12 including a passageway 14 coupled to a pipeline 15 leading from a source of liquid fuel 17. For applications in remote areas it is highly advantageou that the liquid-burner be operable with fuels normally provided for other purposes, thereby simplifying transport and storage problems. To this end, it is desirable that the liquidfuel burners be operable with commercially available automotive gasoline, and especially leaded gasoline.

Passageway 14 opens into the lower end of a vertical and centrally disposed open-ended, tubular member 16 having a number, e.g., 4, longitudinally extending bores 13 therethrough. Mounted on member 16 and extending over the open ends of bores 18 is a deflector 20 having an annular downwardly extending flange 22.

Member 16 provides a first vaporizingregion 18' wherein most of the liquid fuel is vaporized, and to this end, member 16 is heated. This is accomplished by heating an extending portion 24 of casing 12,. the heat received by portion 24 passing by conduction upwardly through casing 12 to member 16 which is firmly secured within an annular flange 26 of casing 12, as by means of a screw thread, not shown. Casing portion 24 may be heated by the exhaust gases from the burner fired by the fuel from the vaporizer, using known heat transferring means, not shown. The liquid fuel, such as gasoline, is fed into the casing passageway 14 at a given rate and at pressures of around 525 p.s.i.g. by known pump means (not shown), and the casing portion 2a is heated at a rate suflicient to maintain the lower end of tubing 16 at a temperature (when gasoline is used) of around 160 C.

Gasoline comprises numerous hydrocarbon constituents having boiling point temperatures ranging from around 40 C. to C. Within the first vaporizing region 18 substantially all of the hydrocarbon constituents of the gasoline are vaporized in the nucleate boiling mode. The higher boiling-point hydrocarbon constituents, that is, heavy-ends of the gasoline, are not vaporized but remain in the liquid state. In general, satisfactory results m) are achieved if the vaporizer is operated to vaporize about 90-95% of the gasoline (by volume) fed to the vaporizer. The unvaporized 10% of the fuel comprises, in general, the gasoline constituents having boiling points above 160 C. If leaded gasoline is used, it is found that the heavy-ends or high-boiling point constituents of the gasoline include some of the tetraethyl lead additive.

After being heated in the first vaporizing region 18', the mixture of vapor and heavy-ends liquid droplets is directed downwardly by deflector 20 into the upper portion of a separating or settling chamber having a volume relatively large in comparison with the volume of the first vaporizing region 18. Settling chamber 30 comprises an outer wall 32 mounted on a flange 34 of casing 12, the upper surface of casing 12 serving as the bottom of chamber 30, and the top end of chamber 30 being closed by a superheating member 40, described hereinafter.

Due to the comparatively large volume of the settling chamber 30, the liquid droplets-vapor mixture has a low velocity, thereby allowin the heavy-ends liquid droplets to separate from the vapor and settle to the bottom of chamber 30. Casing 12 is heated, as described, and the pool of heavy-ends collected in the lower portion of settling chamber 30 is further heated, whereby any lower boiling point constituents of the liquid fuel entrained with the heavy-ends are boiled out of the heavy-ends pool.

Opening into the settling chamber 30 near its lower end is a feed tube 44 which extends through casing 12 and into a discharge or float chamber 46 mounted on casing 12 and having a known type float valve system therein. The heavy-ends drain through the feed tube 44 and into the float chamber 46 where, when suflicient heavy ends accumulate to lift the float and open the valve, the heavy ends are discarded through a drain tube 48. Float chamber 46 is vented by means of a tubing 50 to provide A pressure equalization between the chamber 46 and settling chamber 30.

To prevent condensation of the fuel vapors which pass into and out of the float chamber 46 through tubing 50, float chamber 46 is also maintained at an elevated temperature. This may be accomplished by making the wall of float chamber 46 of a good thermal conductivity material and heat insulating the chamber (by known means, not shown) to prevent heat loss therefrom whereby the Wall conductivity and the circulating hot vapors serve to heat the chamber to a sufficiently high temperature.

superheating member has a vapor inlet 62 dis-posed above the deflector 20 which leads to a passageway 64 extending through member 40 to a spud 66 having a relatively small diameter orifice 68. The vapors in settling chamber 30, mostly free of heavy-ends droplets, pass around and upwardly of deflector 20 and into pass-ageway 64 through inlet 62.

Passageway 64 comprises the second vaporizing or superheating region, and to this end, member 40 is heated. An extending portion '70 of superheating member 40 is heated, preferably also by the hot exhaust gases from the burner, and the heat passes by conduction throughout member 40. In one embodiment, and wherein gasoline is used as the fuel, the operating temperature of superheating member 40 in the immediate region of vapor inlet 62 is around 220-230 C. and decreases to about 190-200" C. at the orifice end of member 40. Within the passageway 64, the vapors are superheated to a temperature higher than the boiling point of the highest boiling point constituents of the raw fuel. This insures that the vapors, which may include small amounts of heavy-ends liquid droplets entrained with the vaporized lighter ends, are virtually devoid of liquid droplets as the vapors approach and pass outwardly through orifice 68.

The vapors are then fed to an injector, such as the one shown in FIG. 3, described hereinafter, where the vapors are mixed with air, fed to a burner, and immediately burned.

Casing 12, the first vaporizing member 16, deflector 20, and the superheating member 40 are preferably made of high thermal conductivity materials having a high resistance to oxidation and chemical attack. Aluminum alloys low in copper content have proven to be satisfactory. Aluminum is suitable for the wall of the settling chamber, and brass and stainless steel are suitable for the float chamber 46. The orifice spud 66 is preferably made of a free-machining aluminum alloy.

The use of Vaporizers as described above avoids many of the problems associated with the use of prior-art liquidfuel burners. Thus, for example, by removing the heavy ends, complete vaporization of the vapors fed to the burner and complete combustion of the fuel-air mixture and avoidance of soot are obtained.

Further, a major detriment to long and unattended operation of liquid-fuel burners is the clogging of small passages and jet orifices by various deposits. One of the main causes of such clogging is the presence of liquid droplets in the vapors stream. It appears that the metal walls of the pipelines act as a catalyst and that the liquid droplets go through chemical reactions which produce various deposits as the end products of the reactions. Use of the present vaporizer greatly reduces such clogging by providing almost complete vaporization of the liquid fuel. This is accomplished, as described, by first removing the diflicult-to-vaporize heavy-end hydrocarbon constituents of the liquid fuel and thereafter superheating the vapor to insure that any liquid-fuel droplets are completely vaporized. In one test of the embodiment shown in FIG. 1, for example, and using a leaded gasoline fuel, the vaporizer was operated in excess of 100 hours in daily 8-hour cycles without the formation of deposits along the pipeline walls and at the orifice 68. In contrast, after as little as five hours of use with known Vaporizers, deposits accumulated at the discharge orifice of the vaporizer which nitieeably impeded the vapor flow from the vaporizer.

It is also found that with known Vaporizers the heaviest fuel-ends, even if vaporized, settle out as a heavy liquid in the pipelines leading to the burner and constitute a fire hazard. Removal of these heavy-fuel ends as herein described avoids this problem. Further, removal of at least some of the tetraethyl-lead additive of leaded gasoline, if used, reduces the formation of salt deposits in the fuel passageways immediately adjacent to the burner combustion zone. Such salts are formed in the flame-front zone during the combustion of the gasoline vapors and tend to condense on and clog the passageways through the Meker-type gridworks normally used in vaporizing-type burners.

The vaporizer 30 shown in FIG. 2 comprises an inverted cup-shaped member 82 haivng an outer or side wall 84 closed by a heat receiving and conducting end member 36. Outer wall 84 includes an upper thin wall section 83 and an intermediate thick wall section having a plurality, e.g., l2, longitudinally extending bores 92 therein, the bores being arranged in a circular array coaxial with member 82. The lower end of the bores open into an annular chamber 94 communicating with a coupling 96 through which a liquid fuel is admitted. The upper ends of the bores 92 are open but have a annular deflector 100 extending thereover from outside wall 84. Received coaxially within tubular member 82 is an elongated inner tubing 102 having a passageway 104 therethrough and a coaxial intermediate cylindrical mem ber 106 disposed around tubing 102. Tubing 102 is spaced from outer wall 34. The lower end of cylindrical member 106 extends below the thick wall section 90 and provides, with an annular member 108 and the lower end 110 of outer wall 84, a float chamber 112. Float chamber 112 is coaxial with tubing 102. The means for assembling and sealing the various vaporizer parts with respect to one another are neither shown nor described since such means will be apparent to those skilled in the art.

Cit

The vaporizer 80, for convenience of illustration, is shown as an integral member.

The liquid fuel is admitted under pressure through coupling 96 into the annular chamber 94 and into the bores 92. The thick wall section 90 is heated by means described hereinafter and the bores 92 provide a first vaporizing region wherein the liquid fuel is heated to a temperature suflicient to vaporize (when gasoline is used) about 90-95%, by volume, of the lower boiling point constituents of the fuel.

The annular space provided by the cylindrical member 106 and the inside wall of the thickened wall section 90 serves as an open-ended separating chamber 114. The chamber 114 connects with bores 92 at its upper end and with the float chamber 112 at its lower end.

Annular deflector 100 has a downwardly extending flange 116 whereby the heated fuel rising upwardly through the bores 92 is deflected by deflector 100 downwardly through the open upper end of separating chamber 114. The volume of the-separating chamber 114 is somewhat larger than the combined volume of the first vaporizing bores92 so that the velocity of the heated fuel in the separating chamber is sufliciently slow to permit gravity separation of the unvaporized heavy ends constituents from the vaporized lighter ends constituents of the fuel. The separated heavy ends pass downwardly through a passageway 118 between cylindrical member 106 and the lower portion of thickened wall section 90 and into the float chamber 112.

Float chamber 112 contains an annular hollow float 120 which cooperates with a known spring-loaded pin valve 122 for opening and closing an orifice in an outlet coupling 124. When sufiicient heavy-ends accumulate in the float chamber to raise the float 120 a suflicient amount, valve 122 is opened thereby permitting discharge of the heavyends through coupling 124.

The vaporized constituents of the fuel pass upwardly and outwardly of the settling chamber 114 through the central opening in .the annular deflector 100 into a chamber 126 formed above deflector 100 and into the passageway 104- extending through tubing 102. Within tubing 102 the gas vapors are superheated to a temperature higher than the highest boiling point constituents of the fuel and then discharged as a jet through an orifice 123 in the lower end of the tubing 102.

For heating vaporizer 80, hot exhaust gases from the burner fired from the vaporizer are used, as described hereinafter, to heat the upwardly extending end member 86 of the vaporizer. The heat transferred to member 86 is then conducted throughout the vaporizer for heating the first vaporizing region (bores 92 within the thick wall section 90), the superheating tubing 102, and the float chamber 112. The superheating tubing 102 is heated to a temperature higher than the temperatures of the first vaporizing region and float chamber, and to this end, tubing 102 is secured .to the heatreceiving member 86 by means of a large cross-sectional area pedestal 132, whereby only a relatively small temperature drop occurs between heat receiving member 86 and tubing 102. Conversely, the thin wall section88 causes a somewhat larger temperature drop between the heat receiving member 86 and the thick wall section 90. Float chamber 112 is heated by conduction of heat through the outer wall 82. Heating of the float chamber 112 prevents condensation of the gas vapors passing in and out of the float chamber through passageway 118.

As shown in FIG. 3, the superheated gas vapors are discharged from the lower end of tubing 102 into an injector 134 of a burner 136. The injector shown is of the compound Venturi type and is generally known in the art. Air passes downwardly through the open end 138 of the Venturi and is entrained and mixed with the fuel vapors injected therein by vaporizer 80. An air regulating shutter 140 is provided for controlling the amount of air mixed with the fuel vapors. The fuel vapor-air mixture passes through the Venturi, past baflies 142 which provide a laminar flow of the fuel, and into the burner head 143 which includes a Meker-type gridwork 14 1. As the fuel mixture passes outwardly of the Meker gridwork 144 it is burned, the gridwork 144 preventing flashback of theburner flame, as known. The burner flame is used 'to heat an enclosing cylindrical element 146, such as a thermoelectric converter (the details of which are not shown), and the hot exhaust gases from the burner are directed into a duct 148 leading to a known type heat exchanger, not shown, for heating the heat receiving and conducting member 86 of the vaporizer 80.

A problem associated with the use of leaded gasoline is that lead salts, such as sulfates and oxides, are formed during the combustion of the gasoline vapors which .tend to deposit on and clog the Meker gridwork ports. The Meker gridwork is so designed, and the flow of fuel to the gridwork so regulated, that deposit of these salts onto the gridwork is largely avoided. This is ,accomplished by designing the gridwork to provide, at a stoichiometric fuel-air mixture and normal firing rate, a mixture velocity-gradient in the gridwork which provides a lifted flame-front anchored only at its extremities. That is, except at the perimeter of the burner head gridwork, combustion of the fuel does not begin. immediately adjacent the gridwork port ends, but at a small distance above the gridwork. In FIG. 3 the combustion zone of the fuel is indicated by the region 150. Under these conditions of combustion, the lead salts, which normallyform in the lower portion of the combustion zone, are not deposited in the gridwork ports, but are volatilized and carried away by the exhaust products.

Design information enabling one to design a burner for operation with liftedflame-fronts is presented in Combustion Flames and Explosions of Gases, by B. Lewis and G. Von Elbe, Academic Press, 1951, pp. 226-308.

In one embodiment, the burner head 143 has a diameter of 2 inches, and the gridwork is formed of .008 inch slotted metal strips to provide 2. %-inch thick gridwork having ports .052 x .052 inch.

The fuel flow is about 1 lb./hr. and the center of the flame-front (on axis) is lifted about 1 inch or more from the top of the gridwork.

What is claimed is:

1. A vaporizing burner for a liquid fuel having different boiling point constituents comprising:

a vertically extending member having a plurality of longitudinally extending bores therethrough,

passage means opening into the lower ends of said bores for entry of fuel therein,

means for heating said member for vaporizing a preselected portion of the lower boiling point constituents of said fuel,

a separating chamber having upper and lower ends and having a volume larger than the combined volume of said bores,

means for directing the heated constituents of said fuel from said first vaporizing bores in a downward direction into the upper end of said separating chamber,

a discharge chamber in communication with the lower end of said separating chamber,

a superheating chamber, said superheating chamber having a vapor inlet in communication with the upper end of said separating chamber,

means for heating said superheating chamber for heating vapors therein to a temperature higher than the boiling point of the highest boiling point constituents of the fuel,

an aspirator,

said superheating chamber opening into said aspirator for passage of said superheated vapors into said aspirator, whereby said vapors are mixed with air,

7 and a burner head,

said aspirator directing said air-vapor mixture into said burner head for consumption of said mixture.

2. A vaporizer for a liquid fuel having different boil ing point constituents comprising:

(a) an upstanding tubular member having therein:

(i) an array of longitudinally extending bores, the

upper ends of said bores being open,

(ii) an annular chamber having an open upper end and having a volume larger than the combined volume of said bores,

(iii) said bores and annular chamber being in communication through the open upper ends thereof, and

(iv) a superheating chamber communicating with said annular chamber through the open end thereof,

(b) a discharge chamber disposed below said annular chamber and in communication therewith,

(c) means for heating said bores and chambers,

(d) passage means for admitting said fuel under pressure into the lower end of said bores for vaporizing a pre-selected portion of the lower boiling point constituents of said fuel,

7 (e) means for directing the vaporized and unvaporized portions of said fuel downwardly through the upper end of said annular chamber, and

(f) said superheating chamber being heated to a temperature for heating vapors therein to a temperature higher than the boiling point of the highest boiling point constituents of said fuel.

3. A vaporizer for a liquid fuel having different boiling point constituents comprising:

(a) an upstanding tubular member having therein, in

coaxial and radially spaced apart relation:

(i) an outer circular array of longitudinally extending bores, the upper ends of said bores being open,

(ii) an intermediate annular chamber having open ends and having a volume larger than the combined volume of said outer bores,

(iii) said outer bores and intermediate chamber being in communication through the open upper ends thereof, and

(iv) an inner chamber communicating with said intermediate chamber through the open end thereof,

(b) an annular discharge chamber disposed below said intermediate chamber and in communication therewith,

(c) means for heating said bores and chambers,

(d) passage means for admitting said fuel under pres sure into the lower end of said bores for vaporizing a pre-selected portion of the lower boiling point constituents of said fuel,

(e) means for directing the vaporized and unvaporized portions of said fuel downwardly through the upper end of said intermediate chamber, and

(f) said inner chamber being heated to a temperature for heating vapors therein to a temperature higher than the boiling point of the highest boiling point constituents of said fuel.

4. A vaporizer for a liquid fuel having different boiling point constituents comprising:

an upstanding tubular member having a closed upper end, the side Wall of said member including an upper thin wall section joined to the upper end of said tubular member and an intermediate thick wall section,

a plurality of longitudinally extending bores in said thick Wall section, the upper ends of said bores being open, and passage means opening into the lower ends of said bores for entry of fuel therein,

a tubing having a passageway therethrough extending axially of said tubular member, said tubing being joined to the upper end of said tubing member by a pedestal having a cross-sectional area larger than the cross-sectional area of said thin wall section,

a cylindrical member coaxial with said tubing and disposed therearound and in spaced relation with said thick wall section,

the space between said cylindrical member and said thick wall section defining an annular separating chamber having a volume larger than the combined volume of said bores,

the lower end of said cylindrical member extending beyond the lower end of said thick wall section and being joined to said side wall for providing an annular discharge chamber coaxial with and in communication with said separating chamber,

the upper end of said separating chamber being open and in communication with the open upper ends of said bores and with said passageway through said tubing,

means for heating the upper end of said tubular member for heating, by conduction, said side wall and said tubing, said thick Wall section being heated to a temperature for volatizing a preselected portion of the lower boiling point constituents of said fuel in said bores, and said tubing being heated to a higher temperature than the boiling point of the highest boiling point constituents of said fuel,

means for feeding said fuel into said bores, and

means for directing said vaporized and unvaporized constituents from said bores downwardly through the upper end of said separating chamber.

5. A vaporizing burner for a liquid fuel having different boiling point constituents comprising:

a vertically extending member having a plurality of longitudinally extending bores therethrough,

passage means extending into the lower ends of said bores for entry of fuel therein,

means for heating said member,

a separating chamber in communication with the upper end of said bores, said separating chamber having a volume larger than the combined volume of said bores,

a discharge chamber in communication with said separating chamber,

a superheating chamber in communication with said separating chamber,

means for heating said superheating chamber, and

a burner head in communication with said superheating chamber.

References Cited UNITED STATES PATENTS 665,112 1/1901 Kitson 158-54X 778,577 12/1904 Hague l5853 FREDERICK L. MATTESON, 111., Primary Examiner.

ROBERT A. DUA, Examiner.

Claims (1)

1. 5. A VAPORIZING BURNER FOR A LIQUID FUEL HAVING DIFFERENT BOILING POINT CONSTITUENTS COMPRISING: A VERTICALLY EXTENDING MEMBER HAVING A PLURALITY OF LONGITUDINALLY EXTENDING BORES THERETHROUGH, PASSAGE MEANS EXTENDING INTO THE LOWER ENDS OF SAID BORES FOR ENTRY OF FUEL THEREIN, MEANS FOR HEATING SAID MEMBER, A SEPARATING CHAMBER IN COMMUNICATION WITH THE UPPER END OF SAID BORES, SAID SEPARATING CHAMBER HAVING A VOLUME LARGER THAN THE COMBINED VOLUME OF SAID BORES, A DISCHARGE CHAMBER IN COMMUNICATION WITH SAID SEPARATING CHAMBER, A SUPERHEATING CHAMBER IN COMMUNICATION WITH SAID SEPARATING CHAMBER, MEANS FOR HEATING SAID SUPERHEATING CHAMBER, AND A BURNER HEAD IN COMMUNICATION WITH SAID SUPERHEATING CHAMBER.

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