CA1042778A - Cyclonic multi-fuel burner - Google Patents

Abstract

ABSTRACT
The disclosure describes an improved heat ex-changer to superheat the atomizing medium and the sonic and/or subsonic vortex of the primary atomizing zone assisted by multiple impingement points and cyclonic tur-bulence and low pressure within the diffuser resulting in micron size droplets of fuel that easily vaporize and greatly improve the reaction process to produce a very efficient flame with fuels ranging down to 3° API.

Description

This invention is generally concerned with a combustion process and the novel means for achieving it and in particular with a method and a fuel atomizing device for burning gaseous and/or liquid fuels which are not considered as being useful fuels, such as pitch and asphaltic compounds.
A burner assembly utilizing the novel fuel atomizing device is described in Applicant's copending Application filed Burner assemblies heretofore used for the combustion of liquid and gaseous fuels are numerous and each has a specific application for which it is best suited.
Such present burner assemblies generally use mechanical methods of atomizing the fuel. This requires high fuel pressure in combination with very small openings which result in these `~ openings readily becoming plugged and therefore require a con-siderable amount of maintenance and steadily degrading efficiency.
~ Heretofore atomizers of the emulsion type and the ex- .`
ternal mixing type were used for all fuels even though the fuel droplets were relatively large and therefore required an extended dwell time in order to vaporize. These atomizers used air or steam as the atomizing medium without any additional heat input.
In some cases the atomizing medium offered no additional advan-tage and at times actually absorbed heat from the fuel.
This invention relates to a method for atomizing fuel to promote efficient burning, comprising:
A. preheating a fluid atomizing medium;

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B. imparting a high velocity tangential motion to at least a portion of the medium to create a vortex;
C. introducing said vortexual motion medium at a first velocity and pressure upstream of a fuel entry point;
D. introducing the fuel into a diffuser at a first pressure;
E. atomizing the fuel within the diffuser by causing the fuel and the medium to intimately mix in the 10diffuser area immediately adjacent the fuel intro-duction point at substantially said first pressure, ' transferring heat from the medium to the fuel; and -~ F. further decreasing the pressure of the mixed fluid by controlled expansion while continuing to subject the fuel to the tangential and shearing action of , the introduced medium vortex.
: This invention also relates to a fuel atomizing device ~` for use in a burner assembly comprising: an atomizer head having means for communication with a fuel source and means for communi-20 cation with an atomizing medium source; :
A. said fuel source communication means defining a conduit having an exit point within said atomizer head;
B. said atomizing medium communication means defining - a plenum upstream of said fuel conduit exit point, a vortex cavity and an ejector nozzle surrounding :
said fuel conduit exit point;

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-C. vortex generating means interposed between the plenum and the vortex cavity so that a high ve-locity vortex is imparted to the flow of the atom-: izing medium which vortex acts on the fuel at and , around the ejector nozzle; and means for diffusing the atomized fuel downstream of said ejector nozzle.
The invention will now be described in reference to theaccompanying drawings, wherein:
Figure 1 is an elevational view showing in cross sec-tion a burner assembly using an atomizer of the invention;

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Figure 2 is an elevational view shown in cross section one embodiment of the atomizer;
Figure 2A is a sectional view of an alternate diffuser providing for impingement of the flow; and Figure 3 is a cross sectional view of another embodi-ment of the atomizer head.

~ j . Referring now to the drawings and particularly to . Figure 1, there is illustrated an embodiment of a burner assembly . for carrying out certain objects of this invention wherein is 20 shown a typical furnace floor 10, to which is attached a burner support bracket 12, which carries burner assembly 14 having a ~ ceramic head and hot gas diffuser 16 extending through floor 10, .~ the assembly comprising a heat exchanger 18 having spaced inner and outer walls 20, 22 with a packing material 24 positioned therebetween and retained by upper and lower packing retainers 26, 28, retainer 26 forming a communication means with upper -~ manifold 30 which is connected to an atomizing medium supply by port 320 Retainer 28 provides a communication means to lower ' ~ -3----' ~-1~2778 manifold 34 and atomizing medium exit port 36, conduit 38 andconnecting tee 40, to which is connected conduit 42 to carry the heated atomizing medium to the atomizer head 44. Conduit 42 surrounds fuel conduit 46 which also communicates with atomizer head 44. Atomizer head 44 has an exit nozzle 48 and turbulator 50. A main gas fuel ring 52 having angled ports 54 is connected to a fuel supply by conduit 56. A primary air register opening 58 is provided for the .

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~ Z7'78 burner. The pilot igniter is shown at 60, and flame sensor viewing tube and sensor at 62, 64 respectively.
The operation of the embodiment as illustrated in Figure 1 under a typical condition to fulfill a specific re-quirement can be described assuming that an atomizing medium is connected to port 32, the main gas conduit 56 is connected to a control valve and the liquid fuel conduit 46 is connected to a preconditioned ~uel supply by way of a manual control valve. The pilot ignitor 58 and the flame sensor 62 are not a part of this disclosure and will not be discussed ~urther other than to note that the pilot is lit and the flame is sensed by the sensor which is connected to prescribed safety control systems old in the artO
The atomizing medium is pressured into the port 32.
Flow is established through port 32 into the manifold 30, through the heat exchanger packing 24 into the bottom manifold 34 by way of the retainer 26, the heat exchanger 18 and the packing support 28. The atomizing medium leaves the manifold 34 by way of the passageway 36 and flows into the atomizer tee 20 40 by way of the conduit 38~ The atomizing medium flows to the atomizer head by way of the conduit 42~ The ~low of the atom-izer medium is around the fuel conduit 46 as it flows toward the head 44. The atomizing medium ~lows through its respective passageways in the head 44 and establishes a vacuum within the liquid fuel tube 46.
The medium exhausts from the nozzle 48 and into ~e combustor by way of the turbulator 50. When the atomizing flow ; has been established the main gas valve is opened and ignition is immediate by way of the pilot flameO As the main flame heats the combustor wall 20 the heat is transferred into the atomizing medium flowing in the heat exchanger 18 by the effect of the packing 24, This pac~ing is of a conductive material such as ceramic or metallic balls or any shape that would r,love the heat from the combustor wall and place it into better con-tact with the flowing atomizing medium. This unique construc-tion has a definite advantage in increasing the heat transfer resulting from the turbulence generated in the heat exchanger by non-lineal ~low and the elimination of the film coefficient on the heated surface by conduction. The temperature of the atomizing medium continues to increase until a heat balance has been reached. Proper design establishes the final temperature by dictating those areas and velocities required based on the heat radiator and the receiver at a given point or operating condition. Water may be inJected to generate steam to serve as an atomizing medium.
When the atomizing medium has reached the proper tem-perature, the preconditioned liquid fuel is admitted into the conduit 46. The fuel, sub~ected to the vacuum generated in fuel conduit 46 by the discharge of the surrounding atomizing medium in conduit 42, also receives heat by transfer from the surround-ing heated atomizing medium. The lowered pressure resultantfrom the atomizing medium discharge from the circular e~ector, lowers the boiling point of the fuel, thus permitting the light ends in the fuel to boil off at a lower temperature and increas-ing the efficacy of the heat transfer. As the liquid fuel dis-charges from the conduit 46 it is subjected to the low pressure resultant therefrom and then to the so~ic velocity tangential flowO This causes a shearing effect on the molecules of fuel while the delta pressures of the angled sonic shock waves form-ing around and immediately downstream of the exit of conduit 46 and the multiple flow directions existing in the high velocity tangential atomizing medium aid in atomizing and mixingO In 778addition, the effect of the density transition as the heavy fuel is ce~trifically forced toward the outer parameter of the tan-gential flow, causes additional shearing of the liquid. The turbulence generated when the sonic flow changes to subsonic flow also provides additional atomization to produce micron drop-lets of fuel that greatly reduces the dwell time required for the transition from liquid to a vapor state.
A novel feature of this unique method of atomizing is the direction of the tangential flow of the atomizing medium, The normal vortex direction north of the equator is counter-clockwise and south of the equator the normal flow is clockwiseO
Better atomization is obtained when the vortex is forced in a direction opposite to that of normal flow. This does not sug-gest or indicate the flow could not be the same direction as the normal flow.
Another important factor and novel feature of the unique method of atomizing liquid fuel is the use of the heated atomizing medium, the high velocity gained by it through heating and the ability of transferring this heat into the fuel.
It will be noted that the combustor is devoid of the usual combustor block. Exhaustive tests have established the fact that such a block is not required with the present novel embodiment. This does not mean that a ceramic could not be used within the combustor if the effect on the heat transfer can be tolerated. It will also be noted that an excess air register is not illustrated. Although the register is necessary in most ap-plications, its usefulness in describing the basic operation of the inventive device is not necessary.
The angled gas ports as illustrated in Figure 1 at 54 perform major functions. The angle has an effect on the turbu-lence generated in the combustor to hold the gas generated flame ;Z77~
front at a specific point within the combustorO Also the angle of these ports greatly e~fects the mixing of the alr and fuel and controls the type of flame entering the furnace when operat-ing on gas only. Likewise, the kinetlc energy of these multiple ports inspirates primary air into the combustorO Additional primary air is inspirated by the kinetic energy of the atomized fuelO The amount of primary air is controlled by the position of the register 58 as it blocks or restricts the flow of air through the port 660 It is also feasible to provide for an alternate loca-tion for maln gas ln~ection at the top of the assembly. This may be accomplished by installing multiple tubes angled at a point where they terminate in the combustor so that they pass through the ceramic head and have their inlet on the external surface of the burner shellO Multiple gas nozzles are piped to these inspirator tubes and positioned so that the gas flow from ; the nozzles will enter the tube and inspirate airO The multiple pipes supplying the nozzles terminate in a suitable manifoldO
Valving is made available so that the assembly can be started and heated with the fuel ringO When the liquid fuel is ignited . the gas is transferred to the top in~ection point and uses the radiant heat of the oil flame to keep the atomizing medium hot.
When the embodiment is used without the atomizer head it is necessary by proper valving or repiping to direct the flow ; of main gas through the heat exchanger~ Care should be exercised ; to insure that the temperature does not reach the cracking tem-perature of the fuel in useO
Likewise, liquified petroleum gas can be directed through the heat exchanger so that it may serve as a vaporizer for the LPG~ Liquid propane and butane have been tested and documented with excellent resultsO
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Referrin~ to Figure 2 there is illustrated an embodi-ment of an atomizer head wherein 46 is the liquid fuel conduit centrally located within the atomizing medium conduit 42, 44 is the atomizer head, 48 is the exit nozzle, 68 is the atomizing medium plenum, 70 is the impingement nozzle annulus, 72 illus-trates the typical multiple impingement openings, 74 is the dif-fuser, 76 is the atomized fuel, 78 is the circular nozzle throat, 80 is the primary atomizing, low pressure, and expansion zone, 82 is the tangential generating slot directed to cause the gen-eration of a vortex opposite to the natural vortex, 84 is thevortex generating plate and 46 A illustrates an alternate loca-tion for the fuel conduitO
In operation the atomizing medium is flowing through conduit 42 and fuel is flowing down conduit 46. This method insures adequate tracing for specific applicationsO The flow of the atomizing medium enters the plenum 68 and the flow is divid-ed into the number of flow paths, on an area ratio basis, that is required for the specific head design. One path is through the annulus 70 where it communicates with the multiple impinge-ment nozzles 72. These are terminated in the wall of the dif-fuser 74, however, the sonic flowg although warped by the angled exit, forms an impingement point within the diffuser. Another path for the atomizing medium is through the tangential slot 82 that is located in the swirl plate 84. As the atomizing medium exhausts from the tangential slot 82 a vortex or tangential flow is generated within the cavity 86 having a swirl opposite in direction to the normal ~low. As the transition section 88 of vortex cavity 86 becomes smaller the vortex flow velocity is in-creased until a critical pressure ratio is reached. At this point the flow velocity is sonic, As the rotating atomizing medium leaves the nozzle 78 formed by the fuel tube 46 and the ~ Q~778 head 44 sonic shocks are formed as the compressed atomizing me-dium attempts to shock down to subsonlc velocities. These shocks are circular and angled corresponding to the tangential flow. Also at the center of this vortex the pressure is below atmosphere. Likewise, the manner of placing the fuel tube 46 in the center of the opening of head 44 to form an annular nozzle 90 creates in essence a circular ejector. The combination of these phenomena provides an ideal low pressure primary area 80 into which the liquid fuel is deposited. In essence this lowers the boiling point of the fuel depending upon the vapor pressure of those elements that make up the fuel in use, In this primary zone 80 the liquid fuel is subjected to sonic conditions and severe pressure changes that tend to shear the fuel molecules, ` while the density variations within the atomizing medium and the liquid fuel causes it to be moved toward the outer edge of the vortex where it is subjected to the sonic shocks that continue to cause molecular shear. As the diffuser 74 accomplishes a form of controlled expansion and begins to convert some of the total ` pressure to static pressure, the atomized fuel is forced into sonic impingement by the multiple flows from the angled nozzles ; 72 within the diffuser body 74. Any rotational fl~w is immedi-ately stopped and the mixture is again sub~ected to the violent action of the impinging sonic jets. As the atomized fuel is ex-hausted from the atomizer head through exit nozzle 48 the fuel droplets are in the micron size and quickly convert from liquid to vapor for immediate and trou~le free combustion.
A modification of the embodiment of Figure 2 is illus-trated in Figure 2A. It depicts an alternate diffuser having an action effecting the impingement flow whereby the impingement area is larger, the static pressure is higher and the velocity is greater than sonic. Like reference numbers denoting like _g_ .:

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1`'.~4Z778 parts, l~6 is the fuel tube, 24lL is the atomizer head, 248 is the diffuser exhaust exit, 270 is the lmpingement nozzle inlet annulus, 76 represents the atomized fuel, 78 is the nozzle throat of vortex cavity 86, 292 is the impingement nozzle inlet throat and 272 is the impingement nozzle diffuser section. The atomizer operation is identical to that already described except that the expansion of the sonic velocity flow downstream of the throat 292 in the diffuser section 272 is controlled in such a manner that the velocity pressure is converted into static pressure and the velocity is increased above sonic. Although the flow is warped due to the angled exit, the amount of atom-izing efficiency is increased.
The atomlzer head as illustrated in Figure 3 is iden-tical to the previous atomizers except it does not have any impingement nozzles nor does it have a diffuser.
As illustrated in the figures at 46A is an alternate method of admitting fuel to the atomizer head for specific fuel applicationsO
The turbulator body 20 is no~ shown on any of the atomizer heads of Figures 2, 2A, or 3~ It is a needed item but is not considered a novel feature and will not be discussed furtherO
The embodiments as disclosed and described herein have been tested with excellent results on the following fuels using air and again using steam as the atomizing mediumO These were naphtha, kerosene, carbon black oil, 40 API crude, 24 API
crude, 19 API crude, Bunker "C" and Ten Pen AsphaltO The amount of air or steam per pound of fuel required for the present ln-vention was less than normally used in state of the art devices and the preheat fuel temperatures were lowerO
From test data and observations the efficiencies dur-~10-7t~8 ing the static firing tests resulted in the following advan-tages over present known devices: Less pollution, greater sta-bllity, better turndown, and the ability to successfully use those fuels that to date have not been considered as useful fuels.
The abllity of the atomizer to form micron droplets makesit very useful for application using fuels that presently require ambient air temperatures~ HoweverJ the atomizing method as disclosed herein requires less atomizing medium weight flow per pound of fuel~ less fuel pressure and produces greater combustion efficiencies that result in a greater heat release.
For some applications the atomizer will pump the fuel by the action of the circular ejector. Tests indicate that it is pos-sible to produce an emulsion with the water vapor and fuel oil merely by the effect of the sonic energy within the atomizer.
A metered amount of water can be injected into the fuel for ad-ditional emulsion water content.
Further studies provide an additional use for atomiz-ing a coal dust slurry. The atom~zing feature can easily be modified for oxygen injection for coal dust or other applica-tions.
For specific applications the fuel is caused to flow tangentially as it enters the atomizing head by use of a swirl vane within the fuel tube.
As apparent, one of the principal ob~ectives of the present invention is to provide an improved heat exchanger to super heat the atomizing medium through the heat usually lost by way of combustor wall radiation and to offer adequate cooling of the combustor and at the same time to put the absorbed heat into the fuel within the atomizer headin such a manner that the atomization of the fuel is greatly improved.

77~3 While the device as disclosed herein has been de-scribed as a liquid fuel burner assembly, the device is useable as a gaseous fueled assembly, a liquid fueled assembly or a com-bination gaseous-liquid fuel assembly. Various tests have been conducted using propane, butane or natural gas as a gaseous fuel, and as a liquid fueled combustor device. Excellent re-sults have been obtained using naphtha, kerosene, 40 API Crude Oil, Bunker "C" and Ten Pen Asphalt. In the preferred embodi-ment, the combustion air is inspirated into the combustor by the kinetic energy of the gaseous fuel or the kinetic energy of the atomized fuel. However~ positive air pressure may be di-rected into the ccmbustor or around the combustor as secondary air. The presently anticipated application for this device will be as a heat source for furnace applications where suitable draft is available to assist in the supplying of the required combustion airO However, this does not suggest nor indicate that the device as disclosed herein cannot be applicable to other uses.
One test condition used saturated steam at 150 pounds pressure (36~F.) at a demand of 130 pounds per hour for a Ten Pen Asphalt flow of 660 pounds per hour at a temperature of 400F. The heat exchanger superheated the steam to 800F. or an increase of 433F. The resulting flame of the aspha~tic fuel was very efficient and smoke free. Other tests using lower steam pressures and air pressures were documented with similar results.
Although particular embodiments of the invention have been illustrated and described, changes and modifications will become apparent to those skilled in the art and it is intended to cover in the appended claims all such changes and modifica-tions as come within the true spirit and scope of the inven-tion.

Claims (6)

The embodiments of the invention in which an ex-clusive property or privilege is claimed are defined as follows:

1. A method for atomizing fuel to promote effi-cient burning, comprising:
A. preheating a fluid atomizing medium;
B. imparting a high velocity tangential motion to at least a portion of the medium to create a vortex;
C. introducing said vortexual motion medium at a first velocity and pressure upstream of a fuel entry point;
D. introducing the fuel into a diffuser at a first pressure;
E. atomizing the fuel within the diffuser by causing the fuel and the medium to intimately mix in the diffuser area immediately adjacent the fuel introduction point at substantially said first pressure, transferring heat from the medium to the fuel; and F. further decreasing the pressure of the mixed fluid by controlled expansion while continuing to subject the fuel to the tangential and shear-ing action of the introduced medium vortex.

2. The method for atomizing fuel defined in claim 1, including:
A. increasing said first velocity and pressure of the vortexual motion medium after introduction upstream of the fuel entry point to a sonic velocity and second pressure prior to said fuel-medium mixing step, B. causing further and additional atomization of the fuel in the diffuser area by subjecting it to the sonic shock resultant from said velocity increasing step above.

3. The method for atomizing fuel defined in claim 2, including:
introducing a second portion of the fluid atomizing medium at a high pressure downstream of the fuel entry port and within the diffuser so that it impinges and further atomizes the fuel being acted upon by the high velocity vortex imparted thereto upstream, the second portion of the atomizing medium resulting on introduction in additional molecular shearing of the fuel droplets.

4. A fuel atomizing device for use in a burner assembly comprising: an atomizer head having means for communication with a fuel source and means for communi-cation with an atomizing medium source;
A. said fuel source communication means defining a conduit having an exit point within said atom-izer head;
B. said atomizing medium communication means defining a plenum upstream of said fuel conduit exit point, a vortex cavity and an ejector nozzle surrounding said fuel conduit exit point;
C. vortex generating means interposed between the plenum and the vortex cavity so that a high velocity vortex is imparted to the flow of the atomizing medium which vortex acts on the fuel at and around the ejector nozzle; and means for diffusing the atomized fuel downstream of said ejector nozzle.

5. The atomizing device as defined in claim 4, wherein:
A. the vortex cavity defined by said atomizing medium communication means has a transition sec-tion which decreases in area to its smallest point substantially coextensive with said fuel source exit point to thereby define an ejector nozzle, the atomizing medium flow therethrough creating a differential pressure of a lesser value in said fuel tube; and B. said vortex generating means comprises a swirl plate having at least one tangential vortex generating slot therein communicating between said atomizing medium communication means defined plenum and the vortex cavity.

6. The atomizing device as defined in claim 5, wherein means are provided to direct a portion of the atomizing medium to said diffuser means, said first named means comprising impingement nozzles communicating the plenum and the diffuser, said nozzles being angled in the downstream direction and impinging fuel in said diffuser means to thereby break up the tangential flow of the fuel following exit from said ejector in said diffuser.