US3710070A - Low voltage, compact electrically augmented burner - Google Patents

Abstract

A compact, low voltage burner capable of supplying high gas temperatures by electrical augmentation provided by a diffuse discharge in the gas stream at substantially less than 1,000 operating volts, including two electrodes spacially separated by less than 2 inches, a pilot stage for supplying a conductive zone between the electrodes, a gas inlet to supply the main gas to be heated to the conductive zone, means for supplying RF energy to said electrodes, and means for supplying an operating voltage of substantially less than 1,000 volts to start and maintain a diffuse discharge in the burner.

Description

United States Patent 1191 1111 3,710,070

Hirtetal. 1 1 Jan.9, 1973 54 LOW VOLTAGE, COMPACT 3,450,926 6/1969 Kiernan ..219 1211 ELECTRICALLY AUGMENTED 3,004,137 10/1901 1011mm ..219/75 BURNER Inventors: Thomas J. Hlrt; Richard 1). Kissinger; Karl H. Frantzen, all of Omaha, Nebr.

Northern Natural Gas Company, Omaha, Nebr.

Filed: June 9, 1971 Appl. No.: 151,266

Assignee:

References Cited UNITED STATES PATENTS 4/1968 l-lirt et a1. ..219/12l PX MAIN STAGE GAS INLET COATING METAL INLET POWER SOURCE Primary Examiner-.l. V. Truhe Assistant ExaminerGale 1R. Peterson Atlorney-Merriam, Marshall, Shapiro & Klose [5 7] ABSTRACT A compact, low voltage burner capable of Supplying high gas temperatures by electrical augmentation provided by a diffuse discharge in the gas stream at substantially less than 1,000 operating volts, including two electrodes spacially separated by less than 2 inches, a pilot stage for supplying a conductive zone between the electrodes, a gas inlet to supply the main gas to be heated to the conductive zone, means for supplying RF energy to said electrodes, and means for supplying an operating voltage of substantially less than 1,000 volts to start and maintain a diffuse discharge in the burner.

7 Claims, 2 Drawing Figures 11.07 INLET IONIZING ADDITIVE INLET PMWEM 9mm 3.71911 MAIN STAGE GAS INLET 48 M ILOT INLET com-ms 2 METAL INLET IONIZING ADDITIVE INLET POWER SOURCE F E G. H

F IG. 2

INVENTORS a6 1 moms .1 H/RT KARL FRA/VTZEN 84 mam/w a KISS/N65? ATTORNEYS LOW VOLTAGE, COMPACT ELEGTRIICAIJILII AUGMENTEI) BURNER This invention relates to apparatus for developing high temperatures, and in particular to a compact, low voltage burner capable of providing high gas temperatures by electrical augmentation with a diffuse discharge in the gas stream.

Many applications involving heat, such as material cutting, welding, metal coating, incineration, etc., can presently be accomplished by small, compact burners utilizing ordinary fuels. It would be especially advantageous in terms of increased heating and operating efficiency in such applications to provide significantly higher gas temperatures without resorting to exotic fuels or cumbersome and expensive apparatus and techniques.

One method for increasing gas temperatures above that usually resulting from burning ordinary fuels is to utilize electric power to augment the heat from fuel 'combustion. Such electrical augmentation can be achieved by an are superimposed on the flame, however, this type of electrical augmentation offers severe disadvantages. In the first place, such an electric are augmented device is characterized by extreme temperature gradients, in that the electrically conductive path contracts into a narrow, superheated pencil-like channel which carries virtually all the current, whereas the surrounding medium remains relatively cool and carries little or no current. Due to the high conductivity of the conducting path, there is a high current density and a low voltage gradient along the path. Thus, to dissipate large amounts of energy in the gas stream, extremely high current levels are required. The high current density creates serious electrode maintenance problems because the area of attachment of the are at any moment is extremely small. This reduces the useful life of the electrodes. A second factor is the increase in energy loss at the electrode which is mainly related to current density.

A second and more useful method for increasing gas temperatures is described in B. Karlovitz US. Pat. No. 3,004,l37 and is known as the diffuse or distributed discharge technique wherein the discharge is distributed substantially throughout the gas stream. In a diffuse discharge, more uniform heating is accomplished with lower current densities and higher voltage gradients resulting in higher heating efficiencies and reduced electrode maintenance costs.

The diffuse discharge is made possible by the addition of an ionizing additive to the gas stream. Gases at ordinary temperatures are very poor electrical conductors, because they have a very low concentration of free electrons and positive ions. At ordinary flame temperatures some materials such as potassium chloride, are sufficiently dissociated to ions and electrons to provide significant and controlled conductivity sufficient to provide a condition whereby a distributed discharge can be carried by the seeded gas stream. The distributed discharge in a turbulent flame prevents lo calization of current flow and resultant local overheating and breakdown into arc filaments.

While the diffuse discharge mode of operation offers many distinct advantages, the various embodiments utilizing this principle as shown in the aforementioned Karlovitz patents are those described in, for instance, U. S. Pat. Nos. 3,122,212; 3,232,746; 3,373,306;

3,376,468; and 3,465,115, all assigned to the same assignee herein, required high voltage inputs ranging from about 1,000 to several thousand volts.

As opposed to such high voltage devices requiring thousands of volts, in many applications for high temperature burners including the aforementioned material cutting, welding, metal coating and incineration, it is desirable to provide the increased temperature available from a diffuse discharge type of electrically augmented operation in a compact, perhaps hand-held burner operable from low voltage power sources, such as the common 1 15 or 230 volts A.C. supplies.

In attempting to construct a low voltage burner from existing components of a prior high voltage diffuse discharge burner several problems were encountered. Initially, the electrode spacing must be decreased from several inches to less than an inch due to the significantly lowered discharge voltage required. Then it was found that the heat losses which were relatively inconsequential in the prior large, high voltage burners, were excessive in the compact, low voltage burner. The lower voltage, closer electrodes, and higher percentages of heat loss were such that effective ionization could not be achieved and the discharge thus could not be started and maintained.

SUMMARY OF THE INVENTION In accordance with the principles of the present invention, there is provided a compact, low voltage diffuse discharge burner providing high gas temperatures which can be in excess of 5,000 F. when operating with ordinary fuels. As an example of the principles of the present invention, a burner for metal coating compositions was constructed. The constructed hand-held burner was operable from a power source of less than lOO volts. In operating the constructed metal coating burner embodiment of the present invention, a coasting rate of about 15 lbs. per hr. was achieved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. II is a sectional view of a burner constructed in accordance with the principles of the present invention and employed for providing high temperatures in metal composition coating; and

FIG. 2 is a sectional view of a gravity coating feeder for supplying metal particles to the burner shown in FIG. il in an alternative embodiment of the invention.

DETAILED DESCRIPTION electrode 112 and a downstream similarly shaped metal.

electrode lid, each adapted for receiving cooling water therethrough via suitable water lines 116. The metal electrodes 12 and 14 are preferably faced with an erosion resistant surface such as a molybdenum surface 54; inch thick. Electrode 12 is connected through lead 18 and terminal 20 to one side of a low voltage power source 22. Similarly, electrode 14 is connected through lead 24 to a terminal 26 connected to the other side of the power source 22. A radio frequency source 28 which can either be a separate source or included within the low voltage power source 22 is also connected to the electrodes 12 and 14 as shown in FIG. I.

A pair of spaced insulating blocks 30 with suitable clamping means 32 maintain the electrodes 12 and 14 in position. The main gas supplied to burner enters through the main stage gas inlets 34 which are connected through metal ring 36 locked between the insulating blocks 30. The gas supplied through inlet 34 enters the diffuse discharge zone 38 in a swirl pattern through swirl inlets 40 on the inside periphery of metal ring 36.

At the upstream end of the burner, a metal tube 42 is mounted to the upstream electrode 12 and supports a pilot flame holder 44 therewithin. Gas for the pilot stage is supplied through pilot stage inlet 46. The pilot gas flows through conduit 48, through flame holder 44, and through the passageways 50 and 52 through ring electrodes 12 and 14, respectively. A suitable ionizing additive, such as potassium chloride, is supplied through the ionizing additive inlet 54 so that the material can be ionized in the vicinity of flame holder 44 and form a uniformly distributed conductive zone within the diffuse discharge zone 38 between electrodes l2 and 14. Suitable mounting and connecting means 56 and 58 are provided for mounting the conduit 48 and ionizing additive conduit 16 to an insulating handle 62 so that the entire burner 10 can be a handheld unit. A small amount of additive carrier gas such as oxygen is also supplied to the ionizing additive inlet 54 to carry the ionizing material.

A metal outlet tube 64 having an outlet nozzle 66 is suitably mounted to the downstream end of electrode 14 for receiving the gases discharged from passageway 52. Outlet tube 64 also is provided with a coating metal inlet 68 for the introduction of a coating material at a metered rate into the discharge flame at the outlet nozzle 66.

Referring now to FIG. 2, there is shown an alternative embodiment for the feeding of the coating material. The coating feeder 80 includes a storage tube 82 for containing the coating material. At the metering end of tube 82, there is located a nozzle 84 adapted for threadably engaging the coating metal inlet 68 on the tube 84 of burner 10. An orifice 86 in nozzle 84 is sized so as to deliver the required amount of coating metal to the outlet nozzle 66. A needle valve 88 is insertable into the orifice 86 for on-off control of the flow of coating material through orifice 86. The other end of needle valve 88 is inserted through the tube lid 90. The needle end of valve 88 is suitably adapted so that the coating material is allowed to flow when control end 92 is moved upwardly. Conversely, the coating material flow is shut off by needle valve 88 by allowing the needle valve to seat within the coating feeder outlet nozzle 84. Thus, the coating feeder 80 shown in FIG. 2 provides a very convenient gravity feed for the powdered coating metal feed to be supplied to burner 10.

As indicated previously, a burner 10 as shown in FIG. 1 for metal deposition coating was constructed. The following details of construction of this embodiment are as follows. The inside diameter of passageways 50 and 52 in electrodes 12 and 14 is X; inch and the spacing between electrodes is 3/l6 inch. The main stage swirl chamber defined by the length of metal tube 36 between the insulating blocks 30 is about 9/16 inch with the metal tube 36 comprising such a length of 1% inch ID pipe.

The device was constructed partially from standard pipe fittings. The pilot stage consists of a A inch pipe which has been drilled out to inch. The output tube 64 is also basically the same size pipe with added parts comprising the electrode 14 and water cooling chamber therein.

The energy levels used with the constructed burner 10 shown in FIG. 1 have been in the 6 kilowatt range, with 3 kilowatts provided by combustion and 3 kilowatts by electrical augmentation. Typical electrical power input using a standard, commonly available electric arc welder supply was 90 amps at about 35 volts. The maximum open circuit voltage available from the welder supply is slightly over volts with either AC or DC operation. The power supply used was a MagnaTran MD-30l made by the Eutectic Corporation.

The low operating voltage makes maintenance of proper operating conditions important. In order to maintain the diffuse discharge, especially with an AC discharge, the flow patterns must be established in a manner that will provide a distribution of the ionizing additive carrying stream between the electrodes, as supplied through the ionizing additive inlet 54. It was found necessary to provide a steady feed of the ionizing additive to the zone between the electrodes to maintain a steady power level in the electrical discharge. The rate of the ionizing additive used in the device has been in the range of l2 to l5 grams per hour of potassium chloride which has been ground and screened to finer than 325 mesh. This material must of course be fed uniformly at the required rate, and there are a number of available feeders for providing such uniform feed rate, such as one manufactured by L. Adams, Ltd., London, England.

The RF source 28 was found convenient as an aid in reliably maintaining the discharge when operating the burner 10 at the typical 35 volts supplied from the electric are welder supply. Such an RF voltage is conveniently provided by components within the welder supply. The RF supply can, of course, be provided separately from the low voltage power source. When operating at the low voltages such as the aforementioned 35 volts, it is believed that the RF aids in insuring that there is a sufficient conductive region between the electrodes to provide a diffuse discharge therebetween and thereby prevent the discharge from breaking down into a filamentary are. It has been found that raising of the described constructed burner operating voltage to at least volts eliminates the need for the RF source. Without the RF present, the burner has been operated at 70 volts, although intermittent break down of the diffuse discharge to an arc was experienced. It must be noted that if reliable diffuse discharge operation is desired at even lower voltages the pilot stage illustrated in FIG. I may be modified to provide more efficient heating and coupling of the conductive gases to the electrodes.

The constructed burner 10 as illustrated in PM 11 was used with several different arrangements of fuel and oxidant. The first arrangement used premixed air and natural gas supplied to the pilot inlet 416, with oxygen used as the carrier gas and supplied to the ionizing additive inlet 54. Natural gas was introduced into the main stage gas inlets 34 to provide additional combustion fuel. The swirl inlet through inlets 410 inside the swirl chamber tended to move the gas and ionizing additives between the electrodes 12 and 114 so as to aid in preventing the formation of arcs and the resulting possible damage due to anchoring of any are discharge in one area. Air was used to convey a nickle and chrome base material used as the coating material at a rate of 15 pounds per hour from a metering, variable speed auger. The coating material introduced into the flame at the outlet nozzle 66 then impinged on the surface to be coated. Natural gas was also introduced into the coating material carrier stream so that the overall composition of the flame would not be oxidizing. An inert gas could also be used instead of air for the material carrier gas.

1n a constructed alternative embodiment of the invention, a gravity coating feeder as illustrated in FIG. 2

-was utilized. In this instance, the powdered coating metal was placed in container tube 82 and the orifice 86 was calibrated to deliver 15 lbs. per hour of the metal.

Other fuels such as propane can also be used with appropriate adjustments of the rates. A convenient arrangement for the combustion is use of propane with oxygen. With this arrangement fewer flows are required and operation is simplified as well as having a hotter flame with or without augmentation. With this combination it is convenient to introduce the propane into the main stage swirl inlets and the oxygen into the pilot stage. The additive carrier oxygen stream can be used to provide all of the oxygen required for the combustion and the rate adjusted accordingly. This arrangement has no combustion in the pilot stage. Due to the rapid combustion in the main stage the additive is heated by combustion to its thermal ionization temperature as when it was introduced into pilot stage flame. An oxygen-propane flame can be established in the pilot stage but operation is not improved significantly by this technique and heat losses are increased due to the increased temperature in the area behind the upstream electrode.

Table 1 gives a summary of flow rates used for the various configurations:

TABLE l Methane Air Rates Main gas 2500-3000 cc/min Pilot gas 800-4600 lPilot Air 11,300 Additive 7,000 Coating carrier air 2,100 Coating carrier gas 1,100 Potassium Chloride 12-15 gram/hr.

Propane Air Rates Main propane 2,800 cc/min Pilot propane 480 Pilot Air 9,000 Additive 02 14,000 Coating Carrier Air 2,100 Coating Carrier Propane 850 Potassium Chloride 12-15 gram/hr.

Propane O Rates Main propane 2,800 cc/rnin Additive 0 14,000 Potassium Chloride 12-15 gram/hr.

The following procedure was used to ignite the combustion flame with the propane-oxygen combustion system.

1. Cooling water flow was started.

2. The propane flow was started at the desired rate.

3. The propane was ignited at the nozzle with a flame or spark.

4. The oxygen flow was immediately started and adjusted to the desired rate. This caused the flame to strike back into the body of the burner.

5. The additive was then adjusted to the desired rate. The electrical discharge could then be established.

With the air-fuel combinations, the air rate was set at a reduced rate, then turned up after ignition.

1n the methane-air and propane-air configurations, the coating metal was metered through a variable speed auger and carried by the carrier gas into coating metal inlet 60. in the propane-oxygen embodiment the coating metal was supplied through the gravity coating feeder shown in FIG. 2.

The following procedure is used to metallize a surface:

1. The surface is prepared by brushing, sand blasting, or grinding.

2. The surface is then preheated without allowing the surface to oxidize. This can be done by keeping the flame gases (non-oxidizing) over the surface and not letting air (oxygen) contact the surface. This could also be aided by an inert gas sheath around the flame.

A small amount of the coating material is fed into the flame and impinged on the surface to be coated. The surface with the slight covering is heated further until the coating material melts. Then additional coating material is added to the molten puddle on the surface and continued until the desired thickness is obtained. The deposition of coating material is best accomplished if electrical augmentation is used during the time the coating material is being applied and fused or melted.

The surfaces we have coated for experimental purposes have been carbon steel. Best bonding has been to a surface cleaned by grinding a thin layer off the surface. The coating material used has been a Eutectic Corporation alloy 10,009 which is a nickel and chrome base material.

Thus, in accordance with the present invention there is provided a compact, electrically augmented burner capable of operating at substantially less than the usually required 1,000 volts with the desired diffuse discharge mode for heating gases to high temperatures. In the described embodiment of the invention, the burner required only 35 volts (operating voltage) in a diffuse discharge mode. The distance between electrodes was only 3/16 inch, and the burner was formed into a compact, hand-held unit.

it must be realized that in accordance with the teachings herein, other burners operating in the diffuse discharge mode at voltages substantially less than the usually required l,000 volts can be provided. As an example, such a burner operating at about 230 volts AC has been constructed with the electrode spacing at slightly over 1 inch.

Furthermore, the burner need not be a hand-held unit. The compact feature aspect of this invention thus can be utilized in a unit which can be readily mounted in a small frame or cabinet and operable from a standard home supplied 115 or 230 volts AC source. The highly efficient diffuse discharge mode for heating gases to high temperatures therefore can be used in the home as an incinerator.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art;

What is claimed is:

l. A low voltage, compact electrically augmented burner for heating gases to high temperatures comprising:

a pilot tube having an input and output end for containing a pilot flame;

a pilot gas inlet for supplying a pilot gas stream to the input end of said pilot tube;

means, intermediate the input end of said pilot tube and said pilot gas inlet, for receiving said gas stream and creating said pilot flame at said tube input end;

an upstream electrode at the output end of said tube for receiving said pilot flame, said upstream electrode having a passageway to enable said pilot gas stream to flow therethrough;

means for introducing ionizing additives to said pilot flame to form a substantially uniformally distributed conductive zone through said passageway in said upstream electrode;

a downstream electrode having a passageway therethrough for alignment and direct communication with the passageway through said upstream electrode,

means for mounting said downstream electrode with respect to said upstream electrode such that the minimum longitudinal distance between said electrodes along an axis aligned along said passageways is about 2 inches or less;

means for supplying a main gas stream to be heated to said conductive zone between said upstream and downstream electrodes; and

diffuse discharge means for maintaining a uniformly distributed electrical discharge through said main gas stream in said conductive zone;

said diffuse discharge means including means for connecting said electrodes to a power source for operating said burner at an operating voltage on the order of lOO volts.

2. A low voltage, compact burner as claimed in claim 1, wherein said means for mounting said electrodes comprises means for maintaining said minimum longitudinal distance at about 3/16.

3. A low voltage, compact burner as claimed in claim 2, including RF means coupled to said electrode for supplying RF energy to said conductive zone.

4. A low voltage, compact burner as claimed in claim 2, including portable support means for enabling said burner to be hand supported during operation.

5. A low voltage, compact burner as claimed in claim 1 for use in applying coating materials to a workpiece, including inlet means for receiving and dispersing said coating material into said flame, said burner directing said flame and coating material to said workpiece for applying a layer of said material thereon.

6. A low voltage, compact burner as claimed in claim 5, including a container for said coating material, said container adapted for connection to said inlet means on said burner, said container including means for gravity feeding said coating material at a predetermined rate into said flame.

7. A low voltage, compact burner as claimed in claim 6, including a handle, and means for mounting said handle to said burner to enable said burner to be handheld and portable during use in applying coating materials to a workpiece.

Claims (7)

1. A low voltage, compact electrically augmented burner for heating gases to high temperatures comprising: a pilot tube having an input and output end for containing a pilot flame; a pilot gas inlet for supplying a pilot gas stream to the input end of said pilot tube; means, intermediate the input end of said pilot tube and said pilot gas inlet, for receiving said gas stream and creating said pilot flame at said tube input end; an upstream electrode at the output end of said tube for receiving said pilot flame, said upstream electrode having a passageway to enable said pilot gas stream to flow therethrough; means for introducing ionizing additives to said pilot flame to form a substantially uniformally distributed conductive zone through said passageway in said upstream electrode; a downstream electrode having a passageway therethrough for alignment and direct communication with the passageway through said upstream electrode, means for mounting said downstream electrode with respect to said upstream electrode such that the minimum longitudinal distance between said electrodes along an axis aligned along said passageways is about 2 inches or less; means for supplying a main gas stream to be heated to said conductive zone between said upstream and downstream electrodes; and diffuse discharge means for maintaining a uniformly distributed electrical discharge through said main gas stream in said conductive zone; said diffuse discharge means including means for connecting said electrodes to a power source for operating said burner at an operating voltage on the order of 100 volts.

2. A low voltage, compact burner as claimed in claim 1, wherein said means for mounting said electrodes comprises means for maintaining said minimum longitudinal distance at about 3/16.

3. A low voltage, compact burner as claimed in claim 2, including RF means coupled to said electrode for supplying RF energy to said conductive zone.

4. A low voltage, coMpact burner as claimed in claim 2, including portable support means for enabling said burner to be hand supported during operation.

5. A low voltage, compact burner as claimed in claim 1 for use in applying coating materials to a workpiece, including inlet means for receiving and dispersing said coating material into said flame, said burner directing said flame and coating material to said workpiece for applying a layer of said material thereon.

6. A low voltage, compact burner as claimed in claim 5, including a container for said coating material, said container adapted for connection to said inlet means on said burner, said container including means for gravity feeding said coating material at a predetermined rate into said flame.

7. A low voltage, compact burner as claimed in claim 6, including a handle, and means for mounting said handle to said burner to enable said burner to be hand-held and portable during use in applying coating materials to a workpiece.

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