US 3209811 A
Description (OCR text may contain errors)
Oct. 5, 1965 R. w. STRANG 3,209,311
COMBINATION HIGH VELOCITY BURNER Filed March 28, 1963 3 Sheets-Sheet l INVEN TOR.
ROBERT W. ST RANG.
Oct. 5, 1965 R. w. STRANG COMBINATION HIGH VELOCITY BURNER 5 Sheets-Sheet 2 Filed March 28, 1963 &
m R MW O S w WT 1% M B ATTORNEYS.
United States Patent 3,299,811 COMBHNATHUN HHGH VELOQHTY BURNER Robert W. Strang, Moon Township, Allegheny County,
Pa, assignor to Loftus Engineering Qorporation, Pittsburgh, Pa, a corporation of Maryland Fiied Mar. 28, 1%3, Ser. No. 268,826 3 (Iiaims. (til. 158-109) My invention relates to burners for the firing of soaking pits with gaseous fuel, and the invention consists in certain new and useful improvements in a burner structure, whereby the recently developed advantages of the highvelocity firing of a soaking pit with a plurality of burners may be more economically obtained by the use of a single burner.
In application for United States Letters Patent, Serial No. 189,820 filed April 24, 1962, for a Method of Operating Soaking Pits, owned by the assignee of my present invention, an improved method of firing soaking pits with high-velocity burners is disclosed. Briefly, the said method consists in firing a soaking pit chamber with gaseous fuel, and with the required combustion air delivered at a velocity of at least 200 feet per second, employing burner means that comprise or have the effect of a plurality of burners.
For purposes of illustration, let it be assumed that three individual high-velocity burners are arranged to fire a pit. During the heating period, that is, the time the pit is being operated to heat a charge of steel ingots, all three burners function at normal maximum firing capacity until the ingots approach the temperature at which they are to be thermally soaked, preparatory to rolling, forging, or otherwise working them into the desired product. As the ingots approach the soaking temperature, one of the burners is cut-back or shut-off, leaving the other two burners in normal operation with about two-thirds normal maximum fuel input until the ingots reach desired temperature. T hereupon, the two burners are cut-back or shutofi? and the firing of the third burner is reinstated and maintained during the period in which the ingots are thermally soaked to obtain substantially uniform working temperature throughout their bodies. Prior to the discovery of the method disclosed in said patent application, Serial No. 189,820, it was practically impossible to obtain sufficient kinetic energy of the fiames and hot pro-ducts of combustion during the soaking period of a gasfired pit, at least without using high amounts of excess combustion air.
The object of my invention is to provide an improved single burner structure that can be operated to provide, during the soaking period, the high kinetic energy required to maintain the pit chamber at substantially uniform temperature throughout, and to provide throughout the bodies of the ingots a substantially uniform temperature.
Another object is to provide a burner which may be effectively fired at high velocity during the soaking period, while maintaining substantially the same ratio of fuel to air as is used during the heating cycle, with the effect that scale loss is held to a minimum.
Still another object to provide a single burner structure possessive of advantages of the sort indicated and yet whose fuel and combustion air piping may be minimized, or held to the equivalent of the fuel and air piping of the conventional or more simplified burner.
A burner embodying the invention is diagrammatically illustrated in FIG. 1 of the accompanying drawing, in association with exemplary components of a combustion system for firing a soaking pit or other heavy industrial furnaces; FIG. 2 is a view to larger scale of the burner, as seen on a medial vertical plane of section; FIG. 3 is a view of the burner in end elevation, as seen from the 32%,811 Patented Get. 5, 1965 right of FIG. 2; and FIGS. 4 and 5 are views similar to FIGS. 2 and 3, respectively, illustrating certain modifications in the structure of the burner.
Referring to the drawings the reference numeral 2 indicates fragmentarily the refractory wall of a soaking pit, through which wall a port 3 opens into the furnace chamber C of the pit located on the right-hand side of wall 2. Mounted on the outside (left-hand side, FIG. 1) of wall 2 is a burner 4 having a hollow body 5 constructed of welded steel plate or cast metal. The body may be lined with refractory material (not shown in FIG. 1, but at 50 in FIG. 2) in accordance with conventional practice. Within the delivery end of the burner a battle 6 is secured, the battle being formed of a suitable ceramic refractory material. A duct 7 for combustion air opens into the hollow interior of the burner body, and this hollow interior includes a longitudinal partition 8 of heat-resisting metal that extends rearwardly from the concentric with the baffle 6 to a transverse partition 9. The partitions 8 and 9 are united, as shown, and serve to divide the hollow interior of the burner body 5 into two chambers 10 and 11.
The refractory baffle 6 includes a circular series of orifices 12 that open from chamber 10 into port 3, and a circular series of air passages or orifices 13 that open from chamber 11 into said port 3. Gaseous fuel flows from a fuel-supply duct 14 into a fuel-delivery passage or duct 15 that extends concentrically of and through the bafiie 6 for jetting fuel through burner port 3 into the chamber C. As shown in FIG. 3, the two circular series of orifices 12 and 13 are, in this case, concentric with the delivery end of the fuel-delivery tube 15.
The air for combustion may be preheated or not, but if it is preheated a recuperator, comprising in an exemplary way two cells 16 and 17, whose heat-transfer tubes 18 of stainless steel, or the like, are positioned in a flue 19 that conducts the hot products of combustion from the soaking pit (or other furnace) fired by burner 4 to a suitable chimney or other outlet, not shown. A powerfully driven fan or blower 20 propells air drawn from the outer atmosphere first through a duct 24 and then downwardly through the tubes 18 of cell 16. The air thus propelled downwardly flows into a header 21 at the bottom of the tubes 18 of recuperator cell 16, and thence through a duct 22 into a header 23 at the bottom of the tubes of recuperator cell 17. From header 23 the air flows upwardly into the duct 7 that supplies combustion air to the chambers 1t and 11 of the burner. As the air flows sequentially through the tubes 18 of the recuperator cells 16 and 17, it absorbs great quantities of heat from the hot waste gases flowing through fine 19 and around the outer surfaces of the tubes 13.
In accordance with conventional practice, a thermocouple 24 is placed at an appropriate point in the soaking pit chamber where it is exposed to pit temperature. The minute electrical currents generated by the thermo-coupie in response to temperature conditions in the pit are magnified by an amplifier and temperature indicator 25 to operate a motor 26 having an arm 27 that swings clockwise and counter clockwise in proportion to the increases and decreases in the electrical currents developed by the thermo-couple 24, the variations in the electrical currents being proportioned to the temperature changes in the pit. The arm 27 is connected by a link 28 to the operating arm 29 of a butterfly valve 30 in the fuel supply line 14, whereby when the temperature in the soaking pit rises above a predetermined value the valve 30 swings to reduce fuel input to the burner 4. Alternately, when the temperature in the pit drops below optimum value the valve 30 moves into a more widely open position to increase fuel flow.
The fuel supply line 14 includes an orifice plate 3 1 and the air supply line an orifice plate 32. The pressures on the upstream and downstream sides of these orifice plates are transmitted via pairs of tubes 33 and 34, respectively, to a fuel-air ratio controller 35 of known construction, whereby the quantity of combustion air delivered through duct 7 to the burner 4 is automatically regulated with respect to the quantity of fuel delivered by supply line 14 to the fuel passage or duct 15 of the said burner. As already mentioned, the quantity of fuel fed to burner 4 is determined by the valve in the fuel supply line 14, and this valve is actuated in response to temperature variations in the pit chamber C. As the fuel flow varies the fuel-air ratio controller sends hydraulic or pneumatic impulses through tubes 38 to a motor 39, and through a linkage 37 the motor 39 swings the butterfly valve 36 in the air supply duct 7 towards a more open or a more closed position according as the flow of fuel increases or decreases. Thus, the ratio of fuel to air delivered to burner 4 may be accurately and automatically controlled at a predetermined value. The ratio is usually one that gives ten (10%) percent more air than is stoichiometrically necessary to burn the fuel delivered by the burner.
In the burner body a flap-valve 40 is pivotally mounted at 41 adjacent to the top edge of partition 9. A motor is adapted through a linkage 42, 43, 44. to actuate the flap-valve, the motor 45 receiving its excitement through an electrical circuit 46 from a fuel flow recorder 47. The diiferential pressure between the opposite sides of fuel orifice plate 31 is transmitted through tubes 33 and 48 to recorder 47; the recorder receives energy from an electrical supply cicuit 49; and in a known way the recorder 47 sends electrical current through circuit 46 to operate the flap-valve in the manner described in the following context.
In service the soaking pit chamber C is charged with ingots to be heated and thermally soaked, preparatory to rolling or forging. When the pit chamber has been charged and the open top of the chamber closed by the usual refractory cover (not shown), the fuel and air are delivered to the burner 4- at normal maximum capacity, the fuel valve 30 and air valve 36 standing in about fully opened positions, with the flap-valve 40 standing in the vertical or open position in which it is shown in FIG 1. Preheated combustion air flows into both chambers 10 and 11 of the burner and thence flows at high velocity, a velocity of at least 200 feet per second, through both sets of orifices 12 and 13, to support the combustion of the gaseous fuel delivered by duct 15 through port 3 into the pit chamber C containing the ingots. The burning fuel and products of combustion transfer heat to the ingots and to the refractory walls and cover of the pit chamber. In a typical case let it be assumed that the ingots are to be heated and soaked to a uniform temperature of 2250" F. In this case the firing of the pit chamber is cont-rolled in such way that the temperature of the steel ingots does not substantially exceed 2250 F., even though the refractory walls and cover during this heating cycle reach a temperature hgher than the temperature of the ingots.
In the interests of high production it is desirable to burn as much fuel in the pit chamber as possible without overheating or washing the ingots. Accordingly, at the start of the heating cycle maximum firing progresses until the walls of the pit chamber reach the control point temperature pre-set in temperature controller 25, at which time the temperature controller operates through circuit 52, motor 26 and linkage 27, 28, 29 to turn the valve 30 and gradually reduce the rate of fuel delivery. When the walls of the pit thus are caused to drop below control point temperature the fiow of fuel is increased until control point temperature is again reached.
During the initial firing of the pit the relatively cold ingots absorb heat fast, and the walls of the pit chamber do not become much hotter than the steel of the ingots; as, however, the temperature of the ingots rises the rate at which the steel ingots absorb heat progressively drops,
and in consequence the temperature of the pit chamber walls rises to the control point. Each time that the temperature of the pit reaches the control point the flow of fuel is reduced, and then is increased again when the temperature of the pit walls drops. As the flow of fuel is thus alternately decreased and increased the flow of air is proportionately decreased and increased by control means 35, 38, 39, 37, 36. This rising of the temperature to the control point and the cutting back of fuel flow is repeated many times during the heating cycle. As the heating of the ingots continues, it takes progressively less than the normal maximum fuel flow to reach the control point. During this first phase of the heating cycle the flap-valve 40 remains in its vertical or wide open position, and during this phase of the heating cycle the degree to which the valve 36 throttles the combustion air is not so extreme as to result in the high velocity of the air flowing from the orifices l2 and 13 falling below 200 feet per second.
When the firing rate of the fuel reaches the status where no more than two-thirds of the normal maximum firing rate is required to reach the control point temperature, the fuel flow recorder 47 (due to pre-set known control devices therein) is effective through mechanism 42, 43, 44, 45, 46, 48 to swing the flap-valve 40 counter-clockwise into horizontal position on the left-hand side of partition 9, with the result that the fiow of combustion air into burner chamber ll l is blanked, as is also the flow of air through burner orifices 13. If, in accordance with usual practice, a single air chamber were provided in the burner and the flap-valve 4t) were eliminated, the firing rate could be reduced and the air fiow correspondingly throttled to any desired value, but such throttling below twothirds of maximum flow would mean that the fiow of air would .be at a velocity of less than 200 feet per second, with the result that the kinetic energy of the flames and products of combustion would be inadequate to maintain uniform temperature throughout the pit chamber and the bodies of the ingots. In the past this situation has been particularly acute during the soaking cycle of pit operation, and a solution of the problem provides one of the cardinal advantages of the present invention, as will presently be described.
With the flap-valve 40 in horizontal position to the left (FIG. 2) of the partition 9, the operation of pit continues with the flow of fuel fluctuating between one-third and two-thirds of the flow during normal maximum firing. As noted, the temperature of the pit chamber walls is never allowed to go substantially above control point. When the ingots reach 2250 F., or substantially so, the mechanism and devices described function to throw the flap-valve 40 through 180 degrees, i.e., into horizontal position on the right-hand side (FIG. 2) of the partition 9, whereby the flow of combustion air to burner chamber 10 and orifices 12 is blanked, leaving the burner chamber 11 and orifices 13 open to flow. The flow of fuel in overall response to the functioning of thermocouple 24 and its associate instrumentalities is increased and dethe pit chamber reach a uniform temperature of 2250 or maybe a few degrees higher, until all of the ingots in the pit chamber reach an uniform temperature of 2250 F., or substantially so. It will be understood that, due to the features of the burner structure described, the air will flow at the high velocity of at least 200 feet per second at all times during normal pit operation, except during the few seconds in which the flap-valve 40 is moving from one position to another. As a consequence, during the soaking cycle (as well as during the heating cycle) of pit operation, sufiicient kinetic energy of the flames and products of combustion in the pit chamber is provided to maintain uniform temperature conditions throughout all portions of the pit chamber and the ingots.
It is unnecessary during the soaking cycle to increase the percentage of excess air delivered with the fuel (as has been the unsatisfactory practice in the past) in an effort to develop suflicient kinetic energy of the flames and products of combustion in the pit chamber. A noteworthy objection to the use of increased excess air during the soaking cycle is that such practice increases the formation of scale on the surfaces of the ingots. By virtue of the present invention the reduction below otherwise normal scale formation is in some instances of sufficient economic value to pay for the cost of the fuel required to heat and soak the full charge of ingots in the pit.
When the ingots have been heated and soaked the cover of the pit chamber is opened, the flow of fuel and combustion air is arrested in conventional way, and an ingot is removed to feed the rolling mill or forging press. After an ingot is removed the cover is reclosed and the firing of the pit is reinitiated as required to restore the thermal conditions in the pit chamber and the remaining ingots, pending the withdrawal of the next ingot.
FIGS. 4 and 5 illustrate that the two sets of air orifices or passages 12a and 13a may be provided in a single circular series distributed around the outlet end of the fuel duct 15a. The passages 12a open from the air chamber or receiver Illa, while the passages 13a are connected by pipes 11a to the air chamber 11b. The chamber 1112 and the interiors of the pipes 11a may be considered an air receiver. The operation of the burner, with its valve means 490, may be substantially that described in connection with burner 4 of FIGS. 1-3, where by during normal maximum firing combustion air will be delivered by all air passages 12a and 13a, or by air passages 12a alone, and/or by the air passages 13a alone.
Such is the nature of the invention herein described, and within the terms of the appended claims many modifications and variations will occur to the skilled engineer or operator without departing from the spirit of the invention.
1. A high-velocity burner for industrial furnaces comprising a burner body including an air chamber and provided with a refractory baffle that forms a Wall portion of said chamber, said burner having a duct that opens through said baflle for delivering gaseous fuel from the burner, partition means in the burner body for dividing said chamber into two compartments, said baffle having two sets of air passages that open severally from said compartments, each set of air passages being distributed with respect to the point of fuel delivery through the bafile, a combustion air duct opening into said burner, a valve movable into several positions relatively to said partition means for directing combustion air selectively into both and into either exclusively of said compartments, and means coordinated with the rate of flow of gaseous fuel from said burner for automatically moving said valve from one to another of said positions.
2. A high-velocity burner for industrial furnaces comprising a burner body including an air chamber and provided with a refractory baffle that forms a wall portion of said chamber, said burner having a duct that opens through said baffle for delivering gaseous fuel from the burner, partition means in the burner body for dividing said chamber into two compartments, said balile having two annular series of air passages severally opening from said compartments, each annular series of passages being substantially concentric with respect to the point of fuel delivery through the baffle, a combustion air duct open ing into said burner, a valve movable into several positions relatively to said partition means for directing combustion air selectively into both and into either exclusively of said compartments, and means coordinated with the rate of how of gaseous fuel from said burner for automatically moving said valve from one to another of said positions.
3. A high-velocity burner for industrial furnaces, said burner having a body including an air chamber, a refractory bafile forming a wall portion of said chamber, a duct connected to the burner body for delivering combustion air into said chamber, a transverse partition in the burner body dividing said air chamber into two compartments, the body of said transverse partition being substantially parallel to the line of flow of combustion air leaving said duct, a fuel-delivery tube extending into the burner body and through said transverse partition, said refractory bafile including a fuel passage in communication with the fuel-delivery tube, said bafiie also including a plurality of air passages distributed in spaced relation around said fuel passage, certain of said air passages communicating with the air compartment on one side of said transverse partition and others of said air passages communicating with the air compartment on the other side of said transverse partition, and a valve mounted for movement relatively to said partition and to the point of entrance of the combustion air into the burner body for selectively directing combustion air into both of said compartments and exclusively into either of the compartments.
References Cited by the Examiner UNITED STATES PATENTS 1,558,529 10/25 Wunsch. 2,167,183 7/39 Naab 158-99 2,244,821 6/41 Bloom 158-990 2,377,497 6/45 Hopkins 15899.0 2,458,543 1/49 Urquhart 158109 X 2,849,221 8/58 Cone et a1 263-43 FOREIGN PATENTS 398,488 7/24 Germany. 819,964 9/59 Great Britain.
OTHER REFERENCES Publication, Iron and Steel Engineering, vol. 35; November 1958; pp. 82-89.
FREDERICK L. MATTESON, JR., Primary Examiner. MEYER PERLIN, Examiner.