US2409272A - Industrial furnace and firing apparatus - Google Patents

Description

@5%. l5, 1946. J. M. GUTHRIE INDUSTRIAL FURNACE AND FIRING APPARATUS Filed Deo. .2, 1942 2 Sheets-Sheet l MTM INDUSTRIAL FURNACE AND FIRING -APPARATS Filed nec. 2, 1942 .2 sheets-sheet 2 Patented Oct. l5, 1946 iNnUsTRIAL FURNACE AND FmING APPARATUS James M. Guthrie, Allison Park, Pa., assigner to Frederick S. Bloom, Pittsburgh, Pa.V

Application December 2, i942, Serial No, 467,586

My invention relates to furnaces, boilers, lehrs, and other equipment heated by the combustion of fuel, and particularly to pre-mix ring systems therefor. A pre-mix firing or combustion system consists in apparatus that mixes the air and fuel for combustion in predetermined proportions at a mixing station remote from the combustion chambers of the furnaces, or other equipment in which combustion is to be maintained.

It has long been realized that more accurate combustion control and better fuel economy can be obtained through the use of pre-mix firing systems, but the fact is that such systems have hitherto been dangerous, this being for the reason that the mixture of air and fuel is essentially an explosive mixture, Which is particularly hazardous when itis confined, as in practice it must be confined, in ducts leading from the mixing station to the point or points at which combustion is to be maintained. The patented art in this field attests to the efforts that have been made to eliminate the danger inherent in the operation of such ring systems.

More particularly, my invention is centered in an improved burner for use in pre-mix i-lring systems. The burner of the invention is provided at its outlet with a valve adapted automatically to close when the pressure of the combustible mixture drops to a value at which there is danger of backfire. Additionally, the burner includes a trap which closes in case a backfire occurs Within the burner structure, the closed trap preventing the spreading of the explosion to the ducts that supply the mixture to the burner. Thus, it will be understood that my burner is characterized by a double safeguard against backflring.

In the accompanying drawings, Fig. I is a diagrammatic view in side elevation of an industrial furnace equipped With a typical firing system in which my burner may be employed, to provide an organization of the invention defined in certain of the appended claims. And Fig. II is a view in Vertical section of an exemplary form of my burner, the Wall of the furnace and the supply duct of the pre-mix firing system with which the burner is organized being shown fragmentarily.

The patented art contains several pre-mix combustion systems in which my burner may be used to obtain the advantages in mind. Preferably,if not essentially, the ring system in which my safety burner is used will itself include one or more devices functioning to safeguard the systern against conditions which might lead to an explosion. The backfire-neutralizing means of my improved burner, brought into functional associ- Achims. (crus-'1) v ation With conventional protective or safety devices for firing systems, afford a solution of the problem.

On September 22, 1942, Letters Patent of the United States, Nos. 2,296,255 and 2,296,256, Were granted for improvements in pre-mix firing systems to one Frederick S. Bloom, the assignee of record of the invention herein disclosed. The ring systems illustrated and described in such Letters Patent embody devices intended to safeguardthe systems against the danger of backfir- `ing, and itis in such safeguarded systems that my burner is particularly, though not exclusively, serviceable. While the ring systems shown in these Bloom patents are considered in and of themselves to be perfectly adapted for certain conditionsof service, there are cases in which the added safety of my improved burner is desirablein some cases indispensable. For purposes of illustration, I shall herein describe my invention as it may be incorporated With the pre-mix firing system of Bloom Patent No. 2,296,256.

Referring to the drawings, the reference numeral la is applied to a furnace, or a lehr, for

heating or heat-treating articles formed ofmetal, glass, or other material. A line of burners 2 is mounted on each of the opposite side Walls of the furnace, and in service these burners are adapted toproject burning columns of fuel and air into the furnace chamber. A supply duct 3a delivers a combustible mixture of air and fuel (the fuel in this case being a combustible gas) into a manifold ila, and from the manifold the mixture is fed through branch pipes 40 to the burners. More specically, gaseous fuel is delivered, undersuperatmospheric pressure, from. a pipe 6 into duct 3a, and air is supplied to the duct, by means of a blower or fan 5, and the mixed air and fuel are delivered from the duct 3a to the burner-feeding manifolds 4a on the opposite sides of the furnace.

The firing or combustion system comprises means for establishing and automatically maintaining at predetermined Value the ratio of air to fuel in the mixture, and such means, including a piece of apparatus |00 obtainable on the open market under the name Askania ratio regulator, are fully described in said Letters Patent No.` 2,296,255. To those skilled in the art it will sufce to say that the duct leading from the blower 5 includes an orifice plate ll and the fuel line B an orifice plate l2; that leads I3 and I4 establish communication between the regulator |00 and the pipes 3a, `and 6 at points on opposite sides of the orifice plates, as shown; that a buttery Valve a I is arranged in the fuel pipe 8 on the upstream side of the orice plate I2; that the plunger 9 of a pneumatic cylinder I 9 is connected to swing such valve; and that leads I'.' and I8 extend from the regulator to the opposite ends of said cylinder. The regulator IBI] operates in known way to vary pneumatic pressures in the two leads I'I and I8 in accordance with variations in the pressure differential between the fuel and the air supplied to the duct 3a, and, as the difference between the pressures in said leads rises and falls, the plungerA 9 shifts in the cylinder IE) in one direction or the.

other, correspondingly swinging the valve I in the fuel line 6 towards open or closed position. In such manner the ratio of air to fuel in the mixture in duct 3a is established and maintained at optimum value, regardless of fluctuations in the supply pressures of the air and uel, and irrespective of the usual variations in the demands or requirements of the furnace. The air and fuel are thus mixed in proportions that will afford highest eciency of combustion and greatest economy of fuel, but it will be understood that such a mixture within a closed ring system is explosive and dangerous. v

The burner included in the pre-mix lfiringsystem embodies several features of design and operation commontothe burners of the abovenoted Bloom patent. Turning to Figure II, the burner of myinvention will be understood to comprise a metal body 28 that includes a valve-y chest or chamber 82. The burner is adapted to be mounted on the sidewall of the furnace, as shown, with the outlet orice or mouth 29 of the burner in registry with the outer and smaller end of a conical passage 3D in a refractory portblock 3I which is, as usual, embodied in the furnace side wall. The combustible mixture of fuel and air enters the chest 82 by way of one of the branchy pipes IB` leading from manifold 4a, and within the chest a valve 32 is arranged to control the mouth or orice 29.

In service the combustion of the gaseous mixturestreaming through orice 29 and port-block 3I into the furnace is initiated in the conical passage 30 in the port-block, and so long as the velocity of the streaming gases is above va critical value, there is no danger of the ame burning back through the oriiice 29. and causing premature combustion andexplosion in the burner body 23 and branch pipe lill. With this circumstance in mind, it is to be understood that the burner structure includes, advantageously, means for adjusting the valve 32 in accordance with variations in the pressure of the combustible mixture supplied, to the burner, so that, regardless of the pressure at which the combustible mixture enters the burner, the velocity of flow through the orice 2,3 will either be held above critical value, or the valve 32 Will shift into position entirely to close the orifice or mouth of the burner.

Such means may consist in a eXible diaphragm 33, to which the stem 34 of valve 32 is secured. AV spring 35, whose eiective force may be adjusted by means of a screw 36, bears upon one side-of the diaphragm, and tends to shift the rod 3l! in right-to-leftA direction and to move the valve 32 towards closed position, While the pressure of the combustible mixture, transmitted through a passage 66 in a partition 3'I in the valye-chest, is eifective on the opposite side of the diaphragm, and, opposing the force of spring 3,5', tends to move the valve away from the mouth or orice 29. As in service the pressure of the combustible mixture supplied to the chest risesA or falls (other things being equal), the valve 32 is shifted to the right or to the left, and accordingly increases or decreases the effective area of the orifice 23, with the consequence that the velocity of the gases flowing through the portblock 3i is maintained above critical valueabove the value at which the flame can work back through the orice 2S and cause an explosion in the burner body 28.

If the pressure of the combustible mixture should drop to a Value at which a safe velocity through orice 23 cannot be maintained, the valve 3 2, under the urging of spring 35, moves into fully closed position, and in such position the valve is effective to prevent explosive back-firing. It is merely a matter of properly adjusting the effective force of spring 35 to insure that the valve shall close before the danger point is reached.'

The body of the valve, it is to be noted, includes one or more small passages 38, which, when the valve is in closed position, permit the flow of a slight but sufficient quantity of the combustible mixture into the throat 39 of the port-block, to sustain a pilot flame.

g The valve 32 is arranged to control the flow of the combustible mixture, not at some point in the line of iiow removed a substantial interval from the inlet end of the passage 29, 3D, but immediately at the inlet end of such passage and preferably immediately at the inlet end 30av of the conical throat of the port-block 3|.

A pipe t9 opens through the burner wall, and through such pipe (as presently will appear) air or other uid under pressure is supplied to the diaphragm chamber within the burner, on opposite side of the diaphragm 33 from that upon which the pneumatic pressure of the combustible mixture is effective. By regulation of the pressure of the air in line 39, the position of the valve d2; may be adjusted, the pneumatic pressure thus established on the right-hand side of the diaphragm supplementing the pressure of the spring 35. Indeed, in some cases the spring may be dispensed with, leaving the valve-shifting diaphragm responsive solely to pneumatic pressures.

Other known pressure-operated devices than flexible diaphragms may be arranged to shift the burner valves in the desired manner, such as the Sylphon illustrated and described in the said Bloom patents.

The rate of combustion is regulated in such manner as to maintain the desired temperature conditions within the furnace. In the exemplary apparatus herein disclosed the rate of combustion is controlled by the same valve 32 as serves to safeguard the burners from back-firing, means being provided for shifting the Valves towards or away from their seats 29 according as the temperature within theV furnace rises or falls from a critical or predetermined value. The means for so` shifting the valves in this case are pneumatic, and are adapted' automatically to vary the differential pressure on the valve-shifting members 33 within the burners.

The air-control pipe 39 of each burner is connected by a lead 4I to a pyrometer 24a, which is in turn connected by a lead 251) to a pipe 25a that leadsV from a supply of compressed air (not shown). A thermocouple, 26a., exposed to the o temperature within the furnace, is connected to the pyrometer. In the illustrated furnace it is. desirable to provide different temperaturesat various points in the length of the furnace, and inl such an installation, Athe burners are arranged' 75 in groups longitudinally of the furnace. and a pyrometer Zfia and a thermo-couple 26a are provided for each group. The burners 2 of the furnace I a, are shown to be arranged in three groups of three burners each, and the pneumatic control pipes 39 of the burners in each group are connected in common to the control pipe l of a pyrometer 2da. The pyrometers include valves (not shown) that open and close in response to the increase and decrease of the thermo-electric currents in circuits Zia, and, as such valves in the pyrometers open and close, the fluid pressure in pipes li leading to the Valve-controlling diaphragrns 33 (which diaphragms are exemplary of the several types of pneumatic motors that may be used) correspondingly rises and falls; that is to say, as the temperatures rise or fall (in the regions of the furnace into Which thermocouples 2te extend) thepressures on the righthand faces of the burner diaphragms increase or decrease relatively to the pressure of the combustible mixture on the left-hand faces of the diaphragms, and in consequence the burner valves are shifted either towards closed positions or into more widely opened positions. Thus the quantity of the fuel and air mixture delivered into the furnace is regulated. in organizing the burners in groups severally controlled by pyrometers that are individually responsive to thermocouples arranged at successive points longitudinally of the furnace, the temperatures at such points or regions of the furnace may be accurately maintained, and the desired temperature gradient in the furnace may be established and held.

The apparatus admits of great versatility in the matter of temperature regulation. The grouping of the burners may be quickly altered to provide the desired temperature gradient from one end of the furnace to the other; one burner on each side of the furnace may be connected to one pyrometer, and ve burners on eachside may be connected to another, and so on; indeed, all of the burners may be connected to a single pyrometer, if the conditions should require a single control. This interchangeability of burner grouping is made practical and economical, due to the ease with which the small tubing 39, :El may be taken apart and re-connected in such Way as to provide the desired burner grouping.

An automatic valve l2 is arranged in the fuel supply line 6. Ii for any reason the pressure of the air, or of the combustible mixture, should fall to the danger point the valve l2 closes and completely shuts oi the supply of fuel. The fan 5 will continue in operation, and in such case will scavenge the lines 3a and ia of the combustible mixture therein. The valve 52 is a known type of pneumatically operated valve, adapted in known way to close the fuel line when the pressure of the gases in pipe 3a falls below critical value.

If for any reason it should prove desirable to close down a burner, other than through the operation of the automatic means described, the attendant may do it. That is to say, a branch 43 is provided for the air line 39 of each burner, and this branch is connected to a supply of air or other fluid under a predominating' pressure. The branch includes a valve di! adjacent to the burner, but it will be understood that this valve may, if desired, be located at a remote control station. The valve is normally closed, and the burner functions in the System, as desired. However, if it becomes desirable to shut the burner down, the attendant merely opens the valve, and a predominating pressure is immediately established on the right-hand face of the diaphragm. The valve 32 is instantly closed. Thus itis that the air line 43 and valve t comprise auxiliaryV means for quickly varying the relative value of the pressures acting on the valve-controlling diaphragm. It will be perceived that the branches 43 of all of the burners of the furnace may be connected through a single valve to the predominating pressure supply, whereby the burners will respond simultaneously to the control of the attendant. In still further rennement the attendants valve or valves may be automatically operated in response to certain critical pressures or temperatures in the installation, but it is needless to involve this specification with this or other refinements and modifications that the engineer may supply.

laying described a firing system that includes instrumentalities of the sort with which the irnprovements of my invention are adapted to be associated, I shall now;turn to a description'of such improvements.

in accordance with the invention each burner 2 includes a trap that serves, in the.event of a backiire in the burner, to prevent the spread oi combustion to the branch pipe lll and other parts of the pre-mix ring system. The backfire trap comprises, in this case a flap-valve 66 arranged in the line of iiow of the combustible mixture between the inlet and outlet of the burner. The nap-valve is pivoted, at 6l, to a member S2 secured in the burner Wall, to receive in threaded union the delivery end of feed-pipe dll. The member E32 is provided with an annular valve-seat @3 which the flap-valve adapted, as will appear below, snugly to engage. Normally the nap-valve is, by the impingement of the gaseous mixture streaming through the burner, held away from the seat $3. If required a light spring E@ may be arranged to assist the streaming mixture of air and fuel in normally sustaining the flap-valve in the open position in which it is illustrated.

If the valve 32 should for any reason fail to function in such way as to prevent a backfire i.' Within the burner, the gaseous pressure produced by the backfire operates to close the flap-Valve 8@ upon seat t3 and thus prevent the spread of combustion to the pipe @15. It will be noted that the nap-valve 5d is normally inclined (when in open position) in the burner body that the pressure produced by a backfire through the inlet of the burner is eiective instantly to drive the flapvalve to its seat.

Advantageously, means are provided for locking the iiap-valve to its seat, once it has been driven there by a backfire, for in such Way the flap or disk-valve is prevented from rebounding from its seat in such way that i'lre momentarily lingering in the burner after the valve has been slapped closed cannot spread. Said means may consist in a resilient catch 65 that engages the edge of the flap-valve as it is slapped into closed position, and locks the valve to its seat. The catch is manually releasable, so that the flap-valve may, after the occurrence of a back-fire, be reset for normal is used), is effective to restore the valve to position for normal operation of the burner.

Means are also provided to safeguard the bur-ner body against rupture under 'the stress of an explosive backre. Such means comprise essentially a pressure-releasing device which may, as here shown for purposes of illustration, consist in a plate 51 normally closing an orice 58 in the burner body. The plate 6l is held in hermetic engagement with the wall of the valve body by means of springs 69, and if and when a dangerous pressure is developed Within the burner, such as is developed by an explosive backre, the plate is forced from its seat, and escape is afforded for the gases under excessive pressure Within the burner.

The foregoing specification gives a full disclosure of the invention, and it will be understood that various modifications and refinements are permissible within the terms and intent of the appended claims.

I claim as my invention:

1. A pre-mix firing system for a furnace installation including a combustion chamber, a burner, and means for supplying a mixture of air and fuel to said burner, the body of said burner having an inlet for said mixture and an outlet for the passage of the mixture into said combustion chamber, a valve arranged in the burner body to regulate the effective area of said outlet, a pneumatic device, a member connecting said pneumatic device to said valve and being movable to adjust the position of said valve in response to variations in the dilerential of two pressures acting in opposition on said member, one pressure being the pressiue of said mixture, with the effect that the velocity of the mixture streaming into said combustion chamber is normally held at backfire-preventing Value, said outlet being disposed adjacent to one end of the burner body and said inlet being disposed between said outlet and said pneumatic device, and a backre trap disposed across the mouth of said inlet in the line of flow between the inlet and the outlet, said backfire trap being movable into closed position on said inlet under the effect of gaseous pressure acting in reverse direction to the normal line of mixture flow between said inlet and said outlet, said outlet valve being arranged and preconditioned to operate under the eiect of said pneumatic device to close said outlet against backre when the mixture pressure in said burner body drops to critical value, and said trap being arranged and preconditioned to move into Yinlet-closing 'position in the event that said valve tails to move into backfire-preventing position said outlet.

2. A'-Ihe structure of claim 1, said backfire trap comprising a valve member hinged adjacent to the edge thereof which is nearer to said outlet and adapted to swing on its hinge into outletclosing position, said last named valve member being inclined from said edge in a direction away from said outlet, substantially for the purpose described.

3. The structure of claim l, together with manually releasable means for locking said trap in closed position, whereby the burner requires manual attention before the system can be returned to normal operation after the trap has been closed by abnormal conditions within the burner.

4. A pre-mix liring system for a furnace lnstallation including a combustion chamber, a burner, and means for supplying a mixture of air and fuel to said burner, the body of said burner having an inlet for said mixture and an outlet for the passage of the mixture into said combustion chamber, a valve arranged in the burner body to regulate the effective area of said outlet, a pneumatic device, a member connecting said pneumatic device to said valve and being movable to adjust the position of said valve in respense t0 variations in the diierential of two pressures acting in opposition on said member, one pressure being the pressure of said mixture, with the effect that the velocity of the mixture streaming into said combustion chamber is normally held at backfire-preventing value and a backfire trap disposed across the mouth of said inlet in the line of flow between the inlet and the outlet, said backre trap being movable into closed position on said inlet under the eiect of gaseous pressure acting in reverse direction to the normal line of mixture flow between said inlet and said outlet, said outlet valve being arranged and preconditioned to operate under the effect of said pneumatic device to close said outlet against backfire when the mixture pressure in said burner body drops to critical value, said trap being arranged and preconditioned to move into inlet-closing position in the event that said valve fails to move into backfire-preventing position in said outlet, and manually releasable means for locking said trap in closed position on said inlet.

JAMES M. GUTHRIE.

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