US2285036A - Furnace - Google Patents

Description

J'ulne 2, .1942. s. KNEAss, JR

FURNACE Filed Feb. 6, 1941 3 Shee ts-Sheet l ATTORNEY June 2, 1942. s. KNEAss, JR

FURNACE Filed Feb; 6, 1941 5 Sheets-Sheet 3 cil JNVENTOR `.saffzlczfLAJs/D KNEAss JR. BY @um/r M ATToRNY Patented une 2, 1942 FURNACE Strickland Kneass, Jr., Boylston, Mass., assignor to Morgan Construction Company, Worcester, Mass., a corporation of Massachusetts Application February 6, 1941, Serial No. 377,699

10 Claims.

This invention relates to furnaces, and more particularly to furnaces having provision for recirculating a portion of the waste gases to'control the combustion conditions. v

The invention is especially useful in connection with soaking pits for heating metal ingots and fired with fuels such as oil or high B. t. u. gas which ordinarily produce high llame temperatures. When such fuels are used, the rate of heat transfer from the flame to the ingots tends to exceed the rate at which the heat will travel inwardly toward the central portions of the ingots. Consequently great care must be used to avoid overheating and washing of the ingot surfaces. Attempts to solve the problem by de-l liberately maintaining an inefficient fuel-air ratio have proven to be highly wasteful of fuel. While recirculation of part of the gaseous products of combustion has been proposed as one method of reducing the llame temperature, no satisfactory means has been known heretofore for controlling this recirculation in a desired manner While maintaining an eicient ratio between the supplies of fuel and air.

It is accordingly one object of the invention to provide a .furnace having an improved means for controlling the combustion of fuel therein by recirculating a portion of the gaseous products of combustion.

It is a further object of the invention to provide for recirculation of gases in a furnace while maintaining anv eflicient ratio between the supplies of fuel and air.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

Referring to the drawings illustrating one embodiment of the invention and in which like reference numerals indicate like parts,

Fig. 1 is a diagrammatic plan View of a regenerative furnace and associated combustion control apparatus, certain parts being shown in section for clearness of illustration;

Fig. 2 is a section on the line 2-2 of Fig. 1;

Fig. 3 is a section on the line 3-3 of Fig. l; and

Fig. 4 is a view similar to Fig. 2, with a slightly modified form of control apparatus.

- The embodiment illustrated comprises a furnace IIJ (Fig. l) havingregenerators II and II' at opposite sides thereof. The regenerators are of well-known construction, and they serve alternately to absorb heat from the outwardly flowing gaseous products of combustion and to deliver heat to the inwardly flowing combustion air. The furnace III may be constructed to serve as a soaking pit for the heating of metal ingots, but the invention is not limited to such furnaces. Oil or other suitable fuel is delivered by a main pipe I2 to a three-way valve I4 from which branch pipes I5 and I5' lead to suitable burners at opposite sides of the furnace. Ducts or passages I6 and I6' lead from the regenerators II and I I' respectively to a pair of stacks I8 and I8' of well-known construction provided with dampers I9 and I9'. Means is provided to supply air to these stacks alternately insuch a manner as to entrain the gases from the corresponding ducts and eject these gases to the atmosphere. For this purpose a fan 2| is arranged to supply air to a main duct 22 having branches 23 and 23' leading to the lower portions of the respective stacks. These branches are provided with slidable shut-off gates 24 and 24' .operated by fluid motors 25 and 25' respectively. As indicated particularly in Fig. 3, a vertical nozzle 26 is provided at the base of each stack to direct the gases upwardly thereto from the gas duct therebeneath, the ejection air flowing upwardly in an annular jet around the outside of the nozzle. With the damper I9 and gate 24 closed, and the damper I9 and gate 24 open, as shown in Fig. 1, all the air from the fan 2| Will be directed into the ejector stack I8', and the gaseous products of combustion will be drawn outwardly from the furnace through the duct I6', the branch pipe I5 supplying the fuel. To reverse the furnace the three-Way valve I4 will be turned 90 degrees in a clockwise direction, the damper I9 and gate 24 will be opened, and the damper I9' and gate 24 will be closed.

TheL rate of flow of the ejection air is preferably controlled automatically to maintain a desired pressure (usually very close to atmospheric pressure) within the furnace Ill. For this purpose the ejection air duct 22 is provided with a damper 28 which is actuated by a fluid motor 29 controlled by a regulator 30. This regulator is of Well-known construction and comprises a ilexible diaphragm 32 which is subjected by means of two conduits 33 to the pressure differential between the interior of the furnace I0 and the atmosphere adjacent the furnace. This diaphragm is connected to a pivotally mounted nozzle 34 supplied with a suitable pressure fluid.

such as oil, through a pipe 36, and arranged to direct this fluid to one or the other of two conduits 31 leading to the opposite ends of the motor 29. The diaphragm may be loaded by means of an adjustable spring 38. With this construction the slightest variation in the furnace pressure will cause movement of the diaphragm 32 and nozzle 34, so that the motor 28 will move the damper 28 and produce the change in ejection air flow necessary to restore the .desired furnace pressure.

Air for combustion of the fuel is supplied in such a manner as to recirculate a portion of the gaseous products of combustion and thereby lower the temperature within the furnace. As shown in Fig. 2, a chamber 39 is provided above the ducts |6 and I6', and two ports 48 and 48' lead downwardly from this chamber to the respective ducts. A nozzle 4| is supported by horizontal trunnions 43 above the chamber 39, with the lower portion of the nozzle extending downwardly through the upper wall or roof 44 of the chamber. 'I'his roof 44 is slidable so that the nozzle may be swung in a vertical plane into alignment with the ports 40 and 40 selectively. 'I'his swinging of the nozzle may be brought about by means of a reversible fluid motor 45 having a suitable control valve (not shown). Combustion air is supplied to the nozzle 4| by means of a fan 41 and a duct 48, this duct leading from the fan to one of the trunnions 43, which is made hollow so that the air may flow therethrough into the nozzle. With the nozzle aligned with port 40, as shown in Fig. 2, a jet of combustion air will be discharged through this port into the duct I6, through which it will flow to the regenerator and thence to the furnace |8. At the same time the air jet will create a suction in the chamber 39 and draw a portion of the waste gases from the duct |6' upwardly through the port 40', so that these gases will be entrained by the combustion air and carried along thereby to the furnace. When the furnace is to be reversed, the nozzle will be swung by means of the motor 45 into the position indicated by the broken lines in Fig. 2, so that gases will be withdrawn from the duct I6 and injected with the combustion air into the duct I6'.

The rate of ow of the combustion air is preferably controlled automatically to maintain a desired fuel-air ratio. For this purpose an axially reciprocable valve 50 (Fig. 2) is mounted within 'the inner end of the nozzle 4| to control the discharge of the air therefrom, this valve being connected by a rod to the slidable piston 52 of a hydraulic motor 53 carried by the outer end of the nozzle. This motor is controlled by a regulator 55 (Fig. l) comprising two opposed flexible diaphragms 56 and 51 which function through an adjustable lever mechanism 59 to actuate a pivotally mounted nozzle 60 supplied with a suitable pressure fiuid, such as oil. through a pipe 6|, and arranged to direct the fluid to one or the other of two conduits 63 leading, through suitable iiexi'ole connections, to the opposite ends of the motor 53. The diaphragm 56 is subjected by means of two conduits 64 to the pressure differential on opposite sides of an orifice plate 65 in the fuel pipe I2, this pressure differential being a function of the rate of fuel supply. The diaphragm 51 is subjected by means of two conduits 61 to the pressure differential on opposite sides of an orifice plate 68 in the combustion air duct 48, this pressure diiferential being a function of the rate of combustion air supply. The forces produced by the loading of the respective diaphragms 56 and 51 are opposed through the lever mechanism, and by swinging the nozzle 60 slightly in one direction or the other they regulate the motor I3 and the valve 98 to control the now of combustion air in accordance with the flow of fuel. By adjusting the lever mechanism, the ratio of air to fuel may be varied as desired.

Referring now to Fig. 2, it will be seen that the ports 48 and 40 are provided with sliding gates or dampers 1|| and 18' respectively arranged to be actuated by means of fiuid motors 1| and 1|. During the operation of the furnace the gate associated with port through which the combustion air is injected is held fully open, while the other gate is utilized to control the quantity of gases to be recirculated, In the embodiment shown in Fig. 2, this other gate is controlled automatically to maintain a' predetermined pressure drop between the duct from which the gases are withdrawn and., the chamber 39. For this purpose a regulator i3 is provided, this regulator comprising a flexible diaphragm 14 connected to a pivotally mounted nozzle 15 supplied with a suitable pressure fluid, such as oil, through a pipe 16. The diaphragm may be loaded by means of an adjustable spring 11. The space at one side of the diaphragm is connected by a conduit 18 to the Ichamber 39, while the space at the other side of the diaphragm is connected by a conduit 19 to a three-way valve 80 from which two branch conduits 8| and 8|' lead respectively to the ducts |6 and I6. Thus the diaphragm is subjected to the pressure drop between one or the other of the ducts |6 and I6 (depending upon the position of the valve and the chamber 39. The diaphragm controls the nozzle 15 from which fluid may be ejected into one or the other of two conduits 83 and 84 leading respectively to two four- way valves 85 and 86. The valve 85 is provided with an exhaust connection 88, and this valve is also connected to the outer ends of the motors 1| and 1| by means of two conduits 89 and 89 respectively. The valve 86 is connected to the iiuid supply pipe 16 by means of a conduit 98, and this valve is also connected to the inner ends of the motors 1| and 1|' by means of two conduits 9| and 9| respectively. With the various parts positioned as indicated in Fig. 2, gate 10 will be held open by the pressure in conduit 9|, While gate 10' will be controlled by the regulator 13 to maintain a predetermined pressure drop from the duct |6' to the chamber 39. When the furnace is reversed, the valves 80, 85 and 86 will all be turned ninety degrees from the positions shown.

It will now be apparent that in the operation of the invention the regulator 30 will control the ejection air damper 28 in such a manner as to maintain a desired pressure within the furnace l0. 'Ihe regulator 55 will control the combustion air valve 50 in such a manner as to maintain the air for combustion in a desired proportion to the supply of fuel, so that the combustion will be efiicient. When the rate of combustion is increased, it is desirable to recirculate more of the waste gases, and this is effected automatically by the action of the regulator 13. An increase in the flow of combustion air from the nozzle 4| will tend to decrease the pressure in the chamber 39, by ejector action, and the regulator 13 will prevent such pressure decrease by opening the gate 18 or 10 (as the case may be) past which the gases flow to enter this chamber. Thus more gases will enter the chamber 39 and become entrained by the air jet. To change the proportion of gases recirculated, it is merely necessary to adjust the regulator spring 11.

In some cases it mayL be desirable to increase the relative proportion of Arecirculated gases 14, and subjected to the pressure differential transmitted by the conduits 18 and 19. A second diaphragm 95 is also provided, this second diaphragm being subjected tothe pressure differential on opposite sides of the orifice plate 68 in the combustion air duct 48, this differential being transmitted through two conduits 96. These two diaphragms 94 and 95 are connected livery thereof to the entrance passage, and a valveat the discharge end of the nozzle to control the flow of said air, the valve being adjustable along the axis of the nozzle.

through an adjustable lever system 9B to a piv- I diaphragme act in the same direction, and they' are balanced by an adjustable spring |68.

In the operation of this embodiment, an increase in the flow of the c-ombustion air in the duct 48 will increase the pressure differential transmitted through the conduits 96 to the dlaphragm 95. This will reduce the force transmitted through the lever system 98 to the diaphragm 94, so that the regulator 93 will open the gate 10 or 19 (as the case may be) past which the gases are flowing into the chamber` 39. At the same time the increased flow of combustion air from' the nozzle 4I will tend toA decrease the pressure in the chamber 39 and increase the pressure differential on the diaphragm 94, causing the gate to be opened still further. It will accordingly be apparent that with this embodiment an increase in the combustion rate will automatically adjust the regulator 93 for a lower pressure differential between the exit passage and the chamber 39, and hence will produce a greater increase in the volume of the gases recirculated than would be the case with the embodiment of Fig. 2. It will also be clear that the adjustable lever system 98 provides a simple and convenient means for predetermining the proportion of gases which will be recirculated at various rates of combustion.

The regulator 55 serves to maintain a predetermined ratio between the supplies of fuel and air by adjusting the valve 56, whether the if.

gas recirculation is controlled by the regulator 13 of Fig. 2 or by the regulator 93 of Fig. 4. Hence the fuel will be burned efliciently at all times. Since this valve 50 is located at the discharge end of the nozzle 4l, the full pressure of the air supplied by the fan 41 will be available to produce an air jet of comparatively high velocity from this nozzle, ensuring eiicient ejector action for entrainment of the waste gases. While the volume of this jet will of course vary with the rate of combustion, its velocity will be maintained substantially constant, since the pressure of the air supplied by the fan 41 will vary only slightly. High furnace temperatures are avoided even at high fuel burning rates, since the volume of recirculated gases is increased automatically upon an increase in the combustion rate.

Having thus described my invention, what I claim as new and desire to secure by Letters .Patent is:

1. A furnace having entrance and exit passages, a nozzle arranged to discharge a ljet of combustion air for entrainment of a portion of the waste gases from the exit ,passage and de- 2. A furnace having entrance and exit passages, means to supplyrfuel to the furnace for combustion therein, a nozzle arranged to discharge a jet of air for entrainment of a portion of the waste gases from the ex'it passage, means to supply all the combustion air for the furnace to the nozzle, means to conduct all the air discharged from the nozzle and the gases entrained thereby to the entrance passage, means to control the flow of the air, and an automatic regulator to adjust the air control means in accordance with the rate of fuel supply.

3. A furnace having entrance and exit passages, means to supply fuel to the furnace for combustion therein, a nozzle arranged to discharge a jet of air for entrainment of a portion of the waste gases from the exit passage, means to supply all the combustion air for the furnace to the nozzle, means to conduct al1 the air discharged from the nozzle and the gases entrained thereby to the entrance passage, a valve at the discharge end of the nozzle to control the flow of the air, and an automatic regulator to adjust the valve in accordance with the rate of'fuel supply.

4. A regenerative furnace having two passages connected thereto and arranged to serve alternately as entrance and exit passages, a chamber having two ports leading therefrom to the respective passages, a nozzle having its discharge end located within the chamber, means to move the nozzle and bring its discharge end into substantial alignment with either of said ports selectively, means to supply air under pressure to the nozzle, a valve at the discharge end of the nozzle to control the discharge of air therefrom, and a motor mounted on the nozzle and connected to the valve to regulate the same.

5. A regenerative furnace having two passages connected thereto and arranged to serve alternately as entrance and exit passages, a chamber having two ports leading therefrom to the respective passages, a nozzle having its discharge end located within the chamber, means including a hollow trunnion pivotally supporting the nozzle so that the discharge end of the nozzle may be swung into substantial alignment with either of said ports selectively, means to supply air under pressure to the nozzle through the hollow trunnion, a valve at the discharge end of the nozzle to control the discharge of air therefrom,

and a motor mounted on the opposite end of the nozzle and connected to the valve to regulate the same.

6. A furnace having entrance and exit passages, a nozzle arranged to discharge a jet of combustion air for entrainment of a portion of the waste gases from the exit passage and delivery thereof to the entrance passage, a damper to control the flow of waste gases toward the jet, and means to regulate the damper in accordance with the pressure differential on oppov site sides of the damper.

'1. A regenerative furnace having two passages connected thereto and arranged to serve alternately as entrance and exit passages, a chamber having two ports leading therefrom to the respective passages, a damper associated with each port, a nozzle mounted within the chamber, means to supply air under pressure to the nozzle, means to move the nozzle at each re- \connected thereto and arranged to serve alternately as entrance and exit passages, a chamber having two ports leading therefrom to the 15 respective passages, a damper associated with each port, a nozzle mounted within thechamber, means to supply air under pressure to the nozzle, means to move the nozzle at each reversal of the furnace into substantial alignment 20 with the port connected with the entrance passage so that the air jet discharged from the nozzle will cause a portion of the waste gases to flow from the exit passage through the chamber to the entrance passage, means to open the damper associated with the-port connected with the entrance passage, and means to regulate the other damper to maintain a substantially constant pressure differential between the exit passage and the chamber.

9. A regenerative furnace having two passages connected thereto and arranged to ,serve alternately as entrance and exit passages, a chamber having two ports leading therefrom to the respective passages, a damper associated with 3.

each port, a nozzle mounted within the chamber, means to supply air under pressure to the nozzle, means to move the nozzle at each re- .versal of the furnace into substantial align- .flow from the exit passage through the chamber to the entrance passage, means to open the damper associated with the port connected with the entrance passage, a regulator arranged to control the other damper in accordance with the pressure differential between the exit passage and the chamber, and automatic means to adjust the regulator for a lower pressure diiferenn tial as the combustion rate in the furnace increasesand vice versa.

10. A regenerative furnace having two passages connected thereto and arranged to serve alternately as entrance and exit passages, a chamber having two ports leading therefrom to the respective passages, a damper associated with each port, a nozzle mounted within the chamber, means tosupply air under pressure to the nozzle, means to move the nozzle ateach reversal of thebfurnace into substantial alignment with the port connected with the entrance passage so that the air jet discharged from the nozzle will causev a portion of the waste gases to flow from the exit passage through the chamber to the entrance passage, means to supply fuel to the furnace, a valve at the discharge end of the nozzle to control the air ow therethrough, means to control the valve lin accordance with the rate of fuel supply, means to open the damper associated with the port connected with the entrance passage, and means to regulate the other damper in accordance with the pressure differential between the exit passage and the chamber.

STRICKLAND KNEASS, JR.

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