US1848184A - Open hearth furnace control - Google Patents

Description

Mme 8, 1932. J. K. MAWHA 193487384 OPEN HEARTH FURNACE CONTROL Filed Sept. 26, 1930 3 Sheets-Sheet l MAW/1 ATTORNEYS March 8, 1932. J K. MAWHA 1,848,184

OPEN HEARTH FURNACE CONTROL Filed Sept. 26, 1930 3 Sheets-Sheet 2 March 8, 1932. J. K. MAWHA OPEN HEARTH FURNACE CONTROL Filed Sept. 26, 1930 3 Sheets-Sheet Patented Mar. 8, 1931? UNITED STATES PATENT OFFICE JAMES K. MAWHA, OF MAPLEWOOD, NEW JERSEY, ASSIGNOR TO SHOOT ENGINEERING CORFOIRATION OF NEW YORK, N. Y., A CORPORATION OF DELAWARE OPEN HEABTH FURNACE CONTROL Application filed September 26, 1980. Serial No. 484,489.

My invention relates to the control of the air supply in open hearth furnaces, and comprises regulating apparatus particularly adapted to automatically control the air supplied to open hearth furnaces of the reversible type. My invention preferably includes a master control means for permitting adjustment from a central point of the total fuel and air supplied to the furnace as well as the ratio of fuel to air, and is equally applicable to furnaces burning liquid fuel, or gas, or a combination of both.

In certain types of regenerative furnaces, two stacks are provided, each including a section made in the form of a Venturi pipe and provided with a controlling damper in the neck of the Venturi section. In these furnaces air is delivered to the furnace at apoint below the Venturi sections. Closure of the damper in one stack causes the air to be deflected into the furnace as a forced draft, simultaneously, the damper in the opposite stack being open, the air passes through the Venturi section, serving as induced draft to withdraw the gases from the furnace. These dampers are so connected that when one is open the other is closed, thus interchanging the function .of the air supply to each. Correlation of the air supplied to each stack in this type of furnace is an essential element in the efficient operation of the furnace, it being necessar at all times to insure a supply of air to the urnace properly proportioned to the fuelsupply, and an exhaust of gases from the furnace such that the proper pres sure conditions will 'exist within the furnace chamber.

It is a practice with this type of furnace to associate a blower with each stack, the

blower alternately serving the purpose of a Y forced draft for an induced draft fan. Heretofore the operation of the blowers .under these conditions has required such a wide speed range to obtain the pro er volume range that it has been costly and inefficient to accurately proportion the air or make the regulators respond to slight pressure fluctuations within the furnace.

My invention particularly relates to means for controlling the air supply so that a wide 5 volume range will be obtained, permitting the versing damper therein in combination with air regulators and so arranged that regardless of the location of the blowing apparatus the reversing damper intersects the conduits at a point between the furnace and the points at which the air is regulated, so dividing the conduit that it alternately connects the regulated air supplies with the opposite stacks. For a better understanding of my invention reference may be had to the accompanying drawings of which:

Figure 1 diagrammatically illustrates an embodiment of my invention applied to a liquid fuel burning furnace in which two constant speed blowers are used, the air supply to the furnace being. controlled by regulating the inlet air to the blowers;

Fig. 2 diagrammatically illustrates an embodiment of my invention applied to a liquid fuel burning furnace in which two constant speed blowers are used, the air supply to the furnace being controlled by regulating the discharge from the blowers;

Fig. 3 is a variation'of some of the ap aratus of Fig. 2 in which variable speed Instead of constant speed blowers are em-.

ployed;

Fig. 4 is a variation of some of the apparatus of Fig. 2 in which a positive displacement blower is employed to supply the forced draft air supply; and

Fig. 5 diagrammatically illustrates one embodiment of my invention applied to a liquid fuel burning furnace in which one constant speed blower discharges into a common conduit, the air su ply to the furnace being controlled by regu ating the discharge from the fan.

The master and the fuel control regulators shown in Fig. 1, being the same for each embodiment, have been omitted from Figures 2 and 3 for simplicity. The regulators are'diagrammatically illustrated, for simplicity, as comprising a balancing lever ar ranged for direct control of the associated damper or valve in response to forces warying as a function of the element controlled and in response to a force transmitted to the lever by the master controller. Preferably these regulators would be of the anti-hunting balancedtype employing auxiliary power fluid for operating the controlled elements. As such regulators are now well known in the art it is not believed necessary to illus trate or describe the same in detail. For example, these regulators may take the form illustrated in Fig. 2 of Smoot Reissue Patent N 0. 16,507, dated December 21, 1926.

Likewise the particular construction of the master controller is immaterial, but preferably I employ a construction similar to that disclosed in the aforementioned reissue patent. As shown in Fig.1, the master controller 60 may comprise a chamber 60a into which air under pressure is supplied through a throttled pipe 606 from any suitable compressor or the like (not shown). A cup valve 600 permits leakage of air from the chamber in an amount dependent upon the pressure acting thereon and upon the tension of a spring 61 tending to raise valve 600 against a downward pressure of the air in chamber 60a. Spring 61 has one end attached to a pivoted lever 62 to which valve 600 likewise attached and has its other end attached to a rack 63. The position of rack 63 and hence the tension of spring 61, is adjusted manually by means of a hand wheel64 mounted on a pinion meshing with the teeth of rack 63. A plurality of chambers 66 receive air under pressure from chamber 60a through restricted orifices 68. Air from chambers 66 bleeds to atmosphere through controlled orifice valves 67 a, 67 b, 670.

The open hearth furnace 1 is diagrammatically illustrated in Fig. 1, as having a furnace chamber 2 and regenerative checker brick passages 3 and 3 leading to stacks 4 and 4' respectively. Stacks 4 and 4; are each fitted witha Venturi section 5 and 5' and damper 6 and 6' fitted to tightly close or completely open the passage through the Venturi section. A blower 7 supplies air through conduit 8 terminating in the stack under damper 6. \Vhen 6 is closed the air is deflected and acts as a forced draft thror the furnace. Simultaneously air is being supplied by blower 7' through conduit 8.

The damper 6 is open and the air jet serves as an exhauster drawing the gases from the furnace 2. The dampers 6 and .6 are suitably interconnected so that upon reversing the furnace cycle the dampers reverse and the air supplied performs the opposite. functlon.

The accurate control of the through conduits 8 and 8 is essential for ellicient operation. Referring to Figure 1, I obtain this result by providing two constant speed blowers 7 and 7 their intakes 9 and 9 leading to an intersection where, due to the position of damper 12, they interconnect with the intake conduits 10 and 11 respectively, 910 serving as an inlet conduit for the forced draft and 9'11 serving as an inlet for the induced draft. By reversing damper 12 to the dotted position conduit 10 would be connected to 9 and conduit 11 connected to 9. In this manner the forced draft air supply is always drawn through conduit 10 and the induced draft air supply is always drawn through conduit 11 regardless of the cycle of the furnace and the regulators 15 and 18 maintaining the same function throughout. A damper 14 is locatedin 10 and controlled by regulator 15, which acts to adjust the damper and keeps a fixed relation between the master pressure transmitted through pipe 19 to chamber 15a and the differential air pressure across a construction 16 transmitted to chambers 15?) and 150 through pipes 20 and 21. A damper 17 is located in 11 and controlled by regulator 18 which acts to adjust the damper and maintain a fixed relation between the furnace pressure transmitted through pipe 22 to chamber 181; and atmospheric pressure.

In the position illustrated in Figure 1, blower 7 is supplying the forced draft. drawing air from atmosphere through conduit 9-10 and discharging it into conduit 8. The stack damper 6 being closed, the air is deflected and passes through the checkerbrick 3 into the furnace 2. Simultaneously blower 7 is supplying induced draft, drawing air from atmosphere through conduit 9'11 and discharging it into conduit 8. The stack air supplied damper 6" being open, the air jct passes through the Venturi section drawing the gases of combustion with it.

As diagrammatically illustrated, an increase in air flow will cause an increase of pressure in chamber 157) causing arm 30 to move in a direction to close damper 14, restricting the orifice and reducing the flow to normal. If the master calls for an increase in air flow, the pressure increase in chamber 15a will cause arm 30 to move in a direction to open damper 14, increasing the orifice and permitting an increase of flow. An increase of pressure in furnace 2 will increase the pressure in chamber 18a causing arm 31 to move in a direction which will open damper 17, permitting an increase of air supply, increasing t-he air flow through the Venturi section withdrawing the gases of combustion and bringing the furnace pressure to normal. The volume supplies of air to the blowers may thus be varied from substantially nil when dampers 14 and 17 are closed to the total volume obtained when the dampers are.

wide open.

Figure 1 illustrates the air control acting in conjunction with the fuel control. The fuel is supplied to burner 32 from the branch line 33 which receives its supply from the main fuel line 34. The fuel is injected by steam delivered from a main supply 36, through branches 37 to burner 32. Regulator 40 controls valve 41 adjusting the fuel supply to maintain a fixed relation between the pressure transmitted through pipe 34, from the master controller and the difl'erential across a constriction 42, in pipe 34, transmitted to regulator 40 through pipes 43-and 44. The injector steam valve 45 is varied by regulator 46 to maintain a fixed relation between the pressure from the master controller pressure transmitted through pipe 47 and the steam pressure transmitted through pipe 48.

When the cycle of the furnace is reversed it is necessary to reverse damper 12 in con duit 9--9. This may be done by any manual or mechanical means, but preferably it is arranged to work in conjunction with cylinders 51 and 51 which reverse stack dampers G and 6'. As illustrated, an auxiliary liquid or air transmits pressure from a source (not shown) through pipe 53 to the relay valve 54 which in the position shown permits the pressure to be transmitted to the cylinders through pipe 55, pipe 56 being open to a drain 57. Reversing lever 54a will connect pipe 53 with pipe 56 and 55 with drain 57, pressure will then be transmitted to' the opposite ends of the cylinders, opening stack damper 6, closing stack damper 6', and swinging damper 12 to the dotted position. Blower 7' will now draw air through 9'1Q and serve as a force draft blower, whereas 7 will draw air through 9--11 and act as an cxhauster. The fuel supply may be changed manually by reversing valves 4950 and 49'-'50', or they may likewise be controlled by valve 54 or by any other suitable mechanical means.

In the embodiment shown in Figure 2. two constant speed blowers are again employed but it difiers from Figure 1 in that the function of the blowersas well as the regulators remain constant. and damper 12 divides the conduitson the discharge side of the blowers. whereas in Figure 1 it divides the conduit on the inlet side. As illustrated. blower 1 discharges into conduit 3-8, stack damper 6 being closed and the air passes into the furnace as forced, draft. Simultaneously blower 2 discharges into conduit 4- stack damper 6' being open the air passes through the Venturi section and produces an induced draft. A damper 14 inserted in conduit 3 is controlled by regulator 15 through arm 30. Regulator 15 acts to maintain a fixed relation between the master pressure transmitted to 15a through pipe 19 and a differential air pressure across constriction 16 transmitted to chambers 15b and 150 through pipes 20. 21. Damper 17 inserted in discharge conduit 4 is controlled by regulator 18 which acts to maintain a fixed relation between the furnace pressure transmitted to chamber 180 through pipe 22 and atmospheric pressure. An increase in air flow across constriction 16 will cause regulator 15 to move arm 30 in adirection which will close damper 14 restricting the conduit and reducing the air flow to normal. ,An increase of pressure from the master will cause arm 30 to move in a direction to open damper 14 permitting a greater flow of air to the furnace. An increase in furnace pressure will be transmitted through pipe 22 to chamber 18a causing it to move arm 31 in a direction to open damper 17 increasing the induced draft and withdrawing the gases from furnace chamber 2 until the pressure equalizes.

Cylinder 13 which operates damper 12 may be controlled by manual or mechanical means but preferably is operated in conjunction with cylinders 51-51' operating dampers 6-6, as explained and illustrated in Fig. 1. If damper 12 is reversed to the dotted position, stack damper 6 opened and 6 closed, the operation of the furnace is reversed but the function of the two blowers remain constant. Blower 1 will continue the supply of forced draft through conduit 3 but damper 12 now deflects the air into the conduit 8' and blower 2 will continue the supply of induced draft through conduit 4, but damper 12 now deflects the air into conduit 8, the functions of regulators 15 and 18 also remaining constant.

Fig. 3 is a variation of Fig. 2 and as illustrated regulator 15 acts to adjust the rheostatof a variable speed motor which drives blower 1.- As the blower always supplies forced draft, the speed range may be reduced to a minimum by proper selection of'the motor. The fan for induced draft may be similarly controlled.

Fig. 4 illustrates another variation of Fig. 2 in which the forced draft is supplied by a positive displacement blower. The regulator 15 now acts to maintain a fixed relation between the master pressure and the speed of the blower. adjusting arm 30 to regulate a rheostat controlling the speed of the blower. the induced draft air supply may be con trolled as shown in Fi 2. or the blowermay be driven by a variable speed motor with a regulator controlled field rbeostat.

Fig. 5 is another embodiment of my invention differing from the others in that only one constant speed blower is used dischargiug into a common conduit :2 which divides into legs 2a and 2b which alternately connectwith conduits 8 and 8 dependent upon the position of reversing damper 12. As illustrated in Fig. 5, 2a connects with conduit 8, stack damper 6 being closed the air acts as a forced draft, and 2?) being connected to 8 and stack damper 6' being open the air supplied acts as an induced draft. A reversal of damper 12 in conjunction with stack dampers 6 and 6' as previously explained will connect 2a with 8 and 2b with 8, but it will be noted that the forced draft is always supplied through leg 2a and the induced draft through leg 25. Itegulators 1:") and 18 per-v form the same functions as explained in Flg. 2.

I have now described several embodiments of my invention. It will be noted that in all embodiments the functions of the regulators are not interchanged, the ducts being so arranged that air for forced draft is always drawn or discharged through the same conduit, likewise air for induced draft is always drawn or discharged through the same conduit, as far as the reversing damper which intersects the conduits and alternately deflects the air to opposite ends of the furnace. This permits the cross-section areas of the conduits which always supply either p y forced or induced draft to be properly proportioned to meet the required conditions, thus minimizing the speed range of the blowers and the range of action required of the regulators. It further eliminates the necessity of individual fans for each furnace except in cases where it is desirable to control the draft by controlling the speed of the blowers- Where the draft is controlled by regulated dampers in the forced draft and induced draft sections of the individual furnace air supply system, the air could be drawn from a common source of supply for several furnaces. thus reducing the number of blowers required.

As shown in the embodiment of Fig. l, and equally applicable to the other embodiments, the air control may be combined with a master controller whereby the air control may be maintained at any-desirable ratio in proportion to the fuel supply, whether liquid or gas. or a combination of the two.

I claim:

1. In a reversing furnace of the type wherein a pair of conduits are adapted to be alternately utilized to deliver air under pres sure for forced draft or air for inducing withdrawal of the gases from the furnace, the combination comprising means for creating the drafts, a forced draft air supply duet, an inducing draft air supply duct, separate means for regulating the drafts in said ducts,

and means for connecting the forced draft duct with either one of said conduits and simultaneously connecting the inducing draft duct with the other of said conduits.

2. The combination according to claim 1 including a regulator for the fuel supply to the furnace chamber adapted to maintain a predetermined rate of flow of fuel thereto and a: master controller connected to said fuel regulator and to the means associated with the said draft regulators for adjusting the total fuel and the air supplies to the furnace and the ratio therehetween.

3. The combination according to claim 1 wherein the furnace is provided with a pair of burners and with liquid fuel and injection steam supply pipe lines therefor branching to each of said burners, and wherein the control system includes a regulator adapted to maintain the flow of liquid fuel through the supply pipe in predetermined ratio with the air flow to the furnace and a regulator for the steam supply pipe adapted to maintain the pressure of the injection steam in proportion to the flow of fuel.

i. In a reversing furnace of the type wherein a pair of conduits are adapted to be alternately utilized to deliver air under pressure for forced draft or air for inducing withdrawal of the gases from the furnace, the combination comprising means for creating the drafts whereby there is one source of supl of air under pressure for both the forced draft and the inducing draft, a forced draft air supply duct, an inducing draft air supply duct, separate means for regulating the drafts in said ducts and means for connecting the forced draft duct with each of said conduits and simultaneously connecting the inducing draft duct with the other of said conduits.

5. In a reversing furnace of the type wherein a pair of conduits are adapted to be alternately utilized to deliver air under pressure for forced draft or air for inducing withdrawal of the gases from the furnace, the combination comprising means for creating the drafts whereby there is one source of supply of air under pressure for forced draft and another source of supply of air under pressure for induced draft, a forced draft air supply duct, an inducing draft air supply duct, separate regulators for controlling the drafts in said ducts, and associated therewith means for applying to the regulator controlling the forced draft a differential pressure varying with the'rat-e of a differential pressure varying with the pressure in the furnace. and means for connecting the forced draft duct with each of said 6. In a reversing furnace of the type wherein a pair of conduits are adapted to be alternately utilized to deliver air under pressure for forced draft or air for inducing withdrawal of the gases from the furnace, the combination comprising a forced draft air supply duct, an inducing draft air supply duct, means for creating the drafts whereby there is one blower for supplying the forced draft and another blower for supplying the induced draft, a regulator for each blower, and associated therewith means for applying to the regulator controlling the blower supplying the forced draft a differential pressure varying with the rate of air flow to the furnace, and to the regulator controlling the blower supplying induced draft a differential pressure varying with the pressure in the furnace, and means for connecting the forced draft duct with each of said conduits, and simultaneously connecting the inducing draft duct with the other of said conduits.

' 7. In a reversing furnace of the type wherein a pair of conduits are adapted to be alternately utilized to deliver air under pres sure for forced draft or air for inducing withdrawal of the gases from the furnace, the combination comprising means for creating ber to which fuel is supplied and from which the air from the other blower induces with- JAMES K.

the drafts whereby one blower supplies air under pressure for both drafts to one conduit, and another blower supplies air under pressure for both drafts to the other conduit, a forced draft air supply duct, ,an inducing draft air supply duct, means for regulating the drafts in said ducts, and means for connecting the forced draft duct-with each of said conduits and simultaneously connecting the inducing draft duct with' the other of said conduits. i

. 8. In areversing furnace of the type wherein a pair of conduits are adapted to be alternately utilized todeliver air under pressure for forced draft or ai'r'for inducing the withdrawal of gases from the furnace, the combination of a blower connected to discharge air under pressure into one of said conduits, a second blower connected to discharge air under pressure to the other conduit, a forced draft air supply intake duct, an inducing draft air supply intake duct, separate means for regulating the drafts in said ducts and means for connecting the forced draft intake duct with the intake of either of said blowers and simultaneously connecting the inducing draft intake duct with the intake of the other of said blowers. 9. In combination with a reversing furnace of the type wherein a pair of continuously operating blowers supply air under pressure into damper controlled Venturi sections of a pair of stacks and the furnace is reversed by reversing the position of the dampers in the stacks to cause the 'air delivered by one blower to be deflected at the closed damper and to thereupon pass into the melting cham-

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