US1812268A - Open hearth furnace control - Google Patents

Description

June 30, 1931. J. K. MAWHA I OPEN HEARTH FURNACE CONTROL Filed April 9, 1930 3 Sheets-Sheet 1 J. K. MAWHA OPEN HEARTH FURNACE CONTROL 3 She'ets-fSheet 3' Filed April 9. 1950 INVENTOR Janms 1C Maw/w;

ATTO R N EYS June 30, 1931.

Patented June 30, 1931 UNITED STATES PATENT; OFFICE JAMES K. MAWHA, OF MAPLE'WOOD, NEW JERSEY, ASSIGNOR TO SMOOT ENGINEERING CORPORATION, OF NEW YORK, N. Y., A CORPORATION OF DELAWARE ormr HEARTH rummcn common Application filed April 9,

My invention relates to the control of combustion in open hearth furnaces and comprises regulating apparatus particularly adapted to automatically control the supply of air to, and the withdrawal of gases from, 1open hearth furnaces of the reversible type. y invention includes also master control means for permitting adjustment from a central point of the total fuel and air supplies to the furnace as well as of the ratio of fuel to air. My invention is equally applicable to furnaces burning liquid fuel or gas or a combination thereof.

In certain types of regenerative furnaces two stacks are provided, each including a section made in the form of a Venturi pipe and I provided with a controlling damper in the neck of the Venturi section. In these furnaces, a blower associated with each stack delivers air thereto below the Venturi section. Closure of the damper in one stack with the damper in the other stack open utilizes the blower delivering air into the first stack as a forced draft blower and utilizes the blower delivering air into the other stack as an exhauster. Upon reversal of the furnace, the formerly closed damper is opened and the formerly opened damper is c:losed, thus interchanging the functions of the associated blowers. My invention is mainly concerned with means for correlating the blower speeds with the reversal of such a furnace to insure at all times a supply of air to the furnace in proper proportion to the fuel supply thereto and an exhaust of gases from the furnace such that proper pressure conditions will be maintained within the furnace chamber.

For a better understanding of my invention reference may be had to the accompanying drawings, of which:

Fig. 1 illustrates diagrammatically .my combustion control applied to a liquid fuel burning furnace of the type above described;

Fig. 2 is an enlarged view of one of the blower regulators of Fig. 1; and

Fig. 3 illustrates my control applied to a gas fired furnace of the same general type.

An open hearth furnace 1 is diagrammatically illustrated in Fig. 1 as having the furnace chamber 2 and regenerative checker pressure within the melting chamber 1930. Serial No. 442,793.

brick passages 3 and 3' leading to stacks 4 and 4 respectively. Stack4 is provided with a Venturi section 5 and with a damper 6 adapted to completely close or open the passage through the neck of the Venturi section. Similarly stack 4 is provided with the Venturi section 5' and with a reversing damper 6'. A blower 7 delivers air under ressurc through a conduit 8 terminating in t e stack 4 beneath the damper 6. When the damper 6 is closed, the air flowing from conduit 8 is deflected at the damper and flows through the checker brick passage 3 to the melting chamber 2 at the entrance to which it mixes with and burns injected liquid fuel delivered to the burner 9 by a branch supply pipe 10 connected to a main fuel supply pipe 11. The liquid fuel is injected by means of steam delivered from a main supply pipe 12 through a branch supply pipe 13 to the burner 9. When the damper 6 is open, air from the conduit 8 passes upward in a jet through the Venturi section 5 drawing with it the gas from the melting chamber 2 and regenerative passage 3. -When damper 6 is open, burner 1 9 is inoperative due to closure of valves 14 and 15 in branch supply pipes 10 and 13 rcspectively, burner 9 connected to fuel and steam supply pipes 11 and 12 by means of branch pipes 10 and 13 is in operation, and damper 6' is closed to cause the air supplied by blower 7 through conduit 8 to be defiected and pass through checker brick passage 3' into the furnace chamber adjacent burner 9'.

So far as I am aware, no comprehensive systemof automatic regulation for the type of furnace above described has heretofore been employed. For most eflicient operation, the speeds of blowers 7 and 7 need to be adjusted for each reversal of the furnace. Furthermore an accurate control of the rate of fuel feed, of the fuel-air ratio, and of the are essential for best operating conditions. Centralized control of the various elements is of great value in permitting adjustment for changing conditions, such as caused by a change in the character of the fuel used, or in the composition of the material treated.

The apparatus which I have devised for automatically regulating such a furnace includes a master controller 16, fuel regulator 17, injection steam pressure regulator 18 and blower regulators l9 and 19'.

The master controller is adapted to deliver controlling air pressure to each of the individual regulators, which air pressure is that determined by manual adjustment. Each individual regulator is arranged to control the element associated therewith in response to the master air pressure and to a force varying as a function of the element controlled.

The particular construction of the mastercontroller and of the power transmitting parts of the individual regulators is immaterial, but preferably I employ a construction similar to that disclosed in Reissue Patent No. 16,507, to Charles H. Smoot, dated December 21, 1926. As shown in Fig. 1, the master controller 16 may comprise a chamber 16a into which air under pressure is supplied through a throttled pipe 165 from any suitable compressor or the like (not shown). A cup valve 160 permits leakage of air from the chamber in amount dependent upon the pressure acting thereupon and upon the tension of a spring 20 tending to raise valve 160 against the downward pressure of the air in chamber 16a. .Spring 20 has one end attached to a pivoted lever 21 to which valve 160 is likewise attached and has its other end attached to a rack 22. The position of rack 22, and hence the tension of spring 20, is adjustable manually by means of ahand wheel 23 mounted on a pinion 24 meshing with the teeth'of rack 22. A plurality of chambers 25 receive air under pressure from chamber 16a through restricted orifices 26. Air from chambers 25 bleeds to atmosphere through Valve controlled orifices 27a, 27b, 27 c and 27 d.

The construction of individual regulators 17, 18, 19 and 19 which may be of generally similar construction, may best be understood by reference to Fig. 2 wherein regulator 19 is shown upon a larger scale. This regulator preferably comprises four chambers 28, 29,30 and 31. Chambers 28 and 29 are separated by a pressure responsive diaphragm 32 to which is rigidly attached an arm 33 pivoted within chamber 29. Chambers and 31 are likewise separated by a diaphragm 34 to which a rod 35 is rigidly attached. Arm 33 carries a rod'36 vertically movable within a bushing 37 carried by the lower wall of chamber 29. Rods 35 and 36 bear upon a balance lever 38 at opposite sides of the pivot 39 to transmit to the lever opposing forces varying with the pressure difierentials in chambers 30 and 31, and 28 and 29 respectively. Unbalance of lever 38 varies the position of a throttle valve 40, which valve controls the pressure of actuating fluid in chamber 41 acting beneath a power piston 42; actuating fluid being delivered to chamber 41 through a throttled pipe connection 43 from any suitable source (not shown) and being withdrawn from the regulator at atmospheric pressure through a pipe 44. Movement of piston 42 operates a power arm 45' linked to the rod 46 of piston 42 and pivoted to a fixed part of the regulator 19.

To prevent hunting of the apparatus one element 4'? of a dash pot is connected to piston 42 and the other element 48 of the dash pot is carried by lever 38.

Chamber 31 is connected to atmosphere by meansofapassage49. Pipes50,51and'52lead respectively to chambers 28, 29 and 30. Pipe 50 may be connected to either of two pipes, 53 and 54, by means of a valve 55. Similarly pipe 51 may be connected with either of pipes 56 and 57 and pipe 52 may be connected with either of pipes 58 and 59 by means of valves 60 and 61 respectively. Valves 55, 60 and 61 are adapted to be operated in unison by means of links connected to a. vertically mov-- able rod 62, which rod is connected with the piston ot' a. relay cylinder 63 (see Fig. 1). With valves 55, 60 and 61 in the position shown in Fig. 2, pipe 50 is in communication with pipe 53, pipe 51 with pipe 56 and pipe 52 with pipe 58. Pipes 53 and 56 lead to opposite sides of an orifice 64 in pipe 8. Pipe 58 leads to one chamber 25 on the master controller. The balance lever 38 of regulator 19 is thus subjected to apressure differential measuring the flow of air through conduit 8 as measured by pipes 53 and 56 and to a master controlling pressure: as transmitted through pipe 58. An unbalance of these forces, calling for an adjustment of the speed of blower 7 causes movement of power arm 45, which arm operates to vary the speed of the blower motor. As diagrammatically illustrated, the motor 65 of the blower 7 is an electric motor having an electrical resistance 66 in circuit therewith varied by movement of arm 45. The arrangement is such that an increase in air flow through conduit 8 causes a movement of arm 45 in a direction to reduce the speed of motor 65 to thereby return the air flow to the desired value, or an increase in master pressure calling for an increase in air flow causes a movement of arm 45 in a diretcion to increase the speed of motor 65. As regulator 19 is preferably identical with regulator 19, and as like parts are identified in the drawings with like numerals but with a prime aflixed thereto, it is not necessary to describe this regulator in detail. It

should be noted, however, that relay cylinders 63 and 63 are so connected by pipes 7 and 68 as to be synchronously but oppositely operated. When valves 55, 60 and 61 are in the position shown, valves 55, 60

and 61 are in a position to connect pipe 50' with pipe 54, pipe 51 with pipe 57 and plpe 52 with pipe 59. In this position erates to maintain the furnace pressure substantially constant and equal to that of the atmosphere. An increase in furnace pressure over that desired'causes arm to adjust resistance 66 in' a direction to increase the s eed of motor to thereby increase the jet 0 air delivered through the Venturi section 5. The increased flow of air through the Venturi section 5 increases the volume of gases withdrawn from the furnace and thus restores the furnace pressure to its initial value.

To insure that damper 6 is closed when regulator 19 is operating as a regulator for the forced draft and that damper 6' is at such time open and regulator 19' operating as a regulator for the induced draft, relay cylinders 69 and 69' controlling dampers 6 and 6' respectively and relay cylinders 63 and 63 are all connected toa master pilot valve 70 preferably located adjacent the master controller 16. Pilot valve 70, of any well known construction, when in one position supplies fluid under pressure from a supply pipe 71 to a pipe 72 and connects a pipe 7 3 with a drain pipe 74, in the other position supplies fluid under pressure from pipe 71 to pipe 73 and drains pipe 72. Pipe 7 2 is connected to pipe 67 in communication with the upper ends of cylinders 63 and 69' and with the lower ends of cylinders 63' and 69. Pipe 73 is connected with pipe 68 in communication with the lower ends of cylinders 63 and 69 and with the upper ends of cylinders 63 and 69. Reversal of pilot valve 70 thus operates to automatically reverse the positions of dampers 6 and 6' and to correspondingly shift the functions of regulators 19 and 19'. Preferably valves 14, 14" and 15 15' in the fuel and steam pipes leadingto the urners, are also connected with the pilot valve 70 to be operated iivm chronously with the reversal of the air ow through the furnace. Such connections from valves 14, 1 1', 15 and 15', however, have not been illustrated as they may be similar to those shown for dampers 6 and 6 and for the valves controlling the blower regulators.

Pilot valve 70 may be operated in any desired manner. -Manual control of this valve by means of the handle 75 is illustrated, but obviously automatic means could be provided to cause the pilot valve to be reversed either by a time switch at predetermined intervals or by a thermostat when predetermined temperature conditions exist inthe furnace according to the desired methods of operation of the furnace.

To cont-r01 the supply of fuel to the furnace in proper ratio with the air supply, and

to permit of the relative adjustment of the fuel-air ratio, regulators 17 and 18 are pro- -v1ded. These regulators may be and erably are, similar in construction to regulators l9 and 19'. Regulator 17 adjusts a; valve 76 in the fuel supply pipe 11 in response to the flow of fuel as measured by the differential in pressure across a constriction 77 and as transmitted by ipes 78 and 79 to opposite sides of the upper diaphragm of the regulator and in response to the master ressure as transmitted through a pipe 80 to t e chamber above the lower diaphragm of the regulator. An increase in thefuel flow over that desired disturbs the balance upon the balance'lever of the regulator and causes operation of the power arm 81 in a direction to close valve 76 sufliciently to restore the fuel flow to the desired'value. An increase in master pressure occasioned by adjustment of wheel 23 or by adjustment of the leakage through the port 27?) causes operation of regulator 17 in a direction to open valve 76 to increase the fuel flow to the value called for by the new master loading.

Regulator 18 adjusts a valve 82 in the steam supply pipe 12 to maintain a predetermined relation between the pressure of the steam delivered to the burners and the master pressure; the steam pressure being transmitted to the upper side of a diaphragm of the regulator by a pipe 84 and the master pressure pref-- being transmitted to the upper side of the lower diaphragm by a pipe 85 connected to one of the chambers 25 of the master controller. Q

In operation of the control system disclosed in Fig. 1, with pilot valve 7 O in the position shown, with valves 14 and 15 open and with valves 14 and 15- closed, air from blower 7 deflected by damper 6-, is preheated by passage through checker brick passage 3. At the entrance to the furnace chamber the air mixes with and burns the fuel delivered by the burner 9. The gases of combustion are drawn through the checker brick 3 by the suction developed in the Venturi section 5 by the upwardly directed jet of air from .blower 7 If for any reason it is desired lator 18, the increase in master pressurev causes a proportionate increase in steam injection pressure. At regulator 19, the increase in master pressure causes a speeding up of blower 7 sufficient to increase the air flow to the furnace in proportion to the change in master pressure and consequently to the change in fuel flow as well. The increase in speed of blower 7 raises the pressure in the furnace chamber which in turn reacts upon regulator 19 to cause it to increase the speed of blower 7 sufficiently to return the pressure in the furnace to that of the atmosphere. If it is desired to change the ratio of fuel to air, as is often the case when it is desired to change from reducing to oxidizing or vice versa conditions in the furnace, the leakage through ports 27a and 27?) may be adjusted at the master to reduce or increase the master loading to the fuel and steam regulators independently of the adjustment of the air regulators 19 and 19. Instead of adjusting the leakage through ports 27 a and 276, that through ports'270 and 27 0! could be adjusted.

After the desiredlength of run of the furnace, valve 70 is reversed to reverse dampers 6 and 6 and to shift the valves associated with regulators 19 and 19. At the same time valves 14 and 15 are closed and valves 14 and 1 5 are opened. The flow of air through conduit 8 is now maintained by regulator 19 in proportion to the master loading transmitted through pipe 58 and the pressure in the furnace is still maintained equal to that of the atmosphere but by reguduit 86, and blast furnace gas, supplied through a conduit 87, are mixed in a conduit 88 connected to branch gas pipes 89 and 89 leading to burners 90 and 90 respectively.

As in Fig. 1, the furnace is provided with a pair of stacks 91 and 91 each including a damper controlled Venturi section. Blowers 92 and 92'. deliver air into stacks 91 and 91 respectively. Regulators 93 and 93, preferably of the same general construction as that shown in Fig. 2, adjust the speed of the motors 94 and 94 driving the blowers 92 and 92' by adjustment of resistances 95 and 95. Regulator 93, like regulator 19, has associated therewith a relay cylinder 96 adapted to connect pipe 97 with either of pipes 98 or 99 and to connect pipe 100 with either of pipes 101 or 102 by operation of valves 103 and 104. Regulator 93 operates in response to the pressures transmitted through pipes 97 and 100 to maintain a predetermined relation therebetween. Pipe 98 is connected to a point measuring the suction at the inlet of the blower 92. The pressure in pipe 98 will vary, therefore, inversely with the amount of air delivered by the blower, and the differential of this pressure with that of the atmosphere, as measured at the regulator 93 when pipes 97 and 98 are in communication, will be as much of a measure of the air flow to the furnace as is the difierntial pressure measured by pipes 53 and 56 in Fig. 1. Pipe 99 is connected to the furnace chamber 103 by means of a pipe 99a to transmit to the regulator a pressure varying with the pressure in the furnace when pipes 97 and 99 are in communication. Pipe 101 is connected to the master controller 104 shownsimilar to the master 16 of Fig. 1 to transmit to regulator 93 amaster loading force when pipes 100 and 101 are in communication. Pipe 102 is open to the atmosphere.

Similarly regulator 93 adjusts the speed of blower 92' either tomaintain the flow of air to the furnace in proportion to the master loading or to maintain atmospheric pressure in the furnace, depending upon the position of the piston of relay cylinder 96. As in Fig. 1, relaycylinders 96 and 96 as well as the relay cylinders 105 and 105 controlling the dampers in the stacks 91 and 91 are connected to a master pilot valve 106. Prefer ably also reversing valves 107 and 107 in the branch gas supply pipes 89 and 89 and valves 120 and 120 in pipes 121 and 121' respectively are connected with pilot valve-106 for operation synchronous with that of the blower regulator and damper relay cylinders 96, 96, 105 and 105'.

The gas supply to the furnace is controlled by a regulator for the gas flow-through each conduit 86 and 87. Regulator 108 adjusts a damper 109 to maintain the flow of coke oven gas as measured across a restriction 110 by pipes 111 and 112 in proportion to the master loading pressure as transmitted to the regulator through a pipe 113. Similarly regulator 114 adjusts a damper 115 to maintain the flow of blast furnace gas as measured across a restriction 116 by pipes 117 and 118 in proportion to the master loading pressure as transmitted to the regulator through a pipe 119.

The operation of the system-described in Fig. 3 is similar to that of Fig. 1. When valves 107 and 120 and the damper in stack 91 are open with valves 107 and 120 and the damper in stack 91 closed, regulator 93 is operating as a forced draft regulator to main tain the flow of air to the furnace in proportion to the master loading, while regulator 93 is operating as an induced draft regulator to maintain constant the pressure within the furnace. The gas regulators 108 and 114 maintain the gas supply in proper proportion to the air supply which proportion is adj ustable at the master 104. Reversal of pilot valve 106 with simultaneous reversal of the position of valves 107, 107, 120 and 120 reverses the flow of air and gases through the furnace and likewise reverses the functions of regulators 93 and 93', while having no'effect upon the gas regulators 108 and 114:.

I have now described two' embodiments of my new regulating sygstem for open hearth furnaces. In each em odiment two air regulators are provided, each adapted to operate either as a forced draft or an induced draft regulator. In each embodiment intercon nec ed controlling means are provided for shifting the regulating function of the air regulators under control of a single pilot valve, which pilot valve may also be in control of the various reversing valves and dampers of the furnace. My invention includes any suitable automatic or manual means for suitably operating the controlling pilot valves for such air regulators. My invention also includes the combination with the above air control of-a master controller adapted to control the fuel supply, to the furnace, whether liquid or gaseous, to maintain any desired ratio between the air and fuel supplies; the master controller being arranged to control at all times one or the other of the air regulators.

Iclaim:

1. In combinationyvith a reversing furnace of the type wherein a pair of continuously operating blowers supply air under pressure into damper controlled Venturi sections ofa pair of stacks and the furnace is reversed by reversing the positions 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 chamber to which fuel is supplied and from which the air from the other blower induces withdrawal ofthe gases of combustion, a control system including a regulator for each blower and means associated therewith for applying to the regulator for the blower supplying air to the furnace a differential pressure varying with the rate of flowof air to the furnace and for applying to the regulator for the blower inducing the withdrawal of gases from the furnace a pressure differential varying with the pressure in the furnace.

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 said blower regulators for adjusting the total fuel and air supplies to the furnace and the ratio therebetween.- r

3. The combination according to claim 1 wherein the furnace is provided with a pair of burners andwith 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 throughthe supply pipe in predetermined ratio with 'melting chamber.

the air flow to the furnace and a, regulator for the steam suppl pipe adapted to maintain the pressure 0 the injection steam in proportion to the flow offuel.

4. In combination with a reversible regen erative furnace provided ,with a melting chamber and with a blower adapted to supply ai'rithereto or to induce withdrawal of sures the differential of which varies with the rate of flow of air delivered by the blower and when in another position adapted to connect said chambers to pressures, the differential of which varies with the pressure in the 5. The combination according to claim 4 I including a second blower for said furnace adapted to supply air thereto when said first blower induces withdrawal of gases from the melting chamber and to induce withdrawal of gases when said first blower is supplying air to the furnace, a regulator for said second blowerprovided with two chambers separated by a diaphragm movable to effect control of the blower, a member when in one position adapted to connect said chambers with pressures the differential of which varies with the rate of flow of air delivered by said second blower and when in another position adapted to connect said chambers to pressures the differential of which varies with the pressure in the melting chamber, and means -for causing movement of said members synchronously with the reversal of the furnace whereby when said first blower is.

supplying air to the furnace the regulator therefor is adjusting in response to the rate of flow of air, said second blower is inducing withdrawal ofgases from the furnace and the regulator therefor is adjusting in response to the pressure in the melting chamber.

I 6. In combination with a reversible furnace provided with a melting chamber and with a blower adapted to supply air thereto or to induce withdrawal of gas therefrom depending upon the direction of operation of the furnace, a regulator for said blower provided with a balance and with power means for adjusting the speed'of the blower brought into operation upon departure of said balance from neutral, a relay cylinder associated-with said regulator and having a piston which in one position causes said balance to be subjected to a force varying with the rate of flow of air supplied by the blower and to an adjustable controlling force, and in the other position causes said balance to be subjected to a force varying with the pressure in the melting chamber and to a force varying with the pressure of the atmosphere, and remote control means for causing the piston of said relay cylinder to move from one position to the other.

7. The combination according to claim 6 wherein the reversal of the air to the furnace is effected by two dampers each under control of a relay cylinder and wherein the remote control means comprises a pilot valve connected to the relay cylinders for the dampers and for said regulator arranged to operate .the same in synchronism.

8. In combination with a furnace having a combustion chamber and provided with a blower for supplying air thereto, a regulator for said blower including a balancing device adapted upon departure from neutral position to effect adjustment of the air supply delivered to the furnace by said blower, a master controller adapted to transmit a controlling force to said balancing device, means adapted to transmit to said device a force varying with the rate of flow of air delivered by said blower, and a relay adapted when in one posit-ion to cause said device to be subjected to said master controlling force and to said force varying with the rate of air supplied by the blower, and when in another position to cause said device to be subjected to a constant force and to a force varying with the pressure in said combustion chamber.

9. In combination with a reversing furnace of the type wherein air under pressure is continuously supplied through conduits into damper controlled Venturi sections of a pair of stacks and the furnace is reversed by reversing the positions of the dampers in the stacks to-cause the air to one Venturi section to be deflected at the closed damper and to .thereupon pass into the melting chamber to which fuel is supplied and from which the air to the other Venturi section induces withdrawal of the gases of combustion, a control system including a regulator for the air sup ply through the conduits to the Venturi sections and means associated therewith for applying to the regulator controlling the air supply to the furnace a differential pressure varying with the rate of flow of air to the furnace and for applying to the regulator controlling the air supply for inducing the withdrawal of gases from the furnace a pressure differential varying with the pressure in the furnace.

10. The combination according to claim 9 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 said air supply regulators for adjusting the total fueland air supplies to the furnace and the ratio therebetween.

11. In combination with a reversible regenerative furnace provided with a melting.

chamber and with a supply of air thereto for forced draft or to induce withdrawal of gases therefrom depending upon the direction of operation of the furnace, a control system including a regulator for said air supply provided with a pair of chambers separated by a diaphragm movable in response to the pressures in said chambers to effect controlof the air supply, a member when in one position adapted to connect said chambers to pressures, the differential of which varies with the rate of flow of air delivered as forced draft and when in another position adapted to connect said chambers to pressures, the differential of which varies with the pressure in the melting chamber.

In testimony whereof, I have signed my name to this specification.

JAMES K. MAWHA.

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