US2176270A - Open hearth furnace - Google Patents

Description

Oct 17, 1939. 'w. RT I 2,176,270

OPEN HEARTH FURNACE A Filed Dec. 17, 1937 5 Sheets-Sheet l A TTORNEYS.

Oct 17, 1939. w. AfMORTCN OPEN HEARTH FURNACE 3 Sheets-Sheet 3 Filed Dec. 17, 1957 I N V EN TOR.

A TTORNEYS.

meme a. 11, 1939 ammo UNITED STATES PATENT orrlcr:

' ammo V OPEN HEART]! macs notation of Penny I Application December 17, 19:1, Serial-No. 180,34:

4 Claims.

This invention relates to new and useful improvements in open hearth furnaces, more particularly in the method of flrings'uch' furnaces and automatically controlling the combustion system, and it is among the objects thereof to provide a furnace structure which shall be adapted for mechanically controlled continuous flring as distinguished from the reversing regenerative type furnaces, and in which the application of a heating ilame is such as will provide regul'able temperatures longitudinally and'transversely of the melting hearth and chamber.

Another object of the invention is the provision of means for directing an adjustable heating flame into the furnace, and s0 removing the waste products therefrom that the atmosphere into which the fuel is directed will be free'of any excess of waste gases to thereby insure maximum thermal em.- clency.

A further object of theinvention is the provision of means for controlling the fuel supply and stack draft in response to variations in pressure of the furnace atmosphere. I

The reversing type furnace is not well adapted to a modern combustion control system. The burner is alternately a burner and a waste gas outlet and with such an arrangement the problem of properly burning the fuel at correct velocities is serious. In this new furnace. a pair of burner ports are provided having an area much smaller than the total area of the two outlets, resulting in better combustion, flame direction and control.

These and other objects of the. invention will become more apparent from a consideration of the accompanying drawings constituting a part hereof in which like reference characters designate like parts and in which:

, Fig. l is a horizontal section of an open hearth furnace talren along the line ll, Fig. 4;

Fig. 2 ahorlzontal section of one-half of the openhearth furnace taken along the :line 2-2, as Fig.6;

A further object of the invention is to conduct Fig. 3 a vertical section taken along the line 3-4, Fig. 2;

Fig. 4 a vertical section taken along the line 4-4, Fig. 6; 1

Fig. 5 a plan view of the complete furnace B viewed from the topof Fig. 6;.

Fig. 6 a vertical cross-section longitudinally of the furnace taken along the line 8-8, Fig. 2;

Fig. 7 a plan view of the open hearth f 3% diagrammaticallyillustrating means for controlto ling the stack draft in response to pressure erential in the furnacechamber; and

Fig. 8 a diagatic view partially in section of the stack draft control means of Fig. 7.

With reference to the several figures of the 515 drawings, numeral 6 designates the roof, 2 the hearth, and 3 and 8 the sidewalls of the furnace. The hearth 2 is provided with a lining it of dolomite or the like which isrenewedfor each charge. Both the roof and hearth are conveg at their go ends as shown in Fig. 6, forming a constricted area constituting firing ports ii and waste gas exit passages l, the firing ports extending into preheated air passages 3 and the waste gas exit ports l communicating with waste gas passages El surroung 5 7 the preheated air passages t. Dampers to. may he provided to distribute the flow oi waste gases around the preheat air passage 8.

Firing ports (-3 are slightly oiic'set from the longitudinal ends of the furnace, and the hea so flame extends from the mouth of the firing port longitudinally of the furnace, and the products of combustion pass in a loop toward and into the waste gas passages l. Burner pipes ill extend into the firing ports t, these being movable longitudig5 nally by means of a motor drive mechanism generally designated by the numeral it for the purpose hereinafter explained, the burner pipes Bil being at a slight inclination to impinge the heating flame downward against the surface or the charge 49 on the furnace hearth.

The'preheeted air and waste gas passages 8 and 9, respectively, extend vertically downward from the furnace to the recuperator structures, generally designated by the reference numeral 62, and which consist of refractory tile l3, forming vertical waste gas passages and horizontal air passages through which the products of combustion from the furnace and the preheated air delivered to the furnace, respectively pass. Poke holes provided 50 with refractory plugs it extend through the roof of the recuperators to render the vertical waste gas passages accessible for cleaning;

As shown. in Fig. e, the waste gases pass down- 'wardly from the exhaust port l around the veris tical preheated air passage 8 in heat exchange relation therewith, into a slag pocket l6, from which slag is removed through a door II. The waste gases pass vertically upward into the collecting chamber above the recuperator tile. thence downwardly through the vertical passages to a common chamber at the bottom of the tile-from the waste gases directly to the stack passage l8, if

desired, thereby regulating the degree of preheat of the recuperator, and for the removal of surplus waste gases. from mixed fuels containing blast furnace gas, to avoid high temperature differentials in the base of the recuperator; and further to compensate for resistance to the waste gas flue in the recuperator toward the end of a campaign when an excess of solids may accumulate in the waste gas flues of the recuperator.

The passages iii are also provided with dampers 22 whereby the amount of gases drawn through the respective recuperators may be regulatecl.

The air to be preheated is conducted into the lower horizontal passage 23 of the recuperator tile structure, Figs. 4 and 5, there being a plurality of inlet passages from a manifold 24, which is provided with a blower 25 to supply the air to the recuperator structure in any desired regulable quantities.

The operation of the above-described open hearth furnace is briefly as follows: When the material is charged in the chamber, it is piled on the lining 5 of the hearth 2 and the burners are lighted and adjusted to deliver a desired amount of heating medium'through the burner port 6. The products of combustion are directed against the material on the hearth and then pass to the waste gas exits I and downwardly through the vertical passage 9 surrounding the preheated air passage 8 to the recuperator-structure. Because of the continuous removal of the products of combustion through the ports I, combustion will take place in an atmosphere continuously cleared of products of combustion. During the initial stages .of firing, it is desirable to retract th burner pipes ill from the firing ports to obtain increased ignition rates by utilizing the stored heat of the refractory walls of the firing ports as an aid to efficient combustion. The burners are then gradually moved to an advanced position at a predetermined rate in the firing port 6 to vary the flame length and extend the area subjected to the products of combustion, as shown in Fig. 6 of the drawings. This movement of the burner pipes is effected by the drive mechanism II which may be operated by a reversing motor through a gear reduction mechanism as shown.

The drive mechanism is designed to gradually move the burner'into the port to change the flame length and concentration of heat during the progress of a melting cycle; thus, for example, when a cold charge is placed in the furnace, it will occupy a substantial portion of the space between the hearth and roof, and it is diflicult to burn a long flame at high temperatures uniformly in the cold furnace at the start of the heat. By properly positioning the burner at the beginning of the heat, the flame is concentrated on the charge adjacent the burner port and melting progressively is advanced toward the center of the hearth. When the burner is drawn back into the burner port, the' mixing of the fuel and air takes place in a confined area and as it progresses into the furnace the heat flame islengthened so that the hotter portion of the flame extends into the charge remote from the burner port. The fuel supply may be gradually diminished as the "melting progresses so that as the flame is lengthened the firing rate or thermal input per unit of time is reduced to obtain the most effective distribution of the fuel to the bath.

Because of the unidirectional continuous firing from both ends of, the furnace, it is desirable to maintain balanced pressures at the exhaust ports, which can be accomplished by pressure recording mechanism that is standard equipment and which is' located in the exhaust passages and which, through suitable control mechanism, automatically regulates the stack dampers to maintain a balanced pressure.

It is evident from the foregoing description of the invention that open hearth furnaces constructed in accordance therewith are adapted'to the melting and refining of steel in an economical and emcient manner, whereby the time of melting is reduced, thereby increasing the production capacity of the furnace.

It is also apparent that by means of the arrangement of waste gas passage and preheat air passage in heat exchange relation in the travel of the air and gases between the furnace and recuperator structures, a much higher preheat for the air is obtainable, and by regulating both the application of heat and the heat intensity from 4 the firing port end toward the center of the furnace, the materials can be melted at a faster rate without creating waste heat in the furnace.

With reference to Figs. 7 and 8 of the drawings, the internal pressure of the furnace chamber is regulated by means of the following mechinder 33, the piston of which actuates the stack damper 34, a manually operated valve 35 being interposed in conduits 3| and 32.

It is desirable during the heating period of the furnace to maintain predetermined pressure in the furnace chamber, this being automatically accomplished by the regulator diaphragm 28 which, by being exposed to both the pressure within the furnace chamber through conduit 26 and the atmosphere through conduit 21, will operate valve 30 in response to variation in the pressure differentials it is desired to maintain.

When the fuel and air supply to the furnace have been reduced after the charge in the furnace has been brought to a molten stage, the pressure decreases in the stack and the furnace pressure drops accordingly. By means of the control mechanism of Fig. 8 the stack draft dampers 34 are automatically adjusted to compensate for the lesser volume of the products of combustion so that the some pressure may be maintained in the furnace,'which is especially desirable where prolonged metallurgical processing is necessary as apparent to those skilled in the art that various modifications may be made in the details of construction without departing from the principles herein ,set forth. I claim:

1. In an open hearth furnace, a hearth, roof and side walls forming \a melting chambenfiring ports at opposite ends of said chamber and waste gas exit ports adjacent the firing ports, burners extending into the firing ports, preheat air passages of substantial length communicating with said firingp'orts. waste gas passages surrounding said air passages, a recuperator tile structure communicating with said preheat and waste gas passages, means for directing. regulable quantities of fuel and preheated air to said firing ports, and means to simultaneously and continuously withdraw the products of combustion through the waste gas exit adJacent said 20 ports whereby the melting-flame is extended into the continuously clearing atmosphere of the fur- 2. In an open hearth furnace, a hearth, roof and side wall structures comprising a melting chamber, firing ports at the respective ends of 1 said chamber, a preheated air passage extending vertically from said firing ports to recuperator structures, waste gas exit ports adjacent the firing ports having a passage coextensive with the preheated air passage and completely surrounding the latter, a recuperator tile structure communicating with said preheat and waste gas es,

means for distributing the fiow of the waste gases aroimd the preheated air passage and burners extending into said firing ports.

3. In an open hearth furnace, a hearth, roof and side wall structures comprising a melting chamber, firing ports at the respective ends of said chamber, a preheated air passageextending vertically from said firing'ports to recuperator structures, waste gas exit ports adjacent the firing ports having a passage coextensive with the preheated air passage and completely surround- .ing the latter, a recuperator tile structure communicating with said preheat and waste gas passages, and means for regulating the volume and heat intensity of the preheated air entering the furnace chamber.

4. Inan open hearth furnace, a hearth, roof and side wall structures comprising a melting chamber, firing ports at the respective ends of said chamber, a preheated air passage extending vertically from said firing ports to recuperator structures, waste gas exit ports arflacent the firing ports having a passage coextensive with the preheated air passage, a recuperator tile structure communicating with said preheat and waste gas passages, means for regulating the rate of exhaust of the waste gases from the melting chamber through the respective recuperator

Images