US2191354A - Open hearth furnace and method of operating the same - Google Patents

Description

Feb. 20, 1940. H. RATEAU ET m. 2,191,354

7 OPEN HEARTH FURNACE AND METHOD 0E OPERATING THE SAME 'Filed Aug. 15, 1959 2 Sheets-Sheet 1 INVENTORS Henry; Rateau EdWardD. 60.5562! 6 M M7M Feb. 20, 1940. H. RATEAU ET AL OPEN HEARTH FURNACE AND METHOD 0E OPERATING THE SAME Filed Aug. 15, 1939 2 Sheets-Sheet 2 gm \N Patented Feb. 20,

OPEN HEARTH FURNACE AND METHOD OF OPERATING THE SAME Henri Rateau, Weirton, and Edward D. Gossett, Hollidays Cove, W. Va.

Application August 15, 1939, Serial No. 290,166

13 Claims.

, This invention relates to open hearth furnaces and the method of operating them and more particularly to a furnace and method of operating a furnace wherein the stagnation of intensely hot gases in certain zones of the furnace is prevented, the heat used to better advantage, and certain portions of the refractory walls of the furnace protected from overheating.

Open hearth furnaces usually comprise an elongated structure having a row of doors along the long front wall thereof and having burner ports in the opposite end walls. The rear wall is usually completely closed, and as they are now commonly constructed, the upper part of the rear wall often slopes upwardly and rearwardly to enable refractory to be charged into the furnace to better advantage. A regenerating system is provided in connection with the furnaces whereby pre-heated air and gas are introduced 0 through the burner ports at one end of the furnace, and the products of combustion are carried out the ports at the opposite end of the furnace, circulated through the regener'ators, and the flow of air and gases is periodically reversed. The infiltration of cold air around the doors in the front wall of the furnace plus the cooling that occurs adjacent the doors tends to drive the hot gases of combustion toward the rear wall of the furnace and toward the top thereof. This causes intensely hot gases to accumulate under the roof adjacent the back'wall, and this condition is particularly aggravated in the case of a furnace having a sloping rear wall. In such a case the portion of the furnace below the roof and over the sloping back wall is out of the direct path of flow of gases from one end of the furnace to the other so that the gases are not swept from one end of the furnace to the other in this zone, and they tend to stagnate in this portion of the furnace. Being remote from the surface of the metal in the bottom of the furnace, these gases are not effective to anyconsiderable extent at least in heating 'themetal bath. On the contrary, they are harmful to the refractory in the walls and 5' roof of the furnace adjacent this zone because they are intensely hot and do not sweep over the surface of the refractory in such manner as to carry heat away from the refractory.

According to the present invention an arrangement is provided whereby the hot gases may be driven out of this portion of the furnace and carried away so that the heat may be utilized, the presence of the stagnant pool or backwash of hot gases avoided, and the refractory walls protected. The invention further provides means and apparatus whereby the flow of gases in this zone of the furnace may be directed and controlled to produce the most effective results according'to the particular type of furnace and the particular conditions of operation encountered. According to our invention pre-heated combustion air is introduced at predetermined locations adjacent this zone of the furnace, and an arrangement is provided whereby the introduction of this air may be varied or changed in accordance with or irrespective of the direction in which the gases are flowing through the furnace according to which method produces the better result in a particular' furnace. The invention further contemplates that the hot combustion air so introduced may force the highly heated gases downwardly toward the surf ace of the metal in the furnace to thus be effectively used in heating the charge. 1

Our invention may be more fully described and understood by reference to the accompanying drawings in which Figure 1 is a horizontal section through an open hearth furnace constructed in accordance with our invention;

. Figure 2 is a detailed view showing one of the auxiliary air inlet ducts, the view being a partial section in substantially the plane of line II-II of Figure 1 but being on a larger scale;

Figure 3 is a detailed view on still a larger scale showing the'valved passageway through which the flow of air through the auxiliary duct is controlled;

Figure 4 is a rear elevation of the open hearth furnace shown in-Figure 1 showing the arrangement whereby heated air from the regenerator system is withdrawn and supplied to the auxiliary ducts;

Figure 5 is a detailed view showing afront elevation of the nozzle or duct for introducing the auxiliary air into the furnace detached from the struc'tureof the furnace itself;

Figure 6 is alongitudinal section through the element shown in Figure 5;

Figure 7 is a fragmentary view similar to Fi ure 1 but showing only one end of thefurnace and showing a slightly modified construction.

Referring to Figure 1 of the drawings, the front wall of the furnace having a number of door openings therethrough is designated 2. The rear wall 3 has ofiset portions 4 adjacent each end thereof. The furnace is of the usual reversing type in which air and gas is first blown in at one end and exhausted through the other and. the flow then reversed for the operation of regenerators. The main ports at each end of the furnace are designated 5, and 6 designates the gas passage for supplying combustion gas to the burners and l designates the customary air passages. Referring to Figure 2, the back wall construction which is more or less typical is more clearly illustrated. The upper part of the back wall 3 slopes upwardly and rearwardly as indicated at 3a. The roof of the furnace is designated 8. In that zone of the furnace which is directly out of the straight line flow of gases from one end of the furnace to the other, particularly the zone which is over the sloping portion 3a. of the rear wall and under the roof 8, intensely hot gases accumulate in furnaces as they are now operated, the gases being more or less stagnant because of being out of the straight line of flow through the furnace, and this condition is aggravated by the fact that cold air enters through and around the doors from the front wall tending to drive the heat toward the rear wall and upwardly.

The present invention aims to eliminate this zone of stagnant hot gases, and for this purpose there are provided auxiliary air ducts which pass through the rear wall preferably at opposite ends of the offset and which serve to blow a volume of hot air into this zone to sweep out the gases that tend to stagnate and prevent overheating in this part of the furnace without, however, chilling the furnace to an undesirable extent. These auxiliary air nozzles or ducts are designated generally as 9. As shown in Figures 1 to 6 inclusive, they are preferably formed of metal, there being a rectangular duct portion ill with a curved hood II at the outer end thereof, the discharge port which opens at the side of the structure being designated i2. The structure is preferably formed with spaced walls providing a water circulating space 13 therebetween, cooling water being introduced into this space through a pipe l4 and being drained out through a nipple connection l5.

For supplying air to each of the auxiliary nozzles 9 there is an air duct at the outside of the back wall of the furnace, these air ducts being designated I6, their location being as shown in Figure 4. In the upper portion of each of ducts IBis a water cooled valve l'l shown in detail in Figure 3 for controlling the flow of air into the discharge nozzle. Each of the ducts or conduits i6 communicates with the nozzle structure 9 through horizontal passage I8 at the rear of the nozzle structure 9. Above the valve II at the rear of each conduit I6 is a clean-out opening l9 over which is a door in which there may be a peep hole 2|. This door enables slag and refractory, particularly refractory which is shoveled into the furnace from time to time, to be poked clear of the outlet portion of the nozzle.

In addition to this, the nozzle structure itself may be provided with an angularly projecting passageway 22 having a closure 23 at the end thereof in which a peep hole may also be provided and through which a poker may be inserted.

The air which is supplied to the nozzles 9 through the ducts P6 is pre-heated, and as shown the left-hand nozzle 8 thus blows into the zone of the furnace along the rear wall in the same direction as the main flow of gases through the furnace, maintaining a circulation of air along the back wall, particularly over the sloping portion 3a thereof and under the roof 8,. The volume of air which is already hot is further heated when it is discharged into the furnace so that it expands tending to drive hot gases along the back wall and near the roof out into the furnace chamber and down against the back of the metal in the bottom of the furnace. When the flow of combustion gases and air through the furnace is reversed, the right-hand valve I1 is opened so that air will blow through the right-hand nozzle 9, and the valve H for the left-hand nozzle will be closed.

In some furnaces it may be desirable to blow air into the furnace simultaneously from both nozzles so that the two streams of auxiliary air introduced at opposite ends of the furnace sweep along the rear wall, meet each other at some point between the two nozzles, and by opposing one another the two streams are diverted and forced outwardly toward the middle of the furnace.

Under other conditions of operation, we contemplate that the furnace may be operated by introducing auxiliary air in a direction opposite to the main flow of air through the furnace. Which of the three methods permitted by Your invention shall be used may be determined by trial in any particular installation.

The nozzles 9 are large enough to accommodate a considerable volume of air, and we prefer, in the operation of the furnace, that the air be introduced at a relatively low velocity but in a relatively large volume. By introducing a relatively large volume of air at relatively low velocity, numerous advantages are secured over introducing a small volume of air athigh velocity. A large volume of air moving at slow velocity and pre-heated to a fairly high temperature which, however, is still much below the temperature in the furnace, prevents excessive localcooling of the refractory wall or roof of the furnace, and the expansive action of a relatively large volume of gas serves to more effectively drive or sweep out stagnant hot gases than would a small stream of cold air and with less tendency toward stratification of the gases into cold and hot layers.

To increase the flexibility of the method of operating the furnace and enable any particular furnace to be more completely adapted to the particular conditions existing within it, our invention further contemplates that the arrange ment more or less generally and schematically illustrated in Figure 7 may be employed. In this arrangement the construction of the furnace and the construction of the air supply ducts is the same as heretofore described, but the nozzles, instead of being rectangular throughout the greater portion of their length, are circular so that they may be rotated through a limited are or through a complete circle as may be desired. In this figure the nozzle designated generally as is connected with the portion l8 of the air supply duct through a flanged or swivel connec tion 3|. While it is preferably of the same general design as that shown in Figures 5 and 6, it.

is preferably circular in cross section so that it may be rotated. No mechanism has been illustrated for affecting this rotation, but' this may be accomplished by motor-driven gearing or counter-weighted levers or in any other manner that may be deemed desirable by those skilled in the art. The advantage of having the nozzles 30 angularly adjustable is that they can be directed at different angles so as to blow the heat down onto the surface of the bath. Moreover, if they are rotatable through an arc of 180", the ports thereof may always be faced in the same direction, i. e., when the gases are traveling through the furnace from left to right,

both nozzles may be rotated to face toward the right and air may be introduced by both of them simultaneously to travel in the same direction and when the flow of combustion gases through the furnace is reversed, the direction of both nozzles may be reversed. Under other conditions of operation, one nozzlemay be directed downwardly and one may be directed upwardly to produce a vertical eddy current or swirl over the face of the back wall.

The use of pre-heated air through the nozzles is important first, to prevent excessive cooling of the refractory or any portion of the furnace and secondly to accelerate combustion, because the flow of air through the main burner portion may be reduced in the same proportion as it is introduced through the auxiliary ports or nozzles, inasmuch as air which is supplied through the auxiliary nozzles is combustion air required for operating the furnace. Thus, the air so introduced by the auxiliary ports does 'not require any increase or substantial increase in the total volume of air introduced in the furnace. The invention effectively eliminates stagnation pockets adjacent the back wall, protects the refractory at the back wall, particularly at the top, from excessive overheating and enables the hot gases in this portion of the furnace to be driven down onto the surface of the bath of metal so that the heat is more effectively utilized. As previously stated, by taking the auxiliary air from the air supply passages leading from the regenerators and introducing it through the auxiliary nozzles, th? total amountof air supplied to the furnace for combustion purposes does not need to be increased, at least to any material extent.

While we have illustrated and described certain specific embodiments of our invention and certain specific methods of operating the same, it will be understood that various changes and modifications may be made in the construction and method of operation within the contemplation of our invention and within the scope of the following claims.

Weclaim:

1. lg'he method of operating an open hearth furnace which comprises introducing pro-heated combustion air into the zone extending along the rear wall of the furnace.

2. The method of operating an open hearth furnace which comprises introducing a relatively large volume of pre-heated combustion air at relatively low velocity into the zone of the furopen hearthfurnace which comprises introducing pre-heated combustion air into the furnace the direction corresponding to the flow of combustion gas through the furnace and in such manner as to sweep along the back wall of the furnace and prevent the accumulation of stagnant bodies of hot gases adjacent such rear wall, and reversing the flow of such air when the flow of gases through the furnace is reversed.

4. The method of operating an open hearth furnace having a regenerative system which comprises withdrawing heated air from the regenerative system and introducing it into the furnace chamber intermediate the ends of the furnace and in a direction to travel along the rearwall of the furnace.

5. The method of operating an open hearth furnace having a regenerative system which comprises withdrawing heated air from the regenerative system, diluting it with atmospheric air, and introducing the mixture into the furnace chamber intermediate the ends of the furnace and in a direction to travelalong the rear wall of the furnace. I

6. An open hearth furnace comprising a furnace structure having end walls, a roof and front and rear walls, and means intermediate the'ends of the furnace for projecting a current of air along the rear wall of the furnace in a direction generally parallel to the direction of the flow of gas through the furnace.

'7. An open hearth furnace comprising an elongated furnace structure having front and rear walls and having end walls and a roof, and nozzles passing through the rear wall of the furnace adjacent each end thereof and opening into the furnace in a direction generally parallel to the longitudinal axis thereof for projecting a current of air along the rear wall, and means'for supplying a current of air to said nozzles.

8. An open hearth furnace comprising an elongated furnace structure having front and rear walls and having end walls and a roof, nozzles passing through the rear wall of the furnace adjacent each end thereof and opening into the furnace in a direction generally parallel to the longitudinal axis thereof for projecting a current of air along the rear wall, means for supplying a current of air to said nozzles, and valve means for selectively controlling the discharge of air from said nozzles.

9. An" open hearth furnace comprising an elongated furnace structure having front and rear walls and having end walls and a roof, and nozzles passing through the rear wall of the furnace adjacent each end thereof and opening into the furnace in a direction generally parallel to the longitudinal axis thereof for projecting a current of air along the rear wall, and means for supplying a current. of air to said nozzles, said nozzles being rotatably adjustable about an axis transverse to the longitudinal axis of the furnace. 10. An open hearth furnace comprising an elongated furnace structure having front and 70 the longitudinal axis thereof for projecting a II current of air along the rear wall, and means for supplying said nozzles with pre-heated air.

11. The combination with an open hearth furnace having a regenerative heating system of auxiliary air nozzles opening into the furnace in a manner to direct a current of air along the face of the rear wall of the furnace adjacent the upper portion thereof, and means for withdrawing combustion air from said regenerative system and delivering it to the nozzles.

12. The combination with an open hearth furnace having a front wall with doors therein, end walls with burner ports arranged therein, a top wall, and a rear wall which is outwardly offset and rearwardly inclined intermediate the ends of the furnace, of a nozzle in the rear wall adjacent each end of the offset portion thereof andopening into the furnace in such manner as to direct the current of air over the face of the rear wall of the furnace, and means for supplying heated air to each of said nozzles.

13. The combination with an open hearth furnace having a front wall with doors therein,- end walls with burner ports arranged therein, a top -wall, and a rear wall which is outwardly offset directions. v

HENRI RATEAU. EDWARD D. GOSSE'I'I.

dusted to discharge air in' selectively different 15

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