US2094471A - Open hearth furnace - Google Patents

Description

Sept. .28, 193-7.

Filed NOV. 27, 1955 3 Sheets-Sheet 2 INVENTOR M. jhannan Sept. 28, 1937. Y M. c. SHANNON 2,094,471

OPEN HEARTH FURNACE (l Filed Nov( 27, 1935 3 sheetssneet s INVENTOR M. .Sha'nnan/ 55 regulation lies Patented Sept. 28, 13937 s'v4 PATE-NT oFFlci: y

OPEN HEARTH FURNACE Maurice C. Shannon,

Alabama City, Ala., assigne or, by mesne assignments, to Republic Steel Corporation, Cleveland,

. New Jersey Ohio, a corporation of a Application November 27, 1935, Serial No. 51,816'

This invention relates to an open hearth steel furnace operated .on thefregenerative principle and is directed toward improvements in the construction and methods of control for proportioning and regulating the volume of gas ,and air and for controlling the direction and -velocity lof iiame in the furnace, l

In the operation of an open-hearth furnace certain established principlesl must govern the introduction of air and gas to obtain the most efcient operation within the furnace and "yet at the same time afford protection to its refractory walls that are exposed to the action of the gases. It is well understood that the roof must be protected by the admission of whatis termed a secondary supply of air which entersfthe furnace in position and volume sufficient to flow along the furnace roof, thereby interposing a protective blanketv between the zone of most lintense vcomtory roof. While this protective blanket of air `is highly desirable, it is of interest in the efcient operation of theAfurnace, that its volume should be in definite andaccurate control so as to reduce the excess air admitted to the furnace beyond the combustion requirements. l

In the operation of an open hearth` furnace, it is important to maintain the' correctl pressure within the furnace, balancing the positive pressure under. which the air and gas enter at one end ofthe furnace against negative pressure induced by the stack Adraft on the opposite end of the furnace, so that there will be in substance a neutralv pressure-opposite the charging doors in the middle zone of the furnace, as a result' of which there will be no marked tendency of gases to escape through these doors nor o f cold air to enter and disturb the heat balance in the furnace. Ithas been -attempted to accomplish 40. this controlled balance of pressures in4 the furnace by interposing a damper operable on the stack-draft so as to increase or diminish its effect in the furnace. According to myv invention I propose to effect 45 a control imposed upon the entering air, both the primary air for mixing with the'` fuel gas and the secondary air for providing the protective blanket between Vthe combustion zone and roof of the furnace and for completing' combustion 50 of the fuel, by valve means adjustable not only to regulate thel total volume of air admitted to the furnace, but also the distribution of this regulated volume to the primary and secondary air supplies. The importance of this distributive bustion of the gases over the bath and the refrac-.g

inthe fact that itis accomplished without a disturbance ofthe regulation of the Y gling with the gas and thereby determines the velocity of the jet and, in a measure, the nature and situs`of the zone of most active combustion derived from the entering gases. In other words, I can thus obtain more or less of the blow torch eiect with a longer or shorter ame and can locate the more intense zone of heat as desired. Thus, a control of the heat functions of the furnace are lobtained by` a regulation of the cold air supply, where a simple and inexpensive valve means can be interposed and economically maintained.

My invention has a further distinctive advantage in respect of existing open hearth furnaces which have been designed for use with producer gas. There are a large number of s uch open hearth furnaces in the United States and their operators have all experienced difficulty in converting these furnaces to the use of' natural gas or a like combustible having a relatively small 'volume as compared with that of producer gas and which is not adapted to regenerative treatment before admission to the furnace. In other words, these furnaces nd themselves with a gas checker considerably smaller than the checker for the main air supply, that must be abandoned or put to use on the air supply to the furnace.

My invention will render vfurnaces of this type readily convertible to the use of natural gas and the likeand will enable the existing checker work systems to be put to effective and eiiicient service and to this end I propose to introduce the natural gas into the primary air intake at a point Where it will become commingled with the primary vair supply which I cause to ow through .the checkers formerly used for the regeneration of the producer gas, and the mingled gas and preheated primary air will reach a state of active combustion withinf the gas port prior to discharge into the furnace. In order 'to protect the gas flue and the primary air intake opposite and above the point of gas inlet, I interpose coolers in the masonry. ,My invention contemplates that the primary and secondary air currents, after they pass the distribution valve, shall be maintained separate, this being essential to volume control of the primary air and, where existing kopen hearth furnaces would permit these air currents to be interconnected either before or after the checkers and thus 'free to divide between the two available iio channels in proportions responsive to the resistance in each channel to the air flow, it will be necessary to close o such connection, but otherwise than this and the interposition of coolers, above referred to, no physical changes are required in the former producer gas red open hearth furnaces, checkers, fiues, etc., to adapt them. to my new method of control.

The practice of my proposed method of control and a suitable apparatus for carrying it into eect will be found illustrated in the accompanying drawings which form a part of this specification, and in which:-

Fig. l is a longitudinal central vertical cross section taken through one end of an open hearth furnace designed and adapted for the practice of my improved method of control.

Figs. 2 and 3 illustrate respectively cross sectional views of the furnace taken on the lines II-II of Fig. 3 and III--III of Fig. 1.

Fig. 4 is a diagrammatic view illustrative of the air and gas distribution mains, their controls, both for reversing and for air regulation and distribution, and the layout of the checkers and slag pockets for a complete open hearth furnace which is shown only fragmentally in the preceding views.

Similar reference numerals refer to similar parts throughout the drawings.

In the embodiment of my invention illustrated, I show an open hearth furnace having its floor 5 resting upon suitable structural supports 6 and protected. by the hearth lining I of suitable refractory material. A tap hole d. is provided in the back wall 9 and charging doors 8 are provided in the front wall il) of the furnace, which may have a hearth of any suitable material and design with the front and back walls of the furnace supporting an arched roof Il and all held together by the customary structural frame Work generally indicated by the numeral l2.

At each end of the furnace I provide a central gas port I3 communicating with a primary air uptake I4 rising from its respective slag pocket |5 and opening under the hood of the port. This uptake I4 is flanked on each side by separate secondary air uptakes I6 leading from a common slag pocket I1 and rising on each side of the uptake I4 so as to deliver the secondary supply of air against the furnace roof on each side of and above the downwardly directed gas port, as will be more apparent by reference to Fig. 3.

I have not illustrated the checkers through which the separated primary and secondary air streams enter the slag pockets I5 and |I at each end of the furnace beyond showing same diagrammatically in Fig. 4 where I8, I8' represent the smaller checkers through which the primary air supply flows to the uptakes I5 on either endof the furnace, and I9, I9' represent the larger checkers through which the secondary air supply ows to theintakes I6 on either end of the furnace.

It will be noted that, in accordance with the customary practice in regenerative furnaces, a duplicate arrangement of checkers, slag pockets and gas ports is provided for opposite ends of the furnace and in the normal operation of the furnace, the gas is rst admitted to one end and exhausted from the other and then is reversed, this reversal being accomplished by the piping system and arrangement of reversing valves therein which are conventionally illustrated in Fig. 4, and which comprise, as a system, the stack having communication by means of a pipe 2| under control of a reversing valve 22 with one or acer-,eti

the other of the mains 23 and 23 which respectively lead to the large checkers i9, H9' at the opposite ends of the furnace. The' stack likewise has communication through the pipes 2li and 24 under control of the cut- oirv valves 25 and 25 with the ducts 25 and 25 leading respectively to the primary air checkers I8, H8 at the opposite ends of the furnace.

The entire supply of air for the operation. of the furnace is admitted through a single intake pipe 2l and passes through an air measuring device here shown as an orifice in a plate 28 before reaching the blower 29, which forces the air in a single air stream through the pipe 3|] and past the volume regulating .valve 3| to the division point where the primary air supply pipe 32 branches from the main or secondary air supply pipe 33, which latter pipe leads to the reversing valve 22 and delivers secondary air to line 23 or 23 according to the setting of that valve.

The primary air stream diverted through the pipe 32 flows through pipes 34 or 34 past cut- olf valves 35 or 35 and enters one or the other of the primary supply air lines 25 and 25. The valve for effecting the division or distribution or for prorating the regulated volume of air to the working checkers i8 or I 8' and I9 or i9 is illustrated at 35 in the main air line 33 just beyond where the primary air line 32 diverts.

I have not shown any control means for reversing valves 22, 25 and 25', 35 and 35', because such valves are of standard construction and are controlled in accordance with the well known existing practice under which, when the reversing valve 22 is set for the admission of air to'the main checkers I9, the valves 25 and 35 will be closed and valves 25 and 35 will be opened. Under such conditions the primary air will enter the checkers i8 and the gases from the furnace, after passing the checkers I8 and i9', will ow through the passages 23', 26 and 24 past valves 25 and 22 and will be conducted to the stack 2G. Under these conditions the air enters the left hand end of the furnace (Fig. 4) and the burning gases are exhausted at the right'hand end. Upon reversal of these several valves the air will be shifted to the checkers I8 and I9' and the gases will escape through the checkers I8 and I9 to the stack.

The main volume control valve 3| is adapted to be adjusted by a suitable control means, such as the cable 31, which leads to a controller 38 in the operating room 39, or this valve may consist of adjustable louvers in the fan. The distribution valve 36 will also be adjusted by any 'suitable control means, such as cable 40, leading to the controller 4| In the operating room. These two valves, as shown, are manually and independently controlled and Valve 3| is set rst to regulate the total volume of air to be admitted to the furnace so that it will be ample for combustion, for the protection of the furance, and for the maintenance of the neutral pressure opposite the charging doors.

Having by means of the elements 28, 29 and 3| or their equivalents regulated the Volume and pressure of the total air supply for the furnace, the division of this volume of air as may be desired to the checkers I8 and I9, or I8 and |9, as the case may be, is then regulated by adjusting the valve 36 in the secondary air line. As this valve 36 is opened, the volume of secondary air flowing through the checkers4|9 or I9 is increased but the requisite volume of primary air to maintain the desired combustion in the fura greater air volume under pressure willbe shunt-y ed into the primary air line and a lesser volume This flows as secondary air into the furnace. division valve enables any difference in the resistance set up to the flow of any through each of the channels for the two air streams supplied to the furnace to be compensated for. The location of this division valve in the pipe 33 is called for because of the greater draft that will be effective in the secondary air circuit because of its larger area than the primary air circuit and also because the fuel gas is charged into the primary air circuit and these unbalancing forces are most effectively controlled by placing the regulating valve 36 in the secondary air circuit.

As the volume of primary air under pressure is increased its velocity in the gas port is increased and the blow torch action of the jet of burning gases and air becomes accentuated and these gases are blown further across the furnace with a larger distribution of the zone of intense heat. As the primary air volume is reduced the jet pressure drops, the highest combustion zone recedes toward the working gas port, and a slower combustion results. As the total volume of air is varied, the positive pressure at the intake end of the furnace will be varied and can be adjusted to neutralizethe negative pressure `atthe opposite end of the furnace induced bythe stack draft, and itself subject to regulation if de-` sired.

I have shown the furnace designed for the burning of natural gas or a combustible of small volume and high B. t. u. This gas I propose to introduce by means of gas supply pipes 42 and 42. One of these supply lines enters the primary air uptake I4 at each endof the furnace at a point about midway of the uptake. The gas and primary air streams thus intersect at right angles and the walls of the uptakes about this zone are protected by the interposition of water coolers 43 in the masonry, a cooler 44 being set in each end wall surrounding its gas inlet. The commingled air and gases enter the downwardly inclined gas port I3, the Walls of which are protected by a water cooler 45 interposed in the masonry. Water is supplied and,withdrawn fromv these coolers by suitable piping connections which are of standard construction and arrangement and need not be described in detail.

The burning gases are thus directed down-- to provide the moving blanket of air that protects the roof from rapid destruction and supplies such additional oxygen as may be needed for the complete combustion of the gas.

It will be noted from Fig. .4 that the ducts carrying the primary and secondary air currents are maintained separate. after they leave the common air supply line 30, and it will be obvious that control may be effected by regulating the action of the single main air supply blower fan 29 both to vary the flow and'increase the pressure from the primary and secondary air supplies in the furnace,l but itis contemplated that all ordinary operating controls can be effected very simply and' effectively by the manipulation of the valve 36 and the valve '3l or, as its equivalent, louvers on fan intake.

It will .of course be understood that a damper valve can be used in the stack, if such be desired, for additional regulation of volume of exhaust gases in conjunction with variations in the input of gas and air, to maintain the neutral pressure about the center of the furnace. While 'I perfer to introduce the gas at the points indicated, it may obviously be supplied to the gas ports at any point desired and its volume may be regulated by any suitable valve means and reversed by the valve 46 when the furnace is reversed.

What I claim iszk l. The method of open hearth regenerative furnace operation, which comprises introducing the total volume of combustion air for the furnace under pressure from a common source, regulating said total volume of air, splitting the regulated volume of air into a primary air stream and a secondary air stream, separately heating the air of each stream, controlling the ratio of air diverted from the total air supply into said streams, which streams are kept separate until they enter the furnace, admitting a non-regenerative fuel gas into the primary air stream, removing the burning gases from the furnace by stack draft, and balancing the total volume of combustion air and fuelgas admitted against the exhaust action of the stack to establish substantially neutral pressure 4at the middle zone of the furnace.

, 2. The method of operating an open'hearthy furnace, designed for the burning of regenerative fuel gas, with non-regenerative fuel gas,. which comprises supplying the air tothe furnace in a main stream Iunder pressure with volume control, splitting said stream into streams vwhich are 'the non-regenerative gas in the latter stream of air after heating such air, and varying the ratio y of air diverted from the secondary air stream to form said split streams.

3. The method of operating an open hearth furnace, designed for the burning of regenerative fuel gas, with non-regenerative fuel gas, which comprises supplying the air to the furnace in a main stream under pressure with volume control, splitting said stream into separate primary and secondary air streams, the latter flowing through the air heating channels of the furnace and the former flowing through the gas regenerative channels of 'the furnace, introducing the nonregenerative gas in the latter stream of air after heating it, varying the volume of air under pressure diverted from the secondary stream to form said primary stream, and varying the total volume of air under pressure before division into said streams to produce a substantially neutral pressure opposite the middle zone of the furnace.

4. In an open hearth steel furnace of the type having at each end a gas port with a middle uptake and means for delivering primary air and fuel to its respective gas port, side uptakes for admitting secondary air, regenerative checker work for heating the primary air, separate regenerative checker work for heating the secondary air, a common air supply inlet associated with means to introduce the total air supply for the furnace under pressure, a stack, and a valve controlled pipe system for reversibly distrihut= ing the air supply under pressure in separate streams through the Working checker Works and uptakes into the intake end of the furnace and for conducting away the gases from the exhaust end of the furnace through the other checker Works to the stack.

5. in open hearth steel furnace according to clanfl in combination with a common means to regulate the total volume and pressureof air :for said streams admitted through said air` supply inlet.

6. open hearth steel furnace according to claim in combination with a blower and valve means to regulate the total volume and pressure ci air admitted through said air supply inlet, and adjustable means to split the admitted air and prorate it to said air streams.

7. in open hearth steel furnace according to claim a, in which the pipe system comprises a large pipe for the secondary air supply connected to saidcornmon air supply inlet, a regulating valve said pipe, and a smaller pipe for the primary air supply connected to said secondary air supply pipe ahead of the said valve therein.

8. An open hearth regenerative furnace,A having at each end a gas port with means to supply primary air and gas thereto, air ports with means to deliver secondary air thereto, and separate checker Works for heating the streams of primary and secondary air, in combination With a piping system for the air and gases comassenti prlslng a main supply pipe for secondary air having a :dow regulating valve therein, a supply pipey streams, a common air supply intake having a regulating valve and a hlovver ian therein for delivering the common air supply under pressure, a stack, and a valve controlled pipe system for reversihly distributing the air supply under pressure in separate streams through the Working checker 'Works and uptakes intoythe intake end of the furnace and for conducting the gases from the exhaust end of the furnace through the other checker Works to the stack, said pipe systern comprising a secondary air supply pipe connected to the common air supply intake and provided with a regulating valve, and a primary air supply pipe having connection with the cornrnon air supply intake at a point between the latters regulating valve and said regulating .valve for the secondary air supply pipe.

` MAURICE C. SHANNON.

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