US1907140A - Open hearth furnace - Google Patents

Description

w. FE. BARTHOLCMEW May 2, 1933.

OPEN HEARTH FURNACE 4 Sheets-Sheet 1 Filed 001:. 23 1950 l l l INVENTOR; WiLL/AM-E BAR mum/15w.

A ORNEYS.

y 1933- w. F. BARTHOLOMEW 0 OPEN HEARTH FURNACE Filed Oct. 23, 1930 4 Sheets-Sheet 2 INVENTOR. WILLIAM EBAnTHoLoMEw.

RNEYS.

May 2, 1 3- w. F. BARTHOLOMEW OPEN HEARTH FURNACE Filed Oct. 23 1930 4 Sheets-Sheet 5 .INVENTOR.

WILL/AME BAR mom/45w.

y 1933- w. F. BARTHOLOMEW OPEN HEARTH FURNACE Filed Oct. 25, 1930 4 Sheets-Sheet 4 I I/ I 1 I) z/ lll INVENTOR. WILLIAM F. BAR THOLOME w.

Patented May 2, 1933 UNITED STATES PATENT OFFICE WILLIAM F. BARTHOLOMEW, F WARREN, OHIO OPEN HEARTH FURNACE Application filed October 23, 1930. Serial No. 490,621.

ried on without the necessity of periodical-s .ly reversing the furnace during the heat as required in the usualtype of regenerative open hearth furnace.

Regenerative open hearth furnaces as at present constructed embody certain disadvantages, among. which may be mentioned the necessity for periodically reversing the furnace during the treatment of a charge, an operation requiring the employment of reversing valves with attendant expense and complications, and one which results in frequent complete change of the direction of travel of the gases through the furnace with consequent more or less uneven heating of the bath as a whole. Additionally, the ports at the ends of the furnace are required to serve alternately as intake and exhaust ports and the furnace designer is thus faced with the problem of making the ports small enough to attain a desirable high velocity for the incoming gases and yet large enough to permit the escape of the exhaust gases at a desirable low velocity. Since it has been impossible to meet both these conditions by the use of ports of fixed size, various means have been suggested for adjusting the size of the ports so that when the latter are 5 serving as inlet ports their effective area can be reduced, and when they are serving as exhaust ports their effective area can be increased, but such arrangements are necessarily complicated and have been found unto satisfactory in practice. Moreover, the action of the exhaust gases on the refractories forming the ports is distinctly inimical thereto at the high temperatures which are employed and in time bring about erosion of the ports which, while not rendering them unserviceable when operating as exhaust ports, nevertheless materially detracts from the efficiency of the furnace when they are being employed as inlet ports.

Because of the foregoing and other reasons, various forms of open hearth furnaces of the recuperative type have been suggested, but as far as I am aware periodic reversal of all of them is necessary to avoid raising the temperatures of the refractories to such a point as to bring about their too rapid deterioration, while the clogging of the recuperative chambers with slag and other impurities carried over thereto by the exhaust gases as well as other disadvantages necessarily inherent in 'such recuperative open hearth furnaces as have heretofore been proposed, has rendered them unsatisfactory for the commercial production of open hearth steel and very few, if any, such furnaces are now being utilized for that purpose. V I

A principal object of my present lIlVG-Il tion, therefore, is to provide a novelrform of open hearth furnace, more particularly of the recuperative type, which does not require reversal of the flow of gases-through the furnace during the heating of the charge. q

A further object of my invention is the provision of an open hearthfurnace having at each end separate inlet and exhaust ports which are respectively adapted to serve as such'throughout'the operation of the furnace with the result that each may be so designed as to operate with maximum efliciency for its intended purpose and the inlet ports thus made small enough to impart to the incoming gases the desirable relatively high velocity and the exhaust ports large enough to permit the escape of the exhaust gases a-t the desirable relatively low velocity while, additionally, the inlet ports are relieved from the erosive action of the exhaust gases and are consequently maintained in proper condition for the performance of their'intended function throughout the life of the furnace. V r

A further object of my invention is to provide an open hearth furnace so arranged that the exhaust gases are substantially freed of entrained particles of slag, dust and other inimical impurities before passing into the recuperator, this result being accomplished through the provision of slag pockets and exhaust fines of novel form and arrangement and, additionally, in certain embodiments of the invention, by a novel manner of directing the course of the gases while adjacent the furnace hearth.

A still further object of my invention is to provide an open hearth furnace which may be so arranged that the, flame used for heating the charge tends to maintain a slow circulation or rotation of the bath with consequent substantially uniform heating of the latter throughout.

Additional objects of my invention are to provide a furnace of the character aforesaid in which mixed fuel and air may be admitted to the hearth at a velocity sufficient toinsure the best results, while the exhaust gases may be withdrawn from the hearth at a relatively low velocity whereby entraining of slag and other solids in the exhaust gases and erosion of the exhaust ports and other parts of the furnace are reduced to a minimum; in which the heat may be so directedduring the heating of the charge as toobtain maximum heating efficiency; in which the roof extending over the hearth may be made of any desired height, since in accordance with my invention, it is relieved from the usual duty of directing the gases in their traverse over the bath. and serves merely as a mirror or reflector to assist in heating the bath by reflected heat; in

which, in certain embodiments, the incoming gases may be so directed from opposite 5 ends of the furnace as to meet substantially at the center of the hearth at relatively high velocity and then, after intermingling. pass upwardly andthence oppositely outwardlv in reverse direction at relatively low velocity'to the exhaust ports, a low velocity area or Zone being thus created adjacent the middle of the hearth with consequent tendency of the heavier particles of slag and other impurities entrained in the gases to drop back into the bath while the gases are rising and during their subsequent traverse to the exhaust ports.

,My invention also comprehends the provision of a novel method of open hearth furnace operation.

Still other purposes. objects and advanages of my invent-ion will" hereinafter be specifically indicated or will appear from the following description of two forms of furnace constructed in accordance therewith and intended for burning liquid fuel. reference being had to the accompanying drawings.

In the said drawings, Fig. 1 is a top plan View, partially in horizontal section, of one of the said forms of furnace, a portion of one ofthe recuperators being broken away to better illustrate the internal construction thereof; Fig. 2 is a vertical longitudinal section substantially on line 2-2 in Fig. 1

with the parts adjacent the inlet port at the left hand end of the furnace shown in fragmentary section on a plane coincident with the median line thereof; Fig. 3 is a vertical section through one of the recuperators, and Fig. 4 a fragmentary vertical section on line 44 in Fig. 1. In Figs. 5 to 8 inclusive I have shown another form of furnace constructed in accordance with my invention; Fig. 5 is a top plan View thereof, partially in horizontal section, and thus generally corresponding to Fig. 1; Fig. 6 is a vertical section on line 66 of Fig. 5 and thus generally corresponding to Fig. 2; Fig. 7 is a vertical staggered section on line 7-7 in Fig. 5, and Fig. 8 is a fragmentary hori- Zontal section on a plane somewhat below the section plane in Fig. 5 through the slag pocket at the left hand end of the hearth when viewed from the front or charging side thereof. The same symbols of reference are used to designate corresponding parts in the several figures as far as possible, and the several sectional views are taken in the directions indicated by the arrows on the respective section lines.

Referring now more particularly to that form of the inventionshown in Figs. 1 to 4 inclusive, the furnace proper 'comprisesthe usual hearth 1, front wall 2, back wall 3, end walls 4 and roof 5. In the front Wall are charging doors 6 of which five are shown, although of course any desired number of such doors may be provided. At each end of the hearth I provide an inlet port 7 having a suitable burner 8 disposed therein and connected to a source of liquid fuel through suitable connections (not shown) The burners may be of any suitable form andconstruction, but I prefer to incline them downwardly toward the hearth and to so arrange them that they can be moved axially toward or away from the hearth as indicated in Fig. 2; hence by ad-' justing the burners in and out the extent of premixture of the air and liquid fuel may be varied and the maximum heating effect of the flame or hot spot thus in eflect may be adjusted longitudinally of the hearth during the heating of the charge and in accordance with the different requirements thereof as the heat progresses. Thus, assuming there is a large amount of cold scrap adjacent the ends of the hearth, it may be desirable to direct the hot spots thereon by moving the burners outwardly with respect to the furnace and thus increasing the extent of premixing in the burner passages 7a, the mouths of which form the inlet ports 7, and as the scrap is successively melted down the burners maybe moved inwardly so as to correspondingly move the hot spots toward the center of the bath. It will of course be understood that the particular fuel employed is a matter of choice as in the furnaces of my invention either liquid fuel, gas, pulverized coal or any other desired fuel may be used, the burners of course being varied in construction in accordance with the particular type of fuel to be employed.

.Air for supporting combustion is supplied to the furnace through vertically directed intakes 10 communicating with the outer ends of the burner passages 7a and with fines extending to the recuperators 11, 11 hereinafter more fully described, and a fan 12 is connected to each recuperator by aconduit 13 and is operative to deliver a continuous streamof air thereto. Since the inlet ports of my improved furnace are never required to serve as exhaust ports, they may therefore be of relatively small size and thus adapted to deliver the air at high velocity into the hearth, thereby leaving a relatively large space adjacent each end of the hearth in which are located exhaust ports 15 disposed on opposite sides of the air intakes and leading downwardly adjacent the front and back walls of the furnace into the subjacent slag pockets 17 Desirably from that end of each slag pocket most nearly adjacent the hearth a passage 18 is extended laterally and thence longitudinally of the furnace in parallelism with the front wall thereof to the adjacent recuperator 11.01" 11; preferably, as best shown in Fig. 4, the bottoms of these passages are somewhat lower than the floors of the adjacent slag pockets, while disposed above the passages 18 are air fiues 19 leading from the recuper ators to the intakes 10. 'Thus when the furnace is in operation, the air coming from the recuperators passes through the flues 19 into the intakes and from thence into the hearth ateach end thereof while the ex haust gases from the hearth pass downwardly through the exhaust ports 15, 15 at opposite ends of the hearth into the subjacent slag chambers 17 and from thence through passages 18 to the recuperators.

The recuperators may be of any design and construction suitable for the performance of their intended functions, namely, to effect transfer to the incoming air to be employed for combustion of much as possible of the heat contained in the exhaust gases before the latter pass into the stack, and two are preferably provided, one for each end of the furnace. In the particular arrangement illustrated the recuperators 11, 11' are disposed side by side, separated by a single wall 20 running at right angles to the median line of the furnace hearth and are located in front of the front wall of the furnace, this arrangement being a convenient one under most conditions and, among other things, presenting the advantage of requiring but one division wall between the recuperators in place of the two walls which would be required if the latter were formed as entirely separate units. Each of the recuperators which I have chosen to illustrate and which under most circumstances I prefer to employ, comprises a pair of generally similar units 21, 21 providing together a continuous tortuous passagev22 through which the exhaust gases are directed after they leave the conduit 18 and from which they ultimately pass into the stack 23 through conduits 24 uniting? in a common conduit 25 leading thereto. Each unit, the walls, roof and other parts of which are desirably made of or lined with refractory firebrick in accordance with the usual practice in the furnace art, is so constructed'as to provide a central chamber 26, 26 and the passage 22 is arranged to extend on opposite sides of the walls forming this chamber and across the top thereof. Each unit is also provided with an end chamber 27, 27 and into the outermost of these, that is, the chamber most remote from the hearth, the conduit '13 is connected, sothat the air forced through the latter by the adjacent fan will be directed into the said. chamber. The several end and central chambers are respectively connected bya plurality ofgroups of pipes 28 and the chamber 26 also similarly connected with the air conduit 19; these pipes may be of steel, refractory or any other heat resisting material, but preferably one having a high heat conductivity, and are disposed horizontally so as to form a plurality of separate ducts through which the incoming air can pass from the chamber 27 at the outer end of the recuperator into the airconduit 19, and as the pipes are heated by the-exhaust gases in their travel through the pas sage 22, the incoming air, by the time it reaches said air conduit, is heated to a relatively high temperature so as to pass substantially at such temperature into the intake 10 and from thence to the furnac hearth.

It will be observed that the slag pockets 17 which are respectively disposed beyond and below the ends of the hearth proper are of relatively large volumetric capacity in comparison with the exhaust ports 15 and downtakes communicating therewith through which the exhaust gases must pass prior to their entry into the slag pockets. The ability to provide slag pockets of such relatively large capacity arises in part from the fact that the conduits 19 are carried in above the slag pockets and therefore do not materially reduce the space which can be conveniently accorded thereto.

For controlling the passages from the recuperators to the stack, dampers 29 may be provided in the former, and in order to afford a convenient means of controlling the temperature of the air passing from the conduits 19 into the intakes, a by-pass conduit 30may be extended from each of the conduits 13 to the conduit 19 and provided with a valve or damper 31. Thus, by operating thesaid valves or dampers, more or less unheated air can be directed into the air conduits 19 so as to correspondingly modify the temperature of the air coming from the recuperators.

In the operation of a furnace of the general character of that hereinabove described air is delivered to the intakes 10 at a high temperature so that maximum flame temperatures are obtained in the hearth and the time required for heating the charge is reduced to a minimum, thereby increasing the rate of production of the furnace. Fur thermore, as the inlet ports in the furnace are relatively constricted, a high velocity flame is obtained with substantially complete combustion of the fuel, while as the air requisite for combustion is supplied through the medium of the fans 12, it is possible to maintain a pressure in the furnace slightly higher than atmospheric and thus prevent infiltration of air through the charging doors or otherwise whereby undesired oxidation ofthe charge is avoided.

Since throughout the heating of the charge the air and fuel for combustion are continuously supplied from both ends of the furnace at relatively high velocity, the burning gases tend to meet substantially midway between the ends of the hearth and there inter-mingle and thence pass upward- 1y toward the roof, thus creating a zone of relatively low pressure at about the middle ofthe hearth in which, while the gases are passing therethrough, a large percentage of the entrained solids tend to separate themselves from the gaseous current an d fall back into the bath. As the gases rise toward the roof, they gradually tend to separate in such manner that the major part of those which initially entered from the right hand end of the hearth turn back in reverse direction and move at a relatively low velocity toward that end of the furnace from which they entered and then pass therefrom through the adjacent exhaust ports 15, while i the major part of those which initially entered from the left hand end likewise turn back and pass through the exhaust ports at that end, thus giving a further oppor' tunity for the entrained solids to drop back into the bath with the result that by the time the gases enter the several exhaust ports they are substantially free from the major portion of the said solids. Of course some small portion of the gases which initially entered at either end of the hearth will continue their original direction of travel oward the opposite end of the furnace and will thus pass into the exhaust ports at the said opposite end along with the gases which have entered at that end and which have been reversed in direction of travel at approximately the center of the furnace. Thus, the gases passing into the slag pockets 17 are relatively clean, and as their velocity is still further reduced in the pockets, the lighter particles of entrained solids which have not already been returned to the bath are deposited in the pockets and to some extent in the relatively long passages 18 extending to the recuperators, so that by thetime the exhaust gases reach the latter they contain substantially nothing except a small amount of'very light dust and the like which has substantially no clogging or other inimical effect on the recuperators.

At this point it may be observed that as separate inlet and exhaust ports are proided at each end of the furnace, the exhaust gases are never brought into contact with the burner tips and associated parts or drawn through the inlet ports, and I thus avoid the frequent replacement thereof or repairs thereto required in furnaces in which the ports are used alternately for incoming and exhaust gases as well as the usual gradual enlargement of the inlet ports with consequent loss of velocity through erosion by the exhaust gases under such circumstanstances, while the inlet and exhaust ports may be made of proper size for the most satisfactory performance of their respective functions.

Additionally, in furnaces of my invenion the roof, as hitherto stated, is not utilized as a directing medium for the incomlng gases but acts simply as a mirror or reflector which tends to throw the heat downwardly on the bath; the roof is therefore less subject to erosion than where the flame traverses the furnace closely adjacent the roof and is to some extent guided directly thereby while, furthermore, the roof may be made of any desired height above the bath and may thus be raised sufliciently to maintain its temperature at a point sufficiently low to prevent injury to thecrefractories of which it is constructed.

In Figs. 5 to 8 inclusive I have shown a slightly different form of furnace constructed in accordance with my invention and which differs from that hitherto described principally in that the inlet ports and burners at the ends of the furnace are not disposed 'on the median line thereof but are set on opposite sides of said line, a construction which will sometimes be preferred.

In this form of furnace the hearth, front, back and end walls, and roof may be substantially similar to those already described, while the recuperators employed may also desirably be similar to those to which I have referred. As stated, however, the inlet ports 7 are set on opposite sides of the median line of the hearth and the burners 8 disposed in the burner passages 7a leading therefrom and preferably arranged for longitudinal or other adjustment so that the angle of incidence and the point of impact of the flame upon the bath and the extent of premixture of the incoming air and fuel may be regulated as desired. hen this construction is employed, desirably but one exhaust port 15 is provided at each end of the furnace and is located on the opposite side of the median line thereof from that on which the inlet port is disposed. From each inlet port an uptake is carried downward, then laterally outward, and then downward to meet a conduit 19 extending parallel to the front of the furnace and communicating with the adjacent recuperator, while the exhaust ports 15 connect through vertical downtakes with the subjacent slag pockets 17. From the top of each slag pocket a flue 36 leads the exhaust gases over a baffle 37 and thence into the passage 18 disposed below the adjacent air conduit 19 and connecting with the adjacent recuperator passage 22 substantially as already described in connection with the furnace shown in Figs. 1 to 4.

It will be observed that because of the fact that the inlet and exhaust ports are preferably staggered with respect to each other instead of being arranged in longitudinal alignment, the direction of travel of the exhaust gases through the slag pockets differs somewhat at the respective ends of the furnace. Thus, at the right hand end when viewed from the charging side, the exhaust port is disposed adjacent the back wall 3 and a depending arch of brick work 38 is provided adjacent the roof of the slag pocket about midway between the back wall and the baffle 37 and parallel thereto so that as the gases pass down through the exhaust port into the slag pocket, they pass under the arch and finally upwardly and outwardly into the flue 36 and passage 18 leading to the recuperator. At the opposite or left hand side of the furnace, however, the ex haust port is disposed adjacent the front wall 2 and from the lower end of the port a short transversely extending wall 39 is carried to the bottom of the slag pocket so that as the gases pass from the exhaust port they are constrained to travel around the end of this short wall or batlie and are reversed in direction before they can pass into the flue 36, this construction being best illustrated in Fig. 8. In either case, the velocity of the gases in their travel through the slag pockets is materially reduced from that at which they left the exhaust ports with the result that subsantially all of the entrained solids are deposited in the slag pockets and the gases thus thoroughly cleaned of tar, slag and the like before their passage into the recuperators, the small amount of dust which may be still present in the gases and thus ultimately deposited in the ,recuperators being substantially 'negligible in effect upon the operation of the latter through the period .of time they are customarily retained in service.

It will be obvious that in the furnace to which reference is. now being made, the gases enteringat either end from the adjacent inlet port traverse the hearth more or less longitudinally and pass out of the furnace through the exhaust port at the opposite end and on the other side of the median line ofthe hearth from that at which they entered, there being no or substantially no reversal of their direction of flow as in the form of the furnace previously described. By suitable adjustment of the burners, the point of and direction. of impingement of the. incoming gases upon the bath may be varied between limits, so that by directing the continuous currents of burning gases longitudinally of the hearth on opposite sides of the medianline and in opposite directions a slow rotational tend-- ency can be imparted to the moltencharge if desired, or the flames can be otherwise directed at various angles so asato obtain the most efficient heating of the charge during the progress of the heat-and/or to enhance the rotational tendencythereof to which I have referred.

It will be understood of course that in the operation of furnaces constructed in accordance with my invention, the heating gases are continuously directed thereinto in opposite directions from points adjacent both ends of the hearth throughout the heat, and not alternately from one end or the other thereof, with consequent reversal of direction of gas flow at relatively short intervals during the progress of the heat as in the usual forms of regenerative open hearth furnace. tirely omit the reversing valves and other auxiliary apparatus necessary in reversing types of furnaces with their. attendant cost, complication, and liability of derangement, and am further enabled'to more efliciently heat the charge with less fuel and in less time than in a reversing type furnace of similar capacity tilting open hearth type since, in'accordance with my invention, I can obtain very high temperatures and consequently with this type of furnace several different slags can be produced during the progress of a heat and consecutively poured off, so that the finished steel will be a cleaner product than that which has been possibleto heretofore produce in a commercial way in accordance with the usual open hearth practice.

While I have herein shown and described with considerable particularity certainforms of furnaces constructed in accordance with I ani thus enabled to en:

Moreover, the principles of my invention may readily be employed in furnaces of the my invention and operated in accordance with theprinciples thereof, it will nevertheless be understood that I do not intend thereby to limit or in any way confine myself specifically thereto as numerous changes and modificationsin the structure and arrangement thereof will readily occur to those skilled in the art and may be made, without departing fromthe spirit and scope of the invention as defined in the appended claims. Having thus described my invention, I claim and desire to protect by Letters Patent of-the United States 1. An open hearth furnace comprising a hearth, front, back and end walls, means for continuously directing heating flames angularly downwardly into the hearth from oppositely disposed points, and a roof extending over the hearth and elevated thereabove sufficiently to substantially clear the zone of said flames during their inward passage over the hearth and'providing a zone effective to decrease the velocity of the products of combustion as they traverse the hearth above said flames.

2. An open hearth furnace comprising a hearth, front, back and end walls, means for continuously directing heating flames angularly downwardly into the hearth from oppositely disposed points, and a roof extending over the hearth, the height of the roof above the hearth being sufiicient to substantially remove it from the zone of erosive action of said flames and to provide a zone for low velocity passage of the products of combustion.

3. An open hearth furnace comprising a hearth, front, back and end walls, means for continuously directing heating flames angularly downwardly into the hearth from oppositely disposed points, and a roof extending over the hearth and operative to assist in heating the charge by reflecting heat thereon while being substantially without effect upon the courseof the flames during their inward passage over the bath and effective to provide a zone remote from the surface ofthe bath affording space for relatively low velocity passage of the products of combustion from the furnace.

In witness whereof, I have hereunto set my hand this 21st day of Oct, 1930.

' WVILLIAM F. BARTHOLOMEW.

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