US2685439A - Open-hearth furnace - Google Patents

Description

Aug. 3, 1954 F. BART ET Al.

oPEN-HEARTH FURNACE Filed June 1, 1950 PRI 0R HRT Patented Aug. 3, 1954 OPEN-HEARTH FURNACE Franz Bart, Millstatt, Carinthia, and Alfred Slesaczek,

Carinthia,

Austria, assignors, by

mesne assignments, to General Refractories Company, Philadelphia, Pa.

Application June 1, 1950, Serial No. 165,467

Claims priority, application Austria June 14, 1949 2 Claims.

The invention relates to open hearth furnaces comprising a laboratory (furnace chamber) and air uptakes issuing into the ends of said laboratory from below.

In hearths of this type, the shape and direction of the flame is most strongly inuenced by the direction and speed of a current which in gasoperated hearths is formed by the stream of gaseous fuel, and in liquid fuel operated hearths by the fuel jet. lt is the level, the cross sectionand the slope of the conduit of this current, or the position and inclination of the nozzle for the liquid fuel jet with respect to the hearth proper that mainly determines the shape and direction of the flame. The latter is, however, also influenced by the current of combustion air which is introduced into the furnace laboratory from below and which changes its ldirection several times until meeting the gas flow or the oil iet as the case may be.

in general, the speed of the combustion air vwhen emerging from the uptakes into the laboratory is so high that the combustion air is little influenced by the action of the fuel current or iet, and rises against the arched roof of the laboratory opposite the outlets of the uptakes. The combustion air impinges on, and is deflected by, the inner surface of said arch in a downward direction towards the fuel current or jet with which it subsequently mixes.

While, as aforesaid, the currents of combustion air are little influenced by the current of the gaseous fuel or by the jet of liquid fuel, they exercise on the other hand a considerable influence on the latter: in the known open hearth furnaces large masses of air impinge on the flame, particularly on the first stretch of its path, at a very steep angle, up to 90, and accordingly ought to have a low speed as compared with that of the gas stream or jet as they would otherwise excessively spread out or even break up the flame. Moreover almost the whole of the energy of flow of the flame has to be provided by the gas stream or fuel jet. 'Accordingly the cross section of the gas ports had to be kept small which on the side of the waste gas discharge towards the gas chamber involved well known difculties such as insufiicient supply to the gas regenerators and insufficient heating of the same in the case of producer gas or mixed gas fired furnaces etc.

It is the main object of the present invention to provide an open hearth of the kind referred to wherein the aforesaid unfavourable influence of the currents of combustion air on the flame are Obviated.

It is a further object of the invention to provide an open hearth of the kind referred to wherein the external angle of intersection between the current of gaseous fuel or the jet of liquid fuel and the current of combustion air is reduced, particularly in the earlier part of the iiame path.

It is another object of the invention to provide an open hearth of the kind referred to wherein the part of combustion air that impinges on the flame on the earlier part is reduced.

It is yet another object of the invention to provide an open hearth of the kind referred to wherein the speed of the current of combustion air is increased so that additional energy of flow is added to the ame by the current of combustion air.

According to a main feature of the invention the outlet ends of the air uptakes and the part of the roof opposite said uptake ends are so arranged that the external angle included between the longitudinal central axis of said uptake ends and the generating line of said part of the roof does not exceed 73. Previous proposals of construction wherein the said external angle was incidentally made slightly smaller or slightly larger than say between 80 and 110 have proved ineffective to obviate the difficulties of the known open hearths as described hereinabove. In particular, a detrimental tendency of the flame of rising and spreading along the inner faces of the front and rear wall of the furnace laboratory encountered with open hearths of the known constructions has remained unaffected by any reduction of the included external angle between 90 and 80.

In contradistinction thereto, our extensive tests have proved, that the shape of the flame is adversely affected no longer when according to the invention the said external angle is further reduced to a maximum of '73 or preferably even less. The minimum value of this angle is 30.

According to a preferred development of the invention, the part of the furnace roof lying opposite the outlets of the air uptakes as described hereinabove has its continuation towards the hearth proper so arranged that the generating line of this last mentioned part of the roof includes an internal angle of less than with the generating line of the first mentioned part of the roof and with the longitudinal central axis of the aforesaid outlets yof the air uptakes includes an internal angle of more than 73. This second part of the roof in conjunction with the first mentioned part of roof strongly deflects the rising combustion air towards the hearth proper which results in an improved guidance of this air after its deflection on and by the roof.

With these general statements of the objects and purposes of our invention we will now proceed to describe embodiments thereof and the manner in which our invention is carried out, and it will be understood that while we have described what may be considered as preferable embodiments of our invention, we do not limit ourselves to the precise conditions or proportions herein set forth, as they may be varied by those skilled in the art in accordance with the particular purposes for which they are intended, and the conditions under which they are to be utilised.

In the accompanying drawings:

Figs. 1 and 2 show diagrammatically one end of an open hearth furnace of a conventional gas Ifired type, Fig. l being an elevation in section along the line I-I of Fig. 2, and Fig. 2 a plan View in section along the line 2 2 of Fig. 1.

Fig. 3 is a diagrammatic sectional elevation of one end of a gas fired open hearth furnace according to the invention.

Fig. 4 is a diagrammatic sectional elevation of a liquid fuel operated open hearth furnace according to the invention.

Fig. 5 is a diagrammatic plan section of a modification of a liquid fuel operated open hearth furnace according to the invention.

Fig. 6 is a diagrammatic sectional elevation of a modification of the open hearth furnace according to the invention.

Referring now first to Figs. 1 and 2, a are the air uptakes, b is the arched roof of the furnace laboratory lc, c is the gas port. The combustion air arriving from below through the air uptakes a leaves the outlets thereof in. the direction of the arrows I. rEhe currents of this combustion air impinge on to the inner surface of the arch b and are deflected in the direction of the streamlines indicated by the arrows I', 2', 3' (Fig. 2) and I", 2, 3" (Fig. 1). In the center of the furnace laboratory lc the streamlines from the two air uptakes a on both sides converge (I, 2', 3', Fig. 2) and are deiiected from the arch b downwards towards the gas stream '4 emerging from the port c (I, 2, 3, Fig. 1). The combustion air from both air uptakes a,

mixes there with the gaseous fuel which they meet under an angle denoted in Fig. 1, from which it will be seen that the component of the mixed flow towards the hearth proper is provided exclusively by the current of gas 4. So far the conventional and well known form of open hearth furnace has been described for the sake of explanation preparatory to that of the following embodiments of the present invention:

Referring now to Fig. 3, the two air uptakes (one only being shown) are again denoted a, the furnace laboratory 7c, and the gas port c. In addition, the outlets of the air uptakes are denoted a and their central longitudinal axis is donated A, the part of the roof opposite the said outlets is denoted g, and the part of the roof forming a continuation of the aforesaid roof part g is denoted h.

The air uptakes a or at least their outlets a' and the part of the roof g are so arranged with respect to one another, that the central longitudinal axis A of each outlet c' includes an external angle a of 70 with the generating line of the arch portion g.

The roof part h which forms a continuation of the aforesaid part g towards the hearth proper has a slope which is defined by the internal angle Fy included between the generating line thereof and the generating line of the roof part o, the said angle y amounting in the present embodiment to 153, the corresponding external angle being accordingly 27. Consequently the internal angle y included between the generating line of the roof part h and the central longitudinal axis A of the outlet a is l70-27=83, i. e. larger than 73. By the slope of the roof part it an improved guidance of the air deflected by the roof part g towards the hearth proper is achieved.

Referring now to Fig. 4, the parts corresponding to those of Fig, 3 and their angular relations are denoted by the same references. However, the gas port c of the embodiment of Fig. 3 is replaced in Fig. 4 by the nozzle for the liquid fuel d, or in Fig. 5 by a plurality of such nozzles, symmetrically arranged to the vertical middle plan of the furnace.

The central longitudinal axis A of the outlet c of the air uptakes a, includes again an external angle a of 70 with the generating line of the part of the roof g opposite the said outlets, and the generating line of the sloping roof part lz, forming a. continuation of said first mentionel roof part g includes an internal angle 'y of 1513 with the generating line thereof, and accordingly an internal angle fy' of 83 with the aforesaid central longitudinal axis A.

In Figs. 3 and 4 the roof part g opposite the outlets a has a horizontal generating line. However, this roof part g could alternatively be arranged at a slope, provided that the angular relations between the longitudinal central axis A. of the outlet portions a. and the generating line of the roof part h as described hereinabove are maintained. Such a modified arrangement according to the invention is diagrammatically shown in Fig. 6 Where the angle of slope of the roof part g is denoted What We claim as our invention and desire to secure by Letters Patent, is:

l. An open hearth furnace comprising a furnace chamber consisting of a hearth proper, front wall, baci; wall, two end walls and a roof, and including at each end a combustion chamber between the end wall and the hearth open to the hearth across the end of the furnace, the combustion chamber having an open interior, in combination with at least one fuel supply unit at each furnace end issuing into the combustion chamber adjacent and transverse to the end wall, and two air ugo-taires issuing into the combustion chamber through the bottom in front of the end wall on both sides of the fuel supply unit and placed at least as near to the hearth as the fuel supply unit, the preheated combustion air issuing from the air 11p-takes being located in the combustion chamber on either side of the fuel issuing from the fuel supply unit, all fuel supply to the furnace at one end being located between the two air up-takes and all air supply to the furnace at one end being located on the two sides of the fuel supply, there being in the said roof a part of the roof adjoining and extending from the end wall arranged opposite the outlets of the up-talres and having a generating line including an external angle not exceeding '73 with the central longitudinal axis of the outlets.

2. In an open hearth furnace comprising a furnace chamber consisting of a hearth proper, front Wall and back wall, two end walls` and a roof in combination, at least one fuel supply unit on each furnace end issuing into the said furnace chamber transverse the end wall and two air uptakes issuing into said furnace chamber through the bottom on both sides of the fuel supply unit for supplying preheated combustion air thereto, all fuel supply to the furnace at one end being located between the two air up-takes, there being in the said roof a rst part of the roof adjoining and extending from the end Wall opposite the outlets of the up-takes and having a generating line including an external angle not exceeding 73 with the central longitudinal axes of the 11p-takes and a second part of the roof arranged in continuation of the first part of the roof towards the hearth proper with respect to the first part, directed in a converging direction towards the hearth with respect to Cil the first part and having a generating line including an internal angle of less than 180 with the generating line of the rst part of the roof and an internal angle of more than 73 with the longitudinal central axes of the outlets of said air up-takes.

References Cited in the le 0f this patent UNITED STATES PATENTS Number Name Date 1,513,828 Kernohan et al. Nov. 4, 1924 1,674,167 Egler June 19, 1928 1,740,288 De Fries Dec. 17, 1929 1,816,497 Schucany July 28, 1931 1,943,957 Godard Jan. 16, 1934 2,044,655 Wilson June 16, 1936 2,542,684 Laverdisse et al Feb. 20, '1951 FOREIGN PATENTS Number Country Date 271,649 Germany Mar. 17, 1914

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