GB2069677A - Installation and process for the production of hot air - Google Patents

Abstract

An installation of the cowper type for the production of hot air comprises an enclosure occupied by a checkerwork of refractory bricks (12), a cold air admission orifice at the base of the enclosure and a hot air outlet (20) at the top of the enclosure. One or more burners (22) in the upper part generate heat during the heating cycle. Each burner is integrated into a refractory wall (16) & has a cavity (30) from which a conical flow of heat is emitted. The burners are orientated to ensure heat flows directly to the upper part of the checkerwork without direct irradiation of the upper walls (14) of the cowper. Combustion fumes are evacuated from the base of the apparatus. In the air period combustion is stopped & cold air entering at the base of the checkerwork recuperates heat from the refractory bricks and hot air is extracted from the orifice (20). In further embodiments the burners are affixed to a circular slab with an upper casing to form an hermetic chamber, the slab and chamber being cooled. <IMAGE>

Description

SPECIFICATION Installation and process for the production of hot air The present invention relates to an installation for the production of hot air, of the cowper type, comprising an enclosure, mainly occupied by a checkerwork of refractory bricks, at least one cold air admission orifice at the base of the enclosure, at least one hot air outlet orifice situated at the top of the enclosure, and one or more burners arranged in the upper part for the purpose of burning the fuels and generating the heat required for the heating of the checkerwork, as well as a process to be employed with this apparatus.

Most of the known installations for the production of hot air are mainly made up of two parts. A first part, known as the combustion shaft, has a burner at the bottom, into which a combustible gas is injected, particularly blast furnace gas, in most cases enriched with coking gas, natural gas, etc. The heat given off by the combustion of this gas rises through the combustion shaft, is deflected by a cupola and redescends into the second part of the cowper, known as the checkerwork shaft, which stores the heat in its checkerwork of refractory bricks. The hot air is produced by causing the air to circulate through the checkerwork shaft in the opposite direction to the circulation of the combustion gases, i.e. from the bottom upwards. In its passage through the checkerwork the air thus recuperates the heat which was stored up in this checkerwork during the combustion of the gases.

Among these known installations a distinction must be drawn between the "separate shaft" type, in which the combustion shaft is completely separated from the checkerwork shaft, and the "incorporated shaft" type, in which the combustion shaft and the checkerwork shaft, although not identical are situated next to each other in one single container.

In these known installations the part on which the gratest demands are made and which is thus most subject to deterioration is the cupola. The fact is that it is directly exposed to the heat and the combustion flames, since its function is to deflect the combustion gases towards the checkerwork shaft. The hottest part of a cowper of this kind is thus invariably the cupola, which is also that most exposed to stresses and therefore the most liable to suffer damage. This high temperature in the cupola reduces its mechanical strength and increases the concentration of NO, ions, which form at high temperatures and which render the cupola particularly liable to develop what is known as "intercrystalline stress corrosion", major drawback of modern cowpers operating at high temperatures and pressures.

The cowpers with incorporated shafts also suffer from the drawback that the refractory separating wall between the combustion shaft and the checkerwork shaft is likewise exposed to an intensified risk of deterioration. This is due to short circuits occuring between the combustion shaft and the checkerwork and manifest themselves in destruction of the refractory material owing to the heat surges produced by the considerable temperature differences between the two sides of the separating wall.

This last problem, inherent in the cowper of the incorporated shaft type, has been solved thanks to another type of installation known as the "Cowper without combustion shaft", in which the combustion is effected above the refractory checkerwork, either in the space underneath the cupola or in a separate combustion chamber above the cupola. An example of an installation of this kind is described in German Patent application 2,123,552. The elimination of the combustion shaft offers the additional advantage of increasing the space available for the checkerwork or reducing the diameter required. A further advantage of this design is its symmetrical construction.

The cowpers without combustion shaft, however, have not provided any solution to the problem arising in the heating of the cupola, the wall of this latter still being the zone subjected to the most intensive heating, since either the combustion occurs immediately below it or the combustion gases are conveyed straight to the said wall. This type of cowper therefore invariably involves the problems of intercrystalline corrosion.

The purpose of the present invention is therefore to provide a new type of cowper without a combustion shaft and free of the drawbacks inherent in the cowpers already known.

For this purpose the invention provides an installation which is characterized by the fact that each burner is integrated into a refractory wall provided with cavities corresponding to each burner and forming with the front portion of the latter a "combustion dish" from which a conical flow of heat is emitted, each of these burners being orientated to ensure that these heat flows act direct on the entire upper surface of the checkerwork without any contact between this surface and the flames.

In this type of burner the combustion takes place in a front "dish" of the burner, and the combustion gases, as well as the heat given off, are conveyed direct to the upper surface of the refractory checkerwork. The resulting advantage is that the heat is transmitted to the place where it is required and without first being reflected from the cupola. This latter therefore no longer has to function as a deflecting device for the combustion gases and the heat, its sole function now being that of an arch or cover serving to close the upper part of the installation. Thanks to this con struction, the temperature of this arch can be reduced by 100-1 50 for comparable operating conditions.

Whereas in conventional cowpers the hottest point, and that subject to the greatest stress and having the least strength, was the cupola, the hottest point in the cowper according to the present invention is that subject to the minimum stress, in addition to being that of which the heat is recuperable, i.e. the upper part of the refractory checkerwork.

A further advantage offered by the adoption of flameless burners and the elimination of the combustion shaft is the reduction of the proportion of NO, ions for a given hot air temperature.

In the simplest version one single burner is positioned in the centre of the arch of the cowper, the hot air outlet orifice being situated by the side of this burner.

In another version the hot air outlet orifice is in the centre of the arch, the burners being distributed around the orifice. In this case there may be either three of four such burners, occupying the points of a triangle or square respectively.

In a further multi-burner version the burners and the hot air outlet orifice are arranged around the centre of the arch.

As this arch will now be subject to less stress, particularly owing to the lower temperature and the reduction of the intercrystalline corrosion, a number of openings can be provided in the arch, in order to position the hot air outlet orifice and the burners without appreciably detracting from the static strenght of the assembly. The arch may be a simple brickwork structure or else a "suspended arch", i.e. consist of refractory bricks suspended by securing hooks from the outer metal cladding.

In another version the burner or burners are simply affixed vertically to a circular slab mounted transversely above the checkerwork and forming together with an upper casing a hermetic chamber into which the supply pipes for the burners penetrate. In this version the hot air outlet orifice may be situated between the slab and the checkerwork or extend out vertically from the centre.

The invention likewise covers a process for the production of hot air in an installation of this last type, this process comprising a combustion period and an air period, and being characterized by the fact that during the said two periods the slab and also the chamber above it are cooled. This cooling can with advantage be effected by introducing combustion air into the chamber during the combustion phase and cold air during the air phase.

The cold air thus circulating in this chamber can be recycled and reintroduced at the bottom of the checkerwork in such a way as to enable its heating to be utilized in the chamber above the slab. In addition to the cooling effect, the circulation of the cold air in this chamber ensures that the pressure on the respective sides of the slab will be balanced out. In a further embodiment of the invention a cooling system is provided in the slab, in which system a supply of water or else air which can be re-used, in the process adopted, is caused to circulate.

Further features and characteristics will become apparent to those skilled in the art from the following detailed description of certain possible embodiments of the invention, by reference to the accompanying drawings wherein like reference numerals refer to like elements, and in which the respective figures are as follows Figure 1: a schematic cross section of a first embodiment of a cowper in accordance with the present invention.

Figure la : a schematic partial plan view of the version shown in Fig. 1.

Figures 2, 2a : analogous view to the preceding figures, showing a second version.

Figures 3, 3a: Views corresponding to those provided by Figs. 1 and 1 a, illustrating a third embodiment.

Figures 4, 4a: corresponding to Figs. 1 and 1 a respectively of the version having one single burner but provided with the suspended type of arch.

Figure 5: a schematic vertical section through the upper part of another type of cowper according to the invention.

Figure Sa: a partial plan view of the version shown in Fig. 5.

Figures 6, 6a: a variant of the version shown in Fig. 5, with a schematic diagram illustrating the process adopted.

Figures 7, 7a: a schematic diagram of the process description with reference to Fig. 6, but this applied to the version shown in Fig.

5.

Figure 8: A schematic diagram of a version similar to that shown in Fig. 6, but with an air-cooled slab.

Figure 8a: a schematic horizontal section in the plane 8a-8a through the slab shown in Fig. 8.

Figure 9, 9a: a variant of the process described, by reference to Fig. 6.

Figure 10: a schematic diagram of a variant of the embodiment shown in Fig. 8, but with a water-cooled slab.

Figure 10a: a schematic horizontal section in the plane 1 0a-1 0a through the slab shown in Fig. 10.

Figures 11, 1 la: an analogous embodiment to that shown in Fig. 2.

Figures 12, 12a: the adaptation of the suspension system of Fig. 11 to the versions provided with a slab.

Figs. 1 and 1 a illustrate the upper part of a first embodiment of a cowper 10. This cowper comprises one single shaft 1 2 formed by a checkerwork of refractory bricks which are alternately heated and traversed by air from the bottom upwards in order to recuperate the heat stored up in the refractory brickwork. The shaft 1 2 is closed at the top by an arch or dome 1 4 consisting of an assembly of refractory bricks 1 6 surrounded by an external metal cladding 18. This arch 14 is provided with an outlet 20 for the hot air rising through the refractory checkerwork of the shaft 12.

The version of the present invention shown in Fig. 1 comprises a burner 22 which may be of the type described in French Patent 1,205,382. This is a burner essentially consisting of an enclosure 24 provided with an inlet 26 for the combustible gases and an inlet 28 for the combustion air, the combustion itself taking place in a "bowl" 30 also containing the tip of a pilot flame, not shown in the drawing.

The characteristic function of this burner is to produce a very high degree of heat radiation, thanks to a whirling flame inside the bowl 30. The burner will be simply affixed to a flange 32 of the cladding 1 8 of the arch 14, while an aperture 34, preferably diverging slightly, with an opening angle corresponding to the angle of the "cone" emitted by the burner 22, will be provided in the refractory brickwork 16. This emission cone is shown schematically by dotted lines and is marked 36.

During the phase in which the refractory brickwork is heated up the combustion gases and combustion air are introduced into the burner 22 at a pressure slightly above the atmospheric, in order to cause the combustion gases to be very rapidly mixed and to form a continuous flow all the way down to the bottom of the checkerwork shaft 1 2. The emission of the combustion gases and that of the thermal radiation take place at a divergent angle represented by the cone 36, the maximum heating occurring on the upper surface of the refractory checkerwork, i.e. where the heat is really required and where it can be recuperated.

On the other hand, the arch 14, contrary to the arches and cupolas of all the installations known up to the present is less exposed to thermal radiations and remains "in the shade" from the heat given off by the burner 22.

To obtain a regulated temperature of 125Q"C for the hot air, as is the case in modern blast furnaces, the temperature of the refractory checkerwork must be increased to 1400or, at all events in its upper part. If this temperature is to be obtained the temperature at the outlet of the burner must reach 1500"C. Now if such temperatures are adopted in conventional installations the temperature of a cupola, which reflects the combustion gases and the heat of the combustion shaft towards the checkerwork will be over the 1400"C to which the temperature of the refractory bricks has to be brought, i.e. the temperature of the cupola may rise to as much as 1450 C and over.At such a temperature, needless to say, its strength is seriously reduced, in addition to which it is exposed to the intercrystalline corrosion phenomenon.

On the other hand, for comparable operating conditions, i.e. the heating of the upper part of the checkerwork to 140û > C and a combustion temperature of 1500 C, the temperature prevailing in the arch 1 4 is only about 1300"C, which is about 1504C lower than the temperature occuring in the cupolas of conventional installations. Now it is a well known fact that a reduction of 100" or even 150"C in the temperature is quite considerable for these thermal conditions, particularly as regards the increase of the static strength of the arch and the reduction of the risk of intercrystalline corrosion.

Furthermore, in view of the short distance between the burner and the refractory checkerwork, and in view of the fact that the burner used is operated more efficiently than the burners employed in the conventional cowpers, it is even possible to adopt less than 1500on at the outlet of the burner in order to heat the bricks to 1 400'C, or else, while still operating at 1500 C, to raise the temperature of the upper part of the checkerwork to above 1400on.

The proximity of the burner 22 of the refractory checkerwork also enables the temperature of the said checkerwork to be regulated more satisfactorily, resulting in better control over the temperature of the hot air at the outlet of the copwer.

A further important advantage is the reduction in the formation of NO,- ions. The fact is that experience has shown that they form to a very considerable extent at high temperatures particularly at those exceeding 1400"C, so that, as already mentioned, it is in the cupola of conventional cowpers that the greatest concentration of NO,- ions is to be found. Now if the temperature of a cupola can be reduced to below 1400on one of the causes or conditions which favour the formation of NO,- ions is eliminated i.e. the concentration of NO,- ions is greatly reduced, the risk of the intercrystalline corrosion phenomenon being rendered far smaller at the same time.

It goes without saying that the elimination of the heating of the parts which do not require to be heated, such as the walls of the combustion shaft and, above all, the cupola, greatly reduces the fuel required for the heating of the refractory checkerwork, or else enables it to be heated more satisfactorily with the same quantity of fuel. In either case there is naturally an energy gain.

Whereas in the case of the cupolas of conventional cowpers it was necessary, owing to the heat stresses suffered by the cupola, to adhere to certain strict conditions as regards its geometrical design and to avoir apertures as far as possible, in order to increase its static strength, there will hence forward be a greater degree of freedom in the selection of the geometrical shape of the arch described in the foregoing, i.e. it can be given any shape which proves most suitable and the necessary apertures can be provided therein. It is thanks to this circumstance that numerous variants can be adopted, some of which will be described hereinafter, by reference to the following figures.

Figs. 2 and 2a illustrate one embodiment in which the hot air outlet 40 is provided in the centre of the arch, above the checkerwork shaft 12. Instead of providing one single burner, as in Fig. 1, four burners 42a, 42b, 42c and 42d are provided, each of exactly the same design as the burner 22 but of a smaller size. These burners are arranged in a "square" at regular intervals around the hot air outlet 40. These burners 42a, 42b, 42c and 42d will preferably be inclined at a slight angle in relation to the longitudinal axis of the shaft, so that the thermal radiation cone of each burner will come in contact with the entire upper surface of the checkerwork shaft.

The shape and the angle of inclination of the apertures in the brickwork of the arch 44 will naturally be in accordance with the angle of inclination of the burners.

In the version shown in Figs. 3 and 3a the arch 54 has been provided with four burners 52a, 52b, 52c and 52d (not shown). These burners 52a. 52b, 52c and 52d are identically similar to those of Fig. 2 but arranged differently. As may be seen, the hot air outlet 50 is no longer in the centre of the arch but by the side of the latter, while the four burners 52a, 52b, 52c and 52d are arranged in a "square" around the centre of the arch 54.

Figs. 4 and 4a illustrate a version analogous to that of Figs. 1 and 1 a, with a same burner 22 positioned in the centre of an arch 63 and with a hot air outlet 20 positioned adjacent to the burner 22. The difference in relation to the version shown in Fig. 1 resides in the fact that the arch 63 no longer constitutes a brickwork assembly and that the internal refractory lining 67 is affixed by means of securing bricks 65 to the external cladding 69 of the arch 63. This enables a flatter construction to be adopted for the arch 63, i.e. the burner 22 to be positioned more closely to the upper surface of the checkerwork shaft 12, thus intensifying the advantages which result from this adaptation in shape, as described in the foregoing.

Needless to say, the versions shown in Figs.

1 to 3. can also be designed with an arch "hooked on", as shown in Fig. 4. These variants, however. will no longer be described in detail.

Figs. 5 and 5a illustrate a version with four burners 64a, 64b, 64c and 64d, mounted inside the head 60 of a cowper immediately above the checkerwork shaft 62. These burners are mounted vertically on a supporting slab 66 positioned transversely above the upper surface of the shaft 62. The burners are arranged symmetrically in a square around a central outlet 68 which rises vertically through the slab 66.

Needless to say, the burners 64a, 64b, 64c and 64d are of the type described previously, the associated apertures in the slab 66 being adapted to the heat radiation cone of the burners, so that the entire upper surface of the checkerwork shaft 62 will be subjected to the heating and to the combustion gas.

The supply to the four burners 64a, 64b, 64c and 64d is effected by means of two main circular pipes 70 and 72 positioned around the head 60 and conveying the combustion air and the combustible gases respectively to the said burners. Each of the four burners is connected to the two circular pipes 70 and 72 via radial pipes 74 and 76, each provided with a shut-off gate 78 and 80.

The head 60 of the cowper is closed by a hermetic casing 82 provided with the inlets 84 required for inspection and replacement of the burners and defining a chamber 86 above the slab 66. This casing 82 thus renders the cowper head hermetic to the outside. This chamber 86 will preferably be cooled by the circulation of a suitable cooling fluid, as will be described in greater detail hereinafter.

Fig. 6 first of all shows a variant of the version illustrated in Figs. 5 and 5a. In this embodiment of the invention there are once again four burners 94a, 94b (not shown), 94c and 94d, mounted with a rim-type configuration on a slab 96, above the checkerwork shaft 92 and inside the head 90 of the cowper. The essential difference between this embodiment and that shown in Figs. 5 and 5a resides in the fact that the hot air outlet 98 is provided in the side wall between the slab 96 and the upper surface of the refractory checkerwork 92.

The supply of combustible gas to the burners is again effected by a circular pipe 102 which is provided around the head 90 and which is connected via radial pipes 104 and a shut-off gate 106 to each of the burners 94a, 94b, 94c and 94d. Contrary to the previous embodiment, however, the combustion air is supplied through a pipe 100 penetrating vertically and axially into the head 90 and connected to each of the burners via stubs 108.

The head 90 is again closed by means of a hermetic casing 110 comprising apertures 11 2 afording access to the burners, and defining a chamber 11 6 which can be cooled.

A casing 110 and also the casing 82 (Fig.

5) are provided with one or more apertures 114 as a means of regulating the pressure and circulation inside the head, in the cham ber formed by the casing 110 and the supporting slab 96 of the burners.

Fig. 6 shows, likewise schematically, in thick lines, an advantageous constructional version for the cooling and for the equalization of the pressure, particularly the pressurization, of the chamber 116.

For the ventilation of the chamber 1 16 the apertures 114 are connected with the external atmosphere via a pipe 11 8 and a gate 1 20.

The checkerwork shaft 92 is likewise connected to the exterior via a pipe 1 22 and a gate 124, leading into a pipe 1 28 provided at the base of the checkerwork shaft 92, the combustion fumes normally emerging through the said gate during the heating of the shaft.

The combustion air supply pipe 1 00 for the burners communicates with the interior of the chamber 11 6 via a number of apertures 1 30, preferably four, these apertures 1 30 being preferably provided with regulating valves shown schematically at 1 32.

The cold air inlet orifice at the base of the checkerwork shaft 92 is shown schematically by the reference number 1 34 and is fed from a main pipe 136 via a gate 142. This main pipe 1 36 for the cold air likewise communicates, via a gate 149, a pipe 138 and a regulating valve 140, with the pipe 100 through which the combustion air is introduced into the burner.

At the beginning of each combustion phase or heating phase for the shaft 92 both the chamber 11 6 and the interior of the shaft have to be ventilated, since these enclosures, during the preliminary phase, were under pressure. For this purpose all that is required is to open the gates 1 20 and 1 24 in order to cause the air to emerge, expanding in the process to atmospheric pressure, from the chamber 11 6 and the shaft 92, via the pipes 11 8 and 11 2 respectively.

During the combustion period the interior of the chamber 11 6 is cooled by causing some of the combustion air penetrating through the pipe 100, via the apertures 1 30 and the regulating valve 132, to emerge through the apertures 114.

At the end of the combustion period and before the air period, i.e. the introduction of cold air via the orifice 1 34 at the base of the checkerwork shaft 92, the chamber 11 6 has to be pressurized in order to adapt the pressure in the said chamber 11 6 to that of the air in the checkerwork, and the said pressure may rise to as much as 6 bars.This equalization of pressure is advantageously effected by placing the main pipe 1 36 in communication not only with the interior of the checkerwork 92, via the gate 142, for the introduction of cold air into the checkerwork 92, but also with the interior of the chamber 11 6, via the valve 140, the pipe 138, the pipe 100, the apertures 1 30 and the regulating valves 1 32.

The pressurization of the chamber 1 16 and that of the shaft 92 will thus proceed parallel with each other, and the pressure differences between one side of the slab 96 and the other will be practically nill throughout the entire period when the shaft 92 is being filled.

In order to prevent the cold air for the equalization of the pressure in the chamber 11 6 from penetrating the shaft 92 via the burners, valves indicated schematically by the reference number 1 33 are provided between each of the burners 94a, 94b, 94c and 94d and the admission pipe 1 00.

The cooling of the chamber 11 6 throughout the period when the cold air is being heated, this being known as the air period, will be effected in similar fashion to the pressurization and following this latter operation. In other words, during the introduction of cold air via the orifice 134 and the main pipe 136, a certain quantity of air will be deflected via the gate 149, the valve 140, open to a greater or lesser extent for the purpose, and the pipe 138, towards the interior of the chamber 11 6. In order to ensure the required circulation and cooling in this latter, the air, heated in this manner, in the chamber 116, is evacuated through the apertures 11 4 and the pipe 11 8 to the atmosphere.During the cooling the valves 1 32 are set to ensure that the circulation in the chamber 11 6 will maintain a substantially constant pressure equal to that obtained during the preliminary pressurization.

Instead of evacuating the air to the atmosphere via the apertures 11 4 and the gate 120, the pipe 11 8 can be connected to the pipe 122, as shown schematically by the dotted lines 1 44, and this air can be returned via the pipe 1 22 and the evacuation orifice 1 28 for the fumes to the interior of the checkerwork shaft 92, where this air will be mixed with the cold air introduced via the orifice 1 34. This system provides a means of benefitting from the heating of the air serving to cool the chamber 116, recuperating the heat evacuated by the cooling. In this case, however, an over-pressure device must be provided in the pipe 138, in order to counteract the pressure lose occuring in the cooling circuit.

In order to remedy any possible failure in the cooling and pressurization circuit for the chamber 116, which may be caused by faulty operation of the valve and which may seriously aggravate the risk of accidents, the casing 110 should preferably comprise an aperture 1 46 connected to a source of cold pressure gas such as nitrogen. A backup circuit of this kind will normally not be in operation but will be caused to come into operation automatically as soon as the temperature in the chamber 11 6 exceeds a certain preselected threshold or the pressure in this chamber 11 6 falls below a certain critical level.

The slab 96 may also be provided with a small aperture connecting the chamber 11 6 to the interior of the checkerwork shaft 92, thus providing an additional degree of safety against an accidentally excessive pressure difference between the respective sides of this slab.

The process for the pressurization and cooling of the chamber 1 16 may also be applied to the version shown in Fig. 5, for the purpose of pressurizing and cooling the chamber 86. In particular, the apertures 1 30 and the regulating valve 1 32, provided in the pipe 100 in the case of Fig. 6. are provided on the pipes 74 where Fig. 5 is concerned. A slightly modified system, which will be described below by reference to Fig. 7, can likewise be adopted.

In the said Fig. 7, the components discussed by reference to Figs. 5 and 5a have been retained, the same reference numbers being used again. This Fig. 7 likewise contains a reproduction of the general diagram provided in conjunction with Fig. 6, identical components being marked with the same reference numbers. Contrary to the method adopted in the case of Fig. 6, however, the auxiliary pipe 1 38 for the cold air leads both into the circular combustion air supply pipe 70 and into an auxiliary circular pipe 148 connected by one or more small tubes 1 50 to the interior of the chamber 86.

During the combustion period some of the combustion air introduced into the burners via the circular pipe 70 is deflected via the regulating valve 1 40 into the circular auxiliary pipe 148 in order to be conveyed into the interior of the chamber 86 for cooling purposes. The evacuation of the air from the interior of the chamber 86 may once again be effected via the apertures 114 and the pipe 118.

During the air period the equalization of pressure in the chamber 86 and the cooling in the interior of this latter are effected by introducing cold air via the pipe 1 38 into the circular auxiliary pipe 148 and conveying it from the latter to the interior of the chamber 86. Supplementary valves, not shown, can be provided in order to isolate the circular pipe 70 from the pipe 1 38 during the combustion period and the pipe 1 38 from the circular conduit 70 during the air period. More complete information will be provided by the description given with reference to Fig. 6. It should be noted, however, that in the version shown in Fig. 7, a supplementary circuit 146 has likewise been provided, serving to introduce additional cooling and pressurization gas.

Needless to say, it is also possible for the example shown in Fig. 6 to be provided with the system for the injection of cooling and pressurization air via a circular auxiliary pipe, as in the case of Fig. 7.

Fig. 8 provides a schematic diagram of the upper part of a cowper similar to that described by reference to Fig. 6, comprising a similar arrangement of burners 94a, 94b, 94c and 94d, and also a similar pressurization and cooling system for the chamber 116. In order to illustrate this variant, however, the apertures connecting the pipe 100 to the interior of the chamber 11 6 are shown at a higher level, marked 1 52 in Fig. 8. These apertures 1 52 are naturally likewise provided with regulating valves, shown schematically by the reference number 1 54.

Contrary to the preceding embodiment of the invention, particularly that shown in Fig.

6, the embodiment illustrated by Figs. 8 and 8a comprises a slab 1 56 within which is provided a cooling circuit consisting of an entire series of tubes 1 58 sunk in the mass of the slab 1 56. In the diagrams these tubes 1 58 are positioned parallel to one another, but they can obviously be positioned differently, particularly in a circle or spiral, in order to cover the entire surface to be cooled. These tubes 1 58 are connected both to a main distributor 1 60 and to a manifold 1 64 connected to each of the said tubes 1 58.

The cooling circuit provided for the slab 1 56 and shown in Figs. 8 and 8a is designed to function with air. It is thus of advantage to connect this cooling circuit of the slab 1 56 to this circuit through which combustion air is supplied to a series of cowpers. It is known, in fact, that installations for the production of hot air for blast furnaces comprise a group of cowpers, i.e. at least two cowpers operating alternately, one in the combustion period and the other in the air period, and then vice versa. One common feed system is thus generally provided for supplying the combustion air to each of the pipes 100 and each of the cowpers.In the case of Fig. 8, therefore, the cooling circuit of the slab 1 56 can be incorporated in the combustion air supply, so that the combustion air passes through the tubes 1 58 before penetrating the burners.

The manifold 1 64 is connected via two pipes 1 68 and 168' (see Fig. 8a) each comprising a gate 1 70 (see Fig. 8) to two combustion air supply pipes 100 for two cowpers.

When the cowper shown schematically in Fig. 8 is operating during the combustion period the gate 1 70 is open and the cooling air circulating in the tubes 1 58 is introduced into the pipe 100 supplying combustion air to the burners. On the other hand, when the cowper changes over to the air period the gate 1 70 is closed and the cooling air for the tubes 1 58 is conveyed through the pipe 168' to another cowper which at this moment is operating in the combustion period. Consequently, in addition to the pressurization and cooling of a chamber 116, which are carried out in the normal manner, as in the case of Fig. 6, the version shown in Fig. 8 guarantees supplementary cooling of the slab 156, both during the combustion period and during the air period.

Fig. 9 shows another variant applied to a cowper of the type described by reference to Fig. 6, this time comprising a supplementary cooling system for the slab 96. This supplementary cooling is effected by means of a flat cooling chamber 1 72 provided specially for this purpose immediately above the slab 96 and separating the latter from the interior of the chamber 11 6. This chamber 1 72 is connected via a pipe 1 74 and an over-pressure device 1 76 to the auxiliary pipe 138, which latter, as in the version shown in Fig. 6, connects the main pipe 1 36 for cold air to the combustion air supply pipe 1 00. The outlet of the cooling chamber 1 72 is connected via a regulating valve and a pipe 1 78 to the exhaust orifice 1 28 provided for the fumes at the base of a cowper. In order to avoid a direct passage from the inlet to the outlet of the chamber 172, the latter is preferably subdivided into compartments in order to form baffles and force the cooling air to circuit throughout the chamber.

During the combustion period some of the combustion air circulating in the pipe 100 passes through the upper part of the pipe 1 38 and is conveyed by the over-pressure device 1 76 into the cooling chamber 1 72. It is discharged from the chamber 1 72 to the atmosphere via the valve 180, the pipe 1 78 and the gate 1 24.

During the air period cold air is introduced into the cooling chamber via the pipe 138, the over-pressure device 1 76 and the pipe 1 74. This air circulating in the cooling chamber 1 72 is preferably recycled via the pipe 1 78 and the orifice 1 28 in order to take advantage of the heat evacuated from the chamber 172.

In addition to the cooling of the chamber 1 72 the pressurization and cooling of the chamber 11 6 are effected in the same manner as in the case of Fig. 6.

Needless to say, the cooling chamber 1 72 in the version shown in Fig. 9 can be replaced by a system of cooling pipes as in the version shown in Fig. 8. Conversely, the system of cooling pipes provided in the version shown in Fig. 8 can be replaced by the cooling chamber provided in the case of Fig. 9.

Figs. 10 and 1 ova illustrate a version analogous to that of Fig. 8 but with a cooling system provided inside the slab 1 56. As in the example shown in Fig. 8, a certain number of pipes 1 58 are accomodated in a mass of the slab. These pipes are connected both to a distributor 1 82 and to a manifold 1 84.

Contrary to the example shown in Fig. 8, however, it is only cooling water that is caused to circulate in the cooling circuit of the slab 1 56. Needless to say, the pipe 1 58 can once again be positioned parallel to one another or in different configurations, particularly circular or spiral, in order to cover the entire surface of the slab 1 56. The cooling and pressurization of the chamber 11 6 are again effected as in the version shown in Fig.

6.

The different variants of the cooling system which are shown in Figs.-8, 9 and 10 have been described in conjunction with a cowper of the type discussed by reference to Fig. 6. It is nevertheless obvious that the versions shown in Figs. 8-10, as well as the processes employed, are equally applicable to an embodiment such as that shown in Fig. 5 or in Fig. 7.

Finally it should be noted that in the version shown in Fig. 10 the circuit 1 58 can be replaced by a cooling chamber analogous to the chamber 1 72 and again serving for the circulation of either water or some other cooling liquid.

Fig. 11 shows an advantageous example for the design of the head of a cowper, particularly applicable to the versions shown in Figs.

1-4, Fig. 11 a being a view of the upper part of a cowper looking downwards. In this example, there are four burners 190a, 190b, 190c and 190d, mounted in a "square" around the centre of an arch 192, the hot air outlet 1 94 being provided at the side. In this example the shape of the arch is better adapted to the burners inasmuch as for each burner the arch forms a cavity 1 96 fitting the refractory part of the burners, and forming an extension thereto, thus combining with them to form the combustion bowl 1 98.

A set of criss-cross beams 200, 202, 204, integral with the cladding of the arch 192, supports both the latter and the burners.

Figs. 1 2 and 1 2a show how the assembly illustrated in Figs. 10 and 1 ova is adapted to the versions shown in Figs. 5-10. The four burners 206a, 206b, 206c and 206d are mounted on a slab 208 which, like the arch 192 in Fig. 11, comprises cavities 210 which fit the shape of the refractory portion and which combine with this latter to form combustion bowls 212. The slab 208 and the four burners 206a, 2Q6b, 206c and 206d are supported by beams. These beams are supported in their turn by the external casing 214 which forms a prolongation for the external cladding of the shaft 92.

Claims (43)

1. An installation for the production of hot air, of the cowper type, comprising an enclosure mainly occupied by a checkerwork of refractory bricks, at least one cold air admission orifice at the base of the enclosure, at least one hot air outlet orifice situated at the top of the enclosure, and one or more burners arranged in the upper part for the purpose of burning the fuels and generating the heat required for the heating of the checkerwork, wherein each burner is integrated into a re fractory wall provided with cavities corresponding to each burner and forming with the front portion of the latter a "combustion dish" from which a conical flow of heat is omitted, each of these burners being orientated to ensure that these heat flows act direct on the entire upper surface of the checkerwork without any contact between this surface and the flames.

2. An installation in accordance with Claim 1 comprising one single burner mounted in the centre of an arch provided above the checkerwork, the hot air outlet orifice being likewise provided, adjacent to the burner, in the said arch.

3. An installation in accordance with Claim 1, wherein the outlet orifice is situated in the centre of an arch and wherein a number of burners are mounted in the arch in a symmetrical configuration around the outlet orifice and are inclined at an angle in respect of the vertical axis of the enclosure.

4. An installation in accordance with claim 3, comprising four burners, arranged in a "square" around the orifice.

5. An installation in accordance with claim 3, wherein the hot air outlet orifice and a number of burners are positioned around the vertical axis of an enclosure in an arch.

6. An installation in accordance with any one of claims 2-5, wherein the arch consists of a brickwork arch formed by an assembly of refractory bricks surrounded by an external metal cladding.

7. An installation in accordance with any one of Claims 2-5, wherein the arch consists of an arch formed by refractory bricks attached by means of securing bricks to an external metal cladding.

8. An installation in accordance with claim 1, comprising a number of burners mounted symmetrically in rim-type configuration and affixed vertically to a circular slab mounted transversely above the checkerwork and combining with an upper casing to form a hermetic chamber.

9. An installation in accordance with claim 8, comprising a central hot air outlet pipe extending vertically out of the said casing and the slab and by external circular pipes serving to supply combustion air and combustible gases to the burners and connected to these latter by radial pipes provided with shut-off gates.

1 0. An installation in accordance with Claim 9, wherein the hot air outlet orifice is provided in the lateral wall of the checkerwork, between the slab and the upper part of the checkerwork, and wherein the supply of combustion air and combustible gases to the burners is effected, respectively, by a pipe penetrating vertically and centrally through the casing, between the rim-shape configuration of burners, and comprising an external circular pipe connected by radial pipes and shut-off gates to each of the burners.

11. An installation in accordance with any one df claims 8-10, wherein the chamber is cooled by means of a cooling liquid.

1 2. An installation in accordance with any one of claims 8-10, wherein the external casing is provided with access apertures for the inspection and replacement of the burners.

1 3. An installation in accordance with any one of claims 8-12, wherein the external casing is provided with apertures for the regu lation'of the pressure in the chamber.

1 4. An installation in accordance with any one of claims 8-1 3, wherein the pipes communicate via a pipe, a valve and a gate, with a main pipe connected to the cold air inlet orifice at the base of the shaft.

1 5. An installation in accordance with claim 13, comprising a pipe connecting the apertures to the atmosphere via a gate.

1 6. An installation in accordance with claim 1 5, wherein the said pipe is connected to an orifice provided at the base of the shaft and serving for the evacuation of the combustion fumes.

1 7. An installation in accordance with one of claims 8-13, wherein the combustion air feed pipe, for each of the burners, communicate with the chamber, via apertures provided with regulating valves.

18. An installation in accordance with any one of claims 8-13, and 1 5-17, comprising a circular auxiliary pipe connecting the chamber to the combustion air supply pipes, on the one hand, and via a pipe and a valve to a main pipe connected to the cold air inlet orifice at the base of the shaft, on the other hand.

1 9. An installation in accordance with any one of claims 8-13, comprising a cooling circuit sunk in the mass of the slab.

20. An installation in accordance with any one of claims 8-18, comprising a flat cooling chamber provided for the slab and positioned immediately above the latter.

21. An installation in accordance with either of claims 19, 20, wherein the cooling circuit or the cooling chamber is connected to a cooling water pipe.

22. An installation in accordance with either of claims 19, 20, wherein the cooling circuit or the cooling chamber is connected to a cooling air pipe.

23. An installation in accordance with claim 22, wherein the inlet of the cooling circuit or of the cooling chamber is connected via an over-pressure device to a main combustion air supply pipe and wherein the outlet is connected via two pipes, each provided with a gate, to the two combustion air supply pipes of two cowpers operating alternately.

24. An installation in accordance with claim 22, wherein the inlet of the cooling circuit or cooling chamber is supplied with cold air through the pipe connected to the main cold air pipe and wherein the outlet is connected via a pipe to the base of the checkerwork shaft and via a gate to the atmosphere.

25. An installation in accordance with any one of claims 8-24, comprising an aperture in the casing of the chamber, this aperture being connected to a supplementary source for the pressurization and cooling of the chamber.

26. An installation in accordance with any one of claims 8-24, comprising a safety aperture in the slab connecting the chamber to the interior of the checkerwork.

27. A process for production of hot air in an installation according to any one of claims 8-26, in which process the refractory checkerwork is heated during a combustion period in which in each of the burners, a combustible gas in burnt in a current of combustion air, the combustion fumes being evacuated through an aperture at the base of the shaft, the combustion period being stopped and an air period being initiated, in which latter cold air is introduced at the base of the checkerwork shaft and the hot air extracted at the top of the shaft, in which process the heat stored up in the checkerwork during the combustion period is recuperated as it passes through the said checkerwork, wherein during both periods the slab and also the chamber above it, containing the burners, are cooled.

28. A process in accordance with claim 27, wherein during the combustion period the said chamber is cooled by introducing part of the combustion air.

29. A process in accordance with claim 27, wherein during the air period the said chamber is cooled by the circulation therein of part of the cold air introduced at the base of the checkerwork shaft.

30. A process in accordance with claim 29, wherein the cooling air is discharged from the said chamber to the atmosphere.

31. A process in accordance with claim 29, wherein the discharge of the cooling air from the said chamber is effected in the form of a recycling operation in which this cooling air is returned to the base of the checkerwork shaft and introduced into the latter.

32. A process in accordance with any one of claims 27-31, wherein prior to the combustion period, the said chamber and the checkerwork shaft are ventilated by connecting them with the atmosphere.

33. A process in accordance with any one of claims 27-31, wherein, at the commencement of the air period, cold air is introduced simultaneously into the checkerwork shaft and into the said chamber, in order to increase progressively and simultaneously the pressure in each of these enclosures, for the purpose of equalizing the pressure on the two sides of the slab supporting the burners.

34. A process in accordance with any one of claims 27-33, wherein, independently of the cooling, pressurization or ventilation of the chamber, the slab is cooled during both periods by means of an auxiliary circuit provided inside the said slab or immediately above it.

35. A process in accordance with claim 34, wherein water is used for the cooling.

36. A process in accordance with claim 34, wherein this cooling is carried out with combustion air by incorporating this cooling circuit into the combustion air supply pipe for the burners, and wherein the air emerging from this cooling circuit of the slab is conveyed to the burners of the cowper concerned during the combustion period of this latter, whereas during the air period this air is conveyed to the burners of another cowper which at that moment is operating in the combustion period.

37. A process in accordance with claim 34, wherein this cooling is carried out with some of the cold air and that this cooling air is recycled during the air period to the base of the checkerwork shaft for the production of hot air.

38. A process in accordance with any one of claims 31, 36, 37, wherein the cooling air is compressed in an over-pressure device.

39. A process in accordance with any one of claims 28-33, wherein a supplementary cooling and pressurization source is provided, being designed to be put into operation automatically as soon as the temperature in the chamber rises above a certain preselected threshold or the pressure in the chamber differs to a certain preselected amount from that prevailing in the checkerwork.

40. An installation in accordance with any one of claims 1-7, wherein the burners and the arch are supported by beams and wherein the arch is provided with cavities adapted to each of the burners.

41. An installation in accordance with any one of claims 8-26, wherein the slab and the burners are suspended from beams supported by the external casing and wherein the slab is provided with cavities adapted to each of the burners.

42. An installation substantially as hereinbefore described and illustrated in the accompanying drawings.

43. A process substantially as hereinbefore described and illustrated in the accompanying drawings.