EP0036609A1 - Process and installation for the ignition of a sinter mixture - Google Patents

Abstract

The invention relates to a method for igniting a sintering mixture consisting of a solid fuel and a sintering material, on a sintering machine, in which the sintering mixture is passed under an ignition furnace with closed front and side walls and a closed ceiling, hot flue gases in the ignition furnace above the Sintered goods are generated and these hot flue gases heat and ignite the surface of the sintered goods by radiation and convection. A quick, uniform and economical ignition is achieved in that flue gases from one or more approximately stoichiometrically operated burners are fed into the upper region of the ignition furnace and that gases with an increased oxygen content are fed into the lower region in such a way that a furnace atmosphere results, which is hotter and less oxygen in the upper area of the ignition hood, and cooler and oxygen-rich in the lower area. Another process variant provides an improvement in the ignition process by using a thermal insulation hood. Devices for carrying out the method are also described.

Description

The present invention relates to a method for igniting a sintering mixture consisting of a solid fuel and a sintering material, in particular a sintering oil mixture, on a sintering machine, in which the sintering mixture is passed under an ignition furnace with closed front and side walls and a closed ceiling, in which hot flue gases are generated in the ignition furnace above the sintered good and these hot flue gases heat and ignite the surface of the sintered good by radiation and convection. The invention further relates to a device for carrying out such a method with a downwardly open ignition furnace with two end walls, two side walls and a ceiling and with a sintering belt below it which can move essentially horizontally in the direction of the connecting line between the end walls, for receiving a sintering mixture, the end walls and the side walls are pulled down to close to the sintered mixture, so that a hood-like ignition furnace space is formed which is largely sealed off from the outside atmosphere.

Ignition furnaces for igniting sintered mixtures are often designed as hoods that are closed at the top and the sides and open at the bottom. Under this ignition The sintering mixture is transported through in a layer thickness of approx. 40 cm on a so-called sintering belt, which usually consists of an infinite series of grate wagons directly adjoining one another. For the steel production, for example, the sinter mixture essentially consists of iron ore as sintered material and coke as a solid fuel, as well as some additives depending on the steel production process.

In order to ignite the sintered mixture as it passes under the ignition furnace, the latter is equipped with burners which generate the temperatures necessary for the ignition. There are intake ducts under the sintering belt, with the aid of which the combustion gases are sucked out of the ignition furnace through the sintering mixture.

For the economical production of a sinter that is adapted to the properties of the subsequent smelting process, it is important with regard to the ignition that the ignition on the surface of the sintered material takes place intensively and quickly, and evenly with respect to the transverse direction to the direction of transport. This should be achieved with the least possible use of fuel, both with regard to the solid fuel in the sintered mixture and with regard to the usually gaseous or liquid fuel for the burners in the ignition furnace. Finally, the economy of the process is significantly influenced by the possible throughput of the system, which in turn depends crucially on the quality and speed of the ignition process.

Ignition furnaces of the type described in the introduction have already become known in various embodiments. For example, there are ignition furnaces in which the burners are arranged obliquely downwards in the ceiling or in the end walls, the burner jets of the individual burners being directed onto the surface of the sintered material. This method leads to a strong heating of the sintered material surface, but to an uneven ignition, because the points of the sintered material surface that lie in the center of the respective burner jet are heated more intensely than the areas that lie between the burner jets. A modification of this type is that the burners are arranged in the end walls of the ignition furnace against each other and directed obliquely downwards. In the middle of the ignition furnace, where the flue gases from the burners collide, a flow is directed towards the ceiling, through which hot pieces of sintered goods are carried upwards, which then lead to ever increasing caking on the roof of the furnace.

In order to eliminate these disadvantages and to achieve an improved ignition, a design has also already been proposed in which the burners are arranged in the two side walls of the ignition furnace and essentially horizontally. With this solution it is avoided that the burner jets are directed onto the surface of the sintered bed. The surface of the sintered bed is heated and ignited more by the radiation from the furnace space of the ignition furnace. However, the influence of the different temperature distribution over the long extension of the respective burner beam is the same for all burners in series and therefore also causes different temperatures in the cross section of the sintered material surface. In addition, with this design, the burner jets collide after only 1 to 2.5 m with the narrow width of the sintering furnace of about 2 to 5 meters, which creates the risk of incomplete combustion and of the sintering bed being stirred up in the middle of the furnace.

It has also been described (Fred. Cappel and Alois Kilian: "Ignition of sinter mixtures" Stahl und Eisen 94 (1974) No. 11 page 453) to extend the actual ignition furnace and to connect a so-called heat treatment part. The burners of the inlet part of the extended ignition furnace are operated with an approximately stoichiometric air ratio, while the burners of the outlet part, i.e. of the heat treatment part to be operated with a larger excess of air. As a result, in the heat treatment part, the oxygen required for reaction with the solid fuel is supplied to the sintered bed in a heated state, as a result of which the ignition is improved.

With this method, the highest possible temperature for a certain fuel input is achieved in the inlet-side section due to the stoichiometric mode of operation of the burners. The oxygen necessary for the combustion is only supplied in the heat treatment part in that the burners are operated there with a larger excess of air. As a result, as the present invention has recognized, the heat generated by the inlet-side burners is only partially used, so that there is an unnecessarily high energy consumption.

The present invention is therefore based on the object of providing a method and a device for igniting a sintered mixture of solid fuel and sintered material, which enable rapid and uniform ignition of the sintered mixture with the lowest possible investment and operating costs (energy consumption).

This object is achieved according to the invention in a method of the type described in the introduction in that flue gases from one or more approximately stoichiometrically operated burners are fed into the upper region of the ignition furnace and that gases with an increased oxygen content are fed into the lower region in such a way that This creates an oven atmosphere that is hotter and less oxygen-rich in the upper area of the ignition hood, and cooler and oxygen-rich in the lower area.

The invention is based on the knowledge that the ignition process is significantly improved if the sintered mixture is simultaneously exposed to the high temperature of an approximately stoichiometric combustion and an adequate supply of oxygen. According to the invention, this can be achieved by the measures described above. A stoichiometrically operated burner is known to be supplied with fuel gas and oxygen (the latter usually as a constituent of atmospheric air) in such a ratio that the oxygen content corresponds to a good approximation to the amounts necessary for complete combustion of the fuel. Contain the flue gases resulting from such combustion only very small amounts of free oxygen, as this was almost completely used up for combustion. With stoichiometric combustion, the highest possible temperature is reached for a given fuel input and other boundary conditions. Because these flue gases are fed into the upper region of the furnace in the present invention, this upper region and in particular the furnace roof are heated to a very high temperature with the least possible use of fuel.

In contrast, a gas with an increased oxygen content is fed into the lower region. This gas can be any gas mixture in which it is only essential that it contains an increased proportion of free oxygen, which is suitable for accelerating the ignition process on the surface of the sintered material. This gas mixture preferably contains at least 5 s, particularly preferably at least 10%, of free oxygen.

The gases with increased oxygen content fed into the lower region of the ignition furnace can, for example, be a preferably hot gas mixture from another process of the same company. Heated air or pure oxygen can also advantageously be fed into the lower region of the ignition furnace. It is only essential that there is a furnace atmosphere in the lower region of the furnace with an increased proportion of free oxygen compared to the upper region. These oxygen-rich gases are generally considerably cooler than the flue gases from stoichiometric combustion in the upper part of the furnace. Surprisingly, however, it has been found that the ignition process, in particular with respect to the surface of the Sinter mixture, but is still significantly improved if you work according to the inventive method. This can be explained by the fact that the heat from the upper flue gas layer is mainly transferred to the sintered mixture by radiation. This heat radiation onto the sintered bed is absorbed only relatively little by the lower flue gas layer, since the latter, in particular because of its excess air, has only relatively little heat-absorbing components.

The terms "upper region" and "lower region" of the ignition furnace are not to be understood as limiting the fact that the gases supplied to the furnace must adhere to certain limits within the furnace volume. It is only essential for the invention that the flue gases fed into the upper region of the furnace heat in particular the furnace roof and the gas layers underneath to very high temperatures and that an atmosphere with an increased oxygen content is maintained above the sintered mixture. The transition between the two areas is necessarily fluid and depends on the details of the respective furnace design.

According to a preferred embodiment of the method according to the invention, the gases with increased oxygen content, which are fed to the lower region of the ignition furnace, consist at least partially of flue gases from a combustion with an air ratio λ equal to 2 to equal to 5. The air ratio; l gives the relation between that Burner actually supplied amount of free oxygen and the amount of free oxygen necessary for stoichiometric combustion. λ = 1 corresponds to stoichiometric combustion, while a larger 1 leads to a flue gas with a corresponding rest of free oxygen. This flue gas then has an increased oxygen content in the desired manner and, as practical tests have shown, when using the limits according to the invention between λ equal to 2 and λ equal to 5, the temperature is also so high that uniform and rapid ignition of the sintered mixture is ensured .

Similar to one of the known methods, according to a preferred embodiment, with the method according to the invention, more flue gases from the approximately stoichiometrically operated burners can be supplied in the entrance area of the ignition furnace, and more of the gases with increased oxygen content in the exit area. This measure is based on the knowledge that particularly high temperatures and relatively little oxygen are required to ignite the top layer in the entrance area of the furnace, while as the ignition process progresses, the burning layer gradually propagates deeper into the sintered bed, thereby preheating the material considerably deeper layers of the sintered mixture is reached. That is why less heat is useful in the rear area of the ignition furnace, but a slightly higher proportion of oxygen makes sense. However, the essential difference from the known method in this embodiment is also that in the entire region of the ignition furnace there is a layer of gases with an increased proportion of free oxygen, preferably at least about 5%, above the sintered mixture.

In principle, the gases in the method according to the invention can be supplied to the different furnace areas in different ways. For example, the stoichiometrically operated burners can be installed in the upper region of the furnace, for example on the side and end walls, and can be operated at a relatively low outflow speed in order to generate the desired hot and low-oxygen atmosphere in the upper region of the furnace. Similarly, nozzles or burners operated with an over-stoichiometric gas mixture can be provided in the side walls or in the end walls of the ignition furnace and serve to supply the gases with an increased oxygen content. However, it is not necessary for the nozzles or burners to be arranged in the furnace area in which they are to act. Rather, the burners or nozzles themselves can also be arranged elsewhere and only the gases emerging from them can be directed in such a way that the desired furnace atmosphere is achieved. Some special arrangements of the burners and nozzles, which have particular advantages, are the subject of further preferred embodiments of the invention.

In the event that an existing ignition furnace is already equipped with so-called side burners, that is burners which are arranged in the side wall of the furnace, which are operated approximately stoichiometrically at least in the entrance area of the furnace and whose flue gases are guided approximately horizontally in parallel flow to the center of the furnace , it is preferably proposed that the gases with increased oxygen content emerge from nozzles which are located below the approximately stoichiometric burner and in the longitudinal direction between these in the Side wall of the furnace are arranged and from which the gases with increased oxygen content are fed horizontally or inclined to the sintered mixture. Such a measure allows the advantages of the method according to the invention to be used with relatively little investment, even in existing systems with side burners.

A particularly simple design of the ignition furnace and a particularly good uniformity of the ignition process are achieved according to a particularly preferred method proposal if the flue gases from the approximately stoichiometrically operated burners and the gases with increased oxygen content from opposite side walls or, which is particularly advantageous in the case of stoves which are not too long is to emerge from the opposite end walls of the furnace. The flue gases from the approximately stoichiometrically operated burners should preferably be directed against the ceiling of the ignition furnace, specifically at an angle of up to 30 °, angles in the range from 5 to 10 having proven particularly advantageous. At the same time the gases with increased oxygen content to below a maximum angle of 50 °, preferably 20 to 35 ⁰ relative to the horizontal by directed at the bottom of the sinter mix to be. As a result of this counter-movement of the gas flows, there is an overall circulating flow in the ignition furnace, as will be explained in more detail elsewhere.

It is expressly emphasized that this circulating flow is also achieved when the two gas flows are each guided horizontally, but the flue gas stream from approximately stoichiometric combustion in the upper region of the furnace, in particular in the vicinity of the furnace roof, and the gas stream with increased oxygen content in the lower region of the furnace, in particular in the vicinity of the sintering mixture, are supplied. This embodiment also results in a circulating gas flow. An embodiment in which the angle with respect to the horizontal is 0 ⁰ for one or both gas flows is therefore expressly included in the embodiment described above.

According to another preferred method proposal, the flue gases from approximately stoichiometric combustion and possibly also the gases with an increased oxygen content are each supplied from the top of the furnace in such a way that the distribution of the furnace atmosphere according to the invention is achieved. The supply from the ceiling is particularly advantageous if a particularly long ignition furnace is used. As is known, the performance of an ignition furnace, that is to say the throughput of sintering mixture per unit of time, is directly dependent on the speed at which the sintering belt is operated. However, since the ignition process, i.e. the penetration of the burning layer of solid fuel, takes a certain time through the entire layer thickness of the sintered mixture, it is necessary that correspondingly long ignition ovens are used at high powers. In this case, the burner and nozzles are attached at the end, which is particularly advantageous for shorter ignition furnaces; disadvantageous in that it may not be uniform Flow can be maintained in a very long igniter. Burners mounted on the side can be disadvantageous insofar as the uniformity of the ignition across the width of the sintered belt is unsatisfactory. These disadvantages are eliminated by supplying the gases from the ceiling, in which case it is possible to adapt the dosage of both the flue gases from approximately stoichiometric combustion and the gases with an excess of oxygen over the entire length of the furnace to the respective process very precisely. This embodiment is also described in more detail in connection with a corresponding device.

To achieve the object specified above, it is proposed according to a further proposed method according to the invention that the sintered mixture is transported immediately after the ignition process taking place under the ignition furnace through a zone in which it is essentially shielded from the flue gases of the ignition furnace and from an oxygen-containing gas , in particular air, is flowed through, whereby it is largely insulated from the top against heat radiation.

This proposal according to the invention is to be used independently of the measures described above. It also leads to a significant improvement in ignition and considerable energy savings in conventional ignition furnaces. However, it is particularly advantageous if the two proposed methods according to the invention or the corresponding devices are used in combination.

By having the sinter mixture immediately afterwards leads to the actual ignition furnace in an area in which it is thermally well insulated upwards and at the same time an oxygen-containing gas, which is largely free of flue gases, flows through, the ignition process is improved in particular to the extent that the upper layers of the sinter mixture in this zone is well ignited.

To explain the advantages of this measure according to the invention, it must be pointed out that the entire sintering process takes place, for example, on a sintering belt that is more than 100 m long, with a typically about 10 to 15 m long ignition furnace located only over the first part. This distance is sufficient to ignite the top layer of the sinter mixture under the ignition furnace. The length of the sintered belt and the speed of its movement are then such that at the end of the sintered belt the burning layer has migrated from top to bottom through the entire thickness of the sintered mixture.

In the known processes, these conditions led to a disadvantage of the upper layers of the sintered mixture in that, in contrast to the lower layers, they were not subjected to a longer preheating process before they ignited. While the layers below are ignited relatively late on the sintering belt and have been warmed up by the hot smoke gases from the upper layers for a long time, the upper layers are ignited in an almost cold state. In order to achieve sufficient sintering of the uppermost layers, the addition of solid fuel to these uppermost layers was necessary in the known processes be coordinated. An excess of solid fuel was then available for the layers below, which was largely uselessly burned.

To improve this state, it was already known to use the extended ignition furnaces already mentioned at the outset, which are equipped with side burners and whose rear, outlet-side area serves as a heat treatment zone. The burners located there are operated with excess air and thus ensure that the sintered material is heated in this aftertreatment part, so that it is also possible to sinter the upper layers of the sintered mixture with a comparatively small amount of solid fuel.

In the context of the present invention, it has now been found that a sinter which is at least comparable in terms of the quality of the sintered material and the solid fuel used can be achieved with a considerably reduced expenditure of energy if the process measures described above are taken.

A corresponding device of the type described at the outset is characterized in that a thermal insulation hood directly adjoining the ignition furnace and having thermally insulating walls which is open at the bottom towards the sintering machine, the side and end walls of which extend up to the sintering mixture and the ceiling thereof Breakthroughs for sucking combustion air has been provided. The combustion air is sucked in, as usual in the known devices, through suction shafts under the grate car of the sintering belt and thus flows through the entire sinter mixture.

The combustion air can advantageously already be preheated in the process, that is to say in the course of any heat-releasing process steps of the same system. The cooling bed of the sintering machine, for example, is suitable for this. The finished sinter falls at the end of the sintering belt onto a sinter cooler through which air is sucked. This air is still heated up considerably, but in contrast to the air that has flowed through the sintering belt, contains very little flue gas, since there is no longer any combustion on the cooling bed. This preheated air is particularly suitable for use in the rest of the process. In particular, it can also be used advantageously as preheated combustion air for the burners in the ignition furnace.

The advantageous effect of using a thermal insulation hood is based essentially on the fact that the heat radiation from the surface of the sintered material to the environment in the area of the thermal insulation hood is largely prevented and is used in the heat exchange with the intake combustion air.

In the known types, including those with a so-called heat treatment part, the surface temperature of the sintered material after leaving the ignition furnace is still many 100 ° C. This means that after leaving the ignition furnace, heat is lost to a considerable extent through radiation, with the known harmful consequence that upper part of the sintered bed is poorly decreased. It is also an advantage that there is only air in the thermal insulation hood according to the invention which is not heavily contaminated by exhaust gases. This is advantageous for the propagation of the combustion in the areas below the surface.

It is further proposed that the openings in the ceiling of the thermal insulation hood are designed so that they consist of fixed parts and on up and down movable parts arranged above. The latter parts are made wider than the gaps between the fixed parts so that they overlap these gaps. As a result, there is no straight line connection between the sintered surface and the environment. With this design, the direct radiation of the heat from the surface of the sintered material to the environment is also prevented at the openings for the intake of the combustion air. This further reduces the heat loss of the surface of the sintered bed in the desired manner.

It is also possible to adjust the size of the openings for the combustion air. As a result, the pressure in the thermal insulation hood can be adjusted so that on the one hand the combustion air is sucked in essentially through the openings in the ceiling and thus a uniform flow distribution in the thermal insulation hood is produced, with only a small part of the air due to the inevitable leaks between sintered grate cars and thermal insulation hood and between the sintered bed and the outlet end wall of the thermal insulation hood. Doing so the opening should only be set as large as required.

• Fig. 1 einen erfindungsgemäßen Zündofen in prinzipieller Darstellung im Längsschnitt,
• Fig. 2 eine andere Ausführungsform eines erfindungsgemäßen Zündofens in prinzipieller Darstellung im Längsschnitt,
• Fig. 3 eine schematische Aufsicht auf die Decke eines Ofens nach Fig. 2 von unten,
• Fig. 4 einen Querschnitt durch eine erfindungsgemäße Thermoisolierhaube in schematischer Darstellung,
• Fig. 5 einen Längsschnitt durch eine Thermoisolierhaube gemäß Fig. 4.

The invention, in particular the proposed devices according to the invention, are explained in more detail below with reference to preferred embodiments shown in the drawing. Show it:

• 1 shows an ignition furnace according to the invention in a basic representation in longitudinal section,
• 2 shows another embodiment of an ignition furnace according to the invention in a basic illustration in longitudinal section,
• 3 is a schematic plan view of the ceiling of an oven according to FIG. 2 from below,
• 4 shows a cross section through a thermal insulation hood according to the invention in a schematic illustration,
• 5 shows a longitudinal section through a thermal insulation hood according to FIG. 4.

1 shows the upper edge 1 of a sintered mixture. The sintered mixture moves in a direction indicated by the arrow 2 at a speed corresponding to the respective process under an ignition furnace, which is provided with the reference number 3 in its entirety. The sintering mixture is located in a known manner on a sintering belt formed from grate wagons and has a thickness of usually about 40 cm. For the sake of clarity, these known details are not shown in the drawing.

The ignition furnace consists of a ceiling 9, an end wall 4 on the inlet side and an end wall 5 on the outlet side. The side walls in FIG. 1 run parallel to the plane of the paper and essentially perpendicular to the sintering belt along its edges. Overall, the ignition furnace 3 thus forms a hood-like closed space. The end walls 4 and 5, like the side walls not shown in the figure, are pulled down in a known manner to just above the surface of the sintering mixture 1. The ceiling 9 of the ignition furnace and also its walls are thermally insulated in a known manner. In the illustrated embodiment, a number of burners are arranged in the end walls 4 and 5, the burner axes of which are provided in the figure with the reference numerals 6 for the inlet-side burners and 7 for the outlet-side burners. The number of burners arranged on the respective side is determined by their performance, the width of the sintering belt and other factors and is not the subject of the invention. In any case, in the preferred embodiment shown, all the burners on the inlet side and all burners on the outlet side are aligned parallel in their axial direction and evenly distributed over the width of the respective end wall.

In the illustrated embodiment, as can be seen in the figure, the inlet-side burners are at an angle of 5 with respect to the horizontal Ignition 3 ceiling directed. The burners on the outlet side are oriented downwards against the surface of the sintered mixture at an angle of 30 ° with respect to the horizontal. This orientation of the respective burner rows on the inlet and outlet sides results in a circulation flow which is shown schematically in the drawing with the reference number 8.

It is essential to the invention that the inlet-side burners are operated with an approximately stoichiometric ratio of fuel and oxygen, while in the outlet-side burners the ratio of fuel and air is set such that an air ratio 2. greater than 1.3 is maintained. These air conditions are maintained in both rows of burners in a conventional manner with the aid of suitable valves and control devices, which are not shown in the figure, since they are not essential to the invention.

The formation of the flue gas roller in the ignition furnace is additionally improved in that, according to a preferred embodiment, the inlet-side burners are designed in a manner known per se in a short-flame design, while the outlet-side burners are designed in a long-flame design.

In the embodiment shown in the drawing, the outlet-side end wall 5 is oriented perpendicular to the associated burner axis 7. This is particularly advantageous in the case of larger inclinations of the burner axis, in order to allow the burner to be easily attached to the respective one Wall and enable a clear guidance of the flue gases.

This preferred design offers the following advantages: It is avoided that the flue gas flow caused by the burner jets forms a jam in the middle of the furnace 3 and, as a result, heated particles of the sintered bed 1 are whirled up and annoying caking occurs. Rather, both the inlet-side and the outlet-side burners act in such a way that a rotating flue gas roller 8 is formed in the ignition furnace 3, the direction of rotation of which is maintained in the same direction by both rows of burners. This roller 8 causes the hot flue gases generated by stoichiometric combustion of the inlet-side burners to flow along the ceiling 9 of the ignition furnace 3 from the inlet side to the outlet side, and their heat at the prevailing temperatures predominantly by direct radiation to the sintering mixture 1 and by indirect radiation also delivered to the sintering mixture 1 via the radiation heating of the blanket 9. It is thus avoided that the individual burner jets are directed onto the sintered bed 1, which causes the described unevenness in the heating. Rather, the heat transfer takes place in the manner described essentially by the heat radiation of the entire gases and the furnace roof 9 in the upper part of the ignition furnace 3, whereby the uniformity of the heating is ensured.

Furthermore, it is advantageous that any irregularities in the heating, which are transverse to the transport direction of the sintering machine occur, can be compensated for by different loading of the burners arranged side by side in the end wall. If it is shown, for example, that the two outer edges of the strip are not heated enough, the two outer burners in the end wall can accordingly be subjected to a greater load.

The solution according to the invention thus combines the advantage of uniform heating by radiant heat transfer from the upper furnace area with the possibility of influencing the heat applied to the parts lying next to one another in the direction of transport. This is important because it is not only necessary to produce a uniform sintered good that the entire sintered bed 1 is heated uniformly, but because it is additionally necessary to adapt the heating to the possible differences in the heat requirements of the different parts of the sintered bed lying next to one another in the transport direction . In the case of the burners on the outlet side, which are inclined downwards in a manner known per se and are operated with excess air, there is no risk of uneven heating. Since these burners are operated with a higher excess of air, the excess temperature of the flue gases compared to the surface temperature of the sintered bed 1 is only slight in this area, so that there is essentially no further reference by these burners. Rather, the function of these burners is to provide hot gases with an increased oxygen content, which are required for the reaction with the solid fuel of the sintered mixture. It is particularly important that the flue gas described roll in the ignition furnace causes the stratification of two flue gas streams one above the other. The upper layer of the hot stoichiometric flue gases emanating from the inlet-side burners causes the sintered bed to be heated by radiation, the heat flow density and the temperature decreasing as a result of the heat quantities transferred from the inlet side to the outlet side. In contrast, the lower flow of less hot but oxygen-rich gases emanating from the outlet-side burners serves to provide the oxygen required for the reaction of the solid fuel. The heat radiation from the upper flue gas layer onto the sintered bed is absorbed only relatively little by the lower flue gas layer, since the latter has flue gas components which absorb relatively little heat radiation, in particular because of its high excess of air. The particular advantage of this preferred type of construction is therefore that a high and uniform heat flow density is provided for the ignition and at the same time the oxygen required for the combustion of the solid fuel is supplied at a temperature. A quick and even ignition is thus brought about by making appropriately heated combustion air available. After the first ignition process of the surface, the temperature and thus the sintering of the top layer of the sintered bed is further improved. This avoids the disadvantageous effect in the known types that the sintering of the top layer remains imperfect. Since the top layer can also be used as a finished sinter, the throughput of the system and the specific heat are thereby reduced consumption per ton of finished sinter reduced.

In principle, the last-mentioned advantages can also be achieved with the aid of other devices in which the method steps described above are observed. In this respect, the preferred embodiments of devices for carrying out the method according to the invention described here are only to be understood as examples of particularly preferred embodiments which, depending on the given requirements, lead to particularly advantageous results.

Another such preferred embodiment is shown in FIGS. 2 and 3. Those components which correspond to the previously described embodiment are identified by the same reference numerals, provided with an additional line.

The essential peculiarity of the device shown in FIGS. 2 and 3 is that both the burners for supplying the flue gases from approximately stoichiometric combustion, and the nozzles for supplying the gases with increased oxygen content are passed through the roof of the furnace. You can see ceiling burners 10, ceiling nozzles of long type 11 and ceiling nozzles of short type 12.

The ceiling burners 10 are preferably designed as so-called ceiling radiation burners. This type of burner known per se is distinguished by the fact that the media (fuel and air) leave the burner with a certain swirl due to the shape of the burner nozzles.

The streamlines of the media spiral outwards and outwards after leaving the burner. This creates a short flame on the one hand and a suction in the center of the burner, on the other, through which the media or flue gases are drawn upwards in the center of the spiral. The basic shape of the streamlines is shown in FIG. 2 insofar as it can be seen in the cross section.

It is essential that a very short flame and a strong heating of the surroundings of the burner is achieved with this type of burner. The heat is emitted essentially by radiation from the flue gases and the furnace ceiling 9 'heated by the burners.

In the embodiment shown, nozzles 11 and 12, which are preferably designed as parallel flow nozzles, serve to supply the gases with an increased oxygen content. Depending on the application, these consist of a tube for air or another oxygen-containing gas mixture or of concentric tubes for fuel and air. They have a smooth surface and overall are designed in such a way that the media emerge at the end of the nozzles relatively slowly and in a laminar flow, so that an elongated flow path is reached towards the surface of the sintered mixture. The nozzles are preferably designed as longer tubes 11 or shorter tubes 12, the longer tubes being more suitable for guiding the gases with increased oxygen content without great mixing with the flue gases from the ceiling burners in the vicinity of the sinter mixture. On the other hand, the pipes must not be made to be of any length, because otherwise they would be subject to increased wear subject to. The determination of the length and design of these nozzle tubes depends on the individual case and is readily accessible to any person skilled in the art, it being only important that the stratification of the gases according to the invention is achieved in the ignition furnace in this case as well.

Fig. 3 clearly shows that the ceiling radiation burner 10 and the ceiling nozzles 11 and 12 are arranged in a checkerboard manner and offset from one another in such a way that the ceiling nozzles 11, 12 are each centered in the fields which are formed by the ceiling radiation burners as end points. Such a uniformly alternating distribution of the ceiling nozzles and ceiling radiation burners results in a particularly uniform ignition of the surface of the sintering mixture.

The individual rows of burners arranged one behind the other in the direction of movement of the sintering belt can also be acted upon with different amounts of fuel and air, for example in such a way that the flow rates that are passed decrease towards the outlet side. However, the distance between the rows of burners can of course also be varied accordingly.

As already described above, an embodiment with flue gases or gases with an increased oxygen content that are supplied through the roof of the furnace is particularly advantageous for long ignition furnaces, where such an embodiment also enables a particularly precise adjustment of the temperature distribution both over the width of the sintering belt and in particular over the length of the igniter allowed. A preferred variant of the device according to the invention is characterized in that there are tubes for supplying the gases with an increased oxygen content, which extend between the side walls of the ignition furnace. These tubes have nozzles, from which the gases exit essentially downwards, be it obliquely or directly vertically. In special applications, horizontal gas routing from the pipes can also be useful. It also makes sense under certain application conditions not to run the pipes continuously from one side wall to another, but only to let a certain part protrude into the furnace chamber from one side or end wall.

4 and 5 schematically show in cross-section or longitudinal section a thermal insulation hood according to the invention, which is provided in its entirety with the reference number 20.

As can be seen from FIG. 5, the sintering belt moves under the thermal insulation hood in the direction of arrow 21. The essential parts of the sintering belt are shown in dashed lines. These are the grate wagons 22 that roll on the rails 26 with wheels 24. Also shown in dashed lines is the outlet end 28 of an ignition furnace. This ignition furnace can be of conventional design. However, an oven according to the invention, as described above, is particularly preferably used.

The thermal insulation hood 20 has two end walls 30 and 32, one composed of a plurality of side wall elements 34 Side wall 36 and a ceiling 38.

The blanket 38 consists of fixed parts 40 and parts 42 that can be moved up and down. As can be seen from FIG. 4, the parts 42 that move up and down are horizontally larger than the gaps between the fixed parts 40. The moving parts 42 thus overlap the fixed parts 40. All walls 30, 32, 36 and 38 of the thermal insulation hood 20 are thermally insulated in a known manner. The overlapping construction of the ceiling elements 40 and 42 ensures that the heat losses under the thermal insulation hood, insofar as they arise from radiation, are largely prevented even when the openings 44 in the ceiling 38 are open.

The thermal insulation hood thus provides good thermal insulation above the sintering mixture located in the grate carriage 22. Under the grate car are the intake ducts, not shown in the drawing, so that oxygen-containing gases, in particular air, are drawn in through the sintered mixture. This air can penetrate into the thermal insulation hood 20 through the openings 44. Depending on the conditions of the system in question, this air can already be preheated in the process. In any case, the thermal insulation hood allows the creation of a controlled and thermally insulated atmosphere in the area of a sintering machine immediately adjacent to the ignition furnace. It has been found that the ignition of the surface of the sintering mixture can be decisively improved by this measure or the fuel expenditure required for this can be considerably reduced.

The construction used to adjust the thermal insulation hood according to the invention is shown only schematically in FIGS. 4 and 5. It consists essentially of a frame 46, from which a common support beam 50 for the various movable ceiling elements 42 is suspended via cables 48. The cable 48 is guided by support rollers 52 and deflection rollers 54 which are fastened to the frame 46. A winch 56, shown schematically, is provided for driving the cable 48. This winch 56 can be controlled in such a way that the movable elements 42 can be brought into any desired distance from the fixed elements 40 of the ceiling 38 and can be locked there.

The fixed elements 40 of the ceiling 38 as well as the end walls 30 and 32 and the elements 34 of the side walls 36 are fastened in a stationary manner above the sintering belt by a construction familiar to the person skilled in the art and not shown in detail in the figures. It is important that the side and end walls extend close to the sintered mixture so that the space below the thermal insulation hood 20 is largely closed.

• Eine konventionelle Anlage hatte einen Zündofen mit zwei stirnseitig angeordneten Brennerreihen mit jeweils neun Brennern, die schräg nach unten auf der einlaufseitigen und auslaufseitigen Seite jeweils gegen das Sintergemisch gerichtet waren. Diese dem Stand der Technik entsprechende Anlage wurde dann umgebaut: Anstelle des vorhandenen Zündofens trat ein Zündofen gemäß Fig. 1 und eine anschließende Thermoisolierhaube gemäß Fig. 4 und 5. Durch die erfindungsgemäßen Maßnahmen konnte der Gasverbrauch der Anlage von 27,4 Normalkubikmeter pro Tonne Fertigsinter (m3/t) auf 13,1 m_n ³/t gesenkt werden. Der Koksverbrauch verminderte sich von 61,0 kg/t Fertigsinter auf 47,7 kg/t. Die Untersuchung des erhaltenen Fertigsinters zeigte, daß dessen Qualitätsmerkmale trotz des erheblich verminderten Energieaufwandes mindestens gleich, in einigen wesentlichen Punkten, beispielsweise der Festigkeit des Sinters, sogar verbessert waren.

Practical experience has shown that with a sintering plant which is operated according to the method and device according to the invention, higher performance, a qualitatively improved sintering and considerable energy savings can be achieved. An example of this is given below:

• A conventional system had an ignition furnace with two rows of burners arranged on the front side, each with nine burners, sloping downwards on the inlet side and the outlet side were each directed against the sintered mixture. This state-of-the-art system was then rebuilt: Instead of the existing ignition furnace, an ignition furnace according to FIG. 1 and a subsequent thermal insulation hood according to FIGS. 4 and 5 were used (m3 / t) can be reduced to 13.1 m _n ³ / t. Coke consumption decreased from 61.0 kg / t finished sinter to 47.7 kg / t. Examination of the finished sinter obtained showed that, despite the considerably reduced energy expenditure, its quality characteristics were at least the same, in some essential points, for example the strength of the sinter, even improved.

Claims (19)

1. A method for igniting a sintering mixture consisting of a solid fuel and a sintering material, in particular a sintering oil mixture, on a sintering machine, in which the sintering mixture is passed under an ignition furnace with closed end and side walls and a closed ceiling, in the ignition furnace hot flue gases are generated above the sintered material and these hot flue gases heat and ignite the surface of the sintered material by radiation and convection, characterized in that flue gases from one or more approximately stoichiometrically operated burners are fed into the upper region of the ignition furnace and that. in the lower ones Area gases are supplied with an increased proportion of oxygen, such that there is an oven atmosphere which is hotter and less oxygen in the upper area of the ignition hood, cooler and oxygen-rich in the lower area. 2. The method according to claim 1, characterized in that the gases fed into the lower region contain more than 5% free oxygen. 3. The method according to claim 2, characterized in that the gases fed into the lower region include flue gases from a combustion with an air ratio between 2 and 5. 4. The method according to any one of the preceding claims, characterized in that more of the flue gases from approximately stoichiometrically operated burners in the entrance area of the ignition furnace, more of the gases with increased oxygen content are supplied in the exit area. 5. The method according to any one of the preceding claims, in which the flue gases produced by approximately stoichiometrically operated burners are guided approximately horizontally in parallel flow from the side walls of the ignition furnace, characterized in that the gases with increased oxygen content from below the approximately stoichiometrically operated burner and in particular nozzles arranged between them are fed horizontally or inclined to the sintered mixture. 6. The method according to any one of the preceding claims, characterized in that the flue gases emerging from the approximately stoichiometrically operated burners at an angle of at most 30 ⁰ , preferably 5 - 10 °, with respect to the horizontal from a side or end wall against the ceiling the ignition furnace are directed so that they brush against the cover of the ignition furnace and that the gases with increased oxygen content from the opposite side and end wall forth at an angle of at most 50 °, preferably 20 - 35 ⁰ relative to the horizontal downwards against the sintered mixture are directed so that they sweep over the sintered mixture and overall there is a circulating gas flow in the ignition furnace. 7. The method according to any one of the preceding claims, characterized in that the flue gases fed into the upper region of the furnace from the approximately stoichiometrically operated burners are supplied from the ceiling of the ignition furnace in such a way that they spread essentially only in the upper part of the ignition furnace and that the gases fed into the lower part of the ignition furnace are supplied with increased oxygen content from the roof of the ignition furnace in such a way that they spread essentially in the lower region of the ignition furnace and over the sintered mixture. 8. The method according to claim 7, characterized in that the flue gases supplied from the ceiling of the ignition furnace from approximately stoichiometrically operated burners are arranged in a manner known per se in the ceiling of the ignition furnace with a vertical axis by a corresponding swirl of the media in the burner are fed in such a way that the media (fuel and air) first move downwards from the burner in a helical movement with a hollow core and then flow back up to the burner axis to a considerable extent centrally along the burner axis and are thus recirculated, the Tangential and axial speeds of the media in the burner are so great in a manner known per se that the resulting circulation flows essentially only fill the upper two thirds of the clear height between the sintered bed and the top of the ignition furnace and that the gases with increased oxygen content come out through the ceiling passed through n nozzles in a manner known per se as Paral Oil flows with approximately vertical flow direction at a low speed (approx. 5 - 30 m / sec.) are blown in downwards, so that they spread out in the lower part of the ignition furnace and, on the way from the ceiling to the lower part of the ignition furnace, relatively little smoke gases of the approximately stoichiometric combustion. 9. A method for igniting a sintering mixture consisting of a solid fuel and a sintering material, in particular a sintering oil mixture, on a sintering machine, in which the sintering mixture is passed under an ignition furnace with closed front and side walls and a closed ceiling, in which the ignition furnace is called Flue gases are generated above the sintered material and these hot flue gases heat and ignite the surface of the sintered material by radiation and convection, characterized in that the sintered mixture is transported immediately after the ignition process taking place under the ignition furnace through a zone in which it is separated from the flue gases of the Ignition furnace is essentially shielded and is flowed through by an oxygen-containing gas, in particular air, whereby it is largely isolated from the top against heat radiation. 10. An apparatus for performing the method according to one of claims 1 to 9, with a downwardly open ignition furnace (3) with two end walls (4, 5), two side walls and a ceiling (9) and with one below it essentially horizontally in the direction the connecting line between the end walls of the movable sintered belt for receiving a sintered mixture (1), the end walls (4, 5) and the side walls being pulled down as close as possible to the sintered mixture, so that a hood-like ignition chamber is largely closed off from the outside atmosphere, characterized in that on the inlet-side end wall ( 4) burners (6) are arranged horizontally or with an inclination of up to 30 ° with respect to the horizontal to the ignition furnace ceiling, and on the outlet-side end wall (5) burners (7) are arranged with an inclination with respect to the horizontal to the material surface of up to 50 ° are, the inlet-side burners are operated approximately stoichiometrically, the outlet-side burners, however, with an air ratio λ greater than 1.3. 11. The device according to claim 10, characterized in that the end walls (4, 5) each extend approximately perpendicular to the burner axis of the burners arranged in them (6, 7). 12. Device according to one of claims 10 or 11, characterized in that the inlet-side burner (6) in a short-flame design known per se, the outlet-side burner (7) are designed in a long-flame design known per se. 13. Device for performing the method according to one of claims 1 to 9, with a downwardly open ignition furnace with two end walls (5 ', 6'), two side walls and a ceiling (9 ') and with one below it essentially horizontally in the direction the connection Line between the end walls movable sintering tape for receiving a sintering mixture (1 '), the end walls and the side walls being pulled down to just above the sintering mixture, so that a hood-like ignition furnace space is formed which is largely sealed off from the outside atmosphere, characterized in that in the ceiling ( 9 ') of the ignition furnace known ceiling burner (10) are arranged, the supply line for fuel and air have actuators that allow adjustment or control to an air ratio λ et wa equal to 1 that the ceiling burner (10) uniform, checkerboard and are arranged offset with respect to one another in the longitudinal direction of the ignition hood, that nozzles (11, 12) with a vertical axis are arranged in the ceiling for supplying the gases with increased oxygen content, said nozzles consisting of a tube for air or concentric tubes for fuel and air as parallel flow nozzles, that the cross sections of these tubes for air and fuel gases are so good are that air and fuel gases at a speed of about 5 - 30 m / sec. emerge and that the nozzles (11, 12) are each centered in the fields which are formed by the ceiling radiant burners (10) as corner points. 14. The apparatus according to claim 13, characterized in that the nozzles (11, 12) for supplying the gas with increased oxygen content are designed as tubes which are guided with a vertical axis through the ceiling (9 ') into the cavity of the ignition furnace. 15. Device according to one of claims 10 to 14, characterized in that for supplying the gases with an increased oxygen content, tubes protrude horizontally from the side walls of the ignition furnace into the lower region thereof, which are provided with obliquely or vertically downwardly directed nozzles. 16. An apparatus for performing the method according to one of claims 1 to 8 with a downwardly open ignition furnace (3) with two end walls (4, 5), two side walls and a ceiling (9) and with one below it substantially horizontally in the direction of Connection line between the end walls of a movable sintering belt for receiving a sintering mixture (1), the end walls and the side walls being pulled down to close to the sintering mixture (1), so that a hood-like ignition furnace space is formed, which is largely closed off from the outside atmosphere, characterized by an immediately the ignition furnace is connected to a thermal insulation hood (20) with thermally insulating walls (30, 32, 36, 38), which is open at the bottom towards the sintering machine, the side (36) and end walls (30, 32) of which extend close to the sintered mixture and whose ceiling (38) has openings (44) for sucking in combustion air. 17. The apparatus according to claim 16, characterized in that the size of the openings (44) for the combustion air is adjustable. 18. Device according to one of claims 16 or 17, characterized in that the ceiling consists of fixed parts (40) which extend in the longitudinal direction of the hood and consists of up and down movable parts (42) which are larger in area than the gaps between the fixed parts (40) so that they overlap the fixed parts and which are suspended on an up and down movable support (50) are substantially vertically movable. 19. Device according to one of claims 16 to 18, characterized in that the thermal insulation hood (20) is divided into a number of individual segments, so that their length can be varied according to the requirements.

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