SI9400073A - Introduction of pulverulent additives into the furnance - Google Patents

Abstract

A method for introducing pulverulent matter into a cupola or a blast furnace is proposed. The introduction takes place in the flue gases or in the oxidising gas feed tuyeres. It is the granules themselves that form the sealing between the pressurised zone and the outside. An alternative form has no moving component in contact with the granules, another one employs an endless screw rotating in a pipe. The method is suited in particular to the reintroduction into the feed tuyeres of dust collected in the flue gases and to the introduction of pulverulent matter into the flue gases. <IMAGE>

Description

The invention relates to industrial furnaces, and in particular to domes or blast furnaces, whose internal atmosphere and gas supply pipes are usually at a different pressure than the ambient pressure, and to which substances in powder form are to be added.

There are several industrial processes for hot processing of fuel-based raw material products, such as e.g. coke mixed with raw material. In this case, the combustion gas, air and / or oxygen is introduced under pressure at one end of the furnace by means of supply pipes, while the flue gas is extracted at the other end. It is often required to add to the furnace certain components that are used to process the substance, either by supplying it with pressurized gas or by introducing a counterflow into the flue gas, but in each the case prevents the inner atmosphere from coming into contact with the outside atmosphere.

Thus, e.g. in the manufacture of rock wool from raw materials based on blast furnace slag and basalt rock and melted in the dome, it is added to the powder form by adding them to the mixture to be glazed.

These processes for making rock wool from high melting point substances are more commonly known as free centrifugation. In this case, the substance to be drawn into the fibers is melted to the circumference of three or four centrifugal rings in a horizontal axis, arranged side by side, so that the substance is poured into the first ring to accelerate and give off the next ring. Each ring converts a portion of the molten substance into fibers and transfers the excess to the next ring.

The substance is usually melted in cupola-type furnaces used in foundries. The domes, which are generally cylindrical in shape and have a vertical axis, are filled by the top with successively alternating layers of fuel, which is generally coke, and the substance to be drawn into the fibers. The combustion area is located in the lower part of the dome near the inlet pipes through which the combustion gas, which is generally air, is blown but which can be optionally enriched with oxygen. The heat released by combustion permits the melting of the substance to be drawn into the fibers and which escapes through the casting openings, which are arranged at a slightly lower level than the level of the supply pipes. Finally, cast iron residues are collected at the bottom of the dome, which is obtained from both the clumps involved in the slag and by reducing the iron oxides in the remainder of the charge. Although cast iron of highest density is naturally eliminated from the substance to be pulled into the fibers in the molten state, the casting opening must be at the highest possible level to prevent the leakage of small amounts of cast iron, which would result in rapid wear of the centrifugal rings .

These melting fences have many advantages, given the very high production of molten products and the low cost of energy for this smelting. In a fence of this type, the rock melts relatively slowly and it must be ensured that combustion gases and combustion gases can circulate very easily in the melting range and, above all, that they can escape towards the chimney. For this reason, the filling should not be too compacted, as otherwise the pressure in the melting area would increase and there would be increased turbulence in the casting area. For this reason, the filling of the raw material is preferably introduced in extruded form, e.g. cylindrical blocks or briquettes.

The process of this type for preparing briquette filling is well known e.g. additionally, these briquettes have the advantage that they preferably consist of products obtained from powders in flue gases, molten products and waste fibers that can be reintroduced into the dome. The process also makes it possible to adjust the composition of the raw materials. However, in the case of products obtained from flue gases, it is relatively difficult to collect them, store them after cooling and transport them at the site of briquette production. Furthermore, the manufacture of briquettes consisting of agglomerating a powder-like substance through a binder is expensive. It would be advantageous to be able to recycle directly on site, which would further save energy in the case of flue-gas powders, avoiding the need to re-heat the powders.

Similarly, in blast furnaces, the process of introducing powder coke and transporting it with combustion gas is known.

Existing processes for crushing crushed coke powder are divided into two main groups, one using additional carrier gas and the other using the Venturi effect. In both groups there is a problem of controlling the amount of powdery substances that have been introduced into each supply pipe. In these two groups of processes, the problems are related to the fact that the amount of powder introduced depends very much on the conditions of the carrier gas flow in the inlet pipes and downstream relative to them in the furnace itself.

It is an object of the invention to provide a process that allows the introduction of certain quantities of powdered matter into a reactor in which solids and gases are processed, such as e.g. furnace for the processing of molten materials, cast iron or glassware, and in particular with furnace gases such as domes or blast furnaces.

In particular, the invention must enable this injection to be carried out at flows independent of the conditions of use of the furnace, such as the gas pressure at the outlet or the gas pressure or velocity at the inlet pipes.

Among the documents that propose procedures for introducing powders into blast furnaces, most suggest introducing powders into combustion gas inlet pipes, e.g. U.S. Patent No. 5,133,632, in which coal dust is stored in silos to be distributed into inlet pipes by means of a distributor that distributes the powder stream uniformly between the conduits leading to each inlet pipe. The document proposes to maintain a constant pressure in each of the ducts by means of additional gas, so that the flow remains constant at the opening of each supply pipe, despite changes in the pressure (and temperature) in the furnace.

Another document, US 5 070 797, proposes that a Venturi system be used to inject various components in powder form, especially coal, into the combustion air of the dome in the supply pipe. The system comprises a pressurized air circuit which narrows and then expands and the injection of powder near the narrowest point. U.S. Patent 5 070 597 also includes a pressure balancing system so that the flow is independent of the pressure fluctuations that can occur in the dome. Substances that are intended to be introduced into the furnace by the means described are as different from the starting by-products as from the powders obtained during the filtration of the dome flue gas.

Known means for introducing powdered matter into a dome or blast furnace require additional systems to provide a certain flow. These systems are relatively complex because they require the detection of changes in pressure in the inlet pipes so that variations in flow rates can be offset.

The object of the invention is a process for introducing a substance into a reactor gas, such as a blast furnace or a dome, in which the substances are in powder form and where the substances in powder form themselves in a compacted joint form a seal between the area to which they are to be brought and the outside. Preferably, the induction is carried out in the inlet pipes of the combustion gas reactor or in the gases obtained from the reactor as they are directed towards the outlet.

This process thus allows granular matter to be introduced into areas where the gases are normally pressurized and / or dangerous and where it is therefore essential to prevent any gas exchange between the inside and outside of the reactor.

According to the invention, the process is used for the introduction of raw materials into the reactor and for recycling in the reactor of endogenous or exogenous waste, if necessary, after crushing or cutting, as well as for recycling in the reactor of powders obtained from the gases generated in the reactor and in the case of the manufacture of fibrous products for recycling in a reactor which have not been pulled into the fibers.

When used in this way, the process according to the invention enables the direct use of raw materials in powder form or the direct recycling of most different substances.

The invention also proposes a device for carrying out a process comprising a tube which feeds the substances to be injected into the powder form and which creates a stopper the thickness of which prevents the passage of gases. Alternatively, the powder-carrying tube exits into the reactor area through which the gases pass before they escape, and in this case the pipe exits into the area through which the combustion gases exiting the dome or the blast furnace pass through. the filter device to subsequently reach the flue gas outlet, and the filter device preferably consists of the raw materials themselves through which the exhaust gases must pass before they exit, or the tube carrying the powdered substance is discharged into the reactor gas inlet and especially in the dome or blast tube for air or oxygen supply.

The tube conveying the powdered substance to form the basis of the device according to the invention is advantageously either an Archimedean screw or a vertical windmill filled with powdery materials to a minimum level and with which the bottom is sealed. Alternatively, the bottom of the tube is sealed with a shut-off valve, which is controlled by maintaining the thickness of the stopper material in powder form greater than the minimum value, or by lowering the bottom as a knee, and maintaining the vibrator in the lower part of the tube at a certain level therein.

It may be found that the preparations provided for carrying out the process of the invention are very simple and inexpensive.

The methods according to the invention allow the influx of the introduction of a substance in powder form into gases to be controlled, either in the case of input of raw materials or exogenous waste with a flow selected in accordance with the manufacturing parameters or in the case of direct recycling of endogenous waste with full instantaneous input waste. However, the inlet flow is always independent of the pressure conditions in the reactor.

The following description and drawings will allow the invention to develop.

Figure 1 is a particle cupola with particles added to the flue gas, Figure 2 is an archimede screw-type intake device, Figure 3 is a device for re-introducing flue-gas powders into the combustion gas inlets, and Figures 4 and 5 of the apparatus using a vertical windmill.

In the manufacture of rock wool, the raw materials are essentially introduced in the form of blocks, which may be natural in the case of fragmented basalt rocks or obtained from pre-treatment, such as e.g. coke or slag, a by-product of cast iron production, or in the form of briquettes, mainly created by the reintroduction of waste and the adjustment of composition. For various reasons, it is advantageous to inject certain components of the mixture directly into powder form. These are, first, substances that are made on site, such as those that have not been pulled into fibers, i.e. grains of substances ejected from centrifuges that could not be formed into fibers, or, in particular, solid residues ejected from the dome and carried away by the flue gases. These latter are compound mixtures of powder and coke. Thus, the product can be adjusted directly because its composition is only slightly different from the composition of the substances that have been introduced into the furnace. In addition, its temperature is high and its direct return saves the heat that would be required to reheat it. It is also required to introduce raw materials in powder form in order to fine-tune the composition of the substance to be processed in the dome. The introduction of wastes of external origin, which are fragmented to powder form, also works favorably.

Figure 1 shows the upper part of the dome in which the glassy material is processed to allow stone wool to be produced by centrifugation.

is the body of the actual dome with its double wall, in which the cooling water 52 circulates. This dome was adapted to introduce the device according to the invention. Typically, the parts marked 53 and 54 do not exist and the filler funnel 55 and the conduit 56 which discharge the flue gases to the cyclone dust trap and to the chimney not shown are both positioned below, i.e., the filler funnel 55 at the upper opening of the cupola furnace at 57 and 56 on wall 58 at the same level as conduit 54 resulting from device 63. The parts added to the conventional cupola are a tube 53 filled with the feedstock 59 and a device 54 for supplying the substance to powder form. This adaptation of the dome made it possible to create a balancing area 60 through which the flue gas passes before being drawn between the outer tube 53 and the inner tube 61, which forms an extension of the hopper 55. In normal operation, the pressure in the balancing area is low, that is, about 1000 Pa.

According to the invention, powdered form substances are introduced into this field. The device according to the invention must:

* allow powders or grains to be introduced in controlled quantities, * prevent them from being drawn along with the flue gases, * prevent flue gas from exiting through the inlet 62 for powders or grains.

The first and third functions are fulfilled by producing 63 upstream of line 54, and the second function is filled with a filter that traps the particles 64 that have just been introduced, allowing them to reach the raw materials 59. A filter of this type is required, because without it, the particles 64 would be taken directly to the flue gas outlet (and most of them would be recovered in a cyclone dust trap located between the gas outlet and the chimney).

In the figure, the filter consists of an assembly of raw materials 59 consisting of pieces or briquettes, which is located between the lower portion 65 of the balancing area 60 and the gas outlet 66 between the two pipes 53 and 61. This distance is sufficiently long and difficult to the particles 64 stop, of course, if they are not subtle, so that they begin to move along with the rest of the mixture. Very fine particles, such as powders collected in the flue gas by means of a cyclone dust trap downstream of the outlet duct 56, would be to go the same route again and in the same direction that they already went between the pieces. . The experimental conditions make it possible to determine the lower limit of particle size to be input at this level.

Apparatus 63 according to the invention comprises a tube in which the powdered substances themselves, in the compacted state, form a stopper between the area to be fed and the outside.

Figure 2 shows an embodiment of a preparation of this type involving an Archimedean screw.

The picture shows a 140 mm diameter pipe, which includes a straight part 30 and a knee 31. On the axis of the straight part there is a snail 34, which is rotated by an adjustable bearing, which is not shown. The side hopper 32 is positioned upstream of the top of the pipe 30 and allows the screw 33 to be fed to the screw 33 driven in the left-hand picture. The inclination of the pipe 30 with respect to the horizontal is not a determining factor. The function of the moving screw 34 is that it forms a stopper 35 from substances that fill the tube 30 completely over the length (thickness of the stopper), e.g. about 20 cm. This length may vary according to the nature and consistency of the substances to be introduced. It is required that it be sufficient that the stopper 35 forms a seal between the downstream portion where the pressure is e.g. about 1000 Pa, and the upper part where there is generally atmospheric pressure. The thickness of the stopper 35 will be greater, for example, if the shredded glass wool is to be introduced than the powdered raw materials.

The snail preparation works very flexibly. In fact, it is sufficient for the distance available between the end 36 of the bolt 34 and the tube 31 to be greater than or equal to the thickness of the stopper necessary to prevent the downstream gases from returning upwards, and the system then operates independently of the rate of introduction of the substance into the hopper 32 and / or the rotation of the snail.

The preparation as shown in Figures 1 and 2 is used to recycle the waste obtained during the production of stone wool, e.g. by the free-spin method described above.

Following this process, any molten glassy substance created by the dome is not converted to fibers. A significant proportion is in the form of substances that have not been pulled into the fibers (droplets), that is, solids, which, in contrast to the fibers which are laterally pushed by the jet of air, fall under the machine and pull some fibers with them. Typically, this waste is agglomerated into briquettes and then re-introduced into the dome together with the raw materials.

The process according to the invention allows this waste to be reintroduced in practice at the same place as the briquettes without having to be converted or even stored. The experiments were able to determine the percentages by weight of about 10% of the recycled droplets relative to the total raw materials using only one preparation.

The invention allows not only the introduction of powdered matter into an area such as the balancing area 60 in Figure 1, where the pressures are low, but also to areas where the pressure is high, such as combustion gas inlets where it can reach 7000 or 8000 Well, or even more.

Figure 3 shows a conventional embodiment of a turret 1 having its double wall 2 cooled by the circulation of water, its filling opening 3 at a normal level, two of its oxygen supply pipes 4, 5 through which oxygen is supplied, its extractor 6 for the flue gas leading to the cyclone dust trap 7, which extracts the powders which then fall down the chimney 8, while the flue gas is directed to the chimney by means of conduits 9. To allow the removal of the powders, the chimney outlet 8 is provided with a shut-off valve, which is not shown. In this same picture, there is a 40 hopper funnel intended to contain the powdered raw materials that need to be inserted into the dome to accommodate the composition. This may be e.g. sand, dolomite, etc. At the outlet of the hopper, the measuring valve 41, which is adjusted by the mechanism 42, adjusts the flow of the additives as required.

When removed from the cyclone dust trap 7, the hot powders (temperature higher than 150 ° C) as well as the fragmented raw materials at the outlet of the funnel 40 are taken over by the conveyor 13, which transports them towards the measuring device 10 according to the invention. Its function is to inject substances into the conduit 11 of the inlet pipe 5 with the flow at which they reach. Injection is carried out via a wind tunnel 12. Said line passes through a tube and supplies hot air (at a temperature of about 500 ° C) which is rich in oxygen.

Figure 4 shows in detail the measuring device. The figure 1 shows the dome 1 with its water jacket 2 and the supply pipe 5 with its cooled end 13. Unlike the figure 3, the supply pipe shown here comprises a pipe end 44 for oxygen supplied through line 45. it runs in the same direction with the supply pipe. The base of the dome is composed of naphane mass, the upper limit of which is 14. At the bottom of the dome, liquid cast iron 15 is covered with liquid glass mass 16, which also contains solid coke 17.

Veterinarian 12 is used to supply inlet pipes with an air pressure of about 8000 Pa. The line 11 has an air velocity of 70 m / s. The device 10 has two parts, the upper part 20 consisting of a tube of e.g. 150 mm, and the bottom, which is a vertical straight tube 18, 70 mm in diameter. This tube 18 is transiently fastened to the upper end of the windmill 12 directly opposite the opening of the inlet line 11 of the inlet pipe 5. The portion 19 of the line 11 opposite the pipe 18 is extended to a diameter of about 128 mm. Both coaxial openings of pipes 18 and 19 are in the same plane.

The upper portion 20 of the apparatus 10 has a vertical upper portion 21 and a similar vertical upper portion 21 which is mounted laterally. Finally, an expanded mouthpiece 23 is provided in the upper portion of the two to provide easy filling with the conveyor 13. The tube 20 is made of a material that is highly resistant to temperature and abrasion by powders obtained from flue gases. and is e.g. made of steel. It is attached to the upper part of the cuff and is equipped with a vibrator at its lower end. It is connected to a small diameter 18 tube with a 28 'feed tube made of suitable material such as asbestos or silicon coated fabric.

The essence of the operation of the device 10 is as follows: while the pipe 20 is separated from the wind 12, e.g. by means of a valve not shown and mounted on the pipe 18, the pipe 20 is rapidly filled with a powder which e.g. it removes at the outlet of the chimney 8 the cyclone dust trap 8. It then takes the form of a slope 26 that prevents the powder from falling. When the powder reaches the predefined level 27, the filling stops. The system starts up and can then function: the valve on the pipe 18 is open, the powder is transported to 23 by means of a conveyor 13 and the vibrator is started as often as necessary to empty the pipe at the bottom and maintain the same level 27. Due to the automatic of operation, the level detector was installed in the same location. This is e.g. a temperature sensor that detects the presence of hot powder inside the pipe. As soon as the powder is no longer at the level of detector 28, the vibrator 25 is stopped and, since the powder is fed continuously, the level immediately rises again and the vibrator resumes operation as soon as a certain level is reached.

Generally, experts will decide whether only the full and continuous type of waste generated within the unit need to be reintroduced, or whether certain quantities of raw materials in powder form need to be added simply by experimentation, with parameter values being selected for on:

the gradient of the intermediate region where the slope 26 is created and the height of the powder column (between 26 and 27) required to compensate for the excess wind pressure.

It was found that in the case of powders recovered from the flue gas of the domes in stone wool production, with particles having a size less than 1 mm, the diameter of 150 mm would be suitable for tube 20, the gradient of the intermediate region of pipe 20, where the vibrator 25 installed is 45 ° and the level difference between the slope 26 and the upper level is 1.10 m. The vibrator is of an eccentric type and has a vibration frequency of 7500 per minute.

The parameters described above make it possible to inject all the powders obtained from the flue gas from the dome by means of a cyclone dust trap, ie quantities exceeding 100 kg per hour, without difficulty. The system described above, which does not comprise any moving mechanical component in contact with the powder, is particularly suited to the introduction of powdery abrasives into the dome.

Figure 5 shows a variant embodiment of the device 10 in Figure 3, which also comprises a vertical windmill. The essential difference with the vibrator system is that the tube is straight and fitted with a valve at its lower end.

The picture shows a 12 windmill and 11 conduits leading to the inlet pipe.

Tube 70 is thus standing, e.g. in a vertical position. Its lower end ends in valve 71;

experiments were performed with a shut-off valve. The valve is open just enough to allow the required flow of substance in powder form to pass through. They are stored at 72 at an altitude sufficient to prevent pressurized gases in the windmill from flowing back toward the outside. The level of substance 72 in powder form, which must remain stable in accordance with the parameters, i.e. the nature of the powder, the flow to be provided and the gas pressures are maintained by means of two level detectors 73 and 74 which can be thermal, such as those in Figure 4, whether mechanical with sensors or even optical.

The choice between the first preparation in Figure 2 and the other two in Figures 4 and 5 depends on the nature of the substance to be introduced. Abrasive powders, such as powders recovered from flue gas from a glass wool dome, are e.g. unsuitable for snail because the wear level is too high, but on the other hand, the passive system in Figure 5 is very suitable for powders of this type.

Similarly, lightweight separates are substances which e.g. they contain significant proportions of fiber waste unsuitable for vertical windmills in Figures 4 and 5 because, in order to create a leak, especially with respect to windmills, the required height of the substance in the pipes is too large.

The two methods described above constitute two embodiments of the principle according to the invention, according to which a substance introduced into inlet tubes itself forms a stopper between the high pressure downstream part and the upper atmospheric pressure part or between the outer atmosphere and the interior where toxic gases. Other devices not described herein will be found to enable the same function to be fulfilled and also be covered by this document. The form of the substance to be injected is very important, i.e. powders are obviously suitable, but grains are also suitable unless they are too large or can be compressed, such as in the case of lumps obtained by cutting fiber pads.

The invention described above is characterized by its great simplicity or even simplicity: a very simple and inexpensive means that consumes little energy because e.g. the vertical wind uses gravity as a means of operation, allowing the separate components to be introduced much more simply than by the state of the art directly into the flue gas or into the combustion gas pipes of the dome or blast furnace.

In the case of the reintroduction of waste, such as droplets or powders obtained from flue gases, the advantage of the invention is much more essential, where expensive briquette production is no longer required, and in the case of flue gas powders, re-entry takes place before cooling (saving on re-heating energy).

In addition, the invention provides a simple means for the reintroduction of exogenous waste into the dome of a stone wool production unit, such as fibrous insulation products (glass wool or stone wool) obtained from industries that manufacture heat insulated devices and which are regulated by environmental protection committed to return worn-out appliances and recycle their components.

Claims (18)

A process for adding substances to a reactor gas such as a blast furnace or a dome, characterized in that the substances are in powder form and that the substances in powder form alone create a seal between the area to be fed and the outside. Method according to claim 1, characterized in that the addition is carried out in the gas pipes of the gas reactor. Process according to claim 1, characterized in that the addition is carried out in gases obtained from the reactor as they are directed towards the outlet. Use of the process according to any of claims 1 to 3 for adding feedstocks to the reactor. Use of the process according to any of claims 1 to 3 for recycling endogenous and exogenous wastes in the reactor, if necessary after crushing or cutting. Use of the process of claim 2 and claim 5 for the recycling of reactor powders collected from gases obtained from the reactor. Use of the method of claim 5 in the processing of fibrous products, in which grains that have not been pulled into the fibers are recycled in the reactor. 8. A device for the addition of a substance in powder form to a reactor gas, characterized in that it comprises a tube which carries the substances to be introduced in the powder form and therein forming a stopper the thickness of which prevents the passage of gas. Device according to claim 8, characterized in that the powder-carrying tube enters the reactor area and is flowed by gases before leaving the reactor. Device according to claim 9, characterized in that the powder-carrying tube exits into the area through which the combustion gases obtained from the dome or blast furnace pass through before passing through the filter device to obtain an outlet flue gas. Device according to claim 10, characterized in that the filter device consists of the raw materials themselves through which the combustion gases must pass before they exit. Device according to claim 8, characterized in that the powder-carrying tube exits into the reactor gas inlet pipe and, in particular, into the air or oxygen inlet tubes at the dome or blast furnace. Device according to any one of claims 8 to 12, characterized in that it comprises the addition of substances in powder form supplied by the Archimedes screw. Apparatus according to any one of claims 8 to 12, characterized in that it comprises a vertical windmill filled with powder-like substances to a minimum level and the lower part of which is sealed. Apparatus according to claim 14, characterized in that the lower part of the tube is sealed with a shut-off valve, which is controlled to maintain the thickness of the stopper of the substance in powder form greater than the minimum value. Apparatus according to claim 14, characterized in that it comprises a vertical windmill containing powdered substances having a knee-shaped lower part and a vibrator in the lower tube and its operation governed by a level control system. Use of a device according to any one of claims 8 to 16 for the addition of grains which have not been converted into fibers during the production of mineral fibers in the dome. Use of a device according to any one of claims 14 to 16 for introducing into the dome or blast furnace powders obtained from flue gases. For