Title of Invention

"A PROCESS FOR COLLECTING AND TREATING REACTION GASES FROM A PRODUCTION PLANT FOR MOLTEN METALS"

Abstract

A process for collecting and treating reaction gases from a production plant for molten metals, in which metal-containing feed materials in solid or liquid form are introduced into a metallurgical vessel and reacted under the action of fuels and reaction materials, and the hot, gaseous and dust-laden reaction gases which leave the metallurgical vessel are fed in part to a primary dedusting process and in part to a secondary dedusting process in associated dust separation devices (11), characterized in that the reaction gases which are fed to the secondary dedusting process flow through a heat accumulator (9) prior to the secondary dedusting process, and heat is released from reaction gases at a reaction gas temperature which is above the wall temperature of the accumulator elements (33) to the heat accumulator, and this accumulated heat is released again to subsequent reaction gases at a reaction gas temperature which is below the wall temperature of the accumulator elements and in that 20% to 70%, preferably 25% to 50%, of the heat quantity transported by the reaction gases is accumulated in the heat accumulator and subsequently released again by the latter. FIG. 1

Full Text

The present invention relates to a process for collecting and treating reaction gases from a production plant for molten metals. The invention relates to a process for collecting and treating reaction gases from production plants for molten metals, in which metal-containing feed materials in solid or liquid form are introduced into a metallurgical vessel and reacted under the action of fuels and reaction materials, and the hot, gaseous and dust-laden reaction gases which leave the metallurgical vessel are fed in part to a primary dedusting process and in part to a secondary dedusting process in associated dust separation devices, and to an associated dedusting installation. In a primary dedusting process, the reaction gases formed during a continuous metal production process are cooled and dedusted, while in a secondary dedusting process the reaction gases which rise up during the charging of scrap and pig iron are preferably treated further. In detail, the invention relates to a process for treating reaction gases from steelmaking plants and to the dedusting installations required for this process, in which iron-containing feed materials, such as for 'example pig iron, scrap, iron ore, etc. in solid or liquid form are introduced into a steelmaking converter, an arc furnace, a cupola furnace or a similar type of metallurgical vessel, and steel is produced under the action of fuels and reaction materials, such as coal, oxygen, natural gas, various slag-forming agents and alloying additions. The reaction gases which are produced in large quantities during the production process are directly discharged from the metallurgical vessel or are largely extracted above the metallurgical vessel and treated further in a primary dedusting process and a secondary dedusting process, with the reaction gases being substantially dedusted before these reaction gases are fed for combustion (burn-off) or storage (if the reaction gases have a sufficient calorific value). US-A 4,050,682 and DE-C 22 39 578 have already disclosed a process of this type and a corresponding apparatus for collecting and treating reaction gases from a steelmaking converter. The reaction gases from the converter are on the one hand transferred into a primary dedusting installation while the production process is ongoing, where they are treated further, and on the other hand, during the charging phase, in which the converter adopts an inclined position, are discharged into a secondary dedusting installation, where they are fed for further treatment. In the primary dedusting installation, the reaction gases, which are produced continuously and substantially in largely predictable quantities that are dependent on the feed materials, are collected in a cooled extractor hood, which substantially covers the converter mouth, and then have the dust which they contain removed from them in a multi-stage, or at least two-stage, dedusting process in scrubbers, preferably venturi scrubbers, and are then cooled and fed for combustion in a flame. During the charging of feed materials, in particular during the charging of scrap, on the one hand there is a high level of dust produced and on the other hand sudden combustion of the impurities charged with the steel scrap, such as paints, oils, plastics, etc. occurs. The reaction gases formed from the inclined converter vessel are collected in a further extractor hood, arranged a distance above the converter, of a secondary dedusting installation and from there are fed for further treatment. This reaction gas stream produced during the short charging times with a tilted converter vessel is likewise fed to a scrubber, with the flow passage intended to transport the reaction gases opening out into the primary dedusting installations between the first and second scrubbers. Furthermore, it is known from DE-C 22 39 578 to feed the purified and cooled reaction gases to a gas store and for them to be used as useful gases for a further application. If the metallurgical vessel for producing molten metals is formed by an electric arc furnace, as the smelting process is ongoing, reaction gases are usually extracted via a roof hole in the furnace vessel and fed to a primary dedusting installation. During the charging of feed materials into the arc furnace, which predominantly comprise scrap, direct reduced iron and hot-briquetted iron, the furnace roof is usually pivoted away and rising reaction gases are trapped by what is known as a canopy hood and fed to a secondary dedusting installation. The dedusting installations are of similar construction to those used for converter vessels. Dedusting installations as are known, for example from USz2L._4_J3.5-.Q-, 682 however, do not satisfy current demands, in particular with regard to the charging of steel scrap of poor quality on account of a high impurity rate. On account of the requirement for comprehensive recycling of automobiles and domestic scrap (domestic appliances), considerable quantities of the scrap are contaminated with a high level of hydrocarbon-containing accompanying substances, such as plastics, paints, other organic substances, oils, etc., as well as aluminum and zinc, which release large heat quantities during combustion. This contaminated scrap additionally has a high moisture level (water, snow). During charging, this scrap is brought into direct contact with liquid metal; in the case of an electric arc furnace, this occurs as a result of basket charging onto a liquid melt bath, and in the case of a blowing converter this occurs as a result either of charging liquid metal onto an existing stock of scrap or by charging scrap into an existing melt bath. On account of the sudden action of heat within a very short time, decomposition products, such as CO, H2, CH4 or similar products and combustion gases, are formed and escape from the metallurgical vessel before being mixed with ambient air. The quantities of these decomposition products and the temperature in the vicinity of the metallurgical vessel are high enough to initiate direct combustion of these decomposition products and to evolve a considerable quantity of reaction gases and significant levels of heat in this region. The secondary dedusting system, in particular the canopy hood of the arc furnace, and the secondary extractor hood of a steelmaking converter are designed to collect and discharge these reaction gases to the maximum possible extent, in order to avoid the build-up of heat in the steelworks and contamination in and outside this area. Dust separation devices (dust filters) are arranged for gas purification in the secondary dedusting system; on account of their design, the gas inlet temperature for these dust separation devices should not exceed 130°C to 160°C. Many steelmakers and manufacturers of nonferrous metals have in recent years considerably increased their scrap feed rate, in particular with a considerable rise in the proportion of scrap contaminated with combustible materials. These circumstances lead to considerably increased energy emissions from the metallurgical vessels during the charging of scrap onto liquid steel or vice versa. The superheated reaction gases cannot be adequately cooled during the short transport time to the dust separation devices and cause overheating damage at the filter devices. The admixing of cooling air, predominantly ambient air, is subject to restrictions, since brief, high quantities of reaction gas require correspondingly high quantities of cooling air, which in turn impose uneconomical overdimensioning of the filter installations. Furthermore, the large quantity of gas which briefly occurs can lead to incomplete combustion of decomposition products formed from the scrap-accompanying materials on account of oxygen deficit and to incompletely burnt reaction gases being sucked into the pipe system of the secondary dedusting installation. If ambient air then enters this pipe system, in particular if cooling air is injected prior to entry to the dust separation device, explosive conflagrations can occur, leading to destruction in particular of the filter devices. Therefore, it is an object of the present invention to avoid the drawbacks of the known prior art and to propose a process and a dedusting installation for reaction gases from a production plant for molten metals, which enable large quantities of hot reaction gases which are produced for a short period of time to be reliably dedusted using installations with the minimum possible dimensions. Furthermore, it is intended to provide existing dedusting installations so that they can accommodate high quantities of reaction gases occurring for a brief period of time. In a process of the type described in the introduction, this object is achieved by virtue of the fact that the reaction gases which are fed to the secondary dedusting process flow through a heat accumulator prior to the secondary dedusting process, and heat is released from reaction gases at a reaction gas temperature which is above the wall temperature of the accumulator elements to the heat accumulator, and this accumulated heat is released again to subsequent reaction gases at a reaction gas temperature which is below the wall temperature of the accumulator elements. The heat accumulator therefore operates according to a regenerative principle, which provides for only brief heat accumulation during and shortly after the scrap charging. This allows a procedure which saves on investment costs in particular compared to a heat exchanger principle. If appropriate, the reaction gases flowing through the heat accumulator may also comprise air from the region surrounding the metallurgical vessel. The heat accumulator is expediently dimensioned in such a way that 20% to 70%, preferably 25% to 50%, of the heat quantity transported by the reaction gases is accumulated in the heat accumulator and subsequently released again by the latter. Reliable protection against overheating in the dust filters is provided if the heat released from the reaction gases to the accumulator elements is used to lower the temperature of the reaction gases to a dust filter inlet temperature of preferably less than 180°C. This temperature level corresponds to that which can withstood by bag filters and conventional filter cloth under brief thermal stressing. Reliable protection against overheating in the dust filters can also be achieved if a cooling gas is additionally fed to the reaction gases after they have flowed through the heat accumulator and before they enter the dust separation device, and the temperature of the reaction gases is lowered to a dust filter inlet temperature of preferably less than 180°C. The combined use of reaction gas cooling by heat accumulation in a regenerative heat accumulator and by cooling with cooling gas is particularly suitable for optimizing the overall secondary dedusting installation. Preferably, the reaction gases are lowered to a dust filter inlet temperature in a temperature range between 130°C and 160°C. A temperature drop in the reaction gases to a correspondingly low dust filter inlet temperature achieved in this way avoids explosive afterburning in the dust filter. The cooling gas quantities required can be optimally defined if the actual value of the dust filter inlet temperature is measured continuously, and the quantity of cooling gases admixed to the reaction gas is controlled as a function thereof. The invention also proposes a dedusting installation for collecting and treating reaction gases from a production plant for molten metals, the production plant comprising a metallurgical vessel for receiving metal-containing feed materials in solid or liquid form and reacting them under the action of fuels and reaction materials, and the metallurgical vessel being assigned a primary dedusting installation and a secondary dedusting installation for the hot, gaseous and dust-laden reaction gases leaving the metallurgical vessel, which dedusting installations at least comprise an extractor hood, a flow passage and a dust separation device. To achieve the object set, a dedusting installation designed in this way is characterized in that a heat accumulator for taking up heat from the reaction gas flowing through it and for releasing heat to the reaction gas flowing through it is arranged in the flow passage of the secondary dedusting installation. The heat accumulator is designed for a cooling capacity which makes it possible to lower the temperature of the reaction gas quantities formed, even with a poor quality of scrap, to a sufficiently low dust filter inlet temperature by the time they enter the dust filter. To enable a large heat quantity to be stored for a brief period of time, the heat accumulator comprises at least one accumulator element having a multiplicity of flow passages. The heat accumulator may equally comprise a multiplicity of accumulator elements, in which case flow passages for the reaction gases to pass through are arranged between adjacent accumulator elements. Preferably, the accumulator elements of the heat accumulator are formed by accumulator plates or accumulator bars that are preferably arranged parallel to one another. A substantially rectilinear direction of flow of the reaction gases in the heat accumulator minimizes the flow resistance presented by the accumulator elements and keeps the additional power consumption of the gas blower at a low level. To provide the accumulator plates with a sufficient accumulator action and to achieve sufficient heat transfer, the accumulator plates have a wall thickness of from 1 mm to 5 mm and a distance between adjacent accumulator plates of from 30 mm to 80 mm. An expedient configuration of the heat accumulator is achieved if the accumulator elements of the heat accumulator have at least 0.5m of cooling surface area per 1 m3/s of reaction gas throughput. The cooling surface area in this context comprises the surface area of the heat accumulator, in particular of the accumulator elements, which is in contact with the reaction gas while the reaction gas is flowing through the heat accumulator. A dedusting installation with minimized investment costs is achieved if an introduction apparatus for introducing a cooling gas into the flow passage is provided between the heat accumulator and the dust separation device. In the event of temperature peaks in the reaction gases, which may occur if there is a particularly high level of plastics in the scrap, and in the event of particularly large quantities of reaction gases at a high temperature level, the temperature can be reduced immediately upstream of the dust separator by additionally injecting or sucking in cooling gas. It is ensured that a predetermined dust filter inlet temperature is complied with if on the inlet side the dust separation device is assigned a temperature-recording device, which is signal-connected to a controller for controlling the introduction apparatus for introducing the cooling gas. The dedusting installation according to the invention is preferably used for metallurgical vessels, such as a converter, arc furnace or cupola furnace. When designing a new dedusting installation or a new production plant for liquid metal with a dedusting installation, use of the heat accumulator according to the invention has the following advantages: • The overall dedusting installation can be made smaller, since only a small amount of cooling air or no cooling air at all is required to reduce the temperature of the reaction gases to a level which is permissible for the dust separation device upstream of the latter. • Especially in the case of metallurgical vessels which evolve high levels of heat, the dedusting system can be designed for an appropriate capacity. The following advantages ensue if a heat accumulator according to the invention is installed in an existing production plant for liquid metal: • later opening of the cooling air supply or elimination of this cooling altogether, • a significantly greater quantity of reaction gas can be removed and treated, • lower emissions in and outside the production halls, • a reduced risk of unburnt reaction gases being sucked in, • a minimized risk of explosions being caused by unburnt reaction gases in the dedusting installation. In general terms, the heat accumulator according to the invention in the secondary dedusting installation gives rise to the following advantages: • the heat accumulator does not need any additional cooling media for its operation, and therefore does not require any additional equipment to provide such media, • the maintenance costs of the heat accumulator are minimal, since scarcely any deposits of dust are formed, • the heat accumulator requires only 7 to 10% of the pressure loss of the secondary dedusting installation. This additional energy demand in terms of blower drive power is compensated or more than compensated for by the lower levels of gas (no cooling air or only a small amount of cooling air). Further advantages and features of the present invention will emerge from the following description of non-restricting exemplary embodiments, in which context reference is made to the appended figures, in which: Fig. 1 shows a secondary dedusting installation according to the invention in conjunction with an arc furnace, Fig. 2 shows a secondary dedusting installation according to the invention together with a converter, Fig. 3 shows a longitudinal section through the heat accumulator of a secondary dedusting installation of modular construction as shown in Figs 1 and 2, Fig. 4 shows a cross section through a module of a heat accumulator on section line A-A in Fig. 3. Figures 1 and 2 diagrammatically depict the secondary dedusting installations according to the invention on the basis of two applications that are typical of the steelmaking basic materials industry. Fig. 1 shows an electric arc furnace 1 as is customarily used to smelt steel scrap. This electric furnace has a roof hole 2 which is adjoined in a sealing manner by a flow passage 3 that forms part of a primary dedusting installation, which is not illustrated in more detail and corresponds to the known prior art. During the continuous smelting process and the subsequent steel treatment processes, reaction gases are sucked out of the interior of the furnace space through the flow passage 3. A canopy hood 4 for collecting reaction gases from the electric furnace which are formed in particular during the operation of charging scrap into an existing stock of liquid steel as a result of combustion of impurities in the scrap, is arranged above the arc furnace, beneath the roof of the furnace room (not illustrated). During the charging operation, the electrodes 5 and the furnace roof 6 have been pivoted out of the operating position of the electric furnace which is illustrated, so that the reaction gases can rise direct to the canopy hood. The sucking action of a blower 7 sucks the reaction gases which have collected in the canopy hood 4 through the flow passage 8 into and through a heat accumulator 9, in which heat is extracted from the reaction gases if they are at a high reaction gas temperature. The heat accumulator 9 is formed by a plurality of series-connected accumulator modules 9a, 9b, 9c, 9d. Then, the reaction gases, which have been cooled to approximately the dust filter inlet temperature, are sucked through the flow passage 10 into a dust separation device 11, which is designed as a multi-stage dust filter and in which the dust is substantially separated out of the reaction gas. Then, this substantially purified reaction gas is discharged by the blower 7 via the stack 12 into the environment. An introduction apparatus 13 for introducing cooling air opens into the flow passage 10 upstream of the dust separation device 11; this introduction apparatus is designed in such a way that along the remaining distance to the dust separation device, substantially uniform mixing and therefore cooling of the reaction gas can take place. This allows reaction gas with peak values in terms of reaction gas quantity and reaction gas temperature to be treated in such a manner that it can be processed by the dust separation device. To optimize the cooling air supply, a temperature recording device 14 is arranged in the flow passage 10 on the inlet side of the dust separation device 11; the measurement signal from this temperature recording device is used in a controller 15 to control the quantity of cooling air to be injected in the introduction device 13 for introducing cooling air. A closure flap 16 can be used, for example, for quantitative control of the cooling air stream. It is advantageous if the heat accumulator 9 is arranged as close as possible upstream of the dust separation apparatus 11 and as far away as possible from the canopy hood 4, since over a long flow passage 8, considerable quantities of heat can be dissipated through the wall of the flow passage to the ambient air, and therefore the reaction gases already enter the heat accumulator 9 at a lower temperature. The intake quantity of the secondary dedusting installation is controlled using a control flap 17 in the flow passage 8, just above the canopy hood. Fig. 2 shows a second application for a secondary dedusting installation of the type according to the invention, for a tiltable blowing converter in a blown steel plant. During the continuous production process, the converter 20 is in the upright position illustrated and a cooled extractor hood 21, which is part of a primary dedusting installation, is arranged a short distance above the converter mouth 22. The converter 20 can be pivoted about the tilting axis 23 into the tilted position indicated by a dot-dashed line 24, in which the scrap charging is carried out. The reaction gases, which escape in large quantities during scrap charging in this position, are trapped by an extractor hood 2 5 and treated further in a secondary dedusting installation. The basic structure of this secondary dedusting installation corresponds to that of the dedusting device which has been described and illustrated in Fig. 1. Figures 3 and 4 illustrate structural details of the heat accumulator. The heat accumulator 9 comprises a housing 30, which is incorporated in the flow passages 8, 10, of which two side walls 30a, 30b are illustrated and which has an inlet opening 31 and an outlet opening 32 for the passage of the reaction gas stream. The reaction gas stream flows through the heat accumulator over a short distance with minimal resistance and without any change in direction. Individual accumulator modules 9a, 9b, 9c, . . . composed of a multiplicity of accumulator elements 33 are inserted into the housing 30, resting via a carrier beam 34 on supporting brackets 3 5 of the housing. The accumulator elements 33 comprise metal plates, preferably thin sheet-metal panels, which are fixed at a predetermined distance from one another by welded-on spacers 3 6 and are clamped using continuous tensioning rods 37 to form a module. The sheet-metal panels are 2 mm thick and arranged at a distance of 60 mm from one another. We Claim: 1. A dedusting apparatus for collecting and treating reaction gases from a production plant for molten metals, the production plant comprising a metallurgical vessel for receiving metal-containing feed materials in solid or liquid form and reacting them under the action of fuels and reaction materials, and the metallurgical vessel being assigned a primary dedusting installation and a secondary dedusting installation for the hot, gaseous and dust-laden reaction gases leaving the metallurgical vessel, which dedusting installations at least comprise an extractor hood (4, 25), a flow passage (8, 10) and a dust separation device (11) characterized in that, a heat accumulator (9) for taking up heat from the reaction gas flowing through it and for releasing heat to the reaction gas flowing through it is arranged in the flow passage (8, 10) of the secondary dedusting installation, and in that the heat accumulator (9) comprises a housing (30) with an inlet opening (31) and an outlet opening (32) for the passage of the reaction gas stream, and in that the heat accumulator (9) comprises either at least one accumulator element having a multiplicity of flow passages or a multiplicity of accumulator elements (33) flow passages being arranged between adjacent accumulator elements. 2. The dedusting apparatus as claimed in claim 1, wherein the accumulator elements (33) of the heat accumulator (9) are formed by accumulator plates or accumulator bars that are preferably arranged parallel to one another. 3. The dedusting apparatus as claimed in claim 2, wherein the accumulator plates have a wall thickness of from 1 to 5 mm, and the distance between adjacent accumulator plates is from 30 to 80 mm. 4. The dedusting apparatus as claimed in one of claims 1 to 3, wherein the accumulator elements (33) of the heat accumulator (9) have at least 0.5 m2 of cooling surface area per 1 m3/s of reaction gas throughput. 5. The dedusting apparatus as claimed in one of claims 1 to 4, wherein an introduction apparatus (13) for introducing a cooling gas into the flow passage (10) is provided between the heat accumulator (9) and the dust separation device (11). 6. The dedusting apparatus as claimed in claim 5, wherein on the inlet side the dust separation device (11) is assigned a temperature-recording device (14), which is signal-connection to a controller (15) for controlling the introduction apparatus (13) for introducing the cooling gas. 7. The dedusting apparatus as claimed in any of the previous claims, assigned to a metallurgical vessel for steel making. 8. A process for collecting and treating reaction gases from a production plant for molten metals, in which metal-containing feed materials in solid or liquid form are introduced into a metallurgical vessel and reacted under the action of fuels and reaction materials, and the hot, gaseous and dust-laden reaction gases which leave the metallurgical vessel are fed in part to a primary dedusting process and in part to a secondary dedusting process in associated dust separation devices (11), characterized in that, the reaction gases which are fed to the secondary dedusting process flow through a heat accumulator (9) prior to the secondary dedusting process, and heat is released from reaction gases at a reaction gas temperature which is above the wall temperature of the accumulator elements (33) to the heat accumulator, and this accumulated heat is released again to subsequent reaction gases at a reaction gas temperature which is below the wall temperature of the accumulator elements and in that 20% to 70%, preferably 25% to 50%, of the heat quantity transported by the reaction gases is accumulated in the heat accumulator and subsequently released again by the latter. 9. The process as claimed in claim 8, wherein the heat released from the reaction gases to the accumulator elements is used to lower the temperature of the reaction gases to a dust filter inlet temperature of preferably less than 180°C. 10. The process as claimed in one of the preceding claims, wherein a cooling gas is fed to the reaction gases after they have flowed through the heat accumulator and before they enter the dust separation device, and the temperature of the reaction gases is lowered to a dust filter inlet temperature of preferably less than 180°C. 11. The process as claimed in one of the preceding claims, wherein the reaction gases are lowered to a dust filter inlet temperature in a temperature range between 130°C and l60°C. 12. The process as claimed in either of claims 10 and 11, wherein the actual value of the dust filter inlet temperature is measured continuously, and the quantity of cooling gases admixed to the reaction gas is controlled as a function thereof. 13. The process as claimed in one of claims 10 to 12, wherein the cooling gas used is cooling air.

Documents:

1393-DELNLP-2006-Correspondence-Others-(22-09-2009).pdf

1393-DELNP-2006-Abstract-(10-02-2009).pdf

1393-delnp-2006-abstract.pdf

1393-DELNP-2006-Claims (29-10-2009).pdf

1393-DELNP-2006-Claims-(10-02-2009).pdf

1393-delnp-2006-claims.pdf

1393-DELNP-2006-Correspondence-Others (29-10-2009).pdf

1393-delnp-2006-correspondence-others 1.pdf

1393-DELNP-2006-Correspondence-Others-(10-02-2009).pdf

1393-delnp-2006-correspondence-others.pdf

1393-DELNP-2006-Description (Complete)-(10-02-2009).pdf

1393-delnp-2006-description (complete).pdf

1393-DELNP-2006-Drawings-(10-02-2009).pdf

1393-delnp-2006-drawings.pdf

1393-DELNP-2006-Form-1-(10-02-2009).pdf

1393-delnp-2006-form-1.pdf

1393-delnp-2006-form-18.pdf

1393-DELNP-2006-Form-2-(10-02-2009).pdf

1393-delnp-2006-form-2.pdf

1393-delnp-2006-form-3.pdf

1393-delnp-2006-form-5.pdf

1393-DELNP-2006-GPA-(10-02-2009).pdf

1393-delnp-2006-gpa.pdf

1393-delnp-2006-pct-210.pdf

1393-delnp-2006-pct-304.pdf

1393-delnp-2006-pct-308.pdf

1393-delnp-2006-pct-409.pdf

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