EP0754247B1 - Method and installation for the heat treatment of materials - Google Patents

Description

The invention relates to a method for heat treating a pourable treatment goods, especially for sintering metallic materials according to the preamble of the claim 1. The invention further relates to an arrangement according to the preamble of claim 12.

Method and arrangement of those used in the invention Genus are first described with reference to Fig. A, in the as a treatment plant, a conventional sintering plant with the the first additional units is shown schematically.

The arrangement shown in Fig. A consists essentially from a sintering plant 1 with one on the inlet side End arranged ignition furnace 3, a sintered bed transport device 5, which is an endless passed through the sintering plant Sinter belt 7, a sinter mixture feed device 9 and an exhaust gas extraction device 11, with the Help also the one that runs from top to bottom through the sintered bed Pressure drop is built up for the sintering process.

The sinter mixture consists of the one described with reference to FIG known sintering process from ores, aggregates, Fuels, especially coke breeze, quicklime and return goods the sintering process itself. A mixing and rolling drum 13 ensures an intimate mixture of granular or pourable Mix components as well as a uniform grain size and shape of the sintered material. The feed device 9 is made up of the mixing and Rolling drum 13 loads and pours the sinter mixture in a substantially uniform layer thickness on the grate of the Sinter belt 7. With the help of an upstream feed device 15 is a finished sintered layer in this known system abandoned as a rust coating on the sintered belt 7, the between the actual sinter bed, i.e. the sintered mixture layer and the grate is arranged and in the manner of a temperature barrier the grate from excessive temperature loads and Protects stress. The finished sintered layer remains of the subsequent sintering process in the sintering plant 1 untouched and disrupts the post-processing steps in a crusher 17, in a sinter cooler 19 and in a cold sieve station 21 until the usable finished sinter is obtained at the issuing point 23 not.

The associated conventional sintering process is as follows From: The sintering belt 7 is first a suitable layer of rust evenly abandoned via the feeder 15. The sinter mixture is placed on the grate in a predetermined Layer thickness over the full width of the bed as evenly as possible heaped up. From the sinter mix feed point the sintering belt 7 moves below the feeding device 9 left to the sinter plant. The sinter bed is from the igniter 3 on the first page facing this when entering the sinter plant 1 ignited. Through the trigger 11 below the bed is in the entire sintering plant 1 in the sintering bed built up a pressure drop through which combustion air introduced into the firing sinter mixture and exhaust gases on the second sintered bed side (bottom) can be removed. After Ignition of the carbonaceous fuel of the sintered mixture a firing zone forms in the sintered bed, which progresses of the sinter bed in the sinter plant from right to on the left in the sintered bed moves from top to bottom, the sintered material is sintered through in this zone and for caking is coming. The course and training of the burning or Sintering zone over the depth of the sintering bed is over the length of the sintered strip in the interior of the sintering plant 1 from FIG. B removable. In this example, the bed depth is 500 mm. How B can be seen from FIG. B, reaches the firing or sintering zone at the end of the sintering process or shortly before it leaves the Sinter plant 1 the bottom of the sinter bed and softens there too the material to be sintered so far that the individual material grains can bake (agglomerate).

This proven sintering process has the disadvantage that that the exhaust gases drawn off from the sintered layer with a high pollutant content that are removed must, before the exhaust gases are discharged into the ambient atmosphere can be. So far, sintered exhaust gases have been cleaned in practice using secondary emission control systems. The Investment costs of secondary emission control systems, which reduce pollutant emissions to acceptable levels, are enormous because the exhaust gas runs along the entire length of the sintered bed is heavily contaminated and with cleaning accordingly large amounts of gas have to be managed. Therefore one the exhaust gas purification on the use of dust filters (Belt dedusting in Fig. A) limited or a little more extensive Exhaust gas cleaning, for example, carried out in car washes. The particularly critical organochlorine substances, Heavy metals and The like, however, were not for cost reasons away.

The invention is therefore based on the object Generated heat treatment process of the generic type Pollutants as far as possible and with a comparatively low level To remove capital expenditure, preferably under Reduction of the exhaust gas volume to be cleaned.

In solving this problem, the invention is based on Recognition that the conventional sintering process described by its nature numerous exhaust gas cleaning systems favorable properties and phases inherent in the previous could not be used appropriately. This is only possible according to the invention, namely procedurally with the features of the claim 1 and in line with the Features of claim 12.

The invention starts from those with extremely high investment costs polluted exhaust gas purification measures on the secondary side for very large gas volumes. It binds in all alternatives Exhaust gas purification solutions are essentially one in the primary Sintering process. Here, the invention proceeds from the consideration from that in the known type of heat treatment a strong adsorbing filter layer is connected downstream of the combustion zone, as long as the burning zone is not yet on the side of the flame opposite exhaust side has broken through. The cleaning effect this "natural" adsorption layer is at used the invention. Before the cleaning effect by burning of carbonaceous (adsorbable) fuel disappears and the burning zone penetrates to the other side, in the first solution according to the invention The pressure drop reverses and a counterburn occurs. On this is the way from the other side into the bed migrating second firing zone is followed by a layer, which can initially act as a filter layer. Before the Union of the two firing zones will be in the second firing zone released chloroorganic substances, for example Dioxins or furans under the influence of the high temperature of the burned in the first combustion zone or from the remaining ones Carbon particles adsorbed and then burned in the same way.

It is known from FR-A 1 397 409, a sintered belt first from top to bottom and then from bottom to top with To apply combustion air. However, this sintered belt formed by closed containers so that it is between the loading station and the discharge point are deflected by 180 degrees can be. So if the sintered material in the area of upper run from top to bottom and in the area of the lower Flumes of combustion air flow from bottom to top , it is, based on the sintered material, a and the same direction of flow.

In a further development of the invention Exhaust gases exiting treatment bed and collected in the Ignition furnace directed. Either everyone in the Treatment plant emerging gases are recycled or only the gases with a critical pollutant content Subphases, especially the final phase of the treatment process. Due to the influence of the high temperature in the ignition furnace, the in the pollutants contained in the exhaust gases destroyed. The exhaust gases are then under the influence of the pressure gradient applied to the treatment bed passed through the treatment bed. They are in the Exposed to high temperatures and further cleaned in this way. The behind the burning zone in the Treatment bed formed "natural" cleaning layer also adsorbs residual pollutants remaining in the exhaust gas.

In an alternative treatment method, the in the end of the process exiting the treatment bed Exhaust gases collected and together with those required for heat treatment Gases in the initial and / or middle phase of the Process passed through the treatment bed. The exhaust gases can distributed over a large area over the treatment bed and be guided through it. The pollutants have to not be focused on the area of the igniter, but can work together with combustion air in lower Concentration can be supplied. The contained in the exhaust gases Pollutants, such as dioxins and furans, are in turn under the influence of the high temperature during the passage of the gas mixture destroyed by the burning zone. Even with this alternative process the cleaning effect is behind the burning zone formed "natural" adsorption layer used. It is only low technical conversion measures to implement the process required, so that the costs incurred are comparatively are low.

In a further alternative method, a deliberate shift of the pollutant profile in the direction of Profile of the exhaust gas temperature and in particular through superimposition the associated profile maxima the pollutants on that section of the plant concentrated, in which the exhaust gas temperature particularly is high. The cleaning of the exhaust gases can therefore affect one limit accordingly short section of the treatment area, in which the pollutant concentration and exhaust gas temperature are maximum. In this way, cleaning systems are sufficient small capacity to a whole treatment plant with very operate lower pollutant emissions. The shift in pollutant concentration profiles will by enriching the treatment bed with pollutant adsorbing Means reached that the pollutants to the last Retain the section of the treatment area (e.g. the sintering machine). Only at the end of the treatment area when the capacity the pollutant adsorbent is exhausted and the burning zone reaches those lower layers in which the pollutants have been retained in a highly concentrated manner the concentration of pollutants in the exhaust gas increases sharply. This then part of the exhaust gases that are heavily contaminated can be separated getting cleaned.

Instead of introducing additional pollutant adsorbents Agents in the treatment bed can be used in applications where the treatment process uses pollutant adsorbing Agents in the treatment bed limited, agents with improved adsorption properties be used. A bigger specific Surface of the individual adsorbent particles can for example, to the desired shift in the pollutant concentration profiles to lead.

The pollutant adsorbing agents are advantageous mixed with the material to be treated and then poured onto the grate, before they are introduced into the treatment area. So it succeeds almost without additional technical effort, that Pollutant-absorbing agents evenly in the treatment bed to distribute.

In a development of the invention it is provided that the Pollutant adsorbent in the lower area of the treatment bed in a higher concentration than in the upper range of the treatment bed. Different concentration ratios between pollutant adsorbents and material to be treated can be produced during mixing. Around a particularly steep concentration profile of the pollutants achieve, it is beneficial to adjust the concentration of the pollutant adsorbing Using the top down in the treatment bed gradually increase. Instead, you can use two or more layers provided with different concentration ratios become.

A preferred embodiment is characterized in that the collected exhaust gases are catalytically cleaned using their high temperature. Effective catalytic cleaning is only possible at temperatures above 300 ° C. The superposition of the pollutant concentration maxima with the temperature maximum achieves the high temperature required for catalytic cleaning in most heat treatment processes. No additional thermal energy has to be added; instead, the heat energy released in the heat treatment process is collected and sufficient as a heat supplier. It is also advantageous that the heat is not released into the environment as waste heat. Various types of pollutants can be removed from the exhaust gas by catalytic cleaning; For example, organochlorine substances such as dioxins and furans can be reduced using suitable reduction catalysts. Nitrogen oxides can also be easily reduced at these temperatures. Catalytic oxidation is possible, for example, for pollutants such as SO ₂ . SO ₂ becomes SO ₃ by oxidation.

As an advantageous development of the invention, that the pollutant adsorbing agents and their concentrations be chosen in the treatment bed so that the concentration profiles of the pollutants generated in the treatment process and in particular their maxima among themselves in the end section overlap the treatment area. The more concentration profiles of different pollutants can be overlapped with each other and ever the steeper the concentration peaks, the lower that becomes partial volume of the exhaust gas to be cleaned and the more effectively it works the inventive method.

In advanced training, the last phase of the Treatment bed emerging exhaust gases of a particle separation subject. For this purpose, a normal electrostatic filter be used. To achieve a particularly high cleaning effect it is favorable to achieve the catalytic particle separation Downstream cleaning.

Instead of the particle separation, the exhaust gas after the catalytic cleaning washed with adsorbent and water become. This happens, for example, with the help of a Spray dryer, in the dusty carbon-containing adsorbent and water are introduced into the flue gas stream. The The water introduced reduces the exhaust gas temperature to such an extent that for example, crystallize salts and chlorides. Around Instead of one, the quality of the exhaust gas can be further improved Spray dryer or in addition to this an activated coke system be used.

Advantageously, the exhaust gas after cleaning Adsorbent and water subjected to particle separation.

Part of the solids that result from particle separation can be recycled and used again as an adsorbent Cleaning can be used. Because the adsorbent-containing Solids their capacity to absorb pollutants at their first Not being able to fully utilize the passage through the exhaust gas, succeeds through the return, the adsorbent to load up to its capacity limit with pollutants and to keep the operating costs low.

It is advantageously used as a pollutant adsorbing agent carbonaceous, pourable material, e.g. Coke breeze and / or activated coke used. This material is inexpensive to acquire. For heat treatments above the ignition temperature coke breeze ignites and releases the heat of combustion released as additional heat to the treatment bed. It no disturbing foreign substances remain in the treatment bed back.

The method according to the invention is preferred during sintering metallic materials used.

Appropriate developments and refinements of the invention are marked in the subclaims.

Fig. 1

eine schematische Darstellung einer Sinteranordnung zur Durchführung eines Sinterverfahrens nach der Erfindung;

Fig. 2A

ein Diagramm der Abgastemperatur, aufgetragen gegen die Länge des Sinterbandes;

Fig. 2B

ein Diagramm der Abgaskonzentration von SO2, aufgetragen gegen die Länge des Sinterbandes;

Fig. 2C

ein Diagramm der Abgaskonzentration von polychloridierten Dibenzodioxinen und polychlorierten Dibenzofuranen, aufgetragen gegen die Länge des Sinterbandes;

Fig. 2E

ein Diagramm der Abgaskonzentration von Stickstoffoxiden, aufgetragen gegen die Länge des Sinterbandes.

The invention is explained in more detail below with reference to exemplary embodiments schematically illustrated in the drawing. The drawing shows:

Fig. 1

a schematic representation of a sintering arrangement for performing a sintering method according to the invention;

Figure 2A

a diagram of the exhaust gas temperature, plotted against the length of the sintering belt;

Figure 2B

a diagram of the exhaust gas concentration of SO2, plotted against the length of the sintering belt;

Figure 2C

a diagram of the exhaust gas concentration of polychlorinated dibenzodioxins and polychlorinated dibenzofurans, plotted against the length of the sintered belt;

Figure 2E

a diagram of the exhaust gas concentration of nitrogen oxides, plotted against the length of the sintering belt.

The embodiment shown schematically in FIG Invention differs from the conventional sintering arrangement in Fig. A on the one hand by a second ignition furnace 4, the arranged near the outlet end of the sintering plant 1 is and the sinter bed ignites from the bottom, and on the other hand by a device for generating a pressure gradient in the opposite direction, i.e. from the bottom of the bed to the top of the bed. This pressure drop generating device has one Exhaust hood 6 and one arranged in a return line 8 Suction pump 10 on.

The exhaust gas discharged via the hood 6 can be via a suitable filter 12 are dedusted. In a mixer 14 the exhaust gas with that in the front or middle area of the sintering plant 1 required combustion air mixed and together with the combustion air through the hood 16 from top to bottom passed through the sinter bed. When passing through the firing zone or through the high temperature area passed by the firing zone of the sintered bed are the organochlorine substances destroyed reliably enough. Pass behind the burning zone those returned or newly created during sintering Exhausts the sintered mixture in which the high carbon Fuel usually in the form of finely divided coke breeze is included. This fuel acts as an adsorbent, in which a substantial part of the pollutants, similar as with conventional secondary cleaning of exhaust gases in activated coke reactors, is adsorbed.

The adsorbent can in the lower layers of the sintered bed in higher concentration than in the upper layers. The adsorbent and the sintered mixture can also be applied to the belt one after the other be applied. Such an adsorbent layer can also in addition to enriching the material to be treated adsorbent material can be used.

The adsorbent itself can be an aggregate and / or one used in conventional sintering processes Be a mixture of substances, its pollutant-absorbing properties are improved in the sense of the invention. It is important that that Concentration profile of the pollutants in adaptation to the exhaust gas temperature profile is moved. This is illustrated in FIG. 2 explained in more detail below.

The sintering process begins below the ignition furnace 3. The Sinter belt 7 moves in the conveying direction, that is in FIG. 2 to the right. Simultaneously with the funding movement of the Sinter bed moves through the sinter zone daily from top to bottom the sinter bed.

2A shows a diagram of the exhaust gas temperatures, plotted against the sintering belt length. The solid line represents the curve for a conventional sintering process and the dashed Line the curve for the method according to the invention This also applies to diagrams B-D. The course of the exhaust gas temperature shows in the rear section of the sintering area a strong maximum, both in the known and in the method according to the invention. The temperature curve will practically not affected by the invention.

2B shows the diagram of the concentrations of SO ₂ in the exhaust gas, plotted against the sintering band length. In known sintering processes (solid line), the SO ₂ concentration in the exhaust gas increases just behind the center of the sintering system. The SO ₂ peak is very wide. In the method according to the invention, the exhaust gas concentration of the SO ₂ is constantly significantly lower in the front and middle sections and only increases significantly later with a relatively steep flank. The peak is shifted backwards and considerably narrower.

The exhaust gas concentrations of polychlorinated dibenzodioxins and dibenzofurans are plotted against the sintering band length in FIG. 2C. In the conventional sintering process, the concentration of organochlorine substances increases in the middle of the sintering process. Analogous to the peak of the SO ₂ exhaust gas concentration, the peak is very broad. In the method according to the invention, the exhaust gas loading with organochlorine substances in the front and middle sections is significantly reduced by the additional adsorption effect of the sintered bed and the maximum is shifted backwards to form a sharper peak.

The exhaust gas concentrations of NO _{x are} plotted against the sintering band length in FIG. 2D. In the conventional sintering process, the NO _x concentration is constant almost over the entire length of the sintering belt. Only at the end of the band does the NO _x concentration drop approximately linearly. As a result, cleaning of the entire exhaust gas volume was previously required to remove the NO _x pollutants. The exhaust gas concentration of NO _x in the process according to the invention is negligibly low in the front and middle sections and only rises to a peak in the rear section of the sintering belt.

With the method according to the invention it is therefore possible to Concentrate pollutants in the rear section of the sintering belt. The pollutant peaks are shifted back, and the concentration maxima agree with the maximum of the exhaust gas temperature match. In this way, only a small subset is required of the resulting exhaust gas volume can be cleaned. The too Part of the cleaning exhaust gas is in the rear section of the sintering machine collected, i.e. where the exhaust gas temperature in the essentially the optimal temperature for catalytic cleaning has reached.

The procedure is for many heat treatment processes with similar advantages applicable, in particular also for roasting processes, for example for the heat treatment of metal sulfides, especially lead, zinc and nickel in an oxidizing atmosphere.

Claims (21)

1. Method for the heat treatment of a flowable treatment material in a treatment bed, especially for the sintering of metallic materials with addition of fuels with high carbon content, wherein the treatment material is distributed in a predetermined minimum layer thickness on a movable grate; the grate together with the treatment bed is moved through a treatment region and the treatment bed on entry into the treatment region is ignited starting from a first side; a combustion zone starting from the ignition side is thereafter formed in the treatment bed with feeding of oxygen and under a pressure drop from the ignition side through the treatment bed; and the combustion zone is displaced, under the influence of the pressure drop, in the direction of a second side of the treatment bed opposite to the first side in the course of further transport of the treatment material, in order to successively thermally treat the treatment material, wherein waste gases emanating from the treatment bed are led away, characterised in that the cleaning effect of the natural absorption layer formed behind the combustion zone is utilised for removal of noxious substances, wherein a counter combustion process is initiated by ignition of the treatment material from the second side of the treatment bed after the treatment bed has been transported on in the treatment plant to a predetermined extent and the combustion zone has attained a specific depth of penetration into the treatment bed, but before the combustion zone has broken through to the second side of the treatment bed; and wherein the treatment bed is subjected at the second ignition point to an opposite pressure drop so that a second combustion zone builds up from the second side and is driven through the treatment bed to such an extent that the fuel particles not yet picked up by the first combustion zone are combusted in the second combustion zone and the entire treatment bed is percolated through.
2. Method according to claim 1, characterised in that the waste gases emanating from the treatment bed in at least one phase of the treatment process are collected and are preferably fed, together with the gases needed for the ignition, during the ignition of the treatment bed so as to destroy, and/or adsorb in an adsorption layer formed in the treatment bed, noxious substances in the ignition zone and/or during throughflow of the treatment bed under the influence of the pressure drop in the combustion zone.
3. Method according to claim 1 or 2, characterised in that the waste gases emanating from the treatment bed in the end phase of the treatment process are collected and are conducted, together with the gases needed for the heat treatment in the initial and/or middle phase of the treatment process, through the treatment bed so as to destroy, and/or adsorb in an adsorption layer formed in the treatment zone behind the combustion zone, noxious substances in the combustion zone.
4. Method according to one of claims 1 to 3, characterised in that the treatment material is deposited and distributed on a substantially inert sinter material layer and is fed on the grate to the ignition point in such a manner that the ignition of the treatment material begins on the side remote from the (inert) sinter material layer.
5. Method according to one of claims 1 to 4, characterised in that the treatment bed is enriched before and/or in the treatment region with media adsorbing noxious substance and noxious substances are so retained in the treatment bed under the influence of the media adsorbing noxious substance that in at least one, preferably the last, phase of the treatment process the concentration profile of at least one kind of noxious substance is matched to the profile of the waste gas temperature and in particular the associated profile maxima of waste gas temperature and kind(s) of noxious substance are brought into overlapping relationship and that the waste gases emanating from the treatment bed in this phase are collected.
6. Method according to one of claims 1 to 5, characterised in that the media adsorbing noxious substance is mixed with the treatment material and thereafter distributed on the grate before it is introduced into the treatment region.
7. Method according to one of claims 1 to 6, characterised in that the media adsorbing noxious substance is present in the lower region of the treatment bed in a higher concentration than in the upper region of the treatment bed.
8. Method according to one of claims 1 to 7, characterised in that the collected waste gases are catalytically cleaned with utilisation of their high temperature.
9. Method according to one of claims 1 to 8, characterised in that the waste gases emanating from the treatment bed in the last phase are subjected to a particle separation, which is preferably connected ahead of the catalytic cleaning.
10. Method according to claim 8 or 9, characterised in that the waste gas is cleaned by adsorption media and water after the catalytic cleaning.
11. Method according to one of claims 1 to 10, characterised in that carbonaceous, flowable material, for example coke fines and/or activated coke, is used as medium adsorbing noxious substance.
12. Arrangement for the heat treatment of granular or flowable treatment material, especially for the sintering of metallic materials with addition of fuels with high carbon content, with a treatment plant (1), a treatment bed transport device (5), which comprises a belt (7) moving the treatment bed on a grate approximately horizontally through the treatment plant, a device (9) for delivery of the treatment material (24) onto the grate before the point of entry thereof into the treatment plant, an igniter furnace (3), which is arranged in the region of the treatment plant inlet, for the igniting of the treatment bed on a first side and a waste gas extraction equipment (11) effective on the second side of the treatment bed opposite the first side, characterised in that a second igniter furnace (4), which ignites the treatment bed on the second side thereof, is arranged in the end section of the treatment plant (1) at the outlet side; and that a separate differential pressure generating plant (6, 8, 10), which produces a pressure drop from the second to the first side of the treatment bed, is effective in the region of the second igniter furnace.
13. Arrangement according to claim 12, characterised in that a separate waste gas collecting device is arranged at least in the end section of the treatment plant at the outlet side; and that a return duct connects the separate exhaust gas collecting equipment with the igniter furnace (3) in order to conduct into the igniter furnace (3) at least waste gas extracted from the end section of the treatment plant at the outlet side.
14. Arrangement according to claim 12, characterised in that a separate waste gas collecting device is arranged in the end section of the treatment plant at the outlet side; that a mixing device (14, 6) for the feed of combustion air for the section of the treatment plant (1) at the inlet side and/or in the middle is provided; and that the mixing device is connected with the separate waste gas collecting device in order to feed back waste gas, which is extracted from the end section of the treatment plant at the outlet side, distributed through the treatment plant.
15. Arrangement according to one of claims 12 to 14, characterised in that a waste gas collecting device is arranged in the end section of the treatment region and coupled with a catalytic cleaning reactor by way of a first take-off duct.
16. Arrangement according to one of claims 12 to 15, characterised in that a first particle separating device, especially an electrostatic filter, is connected into the waste gas flow downstream of the waste gas collecting device.
17. Arrangement according to one of claims 12 to 16, characterised in that an adsorption medium reactor is connected downstream of the catalytic cleaning reactor.
18. Arrangement according to claim 17, characterised in that a second particle separating device, especially a textile filter, is connected downstream of the adsorption medium reactor.
19. Arrangement according to one of claims 12 to 18, characterised in that the waste gas flow is fed back from the waste gas collecting device by way of the catalytic cleaning reactor to the igniter furnace (3) in the front section of the treatment region.
20. Arrangement according to one of claims 12 to 19, characterised in that a separate waste gas collecting device for collection of the waste gases is arranged in the front and centre sections of the treatment region and is connected with a third particle separating device, especially an electrostatic filter, by way of a second take-off duct.
21. Arrangement according to one of claims 12 to 20, characterised in that the second take-off duct is connected with the first take-off duct behind the electrostatic filter.

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