EP0722777A1 - Method for processing slag from waste incineration plants - Google Patents

Abstract

The method involves raw slag being separated into at least two fractions and the first fraction has a particle size of up to 80 mm, pref. 32 mm in a first phase. The screen overflow from the first phase is supplied to the wet slag separator (4). The through-fall through the screen and through the fire rack is sent to a second screen phase (5) to separate the fine material. The screen overflow from the second phase is mechanically pulverised after sorting out the metal and inert materials and the through-fall from the second phase is sent to a melting furnace (7) for separate processing. A third screen phase (8) can be included.

Description

TECHNICAL AREA

The invention relates to a method for treating slag from waste incineration plants, in which the raw slag is separated into at least two fractions after passing through the furnace grate directly and without prior quenching in a water bath, and these two fractions are further treated separately, the coarse fraction being a wet slag remover is fed.

Such a processing method is known for example from EP-0 437 679 B1.

TECHNOLOGICAL BACKGROUND AND PRIOR ART

When municipal waste is incinerated, around 250 kg of slag per ton of waste are generated as residual material. The resulting slag contains pollutants immediately after the furnace, which further use, e.g. as a building material, prevent. The depositing of the slag in landfills poses a risk to the environment if no special precautions are taken, e.g. collecting the leachate.

Typically, the slag is quenched in a wet deslagger immediately after it leaves the furnace. Without additional Washing the slag does not result in a reduction in the heavy metal content in the slag, and considerable amounts of toxins remain in the slag.

EP-0 437 679 discloses a method for treating residues from a waste incineration plant, in which the raw slag is separated into two fractions after passing through the furnace grate. The rust slag, boiler ash and the grate diarrhea are separated into two fractions. The fraction with constituents whose diameter is less than 100 to 300 mm is melted in a separate melting furnace, the larger constituents of the grate and boiler ash are introduced into a wet slag remover.

This comparatively rough classification ultimately leads to the fact that components are supplied to the melting furnace that do not actually require such special treatment.

EP patent 0 372 039 now shows for the first time a way of treating slag from waste and incineration furnaces, the slag being fed to the rough cleaning (removal of unburned coarse material and magnetic parts) in a water bath directly after the furnace without prior quenching . The roughly cleaned slag is then separated into at least two fractions and all particles that are smaller than 2 mm are assigned to one fraction.

This known method is based on the knowledge that the fine fraction contains the majority of the pollutants originally contained in the slag at the slag outlet. It will be given special treatment. The coarse fraction, however, is suitable for direct use as a building material or for storage in landfills.

In the technical implementation of the process according to EP patent specification 0 372 039, there are now certain technical difficulties in separating the fine fraction 0 ... 2 mm on the one hand - conventional screen conveyors or other classifying devices tend to clog, on the other hand, the air seal against the combustion chamber must be ensured be, and the cooling of the coarse fraction is problematic.

SUMMARY OF THE INVENTION

The invention, as characterized in the claims, is based on the object of specifying a method of the type mentioned at the outset which enables simple removal of the fine fraction, air exclusion from the combustion chamber and cooling of the second fraction can be achieved with simple means.

• einfache Abtrennung des Feinanteils mit herkömmlichen Klassiereinrichtungen
• einfach durchzuführender Luftabschluss gegenüber dem Verbrennungsraum, und zwar für beide Partikelströme, wobei insbesondere die Nassentschlackung der Grobfraktion um 30 mm mit bewährter Technologie durchgeführt werden kann

Die Erfindung und weitere mit ihr erzielbare Vorteile werden nachstehend anhand eines Ausführungsbeispiels näher erläutert.The invention is based on the idea of separating the fine fraction contaminated with pollutants in a “dry” way and further processing the coarse low-pollutant fraction “wet”. This procedure - you could describe it as "semi-dry detoxification" - in combination with the two-stage extraction of the fine fraction 0 ... 2 mm offers numerous advantages:

• easy separation of the fine fraction with conventional classifying devices
• air can be easily sealed off from the combustion chamber, for both particle flows, whereby in particular the wet detoxification of the coarse fraction by 30 mm can be carried out with proven technology

The invention and further advantages which can be achieved with it are explained in more detail below on the basis of an exemplary embodiment.

BRIEF DESCRIPTION OF THE DRAWING

Fig.1

eine aus einzelnen Baugruppen zusammengestellten Anlage zum Aufbereiten von Schlacke aus Müllverbrennungsanlagen;

Fig.2

einen vereinfachten Längsschnitt durch einen Teil einer Müllverbrennungsanlage;

Fig.3

einen mehr ins Detail gegehenden Schnitt durch die erste Siebstufe der Anlage gemäss Fig.2.

In the drawing, an embodiment of the invention is shown schematically; shows

Fig. 1

a system composed of individual assemblies for processing slag from waste incineration plants;

Fig. 2

a simplified longitudinal section through part of a waste incineration plant;

Fig. 3

a more detailed section through the first screening stage of the system according to Fig. 2.

WAYS OF CARRYING OUT THE INVENTION

Waste is burned in an incinerator 1. The resulting flue gases and entrained particles (fly ash as boiler ash and filter ash) are processed in a known manner in a separating and filtering stage 2, as described and shown, for example, in EP-0 437 679 B1. The grate ash passes directly from the furnace grate into a first sieving stage 3. This is preferably designed as a sieve conveyor grate. Such devices are known and, in addition to other areas of application, are also used in waste incineration plants for screening out the fine fraction (cf. "Jost Siebförderroste" brochure from Jost AG Maschinenfabrik, CH-3627 Heimberg, FOT 1.92 - 3000, undated). In this first sieving stage, the raw slag is separated into a fine fraction with particle diameters smaller than 25 ... 35 mm and a corresponding coarse fraction. The coarse fraction arrives as a sieve overflow in a wet deslagger 4 of a known type. This also ensures that there is no air on the coarse fraction side from the inside of the furnace.

The fine fraction smaller than 25 ... 35 mm is fed to a second sieve stage, e.g. a strainer sieve or preferably a vibrating sieve, also of a known type. Optionally, the grate diarrhea from the incinerator 1 can also be fed to the second sieve stage 5, which is symbolized in the figure by a dashed line. The sieve diarrhea of the second sieving stage 5 with particles of 0 ... 2 mm is specially treated, e.g. melted in a melting furnace 7. The sieve overflow of the second sieving stage 5 is mechanically comminuted in a grinding stage 6, e.g. in a ball mill. In the example, the ground material is then in a third (optional) sieving stage 8, e.g. a rod sieve, again separated into two fractions, namely a fine fraction with particle size 0 ... 2 mm and a coarse fraction larger than 2 mm. The fine fraction - it contains 5 less pollutants than the fine fraction 0 ... 2 mm of the second sieving stage - is also fed to the melting furnace 7, the coarse fraction - it essentially consists only of inert substances - can be deposited. Under certain circumstances, a sorting stage 9 can be interposed between the grinding stage 6 and the third sieving stage 8 in order to separate out metal parts, preferably separately according to ferrous and non-ferrous metals, and other inert substances.

The still very hot sieve diarrhea from the first sieve stage 3 to the second sieve stage 5 is normally transported by conveying devices known per se. A further development of the invention preferably provides for a discharge element, preferably a screw conveyor 10, which combines cooling and air sealing functions. This screw conveyor 10 also serves as an air sealing element on the fine fraction side of the first sieve stage 3 with respect to the incinerator 1 and also acts as a cooling device for the ash cooling, because with a screw conveyor, the material to be conveyed is spread over a large area with the screw conveyors Comes into contact and the latter can simply be cooled. If the screw conveyor 10 proves to be insufficiently efficient in its function as an air sealing element, this can be followed by a double pendulum flap 11, also referred to in the literature as a double-leaf shut-off flap.

As can be seen from FIGS. 2 and 3, the described “semi-dry process” can be integrated into a waste incineration plant without great effort. In these two figures only those components are shown which relate to the essence of the invention, namely separation of the first fraction with a particle size of 30 mm in the first sieving stage and wet purification of the sieve overflow of this sieving stage.

Burnt-out slag 12 (coarse / fine) falls at the end of the grate 13 into a slag shaft 14, the walls of which are drawn down so far that they dip into the wet slag remover 4. A deflection flap 15 is pivotably arranged in the side wall of the slag shaft. As a rule, this deflection flap 15 is pivoted out of its vertical position and closes the direct access to the wet slag remover 4. Burnt-out slag is then fed directly to the first sieving stage 3, which is preferably designed as a sieve conveyor grate. The screen overflow of the first screen stage 3 goes directly into the wet deslagger 4 below the screen stage 3. The arrangement is such that the screen overflow falls into a shaft 16, the walls 17, 18 of which are drawn down so far that they are below the water level 19 ends. In this way, the air seal with respect to the slag shaft 14 and thus the interior of the furnace is achieved.

The sieve diarrhea is collected in one or more funnels 20, 21 under the first sieving stage 3 and carried out separately and dryly via suitable discharge devices 10, for example screw conveyors or trough chain conveyors, and is further processed as described in connection with FIG. 1. In the event of an accident In the first sieving stage 3, the deflection flap 15 can be set vertically (shown in broken lines in FIG. 3), so that the entire slag can be discharged conventionally (wet).

LIST OF DESIGNATIONS

1

Incinerator

2nd

Separation and filter stage

3rd

first sieve stage

4th

Wet purifier

5

second sieve stage

6

Grinding stage

7

Melting furnace

8th

third sieve stage

9

optional sorting level

10th

Schencken conveyor

11

Double swing flap

12th

burnt out slag

13

rust

14

Slag shaft

15

Deflection flap

16

Shaft

17.18

Walls of 16

19th

Water level in 4

20.21

Collecting funnel

Claims (9)

Process for treating slag from waste incineration plants, in which the raw slag after passing through the furnace grate is separated into at least two fractions directly and without quenching in a water bath, and these two fractions are further processed separately, the coarse fraction being fed to a wet deslagger (4), characterized in that the first fraction with a particle size of up to 80 mm, preferably up to about 32 mm, is separated in a first sieving stage (3) and the sieve overflow of the first sieving stage (3) is fed to the wet purification system that the sieve diarrhea and possibly the grate diarrhea of the furnace grate A second sieving stage (5) is fed in order to separate the fine fraction 0 ... 2 mm, that the sieve overflow of the second sieving stage is mechanically comminuted after sorting out metallic and inert materials, and the sieve diarrhea of the second sieving stage (5) is subjected to a special treatment, e.g. a melting furnace (7) is supplied. Method according to Claim 1, characterized in that the sieve overflow of the second sieving stage is fed to a third sieving stage (8) after mechanical comminution, and the fine fraction 0 ... 2 mmm of this third sieving stage is likewise subjected to a special treatment, preferably together with that in the second sieve stage (5) sieve diarrhea is specially treated. A method according to claim 1 or 2, characterized in that the first sieving stage (3) is integrated in the combustion grate of the incinerator (1) or directly adjoins it. A method according to claim 3, characterized in that a sieve conveyor grate is used as the first sieving stage (3) and / or a vibrating sieve is used as the second sieving stage (5). A method according to claim 3 or 4, characterized in that the screen overflow of the first screen stage (3) is fed directly to the wet deslagger (4). Method according to one of claims 1 to 5, characterized in that the transport of the sieve diarrhea from the first sieving stage (3) to the second sieving stage (5) is carried out by means of a discharge member (10) which simultaneously acts as an air sealing member. A method according to claim 6, characterized in that cooling of the material to be discharged takes place simultaneously in the discharge device (10). A method according to claim 6 or 7, characterized in that the air seal is additionally accomplished by means of a double pendulum flap arrangement (12) which is connected downstream of the discharge member (10). Method according to one of claims 2 to 8, characterized in that a sorting stage (9) is switched on between the second (5) and third sieving stage (8) in order to remove metals, preferably separated according to ferrous metals and non-ferrous metals, and other inert substances.

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