EP0908673A1 - Method for processing residues and/or ash from thermal treatment of refuse - Google Patents

Abstract

A carbon-rich heavy metal-containing slag and/or ash from waste thermal treatment is heated in a rotary kiln to reduce its heavy metal content to metallic form and evaporate volatile heavy metals. Slag and/or ash, from waste thermal treatment, is processed by (a) pyrolyzing, gasifying or partially incinerating the waste (1) to form a carbon-rich heavy metal-containing slag and/or ash (8); (b) heating the slag and/or ash (8) in a rotary kiln (6) to below its melting temperature to convert the heavy metal content into the metallic form by reduction with the carbon content and to convert the volatile heavy metals into the gaseous phase which is entrained with the flue gas (9) from the kiln (6); and (c) discharging a heavy metal-depleted slag (15) from the kiln (6).

Description

Technical field

The invention relates to the field of thermal waste treatment. she relates to a process for the treatment of slag and / or ash from the thermal treatment of garbage.

State of the art

For the thermal treatment of waste / garbage are in addition to the classic waste incineration also known many processes in which the waste is degassed and / or is gasified or combinations of these known methods are used. The resulting solid reaction products can be in different Way, e.g. B. thermal, are further treated, the no longer usable Products are then deposited. For environmental and cost reasons one strives to keep these inevitable amounts of residues as small as possible to keep possible and to process the slags or ashes so that they as Recyclable or inert materials continue to be used.

1. Zur Verbrennung von Hausmüll wird heute üblicherweise das Rostfeuerungsverfahren eingesetzt. Dabei wird der Müll mechanisch über eine horizontale oder geneigte Ebene bewegt und gleichzeitig mit Verbrennungsluft, die von unten durch den Rost ins Müllbett eintritt, durchströmt. Der unbrennbare Anteil des Abfalls wird als Rostasche bzw. Schlacke aus der Verbrennungsanlage ausgetragen. Eine Verschwelung des Mülls und eine anschliessende Schlackenverflüssigung wie beim o. b. Verfahren ist in diesen vielfach bestehenden Anlagen nicht möglich.

2. Zum Einschmelzen der Schlacke im Drehrohrofen sind sehr hohe Temperaturen notwendig, so dass hochwertiges und teures Ausmauerungsmaterial eingesetzt werden muss.

3. Beim Einschmelzverfahren gelangen die umweltschädlichen Schwermetalle trotzdem unkontrolliert in die Umwelt und können nicht zurückgewonnen werden.

4. Nachteilig ist ausserdem der hohe Energieaufwand, der zur Verflüssigung aufgebracht werden muss.

From WO 93/17280, for example, a method for melting combustion residues in slag is known, in which the waste is first carbonized in a low-temperature unit, and then a complete one with the use of sulphurous substances and gases in a high-temperature unit at approx. 1200-1400 ° C Incineration with slag liquefaction is carried out. The end product is a completely burned-out, liquefied slag that can be left to solidify in any form. On the one hand, this slag has a low loss on ignition, ie a low proportion of unburned constituents, on the other hand, highly harmful hydrocarbon compounds, such as dioxins and furans, are below the detection limits, and heavy metal compounds should be incorporated in the slag in a practically insoluble manner. These advantages are offset by the following disadvantages:

1. The grate combustion process is usually used today for the combustion of household waste. The garbage is moved mechanically over a horizontal or inclined plane and at the same time flows with combustion air that enters the garbage bed from below through the grate. The incombustible part of the waste is discharged from the incinerator as rust ash or slag. A smoldering of the waste and a subsequent liquefaction of slag as in the case of the process is not possible in these existing plants.

2. Very high temperatures are required to melt the slag in the rotary kiln, so that high-quality and expensive lining material must be used.

3. During the melting process, the environmentally harmful heavy metals nevertheless get into the environment in an uncontrolled manner and cannot be recovered.

4. Another disadvantage is the high energy expenditure that has to be applied for liquefaction.

EP 0 372 039 B1 describes a process for treating the slag from waste incineration plants known in which the slag dry from the incinerator is carried out, a rough cleaning (removing unburned Coarse goods and magnetic parts) is subjected, and then the coarse cleaned slag is separated into at least two fractions and one of them all particles smaller than 2 mm are assigned. This procedure is based on the knowledge that the fine fraction is the largest part of the original contains pollutants contained in the slag. The fine fraction will a special treatment, while the coarse fraction z. B. as a building material suitable is.

A further development of this method is disclosed in EP 0 722 777 A1. There is a process for the treatment of slag from waste incineration plants claimed, in which the raw slag after passing through the grate directly and without quenching in a water bath in at least two Fractions is separated, and these two fractions treated separately the coarse fraction is fed to a wet slag remover. The The method is characterized in that the first fraction has a particle size less than 80 mm, preferably less than about 32 mm, in a first screening stage is separated so that the screen overflow is fed to the wet purification, that the sieve diarrhea and possibly the grate diarrhea of the furnace grate a second sieving stage is fed in to separate the fine fraction 0 ... 2 mm that the screen overflow of the second stage, if necessary after sorting out is mechanically crushed by metallic and inert materials, and the sieve diarrhea the second stage of special treatment, e.g. B. a melting furnace becomes. In this, for example, carried out in an arc furnace Melting process become a glassy, easy to deposit product and a Metal concentrate produced (see F.-G. Simon and K.-H. Andersson: InRec process - Recycling of residues from thermal waste treatment, ABB technology 9/1995, pp. 15-20). In practice, this processing method has been used for the slag from rust incinerators was used and has proven itself there. On the one hand, the high costs resulting from the use of the Arc furnace result, on the other hand, the many classification and crushing levels for the slag or ashes.

Various volatilization processes for metal extraction are from the iron and steel industry known, for example the rolling process. This with reducing The aim of the process is to use heavy metals such as lead, zinc and conditions To obtain cadmium in the form of highly enriched airborne dust (see Ullmann: Encyclopedia of technical chemistry, 4th edition, p. 429). As starting material serve poor, oxidic, difficult to process zinc lead ores in the rolling process, Zinc-lead-containing dusts and metallurgical waste products. These metal-containing raw materials are with a reducing agent, e.g. B. coke or anthracite, mixed and fed to a rotary kiln. They walk through the oven and heat until the volatilization begins at around 1000 ° C. The volatilization reactions (Reaction of the solid metal oxides with the added carbon to gaseous metals and carbon monoxide) run in the solid layer of the rotary kiln, which is constantly circulated. In the above The volatilization products become gas spaces with an oxidizing atmosphere then reoxidized. These gaseous phase oxidation products are very finely divided so that it is carried away by the flue gas and transported out of the oven and finally separated after the flue gases have cooled down. The low-metal slag is discharged from the furnace, cooled and then opened Dumped.

Presentation of the invention

The invention tries the above. Disadvantages with the known preparation of To avoid garbage slag. It is based on the task of being effective and inexpensive Process for the treatment of slag and / or ash from the provide thermal treatment of garbage, which with a robust and simple technology can be realized and with no additional classification and Crushing stages create an inert slag depleted of pollutants.

According to the invention, this is the case with a method according to the preamble of the patent claim 1 achieved in that the waste in a first process step is pyrolyzed, gasified or partially incinerated, with slag containing heavy metals and / or ash with a comparatively high carbon content is said slag and / or ash in a second process step in a rotary kiln to a temperature below the melting temperature of the Slag and / or ash is heated up that the slag and / or ash before their discharge from the rotary kiln remains in the rotary kiln for a sufficiently long time, so that the heavy metals contained in it by reduction on the own slag Carbon is converted into its metallic form and the volatile Heavy metals such as zinc, lead, arsenic and cadmium are converted into the gas phase and are discharged from the rotary kiln with the flue gas, and that a heavy metal-depleted slag is discharged from the rotary kiln becomes.

The advantages of the invention are that the slag in one of pollutants depleted state arises. The heavy metal contents are clear below the legally prescribed maximum values for inert material landfills of the Swiss Waste Technical Ordinance (TVA) dated 10.12.1990. Highly harmful Hydrocarbon compounds, such as. B. dioxins are below the detection limit. Therefore, the slag prepared in this way can be easily Ferrous and non-ferrous metal separation, for example as a building material in the Road construction used or otherwise used. An expensive one Landfill is unnecessary. In addition, the preparation means in a rotary kiln the advantageous use of robust technology. Time consuming classification and Crushing stages for processing the slag are not necessary.

It is advantageous if the pyrolysis, gasification or partial combustion emerging and separated in a dedusting filter dust Added slag and / or ash and heated them together in a rotary kiln and be depleted of heavy metals. This can also remove the dust from the dust collector in a simple way from heavy metal contamination be freed.

Furthermore, it is useful if both the gasification or partial combustion of garbage and as well as the volatilization of heavy metals from the burning resulting slag / ash in a single aggregate, i.e. in the Rotary kiln, the amount of combustion air is measured so that practically no more oxygen was detected at the end of the rotary kiln can be. This can save costs. However, then only some of the filter dust can be returned to the rotary kiln, because otherwise concentrate the volatile heavy metals in the flue gas.

It is advantageous if the slag and / or ash remain in the rotary kiln is more than an hour because then for the volatilization reactions enough time is available.

It is also advantageous if the flue gases from the rotary kiln are cooled and dusted in a filter, and so the air pollution low is held.

It is convenient if the slag and / or ash dry without water humidification discharged from the pyrolysis, gasification or combustion furnace and before they are fed into the rotary kiln, ferrous and non-ferrous metals be separated. It is also advantageous if the from the rotary kiln discharged slag using magnetic separators and non-ferrous metal separators the rest metallic components are removed.

It is also advantageous if the slag introduced into the rotary kiln and / or ash contains at least 10% carbon, because then one is sufficient large amount of reducing agent for the reduction and volatilization of heavy metals is available.

Finally, it is advantageous if the slag is dry from the rotary kiln is carried out and separated into at least two fractions, the first Fraction with a particle size larger than approx. 32 mm in a first sieving stage is separated as a screen overflow, and the screen diarrhea of a second classification stage for the purpose of separating the fine fraction 0 ... 2 mm, whereby at least part of the fine fraction 0 ... 2 mm from the slag processing on the Air inlet side is returned to the rotary kiln and burned there. Thereby the ash burnout in the rotary kiln is increased and the pollutant content the slag reduced even more.

Brief description of the drawing

Exemplary embodiments of the invention are shown in the drawing.

Fig. 1

eine schematische Darstellung des erfindungsgemässen Verfahrens in einem ersten Ausführungsbeispiel, bei welchem der Müll auf einem Verbrennungsrost teilverbrannt wird und anschliessend die Schlacke und Asche aus der Müllverbrennung einem Drehrohrofen zugeführt und dort aufbereitet werden;

Fig. 2

ein Diagramm, welches einerseits die Zink- bzw. Blei-Konzentrationen in der Schlacke in Abhängigkeit von ihrer Verweilzeit im Drehrohrofen und andererseits die Bett-Temperaturen in Abhängigkeit von der Zeit darstellt;

Fig. 3

eine schematische Darstellung des erfindungsgemässen Verfahrens in einem zweiten Ausführungsbeispiel, bei welchem die Verbrennung des Mülls und die Aufbereitung der Schlacke in ein und demselben Drehrohrofen erfolgt.

Show it:

Fig. 1

a schematic representation of the inventive method in a first embodiment, in which the waste is partially incinerated on a combustion grate and then the slag and ash from the incineration are fed to a rotary kiln and processed there;

Fig. 2

a diagram which on the one hand shows the zinc or lead concentrations in the slag as a function of their residence time in the rotary kiln and on the other hand the bed temperatures as a function of time;

Fig. 3

is a schematic representation of the inventive method in a second embodiment, in which the waste is incinerated and the slag is processed in one and the same rotary kiln.

Only the elements essential for understanding the invention are shown. For example, the charging device for the furnace and Ferrous or non-ferrous metal separator. The direction of flow of the media is marked with arrows.

Way of carrying out the invention

The invention is described below using two exemplary embodiments and 1 to 3 explained in more detail.

1 shows a schematic representation of the method according to the invention in a first embodiment. Rubbish 1, preferably household waste, is disposed of in a Feeding device, not shown, fed to a waste incinerator 2 and burned there on a grate 3 using the grate firing process. The Incinerator 2 is a boiler 4 and a dedusting system 5 on the gas side, e.g. B. an electrostatic filter. The incinerator is on the slag side 2 is followed by a rotary kiln 6.

The waste 1 is burned in the incinerator 2 with the supply of primary air 7, that a slag 8 is produced which has a loss on ignition of at least 10 % having. The loss on ignition is a measure of the unburned portion in the Slag 8 and thus an indirect measure of the carbon content. So this comparatively high loss on ignition and thus high carbon content is achieved, Incomplete combustion must take place in furnace 2. So far she had Incineration using the grate combustion process is always the goal, if possible the waste 1 to burn completely, i.e. a slag with the lowest possible loss on ignition and thus to generate low carbon content. In addition to the slag 8 arise when burning the garbage 1 also flue gases loaded with flue dusts 9, which get into the dedusting system 5 via the boiler 4. There the dusts are separated from the flue gas 9 and as filter dust 10 (= Fly ash) discharged.

The heavy metal and carbonaceous slag 8 from the incinerator 2 falls directly from the grate 3 into the rotary kiln 6 without intermediate cooling Discharged dry without water humidification. The slag 8 has after Rust a temperature of approx. 400 ° C. In the rotary kiln, it is together with the filter dust 10 from the dedusting system 5 by means of an oil burner 16 heated to a temperature of 900 ° C. This temperature is below the Melting temperature of the slag / ash 8, 10, but above the volatilization temperature the heavy metals contained therein. In the present embodiment were a slag amount of 2500 kg / h and a fly ash amount of 200 kg / h used. The rotary kiln 6 is so large that the Residence time of slag / ash 8, 10 in rotary kiln 6 after heating approx. Is 1.5 hours. For this reason, the rotary tube has a length of 8 m and an inner diameter of 2.5 m.

The volatilization reactions (reaction of the heavy metal oxides with that in the Slag containing carbon to gaseous metals and carbon monoxide) run in the solid layer of the rotary kiln 6, which circulates continuously becomes. In the gas space above with an oxidizing atmosphere, the Volatilization products then reoxidized. These reaction products from the gaseous phase are very fine, so that they are entrained by the flue gas 9 become. The flue gas 9 is then cooled in a steam boiler 13 and filtered in a dust filter 14. This filter dust enriched with heavy metals can then be further treated with the aim of being in them recover heavy metals contained. The heavy metal depleted Slag 15 is discharged from the rotary kiln 6, cooled and can after scrapping and non-ferrous metal separation using a magnetic separator or non-metal separator (not shown in Fig. 1) easily used (e.g. as Building materials in road construction) or on a heap.

The following table shows for the exemplary embodiment the contents of heavy metals and dioxin for the starting materials and the end product of the rotary kiln 6 compared to the maximum values for inert landfill quality according to TVA: Fly ash Slag from rust Slag after rotary kiln TVA, inert landfill quality Loss on ignition % 5 > 10.0 <1 Pb ppm 9000 2500.0 400 500 Zn ppm 16000 4000.0 500 1000 CD ppm 2400 13.0 nn 10th Dioxin concentration ng TE / kg 1600 11.5 nn

As can be seen in the table, the heavy metal contents are significantly lower the legally prescribed maximum values for inert material landfills in Switzerland Technical regulation waste, TVA. The highly harmful hydrocarbon compounds, such as B. Dioxins are even below the detection limit.

Fig. 2 shows a diagram to clarify what has just been said on the one hand the zinc or lead concentrations in the slag depending on their residence time in the rotary kiln and on the other hand the bed temperatures depending represents from that time. The course of the curves shows that the slag 8 should stay at least one hour in the rotary kiln 6, because only then a sufficiently large depletion of heavy metals takes place.

The slag prepared in this way can be used, for example, as a building material in road construction used or otherwise used. An expensive landfill is unnecessary yourself. In addition, processing in a rotary kiln is the most advantageous Use of robust technology. Time-consuming classification and shredding stages for the treatment of the slag are not necessary.

Of course, the method can also be successful without the addition of filter dust 10 can be applied by using only the carbonaceous slag 8 the grate combustion is fed to the rotary kiln 6.

3 shows a further exemplary embodiment. Here, waste incineration and slag processing take place in one and the same unit. Untreated domestic waste 1 with a calorific value of approximately 10,000 kJ / kg is introduced into a rotary kiln 6 with a length of 12 m and an inner diameter of 4 m. The amount of waste is 10,000 kg / h. The garbage 1 is now partially burned by the addition of air, the combustion air 7 having been preheated to a temperature of approximately 400 ° C. The amount of combustion air 7 is such that, on the one hand, a temperature of 1000 ° C. is never exceeded in the furnace 6, so that the ash formed is not melted, and on the other hand, practically no oxygen can be detected in the flue gas 9 at the end of the rotary kiln 6. In the present example, the amount of combustion air is 7 12,000 Nm ³ / h. The residence time of the waste 1 in the rotary kiln 6 is approximately 2 hours. This time is sufficient on the one hand to burn garbage 1 (incomplete) and on the other hand to deplete the resulting slag / ash from heavy metals by volatilizing them. The slag 15 is then discharged from the rotary kiln 6, cooled and, as already described in the first exemplary embodiment, can continue to be used after separation of iron and non-ferrous metal. The following heavy metal contents or dioxin concentration are still present in the slag 15 after the process according to the invention has been carried out: Slag after rotary kiln Loss on ignition % <1 Pb ppm 300 Zn ppm 400 CD ppm nn Dioxin concentration ng TE / kg nn

The flue gas 9 from the rotary kiln 6 is then completely burned out by adding secondary air 11 in the afterburning chamber 12, cooled in the boiler 4 (flue gas amount at the end of the boiler approx. 53 600 Nm ³ / h) and cleaned in a flue gas cleaning system 5.

Of course, the invention is not based on the exemplary embodiments shown limited. So z. B. household waste or municipal waste 1 instead of a partial incineration also subjected to pyrolysis or gasification in the first process step become. It is only important that in the slag / ash 8 at least 10% Carbon are included, so the conditions in the second step for a successful reduction and volatilization of the heavy metals in the rotary kiln 6 are given. It is also advantageous if from the slag / ash 8 before they are loaded into the rotary kiln 6 ferrous and non-ferrous metals separated that can be used for other purposes. Finally is it is also appropriate if the slag 15 dry from the rotary kiln 6th is carried out and separated into at least two fractions, the first Fraction with a particle size of approx. 32 mm in a first sieving stage is separated as a screen overflow, and the screen diarrhea of a second classification stage for the purpose of separating the fine fraction 0 ... 2 mm, and at least part of the fine fraction 0 ... 2 mm from the slag processing on the Air inlet side is returned to the rotary kiln 6 and burned there. Thereby the ash burnout in the rotary kiln 6 is increased and the pollutant content the slag further reduced.

Reference list

1

rubbish

2nd

Incinerator

3rd

rust

4th

boiler

5

Dedusting system

6

Rotary kiln

7

Combustion air / primary air

8th

slag

9

Flue gas

10th

Filter dust

11

Secondary air

12th

Afterburner

13

boiler

14

dust filter

15

Slag after the rotary kiln

16

Oil burner

Claims (10)

Process for the treatment of slag and / or ash from the thermal Treatment of garbage, characterized in that the garbage (1) in is pyrolyzed, gasified or partially burned in a first process step, being heavy metal containing slag and / or ash (8) with a comparatively high carbon content that slag and / or ash (8) in a second process step in a rotary kiln (6) to a temperature below the melting temperature of the slag and / or ash (8) is heated so that the slag and / or ash (8) before it is discharged from the rotary kiln (6) in the rotary kiln for a sufficiently long time (6) lingers, so that the heavy metals contained in it Reduction of the slag's own carbon into its metallic form transferred and the volatile heavy metals in the gas phase and are discharged from the rotary kiln (6) with the flue gas (9), and that a heavy metal-depleted slag (15) from the rotary kiln (6) is carried out. A method according to claim 1, characterized in that both the Gasification or partial incineration of the waste (1) and as well as the reduction and volatilization of the heavy metals from the combustion Slag / Ash (8) in a single aggregate, i.e. in a rotary kiln (6), takes place, the amount of combustion air (7) so dimensioned is that at the end of the rotary kiln (6) practically no more oxygen can be demonstrated. A method according to claim 1, characterized in that the pyrolysis, Gasification or partial combustion occurring and in a dedusting system (5) separated filter dust (10) of the slag and / or Ash (8) added and heated together in the rotary kiln (6) and be depleted of heavy metals. Method according to one of claims 1 to 3, characterized in that that the dwell time of the slag and / or ash (8) in the rotary kiln (6) is more than an hour. Method according to one of claims 1 to 4, characterized in that that the flue gases (9) from the rotary kiln (6) cooled and in one Filters (14) are dedusted. Method according to one of claims 1 to 5, characterized in that that the slag and / or ash (8) dry without water humidification is discharged from the pyrolysis or incinerator (2). Method according to one of claims 1 to 6, characterized in that that the slag (15) discharged from the rotary kiln (6) by means of Magnetic separators and non-ferrous metal separators the remaining metallic components be removed. A method according to claim 1, characterized in that the in the Rotary tube furnace (6) introduced slag and / or ash (8) at least 10 % Contains carbon. A method according to claim 1, characterized in that the Slag and / or ash (8) before they are fed into the rotary kiln (6) Ferrous and non-ferrous metals are separated. A method according to claim 1 or 2, characterized in that the Slag (15) discharged dry from the rotary kiln (6) and in at least two fractions are separated, the first fraction with one Particle size larger than approx. 32 mm in a first sieving stage as a sieve overflow is separated, and the sieve diarrhea of a second classification stage for the purpose of separating the fine fraction 0 ... 2 mm, and at least part of the fine fraction 0 ... 2 mm from the slag processing on the air inlet side into the rotary kiln (6) and there is burned.

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