CH701352B1 - Process for the thermal treatment of incineration residues, particularly filter ash from garbage or waste incineration plants and metal recovery. - Google Patents

Abstract

The invention relates to a method for the thermal treatment of combustion residues, in particular of filter ash, from a garbage or waste incineration plant (10), which serves to remove pollutants contained therein, which at least metals, especially heavy metals and especially mercury, furan and / or dioxin. The method comprises the steps: a. Heating the combustion residues to transfer the pollutants to the gas phase, b. Filtering out metals, especially heavy metals, and especially mercury, during the gas phase, c. Returning the dioxin and furan-containing residual gas to the garbage incinerator (10), and d. Collecting and depositing the in steps a.-c. treated combustion residues, in particular the recycled filter ash. Advantageous developments of the method provide for a further treatment of the combustion residues, so that ultimately an over-day dumping of the processed combustion residues is possible, which were freed of pollutants (such as dioxins, furans, mercury and / or metal oxides).

Description

The invention relates to a method for the thermal treatment of combustion residues, in particular filter ash, from refuse incineration plants (KVA).

Flammable household and commercial waste are disposed of in waste or waste incineration plants (KVA) for decades. The waste incineration works perfectly in these modern plants. On the one hand, it has been possible on the one hand to continuously reduce the environmental impact and to improve the ecological balance through increased exhaust air purification and increasing metal recovery from the slag, and on the other to permanently increase electricity and heat production. However, the disposal of contaminated combustion pollutants in the form of filter ash, of which, for example, in Switzerland in 2007 about 60 000 tons accrued and which is mainly burdened with soot, heavy metals, mercury, furan and dioxin, is still unsatisfactorily solved.

Part of this filter ash is still deposited today without pretreatment in underground landfills. Another part of the filter ash is placed in a so-called neutral wash to remove salts. The remaining material from this filter ash is then solidified with cement and can be disposed of in a landfill. In a further alternative treatment process, the filter ash first passes through an acidic wash with hydrochloric acid from the flue gas cleaning. Here, the heavy metals zinc, cadmium and lead are removed and the filter ash then deposited together with the slag from the KVA. Filter ash from the KVA contains up to 5 micrograms of dioxin per kilogram. If this toxic substance comes into contact with oil-contaminated seepage water in case of improper sedimentation, it can be mobilized and washed out. Due to their dangerousness, it is therefore necessary to reduce the dioxin emissions to a minimum. In order to reach the limits set by the European Union of 1 microgram dioxin per kilogram of filter ash, there is a need to develop a method of effectively reducing the dioxin content in the filter ash.

A device and a method of the same applicant relate to the mechanical treatment of the filter ash. The treated with this method filter ash from garbage or waste incineration plants is cleaned so far that a landfill of the resulting after this treatment residues can be carried out in underground landfills. By mechanical means, however, other components of the filter ash (eg dioxins (PCDD), furans (PCDF) and mercury (Hg)), some of which are particularly harmful to health and the environment, as well as recyclable metals can not be removed. The over-day dumping of the remaining filter ash fractions is thus out of the question due to the residual contents of pollutants. But also in the underground landfill the contaminated residues are problematic. In addition, mercury and metal oxides contained in the residues can not be recovered as raw materials and additionally problematize the landfill or prevent their economic recovery.

A disadvantage of the mechanically processed filter ash (a name, which is also used in the following as a synonym for the combustion residues) is that the deposition must be due to the pollution in underground landfills. This goes hand in hand with much higher costs. In addition, the existing underground landfills are reaching their capacity limits. This necessitates the development of new deposits, resulting in further costs and acceptance problems.

The object of the present invention is therefore to provide a method that improves the treatment of incineration residues from refuse or waste incineration plants, in particular the filter ash, to the extent that a treatment takes place, which leads to the most pollutant-free combustion residues.

The object is achieved by a method for the thermal treatment of combustion residues, in particular of filter ash, from a garbage or waste incineration plant according to claim 1. Advantageous developments of the invention are the subject of the dependent claims.

In the novel process for the treatment of such combustion residues first dioxin (PCDD), furan (PCDF), mercury and metals are removed from the combustion residues, so that the thus treated combustion residues are easily underground-dumpable. Due to the thermal treatment, the specific weight of the ash is increased by about 20%, which is ecologically and economically very important. With an optional additional addition of a cement compound as a binder, the leaching of remaining in the filter ash pollutant residues is prevented and increases the compressive strength of the as pressed in block form ashes, so that an overnight deposit of the filter ash after treatment in the inventive method is straightforward. The method also allows the deposition of the mercury contained in the filter ash and recyclable metals. The recoverable fractions of the filter ash thus obtained can either be separately landfilled or subsequently returned to the material cycle, if this appears more meaningful from an economic point of view. The same applies to metal oxides, which are excreted during the temperature treatment of the filter ash from this. The inventive method can be used in conventional filter ash recycling or. Processing plants, including in those with a so-called. Acid laundry, preceded to improve the degree of purification of the ash.

A method according to the invention comprises method steps for the elimination of dioxin and furan and for the recovery of mercury and / or metals from the filter ash to be treated. In a first step, the filter ash is heated to temperatures between 238 ° C and 1000 ° C, preferably to temperatures between 356 ° C and 600 ° C and more preferably at a temperature of 500 ° C. In this process step, the filter ash passes through the heatable part of a treatment plant, in particular a heated screw or a heated rotary tube. Black particles in the filter ash are lighter and float up the product stream in the treatment plant. In particular, the heating of these black particles in the specified temperature range produces gases in a gasification process. In this case, dioxin, furan, mercury and possibly also parts of the metals present are converted into the gas phase or vaporized and thereby removed from the filter ash. This is done at specific temperatures in a step-by-step process. For example, mercury vaporizes at 356.6 ° C, while chlorine vaporizes at 238.5 ° C and sulfur at 444.7 ° C. With the heating to 500 ° C can thus be achieved evaporation of all the aforementioned components to be eliminated. By further increase in temperature up to 1000 ° C and the metal components can be evaporated and then recovered from the gas phase as described above. For example, the economically usable zinc evaporates at 907 ° C and is detected by heating to almost 1000 ° C.

The pollutant (including chlorine and sulfur) and metal residues are transferred here in the gas phase. The ash remaining after heating and degassing thus no longer contains pollutants (such as dioxin). In the further process steps, the vaporized pollutants are recovered from the steam and recycled (in the case of mercury, metals and metal oxides).

The method can be carried out in a treatment plant, which has the garbage or Kehrrichtverbrennungsanlage. Then the heating of the combustion residues in the heated part of this treatment plant or in a reactor with a heated screw or a heated rotary kiln, wherein the reactor of the treatment plant is then arranged downstream. However, it is considered to be particularly favorable when the reactor is designed as a pyrolysis reactor and the heating of the combustion residues for transferring the pollutants into the gas phase takes place under exclusion of oxygen. The treatment of the residues is then depending on the starting material in indirect or direct pyrolysis. To control the pyrolysis and to achieve certain end products here is the ability to add certain pyrolysis excipients and set the pressure ratios, gas mixtures and the duration of treatment precisely, so as to achieve the best possible efficiency.

Preferably, in a further development of the method, a cooling of the hot gas. For this purpose, this is passed through a heat exchanger and thereby cooled. The heat recovered in this case can be used to increase the energy efficiency of the system, to operate a heater or to generate electricity and the like. By cooling the gases before passing through the filter, which is used for filtering out the metals, this is spared and thus extends its service life. It is considered to be advisable to place the filters and / or the filtered-out metals, such as heavy metals, in a separate depot and to store them in order to prevent contamination of the remaining fractions and thus of the environment. It is also possible to exploit the heavy metals, which can be used as an alternative to landfill.

The inventive method further provides for the resulting during the heating of the filter ash and possibly cooled gases to pass through an activated carbon filter in order to remove metals present in the gas phase, in particular mercury. The metals, in particular the said mercury, are thereby bound in the coal of the filter. The remaining after filtration gas now contains only dioxins and furans. The treated with metals, in particular mercury, coal is recycled in an regarded as favorable, additional process step and the metals, especially the mercury, thereby recovered. For this purpose, for example, the retrieved from the vapor mercury resp. the activated carbon, which has taken up mercury, collected in a mercury catch tank and fed to market and environmentally friendly mercury treatment. The same can be done for the collected metals. In a further step of the thermal treatment process according to the invention for filter ash, the gases, which are freed of mercury and / or of metals and still containing dioxins and furans, are introduced into a combustion furnace.

Preferably, a further cooling of the treated filter ash. As low is considered in this context, the ashes (for example, after the passage of the above-mentioned heated screw or the heated rotary tube or after treatment in a so-called rotary table process) to pass through or through a heat exchanger to here to increase energy efficiency further Recover heat and to provide the waste heat for further uses.

As low is considered, if there is a further separation of metal oxides and metals, which were not or not completely evaporated due to low treatment temperatures, a separation of these substances from the treated combustion residues by means of magnetic separation. The magnetic separation can take place immediately before landfilling. However, it is also possible that this is carried out once or several times in or before each of the abovementioned method sections. It can thus be carried out a further reduction in the burden of pending for landfill combustion residues with these substances. In addition, however, there is also the possibility of recovering economically recoverable residual constituents of the filter ash in order to increase the contribution margin.

In a simple embodiment, the filter ash is not desalted or the metal oxide portion removed only incomplete. While the original ash was more flaky, this is converted by the application of the inventive method in a sandy texture and at the same time increases their specific gravity. Since only mercury, metals, dioxin and furan were removed from the filter ash in the process according to the invention, this ash is suitable for underground deposit. It is therefore considered advisable to further treat the treated filter ash for overnight storage.

Further advantages, features and characteristics of the invention will become apparent from the following description of preferred (but not limiting) embodiments of the invention with reference to the schematic drawing. It shows: <Tb> FIG. 1 <SEP> is a schematic representation of the sequence of the method according to the invention.

The inventive method is used for the thermal treatment of combustion residues and in particular for the treatment of dioxin, furan- and heavy metal contaminated, in particular mercury-loaded filter ash from garbage or waste incineration plants (here generally designated by the numeral 10). The process can be preceded or followed by any existing filter ash processing plant. In this case, the upstream is preferable to the downstream, so that the dioxin and furan are removed right at the beginning. It follows thus first a mechanical or chemical treatment of the filter ash and then a thermal treatment. However, it is also conceivable that the thermal of the chemical or mechanical treatment is connected upstream.

In the method shown schematically in Fig. 1 dioxin (PCDD), furan (PCDF) and mercury are removed from the ash, which is taken from the investment filter 20 a KVA 10 or a mechanical / chemical treatment plant 30. The filter ash treated in this way is capable of being disposed of underground after treatment. Due to the thermal treatment, the specific weight of the ash is increased by about 20%, which is ecologically and economically very important. The mercury is recirculated (as are all metal oxides excreted at this temperature).

In the first step of the process filter ash, which is taken from the (a KVA 10 or a mechanical / chemical treatment plant 30 associated) investment filter 20 is heated in a reactor 11 to 500 ° C. This is done for example by a reactor 11 arranged in the heated screw or by a heated rotary tube (both not shown). The black particles in the filter ash are lighter, float up here and are therefore the most heated. This heating of the black particles to 500 ° C produces gases (gasification process). The dioxin, furan and mercury go into the gas phase during the gasification process or evaporate and are thereby removed from the filter ash. For example, at 356.6 ° C mercury evaporates away, but already at 238.5 ° C chlorine and only at 444.7 ° C sulfur. In order to achieve a safe evaporation of all relevant pollutants, a reactor temperature of about 500 ° C is selected in the inventive method. The dioxin-containing residues (including chlorine and sulfur) are thus converted into the gas phase, and in the reactor 11 remains only ash, which contains no dioxin more. In a further method step, the hot gas is introduced into a gas heat exchanger 2, cooled there and thus recovered heat. By this cooling of the gases before passing through the heavy metal filter 3 this is conserved. After the gas heat exchanger 2 heavy metals are filtered out of the gas in the heavy metal filter 3, which can then be spent in the depot 7 and stored.

The resulting in the first steps and subsequently cooled gases flow through the heavy metal filter 3, an activated carbon filter 4, which binds the mercury in the coal. This mercury-laden coal can later be reprocessed and the mercury recovered. The filtration through the activated carbon filter 4 can be further improved by chemical bonding of mercury. The gas is after filtration through the activated carbon filter 4 only dioxin and furanhaltig. The mercury deposited from the gas phase or the activated carbon which has taken up the mercury is collected in a mercury collecting tank 17 and can subsequently be made available from the mercury collecting tank 17 for the environmentally and marketable mercury treatment. The liberated from mercury, but still dioxin and furan-containing gases are returned via a gas inlet 5 (for example, a valve) in the combustion furnace 12 of the KVA 10 and eliminated by the high temperatures prevailing there.

The heated to separate the pollutants ash is passed over or through an ash heat exchanger 8 and the filter ash cooled here. The recovered heat can then be fed, for example, into the heat cycle of the KVA 10 and the efficiency of the system can be increased thereby.

After passing through the ash heat exchanger 8, the processed filter ash is collected in a warehouse 9. Since the filter ash is not yet desalted after removal of mercury, dioxin and furan and since the metal oxides have been removed only incompletely, this ash is usually suitable only for underground landfill. Due to the treatment described above, the filter ash is sandy consistency while at the beginning of the process it was flaky. Also, the specific gravity of this recycled filter ash is higher.

Claims (9)

1. A process for the thermal treatment of combustion residues, in particular of filter ash, from a garbage or waste incineration plant (10), for the removal of pollutants contained therein, comprising at least metals, especially heavy metals and especially mercury and furan and / or dioxin, comprising the steps: a. Heating the combustion residues to transfer the pollutants into the gas phase, b. Filtering out metals, especially heavy metals, and especially mercury, during the gas phase, c. Returning the dioxin and / or furan-containing residual gas to the garbage or refuse incineration plant (10), and d. Collecting and depositing the in steps a.-c. treated combustion residues, in particular the recycled filter ash. 2. The method according to claim 1, characterized in that the heating of the combustion residues in the form of the filter ash to temperatures between 238 ° C and 1000 ° C, preferably to temperatures between 356 ° C and 600 ° C and more preferably at a temperature of 500 ° C takes place 3. The method according to claim 1 or 2, characterized in that the garbage or refuse incineration plant (10) has a treatment plant (30), and that the heating in the heatable part of the treatment plant (30) takes place or in a reactor (11) with heatable Screw or a heated rotary kiln, wherein the reactor (11) of the processing plant (30) is arranged downstream. 4. The method according to claim 3, characterized in that the reactor is designed as a pyrolysis reactor, and that the heating of the combustion residues for transferring the pollutants into the gas phase takes place under exclusion of oxygen. 5. The method according to claim 3 or 4, characterized by the further process step of cooling the hot gas following the heating in the heated part of the treatment plant (30) or the reactor (11) by introducing the gas into a downstream gas heat exchanger ( 2). 6. The method according to any one of claims 1 to 5, characterized in that the filtering out of the metals, in particular the heavy metals and especially of the mercury from the gas phase with an activated carbon filter (4). 7. The method according to any one of claims 1 to 6, characterized by the further step of cooling the heated to transfer the pollutants in the gas phase combustion residues, in particular the filter ash, by passing through an ash heat exchanger (8). 8. The method according to claim 7, characterized in that the refuse or refuse incineration plant (10) has a heat cycle and that the heat recovered by the ash heat exchanger (8) to increase the efficiency in the heat cycle of the garbage incineration plant (10) is fed. 9. The method according to any one of claims 1 to 8, characterized in that before depositing the in steps a.-c. recycled combustion residues, in particular the treated filter ash, in a further process step, a deposition of not completely removed from the combustion residues metals and / or metal oxides formed by means of magnetic separation (26).