EP0814304B1 - Method of improving the quality of the slag produced by a refuse incinerator and incinerator plant for carrying out the method - Google Patents

Description

The present invention relates to a method improving the quality of bottom ash produced by a waste incineration plant and a facility incineration for its implementation.

It relates more precisely to a method of treatment of bottom ash produced by an installation incineration in which the fumes leaving a combustion chamber are evacuated to a set of smoke treatment and according to which bottom ash from the combustion chamber are cooled in a cooling filled with water known as a descaler.

An example of such an installation includes a waste incineration grid.

In such an installation, the waste is discharged into a hopper and fall into a well substantially vertical on a substantially horizontal surface where they are pushed by a pusher on a combustion grate tilted. This grid consists of fixed bars and mobile alternating and provided with air passage holes of combustion and the waste is burned there and gradually translated to the end of the grid where they fall in the scrubber and are cooled. They are then evacuated for recovery. Combustion fumes as for them escape above the grid in a leads to a smoke treatment unit capable of have a recovery boiler, a filter, a hydrochloric acid emission elimination device and / or sulfur dioxide. The fumes are then evacuated by a fireplace. The document FR 2 605 724 describes an installation of this kind.

The invention can however be applied to any waste incineration plant comprising a scrubber, whatever the type of combustion chamber producing bottom ash, whether it be grate like previously described or rotary kiln, fluidized bed or other.

The bottom ash produced by such an installation, after de-railing, consists largely of major elements such as SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , CaO, Na ₂ O, K ₂ O, MgO. These elements are most often combined with one another and form the mineral matrix of bottom ash. Inside this matrix, heavy metals such as lead, mercury, cadmium or chromium are found in trace amounts in various forms, in particular oxides, chlorides, hydroxides, sulfates or carbonates. chemically or not bonded to the mineral matrix.

These clinkers have long been used for their mechanical qualities in road engineering such as underlayment or backfill materials. In this case, it is essential, in order to preserve the environment, that water rain does not percolate heavy metals contained in bottom ash.

To predict the behavior of bottom ash in relation to this phenomenon, laboratory tests have been developed. In France, the leachate test according to the NFx31.210 standard is used by the regulations to set thresholds for the leachate content allowing the quality of bottom ash to be defined according to the table below: VALUATION MATURATION STORAGE (V) (M) (S) IMBRULES% <5 <5 > 5 SOLUBLE FRACTION <5 <10 > 10 POLLUTANT POTENTIALS: mg / kg dry clinker Hg <0.2 <0.4 > 0.4 Pb <10 <50 > 50 CD <1 <2 > 2 Ace <2 <4 > 4 Cr ⁶ <1.5 <3 > 3 SO ⁴ <10,000 <15000 > 15,000 COT <1500 <2000 > 2000

From their production, if the bottom ash presents contents all below the thresholds of category V (recovery), they are immediately recoverable.

If the contents are such that the bottom ash is classified in the intermediate category M (maturation), they require a maturation treatment on the park until they have the characteristics of category V. During this maturation in the park, carbonation progressive elements like lime or certain heavy metals play an essential role in reducing the leachable fraction.

If clinkers are classified in category S (storage), they are stored in a controlled landfill, which represents a significant cost.

The clinkers produced by the installations waste incineration are most often classified as category M and sometimes in category S. The fraction soluble and the lead content of the leachate are the criteria most difficult to meet to reach the category V.

The present invention makes it possible to produce bottom ash. directly recoverable at the outlet of the installation incineration, by carrying out a carbonation integrated into this installation, i.e. without a specific carbonation added.

To do this, in accordance with the invention, fumes are taken from said processing set and are recycled by bubbling in the water from the scrubber.

Accelerated carbonation of bottom ash is thus carried out continuously, without the use of additional chemical substance. This treatment by bubbling in the water of the scourer allows a reaction in three phases, solid, liquid and gas. The dissolved CO ₂ penetrates quickly into the pores of bottom ash and the carbonation time is particularly short.

According to a preferred embodiment, all of smoke treatment comprising downstream of the combustion a recovery boiler, a filter, a hydrochloric acid emission elimination device and / or sulfur dioxide and a chimney, said fumes are taken at the outlet of said elimination device.

As a variant, said fumes can be sampled at the outlet of said filter or at the outlet of said boiler recovery.

Advantageously, the ratio of the smoke flow recycled and the flow of smoke produced is between 2 and 15%.

Preferably, the fumes escaping from the scrubber are returned to the combustion chamber. These fumes then contribute to reducing the formation of nitrogen oxides.

The invention also relates to an installation incineration according to claim 7 for the implementation of this process, the scrubber is equipped with smoke injection means recycled from its processing set fumes.

Said injection means can be ramps placed in the water of the scrubber or injection nozzles arranged on the walls of the scrubber.

The invention is described below in more detail at using a figure representing only one mode of preferred embodiment of the invention.

In a waste incineration plant, these are dumped into a hopper 1 and fall into a well 2 substantially vertical on a substantially surface horizontal where they are pushed by a pusher 3 on a combustion grate 4 inclined in a combustion 7. This grid 4 consists of bars fixed and mobile alternating and provided with through holes combustion air from the blowing chambers 5. The waste is burned there and gradually translated to the end of the grid 4 where they fall into the scrubber 6 and are cooled to form the bottom ash. They are then evacuated for recovery.

As for the combustion fumes, they escape above from grid 4 in a conduit to a set of smoke treatment comprising in series a boiler recovery 9, a bag filter or dust collector electrostatic 10, a device for eliminating hydrochloric acid and / or sulfur dioxide emissions 11, for example by wet washing, and a fan 12. The smoke is then evacuated through a chimney 13. In some installations, filter 10 and device 11 can be integrated.

According to the invention, fumes are taken from said treatment set and are recycled by bubbling in water from the scrubber 6.

Preferably, this smoke is taken at the outlet said elimination device 11 downstream of the fan 12 by a pipe 14 using a fan 15. This mode of advantage has the advantage of using very fumes low in hydrochloric acid and sulfur dioxide and consequently the chlorine and sulphate contents in the water from the scrubber does not increase significantly by compared to the prior art.

Alternatively, this smoke is taken at the outlet of said filter 10 via a line 14 'or at the outlet of said recovery boiler 9 through a pipe 14 ".

The flow rate of recycled fumes depends in particular on the quantity of clinkers produced, on the CO ₂ content in the fumes, on the chemical characteristics of the clinkers such as for example the content of lime and lead. In practice, the ratio of the flow of recycled smoke and the flow of smoke produced is between 2 and 15%.

Tests carried out on an installation of laboratory simulating the operating conditions of a urban waste grid incineration plant have shown that with a smoke recirculation rate of around 5%, it is possible to reduce the leaching of lead by factor greater than 10 and reduce the soluble fraction to a lesser extent.

In an installation as described, the fumes escaping from the scrubber 6 are directly returned to the combustion chamber 7 by the well separating it from the scrubber.

The scraper 6 is equipped with means for injecting fumes which can be ramps arranged in the water of the scraper or injection nozzles arranged on the walls of the scrubber.

Claims (9)

1. A method of treating clinker produced by an incineration installation in which fumes leaving a combustion chamber (7) are evacuated to a fumes treatment system, wherein clinker from the combustion chamber is cooled in a cooling bath filled with water, referred to as declinkering water (6), characterised in that fumes are extracted from said treatment system and are recycled by bubbling them into the water in the declinkering unit (6).
2. A method according to claim 1 of treating clinker produced by an incineration installation, wherein the fumes treatment system includes, downstream of the combustion chamber (7), a heat recovery boiler (9), a filter (10), a system (11) for eliminating emissions of hydrochloric acid and/or sulphur dioxide and a chimney (13), characterised in that said fumes are extracted at the outlet of said elimination system (11).
3. A method according to claim 1 of treating clinker produced by an incineration installation, wherein the fumes treatment system includes, downstream of the combustion chamber (7), a heat recovery boiler (9), a filter (10) and a chimney (13), characterised in that said fumes are extracted at the outlet of said filter.
4. A method according to claim 1 of treating clinker produced by an incineration installation, wherein the fumes treatment system includes, downstream of the combustion chamber (7), a heat recovery boiler (9) and a chimney (13), characterised in that said fumes are extracted at the outlet of said heat recovery boiler (9).
5. A method according to any preceding claim, characterised in that the ratio of the flowrate of the recycled fumes to the total flowrate of the fumes produced is from 2% to 15%.
6. A method according to any preceding claim, characterised in that the fumes exhausting from the declinkering unit (6) are returned to the combustion chamber (7).
7. An incineration installation for implementing the method according to any preceding claim, including a combustion chamber (7) from which exhaust fumes are evacuated to a system for treating said fumes and a cooling bath filled with water, referred to as declinkering water (6), in which the clinker from the combustion chamber (7) is cooled, characterised in that the declinkering unit is equipped with injection means for bubbling into the water recycled fumes extracted from its fumes treatment system.
8. An installation according to claim 7, characterised in that said injection means are manifolds in the water in the declinkering unit.
9. An installation according to claim 7, characterised in that said injection means are injection nozzles on the walls of the declinkering unit.

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