FR2771946A1 - WASTE INCINERATION PROCESS, FLY ASH TREATMENT PROCESS AND DEVICE FOR IMPLEMENTING THESE PROCESSES - Google Patents

Abstract

The invention relates to a process for treating fly ash entrained by the fumes emitted during the incineration of household and / or industrial waste. The process of the invention comprises collecting the ash formed, forming a pulp by supplying water and recycling this pulp in the waste incinerator. The invention finds application in the field of treatment of household and / or industrial waste.

Description

The invention relates to a method for treating fly ash.

  entrained by the fumes emitted during the incineration of household and / or industrial waste, to a process of incineration of household and / or industrial waste comprising such a process for the treatment of entrained fly ash, and to a

  device for implementing these methods.

  During the incineration of waste, whether domestic (or assimilated) or industrial, and whatever the incineration process (on a grid, in a fluidized bed, or even in thermolysis), the gases from combustion

  or thermolysis lead to "fly ash".

  These fly ash are powdery solids made up of unburnt particles, calcium silicates and silico-aluminates, sodium and potassium chlorides, oxides, sulphates and calcium carbonates as well as heavy metals. These fly ash are collected throughout the smoke circuit, including

  they are separated, in particular, by filters.

  These ashes contain a large number of soluble elements and must therefore be stabilized before landfilling. The purpose of stabilization is to reduce the soluble fraction which carries with it many pollutants. A process is known for treating these fly ash which consists in washing them so as to dissolve the soluble fraction, the resulting solid then being free of pollutants. But in this case, the problem is only out of place and then lies in the treatment of

  polluted liquids resulting from this washing.

  It has also been proposed to coat the ashes

  flying in plastics or bitumen.

  Currently known methods for stabilizing fly ash with binders

hydraulic.

  However, these methods require the use of an apparatus or a special installation not integrated into the device for incinerating household and / or industrial waste itself. They also require bringing to the site and using reagents such as hydraulic binder, plastic, bitumen or other to achieve their coating. There is also known a technique for vitrifying these fly ash which has an additional disadvantage compared with the coating or stabilization methods described above which is a high cost due to the use of a high temperature. It has also been proposed to hydrolyze these fly ash, but again, use a non-integrated apparatus or special installation.

  in the waste incineration oven.

  In addition, all of these methods have the drawback of always requiring the storage, in special industrial waste landfills, of the treated or stabilized ash. However, this storage is expensive and the ashes cannot be used and therefore

  valued for example in road techniques.

  The invention aims to overcome the drawbacks of the methods of the prior art by proposing a method for treating fly ash entrained by the fumes emitted during the incineration of household and / or industrial waste by transforming these ashes into

clinker clinkers.

  To this end, the invention provides a method for treating fly ash entrained by the fumes emitted during the incineration of household and / or industrial waste, characterized in that it comprises the steps of: - collecting said ashes along the circuit and fumes, formation of a pulp by adding water to the ashes, - introduction of the pulp thus obtained into the hearth of the waste incinerator to transform the ashes into bottom ash by clinkering and hydrolyze the chlorides they contain, and - recovery from the incinerator, by a

  extractor, bottom ash thus formed.

  According to a variant of the invention, said contribution

  water is produced by adding water alone.

  According to another variant of the invention, said addition of water is carried out by adding wet sludge consisting of water, organic matter and mineral matter such as, for example, sludge from water treatment plants or black liquors of stationeries. According to a feature of the process of the invention, said pulp has a dryness of between 20 and 40% by weight. According to an embodiment of the method of the invention, a mixture of said pulp is produced with household and / or industrial waste before introduction of this mixture by normal means

  for the introduction of household and / or industrial waste.

  According to another embodiment of the process of the invention, household and / or industrial waste is introduced by the normal means of introducing the waste and the pulp is introduced by a separate introduction means located upstream and in cold zone

from the incinerator hearth.

  According to yet another embodiment of the process of the invention, the pulp and the household and / or industrial waste are introduced by separate means, the household and / or industrial waste being introduced by the normal means of introduction of the waste and the pulp being introduced directly into the

home of the incinerator.

  The invention also relates to a method for incinerating household and / or industrial waste, characterized in that it comprises the treatment of fly ash entrained by the fumes emitted during

  of this incineration by the process described above.

  It also relates to a device for implementing the methods described above comprising: - a means for introducing waste into the hearth of an incinerator, - an extractor located at the bottom outlet of the hearth, for recovering the clinkers thus formed , - a means for separating the fly ash from the smoke, to purify this smoke, - a means for extracting and removing the purified smoke, characterized in that it further comprises: - at least one means for recovering the ash flying along the smoke circuit, connected to a mixer, - a means of water supply connected to the mixer, - a means of transporting the pulp formed in the mixer, connecting the lower part of the mixer, directly or indirectly, to the incinerator hearth

to bring the pulp into the hearth.

  According to a characteristic of the device of the invention, said means of transport is connected to the hearth by the introduction means opening into the chute located under the normal hopper for introducing waste

household and / or industrial.

  According to a variant of the device of the invention, said means of transport is connected to the hearth by the hopper for the normal introduction of household and / or industrial waste. According to another variant of the device of the invention, said introduction means is connected

  directly at the fireplace, in a hot zone.

  According to another characteristic of the device of the invention, the means of transporting the pulp is a

pump associated with a conduit.

  According to yet another characteristic of the device of the invention, the means of transporting the pulp consists of mechanical conveyors

mass, band or bucket.

  The invention will be better understood, and other advantages and aims of it will appear better on

  reading of the following explanatory description and

  which is made with reference to the single appended figure which represents a device for implementing the

method of the invention.

  First, the prior art household and / or industrial waste incineration process

  will be described with reference to the single appended figure.

  The waste to be incinerated is introduced through the hopper 11 and the chute 9 into a combustion hearth

o they are cremated.

  The incinerator used in this process can be either an oven without heat recovery, in which case all of the ash is recovered under the filter 2, or a furnace-boiler, that is to say an oven equipped with the hearth 10 and d 'A heat recovery means constituted by the boiler 1, in which case the ashes are recovered on the one hand under the boiler 1 and

on the other hand under filter 2.

  During this incineration, on the one hand, clinkers are obtained which are evacuated at the bottom of the hearth 10 by an extractor 12, and on the other hand, combustion gases or fumes in which the fine particles called fly ash are entrained. These fumes are discharged from the top of the hearth 10 and cooled. They then pass through a filter 2 to separate the solid particles from the gas phase and the gas phase purified in the treatment of fumes 16 is discharged into the atmosphere by a fan 13 and a chimney 14. The ashes retained in the filter 2 are collected under this filter and are routed, for example by screws 3, 4, for storage, for example

in a container not shown.

  The fly ash is then further processed in another device, before storage. In contrast to this conventional process, the invention proposes to process the fly ash continuously and in the same installation as that intended for the

waste treatment themselves.

  To this end, the invention proposes to collect all of the ashes, and to mix them in a kneader 5 with water coming from an introduction means 6. In the kneader 5, a pulp is formed which is then injected by a means of transport 7, 8, into the hearth 10. This reintroduction of the ashes, in the form of pulp into the hearth 10 can be carried out either directly in the hearth 10 and in the hot zone, by an injection device of sludge known per se, either with the waste to be incinerated, in a cold zone. In this case, the pulp can be either mixed with the waste to be incinerated before introduction of this pulp / waste mixture by the hopper 11, or injected by an introduction means.

separate, in chute 9.

  Introducing the recycled ashes directly into the hearth, in the form of pulp, advantageously avoids the immediate entrainment of ashes

by combustion gases.

  In the hearth 10, and whatever the site of introduction of the pulp, hydrolysis of the sodium and potassium chlorides contained in the ashes occurs, when the pulp is brought to a high temperature of approximately 850 C, in the hearth 10. At the same time, the ashes are clinkerized and transformed into bottom ash. Thus, with the process of the invention, there is no longer any need to process or store the fly ash flowing in the incineration plant. Indeed, fly ash turns into bottom ash under the effect of the heat brought

  directly by burning waste.

  The process for treating fly ash of the invention is therefore particularly advantageous since it makes it possible to transform the ash into bottom ash, which is easily recyclable and therefore recoverable. In addition, this process directly uses the thermal energy of the incinerator of household and / or industrial waste and minimizes the thermal energy necessary for the treatment of the ash which then only affects the surface of the grains of the ash and not the whole mass. of these grains, and this without adding reagent. In addition, the chlorine present in these ashes is eliminated in the form of hydrochloric acid by the hydrolysis of alkali and alkaline earth chlorides, this hydrochloric acid then being retained in the smoke treatment system whose incineration plant is legally equipped. This process also removes unburnt carbon in the form of carbon dioxide. Thus the pulp form of the fly ash, in addition to providing the water necessary to obtain an easily transportable mass of ash, more particularly easily pumpable, to simplify the injection process in the incinerator, advantageously allows

  hydrolysis of the chlorides contained in these ashes.

  The water for making an easily transportable pulp, preferably by a pump, and for hydrolyzing the chlorides is supplied by either water alone or, advantageously, by the water contained in

  wet sludge from water treatment plant.

  In the latter case, water is saved which should have been used to make the pulp. In addition, the clinkering of ash and the incineration of sludge from water treatment plants are

  performed in a single operation.

  In the process of the invention, it should be noted that moreover the heavy metals entrained and fixed on the ashes are themselves thus fixed in the silico-aluminous matrix of the ashes by substitution of calcium atoms during the clinkering. In fact, clinkering is a surface vitrification which allows reactions between the particles of calcium silicates and silico-aluminates and the molten sodium and potassium oxides. During this operation at high temperature (800 to 1000 C) the particles agglomerate, become larger and heavier and are not entrained by the flow of smoke: they remain in the bottom clinkers whose characteristics

  physical or chemical are identical.

  Thus, due to this clinkering or surface vitrification, the heavy metals are fixed in calcium silico-aluminates and are not soluble. In order to better understand the invention, we will now describe it by way of examples purely

  illustrative several modes of implementation.

Example 1

  As described with reference to the appended figure, the waste is introduced through the hopper 11 and the ash is collected under the boiler 1 and under the filter 2 and is conveyed by screws 3 and 4 to a mixer 5. For a 1 ton of waste, ashes represent

  approximately a weight of 20 kg of dry matter.

  The mixer 5 is supplied with water by the introduction means 6. The water is metered by a conventional volumetric or mass system so as to obtain

  leaving the mixer a pulp having a dryness, that is to say

  say a dry matter content, which allows it to be easily pumped by a pump 7 known per se. Preferably the pump 7 is volumetric. It sends the pulp through the conduit 8 and the introduction means 15 located in the chute 9 in the hearth 10. The pulp is introduced into the hearth 10 at the same time as the waste and care will be taken to distribute the pulp

  over the entire width of the chute 9.

  Arrival in the hearth, the pulp is subjected to

  hydrolysis and clinkerization reactions described above

  above and is integrated into the bottom clinkers which it has

  the same physico-chemical characteristics.

  In the case where a part of the pulp is reentrained by the fumes, because containing too fine particles, the particles will again be stopped by the filter 2 and recycled to the hearth 10 via the mixer 5 and the reformed pulp. Thus, the invention allows continuous treatment and a complete elimination of the need to evacuate the

fly ash.

Example 2

  In the same way as in Example 1, 20 kg of ash from the incineration of 1 ton of waste is collected under the boiler 1 and under the filter 2 and is conveyed by screws 3 and 4 to the

mixer 5.

  Unlike Example 1, the mixer 5 is supplied, by the introduction means 6, with wet sludge from water purification stations. In this case, 150 kg of sludge at 20% by weight of dry matter is used, which gives a pulp having a dryness of 30% which is still easily transportable, for example by pumping. However, a mechanical means of transport is used here consisting of a series of mass or belt conveyors and a bucket elevator. The pulp is mixed with the waste to be incinerated before introduction of this mixture through the hopper 11. The pulp / waste mixture to be incinerated is then sent to the hearth 10 where the fly ash undergoes the

  hydrolysis and clinkerization reactions described above

  above and are integrated into the bottom ash resulting from

  incineration of the waste itself.

  As in Example 1, the clinkerized ashes

  then have the same physical and

chemicals than bottom ash.

  Example 3 The procedure is as in Example 1, except that the pulp is directly introduced into the hearth 10. Again, the pulp will be hydrolyzed and clinkerized and integrated into the

  clink as in examples 1 and 2.

  As can be seen from the above, while in the processes of the prior art, the ashes are considered as special waste and disposed of, after costly stabilization, in special industrial waste landfills, thanks to the invention, these ashes are freed from the chlorine they contain and are thermally stabilized by clinkering

  and transformed into recoverable bottom ash.

  The method and the device for treating fly ash entrained by the fumes from the incineration of household and / or industrial waste according to the invention and as described above, can of course be integrated into a method and a device, respectively, waste incineration

  industrial and / or household appliances of the prior art.

  Consequently, the invention also encompasses all the methods of incineration of household and / or industrial waste which comprise the stage of treatment of the ash entrained by the fumes resulting from the incineration of household and / or industrial waste and which consists to collect these ashes, to transform them into aqueous pulp and to recycle them, in the waste incinerator, to clinkerize them and integrate them into

  clinkers produced in this incinerator.

  Similarly, any device for incinerating household and / or industrial waste which includes the device for treating ash entrained by the fumes from the incineration of household and / or industrial waste and which includes a means of processing, recovery and transformation of ash into aqueous pulp and a means of injection and recycling of this aqueous pulp in the incinerator is

encompassed by the invention.

  The method and the device of the invention are not limited to the means of injection, transport of pulp, obtaining of pulp and recycling of this pulp in the hearth described and illustrated here, as long as these means serve to recycle the ash entrained in the gases from the incineration of household and / or industrial waste, in the form of aqueous pulp, in

the incinerator itself.

  This means that the invention is in no way limited to the means described and illustrated. On the contrary, it includes all the technical equivalents and variants of these means if they are implemented according to its spirit.

Claims (14)

  1. A method for treating fly ash entrained by the fumes emitted during the incineration of household and / or industrial waste, characterized in that it comprises the steps of: - collecting said ashes along the smoke circuit, - formation of '' a pulp by adding water to these ashes, - introduction of the pulp thus obtained into the hearth (10) of the incinerator (1) of waste, to transform the ashes into bottom ash by clinkering and hydrolyze the chlorides which they contain, and - recovery from the incinerator (1) by   the extractor (12) of clinkers thus formed.   2. Treatment method according to claim 1, characterized in that said supply of water is carried out by adding water alone.   3. Method according to claim 1, characterized in that said supply of water is carried out by adding wet sludge consisting of water, organic matter and mineral matter such as for example sludge from water treatment plants or the black liquors from paper mills.   4. Method according to any one of   previous claims, characterized in that said   pulp has a dryness of between 20 and 40% by weight.   5. Method according to any one of   previous claims, characterized in that   mixes said pulp with household and industrial waste before introduction of this mixture, by means of introduction (11) of the waste industrial and / or household.   6. Method according to any one of   claims 1 to 4, characterized in that said   household and / or industrial waste is introduced by the normal introduction means (11) and in that said pulp is introduced by a separate introduction means   (15) located upstream and in the cold zone of the hearth (10).   7. Method according to any one of   claims 1 to 4 characterized in that said pulp   and said household and / or industrial waste is introduced by separate introduction means, household and / or industrial waste being introduced by the normal introduction means (11) and the pulp being introduced directly into the hearth (10) of the incinerator (1).   8. Method for incinerating household and / or industrial waste, characterized in that it comprises the treatment of fly ash entrained by the fumes emitted during this incineration by the process   according to any one of claims 1 to 7.   9. Device for implementing the method   according to any one of the preceding claims,   comprising: - a means for introducing waste (11) into the hearth (10) of an incinerator (1), - an extractor (12) located at the bottom outlet of the hearth (10), for recovering the clinkers thus formed, - a means for separating (2) the fly ash from the fumes, to purify these fumes, - a means of extraction (13) and evacuation (14) of the purified fumes and, characterized in that it further comprises: - at least one means of recovery (3, 4) of fly ash along the smoke circuit connected to a mixer (5), - a means of supplying an aqueous solution (6) connected to the mixer (5), - a means of transport (7, 8) of the pulp formed in the mixer (5), connecting the lower part of the mixer (5), directly or indirectly, to the hearth (10) of the incinerator (1) to bring the pulp into the fireplace (10).   10. Device according to claim 9, characterized in that the transport means (7, 8) is connected to the hearth (10) by the introduction means (15) opening into the chute (9) located under the hopper (11 ) normal introduction of household and / or industrial waste. 11. Device according to claim 9 characterized in that the transport means (7, 8) is connected to the hearth (10) by the hopper (11) of introduction   normal household and / or industrial waste.   12. Device according to claim 9, characterized in that the means of transport (7, 8) is   directly connected to the fireplace (10) in the hot zone.   13. Device according to any one of   claims 9 to 12, characterized in that the means for   transport (7, 8) is a pump (7) associated with a conduit (8). 14. Device according to any one of   claims 9 to 12, characterized in that the means for   transport (7, 8) consists of transporters   mechanical mass, belt or bucket.