EP0692677B1 - Process and installation for the thermolysis of waste - Google Patents

Abstract

Procedure for thermal treatment of waste consists of pyrolysis of the waste, recycling of the pyrolysis gas as a combustible for the pyrolysis and post-treatment of the solids output of pyrolysis in that the combustible solids output at the post treatment of the pyrolysis solids can be burnt in a cyclone furnace (5) or stocked. The hot gas output of the cyclone furnace can be used to recoup energy (11), and the post-treatment consist essentially of purification of carbon solids. The pyrolysis gas can be burnt in the cyclone furnace (5) or in the means of recouping energy (11). The post-treatment consists of cooling the solids, extracting and rinsing the mineral materials, hot washing to dissolve notably chlorine salts, and separating the water and carbon solids. <IMAGE>

Description

The present invention relates to the field of treatment thermal treatment of waste, including a treatment thermolysis of waste.

The waste likely to be treated according to the invention is preferably solid, heterogeneous and not dangerous.

It is therefore primarily household waste but also ordinary industrial waste such as automobile shredding, used tires, waste plastics, industrial or sewage sludge, etc.

As will become clear from the description which follows, the invention advantageously makes it possible to treat waste from very variable sizes, at very variable flow rates also.

We already know, in the field of heat treatment of waste, installations intended to carry out thermolysis, which also allow most of them to treat either thermolysis is the solids from thermolysis.

Among the documents concerning oriented devices towards the treatment of thermolysis solids, we can cite by example German patent DE 4308551 or applications French FR 2 679 009 and FR 2 678 850 both filed in the name of the plaintiff.

German document DE 4308551 presents the characteristic of gasifying the fine carbon-rich fraction of solid residues to produce synthesis gas and slag of fusion.

The two aforementioned French patent applications disclose in in particular washing the solids from thermolysis.

Other documents more particularly reveal a treatment of effluents or thermolysis gas: in this category can be mentioned the French patent application FR 2 668 774, or even document EP-A1-0302310.

According to French request FR 2 668 774 a treatment of gases at hot, in the thermolysis oven itself, can be operated: this allows to be able to directly re-use the pyrolysis gases, without further treatment. More particularly according to this document, the pyrolysis gases are used to heat, directly or indirectly, waste.

Document EP-A1-0302310 discloses in particular a combustion combustion effluents at very high temperatures.

This prior art makes it possible, as we can see, to improve the thermolysis process in terms of the implications for the gaseous or solid discharges that it generates. Increasingly stringent environmental standards, planned or already in force in most industrialized countries, force operators to install less and less polluting installations. Releases of N0 _x and MCI, HF, SO ₂ , Co, fly ash, clinker, etc. are in particular subject to increasingly strict standards.

We also know the document EP-A2-0 312 742 which describes a combustion process where the waste is first subjected to a incomplete combustion at low temperature in a cyclone hearth, then unburnt elements are subjected to high temperature combustion.

However, the aforementioned prior art improves only one or the other of the thermolysis products, namely either gaseous effluents or products solid.

In addition to energy, consumption and especially the balance sheet energy consumption remain underestimated or even neglected parameters in the prior art.

The object of the present invention is to remedy these drawbacks. It allows in particular a better valorization of the energy content garbage.

In addition, the present invention makes it possible to minimize self-consumption. of energy required to carry out the process.

• une thermolyse desdits déchets;
• un recyclage d'une partie des gaz de thermolyse comme combustible pour la thermolyse;
• un post-traitement des solides issus de la thermolyse consistant essentiellement en une épuration des solides carbonés.

The present invention therefore relates to a process for the thermal treatment of waste, comprising in particular:

• thermolysis of said waste;
• recycling part of the thermolysis gases as fuel for thermolysis;
• post-treatment of solids from thermolysis consisting essentially of a purification of carbonaceous solids.

• les combustibles solides issus du post-traitement des solides de thermolyse sont brûlés au moins en partie dans un foyer-cyclone et/ou stockés;
• les gaz chauds issus du foyer-cyclone alimentent au moins un moyen de récupération d'énergie, et en ce qu'il consiste en outre à contrôler la quantité de combustibles solides brûlés dans le foyer-cyclone et la quantité de combustibles solides stockés, en fonction du bilan énergétique.

According to the invention:

• the solid fuels resulting from the post-treatment of the thermolysis solids are burned at least in part in a cyclone hearth and / or stored;
• the hot gases coming from the cyclone hearth supply at least one energy recovery means, and in that it also consists in controlling the quantity of solid fuels burned in the cyclone hearth and the quantity of solid fuels stored, in function of the energy balance.

More particularly, the thermolysis gases can be burnt less partially as fuel either in the cyclone hearth or in at least one of said energy recovery means.

• un four de thermolyse;
• au moins un moyen de combustion des gaz de thermolyse;
• un moyen de récupération d'énergie; et
• un moyen de post-traitement des solides de thermolyse, qui réalise une épuration des solides carbonés.

The present invention further relates to a thermal waste treatment installation comprising:

• a thermolysis oven;
• at least one means for combustion of the thermolysis gases;
• energy recovery means; and
• a means of post-treatment of thermolysis solids, which performs a purification of carbonaceous solids.

• un moyen de stockage des solides carbonés epurés
• un foyer-cyclone alimenté par une partie au moins des combustibles solides issus du moyen de post-traitement,
• un moyen destiné à véhiculer les gaz chauds issus dudit foyer-cyclone vers ledit moyen de récupération d'énergie, et
• un moyen destiné à contrôler la quantité de combustibles solides brûlés dans le foyer-cyclone et la quantité de combustibles solides stockés, en fonction du bilan énergétique.

The installation also includes:

• a means of storage of purified carbon solids
• a cyclone hearth supplied with at least part of the solid fuels from the post-treatment means,
• means for conveying the hot gases from said cyclone hearth to said energy recovery means, and
• means for controlling the quantity of solid fuels burned in the cyclone hearth and the quantity of solid fuels stored, as a function of the energy balance.

More specifically, the means of combustion of the thermolysis gases includes said hearth cyclone.

According to the invention, the means for combustion of the thermolysis gases and the energy recovery means are arranged so that the combustion means is powered by thermolysis gases and the means of energy recovery is supplied by the effluents of the means of combustion and, under certain operating conditions, by gases hot from the cyclone hearth.

In addition, the installation according to the invention may comprise a means filtration of the fumes from the energy recovery means 11, an outlet of said filtration means being connected to an inlet of the hearth cyclone.

• La figure 1 est une représentation schématique fonctionnelle d'une installation selon un mode de réalisation de l'invention;
• La figure 2 est une représentation schématique fonctionnelle d'un autre mode de réalisation de l'invention ; et
• La figure 3 est une représentation schématique fonctionnelle d'un ensemble de post-traitement des solides de thermolyse selon l'invention.

Other characteristics, improvements and advantages of the invention will appear better on reading the description which follows, given by way of illustration and in no way limitative with reference to the appended drawings according to which:

• FIG. 1 is a functional schematic representation of an installation according to an embodiment of the invention;
• Figure 2 is a functional schematic representation of another embodiment of the invention; and
• FIG. 3 is a functional schematic representation of an assembly for post-treatment of thermolysis solids according to the invention.

According to Figure 1, the referenced raw waste (DB) can undergo first of all a pretreatment, the complexity of which depends on the type of treated waste, which uses traditional techniques: grinding, partial sorting, de-steeling, drying, etc. The purpose of this stage of pretreatment is to recover easily separable materials and recoverable, and homogenize waste. This part of the installation does does not in itself have an innovative character since the techniques used have long been used in the waste industry. This pre-treatment has no advantage of a character mandatory.

Following this pretreatment, the pretreated waste (DP) are introduced into a rotary furnace 1 with external heating or internal indirect via a device 2 allowing to guarantee the watertightness of the oven with the outside and to prevent thus any air entry into the oven. Device 2 which allows achieving this seal can be an Archimedes screw, or else a load introduction system by compacted bale.

Without departing from the scope of the invention, the rotary kiln can be as that disclosed in the French patent application IN. 94/06660, with indirect internal heating.

During their progress in oven 1, the waste undergo thermal degradation to result in formation a gas phase (GT) and a solid residue rich in matter carbonaceous (SC). Waste and gases from their decomposition thermal circulate co-current in the oven. This operation is conducted at a temperature between 200 and 800 ° C and preferably between 350 and 600 ° C. The rotary kiln is surrounded a double jacket 3 equipped with combustion means like burners (not referenced), allowing to generate the thermal power required to heat the waste. The burners can be supplied, in known manner, by a party GT1 thermolysis gases, or by any other fuel such as fuel oil or natural gas.

The reaction conditions of thermolysis allow the retention in carbon solids of almost all gases acids, in particular hydrochloric acid produced during the thermal decomposition of chlorinated plastics such as PVC. This self-neutralization of acid components by materials always present in the waste is favored, between others, by the reducing atmosphere as well as the bass temperatures to which the waste is subjected during the thermolysis. By increasing the basic component of waste by adding calcium or sodium absorbent, the yield is improved of capture of acid gases by carbonaceous solids. Purification carbonaceous solids which is described below makes it possible to eliminate in in particular the chlorine salts resulting from the capture of gases acids. Likewise, the processing temperatures being low and thermolysis being carried out away from oxygen, metals heavy are neither volatilized nor oxidized, and therefore remain concentrated in carbon solids (SC).

At the outlet of the rotary kiln 1, the carbonaceous solids (SC) are evacuated by a device 4 ensuring tightness with respect to outside (rotary valves, guillotine airlock, or any other equivalent device to perform this function). Carbon solids (CS) are transported to a device treatment plant 6 which aims to separate part of the materials inert and to remove soluble pollutants, including chlorine, present in carbonaceous solids. Details of the device of carbonaceous solids 6 is described in more detail more bottom, in relation to figure 3. Following the treatment purification, purified carbon solids (SCE) can be directed to a combustion device 5, here consisting of a hearth cyclone with molten ash.

As already mentioned, part of the thermolysis gas (GT1) can be used to heat the rotary kiln by combustion for example in burners located in the double envelope 3 surrounding the rotary kiln 1. The fraction excess (GT2) thermolysis gas can be directed to a combustion device, for example the cyclone molten ash 5.

The cyclone molten ash hearth 5 is a hearth suitable for the combustion of solid fuels heavily loaded with low melting ash. It is characterized by turbulence high and a rotation of the flow, which allows obtain a significant residence time of the fuel and a good ash retention. It operates at temperatures of around 1000 to 1500 ° C. At these temperatures, the ashes melt and flow in the molten state out of the reactor.

The advantages of this type of fireplace compared to traditional combustion devices are: small amount of unburnt due to the long residence time of the particles in the hearth, inert as vitrified ash, a significant compactness due to the high fire density of installation, possibilities for staging the combustion air to minimize the formation of nitrogen oxides, and a stable combustion even when the characteristics of the fuel vary significantly.

The interior of the cyclone hearth 5 may preferably be covered with a refractory ceramic coating capable of withstand temperatures of the order of 1500 ° C. The injection of purified carbon solids (SCE) is done pneumatically by a or more tangential rectangular or circular inputs distributed over a perimeter of the cyclone. We can also inject one or more of these inputs with a complement combustion air and / or all or part of the excess gas GT2 thermolysis. On a second perimeter of the cyclone hearth, other tangential inputs can be installed so perform additional injections of combustion air or gaseous fuel as all or part of the surplus of the GT2 thermolysis gas. Finally, an additional air injection can be carried out at the upper outlet of the cyclone hearth, so improve combustion efficiency.

Combustion in the cyclone hearth is optimized to minimize emissions of gaseous pollutants. The sharing of combustion air between the different inlets will therefore be carried out so as to ensure total combustion purified carbon solids and thermolysis gas, and minimize the formation of nitrogen oxides and unburnt materials. Else part, we can preheat all or part of the combustion air, to facilitate obtaining high temperatures in the hearth cyclone.

The cyclone hearth with molten ash allows advantageously to immobilize the elements definitively pollutants present in purified carbon solids, in particular heavy metals, by trapping in the vitreous matrix formed during the melting of the mineral materials contained in the purified carbon solids. The temperatures obtained during the combustion of purified carbon solids (SCE) and of the surplus of GT2 thermolysis gases are sufficient to melt these materials mineral. The ashes thus melted (CF) flow out of the hearth 5 and fall into a water tank 10 where they are cooled. When from their cooling, the ash forms the aggregates solid. These aggregates are inert with respect to leaching which allows them to be recycled and reused in applications road or public works for example.

The hot fumes (F) from the mixed combustion of purified carbon solids and part of the thermolysis gases in the cyclone focus 5 are then directed to a device for energy recovery 11 such as a heat exchanger, boiler producing steam or hot water, or a boiler coupled with a turbine making it possible to produce electricity. Then these fumes are dedusted in a device 12 which can be a bag filter or a dust collector electrostatic, and returned to the atmosphere via an extractor 13 and a chimney 14 via a line 35. The ash from the recovery device respectively energy 11 and dust collector 12 are mixed with purified carbon solids then sent to cyclone 5 via lines 36 and 37 respectively. The ashes are vitrified in the cyclone 5 hearth, thus enabling inerting of pollutants adsorbed on this dust.

A second embodiment of the invention is shown in Figure 2. The essential difference between the mode of realization already described and the one which will be described now resides in that the purified carbon solids and the gases from the thermolysis of the waste is burned in two separate devices. As in the first embodiment of the invention, a part of the thermolysis gas (GT1) is used to heat the oven rotating by combustion for example in burners located in the double envelope 3 surrounding the rotary kiln 1. Here the excess fraction (GT2) is sent to a room conventional combustion 15 equipped with a gas burner. The burner and combustion chamber configurations minimize the formation of nitrogen oxides during the combustion of thermolysis gas, and guarantee destruction of all organic compounds thanks to a residence time of gas of at least 2 seconds at 850 ° C.

Purified carbon solids (SCE) are burned in a fireplace cyclone with molten ash 5 of a design identical to that described above but with a lower thermal power, in mixing with the ashes from the dedusting device smoke 12 and energy recovery device 11. As before, the temperature reached during combustion of purified carbon solids is sufficient to allow the ash to melt and therefore trap the pollutants in the glass matrix. On leaving the foyer, the molten ash (CF) flows into a water tank 10 where it are cooled and solidified to produce aggregates inert. The combustion air is staged as described previously and all or part of this air could also be preheated to improve the heat balance of the operation.

The hot fumes (F) from the combustion of thermolysis (GT2) in combustion chamber 15 and those from the combustion of purified carbon solids (SCE) in the cyclone 5 focus are mixed and sent to a energy recovery 11 such as a heat exchanger, boiler producing steam or hot water, or a boiler coupled with a turbine making it possible to produce electricity. Then these fumes are filtered in a device 12 and returned to the atmosphere via an extractor 13 and a chimney 14. The ashes and dust from the energy recovery device 11 and dust collector 12 are mixed with the purified carbon solids and then sent in the cyclone 5 hearth in order to be vitrified, thus allowing the final inerting of the pollutants adsorbed on this dust.

The embodiment of the invention according to Figure 2 has a more flexible operation than that according to the figure 1. In particular it is possible in accordance with this mode of realization of stopping the hearth-cyclone 5 when consumption overall energy is low. In this case, the carbonaceous solids purified (SCE) are not sent to the home-cyclone 5, but stored. However, in times of high energy demand (winter, for example), the cyclone 5 fireplace functions as indicated above. The stored fuels can then be burned in this period.

This embodiment of the invention therefore allows a very good match between energy demand and need.

The device for purifying carbonaceous solids 6 such as shown in Figure 3 will now be described.

At the outlet of the rotary kiln 1, the carbonaceous solids (SC) are evacuated via a waterproof device 4 and fall by gravity into a stirred tank 16 filled with room temperature water, which allows cooling of solids. The agitation of the mixture, ensured for example by rotation of a shaft carrying blades 17, is such that the heaviest particles composed mainly of metals, mineral matter or glass, deposit at the bottom of the tank, while the lighter particles rich in carbon are kept in suspension. In the bottom of the tank 16 can be immersed a screw, a carpet, a scraper or any other equivalent device 18 allowing continuous extraction mineral matter deposited at the bottom of the tank.

This first tank 16 therefore allows the cooling of carbon solids as well as the separation of part of the materials minerals contained in carbonaceous solids.

Inert mineral matter extracted by the device 18 are then rinsed with water on a vibrating screen 19 surmounted by a water spray boom 20, so eliminate carbon particles deposited on these materials mineral. Rinsing water contaminated by these carbon particles can be sent by a pump 21 to the first tank decantation 16.

The mineral material flushing operation may well heard to be achieved by other means than those who come to be described without departing from the scope of the present invention.

In addition, the mixture of water and carbonaceous solids in suspension in the tank 16 is taken up by a pump 22, then sent to a second perfectly agitated washing tank 23 containing water maintained at a temperature between 40 and 95 ° C, and preferably between 75 and 85 ° C. This temperature is maintained constant in tray 23 thanks to temperature regulation 24 connected to an electrical resistance or to any other device equivalent to maintain the water temperature at a setpoint. The residence time of carbonaceous solids in tray 23 is between 15 and 120 minutes. The report mass water / carbon solids is between 1 and 100 and preferably between 5 and 15. This operation makes it possible to dissolve essentially the chlorinated salts formed during the thermolysis. Heavy metals are not dissolved and remain concentrated in carbon solids.

Before their introduction into the stirred tank 23, the solids carbonaceous can be ground in a mill 25 operating in liquid phase, in order to decrease the average particle size of carbon particles and speed up the washing step. This step can also be followed by a separation step on a 26 calibrated sieve to separate the aluminum sheets contained in carbon solids (SC). This operation is especially necessary when carbonaceous solids come thermolysis of household waste. Water spray 27 is kept on the sieve containing the aluminum sheets in order to remove the carbon particles deposited on the surface of these. This last operation makes it possible to recover the aluminum sheets which can then be recycled and valued.

At the outlet of washing tank 23, the water-solids suspension carbonaceous is taken up by a pump 28 and then directed to a filtration device 29 which aims to remove the charged water in chlorides of carbonaceous solids. This operation can be performed with a centrifuge, a vacuum belt filter, or any other filtration device to separate water from carbon solids.

At the outlet of the filtration device 29, the carbonaceous solids purified dry, or containing only a reduced quantity of humidity, are stored in a silo 30. The waste water from filtration are directed if necessary to a device for water treatment 34 making it possible to precipitate the chlorinated salts, then reinjected into the first settling tank 16. A new water is constantly added thanks to the devices 20 and 27.

In some cases, the decanting and washing steps such as described above can be carried out in the same tank, simultaneously fulfilling the functions of tanks 16 and 23, the temperature is maintained between 40 and 95 ° C. The device previous is then simplified.

After this purification operation, we have a fuel rich in carbonaceous materials and free of part of these pollutants, which can be immediately burned to generate energy in the cyclone ash hearth fondues, or be stored for later combustion.

From the above it appears that the present invention allows the recovery of the energy content of waste thanks to the production of solid fuel and gaseous fuel purified, and their combustion.

In addition, the device 6 for purifying carbonaceous solids according to the invention eliminates part of the materials mineral and recover recoverable materials such as aluminum. This device also makes it possible to increase the quality of the fuel produced, by reducing its ash rate and its content of pollutants. Finally he increases his power calorific.

Furthermore, the use according to the invention of a cyclone hearth molten ash with combustion air staging allows to burn the purified carbon solids and / or all or part of the gases from thermolysis of waste, and this without emission of polluting compounds in gaseous or solid effluents from the combustion.

The waste treatment method according to the invention avoids the dispersion of pollutants, since almost all of the pollutants are concentrated in carbon solids. Some of these pollutants are then removed by treatment purifying carbonaceous solids, the other part being immobilized in inert pellets from combustion in the hearth cyclone with molten ash.

The invention relates to the realization of a complete system of waste treatment that removes pollutant emissions in the fumes from the combustion of thermolysis gases and carbonaceous solids, so the only smoke treatment to implement is a simple dusting. The invention thus avoids the installation of treatment devices of smoke by washing, which reduces the cost of treating waste compared to that of conventional techniques like incineration.

Claims (12)

1. A method of heat treatment for waste, in particular consisting of:

   thermolysis of said waste;

   recycling some (GT1) of the thermolysis gas as a fuel for the thermolysis process;

   a post-treatment of the solids produced by thermolysis, essentially consisting of cleaning the carbon-containing solids,

   characterised in that :

   the solid fuels resulting from the post-treatment of the thermolysis solids are at least partially burned in a cyclone furnace (5) and/or stored;

   the hot gases from the cyclone furnace supply at least one energy recovery means (11); and

   in that the quantity of solid fuels combusted in the cyclone furnace and the quantity of solid fuels put to storage are controlled, depending on energy requirements.
2. A method as claimed in claim 1, characterised in that the thermolysis gases (GT) are burned at least partially as a fuel either in the cyclone furnace (5) or in at least one of said energy recovery means (11).
3. A method as claimed in claim 1, characterised in that the process of cleaning the carbon-containing solids essentially consists in:

   cooling said solids;

   extracting and rinsing the mineral substances;

   a process of hot washing intended to make the chlorine salts in particular soluble;

   separating the water from the carbon-containing solids.
4. A method as claimed in claim 3, characterised in that it also incorporates in a treatment followed by a recycling of the water used during the cleaning step.
5. A method as claimed in any one of claims 3 or 4, characterised in that it also incorporates a process of crushing the carbon-containing solids and/or separating the aluminium sheets.
6. A method as claimed in any one of the preceding claims, characterised in that the effluent from the energy recovery means is filtered and the particles resulting from said filtration can then be introduced into the cyclone furnace.
7. A heat-treatment plant for waste designed to implement the method as claimed in one of claims 1 to 6, comprising:

   a thermolysis furnace (1);

   at least one means (5; 15) for burning the thermolysis gases;

   an energy recovery means (11); and

   a means (6) for post-treatment of the thermolysis solids, which cleans the carbon-containing solids,

   a means for storing cleaned carbon-containing solids;

   characterised in that it also has :

   a cyclone-furnace (5) supplied by at least some of the solid fuels (SCE) resulting from the post-treatment means;

   a means (F) designed to convey the hot gases from said cyclone furnace (5) to said energy recovery means (11); and a means designed to control the quantity of solid fuels burned in the cyclone furnace and the quantity of solid fuels put to storage, depending on energy requirements.
8. A treatment plant as claimed in claim 7, characterised in that the means for combusting the thermolysis gases is said cyclone furnace (5).
9. A plant as claimed in claim 7, characterised in that the means for combusting (15) the thermolysis gases and the energy recovery means (11) are arranged so that the combustion means (15) is supplied by the thermolysis gases (GT2) and the energy recovery means (11) is supplied by the effluent (F) from the combustion means (15) and, under certain operating conditions, by the hot gases from the cyclone furnace (5).
10. A plant as claimed in anyone of claims 7 to 9, characterised in that the means designed to clean the carbon-containing solids consists of:

    a first tank (16) for cooling the solids;

    a means (18) for extracting the mineral substances present in said tank (16);

    a hot-washing tank (21); and

    a filtration and/or rinsing means (27) designed to separate the water from the cleaned carbon-containing solids.
11. A plant as claimed in any one of claims 7 to 9, characterised in that it also has a means (12) for filtering the fumes given off from the energy recovery means (11), an outlet (37) of said filtering means being connected to an inlet of the cyclone furnace (5).
12. A plant as claimed in any one of claims 7 to 11, characterised in that it also has a means (0) for pretreating waste such as a dryer arranged upstream of the thermolysis furnace.

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