EP2843309B1 - System and method for the vitrification of waste - Google Patents

Description

Technical field of the invention

The invention relates to the field of waste treatment. In particular, it involves vitrifying a quantity of particular waste, such as bottom ash from incineration of non-hazardous waste.

The subject of the invention is more particularly a method and a device for treating waste.

State of the art

The economic development of countries leads to an increase in the quantity of waste produced. If the objective of all must be the prevention of waste at the source, the reuse, or the recycling of waste, there remains a significant quantity of residual waste to be treated.

Treatment methods vary a lot from country to country. The thermal treatment of waste is one of the most widespread processes in Europe since in 2011, 23% of European waste was incinerated. Only six European countries do not currently use incineration.

Thus, it is currently known to incinerate the non-hazardous waste collected. This technique results in the production of bottom ash, which are residues from incineration.

Thus, approximately 200-250 kg of bottom ash per tonne of incinerated waste is produced. These bottom ash constitute the largest production of residues from incineration. More than 16 million tonnes of bottom ash were produced in 2009 in Europe and their recovery is therefore an important issue in the economic and environmental assessment of thermal waste treatment facilities.

The document EP 1 310 733 A discloses waste treatment.

It has already been imagined to enhance bottom ash by developing vitrified materials, or vitrifiates, from bottom ash. The vitrification of bottom ash is a high temperature melting treatment, between 1100 ° C and 1500 ° C, making it possible to obtain, after cooling, a non-crystalline (amorphous) solid.

• la réduction du volume spécifique des mâchefers,
• la destruction à haute température de leurs imbrûlés carbone,
• la destruction à haute température des dioxines et furannes,
• la récupération facilitée des ferreux et non-ferreux résiduels, contenus dans les mâchefers.

The main advantage of vitrification of bottom ash is that it renders them inert: the heavy metals contained in bottom ash are trapped in the glass matrix and are no longer transferable to the environment. The main obstacle to the recovery of bottom ash has therefore been removed. This process also has other advantages:

• reduction of the specific volume of bottom ash,
• destruction at high temperature of their unburnt carbon,
• high temperature destruction of dioxins and furans,
• facilitated recovery of residual ferrous and non-ferrous contained in bottom ash.

Cooling of molten bottom ash can be slow or fast. In the first case, the molten casting is collected in ingot molds, the cooling being natural and leading to an amorphous vitrify, comparable to a pebble. In the second case, the molten bottom ash is poured in a water tank, in the form of granular vitrifiates, more or less divided, in the form of vitreous solids.

The quality of the vitreous material obtained strongly depends on the mineral composition of the treated residues, in particular on their initial distributions in oxide elements such as SiO ₂ , Al ₂ O ₃ , CaO, which can lead to poorly or non-fusible materials, as well as of the cooling rate.

Following their vitrification, the bottom ash can then be upgraded in various fields of application.

Bottom ash vitrifies, in particular in granular and non-amorphous form, can also be used in civil engineering, their inert properties making them a draining and stabilizing material. Industrial applications are, for example, the use in road technology as an aggregate of mixes in a bituminous matrix or even as a road sub-layer. They can also be used as backfill material, as a coating material or as concrete blocks.

Bottom ash are not pure substances and therefore do not have a defined melting point. In general, the melting of the mixture of the mineral compounds which constitute them, takes place in a temperature interval between the liquidus temperature and the solidus temperature of the mixture, the latter varying according to the composition of the bottom ash. However, it could be observed that the liquidus and solidus temperatures of the bottom ash were a priori close to 1150 ° C and 1450 ° C, respectively, with an average melting temperature of 1250 ° C. The calorific energy required to provide a unit mass of bottom ash, assumed to be at ambient temperature, to bring it from 20 ° C to 1200 ° C and melt it, is of the order of 0.8 kWhth per kg of bottom ash .

• les fours à oxy-fuel ou oxy-gaz, fonctionnant à l'air enrichi ou à l'oxygène,
• les fours à arc électrique ou électrodes, en bain de fusion,
• four à résistance électrique rayonnante,
• les fours à torche plasma (arc soufflé ou transféré),
• les fours de chauffage par induction en creuset froid.

Several types of furnaces allowing vitrification after incineration are listed, using a supply of calorific energy by a fuel or by electricity:

• oxy-fuel or oxy-gas furnaces, operating with enriched air or oxygen,
• electric arc furnaces or electrodes, in a molten bath,
• radiant electric resistance furnace,
• plasma torch furnaces (blown or transferred arc),
• cold crucible induction heating furnaces.

If the recovery of bottom ash by vitrification therefore has the advantages already mentioned, its main drawback is, on the other hand, a high energy consumption necessary to raise the bottom temperature and melt them. The use of a conventional energy source (electricity, gas etc.) becomes particularly problematic in the environmental assessment of the recovery of bottom ash by the vitrification technique.

Although these issues relate in particular to bottom ash from the incineration of non-hazardous waste, they can be extended to any other category of waste to be vitrified.

Object of the invention

The aim of the present invention is to provide a solution for recovering solid residual waste resulting from waste incineration which overcomes the drawbacks listed above.

In particular, an object of the invention is to provide a solution which improves the balance from an environmental point of view.

An object of the invention is to provide a solution which is particularly suitable, but not exclusively, for the vitrification of bottom ash resulting from the incineration of non-hazardous waste (waste of the first type).

These objects can be achieved by means of the appended claims, in particular by a waste treatment method according to claim 1.

Waste of the second type can be chosen from biomass, solid recovered fuels, wood containing chemicals such as gluing, finishing and preserving substances.

• une étape d'incinération d'une quantité de déchets de base, de type dangereux et/ou de type non dangereux, produisant une quantité de résidus solides d'incinération,
• puis une étape de refroidissement desdits résidus solides d'incinération au-delà d'une première valeur seuil réalisée de sorte que la température des résidus solides d'incinération reste supérieure à 600°C et/ou une étape de maintien d'un taux de carbone dans les résidus solides d'incinération supérieur à une deuxième valeur seuil, préférentiellement égale à 2% en masse.

According to one mode of implementation, the step of providing a quantity of waste of the first type comprises

• a step of incineration of a quantity of basic waste, of the hazardous type and / or of the non-hazardous type, producing a quantity of solid incineration residues,
• then a step of cooling said solid incineration residues beyond a first threshold value carried out so that the temperature of the solid incineration residues remains above 600 ° C and / or a step of maintaining a level of carbon in the solid incineration residues greater than a second threshold value, preferably equal to 2% by mass.

The vitrification step can comprise a post-combustion step, carried out in the melting furnace, by oxidation in an oxidizing atmosphere of the combustible synthesis gas produced in the gasification step so as to produce a quantity of heat energy and a step melting the quantity of waste of the first type in a melting furnace and using said quantity of heat energy produced by oxidation.

The treatment process may include a step of heat exchange between the fumes generated during the post-combustion step and the quantity of waste of the first type present in the melting furnace. The post-combustion of the combustible synthesis gas can be controlled so that the temperature in the melting furnace is such that the dynamic viscosity of the quantity of waste of the first type in fusion is less than or equal to 25 Pa.s.

According to an alternative embodiment, the temperature in the melting furnace is controlled so that the quantity of waste of the first type reaches a temperature greater than or equal to 1400 degrees.

The melting step may comprise a step of introducing at least one melting agent into the melting furnace, in particular cullet and / or sodium oxide, chosen so as to lower the melting temperature of the quantity waste of the first type and / or to lower the dynamic viscosity of the quantity of waste of the first type in fusion.

The melting step can comprise a step of introducing at least one carbon-containing agent into the melting furnace, configured so as to reduce the metal oxides initially contained in the charge, to metals.

According to the invention, the vitrification step comprises a step of casting out of the melting furnace the waste of the first type in fusion and then a step of cooling the waste of the first type in a cooling tank in a manner generating said vitrify, the cooling tank being a water bath.

Following the step of cooling the waste of the first type in the cooling tank, the method according to the invention comprises a step of separating the basaltic granular materials from the vitrify, the ferrous and non-ferrous metals and the metal oxides previously contained. in the amount of waste of the first type and reduced in the melting furnace.

The vitrification step can comprise a step of admitting air, optionally enriched with oxygen, into the melting furnace and the method can comprise a step of heat exchange between the air admitted into the melting furnace and the fumes. generated by the vitrification step.

The method may comprise a step of treating the fumes generated by the vitrification step, in particular by the dry process, then a step of discharging the treated fumes into the atmosphere.

The temperature of the combustible synthesis gas produced in the gasification step is preferably between 600 and 800 ° C, in particular between 650 and 750 ° C.

A second aspect of the invention relates to a waste treatment installation according to claim 14.

The waste treatment installation may include a heat exchange device between the air admitted into the melting furnace at a third inlet of the melting furnace and the fumes generated in the melting furnace and / or in the cooling tank, the heat exchange device being in particular separate from the melting furnace.

Brief description of the drawings

• la figure 1 est un organigramme de principe d'un exemple de traitement de déchets selon l'invention,
• la figure 2 illustre un exemple de réacteur de gazéification utilisé dans le traitement de déchets selon l'invention,
• et la figure 3 illustre un exemple de l'enceinte de vitrification utilisée dans le traitement de déchets selon l'invention.

Other advantages and characteristics will emerge more clearly from the following description of particular embodiments of the invention given by way of non-limiting examples and shown in the accompanying drawings, in which:

• the figure 1 is a block diagram of an example of waste treatment according to the invention,
• the figure 2 illustrates an example of a gasification reactor used in the treatment of waste according to the invention,
• and the figure 3 illustrates an example of the vitrification enclosure used in the treatment of waste according to the invention.

Description of preferred embodiments of the invention

• une étape de fourniture d'une quantité 10 de déchets d'un premier type,
• une étape de fourniture d'une quantité 11 de déchets d'un deuxième type différent du premier type de déchets et comportant essentiellement une matière carbonée,
• une étape de gazéification durant laquelle la quantité 11 de déchets du deuxième type est transformée d'une manière produisant un gaz de synthèse combustible 12,
• une étape de vitrification durant laquelle la quantité de déchets du premier type, alimentée en continu, est transformée en continu en vitrifiat 14 en utilisant la chaleur libérée par l'oxydation complète du gaz de synthèse combustible produit à l'étape de gazéification.

The waste treatment process according to claim 1, continuously, which will be described in detail hereinafter with reference to figures 1 to 3 , includes:

• a step of supplying a quantity of waste of a first type,
• a step of supplying a quantity 11 of waste of a second type different from the first type of waste and essentially comprising a carbonaceous material,
• a gasification step during which the quantity 11 of waste of the second type is transformed in a manner producing a combustible synthesis gas 12,
• a vitrification step during which the quantity of waste of the first type, supplied continuously, is continuously transformed into vitrify 14 using the heat released by the complete oxidation of the combustible synthesis gas produced in the gasification step.

The gasification step uses a dense fluidized bed type gasification reactor, into which the quantity of waste of the second type to be gasified is continuously introduced.

The quantity of waste of the first type, intended to be vitrified via the use of synthesis gas, is formed by residues resulting from the incineration of waste, in particular household waste. The waste of the first type is in particular formed by solid incineration residues resulting from the incineration of a quantity of basic waste. He These are mainly bottom ash from the incineration of non-hazardous waste.

A waste treatment installation is also described, according to claim 14, comprising the software and / or hardware elements implementing the waste treatment method described below.

Preferably, the waste of the second type constituting the quantity 11 is chosen from biomass (for example, forest chips), solid recovered fuels, so-called class B wood, that is to say containing chemical substances. such as gluing, finishing and preserving substances.

Solid recovered fuels also known by the acronym “CSR” are preferentially substitute fuels derived from waste used for their high calorific value for energy recovery purposes as a substitute for conventional fossil fuels (coke, fuel oil, etc.) . By way of example, the waste used to manufacture solid recovered fuels can be ordinary industrial waste and bulky waste from waste reception centers of heterogeneous quality or too large to be recovered in the incineration and co-incineration energy recovery units. They are notably composed of wood, plastics, paper and cardboard, polyurethane foam, etc.

However, it is still conceivable that the quantity of waste of the second type could include hazardous waste, such as for example so-called class C wood, that is to say treated to the heart, soiled or fireproof.

In this document, the term “hazardous waste” will preferably be considered as meaning waste which presents one or more of the properties listed in appendix I of Decree n ° 2002-540 of April 18, 2002 relating to the classification of waste. They are indicated by an asterisk in the list of wastes in Annex II of the same decree.

In this document, the term “non-hazardous waste” will preferably be considered to mean any waste that is not defined as hazardous by decree n ° 2002-540 of April 18, 2002.

The gasification step comprises a step of continuously introducing the quantity 11 of waste of the second type into the gasification reactor 13 of the dense fluidized bed type, then a pyrolysis step in which the waste of the second type constituting the quantity 11 are decomposed in the gasification reactor 13 in a manner producing volatile compounds in the form of gaseous hydrocarbons and organic vapors and pyrolysis coke, followed by a step of converting the hydrocarbons and coke in a manner producing the fuel synthesis gas 12.

The thermochemical conversions are carried out in a reducing atmosphere and are generally endothermic.

The heat energy necessary for the pyrolysis step and the conversion step is provided by exothermicity of the partial oxidation of a fraction of the carbon contained in the quantity 11 of waste of the second type, so that the gasification reactor 13 can advantageously have a self-thermal operating mode.

The pyrolysis step and the conversion step can be carried out in the same thermal chamber, or in two separate chambers, by the action of a fluidizing agent 16, such as water or carbon dioxide. carbon, in a reducing atmosphere admitted into the gasification reactor 13.

The combustible synthesis gas 12 comprises carbon monoxide and dihydrogen. It can also contain carbon dioxide, methane, tars and water vapor. It is also known as "syngas".

Thus, the main reactions involved in the gasification reactor 13 are, a devolatilization reaction, followed by a reaction in which the water vapor reacts with the fixed carbon of the quantity 11, to give hydrogen and carbon monoxide. , a second reaction in which the carbon of quantity 11 reacts with carbon dioxide to give carbon monoxide and a third reaction in which the carbon of quantity 11 reacts with oxygen to give carbon monoxide.

The temperature of the combustible synthesis gas 12, produced in the gasification step, is preferably between 600 and 800 ° C, in particular between 650 and 750 ° C. These are therefore advantageously moderate temperatures so as on the one hand to ensure the selectivity of the thermochemical conversion reactions and on the other hand in order to avoid the problems of agglomeration of the feed, by softening and / or melting of its. inert fraction, due to the frequent presence of high alkali content in biomasses (Na, K).

In general, the term “gasification” is understood to mean any method allowing the carbonaceous material of the quantity of waste of the second type to be transformed at high temperature into combustible gas, the main constituents of which are carbon monoxide and hydrogen.

The vitrification step is carried out continuously. It is implemented in a vitrification chamber 15 which comprises a melting furnace 151 and a cooling tank 152. The union of the melting furnace 151 and the cooling tank 152, illustrated on figure 3 , constitutes the vitrification chamber 15 taking as input in particular the combustible synthesis gas 12 coming from the gasification reactor 13 and the quantity 10 of waste of the first type, supplied continuously, and delivering mainly the vitrify 14 as well as fumes at the outlet 19 generated by the oxidation of syngas, at the level of the melting furnace 151 and / or the cooling tank 152.

• le réacteur de gazéification 13 de type à lit fluidisé dense, ayant une sortie évacuant le gaz de synthèse combustible 12 produit dans le réacteur de gazéification 13,
• un premier dispositif d'alimentation 28 (figure 2) alimentant, notamment en continu, une première entrée du réacteur de gazéification 13, par exemple via une trémie et un convoyeur alimentant un sas d'introduction, avec la quantité 11 de déchets du deuxième type, ou par une vis doseuse permettant une alimentation en continu du réacteur de gazéification 13, sans introduction d'air parasite dans le réacteur de gazéification,
• le four de fusion 151 ayant une première entrée alimentée en continu par le gaz de synthèse combustible 12 sortant du réacteur de gazéification 13 au niveau de sa sortie,
• un dispositif de liaison, notamment calorifugé, conduisant le gaz de synthèse combustible 12 de la sortie du réacteur de gazéification 13 à la première entrée du four de fusion 151,
• un deuxième dispositif d'alimentation 27 (figure 3) alimentant, notamment en continu, une deuxième entrée du four de fusion 151 avec la quantité 10 de déchets du premier type,
• le bac de refroidissement 152 alimenté en entrée par la quantité 10 de déchets du premier type en fusion, coulant hors du four de fusion 151 au niveau d'une première sortie du four de fusion 151.

The continuous waste treatment facility more generally includes the following:

• the dense fluidized bed type gasification reactor 13, having an outlet discharging the combustible synthesis gas 12 produced in the gasification reactor 13,
• a first feed device 28 ( figure 2 ) feeding, in particular continuously, a first inlet of the gasification reactor 13, for example via a hopper and a conveyor feeding an introduction lock, with the quantity 11 of waste of the second type, or by a metering screw allowing a supply of continuous gasification reactor 13, without introduction of parasitic air into the gasification reactor,
• the melting furnace 151 having a first inlet fed continuously with the combustible synthesis gas 12 leaving the gasification reactor 13 at its outlet,
• a connecting device, in particular heat-insulated, leading the combustible synthesis gas 12 from the outlet of the gasification reactor 13 to the first inlet of the melting furnace 151,
• a second feed device 27 ( figure 3 ) feeding, in particular continuously, a second inlet of the melting furnace 151 with the quantity of waste of the first type,
• the cooling tank 152 fed at the inlet with the quantity 10 of waste of the first type in fusion, flowing out of the melting furnace 151 at a first outlet of the melting furnace 151.

The cooling tank 152 is preferably a water bath, in particular a cold water bath to achieve very rapid cooling by immersion in this cold water bath and allowing a thermal shock, causing, in particular, the division of the vitreous matrix.

The gasification reactor 13 of the dense fluidized bed type, called “LFD”, is particularly suitable. This is a reactor in which the quantity 11 to be gasified is introduced continuously into a bed of inert particles (for example sand) suspended in the reactor, by an upward current of air, which promotes thermal and mass exchanges between the solid and the gas. The dense fluidized bed reactor 13 provides for a relatively low fluidization rate (1 to 2 m / s) without bed entrainment. The fluidization agent 16 is blown under a fluidization grid.

• permet au réacteur de gazéification 13 de pouvoir fonctionner à température uniforme et modérée (entre 650 et 750 degrés notamment),
• permet de pouvoir contrôler le réacteur 13 en température par des parois refroidies,
• permet que le réacteur 13 présente un encombrement modéré,
• permet de s'accommoder aisément à des situations d'exploitation nécessitant l'arrêt et le démarrage du réacteur de gazéification 13.

It is particularly well suited to the present case for the following reasons:

• allows the gasification reactor 13 to be able to operate at uniform and moderate temperature (between 650 and 750 degrees in particular),
• allows the temperature of the reactor 13 to be controlled by cooled walls,
• allows the reactor 13 to have a moderate size,
• makes it easy to adapt to operating situations requiring stopping and starting the gasification reactor 13.

In fact, in the gasification reactor 13 of the dense fluidized bed type, the introduction of fluidization agent 16 intended to carry out the partial oxidation of the quantity 11, so as to supply the heat energy necessary for the gasification reactions. in self-thermal conduct, is carried out at a flow rate corresponding in practice to the flow rate of fluidization air in dense regime. It is distributed uniformly in the quantity 11, mixed with the inert fluidization medium, through the fluidization grid. The presence of a fluidization medium (sand) also makes it possible to obtain a uniform bed temperature, limiting the agglomeration processes by softening the load. The bed plays, moreover, a role of thermal buffer, vis-à-vis a variation of the lower calorific value of the incoming quantity, contributing to the uniformity of its temperature.

In the gasification reactor 13 of the dense fluidized bed type, the enclosures are static and can easily be produced as cooled walls (membrane walls with water or oil tubes, integrated into a heat recovery circuit, double-flushing. air casing) and sealed against parasitic air inlets. In addition, the agent 16 is uniformly distributed therein in the quantity 11, via the fluidization grid, making it possible to avoid hot spots which may lead to the softening of the mineral compounds of the incoming quantity 11 and of the processes. clogging of walls and deposits in downstream conduits.

In the dense fluidized bed type gasification reactor 13, the internal transfer coefficients between the fluidizing agent 16 and the divided quantity 11 to be treated, as well as between the bed and the cooled walls, can reach values ranging from 500 to 800 W / m ² ° C, allowing at the same flow rate, to reduce the volumes of enclosures involved. Higher values of heat transfer coefficients can be reached with other reactor technologies gasification 13 but to the detriment of bulk.

In the gasification reactor 13 of the dense fluidized bed type, stopping the feed practically instantly stops the production of synthesis gas 12, given the low effective retention of the quantity 11 to be gasified in the gasification reactor. bed.

The introduction of a small amount of air into the gasification reactor 13 of the dense fluidized bed type, also corresponding to the fluidization agent 16, makes it possible to achieve self-thermal operation of the reactor by partial oxidation of the gas. incoming quantity 11.

In the gasification reactor 13, the reactor is cooled by flushing with ambient air or with water.

The establishment of a device for extracting unwanted from the incoming quantity can be achieved by installing a screw at the bottom of the bed. The inert part of these undesirable can be advantageously introduced into the melting furnace 151.

An example of the arrangement of the gasification reactor 13 is illustrated on figure 2 . The fluidization agent (air) 16 is for example admitted into the lower part of the reactor 13 via a fan, at a second inlet of the gasification reactor 13.

The second feed device 27 comprises for example a hopper for receiving and storing the quantity 10 of waste from the first type, the outlet of which feeds a conveyor which itself feeds the second inlet of the melting furnace 151. The continuous introduction of the gasifiable charge is carried out via a double airlock device or via a metering screw, allowing, in the two cases, to limit the entry of parasitic air into the reactor.

The start-up sequence of the gasification reactor begins with the preheating of the inert sand-type media, by the preheating of the fluidization air via an external burner. The charge to be gasified is introduced when the medium has reached a temperature in the region of 450 to 500 ° C. Therefore, the gasification of the incoming charge takes place homogeneously in the hot inert medium, its maintenance being ensured by the partial oxidation of a fraction of the incoming charge, by the fluidization air itself. The burner for preheating the fluidizing air can therefore be gradually stopped.

The vitrifies 14 continuously exit out of the vitrification enclosure 15 at the level of a first outlet of the vitrification enclosure 15 while the fumes 19 exit out of the vitrification enclosure 15 at the level of a second outlet.

The vitrification step preferably comprises a step of post-combustion by oxidation in an oxidizing atmosphere of the combustible synthesis gas 12 produced in the gasification step so as to produce a quantity of heat energy allowing a step of melting the quantity 10 of waste of the first type in the melting furnace 151 and using this amount of heat energy produced by oxidation.

Preferably, the post-combustion step is carried out in the melting furnace 151 but it could be deported by providing for a transfer of the quantity of heat energy produced during the post-combustion to the melting furnace. Within the melting furnace 151, a step of heat exchange between the fumes generated during the post-combustion stage and the quantity of waste of the first type present in the melting furnace 151 can advantageously be implemented.

It emerges from the foregoing that the solution described here makes it possible to ensure that the heat input necessary for the melting of waste of the first type, for example bottom ash from incineration of non-hazardous waste, following their introduction. in the melting furnace 151 is obtained by an oxidative postcombustion (air 20 possibly enriched with oxygen being also introduced into the melting furnace 151) of the combustible synthesis gas 12 previously produced in the auto-thermal gasification reactor 13 of wastes from waste gasification based on carbonaceous material. The post-combustion releases the heat necessary for melting the waste of the first type introduced into the melting furnace 151.

Thus, the high specific amount of conventional energy (electricity, gas, etc.) used in the prior art to carry out the melting of bottom ash is advantageously replaced by the energy obtained by post-combustion of the synthesis gas itself obtained. by an operation of gasification of waste of another nature, that is to say based on carbonaceous material. The solution is therefore particularly interesting from an overall economic and environmental point of view. By virtue of the treatment method described, the waste of the first type and the waste of the second type are jointly treated. The external energy, based on fossil fuels and / or electricity from the grid, to be supplied for vitrification is considerably reduced. These advantages apply whatever the nature of the waste of the first type to be vitrified and are interesting in the particular example of bottom ash resulting from the incineration of non-hazardous waste.

The tars possibly present in the synthesis gas 12 produced by the gasification reactor 13 are advantageously directly thermally cracked in the melting furnace 151, thus recovering their thermochemical content by combustion. In the case of a gasification reactor 13 of the dense fluidized bed type, the synthesis gas 12 also comprises significant quantities of particulate flights of the inert fraction of the incoming quantity 11. As the synthesis gas 12 is oxidized in the melting furnace 151 disposed downstream of the gasification reactor 13, the particulate pollutants are recovered by the molten bath from the quantity of waste of the first type in fusion and the tars are thermally destroyed. .

With reference to the figure 3 , the vitrification step can comprise a step of casting out of the melting furnace 151 the waste of the first type in fusion and then a step of cooling the waste of the first type in the cooling tank 152 in a manner generating said vitrify 14. The tank 152 is for example a water bath. The vitrifies 14 are evacuated out of the cooling tank 152 via a conveyor marked 26, for example consisting of a continuous extraction screw. Furthermore, the melting furnace 151 can also be supplied at its second inlet with cullet 24 and at its first inlet with natural gas 25. The addition of fixed carbon in the bath is also possible, so to be carried out in the molten bath, the reduction of the metal oxides present, making it possible to increase the subsequent recovery of metals. This addition of fixed carbon can come from the inert part of the undesirable substances resulting from the gasification reactor 13. The natural gas 25 and the cullet 24 are only used when starting the melting furnace 151. It is in particular a furnace. with bubbling bath tub. A silo for storing the cullet 24 can be provided, as well as a line supplied with natural gas 25. The installation is started up. using cullet, melted by the combustion of natural gas. Once the bath is formed, the cullet feed is reduced by substituting it for the amount of waste of the first type. The natural gas 25 is then gradually replaced by the synthesis gas 12 supplied by the gasification reactor 13. A silo for storing the vitrifiates can be provided, as well as a fume evacuation duct 19 leaving the furnace 151 and directed, using an extractor, at the inlet of the main boiler relating to the incineration stage.

Following the step of cooling the waste of the first type in the cooling tank 152, the method according to the invention comprises a step of separating the basaltic granular materials from the vitrify, the ferrous and non-ferrous metals and the metal oxides previously contained. in the amount of waste of the first type and reduced in the melting furnace. The addition of fixed carbon in the molten bath is likely to increase the rate of recovery of the metals, by reducing the metal oxides previously contained in quantity 10. Ferrous / on-ferrous metals and the remaining quantity may be the object separate valuation.

The melting step may comprise a step of introducing at least one melting agent 17 into the melting furnace 151, in particular cullet and / or sodium oxide, chosen so as to lower the melting temperature of the quantity of waste of the first type and / or to lower the dynamic viscosity of the quantity of waste of the first type molten. The melting furnace 151 therefore includes a third inlet for this purpose. The addition of Na ₂ O, supplied in the form of Na ₂ CO _3, makes it possible to obtain glasses at temperatures between 1100 and 1200 ° C. A typical composition by mass, in majority compounds, is then: SiO ₂ = 40%, Al ₂ O ₃ = 8%, CaO = 18%, Na ₂ O = 26%.

The melting step comprises a step of introducing at least one carbon agent 17 into the melting furnace, with the aim of reducing the metal oxides initially contained in the charge, to metals.

The post-combustion of the combustible synthesis gas 12 is preferably controlled so that the temperature in the melting furnace 151 is such that the dynamic viscosity of the quantity of waste of the first type in fusion is less than or equal to 25 Pa.s. It is in fact considered that above this limit, the viscosity reached does not allow the casting of the vitrified material 14 out of the furnace 151. In particular, the temperature in the melting furnace 151 is controlled so that the quantity of waste from the first type reaches a temperature greater than or equal to 1400 degrees, preferably of the order of 1450 ° C.

The vitrification step preferably comprises a step of admitting air 20, optionally enriched with oxygen, into the melting furnace 151. The melting furnace 151 therefore comprises a fourth inlet for this purpose.

The post-combustion of the synthesis gas 12 being carried out in a homogeneous phase (gas-gas combustion), the excess air 20 to be carried out in order to obtain complete combustion are low (included in a range going from 5 to 8%) so that the adiabatic flame temperature obtained is high (of the order of 1500 ° C.) and the volume of the fumes 19 is reduced. It should be noted that the use of air 20 enriched with oxygen for the post-combustion of the gas 12 makes it possible, if necessary, both to increase the flame temperature and to reduce the volume of fumes 19, by reducing the nitrogen ballast. With such a flame temperature, the temperature level necessary for melting waste of the first type, ie beyond 1400 ° C. in the example of bottom ash from incineration of non-hazardous waste, is easy to achieve.

The installation therefore optionally comprises an intake air enrichment unit 20 supplying air enriched between 40 and 50% dioxygen, replacing the standard air which comprises 21% dioxygen, to significantly increase the temperature of the 10 molten quantity and therefore facilitate its pouring out of the furnace 151.

A heat exchange step can advantageously be implemented between the air admitted 20 into the melting furnace 151 and the fumes 19 generated by the vitrification step.

For this purpose, the installation comprises a heat exchange device 21 between the air admitted 20 into the melting furnace 151 at a third inlet of the melting furnace 151 and the fumes 19 generated in the melting furnace 151 and / or in the cooling tank 152. This heat exchange device 21 is very preferably separated from the melting furnace, that is to say arranged outside,

It is in fact conceivable to preheat the air admitted 20 to a temperature between 700 and 800 ° C, before it enters the fluidization furnace 151 so on the one hand to avoid the injection of cold air into the bath. melting and on the other hand increasing the adiabatic temperature of the afterburner in the furnace 151, lowering the dynamic viscosity of the quantity of waste of the first type in the molten state and thus facilitating its pouring out of the melting furnace 151. This also makes it possible to lower the temperature of the fumes 19 to a temperature compatible with a subsequent treatment of the fumes carried out in a device 18 for treating the fumes mentioned below.

It can be implemented to cool the fumes from the melting furnace by injecting water, followed by the aforementioned heat exchange step in the device 21.

• une étape d'incinération d'une quantité de déchets de base, de type dangereux et/ou de type non dangereux, produisant une quantité de résidus solides d'incinération,
• puis une étape de refroidissement des résidus solides d'incinération au-delà d'une première valeur seuil et/ou une étape de maintien d'un taux de carbone dans les résidus solides d'incinération supérieur à une deuxième valeur seuil. La deuxième valeur seuil est préférentiellement égale à 2% en masse. L'étape de refroidissement pourra avantageusement être réalisée de sorte que la température des résidus solides d'incinération reste supérieure à 600°C, notamment par contrôle de la vitesse de défilement des déchets dans l'incinérateur de déchets. Toutefois, il peut tout à fait être envisagé que la première valeur seuil soit inférieure à 600°C.

In a manner not shown, the step of providing a quantity of waste of a first type may preferably comprise, although this is not exclusive:

• a step of incineration of a quantity of basic waste, of the hazardous type and / or of the non-hazardous type, producing a quantity of solid incineration residues,
• then a step of cooling the solid incineration residues beyond a first threshold value and / or a step of maintaining a level of carbon in the solid incineration residues above a second threshold value. The second threshold value is preferably equal to 2% by mass. The cooling step could advantageously be carried out so that the temperature of the solid incineration residues remains above 600 ° C., in particular by controlling the speed of travel of the waste in the waste incinerator. However, it is quite possible for the first threshold value to be less than 600 ° C.

Maintaining a deliberately higher carbon rate than current practice in incineration techniques, for example beyond 2% by mass, aims to take into account the fact that this fixed carbon participates, through its lower calorific value, to reduce the specific energy demand of the melting furnace 151. In fact, the introduction of air 20 into the melting furnace 151 causes the exothermic oxidation of this carbon fraction. The addition of biomass directly into the molten bath formed by the molten quantity is also possible. Thus, for example for a quantity containing 5% of fixed carbon, the specific allothermal energy to be provided for the vitrification is 0.34 kWh / kg while it is 0.8 kWh / kg for a carbon mass percentage of 2%.

Maintaining a relatively high bottom ash temperature, for example greater than 600 ° C., makes it possible to reduce the specific heat energy required for the quantity 10 to melt into the furnace 151 and therefore for the vitrification. For example, this makes it possible to go from around 0.8 kWhth / kg (for an initial temperature at the inlet of furnace 151 of 20 ° C) to around 0.62 kWhth / kg (for an initial temperature at the inlet oven 151 of 600 ° C).

It can also be implemented a step of recovery by the melting furnace 151 of all or part of the ash collected under the boiler of the basic waste incinerator which produces a quantity of solid incineration residues. The sizing of the melting furnace 151 must then take into account the volumes of such ash to be vitrified in the vitrification chamber 15.

The hot fumes 19 (of the order of 1400 ° C.) generated by the vitrification step are then treated, after cooling by injection of water and passing through the exchanger 21, into the treatment device 18, in particular by dried. Then the fumes 22 treated by the treatment device 18 are discharged into the atmosphere. The fumes 19 contain, in particular, chlorides, sulfur compounds, mercury and certain heavy metals, not solubilized in the molten bath in the furnace 151. The treatment device 18 can be constituted by the device for treating the fumes obtained from the basic waste incineration step or by an autonomous treatment device 18.

Finally, the residues resulting from the treatment of the fumes 19 carried out in the treatment device 18 are identified 23 and recovered.

Although the previous solution is particularly aimed at solving the problems associated with the treatment of bottom ash from non-hazardous waste incineration, it remains fully applicable to waste to be vitrified of any other nature.

An example of pre-dimensioning of a solution as set out above is presented below. This is a particular example of application, not limiting the field of application of the invention, implementing vitrification of a quantity of waste of the first type consisting of bottom ash from incineration of non-waste. dangerous. It is therefore recalled that the waste of the first type can be of another nature, such as hazardous waste, such as, for example, ash in a boiler.

This is an installation authorized to treat 115,000 t / year of non-recyclable waste. A quantity of close to 20,000 tonnes of bottom ash is produced annually, ie around 17% of the pre-treated waste entering the incinerator. A separation operation of ferrous and non-ferrous metals is implemented. Assuming that the recoverable ferrous and non-ferrous metals represent of the order of 6% of the quantity of raw bottom ash, the annual quantity is 18,800 t / year which should be treated.

It should be remembered that the bottom ash produced has naturally not insignificant lower calorific values, due to their often high contents (between 2 and 5%) of residual unburned carbon. In the solution proposed in this document, this fixed carbon being oxidized in the melting step of the quantity 10 in the furnace 151 in an oxidizing atmosphere, the heat energy released by the exothermicity of the oxidation reactions can be directly recovered in the bath melt formed by the molten amount. This makes it possible to reduce the external heat energy input necessary for the fusion.

In this example, it is assumed that the residual carbon content in the quantity of waste of the first type is 4% and that their humidity, after cooling, is 10%. Under these conditions, the calorific value of this quantity is 262 kcal per kilogram.

The specific demand for external heat energy to be supplied to obtain the melting of quantity 10 is therefore 0.5 kWh / kg, or 0.5 MWh / t. It should be remembered that this energy demand could be reduced by increasing the residual fixed carbon content of the quantity at the outlet of the incinerator, for example by simply increasing the speed of advance of the waste on the grate of the incinerator.

• la teneur en humidité est faible (comprise entre environ 4 et 6%) et le pouvoir calorifique inférieur est élevé (compris entre environ 4 et 4,5 kMh/kg),
• ils sont actuellement disponibles facilement.

It is taken as an example a quantity 11 of waste of the second type consisting of class B wood. They are indeed interesting because:

• the moisture content is low (between around 4 and 6%) and the lower calorific value is high (between around 4 and 4.5 kMh / kg),
• they are currently readily available.

It is assumed here that the lower calorific value is 4 kMh / kg.

Assuming a heat loss rate of around 7%, the effective annual demand for heat energy in the vitrification step is 10 GWh / year. Assuming a gasification efficiency of 96%, the amount of Class B wood required is therefore 2604 t / year.

For operation at a rate of 8000 h / year, the hourly quantity 11 of class B wood feeding the reactor 13 is 0.326 t / h, corresponding to a power entering the reactor 13 of 1.3 MWth.

It is recalled that other types of waste can be used in the gasification step.

Claims (15)

1. Process for the continuous treatment of waste, comprising:

   - a stage of providing an amount (10) of waste of a first type formed by residues resulting from the incineration of waste, in particular formed by clinker resulting from the incineration of non-dangerous waste,

   - a stage of provision of an amount (11) of waste of a second type different from the first type of waste and essentially comprising a carbon-based material,

   - a gasification stage during which the amount of waste of the second type is converted in a way producing a combustible synthesis gas (12), using a gasification reactor (13) of dense fluidized bed type,

   - a vitrification stage during which the amount of waste of the first type is converted into vitrified product (14) using the heat released by the complete oxidation of the combustible synthesis gas produced in the gasification stage,

   the process being characterized in that the amount (11) of waste of the second type to be gasified is introduced continuously into the gasification reactor (13), in that the vitrification stage comprises a stage of running the molten waste of the first type out of a melting furnace, then a stage of cooling the waste of the first type in a cooling tank (152) in a way generating the said vitrified product, the cooling tank being a bath of cold water for carrying out very rapid cooling by an immersion in this bath of cold water and making possible a thermal shock, and in that, subsequent to the stage of cooling the waste of the first type in the cooling tank, the process comprises a stage of separation of the ferrous metals present beforehand in the amount of waste of the first type.
2. Process for the treatment of waste according to Claim 1, characterized in that the waste of the second type is chosen from biomasses, solid recovered fuels, wood containing chemical substances, such as adhesives, finishing substances and preservatives.
3. Process for the treatment of waste according to either of Claims 1 and 2, characterized in that the stage of providing an amount (10) of waste of the first type comprises:

   - a stage of incineration of an amount of base waste, of dangerous type and/or of non-dangerous type, producing an amount of solid incineration residues,

   - then a stage of cooling the said solid incineration residues beyond a first threshold value carried out so that the temperature of the solid incineration residues remains greater than 600°C and/or a stage of maintaining a content of carbon in the solid incineration residues greater than a second threshold value, preferentially equal to 2% by weight.
4. Process for the treatment of waste according to one of Claims 1 to 3, characterized in that the vitrification stage comprises a post-combustion stage, carried out in the melting furnace, by oxidation in an oxidizing atmosphere of the combustible synthesis gas produced in the gasification stage, so as to produce an amount of calorific energy, and a stage of melting the amount of waste of the first type in a melting furnace (151) using the said amount of calorific energy produced by oxidation.
5. Process for the treatment of waste according to Claim 4, characterized in that it comprises a stage of heat exchange between the flue gases (19) generated during the post-combustion stage and the amount of waste of the first type present in the melting furnace.
6. Process for the treatment of waste according to either of Claims 4 and 5, characterized in that the post-combustion of the combustible synthesis gas is managed so that the temperature in the melting furnace is such that the dynamic viscosity of the amount of molten waste of the first type is less than or equal to 25 Pa.s.
7. Process for the treatment of waste according to Claim 6, characterized in that the temperature in the melting furnace is controlled so that the amount of waste of the first type reaches a temperature of greater than or equal to 1400 degrees.
8. Process for the treatment of waste according to one of Claims 4 to 7, characterized in that the melting stage comprises a stage of introduction of at least one flux (17) into the melting furnace, in particular cullet and/or sodium oxide, chosen so as to lower the melting point of the amount of waste of the first type and/or to lower the dynamic viscosity of the amount of molten waste of the first type.
9. Process for the treatment of waste according to one of Claims 4 to 8, characterized in that the melting stage comprises a stage of introduction of at least one carbon-based agent into the melting furnace, configured so as to reduce the metal oxides initially present in the charge to give metals.
10. Process for the treatment of waste according to one of Claims 1 to 9, characterized in that, subsequent to the stage of cooling the waste of the first type in the cooling tank, the process comprises a stage of separation of the basaltic granular materials of the vitrified product, of the nonferrous metals and of the metal oxides present beforehand in the amount of waste of the first type and reduced in the melting furnace.
11. Process for the treatment of waste according to one of Claims 1 to 10, characterized in that the vitrification stage comprises a stage of admission of air (20), optionally enriched in oxygen, into the melting furnace and in that it comprises a stage of heat exchange between the air admitted into the melting furnace and the flue gases generated by the vitrification stage.
12. Process for the treatment of waste according to one of Claims 1 to 11, characterized in that it comprises a stage of treatment of the flue gases generated by the vitrification stage, in particular by the dry route, followed by a stage of discharge to the atmosphere of the treated flue gases (22) .
13. Process for the treatment of waste according to one of Claims 1 to 12, characterized in that the temperature of the combustible synthesis gas produced in the gasification stage is between 600 and 800°C, in particular between 650 and 750°C.
14. Plant for the continuous treatment of waste comprising software components and/or equipment carrying out a process for the treatment of waste according to any one of the preceding claims and which comprises:

    - a gasification reactor (13) of dense fluidized bed type, having an outlet discharging the combustible synthesis gas produced in the gasification reactor,

    - a first feed device (28) continuously feeding a first inlet of the gasification reactor with the amount of waste of the second type, of metering screw type making possible continuous feeding of the gasification reactor, without introduction of secondary air,

    - a melting furnace (151) having a first inlet fed by the synthesis gas (12) exiting from the gasification reactor at the level of its outlet,

    - a connecting device, in particular a lagged connecting device, leading the combustible synthesis gas from the outlet of the gasification reactor to the first inlet of the melting furnace,

    - a second feed device (27) continuously feeding a second inlet of the melting furnace with the amount of waste of the first type,

    - a cooling tank (152), being a water bath, fed at the inlet by the amount of molten waste of the first type flowing out of the melting furnace at the level of a first outlet of the melting furnace,

    - a vitrification component for converting into vitrified product (14) the amount of waste of the first type using the combustible synthesis gas produced by the gasification reactor,

    - a means for running the molten waste of the first type out of the melting furnace,

    - a means for cooling the waste of the first type in the cooling tank in a way generating the said vitrified product, the cooling tank being a bath of cold water for carrying out very rapid cooling by an immersion in this bath of cold water and making possible thermal shock,

    - a means for separation of the ferrous metals present beforehand in the amount of waste of the first type.
15. Plant for the treatment of waste according to Claim 14, characterized in that it comprises a device for heat exchange (21) between the air (20) admitted into the melting furnace at the level of a third inlet of the melting furnace and the flue gases (19) generated in the melting furnace and/or in the cooling tank, the heat exchange device (21) being in particular separated from the melting furnace.

Images