EP0235473B1 - Process for destroying organic products having toxic properties, and equipment for performing this process - Google Patents

Abstract

1. A process for destroying organic products having toxic effects, such as waste from the electrical, chemical or nuclear industries, without the risk of forming secondary decomposition products which are equally toxic, comprising as its main step a vapo-cracking operation.

Description

The present invention relates to a process for destroying organic products with toxic effects avoiding pollution of the surrounding environment after an incident, accident or any other case requiring the decommissioning of these products.

The invention also relates to installations implementing this method.

More specifically, in certain fields the industry is currently using organic compounds of the type, for example, polychlorinated biphenyls (usually called PCBs) because they have advantageous characteristics and in particular good thermal stability, good chemical inertness and a high dielectric constant thus justifying their intensive use in particular as fluids for transformers and / or capacitors.

• - le brevet français N_° 2.323.432 sur un procédé catalytique de décomposition de composés organiques halogénés ;
• - le brevet N_° WO 82/00509 sur un procédé de décomposition utilisant un brûleur au plasma entre 3000 et 4000_°C ;
• - le brevet WO 80/022116 sur un procédé de décomposition utilisant un sel fondu et une source d'oxygène ;
• - le brevet européen 0 060 089 sur un procédé de décomposition à l'aide d'un réactif comprenant un polyglycol et un hydroxyde alcalin en présence d'oxygène.

However, in recent years, studies have shown that such products are not biodegradable and that there are significant traces of accumulation in the food cycle. In addition, these studies have shown a high toxicity of these products and an activity which may be carcinogenic. In view of this research, the administrations concerned in different countries have issued regulations relating to the use, storage and destruction of these products. As a result, various industrial processes have therefore been developed. Most of these processes involve an incineration process with excess air or oxygen in devices such as cement kilns or household waste incinerators. This is how we can cite:

• - French patent _No. 2,323,432 on a catalytic process for the decomposition of halogenated organic compounds;
• - Patent _No. WO 82/00509 on a decomposition process using a plasma burner between 3000 and 4000 _° C;
• - Patent WO 80/022116 on a decomposition process using a molten salt and a source of oxygen;
• - European patent 0 060 089 on a decomposition process using a reagent comprising a polyglycol and an alkali hydroxide in the presence of oxygen.

Such methods have been found to be partially effective in that they present, during their implementation, the main risk of causing the formation of decomposition and restructuring products of the molecule which it is desired to destroy, which are very toxic and everyone knows the dangers of a dioxin-like decomposition product in the case of PCBs, dioxin obtained by degradation of chlorinated molecules in the presence of oxygen. Mention will also be made of the very large formation of volume of gas released of the C0 ₂ and N0 _{2 type} , which requires corresponding treatment installations.

However, the present invention proposes to avoid these drawbacks and it provides a process for destroying toxic organic molecules without having the risk of the dangers mentioned above, in particular of the formation of very toxic degradation products, while minimizing the volume of gas released, this process being characterized by the fact that it comprises as main stage a steam cracking operation.

According to a particularly advantageous embodiment, this steam cracking is carried out in a reducing medium in the presence of hydrogen.

According to an advantageous procedure of this process, the quantity of hydrogen chosen as the reducing medium is between 1 and 1.5 Nm ³ / kg of product to be treated. The presence of such a reducing medium has the effect of preventing the oxidation of organic products leading to very toxic by-products of the dioxin type in the case of the destruction of a compound of the PCB family.

Advantageously, the reaction temperature is between 1000 and 1500 ° C.

In particular, the process is carried out by injecting superheated steam and oxyhydrogen combustion.

Advantageously, the quantity of hydrogen necessary for this oxyhydric combustion corresponds to an excess of 2 to 10% compared to the stoichiometric conditions.

Thus, for the implementation of this method, the invention covers any installation comprising a combustion and mixing chamber with admission of hydrogen, oxygen and water vapor; at least one reactor receiving the mixture resulting from such combustion and the product to be treated and, at the outlet of this reactor, stations for condensing and treating the solid, liquid and gaseous reaction products.

Other characteristics and advantages of the invention will emerge more clearly from the description which follows, given with reference to the appended figure, illustrating very schematically an installation implementing the method of the invention.

The installation shown in the figure consists of a known diffusion burner 1, a combustion and mixing chamber 2, a reactor 3, a condenser 4, a tank 5 for storing products condensates and an evacuation 17 of the gases to a conventional treatment device not shown.

The diffusion burner 1 comprises a pipe 6 for injecting hydrogen or nitrogen, a pipe 7 for injecting oxygen or air. These two pipes supply a plurality of diffusers. The diffusion burner 1 also includes a pipe 8 for propane and oxygen injection supplying the ignition pilot flame and a water supply circuit 9 for cooling the burner jacket.

The combustion and mixing chamber 2, placed above the burner 1 and comprising a supply of water vapor 10 modulates the temperature and the residence time.

In the body of the reactor 3, the product 11 to be treated is injected, for example pyralene and water vapor 12 serving as carrier gas and steam trap. Product 11 is admitted into an ultrasonic resonance injector requiring an ap point for example water vapor 12, which improves the spraying and thereby the efficiency of the reaction. The chamber 2 and the reactor 3 have nozzles 13 and 13a for thermocouples and operating control manometers.

The condenser 4 has in its upper part an inlet for water 15 ensuring the condensation of the water for cooling the gases and an inlet for a basic product 16 for example diluted sodium hydroxide allowing the neutralization of the hydrochloric gas formed in the case treatment of chlorinated products.

• - mise en route :
• . purge de la canalisation 6 d'hydrogène avec un gaz inerte tel que l'azote par dilution sous pression,
• . établissement des refroidissements 9,
• . établissement du débit d'air comprimé dans les diffuseurs par la canalisation 7,
• . mise en route de la flamme pilote d'allumage,
• . établissement du débit d'hydrogène ; au départ un cinquième du débit nominal,
• . remplacement de l'air comprimé par l'oxygène dans la canalisation 7,
• . réglage des débits d'hydrogène et d'oxygène de manière stochiométrique pendant une première phase,
• . introduction de la vapeur d'eau dans la chambre 2,
• . extinction de la flamme pilote,
• . mise en régime thermique pendant une heure;
• - réaction :
• . La réaction de destruction intervient dans le réacteur 3 réalisé, de préférence, en matériau résistant à la température de 1500_°C par exemple de l'acier inox réfractaire. le produit, par exemple le pyralène, est injecté dans une canalisation 11 à l'aide d'une pompe. L'injecteur à résonance ultrasonore utilisé nécessite un fluide auxiliaire, dans le cas présent de la vapeur d'eau surchauffée à 120_°C par une gaine chauffante. Un piquage 13 pour un thermocouple mesure la température d'injection dans le réacteur, un autre piquage 13a permet de mesurer la pression. Enfin un piquage 14 assure une possibilité de prélèvement des gaz pour analyses.

The operation of the device includes the following steps:

• - start-up:
• . purging of the hydrogen line 6 with an inert gas such as nitrogen by dilution under pressure,
• . establishment of the coolings 9,
• . establishment of the compressed air flow in the diffusers via the pipe 7,
• . starting the pilot ignition flame,
• . establishing the hydrogen flow rate; initially one fifth of the nominal flow,
• . replacement of compressed air with oxygen in line 7,
• . adjustment of the hydrogen and oxygen flow rates stochiometrically during a first phase,
• . introduction of water vapor into chamber 2,
• . extinction of the pilot flame,
• . thermal regime for one hour;
• - reaction:
• . The destruction reaction takes place in the reactor 3, preferably made of a material resistant to the temperature of 1500 _° C., for example refractory stainless steel. the product, for example pyralene, is injected into a pipe 11 using a pump. The ultrasonic resonance injector used requires an auxiliary fluid, in this case water vapor superheated to 120 _° C by a heating sheath. A tap 13 for a thermocouple measures the injection temperature in the reactor, another tap 13a makes it possible to measure the pressure. Finally a tap 14 provides a possibility of sampling gases for analysis.

• - récupération des rejets liquides, solides et des gaz :
• . une injection d'eau 15 complète le lavage des gaz, l'injection de soude diluée 16 assure la neutralisation du gaz chlorhydrique résultant de la réaction de combinaison d'hydrogène sur le chlore libéré par la destruction des produits organiques chlorés ;
• . une cuve 5 permet le stockage des liquides condensés tandis que les gaz après dévésiculation sont dirigés vers un système de dépollution classique non représenté qui comporte en sortie une torchère propane-air pour brûler l'excès d'hydrogène ainsi que les hydrocarbures légers.

The hydrogen-oxygen reaction ensures the heat supply of the steam cracking which, by diluting the products with an inert vapor, promotes the decomposition of molecules;

• - recovery of liquid, solid and gas discharges:
• . an injection of water 15 completes the washing of the gases, the injection of dilute sodium hydroxide 16 ensures the neutralization of the hydrochloric gas resulting from the reaction of hydrogen combination on the chlorine released by the destruction of the chlorinated organic products;
• . a tank 5 allows the storage of condensed liquids while the gases after demistering are directed to a conventional depollution system not shown which includes at the outlet a propane-air flare to burn excess hydrogen as well as light hydrocarbons.

The following example is given by way of illustration and in no way limits the present invention.

Example Pyralene test

200 g of pyralene used in the transformers containing 60% polychlorobiphenyl and 40% trichlorobenzene were injected into the reactor. Chromatography measurements made it possible to show that 99.9985% of the pyralene was destroyed.

The decomposition by-products include in particular naphthalene, diphenyl, phenanthrene, fluoranthene, heavy hydrocarbons.

The gases released consist of excess hydrogen and light hydrocarbons: C2 / C3 fraction; these gases are burnt in a flare but can advantageously on large units be used as a heat source for the production of water vapor necessary for the process.

No trace of dioxin was detected at the method analysis threshold, ie 2 ppm (parts per million) for the by-products and less than 15 ppt (parts per trillion) for the washing water.

• - des solvants de nettoyage du pyralène en particulier du fréon,
• - des produits (huiles de lubrification et autres solvants) contaminés radioactivement par des sels métalliques notamment du type césium et cobalt par exemple des liquides de scintillation du type 1-5 di- phényloxazol, 1-4 di 2 (5 phényloxazolyl)benzène, etc... Les ions métalliques formant des chélates, ce procédé décompose ces molécules, assure leur minéralisation et la dissolution des sels métalliques radioactifs qui une fois en phase aqueuse peuvent être alors facilement concentrés et traités par des procédés classiques de l'industrie nucléaire.

The present invention has only been described by way of illustration and in no way limiting; in fact, it is capable of receiving various variants coming within its scope and of allowing the treatment of all liquid, gaseous and solid organic products, in particular:

• - cleaning solvents for pyralene, in particular freon,
• - products (lubricating oils and other solvents) radioactively contaminated with metal salts, in particular of the cesium and cobalt type, for example scintillation liquids of the 1-5 di-phenyloxazol, 1-4 di 2 (5 phenyloxazolyl) benzene type, etc. ... The metal ions forming chelates, this process breaks down these molecules, ensures their mineralization and the dissolution of radioactive metal salts which once in the aqueous phase can then be easily concentrated and treated by conventional methods of the nuclear industry.

The applications envisaged thus relate to the treatment of waste from the electrical industries (transformers, capacitors), chemical or even nuclear.

Furthermore, it will be readily understood that the sources of hydrogen suitable for carrying out the process can be any, that is to say that the hydrogen can be supplied by an industrial gas (coke oven gas, flue gas ...) or by domestic gas.

The quantities admitted will then of course be a function of the hydrogen content to satisfy the operating conditions.

Claims (9)

1. A process for destroying organic products having toxic effects, such as waste from the electrical, chemical or nuclear industries, without the risk of forming secondary decomposition products which are equally toxic, comprising as its main step a vapo-cracking operation.

2. A process according to claim 1, wherein the said vapo-cracking is effected in a reducing medium in the presence of hydrogen.

3. A process according to claim 2, wherein the quantity of hydrogen is between 1 and 1.5 Nm3/kg of the product to be treated.

4. A process according to claim 2 or claim 3, wherein the hydrogen required is supplied by an industrial gas or a domestic gas.

5. A process according to claim 4, wherein the industrial gas is a coking plant gas or a flue gas.

6. A process according to claim 1, wherein the va- po-cracking is effected at a temperature of between 1000 and 1500_°C.

7. A process according to claim 1, wherein the va- po-cracking is effected by or with superheated water vapour and oxyhydrogen combustion.

8. A process according to claim 7, wherein the quantity of hydrogen necessary for oxyhydrogen combustion corresponds to an excess of 2 to 10% in relation to the stoichiometric conditions.

9. Processing plant for carrying out the process according to claim 1, comprising a combustion and mixing chamber with means for admitting hydrogen, oxygen and water vapour; at least one reactor for receiving the mixture from the combustion chamber and the product to be treated and, at the exit from this reactor, stations for condensing and treating the products of the reaction.

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