EP0598639A1 - Process for the thermal treatment of an effluent containing organic polluting materials or an inorganic compound - Google Patents

Abstract

Process for the treatment of an effluent containing polluting organic matter and/or an inorganic compound with a view to recovering a clean effluent rid of this organic matter or recyclable. This process if of the type in which a first oxidant is introduced into a first zone (2) via (6) and a fuel via (7), whereby a combustion phase is produced, the oxidant being introduced along a helical trajectory; the said combustion phase is then forced into a second zone (13), through a restricted passage (11), whereby it is given a vortex-sink flow exhibiting an axis of symmetry; the effluent is introduced into the zone of axial symmetry (9) of the said vortex-sink flow; this process is characterised in that a supplementary oxidant is additionally introduced via (10) into the said zone of axial symmetry. <IMAGE>

Description

The present invention relates to a method for treating an effluent comprising polluting organic materials and / or an inorganic compound with a view to recovering a clean effluent free of these organic materials or recyclable.

The invention is particularly applicable to the treatment of methionine manufacturing effluents.

It is known that the chemical industry implements numerous processes which give rise to the emission of discharges or effluents comprising polluting organic impurities. For obvious reasons of respect for the environment, these effluents cannot be discharged without treatment. In addition, in certain cases, these effluents may contain, alone or in combination with pollutants, inorganic chemical species which are of interest to recover. In such cases, it is advantageous for the economy of the processes to also be able to treat the effluents so that the chemical species concerned are sufficiently free of impurities to be recoverable or that the effluents can possibly be recycled in the process taking into account their purity after treatment.

Among the processes used for the treatment of effluents comprising organic impurities and / or inorganic compounds, some consist of a combustion of these impurities or in a heat treatment of the inorganic compounds. The effluents are for example introduced into static vertical ovens where they are atomized in a stream of hot gases resulting from the combustion of a fuel-air mixture for example. The problem with this type of process is that the gas-liquid contacts are made in a completely random manner taking into account the respective trajectories of the gases and the liquid. This has the essential consequence of allowing only imperfect or incomplete combustion or heat treatment of the organic materials or inorganic compounds respectively. With regard to combustion, the destruction yields are generally between 96 and 98% which may be insufficient with regard to recent environmental standards.

The known methods can also pose other problems, in particular in the case of effluents comprising salts as inorganic compounds, such as for example sodium sulfate. In this case, when the melting temperature of these salts is reached, they can be deposited on the apparatus, thus causing the risk of fouling and clogging of the installation, risks aggravated by the corrosive nature of certain salts such as sodium sulphate.

There is therefore a definite need for a treatment method whose efficiency is improved compared to existing methods and whose implementation is safer.

For this purpose, the method according to the invention for treating an effluent comprising organic materials or an inorganic compound or a mixture thereof, is of the type in which a first oxidizing fluid and a fluid are introduced into a first zone. fuel, whereby a combustion phase is carried out, at least one of said fluids being introduced along a helical path; said combustion phase is then forced into a second zone, through a restricted passage, whereby it is given a well-vortex flow having an axis of symmetry; said effluent is introduced into the zone of axial symmetry of said well-vortex flow; this process is characterized in that a second additional oxidizing fluid is also introduced into said zone of axial symmetry.

The method of the invention makes it possible to achieve destruction yields clearly greater than 98%, for example at least 99% and even at least 99.9%.

• la figure 1 est une vue en coupe schématique d'un brûleur utilisable dans le cadre du procédé de l'invention;
• la figure 2 est une vue schématique d'une installation mettant en oeuvre le procédé de l'invention.

Other characteristics, details and advantages of the invention will appear more clearly on reading the description which follows, given with reference to the appended schematic drawings of an embodiment of the invention in which:

• Figure 1 is a schematic sectional view of a burner used in the context of the method of the invention;
• Figure 2 is a schematic view of an installation implementing the method of the invention.

The process of the invention can be used for any type of liquid or gaseous effluent. It is particularly suitable for liquid effluents.

It applies first of all to effluents containing polluting, combustible impurities or organic matter or which may be degraded by the action of temperature. The process is particularly suitable for cases where the impurities contained in the effluent are organic sulfur materials.

The process of the invention is also particularly suitable for the case of effluents comprising an inorganic compound whose recovery or recycling is advantageous. One can cite as an example the effluents comprising a sulphate, in particular an alkali sulphate such as sodium sulphate or also residual sulfuric acids.

Of course, the process of the invention can be used very particularly for effluents comprising both organic materials and inorganic compounds.

The process of the invention can thus be used for the treatment of effluents from the manufacture of amino acids comprising sulfur. A particular example is the treatment of effluents from the production of methionine and in particular of the mother liquors of the crystallization of the latter. In the latter case, the effluent to be treated comprises, in addition to sodium sulphate, numerous organic impurities such as compounds for the degradation of methionine with one or more sulfur atoms. Furthermore, the gases from the combustion treatments of the type described above contain a large amount of sulfur products.

As another example of effluents capable of being treated advantageously by the process of the invention, mention may be made of those resulting from the manufacture of certain esters with sulfuric catalysis such as ethyl phthalate or also the mother liquors of crystallization in the preparation. itaconic acid.

The principle of the process of the invention will now be described.

The first step in the process is to produce a combustion phase under specific conditions. To do this, a first oxidizing fluid and a combustible fluid are introduced into a first zone.

Generally these two fluids are used in gaseous form. Usually used as the first oxidizing fluid is air possibly enriched with oxygen. The combustible fluid can be a gas such as methane or propane or a light hydrocarbon for example. Natural gas is usually used.

Furthermore, according to a characteristic of the invention, at least one of these two fluids, generally the oxidizing fluid, is introduced into the aforementioned zone along a helical path. This fluid is introduced with a slight overpressure relative to the pressure prevailing downstream in the second zone. This overpressure is generally at most 1 bar and preferably between 0.2 and 0.5 bar.

The ignition of the fuel and of the oxidizer is caused and in the first aforementioned zone there is obtained a combustion phase which is itself animated by a movement along a helical trajectory.

This phase is then brought into a second zone via a restricted passage so as to give it a well-vortex movement. having an axis of symmetry. This well-vortex movement in fact corresponds to a movement of gases along a set of trajectories confused with families of generators of a hyperboloid. These generators rest on a family of circles located near and below the reduced passage, before diverging in all directions in the second zone.

It should be noted that following this movement is created in a zone of axial symmetry with respect to the path of the gases, a relative depression with respect to the rest of the first zone. The term “zone of axial symmetry” is understood here and hereinafter to mean the zone extending in the vicinity of the axis of symmetry of the above-mentioned trajectory.

The effluent to be treated is introduced into the zone of axial symmetry of the well-vortex movement. Preferably this introduction is done axially.

Preferably also, the place of introduction is located in the immediate vicinity of the restricted passage, upstream thereof or at the same level of said passage.

According to the main characteristic of the invention, a second oxidizing fluid is also introduced into the above-mentioned axial zone. What has just been said about the place of introduction of the effluent also applies to the second oxidizing fluid. More preferably, this introduction takes place axially. In addition, according to a particular embodiment, the effluent and the second oxidant are introduced coaxially.

As the second oxidizer, pure oxygen is usually used. It is nevertheless possible to envisage the use of oxygen-inert gas mixtures.

Given the vacuum effect in the effluent introduction zone, it is sucked in and then, as a result of a transfer of momentum between the effluent and the combustion phase, it is sprayed . There is thus obtained at the entrance to the second zone an isorepartiated and practically instantaneous dispersion in a spectrum of fine particles which will then be vaporized in a homogeneous and rapid manner.

In practice, the effluent is introduced at a low initial speed, preferably less than 10 m / s and more particularly at 5 m / s so as not to have to excessively increase the initial momentum of the combustion phase, the ratio of the amounts of movement of these two elements being at least equal to 100, preferably between 1,000 and 10,000.

On the other hand, one works under conditions such that the temperature reached by the effluent after vaporization is higher than the auto-ignition temperature of the latter.

The principle of bringing the combustion phase into contact with the effluent as just explained is more particularly described in the patents French n 2257326, 2431321 and 2551183 whose teaching is incorporated here by reference.

The contacting of the vaporized effluent and of the second oxidizing fluid will cause in the second zone, the combustion or the degradation of the organic impurities as well as a heat treatment of the inorganic compounds such as drying, melting, thermal decomposition etc.

At the exit of this second zone, a second essentially gaseous phase is obtained, but which may include a liquid and / or a solid, which is treated in a manner known per se to recover the recoverable compounds and ensure compliance with discharge standards .

This second phase can thus be subjected to quenching. It can also be cooled so that the solids can be recovered on the filter.

Finally, the gases can be treated by sprinkling with any suitable liquid to remove impurities or annoying combustion products before rejection, for example to absorb sulfur species such as SO₂.

In order to illustrate the invention and to better understand the process which has just been described, an example of a device for implementing the invention will now be studied with reference to the accompanying drawings.

FIG. 1 shows a burner 1 comprising a combustion chamber 2.

This combustion chamber consists of an outer cylinder 3 and an inner cylinder 4 coaxial thus defining a central area and an annular peripheral area 5 having perforations 6 distributed over several circles spaced axially. The upper part of the chamber 2 also includes an inlet 7 for the introduction of the combustible fluid.

The combustion chamber 2 is further provided in its axial upper part with a liquid or gas inlet 8 constituted here by two coaxial tubes 9 and 10 surrounded by an insulating lining and serving respectively for the introduction of the effluent to be treated and the second oxidizing fluid.

The chamber 2 ends downstream by a convergent 11 defining a neck 12 allowing passage into a second zone 13. It will be noted here that in the embodiment shown the inlet 8 opens just at the neck 12 and is located on the 'axis of symmetry of it.

The operation of the burner described above is as follows. The first oxidizing fluid is introduced through an orifice, not shown, made in the annular zone, it enters zone 2 through the perforations 6 and then follows the helical path shown in FIG. 1. It mixes with the fuel and the assembly is ignited by any known means, for example by a candle between the electrodes from which a spark bursts.

It is on passing through the neck 12 that the combustion phase will be animated by the movement or well-vortex flow described above.

The effluent is introduced at 9 and it meets the combustible phase substantially at the level of the neck 12 where it is then fractionated into a multitude of drops, each of them being transported by a volume of the gaseous combustion phase.

FIG. 2 illustrates the whole of an installation implementing the method of the invention. This assembly includes a burner of the same type as that described above, the element 14 representing the oxidizer inlet pipe.

Downstream of the burner 1, the second zone 13 consists of an oven 15 with a refractory wall. This oven is itself extended by a quenching device 16 which can for example be a water device such as a spray ring.

The installation further comprises a tank 17 ensuring the reception and separation of the liquid and the gases. These leave the installation through the chimney 18 which is equipped with a sprinkling device 19. The effluent is collected by a purge 20. It can be partly recycled through the pipe 21 to the quenching device 16 and / or when spraying gas. A pipe 22 is provided to add water to the installation.

A nonlimiting example will now be given.

Example

The devices of Figures 1 and 2 are used.

An effluent consisting of the mother liquors of crystallization of methionine is introduced by 9, the composition by weight of which is as follows: sodium sulfate (Na2SO4): 18-22%; methionine: 2-2.5%; organic products: 5-15%; the tests being carried out on lots of total organic carbon (TOC) content of 45 to 80 g / l. Air boosted to 0.5 bar is supplied by 14, methane by 7 and oxygen by 10.
The rates are as follows: Air Methane Oxygen Effluent Debit 695 Kg / h 2.23 Kmole / h 42 Nm³ / h 210 Kg / h

Furthermore, the temperature at the base of the quenching device 16 is 88 ° C, that at the bottom of the oven 13 is 1100 ° C, which by calculation gives a temperature at neck 12 of 1400 ° C. and a methane flame temperature at the bottom of the burner of 1680 ° C. taking into account the thermal losses of the installation.

The analyzes give the results below: Effluent (a) Purge (20) (b) Gas (c) COT g / h 8536 1.91 1.05

We obtain a total not destroyed in TOC g / h d = b + c of 2.96 and therefore a yield (a-d) / a of 99.965% as well as a liquid yield (a-c) / a of 99.978%. Finally, it should be noted that the fumes emitted are odorless.

Claims (10)

1) Process for treating an effluent comprising organic materials or an inorganic compound or a mixture thereof, of the type in which a first oxidizing fluid and a combustible fluid are introduced into a first zone, whereby a combustion phase, at least one of said fluids being introduced along a helical path; said combustion phase is then forced into a second zone, through a restricted passage, whereby it is given a well-vortex flow having an axis of symmetry; said effluent is introduced into the zone of axial symmetry of said well-vortex flow; characterized in that a second additional oxidizing fluid is also introduced into said zone of axial symmetry. 2) Method according to claim 1, characterized in that at least one of the above-mentioned effluent and second fluid is introduced axially into the aforementioned zone of symmetry. 3) Method according to claim 1 or 2, characterized in that the effluent and the aforementioned second fluid are introduced coaxially into the zone of symmetry 4) Method according to any one of the preceding claims, characterized in that an effluent is treated comprising as inorganic compound a salt such as a sulfate, in particular a sodium sulfate. 5) Process according to any one of the preceding claims, characterized in that a residual sulfuric acid is treated as an effluent. 6) Process according to any one of the preceding claims, characterized in that an effluent comprising sulfur-containing organic materials is treated. 7) Process according to any one of the preceding claims, characterized in that an effluent resulting from the production of methionine is treated, in particular the mother liquors from the crystallization of methionine. 8) Method according to any one of the preceding claims, characterized in that the ratio of the momentum of the combustion phase to that of the effluent is at least equal to 100, preferably between 1,000 and 10,000. 9) Method according to any one of the preceding claims, characterized in that at the exit from the second zone, the second phase obtained in this second zone is subjected to quenching. 10) Method according to any one of the preceding claims, characterized in that the second oxygen-oxidizing fluid is used.

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