EP0441942B1 - Process and installation for the combustion of oxygen-free toxic gas effluents - Google Patents

Abstract

Process for the combustion of oxygen-free toxic gaseous effluents in a flame, including an inner cone (8) supplied with combustible gas (6) and with a so-called primary oxidant gas (7). Said effluent gas (10) and a so-called secondary oxidant gas (9) are introduced separately at the level of the inner cone. The secondary oxidant gas is introduced in the form of at least one jet directed at the axis (D) of the inner cone at a flow rate and speed which are sufficient to ensure an excess of oxidant, as well as maintaining the temperature, and creating a turbulent gaseous mass at the level of the inner cone. The toxic gas effluent (10) is then introduced into the resulting turbulent gaseous mass. The invention also relates to an installation for the implementation of said process, which takes place at negative pressure.

Description

The invention relates to a method and an installation for the destruction by combustion of toxic oxygen-free gaseous effluents.

The problem of eliminating such effluents has arisen in particular in integrated circuit manufacturing units where, to boost materials, gases loaded with arsenic hydrides (arsines), and / or phosphorus hydrides ( phosphines) and / or silicon hydrides (silanes) ...

These gases are toxic and the gas stream containing them must absolutely be purified before being released into the atmosphere.

A known treatment method consists in burning said gases; the combustion products are not toxic or can be easily eliminated (for example by filtration for arsenious oxide).

Patent FR 87 03 729 published under the number 2 612 606 describes such a process with its associated device. According to this patent, the effluent is brought into a combustion zone by a central duct surrounded by a tube bringing the combustible gas, itself surrounded by three annular conduits bringing the combustion air. We try to stay as long as possible in laminar flow beyond the burner to push back the inflammation zone to avoid the deposition of oxides on the burner. The gas injection rates and speeds are regulated for this purpose. For the same purpose, the combustible gas stream constitutes a protective sheath for the effluent vis-à-vis the oxidizing gas.

DE-A-2 857 224 has also described a process and its associated device for the incineration of explosive gases. Said method possibly involves an auxiliary fuel and, in order to prolong the residence time of the gases to be incinerated in the combustion chamber, it imposes a reflux of these in said combustion chamber.

The Applicant currently offers a combustion process in which, unlike that described in FR-A-2 612 606, a significant turbulence is created.

• il est mis en oeuvre en dépression ;
• un gaz comburant dit secondaire est introduit au niveau dudit dard, sous la forme d'au moins un jet dit fixe, à débit et vitesse constants et suffisants pour générer une masse gazeuse turbulente au niveau dudit dard et maintenir la température de combustion voulue et d'au moins un jet dit modulable, à débit variable pour stabiliser ladite température de combustion ; lesdits jets, dirigés vers l'axe dudit dard, assurant également l'apport de comburant en excès dans la zone de combustion ;
• ledit effluent gazeux à brûler est introduit au niveau dudit dard, séparément dudit gaz comburant secondaire, dans ladite masse gazeuse turbulente générée ;
• les gaz issus de ladite zone de combustion sont envoyés dans une zone de post-combustion.

More specifically, the subject of the invention is a process for the combustion of toxic gaseous effluents devoid of oxygen in a flame comprising a stinger supplied with combustible gas and so-called primary oxidizing gas, process characterized in that:

• it is implemented in depression;
• a so-called secondary oxidizing gas is introduced at the level of said sting, in the form of at least one so-called fixed jet, at constant rate and speed and sufficient to generate a turbulent gaseous mass at the level of said sting and to maintain the desired combustion temperature and d '' at least one so-called modular jet, with variable flow rate to stabilize said combustion temperature; said jets, directed towards the axis of said dart, also ensuring the supply of excess oxidant in the combustion zone;
• said gaseous effluent to be burned is introduced at said dart, separately from said secondary oxidizing gas, in said turbulent gaseous mass generated;
• the gases from said combustion zone are sent to a post-combustion zone.

The invention therefore consists of a method of combustion of toxic gaseous effluents, devoid of oxygen. Such effluents are not, in themselves, explosive. They can become so in the presence of oxygen.

They consist of a carrier gas loaded with impurities. Said carrier gas can be hydrogen, nitrogen, etc. or a mixture of gases. Air and oxygen are obviously excluded.

Said gaseous effluents to be burned according to the process of the invention can, as indicated above, come from the electronics industry. Such effluents are loaded with hydride, in particular phosphines, arsines ... and / or silanes ... and / or other chemical compounds containing in particular the atoms B, P, As, Te, Se, Cl, F .

Said gaseous effluents can also come from the nuclear industry. It can be pyrolysis gas and / or gas loaded with tritium, radioactive.

The dart is obtained from a conventional burner placed at the head of the combustion zone, supplied with combustible gas (natural gas for example) and oxidizing gas (air for example). This oxidizing gas is called primary in the text of the present application to distinguish it from other oxidizing streams. Advantageously, the flow rate of this primary oxidizing gas is adjusted so as to ensure combustion, with a small excess of oxidizing gas (approximately 10%).

According to the invention, so-called secondary oxidizing gas is sent to the dart in the form of jets, at a rate sufficient to ensure an excess of oxidizer, relative to the quantity necessary for the combustion of the toxic effluent, and at a speed sufficient to create a turbulent gaseous mass at the level of the stinger.

The secondary oxidizing gas is for example air.

The flow and speed of the secondary oxidizing gas are such that the appearance of the stinger is modified: it changes color, its shape is disturbed and we observe vortex movements. We then say that the gas mass is turbulent. This phenomenon is known to those skilled in the art.

The flow rate and speed of the secondary oxidant gas must also be determined to maintain the temperature in the combustion zone and the excess of oxidant.

The speeds can go up to several tens of m / s.

The secondary oxidizing gas is introduced in the form of at least two jets directed towards the axis of said dart. These jets can converge towards the axis of the dart or else be directed so as to create a swirling movement of the oxidant around said dart; in this case also, the orientation of the jet participates in the creation of turbulence.

The method of the invention is implemented, under vacuum with respect to the atmosphere outside the combustion zone (ambient atmosphere). Such a vacuum makes it possible to avoid the formation of gas pockets, to avoid a possible dispersion of the gases towards the outside. It also facilitates the extraction of gases from the installation in which the method is implemented.

This depression is of the order of 0.5 to 6 mbar (or 50 to 600 Pa).

• au moins un jet dit fixe avec un débit et une vitesse constants et suffisants pour obtenir une masse gazeuse turbulente, et la température de combustion voulue ;
• au moins un jet dit modulable avec un débit variable pour maintenir la température ;

lesdits jets assurant également l'apport de comburant en excès.Typically, the secondary oxidant gas is supplied by two different circuits producing:

• at least one so-called fixed jet with a constant flow and speed sufficient to obtain a turbulent gas mass, and the desired combustion temperature;
• at least one so-called modular jet with a variable flow to maintain the temperature;

said jets also ensuring the supply of excess oxidant.

The adjustable (secondary) oxidant gas stream cools the gas mass and makes it possible to lower the temperature of the combustion zone, if necessary. By the absence of said current, the temperature is brought up, which can be accelerated by adjusting the flow rate of fuel gas / primary oxidant.

It is sufficient, in the context of the invention, for the toxic gaseous effluent to be introduced in the form of a jet into the turbulent gas mass (one or more jets). No matter where the effluent jet (s) arrive (s) in relation to the secondary oxidant gas arrivals, it is sufficient that turbulence is created on the gas mass.

When the toxic effluents are of a different nature, they can be introduced in the form of separate jets at the level of the dart, or else be mixed before being introduced.

The toxic effluent can be introduced sporadically. The flow of secondary oxidant gas is generally controlled by the measurement of the temperature in the combustion zone. The method of the invention advantageously makes it possible to treat effluents whose flow and speed are not controlled; it then suffices to adjust the flow rates and speeds of oxidizing gas in order to achieve combustion.

The temperature in the combustion zone is generally greater than 900 ° C. for the treatment of the toxic gases previously mentioned. Said temperature is advantageously chosen so as to obtain at least 99% destruction of the toxic gases over the entire installation - that is to say combustion zone possibly supplemented with an after-combustion zone in which the reaction ends in which the method of the invention is implemented.

In any case, it will be chosen, by a person skilled in the art, above a critical temperature: the explosive temperature of the gas mixture in the combustion zone. What that said mixture is, a person skilled in the art situates this critical temperature at around 800 ° C.

In the absence of effluent to be treated, it is advantageous to put on standby at a temperature very slightly higher than the explosive temperature of the gases then present in the combustion zone.

To allow the combustion reaction to continue, the gases from the combustion zone are sent to a so-called post-combustion zone containing a lining of refractory materials. Said lining is advantageously brought to a temperature higher than the combustion temperature in the combustion zone. Said packing also ensures the filtration of gases and a better distribution of calories in the installation.

Said post-combustion zone is obviously also under vacuum (preferably 0.5 to 6 mbar).

It may be advisable to cause a leak at the top of the post-combustion zone (part opposite the bottom containing the lining) leading to a slight stream of so-called tertiary oxidant gas (air in general) which guarantees an excess of oxidant in the zone post-combustion.

The flow rates and speeds of the oxidizing gases are adjusted so as to obtain a temperature of 900 to 1,200 ° C, approximately 1,000 ° C preferably in the post-combustion zone, in the context of an application to the toxic effluents listed. above.

The outgoing gases can be released directly into the atmosphere or be treated, depending on the amount of residual toxicants and the applicable discharge standards.

• au moins deux tubulures , au moins une pour un jet dit fixe et au moins une autre pour un jet dit modulable, pour amener le gaz comburant secondaire au niveau dudit fond dudit tunnel ; lesdites tubulures étant orientées pour diriger en cours de fonctionnement ledit gaz comburant secondaire en jets vers ledit dard ;
• au moins une tubulure pour amener l'effluent gazeux toxique au niveau dudit fond dudit tunnel , la(les)dite(s) tubulure(s) étant orienté(e)s pour diriger, en cours de fonctionnement, ledit effluent en jet(s) convergent(s) vers l'axe (D) dudit dard ;
• une zone de post-combustion prolongeant ledit tunnel de combustion ;
• un dispositif d'extraction des gaz créant une dépression dans ledit tunnel et ladite zone de post-combustion .

The present invention also relates to an installation for the combustion of toxic gaseous effluents devoid of oxygen, in which the method described above can be implemented. Said installation comprises a combustion tunnel at the bottom of which is a burner, supplied with combustible gas and with so-called primary oxidizing gas, and is characterized in that:
- The bottom of said tunnel is constituted by a conical wall open on said tunnel, of the same axis (D) as it, said burner being disposed on this axis (D) at a depth such that the base of the stinger is located, during operation, near said bottom of said tunnel; and
in that it further comprises:

• at least two pipes, at least one for a so-called fixed jet and at least one other for a so-called modular jet, for bringing the secondary oxidizing gas to said bottom of said tunnel; said pipes being oriented to direct during operation said secondary oxidizing gas in jets towards said stinger;
• at least one tube for bringing the toxic gaseous effluent to the level of said bottom of said tunnel, the said tube (s) being oriented to direct, during operation, said jet effluent (s) ) converge (s) towards the axis (D) of said sting;
• a post-combustion zone extending said combustion tunnel;
• a gas extraction device creating a vacuum in said tunnel and said post-combustion zone.

The installation according to the invention comprises a combustion tunnel, the bottom of which consists of a conical wall. This wall is generally made of refractory materials over a thickness sufficient to ensure the thermal insulation of the installation from the outside.

In the bottom of the cone is a recess for the burner. The burner comprises a pipe for the arrival of the combustible gas and another pipe for the arrival of the primary oxidizing gas.

It can for example be a workman formed at the bottom of the tunnel, into which the burner opens, the dart then developing in the workman.

In another embodiment, the burner comprises two concentric pipes, and the fuel supply pipe is set back from the bottom of the tunnel cone, in order to facilitate the fuel / primary oxidant mixture before the development of the dart, the base of the dart being practically at the bottom of the cone of the combustion tunnel.

Flow adjustment means are provided on these pipes; they are preferably controlled by the temperature measurement in the installation.

On the conical wall of the combustion tunnel, lead to the arrival of secondary oxidant gas and toxic effluent.

The secondary oxidizing gas is supplied by at least two pipes which pass through the conical wall over its entire thickness; the pipes are dimensioned so that the gas escapes in the form of a jet. These tubes can be given a slit shape so as to cover the jets with a larger surface.

A more favorable embodiment consists in providing several pipes, for example three or four, regularly arranged around the periphery of the conical wall. Depending on the case, the pipes are arranged so that the jets converge towards the axis of the dart substantially at the same point, or else they are inclined identically around the periphery of the conical wall so as to create a rotary movement of the oxidizing gas introduced. .

The tubing (s) bringing the effluent, also passes through the conical wall and is (are) arranged so as to direct the jet (s) of effluent towards the axis of the dart substantially at the same point. Preferably, there are several pipes regularly distributed around the periphery of the conical wall.

Secondary oxidant gas pipes for so-called fixed jets and pipes for so-called modular jets are provided, each type of jet being piloted independently of the other.

In a particular embodiment, there are provided tubes separated into two parts by a wall, the jets then opening out substantially in the same place.

The dimensions of the combustion tunnel are determined by a person skilled in the art as a function of the products treated, the combustion temperature to be obtained, the residence time, etc.

A device, for example an exhaust fan, is mounted on the gas extraction pipe to create the vacuum in the installation.

Said installation comprises a combustion tunnel followed by a post-combustion zone, said zone also comprising refractory walls and its axis advantageously making an angle with that of the combustion tunnel. The bottom of said zone is provided with a lining of refractory material and a lateral tube allows the exit of the gases having passed through said lining.

At the top of the post-combustion zone (the top being opposite the bottom), an intake valve can be fitted, allowing the passage of oxidant (tertiary oxidant) towards the bottom of said post-combustion zone. Advantageously, said valve is used as an expansion valve, to compensate for accidental overpressures.

• les figures 1A et 1B représentent des réalisations préférées de l'installation selon l'invention ;
• les figures 2A, 2B et 3A montrent en coupe (vue selon l'axe du tunnel de combustion) le fond du tunnel avec le brûleur et les tubulures pour les gaz, la figure 3B montre une vue en coupe de l'installation 1B selon la direction F.

The figures below illustrate the invention:

• Figures 1A and 1B show preferred embodiments of the installation according to the invention;
• FIGS. 2A, 2B and 3A show in section (seen along the axis of the combustion tunnel) the bottom of the tunnel with the burner and the gas pipes, FIG. 3B shows a sectional view of the installation 1B according to the direction F.

FIG. 1A shows an installation comprising a combustion tunnel 1 of axis (D) followed by an afterburner zone 2 arranged perpendicular to said tunnel.

The bottom of the tunnel 1 is constituted by a conical wall 3 open on the tunnel. The tunnel with its bottom is surrounded by a thickness 4 of bricks (or other material) refractory to ensure thermal insulation.

At the bottom of the tunnel, a recess is arranged along the axis (D) and over the entire thickness of the conical wall. A burner 5 is embedded therein, which comprises a line 6 for the supply of combustible gas (natural gas) and a line 7 supplying the primary oxidizing gas (air). A dart 8 develops at the bottom of the tunnel.

In FIG. 1A, the base of the dart is at the bottom of the cone of the conical wall; in FIG. 1B, it is located in the opening placed on the recess arranged in the bottom of the cone.

Tubes 9 and 10 pass through the conical wall to supply the secondary oxidizing gas (air) and the toxic effluent respectively.

In the example illustrated in FIGS. 1A and 2A, three tubes 9 and three tubes 10 are placed. The tubes 9 are arranged so that their axes converge on the axis (D) of the tunnel at a point A, the tubes 10 in point B and point B is located beyond point A.

On the other hand, in FIG. 18, the tubes 9 converge at points A1 and A2, the tubes 10 at point B and the points A1 and A2 are located beyond point B.

In the section in FIG. 2A, according to an embodiment of the invention, the pipes 9 supplying the secondary oxidizing gas have a slit shape while the pipes 10 have a circular shape.

FIG. 3A presents a preferred variant, in which the pipes 9 are separated into two parts by a partition 11. In part 12, the closest to the burner, circulates the secondary oxidizing gas with fixed jet and in part 13 the oxidizing gas secondary with modular jet. The two parts are then supplied by different pipes. Appropriate means of adjusting the flow and speed are placed on the supply pipes.

FIG. 18 shows separate tubes 9A and 9B for supplying the secondary oxidizing gas in the form of a respectively modular and fixed jet.

FIG. 28 shows in section the tubes 9B inclined so as to create a rotary movement of the secondary oxidizing gas known as a fixed jet around the stinger.

The tubes 10 are divided into three groups of three tubes 10A, 108, 10C which each bring a toxic effluent of different nature, for example. The tubing of the groups is regularly arranged around the periphery of the conical wall.

According to Figure 1A, the gases from the combustion tunnel 1 are diverted to the post-combustion zone 2 which contains at its bottom a lining 14 (made of silicon carbide for example) which can be evacuated by a withdrawal door 15 and brought by a door 16. The door 16 may include a valve 17 through which the tertiary oxidant (air) which is entrained with the combustion gases towards the lining. The gases having passed through the lining, leave the installation through the piping 18.

The invention is illustrated by the example below. In an installation of the type described above, the cylindrical combustion chamber of which has an external diameter of approximately 1,200 mm, an internal diameter of approximately 400 mm, an approximate internal length of 1,600 mm and of which the post- combustion -which follows said combustion chamber- contains aggregates of silicon carbide, a gas loaded with arsine, at 6000 ppm by volume, was treated at a flow rate of 14 Nm³ / h.

At the head and in the axis of the combustion tunnel, there is a burner flue supporting the burner itself and the air and gas inlets.

• hydrogène 10,2   Nm³/h
• azote 3,0   Nm³/h

The carrier gas loaded with arsine is sent into the quarry towards the combustion tunnel. It is composed of :

• hydrogen 10.2 Nm³ / h
• nitrogen 3.0 Nm³ / h

The fuel involved is natural gas, delivered at a rate of 1.1 Nm³ / h at the nose of the burner previously mixed in the burner with 6 Nm³ / h of primary air (primary oxidant). The air / gas ratio was kept constant, whatever the burner flame, with a 10% excess of air compared to the stoichiometry.

• un air à débit constant (33 Nm³/h) et à vitesse constante (12 m/s) pour le balayage turbulent du tunnel de combustion,
• un air modulé à débit variable (de 0 à 35 Nm³/h) pour le maintien en température.

The secondary oxidizing gas composed of: also arrives through the burner opening, at a speed of 12 m / s:

• air at constant flow (33 Nm³ / h) and at constant speed (12 m / s) for turbulent sweeping of the combustion tunnel,
• modulated air with variable flow (from 0 to 35 Nm³ / h) for maintaining the temperature.

The depression in the tunnel is 5 mbar.

The temperature measured before the silicon carbide packing is 1000 ° C. The smoke volume at this temperature is 90 Nm³ / h.

Said fumes are then cooled from 1000 ° C to 700 ° C in a heat exchanger and then undergo a dilution, by ambient air, of a factor of 4 (325 Nm³ / h) to be brought back to a temperature of 100 -120 ° C before very high efficiency filtration (to stop 99.99% of particles of the order of 0.3 ”m) aimed at retaining arsenious acid, solid, formed, before discharge to the chimney.

At this level, the arsine charge is no more than 0.5 ppm by volume. The purification yield ensured by the installation is therefore 99.966%, higher than the 99.95% required (after taking into account the dilution on cooling).

• azote   80,0 %
• oxygène   18,0 %
• eau (vapeur)   1,5 %
• gaz carbonique   0,5 %

In addition, the composition of the smoke from the chimney was approximately as follows:

• nitrogen 80.0%
• oxygen 18.0%
• water (steam) 1.5%
• carbon dioxide 0.5%

Such an installation is particularly well suited for purifying gases from the electronic industry: not only is there almost complete combustion of toxic combustible elements, but the formation of nitrogen oxides or other toxic gases is avoided.

Claims (10)

1. Process for the combustion of toxic gaseous effluents bereft of oxygen, in a flame comprising an inner cone supplied with combustible gas and with so-called primary combustion-supporting gas, characterized in that:

   - it is carried out at reduced pressure;

   - a so-called secondary combustion-supporting gas is introduced at the level of said inner cone, in the form of at least one so-called fixed jet at a sufficient flowrate and speed to create a turbulent gaseous mass at the level of said inner cone and to maintain the desired combustion temperature and of at least one so-called modulable jet, of variable flowrate for stabilizing said combustion temperature; said jets being directed towards the axis of said inner cone, further ensuring the supply of an excess of combustion-supporting gas in the combustion zone;

   - said gaseous effluent to be burned is introduced at the level of said inner cone, separately from said secondary combustion-supporting gas, into said created turbulent gaseous mass;

   - the gases issued from said combustion zone are sent into a post-combustion zone.
2. Process according to claim 1, characterized in that the flowrate of the modulable jet(s) is servo-controlled by the measurement of the temperature in the combustion zone.
3. Process according to one of claims 1 or 2, characterized in that the combustion zone and the post-combustion zone are at a pressure of 50 to 600 Pa below the ambient pressure.
4. Process according to any one of claims 1 to 3, characterized in that an additional stream of combustion-supporting gas (called tertiary combustion-supporting gas) is introduced in the gases issuing from the combustion zone, in order to guarantee an excess of combustion-supporting gas in the post-combustion zone.
5. Process according to any one of claims 1 to 4, charaterized in that there prevails in the post-combustion zone a temperature of between 900 and 1200°C, and preferably a temperature of about 1000°C.
6. Process according to any one of claims 1 to 5, characterized in that the treated effluent contains at least one of the following constituents: silane, B, P, As, Te, Se, Cl, F.
7. Installation for the combustion of toxic gaseous effluents bereft of oxygen by carrying out the process according to any one of the preceding claims, said installation comprising a combustion tunnel (1) in the bottom of which lies a burner (5), supplied with combustible gas and so-called primary combustion-supporting gas, and being characterized in that:
      - the bottom of said tunnel (1) is constituted by a conical wall (3) open on said tunnel (1) and of same axis (D) thereas; said burner (5) being disposed on this axis (D) at such a depth that the base of the inner cone lies in the vicinity of the bottom of said tunnel (1) during operation; and
   in that said installation further comprises:

   - at least two pipes (9), at least one for a so-called fixed jet and at least another for a so-called modulable jet, for supplying the secondary combustion-supporting gas to the level of said bottom of said tunnel (1); said pipes (9) being oriented so that during operation, said combustion-supporting gas is directed as jets towards said inner cone,

   - at least one pipe (10) for supplying the toxic gaseous effluent to the level of said bottom of said tunnel (1), said pipe(s) (10) being oriented so that, during operation, said effluent is directed in jet(s) converging towards the axis (D) of said inner cone,

   - a post-combustion zone (2) extending said combustion tunnel (1);

   - a gas extraction device creating a reduced pressure in said tunnel (1) and in said post-combustion zone (2).
8. Installation according to claim 7, characterized in that said pipes (9) supplying the secondary combustion-supporting gas are in the form of a slot.
9. Installation according to one of claims 7 or 8, characterized in that the axis of said post-combustion zone (2) makes an angle with that (D) of said tunnel (1) and in that said post-combustion zone (2) is provided, in its bottom, with a lining (14) of refractory materials.
10. Installation according to claim 9, characterized in that a flap valve (17) is disposed in the top part of the post-combustion zone (2).

Images