GB2053452A - Method of burning corrosive residues and apparatus for applying the method - Google Patents

Abstract

In the combustion of corrosive residues, a swirling air stream is introduced at the bottom of the flame, the said air is caused to swerve so as to give it the form of a swirling-well flow, and at least one additional air stream is introduced co-currently around the mixture comprising the residues and the swirling air at the level of the upstream portion of the combustion zone. In apparatus for applying the said method, base 46 of combustion chamber 5 contains apertures for swirling air, which are formed in the supporting plate 43, and at least one aperture 44 and/or 45 for at least one additional air stream; the air for injecting and dispersing the corrosive residues being admitted through the injector 21, and the apertures being arranged concentrically relative to the axis of symmetry of the said injector; the apertures for the passage of the swirling air further being associated with a box 31, comprising tangential peripheral orifices 32 and frustoconical deflectors 33 and 34. <IMAGE>

Description

SPECIFICATION Method of burning corrosive' residues and apparatus for applying the method The invention concerns a method of and apparatus for burning corrosive residues such as those containing halogenated, especially chlorinated, hydrocarbons.

Industrial preparation of organic compounds containing chlorine, which is steadily increasing throughout the world, inevitably produces large quantities of residues, often with a chlorine content. These residues may be in the gaseous state, as in the case of the preparation of vinyl chloride or its homopolymers and copolymers, or in a liquid state and/or in the form of tarry solids obtained in the manufacture of chlorinecontaining aliphatic, cyclo-aliphatic and/or aromatic hydrocarbons. The composition of these chlorine-containing residues varies according to their source. Some residues comprise chlorinecontaining tarry residues where at least some of the constitutents contain over seven carbon atoms per molecule. Other chlorine-containing residues comprise chlorine-containing C4 and/or C6 compounds.These residues may be accompanied by other compounds with chlorine-containing C, to C4 constituents.

The discharge of such waste products into rivers or the sea is prohibited. The discharging provisionaliy allowed is restricted to limited quantities and strictly controlled. The rough treatment currently still tolerated, which involves simple combustion at sea, thus allowing corrosive emanations to escape into the atmosphere, is only a last resort. The results of the pollution inevitably produced, which are not normally acceptable near urban centres, are hardly visible here in the short term because of the dilution. However, it is far from certain that in the long term such treatment at sea will not constitute a serious threat to the environment.

One of the well known means for resolving the serious problem of the accumulation of these residues and of the air and water pollution which would result from it is to burn the residues at high temperatures of over 6000 C, e.g. 900-1 4500C, in a combustion chamber with simultaneous recovery of hydrochloric acid gas, which can be put into the form of an aqueous solution, and possibly production of steam.

The burning of the residues is vigorous, with flames. Stable continuous combustion can be obtained only in apparatus specially adapted to the purpose.

Various pieces of apparatus have already been described, adapted to the combustion of products with well defined properties, such as specially refined hydrocarbons used to obtain heat energy.

Such apparatus does not generally allow for the special properties or the absence of well defined properties in the chlorinated residues to be treated. In such cases it is very difficult to obtain stable combustion and consequently a stable flame; burners and spray nozzles frequently become blocked, particularly when the residues are viscous; and it is difficult to effect adjustments with a view to obtaining total combustion and to give hydrochloric acid containing only a minumum of free chlorine, together with virtually zero carbon production. Furthermore, corrosion is experienced in the apparatus, posing problems that are far from negligible and involve considerable maintenance costs.

Moreover, it is often very difficult to avoid rapid degradation of the compounds of a burner if some members or walls of the apparatus are not protected by a refractory and/or anti-acid coating or by special devices, e.g. for injecting a large volume of cold non-combustible gas around the flame.

Finally, a considerable difficulty resides in extrapolating the arrangement to a very large apparatus, e.g. one capable of treating three tonnes per hour of residues, by reason of the very large quantities of residues to be treated.

The invention aims at avoiding the above disadvantages and providing a method and apparatus for the buring or complete combustion of corrosive residues which may be liquids, pastes, solids or charged with solids or even gases.

According to the invention, residues that are corrosive or liable to give corrosive products, particularly halogenated hydrocarbons and residues containing them, are burnt in a combustion zone that is cooled in its upstream portion and where the flame is stabilised with axial introduction and dispersion of a mixture of residues to be burnt and of spraying air in the upstream portion of the combustion zone, in which a swirling air stream, co-axial of revolution of the combustion zone, is introduced at the base of the flame, the swirling air is caused to swerve inwards so as to give it the form of a vortex-well flow which is extended into the zone of dispersion of the said mixture; and at least one additional air stream is introduced co-currently around the mixture comprising the residues and swirling air at the level of the upstream portion of the combustion zone.

The swirling air stream is thus generally surrounded by the additional air stream or streams. In accordance with the invention, the additional air stream may in fact, as the case may be, include or consist of one, two three or more separate streams.

By proceeding in accordance with the invention, it is possible to attain complete satisfaction from the point of view of the regulations on the protection of the environment and has many other advantages, particularly flexibility in operation, reliability of the process, safety and efficiency in the essential purpose being followed, which is the fight against pollution, and a yield of hydrohalic, preferably hydrochloric, acid recovered of about 95% of the halogen when the corrosive residues to be burnt contain halogen. Furthermore, the recovery of hydrohaiic acid from the combustion process enables the cost of an installation including such recovery means to be paid off relatively quickly.

In an advantageous embodiment of the invention a zone of constriction of the swirling air stream is set up. This makes it possible to create turbulences which, in the case of a residue in liquid or paste form, will favour the completion of the dispersion of already dispersed droplets.

In another advantageous embodiment of the invention, at least one zone of construction or restricted passage, through which at least one additional air stream is passed, is provided. One effect of the zone of constriction is to complete the modelling of the flame and to cool the zone where the stabilised flame has come to rest, while at the same time forming an additional supply of combustion-supporting oxygen.

In a special embodiment of the invention, the spraying air is passed through a zone of constriction. The effect of the zone is to prevent the flame from widening out excessively and thereby avoiding excessive thermal strain on the members of the burner.

In another preferred embodiment of the invention, all the air streams are introduced concentrically relative to the axis of revolution (or of repetition or of symmetry) of the flame, around the mixture comprising the residues.

In a special embodiment of the invention, an annular escape space is formed at the base of the combustion zone, and the sheet of additional air is circulated through this space into the zone where the residue to be burnt is brought into contact with the combustion-supporting oxygen. The purpose of this is to provide heat insulation and effective cooling for the whole burner, and thus to prevent deformation, buckling or sagging, which would be caused by overheating of the burner components, which would inevitably take place without such an arrangement.

In another preferred embodiment of the invention, the zone where the flame is formed is ringed. This has the effect of making the flame which is set in rotation by the swirling air come to rest and thus stabilising it.

In another embodiment of the invention, at least one of the spraying, swirling and/or additional air streams is drawn into the combustion zone by setting up an adjustable low pressure. The low pressure may correspond to value of 1 to 40 mm of mercury below atmospheric pressure, allowing the various air streams introduced in the upstream portion of the combustion zone to be sucked in through the burner.

However, it is possible to introduce at least one of the said air streams at a pressure above atmospheric, e.g. swirling air. Particularly when the residues are in liquid or paste form, it is convenient to atomise and disperse the liquid phase with air under a pressure e.g. of 2 to 10 bars absolute.

In a special embodiment of the method, the combustion zone is vertical and has a symmetry of revolution.

Residues that are corrosive or liable to give corrosive products, such as halogenated hydrocarbons and more particularly chlorinated hydrocarbons, may be in liquid form, possibly charged with solid particles, or may be pastes, solids or gases. In the special case of chlorinated industrial residues in liquid, pasty or solid form, the burning method of the invention is particularly well adapted to residues containing over 40% or even over 75% by weight of chlorine, while gaseous residues at ambient temperature, apart from the nitrogen and oxygen which may also be present, contain over 50% by weight and more often from 53 to 74% by weight of chlorine. But the burning method of the invention may of course be used for combustion of corrosive products containing far less than 40% by weight of halogen, e.g. from 5 to 35%.

The invention also provides an apparatus for carrying out the said method. It comprises a chamber for bringing into contact, for forming the dispersion and for combustion, and means for forming the dispersion of the corrosive residues to be burnt, the said chamber being closed at the bottom by a base plate, except for at least one aperture for the said dispersion means. The base of the combustion chamber contains apertures for the swirling air and for at least one additional air stream, introduced into the said contact and combustion chamber co-currently with the air for injecting and dispersing the corrosive residues, which are let in through the means for forming the dispersion.The apertures are arranged concentrically relative to the axis of symmetry of the means for forming the dispersion; and the apertures for the passage of the swirling air are further associated with means for setting the said air in rotation to pre-stabilise the flame, and with deflecting means for causing the swirling air to swerve in the form of a swirling-well flow, thus modelling the shape of the flame to prevent it from widening out.

The dispersing air in turn starts to build up the shape of the flame. In a special embodiment of the invention, however, means for constricting the spraying air are provided to prevent the flame from widening out too far. The constricting means may be provided with means for controlling the restriction, thus enabling the air speed and hence the dispersing action and the constricting action of the spraying air to be adjusted.

The apparatus of the invention preferably comprises means for definitively stabilising the flame which is set in rotation by the air, the air being caused to swerve by deflecting means in order to prevent the flame from widening out too far. The stabilising means allows the flame to come to rest and gives it its stability. These means are outside the means for deflecting the swirling air and outside the means for dispersing the corrosive residues undergoing combustion.

In an advantageous embodiment of the invention, the apparatus further comprises means for constricting and deflecting the additional air stream or streams. These constricting and deflecting means force the additional air stream or streams to pass through them, and the resultant constricting action completes the moddelling of the flame and cools the means for stabilising it.

In another advantageous embodiment of the invention, the apparatus has means for constricting the swirling air stream.

The apparatus may further comprise a multiplicity of apertures for the introduction of the additional air stream or streams at the base of the combustion chamber, surrounding and having the same axis of symmetry as the means for forming the dispersion of the corrosive residues.

In a special embodiment of the apparatus, an annular leakage space at the base of the combustion chamber is adapted so that means are fitted for controlling the apertures which let in the additional air stream or streams. The annular space and/or apertures can thus be closed at least partially, enabling a varying excess of air to be obtained in the combustion chamber.

In a particularly advantageous embodiment, the combustion chamber is associated with depressing means such as venturis or fans.

The means for stabilising the flame and for constricting and deflecting the additional air stream or streams have one and the same axis of symmetry, which is the axis of revolution that forms the shape of the flame.

In a special form of the apparatus, the chamber for combustion of the said corrosive residues is vertical and has symmetry of revolution.

A preferred form of the apparatus will now be described to illustrate the invention. The apparatus is particularly suitable for burning chlorinated residues in liquid or paste form, with or without solid particles in suspension; it comprises means for recovering hydrochloric acid at the outlet of the apparatus, although these are not shown in the accompanying drawings.In the drawings: Figure 1 is a sectional view of the whole burner which fits the combustion chamber; Figure 2 is section through a means for dispersing the residues to be burnt (central injector); Figure 3 is a section through a means for supplying the stream of swirling air and for deflection (box for setting the air in rotation); Figure 4 is a section through a means for stabilising the flame and constricting the additional air stream, associated with a supporting plate for the burner located at the bottom of the combustion chamber (centring ring and stabilising air); and Figure 5 is an assembled view of Figures 2 to 4, again in section, showing the components of the burner in position.

In Figure 1 burner unit 1 is made integral with a circular supporting plate 2, which is fixed by bolts 3 to flat sole plate 4 of a cylindrical furnace or combustion chamber 5 which is connected to the downstream part of the unit (not shown). Outlet 6 for the combustion gases is located laterally in the upper part of the combustion chamber 5. The top of the furnace is fitted with a rocking cover 7 which has two functions, one being to open the cover when the process is stopped to cool the furnace, and the other to divert the flow of heat into the atmosphere in the case of failure in the downstream part of the unit.

The whole unit is kept at an adjustable low pressure, preferably from 3 to 20 mm of mercury below atmospheric pressure. The low pressure thus created in the furnace allows the various air streams to be sucked through the burner unit.

Their function is to support combustion, to disperse the droplets of fuel, to shape the flame and to cool the burner unit.

In Figures 2 and 5 injector 21 comprises dispersing means including a central tube 22 conveying the residues to be burnt, an annular concentric space between tubes 22 and 23 through which made-up fuel can be introduced when necessary, and a second annular space 24 provided for the air for atomising or spraying the corrosive residues, which is generally kept at a relative pressure of 2 to 4 bars.

The ducts 22, 23 and 24 discharge in the same plane as where the flame is formed in combustion.

A double circular chamfered edge 25 has a constricting effect on the atomising air. This prevents the flame from widening out excessively and thereby prevents excessive heat strain on the flame-stabilising ring, which will be described in connection with Figure 4. A screw thread 26 enables top cap 27 of the injector 21 to be positioned so that it controls space 28 between the two chamfered edges 25, thereby adjusting the air speed and thus the spray action and constricting force. The injector 21 can slide within its tubular guide 29, thus providing full scope for proper vertical adjustment relative to the burner unit.

In Figures 3 and 5 cylindrical box 31 contains four tangential peripheral orifices 32 through which the outside air is sucked, thereby setting the interior of the cylindrical box 31 in rotation. The stream of swirling air is then taken over by two frustoconical deflectors 33 and 34, arranged in series and representing the means for deflecting the swirling air, which is brought to where the flame is formed near the adjustable plane of the outlet from the injector 21 in Figures 2 and 5.

The swirling air has several functions. Thus it produces turbulence which completes the dispersion of the droplets atomised by the spraying air; it supplies most of the combustion supporting oxygen required; it shapes the flame to prevent it from widening out and completes the effect initiated by the spraying air in the injector; and it pre-stabilises the flame by setting in rotation.

It is possible to control the intensity of the effects described above, by throttling to a greater or less degree with closing devices or screens (not shown) fitting the four tangential suction orifices 32.

In Figures 4 to 5 cylindrical member 41 comprises a centring ring on which the flame, which is set in rotation by the swirling air, comes to rest and is definitively stabilised. A frustoconical stabilising member 42, located at the top of the ring and forming a constriction around it, enables an additional air stream to be supplied on the edges of the ring. The functions of the additional air stream are to model the flame for the last time by a constricting action, to provide additional combustion-supporting oxygen and to permanently cool the top of the centring ring, thereby avoiding eccessive thermal stresses.

The centring ring 41 and the frustoconical stabilising member 42 are fixed on a supporting plate 43, which contains two concentric series of holes 44 and 45, respectively six and four in number. The series of six holes 44, located nearer the centre, supplies air to the space between the ring 41 and the frustoconical member 42 just described. The outer series of four holes 45 controls a varying excess of air in the combustion chamber. The holes may be partially or totally blocked by closing screens (not shown).

The supporting plate 43 is fixed by bolts (not shown)-see component 4 in Figure 1-on the flat bottom 46 of the combustion chamber, forming an annular escape space 47 of a height defined by stud blocks 48. This creates a sheet of circulating air, owing to the low pressure prevailing in the combustion chamber; this is particularly effective in heat-insulating and cooling the burner unit, thus avoiding deformation, buckling and sagging caused by overheating of the equipment, which is usually made of metal. This would be inevitable without this arrangement.

The hydrochloric acid gas leaving the combustion chamber is cooled rapidly by means of an arrangement described in French Patent No.

2,086,574 and is then absorbed by an aqueous hydrochloric acid solution. The acid solution thus concentrated is drawn off and may either be returned to the store, possibly after concentration of the HCl, or neutralised and sent down the drain.

The method and apparatus just described enable the following to be obtained: (1) very fine atomisation of the products to be burnt, promoting rapid vaporization of the resultant droplets, which is indispensable to good combustion; (2) an adequate intake of air (a) to the flame zone and (b) to its periphery; (3) a stable flame; (4) flexible operation, since the burner of the invention can be adjusted within a very wide range of flow rate, e.g. from single to quadruple, and starting from cold without any difficulty:: (5) simultaneous burning of more than one fuel, such as light fuels, heavy fuels or natural gas, when the residues to be burnt have too little energy, thus enabling the temperature of the flame to be raised to the appropriate level; (6) simple construction without any movable components (the wear on which would necessitate excessive maintenance work), giving a very strongly built apparatus; (7) economy in energy consumption, represented by supplementary driving fluids such as air and steam; and (8) freedom from corrosion: the very nature of the halogenated residues to be burnt causes large quantities of halohydric gas to appear in the flame zone, this gas not being corrosive under normal operating conditions. Corrosion may occur in the event of unvaporized residues coming through.

The geometric design of the burner according to the invention eliminates any risk of this happening.

The fact that the burner unit is free from corrosion makes it unnecessary to use special metals or alloys such as tantalum or that sold under the trade mark Inconel.

The apparatus described above by way of example may very easily be adapted to burning residues in solid or gaseous form. In the case of previously pulverised solid residues that have been conveyed pneumatically through the tube 22 (Figure 2), it is not necessary to use the spraying air, and the second annular space 24 in Figure 2 is then simply closed. Similarly, the series of holes 45 in Figures 4 and 5 is closed, thus preventing an excessive amount of air from being admitted.

If the residue to be treated is a gas, the second annular space 24 in Figure 2 is blocked as for solid residues, but the holes 45 in Figures 4 and 5 are not closed.

The following examples are given as a nonrestrictive example of the invention, to explain the operation of the process and apparatus.

EXAMPLE 1 A toxic gaseous effluent from a factory producing poly(vinyl chloride) is to be destroyed by total combustion. It is of the following composition: vinyl chloride 28.9% by weight nitrogen 67.3% by weight oxygen 3.8% by weight and have the empiral formula C2H3ClOo.52NloA2.

The gaseous effluent is discarded in essentially variable quantities by the factory producing the poly(vinyl chloride). The flow rate is regularised at a constant value of 488.7 kg/h using a gasometer with a capacity of 250 m3.

A burner located at the base of a combustion chamber on the principle illustrated in the accompanying Figure receives the effluent in question in the central tube 22 of its injector (Figure 2), while a make-up fuel in the form of 98% propane gas is passed into the annular space between the tubes 22 and 23 at a flow rate of 5 Nm3/h.

A depression of 6.6 mm of mercury relative to atmospheric pressure is maintained in the whole enclosure of the combustion chamber, by means of a fan located at the end of the installation downstream of the combustion chamber, i.e. by means of control shutters located at the inlet to the fan.

In this way a strong current of air is sucked through the four tangential peripheral orifices 32 (Figures 3 and 5). This gives the air a rotating movement (swirling air), of a rapidity which is increased by successive passage into two frustoconical members 33 and 34, to form a swirling-well flow. The flow rate of this induced air stream is set to 1 80 Nm3/h.

Still by means of the depression prevailing in the combustion chamber, an additional air stream is sucked co-currently through the circular orifices 45 (Figures 4 and 5) at a flow rate of 300 Nm3/h. In the same way another additional air stream is sucked through the annular escape space 47, again at 180 Nm3/h.

A clear perfectly stable flame becomes established, sufficient to create a temperature of 1 1000C in the combustion chamber. Allowing for certain internal re-cycling within the unit, the fumes leaving the combustion chamber are of the following composition by weight: 02 2.6% N2 71.85% CO2 14.5% Cl2 0.05% HCI 6.4% H20 4.6% The fumes are quenched rapidly in an appropriate apparatus, passed into a series of absorbers, where they are put into contact with demineralised water and lose there HCI, and then sent through a caustic soda neutralising tower. A perfectly clear hydrochloric acid solution is obtained in this way, containing 32% by weight of HCI, while the fumes discarded into the atmosphere contain no discernible trace of carbon or free chlorine and no kind of organic compound.

As a result of the cooling provided by the annular escape air, the base plate supporting the burner is kept at a temperature of 600C.

EXAMPLE 2 Solid residues consisting of a mixture of stereoisomers of hexachlorocyclohexane have to be destroyed by total combustion. The mixture is the residue from the extraction of lindane (gamma isomer), and is in the form of white powder consisting of particles of an average diameter of approximately 80 microns. Such a mixture is described as "sterile", owing to the fact that, unlike the gamma isomer which is active in insect control, it has no important action in that field but does have recognised toxic properties.

The powdered residue is conveyed pneumatically at 350 kg/h by means of 140 Nm3/h of air at a slightly raised pressure (0.1 bar above atmospheric). This is passed into the burner/combustion chamber unit illustrated in the Figure through the central tube 22 (Figure 2).

65 kg/h of liquid make-up fuel (domestic fuel oil) is supplied to the burner at the same time through the concentric tube 23.

In the fumes circuit, downstream of the combustion chamber, and following the rapid cooling of the fumes, there is a washing tower and two venturi-shaped water-type absorbers (not shown). These each create a depression in the unit, so that the total depression within the combustion chamber is 8.8 mm of mercury. The depression creates a very strong current of air induced by suction through the tangential peripheral orifices 32 (Figures 3 and 5). This gives the air a rotating movement, which is accelerated by successive passage into the two frustoconical members 33 and 34, so as to form a swirling-well flow. The flow rate of the induced air stream becomes established at 2800 Nm3/h.

Still by means of the depression prevailing in the combustion chamber, an additional air stream is sucked through the annular escape space 47 (Figures 4 and 5), with a flow rate of 1500 Nm3/h.

This enables the burner/supporting plate unit 43 to be kept at a temperature of about 350C, thus ensuring that the unit has excellent mechanical strength.

A stable orange-yellow flame becomes established, creating a temperature of 1 2200C in the combustion chamber. Allowing for certain internal recycling, the fumes leaving the combustion chamber of the following composition by weight: O2 14.1% N2 74.1% CO2 5.6% Cl2 0.1% HCI 4.6% H20 1.5% By passing the fumes into the two above mentioned absorbers and then into a caustic-soda neutralising tower, a perfectly clear hydrochloric acid solution containing 5% of HCI can be obtained, while the fumes discarded into the atmosphere contain no discernible trace of carbon or free chlorine and no kind of organic compound.

EXAMPLE 3 The residues to be destroyed are liquid at ambient temperature and consist of: 1,3-dichloropropane 30% by weight 1,2,2-trichloropropane 31% by weight perchlorethvlen;?, 39% bv weight The complete installation comprises: a burner unit (Figures 2, 3, 4 and 5) and a combustion chamber (Figure 1), together with a washing apparatus and a series of three venturitype absorbers with a neutralising tower, which are not shown in the drawings.

The depression created in the combustion chamber by the three venturis in series is 7.3 mm of Hg. This makes it possible to create a very strong induced air stream by suction through the tangential peripheral orifices 32 (Figures 3 and 5), giving the air a rotating movement which is accelerated by successive passage into two frustoconical members 33 and 34. The flow rate of the air stream becomes established at 700 Nm3/h. The vigorous rotation of the air on leaving the injector creates a phenomenon known as a vortex-well or swirling well, which generates a depression sufficient to suck 625 kg/h of residues to be burnt through the central injecting tube 22 (Figure 2) without any pumping means being required for the liquids. Very fine atomisation of the liquid residues is obtained by these means.

The atomisation is completed by blowing in 30 Nm2/h of spraying air at 4 bars absolute, the air being let into the annular space 28 between the tube 23 and the adjustable cap 27 (Figure 2).

The depression created in the combustion chamber by means of the downstream apparatus described above generates three additional air streams: (1) an additional air steam of 175 Nm3/h, sucked through the six holes 44 (Figures 4 and 5), which completes combustion while pinching the flame and cooling the upper edges of the ring 41 and frustoconical member 42; (2) a second additional air stream of 330 Nm3/h, sucked through the four holes 45 and providing sufficient excess of air in the chamber to avoid any risk of poor combustion in the case of fluctuation in the flow rate and/or composition of the residues; (3) a third additional air stream of 470 Nm3/h, sucked through the annular escape space 47. The temperature of the burner/supporting plate unit 43 is thus kept at approximately 420C.

A stable, light-orange-to-yellow flame becomes established, creating a temperature of 11 8O0C in the combustion chamber. Allowing for certain internal recycling within the unit, the fumes leaving the combustion chamber are of the following composition by weight: O2 3.0% N2 52.7% CO2 16.3% Cl2 0.2% HCI 18.2% H20 9.6% The fumes are quenched rapidly by means of an appropriate apparatus then passed successively into the three above mentioned absorbers and into a caustic-soda neutralising tower. A perfectly clear hydrochloric acid solution containing 35% of HCI is produced, while the fumes discarded into:the atmosphere contain no discernible trace of carbon or free chlorine and no kind of organic compound.

EXAMPLE 4 An installation fundamentally similar in all points to that described in Example 3 is used to burn 125 kg/h of residue comprising a mixture of hexachlorobenzene, hexachlorobutadiene, hexachlorethane, trichloroethylene and dichloropropane corresponding to an empirical formula C2Hoos4scl3es3s The residues are fed into the burner through the central tube 22 of the injector (Figure 2), while 25 kg/h of heavy fuel is supplied through the tube 23, so as to provide sufficient heat to keep the temperature of the combustion chamber at 11 600C.

The depression in the chamber is kept at approximately 5.9 mm of Hg.

The swirling air stream sucked through the orifices 32 (Figures 3 and 5) is at 240 Nm3/h.

The spraying air blown in through the annular space 28 (Figure 2) has a flow rate of 10 Nm3/h.

The additional air stream sucked in through the six holes 44 (Figures 4 and 5) has a flow rate of 30 Nm3/h.

The second additional air stream sucked through the four holes 45 has a flow rate of 180 Nm3/h.

The third additional air stream sucked through the annular space 47 (Figures 4 and 5) has a flow rate of 120 Nm3/h, so that the temperature of the burner/supporting plate unit 43 is approximately 600C. Allowing for certain internal recycling within the unit, the composition of the fumes leaving the combustion chamber is as follows, by weight: 02 5.9% N2 62.5% CO2 16.4% Cl2 0.4% HCI 11.9% H2O 2.9% When the fumes have been treated as in Example 3 a clear hydrochloric acid solution is obtained, containing 32% by weight of HCI.

The findings in respect of the flame and the fumes discarded into the atmosphere are similar to those described in Example 3.

EXAMPLE 5 An installation fundamentally similar in all points to that in Example 3 is used to burn 480 kg/h of chlorinated liquid residues of the empirical formula: C2s87 H44s2 C 54 O,,,.

The residues are fed into the burner through the central tube 22 of the injector (Figure 2). The temperature of combustion chamber is 1 2400C, and the depression prevailing therein is 5.5 mm of Hg.

The induced swirling air stream sucked through the orifices 32 (Figures 3 and 5) is at 1030 Nm3/h.

The atomising air blown in through the annular space 29 (Figure 2) has a flow rate of 25 Nm3/h.

The additional air stream sucked through the six holes 44 (Figures 4 and 5) has a flow rate of 570 Nm3/h.

The second additional air stream sucked through the four holes 45 has a flow rate of 460 Nm3/h.

The third additional air stream sucked through the annular space 47 has a flow rate of 570 NmVh, so that the temperature of the burner/supporting plate unit 43 is approximately 300C.

Allowing for certain internal recycling within the unit, the composition of the fumes leaving the combustion chamber is as follows, by weight: O2 6.9% N2 60.7% CO2 12.7% Cl2 0.07% HCI 9.33% H2O 10.3% When the fumes have been treated as described in Example 3, a clear hydrochloric acid solution is obtained, containing 28% by weight of HCI. The findings in connection with the flame and the fumes discarded into the atmosphere are similar to those described in Example 3.

EXAMPLE 6 The following are burnt together in an installation which is identical in all points with that in Example 3: 1 395 kg/h of a type (A) residue, with an empirical formula of C2H2CI2 and 500 kg/h of a type (B) residue, containing hexachlorobenzene, hexachlorobutadiene, hexachloroethane and perchloroethylene.

The empirical formula for the mixture of the two streams of residues (A " B) is: C2H22oCI203 The residue (B) is a very viscous liquid, which has to be handled at 1 800C (crystallisation point 1 500C). It is supplied to the burner through the central tube 22 of the injector (Figure 2).

The type (A) residue is a liquid which is fairly fluid at ambient temperature and which does not require any special precautions. It is fed to the burner through a tube coaxial with the tube 22 (not shown in Figures).

20 kg/h of make-up fuel is fed through the tube 23, so as to provide sufficient heat to keep the temperature of the combustion chamber at 11 900C. The depression prevailing in the chamber is 8.1 mmofHg.

The induced swirling air stream sucked through the orifices 32 (Figures 3 and 5) flows at 3200 Nm3/h.

The atomising air blown in through the annular space 28 (Figure 2) has a flow rate of 40 Nm3/h.

The additional air stream sucked in through the six holes 44 (Figures 4 and 5) has a flow rate of 1600 NmVh.

The second additional air stream sucked through the four holes 45 has a flow rate of 800 Nm3/h.

The third additional air stream sucked through the annular escape space 47 has a flow rate of 1200 Nm3/h, so that the temperature of the burner/supporting plate unit 43 is approximately 350C.

Allowing for certain internal re-cycling within the unit, the composition of the fumes leaving the combustion chamber is as follows, by weight: 02 3.1% N2 52.3 CO2 17.1% Cl2 0.2% HCI 17.7% H20 9.6% When the fumes have been treated as described in Example 3, a clear hydrochloric acid solution containing 33% by weight of HCI is obtained. The findings relating to the flame and the fumes discarded into the atmosphere are similar to those described in Example 3.

Claims (22)

1. A method of burning residues that are corrosive or liable to give corrosive products, particularly halogenated hydrocarbons and residues containing them, carried out in a combustion zone which is cooled in its upstream portion and where the flame is stabilised with axial introduction and dispersion of a mixture of residues to be burnt and of spraying air in the upstream portion of the said combustion zone, in which a swirling air stream, co-axial of revolution of the combustion zone, is introduced at the base of the flame, the said swirling air is caused to swerve so as to give it the form of a vortex-well flow which is extended into the zone of dispersion of the said mixture; and at least one additional air stream is introduced co-currently around the mixture comprising the residues and swirling air at the level of the upstream portion of the said combustion zone.

2. A method as claimed in Claim 1, in which at least one zone of constriction is set up through which at least one additional air stream is passed.

3. A method as claimed in Claim 1 or 2, in which the additional air stream may include or consist of one, two, three or more separate streams.

4. A method as claimed in any preceding claim, in which all the air streams are introduced concentrically relative to the axis of revolution of the flame, around the mixture comprising residues.

5. A method as claimed in any preceding claim, in which the swirling air stream is surrounded by the additional air stream or streams.

6. A method as claimed in any preceding claim, in which a zone of constriction of the swirling stream is set up.

7. A method as claimed in Claim 1, in which a zone of constriction of the air for spraying the residues to be burnt is set up.

8. A method as claimed in any preceding claim, in which the zone where the flame is formed is ringed.

9. A method as claimed in any preceding claim, in which an annular escape space is formed at the base of the combustion zone through which an additional air stream in the form of a sheet is circulated with the combustion-supporting oxygen.

10. A method as claimed in any preceding claim, in which the spraying, swirling and additional air streams are drawn into the combustion zone by creating an adjustable low pressure.

11. Apparatus for carrying out a method according to any of Claims 1 to 10, comprising a chamber for bringing into contact, for forming the dispersion and for combustion, and means for forming the dispersion of the said residues, the said chamber being closed at the base by a base plate apart from at least one aperture for the said means for forming the dispersion, in which the base of the combustion chamber contains apertures for the swirling air and for at least one additional air stream, which are let into the said chamber for contact and combustion co- currently with the air for injecting and dispersing the corrosive residues admitted through the means for forming the dispersion, the said apertures being arranged concentrically relative to the axis of symmetry of the dispersion means, the apertures for the passage of the swirling air further being associated with means for setting in rotation and means for deflecting the said air.

12. Apparatus as claimed in Claim 11, in which means for contricting the spraying air is provided, equipped with means for controlling the constriction.

13. Apparatus as claimed in Claim 11, that includes means for definitively stabilising the flame.

14. Apparatus as claimed in any one of Claims 11 to 13, that further comprises means for constricting and deflecting the additional air stream or streams.

1 5. Apparatus as claimed in any one of Claims 11 to 14, that comprises means for constricting the swirling air.

16. Apparatus as claimed in any one of Claims 11 to 15, that comprises a large number of apertures for introducing the additional air stream or streams at the base of the combustion chamber, surrounding and with the same axis of symmetry as the means for forming the dispersion of the corrosive residues.

1 7. Apparatus as claimed in any one of Claims 11 to 16, in which an annular escape space at the base of the combustion chamber can be at least partially closed as well as the apertures to let in the additional air stream or streams, in order to heat-insulate the burner unit.

18. Apparatus as claimed in any one of Claims 13 to 17, in which the means for definitively stabilising the flame are outside the means for deflecting the swirling air and outside the means for forming the dispersion of the residues to be burnt.

19. Apparatus as claimed in any one of Claims 11 to 18, in which the combustion chamber is associated with depression means.

20. Apparatus as claimed in any one of Claims 11 to 19, in which the chamber for combustion of the said corrosive residues is vertical and has symmetry of revolution.

21. Apparatus as claimed in Claim 11, substantially as hereinbefore described with reference to the accompanying drawings.

22. A process as claimed in Claim 1 carried out substantially as hereinbefore described in any one of the Examples.