FR2582541A1 - Process for the treatment of a fluidised bed and plant comprising application of this process - Google Patents

Abstract

Process and plant for the treatment of a fluidised bed. This plant comprises essentially a reactor 1 with a vertical axis, one or more torches 9 for side injection of plasma into the reactor 1, means for injecting a gas stream 4 into the bottom part 2 of the reactor 1, means 6 for feeding pulverulent material into the reactor 1, a circuit 15, 16 for recycling hot particles into the reactor 1, and a circuit 21, 22, 23 for recycling hot gases towards the plasma torches 9 and towards the bottom part 2 of the reactor 1. This plant applies, for example, to ore roasting, to coal gasification, or to the chemical synthesis of various solid or gaseous products.

Description

 The present invention essentially relates to a process for treating a fluidized bed in a reactor.

 It also relates to an installation for the implementation of this process.

 It has been known for a long time that the formation of a fluidized bed can be obtained by suspending in a gas stream a finely divided material in the form of particles. More precisely, the fluidized bed can be formed in a chamber or a reactor into which a powder material to be treated is introduced, as well as a fluidizing gas which is injected at the bottom of the reactor to keep the particles of the material in suspension and in motion. powdery.

 In this way, a number of chemical reactions can be carried out in heterogeneous phases due to the significant heat transfers between the fluidizing gas and the particles, as well as due to the permanent agitation of the particles in suspension.

 It is also possible in this way to carry out reactions in gaseous phases, the fluidized bed constituting for example a catalytic bed. It is also possible to carry out purely physical treatments such as for example the drying of pulverulent materials or the roasting of ores.

 To heat the fluidized bed, various means have already been proposed such as for example plasma torches which can be fixed laterally on the wall of the reactor in which the fluidized bed is formed.

 However, the use of plasma torches, as has hitherto been recommended on fluidized bed reactors, provides a certain number of drawbacks, such as for example significant entrainment of the particles by the hot gas increased by the speed of the plasma and its viscosity thereby causing the instability of the fluidized bed, which is obviously detrimental to the reactions that iton wants to do in the reactor. If for example the particles in suspension have to undergo a heat treatment which is very brief, it is understood that this treatment will not be adequate, especially if the circulation of the fluidized bed in the reactor is practically zero.

 Also, the present invention aims to remedy the above drawbacks by providing a method and an installation for treating a fluidized bed which are particularly advantageous for efficiently carrying out reactions of various types.

 To this end, the subject of the invention is a process for treating a fluidized bed, according to which a pulverulent material is introduced into a reactor and suspended using a gas stream injected at the bottom of the reactor to forming a fluidized bed therein which is heated by at least one plasma torch, characterized in that one causes, thanks to the plasma emanating from the torch; forced and vertical circulation of at least a portion of the particles of the pulverulent material of the fluidized bed from the bottom to the top of the reactor to allow in particular the at least partial recycling of the hot particles collected at the top of the reactor and reinjected into the fluidized bed.

 It is therefore understood that, thanks to the plasma jet leaving one or more torches, an energetic vertical circulation of at least part of the particles of the fluidized bed will be carried out, which will improve the mixing of the particles and of the fluidization gas and advantageously will allow a controllable recycling of these particles and of this gas.

 According to another characteristic of this process, the hot particles collected in the upper part of the reactor are recycled by injecting them above and / or below the introduction of the plasma into said reactor.

 According to yet another characteristic of this process, at least a fraction of the hot gases is recycled in the upper part of the reactor in the plasma torch and / or in the gas stream injected in the lower part of the reactor.

 It should also be noted here that the number of recycling of hot particles and / or the operation of the plasma torch can or can be adjusted as a function of the treatment time necessary for the completion of the reactions in the reactor.

 The invention also relates to an installation for implementing the above method, and of the type comprising a reactor with a vertical axis, at least a united torch for lateral plasma injection into said reactor, means for injecting a gas stream in the lower part of the reactor, as well as means for supplying pulverulent material to the lower part of the reactor, characterized in that the upper part of the reactor is associated with a cyclone or the like, the outlet of which comprises at least one recycling of hot particles which opens laterally into the reactor above or below the plasma torch.

 This installation is further characterized by the fact that the upper part of the aforementioned cyclone is connected by at least one conduit to the plasma torch and / or to the lower part of the reactor.

 According to another characteristic of this installation, the means for supplying pulverulent material comprise at least one pipe opening into the reactor between its lower part and the plasma torch.

 It will also be specified that a valve can be provided at the outlet of the cyclone and allow communication of this cyclone either with the above-mentioned pipe or with a storage tank for the pulverulent material discharged by the reactor.

However, other characteristics and advantages of the invention will appear more clearly in the detailed description which follows and refers to the appended drawings, given solely by way of example, and in which
FIG. 1 is a schematic view in vertical section of an installation in accordance with the principles of the invention, and
- Figure 2 is a schematic view in vertical section of a second embodiment of installation according to this invention.

 According to the embodiment shown in Figure 1, we see that an installation according to the invention essentially comprises a reactor i with a vertical axis extending over a certain height and in the lower part 2 of which is introduced by an orifice 3, a pressurized gas materialized by the arrow 4.

 A powdery material 5 contained in a hopper 6 is introduced into the lower part of the reactor 2 by a preferably oblique pipe 7. The powdery material 5 is retained by a grid 8 arranged inside and in the lower part 2 of the reactor 1.

 One or more plasma torches 9 are fixed perpendicularly or at a certain angle to the horizontal, on the wall of the reactor 1. As is known, the torches 9 are for example constituted by a quartz tube 10 surrounded by a self 11 generating a plasma jet 12 or even an arc plasma torch (not shown) which, in the present case, causes in particular the entrainment of at least part of the fluidized bed 13 from the bottom part 2 of the reactor 1 to the upper part 14 of said reactor.

 This upper part 14 is connected to the upper part of a cyclone 15, the outlet of which comprises a pipe 16 which opens at 17 into the reactor 1 above the plasma torch 9.

 The outlet of the cyclone can also be equipped with another pipe 18 connected to a storage tank 19 for the particles of the pulverulent material already treated in the reactor 1. A valve has been shown at 20 allowing communication of the cyclone 15 either with the tank 19, or with the interior of reactor 1.

 In the upper part of the cyclone 15, there is provided a conduit 21 allowing the recycling of the hot gases in the plasma torch 9 and / or with the gas stream 4 injected into the lower part 2 of the reactor 1, as shown schematically by dashed lines marked respectively at 22 and 23, it being understood that a valve (not shown) could perfectly well be provided at the intersection 24 of the conduits 22 and 23 for supplying recycled hot gas either the torch or torches 9 or the lower part 2 of reactor 1.

 A valve has also been shown at 25 between the hopper 6 for supplying pulverulent material and the pipe 7 for conveying this material into the reactor 1.

 The same references have been used in FIG. 2 as in FIG. 1 to designate the elements common to the installations shown in these two figures.

 The only difference between the installation shown in Figure 2 and that shown in Figure 1, is at the recycling of hot particles in the reactor 1. Indeed, in the case of Figure 2, we see that the outlet from cyclone 15 is provided a pipe 26 which opens out at 26a not above the plasma torch 9, as in FIG. 1, but below this plasma torch.

 We will now briefly describe the operation of the installation which has just been described and which is moreover the same for the two embodiments shown.

 The pulverulent material arriving via the pipe 7 is suspended in the lower part 2 of the reactor 1 by virtue of the flow of pressurized gas 4 penetrating through the orifice 3. The plasma jet 12 emanating from the torch or torches 9 is injected into the fluidized bed thus formed, under a very variable pressure which can be between 0.5 and 50 bars.

 The high volume flow rate of hot plasma gases and their very high ejection speed, as well as their high viscosity, cause the particles to be agitated as well as a significant circulation of the fluidized bed towards the upper part 14 of the reactor. 1 as shown by the arrows F.

 We therefore obtain an optimal interpenetration of the two media constituted by the plasma and the fluidized bed, as well as a very significant heat transfer between the plasma gas and the particles.

 It will also be noted that the particle flow can be adjusted so that the walls of the reactor are protected against corrosive attack, by virtue of the circulation of particles along the walls which absorb the thermal energy and the kinetic energy of this plasma.

 When they reach the upper part 14 of the reactor 1, the hot particles are separated in the cyclone 15 and are recycled in the reactor 1, ie above the plasma jet 12 in the case of rapid recycling at high temperature (Figure 1), or below this jet in the case where a slower recycling is sought (Figure 2).

 It should be noted here that the number of cycles undergone by the hot particles, as well as the operation of the torch or plasma torches 9 can be adjusted as a function of the treatment time necessary for the completion of the reactions to be carried out. We thus perfectly master the optimal treatment time.

 Furthermore, thanks to the partial or total recycling of the hot gases leaving the reactor 1 and of the cyclone 15, it is possible to control the temperature of the fluidizing gas 4 before its introduction, which makes it possible to obtain in the reactor a suitable temperature at the same time for the reaction or reactions to be carried out and for the good behavior of the walls of the reactor.

 In addition, it is possible, with an installation in accordance with the invention, to choose the appropriate plasma gas or gases as a function of the reactions to be carried out in reactor 1.

 Finally, it should be noted that this installation allows treatments of very diverse materials, among which we can cite the roasting of ores, the gasification of coal, quenching in a catalytic bed, chemical synthesis of solid or gaseous products, drying and encapsulation. .

 Of course, the invention is in no way limited to the embodiments described and illustrated which have been given only by way of example.

 On the contrary, the invention includes all the technical equivalents of the means described and their combinations if these are carried out according to the spirit

Claims (8)

 1.- Process for treating a fluidized bed, according to which a pulverulent material is introduced into a reactor and is suspended using a gas stream injected at the bottom of the reactor to form a fluidized bed therein which is heated by at least one plasma torch, characterized in that it causes, thanks to the plasma emanating from the torch, a forced and vertical circulation of at least part of the particles of the pulverulent material of the fluidized bed from the bottom to the top of the reactor to allow in particular at least partial recycling of the hot particles collected at the top of the reactor and reinjected into the fluidized bed.  2.- Method according to claim 1, characterized in that the hot particles collected in the upper part of the reactor are recycled by injecting them above and / or below the introduction of the plasma into said reactor.  3.- Method according to claim 1 or 2, characterized in that at least a fraction of the hot gases is recycled in the upper part of the reactor in the plasma torch and / or in the gas stream injected in the lower part of the reactor.  4.- Method according to one of claims 1 to 3, characterized in that the number of recycling of hot particles and / or the operation of the plasma torch is or are adjusted according to the treatment time necessary for the accomplishment reactions in the reactor.  5.- Installation for the implementation of the method according to one of claims 1 to 4 and of the type comprising a vertical axis reactor, at least one lateral plasma injection torch in said reactor, injection means d '' a gas stream at the bottom of the reactor, as well as means for supplying pulverulent material to the bottom of the reactor, characterized in that the top of the reactor is associated with a cyclone, the outlet of which comprises at least one pipe or the like for recycling hot particles which opens laterally into the reactor above or below the plasma torch.  6.- Installation according to claim 5, characterized in that the upper part of the aforementioned cyclone is connected by at least one conduit to the plasma torch and / or to the lower part of the reactor.  7.- Installation according to claim 5 or 6, characterized in that the means for supplying pulverulent material comprise at least one pipe opening into the reactor between its lower part and the plasma torch.  8.- Installation according to one of claims 5 to 7, characterized by a valve provided at the outlet of the cyclone and allowing communication of the cyclone either with the aforementioned pipe or with a storage tank for the pulverulent material discharged by the reactor.