EP0142437A2 - Method and device for reinjecting flyash particles into a boiler for solid fuel - Google Patents

Abstract

The present invention relates to a method and a device for reinjecting flown particles into a solid fuel boiler.

In a boiler supplied with fuel by a sprayer (17) and comprising a so-called "retro" grid (3), the fumes are taken up and pass successively through means (36) for separating the largest flown particles and means (43) separation of the finer particles, before being discharged; the larger particles are reinjected into the boiler in a possibly known manner; in addition, the irregular flow, in particles, of the second separation means (43) is transformed into a continuous flow, at least approximately proportional to the load of the boiler, and this continuous flow of particles is introduced into a continuous flow of transport air with which it is injected into part of the trajectory (20) of the fuel coming from the sprayer (17) which is close to the grid (3); thus, it is possible to re-inject and burn all the particles which have gone up with the fumes in the boiler, without disturbing the operation of the boiler.

Description

The present invention relates to a method and a device for re-injecting flown particles into a solid fuel boiler of the so-called "jet engine with retro grid" type.

Such a boiler is characterized by the fact that it is supplied with fuel, for example coal with a particle size of up to several tens of millimeters, or else wood, bark, bagasse, that is to say sugar cane, or other comparable solid fuels, by means arranged in a first zone of the boiler and which continuously project a determined charge of the fuel along a trajectory bringing the latter into a second zone of the boiler, on a grid animated by a return movement from this second zone to the first; combustion begins during said trajectory and continues not only during the end thereof but also on the grate, where this combustion ends so that the grate brings only clinkers into the first zone, where these bottom ash are evacuated.

When compared with boilers of other known types, boilers of this type have a number of interesting advantages.

Compared to mechanical grate boilers, in which combustion takes place exclusively on the grate, they bring advantages linked to the fact that part of the combustion takes place during the fuel projection trajectory, namely of a on the one hand an increase in the combustion rate with the consequence of the possibility of reducing the surface of the grate, and on the other hand increased operating flexibility, making it possible to admit rapid load variations under better conditions.

Compared with pulverized coal boilers, boilers of this type provide the advantage of using coals of varied particle size, and in particular coals of much larger particle size, which dispenses grinding means, costly in investment, maintenance and energy consumption, inextricably linked to pulverized coal boilers.

However, the development of boilers with sprayer and retro grids has so far been limited, due to a lower yield than that of boilers of other types, and more precisely due to a too high rate of unburnt combustible particles. .

In fact, the supply of fuel by spraying it allows the flight, with the fumes given off by combustion, of fuel particles sufficiently light to be thus entrained but nevertheless too large to burn completely during the trajectory of projection ; this drawback is appreciable with respect to boilers with a fixed grate, where there is no projection, and with respect to boilers with pulverized coal, which use a coal of sufficiently fine particle size so that the rate unburned is minimal; in comparison with these other types of boilers, one notes during the use of boilers with sprayer and retro grid an increase in the proportion of solid particles extracted from the fumes, before evacuation to the atmosphere, by appropriate dust collectors, with a content of these larger carbon particles; in other words, there is an increase in losses by unburnt solids; in addition, the evacuation of solid particles extracted from the funerals by the dust collectors can present difficulties because of their abundance.

To overcome these drawbacks of boilers with sprayer and retro grid, it has been proposed to reinject into the boiler a part of the solid particles flown away with the tailpipes, after having collected them at the outlet of the boiler by means of dust collectors or separators used to purify these spindles before they are released to the atmosphere.

In practice, such dust collectors or separators being usually provided in series, to extract fumes I first the larger particles and then increasingly fine particles, we have so far reinjected the coarsest particles separated in first, but so far we have not managed to also reinject the finer particles, which are particularly difficult to burn before they fly away again, carried away by the fumes, and to prevent them from flying away when 'they possibly burned; in other words, we have so far limited ourselves to a reinjection of the larger particles insofar as there was a significant risk that the reinjection of the finer particles would result in a new immediate shipment, with or without combustion, together with the finest particles of the charge introduced by the projector, resulting in rapid stuffing of the installation.

The purpose of the present invention is to eliminate such a risk, to allow a total reinjection of the solid particles sampled by the various successive dust collectors or separators, including the finest particles separated immediately before rejection of the fumes into the atmosphere.

• - de façon éventuellement connue en ce qui concerne les particules les plus grosses et,
• - en ce qui concerne les particules les plus fines, fournies par les moyens de séparation correspondants selon un débit irrégulier, au moyen des opérations consistant à :
  • a) transformer ce débit irrégulier en un débit continu de particules, au moins approximativement proportionnel à la charge de la chaudière,
  • b) introduire en continu ce débit continu de particules dans un débit continu d'air de transport,
  • c) au moyen de ce débit d'air, acheminer ces particules en continu jusqu'à proximité de la deuxième zone de la chaudière et les injecter dans cette zone, dans une partie de ladite trajectoire proche de la grille.

To this end, the method according to the invention, consisting in a known manner of removing from the projection boiler and retro grid the fumes released by combustion, entraining solid particles, then conveying them successively in means of separation of the particles larger and in means for separating finer particles, and to evacuate the fumes after this separation while re-injecting into the boiler, separate particles, is characterized in that we re-inject into the boiler all of the separate particles,

• - in a possibly known manner with regard to the largest particles and,
• - as regards the finest particles, supplied by the corresponding separation means at an irregular flow rate, by means of the operations consisting in:
  • a) transform this irregular flow into a continuous flow of particles, at least approximately proportional to the load of the boiler,
  • b) continuously introducing this continuous flow of particles into a continuous flow of transport air,
  • c) by means of this air flow, convey these particles continuously to the vicinity of the second zone of the boiler and inject them into this zone, in a part of said path close to the grid.

By thus reinjecting the fine particles into the projection trajectory of the fuel, that is to say precisely where the finest particles thereof burn, it facilitates the ignition of the particles thus reinjected and, by choosing cam part of the trajectory in which in practice this reinjection the part of this trajectory closest to the grid, it facilitates a drive of the particles reinjected towards the latter, on which the latter are consequently deposited after combustion; this deposition takes place in the area of intersection of the grid with the fuel projection path; however, this zone constitutes precisely the hottest zone of the grid, which favors sintering of the reinjected particles which have thus burned. , that is to say the formation of clinkers which one should no longer fear the take-off, and which one evacuates with the other clinkers when they reach the first zone of the boiler, under the effect of the movement of the grid.

It will be noted that the flow rate, in fine particles, of the corresponding separation means may even tuuel be very irregular, for example during an accidental or voluntary unclogging of these, or by repercussion, after a certain time, of a significant variation in the load of the boiler, and that, however, the transformation of this flow irregular in a continuous flow, at least approximately proportional to the load of the boiler, makes it possible not to disturb by the reinjection the combustion in this boiler, that is to say to reinject at all the load values without irregularity of heating , whatever the disturbances which may affect the instantaneous flow rate of the means for separating fine particles.

Naturally, the flow of transport air must be such that this air does not disturb the combustion inside the boiler either, and in particular that it does not disturb the combustion of the reinjected particles thus transported; taking into account the high carbon content of these particles and their almost zero volatile matter content, the concentration of fine particles reinjected relative to the air which transports them should be sufficiently high, and we have obtained good results with a ratio of the mass flow rate of fine particles to the mass flow rate of transport air of the latter of between ¹ and 10 approximately, these figures being given by way of nonlimiting example.

In addition, the volume flow rate of the transport air is advantageously substantially constant, although adjustable, only the flow rate of fine particles in this air varies, in order to ensure a regular injection speed.

Thus, the method according to the invention makes it possible to reinject all of the solid particles taken from the flue gases before evacuation of the latter to the atmosphere, and to burn the combustible part of these particles under the best conditions, which allows savings sensitive fuel without moreover, it results in a complication of the installations; this results in an optimal use of the fuel, in every respect comparable to that obtained by a pulverized coal boiler, without the need to provide a grinder, a particularly significant drawback of such boilers.

It is further noted that the total reinjection makes it possible to extract waste, in practice clinkers, only in a single zone and in a space-saving form which is easy to reprocess.

• - des moyens de prélèvement de fumées dans la chaudière,
• - des moyens d'évacuation de fumées,
• - des premiers moyens de séparation de particules,
• - des seconds moyens de séparation de particules,
• - des moyens dacheminement de fumées des moyens de prélèvement aux premiers moyens de séparation, des premiers moyens de séparation aux seconds moyens de séparation, des seconds moyens de séparation aux moyens d'évacuation de fumées,
• - des moyens de prélèvement de particules dans les premiers moyens de séparaticn, et de réinjection de telles particules dans la chaudière,
• - des moyens de prélèvement de particules dans les seconds moyens de séparation,

ce dispositif étant caractérisé en ce que les moyens de prélèvement de particules dans les seconds moyens de séparation comportent:

• a) une capacité tampon
• b) des moyens de déversement de particules des seconds moyens de séparation dans la capacité tampon, interdisant une commu- nicaticn directe entre ces derniers,
• c) des moyens de prélèvement continu de particules dans la capacité tampon, selon un débit réglable,
• d) des moyens pour asservir à la charge de la chaudière le débit des moyens de prélèvement continu de particules dans la capacité tampon,

et en ce qu'il est prévu :

• - une source d'air sous pression,
• - des moyens d'injection disposés à proximité de la deuxième zone de la chaudière et débouchant vers une partie de ladite trajectoire proche de la grille, dans cette deuxiàme zone,
• - une conduite de transport pneumatique reliant la source d'air sous pression aux moyens d'injection, les moyens de prélèvement continu de particules dans la capacité tampon débouchant dans ladite conduite.

For the implementation of this method, the present invention also provides a device comprising:

• - means for drawing smoke from the boiler,
• - smoke evacuation means,
• - first means of particle separation,
• - second means for separating particles,
• means for conveying smoke from the sampling means to the first separation means, from the first separation means to the second separation means, from the second separation means to the smoke evacuation means,
• means for sampling particles in the first separation means, and for reinjecting such particles into the boiler,
• means for sampling particles in the second separation means,

this device being characterized in that the means for sampling particles in the second separation means comprise:

• a) a buffer capacity
• b) means for discharging particles from the second separation means into the buffer capacity, preventing a commu- direct nicaticn between these,
• c) means for continuous sampling of particles in the buffer capacity, at an adjustable rate,
• d) means for controlling the flow rate of the means for continuous sampling of particles in the buffer capacity to the load of the boiler,

and that it is planned:

• - a source of pressurized air,
• injection means arranged near the second zone of the boiler and opening towards a part of said trajectory close to the grid, in this second zone,
• - A pneumatic transport line connecting the source of pressurized air to the injection means, the means for continuous sampling of particles in the buffer capacity opening into said line.

In an advantageous embodiment of the device, for pneumatic conveying is carried out the connection between on the one hand, the average particle spill second sé ^p means a-ration in the buffer storage and, on the other hand, this last, which makes it possible to dissociate it from these dumping means and in particular to juxtapose it with the latter, that is to say not to place it immediately below; for this purpose, the device comprises a second source of pressurized air, a second pneumatic transport line connecting this second source at the buffer capacity, the means for discharging particles from the second separation means into the buffer capacity opening into this second pipe by preventing direct communication between the latter and the second separation means.

Advantageously, it can then be expected that the. pressurized air source mentioned first, intended to supply the pneumatic conveying line leading to means for continuous sampling of particles in the buffer capacity by means of injection into the boiler, ie constituted by an upper part of the buffer capacity; in other words, the same transport air is then used to successively route the particles from the discharge means to the buffer capacity, then to the particles from the buffer capacity to the boiler.

In addition, when the second separation means comprise a plurality of separators connected in series and / or in parallel, between the first separation means and the smoke evacuation means, by the smoke transport means, it is then possible to provide for a discharge of all of these separators in a single tanpon capacity without being obliged to communicate to the latter dimensions in plan corresponding to those of all of the second separation means thus formed; the device according to the present invention is then characterized in that means are provided for discharging particles from each of the separators into the single buffer capacity, these discharge means opening into said second pipe, which is common, by prohibiting communication direct between this pipe and the separators.

This solution is advantageous not only in terms of space, but also in terms of simplification of the means used for regulating the operation, simply because of the uniqueness of the buffer capacity.

• a) une pluralité de capacités tampons dont chacune est associée à au moins un séparateur,
• b) des moyens de déversement de particules de ce séparateur dans la capacité tampon associée, interdisant une commmi- cation directe entre ces derniers,
• c) des moyens de prélèvement continu de particules dans chaque capacité tampon, selon un débit réglable,
• d) des moyens pour asservir à la charge de la chaudière le débit de chacun des moyens de prélèvement continu de particules dans une capacité tampon,

et que les moyens de prélèvement continu de particules dans différentes capacités tampons débouchent dans la conduite de transport pneumatique précitée, qui est ccnmune.However, when the second separation means comprise a plurality of separators connected in series and / or in parallel, between the first separation means and the smoke evacuation means, by the smoke conveying means, provision may also be made that the means for sampling particles in the second separation means include:

• a) a plurality of buffer capacities, each of which is associated with at least one separator,
• b) means for discharging particles from this separator into the associated buffer capacity, preventing direct communication between them,
• c) means for continuous sampling of particles in each buffer capacity, at an adjustable rate,
• d) means for slaving to the charge of the boiler the flow rate of each of the means for continuous sampling of particles in a buffer capacity,

and that the means for continuous sampling of particles in different buffer capacities open into the aforementioned pneumatic transport line, which is common.

It is thus ensured that samples are taken from each buffer capacity that are both regular and suitable for the average production of the associated dust collector.

Advantageously, the means for controlling the flow rate of the means for continuously sampling particles in the or each buffer capacity to be charged to the boiler include means for controlling this flow rate to maintain an average level of particles in this buffer capacity, which makes it possible to gradually absorb, without disturbing the reinjection and combustion of the particles in the boiler, any sudden variations in the charge of particles received by the buffer capacity due to the repercussion, with delay, of an abrupt variation in the charge of the boiler, or also of unclogging the second separation means and more precisely, when the latter comprise several dust collectors, of unclogging one of these dust collectors or more of them.

• - La figure 1 montre le schéma d'une chaudière à projeteur et grille rétro, équipée d'un dispositif de réinjection mettant en oeuvre le procédé selon l'invention.
• - La figure 2 montre le schéma d'une chaudière à projeteur et grille rétro, équipée d'une variante du dispositif de réinjection selon l'invention.
• - Les figures 3 et 4 illustrent deux variantes de branchement des seconds moyens de séparation, dans le cadre de cette variante du dispositif.

Other characteristics and advantages of the method according to the invention and of the device proposed for this implementation will emerge from the description below relating to nonlimiting examples, as well as from the appended drawings which form an integral part of this description.

• - Figure 1 shows the diagram of a projector boiler and retro grid, equipped with a re-injection device implementing the method according to the invention.
• - Figure 2 shows the diagram of a projector boiler and retro grid, equipped with a variant of the reinjection device according to the invention.
• - Figures 3 and 4 illustrate two variants of connection of the second separation means, in the context of this variant of the device.

We will first refer to Figure 1, where we have designated by 1 a coal boiler, internally having a hearth 2 delimited downwards by an approximately horizontal grid 3 constituted by an endless conveyor 4 passing right through share the boiler 1, approximately horizontally, and respectively bypassing on either side thereof deflection means 5, 6 which define in particular in the conveyor 4 an upper strand 7, approximately horizontal, including an intermediate zone between the means bypass 5 and 6 constitutes grid 3; motor means, not shown, animate the conveyor 4 with a movement such that its upper strand 7, that is to say the grid 3, performs an approximately horizontal translational movement 8.

Above a downstream zone 9 of the grid 3, with reference to the direction 8, open into the hearth 2 means 10 for supplying coal, comprising a storage hopper 11 external to the boiler 1 and opening downwards above an endless conveyor 12 also external to the boiler 1, leguel has an approximately horizontal upper strand 13 receiving the coal 14 from the storage hopper 11, and motor means 16 driving the endless conveyor 12 of a movement such that its upper strand 13 moves in the direction 15 of approximation with respect to the boiler 1, to convey the coal 14 to above a spraying device 17 disposed above the area downstream 9 of the grid 3 and comprising paddles 18 which a motor, not shown, drives a rotary movement about a horizontal axis and a fixed peripheral guide 19; thus the coal brought by the upper strand 13 of the conveyor 12 to near the boiler 1 falls on the device 17 and the latter projects this coal inside the hearth 2, along a path 20 intersecting the grid 3 in a zone 21 which constitutes its upstream zone with reference to the direction 8; in other words, the coal introduced by the spraying device 17 passes through the hearth 2 right through, to deposit on the grid 3 in the zone of the hearth opposite to the zone of its introduction into the latter; the volume flow rate of coal supply 14 from the hopper 11 is adjusted by adjusting the speed of movement of the upper strand 13 of the conveyor 12 in the direction 15, that is to say by adjusting the output speed of the motor 16, the pallets 18 being driven to rotate about their horizontal axis at a speed chosen as for it as a function of the path 20 to be accomplished, as defined above.

A combustion of the coal thus introduced into the hearth 2 begins during the crossing of the path 20 and continues on the grate 3, facilitated by an injection of primary air into the hearth 2 via a sheath 22 opening out inside it. Ci under the upper strand 7 of the conveyor 4, that is to say under the grid 3, and by an injection of secondary air by nozzles such as 23, 24 opening into the hearth 2, in the faces 108, 109 of the boiler corresponding respectively to the upstream 21 and downstream 9 zones of the grid 3, at an intermediate level between that of the grid 3 and that of the spraying device 17 as well as, preferably, at a level higher than that of the spraying device 17, and neighbor of this level.

The speed of movement of the grid 3 in the direction 8 is established so that the coal deposited on this grid in the upstream zone 21 thereof is reduced to clinker state upon its arrival in the downstream zone 9, this bottom ash being evacuated by gravity bypassing, by the conveyor 4, the deflecting means 6 placed downstream if one refers to the direction 8, as has been shown diagrammatically at 25.

The combustion of coal during the crossing of the path 20 and on the grid 3 causes a release 26 of smoke that the walls 27 of the boiler, delimiting the hearth 2 laterally and upward, guide entirely to a duct 28 approximately horizontal, by making them pass through an evaporator 29 comprising a network of vertical tubes connecting a lower balloon 30 to an upper balloon 31 to vaporize a liquid completely filling the lower balloon 30 and the network of tubes, and partially the upper balloon 31; the latter is connected above the level of the liquid to a manifold 32 for steam outlet from the boiler, by means of a superheater 34 placed on the forced passage of the fumes, and below the level of the liquid to a manifold 33 water inlet into the boiler, via an economizer exchanger 35 also placed on the forced passage of fumes.

The output speed of the motor 16 is controlled by the flow of steam to be produced to meet the needs of the user, or load of the boiler.

. Boilers of this type are well known to those skilled in the art, who know the practical embodiment of the various elements which have just been described.

The conduit 28 successively routes the fumes taken from the boiler 1 to first separation means 36 intended to separate the larger particles, then to second separation means 43 intended to separate the finer particles before routing the fumes thus dedusted towards means of evacuation to the atmosphere, shown schematically in 44.

the first separation means 36 can be constituted by any known device, capable of carrying out coarse dusting; they can be constituted for example by a mechanical deduster, for example cemtrifuge, or by the first field of an electrostatic separator.

As is already known per se, means are provided for removing from these first separation means 36 the particles separated by the latter and re-injecting them into the boiler 1; in the preferred exemplary embodiment illustrated, where only the lower separation means 36 have been indicated as a lower hopper 37, these removal means and of reinjection comprise a vertical pipe 38, provided with two juxtaposed valves 39, 40 and in which the hopper 37 opens downwards, this pipe 38 opening itself downwards in an intermediate zone of a horizontal pipe 84 for pneumatic transport joining a source of pressurized air 42 to the hearth 2 of the boiler 1, into which this pipe 84 opens approximately horizontally, as indicated at 41, above the upstream zone 21 of the grid 3, at a corresponding level approximately to that of the projector 17 or at a lower level, so that the particles thus reinjected at 41 inside the boiler 1 are taken up by the coal projected along the path 20 by the designer 17, and follow then this trajectory with the coal thus projected.

The parameters of this reinjection of the largest particles separated from the fumes in the means 36 can be easily determined by those skilled in the art; one could also choose other modes, already known, of reintroducing such particles into the home, such as for example reintroduction by the designer 17 _; taking into account the granulanetry of the particles thus reinjected at 41, the combustion of these particles without re-flight, together with the coal introduced along the path 20 by the designer 17, does not pose the particular problems mentioned above, linked to the reinjection particles of finer particle size, which are resolved in accordance with the present invention.

It will be noted that all of the larger particles separated from the smoke by the first separation means 36 are thus reinjected at 41 into the hearth 2; the means making it possible also to reinject all of the finer particles then separated, into the second separation means 43 to which the duct 28 routes the fumes after they have got rid of the coarsest particles in the first separation means 36 and before to be evacuated to the atmosphere by means 44, wind will now be described.

By way of nonlimiting example, the case has been illustrated where the second separation means 43 consist of three separators 45, 46, 47, that the smoke travels successively in this order, in series, losing particles of increasingly fine collected in a respective lower hopper 48, 49, 50 of these separators 45, 46, 47; these separators can be either fields of the same electrostatic dust collector, or dust collectors of a different type.

Each of these hoppers 48, 49, 50 opens downwards onto a respective valve 51, 52, 53 capable of closing it in a gas-tight manner or of opening it to allow the descent, by gravity, of the solid particles collected.

Under each of the valves 51, 52, 53 is disposed a respective intermediate hopper 54, 55, 56, sealed, having an interior volume such that each opening of the associated valve 51, 52, 53, it can receive all of the load of solid particles from the lower hopper 48, 49, 50 of the associated separator 45, 46, 47.

For this purpose, in service, an opening and then closing of each valve 51, 52, 53, normally closed, to empty the lower hopper 48, 49, 50 of the corresponding separator is carried out either when the latter contains a predetermined volume of particles, in function of which is chosen the volume of the associated intermediate hopper 54, 55, 56, or cyclically with a chosen periodicity so that the volume of particles in this lower separator hopper never exceeds this predetermined volume.

Each of the intermediate hoppers 54, 55, 56 opens downwards onto a valve 57, 58, 59 at any point similar to the valves 51, 52, 53.

Inside each of the intermediate hoppers 54, 55, 56, at the bottom of the lower part thereof, there opens a respective pipe 100, 101, 102 connected in branch on a pipe 97 which will be described later, and a vehicle air under p _res - sion provided by a volumetric blower 98; each of these pipes 100, 101, 102 makes it possible to inject into the associated intermediate hopper 54, 55, 56, an air for fluidizing the particles therein, the flow rate of this air being able to be adjusted individually by an appropriate valve 103 of line 100, 104 of line 101, 105 of line 102.

The particles are thus maintained, in each of the intermediate hoppers 54, 55, 56 in a state of fluidity such that they can easily flow down out of it when the valve 57, 58, 59 is open.

Downwards, each valve 57, 58, 59 opens onto a respective vertical gravity discharge pipe 94, 95, 96 and the various pipes 94, 95, 96 themselves open down into the pipe 97 mentioned above. , approximately horizontal, in locations distributed along it downstream of the zone from which the fluidization air lines 100, 101, 102 are derived, if one refers to a direction 99 of circulation of the air in this pipe 97, imposed by the volumetric booster 98; a diaphragm 106 is interposed in the pipe 97 between the outlet of the various pipes 94, 95, 96 and the mouth of the pipes 100, 101, 102 to cause air to pass through them.

As a result, the air conveyed by the pipe 97 at a flow rate adjusted by adjusting the volumetric booster 98 can successively take charge of the particles taken from the intermediate hopper 56 when the valve 59 is open, and which fall via the pipe 96, the particles taken from the intermediate hopper 55 when the valve 58 is open, and which fall via the line 95, and the particles taken from the intermediate hopper 54 when the valve 57 is open, and which fall via the line 94; it will be noted that this order, chosen by way of example, is not characteristic of the invention and is therefore not limiting of the latter.

Downstream of the connection of all the pipes 94, 95, 96 if one refers to direction 99, the air circulating in the pipe 97 conveys in this direction 99 all the particles thus received up to the upper part 107 with a single buffer capacity 60, sealed, delimiting an internal volume greater than the sum of the respective volumes of the intermediate hoppers 54, 55, 56 of so that it can permanently contain a volume of particles much greater than the volume which can reach the intermediate hoppers 54, 55, 56 when the valves 51, 52, 53 connecting them with the respective separators 45, 46 , 47 are open; in addition, the volume and the shape of the buffer capacity 60 are such that, when the latter receives, via the pneumatic conveying line 97, intermediate hoppers 54, 55, 56 a load of solid particles by opening the valves 57, 58, 59, there follows in the buffer capacity a small variation in the level of the charge of solid particles therein.

The practical arrangements which may be adopted for this purpose can vary to a great extent, and will be chosen by a person skilled in the art without departing from the scope of the present invention.

For example, the buffer capacity 60 has a lower hopper-shaped portion, tapering progressively downward, and an upper portion 107 of constant cross section in a horizontal plane, the lower portion being intended to be permanently filled with particles on the whole of its height, as well as the upper part 107 over part of its height.

Buffer capacity 60 is thus associated with an upper average level 63 of its particle charge; a level sensor 91, associated with the buffer capacity 60, makes it possible to detect and either quantify or compare to a predetermined threshold or to several predetermined thresholds, the possible differences between the actual level of particles in the buffer capacity and the level predetermined means 63, corresponding to this buffer capacity; such sensors are known to those skilled in the art.

Each intermediate hopper 54, 55, 56 constitutes an airlock allowing the passage of particles from the lower hopper 48, 49, 50 of the separator respectively associated 45, 46, 47 to the buffer capacity 60, via line 97, while prohibiting direct communication, with the possibility of gas passage, between the internal volume of this buffer capacity and the separators 45, 46, 47; for this purpose, in service, each of the valves 51, 52, 53 is only open on condition that the valve 57, 58, 59 associated with the same intermediate hopper 54, 55, 56 is closed, and each of these valves 57, 58, 59 is only open on condition that the valve 51, 52, 53 associated with the same intermediate hopper 54, 55, 56 is closed; in practice, an opening then closing of each valve 57, 58, 59, normally closed, to empty the associated intermediate hopper 54, 55, 56 occurs after each opening-closing of the corresponding valve 51, 52, 53.

Other means could naturally be chosen to allow the passage of the solid particles collected by one of the separators 45, 46, 47 to the buffer capacity 60, but the choice of such airlocks made it possible to obtain all satisfaction under the conditions of operation of the device, that is to say taking into account that the solid particles considered are present in the pulverulent state.

Inside the buffer capacity 60, at the bottom of the lower part thereof, there is a pipe 85 which makes it possible to inject into the buffer capacity 60 a fluidizing air of the particles therein, the flow rate of this air can be regulated by a suitable valve 88 of the pipe 85; this air comes for example from the source 42, the pipe 85 then being connected in bypass on the pipe 84, between this source 42 and the outlet of the pipe 38, in a manner not shown but similar to what has been described with reference to lines 100, 101, 102 and 97.

The particles are thus maintained, in the buffer capacity 60, in a state of fluidity such that they can be easily sampled by means of sampling at a continuous, adjustable flow rate, onto which this buffer capacity 60 opens down; these removal means are advantageously designated by 69 constituted by a rotary airlock or alveolar distributor, comprising, as is known, a plurality of pallets driven to rotation about an axis, by a motor 72, inside a envelope with which these pallets delimit cells which the rotation of the pallets puts in communication alternately with the buffer capacity 60, upwards, and, downwards, with a vertical evacuation pipe by gravity 75; the flow rate of such a honeycomb distributor, in terms of volume flow rate or mass flow rate, is controlled by the speed of rotation of the pallets, that is to say by their driving speed by the associated motor 72.

Downwards, the pipe 75 opens into an approximately horizontal section of a pipe 66 which takes up the air under pressure, supplied by the volumetric booster 98 via the pipe 97, in the upper part 107 of the buffer capacity 60 and conveys this air in a direction of flow 78; a throttle 68 is interposed in the pipe 66, between its mouth in the upper part 107 of the buffer capacity 60 and the outlet of the pipe 75 in this pipe 66, to establish at the outlet of the pipe 75 a pressure lower than that which prevails in the upper part 107 of the buffer capacity 60.

Therefore, the air conveyed by the pipe 66, at a flow rate adjusted by adjusting the volumetric booster 98, takes care of the particles taken from the buffer capacity 60 at a flow rate determined by the alveolar distributor 69, and which fall via line 75.

Downstream of the connection of the pipe 75, if one refers to the direction 78, the air circulating in the pipe 66 conveys in this direction 78 the particles thus received up to injection means 79 of any type known in itself, used for injecting pulverulent materials into boilers, which injection means 79 open into the hearth 2 approximately horizontally, above the upstream zone 21 of the grid 3, at a level which is intermediate between the levels nozzles 23, 24 for injecting secondary air and corresponds to at least approximately the level of injection 41 of the largest particles separated by the first separation means 36; the injection means 79 are oriented towards the path 20, and more precisely towards a part thereof close to the grid in the upstream region 21 thereof, to favor the handling of the fine particles thus injected at 79 by the coal projected by the spraying device 17 along the path 20, and the monitoring of this path to the grid 3 by these fine particles.

In accordance with the present invention, the flow of air for transporting the particles in the pipe 66 and the flow of particles in this air, via the withdrawal means in the buffer capacity 60, here constituted by the alveolar distributor 69, are continuous, and the flow of particles downstream from the outlet of the pipe 75 in the pipe 66, expressed in terms of mass flow or volume flow, is at least approximately proportional to the load of the boiler, for example to the flow of the supply means 10 expressed in the same units, which is representative of this charge.

For this purpose, the flow rate of the withdrawal means in the buffer capacity 60, that is to say of the cellular distributor 69, is controlled by the load of the boiler so as to be at least approximately proportional to it.

Taking into account that, in steady state, with a substantially constant load of the boiler and for a coal of determined characteristics, the flow of solid particles received in the dust collectors 45, 46, 47 then conveyed to the buffer capacity 60 is substantially proportional to the feed rate of the coal boiler 14 from the hopper 11, itself representative of the load of the boiler, there is provided for this purpose, in the illustrated embodiment, a servo motor 72 to the information supplied by the level sensor 91, so as to limit the variations in the level of particles in the buffer capacity 60 in comparison with the predetermined average level 63; it will be noted that in this way it is also ensured that the sampling means 69 receive particles, in the buffer capacity 60, an approximately constant force allowing them to work under conditions themselves approximately constant, independently of the respective emptying intermediate hoppers 54, 55, 56.

The means making it possible to control the speed of rotation of the motor 72 to the information supplied by the level sensor 91 have been shown diagrammatically by a link in dashed lines 81; they can be chosen by a person skilled in the art from a wide range of possibilities without departing from the scope of the present invention, depending in particular on the type of level sensor 91 used, offering, depending on the case, a possibility of correction step by step or a possibility of continuous correction.

• - à la mise en service de l'installation, la capacité tampon 60 étant supposée initialement vide, et jusqu'à ce que le niveau haut 63H soit atteint du fait des déversements successifs des trémies intermédiaires 54, 55, 56 dans la capacité tampon 60, on impose au moteur 72 une vitesse de rotation minimale prédéterminée, ce qui correspond à une réinjection de particules en 79 selon un débit minimal ;
• - lorsque le niveau 63H vient d'être atteint, ce que confirme l'émission, par le capteur 91, d'un nombre prédéterminé d'impulsions correspondantes, les moyens d'asservissement 81 provoquent une augmentation de valeur prédéterminée de la vitesse de rotation du moteur 72 ; si, ensuite, un même nombre prédéterminé d'impulsions émises par le capteur 91 témoigne de ce que le niveau 63H est toujours atteint ou dépassé, les moyens d'asservissement 81 provoquent une nouvelle augmentation de la vitesse du moteur 72, de la même valeur prédéterminée, et ce processus d'augmentation de vitesse du moteur 72 se poursuit jusqu'à ce que le niveau réel de particules dans la capacité tampon 60 redescende en dessous du niveau haut 63H, ce dont témoicment les impulsions fournies par le capteur 91 ;
• - lorsque le niveau haut 63H est ainsi dégagé, le niveau réel de particules restant néanmoins au-dessus du niveau bas 63B, les moyens d'asservissement 81 maintiennent constante la vitesse de rotation du moteur 72 ;
• - si le niveau réel des particules dans la capacité tanpon 60 remonte jusqu'à atteindre à nouveau le niveau 63H, le processus précité recommence ;
• - si le niveau dans la capacité tampon 60 redescend en dessous du niveau bas 63B, l'émission par le capteur 91 dudit norrbre prédéterminé d'impulsions correspondantes provoque, par les moyens d'asservissement 81, une réduction de la vitesse de rotation du moteur 72, selon la valeur prédéterminée précitée ; ce processus peut se répéter soit jusqu'à ce que le niveau bas 63B soit à nouveau atteint, et s'interrompre alors, soit jusqu'à ce que la vitesse minimale précitée soit atteinte, si le niveau réel des particules dans la capacité tampon 60 n'atteint pas à nouveau le niveau bas • 63B ;
• - notamment, à l'arrêt de l'installation, le dégagement du niveau bas 63b ramène la vitesse de rotation du moteur 72 à la vitesse minimale précitée, ce qui ramène l'installation dans l'état initial.

For example, according to a currently preferred embodiment, the level sensor 91 makes it possible to detect the passage of the actual level of particles in the capacity 60 at two different levels, at the rate of a low level 63B and a high level 63H, the average of which defines the average level 63, and emits pulses representative of that of these two levels which is eventually reached by the particles; servo-control of the flow rate of the alveolar distributor 69, that is to say of the speed of the motor 72 thereof, to the information thus supplied by the sensor 91 can be carried out in the following manner in this case:

• - when the installation is put into service, the buffer capacity 60 being assumed initially empty, and until the high level 63H is reached due to the successive discharges from the intermediate hoppers 54, 55, 56 into the buffer capacity 60 , a minimum predetermined speed of rotation is imposed on the motor 72, which corresponds to a reinjection of particles at 79 at a minimum flow rate;
• - When the level 63H has just been reached, which is confirmed by the emission, by the sensor 91, of a predetermined number of corresponding pulses, the control means 81 cause an increase in the predetermined value of the speed of rotation motor 72; if, then, the same predetermined number of pulses emitted by the sensor 91 shows that the level 63H is always reached or exceeded, the control means 81 cause a further increase in the speed of the motor 72, by the same value predetermined, and this process of increasing the speed of the motor 72 continues until the actual level of particles in the buffer capacity 60 drops below the high level 63H, as evidenced by the pulses supplied by the sensor 91;
• when the high level 63H is thus released, the real level of particles nevertheless remaining above the low level 63B, the control means 81 keep the motor rotation speed 72;
• - if the real level of particles in the tanpon capacity 60 rises until reaching level 63H again, the above-mentioned process begins again;
• - If the level in the buffer capacity 60 drops below the low level 63B, the emission by the sensor 91 of said predetermined number of corresponding pulses causes, by the servo means 81, a reduction in the speed of rotation of the motor 72, according to the aforementioned predetermined value; this process can be repeated either until the low level 63B is reached again, and then stops, or until the abovementioned minimum speed is reached, if the actual level of the particles in the buffer capacity 60 does not reach the low level again • 63B;
• - In particular, when the installation is stopped, the release of the low level 63b reduces the speed of rotation of the motor 72 to the aforementioned minimum speed, which brings the installation back to the initial state.

In addition, it is advantageously possible to provide for detection of the possible passage of the level of particles, in the buffer capacity 60, above a so-called security level 63S greater than the level 63H, by means of the sensor 91 or of another sensor. level, with a servo such that exceeding this level 63S stops the extraction of the particles in the intermediate hoppers 54, 55, 56 and their pneumatic transport, via line 97, to the buffer capacity 60, this extraction and this transport automatically resumes when the security level 63S is again released.

Advantageously, to allow absorption of the variations in the quantity of particles received by the dust collectors 45, 46, 47 following the repercussion, with delay, of a significant variation in the load of the boiler or even after a de-clogging of these dust collectors, without disruption of transport via line 66 and without reinjection into the hearth at 79 causes excessive variations in the heating rate, provision may be made for regulating the output speed of the motor 72 as a function of the information provided by the level sensor 91, by means of a trend signal representative at all times of the charge of the boiler and which is operated in the direction of proportionality of the flow rate of the withdrawal means in the buffer capacity 60, that is to say of the alveolar distributor 69, at this charge ; the means used for this purpose, which can be chosen by a person skilled in the art from a wide range of possibilities and have therefore only been shown diagrammatically by a dashed line 80, tend, for example, to link in a predetermined proportionality relationship , as a function of the quantities of solid particles expected in the dust collectors 45, 46, 47 for determined loads of the boiler, taking into account in particular the characteristics of the coal used, the speed of rotation of the motor 72 to that of the motor 16, which is representative of the load of the boiler.

This ensures regular reinjection of the particles.

• inversement, le mode qui vient d'être décrit pourra être adopté pour l'ensemble ou pour chacune des capacités tampon qui seront décrites en référence aux figures 2 à 4.

It will be noted that the node for controlling the flow rate of the withdrawal means in the buffer capacity 60 charged to the boiler, in the direction of at least approximate proportionality, which has just been described, giving priority to the detection of the level of particles in buffer capacity 60 and involving only in terms of trend the load of the boiler at the instant considered, could be replaced by a control mode in the direction of such proportionality which will be described more far with reference to FIGS. 2 to 4, involving first of all the charge of the boiler and by way of correction the level detection in the buffer capacity or in each buffer capacity;

• conversely, the mode which has just been described may be adopted for all or for each of the buffer capacities which will be described with reference to FIGS. 2 to 4.

The flow of particles in the pipe 66 being thus determined, the flow of transport air in this pipe, preferably constant in volume flow lands, is adjusted by action on the voluretric booster 98 so that the mass flow of the particles introduced into line 66 either in relation to the mass flow rate of air in this line, between 1 and 10 approximately; these figures, given by way of nonlimiting example, correspond to a high concentration of the particle-air suspension injected at 79 into the boiler, such a high concentration being favorable to the combustion of the particles upon their arrival in the boiler and to their sintering in the form of bottom ash once they have burned and they are on the grid 3.

Illustrated in phantom in Figure 1, two variants of the device which has just been described.

These two variants have the common characteristic that instead of being supplied with pressurized air by the volumetric booster 98, via the pipe 97 and the upper part 107 of the tarpon capacity 60, the pipe 66 ensuring pneumatic transport to the injection means 79, particles taken from the latter by the means 69 is supplied by a clean fan (variant not shown) or by the same fan 42 as the pipe 84 as illustrated in 66a; then, the air introduced into the upper part 107 of the buffer capacity 60 by the volumetric booster 98 can either be evacuated to the open air, as shown diagrammatically in 66b, after filtering by appropriate means, or more advantageously be reinjected in the second separation means 43, as shown schematically at 66c.

We will now refer to Figure 2, where we find under the same references, identically and in an identical cooperation, the elements 1 to 59 and 84 of Figure 1, possibly shown more schematically.

This variant embodiment of the device differs from that of FIG. 1 in that each valve 57, 58, 59 opens downwards onto a respective buffer capacity 360, 361, 362 sealed, delimiting an interior volume greater than that of the intermediate hopper 54, 55, 56.

associated so that it can permanently contain a volume of particles much greater than the volume which can reach the associated intermediate hopper 54, 55, 56 when the valve 51, 52, 53 connecting the latter with the associated separator 45, 46, 47 is open; in addition, the volume and the shape of each buffer capacity 360,361,362 are such that, when the latter receives from the associated intermediate hopper 54, 55, 56 a load of solid particles by opening the valve connecting them 57, 58, 59 it there follows in the buffer capacity a small variation in the level of the charge of solid particles therein.

The practical arrangements which may be adopted for this purpose can vary to a great extent, and will be chosen by a person skilled in the art without departing from the scope of the present invention.

For example, each of the buffer capacities 360,361,362 has a hopper-shaped lower part, progressively narrowing downwards, and an upper part of constant section in a horizontal plane, the lower part being intended to be permanently filled with particles on the its entire height, as well as the upper part over a portion of its height.

Each buffer capacity 360,361,362 is thus associated with an upper average level 363,364,365 of its charge in particles; a level sensor 391,392,393 respectively associated with each buffer capacity 360,361,362 makes it possible to detect and either quantify or compare to a predetermined threshold or to several predetermined thresholds, the possible differences between the actual level of particles in the buffer capacity considered and the level predetermined means 363, 364,365 corresponding to this buffer capacity; such sensors are known to those skilled in the art.

Each intermediate hopper 54, 55, 56 constitutes an airlock allowing the passage of particles from the lower hopper 48, 49, 50 of the separator respectively associated 45, 46, 47 to the capa corresponding buffer city 360,361,362 without at any time, the internal volume of the latter being put in direct communication, with the possibility of gas passage, with the separator 45, 46, 47; for this purpose, in service, each of the valves 51, 52, 53 is only open on condition that the valve 57, 58, 59 associated with the same intermediate hopper 54, 55, 56 is closed, and each of these valves 57, 58, 59 is only open on condition that the valve 51, 52, 53 associated with the same intermediate hopper 54, 55, 56 is closed; in practice, an opening and then closing of each valve 57, 58, 59, normally closed, to empty the associated intermediate hopper 54, 55, 56 occurs after each opening-closing of the corresponding valve 51, 52, 53.

Other means could naturally be chosen to allow the passage of the solid particles collected by one of the separators 45, 46, 47 to the respectively associated buffer capacity 360,361,362, but the choice of such airlocks made it possible to obtain all satisfaction in the operating conditions of the device, that is to say taking into account that the solid particles considered are present in the pulverulent state.

Inside each of the buffer capacities 360,361,362, at the bottom of the lower part thereof, there emerges a respective pipe 385,386,387 connected in diversion to a pipe 366 which will be described later, and which conveys pressurized air supplied by a fan 367; each of these pipes 385,386,387 makes it possible to inject into the associated buffer capacity 360,361,362, an air for fluidizing the particles therein, the flow rate of this air being able to be adjusted individually by a suitable valve 388 of the pipe 385,389 of the pipe 386,390 of driving 387.

The particles are thus maintained, in each of the buffer capacities 360,361,362 in a state of fluidity such that they can be easily withdrawn by means of sampling at a continuous, adjustable flow rate, onto which this buffer capacity 360,361,362 opens downwards; these withdrawal means associated with the buffer capacity 360,361,362 respectively have been designated by 369,370,371; each of these removal means 369,370,371 is advantageously constituted by a rotary airlock or alveolar distributor, comprising, as is known, a plurality of pallets driven to rotation about an axis, by a respective motor 372,373,374, inside a envelope with which these pallets delimit cells which the rotation of the pallets brings into communication alternately with the associated buffer capacity 360,361, 362, upwards, and, downwards, with a vertical evacuation pipe by gravity 375,376,377; the flow rate of such a cellular distributor, in terms of volume flow rate or mass flow rate, is controlled by the speed of rotation of the pallets, that is to say by their driving speed by the associated motor 372,373,374.

Downwards, each of the pipes 375,376,377 opens into the pipe 366 mentioned above, approximately horizontal, in locations distributed along it downstream of the zone from which the fluidization air pipes 385,386,387 derive therefrom if the 'We refer to a direction of air circulation 378 in this line 366, imposed by the fan 367; a diaphragm 368 is interposed in the pipe 366 between the outlet of the various pipes 375,376,377 and the mouth of the pipes 385,386, 387 to cause an air passage in the latter.

Therefore, the air conveyed by the pipe 366, at a flow rate adjusted by adjusting the fan 367, successively takes care of the particles taken from the buffer capacity 362 at a flow rate determined by the alveolar distributor 371, and which fall via the line 377, the particles taken from the buffer capacity 361, at a flow rate determined by the alveolar distributor 370, and which fall via line 376, and the particles taken from the buffer capacity 360 at a flow rate determined by the alveolar distributor 369, and which fall via line 375; it will be noted that this order, chosen by way of example, is not characteristic of the invention and is therefore not limiting of the latter; other connection methods will also be described later, with reference to FIGS. 3 and 4.

Downstream of the connection of all of the pipes 375, 376, 377 if one refers to direction 378, the air circulating in the pipe 366 conveys in this direction 378 all of the particles thus received up to means injection 379 at all points similar to the injection means 79 described with reference to FIG. 1, and arranged in the same way as the latter with respect to the grid 3, to the nozzles 23 and 24, and at the level of the injection 41 of the larger particles separated by the first separation means 36; in particular, the injection means 379 are oriented towards the path 20, and more precisely towards a part thereof close to the grid in the upstream zone 21 thereof, to favor the handling of fine particles as well injected in 379 by the coal projected by the spraying device 17 along the path 20, and the monitoring of this path to the grid 3 by these fine particles.

In accordance with the present invention, both the air flow in line 366, considered canine, a transport air flow taking into account the negligible nature of the part of this flow used for fluidization in the buffer capacities 360, 361, 362, and the flow of particles in this air, via the sampling means in the buffer capacities 360, 361, 362 here constituted by the alveolar distributors 369, 370, 371, are continuous, and the particle flow downstream of all the pipes 375,376,377, expressed in terms of mass flow or volume flow, is at least approximately proportional to the load of the boiler, for example to the flow of the supply means 10 expressed in the same units.

To this end, in accordance with the example of implementation illustrated in FIG. 2, it is the flow rate of each of the withdrawal means in the buffer capacities 360,361,362, that is to say of each of the alveolar distributors 369,370,371, which is thus controlled by the load of the boiler so as to be at least approximately proportional thereto, and for this purpose, provision has been made for control of each of the motors 372,373,374 to the motor 16, so as to link in a predetermined proportionality ratio the respective output speeds of these motors; these control means, shown diagrammatically by a dashed line link 380, can be chosen by the fall of the trade from a wide range of possibilities and will therefore not be described.

By an appropriate adjustment of the proportionality ratio, as a function of the quantities of solid particles expected in each of the dust collectors 45, 46, 47 for determined loads of the boiler, taking into account in particular the characteristics of the coal used, it is thus possible to ensure a regular reinjection of these particles; note that the ratio may be different for the different engines 372,373,374.

To allow absorption of variations in the quantity of particles received by the dust collectors 45, 46, 47 following the repercussion, with delay, of a variation in the load of the boiler or even after unclogging these dust collectors, without disturbing the transport via line 366 and without reinjection into the hearth at 379 causing excessive variations in the heating rate, provision is also made for slaving the output speed of each of the motors 372, 373, 374, that is to say -display the flow rate of the withdrawal means 369,370,371, to the variations in the level in the buffer capacity respectively associated 360,361,362, in comparison with the predetermined average level 363,364,365; for this purpose, means are provided for correcting the servo-control of the output speed of each of these motors, as defined by the means 380, as a function of the information provided by the level sensor 391,392, 393 so that a passage of the actual level of particles in one of the buffer capacities above the predetermined average level causes a flow rate of the corresponding sampling means 369,370,371 greater than the flow rate calculated by proportionality with the load of the boiler, and that, on the contrary, a reduction in the level below the predetermined level causes a reduction in the flow rate with respect to the flow rate calculated by proportionality with the load of the boiler; it will be noted that in this way, it is also ensured that the sampling means 369,370,371 receive particles, in the corresponding buffer capacity 360,361,362, an approximately constant effort allowing them to work under approximately constant conditions, independently of the successive emptying of the hoppers. associated intermediaries.

The means making it possible to correct, step by step or continuously, depending on the type of level sensor 391,392,393 used, the speed of rotation of each of the motors 372,373,374 in a slave manner to the measurement of the level sensor 391,392,393 associated with the same capacity buffer 360,361,362 were simply diagrammed by broken lines 381,382,383; like the means 380, they can be chosen by a person skilled in the art from a wide range of possibilities, without departing from the scope of the present invention.

The flow of particles in the pipe 366 being thus determined, the air flow in this pipe, considered as a transport air flow taking into account the small part of this flow which is taken for the fluidization in the capacities. buffers 360,361,362 and preferably constant in terms of volume flow, is adjusted by action on the fan 367 so that the mass flow of the particles introduced into line 366 is in relation to the mass flow of air in this line, inclusive between 1 and 10 approximately; these figures, given by way of nonlimiting example, correspond to a high concentration of the particle-air suspension injected at 379 into the boiler, such a high concentration being favorable to the combustion of the particles upon their arrival in the boiler and to their sintering in the form of bottom ash once they have burned and they are on the grid 3.

Naturally, in addition to the characteristic arrangements of the invention which have just been described, the person skilled in the art will provide all the usual safety devices and accessory arrangements; among these accessory arrangements, there will be found in particular means (not shown) for emptying the entire installation to means for storing suitable solid particles, and in particular means for emptying the separators 45, 46, 47 but note that instead of being used in steady state as is traditionally the case, these means will be used exclusively during installation maintenance operations, the steady state corresponding to a reinjection into focus 2 of all the particles extracted from the fumes before being discharged into the atmosphere by the means 44.

In addition, a person skilled in the art will be able to provide numerous variants of the device which has just been described, without thereby departing from the scope of the present invention; these variants may in particular relate to the practical constitution of second separation means 43, constituted in the example illustrated by three fields of an electrostatic dust collector connected in series by the conduit 28 for conveying the fumes; whatever their nature, we could provide a different number of these separators constituting the second separation means, and a different mutual connection mode, and FIGS. 3 and 4 precisely illustrate two modifications, in this direction, of the device illustrated in FIG. 2.

In the case of the variant illustrated in FIG. 3, a flue duct 128, corresponding to the ducts 328 and connected like this to a boiler, not shown, branches out into two parallel branches 128a and 128b, each of which connects in series two separators, respectively 145a, 146a for line 128a, and 145b and 146b for line 128b.

Each of these separators 145a, 146a, 145b, 146b has a respective lower hopper 148a, 149a, 148b, 149b opening downwards, via a respective valve 151a, 152a, 151b, 152b, in a respective intermediate hopper 154a, 155a, 154b , 155b opening itself down, via a respective valve 157a, 158a, 157b, 158b, in a respective buffer capacity 160a, 161a, 160b, 161b; this buffer capacity itself opens downwards by continuous withdrawal means, at an adjustable flow rate, such as a cellular distributor respectively 169a, 170a, 169b, 170b, on an upper end of a vertical pipe, respectively 175a, 176a, 175b, 176b; these elements carry numerical references resulting from a decrementation of 200 compared to the numerical references assigned to elements already described with reference to FIG. 2, to which these elements of FIG. 3 are similar in their structure, their interrelation and their operation.

In this variant, despite a connection of the separators 145a, 146a, 145b, 146b in series-parallel, a single pneumatic transport line 166, at any point ccm- comparable to the line 366 described above and supplied as it in pressurized air by a fan 167 at any point comparable to the fan 367, receives in a distributed manner the lower ends of the different lines 176b, 176a, 175a, 175b, in this order, to convey the particles which it receives from these lines , suspended in the air, up to single injection means 179, at any point comparable to the means 379 described above, at the hearth of the boiler (not shown).

In the case of the variant illustrated in Figure 4, we find all the elements illustrated in Figure 3, assigned reference incremented by 100 relative to the references that these elements bear in Figure 3, except that the single line 166 and the single fan 167 are split; more precisely, the lines 275a and 276a, respectively correspond to the lines 175a and 176a, open into a first transport air line 266a and the lines 275b and 276b corresponding respectively to the lines 175b and 176b open into a second pneumatic transport line 266b , each of the pipes 266a and 266b having a first end connected to a respective fan 267a, 267b injecting transport air therein at an adjustable and preferably constant flow rate, and a second end to which the two transport pipes 266a and 266b are connected in a single pneumatic conveying line 266 ending at the hearth of the boiler (not shown) by injection means 279 at all points comparable to means 179, 79 or 379, such as an injection nozzle.

In the case of this variant, it is however also possible to supply the two pipes 266a and 266b with transport air in parallel, by means of a single ccnmun fan 267 instead of providing a fan specific to each of them. and / or provide separate paths from these two pipes to the boiler, at the home of which they then open by means own injection 279a and 279b, fully comparable to means 179, 79 or 379, instead of leading to it by common injection means 279; these two possibilities have been shown in dashed lines in FIG. 4.

Naturally, in the case of these two cam variants in the case of the embodiment illustrated in FIG. 2, the number of separators traversed in series by the flue gases, and the nature of these separators can vary to a large extent depending on the needs. estimated by the skilled person; in the case of the embodiments illustrated in FIGS. 3 and 4 in addition, the number of branches derived from the smoke delivery duct 128 or 228 could be greater than two, the ducts then corresponding to the ducts 175a, 176a, 175b, 176b or 275a, 276a, 275b, 276b which can open into a single pneumatic transport line of the type illustrated in 166 in FIG. 3, or into parallel pneumatic transport lines of the type illustrated in 266a and 266b in FIG. 4, or else in series in pneumatic conveying lines connected in parallel.

Naturally, although the above description refers to a coal-fired boiler, it would not go beyond the scope of the invention to apply the latter to boilers burning other solid fuels, such as, for example, wood, bark, bagasse.

Claims (24)

1. Method for reinjecting particles which have flown off in a solid fuel boiler, supplied with fuel by means (10) arranged in a first zone (9) of the boiler and which continuously project a determined charge of fuel along a trajectory (20 ) bringing the latter into a second zone (21) of the boiler, on a grid (3) driven by a movement (8) returning from the second zone (21) to the first (9), combustion taking place on said trajectory (20) and on the grid (3) by means of a release (26) of fumes entraining solid particles,
this process consisting in taking the fumes in the boiler, then conveying them successively in means (36) for separating the largest particles and in means (43) for separating the finer particles, and in evacuating (44) the fumes after this separation while re-injecting into the boiler, separate particles,
this process being characterized in that all of the separated particles are reinjected into the boiler, - in a possibly known manner with regard to the largest particles and, - as regards the finest particles, supplied by the corresponding separation means (43) at an irregular flow rate, by means of the operations consisting in: a) transform this irregular flow into a continuous flow of particles, at least approximately proportional to the load of the boiler, b) continuously introducing this continuous flow of particles into a continuous flow of transport air, c) by means of this air flow, convey these particles continuously to the vicinity of the second zone (21) of the boiler and inject them into this zone, in a part of said trajectory (20) close to the grid (3). 2. Method according to claim 1, the means (43) for separating the finer particles comprising a plurality of separators (45, 46, 47) each of which provides particles according to an irregular clean flow, characterized in that one puts implementing the operations a) and b) above by transforming each of these irregular clean flows into a continuous clean flow of particles, at least approximately proportional to the load of the boiler, and by successively introducing, continuously, these continuous clean flows of particles in said continuous flow of transport air. 3. Method according to claim 1, characterized in that the said continuous flow of particles is controlled by the flow of the means (43) for separating the finer particles. 4. Method according to claim 2, characterized in that each continuous clean flow of particles is controlled by the clean flow of the separator (45, 46, 47) corresponding. 5. Method according to any one of claims 1 to 4, characterized in that the transport air flow is substantially constant, in terms of volume flow. 6. Method according to any one of claims 1 to 5, characterized in that, during operation b), the continuous flow of particles is introduced into the continuous flow of transport air in a ratio of the mass flow of particles with a mass flow of transport air between 1 and 10 approximately. 7. Device for reinjecting particles flown away in a solid fuel boiler, supplied with fuel by means (10) arranged in a first zone (9) of the boiler and which continuously project a determined charge of fuel along a trajectory (20) bringing the latter into a second zone (21) of the boiler, on a grid (3) driven by a movement (8) returning from the second zone (21) towards the first (9) , combustion taking place on said path (20) and on the grate (3) by means of a release (26) of fumes entraining the solid particles, this device comprising - Means (27) for extracting the fumes from the boiler, - means (44) for evacuating smoke, - first separation means (36), for the separation of relatively large particles, - second separation means (43), for the separation of relatively fine particles, - means (28) for conveying smoke from the sampling means (27) to the first separation means (36), from the first separation means (36) to the second separation means (43), from the second separation means ( 43) the means (44) for evacuating smoke, means (37, 38, 39, 40, 41, 42, 84) for sampling particles in the first separation means (36) and for reinjecting such particles into the boiler, - means for sampling particles in the second separation means (43),
this device being characterized in that the means for sampling particles in the second separation means (43) comprise a) a buffer capacity (60, 160,161,162,260,261,262,360, 361,362). b) means (51 to 59) for discharging particles from the second separation means (43) into the buffer capacity (60,160,161, 162,260,261,262,360,361,362), preventing direct communication between them. c) means (69,169,170,269,270,369,370,371) of direct debit continuous of particles at the bottom of the buffer capacity (60, 160,161,162,260,261,262,360,361,362), according to an adjustable flow. d) means (80,81,380,381,382,383,391,392,393) for controlling the flow of the means of the boiler (69,169,170, 269,270,369,370,371) for the continuous collection of particles in the buffer capacity (60,160,161,162,260,261,262,360,361,362), and in what is provided: - a source (98,107,42,167,267,367) of pressurized air, injection means (79,179,279,379) arranged near the second zone (21) of the boiler and opening out towards a part of said path (20) close to the grid (3) in this second zone (21), - a pneumatic conveying pipe (66,166,266,366) connecting the source of pressurized air (98,107,42,167,267,367) to the injection means (79,179,279,379), the means (69,169,170,269,270, 369,370,371) for continuous sampling of particles in the buffer capacity (60,160,161,162,260,261,261,261,261,262,262,262,262,262,262,262,262,262,262,262,262,262,262,262,262,262,262,262,262,362 opening into said pipe (66,166,266,366). 8. Device according to claim 7, the second separation means (43) comprising a plurality of separators (45, 46, 47, 145a, 146a, 145b, 145b, 245a, 246a, 245b, 246b), connected in series and / or in parallel, between the first separation means (36) and the smoke evacuation means (44), by the means (28, 128, 228) for conveying smoke, characterized in that the means for taking off particles in the second separation means (43) comprise: a) a plurality of buffer capacities (160a, 161a, 160b, 161b, 260a, 261a, 260b, 261b, 360, 361, 362), each of which is associated with at least one of said separators and placed under it, b) means (51 to 59), 151a, 152a, 151b, 152b, 154a, 155a, 154b, 155b, 157a, 158a, 157b, 158b, 251a, 252a, 251b, 252b, 254a, 255a, 254b, 255b, 257a, 258a, 257b, 258b) of particles of this separator in the associated buffer capacity, preventing direct communication between them, c) means (169a, 170a, 169b, 170b, 269a, 270a, 269b, 270b, 369, 370, 371) for continuous sampling of particles at the bottom of each buffer capacity, according to an adjustable flow rate, d) means (380,381,382,383,391,392,393) for slaving the charge of the boiler to the flow rate of each of the means for continuous sampling of particles at the bottom of a buffer capacity,
and in that the means for continuous sampling of particles at the bottom of the various buffer capacities open into said pipe (66,166,266,366), which is common. 9. Device according to claim 7, characterized in that the means for discharging particles from the second separation means (43) in the buffer capacity (60,160,161,162,260, 261,262,360,361,362) include an airlock (54,55,56,154,155,156,254,255, 256) of useful volume small in front of that of this buffer capacity (60, 160,161,162,260,261,262,360,361,362). 10. Device according to claim 8, characterized in that the means for discharging particles from a separator (45,46,47) in the associated buffer capacity (60,160,161,162,260, 261,262,360,361,362) include an airlock (54,55,56,154,155,156,254, 255,256 ) of useful volume small compared to that of this buffer capacity. 11. Device according to any one of claims 7 to 10, characterized in that the means (380,381,382,383,391,392, 393) for controlling the load of the boiler the flow rate of the means (69,169,170,269,270,369,370,371) for continuous sampling of particles in the or each capacity buffer (60,160,161,162,260,261,262,360, 361,362) include means (381,382,383,391,392,393) for controlling this flow rate to the maintenance of an average level (363,364,365) of particles in the latter. 12. Device according to any one of claims 7 to 11, characterized in that it comprises means (385 to 390) for fluidizing the particles in the or each buffer capacity (360, 361,362). 13. Device according to any one of claims 7 to 12, characterized in that the means (69,169,170,269,270,369,370, 371) for sampling particles in the or each buffer capacity (60,160,161,162,260,261,262,360,361,362) comprise a cellular distributor. 14. Device according to claim 7, characterized in that it comprises: - a second source (98) of pressurized air, - a second pneumatic transport pipe (97) connecting this second source (98) to the buffer capacity (60), said means (51 to 59) for discharging particles from the second separation means (43) in the buffer capacity (60 ) opening into this second pipe (97) by prohibiting direct communication between the latter and the second separation means (43). 15. Device according to claim 14, the second separation means (43) comprising a plurality of separators (45, 46, 47), connected in series and / or in parallel, between the first separation means (36) and the means (44) smoke evacuation, by the means (28) for conveying smoke, characterized in that the buffer capacity (60) is unique, in that there are provided means (51 to 59) for discharging particles from each of the separators (45 to 47) in the single buffer capacity (60), these discharge means opening into said second pipe (97), which is common, by preventing direct communication between the latter and the separators. 16. Device according to claim 14, characterized in that the means for discharging particles from the second separation means (43) into the buffer capacity (60) comprise an airlock (54, 55, 56) of small useful volume in front of that of this buffer capacity (60). 17. Device according to claim 15, characterized in that the means for discharging particles from a separator (45, 46, 47) into the single buffer capacity (60) comprise a respective airlock (54, 55, 56), the cumulative useful volume of airlocks being less than that of this buffer capacity. 18. Device according to any one of claims 16 and 17, characterized in that it comprises means (100 to 105) for fluidizing the particles in the or each airlock (54, 55, 56). 19. Device according to any one of claims 14 to 18, characterized in that the means (80) for controlling the load on the boiler the average flow rate of the means (69) for continuous sampling of particles in the buffer capacity (60 ) include means (81, 91) for controlling this flow rate to maintain an average level (63) of particles in the latter. 20. Device according to any one of claims 14 to 19, characterized in that it comprises means (85, 88) for fluidizing the particles in the buffer capacity (60). 21. Device according to any one of claims 14 to 20, characterized in that the means (69) for removing particles from the buffer capacity (60) comprise a cellular distributor. 22. Device according to any one of claims 14 to 21, characterized in that the first source (98, 107) is constituted by an upper part (107) of the buffer capacity (60) and by the second source (98) . 23. Device according to any one of claims 14 to 21, characterized in that provision is made for return means (66b) of the gases from the buffer capacity (60) to the second means separation (43), and in that the two sources (98; 42) are dissected. 24 .. Device according to any one of claims 14 to ₂₁ , characterized in that the buffer capacity is open to the open air via a filter (66b), and in that the two sources (98, 42) are dissociated .

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