EP0675323A1 - Device for feeding large solid fuels into a furnace, for example whole scrap tyres - Google Patents

Abstract

The incinerator consists of a furnace (4) with a feed hopper (2) through which the objects to be burned drop by gravity. The lower part (2c) of the hopper is angled and equipped with an adjustable mechanical deflector (10) to control the trajectory of objects dropping into the furnace, and its bottom edge (3) is situated at a distance above the furnace bed (14) at least as great as the largest dimension of the objects being incinerated. The furnace bed (14) is in the form of a grating with horizontal (14) and sloping (15) sections, each made up of a series of bars (15, 15'). The bars in the first section are inclined upwards, with their upper ends forming a horizontal surface, and those in the second section are set horizontally and stepped to form the sloping surface. The furnace is fed with primary air through a pipe (19) beneath the grating, and with secondary air and recycled gases through nozzles in its side walls. <IMAGE>

Description

The present invention relates to a device for charging large solid fuels of the industrial waste type, into a combustion chamber or a fireplace, for example for a rotary kiln installation or a grate boiler.

Such installations or boilers are intended for the combustion or incineration of industrial waste belonging to two main categories of fuels.

A first category consists of aggregates of reduced size, such as manufacturing waste, shredded pneumatic tires or the like, allowing a continuous supply of fuel to the hearth.

The second category consists of larger individual elements, such as whole used pneumatic tires, large agglomerated plates or the like, which are introduced into the hearth by successive charging.

The charging of fuels belonging to this second category has many drawbacks, in particular, in the case of combustion on a grid of whole used tires, the distribution of fuel on the grid is very irregular at the start of combustion due to the low density of whole tires (approximately ten tires per m³, ie a density of 0.06) resulting from their "airy" shape.

This irregular distribution of the fuel at the start of introduction into the hearth is detrimental to the combustion efficiency, since the density on the grate varies suddenly during the movement of the fuel thereon to achieve a significantly higher density value of around 4.8, about 80 times more than the initial density, and the fact that the fuel generally burns during the first minute following its introduction into the fireplace, releasing approximately 75% of the total energy supplied by the fuel.

A known device for charging large solid fuels into a boiler is of the type comprising an inclined feed chute into which the fuel falls under the effect of gravity, said chute opening flush with the grid of the boiler, said grid extending in the hearth of the boiler passing under an entry vault of refractory material to cause the ignition of the returning fuel.

This known device is not satisfactory because direct contact between the material being burned and the fuel entering the hearth is possible, which can lead to the distillation and sticking of the fuel (formation of "gratons") on the introduction device and possibly combustion primers may appear in the feed chute of the device.

Similar problems arise in rotary kiln installations.

The object of the present invention is therefore to eliminate the aforementioned drawbacks and to propose a device for placing large solid fuels in a hearth which makes it possible to optimize the distribution of the fuel as soon as it is introduced into the hearth and which is reliable and simple and economical manufacturing.

To this end, the subject of the present invention is a device for charging solid fuels into a fireplace, comprising a feed chute into which the fuel falls under the effect of gravity, the lower part of said chute being inclined and fitted with an adjustable mechanical deflector to deflect the path of the fuel entering the hearth, the lower end of the chute opening into the hearth at a level higher than the wall of the hearth receiving the burning fuel, characterized in that the device being intended for large fuels, the difference in level is substantially equal to or greater than the largest dimension of the fuel to be burned.

This difference makes it possible to avoid any direct contact between the material being burned and the fuel entering the hearth.

In a pictorial way, the mechanical deflector acts as a ski jump spring making it possible to adjust approximately the point of fall of the fuel on the wall of reception of the hearth, according to the size and the weight of this fuel.

The abovementioned drop is advantageously between 1 and 3 m, depending on the size of the fuel to be burned.

According to another characteristic of the invention, a source of cooling air or combustion gases recycled under pressure scans the lower and upper faces of the deflector as well as the external face of the lower wall of the chute.

This characteristic makes it possible to limit the influence of the heat of the hearth on the part of the device which is the no longer subject to radiation and the significant heat flow released during the ignition of the fuel returning to the fireplace, and therefore to improve the mechanical strength and longevity of this part of the device.

According to yet another characteristic of the invention, the receiving wall of the hearth is cooled jointly by a circulation of water and by a source of air or recycled combustion gases or an air-gas mixture.

Cooling the grate of the hearth with water or with the combustion gases makes it possible to reduce the supply of oxidizer, and consequently to limit the temperature and the "violence" of the beginning of combustion.

The adjustable mechanical deflector can consist of a flap articulated at one end, the pivoting of which can be controlled by an actuating means such as a hydraulic cylinder.

The device of the invention may include a retractable closure means associated with the chute to separate the upper part of the chute from its lower part in a gas-tight manner.

Such a closure means can optionally be formed by an airlock associated with a source of air or recycled combustion gases or an air-gas mixture under pressure to ensure a gaseous barrier between the two parts of the airlock to the fumes produced. in the foyer.

An airlock type closure system makes it possible to supply the fireplace with fuel as regularly as possible at a rate that depends on the load requested.

According to an advantageous characteristic of the invention, at least one side wall of the hearth comprises a heat exchanger device made up of bundles of substantially parallel tubes traversed by a heat-transfer agent, such as water, and connected together by fins, through which are provided nozzles for projecting air or combustion gases recycled under pressure.

Certain tubes of the above-mentioned bundles of tubes can be bent in the manner of an S to provide a passage between the tubes for the air projection nozzles which are housed respectively in each loop of the S, the line passing through the two nozzles associated with each S-tube being inclined relative to the vertical.

Advantageously, the nozzles belonging to the same side wall of the hearth are symmetrical with respect to a median plane perpendicular to said side wall, so as to form an air flow in chevron or V reversed in the hearth.

According to a first embodiment of the invention, the device is mounted in a rotary kiln installation, the wall for receiving the burning fuel being formed by the rotary wall made of refractory material from the kiln.

According to another embodiment of the invention, the device is associated with a grate boiler, the grate forming the wall for receiving the hearth.

The grid may include a first substantially horizontal part for receiving the fuel entering the hearth and extending by a second sloping part ensuring the movement of the fuel in progress. incineration to a gravity discharge opening.

When the grid consists of a plurality of bars, the bars of the first part of the grid are inclined upwards so that their vertices define a substantially horizontal plane, while the bars of the second part are superimposed in planes horizontal, and are offset in the direction of movement of the fuel during incineration so that their free ends define a sloping plane.

If the mechanical deflector makes it possible to determine the fuel drop point on the grid, the angle formed between the fuel and the plane of the grid has an influence on the rebound of the fuel on the grid and more generally on its behavior after its impact. on the grid.

The bars of the first substantially horizontal part being inclined upwards, the angle formed for example by a tire and a bar inclined during the impact on the grid is greater than on a horizontal bar, which increases the probability that the tire falls back onto the grid near the side wall of the fireplace.

In an alternative embodiment, the upper wall of the chute extends into the hearth beyond its lower wall, so as to form a pre-combustion chamber partially extending over the inlet of the grate, to protect the first bars of the grate which are generally little covered with fuel, from the intense thermal radiation produced by combustion in the hearth.

Provision may also be made for the upper wall of the chute to extend into the hearth up to a height relative to the grate, which is substantially less than the size of the fuel to be burned, so as to act as a stop and to fold the fuel towards the first bars of the grid.

According to another characteristic of the invention, air projection nozzles or recycled combustion gases are provided in the side wall of the hearth under the lower end of the chute and above the fuel receiving wall.

Such an air source provided under the fuel introduction chute in the hearth, makes it possible to develop a flame in the fire zone located just above the freshly introduced fuel and promotes the ignition of the fuel, in a similar manner to classic entry vaults in refractory material.

This characteristic therefore makes it possible to eliminate the refractory vault at the level of the entry on the grid, and to achieve savings in maintenance since the refractory materials are generally fragile and require regular maintenance.

This so-called secondary air source also makes it possible to stage the combustion in the hearth and to push the main flame towards the center of the hearth.

The invention will be better understood and other objects, characteristics, details and advantages thereof will appear more clearly during the explanatory description which will follow of several particular currently preferred embodiments of the invention, given solely by way of illustrative and nonlimiting examples, with reference to the appended schematic drawings, in which:

Figure 1 is a schematic, partial and sectional view of a first embodiment of the device of the invention, associated with a grate boiler.

FIG. 2 is a schematic and partial view of a side wall of the boiler of FIG. 1.

Figure 3 is a view similar to Figure 1, but showing an alternative embodiment equipped with a pre-combustion chamber.

Figure 4 is a schematic, partial and sectional view of a second embodiment of the device of the invention, associated with a rotary kiln installation.

According to the embodiment shown in Figure 1, the device of the invention is associated with a grate boiler 1 which includes a fuel supply chute 2 opening at its lower end 3 into a combustion chamber or hearth 4 .

The chute 2 comprises a first upper vertical part 2a which defines a bend 2b with a lower inclined part 2c opening into a side wall 5 of the hearth 4.

The upper end 6 of the chute 2 has a substantially flared shape to allow fuel to be placed in the oven, for example tires 7.

An airlock of the double flap type is mounted in the vertical part 2a of the trough 2 to ensure both the sequential introduction of the fuel into the hearth 4 and a seal against any combustion risers in the chute 2.

The airlock is here formed of an upper flap 8a and a lower flap 8b both hinged with respect to a horizontal axis.

Pressurized air is projected by a nozzle 9 between the upper 8a and lower 8b flaps to form an air barrier in the airlock (the air projection is materialized by an arrow).

This air barrier establishes an overpressure between the two flaps 8a and 8b of the airlock to prevent the gases produced in the hearth 4 from going up into the chute 2.

It is also possible to use, instead of air, recycled combustion gases which have a lower oxygen content and are therefore less likely to serve as oxidizer, or even an air-gas mixture.

Of course, in an alternative embodiment not shown, the airlock can consist of two horizontal plates closing the path of the chute 2 and movable in translation under the action for example of a jack.

An articulated flap forming a deflector 10 is provided on the lower wall 11 of the inclined part 2c of the trough 2.

The pivoting of the deflector 10 around a horizontal axis 12 can be carried out manually or be controlled by any actuation means such as a hydraulic cylinder.

The upper and lower faces of the deflector 10 as well as the external face of the lower wall 11 of the chute are swept by air projected by a source of pressurized air 13 to cool the assembly. A fan is generally used as a source of pressurized air.

However, the air can also be replaced by the recycled combustion gases.

The lower end 3 of the chute 2 is vertically separated by a drop D of the grid 14 for receiving fuel.

This drop D must be sufficient to allow the fall of the tire 7, and preferably greater than 1.5 m.

The grid 14 is of the type with bars 15 and 15 ′ which can be moved under the action of control jacks generally indicated at 16. A few cylinder rods are shown schematically by dashed lines 17.

The arrangement between the control cylinders 16 and the bars 15 is neither shown nor described in the present application because such an arrangement is generally known in the state of the art.

For example, provision can be made for only one bar in two to move in translation in order to ensure the movement of the fuel towards an opening 18 for evacuation by gravity of the bottom ash and other combustion ashes.

The ashes correspond to the residues left by the fuel when it is completely burned. In the case of pneumatic tires, these are mainly steel corresponding to the metal reinforcements, zinc oxide and an alumina silicate, used in the composition of tires.

A source 19 of said primary air projection is associated with the grid 14 by means of a plurality of partitioned compartments 20 which are arranged under the bars 15 and 15 ′ of the grid. This projection of primary air participates in the start of combustion as well as in the combustion of solid unburnt products and its flow rate is adjusted by means of the aforementioned compartmentalized compartments 20.

The primary air may alternatively be replaced by the recycled combustion gases or by an air-gas mixture.

A cooling water circuit (not shown) is also associated with the grid 14 to ensure its cooling together with the projection of primary air or gas.

A first part of the grid 14 consists of bars 15 'oriented upwards so that their vertices define a substantially horizontal plane for the reception of the fuel 7' entering the hearth 4.

A second part of the grid 14 consists of bars 15 superimposed along horizontal planes and which are offset in the direction of movement of the fuel during incineration so that their free ends define a sloping plane opening onto the opening 18 .

An alternative embodiment of the boiler 1 is shown in FIG. 3 which shows a pre-combustion chamber 4a upstream from the hearth 4.

This pre-combustion chamber 4a is formed by the upper wall 26 of the chute 2 which extends into the hearth 4 beyond the lower end 3 of the chute and extends partially above the inlet on the grid 14 which here consists only of horizontal bars 15 defining a plane sloping towards the opening 18.

It is of course possible to provide, as a variant, a rotating, tilting or vibrating grid for example.

The upper wall 26 opens into the hearth 4 at its end 26a which is at a height H relative to the grid 14, this height being substantially less than the size of the tire 7 to force it to lie on the grid and thus better distribute the fuel on it from the first bars.

7a shows a tire at the pre-combustion chamber 4a, already deformed by heat but not yet on fire, which makes it possible to delay the combustion of the tire until it enters the hearth proper.

The non-volatile materials in the fuel require a considerable residence time in the hearth to burn completely, which residence time depends on the size of the particles. In the case of tires, the non-volatile materials consist in particular of carbon black, which represents approximately 23% of the mass of the tire, and burn in 20 minutes, when the temperature is above 1100 ° C, releasing the 25 % of energy remaining.

This non-volatile material is conveyed to the discharge opening 18 by the movable bars 15 and 15 '.

The mechanical deflector 10 deflects the trajectory of the tire 7 sliding in the chute 2 and the tire forms a spray 7 'penetrating into the focus 4.

The angular position of the mechanical deflector 10 makes it possible to determine the point of impact of the burning tire 7 'on the grid 14 so that this burning tire 7' rocks on the grid 14 as close as possible to the side wall 5 of the hearth 4 (see curved arrow).

When the fuel is introduced into the hearth, the volatile matter of the latter quickly escapes on burning and forms a so-called flame front zone. In the case of tires, volatile matter represents approximately 60% of its mass, which volatile matter, when the temperature is above 1100 ° C, burns during the first minute following the introduction of the tire into the firebox, producing in particular gas NO _X.

Under these conditions, to create good combustion conditions, that is to say to stage the oxidant so as to minimize the production of NO _X gas and spread the heat flux in the hearth, projection nozzles are provided. so-called lift air 21, front secondary 22a, rear secondary 22b, front tertiary 23a and rear tertiary 23b.

The lift nozzles 21 are formed in the side wall 5 of the hearth 4 between the lower end 3 of the chute 2 and the grid 14.

The projection of air through the nozzles 21 promotes the ignition of the fuel, as indicated by the burning tire 7'represented in broken lines in FIG. 1.

The nozzles 22a for front secondary air projection and the nozzles 22b for rear rear air projection are formed respectively in the side wall 5 above the chute 2 and in an opposite wall 24 thereof, to assist the combustion of volatile materials released by the fuel.

The nozzles 23a for front tertiary air projection and the nozzles 23b for rear tertiary air projection are provided respectively above the nozzles 22a and 22b and are used to complete the combustion of volatile matter and fine particles in suspension and to filter smoke or combustion gases.

The nozzles 22 and 23 are all oriented downwards so as to cause the return, by pneumatic transport, to the combustion zone of the unburnt particles which take off.

The nozzles 22a are supplied by a front secondary air source 25 which scans the upper wall 26 of the inclined part 2c of the chute 2 to ensure its cooling.

Of course, the nozzles 21, 22 or 23 can project recycled combustion gases in place of air.

A monitoring window 27 is provided in the side wall 24 of the hearth 4 at the level of the discharge opening 18.

The fact of providing several sources of air projection in the fireplace makes it possible to stage the combustion by adjusting the flow rate, the pressure and the temperature of the projected air.

It can be seen in FIG. 2 that the side wall 5 of the hearth comprises a heat exchanger device made up of bundles of tubes 28, 28 ′ which are substantially parallel and connected together, for example by welding, in a gas-tight manner by means of '' sheet metal fins 29.

Certain tubes 28 ′ have a double curvature in the manner of an S to provide a space between the tubes for the air projection nozzles 21 which are housed respectively in each loop of the S.

The fact of providing certain tubes 28 'bent in S makes it possible to have two nozzles on either side of the same tube and to offset them both laterally and in altitude.

We can provide for example that the line 31 passing through two nozzles 21 associated with a tube 28 'in S is inclined at an angle ϑ between 15 and 45 ° relative to the vertical 30, and preferably of the order of 30 °.

In FIG. 2, the nozzles 21 belonging to the same side wall 5 of the hearth are symmetrical with respect to a median plane 30 perpendicular to said side wall 5, so as to form an air flow in chevron 31 or in inverted V in the home.

This chevron flow slows the upward flow of smoke resulting from the combustion of volatile matter, and separates the unburnt particles which fly away.

FIG. 4 represents the device of the invention associated with an installation 33 with a rotary kiln 32.

The rotary kiln 32 is slightly inclined relative to the horizontal, for example along a slope of 2%, to ensure the displacement of the unburnt residues from the kiln towards a post-combustion boiler 33a, 33b.

The combustion of solid waste and unburnt material leaving the oven 32 is received on an incineration grid 14 'allowing the post-combustion of unburnt materials by air projection under the grid 14' and which consists of two retractable flaps 34 to allow disposal of ashes and other solid residues to a storage space indicated by an arrow 35.

The boiler shown in FIG. 4 is of the type with two vertical compartments 33a and 33b, or with at least two compartments, which communicate with each other at the upper end of the boiler.

Schematically shown at 36 are water or steam heat exchanger devices formed for example by bundles of tubes 36a.

The arrow 37 indicates the direction of flow of the smoke towards a smoke treatment installation such as a dust collector (not shown) or towards a combustion gas recycling installation to supply the aforementioned nozzles.

The feed chute 2 opens into the oven 32 through a substantially vertical fixed wall 38.

A lift air projection nozzle 21 'is formed in the wall 38 under the lower end 3 of the chute 2. The nozzle 21' is here oriented upwards, but it can be provided horizontal.

The internal wall of the rotary kiln 32 constitutes the wall for receiving the fuel.

There is shown diagrammatically at 39 and 40, respectively rotation drive and rolling means for the rotary kiln 32.

Although the invention has been described in conjunction with several particular embodiments, it is obvious that it is in no way limited thereto and that it can be brought to many variations and modifications, without going beyond its scope or of his mind.

Claims (14)

Device for charging solid fuels into a hearth (4, 32) comprising a feed chute (2) into which the fuel falls under the effect of gravity, the lower part (2c) of said chute being inclined and provided an adjustable mechanical deflector (10) for deflecting the path of the fuel (7) entering the hearth, the lower end (3) of the chute (2) opening into the hearth (4, 32) at a higher level (D, D ') as the wall (14) of the hearth receiving the burning fuel (7'), characterized in that, the device being intended for large fuels (7), the difference in height (D, D ') is substantially equal to or greater than the largest dimension of the fuel to be burned (7). Device according to claim 1, characterized in that it is associated with a grate boiler (1), the grate (14) forming the wall for receiving the fuel entering the hearth (4). Device according to claim 2, characterized in that the grid (14) has a first substantially horizontal part for receiving the fuel (7 ') entering the hearth (4) and being extended by a second sloping part, ensuring movement molten fuel to a gravity discharge opening (18). Device according to claim 3, characterized in that the grid consists of a plurality of bars (15, 15 '), the bars (15') of the first part of the grid being inclined upwards so that their vertices define a substantially horizontal plane, while the bars (15) of the second part are superimposed in horizontal planes, and are offset in the direction of movement of the fuel during incineration so that their free ends define a sloping plane. Device according to claim 2, characterized in that the upper wall (26) of the chute (2) extends into the hearth (4) beyond its lower wall, so as to form a pre-combustion chamber (4a ) partially extending over the entrance to the grid (14). Device according to claim 5, characterized in that the upper wall (26) of the chute (2) extends into the hearth (4) up to a height (H) relative to the grid (14) which is substantially lower the size of the fuel to be burned (7). Device according to claim 1, characterized in that it is mounted in a rotary kiln installation (33), the wall for receiving the burning fuel being formed by the rotary wall made of refractory material from the kiln (32). Device according to any one of the preceding claims, characterized in that the difference in height is between 1 and 3 m, and preferably greater than 1.5 m. Device according to any one of the preceding claims, characterized in that nozzles (21, 21 ') for spraying recycled air or combustion gases are provided in the side wall (5, 38) of the hearth (4, 32 ) under the lower end (3) of the chute (2) and above the wall (14) for receiving fuel. Device according to any one of the preceding claims, characterized in that at least one side wall (5, 24) of the hearth (4, 33a) comprises a heat exchanger device consisting of bundles of tubes (28, 28 ') substantially parallel, traversed by a heat transfer agent, such as water, and through which are provided nozzles (21, 22, 23) for spraying air or combustion gases recycled under pressure and in that certain tubes ( 28 ') are bent in the manner of an S to create a space between the tubes for the nozzles (21) which are housed respectively in each loop of the S, the line (31) passing through the two nozzles associated with each tube in S being inclined relative to the vertical (30). Device according to claim 10, characterized in that the nozzles (21) belonging to the same side wall (5) of the hearth are symmetrical with respect to a median plane (30) perpendicular to said side wall, so as to form a flow of chevron air (31) in the hearth (4). Device according to any one of the preceding claims, characterized in that a source (13) of cooling air or combustion gases recycled under pressure scans the lower and upper faces of the deflector (10) as well as the external face of the lower wall (11) of the chute (2). Device according to any one of the preceding claims, characterized in that the receiving wall (14) of the hearth (4) is cooled jointly by a circulation of water and by a source (19) of air or combustion gases recycled or an air-gas mixture. Device according to any one of the preceding claims, characterized in that it comprises an airlock forming retractable closing means (8a, 8b) associated with the chute (2) to separate the upper part (6) from the gas the chute of its lower part (2c) and to a source (9) of air or recycled combustion gases or a pressurized air-gas mixture to ensure between the two parts (8a, 8b) of the airlock gas barrier to the fumes produced in the hearth (4, 32).

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