EP0882201A1

EP0882201A1 - Boiler continuously supplied with solid fuel batches

Info

Publication number: EP0882201A1
Application number: EP97905203A
Authority: EP
Inventors: René Tabel
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-02-20
Filing date: 1997-02-14
Publication date: 1998-12-09
Anticipated expiration: 2017-02-14
Also published as: FR2745072B1; ES2154892T3; EP0882201B1; DE69703875D1; ATE198659T1; FR2745072A1; WO1997031224A1; DE69703875T2

Abstract

A boiler continuously supplied with solid fuel batches is disclosed. The boiler consists of two levels (6, 10) located one above the other, i.e. a lower level with a vertically extending tubular combustion chamber (12) into which the fuel is fed via feed means (2, 26), and an upper level containing an exchanger (8) and a smoke discharge pipe (20). The two levels communicate via a nozzle (14) enabling the flames to be spread by air circulation means (22) from the base of the combustion chamber (12) towards the smoke discharge pipe (20).

Description

SOLID FUEL CONTINUOUS SUPPLY BOILER

PARCELLIZED.

The invention is in the field of heating techniques, and it relates to a boiler with continuous supply of parceled solid fuel.

Boilers are known comprising two superimposed stages, one lower housing a combustion chamber and the other upper housing a heat exchanger. An access is provided in the combustion chamber for the supply of solid fuel, in particular wood. We can more particularly refer to patents FR 582578 (Ets DELOR and THIBAULT) which describe boilers of this kind. A problem with these boilers is that they do not allow a continuous supply of fuel to the combustion chamber. Indeed, the fuel is supplied by the loading door, which remains closed during combustion so as not to induce disturbing air circulation; it is recalled that in general, the modes of air circulation in the combustion chambers are essential for the maintenance of combustion, and therefore constitutes a problem to be solved in the case of a continuous supply of solid fuel.

The evolution of techniques has led to the development of combustion devices comprising a closed combustion chamber continuously supplied with parceled solid fuel, wood waste in particular. The fumes released by combustion are removed from the enclosure by a conduit, and the heat they give off is removed, by means of a water exchanger for example.

These devices meet the dual objective of eliminating waste by combustion, and seizing the opportunity of the heat produced to heat premises. It follows from this approach that the designers have not optimized the combustion and the exchange of known devices of the genre, to the detriment of their performance. In addition, changes in regulations require control and control of the fumes released, both in terms of their temperature and their pollution. To meet these constraints, the designers were led to arrange the combustion chamber to introduce outside air, not only to fan the combustion by an air blowing, said primary, but also by a contribution of additional air, called secondary air, to control the composition of the fumes. Such arrangements are all the more delicate to implement since the fuel supply is effected by supply means overhanging the combustion chamber, such as a worm screw connected to a silo, which induces a potential risk of fuel reserve fire.

These complex and costly arrangements hinder the development of devices of this type.

Thus, the previous approaches to the design of combustion devices with continuous supply of parceled solid fuel, and the arrangements necessary for bringing them into conformity, induce a manufacturing cost for a low yield such that on the one hand they are not competitive compared to heating devices supplied from another source of energy, such as fuel oil, and secondly that they appear to be obsolete in the light of technological developments.

The object of the invention is to provide a boiler with continuous supply of parceled solid fuel, which offers a high efficiency and a reliable control of the combustion and of the composition of the fumes, the operation of which is carried out naturally in complete safety, and which is of a simple structure, and therefore of a competitive cost price, both with respect to devices of this type and to those using a fuel of another nature. According to the invention, a boiler with continuous supply of parceled solid fuel, is generally characterized in that it is mainly composed of two superposed stages, one of which is lower, in which is located a tubular combustion chamber with vertical extension in which lead to fuel supply means, and of which another superior, in which are located an exchanger and a smoke evacuation duct, the two stages communicating via a nozzle for the escape of the flames out from the combustion chamber to the exchanger, under the effect of means of air circulation, said primary, from the base of the combustion chamber and axially through its interior space, towards the smoke evacuation duct.

The abovementioned organization of the boiler has the result of offering a high efficiency, due to the optimization of the combustion and the removal of the heat produced, optimization obtained by means of upward ventilation from the base of the combustion chamber. up to the smoke evacuation duct, after their passage in the exchanger, upward ventilation means comprising in particular the organization of the boiler in two superposed stages communicating by a nozzle for escaping flames from combustion, and the tubular configuration of the combustion chamber which is arranged vertically.

According to another aspect of the invention, the air circulation means are means for depressurizing the upper and lower stages from downstream of the upper stage.

It results from the choice of means of the "vacuum" type rather than of the "pulse" type, that the air circulating between the floors cannot, naturally, follow a path other than that which has been imposed on it since the base of the combustion chamber to the flue gas exhaust pipe, and finally that the boiler offers reliable safety in use, the combustion can naturally not extend outside the enclosure formed by the boiler, in the fuel supply means in particular.

The combustion chamber is preferably arranged in a primary air intake chamber, its base opening into the latter, inside which intake chamber is introduced in a controlled manner the primary air from outside the boiler, prior to its introduction into the combustion chamber.

Such arrangements, during operation of the boiler, constitute means of preheating, in contact with the external wall of the combustion chamber, of the primary air introduced into the intake chamber prior to its introduction into the combustion chamber. .

According to a preferred embodiment, the boiler is equipped with means for self-regulating its operation, said means comprising: a) means for selection by the user of at least one set temperature at the outlet of the exchanger , and thermostatic means for controlling the starting and stopping of the means for putting under vacuum, respectively below and above the threshold of the, or of the so-called set temperatures, and b) a vacuum switch for measuring the vacuum inside the air intake chamber, and to control the starting and stopping of the fuel supply means of the combustion chamber, respectively above and below a determined threshold of said depression, determined and preset threshold as a function of the maximum tolerated pressure losses resulting from the resistance offered by the fuel present in the combustion chamber against the introduction of the primary air in the latter, and therefore determined and preset according to the maximum amount of fuel tolerated in the combustion chamber. These provisions allow self-regulation of the boiler: the temperature of the water in the exchanger does not reach the set temperature (or the highest temperature in the case where the selection means make it possible to determine a temperature range of setpoint) and the means of depressurization being therefore implemented, the fuel supply to the combustion chamber continues as long as the depression has not dropped below the determined threshold, due to the insufficiency of fuel present in the combustion chamber, and / or due to an always insufficient temperature of the water, and therefore of the maintenance in operation of the means of depression.

Preferably, the fuel supply means are also placed under the dependence of timing means, to compensate by successive short on-off cycles for the reaction times of the boiler to abrupt variations in combustion and pressure ( depression) inside the combustion chamber, resulting from a fuel supply in the latter.

According to particular arrangements of the boiler of the invention, the latter further comprises means of air intake, called secondary, inside the combustion chamber through at least one radial orifice formed at its top and opening out at the base of the nozzle, and means for adjusting the quantity of secondary air admitted for adjusting the composition of the fumes, and therefore the pollution levels of the fumes discharged from the boiler.

According to another aspect of the invention relating to the maintenance of the boiler, the nozzle opens into the upper stage in a combustion pot which constitutes a means for causing a fallout of the ashes and solid particles not consumed in the nozzle and prohibiting dispersion in the upper floor of ash and unburned particles, in particular to limit fouling of the upper floor. In addition, the upper floor is advantageously provided at its top with an access door to

The exchanger, then to the combustion chamber through the nozzle, to facilitate maintenance of the boiler and in particular cleaning of the exchanger.

The exchanger is for example generally formed of a double-walled cylinder disposed around the combustion pot, between which walls extend axially to the exchanger a plurality of tubes for the circulation of smoke, the cylinder being provided with its top of a refractory cover overhanging the burn pot to send back to the nozzle the flames that escape, the heads and unburnt particles.

The tubes are advantageously provided internally with helical cores intended to force the passage of smoke along the wall of the tubes, and therefore to promote heat exchange.

According to a preferred embodiment, in which the said fuel supply means are of the "worm" type, the said screw passes through the wall of the combustion chamber to open, at one of its ends, at the in the vicinity of the top of the latter, the other end being intended to communicate with the outlet of a silo containing a reserve of parceled solid fuel.

The outlet of the silo is preferably closed off by means of additional division of the fragmented fuel which it contains, so that only materials whose dimensions do not exceed a determined threshold are admitted into the supply screw.

Said means of dividing the fuel are for example constituted by a plate closing the outlet of the silo provided with a passage for materials, and by a disc driven in rotation superimposed on the plate and itself provided with a material passing light, so that too much material long are sheared between the rotating disc and the plate when they fall out of the silo.

Preferably, the silo is provided with a centrifugal arm for stirring the fuel that it contains and for supplying the fuel from the walls of the silo to its outlet.

The present invention will be better understood, and details will become apparent from the description which will be made of a preferred embodiment, in relation to the figures in the accompanying plate, in which: fig.l is an illustration in section of a preferred embodiment of a boiler of the invention, FIGS. 2 and 3 are diagrammatic representations in perspective, respectively in exploded and assembled view, of the members equipping the outlet of a silo for the supply of fuel to a boiler of the invention. Fig.4 is a sectional illustration of an improved embodiment of a boiler such as that shown in Fig.l.

In fig.l, a boiler is supplied with solid fuel parceled out by means of an endless screw 2 connected to a silo 4.

The boiler generally consists of an upper stage 6 in which is disposed a water exchanger 8, and a lower stage 10 in which is disposed a vertical tubular combustion chamber 12 inside which opens the worm 2. The two stages 6 and 10 communicate with each other by means of a nozzle 14 through which the flames escape from the combustion chamber 12 towards the exchanger 8. The combustion is maintained by an ascending stream of primary air taken from outside the boiler, which first circulates in a primary air intake chamber 16 surrounding the combustion 12, then axially through the latter 12 from its base towards the nozzle 14, and in a second step, in the form of flue gases, through the tubes 18 for heating the exchanger 8 towards a duct 20 for discharging the fumes out of the boiler.

The primary air circulation is obtained by means 22, such as a turbine, generating a vacuum inside the upper 6 and lower 10 stages, the said means 22 being located downstream of the upper stage 6 for create an air intake through the nozzle 14, through the combustion chamber 12 from its base, and through the primary air intake chamber 16 from the outside of the boiler.

The boiler is self-regulated by means of monitoring and controlling its operation: the user has means 72 for selecting a set temperature of the water in the exchanger 8 measured by thermostatic means 70. In the if the water temperature is lower than the set temperature, the thermostatic means 70 control the starting of the turbine 22.

A vacuum switch 24 controls, depending on the vacuum prevailing in the primary air intake chamber 16, the implementation of the means 2 for supplying fuel to the combustion chamber 12, in the case where said vacuum is greater than a determined and preset threshold. When the vacuum reaches said threshold, the vacuum switch 24 controls the stopping of the fuel supply means 2. When the temperature of the water in the exchanger 8 is reached and / or is higher than the set temperature, the thermostatic means 70 control the stopping of the means 22 for placing under vacuum. Stopping the primary air intake, and therefore the absence of vacuum in the chamber 16 measured by the vacuum switch 24, induces the latter 24 to stop the supply means 2. The nozzle 14 opens into a combustion pot 28 and is overhung by a cover 30 of refractory material resting on the exchanger 8, to cause a fall of the ash and unconsumed solid particles in the nozzle 14.

Secondary air, intended to complete the combustion, is introduced under the effect of the means 22 generating vacuum, from the outside of the boiler through a closed chamber 32 surrounding the top of the combustion chamber 12, then to through radial orifices 34 formed in the latter 12.

It will be noted that the quantities of air admitted inside the boiler, both secondary air and primary air, are adjustable by means of respective adjustment valves 36 and 38, but that during operation of the boiler, self-regulating in the manner just described, the user only has to perform the selection of the set temperature.

According to an advantageous arrangement, the opening of the valve 38 for primary air intake inside the intake chamber 16 is placed under the dependence of an electromagnet 74, the implementation of which is controlled by the said thermostatic means 70 simultaneously with that of the means 22 generating vacuum.

In the example illustrated in FIG. 1, the valve 38 is shaped as an air inlet airlock, one of the openings of which is closed by a first flap 76, for pre-setting the maximum quantity d admissible air inside the boiler, and the other opening of which is closed by a second flap 78 which can be operated by said electromagnet 74. The latter 74 constitutes a means for firmly holding the second flap 78 in the position of opening, in order to avoid variations in the admitted air flow which would result from instability and oscillations of the flap 78 in the open position under the effect of turbulence, which would affect control of the composition of the fumes discharged from the boiler. In the closed position of the second flap 78, a determined quantity of primary air is nevertheless admitted inside the intake chamber 16 coming from the airlock, so that the valve 38 offers two possible admission flow rates d air, one maximum when the vacuum means 22 and the electromagnet 74 are active, the other minimum when the vacuum means 22 are stopped and the second flap 78 in the closed position, minimum flow just enough to maintain combustion.

In this arrangement, the outlet of the vacuum switch 24 is arranged inside the airlock 38, in order to obtain a certain shutdown of the means 2 for supplying fuel in the event of failure of the electromagnet 74, and therefore in case da inoportune closure of the second flap 78 under the effect of its own weight, while the depression means 22 are active.

Note also the presence of an access door 40 to the exchanger 8 and to the combustion chamber 12, after removal of the cover 30, articulated at the top of the upper stage 6.

According to a simple and preferred embodiment, the stages 6 and 10 comprise a respective enclosure each formed by a box 42 and 44, the boxes 42 and 44 being assembled to one another, by bolting 46 in particular. The combustion chamber 12 consists of a rolled sheet 48 inside which is molded a refractory lining 50, said sheet 48 then being welded to the upper wall of the box 44 of the lower stage 10, so as to be supported by the latter in suspension and therefore clear the opening of the base of the combustion chamber 12 to allow the passage of primary air. Equivalently but nonetheless not preferred, the combustion chamber 12 could rest on the bottom of the lower box 44 by means of a base forming at the base of the combustion chamber 12 sufficient clearance for primary air circulation.

It will also be noted the advantageous presence of helical cores inside the tubes 18 for the passage of the smoke from the exchanger 8.

Note also the presence of a door 54 formed at the base of the lower stage 10 for access to the base of the combustion chamber 12, for the ignition of the boiler and the evacuation of ash, an ashtray, not shown in the figures, preferably being placed under the combustion chamber 12.

In fig.l, 2 and 3, the outlet of the silo is closed by a plate 56 provided with a light 58 for the passage of materials, and by a disc 60 superimposed on the plate 56 and connected to means 64 of rotational drive, disc 60 itself provided with the same lumen 58, so that the materials can be admitted into the worm 2 only on condition that their parcelling is sufficient. A centrifugal arm 66 connected to means 64 for driving in rotation is provided for driving the materials contained in the silo 4 towards its outlet. This arm 66, crenellated and driven in rotation on itself, rolls on a ring gear 68 equipping the silo 4 around the axis of the latter.

It will be noted that advantageously the means 64 for driving in rotation the disc 60 and the arm 66 are combined.

Referring to FIG. 4, it will be noted that the tubular combustion chamber 12 delimits an interior volume which is preferably conical, in particular in order to obtain a fall of the fuel in its axial zone rather than along its wall, thanks to which the fuel is naturally distributed at the base of the combustion chamber 12. It will also be noted that thanks to these provisions, the combustion chamber 12 is all the more robust, which is preferable insofar as it where it participates in support of the burn pot 28. According to the improvements shown in fig.4, the boiler of the invention is further equipped with an automatic ignition device, comprising means 80,82,84,86 for drawing a stream of hot air, such as at a temperature between 480 ° C and 520 ^β C, at the base of the combustion chamber 12. This device comprises means 80 for taking the air outside the boiler and circulating it through a resistance 82 for heating, then through a conduit 86 to the base of the combustion chamber. The implementation of the pulsing means 80 is placed under the dependence of timing means 84, so that the burning air is spontaneously maintained drawn from the base of the combustion chamber for a predetermined period, from 1 to 5 minutes per example, when switching on the boiler. It will be noted that thanks to these arrangements, the blower 80, air heating 82, and timer 84 means are disposed away from the combustion chamber, and even preferably outside the boiler, thanks to what the said means do not require special arrangements to preserve them from the heat of the hearth, and finally thanks to which their manufacturing cost is reduced.

The boiler of the invention is preferably equipped with means for de-ashing the base of the combustion chamber 12, in order to avoid engorgement which is detrimental to the free circulation of air through the combustion chamber 12. These means include a squeegee 92 animated by a back and forth movement (arrow 1) for dropping the ashes in a tank 88, disposed at the base of the boiler, through ports 90 for communication between the ash tank 88 and the chamber air intake 16, said lights 90 opening in the vicinity of the periphery of the combustion chamber 12. The movement of the squeegee 92 can be generated, either manually by the user at his discretion, or and preferably regularly by means of motors 94, by means of a pinion comprising a rack 96 fitted to the squeegee 92.

Claims

1.- Boiler with continuous supply of parceled solid fuel, characterized: in that it is mainly composed of two superimposed stages (6, 10), one of which is lower (10), in which is located a tubular combustion chamber with extension vertical (12) into which fuel supply means (2.26), and another, upper (6), in which are located a heat exchanger (8) and a flue exhaust pipe (20) , the two stages (6,10) communicating via a nozzle (14) for the escape of flames out of the combustion chamber (12) towards the exchanger (8), under the effect of means (22) air circulation, said primary, from the base of the combustion chamber (12) and axially through its interior space, towards the flue exhaust duct (20);

2.- Boiler according to claim 1, characterized: in that the means (22) for air circulation are means for putting the upper (6) and lower (10) stages into depression from downstream of the stage upper (6);

3.- Boiler according to claim 2, characterized: in that the combustion chamber (12) is disposed in a chamber (16) for primary air intake, its base opening into the latter, inside which intake chamber (16) is introduced in a controlled manner (38) the primary air prior to its introduction into the combustion chamber (12);

4.- Boiler according to claim 3, characterized: in that it is equipped with means for self-regulating its operation, said means comprising: a) means (72) for selection by the user of at least one set temperature of the water at the outlet of the exchanger (8), and thermostatic means (70) for controlling the switching on and stopping of the means (22) for placing under vacuum, respectively below and above the threshold of said set temperature at least, and b) a vacuum switch (24) for measuring the vacuum prevailing in the chamber (16) d primary air intake, and to control the starting and stopping of the means (2) for supplying fuel to the combustion chamber (12), respectively above and below a determined threshold of the flow rate primary air intake;

5. A boiler according to claim 4, characterized: in that the means (2) for supplying fuel are also placed under the dependence of time delay means;

6.- Boiler according to claim 1, characterized: in that it further comprises means (22,32) of air intake, said secondary, inside the combustion chamber (12) through at least one radial orifice (34) formed at its top, and means for adjusting (36) the quantity of secondary air admitted;

7.- Boiler according to claim 1, characterized: in that the nozzle (14) opens into the upper stage in a combustion pot (28) which constitutes a means for causing a fallout of the ashes and solid particles not consumed in the nozzle (14) and prohibit a dispersion in the upper stage of ash and unburnt particles;

8.- Boiler according to claim 7, characterized: in that the exchanger (8) is generally formed by a double-walled cylinder arranged around the combustion pot (28), between which walls extend axially at the exchanger (8) a plurality of tubes (18) for the circulation of smoke, the cylinder being provided at its top with a cover (30) in refractory material overhanging the combustion pot (28) to return to the nozzle (14) the flames which escape therefrom, the ashes and the unburned particles;

9.- Boiler according to claim 1, characterized: in that the upper stage (6) is provided at its top with an access door (40) to the exchanger (8) and to the combustion chamber ( 12) through the nozzle (14);

10.- Boiler according to claim 1, said fuel supply means being of the "worm" type, characterized: in that said screw (2) passes through the wall of the combustion chamber (12) for lead, at one of its ends, in the vicinity of the top of the latter (12), the other end being intended to communicate with the outlet of a silo (4) containing a reserve of parceled solid fuel;

11.- Boiler according to claim 10, characterized: in that the outlet of the silo (4) is closed by means (56,58,60,62,64) of additional division of the fragmented fuel it contains; so that only materials whose dimensions do not exceed a given threshold are admitted into the supply screw (2);

12.- Boiler according to claim 11, characterized: in that the said fuel division means consist of a plate (56) for closing the outlet of the silo (4) provided with a light (58) for passage of materials, and by a disc

(60) driven (64) in rotation superimposed on the plate (56) and itself provided with a light (62) for passage of the materials, so that excessively long materials are sheared between the rotary disc (60) and the plate (56) when they fall out of the silo ;

13.- Boiler according to claim 11, characterized: in that the silo (4) is provided with a centrifugal arm (66) for stirring the fuel which it contains and for supplying the fuel from the walls of the silo (4 ) towards its outlet;

14.- Boiler according to claim 1, characterized: is further equipped with an automatic ignition device, comprising means (80,82,84,86) for drawing a stream of hot air at the base of the chamber combustion (12).