IT201700018014A1 - BOILER FOR THE COMBUSTION OF GRANULAR BIOMASSES. - Google Patents

Description

BOILER FOR COMBUSTION OF GRANULAR BIOMASS

DESCRIPTION

The present invention relates to a boiler for the combustion of granular biomass, and more particularly for so-called "poor" granular fuels such as pomace pits, cereal waste, corn, etc.

Boilers are known in the art which comprise inside them a wall provided with a cavity for containing a fluid to be heated, which delimits a compartment which houses a burner.

The burner is generally provided with a grill, on which the fuel to be burned is arranged, which divides the space inside the aforesaid wall into an upper area and a lower area.

While the upper zone is intended to receive and contain solid fuels of different types, the lower zone comprises a combustion chamber and heat exchange means, suitably arranged to heat the fluid contained in the above-mentioned cavity.

Combustible products are generally supplied by means of suitable supply means, while the combustion air arrives through suitable supply means.

Known boilers, however, have some drawbacks, especially if they are used to burn granular fuels of vegetable origin generally defined as "poor" due to their low calorific value, such as pomace pits, cereal waste, corn, etc., for example.

In fact, these fuels typically have a high degree of humidity and this generally makes ignition difficult, which is obtained only by using high electrical powers, as well as making their combustion difficult.

In this regard, it should be considered that the combustion of poor granular biomass occurs most of the time at low temperatures, with the consequent formation of unburnt materials which tend to deposit in the form of refractory concretions, which rapidly and significantly compromise the efficiency of the burner. and boiler heat exchangers.

The problems due to deposits in the boiler are generally divided into two broad categories, and concern the encrustations respectively identified with the English terms "slagging" and "fouling".

More specifically, the "slagging" deposits are formed by the unburnt particles of ash that stick to the hot walls of the boiler giving rise to the clinker, while the "fouling" deposits are formed by inorganic vapors which condense on the colder surfaces of the boiler.

These types of encrustations, although characterized by different formation mechanisms, are both closely related to low combustion temperatures.

Another drawback relates to the fact that the flame is almost always turned upwards, contrary to what would actually be desirable in a boiler of the type described above, with significant combustion and efficiency losses.

A further critical aspect then concerns the fact that ignition is generally manual, and therefore known boilers are also not very comfortable to use.

The aim of the invention is therefore to provide a boiler for the combustion of granular biomass which overcomes the drawbacks of the known art.

Within the scope of the above aim, a particular object of the invention is to provide a boiler which operates using so-called "poor" granular fuels such as pomace pits, cereal waste, corn, etc., while still guaranteeing high levels of efficiency and of efficiency.

Another object of the invention is to provide a boiler in which the formation of any unburnt residues is minimized.

Another object of the invention is to provide a boiler capable of automatically regulating its operation, limiting fuel consumption and ensuring optimal combustion.

Not least object of the invention is to provide a boiler which is comfortable to use and advantageous also from the point of view of energy consumption.

The aforementioned task, as well as the aforementioned purposes and others which will appear better later, are achieved by a boiler for the combustion of granular biomass, comprising a compartment delimited by a wall equipped with a cavity for containing a heat exchange fluid; said compartment at least partially accommodates a burner unit comprising a separating wall, provided with one or more through openings, which divides the compartment into an upper area and a lower area; said upper zone is adapted to receive and contain combustible products; said lower zone comprises a combustion chamber, placed in depression by suction means, and heat exchange means, in thermal connection with said wall; said boiler further comprises means for feeding at least one combustible product to said burner unit and means for supplying combustion air to said burner unit; said boiler is characterized in that said burner assembly comprises a burner with lean granular fuels and a pellet burner, said pellet burner cooperating with said burner with lean granular fuels to favor the combustion of said poor granular fuels.

Further characteristics and advantages will become clearer from the description of preferred but not exclusive embodiments of a boiler according to the invention, illustrated by way of non-limiting example in the accompanying drawings in which: Figure 1 is a front view of a boiler according to 1 'invention;

Figure 2 represents a section along the line II-II of Figure 1;

Figure 3 represents a section along the line III-III of Figure 2;

Figure 4 represents a section along the line IV-IV of Figure 1 and schematises the operation of the boiler according to the invention;

figure 5 represents a section along the line V-V of figure 1 and relates to a variant embodiment of the boiler according to the invention

figure 6 represents a section along the line VI-VI of figure 5;

Figure 7 represents a section along the line VII-VII of Figure 1 and relates to another variant embodiment of the boiler according to the invention;

figure 8 represents a section along the line VIII-VIII of figure 7.

With reference to the aforementioned figures 1 to 4, a boiler for the combustion of granular biomass is indicated as a whole with the reference number 1.

The boiler 1 is particularly suitable for the combustion of granular fuels of vegetable origin generally defined as "poor", such as pomace pits, cereal waste, corn, etc., which typically have a low calorific value and a high degree of humidity, resulting therefore difficult to ignite and burn.

The boiler 1 comprises a substantially box-like body 2 inside which a wall 3 is housed provided with a cavity 4 suitable for containing a heat exchange fluid.

Wall 3 delimits a compartment which at least partially accommodates a burner assembly 5 comprising a separating wall 6 provided with one or more through openings.

The separating wall 6 divides the compartment delimited by the wall 3 into an upper zone 7 and a lower zone 8, which are in fluid communication with each other.

More specifically, while the upper zone 7 is intended to receive and contain combustible products fed by suitable feeding means 9, the lower zone 8 comprises a combustion chamber in which a mixture consisting of the gas resulting from the partial combustion of the combustible products is burned. and by combustion air fed by suitable supply means 10.

Conveniently, the combustion chamber is equipped with a channel 11 for evacuating the fumes, which comprises suction means 12 such as to place the entire lower zone 8 in depression.

In the lower zone 8 there are also housed heat exchange means 13, already known per se, which result in thermal connection with the wall 3.

During the operation of the burner assembly 5, the heat exchange means 13 are lapped by the fumes produced by combustion and absorb the heat thereof, causing the heating of the heat exchange fluid contained in the interspace 4.

Advantageously, the heat exchange means 13 are assisted by a catalyst 14 whose main purpose is to prevent the flame from directly touching the underlying area.

In practice, the catalyst 14 creates a smoke circuit which, in addition to allowing a total exploitation of the heat produced by the flame, allows to obtain clean exhaust fumes; in fact, the longer the time during which the combustion products remain at high temperatures, the lower the unburnt products.

According to the present invention, the burner assembly 5 comprises a burner with lean granular fuels 20 and a pellet burner 40 which cooperate with each other in order to favor the complete combustion of these poor granular fuels, which have already been better defined above.

The lean granular fuel burner 20 is essentially constituted, in its lower part, by the through openings obtained in the separating wall 6, which also acts as a support for the lean granular fuel which preheats on it by drying.

More in detail, the separating wall 6 comprises a plate-like body 21, preferably made of refractory material, which is arranged in a substantially horizontal position inside the compartment delimited by the wall 3.

Central to the plate-like body 21 there is a through seat 22, in which a counter-shaped deflector element 23 is housed, conceived in such a way as to define a plurality of passages 24 suitable for putting the upper zone 7 in fluid communication with the lower zone 8.

It is important to point out that the deflector 23 prevents the direct passage of the lean granular fuel in the lower zone 8 through the passages 24, instead retaining it in the upper zone 7 where its gasification begins.

During the operation of the boiler 1, the flame generated by the poor granular fuel burner 20 passes through the passages 24.

In this case, the deflector element 23 consists of an elongated body, preferably made of refractory material, or of suitable metal materials such as cast iron or steel, which has a portion 25 with a mushroom section joined to a portion 26 with trapezoidal section.

During normal use of the deflector element 23, the portion 25 with the mushroom section faces inwards of the upper zone 7.

Advantageously, at the two opposite ends of the portion 25 with a mushroom-shaped section there are defined support elements 27 suitable for keeping the deflector element 23 in suspension in the through seat 22, so as to form the passages 24 and ensure the communication of fluid between the upper zone 7 and lower zone 8.

The lean granular fuel burner 20 is fed by a first duct 30 for feeding the lean fuel granules, of relatively small size, which reach the separating wall 6 by falling, that is, to the plate-like body 21 and to the deflector element 23 depositing thereon. upstairs.

The first duct 30 comprising at least one tubular element, transversal to the separating wall 6, which is provided with at least a first inlet mouth 31 and at least one first outlet mouth 32 arranged inside the upper zone 7.

Conveniently, the first duct 30 is also provided with a first peephole 33 for controlling the flame.

Furthermore, in a different embodiment, the first duct 30 can rotatably accommodate a first worm screw moved by a first gearmotor.

Advantageously, the first outlet 32 of the first duct 30 is placed above the pellet burner 40, or in any case at a height such as to allow the pellet burner 40 to preheat the lean fuel, intended to feed the fuel burner. poor granules 20, both during its fall and when it is accumulated on the separating wall 6, as illustrated by way of example in Figure 4.

In this regard, it should be noted that the pellet burner 40 comprises a brazier 41 advantageously arranged to generate a mainly horizontal flame, positioned above the separating wall 6, that is, above the plate-like body 21 and the deflector element. 23; this allows the pellet burner 40 to preheat the lean fuel, drying it before the combustion operated by the lean granular fuel burner 20 takes place.

Direction of the flame is facilitated by a suitable mouthpiece 42 placed near the brazier 41.

In this case, the mouthpiece 42 has a substantially circular or elliptical section, however, in a different embodiment it could have a polygonal section.

The pellet burner 40 also comprises combustion start-up means 43, preferably an electric resistance, which favor the start of combustion of the pellets in the brazier 41.

The pellet burner 40 is fed by a second duct 35 for feeding the pellets, which by gravity accumulates in the brazier 41.

The second duct 35 comprising at least one tubular element, transversal to the separating wall 6, which is provided with at least a second inlet mouth 36 and at least one second outlet mouth 37 arranged inside the upper zone 7 near the brazier 41 .

Conveniently, the second duct 35 is also provided with a second peephole 38 for controlling the flame.

Furthermore, in a different embodiment, the second duct 35 can rotatably accommodate a second worm screw moved by a second gearmotor. The operation of the boiler 1 is assisted by management and control means 50, which are operatively connected to the burner. to poor granular fuels 20, to the pellet burner 40 and to the feeding means 9.

More specifically, the management and control means 50 are programmed to automatically activate the pellet burner 40 with different flame intensities during the ignition, modulation and shutdown phases of the boiler 1.

More in detail, when the boiler according to the invention is switched on, the pellet burner 40 is initially ignited, which is followed by the gasification of the lean granular fuel, i.e. the formation of the gas which, mixed with the air, will then feed the fuel. poor granular fuel burner 20.

The pellet burner 40 is then brought to a minimum operating speed during the modulation phase of the boiler, to ensure that the poor granular fuel remains on and at the end, in the extinguishing phase, the flame of the pellet burner 40 is raised again. to avoid that unburnt residues of poor granular fuel remain.

Basically, once a preferred temperature regime has been reached, during which the boiler modulates its power, the function of the pellet burner 40 remains that of preheating the fuel that feeds the burner with poor granular fuels 20 before its transformation into gas takes place. , as illustrated by way of example in Figure 4.

As already highlighted in part, thanks to the preheating operated by the pellet burner 40 it is certain that the gasification of the lean granular fuel begins and that the gasification temperature is higher, consequently limiting the unburnt products.

Another important function of the management and control means 50 is that of implementing an algorithm capable of optimizing the combustion of the pellet burner 40; in practice, the boiler 1 adjusts itself in such a way as to limit the consumption of pellets, since they are the most valuable and expensive fuel, trying to favor as much as possible the use of poor granular fuel.

In a variant embodiment illustrated in Figures 5 and 6, in which the boiler according to the invention has been indicated with the reference number 101, the burner with poor granular fuels 120 is essentially constituted, in its lower part, by a plate-like body 121 , preferably made of refractory material, arranged in a substantially horizontal position inside the compartment delimited by the wall 3, and by a grid 123 housed in a through seat 122.

Advantageously, the grid 123 is surmounted by a protection tile 124 shaped and positioned so as to cover and protect the slots 125 of the grid 123 which put the upper zone 7 in fluid communication with the lower zone 8.

In practice, the protection tile 124 prevents the lean granular fuel from passing directly into the lower zone 8 through the slots 125, instead retaining it in the upper zone 7 where its gasification begins.

During the operation of the boiler 101, the flame generated by the poor granular fuel burner 120 passes through the slots 125 instead.

In this case, the protection tile 124 consists of a portion with a curved section provided with lateral supports 126 which keep it raised with respect to the grid 123, guaranteeing the functionality of the slots 125.

The convexity of the portion with curved section of the protection tile 124 faces the upper zone 7 in order to distribute the lean granular fuel on the plate-like body 121.

According to a further variant embodiment illustrated in Figures 7 and 8, the protection tile, now indicated with the reference number 150, consists of a portion with a trapezoidal section equipped with support feet 151 which keep it raised with respect to the grid 123 ensuring the functionality of the slots 125.

Obviously, the function of the protective plate 150 is substantially equivalent to that of the protective plate 124.

The upper edge of the trapezoidal section portion of the protection tile 150 faces the upper zone 7 in order to distribute, in this case too, the poor granular fuel on the plate-like body 121.

For the embodiment variants illustrated in Figures 5 to 8, the elements which correspond to the elements already described with reference to the embodiment illustrated in Figures 1 to 4 have been marked with the same reference numbers.

In practice it has been found that the invention achieves the intended aim and objects by having created a boiler for the combustion of granular biomass with an innovative burner unit that allows to burn poor fuels without the generation of unburned products and therefore without encountering the problems of "slagging" and "fouling" encrustations which would quickly compromise the functionality of the boiler.

In the boiler according to the invention, these problems are overcome by assisting the combustion of the granular biomass with a pellet burner which preheats the lean fuel before gasification takes place.

Thanks to the preheating operated by the pellet burner, you can be sure that the gasification starts and that the gasification temperature is higher, significantly limiting the unburned products.

Another advantage of the boiler according to the invention consists in the fact that thanks to an appropriate management and control system it is able to automatically adapt to the situation and autonomously manage the ignition and shutdown of the pellet burner, modulating its intensity. of the flame according to the different operating phases of the boiler.

Another advantage of the boiler according to the present invention is constituted by the fact that the consumption of pellets is optimized and reduced to the minimum necessary.

The boiler for the combustion of granular biomass is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept; moreover, all the details can be replaced by other technically equivalent elements.

Of course, the materials used, provided they are compatible with the specific use, as well as the contingent shapes and dimensions, may vary according to requirements and the state of the art.

Claims (12)

CLAIMS 1. Boiler for the combustion of granular biomass, comprising a compartment delimited by a wall equipped with a cavity for containing a heat exchange fluid; said compartment at least partially accommodates a burner unit comprising a separating wall, provided with one or more through openings, which divides the compartment into an upper area and a lower area; said upper zone is adapted to receive and contain combustible products; said lower zone comprises a combustion chamber, placed in depression by suction means, and heat exchange means, in thermal connection with said wall; said boiler further comprises means for feeding at least one combustible product to said burner unit and means for supplying combustion air to said burner unit; said boiler is characterized in that said burner assembly comprises a burner with lean granular fuels and a pellet burner, said pellet burner cooperating with said burner with lean granular fuels to favor the combustion of said poor granular fuels. 2. Boiler, according to the preceding claim, characterized in that said separating wall comprises a plate-like body arranged in a substantially horizontal position inside said compartment; said plate-like body comprises at least one through seat, in which at least one deflector element is housed; said deflector element is shaped and arranged in such a way as to define a plurality of passages adapted to put said upper zone in fluid communication with said lower zone. 3. Boiler, according to one or more of the preceding claims, characterized in that said deflector element comprises an elongated body consisting of a portion with a mushroom section joined to a portion with a trapezoidal section; in use, said portion with a mushroom-shaped section faces towards said upper region; said elongated body has support elements adapted to keep said deflector element in suspension inside said through seat to define said plurality of passages. 4. Boiler, according to one or more of the preceding claims, characterized in that said separating wall comprises a plate-like body arranged in a substantially horizontal position inside said compartment; said plate-like body comprises at least one through seat, in which a grid is housed; said separating wall further comprises a protective tile designed to overhang said grid to prevent said poor granular fuels from falling into said lower zone through the slots of said grid and to preserve the functionality of said slots; said protection tile is shaped and arranged in such a way as to define a plurality of passages adapted to put said upper region in fluid communication with said lower region. 5. Boiler, according to one or more of the preceding claims, characterized in that said protection tile comprises a portion with a curved section provided with lateral supports; in use, said protective tile is raised with respect to said grid, and the convexity of said portion with curved section faces towards said upper region. 6. Boiler, according to one or more of the preceding claims, characterized in that said protection tile comprises a portion with a trapezoidal section provided with supporting feet; in use, said protective tile is raised with respect to said grid, and the upper edge of said portion with trapezoidal section faces said upper region. 7. Boiler, according to one or more of the preceding claims, characterized in that said tile has such a width and length as to allow it to cover and protect the slots of said grid and prevent said poor granular fuels from falling into said lower area through said slots . 8. Boiler, according to one or more of the preceding claims, characterized in that said pellet burner comprises a brazier designed to generate a mainly horizontal flame, positioned above said separating wall; said pellet burner comprises a mouthpiece placed in proximity to said brazier. 9. Boiler, according to one or more of the preceding claims, characterized in that said feeding means for at least one combustible product comprise at least a first feed duct for the fall of said poor granular fuels onto said separating wall. 10. Boiler, according to one or more of the preceding claims, characterized in that said means for feeding at least one combustible product comprise at least a second feed duct for the fall of said pellet onto said brazier of said pellet burner. 11. Boiler, according to one or more of the preceding claims, characterized in that it comprises management and control means operatively connected to said burner assembly and to said means for feeding at least one combustible product; said management and control means are adapted to activate said pellet burner with different flame intensities during the ignition, modulation and shutdown phases of said boiler. 12. Boiler, according to one or more of the preceding claims, characterized in that said management and control means are adapted to implement an algorithm for optimizing the combustion of said pellet burner and limit the consumption of said pellet.