EP3604921B1

EP3604921B1 - Biomass heat generator for domestic use

Info

Publication number: EP3604921B1
Application number: EP19182908.4A
Authority: EP
Inventors: Angelo Zardi
Original assignee: Individual
Current assignee: Individual
Priority date: 2018-08-02
Filing date: 2019-06-27
Publication date: 2021-03-10
Anticipated expiration: 2039-06-27
Also published as: IT201800007792A1; ES2880039T3; EP3604921A2; PL3604921T3; EP3604921A3; DK3604921T3

Description

The present invention relates to a biomass heat generator for domestic use.
In the domestic field, stoves or boilers are known which exploit combustion of biomass for heat generation.
As is known, biomass is an organic material which is obtained by means of a biological process and enables heat to be sustainably obtained, by limiting the emissions of CO₂ during combustion.
Notwithstanding variant embodiments, the operating principle is based on the injection of stoichiometric air inside the firelplace. By increasing the supply of air, the performance improves but so do the emissions in terms of pollutant fumes and particles which, in a certain percentage, are evacuated into the atmosphere.
A more ecological and efficient heat generating technology is represented by pyrolysis and gasification.
Pyrolysis is a process of thermo-chemical decomposition of biomass in the absence of oxidising elements and at high temperatures, generally higher than 400°C.
Differently to pyrolysis, gasification is a thermochemical conversion process of a solid/liquid fuel into "syngas", by means of an external agent (for example air or oxygen or vapour) in adequate quantities.
Pyrogasification is already in use in some industrial sectors, for example in waste combustion plants or cogeneration.
Also known are patio heaters and stoves for cooking in the open, or in semi-closed environments which exploit pyrogasification.
In the domestic field, some stoves are known that function using single-load pyrogasification. In particular, the Applicant has developed some hybrid solutions in which the reaction is a sub-stoichiometric combustion, i.e. poor in oxidising agent. In these solutions no smoke visible to the naked eye is emitted. Further, owing to the fact that temperatures around 700°C and above are generated there is a complete combustion of all the substances, including PAHs (polycyclic aromatic hydrocarbons).
These solutions include the introduction of biomass with a single load carried out from above into the combustion chamber, which is usually delimited by a cylindrical or parallelepiped container. The reaction is not easily controllable, i.e. it is poorly modulable as a function of the heat generated and can be interrupted only with a jet of water into the inside, with an obvious dispersion of smoke into the environment, or by capping the container above and below. Further, the introduction of cold fuel lowers the internal temperature, so the infeed of further fuel, once the reaction has been triggered, is not practicable if not very slowly. The risk is in fact that of interrupting the reaction.
Document WO 2014/064300 describes a biomass heat generator for domestic use according to the preamble of claim 1.
Document US 2007/234937 describes a biomass heat generator comprising two grilles.
In this context, the technical task underlying the present invention is to provide a biomass heat generator for domestic use which obviates the drawbacks in the prior art as described above.
In particular, an object of the present invention is to propose a biomass heat generator for domestic use that has a higher performance and lower emissions with respect to known solutions.
Another object of the present invention is to propose a biomass heat generator for domestic use that enables a continuous supply of the fuel under conditions of safety.
Another object of the present invention is to propose a biomass heat generator for domestic use that is easily controllable, in particular in order to enable modulation of the intensity of the flame on the basis of the amount of heat desired.
Another object of the present invention is to propose a biomass heat generator for domestic use, in which the interruption of the combustion takes place over a short time and without generation of unpleasant emissions.
Another object of the present invention is to propose a biomass heat generator for domestic use that generates fewer combustion residues with respect to known solutions.
Another object of the present invention is to make available a biomass heat generator for domestic use that is compact, structurally simple, easy to maintain, modular, enabled for heating and/or cooking.
The technical task set and the objects specified are substantially attained by a biomass heat generator for domestic use, according to one or more of the accompanying claims.
Further characteristics and advantages of the present invention will become more apparent from the following indicative, and hence nonlimiting, description of a preferred, but not exclusive, embodiment of a biomass heat generator for domestic use as illustrated in the appended drawings, in which:

figure 1 schematically illustrates a biomass heat generator for domestic use according to the present invention in a sectioned view;
figure 2 illustrates a part (first grille) of the biomass heat generator of figure 1, according to a first embodiment;
figures 3a, 3b, 3c illustrate three embodiments of the first grille of figure 2;
figures 4a and 4b illustrate a part (second grille) of the biomass heat generator of figure 1, according to two further embodiments.

With reference to the figures, reference numeral 1 relates to a biomass heat generator for domestic use.
The generator 1 comprises a main box-like casing 2 and a secondary box-like casing 5, both having elongated extensions and branching off from one another.
In particular, the main box-like casing 2 encloses a reaction chamber 3 and a combustion chamber 4 of the gases coming from the reaction chamber 3.
As can be seen in figure 1, the main box-like casing 2 extends substantially vertically, i.e. in height, with the reaction chamber 3 being situated under the combustion chamber 4.
The secondary box-like casing 5 branches off from the main box-like casing 2 at the reaction chamber 3 and has an open end 5a for introducing the biomass.
In branching off from the main box-like casing 2, the secondary box-like casing 5 forms therewith a pre-established angle, denoted by "a", in such a way as to enable descent by force of gravity of the biomass introduced via the open end 5a.
The pre-established angle a is preferably an acute angle, more preferably comprised between 25° and 45°.
The main box-like casing 2 and the secondary box-like casing 5 are preferably tubes having rectangular or square or circular section.
In particular, a hole is made in the main box-like casing 2 at the reaction chamber 3 so as to enable coupling (e.g. by welding) the secondary box-like casing 5.
In a variant embodiment, the secondary box-like casing 5 is a tube that is tapered from its open end 5a towards the branch-off from the main box-like casing 2. Therefore, the diameter of the secondary box-like casing 5 is at a maximum at the open end 5a thereof and reduces as it goes towards the main box-like casing 2.
The main box-like casing 2 and the secondary box-like casing 5 are made of metal or a metal alloy. For example, iron can be used, which has the advantage of being a catalyser. Alternatively, steel can be used.
Means (not illustrated) are preferably provided for interrupting the inflow of fuel from the secondary box-like casing 5 towards the main box-like casing 2. For example, an internal shutter can be used, inside the secondary box-like casing 5, which is moved to open or close using a manual lever outside the secondary box-like casing 5.
The generator 1 preferably further comprises a connecting shield (not illustrated) between the secondary box-like casing 5 and the main box-like casing 2.
The connecting shield is in fact a hood screen which enables retaining the heat emitted by the main box-like casing 2 in the reaction chamber 3, facilitating:

i) formation of an internal hot zone which heats the fuel before entry thereof into the main box-like casing 2
ii) maintaining the heat in the reaction chamber 3

An access hole for igniting the combustion is further afforded in the main box-like casing 2. For example, the access hole (to which a hatch door is associated) is located above the reaction chamber 3. This arrangement enables carrying out ignition from above which occurs immediately and without releasing fumes.
The generator 1 further comprises:

at least a first inlet 6 for the air inside the reaction chamber 3;
at least a second inlet 7a, 7b, 7c for the air into the combustion chamber 4;
a first grille 8 housed inside the main box-like casing 2 underneath the reaction chamber 3;
a second grille 9 housed inside the main box-like casing 2 between the combustion chamber 4 and the reaction chamber 3 at the branching off of the secondary box-like casing 5.

The first inlet 6 for the air is obtained in the main box-like casing 2 below the first grille 8.
In particular, the first inlet 6 is interposed between the first grille 8 and a drawer for the collection of the residues of combustion, denoted by reference numeral 10. The drawer 10 closes the main box-like casing 2 below, i.e. it constitutes the bottom thereof.
The zone between the drawer 10 and the first grille 8 has the purpose of causing the air coming from the first inlet 6 to circulate. In figure 1, the first inlet 6 is constituted by a conduit which opens into the main box-like casing 2. The first inlet 6 is preferably protected by a movable hatch door (not illustrated). In this zone, when the combustion is in full working rhythm the temperatures are maintained very high because there are hot charcoals which are consumed on contact with air. The required quantity of air is modest, thus it is sufficient to open the hatch door of the first inlet 6 only by a little to inject the air necessary, in this way preventing too much heat from being dispersed to the outside.
The second inlet 7a, 7b, 7c for the air is obtained in the main box-like casing 2 above the second grille 9.
In figure 1 the second inlets for the air inside the combustion chamber 4 are three in number, denoted by 7a, 7b, 7c. They are obtained at different heights in the main box-like casing 2 and/or at opposite sides with respect to the combustion chamber 4.
The second inlets 7a, 7b, 7c for the air in the combustion chamber 4 have the function of efficiently burning the gas mix coming from the reaction chamber 3, helping to keep temperatures high.
Realising the inlets at different levels (i.e. heights) in the main box-like casing 2 and on opposite sides thereof with respect to the combustion chamber 4 facilitates the air-gas mixture. In particular, some of the inlets have a fixed inflow rate in order to guarantee a necessary minimum inflow of air. One or more of the inlet holes have an adjustable inflow rate with the purpose of modifying the mixing parameters.
In order to ensure that the air injected into the combustion chamber 4 is already hot, closed pathways are realised (using screening or shields or conduits) which partially envelop the main box-like casing 2, from which they receive heat and reach progressively higher temperatures up to arriving at the inlet (or inlets 7a, 7b, 7c) realised in the main box-like casing 2. The heating of the air injected into the combustion chamber 4 (in the jargon known as "secondary air") is of fundamental importance for increasing the combustion performance.
In the most advantageous solution experimented up to now, a conduit is included which starts from the zone beneath the drawer 10 and extends upwards, being welded to the main box-like casing 2 up to one or more of the inlets 7a, 7b, 7c in the combustion chamber.
The first grille 8 has a curvilinear shape with concavity facing the reaction chamber 3 in such a way as to collect the biomass coming from the secondary box-like casing 5.
In the embodiment of figure 2, the first grille 8 comprises a first frame 18 on which a plurality of first bars 28 is fixed, the plurality of first bars 28 being parallel and bent in such a way as to give the curvilinear shape to the first grille 8.
In particular the first frame 18 has a substantially rectangular shape.
As is visible from figures 3b-3c, the first bars 28 can be bent in such a way as to define a more or less accentuated curve and extend between two opposite sides of the first frame 18.
The distance between adjacent bars 28 is preferably equal to or less than 4 mm. In fact, starting from 6 mm wood pellets, the dimension of the charcoal after contraction by effect of the energy release will be about 4.5 mm. With a distance between the bars 28 of equal to or less than 4 mm, the charcoal is retained by the first grille 8 and thus is subject to the primary air (i.e. coming from the first inlet 6) to be consumed.
The first grille 8 is preferably fitted removably, i.e. not fixed, inside the main box-like casing 2 so that the first bars 28 are parallel to the incoming direction of the biomass from the secondary box-like casing 5.
The first frame 18 is preferably fitted flush with the secondary box-like casing 5 so as to enable a continuous descent of the fuel, i.e. a descent with no jamming.
The first grille 8 is preferably fitted inside the main box-like casing 2 so that the first bars 28 are parallel to the incoming direction of the biomass from the secondary box-like casing 5. In this way, there is a scraping effect on the first grille 8 which facilitates the fall of the cinders and minerals created by the combustion of charcoal.
The variant of the first grille 8 illustrated in figure 3a demonstrates that the first bars 28 do not extend between two opposite sides of the first frame 18 (as in figures 3b-3c). On the contrary, the first bars 18 extend from one side of the first frame 18 up to meeting a flat plate 38 which connects them to the opposite side of the first frame 18.
The second grille 9 comprises a second frame 19 on which a plurality of second bars 29 is fixed, said second bars 29 being reciprocally parallel and being spaced and in a number that allows a quantity of passage of air comprised between 22% to 40%.
The second frame 19 preferably has a substantially rectangular shape. The second bars 29 extend between two opposite sides of the second frame 19. For example, as illustrated in figure 4b, each bar is constituted by a hollow tube having a square section. Alternatively, the tube can have a rectangular or circular section.
Figure 4a instead illustrates a variant in which each bar 29 has the shape of a bent metal sheet with a V or U-shaped transversal section.
The functions of the second grille 9 are:

i) to concentrate the gases that form inside the reaction chamber 3 in such a way as to have a more condensed and rapid flow of combustible gases;
ii) to prevent the secondary air from entering into contact with the fuel, especially during the ignition step, given that the flow of exiting gases distances the secondary air;
iii) to create a turbulence in the expelled gases that as soon as they leave, slow down and mix with the secondary air;
iv) owing to the high temperatures, the material of the second grille 9 (which is made of metal or an alloy) becomes very hot and, especially in the central part thereof, helps in the decomposition of the pollutants
v) to guide the fuel in inlet from the secondary box-like casing 5 to the main box-like casing 2.

Above the combustion chamber 4, the pathway of the gases branches off to then recombine thanks to an annular structure 11 (in the technical jargon called "smoke circuit"), which has the following aims:

i) to absorb the heat emitted from the combustion and radiate it outside into the environment, through an exhaust pipe 12 to which a valve 13 is associated;
ii) to create a mixing zone of the gases sent towards the outlet which, by striking against the walls of the two branches 11 a, 11b of the annular structure 11 slow down and thus facilitate the depositing of the particles.

The annular structure 11 illustrated here is suitable for heating the environment and can vary in shape and dimensions. The annular structure 11 is preferably fitted on the main box-like casing 2 and can be demounted and replaced by other structures suitable for different uses (for example, a cooking hob, a boiler for heating liquids, etc.).
The valve 13 of the exhaust pipe 12 regulates the speed of the overall reactions of the generator 1, thus also enabling regulation of the heat emitted.
The operation of the biomass heat generator for domestic use here proposed is briefly described in the following.
The biomass, having been introduced via the secondary box-like casing 5, enters the reaction chamber 3 and is deposited on the first grille 8. A lighter liquid is sprayed through the access hole realised in the main box-like casing 2 onto the second grille 9 which, as it percolates through the openings thereof, reaches the underlying biomass. The flame can be lit using a long-nozzle lighter.
In this step it is advisable to completely open the valve 13 of the exhaust pipe 12 so as to achieve maximum draught and thus accelerate ignition. As the pyrolysis takes place almost instantaneously, the emission of fumes is practically imperceptible.
The flames fan out to the whole surface area of the biomass and spread to the underlying zone so that the whole volume of biomass present is subjected to pyrolysis.
This step lasts for about 13-20 minutes (as a function of the quantity of biomass injected in the reaction chamber 3) and it is of fundamental importance as it enables reaching the optimal thermal conditions for the following step.
No smoke is emitted as this is a pyrolytic step. In the reaction chamber 3, the fuel undergoes a dimensional reduction due to the yielding of energy and is transformed into charcoal. The volume thus-freed is filled by fresh fuel which falls by force of gravity continuously from the secondary box-like casing 5. The new fuel, thus injected, heats both by the effect of the underlying bed of embers and due to the rising gas flow, and starts pyrolysing. Prior to pyrolysation of all the fuel below, the pyrolysis of the fuel continuously injected via the secondary box-like casing 5 already initiates.
When the parts of biomass below have completed pyrolysis, the gasification of the residual charcoal commences which, in contact with the primary air, dissolves and generates gases and releases heat. The gas generated in this way rises through the coals, mixes with the pyrolysis generated by the fuel, and reaches the combustion chamber 4. In practice, the layer of charcoal is located in the middle, between two different contemporaneous reactions, the pyrolysis above and the gasification below. These reactions thermally sustain one another in order to maintain the overall reaction high.
The descending biomass is already very hot and quickly enters reaction; further the gasification of the charcoal absorbs and burns the oxygen coming from the primary air and removes it from the pyrolytic reaction that takes place above. As it continues to be consumed, the charcoal reduces volume with downwards displacements, leaving space above for inflow of new fuel, already hot (and therefore only a little moist, if at all) as it is heated before entering into the reaction chamber 3.
During this step, the opening of the valve 13 of the exhaust pipe 12 can be regulated to obtain the heat required within a minimum and a maximum.
The continuous downwards flow of charcoal causes a sort of "scraping" of the first grille 8, so that inorganic particles and cinders fall into the drawer 10 beneath.
The reactions continue in the same succession as long as there is fuel in inlet from the secondary box-like casing 5.
To terminate the operation of the generator it is sufficient to interrupt the supply of fuel, for example by capping the free end 5a of the secondary box-like casing 5 with a cover. Alternatively, it is possible to include a flow regulating valve inside the secondary box-like casing 5. The residual fuel downstream of the cover or of the valve continues to flow into the reaction chamber 3. As long as there is fuel present to be pyrolysed, the two reactions continue; when the fuel terminates there is only gasification of the remaining charcoal.
The combustion of the final charcoal alone can last for about 15-20 minutes. During this step there is the maximum emission of CO of the whole process, which is however very modest, practically insignificant.
Before starting a new process, it is wise to remove the residues that have remained on the first grille 8.
From the description provided the characteristics of the biomass heat generator for domestic use according to the present invention are clear, as are the advantages.
In particular, the generator proposed is based on two contemporary reactions which mutually support one another to maintain a high thermal level. This leads to gas emission at high temperature that actuates the cracking of the tars (tar residues, aromatic hydrocarbons).
The gas produced by gasification rises through the overlying layer of charcoal which functions as a filter. A high-temperature reaction environment, as is known, leads to a lower production of chars, but with greater thermal power, and also leads to a greater production of syngas of high thermal quality, given the calorific value of the Tar, which is in combustion-ready conditions.
The heating and drying of the biomass is obtained prior to entry into the reaction chamber, again inside the secondary box-like casing.
The heat generation process takes place in continuous mode and is not dependent on blocks of load.
The generator is compact and thus suitable for use in domestic or assimilated environments.
The operation using natural air is further very advantageous as it makes the generator usable also in geographical areas not on the national electricity grid, or where the connection has been lost due to external causes (i.e. earthquakes).
Further, the generator is easy to assemble and dismantle even by non-expert personnel, i.e. not technical personnel. The modular structure enables easy transportability and maintenance.
The regulation of the heat is also within the grasp of non-technical personnel, as it is sufficient to open/close the valve of the exhaust pipe.
The emissions of pollutant gases are negligible and, even in the worst operating conditions (maximum emissions), are always much lower than the known solutions.

Claims

Biomass heat generator (1) for domestic use, comprising:
a main box-like casing (2) having an elongated extension inside which there are arranged a reaction chamber (3) and a combustion chamber (4) of the gases coming from said reaction chamber (3), said reaction chamber (3) being situated under said combustion chamber (4);

a secondary box-like casing (5) having an elongated extension and branching off from said main box-like casing (2) at said reaction chamber (3), said secondary box-like casing (5) having an open end (5a) for introducing the biomass and defining a pre-established angle (a) with respect to said main box-like casing (2) in such a way that it allows the biomass to descend because of gravity;

at least a first inlet (6) for the air in said reaction chamber (3);

at least a second inlet (7a, 7b, 7c) for the air in said combustion chamber (4);

a first grille (8) housed inside said main box-like casing (2) underneath said reaction chamber (3),

characterised in that it comprises:
a second grille (9) housed inside said main box-like casing (2) between said combustion chamber (4) and said reaction chamber (3) at the branching off of said secondary box-like casing (5) so as to concentrate the gases, said first grille (8) having a curvilinear shape with concavity facing said reaction chamber (3) in such a way as to receive the biomass coming from said secondary box-like casing (5).
Biomass heat generator (1) according to claim 1, wherein said pre-established angle (a) is comprised between 25° and 45°.
Biomass heat generator (1) according to any one of the preceding claims, wherein said first grille (8) comprises a first frame (18) on which (18) a plurality of first bars (28) is fixed, bent in such a way as to give the curvilinear shape to the first grille (8) and parallel to one another.
Biomass heat generator (1) according to claim 3, wherein said first bars (28) are parallel to the incoming direction of the biomass from said secondary box-like casing (5).
Biomass heat generator (1) according to any one of the preceding claims, wherein said second grille (9) comprises a second frame (19) on which a plurality of second bars (29) is fixed, said second bars (29) being parallel to one another and being spaced and in a number that allows the passage of air comprised between 22% and 40%.
Biomass heat generator (1) according to any one of the preceding claims, wherein said at least one first inlet (6) for the air is obtained in the main box-like casing (2) below the first grille (8).
Biomass heat generator (1) according to any one of the preceding claims, wherein said at least one second inlet (7a, 7b, 7c) for the air is obtained in the main box-like casing (2) above the second grille (9).
Biomass heat generator (1) according to claim 7, comprising a plurality of second inlets (7a, 7b, 7c) for the air in said combustion chamber (4), said second inlets (7a, 7b, 7c) being obtained at different heights in the main box-like casing (2) and/or at opposite sides with respect to said combustion chamber (4).
Biomass heat generator (1) according to any one of the preceding claims, wherein said main box-like casing (2) and said secondary box-like casing (5) are tubes having rectangular or square or circular section.
Biomass heat generator (1) according to claim 9, wherein said secondary box-like casing (5) is a tube that is tapered from its open end (5a) toward the branching off from said main box-like casing (2).