WO2014029933A1

WO2014029933A1 - Micro-cogeneration device suitable for biomass boilers

Info

Publication number: WO2014029933A1
Application number: PCT/FR2013/051878
Authority: WO
Inventors: Alain MEMPONTEIL; Alain BENGAOUER; Thiébaut KIENTZ
Original assignee: Commissariat A L'energie Atomique Et Aux Energies Alternatives; Exoes
Priority date: 2012-08-23
Filing date: 2013-08-05
Publication date: 2014-02-27
Also published as: FR2994729A1

Abstract

The invention relates to a domestic device for the cogeneration of electricity and heat, suitable for extracting heat energy from a biomass boiler, said biomass boiler comprising: a furnace; a chamber in contact with the furnace; and substantially tubular cavities arranged close to the outer periphery of the chamber, and said device comprising: a first heat exchanger forming an evaporator capable of being inserted in said chamber of said biomass boiler; an electric generator capable of generating electricity from a driving thermodynamic cycle, said electric generator being connected to said evaporator, a first closed fluid circuit feeding a fluid released from said evaporator toward the inlet of said electric generator, and said fluid released from said electric generator toward the inlet of said evaporator; a second heat exchanger, in contact with said substantially tubular cavities located on the outer periphery of the chamber of said biomass boiler; and a second fluid circuit forming a domestic heating circuit, said second heat exchanger being connected to said domestic heating circuit, said evaporator having, opposite the furnace, a surface for capturing heat radiation, and having a thermally insulating layer on the outer periphery of said evaporator, said evaporator forming a heat screen between the radiation from the furnace and the walls of the chamber, said surface including a tube system forming a circulation path for said fluid.

Description

DEVICE FOR MICRO-COGENERATION ADAPTED TO BIOMASS BOILERS

FIELD OF THE INVENTION The present invention relates to the micro-cogeneration of electricity and heat for essentially domestic applications. The term micro-cogeneration refers mainly to low to moderate powers, of the order of a few kilowatts of electricity. More particularly, the invention relates to a device that is installed on a biomass boiler to draw its thermal energy to both produce electricity and heat the water of a building.

STATE OF THE ART The increasing energy needs of the world's population require the development of increasingly sophisticated techniques of local energy production. In this context, energy production tends to become more and more decentralized and respond to moderate energy needs. Indeed, the production of electrical powers of the order of a few kilowatts for localized applications is an interesting alternative to medium and large power plants, especially in isolated sites. Thus, the use of biomass is part of today's energy mix. Biomass is an abundant resource of organic matter of plant origin that releases chemical energy during its combustion. The energy produced by the combustion of biomass comes from a two-phase process. In a first phase, the biomass is pyrolyzed with production of combustible gas. In a second phase, the residual carbon is oxidized in an exothermic reaction in two stages: a first transformation to slightly exothermic carbon monoxide (CO), and oxidation of CO to carbon dioxide (CO ₂ ) corresponding to a very exothermic reaction . The gases generated during the two phases release energy into the combustion volume of the biomass boiler in the presence of oxygen injected either through the biomass bed or directly into the combustion volume of the gases.

This heat is produced by combustion in biomass boilers, which are now available on the market and which are available in several architectures to optimize energy efficiency. These different architectures play on the modes of combustion. For example, natural draft combustion or reverse combustion with forced or forced draft. On the other hand, the Fuel conditioning has improved the performance of biomass boilers. It is however also necessary to optimize the techniques for collecting this heat to return it in a useful form, for example in the form of electricity or hot water.

The heat resulting from the combustion of the biomass can advantageously be collected in two stages, by the use of two exchangers placed in series on the path of the fumes emitted by the boiler. Thus, as proposed in document US Pat. No. 4,583,495, a first exchanger placed in the zones where the combustion of the biomass takes place, at temperatures in the region of 800 ° C., makes it possible to vaporize the water of a circuit connected to a domestic tank. A second exchanger placed downstream of the first exchanger in an area where the smoke is at lower temperatures (of the order of 200 ° C.) makes it possible to collect an additional quantity of the thermal energy emitted by the boiler and to restore it to the same domestic tank. The device described in this document however does not include efficient means for the micro-cogeneration of electricity and heat, and is a biomass boiler per se, unable to adapt to a biomass boiler that is found in the trade.

There are also biomass boilers designed for micro-cogeneration, as for example that proposed by Jozef Huzvàr and Patrik Nemec in "Proposai of heat exchanger in micro-cogeneration unit, configuration with biomass combustion", the reference being accessible on the link next :

(htip: y Ywww.mtf.stuha.sk/ 'docs / internetovy ^ asopis / lOll / mimoriadne ^ islo / hiizvarj em ec.pdf).

The device proposed in this document is an original biomass boiler, extracting heat from high temperature zones by means of a heat exchanger to drive a current generating motor and extracting thermal energy from the lower temperature zones at the same time. using a second exchanger communicating with a fluid circuit for heating with domestic water.

Another example of a biomass boiler designed for micro-cogeneration is the Bison boiler marketed by Exoès (see, for example, http://www.exoes.com/bison/produitphp). This pellet boiler produces electrical energy from the combustion of biomass through a thermodynamic Rankine cycle fed by heat drawn with an evaporator whose geometry is designed to extract the convective thermal energy in the enclosure of the boiler. The evaporator of this boiler does not optimize the thermal energy extracted by the radiative transfer mode. The use of heat-absorbing structures transmitted by convection into the flue gases for rendering it in the form of radiation is an advantageous practice proposed, for example, in the documents US Pat. No. 5,365,888, US Pat. No. 4,113,009 and WO 96/41101. However, these techniques are not applicable to domestic biomass boilers, since the latter sometimes have geometries designed to promote convective heat transfer, especially for heating applications and for which the structures proposed in these documents. do not transpose directly into such devices.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a device for the micro-cogeneration of electricity and heat that can be installed on a domestic biomass boiler of the type found on the market, by optimizing the portion of thermal energy converted into electricity.

To achieve this, the present invention relates to a cogeneration device for electricity and domestic heating capable of extracting thermal energy from a biomass boiler, said biomass boiler comprising:

• a home,

• an enclosure in contact with the fireplace,

Substantially tubular cavities arranged near the outer periphery of the enclosure,

the device further comprising:

^■ a first heat exchanger forming an evaporator adapted to be inserted into said chamber of said biomass boiler,

^■ an electricity generator adapted to generate electricity from a thermodynamic cycle engine, said power generator being connected to said evaporator,

^■ a first closed fluid circuit carrying the fluid exiting from said evaporator to the input of said power generator, and the fluid exiting from said power generator towards the inlet of said evaporator; a second heat exchanger, in contact with said substantially tubular cavities, located on the outer periphery of the enclosure of said biomass boiler, ^■ a second closed fluid circuit, forming a domestic heating circuit said second heat exchanger being connected to said domestic heating circuit.

In this device, the evaporator has, facing the focus, a thermal radiation capture surface, and having on the outer periphery of the evaporator, a thermally insulating layer. The evaporator thus forms a heat shield between the radiation from the hearth and the walls of the enclosure. More specifically, the thermally insulating layer is interposed between the first heat exchanger and the walls of the enclosure in particular to thermally isolate the two heat exchangers. The radiation capture surface includes a tubing, describing a fluid flow path.

The device proposed by the Applicant is therefore a set of elements allowing the extraction of a fraction of the heat produced inside a biomass boiler. A biomass boiler having at least one fireplace, and an enclosure surrounding the fireplace is required to accommodate the characteristic evaporator. This evaporator forms a heat exchanger which extracts the heat transmitted via a substantially radiant transfer mode in the enclosure surrounding the focus of the biomass boiler. Indeed, in this zone, the combustion of the biomass requires having a high temperature, generally between 500 ° C and 900 ° C. At these temperatures, the gases, the dust and the hot walls inside the enclosure surrounding the hearth radiate thermal energy that is captured by the evaporator. Convection is another mode of transfer that participates in heat transfer to the evaporator, although it occupies a less important place. The particular geometry of the evaporator, arranged all around the furnace of the boiler makes it possible to avoid losses of radiation towards the outside of the enclosure surrounding the furnace, while optimally capturing the radiation produced in the center of the furnace. pregnant surrounding the hearth. The thermally insulating layer formed on the outer periphery of the evaporator makes it possible to limit the radiative leakage from the enclosure containing the hearth towards the walls of the enclosure containing the hearth. The evaporator transmits this sensed thermal energy to the fluid flowing through it, which fluid can advantageously pass from the liquid state to the vapor state, and then actuates a motor thermodynamic cycle in an electricity generator. The object of the invention is therefore essentially to optimize the share of electric energy produced in a biomass boiler for the cogeneration of electricity and heat by optimizing the portion of energy, essentially radiative, transmitted to the evaporator inserted in a biomass boiler. The first heat exchanger, the electricity generator and the first fluid circuit thus form a closed fluid circuit, making it possible to transform part of the thermal energy of the furnace hearth into electricity. Advantageously, the first heat exchanger is placed in an area of the boiler where the temperature is high, between 500 ° C and 900 ° C, in order to evaporate a fluid flowing through the heat exchanger to actuate a thermodynamic cycle of an electric generator .

On the other hand, the biomass boiler, on which the Applicant's device is installed, advantageously has an architecture for installing a second heat exchanger on a substantially peripheral area to the enclosure surrounding the fireplace. In this zone, where substantially tubular cavities allow the fumes produced by the combustion of biomass to follow a path leading ultimately to the external environment of the biomass boiler, the flue gas temperature is lower, and the transfer mode dominant thermal is convection. The second heat exchanger which is installed in contact with the substantially tubular cavities is part of a closed second fluid circuit which is heated by the flue gases circulating in the substantially tubular cavities. These fumes transmit the thermal energy by convection to the walls of the exchanger, to raise the temperature of a fluid flowing in the second closed fluid circuit and used for home heating.

The first circuit and the second circuit form two separate closed fluidic circuits to allow the first fluid circuit to generate electricity and the second fluid circuit to provide home heating. The need for thermal energy being different for these two applications, the two fluid circuits are advantageously separate to optimally convert the thermal energy produced by the biomass boiler. The first heat exchanger is placed in the enclosure in contact with the fireplace to allow the transfer of sufficient thermal energy for the operation of an electricity generator. The second heat exchanger is placed outside and on the periphery of the enclosure to provide the thermal energy necessary for domestic heating. Specifically, the first heat exchanger is in contact with a zone whose temperature is generally between 500 ° C and 900 ° C, the second heat exchanger is in contact with areas where the temperature of the smoke is around 200 ° C. A thermally insulating layer is advantageously interposed between the two heat exchangers in order to maintain this temperature difference between the exchangers.

According to a particular embodiment, the nozzle of the evaporator is configured in a helicoid with contiguous turns. This particular geometry of the evaporator makes it possible to encircle the inner periphery of the enclosure surrounding the hearth, and thus to optimize the share of thermal energy transmitted by radiation to the evaporator. Since the turns are contiguous, the total area that the evaporator occupies on the side walls of the enclosure surrounding the hearth is increased, and the radiative leakage from the enclosure surrounding the hearth and between the helical-forming turns are greatly reduced. It is possible, however, that the turns are not completely contiguous, radiative leakage to the outside of the enclosure containing the focus being limited by the presence of a thermally insulating layer on the outer periphery of the evaporator.

According to another embodiment, the evaporator is the assembly of at least one substantially cylindrical metal plate corrugated on a substantially cylindrical metal plate, the corrugations of the substantially cylindrical corrugated metal plate defining a circulation path of the fluid on the periphery inside the evaporator.

This particular geometry of the evaporator makes it possible to encircle the inner periphery of the enclosure surrounding the hearth, and thus to optimize the share of thermal energy transmitted by radiation to the evaporator. The substantially cylindrical metal plate may for example be a sheet. The non-corrugated sheet forms a heat shield that does not allow the radiation to pass through the depressions formed by the corrugated sheet. Thus the radiative leakage from the enclosure surrounding the hearth is greatly reduced. Ultimately, this particular embodiment has substantially the same advantages as a helicoid with contiguous turns. It may also have a greater freedom in terms of design: it may for example lead to the realization of more advantageous forms for the heat transfer and / or the mechanical strength of the evaporator and / or its manufacturing cost. A method of manufacture by hydroforming can meet these criteria.

In particular, the boiler may comprise a structure forming a heat shield advantageously having a skirt shape, in the extension of the evaporator, the skirt being integral with the evaporator and being disposed on one end of the evaporator.

This heat shield makes it possible, on the one hand, to participate in maintaining a higher temperature in the enclosure surrounding the hearth, which makes it possible to burn the fuel better. biomass, and allows on the other hand to increase the proportion of thermal energy transmitted to the evaporator.

According to one embodiment, the biomass boiler also comprises a tubular metal structure forming a ferrule positioned above the hearth.

Different architectures of bio mass boiler are suitable for the installation of the device forming the invention. Biomass boilers that include a ferrule above the fireplace can improve combustion in the enclosure surrounding the home by restricting the flow of fumes from the combustion of biomass. On the other hand, such a ferrule participates in the emission of heat by radiation, because of its high temperature. The radiation of the ferrule is thus transmitted to the evaporator, contributing to an optimization of the proportion of thermal energy of the biomass boiler transmitted to the evaporator to supply the electricity generator.

According to a particular embodiment, the thermally insulating layer of the evaporator may be a layer made from a fibrous material.

The insulation of the surface forming the outer periphery of the evaporator is preferable to prevent the walls of the evaporator from transmitting a portion of the heat stored by these walls to the wall of the enclosure surrounding the fireplace. The thermal energy that would be transmitted to the wall of the enclosure surrounding the hearth would not participate in raising the temperature of the fluid flowing in the evaporator, and would therefore be considered lost. By thermally insulating the surface forming the outer periphery of the evaporator, such heat losses do not occur. The use of fibers, such as rock wool, or a rigid material such as ceramic fiber, advantageously meet the need for thermal insulation formulated above. According to another embodiment, the device comprises a metal element forming a radiating web disposed at least partially facing the inner surface of the evaporator.

The use of a radiating veil provides several advantages. On the one hand, at high temperature, for example when the biomass boiler is operating, which corresponds to temperatures typically between 500 ° C. and 900 ° C., the radiating web re-emits heat by radiation, which heat is absorbed at less in part by the evaporator. On the other hand, the radiating veil can by its geometry particular to participate in a stabilization of the temperature in the enclosure surrounding the hearth. The temperature in the enclosure surrounding the fireplace varies as the rate of oxidizer (oxygen) fluctuates in the fireplace. As the rate of oxidizer increases, the temperature decreases, and convection becomes an increasingly important heat transfer mode in the heat exchange in the enclosure surrounding the hearth. The radiating web captures this thermal energy by convection, and restores it by radiation, this radiation being absorbed at least in part by the evaporator.

According to a particular embodiment, the radiating web comprises a set of substantially rectangular metal plates disposed in a circle and perpendicular to the perimeter of said circle.

According to a particular embodiment, the pads of the radiating web are all connected by two metal rings, these rings being in contact with two diametrically opposite ends of each of said plates, said plates comprising two diametrically opposed strips partially cut on two opposite sides of said plate and folded in opposite directions.

These particular geometries of the radiating web are designed so as to optimize the absorption of thermal energy by convection of the fumes in the enclosure surrounding the hearth and in the vicinity of the radiating web.

According to another embodiment, the first closed fluidic circuit is provided with means adapted to actuate a mechanism for bypassing the electricity generator.

This bypass mechanism ensures the maintenance of the flow in the first fluid circuit in the event of failure of the electricity generator and / or in the starting and / or stopping phases of said electricity generator. Moreover, this bypass mechanism can advantageously be controlled remotely and automatically in case of failure or problem on the apparatus serving as an electricity generator according to a motor thermodynamic cycle.

According to another embodiment, the first closed fluidic circuit comprises a condenser connected to the electricity generator, able to exchange the residual heat output of the electricity generator with the domestic heating circuit. This heat energy can also be returned to the domestic heating circuit, whether in a hot water tank or at any other point in the domestic heating circuit. According to another embodiment, the first closed fluidic circuit comprises a condenser connected to the electricity generator, able to exchange the residual heat output of the electricity generator with a third closed fluid circuit.

The use of a condenser makes it possible to recover the residual heat energy at the output of the apparatus serving as an electricity generator according to a motor thermodynamic cycle. This thermal energy is thus transferred to a third closed fluid circuit, said thermal energy can then be reused elsewhere according to the needs of the user. According to another embodiment, the third closed fluidic circuit comprises a recuperative heat exchanger in contact with the domestic heating circuit.

In this particular embodiment, the residual thermal energy recovered in the third closed fluid circuit is returned to the second domestic heating fluid circuit to further heat the fluid flowing in this circuit.

SUMMARY DESCRIPTION OF THE FIGURES

The invention will be better understood on reading the description which follows, given solely by way of example, and made with reference to the appended drawings, in which the same references denote identical or similar elements and in which:

Figure 1 is a schematic sectional view of a biomass boiler provided with a micro-cogeneration device of electricity and heat showing three fluid circulation circuits, according to a first embodiment; and

Figure 2 is a schematic perspective view of an evaporator provided with a heat shield skirt; and

Figure 3 is a perspective view of a radiating web; and

- Figure 4 is a schematic sectional view of a biomass boiler equipped with the micro-CHP of the invention according to the first embodiment of the invention; and FIG. 5 is a diagrammatic representation of a possible arrangement of the fluidic circuits of a biomass boiler equipped with the microcheater of electricity and heat of the invention according to a second embodiment of the invention; and

FIG. 6 is a diagrammatic representation of a possible arrangement of the fluidic circuits of a biomass boiler equipped with the microcheater of electricity and heat of the invention according to a third embodiment of the invention; and

FIG. 7 is a schematic perspective view of an evaporator according to a fourth embodiment, and

Figure 8 is a schematic sectional view of a biomass boiler equipped with the micro-CHP of the invention according to a fifth embodiment of the invention; and Figure 9 is a schematic sectional view of a biomass boiler equipped with the micro-CHP of the invention according to a sixth embodiment of the invention.

Some elements of these figures have been enlarged to facilitate their comprehension and are therefore not scaled.

DETAILED DESCRIPTION OF THE INVENTION

It will now be described a device for the micro-cogeneration of electricity and heat that can be installed on a domestic biomass boiler.

The device, as illustrated in Figure 1, comprises a domestic biomass boiler of the type found on the market. The boiler architecture shown in FIG. 1 is that of a forced draft rising heat type boiler, but the proposed device can also be used for other boiler architectures provided that it possesses the elements that are presented. hereinafter.

The boiler of FIG. 1, shown diagrammatically in section, has a duct 1 for conveying the biomass fuel (pellet, wood, organic material) as well as providing an air inlet 2, forming a source of oxidant (oxygen) , and therefore oxygen to the furnace 3 of the boiler in which fuel and oxidant (oxygen) can generate the exothermic reactions. A shell 4 placed above the firebox 3, confines the combustion of the biomass and makes it possible to constrain along a substantially vertical axis the flow of smoke and gases escaping from the hearth 3 when the boiler is operating. In operation, the fumes from the boiler escape the hearth 3 to stay inside an enclosure 5 in which the exothermic reactions continue. This enclosure 5 is closed on its upper part by a cover 23 making the enclosure 5 thermally insulated. The residence time of the fumes in the chamber 5 is long enough to allow complete combustion of the biomass. In addition, the absence of convection on cold surfaces makes it possible to avoid a large local cooling of the gases that can affect the efficiency of the combustion. By maintaining a high temperature, typically between 500 ° C. and 900 ° C., the exothermic reactions can continue until the end, that is to say that a large part of the chemical energy of the biomass can be extracted, thus increasing the efficiency of the boiler. The enclosure 5 has in its lower part, near the hearth 3, openings forming a passage 10 allowing the smoke to escape.

Smoke is understood to mean both the combustible gases produced by the pyrolysis of the biomass and the oxidation of the residual carbon that the flue gases contained in the boiler.

Under the enclosure 5, the fumes produced by the combustion of the biomass pass through a second chamber before going up through substantially tubular cavities 11 that can advantageously be cylindrical or constitute a tubular ring, distributed over at least a portion of the circumference of the boiler. These cavities 11 are not in direct contact with the outer walls of the enclosure 5. Indeed, the cavities 11 may and preferably are themselves surrounded by an empty cavity in which a fluid can flow. This set of cavities may serve to define an exchanger 12. The smoke rises along these cavities 11 to reach a third chamber 13 in the upper part of the boiler, which may advantageously comprise means for sweeping 24 tar and dust depositing inevitably in this part of the boiler, as well as on the walls of the cavities 11.

Ventilation means 14 are placed on the outlet of the flue gas path resulting from the combustion of the biomass, in order to impose a flow direction on said flue gases. It is apparent from the description that has just been made of the path of the smoke produced by the biomass boiler that this smoke follows a sinuous path from the hearth 3 to the third enclosure 13. This type of path makes it possible to separate areas where the temperature of the smoke is high (around 700 ° C near the hearth 3), areas where the temperature of the smoke is more moderate (around 200 ° C in cavities 11). On the other hand, by lengthening the path that follows the smoke, the temperature gradient of said smoke in the boiler is lower and avoids sudden temperature changes, while decreasing the temperature of the smoke output of Boiler. All the elements described so far are specific to a particular type of boiler, present in the trade, and compatible with the device that constitutes the invention described below. It is also possible to adapt the device of the invention to other boiler architectures, provided that they contain most of the elements that have just been presented. In particular, and by way of example, it is possible to install the invention on biomass boilers with reverse combustion forced draft or not.

As represented in FIG. 1, and according to one embodiment of the invention, the enclosure 5 of a biomass boiler as described above, is equipped with a first heat exchanger 6 also called an evaporator, forming part of integral part of a closed fluidic circuit 100. The evaporator 6 comprises a pipe made of a material having good properties of mechanical and thermal conduction, wound so as to form a helicoid with contiguous turns, describing a circulation path on a surface intended to to be arranged facing the focus 3 and / or the shell 4, and at least partially in contact with the walls of the enclosure 5. A detailed diagram of an evaporator 6 according to this embodiment of the invention is shown in Figure 2. It may be in an alternative embodiment that the turns of the evaporator 6 described above are not contiguous. It is also conceivable to make an evaporator 6 having a different geometry, so for example to adapt to the size and shape of the enclosure 5 of the biomass boiler. In the interest of a better collection of thermal energy it is advantageous to manufacture an evaporator 6 having a surface and a form factor maximizing the heat exchange while modifying only marginally the flow of smoke and heat. In particular, it is possible to adapt the total area occupied by the evaporator in the chamber 5 to extract a more or less significant fraction of the radiant heat energy. The larger the surface occupied by the evaporator 6 in the enclosure 5, the greater the portion of thermal energy converted into electricity in the biomass boiler for micro-cogeneration. The evaporator pipe 6 is designed to circulate a fluid within said pipe, and withstand the high pressures of a gas able to flow in the pipe. Because of its small size, the evaporator 6 does not require specific approval and does not present any particular risk arising from the possible presence of high pressure gas in the pipe constituting the evaporator 6. Connections are provided for connect the ends of the pipe of the evaporator 6 to the closed fluid circuit 100. On the other hand, the boiler may also comprise a skirt 7, integral with the evaporator 6 and arranged in the extension of the helical structure with contiguous turns formed by the pipe. This skirt 7 serves radiative screen so as to avoid a loss of heat inside the chamber 5 by radiation under the evaporator 6. Indeed in this area, the radiation of the shell 4 can escape of the enclosure 5 without transferring heat to the fluid of the evaporator 6. The skirt 7 radiating screen makes it possible to return this thermal energy to the enclosure 5, which contributes to not unnecessarily lowering the temperature of the enclosure 5 and thus to favor a better combustion of the mass mass and to guarantee a higher temperature in the enclosure 5.

According to another embodiment of the evaporator 6, shown in Figure 7 the evaporator 6 may be the arrangement of at least two metal plates or at least two sheets. These sheets can be welded to each other so as to describe a circuit, and the injection of a pressurized fluid into the non-welded space between the two sheets allows by hydroforming to create ripples in space between the two sheets thus defining a tubular flow path for a fluid, over the entire surface formed by the sheet defining the outer wall of the evaporator 6. According to this embodiment, the evaporator 6 does not show, as in the case of the helicoid with contiguous turns, no through opening can let out thermal energy by radiation between two corrugations of the tubing defining the flow path of the fluid. On the other hand, the sheet defining the outer wall of the evaporator may have thermal insulation properties.

As indicated in FIGS. 1, 4, 8 and 9, the evaporator 6, 60, 600 comprises a layer of thermal insulation 8, 80, 800 disposed on the outer periphery of the evaporator 6, 60, 600, interposed between the walls of the enclosure 5, 50, 500 and the evaporator 6, 60, 600. This thermal insulation 8, 80, 800 also allows to avoid heat losses by radiation to the outside of the enclosure 5, 50, 500 from the evaporator 6, 60, 600. Thus, the heat energy transmitted by radiation is used more effectively in the enclosure 5, 50, 500. This thermally insulating layer 8, 80, 800 , in particular makes it possible to obtain less than 20% loss of thermal energy captured by the evaporator 6, 60, 600. It can be fibrous, and comprise rock wool or ceramic fiber for example. It can also be rigid, comprising a ceramic material. It can also be envisaged to make it by projection of alumina on the outer periphery of the evaporator 6, 60, 600. According to one particular example, a 15 mm thick ceramic fiber layer is used. It has a thermal conductivity of the order of 0.1 Watt / m / ° C. The skirt 7 and the insulating layer 8 are elements that are useful for optimizing the heat transfer modes in the chamber 5 towards the evaporator 6. By making it possible to maintain the temperature in the enclosure 5 without loss of heat to the outside of the enclosure 5, these elements allow an increase in the temperature of a value close to 100 ° C, to reach up to 900 ° C in a domestic biomass boiler. Such a temperature makes it possible, on the one hand, to increase the emission of radiation, and therefore to give greater advantage to this mode of heat transfer in the enclosure 5 towards the evaporator 6. Thus, the particles with a high temperature of the smoke produced by the combustion of the biomass in the enclosure 5, the walls of the shell 4, the walls of the evaporator 6 and so-called participative gases (such as carbon monoxide and water vapor), radiate from the energy which is at least partially transmitted in fine to the fluid flowing in the evaporator 6. The radiation is the dominant heat transfer mode in the chamber 5 and it has the additional advantage of extracting thermal energy the entire volume of smoke, gases and particles present in the chamber 5, and not only the energy of the gases and particles in direct contact with the walls of the evaporator 6. The other two modes of heat transfer, namely conduction and convection are themselves if implemented to heat the fluid of the evaporator 6. The circulation, although reduced and strongly constrained, of the smoke inside the chamber 5, ensures homogenization of the temperature in the enclosure 5 and therefore contribute to convective heat transfer. The main thermal transfer mode implemented in the evaporator 6 between the metal pipe forming a helicoid with contiguous turns and the fluid flowing in said pipe is the conduction in the material forming said pipe. An elevated temperature in the enclosure 5, favoring radiation heat transfer, provides another considerable technical advantage which is that of significantly reducing the fouling of the walls of the enclosure 5 and the evaporator 6. lower temperatures favor the deposition of tar, dust and other substances which increase, by depositing, the thermal resistance of the various elements present in the enclosure 5, decreasing the energy efficiency of the biomass boiler. Thanks to the improvements provided by the present invention, it is not necessary to provide a regular sweeping of the enclosure 5. In addition to a higher temperature and more homogeneous than in boilers not equipped with the device of the invention, the reduced size surfaces constituting the enclosure 5 and their simple shape which does not present particular roughness, also contributes to reduce fouling in the latter. The enclosure 5 is advantageously a cavity, of which the only thermal outlet for the radiative energy, with the exception of the flue gas outlet, is the evaporator 6 and in which all the walls are thermally insulated. It is also advantageous to have a reduced contact surface between the fumes at high temperature and the walls and elements at low temperature present in the enclosure 5 so as not to undergo heat loss by convection (and a fortiori by conduction in the walls) without this heat being transmitted to the evaporator 6 and therefore without it being recovered later. The mode of convective heat transfer is however also implemented and makes it possible to transfer heat in contact with the evaporator 6, thanks to the circulation of smoke, gases and particles in the enclosure 5.

It is possible to optimize the radiation heat transfer by placing a second device forming a radiating web around the shell 4 located above the firebox 3. This radiating web 9 as represented in FIG. 3 , is in the form of a set of plates 92 arranged on the perimeter of a circle, each plate 92 being disposed perpendicularly to said circle, and said plates 92 are all held at their upper and lower ends by two metal annular structures 91 connecting the plates 92 by diametrically opposite ends. As shown in FIG. 3, the plates 92 advantageously have strips 93 partially cut in said plates 92 near two opposite ends of said plates 92, and folded in opposite directions so as to generate convection movements of the smoke in the lower part of the enclosure 5. This particular radiating sail geometry 9 creates a flow of smoke favoring the convective transfer of heat to the radiating veil 9. The absorption of this heat by the radiating veil 9 raises the temperature of the latter which re-emits thermal energy by radiation in part towards the evaporator. Other geometries are conceivable to constitute a radiating veil 9, and their manufacture is now well documented in the prior art. The radiating veil 9 also fulfills other interesting functions. Its temperature being higher than that of the evaporator 6, the gases of the smoke in contact with the radiating web 9 remain at temperatures sufficient for the combustion to continue in the enclosure 5, which among other things has the effect of reducing moreover the fouling in this part of the enclosure 5. The shape of the radiating web can be optimized so as to promote a good mixture between fuel and oxidant (oxygen), so as to further improve the efficiency of the boiler . Moreover, the radiating veil plays a stabilizing role on the temperature inside In fact, the variations in concentration in the fuel / oxidant mixture cause temperature changes in the boiler, insofar as a higher concentration of oxygen (oxidizer) decreases the combustion temperature and gives rise to a decrease in radiative transfer. As the oxygen concentration increases, the convection in the enclosure 5 also increases due to the larger volume of smoke. Thanks to the radiating veil 9, this increase in convection contributes to raising the temperature of the radiating web which retransmits this heat by radiation to the evaporator 6. The heat, resulting from the combustion of the biomass, and collected in the enclosure 5 by the fluid flowing in the evaporator 6, makes it possible to change the liquid / gas phase of the fluid flowing in the evaporator 6. It is also possible to simply raise the temperature of the circulating liquid in the evaporator 6 without necessarily induce phase change, although this is not a preferred mode of operation of the device. The pressurized gas generated by this heat transfer in the evaporator 6 then travels along the closed fluidic circuit 100 firstly up the evaporator 6 to an electricity generator advantageously operating according to a motor thermodynamic cycle of the type Rankine 16. The pressurized gas is used to start a Rankine cycle in this electricity generator 16, which generates electricity by operating an alternator. This electricity is then transferred to an electrical network 17, or stored in a battery or other device for storing the electrical energy provided for this purpose. The lower temperature and pressure gas at the output of the electricity generator 16 is then sent to a condenser 18 acting as a heat exchanger. As shown in FIG. 1, the valve 15 makes it possible to configure the closed fluidic circuit 100 in two positions, namely: a first position of the valve 15 connects the evaporator 6 to the electricity generator 16, and a second position of the valve 15 connects the evaporator 6 directly to the condenser 18 without passing through the electricity generator 16. This switching from one position to the other can be operated automatically in the event of failure of the electricity generator 16 or during the phases of operation. stop and start. Moreover, other means of bypassing the motor valve 15 are possible. In particular, a so-called "by-pass" device can be envisaged. As indicated in FIG. 1, the closed fluidic circuit 100 comprises a lifting pump 19 connecting the condenser 18 to the evaporator, ensuring a continuous circulation of the fluid in the closed fluidic circuit 100, and making it possible to maintain an adequate pressure of the fluid in upstream of the electricity generator 16. By following the path taken by the smoke in the boiler, and as shown in FIGS. 1 and 4, the gases, particles and other emissions due to the combustion of the biomass flow from the enclosure 5 through the openings forming a passage 10 to a second chamber located under the enclosure 5 and then to the cavities 11 located around the enclosure 5 and on at least a portion of the circumference of the biomass boiler. As shown in Figure 1, a second fluid circuit 200 adjacent the walls formed by the cavities 11. This fluid circuit 200 corresponds for example to the water heating of a building. It may, for example, include domestic heating means, such as radiators 22. The sections of this second fluid circuit 200 in contact with the walls of the cavities 11 form a second heat exchanger 12. The temperature of the flue gases in the ducts 11 being of the order of 200 ° C, the main mode of heat transfer in this second exchanger 12 is not the radiation but the convection of the smoke in the ducts 11, followed by a conduction of heat in the walls of the second exchanger 12. Due to the lower temperatures of the order of 200 ° C prevailing in the ducts 11, the walls of these ducts are obviously more prone to fouling than the enclosure 5. For this reason, it is advantageous to provide means for sweeping 24 ducts 11, which may for example be arranged in the chamber 13 located on the upper part of the biomass boiler.

Such an arrangement for the second fluidic circuit 200 has been experimentally validated as making it possible to optimize the proportion of electrical energy produced from the heat extracted from the combustion of the biomass. Indeed, it is recommended to extract most of the heat generated by the combustion of the biomass by a transfer mode radiating in the chamber 5, which implies inter alia having a low surface area to volume ratio, and to draw the remaining thermal energy by an essentially convective mode of heat transfer in a zone of lower temperature, which implies having a high surface area to volume ratio. The conversion of thermal energy into electrical energy is thus optimized, and the temperature difference between the fumes at about 200 ° C. in the ducts 11 on the one hand and the fluid flowing in the second fluid circuit 200 on the other hand, is enough to efficiently heat a building. Furthermore, the contact surface between the smoke flowing in the ducts 11 and the walls of said duct 11 is greater than in the enclosure 5, which is relevant to promote heat exchange based on convection.

As indicated in FIG. 1, the invention may also comprise a third closed fluid circuit 300, which makes it possible to reuse the residual heat energy in output of the electricity generator 16 in the condenser 18 to reinject it into the second fluid circuit 200 via a recuperator exchanger 21. Thus, the condenser 18 serves as an interface between the first closed fluid circuit 100 and the third closed fluid circuit 300, while the recuperator exchanger 21 serves as an interface between the third closed fluid circuit 300 and the second fluid circuit 200. The third closed fluidic circuit 300 can be traversed by a fluid having a high heat capacity, for example water. Moreover, to facilitate the circulation of this fluid in this third closed fluidic circuit 300, the latter can advantageously comprise a pump 20. This recovery of the residual heat energy at the output of the electricity generator 16 makes it possible to obtain cogeneration substantially equal to the efficiencies obtained in heating systems without cogeneration devices.

The preferred embodiment of the invention which has just been described may include variants without however departing from the general idea of the invention. For example, the architecture of the domestic boiler on which the device is installed can be substantially different in its shape, its dimensions and its mode of combustion.

FIG. 8 shows, by way of nonlimiting example, a variant of a biomass boiler for the micro-cogeneration of electricity and heat in which the arrangement of the various elements presented above differs substantially from a biomass boiler. with forced draft heat. Thus, in this Figure 8, the fumes follow a sinuous path from the fireplace 30 to the ventilation means 140 to the outside. In this configuration, the exchanger 120 associated with the domestic heating circuit 200, is distributed both on the outer periphery of the enclosure 50, and at a distance from this enclosure, in the vicinity of the outlet mouth of the fumes. According to the embodiment shown in FIG. 8, the biomass boiler for the micro-CHP does not contain a ferrule around the hearth 30, but an enclosure made of refractory materials 40. This enclosure 40 fulfills the same functions as a ferrule, namely ensure guiding fumes and promote a rise in the combustion temperature. The enclosure 50 comprises on its side walls an evaporator 60, a skirt 70, a thermally insulating layer 80 and its upper part is covered by a wall 230 partially forming a lid. The mouth of the chamber 40 containing the hearth 30 may be equipped with a radiating web 90. The smoke escapes from the enclosure 50 through an opening disposed on the upper part of one of the side walls of the enclosure 50, as shown in FIG. 8. Figure 9 shows another variant given by way of non-limiting example of a biomass boiler for the micro-cogeneration of electricity and heat equipped with the device of the present invention. The biomass boiler shown in Figure 9 is a forced draft reverse combustion boiler. According to this embodiment, a ventilation means 1401 conveys oxidant into a hearth 330 and forces the gases and fumes produced by combustion to circulate to an enclosure 500 located below said hearth 330. The enclosure 500 comprises an evaporator 600 on its side walls and an insulating layer 800, a skirt 700, but the fumes escape from the enclosure 500 through substantially tubular zones 1100 located above the hearth 330 and not on the immediate outer periphery of enclosure 500. The substantially tubular zones have walls in contact with the second heat exchanger 1200 associated with the domestic heating circuit 200.

The arrangement of the various fluidic circuits may also vary according to the embodiments of the invention. For example, as shown in FIG. 5, the heating circuit of a building 200 can be directly connected to the condenser 18 of the first closed fluid circuit 100. In this way, it is not necessary to use a third fluid circuit. closed 300. In Figure 6, a variant proposes to connect the third closed fluid circuit 300, when present, directly to the domestic heating means 22, which may be radiators, water tanks or other.

Ultimately, the invention described above provides the following advantages:

To propose a device integrating on a domestic biomass boiler of the type of those which one finds in the trade.

Offer overall returns that are substantially identical to systems offering only domestic heating means by optimizing the convective heat transfer for heating and recovering the residual heat energy at the output of an electricity generator.

- Optimize radiant heat transfer in areas where biomass combustion takes place.

To allow a reduction in the size of domestic biomass boilers through this optimization, ensuring a low surface-to-volume ratio in areas where combustion takes place and a high surface-to-volume ratio in areas where convection exchange with Fluidic circuit heating of a building takes place.

- Do not require approval and specific safety measures due to the presence of an evaporator, because of its reduced dimensions.

Claims

An electricity and domestic heating cogeneration device capable of extracting thermal energy from a biomass boiler, said biomass boiler comprising:

• a home (3),

An enclosure (5) in contact with the hearth (3),

Substantially tubular cavities (11) arranged near the outer periphery of the enclosure (5),

and said device comprising:

^■ a first heat exchanger forming an evaporator (6) insertable into said enclosure (5) of said biomass boiler,

^■ an electricity generator (16) adapted to generate electricity from a thermodynamic cycle engine, said power generator (16) being connected to said evaporator (6),

^■ a first closed fluid circuit (100) conveying a fluid exiting said evaporator (6) to the input of said power generator (16) and said fluid exiting from said power generator (16) to the inlet of said evaporator (6 );

^■ a second heat exchanger (12) in contact with said substantially tubular cavities (11) located on the outer periphery of the enclosure (5) of said biomass boiler,

^■ a second closed fluid circuit (200), forming a domestic heating circuit said second heat exchanger (12) connected to said domestic heating circuit (200);

said evaporator (6) having, facing the hearth (3), a heat radiation capture surface, and comprising a thermally insulating layer (8), disposed on the outer periphery of the evaporator, interposed between the walls of the enclosure and the evaporator, said evaporator (6) forming a heat shield between the radiation from the hearth (3) and the walls of the enclosure (5), said surface including a tubing, describing a flow path of said fluid.

2. Device according to claim 1, characterized in that the tubing of the evaporator (6) is configured in a helicoid contiguous turns.

3. Device according to claim 1, characterized in that the evaporator (6) is the assembly of at least one substantially cylindrical corrugated metal plate on a substantially cylindrical metal plate, the corrugations of said metal plate defining a fluid flow path on the inner periphery of the evaporator (6).

Device according to any one of claims 1 to 3, characterized in that the boiler comprises a structure forming a heat shield having a skirt shape (7), in the extension of the evaporator (6) and arranged on one side. ends of said evaporator (6).

Device according to one of claims 1 to 4, characterized in that the biomass boiler also comprises a tubular metal structure forming a ferrule (4) positioned above the hearth (3).

Device according to any one of the preceding claims, characterized in that the thermally insulating layer of the evaporator (6) is a layer made from a fibrous material.

Device according to any one of the preceding claims, characterized in that it comprises a metallic element forming a radiating web (9) arranged at least partially facing the surface forming the inner periphery of the evaporator (6).

Device according to claim 7, characterized in that the radiating web (9) comprises a set of substantially rectangular metal plates (92) arranged in a circle and perpendicular to the perimeter of said circle.

Device according to claim 8, characterized in that the plates (92) of the radiating web (9) are all connected by two metal rings (91), said two rings (91) being in contact with two diametrically opposite ends of each of said plates (92), said wafers (92) comprising two diametrically opposed strips (93) partially cut on two opposite sides of said wafer (92) and bent in opposite directions.

10. Device according to any one of the preceding claims, characterized in that the first closed fluidic circuit (100) is provided with means (15) adapted to actuate a bypass mechanism of the electricity generator (16).

11. Device according to any one of the preceding claims, characterized in that the first closed fluidic circuit (100) comprises a condenser (18) connected to the electricity generator (16), able to exchange the residual heat output of the generator of electricity (16) with the domestic heating circuit (200).

12. Device according to any one of the preceding claims, characterized in that the first closed fluidic circuit (100) comprises a condenser (18) connected to the electricity generator (16), able to exchange the residual heat output of the generator of electricity (16) with a third closed fluidic circuit (300).

13. Device according to claim 12, characterized in that the third closed fluid circuit (300) comprises a heat exchanger (21) in contact with the domestic heating circuit (200).