Field of the invention

[0001]. The present invention is directed to a separated chambers pyrolysis furnace and to its use for the combined production of electricity and domestic hot water. Particularly, the present invention related to a separated chambers pyrolysis furnace, fed by organic fuel (e.g.: pellets, woodchips, nut shells, sawdust, biomasses) comprising a first pyrolysis chamber, wherein syngas is produced, and a second combustion chamber wherein the pyrolyzed fuel is combusted in the presence of air. The heat generated in the second chamber is used to heat the first chamber and bring the fuel to the pyrolysis temperature, and to heat domestic water. Syngas is used as a fuel for a generator producing electricity. The invention is also directed to a domestic apparatus for the production of electricity and hot water, the apparatus comprising the above defined pyrolysis furnace, a heat exchanger to heat domestic water by the hot gasses of the second combustion chamber, and a generator to produce electricity by combustion of the syngas produced in the pyrolysis chamber.

Background of the invention

[0002]. Pellet stoves are becoming more and more popular due to the lower cost of fuel compared to methane or gas oil. It is also known the use of organic fuel as defined above for the production of syngas. Nevertheless, these processes cannot find practical application in the domestic use because of high bulk of syngas filtration section, because generally, during conventional processes, the gas contains residue of fuel (ashes). The abatement of these ashes not only makes the apparatus bulky, but also implies a significant maintenance, which make this type of apparatuses unsuitable for domestic use.

Summary of the invention

[0003]. It has been surprisingly found that it is possible to make the production of syngas particularly advantageous thanks to the use of a two-chamber pyrolysis furnace. In a first chamber, the organic fuel is heated in the absence of significant quantity of oxygen at a temperature capable of causing pyrolysis of fuel itself. Once pyrolyzed, the fuel passes through a second combustion chamber where, in the presence of air, the fuel is completely combusted. Therefore, the heat generated inside the second chamber is partly used to pyrolyse the fuel and partly used to heat domestic water. It is important that the first chamber is separated from the second chamber. With the term "separated" it is intended that the gas present in the second chamber cannot enter the first chamber. In fact, in the second chamber air is used for the combustion of pyrolyzed fuel, while in the first chamber pyrolysis is performed in the absence of oxygen. Furthermore, the gas of the second chamber is mainly composed of nitrogen and carbon dioxide, and mixing it with syngas would be negative since it would lower the caloric power of syngas.

Detailed description of the invention

[0004]. Fig. 1 shows a scheme of an embodiment of the two-chamber reactor according to the invention. The first chamber, i.e. the pyrolysis chamber (10), is formed by a pipe containing a cochlea (10) The fuel (e.g. woodchips) is fed through the cochlea and moves forward thanks to the movement of the cochlea. During the stay in the pyrolysis chamber (10), the fuel is heated by the combustion gases of the second chamber (20). The heating of woodchip in the first chamber at a suitable temperature and in the absence of oxygen produces pyrolysis of woodchip itself.

[0005]. Fig. 2 represents a second embodiment of the invention wherein the fuel is fed to the pyrolysis chamber by star valve (15), and the passage from the first chamber (10) to the second chamber (20) takes place by gravitation. In this embodiment, syngas is withdrawn at the top of the loop where pyrolyzed fuel falls into the combustion chamber, and there is no need for a pipe (60) since no depression is created in this embodiment in the cochlea (10). Fig. 2 further shows pipe (70) which is used when the amount of syngas produced exceeds the needs for electricity production and, consequently all or part of syngas is burned for the production of hot water. In the area (100) it is located the heat exchanger (not shown), and pipe (40) represents the pipe of exhaust fumes after heat exchange. Air is feed through pipe (12) and fan (80).

[0006]. Thus, the furnace according to the invention is provided with an entrance for the solid fuel, which entrance might be provided with a star valve (15) for transferring the fuel from a reservoir (30) to the first combustion chamber (10). The furnace further comprises a second entrance (12) for air which is fed to the second chamber (20). The furnace also comprises two separate exits, the first exit (50) located in the first chamber for syngas removal, and an exit (40) in the second chamber for removal of the exhausted fumes.

[0007]. A star valve (11) is optionally placed at the end of the cochlea (10) allowing the passing of the pyrolyzed woodchip from the first chamber (10) to the second chamber (20). Here the woodchip is burned in the presence of an air flux sufficient to produce a complete combustion of the woodchip, but with a low amount of oxygen in the exhaust fumes.

[0008]. When a star valve is used between the two chambers, preferably, in order to avoid a depression near the star valve (11), some of the exhaust fumes are introduced in the cochlea near the star valve through pipe (60). Thus, it is important that the exhaust fumes contain a quantity of oxygen below the fuel combustion threshold. However, the amount of gas introduced in the cochlea from the second chamber is preferably very low, to avoid dilution of syngas. [0009]. In another preferred embodiment, there is no start valve separating the first and second chamber, and the fuel passes from the first chamber to the second chamber by gravity. In this embodiment, syngas is preferably removed from the upper part of the vertical section where the fuel falls from the first chamber to the second chamber. In this embodiment, the first chamber does not receive any exhausted gas from the second chamber.

[0010]. A lambda probe is preferably placed inside the second combustion chamber (20), to determine the quantity of oxygen present on the combustion fumes.

[0011]. A filter is optionally present in pipe (60), which is used in some embodiments to balance pressure in the upper part of the star valve (11). The filter is useful for the abatement of residual ashes present in the fumes.

[0012]. In a preferred embodiment, wherein the pyrolysis furnace is used in a house or an apartment for the production of electricity and for the production of domestic hot water, syngas obtained through pyrolysis is sucked through pipe (50) by a pump which feeds syngas to a generator, not shown in figure. The generator preferably charges a pack of batteries which supplies electricity to the house.

[0013]. Combustion fumes enter pipe (40) which leads to a heat exchanger wherein heat is transferred to water of the domestic heater apparatus. Preferably, the temperature of fumes exiting the exchanger is equal or higher to 70°C, to avoid moisture problems.

[0014]. It is also possible to modify the distribution of energy between the two purposes. For example, in the event that water of the heating apparatus does not reach the desired temperature by using the combustion fumes, it is possible to use part or all the syngas to heat domestic water through a burner, or by feeding part or all the syngas to the second combustion chamber (20) through pipe (70).

[0015]. On the contrary, being the domestic water already at the desired temperature, combustion fumes can be diverted not to pass through the heat exchanger, to avoid overcoming the set temperature.

[0016]. The pyrolysis furnace according to the invention comprises a tank (30) for the storage of organic fuel, e.g. woodchips. The tank might have different size depending on several factors, such as the fuel type, the easiness of supply and the power range of the apparatus. When the pyrolysis furnace according to the present invention is inserted in a medium range apparatus (e.g. 25 kW thermal and 4,5 kW electrical) the tank (30) has a dimension preferably comprised between 100 and 300 litres, more preferably between 150 and 250 litres.

[0017]. The tank (30) feeds the cochlea (10) preferably through a star valve, which guarantees the tank insulation from the combustion chamber for safety reasons. Preferably the tank is equipped of a level sensor and charging cells.

[0018]. The furnace working is preferably managed via software optimizing functioning conditions. Preferably, the software calculates the fuel density and regulates functioning conditions on the basis of density, and therefore of the fuel energy input. Furthermore, in a preferred embodiment, the managing system receives the information about oxygen content from the lambda probe and regulates the air flow (12) to the combustion chamber (20) so to maintain the oxygen content on the combustion fumes between the optimal range.

[0019]. The optimal oxygen content in the fumes is the one providing the better compromise between a good combustion inside the chamber (20) and a quantity of oxygen present in the fumes sufficiently low to avoid combustion risk in the pyrolysis chamber. Basically, with the term in the absence of oxygen, it is intended an oxygen content preferably lower than 3% in weight, more preferably lower than 2%, even more preferably lower than 1%.

[0020]. Concerning the energy build-up, in a preferred embodiment, the generator is connected to a lithium battery pack able to guarantee a power comprised between 3 and 6,3 kW, preferably between 4,5 and 6,3 kW.