Background Art It is known that there is a great availability of granular biomasses, constituted for example by maize or pellets obtained from vegetable substances, which have a high heat value and a low cost and further constitute renewable energy sources and therefore are considered ideal fuels for boilers, particularly in homes.

The combustion of granular biomasses, however, raises considerable problems, and up to now this fact has limited their utilization.

Disclosure of the Invention The aim of the present invention is to provide a burner for burning granular biomasses in a boiler that allows to provide combustion in optimum terms while protecting the integrity of the materials used.

This aim is achieved by a burner for burning granular biomasses in a boiler, according to the invention, characterized in that it comprises: -- a combustion chamber that is associated with the boiler and is placed in partial vacuum by way of fume aspirator means; -- a duct for gravity-feeding combustible granules to said combustion chamber; -- a duct for feeding primary air to said combustion chamber at a region for collecting the combustible granules proximate to the bottom, said duct having means for heating incoming air before feeding said air to the combustion chamber; -- a motorized sleeve rotatable about its own axis, and located proximate to the bottom of said combustion chamber within the region for collecting the combustible granules, said sleeve being supplied with secondary air and being provided with wall nozzles adapted to introduce said air among said

granules.

Brief Description of the Drawings Further characteristics and advantages of the present invention will become better apparent from the description of a preferred but not exclusive embodiment of the invention, illustrated by way of nonlimiting example in the accompanying drawings, wherein: Figure 1 is a schematic perspective view of a boiler provided with a burner according to the invention; Figure 2 is a perspective view, shown in phantom lines, of a detail of the burner according to the invention; Figure 3 is a sectional view of the burner, taken along a longitudinal plane.

Ways of carrying out the Invention With reference to the figures, the reference numeral 1 generally designates the burner according to the invention, which is inserted in a boiler 2 provided with a duct 3 for evacuating the fumes produced by the combustion which comprises means for aspirating such fumes, said means producing a partial vacuum in the entire portion of space occupied by the burner 1.

The burner comprises a combustion chamber 4, associated inside a front 5 of the boiler, and a chamber 6 is associated thereat on the outside of said front ; the chamber 6 is provided, at the cover, with a duct 7 for feeding combustible granules such as 8 that arrive by gravity, encounter an inclined plane 9, and are conveyed toward a port 10 for introduction in the combustion chamber 4 and collect on a bottom 4a thereof.

A duct for feeding primary air to the combustion chamber 4 at the region where combustible granules collect proximate to the bottom 4a is designated by the reference numeral 11 and is provided with means for heating incoming air before such air is fed to the chamber due to the partial vacuum that is present therein. Such heating means comprise an electric resistor 12

(controlled by a thermocouple) inserted in a container 13, which is connected to the outside at a nozzle 13 a and is connected to the duct 11.

The electric resistor is controlled by a thermocouple, which acts as a temperature detector in order to adjust the automatic operation of the device.

Furthermore the reference numeral 14 designates a motorized sleeve that rotates about its own axis by means of an electric gearmotor 15. The sleeve is located proximate to the bottom 4a of the combustion chamber 4 in the region where the combustible granules collect, and is substantially as long as the bottom 4a of the combustion chamber and is supported at one end by the front 5 of the boiler and at the other end by a fixed sleeve 16 that lies outside the combustion chamber and more specifically by an end 16a of the fixed sleeve 16.

The sleeve 14 is supplied with secondary air, which enters the chamber 6 through adjustable openings such as 6a and penetrates it at its two ends respectively by way of holes such as 14a and by means of the fixed sleeve 16, in order to introduce it by means of nozzles such as 14b among the combustible granules collected on the bottom of the combustion chamber 4.

The burner 1 is of course provided with means for automatic adjustment of its operation: such means comprise a photoresistor 17 adapted to detect the combustion conditions.

At boiler ignition, the electric resistor 12 is activated immediately, and once the preset temperature has been reached, the aspirator means at the base of the duct 3, which are adapted to produce a partial vacuum in the combustion chamber 4 and the chamber 6, are activated, causing a consequent inflow of primary and secondary air as indicated by the arrows of Figure 3.

The combustible granules are introduced at the same time and reach the combustion region proximate to the bottom 4a of the chamber 4, where they are ignited due to the primary air heated to a suitable temperature.

This produces steady-state combustion, controlled by the photoresistor

17.

The role of the rotating sleeve 14, introduced among the granules during combustion, is critical.

First of all, it ensures an effective inflow of the secondary air for optimum completion of combustion, and it is also important that such secondary air is preheated when it is introduced in the fuel.

Furthermore, the sleeve ensures effective mixing of the fuel and performs an important action for retaining the combustible granules, preventing their movement away from the combustion region, which might occur due to aspiration.

Finally, the sleeve, which is protected in its integrity despite being placed within the incandescent fuel because it is cooled from the inside by way of the secondary air that flows through it, ensures, with its rotation, the expulsion of the combustion residues.

The described invention is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims. Thus, for example, the fixed sleeve 16 can be omitted and the wall of the combustion chamber 4 can be provided with an interspace that is adapted to receive air from outside in order to send it, after preheating, to the container 13 of the electric resistor 12.

The disclosures in Italian Patent Application No. MN2002A000037 from which this application claims priority are incorporated herein by reference.