SOLID FUEL BOILER WITH NATURAL DRAFT Technical field

The present invention relates to a solid fuel boiler with natural draft. Background art It is known that boilers designed to heat, in heating systems, a fluid which is commonly constituted by water or by diathermic oil or air, and operating with a solid fuel, which can be wood, peat or a granular fuel, have a chamber which is lined by an interspace for containing the fluid to be heated and is provided at the base with a grate adapted to support the fuel that fills the chamber and to allow the passage of the primary combustion air, which enters through one or more ports located in a position below such grate.

In known boilers, the combustion air encounters great resistance in passing through the mass of the fuel that lies above the grate and consequently is in starved conditions which determine the presence of a large quantity of unburned material in the products of combustion when they are inserted in the ducts for conveyance to the evacuation stack.

As a consequence, operation of known boilers is anything but optimum efficiency. Disclosure of the invention

The aim of the present invention is to provide a solid fuel boiler which has a great increase in efficiency with respect to currently commercially available boilers and which further minimizes atmospheric pollution caused by combustion. This aim is achieved by a solid fuel boiler with natural draft, according to the invention, characterized in that it comprises a chamber which is delimited at side walls and at the ceiling by an interspace which contains the fluid to be heated, said chamber being provided, at the base, with a fuel supporting grate which is located above at least one primary combustion air intake port and, at the ceiling, with at least one duct for

conveying the products of combustion to the stack, said chamber being further provided with a hatch for loading the fuel at a storage region which lies directly above the grate, said chamber comprising means adapted to determine the presence of the fuel in a clearly delimited portion of space, so as to form at least one free passage in contact with a side wall, and further comprising, at the top of the storage region, at least one secondary combustion air intake port. Brief description of the drawings

Further characteristics and advantages of the present invention will become better apparent from the description of some preferred but not exclusive embodiments thereof, illustrated by way of non-limiting example in the accompanying drawings, wherein:

Figure 1 is a side view of the boiler according to the invention;

Figure 2 is a sectional view of the boiler according to the invention, taken along the line H-II of Figure 1 ;

Figure 3 is an enlarged-scale sectional view, taken along the line III- III of Figure 2;

Figure 4 is another sectional view as in Figure 2, loaded with different wood; Figures 5, 6, 7, 8, 9 are sectional views of the boiler of the type of

Figure 3, according to different embodiments;

Figures 10, 1 1, 12 are sectional views of the boiler of the type of Figure 2, according to further different embodiments. Ways of carrying out the invention With reference to the Figures 1, 2, 3, the reference numeral 1 generally designates a boiler which comprises a chamber 2 delimited at side walls and at the ceiling by an interspace 3 which contains the fluid to be heated and provided at the base with a grate 4 for supporting fuel formed by pieces of wood 5, which is located above at least one primary combustion air intake port 6; at least one duct 7 for conveying the products of

combustion to a stack is arranged at the ceiling of the chamber 2.

The chamber 2 is provided with a hatch 8 for loading the fuel 5 at a lower storage region, which lies directly above the grate 4 and is delimited by four flat side walls and comprises means constituted by containment bars 9 which are adapted to delimit the presence of the fuel 5 in the central portion of space, so as to form at least one and preferably four free passages 10 in contact with the four side walls.

At the top of the lower storage region of the chamber 2 there is at least one secondary combustion air intake port 6a and there are also means adapted to stir the fluid currents that exit from the storage region, as described in greater detail during the description of operation.

Such means comprise a plate 11 , whose surface directed toward the storage region is flat; the plate 1 1 is provided with a central hole 11a which is surmounted by a baffle 12, both of which are made of refractory material. Finally, the reference numerals 13a, 13b, 13c designate portions of refractory material which are arranged so as to line the side walls of the chamber 2.

Operation of the invention is as follows.

The primary combustion air, which has entered through the port 6, passes through the grate 4, activates the combustion of the bed of embers that is present on the grate and then splits into two streams.

While a first stream, which is minor due to the great load losses that it encounters, passes through the entire mass of fuel 5 and exits from it while it is still rich in unburned material which must complete combustion, the second stream is conveyed by the free passages 10 and strikes the fuel mass, providing an action which is positive in many respects.

First of all, it strikes the lower part of the mass of fuel, activating its combustion, and subsequently strikes the upper part of the mass, drying it so as to prepare it for the combustion that awaits it; finally, it mixes with the first stream and, being still rich in oxygen, contributes to completion of the

combustion of the unburned substances that are present in such stream.

The mixing of the two streams and of the secondary combustion air which, having entered through the port 6a, balances the proportion between the streams, applying a sort of adjustment which leads to an optimization of combustion, is of course facilitated by the conveyance of the entire flow applied by the hole 11a against the baffle 12 before access to the ducts 7 for conveyance to the stack.

It should be noted that the mixing of the two streams described above and of the secondary air might occur also in the absence of particular means arranged above the storage region, and it should also be noted that such means, where present, may assume the most disparate configurations, as described hereinafter.

Figure 4 illustrates in cross-section the embodiment of the invention described in the preceding figures, simply loaded with wood 14 cut in the shape of parallelepipeds.

Figures 5, 6, 7 are sectional views of three embodiments of the boiler according to the invention which, as regards everything that is not shown, repeat identically what has been stated with reference to Figures 1, 2, 3.

In the embodiment of Figure 5, the bars 9 delimit a portion of space for containing wood 15 which is adjacent to one of the side walls of the storage region, thus forming three free passages 16; in the embodiment of

Figure 6, the bars 9 delimit a portion for containing wood 17 which is adjacent to two walls, so as to form two free passages 18, and finally in the embodiment of Figure 7 the portion for containment of wood 19 is delimited by the bars 9 adjacent to three walls, and in this manner a single free passage 20 is provided.

Figures 8 and 9 are views of embodiments of the means provided at the fuel storage region, which are adapted to determine the presence of the fuel in a clearly delimited portion of space: thus, in the embodiment of Figure 8 such means comprise portions of perforated metal plate 21, and in

the embodiment of Figure 9 the side walls of the storage region have expansions 22 whose shape and dimensions are such as to not allow the fuel to occupy them.

As mentioned earlier, the means for mixing the fluid streams that exit from the storage region may assume, where present, different shapes, such as for example a plate 23 with a central hole 23a provided with protrusions 23b which activate the vortical motions of the streams and the transmission of heat to the plate, shown in the embodiment of Figure 10, or baffles 24 shown in the embodiment of Figure 11, or finally a diaphragm 25 provided with a port with converging walls 25a, which is visible in the embodiment of Figure 12; all these embodiments are otherwise identical to what is described with reference to Figures 1, 2, 3.

A further embodiment of the mixing means, not shown in the figures, might be constituted by a diaphragm provided with a port with converging and diverging walls.

The described invention is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims; thus, for example, an ignition hatch can be provided located at the base of the storage region and adapted for introducing fme-cut wood at the grate. In the practical embodiment of the invention, all the details may be replaced with other technically equivalent elements.

The disclosures in Italian Patent Application No. MN2007A000023 from which this application claims priority are incorporated herein by reference. Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.