DEVICE FOR REMOVING THE RESIDUAL AGGLOMERATED MATERIAL GENERATED BY THE COMBUSTION OF PELLET

OR SOLID FUEL IN GENERAL ***

The present invention relates to the sector of burners fuelled with solid fuel in general, and in particular pellets. In particular, it relates to a device for removing the agglomerate ashes that form following combustion reactions of solid material containing substances that tend to melt down, forming red-hot blocks. The same inventive solution described below can therefore be advantageously applied to all that solid fuel which, in burning, produces the same type of agglomerate ashes indicated above. Moreover, in the present description, by the term pellet is meant both fuel deriving from a process of transformation of powdered material into cylindrical or round granules, and solid fuel which is not in pellet form but which comes in small pieces and during combustion behaves like pellet. The burner, with which all pellet boilers are equipped, essentially comprises a combustion chamber, a gasification grille supporting the solid fuel during the combustion phase, a fuel supply system, means for blowing combustion air into said chamber and an ignition device. To supply the burners, in particular biomass burners, the use is known of pellets generally obtained from wood shavings, sawdust, but also from lower-quality materials, such as straw, not-fresh sawdust, biomass in general with any natural binding agents. The solid material forming after combustion, generically called "ash",

is normally conveyed, through the above grille, into an underlying collection area, from which it is later removed by the blowing of air by means of dedicated nozzles.

One disadvantage that can occur, following the use of pellets produced using low-quality materials is the formation of agglomerates. These agglomerates, which consist of residues of material unable to be completely burned, but which rather tend to melt down and aggregate, obstruct the flow of primary air and the exit towards the combustion chamber, as well as the holes generally featured on the gasification grille.

The inert material and granular ashes on the other hand, tend to separate from the agglomerate and deposit underneath the grille bottom.

The above problems are currently overcome by using mobile grilles, whose task is to cause the pellets and any agglomerated combustion residues to move beyond the combustion chamber, but the problem with such grilles is that they can only be fitted to large machines, where mechanical handling problems remain associated with the consolidation of the agglomerate ashes and the high temperature which can affect the grille itself.

The aim of the present invention is to overcome the previously mentioned drawbacks.

The aim of the invention is achieved through the fitting of a device for pushing the agglomerate material, inside static-type pellet burners, suitable for permitting the forward movement of said material on the

gasification grille, towards the combustion chamber exit. The aim is achieved by a device for removing the agglomerated solid residual material produced by the combustion of pellets or solid fuel in general in burners comprising a combustion chamber and a pellet support grille, characterised in that said device comprises at least one rod positioned above said grille, associated with a mechanism able to generate an alternate movement. Advantageously, said rod is flanked by other rods connected to a common support to form the teeth of a sort of "comb" or "fork" linked to a piston type linear movement mechanism. The idle moving rods are external to the combustion chamber, but the presence of transit holes in the front wall of the burner does in any case ensure the access of such elements in the chamber itself. This way the teeth are able to cool down between one contact and the other with the burning-hot ashes. The teeth, fastened at one extremity, are advantageously free at the opposite extremity, so as to produce a substantially punctiform contact with the mass of the ashes and of the fuel material, so as to remove from the combustion chamber only the material producing the melting agglomerate, but not the embers and the fresh fuel. Preferably there are an odd number of teeth, so the central tooth is lined up with the ignition device. To avoid disturbing the pellet situated close to the ignition device too much, the central tooth can have a smaller section than the others.

In a preferred embodiment the alternate movement generation device consists of a double-acting pneumatic piston, the rod of which is

connected to the common support of the teeth of the removal device. As is obvious to any skilled man, to obtain the same type of movement, other types of pistons or other known kinematic mechanisms can be used, driven by fluids or a motor. An electronic control device can allow regulating the movement speed of the comb, the work and interval times, and any other parameters needing to be changed at will.

The main advantage achieved by fitting the device to pellet burners consists in the improvement of combustion resulting from the fact that the teeth making up the removal device only push the agglomerate material, leaving the fresh fuel and the burning embers undisturbed in a suitable position on the grille.

Further characteristics and advantages of the invention will be more evident from the detailed description provided below, with the aid of drawings representing a preferred embodiment, illustrated by way of non-limiting example.

The figure 1 shows, in longitudinal section according to a vertical plane, a burner for pellet fuel complete with a residual agglomerate material removal device produced by the combustion of pellets made in conformity with the present invention.

The figure 2 shows, in longitudinal section according to a horizontal plane, the same burner shown in the figure 1.

The figure 3 shows a cross section of the combustion chamber which extends along the plane III - III of figure 1. With reference to the figure 1 , the pellet burner 1 comprises a fuel

supply duct 2, a combustion chamber 3, an igniter 4, a grille 5, a primary air distribution chamber 6, a support surface 40 for nozzles 13 which blow primary air in radial direction, a chamber 20 for supplying the nozzles 13 with combustion air. The residual agglomerate material removal device essentially comprises at least one piston 7, a support 8, a rod or tooth 9.

The figures 1 and 3 show, in a more detailed way, the presence of the double-acting pneumatic piston 7, a part able to produce an alternate rectilinear movement. The piston, by means of the rod 21 , is directly connected to the support 8 and to the teeth 9, an odd number of which are generally present. The teeth 9 are free at the front extremity, are independent the one from the other and each slides fastened to the front wall of the burner 1 by means of a bushing 10, which acts as a support during movement.

The length of the teeth 9 is such as to avoid protruding inside the combustion chamber when the support 8, associated with the rod 21 , is in retracted position (indicated by unbroken lines in the drawings), and to ensure that the teeth extremity does not move beyond the grille 5 when the support 8 is in forward position (indicated by the broken line in the drawings).

The figures 1 and 3 show the arrangement of the teeth 9 on the support 8, which follows the concave shape of the fuel support grille 5 so the teeth are parallel with each other and substantially all at the same distance from the surface of the grille in all working positions. The section of the tooth 9 positioned in line with the igniter 4 can be

reduced with respect to the others, to prevent both removing too much material from the combustion ignition area, but above all to avoid the burner switching off at the start of the combustion cycle. The grille 5, which is provided with slots 11 , represents both the support for the fuel coming from the supply duct 2, through a supply opening or "mouth" 12, and a protection for the nozzles 13 placed underneath it and through which the combustion air is blown. On the grille therefore, the agglomerated residues that form have to be removed so as not to impair the efficiency of the burner. The movement of the pushing device is regulated by means of a programmable electronic device, not shown, that allows extending or reducing the work time interval and if necessary the speed of movement, as well as other parameters, if this becomes necessary. At the same time as the movement of the agglomerated material pushing device, compressed air can be blown below the grille 5, in the primary air distribution chamber 6.

The compressed air blown below said grille 5, through dedicated nozzles 30 placed on the front wall of the burner, removes the finer ashes from the air distribution chamber 6 and these are pushed back towards the combustion chamber 3 through the slots 11 which had allowed their fall into the chamber 6. This is due to the fact that the inter-space between the support grille 5 and the wall from which the nozzles 13 exit is closed on all sides.

According to the present invention, when the removal device of the agglomerated residual material produced by pellet combustion is idle,

the teeth 9 are all substantially outside the combustion chamber and are brushed by the supplied combustion air in the chamber 20, which cools them. When instead the device is moving to maximum extension, the teeth 9 slide in the bushings 10 and move forward in the combustion chamber 3 parallel to the grille 5, moving the agglomerated residual material forward towards the extremity of the grille. When such material moves beyond the end of the grille, it falls into a special underlying collection compartment from where it is afterwards removed.

The advantages provided by the present invention essentially consist in the fact that the alternate rectilinear motion of the piston 7, together with the presence of teeth 9 able to promptly touch the agglomerate of burnt ashes, ensures greater removal efficiency of the compact residues, leaving the fresh pellet and that in ignition phase substantially undisturbed.

The above-illustrated embodiment is also preferential for its conformation as well as its efficiency.

Naturally, without prejudice to the principle of the invention, the embodiments can be widely varied according to known technique, without because of this moving out of the scope of protection of the invention as described and illustrated and for the specified purposes.

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