DESCRIPTION

The present invention relates to a grate for solid fuel burners or gasifiers.

The grate comprises a solid fuel inlet portion, a deposit portion for the deposit of ashes and char produced by the pyrolysis/gasification of the solid fuel and an outlet portion for said ashes.

The configuration just described is the common configuration of a grate for solid fuel gasifiers or burners, particularly for biomass gasifiers.

Solid fuel gasifiers known in prior art are composed of an outer body delimiting a combustion chamber, providing at least one grate where the combustible material is placed, which is inserted through an inlet portion provided under the grate.

Gasifiers known in prior art further provide an outlet port of the combustion chamber for discharging the obtained gases, as well as members for feeding primary air intended to feed air inside the combustion chamber under the grate, so called primary air .

Moreover gasifiers known in prior art provide means for feeding air above the grate for the combustion of pyrolysis gases, of tar and part of the char of the pile, so called secondary air, as well as means for feeding air in the post-combustion portion, so called tertiary air. It is specified that in prior art known gasifiers a pile is created, that is a store of biomass inside the system above the grate. The pile is always subjected to pyrolysis and pyrolysis produces gaseous products, gas and tar, and solid products , char .

Such products are exothermic and help the gasification and under proper thermo-chemical conditions gasification takes place.

Therefore the first products are char and gaseous products: the former continue to burn inside the pile, the latter burn in the top portion of the combustion chamber creating a flame generating the energy necessary for the gasification.

Inside the pile the resulting ash and the char tend to move towards the bottom.

Therefore fuel introduced inside the combustion chamber is subjected to pyrolysis/gasification process to obtain gases of interest.

Such process forms, as described, char and waste ashes, the latter deriving partially also from the progressive combustion thereof throughout the radial development of the grate.

Both char and ashes have to be removed such to prevent the grate and the combustion chamber from being clogged, since such clogging decreases the efficiency of the pyrolysis/gasification process, resulting in the decrease of the quality and amount of the product of interest.

Moreover, as it will be described below, it is important for the char to continue to burn such to provide the energy necessary for the system and such to remove the unburned components inside the waste material .

Therefore the removal of ashes and char is a very important aspect for optimizing biomass pyrolysis/gasification process.

Therefore the aim is to provide a grate moving the ash and completing the char combustion while moving the residues towards the peripheral parts of the system where the discharge takes place.

In order to overcome such drawback, gasifiers known in prior art have types of grate intended to facilitate the removal of ashes.

A first example is a movable compartment grate, namely a grate providing a kind of trapdoors that open and discharge the ashes under the grate in a discharge region.

As an alternative gasifiers known in prior art provide a grate mounted on shaking supports, which, once operated, shake the grate such that ashes are pushed outside the grate, towards a discharge region.

In addition to difficulties related to the implementation, such solutions do not consider another important factor, since not only ash removal is important, but also the time spent for the combustion of char and the time spent for removing ashes are important.

It is important for discharged ashes to be completely spent, without the presence of unburned products, present in the char, that affect both the quality of the pyrolysis/gasification process and the pollution generated by waste products.

The need of increasingly exploiting waste material therefore requires prior art known grates to be re-designed for being able to handle the process for materials that are deeply non-homogeneous and having impurities in the composition (presence of low-melting compounds, high humidity, low thermal value .. ) .

In order to optimize the process it is necessary for the fuel to have a path and a sufficient residence time inside the combustion chamber such to obtain only ash free from unburned components in the discharge areas.

The present invention achieves the above aims by providing a grate for solid fuel burners or gasifiers as described hereinbefore, wherein the deposit portion comprises at least two portions, of which a movable part and a fixed part, in such a way that the movable part has a relative displacement with respect to the fixed part and with respect to the inlet portion .

The movable part overlaps at least in part the fixed part, in such a way to push ashes and char towards the outlet portion.

Thus a system is generated for the automatic removal of ashes and for char combustion allowing the fuel to be optimally burned/gasified. The removal of the ashes prevents the combustion chamber from being clogged and low-melting compounds from being formed that can create problems to the operation of the burner .

The grate of the present invention helps the pyrolysis/gasification process inside gasifiers such to facilitate the combustion of syngas that is formed and of carbon residues, usually called as char and tar, in the same combustion chamber. The grate of the present invention, in addition to provide an advanced system for the removal of ashes and combustion of char for burners/gasifiers , allows ashes to be discharged throughout areas intended for the discharge such to optimize the removal thereof .

A further advantage of the grate of the present invention is to allow the input fuel to pyrolyse and to gasify such that the grate can burn char and residual ashes from the pyrolysis/gasification process therefore providing the energy amount necessary for triggering the process.

Accordingly the grate of the present invention allows char combustion to be completed and residual ashes to be discharged.

According to a preferred embodiment the movable part is placed in proximity to the inlet portion, while the fixed part is placed in proximity to the outlet portion.

As it will be noted in the description of some embodiments, ashes depositing near the inlet portion are pushed by the movable part towards the outlet portion .

Moreover advantageously in order to make possible the pyrolysis/gasification process the movable part and/or the fixed part have holes for allowing primary air to pass inside the burner/gasifier , in particular inside the combustion chamber .

According to a first embodiment, the deposit portion is composed of at least two annular elements surrounding the inlet portion, of which a movable annular element and a fixed annular element, supported by a movable tubular element and a fixed tubular element respectively, arranged one inside the other and with their longitudinal axes parallel, such that the movable tubular element rotates around its longitudinal axis.

Moreover the movable annular element rotates in an eccentric way with respect to the fixed annular element .

In order to obtain the eccentric rotation of the movable annular element it is possible to provide two different solutions.

According to a first solution it is possible to place the movable tubular element in an eccentric manner with respect to the fixed tubular element, such that both the movable annular element and the tubular element move in an eccentric manner with respect to the fixed elements.

According to a preferred alternative, it is possible to provide the movable annular element to be fastened in an eccentric manner to the movable tubular element, such that the longitudinal axes of the movable tubular element and of the fixed tubular element are coincident.

Unlike grates known in prior art such as for instance the grate according to documents WO 95/32392 and CH226199, such configuration allows different advantages to be obtained, both as regards the constructional point of view and as regards the efficiency of the grate, that will be shown below.

A first particularly advantageous aspect is the fact that the grate of the present invention can be made with reduced dimensions since it develops on the inside the whole system, having on the outside only the mechanisms for moving the movable tubular element or elements .

The reduced dimensions of the grate allow it to be installed also in plants that develop limited powers, also lower than 2 MW thermal power.

Grates known in prior art, such as for instance the grate described in document W095/32392, need larger spaces since they have movement mechanisms installed between fixed and movable tubular elements.

This causes prior art known grates to be developed in wideness, preferring a combustion process with a homogeneous distribution of the combustion bed.

In the grate according to the present invention on the contrary the biomass is distributed according to a pile arrangement and the grate acts for moving such pile. It results that the reduced dimensions help pyrolysis and gasification process.

Moreover it results in a greater overlapping of the movable annular element on the fixed annular element, guaranteeing the whole system to be more clean and more efficient.

According to an improvement the deposit portion is composed of a plurality of movable annular elements and of fixed annular elements arranged alternating with each other.

Moreover the movable and fixed annular elements have diameters that increase as they get farther from the inlet portion and are arranged one above the other one, such that the annular element with the smaller diameter is placed in the highest point and the one with the larger diameter is placed in the lowest point. Thus the rotation of the movable annular elements causes areas to be overlapped such that ashes and char are pushed outwardly. The movement leads to a continuous cleaning of the portions where the fuel is provided with a consequent continuous fall of the fuel, that is char, and ashes towards the peripheral and lowest areas.

As mentioned above the char in such path continues the combustion/pyrolysis process in order to provide energy to the gasification process.

It is clear how the reduction of the dimensions described above has clear advantages also in the case when there is a plurality of movable elements and fixed elements.

In addition to the advantages described above, a more easy maintenance is obtained, by the possibility of removing the individual components of the grate, as well as an assembling easiness, with no need of fastening and/or welding parts, but by means of simple snap actions .

Moreover the reduced spaces between tubular elements allow ash to be handled better, by insufflating interstitial air, that will be described below.

This leads to more rapid cooling, and to the possibility of handling at best the possible perforation of the grate, nearly as it was a fixed grate .

As it will be more clear from the description of some embodiments, the particular described configuration of the different components of the grate of the present invention allows the components to be made also by a melting process. According to a variant embodiment each annular element in its peripheral portion has a thickness greater than the remaining part.

According to a first embodiment the peripheral portion with greater thickness of each annular element is in contact with the preceding and following annular element.

It is clear how such configuration allows friction of movable annular elements on fixed annular elements and vice versa to be optimized, while keeping the action cleaning the fixed and movable annular elements .

In order to further limit the friction it is possible to provide a particular shape of the profile of the end part of greater thickness.

For example it is possible to provide a profile of such portion having a half-sphere shape, such that only the minimum point of the half-sphere is in contact with the preceding and following annular element.

As an alternative it is possible to provide the end portion of greater thickness not to be in contact with the preceding or following element, but to provide a gap portion between the part of greater thickness and the preceding and following annular element .

In this case, according to one embodiment, it is possible to provide to deviate the flow of primary air introduced inside the combustion chamber, such that a part of the primary air is introduced into the combustion chamber and such that the remaining part of it is deviated towards the gap portion between one and another annular element. The flow of deviated primary air allows the depositing ashes and char to be pushed towards the outermost annular elements, such to facilitate them to be exhausted and discharged.

Such configuration, that is the deviation of the stream of primary air, can be provided also in combination with the variant embodiment that provides the portion of greater thickness of the annular element to be in contact with the preceding or following element.

In this case it is possible to provide a groove obtained in the end part of greater thickness such to allow the flow of deviated primary air to pass.

Advantageously the annular element with the greater diameter is a fixed annular element, having at least one discharge hole to allow ashes to pass to the outlet portion.

The ashes free of the unburned materials are pushed towards the annular element with the larger diameter and from that annular element the ashes fall into the outlet portion by the presence of the hole.

As set forth ashes and char by passing from the inlet portion to the outlet portion, during the passage from one to another annular element, completely burn, generating the energy necessary for the pyrolysis/gasification process and eliminating all the unburned products resulting from the pyrolysis/gasification process.

According to a further embodiment the deposit portion is composed of a first series of step elements, of which movable step elements and fixed step elements, arranged alternating with each other and in a helical manner around the inlet portion, from an upper point in proximity to the inlet portion to a bottom point in proximity to the outlet portion.

The movable step elements are fastened to the outer surface of a tubular element, that is mounted so as to oscillate about its own longitudinal axis.

Moreover the inlet portion has a plate element mounted so as to rotate independently from the tubular element, which plate element has at least one fixed spillway element intended to push ashes and char towards the step element positioned in the upper point during the rotation of the plate element.

The operation of such variant embodiment will be clear by some embodiments .

Also in this case the ashes and char produced by the pyrolysis/gasification process travelling through all the step elements, from the uppermost point to the lowermost point, are completely burned and are pushed in the outlet portion once all the unburned components are eliminated.

According to a preferred variant embodiment it is possible to provide two series of step elements arranged according to a double helix about the inlet portion .

In this case the plate element has two spillway elements , such to push ashes and char towards the step elements placed in the upper points.

The provision of the double helix allows a higher amount of ashes to be burned and the process to be optimized, without creating obstructions throughout the fall of the ash.

According to an improvement of the variant embodiment just described, the plate element at its peripheral edge has a delimiting barrier that has an opening at the step element placed in the upper point .

Ashes and char depositing on the plate element, during the movement thereof, by the provision of the delimiting barrier, do not fall outside, but they are only pushed on the uppermost step, due to the action of the spillway element.

According to a variant embodiment of the grate of the present invention, each step element in its end part has a thickness greater than the remaining part .

As set forth for the variant about the annular elements it is possible to provide only the peripheral part of each step element to be in contact with the preceding and following step element.

Likewise what described as regards the embodiment of annular elements, also in this case it is possible to provide the flow of primary air to be deviated such to push ashes and char deposited on the step elements towards the lowermost step elements.

Due to the advantages related to the grate, the present invention also relates to a solid fuel gasifier comprising an outer body delimiting a combustion chamber, which combustion chamber provides at least one grate where the combustible material is placed.

The gasifier provides at least one inlet compartment for the combustible material provided under the grate, as well as an outlet port of the combustion chamber for exhausting the obtained gases.

There are further provided members for feeding primary air intended to feed air inside the combustion chamber under the grate. In particular the gasifier of the present invention provides a grate having one or more of the characteristics described above, as an alternative or in combination with one another.

These and other characteristics and advantages of the present invention will be more clear from the following description of some embodiments shown in the annexed drawings wherein:

Figs, la, lb and lc are three views of a first embodiment of the grate of the present invention;

Fig.2 is a section of the grate of the present invention according to the embodiment of figures la, lb and lc;

Figs.3a to 3c are three sections of the gasifier of the present invention providing to use the grate of the previous figures;

Figs.4a and 4b are the grate of the present invention according to a further embodiment;

Fig.4c is a detail of the embodiment of the grate shown in figures 4a and 4b;

Fig.5 is a section of the gasifier of the present invention providing to use the grate of the previous figures;

Figs. 6a to 6d are some views of the mechanism moving the movable elements belonging to the grate of the present invention.

It is specified that the annexed figures in the present patent application are shown in order to better specify and understand the advantages and characteristics of the grate of the present invention .

Therefore such embodiments have to be intended for explanatory purposes and not as a limitation to the inventive concept of the present invention, that is to provide a grate for solid fuel gasifiers allowing ashes and char to be properly discharged and char to be completely burned, intended to eliminate the presence of unburned components inside waste products .

The present invention relates to a grate for solid fuel burners or gasifiers comprising a solid fuel inlet portion, a deposit portion for ashes and char obtained by pyrolysis/gasification of solid fuel and an ash outlet portion.

The inventive concept of the present invention provides the deposit portion to comprise at least two parts, of which a movable part and a fixed part, such that the movable part has a relative displacement with respect to the fixed part and to the inlet portion .

Moreover the movable part overlaps at least partially the fixed part, such to push ashes and char towards the outlet portion.

As it will be seen in embodiments below, such movement allows not only ashes to be pushed towards the outlet portion, but also the movable part and the fixed part to be cleaned.

Regardless of the embodiment, the movable part is preferably placed in proximity to the inlet portion, while the fixed part is placed in proximity to the outlet portion.

Moreover preferably the movable part and/or the fixed part have holes to allow primary air to pass inside the burner/gasifier .

Figures 3a and 5 show two embodiments of the grate inserted within a gasifier. Particularly the grate has an inlet portion 1 through which the combustible material is fed inside the combustion chamber 4 , and by the provision of a feeding auger 41.

The solid fuel inside the combustion chamber is subjected to pyrolysis/gasification process and the product of such process is collected through the outlet port 5.

Moreover such process produces waste material, namely ashes and char, that again are deposited on the grate, particularly on the area surrounding the inlet portion 1, that is the deposit portion 2.

Particularly the feeding auger 41 feeds the grate, namely the inlet portion 1, in a symmetric manner. The grate of the present invention allows solid products, i.e. waste products, of the process to be homogeneously fed towards the peripheral and circumferential part of the system.

Ashes are moved in the outlet portion 3 through the deposit portion 2, by processes that will be described below.

The outlet portion 3 is not shown in details, but it can be made in any manner known in prior art.

Figures la to 3 show a first embodiment of the grate of the present invention, particularly of the deposit portion 2.

According to such embodiment the deposit portion 2 is composed of at least two annular elements 21, 22, 23, 24, 25 and 26 surrounding the inlet portion 1, of which a movable annular element 21, 23 and 25 and a fixed annular element 22, 24 and 26.

Each movable annular element and each fixed annular element is supported by a movable tubular element and a fixed tubular element respectively, denoted for illustrative purposes by numeral 27, arranged one inside the other and with their longitudinal axes parallel, such that the movable tubular element 21, 23 and 25 rotates about its own longitudinal axis.

Moreover the movable annular element 21, 23 and 25 rotates eccentrically with respect to the fixed annular element 22, 24 and 26, see figure lb.

With a particular reference to figures la to 2 it is possible to provide the supporting tubular elements 27 to be inserted one inside the other with their longitudinal axes as coincident and the movable annular elements 21, 23 and 25 to be fastened so as to be eccentric with respect to the fixed annular elements 22, 24 and 26.

Particularly the grate of the present invention has a symmetric movement system/mechanism, namely the tubular elements 27: the movable annular elements 21, 23 and 25 are eccentric with respect to the movable tubular elements 27, while the fixed annular elements 22, 24 and 26 are concentric with respect to the fixed tubular elements.

According to the embodiment shown in figures la to 3c, the deposit portion 2 is composed of a plurality of movable annular elements 21, 23 and 25 and of fixed annular elements 22, 24 and 26 arranged alternating with each other.

The movable annular elements 21, 23 and 25 and the fixed ones 22, 24 and 26 have diameters that increase as they get farther from the inlet portion 1 and are arranged one above the other one, such that the annular element 21 with the smaller diameter is placed in the highest point and the one 26 with the larger diameter is placed in the lowest point.

Such arrangement is particularly evident in figure 2, wherein each movable annular element 21, 23 and 25 is placed above a fixed annular element 22, 24 and 26.

The movable annular elements 21, 23 and 25 are eccentric with respect to the tubular elements to which they are fastened while the fixed annular elements 22, 24 and 26 are centered.

Preferably the first annular element 21 is movable and the other odd rings 23 and 25 as well .

As said above, in order to transmit the movement the concentric tubular elements 27 are used to which rotating mechanisms are connected, such as for example wheels on rails and rods that is pistons that act on gear wheels connected to "spokes" welded on the rotating tubular element.

According to the embodiment shown in figures, the movable annular elements 21, 23 and 25 are connected through the movable tubular elements to rail-like profile beam spokes resting on supporting wheels. Rotation is transmitted through pairs of pistons arranged at 180° resting, by pairs, on a gear wheel obtained from the "movable" beam spokes.

The fixed annular elements 22, 24 and 26 are connected to a fixed structure with the rest of the burner/gasifier system, for example through fixed concentric tubes that are connected to beam spokes.

Figure 3b shows a possible preferred embodiment of the system moving the supporting tubular elements 27. Such embodiment is shown in details in figures 6a to 6d.

According to such embodiment, each movable supporting element 27 is fastened to a gear wheel 271 engaging a central pinion 272: the central pinion 272 is fastened to a fixed structure and the movement of each central pinion 272 causes the movable supporting elements 27 to rotate.

It is clear how such arrangement allows dimensions of the grate to be minimized, by moving the mechanisms moving the tubular elements 27 in the lower part of the grate, such that the tubular elements 27 can be inserted one inside the other while taking as less space as possible.

As an alternative to such solution, figure 3c shows a possible embodiment of the system moving the supporting tubular elements .

According to such embodiment each movable tubular supporting element 27 has supporting wheels 273 that provide the motion to be transmitted by means of pistons 274 coupled at 180° for each movable tubular supporting element.

Regardless of the movement, ashes are deposited in the area surrounding the inlet portion 1, in particular on the first annular elements 21, 22 and 23.

The eccentric rotation of the movable annular elements 21, 23 and 25 pushes ashes downwards and contemporaneously cleans the surface of the annular elements 21, 22, 23, 24, 25 and 26.

Accordingly ashes move from the top, annular element 21, to the bottom, annular element 26, then to be discharged while completing their combustion. Advantageously such as shown in figure lb, the annular element 26 with the larger diameter is a fixed annular element and it has at least one discharge hole 261 for allowing ashes to pass to the outlet portion 3.

Particularly the annular element 26 is equipped with circular or shaped holes 261 placed at 45° to allow ashes to fall down.

Finally such as shown by the detail of figure lc, each annular element 21, 22, 23, 24, 25 and 26 in its peripheral part has a thickness greater than the remaining part, such that only the peripheral part of each annular element 21, 22, 23, 24, 25 and 26 is in contact with the preceding and following annular element.

Figures 4a to 5 show a different embodiment of the grate of the present invention.

According to such embodiment, the deposit portion 2 is composed of a first series of step elements 21, 22, 23, 24, 25 and 26 of which movable step elements 21, 23 and 25 and fixed step elements 22, 24 and 26 arranged alternating with each other and in helical manner about the inlet portion 1, from an upper point in proximity to the inlet portion 1 to a bottom point in proximity to the outlet portion 3.

The movable step elements 21, 23 and 25 are fastened on the outer surface of a tubular element 211, see figure 4c, which is mounted so as to oscillate about its own longitudinal axis.

The inlet portion 1 has a plate element 11 mounted to as to rotate independently from the tubular element 211, which plate element 11 has at least one fixed spillway element, not shown, intended to push ashes towards the step element 21 placed in the upper point during the rotation of the plate element 11.

Advantageously according to the variant shown in figure 4a to 5, there are provided two series of step elements 21, 22, 23, 24, 25 and 26 arranged according to a double helix about the inlet portion 1, the plate element having two spillway elements, such to push ashes towards the step elements 21 placed in the upper points .

The grate according to such embodiment acts in a way like the previous grate, but it exploits the movement of different members in order to move ashes on the different sections of the grate, since ashes deriving from pyrolysis/gasification process are discharged on different step elements 21, 22, 23, 24, 25 and 26 such to be then discharged.

The combustible material arrives on the plate element 11.

Figures 4a and 4b are different from each other only because figure 4a shows a cone for the entry of the combustible material that allows it to be distributed more homogeneously on the plate element 11.

The combustible material introduced after the pyrolysis, pyrolyses and it generates syngas and char .

The plate element 11 rotates slowly and the presence of the two spillway elements, not shown, allows residual ashes to be transferred slowly on the double side helix each one being formed by the step elements 21, 22, 23, 24, 25 and 26. In particular, since the rotation of the plate element 11 is independent from the oscillation of the movable step elements 21, 23, and 25 ashes are pushed on the highest movable step element 21.

The step elements 21, 23 and 25 are movable since are splined on the tubular element 211 able to rotate .

Fixed step elements 22, 24 and 26 can be splined on an outer fixed cylinder or on the gasifier walls.

The movement generates a partial rubbing of each step element with the following and preceding step element while allowing the combustion/gasification products to proceed towards the discharge portion and to complete oxidation.

At the end of each series of step elements it is possible to provide an abutment door hinged on the top side able to perform an abutment swinging action. The arrival of ashes pushed by the last movable step causes the door to be opened and ashes to be discharged into the dedicated compartment.

It is specified that the series of step elements can be in any number, also more than two.

Moreover the step elements 21, 22, 23, 24, 25 and 26 can have different widths due to volume requirements necessary for the process.

The oscillation of the tubular element 211 allows each step element to push ashes towards the lowest step and contemporaneously to clean itself from the ashes.

Taking for example in consideration the step element 23, an oscillation of the tubular element 211 towards the step element 24 allows the step element 23 to push ashes present on the step element 24 towards the step element 25, while an oscillation in the opposite direction allows the step element 23 to be cleaned from ashes present on its surface by the abutment with the step element 22.

According to a possible embodiment, the movement of the step elements is transmitted by fifth wheels acting on dedicated cylinders.

As mentioned above, the plate element 11 and the tubular element 211 are unconstrained, the plate element 11 rests on a fifth wheel arranged about the tube containing the feeding auger 41.

At the same manner the tubular element 211 is constrained on a fifth wheel fastened on the outer wall or on wheels coupled to rails to generate the rotation thereof.

The rotation is transmitted by pistons (rods) coupled at 180° one with the other for each rotating member. Rods alternatively operate the gear wheel splined on the rotating tubular element.

According to the variant shown in figures 4a and

4b, the plate element 11 at its peripheral edge has a delimiting barrier 111 having an opening at the step element 21 placed in the upper point.

The combined action of the opening of the barrier 111 and of the spillway elements guarantees ash to be conveyed only on the step element 21 that later pushes it towards the following step elements.

In particular the delimiting barriers 111 prevent ashes from falling on the step elements 22, 23 , 24 , 25 and 26 different from the initial steps 21.

Finally as mentioned with reference to the previous variant embodiment, each step element 21, 22, 23, 24, 25 and 26 in its end part has a thickness greater than the remaining part, such that only the peripheral part of each step element is in contact with the preceding and following step element.

As mentioned above friction created during the movement of the movable step elements 21, 23 and 25 occurs only between the end part of each step element and the upper surface of the following step element.