EP3997197A1

EP3997197A1 - An improved reactor for the gasification of wood-cellulose residual materials

Info

Publication number: EP3997197A1
Application number: EP20746863.8A
Authority: EP
Inventors: Domenico CIRILLO; Maurizio LA VILLETTA; Mariana NEGRI
Original assignee: Cmd Costruzion Motori Diesel
Current assignee: Cmd Costruzion Motori Diesel
Priority date: 2019-07-09
Filing date: 2020-07-06
Publication date: 2022-05-18
Also published as: WO2021004658A1; IT201900011208A1

Abstract

The present invention concerns an improved reactor (1) for the gasification of wood-cellulose residual materials, comprising: a reaction chamber (2) with a reduction cone (3), inserted in a containment body (4); - an apparatus (12) for loading the wood-cellulose residual materials, associated to said reaction chamber (2); a first (17) or a second (22) apparatus for unloading the ashes deriving from the gasification of said residual materials in said reaction chamber (2); devices for management and control of above-mentioned elements. In said reactor (1), the apparatus (12) for loading the materials and the apparatuses (17, 22) for unloading ashes cooperate with said reaction chamber (2) so as to avoid the occurrence of phenomena of "slagging" and/or "bridging channelling" and the consequent bad working or complete stall of said reactor (1).

Description

AN IMPROVED REACTOR FOR THE GASIFICATION OF WOOD- CELLULOSE RESIDUAL MATERIALS

The present invention concerns the field of reactors for the gasification of solid organic materials.

More in detail, the present invention concerns an improved reactor for the gasification of wood-cellulose residual materials. As it is already well known, the gasification of wood-cellulose residual materials, specially when performed by means of downdraft-lmbert gasification reactors, may cause in said gasification reactors the formation of waste due to the fusion and the subsequent agglomeration of the ashes contained in the chemical structures of the gasified materials (“slagging”).

Said slags may determine, as a negative effect, the reduction of the functioning time of said gasification reactors, of the plants integrating the same and thus a negative increase of the maintenance intervals. Furthermore, said slags may also determine the complete stall of the gasification reactors and of the plants integrating the same, due to the blockage of the reaction beds and to the following clogging of the grids for removing the ashes produced by the gasified materials. The formation of said slags depends on the content of ashes (high or low) in the starting residual materials, on the fusion temperature (high or low) of the ashes produced by the starting residual materials and on the distribution of the internal temperature in the gasification reactors. Laboratory and field tests have shown that in case of residual materials with an ashes content lower than 5-6%, there is no slag production inside the gasification reactors. On the contrary, laboratory and field tests have shown that in case of residual materials with an ashes content equal or higher than 12%, there are critical regimes inside said gasification reactors which may determine the formation of slags in quantities not sustainable for the gasification processes.

Even the size and the apparent density (“bulk density”) of the starting residual materials may affect the correct execution of the gasification processes.

Laboratory and field tests have shown that reduced size (<G10, which is a dimension corresponding to a medium size passing through a mesh sieve 10mm x 10mm)and apparent low density of the starting residual materials may determine a lowering of permeability of said gasification reactors and the consequent onset of strong pressure changes in the reduction zone.

Laboratory and field tests have also shown that big sizes (>G30, which is a dimension corresponding to a medium size passing through a mesh sieve 30mm x 30 mm) of starting residual materials may determine a reactivity lowering of said materials to the gasification processes and a consequent penalization of syngas production (“bridging channelling”).

The reactivity lowering of the starting residual materials to the gasification processes also determines a higher production of coals (charcoal) and condensable gases (TAR) inside said gasification reactors.

The aim of the present invention is to overcome above mentioned negativities specific to the gasification reactors known, in particular of the downdraft-lmbert kind, used for performing gasification treatments of wood-cellulose residual materials.

The aim set forth is reached according to independent claim 1 , by means of an improved reactorfor the gasification of wood-cellulose residual materials. Further features of the improved reactor for the gasification of wood-cellulose residual materials according to the present invention are described in the independent claims.

The improved reactor for the gasification of wood-cellulose residual materials according to the present invention obtains the following important advantages:

- it allows the gasification of wood-cellulose residual materials according to their specific chemical-physical features;

- it allows the continual gasification of wood-cellulose residual materials with ash content lower than 5-6%;

- it allows the gasification of wood-cellulose residual materials with ash content equal or higher that 12%, avoiding the formation of slag caused by the fusion and the agglomeration of the ashes (“slagging”) and the consequent stall due to slag amounts not sustainable by the gasification processes;

- it prevents the reduction of continuous working hours and the increase of maintenance intervals due to the stall conditions caused by slag amounts not sustainable by said gasification processes;

- it allows the gasification of wood-cellulose residual materials with sizes from G10 (which is a dimension corresponding to a medium size passing through a mesh sieve 10mm x 10mm) to G30 (which is a dimension corresponding to a medium size passing through a mesh sieve 30mm x 30mm), thus avoiding the lowering of permeability and following pressure changes in the reduction zone, as well as reactivity lowering in the gasified materials, with consequent penalization of syngas production (“bridging channelling”).

Further features and advantages of the improved reactor for the gasification of wood-cellulose residual materials according to the present invention will appear more evident from the following detailed description and the enclosed drawings showing preferred embodiments, in which: - figures 1 , 2 show in a vertical flat section and in exploded axonometric view, the structural conformation of an improved reactor for the gasification of wood-cellulose residual materials according to the present invention;

- figures 3, 4, 5 show an axonometric view, construction details of said improved gasification reactor;

- figure 6 shows a flat vertical section of a construction variant of said improved gasification reactor, specific for the use of residual materials with high ash content. Referring now to the details of the figures, an improved reactor 1 for the gasification of wood-cellulose residual materials according to the present invention, mainly comprises:

- a reaction chamber 2 with a reduction cone 3 inserted into a containment body 4;

- a loading apparatus 12 of the residual wood-cellulose material, associated to said reaction chamber 2;

- a first 17 or a second 22apparatus for unloading the ashes of the gasification of said residual materials from said reaction chamber 2, reversibly associated to said containment body 4 of said reaction chamber 2;

- devices for managing and controlling above mentioned elements.

More in detail, said reactor 1 comprises:

- an inlet 5 of wood-cellulose residual materials, provided by said loading apparatus 12;

- a rotating blade sensor 6 for said loading apparatus 12, depending on the presence of residual material in said reactor 1 ;

- an inlet 7 for a gasifying agent, preferably but not exclusively of atmospheric air kind;

- pipes 8 for preheating the gasifying agent, having first descending sections external to the oxidation area of reaction chamber 2 and connected, by means of fittings 9 provided in correspondence of the reduction area of said reaction chamber 2, to second ascending sections passing inside said reaction chamber 2;

- a plurality of nozzles 10 provided along the inner circumference of said reaction chamber 2 and associated to said second ascendant sections of pipes 8, for determining a uniform distribution of the gasification agent, preheated in correspondence with said reduction cone 3;

- an electric resistance 11 of the spark plug type, for starting the gasification of the residual materials introduced in said reaction chamber 2;

- an outlet line for the syngas produced with the gasification of the residual materials introduced into said reaction chamber 2;

- a protection shield reinforcing the thermomechanical resistance of said reaction chamber 2, indicatively toroidal in shape, provided at the base of said reduction cone 3;

- a heat-insulating coating T realized with layers of insulating materials like fibreglass, provided on the inner and outer surface of said containment body od said reaction chamber 2.

Above mentioned elements are out of metal materials, preferably AISI 316L steel, with thickness variable between 2 mm and 3 mm.

More in detail, the loading apparatus 12 associated to the reaction chamber 2 of reactor 1 comprises:

- a roto-valve 13 for dosing the wood-cellulose residual materials having size between G10 ((which is a dimension corresponding to a medium size passing through a mesh sieve 10mm x 10mm) and G30 (which is a dimension corresponding to a medium size passing through a mesh sieve 30mm x 30mm);

- a collection chamber 14 of said materials, indicatively truncated-pyramidal in shape;

- a tubular channel 15, communicating with said collection chamber 15 and with said inlet 5 to reaction chamber 2 of said gasification reactor 1 , comprising a motorized auger for conveying said materials from said collection chamber 14 to said reaction chamber 2 through said inlet 5. The loading apparatus 12 allows reactor 1 to perform gasification treatments on wood-cellulose residual materials with predetermined size comprised between G10 (which is a dimension corresponding to a medium size passing through a mesh sieve 10mm x 10mm) and G30 (which is a dimension corresponding to a medium size passing through a mesh sieve 30mm x 30mm) and consequently avoiding the onset of “bridging channelling”.

Said loading apparatus 12 is made out of metal materials, preferably out of AISI 316L steel.

More in detail, the first ashes unloading apparatus 17 that may be associated to containment body 4 of reaction chamber 2 of said reactor 1 , comprises:

- a vibrating grid 18 for the reduction of the gasified residual material bed, operated by an eccentric electric motor MC, according to a timing depending on a control logic based on temperature and depression values measured along the outlet line of syngas;

- a structure 19for collecting the ashes from said grid 18, indicatively conical in shape;

- a tubular channel 20 communicating with the conical collection structure 19 and integrating a motorized auger 21 for conveying the ashes from said conical collection structure 19 to accessory apparatuses for treatment or stocking.

The first ashes unloading apparatus 17 allows said reactor 1 to perform a continuous gasification on wood-cellulose residual materials with an ash content lower than 5-6% of the gasified materials, removing the gasification ashes thereof by means of a properly timed control logic. More in detail, the second ashes unloading apparatus 22, that may be associated to the containment body 4 of the reaction chamber 2 of said reactor 1 , comprises:

- a fix grid 23 for the deposit of the reduction bed of the gasified residual materials;

- a stirrer 24 with blades PL placed at the centre inside said reaction chamber

2, operated by an electric motor ME with an independent timing by a control logic based on values of pressure drops detected between a couple of points P1 , P2 respectively placed upstream of said reduction cone 3 and downstream of said grid 23;

- a collection structure 25 for the ashes supplied by grid 23 and/or by stirrer

24, indicatively trunk-cylindrical in shape, with an inclination of 30° to the horizontal plane of said reactor 1 ;

- a tubular channel 26 communicating with the trunk-cylindrical collection structure 25 and comprising a motorized auger 27 for conveying the ashes from the trunk-cylindrical collection structure 25 to accessory apparatuses for treatment or stocking.

The second ashes unloading apparatus 22 allows the reactor 1 to perform gasification treatments on wood-cellulose residual materials with ash content equal or higher that 12% of the gasified materials, without the onset of “slagging” phenomena, removing the gasification ashes and the gasification wastes (residual mineral structures etc.) by means of a properly timed control logic.

The first 17 and second 22 ashes unloading apparatuses may further comprise:

- opening valves 28 and exit invitations 29 provided on tubular channels 20,

26 for the transfer of the ashes from collection structures 19, 25 to accessory apparatuses of treatment or stocking;

- guillotine type, or similar, isolation or segmentation devices. The first 17 and second 22 ashes unloading apparatuses are alternative one to another and reversibly associable to said containing body 4 of said reaction chamber 2, without any modification to the remaining parts of said reactor 1 , inside the same.

Geometrical and dimensional characteristics of reactor 1

The reaction chamber 2 and the reduction cone 3 of said reactor 1 provide design solutions resulting from specific numerical-experimental tests. In particular, the proportioning of said reactor 1 , which has allowed to maximize the conversion efficiently reducing at the same time the tars production, has also allowed the correct relative positioning of the three characteristic zones of said reactor, i.e. the pyrolysis zone, the oxidation zone and the reduction zone.

The correct relative positioning of above-mentioned zones has been defined through the study of the geometrical-dimensional parameters of said reactor 1. With particular accuracy have been defined:

- the relationship between the diameter of the reduction cone 3 and the diameter of said reactor 1 (ratios of throat to gasifier diameter). In literature is shown that an accurate relationship between the reduction cone and the diameter of the reactor means a significant impact on the formation of the chemical species forming the syngas, as it directly affects the speed of the gas through the throat, it assures a good mixing between the volatile substances and the gasifying agent (air), and it simultaneously improves the distribution and the uniformity of temperature in the oxidation zone. The high temperature obtained in the oxidation zone following to a good mixing, allows to reduce the tar formation in the gas flow. Numerical and experimental analysis have shown that this may be achieved by establishing the relationship equal to 0.40 between the diameter of the reduction cone ad the diameter of the reactor. The gasification reactor 1 according to the present invention has a relationship between the diameter of the reduction cone 3 and the diameter of the reactor itself equal to 0.41 , and the measured temperature of >120°C. The geometrical profile of the reduction cone 3 is of the converging-diverging type, and this is why it has been properly shaped in such a way as to obtain a correct speed of the gas through the throat, because in this shape the best mixing possible between the volatile substances and the gasifying agent has been obtained.

- The positioning optimization of the air inlet points through said nozzles 10 inside said reaction chamber 2 with respect to the throat of said reduction cone 3. The geometrical relation between the diameter of the cone’s throat, the diameter of the reactor and the position of the air inlet nozzles, has an effect on the distribution of the temperature and of the properties of syngas. Studies and literature show that the relative positioning between the nozzles and the diameter of the cones’ throat may directly affect on the formation of H₂, CO and CH₄ as well as on the uniformity of the temperature in the oxidation zone, while it does not seem to have a particular impact on the formation of C0₂ and on the distribution of the temperature in the pyrolysis and reduction zones. Moreover, it has been noted that if the air inlet nozzles are placed a few centimeters (<8 cm) above the throat’s diameter and in correspondence with the beginning of the inclined converging section of the cone it is possible to produce cold points around the oxidation zone, with the consequent reduction of the local temperature. A low and uneven local temperature around the oxidation zone (<1000°C) may inhibit the tars destruction process by means of a thermic cracking. For these reasons, in the gasification reactor 1 according to the present invention the nozzles 10 have been placed at about 11.5 cm above the diameter of the throat of the reduction cone 3, and seats have been created for said nozzles 10 in correspondence with the beginning of the inclined section of said cone 3, through the removal of material.

- The optimization of the inclination angle of said reduction cone 3 (throat angle). The inclination angle of said reduction cone 3, referred to the angle formed between a horizontal axispassing through the throat and the divergent portion of said cone affects conversion efficiency. In literature studies are known showing the conversion trend along the axis in the reduction zone for inclination angles of said cone variable between 30° and 90° (degenerate cone in a cylinder). Small inclination angles tend to increase the conversion efficiency, while great angles tend to reduce the same as the divergent effect of the cone globally reduces the temperature reached in the reduction zone and consequently the relative reaction speed. However, the smaller angles also need a high length in said reduction zone to achieve optimal efficiency. A greater length would allow the gasifier to work at the maximum efficiency but at the same time the production costs of the product would increase. On the other hand, a smaller height of the reduction zone is not desirable because the gasifier would work below its project capacity due to insufficient length for a correct conversion of the char. On the basis of these considerations, for the reactor 1 for gasification according to the present invention an inclination angle of the divergent portion of said reduction cone 3of 60° has been chosen, so as to mediate the effects from a cost/benefit point of view. Instead, as far as the opening angle of the convergent portion of said reduction cone 3 is concerned, an angle of 50° has been chosen so as to guarantee, as previously illustrated, a proper speed of the gas through the throat for the correct mixing between the volatile substances and the gasifying agent.

Peculiarities of said apparatus 12 for loading the material Said apparatus 12 can be adapted without any mechanical modification both to screw-type transport systems of the materials, in case it is used with materials similar to wood chips or shells (walnuts, hazelnuts and the like, with size <1 cm), and to conveyor belt material transport systems, in case it is used with briquettes obtained by densification processes of residual materials with size <1 mm. If screw-type loading systems are used for moving the briquettes, during transport the occurrence of both impulsive forces and actions produced by sliding friction could be noted, inducing the activation of briquette fragmentation mechanisms that will produce particles of <1 mm. Said apparatus 12 can manage indifferently wood chips, shells and briquettes, as well as other residual materials comprised in the dimensional range G10-G30. Motorized screw 16 in the collection chamber 14 of apparatus 12 is optimized for the transport of briquettes and has a geometrical profile such as to accompany them without producing the occurrence of impulsive forces.

Said apparatus 12 allows said reactor 1 to perform gasifying treatments on wood-cellulose residual materials with predetermined size in the range G10-G30, mitigating the occurrence of phenomena like the “bridging channelling”. In particular, studies in literature show that in gasifiers with a fixed bed there is a limitation on the size to use, and the optimal use for achieving the lowest tendency to said phenomenon of “bridging channelling” appears to be confined within the range G10-G30. Indeed, small biomasses significantly increase the conversion efficiency as the heat transfer zone increases with the reduction of the particles’ size, improving the release of volatile material during the pyrolysis process. Nevertheless, the gasification of materials with particles’ size <G10 and of products with low density, may present problems related to a strong pressure drop inside said reactor determining the occurrence of preferential channels for the passage of the gasifying agent (“bridging channelling” phenomenon), as well as a higher content of dust contained in the syngas. Likewise, biomasses in the range >G30 favour the formation of preferential channels for the passage of air, inducing a low reactivity and generating less syngas at the expense of greater production of particulate matter and tar. In this sense, provided that the size must be previously set within the range G10-G30, the loading apparatus 12, thanks to the perfect coordination produced by the feedback of sensor 6 depending on the presence of the biomass inside said reactor 1 , allows to precisely dose the material and to distribute it evenly inside said reaction chamber 2, mitigating the occurrence of “bridging-channelling” and at the same time minimizing another phenomenon, the one of cohesive arch. Such phenomenon occurs when cohesive particles form an obstruction above the outlet of the throat of reduction cone 3, usually in the shape of an arch or a bridge, that prevents the progress of the material. The cohesive arch may be generated both by particles of the material, mechanically welded to each other so as to form the obstruction, and by rigid structures generated by the variously arranged briquettes. The management system of said reactor 1 allows, through a PLC (Programmable Logic Controller), setting the drive of loading apparatus 12 according both to the type of biomass/residual material (physical and chemical features and density), and to its characteristic size, expressed as a function of the value assumed by the parameter “aspect-ratio”

(proportions). In particular, primarily in case of woodchips and wood- cellulose shells, their irregular shape may cause difficulty in accurately measuring their dimensions as far as length and width are concerned. The “aspect-ratio” parameter, which affects the heat transfer during the thermochemical conversion of the material inside said reactor 1 , has been evaluated and successively implemented in the relative macro-categories management system of residual materials (woodchips, shells and briquettes), as well as the relationship between the minimum width and the maximal length detectable in the particle of the representative sample of the respective population.

The feedback of sensor 6 is guaranteed by the physical contact between the material present in said reactor 1 and the rotating blade of said sensor.

In absence of said material, the blade freely rotates around its own axis and its rotation is registered by the management system of said reactor 1 , which activates the movement of the material in said collection chamber 14, by means of said screw 16. At the same time, the correct dosage of the material in said collection chamber 14 is guaranteed both by said roto- valve 13 and by a loading screw which takes the material from a biomass stocking reservoir and conveys it to said roto-valve 13. When the contact between sensor 6 and the material present in said reactor 1 is achieved, thus preventing the free rotation of the blades of said sensor 6, a stop feedback is generated of said screw 16, of said roto-valve 13 and of the loading screw. Finally a further level sensor in the biomass stocking reservoir, allows the management system of said reactor 1 to verify the presence or not of material inside said stocking reservoir. Said management system of said reactor 1 allows to reach the correct level of material inside said reactor, independently from the macro-category of the residual materials (woodchips, shells and briquettes) that may be used in feeding it.

Peculiarities of the first ashes unloading apparatus 17

In said apparatus 17, the vibrating storage grid 18 of the reduction bed defines the selectivity of the coal and ash particles and the residence time of the material inside said reactor 1 , both through 12 mm passage holes and in function of the driving of the eccentric electric motor MC, which produces a shaking of the reduction grid with respect to an axis passing through the barycentre of said grid, facilitating the expulsion of said particles. The timing of the driving of said eccentric electric motor MC depends on the temperature and depression values detected along the outlet line of the syngas inside said reactor 1 , as well as on the optimal residence time that may be set by means of the management system of said reactor 1 , both according to the typology of the biomass/residual material (physical-chemical features and density) and to its characteristic dimension, expressed in function of the value assumed by the parameter “aspect-ratio” (proportions).

Said apparatus 17, in which a vibrating grid 18 is provided, driven by eccentric electric motor MC, is classified in literature as of the type “vibrating grate”, wherein the oscillation of the grid with respect to an axis passing through the barycentre of said grid, allows to destroy the structures responsible for the packing phenomenon of the material. The eccentrics, defined by the weight of two masses off-axis with respect to the rotation axis of electric motor MC, allow both to produce the oscillation of the grid and to trigger additional dynamic actions such as to put onto oscillation the entire reactor 1 as well as the entire column of biomass/residual material placed above said vibrating grid 18.

Therefore, said apparatus 17 allows to prevent the packing phenomena of the material between the reduction cone 3 and the reduction bed, produced by rough cohesive particles having the characteristic of getting mechanically welded one to another due to the high temperature generated in the oxidation zone, and consequently to mitigate the formation and occurrence of preferential channels for the passage of the gasifying agent “air” through said material (“bridging-channelling” phenomenon).

Peculiarities of the second ashes unloading apparatus 22 Apparatus 22 defines the selectivity of coal and ash particles through a fix grid 23 with 12 mm passing through holes. In this case, the management of this apparatus appears to be somewhat more complex as far as the residence time is concerned, because said apparatus is to be used for biomasses/residual materials containing ashes equal or superior to 12%: - the use of an agitator 24 provided with blades PL and driven by an electric motor ME is provided. Blades PL scrape the bottom of said fix grid 23 and thereby facilitate the removing of coal ad ash particles, thus avoiding the occlusion of the passing through holes. Furthermore, the speed and the direction of the rotation of the blades PL may be varied by means of the managing system of said reactor 1 , and this allow to produce a minimum quantity of dusts potentially transportable by syngas;

- the architecture of apparatus 22 allows to place fix grid 23 at a different height of the deposit of the reduction bed of the gasified residual materials. It is possible to adjust the height of said grid 23, i.e. the height of the reduction zone, by means of appropriate positioning feet placed inside said containment body 4 of the reaction chamber 2 of said reactor 1. In this sense, literature shows that the choice of the correct positioning of the grid, and therefore the definition of the length of the reduction zone crossed by the gas, appears to be a parameter of fundamental importance for the design of “downdraft” gasifiers, as it affects directly the residence time of the biomass, the char conversion and therefore the conversion efficiency. As the conversion efficiency mainly depends on the inclination angle of the reduction cone, on the length of the reduction zone, on the dimension of the solids and on the moisture of the biomass, on the heat dispersion to the outside, besides the possible pre-heating of the gasifying agent (air) entering the reactor, according to the typology of product to use in supplying said apparatus 22 allows to vary the dimension of the reduction zone and therefore to maximize said efficiency, allowing to place said grid 23 at a lengthvariable, as appropriate, from 120mm to 250mm with respect to the end part of said reduction cone 3;

- similarly to apparatus 17, it is possible to vary the residence time according to the typology of biomass/residual materials and to its“aspect-ratio”, that may be set by the management system of reactor 1.

Through a proper management of the movement of the blades PL of stirrer 24, apparatus 22 allows to destroy in the bud the“bridging-channelling” phenomenon, effecting a mixing of the material both near the oxidation zone and near the reduction zone, reacting to the measure of the pressure drop detected between a couple of points P 1 , P2 respectively upstream from reduction cone 3 and downstream of grid 23. Said pressure values, acquired by the management system of reactor 1 , appear to be decisive in identifying the pressure drop, understood as a precursor physical value at which it is necessary to operate the stirrer 24 to destroy in the bud material packing phenomena. The inclination, the pitch and the geometry of blades PL allow to move the material in radial as well as in longitudinal direction (upwards and downwards), according to the rotation direction defined by the managing logic.

A further advantage produced by stirrer 24 is to mitigate also the so-called “slagging” phenomenon concerning special material types. In particular in the thermo-chemical conversion processes the fusion of the relative ashes represents a big problem as it can lead to a reduction of the performance associated with the generation waste, scale and agglomerates. For specific categories of materials, depending on the values assumed by the main elements forming the ashes (Fe, Ca, Mg, K, Na, Al, Si, K, Cl, Zn and Pb) they may determine relevant effects for the fusion thereof and the consequent deposit of amorphous conglomerates in the reactor. Such elements have a different reaction depending on their volatility and this is the reason why the lighter species, like K, Na, Si, Cl, Zn and Pb turn to their gaseous phase due to the high temperature generated in the combustion zone. Once they reach zones with a lower temperature, said gaseous phases turn to the condensation phase on the surface of the particles present in the gas flow, forming nucleation centres for ashes. In literature is has been shown that wooden biomasses are characterized in a high Ca content and a low Si and K content, that typically have a high fusion temperature and form nucleation elements of ashes. Other non- wooden materials usually have a high Si and K content and therefore ae more likely to form potassium silicates with potential formation of nucleation centres and amorphous deposits. In this sense, the use of stirrer 24 allows to destroy in the bud the possible formation of agglomerates produced by the fusion of ashes if products are used containing an ashes percentage greater or equal to 12% (referred to the original biomass). The slags, destroyed in the bud by stirrer 24 and consequently having a particle size similar to the one of the ashes, can now be removed from said apparatus 22.

This means that, as far as the residence time is concerned, said apparatus 22 facilitates its management thanks to the following options:

- to use said stirrer 24 according to a timing depending from a control logic based on the values of pressure drop detected between a couple of points P1 , P2, respectively placed upstream of said reduction cone 3 and downstream of said grid 23;

- to set the optimal residence time according to the typology of biomass/residual material (physical-chemical features and density) and to its characteristic dimensions, expressed as a function of the value assumed from the parameter “aspect-ratio”, through the management system of said reactor 1 ;

- to place said fix grid 23 at different heights and consequently to vary the height of the reduction bed, through positioning feet placed inside said containment body 4 of the reaction chamber 2 of said reactor 1.

As far as the “bridging-channelling” and “slagging” phenomena are concerned, said apparatus allows the mitigation thereof due to the following options:

- to use said stirrer 24 to destroy on the bud the “bridging-channelling” phenomenon per forming a mixingof the material, by means of said blades PL, in the oxidation/reduction zone on the basis of a timing depending on a control logic, based on the pressure drop values detected between the couple of points P 1 , P2. Such pressure values indicate the pressure drop in said reactor 1 : when said drop has been achieved, it is necessary to operate said stirrer 24 in order to prevent the occurrence of material packing phenomena;

- to use said stirrer 24 to destroy on the bud, through said blades PL, the formation of agglomerations produced by the fusion of ashes (“slagging”), in case materials are used with an ash content equal or superior to 12%. The waste, having a particle dimension similar to the one of ashes, destroyed by said stirrer 24 may now be removed by said apparatus 22. In addition, le presence of the structure 25 for the collection of the ashes supplied from said grid 23 and of said stirrer 24, indicatively trunk- cylindrical in shape and with a 30° inclination to the horizontal plane of said reactor 1 , allows a more efficient outflow of said ashes towards the tubular channel 26 containing the motorized removal auger 27.

More peculiarities of ash unloading apparatuses 17, 22 Apparatus 17 is optimized for use with high quality wood-cellulose residual materials, containing a massive fraction of ash equal or superior to 12%.

Both apparatuses 17 and 22 can mitigate the“bridging-channelling”, but only apparatus 22 can manage the“slagging”.

The more appropriate apparatus will be chosen on the basis of the used material and therefore associated to reactor 1 just replacing it with the other one.

The interchangeability of said apparatuses 17, 22 does not require mechanical modifications to said reactor 1 as the anchor points to said containment body 4 are the same. Likewise, once the apparatus has been replaced, the management system of said reactor 1 allows to choose the control logic corresponding to apparatus 17 or 22 associated thereto.

Both apparatuses 17 and 22 have opening valves 28 and isolation and/or segmentation devices controlled by the managing system of said reactor 1 , for separating the atmospheric pressure ambient from said apparatuses 17, 22, working in depression, ad consequently for allowing the ashes unloading without stopping said reactor 1 and without incurring the gas short circuit to the outside, with possible danger for the operators.

Both apparatuses 17, 22 have exit invitations 29 which facilitate the outflow of the ash towards the stocking reservoirs, using the inclination of the tubular profiles.

Peculiarities of further elements of said reactor 1

As far as inlet 7 and pipes 8for pre-heating the gasifying agent (air), with ascending and descending sections in correspondence with the reduction zone of reaction chamber 2, literature shows that the use of air at the reactor’s inlet at a temperature superior to the ambient one, improves the conversion efficiency. In said gasification reactor 1 according to the present invention, the warm air supplies an energetic contribution necessary for the reaction, recovering it from the heat dispersed through the walls of the reactor itself. Said solution allows to preheat the air up to a temperature of about 150°C-200°C.

As far as the plurality of nozzles 10 is concerned, placed along the inner circumference of said reaction chamber 2, their distribution has been designed to balance the pressure drops ensuring, through all the nozzles, the same flow of gasifying agent conveyed to said reactor 1. The uniform distribution of air in the oxidation zone allows to obtain a proper temperature profile without generating strong thermal gradients on the circumference.

For what concerns the electrical ignition resistance 11 of the gasification of the materials introduced in said reaction chamber 2, it allows to activate the reaction in the very first ignition phases of said reactor 1 , without using devices generating combustion flames. Thanks to the very high temperatures achieved by the resistance’s 11 surface (>1 ,500°C) it is possible to start the combustion of the material that gets into contact with the same and therefore start the gasification process.

As far as the thermal insulating coating T provided on the inner and outer surface of said containment body 4 of said reaction chamber 2, studies in literature have shown that the heat dispersion to the outside through the reactor’s walls is the physical parameter most influencing the conversion efficiency, which is estimated to decrease by 11 % for each 5% increase of heat dispersion. In particular, the high heat transfer to the outside causes a temperature decrease inside the reactor, reducing at the same time the reactions speed. For this reason, the gasification reactor 1 according to the present invention has a thermal-insulating coating realized with layers of insulating materials like fibreglass, placed on the inner and outer surface of said containment body of said reaction chamber 2. Detailed working of the reactor for the gasification of wood-cellulose residual materials according to the present invention The loading apparatus 12 conveys the residual materials first into a collection chamber 14, by fall, through a roto-valve 13, and then into a reaction chamber 2 of a reactor 1 , by pushing, through a motorized screw integrated in a tubular conduit 15 communicating with said collection chamber 14 and with inlet 5 of said reaction chamber 2.

An inlet 7 introduces atmospheric air with the function of gasifying agent into reaction chamber 2 of reactor 1 , while a plurality of nozzles 10, placed along the inner circumference of reaction chamber 2, uniformly distributes the atmospheric air in correspondence with reduction cone 3.

For increasing the efficiency of the whole gasification process, the atmospheric air supplied at the inlet 7 will be pre-heated making it pass first outside reaction chamber 2 and in correspondence with the oxidation zone, through first descending sections of pipes 8, and then inside said reaction chamber 2, through second ascending sections of said pipes 8, connected to said first descending sections by means of joints 9 placed in correspondence with the reduction zone, and communicating with nozzles 10. For increasing the thermal insulation of reactor 1 and consequently further increasing the efficiency of the whole gasification process, the containment body 4 of the reaction chamber 2 comprises a thermal-insulating coating T made out of layers of insulating material like fibreglass, placed on the inner and outer surface.

For increasing the resistance to thermal-mechanical stress of reaction chamber 2, reduction cone 3 comprises, at the base, a protective shield indicatively toroidal in shape, for preventing breaking due to thermal corrosion in correspondence with joints 9 of those pipe 8 sections placed between the oxidation and the reduction zone.

An electric resistance 11 of the spark plug type, starts the gasification process of the residual materials present in reaction chamber 2, thus determining a controlled overheating.

Therefore, in reaction chamber 2 the chemical reactions occur in the homogeneous and in the heterogeneous phase determining the gasification process of the residual materials (the whole of reactor 1 is in depression).

During the gasification process, the atmospheric air supplied at inlet 7 and heated by pipes 8 and distributed by nozzles 10, burns part of the residual materials in reaction chamber 2 (localized combustion), providing the thermal energy needed for starting the successive drying, pyrolysis and gasification phases.

The pyrolysis phase leads to the formation of condensable gases (TAR and H₂0 in the liquid state), non-condensable gases (CO, C0₂, H₂, H₂0 in the vapor state; CH₄, N₂) and coal (char).

Below the combustion zone (in front of nozzles 10) is the reduction bed (up in correspondence with deposit grids 18, 23), where the gaseous products of the pyrolysis, of drying and of combustion are made react with coal (char), thus obtaining a further fuel mixture mainly consisting of CO, C0₂, H₂, H₂0, CH_4I N₂ (present in the atmospheric air).

The syngas obtained by the gasification process of residual materials will be conveyed, through an outlet line, towards accessory devices for the removal of TAR and carbonaceous particles and thus reused directly on the site or conveyed to accessory devices for reuse or stocking. Through the first 17 or second 22 ash unloading apparatus, associated to containment body 4 of reaction chamber 2 of reactor 1 , the ashes produced by the gasification process of residual materials are unloaded from reactor 1 and transferred towards accessory devices for treatment or stocking.

The first ash unloading apparatus 17 is a vibrating grate.

In said first ash unloading apparatus 17, a deposit grid 18 of the reduction bed is operated by an eccentric electric motor MC according to a timing depending on a control logic, of the “safety” kind as well, based on temperature and depression values detected along the syngas outlet line.

A conical structure 19 collects the ashes supplied by grid 18 while a tubular channel 20, communicating with said structure 19 and integrating a motorized auger 21 conveys the collected ashes towards accessory devices for treatment and stocking.

The second ash unloading apparatus 22, instead, is of the kind with rotating blades (“stirrer”).

In such second ash unloading apparatus 22 a fix deposit grid 23 of the reduction bed is associated to a stirrer 24 with blades PL, internal to reaction chamber 2, for the destruction of the waste that cause the occurrence of the“slagging” phenomena, without causing stress to grid 23.

Stirrer 24 is driven by an electric motor ME and operated by a control logic in function of pressure drops DR= (Pi - P₂), detected upstream the throat of reduction cone 3, and downstream of grid 23.

If the value DR indicates the onset of “slagging” phenomena, the control logic drives the electric motor ME operating stirrer 24, thus determining the rotation of blades PL and the consequent destruction of the waste in formation.

A a trunk-cylindrical structure 25 collects the ashes supplied by grid 23 and/or by stirrer 24, while a tubular channel 26 communicating with said structure 25 and integrating a motorized auger 27, conveys the collected ashes towards accessory devices for treatment or stocking.

To introduce the stirrer 24 into the reaction chamber 2 of reactor 1 , the collection structure 25 is realized with a 30° inclination to the horizontal plane of said reactor 1. Furthermore, the height of the reduction bed is optimized for increasing the catalytic effet produced by the coal on said deposit grid 23 of the reduction bed.

The first 17 and second 22 ash unloading apparatus may further comprise:

- opening valves 28 and exit invitations 29 provided on tubular channels 20,

26 for the transfer of the ashes from collection structures 19, 25 to accessory devices of treatment or stocking;

- guillotine type, or similar, isolation or segmentation devices.

Laboratory and field tests have proved the efficiency of the first ash unloading apparatus 17 in the gasification process of wood-cellulose residual materials (e.g. chipped wood), with the following specifications:

- a low humidity content (M<30% as such (ar));

- a high ratio between the carbon content and the nitrogen content (C/N>30 ratio);

- a ratio as low as possible between the hydrogen content and the carbon content (H/C<1.6 ratio);

- a ratio as low as possible between the oxygen content and the carbon content (O/C<0.7 ratio);

- an ashes content <3% so as to reduce the problems connected with the formation of waste (“slagging”); - the sizes of the pieces comprised between G10 (which is a dimension corresponding to a medium size passing through a mesh sieve 10mm x 10mm) and G30 (which is a dimension corresponding to a medium size passing through a mesh sieve 30mm x 30mm), thus avoiding the lowering of permeability and following pressure changes in the reduction zone, as well as reactivity lowering in the gasified materials, with consequent penalization of syngas production (“bridging channelling”).

Laboratory and field tests have further proved the efficiency of the second ash unloading apparatus 22 in the gasification process of wood-cellulose residual materials outside above mentioned specifications, and in particular with an ash content equal or superior to 12%.

Claims

1. An improved reactor for the gasification of wood-cellulose residual materials, comprising:

a reaction chamber (2) with a reduction cone (3) inserted into a containment body (4),

characterized in that it comprises:

a loading apparatus (12) for the residual wood-cellulose material, associated to said reaction chamber (2);

a first (17) or a second (22) apparatus for unloading the ashes of the gasification of said residual material from said reaction chamber (2);

devices for managing and controlling above mentioned elements, wherein said apparatus (21 ) for loading the materials and said interchangeable apparatuses (17, 22) for unloading the ashes cooperate with said reaction chamber (2) for avoiding the onset of “slugging” or “bridging channeling” and consequent malfunctioning or complete stalls of said reactor (1 ).

2. An improved reactor (1 ) according to claim 1 , characterized in that it comprises:

- an inlet (5) of wood-cellulose residual materials, provided by the loading apparatus (12);

- a drive sensor (6) for the loading apparatus (12) according to the presence of residual material in said reactor (1 );

- an inlet (7) for a gasifying agent;

- preheating pipes (8) of the gasifying agent, having first descending sections external to the oxidation area of the reaction chamber (2) and connected by means of fittings (9), provided in correspondence of the reduction area of said reaction chamber (2), and second ascending sections passing inside said reaction chamber (2);

- a plurality of nozzles (10) provided along the inner circumference of said reaction chamber (2) and associated to said second ascending sections of pipes (8), for determining a uniform distribution of the preheated gasifying agent in correspondence with aid reduction cone (3);

- an electrical resistance (11 ) for starting the gasification of the residual materials introduced in said reaction chamber (2);

- an outlet line for the syngas deriving from gasification of the residual materials introduced into said reaction chamber (2);

- a protection shield reinforcing the thermomechanical resistance of the reaction chamber (2) provided at the base of said reduction cone (3);

- a heat-insulating coating (T) provided on the inner and outer surface of the containment body (4) of said reaction chamber (2).

3. An improved reactor (1 ) according to claim 1 , characterized in that the loading apparatus (12) comprises:

- a valve (13) for dosing the wood-cellulose residual materials with size comprised in a dimensional interval corresponding to a medium size that passes through a mesh sieve 10mm x 10mm and a mesh sieve 30mm x 30mm;

- a collection chamber (14) of said materials;

- a tubular channel (15) communicating with said collection chamber (14) and with inlet (5) to reaction chamber (2) of said reactor (1 ), comprising a motorized auger for conveying said materials from said collection chamber (14) to said reaction chamber (2) through said inlet (5).

4. An improved reactor according to claim 3, characterized in that the loading apparatus (12) allows reactor (1 ) to perform gasification treatments on wood-cellulose residual materials with predetermined size comprised in an dimensional interval corresponding to a medium size that can pass through a mesh sieve of 30mm x 30mm, and consequently avoiding the onset of“slugging” or“bridging channeling”.

5. An improved reactor (1 ) according to claim 1 , characterized in that the first ashes unloading apparatus (17) comprises: - a vibrating grid for the reduction bed of the gasified residual materials, operated by an eccentric electric motor (MC);

- a structure (19) for collecting the ashes provided by said grid (18);

- a tubular channel (20) communicating with the collection structure (19) and integral with a motorized auger (21 ) for conveying the ashes from the collection structure (19) to accessory apparatuses for treatment or stocking;

- a control logic determining the operating of said vibrating grid (18) according to a timing based on temperature and depression values measured on the syngas outlet line.

6. An improved reactor (1 ) according to claim 1 , characterized in that the second ashes unloading apparatus (22) comprises:

- a fix grid (23) for the deposit of the reduction bed of the gasified residual materials;

- a stirrer (24) with blades (PL) placed at the centre inside said reaction chamber (2), operated by an electric motor (ME) with an independent timing by a control logic based on values of pressure drops detected between a couple of points (P1 , P2) respectively placed upstream of said reduction cone (3) and downstream of said grid (23);

- a collection structure (25) for the ashes supplied by grid (23) and/or by stirrer (24), indicatively trunk-cylindrical in shape, with an inclination of 30° to the horizontal plane of said reactor (1 );

- a tubular channel (26) communicating with the trunk-cylindrical collection structure (25) and comprising a motorized auger (27) for conveying the ashes from the trunk-cylindrical collection structure (25) to accessory apparatuses for treatment or stocking;

- a control logic for determining the operating of the stirrer (24) according to a timing based on values of pressure drops measured between one couple of points (P1 , P2) respectively placed upstream and downstream of said reduction cone.

7. An improved gasifying reactor (1 ) according to claims 5 or 6, characterized in that the first (17) or the second (22) ashes unloading apparatus comprises:

- opening valves (28) and exit invitations (29) provided on tubular channels (20, 26) for the transfer of the ashes from collection structures (19, 25) to accessory apparatuses for treatment or stocking;

- guillotine-type insulating or segmentation devices.

8. An improved reactor (1 ) according to claim 5, characterized in that the first (17) apparatus for unloading ashes allows said reactor (1 ) to perform continuous gasifying treatments onto wood-cellulose residual materials with a content of ashes inferior to 5-6% of the gasified materials, removing the gasifying ashes from said reaction chamber (2) on the timing supplied by the relative control logic.

9. An improved reactor (1 ) according to claim 8, characterized in that the first (17) apparatus for unloading ashes allows said reactor (1 ) to perform continuous gasifying treatments of wood-cellulose residual materials having the following further features:

- a moisture content below 30%;

- a relationship between the carbon and nitrogen content above 30;

- a relationship between the hydrogen and carbon content below 1.6;

- a relation between the oxygen and carbon content below 0.7;

- a dimension of the pieces comprised in a dimensional interval corresponding to a medium size that can pass through a mesh sieve of 10mm x 10mm and of 30mm x 30mm.

10. An improved reactor (1 ) according to claim 6, characterized in that the second (22) apparatus for unloading ashes allows said reactor (1 ) to perform gasifying treatments on wood-cellulose residual materials with an ashes content equal or higher than 12% without the risk of onset of “slugging”, removing the gasification ashes and slags from said reaction chamber (2) according to the timing provided by the relative control logic.