FR2511028A1 - Gasifier for carboniferous materials - employing downwards air flow through combustion zone surrounded by distn. zone before gasification - Google Patents

Abstract

Combustion chamber for the gasification of carboniferous material contg. a high proportion of volatile materials and water employs an inverted cone through which solids and combustion air and gases flow downwards. Prim. air is injected radially to form a drying and distn. zone for removal of water and volatiles which are carried into a central combustion zone where they burn in injected secondary air. Gasification occurs beneath the combustion zone as hot gases pass towards the radial gas outlet. Used in the gasification of wood and waste vegetable matter for automotive and industrial applications, the device produces gas having a low tar content.

Description

 The present invention relates to a process for the gasification of carbonaceous materials with a high content of volatile products, such as wood. And vegetable waste which can be wet for the production of a combustible gas, clean and free of tar, usable for heating, the operation of internal combustion engines or as a gas this synthesis.

 The invention also relates to an installation for implementing the above method.

 Known gas generators, with reverse gas circulation, make it possible to obtain a combustible gas and have been widely used for supplying fuels to car or truck engines.

In these gasifiers, the gases formed travel the same downward path as the solid fuel to be gasified and slurried mt successively from top to bottom of the gasifier, drying, distillation, cracking and combustion zones and finally, gasification.
The pyroligneous and tars produced in the upper part of the gasifier are destroyed in the middle zone at high temperature, which makes it possible to obtain a sufficiently clean combustible gas, not giving rise to deposits such as soot or condensations (tars, acids).

 However, for the combustion of pyroligneous and tars to be complete, it is necessary to respect, at all levels of the gasifier, perfect homogeneity of the temperatures and flows of the gas and the carbonaceous matter. This perfect homogeneity is all the more difficult to obtain the larger the size of the gasifier. In addition, in large gas generators, there is an increased risk of the air injectors being blocked by molten ash.

 To facilitate the destruction of tars and improve the uniformity of temperatures and gas flow, it has been proposed to reverse the gas circulation in the upper part of the gasifier, to collect the distillation gases at the top of the apparatus , discharge these gases by means of a suction pump into an external combustion chamber and reinject the gases at high temperature into the middle zone of the enclosure of the gas generator.

Thus, a part of these gases rises in the apparatus and is recycled, after having caused the distillation of the fresh carbonaceous material and another part redes cent in the apparatus where it gasifies the coal resulting from the distillation of the carbonaceous material , to give rise to a clean combustible gas free of heavy hydrocarbons.

 The industrial development of this type of gasifier has been limited by the difficulties of extrapolation to the big powers.

 To remedy this difficulty, a gasifier with a fixed horizontal or inclined bed recently made of solid carbonaceous materials has been proposed, in which the combustion of the distillation gases takes place within the gasifier itself, above the layer of carbonaceous materials. . Part of the combustion gases is recycled through the layer of fresh carbonaceous materials which it helps to distill and the other part of the gases passes through a embankment of charcoal which it gasifies. Tar is thus destroyed in the combustion chamber located outside the charge of carbonaceous materials. The use of a ventilation turbine to recycle the gases makes it possible to significantly increase the flow rates and speed up exchanges with the mass of carbonaceous materials.

 The difficulties encountered in such an installation result, on the one hand, from its complexity (fan working at high temperature) and, on the other hand, in the entrainment of ash and coal in the recycling circuit where they cause deposits and a wear of the ventilation turbine by abrasion.

The aim of the present invention is to remedy the drawbacks of known embodiments, by creating a process and an installation for gasifying solid carbonaceous materials, with a high content of volatile products, allowing:
- to treat relatively wet carbonaceous materials,
- to produce clean combustible gases, without tar and with a very low hydrocarbon content,
- obtain high energy efficiency,
- A possible extrapolation to very high powers, while being simple and inexpensive to implement.

 In the process targeted by the invention, a drying and distillation zone for the carbonaceous material is created in an enclosure supplied with air and carbonaceous materials, a combustion chamber for: distillation products of the carbonaceous material, and a gasification zone for the carbon resulting from the distillation, the latter being traversed by the gases of combustion of the distillation products.

 According to the invention, this process is characterized in that the combustion chamber for the distillation products is created in an area located outside the carbonaceous material, and simultaneously on the path of the gases and of this carbonaceous material, between the drying and distillation zone and the de-gasification zone of the carbon resulting from the distillation.

 The distillation products formed in the drying and distillation zone enter the adjacent combustion chamber where they are destroyed.

The gases resulting from this combustion are then forced to pass through a layer of carbon resulting from the distillation, gasifying the latter in the gasification zone, before escaping outside the enclosure.

 Experience has shown that thanks to the fact that the combustion chamber for the distillation products is created in an area external to the carbonaceous material and simultaneously on the path of the gases and of this carbonaceous material, between the drying and distillation zone and the gasification zone, it was possible to obtain a clean combustible gas, without tars and with a very low content of heavy hydrocarbons, even in the case where the enclosure has a very high treatment capacity.

 According to an advantageous version of the invention, the drying and distillation zone is formed by a relatively thin layer of carbonaceous materials moving towards the gasification zone, this layer partially limiting the combustion chamber of the distillation products, jets d primary air being blown through said layer and secondary air jets being blown into the combustion chamber.

 The formation of a thin layer of carbonaceous materials in contact with the combustion chamber and upstream of the gasification zone, makes it possible to obtain an excellent heat exchange between the solid phase of this layer and the gas phase, which allows access - speed up the drying and distillation process.

 Preferably, the jets of secondary air are blown towards the gasification zone, which improves the homogenization of the gases during combustion before crossing the gasification zone and thus makes it possible to increase the yield of the gasification reaction. .

 According to another aspect of the invention, the installation targeted by the invention comprises an enclosure, means for supplying the latter with solid carbonaceous materials, means for extracting from this enclosure the residual carbon and the combustible gases formed, means to create in this enclosure a zone for drying and distilling the carbonaceous material, and a zone for gasifying the carbon resulting from the distillation, means being provided for blowing air into said drying and distillation zones and into said combustion chamber. This installation is characterized in that the enclosure comprises means for creating the combustion chamber in an area located outside the carbonaceous material and simultaneously on the path of the gases formed and of the carbonaceous material, between the drying and distillation zone and the gasification zone.

 According to a preferred version of the invention, the enclosure has an upper part flared upwards, this part enclosing a partition whose peripheral edge delimits with the wall of this flared part, an annular passage allowing the flow of the carbonaceous material. along the aforementioned wall, in the form of an annular layer, this partition having orifices for sending jets of secondary air into the combustion chamber and the wall of the flared part, having opposite the annular layer of carbonaceous materials of the openings to inject primary air jets through this layer.

 According to another embodiment of the invention, the installation particularly applied to the gasification of bulky objects made of solid carbonaceous material, separated by layers of air, such as pallets or wooden packaging boxes, comprises a zone of drying and distillation which is constituted by a stack of objects separated by layers of air, means for blowing air through this stack, the combustion chamber being adjacent to this stack and comprising means for blowing air air in it, this combustion chamber being delimited opposite to the stack by a wall whose lower edge is located at a certain distance above the bottom of the enclosure and upstream of a chimney d evacuation of the gases formed, this distance defining the height of the gasification zone.

 Other particularities and advantages of the invention will appear in the description below.

In the accompanying drawings, given by way of nonlimiting examples:
- Figure 1 is a schematic longitudinal sectional view of an installation according to the invention;
- Figure 2 is a sectional view along the plane II-II of Figure 1;
- Figure 3 is a section along the plane IIIo of Figure 1;
- Figure 4 is a longitudinal sectional view of another installation according to the invention;
- Figure 5 is a sectional view along the line VV of Figure 4.

 We will first describe, with reference to Figures 1 to 3, a preferred installation according to the invention, then we will expose the method according to the invention at the same time as the operation of the above installation.

 In the embodiment of FIGS. 1 to 3, the installation comprises an enclosure 1, the upper part 2 of which is constituted by a hopper 3 for supplying solid carbonaceous materials such as wood or agricultural waste, and the narrowed lower part 4 of which opens into a compartment 5 comprising a horizontal and movable grid 6. This grid 6 is located above an ashtray 7.

 The compartment 5 is provided at its upper part with a conduit 8 for evacuating the gases formed.

 The wall 9 of the enclosure 1 between the hopper 3 and the narrowed lower part 4 is frustoconical. It forms a slope of the order of 500.

 This frustoconical wall 9 surrounds a conical partition 10, the apex of which is directed upwards and situated on the axis of the frustoconical part 9.

 The peripheral edge 11 of the partition 10 defines with the frustoconical wall 9 an annular passage 12 allowing the flow of the carbonaceous material along the wall 9, in the form of an annular layer 13.

 The wall 9 has, opposite this annular layer 13, openings 14 for blowing jets of primary air through this layer. These air jets are directed radially towards the axis X-X 'of the enclosure 1.

 Furthermore, the partition 10 has orifices 15 for blowing jets of secondary air into the chamber 16 which is delimited by this partition 10 and by the annular layer 13 of carbonaceous materials.

These secondary air jets are directed towards the bottom of the enclosure and towards the axis XX '.

 The annular layer 13 adjacent to the openings 14 of the primary air jets constitutes the drying and distillation zone of the carbonaceous material.

 The chamber 16 is the combustion chamber for the products resulting from the distillation of the carbonaceous material which constitutes the layer 13.

 Under the chamber 16 and the annular layer 13, there is the zone 17 for carbonation of carbon resulting from the distillation of the carbonaceous material.

 It can therefore be seen, in FIG. 1, that the enclosure 1 comprises arrangements which make it possible to create a combustion chamber 16 in an area situated outside the carbonaceous material and simultaneously on the path of the gases formed in this chamber 16 and carbonaceous material, between the drying and distillation zone 13 and the gasification zone 17.

 We see on the other hand, in Figure 1 that the openings 14 located opposite the annular layer 13 communicate with two separate annular compartments 18, 19 juxtaposed according to the height of the frustoconical wall 9. These superimposed compartments 18, 19 are supplied individually in air by pipes 20, 21 connected to means making it possible to adjust the air flow in each of these compartments.

 Furthermore, the conduit 8 for evacuating the gases formed, also annular, is in contact with the superimposed compartments 18 and 19, which allows a heat exchange between the evacuated gases and the primary air blown into the enclosure 1.

 The secondary air is brought above the perforated partition 10 by a tube 22 which opens into a compartment 23 adjacent to the partition 10 and which separates the latter from the carbonaceous material.

The operation of the installation which has just been described is as follows:
The carbonaceous material introduced at the top of the enclosure 1 flows along the wall 9, forming an annular layer 13 around the combustion chamber 16 and facing the openings 14. The primary air is blown through these openings 14 through the layer 13 towards the combustion chamber 16. The secondary air is blown through the orifices 15 households in the frustoconical partition 10. After the initial ignition of the carbonaceous material, there occurs in the zone of the layer 13 drying and distillation. The resulting volatile products penetrate into chamber 16 where they are completely burned.

 The distillation is carried out with very good yield, thanks to the excellent thermal contact of the solid phase of the annular layer 13 with the gas phase.

 Furthermore, the destruction of the distillation products is complete thanks to the high temperatures prevailing in the chamber 16 and to the uniform distribution of the latter. Maintaining a high temperature in the chamber 16 is achieved by limiting heat loss to the outside thanks to the presence of the annular layer 13 and the compartments 18, 19 and 23 of primary and seeondair air supplies. The compartment 23 moreover, which separates the carbonaceous material from the combustion chamber 16 avoids any excessive heating of this material, while allowing a certain pre-drying of the latter.

 On the other hand, optimal distribution of primary air in the combustion chamber 16 is achieved through the use of separate compartments 18 and 19 supplied with air at adjustable rates.

 The charcoal resulting from combustion penetrates by gravity into the gasification zone 17 which is defined by the narrowed part 4 of the enclosure 1.

This zone 17 is crossed by the gases at high temperatures resulting from the combustion of the distillation products, which has the effect of gasifying the charcoal according to an endothermic reaction. The resulting gases are evacuated from the enclosure 1 by the annular duct 8 which is in thermal contact with the compartment 18, 19 thereby ensuring preheating of the primary air which is blown through the layer 13.

 The fuel gas formed is clean, free of tar and has a very low content of heavy hydrocarbons even in the case where the carbonaceous material is initially very humid. This gas can be used directly for heating or for the operation of heat engines.

 The installation according to the invention can be very large. It can, for example, process several tens of tonnes of fuel per hour.

 Furthermore, the installation, instead of being supplied with air, can also be supplied with oxygen and / or vapor, or C02 optionally, under a pressure higher than atmospheric pressure.

 The size of the installation is relatively small due to the absence of additional members placed outside the enclosure 1.

 The construction is particularly simple, in particular due to the absence of mechanical stirring and ventilation means as well as mechanical means for ensuring the displacement of the carbonaceous material.

 In the embodiment of Figures 4 and 5, there is shown an installation applied to the gasification of bulky objects in solid carbonaceous material, such as pallets or wooden packaging boxes.

 This installation comprises an enclosure 24 whose walls are internally coated with a refractory material 25. This enclosure has at one of its ends a door 26 for the introduction of the carbonaceous material and at its other end a vertical chimney 27 for the evacuation of gases formed by gasification of the carbonaceous material.

 The upper wall 28 has a duct 29 which connects the interior of the enclosure with the chimney 27.

At the intersection of this conduit 29 with the chimney 27 is provided a flap 30 intended to be folded down towards the chimney 27 to close off the latter during the initial phase of operation of the installation and to be folded down then towards the conduit 29 for shut off the latter, when the installation is in normal operating condition.

 The compartment 31 adjacent to the entrance contains a stack of pallets 32 separated by layers of air 33. This stack constitutes the zone for drying and distilling the carbonaceous material constituted by the wood of the pallets 32.

 Along the two longitudinal walls 34 of the enclosure 24 are arranged two vertical air supply conduits 35 having orifices for blowing jets of primary air 36 towards the stack of pallets 32, so that this air penetrates between the pallets 32 and crosses the stack of the latter.

 The installation also comprises a vertical wall 36a whose lower edge 37 is located at a certain distance above the bottom 38 of the enclosure 24. This lower edge 37 of the vertical wall 36 is located upstream of the inlet 39 of the chimney 27 for evacuating the gases formed, relative to the direction of movement of the latter.

 The upper wall 28 and the vertical wall 36a of the enclosure 24, as well as the surface 40 of the coal 41 formed by the combustion of the pallets 32 and which spreads over the bottom 38 of the enclosure, delimit a combustion chamber 42 .

 Behind the vertical wall 36a are arranged superimposed compartments 43, 44, 45, 46 supplied with air and arranged to inject secondary air jets 47 into the chamber 42 towards the stack of pallets 32.

 The part of the coal 41 spread over the bottom 38 of the enclosure and located downstream of the lower edge 37 of the vertical wall 36a, represents the gasification zone. The height of this zone is therefore defined by the distance between the lower edge 37 of the vertical wall 36a and the bottom 38 of the enclosure.

 It can therefore be seen that the installation shown in Figures 4 and 5 has in common with that shown in Figures 1 to 3, the fact that the combustion chamber is created in an area located outside the carbonaceous material and simultaneously , on the path of the gases and of this carbonaceous material, between the drying and distillation zone and the gasification zone of the carbon resulting from the distillation.

 This arrangement makes it possible to obtain both a complete destruction of the tars and other volatile materials originating from the distillation of the wood from the pallets 32 and an excellent yield from the gasification reaction.

 These excellent yields are explained on the one hand, by the optimal heat exchanges carried out between the different zones in contact and by the fact that the primary air jets 36 are sent in contact with thin layers of fresh fuel 32 and the jets d the secondary air 47 causes an internal recirculation of the gases in the combustion chamber 42 which makes it possible to obtain an optimal homogenization of the temperatures and of the compositions of the gases before passing through the layer of coal 41.

 As in the case of the previous embodiment, the gas formed in the combustion chamber 16, after destruction of the tars and other volatile products, is forced to pass through the carbon layer 41, thereby achieving with excellent efficiency, the gasification of this coal 41.

 On the other hand, as in the case of the previous embodiment, the combustible gas formed and evacuated by the chimney 27 is clean and free of tar, even in the case where the pallets 32 or other carbonaceous materials used are wet.

 Of course, the invention is not limited to the examples which have just been described and many modifications can be made to them, without departing from the scope of the invention.

 Thus, the method according to the invention can be implemented in an installation in which a continuous layer of carbonaceous material is moved continuously in an enclosure, using mechanical means such as conveyor belt, screws or the like, towards a fixed bed gasification area. In this case, the primary air is blown through the layer, into the combustion chamber located above this layer. Secondary air is sent into this chamber to the layer of carbonaceous material and to the gasification zone.

 Furthermore, in the case of the embodiment according to FIGS. 4 and 5, the stack of pallets 32 can be replaced by other bulky wooden objects such as packaging boxes stacked on top of each other so as to create layers of air between them.

 On the other hand, in the case of the embodiments according to FIGS. 4 and 5, it is possible to provide an external energy supply, for example electrical, by means of heating resistors or arcs to obtain in the combustion chamber 16, 42 the desired temperature, with a view to reducing oxygen consumption or enriching the gas.

Claims (10)

 1. A process for the gasification of carbonaceous materials with a high content of volatile products, in which a zone (13, 31) for drying and distilling the carbon is created in an enclosure (1, 24) supplied with air and carbonaceous materials. carbonaceous material, a combustion chamber (16, 42) of the products of distillation of the carbonaceous material, and a gasification zone (17, 41) of the carbon resulting from the distillation, the latter being traversed by the combustion gases of the products of distillation, characterized in that the combustion chamber (16, 42) of the distillation products is created in a zone situated outside the carbonaceous material and simultaneously on the path of the gases and of this carbonaceous material, between the zone ( 13, 31) for drying and distillation and the carbon gasification zone (17, 41) resulting from the distillation.  2. Method according to claim 1, characterized in that the drying and distillation zone (13) is formed by a relatively thin layer of carbonaceous materials moving towards the gasification zone (17), this layer (13) limiting at least partially the combustion chamber (16) of the distillation products, in that jets of air or primary gasification fluid are blown through said layer (13) and in that jets of air or secondary gasification fluid are blown into the combustion chamber (16).  3. Method according to claim 2, characterized in that secondary air jets are blown towards the gasification zone (17).  4. Method according to any one of claims 2 or 3, characterized in that an annular layer (13) of carbonaceous materials is formed in said drying and distillation zone, around the combustion chamber (16) of distillation products.  5. Installation for implementing the method according to any one of claims 1 to 4, comprising an enclosure (1, 24), means (2, 26) for supplying the latter with solid carbonaceous materials, means ( 8, 27) for extracting from this enclosure the residual carbon and the combustible gases formed, means for creating in this enclosure, a zone (13, 31) for drying and distilling the carbonaceous material,  a combustion chamber (16, 42) and a zone (17, 41) for gasifying the carbon resulting from the distillation, means being provided for blowing air into said drying and distillation zones and into said combustion chamber , characterized in that the enclosure (1, 24) comprises means for creating the combustion chamber (16, 42) in an area situated outside the carbonaceous material and simultaneously, on the path of the gases formed and of the carbonaceous material, between the drying and distillation zone (13, 31) and the gasification zone (17, 41).  6. Installation according to claim 5, characterized in that the enclosure (1) has an upper part (9) flared upwards, this part enclosing a partition (10) whose peripheral edge (11) delimits with the wall (9) of this flared part, an annular passage (12) allowing the flow of the carbonaceous material along the aforementioned wall, in the form of an annular layer (13), in that this partition (10) has orifices (15) for sending jets of secondary air into the combustion chamber (16) and in that the wall of the flared part (9) has, opposite the annular layer (13) of carbonaceous materials, openings (14) to inject primary air jets through this layer (13).  7. Installation according to claim 6, characterized in that the partition (10) is substantially conical, its apex being directed upwards and situated on the axis (X-X ') of said flared part (9).  8. Installation according to any one of claims 6 or 7, characterized in that the openings (14) located opposite the annular layer (13), communicate with several compartments (18, 19) juxtaposed according to the height of the wall (9) of the flared part, means (20, 21) being provided for supplying air separately and at adjustable flow rates, each of these compartments.  9. Installation according to claim 5, applied to the gasification of bulky objects in solid carbonaceous materials, sep; layers of air, such as pallets (32) or wooden packaging boxes, characterized in that the drying and distillation zone (31) consists of a stack of objects (32) separated by layers of air (33), means (35) for blowing air through this stack, the combustion chamber (42) being adjacent to this stack and comprising means (43, 44, 45 and 46) for blowing air air in it, in that this combustion chamber is delimited opposite to the stack of objects (32) by a wall (36a) whose lower edge (37) is located at a certain distance from the bottom (38) of the enclosure (24) and upstream of a chimney (27) for evacuating the gases formed, this distance defining the height of the gasification zone (41).  10. Installation according to any one of claims 5 to 9, characterized in that it further comprises means for heating the interior of the combustion chamber (16, 42) using a contribution d external energy.