EP2753677B1 - Carbonaceous solid fuel gasifier. - Google Patents

Description

Field of the invention

The invention relates to a gasifier for the gasification of a carbonaceous solid fuel, such as for example solid biomass.

More particularly, the invention relates to such a gasifier, comprising at least a first vertical tank provided with introduction means for introducing the fuel from above into said first tank and having a pyrolysis zone to pyrolyze the fuel, a combustion zone for burning pyrolysis gases from the pyrolysis zone, a reduction zone for gasifying carbonized fuel from the pyrolysis zone, and an outlet for collecting gases produced in the reduction zone, said first vessel comprising moreover, a horizontal plate mounted in a fixed manner between the introduction means and the pyrolysis zone for receiving and retaining the fuel introduced into the tank.

The invention also relates to a gas production and combustion unit comprising such a gasifier for producing said gas.

State of the art

Such gasifiers are known and make it possible to produce a combustible gas from a carbonaceous solid fuel, in particular from wood waste, such as those originating, for example, from sawmills or from forestry operations, or from - agricultural products (straw, etc ...), or from recycled wood. This combustible gas contains in particular carbon monoxide and hydrogen and can then be used for various purposes such as, for example, for supplying a gas turbine or an internal combustion engine or a boiler or an oven.

In order to supply the first tank with fuel, it is known to provide fuel introduction means that are gas-tight that will be produced in the tank. This sealing prevents the gases produced in the tank from going back to the storage and fuel supply systems, so that said gases will essentially go to the outlet when the gasifier is in operation. It is known to use for this purpose a lock mechanism at the entrance of the first tank.

The patent application WO 2007/081296 discloses a gasifier having a rotary valve located in the upper part of the reactor. This device has the advantage of being able to properly dose the fuel supply, but it however has the disadvantage of not being sufficiently gas-tight and require an additional sealing mechanism upstream, which increases the cost. In addition, the valve must be able to withstand the high temperatures that prevail in the first tank when the gasifier is in operation, which requires particularly expensive valves. The document NL8200417A discloses a similar gasifier and having the same disadvantages as WO 2007/081296 from a thermal point of view.

Other mechanisms use only a two-valve lock in place of the rotary valve discussed above. In addition to the fact that this type of mechanism is less efficient in terms of material dosing (batch dosing), the lower valve must also withstand said high temperatures and is therefore expensive.
The patent application WO 2001/051591 discloses a gasifier having an airlock arranged laterally with respect to the upper part of the reactor, which makes it possible to obtain a good gas-tightness, as well as a lateral pipe provided with an endless screw acting as a link between the airlock and the first tank, which also allows to properly dose the material supply. However, such a device is expensive and bulky. The auger is also prone to fouling, which requires maintenance, and / or blocking by pieces of fuel. In addition, since the end of the screw opens into the tank, it is subjected to the high temperatures that prevail when the gasifier is in operation, which requires the use of an expensive screw. The document EP0273656A1 discloses a gasifier similar to that of WO 2001/051591 . It comprises a pyrolysis tank including a plurality of retractable trays that allow the material to be lowered in a stepped manner into said pyrolysis vessel. The pyrolysis gases are then burned in a separate combustion chamber. This device has the same disadvantages as WO 2001/051591 from a thermal point of view if one can imagine using it as it is intended to use a gasifier according to the invention. In addition, retractable trays are expensive and complex device because at least a portion is outside the pyrolysis tank, which also poses sealing problems.

The patent application WO 2010/109501 discloses a gasifier in the form of a tank, in the upper part of which the fuel is introduced laterally. The fuel is then retained in a drying zone of the tank by means of a horizontal wall pierced with an orifice at its center. Through this orifice is placed vertically an endless screw which transfers the fuel from the drying zone to a pyrolysis zone located just below the horizontal wall. This auger opens into the pyrolysis zone and must be able to withstand the high temperatures that prevail when the gasifier is in operation, which requires screws particularly resistant and expensive. The auger is also prone to fouling, which requires maintenance, and / or blocking by pieces of fuel.

Summary of the invention

An object of the invention is to at least partially solve the problems of gasifiers mentioned above.

To this end, the gasifier according to the invention is characterized in that the first vessel comprises a mobile pusher mounted between the introduction means and the horizontal plate, said mobile pusher being designed to push the fuel retained on the horizontal tray to the pyrolysis zone and being positioned or positionable above the horizontal tray.

With such a configuration, the horizontal plate will form a heat shield that will protect both the fuel introduction means and the pusher against the high temperatures that prevail in the first tank (against radiation and flames in particular). This makes it possible to use less expensive material transfer mechanisms (introduction means, pusher) and / or to increase their durability and / or reliability.

Such a mobile pusher also takes up less height and is simpler and more reliable than the vertical worm (12) proposed in the patent. WO-2010/109501 .

Preferably, the movable pusher comprises at least one leg extending horizontally above the plate and rotatably mounted about a first vertical axis. A rotary pusher makes it possible to better distribute the fuel on the fuel bed in the pyrolysis zone, which improves the quality of the pyrolysis reaction. In particular, this makes it possible to reduce the tar content of the product gas.

Various mechanisms have also been devised in the past to better distribute the fuel on the fuel bed after its introduction into the first tank.
The US Patent 5,755,837 (see his figures 4 and 5 ) proposes for example to provide the upper part of the first tank with an inclined weir. This device will nonetheless cause a greater accumulation of material at the point of their drop points on the fuel bed. In particular, the fuel level will be greater on the peripheral part of the first tank than in its central part.
The patent GB 696682 proposes for its part to provide the upper part of the first tank with a mechanism with two rotating plates pierced with orifices. Here too, the fuel will settle preferentially to the right of the orifices. Moreover, this mechanism is likely to become fouled and / or blocked by pieces of fuel.

In order to address these problems, the gasifier according to the invention preferably comprises leveling means capable of leveling at least partially an upper surface of the solid fuel bed in the pyrolysis zone. The inventors have thus provided a mechanism acting directly on the fuel bed rather than acting on the spill of fuel on the bed, reducing or eliminating the disadvantages of the known mechanisms. The leveling means make it possible to further distribute the fuel on the fuel bed in the pyrolysis zone, which improves the quality of the pyrolysis reaction.

According to a preferred embodiment, the leveling means comprise at least one arm extending horizontally at the upper surface of the solid fuel bed in the pyrolysis zone, said at least one arm being rotatably mounted around a second vertical axis C. This is indeed a simple, reliable and effective way to distribute the solid more uniformly on the bed of material in the pyrolysis zone.

Brief description of the figures

Fig.1

montre schématiquement une coupe frontale d'un gazéifieur selon l'invention;

Fig.2

montre schématiquement une coupe frontale d'un mode de réalisation préféré d'un gazéifieur selon l'invention;

Fig.3

montre schématiquement une coupe transversale du gazéifieur de la Fig.2;

Fig.4

montre schématiquement une coupe frontale d'un mode de réalisation plus préféré d'un gazéifieur selon l'invention;

Fig.5

montre schématiquement une coupe frontale d'un mode de réalisation encore plus préféré d'un gazéifieur selon l'invention;

Fig.6

montre schématiquement une coupe transversale du gazéifieur de la Fig.5 ;

Figs.7a et 7b

montrent schématiquement, respectivement une coupe frontale et transversale d'un mode de réalisation encore plus préféré d'un gazéifieur selon l'invention ;

Figs.8a et 8b

montrent respectivement une coupe frontale et une coupe transversale d'un mode de réalisation préféré d'un gazéifieur selon l'invention.

These and other aspects of the invention will be clarified in the detailed description of particular embodiments of the invention, with reference to the drawings of the figures, in which:

Fig.1

shows schematically a frontal section of a gasifier according to the invention;

Fig.2

shows schematically a frontal section of a preferred embodiment of a gasifier according to the invention;

Fig.3

schematically shows a cross-section of the gasifier of the Fig.2 ;

Fig.4

shows schematically a frontal section of a more preferred embodiment of a gasifier according to the invention;

Fig.5

shows schematically a frontal section of an even more preferred embodiment of a gasifier according to the invention;

Fig.6

schematically shows a cross-section of the gasifier of the Fig.5 ;

Figs.7a and 7b

schematically show respectively a frontal and transverse section of an even more preferred embodiment of a gasifier according to the invention;

Figs.8a and 8b

show respectively a frontal section and a cross section of a preferred embodiment of a gasifier according to the invention.

The drawings of the figures are not to scale. Generally, similar elements are denoted by similar references in the figures.

Detailed description of particular embodiments

The embodiments described below relate to a co-current gasifier, fixed bed, and formed by a single vessel comprising both the pyrolysis zone, the combustion zone and the reduction zone. It will be obvious that the invention is not limited to this type of gasifier but relates to all the gasifiers having the characteristics of the preamble of the first claim, such as, for example, countercurrent gasifiers, or gasifiers comprising several tanks put next to each other, the first tank being the one where the pyrolysis reactions of the fuel take place.

Similarly, the embodiments described below use solid biomass as an exemplary fuel, but it will be obvious that any other type of carbonaceous solid fuel will also be suitable.

• un sas d'entrée (5) permettant d'introduire de la biomasse (2) dans la cuve selon un axe vertical (A),
• une zone de pyrolyse (10) pour pyrolyser la biomasse introduite dans la cuve,
• une zone de combustion (20) pour bruler des gaz de pyrolyse provenant de la zone de pyrolyse,
• une zone de réduction (30) pour gazéifier de la biomasse carbonisée provenant de la zone de pyrolyse,
• une sortie (6) pour récolter des gaz provenant de la zone de réduction, et
• une zone (40) pour collecter et évacuer des cendres.

The Fig.1 shows schematically a frontal section of a gasifier (1) according to the invention. In this example, it is a cocurrent and fixed bed gasifier. This gasifier is essentially formed by a reactor having the shape of a vertical tank (4) comprising successively and from top to bottom:

• an airlock (5) for introducing biomass (2) into the vessel according to a vertical axis (A),
• a pyrolysis zone (10) for pyrolyzing the biomass introduced into the tank,
• a combustion zone (20) for combusting pyrolysis gases from the pyrolysis zone,
• a reduction zone (30) for gasifying carbonized biomass from the pyrolysis zone,
• an outlet (6) for harvesting gases from the reduction zone, and
• an area (40) for collecting and discharging ashes.

It should be noted that the entry lock can take various forms, such as for example a rotary valve and / or a lock with two valves and / or any other means of introduction known to those skilled in the art.

The biomass (2), for example wood chips, is introduced into the tank (4) from above through the inlet lock (5) and then arrives - via the intermediate device (50, 51) described in more detail hereinafter - in the pyrolysis zone (10) where it decomposes, under the effect of heat, into volatile matter and into a solid residue rich in carbon generally called "char" or "coke". This reaction typically occurs in a temperature range of 300 ° C to 700 ° C.

In order to reach these temperatures, the tank generally comprises first means of admission of a pyrolysis agent (11) - for example one or more nozzle (s) opening laterally into the tank at the level of the pyrolysis zone - and which allow to introduce a gas which will bring directly or indirectly the energy necessary for the decomposition of the biomass in volatile materials and in "char". Said pyrolysis agent may for example be an oxygen-containing reactive gas which, by burning a fraction of the biomass or products of the decomposition of the biomass, will release the energy necessary for pyrolysis. It can also be an inert gas (such as carbon dioxide, nitrogen, water vapor) which, preheated, will provide the energy necessary for pyrolysis. It can also be a combination of both types of gas.

The "chariot" is then transferred to the reduction zone (30) by well known means, for example those described in the patent application. EP11171156 .

Volatiles (also known as "pyrolysis gases") entering the combustion zone (20) are partially or totally burned. In order to promote this combustion, the tank preferably comprises second means for admitting a gasifying agent (21). These second intake means may for example comprise a plurality of nozzle (s) opening laterally into the tank at the combustion zone. By "gasifying agent" is meant a gas capable of reacting with the carbon and / or hydrogen contained in the solid fuel. Said gasifying agent may therefore for example be ambient air, a gas with a higher concentration of oxygen, water vapor, carbon dioxide or a mixture of these gases. This combustion produces mainly carbon dioxide (CO ₂ ), water (H ₂ O), and of course heat. Typically, temperatures above 1100 ° C are attainable in the combustion zone.
The "tank" that has been transferred to the reduction zone will react with the combustion products to form carbon monoxide (CO) and hydrogen (H ₂ ).
In the case for example of an autothermic reaction of lignocellulosic materials - such as wood - and the use of ambient air at room temperature as a gasifying agent, this reaction typically occurs in a temperature range. between 300 ° C and 800 ° C. This temperature may nevertheless be higher and reach or even exceed 1300 ° C in the case where a higher carbon fuel is used and / or preheated reagents are used. The gases produced by this reaction will be collected at the outlet (6) of the reactor which is located in the bottom of the tank (4). There is thus at the outlet (6) a fuel gas typically comprising about 15% to 30% CO, 10% to 25% of H ₂ , 0.5 to 3% of CH ₄ , 5% to 15% of CO ₂ and 49 % N ₂ when using ambient air as a gasifier.
The ashes can be collected in the bottom (40) of the tank.

Such gasifiers are known and therefore will not be entered in more detail in their design or operation.

Attention will now be focused on the device (50, 51) located just below the entrance lock (5).

This device comprises firstly a horizontal plate (50) fixedly mounted between the entry lock (5) and the pyrolysis zone (10). Said plate (50) is positioned and sized to receive and at least partially retain the fuel (2) introduced into the tank (4) via the input lock (5).
Preferably, the plate is positioned and dimensioned so that it completely retains the fuel and that the latter can only flow to the pyrolysis zone under an external action, such as under the action of the pusher described herein. -after.
To this end, the position and the size of the plate will be adapted to the flow properties of the fuel used, in particular its slope angle (eg for wooden copula, the angle of repose is of the order of 60 °).

The device further comprises a movable pusher (51) mounted between the entry lock (5) and the horizontal plate (50). Said pusher (51) is positioned above the horizontal plate (50), so that the horizontal plate forms a heat shield protecting the pusher from the heat prevailing below the plate when the gasifier is in operation. As illustrated in the figure, it may be for example a horizontal cylinder and at the end of which is mounted a vertical plate acting as a pusher. When the cylinder is actuated, the fuel retained on the plate will be pushed by the plate and fall by gravity into the pyrolysis zone (10). The fuel dosage can be achieved by controlling the movement of the cylinder.

The Fig.2 shows schematically a frontal section of a preferred embodiment of a gasifier according to the invention. According to this preferred mode, the mobile pusher (51) comprises at least one branch (52) extending horizontally above the tray horizontal (10) and rotatably mounted about a first vertical axis (B). This branch may for example be constituted by a vertical plate.
One end of the branch is here connected to a shaft of a motor (M) to allow the rotation of the branch. The movable pusher (51, 52) is thus positionable above the horizontal plate (50), which allows the plate to fulfill its role of heat shield when the pusher is actually positioned above the plate. It will be understood that the pusher may temporarily overflow the tray when the motor (M) is rotated, but it is important that the pusher can at one time or another be positioned above the tray.
Preferably, the motor (M) is provided with a speed reducer in order to increase the torque and the precision of the movement transmitted to the first branch. Preferably, the motor (M) is mounted above the plate so that the plate also forms a heat shield vis-à-vis the engine. More preferably, the motor (M) is mounted outside the tank, in which case its shaft will pass through the upper part of the tank via a seal or a sealed bearing to be subsequently connected to the first branch (not a case). -illustrated).

Preferably, the first axis (B) is offset with respect to the axis (A).

The Fig.3 schematically shows a cross-section of the gasifier of the Fig.2 . It shows an example of the shape that can have the horizontal plate (50) and the branch (52) of the pusher and how these two elements can be arranged relative to each other.

Preferably, the gasifier comprises a motor (M) for driving the at least one branch (52) of the pusher in rotation about the first axis (B) and first control means (60) able to control the motor (M) to give a rocking movement to said at least one branch (52) about said first axis (B). For this, one can use for example a motor whose direction of rotation can be reversed, such as for example a DC motor.

This makes it possible to overflow the biomass by a first end (56) of the plate when the engine rotates in a first direction of rotation and to overflow the biomass by a second end (57) of the plate, opposite to the first side, when the engine rotates in a second direction of rotation opposite the first direction of rotation. This makes it possible to obtain a more uniform distribution of the fuel on the bed in the pyrolysis zone.

Preferably, the first control means (60) are able to adjust a starting angular position (P1) as well as an amplitude (A1) of the pendulum movement, which makes it possible to regulate even more precisely the transfer of biomass from the plateau towards the pyrolysis zone. For this purpose, it is possible, for example, to use a stepper motor provided with an encoder wheel for the angular position of the motor shaft, as well as a suitable controller, this type of assembly being largely known as such.

The Fig.4 schematically shows a frontal section of a more preferred embodiment of a gasifier according to the invention.
Here, the first tank (4) further comprises leveling means (70) capable of leveling at least partially an upper surface (80) of the biomass bed in the pyrolysis zone (10). As illustrated in the figure, these leveling means comprise for example a horizontal cylinder whose end is provided with a scraper. Said scraper is located at the upper surface (80) of the biomass bed in the pyrolysis zone (10). Preferably, the scraper has the shape of a rake whose teeth are oriented downwards. Actuation of the jack will thus level said upper surface (80) of the biomass bed.

The Fig.5 schematically shows a frontal section of an even more preferred embodiment of a gasifier according to the invention. According to this more preferred version, the leveling means (70) comprise at least one leveling arm (71) extending horizontally at the top surface (80) of the solid fuel bed in the pyrolysis zone (10), said at least one leveling arm (71) being mounted rotatable about a second vertical axis (C). The leveling arm may for example be constituted by a vertical plate or a rake whose teeth are oriented downwards.
One end of the leveling arm (71) is here connected to a shaft of a motor (M) to allow the rotation of said arm (71). Preferably, this motor (M) is provided with a speed reducer in order to increase the torque and the precision of the movement transmitted to the arm (71). The operation of the engine will thus level the upper surface (80) of the biomass bed when the gasifier is in operation.
The Fig.6 schematically shows a cross-section of the gasifier of the Fig.5 . There is better the leveling arm (71) and its rotary movement.

Preferably, the leveling means comprise six arms mounted radially every 60 degrees around a rotary shaft of axis C.

Preferably, the axis B and the axis C are merged. More preferably, the at least one leg (52) of the pusher and the at least one arm (71) of the leveling means are mounted on the same rotary shaft (75). An exemplary embodiment is provided to Figs. 7a and 7b .
Here, a single motor (M3) drives both the branch (52) of the pusher and the leveling arm (71) via a common rotary shaft (75), which simplifies the assembly and thus makes it less expensive, less bulky and more reliable.
In such a configuration, the branch (52) of the pusher and the leveling arm (71) are preferably mounted in opposition, that is to say angularly offset by 180 degrees, as can be seen better on the Fig. 7b . When the common motor (M3) is controlled to print a pendulum movement to the branch (52) and to the arm (71), this makes it possible to ensure that, during each forward or backward movement, the arm (71) will pass above the biomass discharged previously on the bed (80) of biomass by the branch (52) of the pusher. This gives a very good equalization of the surface of the biomass bed in the pyrolysis zone, which improves the pyrolysis reaction.

The Figs.8a and 8b show respectively a frontal section and a cross section of a preferred embodiment of a gasifier according to the invention. Here, the tray is formed by a fixed plate (50) which extends substantially over the entire cross section of the vessel (4). The plate (50) is furthermore provided with at least one opening (58) through which the pusher (52) can push the fuel (2) retained by the plate so that it falls by gravity into the pyrolysis zone. (10). The opening (58) is offset relative to the intake means (5) so that the fuel can not fall directly into the pyrolysis zone. For the rest, this gasifier is similar to those described above.
As we see on the fig.8a , the motor (M3) will preferably be deported out of the tank (4) in order to access it more easily and so that it is not subjected to the conditions prevailing inside the tank (temperature, presence of gas, etc ...).

Many other forms of tray and pusher can be envisaged, as long as the tray is able to retain the fuel from the introduction means (5) and the pusher (52) is able to push and to fall by gravity the fuel retained, to the pyrolysis zone (10).

The invention also relates to a gas production and combustion unit comprising a gasifier according to any one of the preceding claims for producing said gas. It can act for example an assembly comprising a gasifier as described above and an internal combustion engine, the outlet (6) of the gasifier being connected to a fuel system of the combustion engine internal.

The present invention has been described in relation to specific embodiments, which have a purely illustrative value and should not be considered as limiting. In general, it will be apparent to those skilled in the art that the present invention is not limited to the examples illustrated and / or described above. The invention includes each of the novel features as well as all their combinations.

The presence of reference numbers in the drawings can not be considered as limiting, even when these numbers are indicated in the claims. The use of the verbs "to understand", "to include", "to include", or any other variant, as well as their conjugations, can in no way exclude the presence of elements other than those mentioned.
The use of the indefinite article "a", "an", or the definite article "the", "the" or "the", to introduce an element does not exclude the presence of a plurality of these elements.

In summary, the invention can also be described as follows: a carbonaceous solid fuel gasifier (2) having at least a first vertical vessel (4) and introduction means (5) for introducing the fuel (2) into a upper portion of the first vessel above a pyrolysis zone (10), said pyrolysis zone being an area where the fuel introduced is pyrolyzed to produce pyrolysis gases and carbonized fuel. The gasifier also has a combustion zone (20) for burning said pyrolysis gas, a reduction zone (30) for gasifying the carbonized fuel from the pyrolysis zone (10) to produce synthesis gases and ashes, and an outlet (6) for harvesting said synthesis gases. The first tank (4) comprises a fixed horizontal plate (50) mounted between the introduction means (5) and the pyrolysis zone (10) in order to retain the fuel introduced therein, as well as a movable pusher (51). mounted between the introduction means (5) and the plate (50) for transferring the fuel retained on the plate to the pyrolysis zone (10). The plate (50) forms a thermal shield at least partially protecting the introduction means (5) and the movable pusher (51) against the high temperatures prevailing in the first tank (4) when it is in operation.

Claims (10)

1. Gasifier (1) for gasification of carbonaceous solid fuel (2) comprising at least one principal vertical tank (4) equipped with an input system (5) for adding the fuel (2) from the top in the said principal tank (4), having successively from top to bottom:

   - a pyrolysis zone (10) where the fuel is pyrolysed, which comprises the principal admission system (11) for a pyrolysis agent,

   - a combustion zone (20) for burning the pyrolysis gas from the pyrolysis zone (10), which comprises a secondary admission system (21) for a gasification agent, where the said secondary admission system (21) is different from the said principal admission system (11),

   - a reduction zone (30) for gasifying the carbonised fuel from the pyrolysis zone (10),

   and comprising an outlet (6) for collecting the gases produced in the reduction zone, characterised in that the said principal tank (4) comprises a horizontal plate (50) fixedly mounted between the input system (5) and the pyrolysis zone (10) for receiving and holding the fuel (2) added to the tank (4),
   and in that the principal tank (4) comprises a movable tappet (51) mounted between the input system (5) and the horizontal plate (50), where the said movable tappet (51) is designed for pushing the fuel held on the horizontal plate towards the pyrolysis zone and is positioned or can be positioned on top of the horizontal plate (50);
2. Gasifier according to claim 1, characterised in that the movable tappet (51) comprises at least one arm (52) extending horizontally over the plate (10) and disposed to rotate around a principal vertical axis (B);
3. Gasifier according to claims 1 or 2, characterised in that it comprises a motor (M) for driving at least one arm (52) of the tappet rotating around the principal axis (B) and principal control system (60) for controlling the motor (M) to produce a pendulum swing to the said arm (52) around the said principal axis (B);
4. Gasifier according to claim 3, characterised in that the principal control system (60) is capable of setting an angular starting position (P1) as well as the range of the pendulum swing,
5. Gasifier according to any of the preceding claims, characterized in that the principal tank (4) comprises a levelling system (70) for at least partially levelling the upper surface (80) of the said solid fuel in the pyrolysis zone (10);
6. Gasifier according to claim 5, characterized in that the levelling system (70) comprises at least one levelling arm (71) that extends horizontally over the level of the upper surface (80) of the said solid fuel in the pyrolysis zone (10), where the said arm is mounted to rotate around a second vertical axis (C);
7. Gasifier according to claim 6, characterized in that the levelling system comprises six arms mounted radially at every 60 degrees around a rotating shaft of axis C;
8. Gasifier according to claims 6 or 7, characterized in that the axis B and axis C are aligned;
9. Gasifier according to claim 8, characterized in that at least one arm (52) of the tappet and at least one arm (71) of levelling system is mounted on the same rotating shaft (75);
10. Gas production and combustion unit that comprises a gasifier in one the preceding claims for producing the said gas.

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