Background

For environmental and energy security reasons there is an increased need to produce syngas and other gaseous fuels, which may be produced using a variety of types of biomass like woodchips, grain residue or sawdust. Syngas consists primarily of a mixture of carbon monoxide and hydrogen gas.

A conventional way to produce such gas and which is beneficial for small scale production is to use “fixed bed” syngas reactors, so called Imbert- type gasifiers. For these, a reaction takes place on a reducing surface. Biomass may be pyrolyzed, oxidized and reduced producing syngas.

Conventional “fixed bed” reactors are however sensitive for the grain size fraction of the biomass since clogs are formed which may damage the drift. The biomass used can, especially if the grain size is smaller, stack up and build so-called bridges which cause a lower efficiency of the reactor. This can also cause fluctuating operations and may disturb the robustness of the production of the syngas.

There is therefore a need for a solution which mitigates the above- mentioned problems.

There is an object of the present invention to provide a solution which mitigates the above-mentioned problems. Further there is an object to provide a gasifier for generating synthesis gas and a method for generating synthesis gas by gasification of a biomass.

According to one aspect of the present invention there is provided a gasifier for generating synthesis gas. The gasifier comprises a gasification chamber comprising a biomass inlet, and an oxidation zone wherein the biomass inlet is arranged axially above the oxidation zone so that the biomass is moved towards the oxidation zone by means of gravity when in use. The gasifier further comprises a rotating shaft which extends within the gasification chamber.

In one embodiment the biomass inlet is open- and closable by a valve mechanism so as to separate the gasification chamber from the ambient air

The rotating shaft comprises first biomass engaging means configured to transport engaged biomass upwards, away from the oxidation zone, upon rotation of the rotating shaft so as to mix the biomass.

Hereby, the rotating shaft with the first biomass engaging means contributes to a better mixture of the biomass which gives a higher efficiency of the pyrolysis and combustion than that of conventional syngas reactors.

It further contributes to a more robust production of syngas, since the mixing of the biomass may enhance the continuous flow of the biomass and thus avoid fluctuations in the operations of the reactor.

Better mixing of the biomass prevents the forming of clogs which may damage the operation of the reactor.

In one embodiment the gasification chamber comprises ceramic walls along the extension of the oxidation and/or reduction zone. The ceramic walls may be heated to a high temperature.

In one embodiment the walls of the gasification chamber may be heated, preferably to 200-900°C, more preferable 300-600°C.

The walls may be heated by electricity, and/or by the hot synthesis gas produced in the gasification chamber.

In one embodiment the gasifier may further comprise an outflow channel configured to channel syngas upwards from the oxidation zone through the outflow channel along walls of the gasification chamber.

In one embodiment the walls of the gasification chamber may be double walls. In one embodiment the outflow channel may be arranged inside the walls of the gasification chamber so as to heat the walls of the gasification chamber by means of the synthesis gas.

When biomass comes into contact with the walls of the reactor, it contributes to a higher efficiency since the walls at least to some extent have a high temperature which enhances reactions of the gasifier.

The present invention enhances the use of fixed bed reactors on a larger scale and decreases the need for fluid size reactors.

In one embodiment the biomass inlet is located axially above a pyrolysis zone of the gasifier. Thereby the biomass may go through the entire pyrolysis zone contributing to higher reaction efficiency.

In one embodiment the first biomass engaging means are protruding axially outwards from the rotating shaft.

In one embodiment the first biomass engaging means is an auger.

The auger may provide an efficient way of mixing the biomass. The auger may enable biomass to be transported from the bottom part of the auger to the top part of it. Biomass that is disengaged from the auger may fall down radially outside of the auger due to gravity and be engaged to the auger at a location further down.

In one alternative embodiment the first biomass engaging means may be paddles which may be angled so as the biomass is transported upwards or downwards.

In one embodiment the gasification chamber further comprises a pyrolysis zone above the oxidation zone and a reduction zone below the oxidation zone.

In one embodiment the temperature in the pyrolysis zone may be 200- 900 °C.

The walls of the pyrolysis zone may be heated to a temperature of about 200-900°C, or preferably to about 300-600°C. The pyrolysis zone may be preheated by means of a double wall channelling the hot syngas produced by the gasifier.

In one embodiment, the syngas is produced in the oxidation zone and flows via the reduction zone out at the bottom of the gasifier and is subsequently led up through the double walls to the level of the pyrolysis zone above the oxidation zone. At the level of the pyrolysis zone the hot syngas may heat the fuel indirectly through the walls so that the fuel is pyrolyzed.

In one embodiment, the volume between each of the walls in the double wall forms a space constituting at least a portion of the outflow channel.

In the pyrolysis zone reactions may take place in the absence of oxygen, so as combustion does not occur. Syngas, higher hydrocarbons and char may be produced from the biomass. The gases produced in the pyrolysis zone may move downwards in the chamber.

In one embodiment the temperature in the oxidation zone may be GOO- OO °C. Remaining combustible gas including methane from the pyrolysis zone may as well as carbon of produced char react with oxygen, with carbon monoxide and hydrogen gas as reaction products, together forming carbon dioxide and water vapour. Said reactions are exothermic and contributes to achieving said temperature in the oxidation zone. The gases produced in the oxidation zone may be transported downwards due to an under pressure, at a gas outlet, which may be created by e.g. a combustion engine or other pressure generating means. Additionally or alternatively the gases are moved by means of a blower. The combustion engine or other pressure generating means such as a blower may thereby force the gas down through the fuel in the reduction zone and further out through the channels in the walls and out of the outlet.

In the reduction zone still remaining carbon from the char may react with carbon dioxide, water and hydrogen and form the products carbon monoxide, hydrogen and methane. Methane may react with water vapour and carbon monoxide and form hydrogen gas, carbon monoxide and carbon dioxide, respectively. The net result of the reactions in the reduction zone may be a higher content of syngas and a lower content carbon dioxide. The temperature in the reduction zone may be 700-1000 °C. Gas which has been produced in the oxidation zone may thereby be reduced in the reduction zone.

In one embodiment the gasifier comprises an outflow gas channel outside and along the walls of the gasification chamber, said channel being configured to channel gas produced in the reduction zone upwards. The channel may be shaped so as the produced gas may heat the walls of the gasification chamber. The walls may be heated to a temperature of about 200-900°C, or preferably to about 300-600°C, by the produced gas.

Thereby the walls of the gasification chamber may be heated by the produced syngas and the produced syngas may be cooled by the walls.

The rotating shaft may extend through the entire pyrolysis zone and oxidation zone of the gasification chamber along a longitudinal direction of the chamber.

The first biomass engaging means may extend along the entire or a portion of the rotating shaft which extends within the pyrolysis zone.

The pyrolysis zone may be of a longer type or a shorter model. If a shorter model is used, the biomass may be pre-pyrolyzed before being fed into the gasifier.

In one embodiment the rotating shaft comprises an oxidation gas channel providing the oxidation zone with oxidation gas from an oxidation gas inlet.

The rotating shaft comprising an oxidation gas channel may provide an efficient transportation of oxidation gas into the oxidation zone. The oxidation gas inlet being at the rotation shaft in the oxidation zone may enhance the process by having an oxidation gas inlet where the mixing is larger so as the oxidation gas is more evenly distributed over the biomass. The oxidation gas may be air, oxygen or any mixture of gas comprising oxygen.

The oxidation gas channel may provide the oxidation zone with oxidation gas in a sufficient flow as to keep the temperature at an optimal level around 1100°C.

In one embodiment the rotating shaft comprises a second portion having second biomass engaging means configured to transport engaged biomass in a downward direction and the first biomass engaging means are arranged in a first portion of the rotating shaft.

The second biomass engaging means may be located above the first biomass engaging means on the rotating shaft in an axial direction, wherein the second portion is an upper portion of the rotating shaft. The second biomass engaging means may force the biomass to move along and close to the hot walls of the pyrolysis zone, enhancing the pyrolysis of the biomass and ensuring a low content of tar in the produced syngas.

The biomass engaging means of the lower portion of the rotating shaft may force the biomass downwards towards the oxidation zone to prevent the biomass from clogging at a border between the pyrolysis zone and the oxidation zone.

In one embodiment the second biomass engaging means are an auger threaded in the opposite direction compared to the first biomass engaging means.

The auger threaded in the opposite direction may transport biomass downwards from the uppermost part of the chamber. In combination with the first biomass engaging means transporting biomass upwards, biomass may in between the first and second biomass engaging means be moved towards the walls of the chamber. The hot temperature of the walls may contribute to a higher efficiency of the gasification process. More biomass getting into contact with the walls may thereby increase said efficiency. The inclusion of an auger which is threaded in two opposite directions may be an efficient solution to achieve this effect since the auger may rotate in one direction and give rise to two opposite directions of the transportation of biomass dependent on in what direction a specific portion of an auger is threaded.

In one embodiment the rotating shaft extends along a central axis of the gasification chamber, and the first engaging means have a radial extension of less than 2/3, preferably less than >2, more preferably less than 1/3, of the distance between the rotating shaft, and the inner walls of the gasification chamber.

This may enhance the mixing of the biomass since the biomass is allowed to fall down in the outer region to which the lower biomass engaging means does not reach. Thereby a circulation may be achieved in which the biomass is transported upwards in a radially inner region and falls down in a radially outer region of the chamber.

In one embodiment the second engaging means have a radial extension being larger than the first engaging means.

Because of the upper engaging means having a larger radial extension than the lower engaging means, a net flow with downward direction of the biomass may be achieved.

In one embodiment the rotating shaft comprises at least one oxidation gas outlet which protrudes from the rotating shaft.

The at least one oxidation gas outlet may me formed and distributed for an even provision of oxygen into the biomass.

The at least one oxidation gas outlet may be sized and formed to provide an even temperature in the oxidation zone.

The at least one oxidation gas outlet may protrude out from the rotating shaft to contribute to mixing the biomass in the oxidation zone.

The at least one oxidation gas outlet may be a nozzle or a hole. The at least one oxidation gas outlet may comprise any number of outlets, e.g. 1 , 2, 4, 8, 12, 20 or 100 outlets. By having a plurality of outlets, a more even distribution of oxidation gas is achieved.

In one embodiment the chamber has a tapered form, which is narrowing in the downward direction.

The gasification chamber having a tapered form helping biomass to flow smoothly along the walls and may as well increase the contact between the biomass and the walls of the chamber so as to increase the reaction rate due to the high temperature of said walls.

In one embodiment there are third biomass engaging means at a third portion of the rotating shaft being below said first and second portion of the rotating shaft. The third biomass engaging means may move the biomass along a third portion of the rotating shaft downwards, which may be important since the bottom of the pyrolysis zone is narrowest and the risk of clogging there may be biggest.

In one embodiment the gasifier further comprises a control unit, which is arranged to control the rotational movement of the biomass engaging means.

In one embodiment the rotational movement controlled by the control unit includes both rotational direction and rotational speed.

The control unit may change direction and rate of rotation of the rotating shaft due to input from e.g. a sensor unit. Changing direction may reduce occurrence of clogging of the biomass or other operational or safety problems by which the movement of the rotational shaft could be changed or halted. The direction may alternatively be reversed periodically. For instance, the direction may be reversed for 5-10 s every minute, for 10 s-1 minute every tenth minute or 1-5 minute every hour.

According to a second aspect of the inventive concept there is provided a method for generating synthesis gas by gasification of a biomass in a gasifier comprising a gasification chamber. The method comprises the steps of feeding biomass to the biomass inlet from which biomass inlet the gravity transports the biomass downwards towards an oxidation zone and to mix the biomass by transporting biomass upwards away from the oxidation zone by a first portion of a rotating shaft comprising first biomass engaging means.

Said method provides the same benefits as the gasifier. With said method synthetic gas may be produced with higher efficiency than for conventional fixed bed reactors. By transporting the biomass upwards with the first biomass engaging means, biomass may be efficiently mixed and heated, contributing to higher reaction rate and high amount of produced gas for a specific amount of biomass. The biomass may be heated by means of hot walls of the pyrolysis zone.

In one embodiment the method may further comprise the steps of heating the biomass by means of heated walls of the gasification chamber.

In one embodiment the walls of the gasification chamber may be heated by the synthesis gas channelled upwards through an outflow channel along the walls of the gasification chamber so that the synthesis gas heats the walls and the synthesis gas is cooled by the walls by conducting heat to the biomass inside the gasification chamber.

In one embodiment the walls of the gasification chamber may be heated to a temperature of about 200-900°C, or preferably to about 300- 600°C

In one embodiment the method further comprises the steps of to provide an oxidation gas into an oxidation zone through a channel of the rotating shaft, and to let the biomass react with the oxidation gas in the oxidation zone.

By providing an oxidation gas through a channel of the oxidation shaft oxidation gas may enter the chamber close to the radial centre of the chamber and at points where the mixing is as highest contributing to a consistent distribution of oxidation gas, leading to a high efficiency for intended reactions taking place in the oxidation zone.

In one embodiment the gasifier of the method further comprises a control unit, and wherein the method further comprises controlling the rotational movement of the biomass engaging means.

In one embodiment the method further comprises a step of re-mixing the biomass by transporting biomass downwards towards the oxidation zone with the first portion of the rotating shaft comprising the first biomass engaging means by rotating the rotating shaft in an opposite direction relative the direction during the first step of mixing the biomass.

By remixing it is meant that the rotation is adjusted, reversed or halted. Remixing may be made input from e.g. a sensor. Changing direction reduce occurrence of clogging of the biomass or other operational or safety problems by which the movement of the rotational shaft should be changed or halted. The direction may alternatively be reversed periodically. For instance, the direction may be reversed for 5-10 s every minute, for 10 s-1 minute every tenth minute or 1 -5 minute every hour. The direction may be dependent on the chemical load or reaction rate of the gasifier. This may be controlled either manually or by detection of one or several sensors for detecting the load in terms of chemical reactions. Hereby, there may be more fuel fed into the oxidation zone if the chemical load increases. The sensors may detect temperature and/or gas composition to determine the load.

In one embodiment, the amount of carbon dioxide of the biofuel may be reduced in a reduction zone.

In the reduction zone reactions may take place between carbon dioxide and char forming carbon monoxide, which is one of the components of syngas.

In one embodiment produced syngas from the gasification chamber is channelled upwards through an outflow channel extending along and outside the walls of the gasification chamber, said outflow channel starting from a bottom portion of the gasification chamber.

In one embodiment the channelled syngas may heat the walls of the gasification chamber from the outflow channel outside of the walls.

The walls may be heated to a temperature of about 200-900°C, or preferably to about 300-600°C.

In one embodiment the oxidation gas is led through a channel of the rotating shaft and into the oxidation zone through an oxidation gas outlet of the channel.

Any features or functions described in connection to the product is to be understood to be combinable with the method. To provide a non- exhaustive example, the product is described to use an auger, which is equally applicable of the method using said auger for the transportation of biomass.

Brief Description of the Drawings

Fig. 1 is a schematic view of the gasifier according one embodiment.

Fig. 2 is a schematic view of the gasifier according to an embodiment in which the pyrolysis zone has a tapered form.

Fig 3 is a schematic view of the oxidation zone and the oxidation gas outlets.

Fig. 4a-4b is schematic views of a gasifier according to an embodiment where the rotating shaft comprises second biomass engaging means and/or third biomass engaging means.

Fig. 5 is a schematic view of a gasifier according to an embodiment in which oxidation gas is provided to the oxidation zone through an oxidation gas channel.

Fig. 6 schematically illustrates the method steps of generating synthesis gas. Fig. 7 schematically illustrates the steps including optional further steps of the method.

Detailed Description

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled addressee. Like reference characters refer to like elements throughout. Fig. 1 schematically illustrates a gasifier for generating synthesis gas according to one embodiment. The gasifier 1 comprises a gasification chamber 10.

The gasification chamber 10 according to this embodiment is housing a pyrolysis zone 104, an oxidation zone 102 and a reduction zone 105. The oxidation zone 102 is oriented axially above the reduction zone 105. The pyrolysis zone 104 is oriented axially above the oxidation zone 102. A biomass inlet 101 is arranged above the pyrolysis zone 104. In another embodiment the biomass inlet 101 may be arranged within the pyrolysis zone 101. The biomass inlet 101 is open and closable to isolate the gasification chamber from ambient air.

The gasification chamber 10 has walls which may be made of different material along the different zones. For instance, the walls may be made of a refractory material such as metal along the pyrolysis zone 104 and the reduction zone 105 or a ceramic material along the oxidation zone 102 and the reduction zone 105. Different portions of the walls extend along different zones of the gasification chamber. There is arranged an outflow channel outside of the circumference of the walls of the gasification chamber leading from the reduction zone upwards to a syngas outlet 0.

A rotating shaft 103 extends through the centre of the gasification chamber. The rotating shaft extends at least through the pyrolysis zone 104 and the oxidation zone 102. The rotating shaft 103 may further extend through the reduction zone 105.

The rotating shaft 103 comprises at least first biomass engaging means 1031. The first biomass engaging means 1031 are arranged to transport the biomass upwards in the pyrolysis zone 104 in an axial direction, away from the oxidation zone 102 during normal operation.

The first biomass engaging means 1031 may be a flighting section of an auger. In another embodiment the first biomass engaging means 1031 may be paddles or interrupted flighting sections.

The rotating shaft and the biomass engaging means 1031 may be made of steel or another material suitable for elevated temperatures.

As have been mention in the summary, the rotating shaft may be rotated in an opposite direction relative the normal operation direction, so as to move the biomass downwards in the reduction zone to avoid e.g. clogging.

The rotating shaft 103 is preferably driven by an electrical motor 20 and controlled by a control unit 22 (illustrated in figs 2, 4-5). The control unit 22 may be a separate unit or embedded in the motor or any other electrical component of the gasifier or a related system. The control unit controls the rotating shaft based on input such as operator input or input from sensors which monitor the occurrence of clogging and the temperatures in the gasification chamber 10. The sensors which may be lambda sensor or also known as oxygen sensors, may also detect the gas composition.

Fig. 2 schematically illustrates the gasifier 1 according to another embodiment. The pyrolysis zone 104 has a tapered form, narrowing down in a downward direction. The walls of the pyrolysis zone have an inclination of between 5 and 50 degrees from the vertical direction. The downward velocity of the biomass is thereby higher further down in the gasification chamber. This does better enable the biomass near the oxidation zone 102 to be transferred to the oxidation zone 102 without clogging or building bridges of biomass and therefore enables even more robust working operations.

Fig. 3 schematically illustrates the oxidation zone 102. The at least one oxidation gas outlet 1034 is illustrated as a nozzle protruding outwardly in a radial direction from the rotating shaft 103. The oxidation gas outlets 1034 are distributed on the rotating shaft 103 in the oxidation zone 102 so as to provide the oxidation zone 102 with oxidation gas.

The oxidation gas outlets 1034 may be spaced apart with a distance d1 or d2 and hight hi and h2. The distance d1 and the distance d2 may be the same or different. The hight hi and hight h2 may be the same or different. The oxidation gas outlets 1034 are spaced apart and distributed in the oxidation zone 102 so as to supply sufficient oxidation gas for an oxidation process of the biomass. The flow of oxidation gas may as well be controlled actively by the controller unit 22 by means of a blower, or by the means of an underpressure at the output O created by the suction of a gas consumer, for example an engine or a burner unit.

Fig. 4a schematically illustrates a gasifier comprising second biomass engaging means 1031 b. The second biomass engaging means 1031 b are provided on the rotating shaft 103 above the first biomass engaging means 1031a in an axial direction. The second biomass engaging means 1031 b are threaded in an opposite direction compared to the first biomass engaging means 1031a. The second biomass engaging means 1031 b has a larger radial extension than the first biomass engaging means 1031a. When the biomass is transported upwards by the first biomass engaging means 1031a, when the biomass reaches the second biomass engaging means 1031 b, it will force the biomass downwards and towards the hot walls of the pyrolysis chamber. Fig. 4b schematically illustrates a gasifier comprising third biomass engaging means 1031c. The third biomass engaging means 1031c are provided on the rotating shaft 103 below the first biomass engaging means 1031a in an axial direction. The third biomass engaging means 1031c are threaded in an opposite direction to the first biomass engaging means 1031a. When the biomass has fallen to the lower parts of the pyrolysis zone 104, the third biomass engaging means 1031c will help transporting the biomass towards the oxidation zone 102.

In some embodiments the gasifier may comprise the first biomass engaging means 1031a, second biomass engaging means 1031 b and third biomass engaging means 1031c.

Fig. 5 schematically illustrates the gasifier 1 according to another embodiment. In this embodiment oxidation gas is provided into the oxidation zone through an oxidation gas channel 1033 which goes through the wall of the gasifier 1 . The gasifier 1 may have more than one oxidation gas channel 1033. There may be one single hole extending through the wall, but several oxidation outlets 1034 in the oxidation zone 102. There may also be several oxidation channels 1033 through different portions of the wall of the gasifier 1 . There may be at least one oxidation gas channel 1033 extending through the wall and an oxidation gas channel 1033 extending through the rotating shaft 103.

Fig. 6 schematically illustrates the steps of generating synthesis gas. The biomass is fed S1 through the biomass inlet 101. By gravity, the biomass is transported towards the oxidation zone 102.

The biomass is mixed S2 by the first biomass engaging means 1031 , transporting the biomass located closest to the rotating shaft 103 upwards in the pyrolysis zone 104, so as to prevent the biomass from clogging or stacking when transported towards the oxidation zone 102.

Due to a much longer pyrolysis zone in comparison to conventional gasifiers, the biomass will be pyrolyzed when being in near contact with the hot walls of the gasification chamber 10. In the pyrolysis zone combustible gases and char and possibly some syngas are produced from the biomass.

Fig. 7 schematically illustrates the steps including optional further steps of the method.

In one embodiment there are further steps than what was described in relation to fig. 6 above. In fig. 7 a subsequent optional step is illustrated as being the step of re-mixing the biomass S2a by transporting biomass downwardly towards the oxidation zone 102. This may be done with the first portion of the rotating shaft comprising the first biomass engaging means 1031 by rotating the rotating shaft 103 in an opposite direction relative the direction during the first step of mixing the biomass S2. Thereby the reactions taking place in the pyrolysis zone may be enhanced. The hot syngas produced is lead through channels near the walls of the gasifier 1 to heat the pyrolysis zone 104 and then to a syngas outlet O. The hot syngas may then heat the walls of the pyrolysis zone 104, thereby heating the pyrolysis zone 104. The char ash may fall to the bottom of the gasifier 1 and can be removed from there by a closable opening or an auger.

The biomass is transported to the oxidation zone 102. In one embodiment this is done by gravity and the biomass falls down into the oxidation zone 102. In another embodiment the rotating shaft 103 comprises third biomass engaging means 1031c, arranged below the first biomass engaging means 1031a on the rotating shaft 103, to transport biomass in the bottom of the pyrolysis zone 104 downwards into the oxidation zone 102.

Oxidation gas is provided S3 to the oxidation zone 102 through the oxidation gas channel 1033 in the rotating shaft 103 and/or through the ceramic walls.

The oxidation gas is allowed to react with the biomass S4 in the oxidation zone. Methane and other combustible gases produced in the pyrolysis zone may as well as carbon of produced char react with oxygen forming water vapor and carbon dioxide. In the reduction zone 105, products of the oxidation process react with carbon and carbon monoxide and hydrogen gas are formed as reaction products, together forming syngas. The produced syngas enters the outflow channel which is arranged outside of the circumference of the gasification chamber. The syngas is channelled upwards through the outflow channel along the walls of the gasification chamber so as the syngas heats the walls and the syngas is cooled by the walls by conducting heat to the biomass inside the reactor. The walls may be heated to a temperature of about 200-900°C, or preferably to about 300-600°C. The syngas continues out of the outflow channel through the outlet 0.

Although exemplary embodiments of the present invention have been shown and described, it will be apparent to the person skilled in the art that a number of changes and modifications, or alterations of the invention as described herein may be made. Moreover, the different embodiments described above may be combined in different ways without departing from the scope of the inventive concept. Thus, it is to be understood that the above description of the invention and the accompanying drawing is to be regarded as a non-limiting example thereof and that the scope of the invention is defined in the appended patent claims.