Device and method for gasifying biomass

description

DEVICE AND METHOD FOR GASIFYING BIOMASS

The invention relates to a reactor for gasifying biomass, in particular wood, having a feed chute and an ash bed arranged under the feed chute.

The invention further relates to a method for gasifying biomass in a reactor, in particular in a reactor of the type mentioned, to form a product gas.

Biomass gasifiers are known as such from the prior art. For example, from WO 2008/004070 A1 a device is known with which biomass such as wood, straw or biological waste is gasified in a reactor and a resulting gas is then passed into a gas-powered motor, where this gas is converted into mechanical energy by combustion . The motor is connected to a generator with which the mechanical energy is converted into electrical energy.

Devices of the prior art have the disadvantages that a system efficiency is only low, since on the one hand product gas exits the reactor at high temperatures, which affects the efficiency of a downstream internal combustion engine, on the other hand a consistency of the biomass often leads to sticking in the reactor, so that frequent and expensive maintenance is the result. Furthermore, the high expenditure for the disposal of filter media that are required for product gas cleaning also has a negative effect on the system efficiency.

The object of the invention is to eliminate or reduce the disadvantages of the prior art by providing a reactor with which a more efficient process is possible.

Furthermore, a method is to be specified which eliminates or reduces the disadvantages of the prior art.

The first object is achieved in that in a reactor of the type mentioned a device is provided with which adhering biomass to the hopper is detachable and / or a heat exchanger is provided with which a product gas generated from the biomass heat releases biomass tracked in the hopper and to an oxidizing air.

Since the biomass must be moved during operation through the hopper from a first end to a second end at a flow rate, adhering to the hopper prevents movement and thus a proper operation. An advantage of the device with which biomass adhering to the filling shaft can be removed can therefore also be seen in particular in the fact that downtimes during which the reactor has to be shut down for maintenance purposes can be significantly reduced. This increases the system efficiency for a system operator.

The heat exchanger, with which the heat of the product gas can be transferred to the biomass tracked in the filling shaft and the oxidation air, has the particular advantage that the energy required for pyrolysis and preheating of the oxidation air can be taken from the product gas, so that less energy has to be taken from the biomass and a temperature of the product gas can be reduced. If the product gas is processed further directly in an internal combustion engine, a lower temperature increases the thermodynamic efficiency in the internal combustion engine. A heat transfer from the product gas to the oxidation air and biomass thus has several positive effects on the system efficiency.

Thus, with the device, biomass can be converted fully automatically into electrical energy.

It is preferably provided that a waste heat heat exchanger is provided with the / 15

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It is advantageous if a fine filter for cleaning a product gas generated from biomass contains biomass as the filter medium. This biomass can preferably contain wood chips according to ÖNORM M7133 G50 or G30 as well as sawdust. The advantage of this design is that the filter medium can be transported to the fuel store after a long period of use and processed like biomass in the reactor, so that this filter medium can be recycled in the simplest possible way. The product gas flows through this filter medium in the fine filter, preferably from bottom to top, with impurities in the product gas, in particular tar, being deposited on the biomass. The biomass can be stored on one or more levels. A sensor can also be provided which measures a pressure loss across the filter and thus determines the optimal point in time for transferring the contaminated biomass to the fuel store and for filling the filter with new biomass. Alternatively, a time-based refilling with biomass is possible.

Instead of wood chips and sawdust, another type of solid biomass can of course also be used, the filtration effect changing with the filter medium. It is advantageous that the filter medium lies on several levels in the filter on porous perforated bases, preferably perforated metal sheets, and the product gas can flow through it in series from bottom to top. A bottom layer has around 20% wood chips and around 80% sawdust and a top layer has around 70% wood chips and around 30% sawdust. In the intermediate layers, a proportion of wood chips lies above that of the bottom layer and rises to the top layer. It is preferred that wood chips and sawdust are made from spruce wood.

A fine filter as described above is preferably used for cleaning a product gas generated from biomass, in particular for separating tar. A particularly cost-effective and environmentally friendly type of product gas cleaning can thus be achieved.

The second object is achieved according to the invention in that in a method of the type mentioned at the beginning, biomass adhering to the filling shaft is dissolved and / or heat is given off from the product gas to biomass and an oxidation air.

[0016] By, in particular intermittently, loosening biomass adhering to the filling chute, contamination of the filling chute with biomass, which would severely impair its function, can be avoided. This can reduce maintenance times and increase system efficiency. A transfer of heat from the product gas to biomass and an oxidation air can minimize the amount of energy that leaves the reactor in the form of heat in the product gas.

It is preferably provided that a vibrator at certain intervals, preferably at intervals of 10 to 30 minutes, in particular 15 to 25 minutes, preferably about 20 minutes, for a period of less than 5 minutes, preferably less than 1 minute, particularly preferably for about 5 seconds, is activated in order to loosen biomass adhering to the hopper. In this way, on the one hand, adhering impurities can be loosened particularly favorably and, on the other hand, mechanical stresses on a material due to vibrations remain minimal, so that the reactor has a long service life.

It is advantageous that a flow rate of the biomass in a lower region of the feed chute is kept approximately constant in this area via a conical design of the feed chute. Since the biomass changes its volume in the lower area due to chemical reactions, a conical design of the filling shaft, which leads to a uniform flow rate, has a particularly favorable effect on the framework conditions of these chemical reactions, such as pressure or temperature.

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It is advantageous that a multiple jacket is provided with which heat from the product gas can be transferred to the oxidation air and tracked biomass. This multiple jacket thus fulfills not only a mechanically supporting function but also the function of the heat exchanger, which means that the reactor can be manufactured particularly inexpensively. The multiple jacket is preferably designed in such a way that it has several, approximately concentric, approximately cylindrical jackets, with product gas between a first jacket, which forms the filling shaft, and a second jacket, which encloses the first jacket, in the case of a preferred vertical installation due to the thermal buoyancy can flow from the bottom to the top and a third jacket is arranged around this second jacket in such a way that that the area between the second jacket and the third jacket can be flown through by oxidizing air. In this way, heat can be transferred from the product gas via the first jacket or to biomass in the filling shaft and via the second jacket to oxidizing air and the temperature of the product gas can be minimized until it exits the multiple jacket. The multiple jacket is preferably made of steel, the first jacket, which borders on the one hand on the biomass and on the other hand on the product gas, preferably consists of temperature and acid-resistant material, for example an austenitic chromium-nickel-molybdenum steel. The second jacket, which adjoins the oxidizing air and the product gas, is preferably made from heat-resistant steel only in a lower area and from a normal boiler plate in an upper area in order to minimize manufacturing costs. It is advantageous if an insulation layer made of a heat-insulating material is applied around the third jacket, which is preferably also made of steel, in order to prevent heat from the oxidizing air from being given off to the environment.

In order to reduce maintenance times, it is particularly advantageous that a vibrating device is provided with which the filling chute can be made to vibrate so that adhering biomass can be released from the filling chute. Due to the broad spectrum of possible constituents and possible consistencies of the biomass, biomass can adhere to the filling shaft during operation, which can severely impair the functionality of the reactor. In order to loosen any adhering biomass in a particularly favorable manner, the filling chute can be made to vibrate by means of the vibrating device. The vibrating device can consist of a motor and an imbalance connected to the motor or other electromagnetic or mechanical devices, with vibrations from the vibrating device preferably being transmitted to the filling chute by means of shaped tubes. These shaped tubes can form a direct connection between the vibrating device and the filling chute; but it can also be provided that the vibrating device is indirectly connected to the filling chute via flexible connecting elements. The connection between the vibrating device and the filling chute is preferably designed in such a way that temperature-related mechanical stresses in the entire reactor are minimized and the tightness of the filling chute is permanently guaranteed. The vibrating device is preferably activated at regular intervals of between 10 and 30 minutes, preferably between 15 and 25 minutes, particularly preferably of about 20 minutes for a period of a few seconds, preferably for about 5 seconds.

It has been proven that a wedge slide is provided with which the biomass can be fed to the hopper. In this way, the biomass can be fed to the filling shaft in a particularly simple and energy-efficient manner. The wedge slide preferably comprises a slide plate which is guided in a linearly movable manner in a groove of a frame rigidly connected to the filling chute. The wedge slide and the frame are preferably components of a sluice via which the biomass is fed to the filling shaft. The connection of the slide plate to the frame is preferably carried out in a particularly low-wear manner via one or more ball bearings. Other types of storage are also possible. Due to the acidic atmosphere in the hopper, the entire wedge slide or parts thereof are made of an acid-resistant material, preferably an acid-resistant steel.

It is advantageous that a sealed feed device is provided with which the biomass can be fed to the filling shaft with the exclusion of oxygen. This is especially 3/15

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To allow the hopper to enter in order to be able to trigger specific chemical reactions in the hopper that are dependent on a controlled or regulated air ratio.

It is preferably provided that the filling chute is tapered in a lower region, in particular with a ratio of a filling chute cross-section to a fire zone cross-section of 1.2 to 10, preferably 1.4 to 3, particularly preferably about 1.9. In this calculation, the feed chute cross-section is measured in a cylindrical upper area of ​​the feed chute and the fire zone cross-section in a fire zone. Since the biomass changes its volume during the pyrolysis taking place in this lower area when moving through the lower area, it is advantageous if the filling shaft is adapted to a change in volume of the biomass in order to ensure a uniform flow rate of the biomass and optimal conditions for the chemical that is running off Enable processes. A cone angle between a cone axis and a lateral surface of the conically designed lower region is preferably between 20 ° and 60 °, particularly preferably between 30 ° and 50 °, in particular approximately 40 °. While the fire zone adjoining this conical area is preferably cylindrical, a lowest area further adjoining the fire zone between the fire zone and a constriction is preferably also conical in order to constructively take account of a change in volume of the biomass in this lowest area as well. A cone angle of this lowermost region is preferably between 20 ° and 60 °, particularly preferably between 30 ° and 50 °, in particular approximately 40 °. This cone angle can also correspond to the cone angle of the lower area.

It has been proven that an oxidizing air supply is connected via an intermediate area and an oxidizing air ring with oxidizing air nozzles which open into a fire zone. The oxidation air can be preheated both in the intermediate area, which is preferably thermally connected to a product gas area, and in the oxidation air ring, which is preferably thermally connected to the fire zone. Preheating of the oxidation air is thus made possible in a particularly favorable manner. Another advantage can also be seen in the fact that the oxidizing air can enter the fire zone evenly over a circumference and thus can be evenly distributed in the fire zone.

An air outlet speed at the oxidation air nozzles, which has a high influence on a chemical reaction in the fire zone, can be particularly favorably influenced via a cross section of the oxidation air nozzles and an air pressure. A higher air outlet speed results in a higher temperature in the fire zone, but the spatial expansion of a glow zone is smaller. An optimal air inlet cross-section can change according to a composition and a calorific value of the biomass. It has proven particularly useful that a sum of all cross-sections of the oxidation air nozzles corresponds to between 1% and 10%, preferably between 2% and 8%, in particular approximately 4%, of a constriction cross-section. The constriction cross-section is that cross-section of the filling shaft at which the biomass can escape from the filling shaft to the ash bed.

It has been proven that the oxidation air nozzles are distributed so evenly over a circumference of the fire zone that between each two oxidation air nozzles on the circumference of the fire zone a distance of between 2 and 30 cm, preferably between 5 and 20 cm, in particular about 10 to 12 cm. The oxidation air nozzles are preferably arranged in one plane, but an arrangement in several planes is also possible. Depending on the circumference of the fire zone, this results in a particularly favorable number of oxidation air nozzles for the chemical reaction in the fire zone and a favorable air speed.

It can preferably be that a rotating grate with at least one agitator pin is provided on the ash bed, with which packings of biomass can be detached. The rotating grate enables the biomass to burn evenly and also serves to discharge ash into an ash bin below. The rotating grate is preferably driven by means of a

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Linear motor via a drive linkage. Other types of drive are also possible. The drive linkage is preferably sealed in a gas-tight manner by means of a stuffing box which has a temperature-resistant graphite sealing cord for creating a seal. The at least one agitator pin enables biomass that is clinging to the rotating grate to be loosened in a particularly favorable manner.

It has been proven that sensors are provided with which a pressure can be measured upstream and downstream of the ash bed in order to use data obtained during a measurement to control and / or regulate the stirring pins. With this arrangement, packings of biomass on the rotating grate are particularly easy to recognize, since packings lead to an increased difference between a pressure before and a pressure after the rotating grate. In this way, the stirring pins can be activated precisely when further handling would lead to problems and wear and tear on the stirring pins can be minimized.

In order to produce a product gas from biomass, it is advantageous that in a device for generating a product gas from biomass, comprising a fuel store for the biomass, a reactor for gasifying the biomass, at least one conveyor for transporting the biomass from the fuel store in the reactor and at least one filter system for cleaning product gas generated from the biomass, the reactor is designed according to the invention.

In this way, biomass can be transported fully automatically from a fuel store into the reactor and the product gas can then be cleaned in a filter system. In particular because of the particularly efficient reactor, the system efficiency of the entire device is thus better than in the case of devices of the prior art.

It is preferably provided that at least one cyclone filter is arranged downstream of the reactor. The product gas is freed from dust and fly ash in the cyclone filter, so that the product gas is of higher quality for further use. Three cyclone filters connected in parallel are preferably provided, with only one cyclone filter or more than three cyclone filters also being possible. Several cyclone filters can be arranged so that gas can flow through them in parallel or in series, a cyclone filter ash container being arranged such that an ash that can be separated in the at least one cyclone filter is preferably automatically directed into the cyclone filter ash container. If the cyclone filter ash container is arranged below the cyclone filter, this is particularly easy. The functionality of the cyclone filter is known and is based on a centrifugal force with which dust and fly ash in the cyclone filter are pushed outwards.

It is advantageous that at least one fine filter is connected downstream of the reactor, which contains biomass as a filter medium. This fine filter can be connected downstream of the cyclone filter, as it can also be used to remove smaller particles and tar residues.

It is advantageous that an internal combustion engine is provided in which the product gas can be conducted, and the internal combustion engine is coupled to a generator for generating electrical energy. As an alternative to the internal combustion engine, another internal combustion engine, for example a gas turbine, can also be provided.

It is advantageous that in a lowermost area of ​​the filling chute, in particular in the area of ​​a constriction, in more than 50%, in particular more than 70%, preferably more than 90% of the biomass, a temperature between 1000 ° C and 1600 ° C, in particular 1200 ° C and 1500 ° C, preferably 1220 ° C and 1470 ° C. Cracking of long-chain hydrocarbons (tars) can thus be ensured and accumulation of long-chain hydrocarbons in pipelines and in any downstream internal combustion engine can be avoided or at least reduced.

It has been proven that a pressure loss over an ash bed is measured continuously and a stirring device is activated in the ash bed when a predetermined limit value is exceeded. This allows packings of biomass on the ash bed or on a rotating grate to be recognized and detached, so that the functioning of the device is guaranteed

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It is advantageous that the oxidation air flows from an intermediate jacket via an oxidation air ring to air nozzles in a fire zone, where an oxidation of biomass is caused. This ensures that the oxidation air is sufficiently preheated so that higher product gas temperatures are achieved after the oxidation zone. The air can enter the fire zone evenly distributed via the oxidizing air ring and the oxidizing air nozzles, so that even temperatures are achieved.

It is advantageous if a product gas is used to drive an internal combustion engine and a generator for generating electrical energy is driven with this. A fully automatic conversion of chemical energy stored in biomass into electrical energy can thus be achieved in a particularly simple manner.

It is preferably provided that heat from an exhaust gas of the internal combustion engine is used to preheat the biomass. The efficiency of the method can thus be increased further, since waste heat from the internal combustion engine is fed back into the method. Alternatively, this waste heat could also be used for heating purposes or other thermal processes.

[0039] Further features, advantages and effects of the invention emerge from the exemplary embodiment shown below. In the drawings to which reference is made:

1 shows a schematic representation of a reactor according to the invention for gasifying biomass;

[0041] FIG. 2 shows a schematic representation of a device for generating a product gas from biomass;

3 shows a representation of a fine filter with biomass as the filter medium.

Fig. 1 shows a schematic representation of a reactor 1 for gasifying biomass, in particular wood. Via a sluice 6, the biomass can be introduced into the reactor 1 or a filling shaft 7 with a wedge slide valve at the top, which is sealed gas-tight by means of a temperature-resistant graphite sealing cord in order to be able to precisely control the oxygen content in the reactor 1. The wedge slide is designed with position sensors so that the current position of a slide plate can be recorded at any time for automatic operation. The slide plate is driven by an electric motor. Attached to the side of the reactor 1 is a vibrating device 8 with which biomass adhering to the filling shaft 7 can be detached. For this purpose, a vibrating movement can be transmitted from the vibrating device 8 to the filling chute 7 via one or more shaped tubes 9. It is also possible to transfer the vibrating movement with other structural components instead of a shaped tube 9, for example mechanically softer or stiffer components, in order to achieve an optimal vibrating result. In the reactor 1 shown in the exemplary embodiment, the vibrating device 8 is activated regularly every 20 minutes for about 5 seconds in order to loosen adhering biomass from the filling shaft 7. The choice of longer intervals between the shaking intervals and longer shaking intervals are just as possible as the choice of shorter times for these intervals. It is also possible to regulate the vibrating device 8 via a sensor which detects a volume or a mass of adhering biomass and activates the vibrating device 8 in a coordinated manner. Alternatively, it is also possible to remove adhering biomass using other mechanical methods, such as direct or indirect exposure to a solid, liquid or gaseous medium.

The filling chute 7 is formed by a first jacket 23 in which the biomass is moved during operation from a first end in an upper region 10 to a constriction 17 by means of gravity. Chemical processes take place in the biomass during movement. Due to the chemical processes and the resulting chemical constituents, the first jacket 23 is made of an austenitic material, at least in the lower region 12

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Made of chrome-nickel-molybdenum steel. Alternatively, other heat and acid-resistant materials can be used. The first jacket 23, which is cylindrical in the upper region 10 and a central region 11, is enclosed by a second jacket 24 lying concentrically therewith. This second jacket 24 is further enclosed by a third jacket 25 lying concentrically therewith. On an outer side of the third jacket 25, an insulating layer 26 consisting of heat insulating material is arranged, which minimizes heat emission from oxidizing air to an environment. The first jacket 23, second jacket 24 and third jacket 25, which are preferably made of steel, are essentially rotationally symmetrical, and the second jacket 24 and third jacket 25 are essentially continuously cylindrical. In the lower region 12 and a lowermost region 14 of the filling chute 7, the first casing 23 is partially conical, an angle between a cone axis and a cone casing being approximately 40 °. The conical design is interrupted by a cylindrically designed fire zone 13 and ends at a constriction 17 at which the biomass can emerge from the filling shaft 7 to an ash bed during operation. A constriction ratio of a fire zone cross section to a filling chute cross section is approximately 1: 1.9, the constriction ratio being formed with the cross section of the filling chute 7 in the cylindrical upper region 10. This constriction ratio and the angle are dependent on a composition of the biomass and can also be smaller or larger depending on the application. The constriction ratio is about 1: 1.8 for softwood as a main component of the biomass and about 1: 2 for hardwood as a main component of the biomass. However, this can change upwards or downwards depending on the biomass used or the type of wood used. Constriction ratios of 1: 4 to 1: 1.1 are also possible, depending on the application.

In the lower region 12 of the hopper 7, an oxidation air ring 15 is arranged around the hopper 7, which is connected to the intermediate region via a compensator which can compensate for thermal expansions. Oxidation air nozzles 16 protrude from the oxidation air ring 15 in one plane into the fire zone 13. In the exemplary embodiment, the number of oxidation air nozzles 16 is selected such that a distance of approximately 10 to 12 cm in the circumferential direction remains between the centers of the oxidation air nozzles 16 over a circumference of the fire zone 13. The cross section of the oxidation air nozzles 16 is selected such that the sum of all cross sections corresponds to approximately 4% of a constriction cross section. However, the function is also given at least to a limited extent with other cross-sectional ratios, for example 1% to 20%, or distances between the oxidizing air nozzles 16, for example 1 to 30 cm. The constriction cross-section is the smallest cross-section of the feed chute 7 through which the biomass exits from the feed chute 7 to the ash bed.

Below the constriction 17 is the ash bed on which the biomass falls after it has passed through the reactor 1. The ash bed comprises a rotating grate 18, which is connected to a motor, preferably a linear motor 20, via a drive linkage and can be driven by this. A gas-tight passage of the drive rod from the rotating grate 18 to the motor located outside the reactor 1 is achieved via a stuffing box which is sealed with a temperature-resistant graphite sealing cord.

On the rotating grate 18 stirring pins 19 are arranged with which biomass adhering to the rotating grate 18 can be detached. Adhering biomass prevents ash from being discharged into an ash bin 21 arranged below the rotating grate 18 and, due to an increased pressure loss on the rotating grate 18, prevents the product gas from flowing out unhindered. The optimum point in time at which the agitator pins 19 are activated and biomass is released from the rotating grate 18 is determined by measuring the pressure difference. As a result, a function of the reactor 1 is also constantly monitored.

In a space between the first jacket 23 and the second jacket 24, a product gas flows from the constriction 17 upwards out of the reactor 1 during operation. In the space between the second jacket 24 and the third jacket 25, an oxidizing air flows from an oxidizing air supply 43 to an oxidizing air ring 15. In the filling chute 7 there is biomass, which is brought into the filling chute 7 by the wedge slide and runs through it from top to bottom.

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The product gas gives off heat via the first jacket 23 to the biomass located in the filling shaft 7 and via the second jacket 24 to the oxidizing air. Biomass adhering to the filling shaft 7 is released in that the vibrating device 8 is activated for 5 seconds every 20 minutes. The biomass is dried and preheated in the upper region 10 of the filling shaft 7 by the heat of the product gas. In the middle area 11, the pyrolysis begins, during which, in the course of thermal decomposition, among other things, organic acids such as acetic acid, methyl alcohol and tar are formed. Furthermore, hemicellulose, which is contained in the biomass, at most, decomposes in this central region 11 at a temperature of 200 ° C. to 300 ° C. With further heating, the cellulose contained in the biomass between 325 ° C and 375 ° C is broken down and carbon dioxide, methane and organic acids, especially acetic acid, are produced. If the temperature continues to rise above 375 ° C, lignin breaks into smaller chemical compounds. Hydrocarbons and tars are also obtained in this central area 11. Oxidation of the biomass begins in a lower region 12 of the filling chute 7. A continuous flow rate and a high pressure, which are achieved in this area due to a decreasing solid volume of the biomass via the conical design of the filling shaft 7, are necessary in order to ensure an optimal course of the oxidation. In the fire zone 13, the biomass is supplied with the oxidizing air via the oxidizing air nozzles 16 and carbon and hydrogen burn substoichiometrically with the release of energy. The temperature is around 650 ° C to 850 ° C, with carbon dioxide, water and methane being produced. A temperature range can be controlled particularly favorably via the amount of oxidizing air supplied and a speed at which the oxidizing air penetrates. A chemical reduction takes place below the fire zone 13 in the lowermost area 14 of the hopper 7. Here, the formation of combustible gas is made possible, among other things, by gasifying carbon. In this lowermost region 14, the intermediate products formed during the oxidation, such as carbon dioxide and water, are reduced at hot points, with carbon monoxide, hydrogen and higher hydrocarbons being formed. Due to the special design of the reactor 1 in this lowest area 14, ideal temperatures between 1220 ° C. and 1470 ° C. are reached here, in particular also in the area of ​​the constriction 17, which are close to the ash melting point of the biomass. A restricted function is also possible in a temperature range from 1000 ° C to 1600 ° C. Due to the conical design of the filling chute 7 in the lowest area 14, a constant temperature can be achieved over a large part of the volume of the biomass, especially in the area of ​​the constriction 17, with which a cracking of long-chain hydrocarbons (tars) is guaranteed and thus tars are accumulated, especially in pipes be minimized. Due to the temperatures close to an ash melting point of biomass, biomass adhering to the rotating grate 18 occurs during operation and is loosened with the stirring pins 19. Since the correct choice of stirring intervals or pauses between the stirring intervals is relevant in order to achieve an optimal result of the chemical reaction in the reduction zone, the stirring pins 19 are actuated exactly to the extent necessary to loosen adhering biomass. For this purpose, a pressure difference is measured upstream and downstream of the rotating grate 18 and these values ​​are used to regulate the stirring pins 19. By means of a movement of the rotating grate 18, ash is discharged particularly favorably into the ash bin 21, from where it is automatically conveyed by means of an ash conveyor 22 into an ash storage container 42. This process results in a gas yield of up to 2 standard cubic meters of product gas per kilogram of biomass supplied.

FIG. 2 shows a device 2 in which the reactor 1 is embedded in order to generate a product gas from biomass. The biomass can be transported from a fuel store 3 into the reactor 1 by means of a conveyor 4 via a biomass dryer 5. A gas outlet of the reactor 1 is connected to cyclone filters 27, where the product gas can be freed from dust and fly ash. Three parallel cyclone filters 27 are provided, through which gas can flow uniformly and in parallel. In the cyclone filters 27, the product gas can be guided in a circular path at a very high speed, so that, due to a centrifugal force, dust and ash are pressed radially outward, from where they are directed

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Downstream of the cyclone filter 27 is a fine filter 29 in which the product gas is cleaned by means of wood chips and sawdust. A particular advantage of the wood chips as filter material in this fine filter 29 is that the wood chips, after they are saturated with impurities, can be fed to the fuel storage room and can thus be recycled directly. There is no filter waste in this way. The fine filter 29 is preferably designed in such a way that the product gas flows through it from bottom to top during operation, with dirt and tar being able to attach to the wood chips. A pressure sensor can be provided by means of which an optimal point in time for emptying this filter can be determined. Alternatively, purely time-based emptying of the filter would also be possible.

A gas outlet of the fine filter 29 is connected to a four-cylinder Otto engine or generally an internal combustion engine 30, which drives a generator 31 and can thus convert the energy of the gas into electrical energy. Alternatively, it is also possible to use a gas turbine or other machines that can convert the chemical energy of a product gas into mechanical energy and then into electrical energy. Downstream of the gas engine is a waste heat exchanger 32, which makes waste heat from the gas engine usable for preheating the biomass and for any heating purposes. A biomass preheating line 33 can also be seen in FIG. 2, of which at least part of the residual heat of the product gas can be used for preheating biomass in the biomass dryer 5. A heat store 34 is also provided for intermediate storage of waste heat.

The method for cleaning product gas obtained from biomass as well as further processing into electrical energy works with the device 2 in such a way that the biomass is fed from the fuel store 3 by means of the conveying means 4 via the lock 6 to the filling shaft 7. The biomass is then gasified as described above in reactor 1 to form product gas. After exiting the reactor 1, the product gas is cleaned in the cyclone filters 27 and in the fine filter 29 before it is passed into the internal combustion engine 30. There the chemical energy of the gas is converted into mechanical energy, which is then converted into electrical energy in a generator 31. When the product gas is burned, the gas engine is regulated to an air ratio of lambda equal to 1.15. This achieves particularly favorable pollutant values ​​in the exhaust gas. Waste heat from the internal combustion engine 30 is released via the waste heat exchanger 32 to a heat transfer medium and partly stored for heating purposes in the heat storage 34 and partly used via the biomass preheat pipe 33 to dry the biomass in the biomass dryer 5 before it enters the reactor 1. A high maintenance and disposal effort is avoided with this method in that the filling shaft 7 is regularly freed of adhering biomass by shaking and the filling shaft 7 is cleaned of packings by regular stirring with stirring pins 19 and contaminated wood chips in the fine filter 29 in a particularly favorable way Return to the fuel store 3 can be recycled.

3 shows an illustration of the fine filter 29 in which biomass is used as the filter material. The product gas can enter the fine filter 29 via a product gas inlet 35 at a lower end. The filter medium is distributed over four layers 38, 39, 40, 41 on perforated floors 37 through which the product gas can flow. The perforated bottoms 37 are preferably formed from metal sheets with a large number of bores, but another type of porous bottom can also be selected, which is preferably designed to be temperature-resistant. Alternatively, it is of course also possible to use only a single layer or to use more than four layers. The product gas flows through the fine filter 29 from bottom to top during operation and flows in series through the individual levels until it leaves the fine filter 29 cleaned at the product gas outlet 36. When flowing through the individual layers, particles in the product gas, in particular tars, dust and impurities, are largely attached to the filter material. The filter medium of layer 38 consists of 20% wood chips and 80% sawdust, the filter medium of layer 39 too

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Patent Office% from wood chips and 70% from sawdust, the filter medium in position 40 is made up of 50% wood chips and 50% from sawdust and the filter medium in position 41 is made up of 70% wood chips and 30% from sawdust. Wood chips and sawdust are preferably made from spruce wood, but the use of other types of biomass is also conceivable, the filter performance depending on the biomass used. A particular advantage of using biomass as a filter medium is that the biomass after contamination in the fine filter 29 can be fed to the fuel store 3 and can thus be recycled in the simplest possible way. An optimal point in time for replacing the filter media due to contamination can be determined by measuring the pressure difference, with a pressure loss across the fine filter 29 being measured. Alternatively, a purely time-dependent exchange of the filter media is also possible. If the filter media are replaced depending on the time, it is recommended to replace them after about 100 hours of operation.