Co-current gasifier

Abstract

 This invention is concerned with an improved construction of a co-current gasifier, wherein a guide (11) is placed in the lower part of fuel silo (3) of fuel tank (1) before burning air jets (7) located in the burning chamber (2), which enables to create free space for burning air in the middle of burning zone of the burning chamber, thereby intensifying the reactions of generating gas. At the same time, the guide (11) enables to extend the burning zone of the gasifier to the pyrolysis zone, resulting in the ignition of tar created as pyrolysis by-product. As a result, the tar content of generated gas output by the gasifier decreases.

Description

Technical Field

[0001] This invention is concerned with gasifying solid biomaterials (biomass), wherein the pyrolysis step includes the decomposition of biomass into pyrolysis products and the reduction step or gasifying step includes the gasifying of pyrolysis products, and more specifically, this invention is concerned with an improved construction of a gasification device used to obtain inflammable gas from biomass, i.e. gasifier.

Background art

[0002] One option for thermal processing of biomass to obtain wood gas is the use of pyrolysis, which is dry distillation of biomass on temperatures exceeding 430 °C without air contact, wherein the heating value of the obtained wood gas is approximately 1.25 MWh/1000m³ (100 kg of wood produces 34-40 m³ of wood gas).

[0003] The pyrolysis of wood generally begins on the temperature of 200-300 °C and results in gas, liquid products and solid waste (primarily carbon). One of the most important characteristics of gasifiers is tar content in the obtained gas and the amount of tar in the pyrolysis process; excessive amounts of tar cause failures in the work of the gasifier.

[0004] The state of the art knows various devices for gasification of solid biomass or gasifiers, wherein wood gas is obtained for example by thermal gasification of wood. The fuel is generally wood, wood scraps or peat, pellets, etc., it is also possible to use organic waste suitable for obtaining gas. Pursuant to the working principle of gasifiers, they are divided into fixed layer gasifiers, counter current gasifiers, cross-draught gasifiers, co-current gasifiers. Co-current gasifiers contain a vertical reactor in which the biomass is gasified. The biomass as fuel is added to the reactor from the top and the fuel moves downward due to gravity. Air necessary for gasifying is added to the reactor in the middle part and the obtained gas is removed from the reactor from the bottom.

[0005] A co-current gasifier reactor contains the following working zones for the gasifier: the upper part of the reactor is a drying zone where fuel is heated and dried (excess moisture is detached from the fuel). The heat necessary for drying is obtained from the hotter part of the gasifier lower down, where it moves upwards along the reactor walls and through the layer of fuel. As the layer of fuel is a relatively poor heat conductor, the height of the drying zone is relatively tall compared to the height of the whole reactor. Beneath the drying zone is the pyrolysis zone, where fuel is heated in oxygen-free conditions (no contact with air). In this zone, volatile agents are removed from the fuel, primarily tar and pyrolysis gases, and solid carbon waste is created (charcoal). Pyrolysis takes place between the temperatures 200 °C to 500 °C. Beneath the pyrolysis zone is the burning zone, wherein the remaining carbon burns at high temperatures of up to 1200 °C. Burning is supported and maintained by providing air or oxygen in the burning zone. When pyrolysis gases and vaporized initial tar move through the burning zone, the tar compounds are cracked and disintegrated into smaller compounds. In the burning zone, where the remaining carbon reacts with carbon dioxide and water vapour, gasification takes place and generator gas is formed, containing carbon dioxide, carbon monoxide, hydrogen and methane. Gasification generally takes place between the temperatures 600 °C to 1000 °C. The lower part of the reactor generally contains a narrowed area and beneath it is the burning chamber, where generator gas obtained in gasification is removed. Document WO2008068596 describes a gasifier with an unmoving layer, wherein one goal is to increase the purity of the gas, and primarily to decrease its tar content. The described gasifier is co-current and shaped like a tower wherein the top part contains an aperture for biomass, the gasifier tower has a narrower part or throat, where channels for air access are located. The tower widen again beneath the throat and forms a reduction chamber, restricted with a grate underneath, which supports a layer of solid charcoal. Beneath the grate is the gas output aperture, through which the obtained gas exits, wherein carcinogenic waste and ash settle in the bottom of the tower. Biomass passes four zones to reach the lowest part of the gasifier tower - the drying zone, the pyrolysis zone, thereafter the biomass reaches the throat, forming the burning zone and where the majority of gas is formed. The burning zone involves intensive mixing of biomass due to turbulence and high temperatures, this zone also promotes the cracking of tar to decrease its content in gas. Beneath the burning zone is the reduction zone. The gas passes the reduction zone and grate and exits from the output aperture.

[0006] The document WO2008/145814, 04.12.2008, T:MI EK Kaasu describes a method for gasifying solid fuels and a relevant device (co-current gasifier). The device involves a fuel silo and burning chamber, which are separated by two plates, in which there is an aperture for the inner cylinder of the burning chamber. This solution attempts to decrease the problem of tar accumulation and removal with a solution where fuel silo is rotating and a catcher is placed on the upper plate for breaking up dense fuel, which scrapes the bottom layer of biomass in the fuel silo and directs scraped fuel into the burning zone through the aperture (narrowing) in the plate. In addition, one solution for decreasing tar accumulation is the prior warming of input burning air. A weakness of the solution is the need for a toothed belt and toothed transmission necessary to turn the fuel silo, which makes the solution less reliable due to the large difference in the masses of the fuel silo and the turning cogwheel. The cogwheel may break, causing the gasifier to stop, because the necessary amount of fuel no longer drops into the burning zone from the silo. Generally, the purity of generated gas changes depending on the load of the device; if the load drops, i.e. air input into the burning zone decreases, the tar content in generated gas increases immediately. This is of particular importance upon starting the device. The weakness of the described solution is the accumulation of excess tar upon starting up, tar content decreases only when temperatures in various zones have reached the optimum level. However, the device does purify gas due to the space between the burning zone and the silo, which keeps the heat of the burning zone from rising up into the pyrolysis zone, meaning that pyrolysis begins immediately before the burning zone.

[0007] The document DE 10 2005 028 377 A1, 04.01.2007, Joos, Bernd describes a gas reactor for producing burning gas, involving a reactor with at least one oxidation or burning zone and a narrowing to speed the generating of gas. Fuel is constantly input in the gasifier with a constant work cycle, therefore the amount of tar in the generated gas remains constant. At the same time, pyrolysis always initially generates a large amount of tar upon every time new amounts are added, because fuel has not had time to dry, due to pyrolysis taking place practically in the entire fuel tank.

Summary of invention

[0008] The main purpose of this invention is maintaining the purity of gas in transmission stages, primarily upon the starting of the gasifier and for example when using a gasifier for means of transport (for example, when a means of transport/a passenger car stops, capacity decreases and tar is immediately added to generated gas because air input in the burning zone has decreased).

[0009] Therefore, the purpose is improving the structure of the gasifier in such a way that the temperature in the burning zone does not drop upon change in the work of the gasifier and that all tar compounds created in pyrolysis are disintegrated and tar content in generated gas does not increase upon the decrease of the load of the device.

[0010] The purpose of this invention is also to provide an improved construction of a two-tier gasifier intended for gasifying biomass, which enables to significantly decrease the amount of tar in generated gas and also completely crack tar compounds created in pyrolysis.

[0011] To achieve the goals of the invention, the construction of the gasifier according to this invention has increased the height of the burning zone with a cone-shaped guide located over the burning zone in the fuel silo, which enables to stretch the burning zone into the cone-shaped guide and expand it underneath the guide, wherein the height of the pyrolysis zone remains the same (the pyrolysis zone remains above the cone). This solution enables the gasifier to work more efficiently with changing loads and the creating of excess tar in generated gas upon starting the gasifier is avoided. This construction is also significantly simpler compared for example to the construction of co-current gasifier described in the document WO2008/145814.

[0012] The goals are solved with a two-tier gasifier incorporating a free fall, containing a fuel silo for the gasified fuel, wherein the fuel silo is surrounded by the outer cylindrical housing of the gas generator, and a burning chamber.

[0013] A guide has been placed in the burning chamber of the gasifier at the transmission of fuel silo before the burning area and burning air jets, which may be a cone-shaped guide narrowing upwards, which is attached to a rod reaching through the fuel silo and lid of the housing of the gasifier. The rod can be rotated to check the even descent of charcoal particles created in pyrolysis down the pyrolysis zone along the side of the guide into the burning zone, where additional heat is released and the gas mix is purified. Thence, hot gases move through the lower narrowing and a layer of charcoal into the reduction zone where gas is generated. The base of the cone-shaped guide, i.e. the wide part is located above burning air jets in a way that free space for burning is created in the middle of the burning zone. The presence of this room is particularly important for reaching the goals of the invention, i.e. for burning tar created in pyrolysis, because the burning process is intensified due to free space underneath the guide and tar created in pyrolysis reaches the temperature required for ignition (>200 °C). With the cone-shaped guide, the burning zone is stretched longer than in solutions known in the state of the art.

[0014] Upon starting the gasifier according to the invention, the guide improves the ignition of fuel, because free space for burning is retained under the cone, because the air input through the burning air jets into the burning part underneath the cone is no longer hindered by the gasified fuel in the burning zone.

Brief description of drawings

[0015] The gasifier according to this invention is described in more detail below with reference to figures, wherein

Fig 1 provides the cross-cut of the gasifier according to the invention,

Fig 2 provides an alternative solution for the gasifier according to the invention,

Fig 3 provides the guide in the fuel silo of the gasifier according to the invention.

Description of embodiments

[0016] Two-part co-current gasifier provided on figure 1 involves fuel tank 1 and burning chamber 2 connected to its lower part. Fuel tank 1 contains fuel silo 3, which is surrounded by the outer housing 4 of the gasifier fuel tank 1, wherein the lower part of the housing, which is for example conical, is directed into burning chamber with double walls 2. Fuel silo 3 of the fuel tank 1 is separated from outer housing 4 of the fuel tank with a layer of insulating material 5 to avoid the heating of outer housing 4 of gasifier fuel tank 1 when the gasifier is working. The upper end of fuel silo 3 can be sealed airtight with a removable lid 6 to add the gasified fuel in the gasifier. In an alternative solution, wherein the automatic constant input of fuel is ensured, the fuel silo 3 may be closed from the top and the input of fuel (biomass, which could be for example wood chips) takes place for example with screw conveyor 20 (see Fig. 2) directed to the upper part of fuel silo 3. To ensure the airtightness of fuel silo 3, the screw conveyor 20 may be placed tilted downwards in relation to outer housing 4 of the gasifier, i.e. the fuel moves from the input of screw conveyor into its muzzle from the bottom up. Thus, a gas lock is created out of input fuel into the muzzle of the screw conveyor immediately before the fuel falls into the fuel silo.

[0017] Upon the working of the gasifier, at least three zones are formed in it: a) the pyrolysis zone, where fuel is disintegrated at 200-500 °C into fuel intermediate, b) the burning zone, where the cracking (disintegrating, burning) of tar compounds generated in pyrolysis also takes place, and c) the reduction zone, where gas is generated.

[0018] In the transfer of fuel silo 3 into burning chamber 2 of the gasifier, burning air jets 7 are placed along the perimeter of the upper part of burning chamber 2, through which burning air or oxygen necessary for burning fuel is input in the burning zone of the gasifier, the so-called ring of fire. Underneath burning air jets of burning chamber 2, plate 9 supported by supports 8 is attached to the inner wall of burning chamber 2; in this plate is an aperture which has a smaller diameter than the diameter of the burning chamber, thereby creating a narrowing beneath the burning zone so that fuel moving downwards does not immediately fall into the reduction zone due to gravity. Beneath supports 8 and plate 9 is the so-called reduction zone of the gasifier, where the gasifying is completed. In the narrowing 10 between the two zones, the speed of gas increases and reaction speed for gasifying increases and gasifying efficiency increases, wherein burning gases can only move towards the lower part of burning chamber 2 through the narrowing 10.

[0019] Guide 11 has been placed above the burning air jets 7 of the burning zone in the lower party of the fuel silo 3. The guide 11 is attached to rod 12, which reaches out of the upper part of fuel silo 3. At that, the passage 13 between rod 12 and lid 6 of fuel silo 3 or upper part of fuel silo 3 is made airtight. The rod 12 is also attached to the upper part of the gasifier so that the rod cannot fall down into the burning chamber together with the guide. The attachment may be a collar around the rod (nut, axis crossing the rod, etc.) which is supported by the other surface of the fuel tank lid of the gasifier, the rod may also be attached in another way which prevents it from falling down which is known to a person skilled in the art.

[0020] Fig 1 provides an example wherein guide 11 is a cone-shaped guide which narrows upwards (e.g. sheet metal material bent into a bottomless cone and welded), wherein the upper narrow end of the cone is attached to rod 12 and a throat which narrows downwards is formed between the cone-shaped guide and the wall of the fuel silo.

[0021] Rod 12 can be rotated (in the case of gasifiers with low power, the rod can be rotated manually, e.g. with an attached crank, handle or wheel, in the case of gasifiers with more power, the rod can be rotated with an engine attached to the rod with necessary transmissions and attached to the outer housing of the gasifier's fuel tank). The guide requires rotating to get carbon particles created in the pyrolysis of fuel to sink evenly downwards from the pyrolysis zone along the guide into the burning zone where heat is released and the gas mix (H₂O and CO₂) is purified. From there, hot gases created in burning move on through a layer of charcoal into the reduction zone where wood gas is generated. The bottom or wider part of the cone-shaped guide 12 is located above burning air jets 7 in a way that a fuel-free space is formed in the middle of the burning zone, where the burning process is intense due to the burning air reaching it uninterrupted. The existence of this space is of particular importance for reaching the goals of the invention, which is the burning of tar created in pyrolysis of fuel, because the burning process intensifies due to free space underneath the guide and the tar created in pyrolysis easily reaches ignition temperature (>200 °C). The presence of this free burning zone also enables the easy start-up of the gasifier, because fuel is immediately burned in this empty zone due to the burning air within, meaning that burning temperatures rises to the necessary level quickly and therefore excess tar is not created due to insufficient burning due to lack of air.

[0022] The cone-shaped guide 11 may be equipped with longitudinal slits 14 (Fig 3), which promote the pyrolysis of fuel on the surface of guide 11 and around it due to heat rising from the burning zone, wherein the longitudinal slits 14 in the cone of guide 11 enable to direct heat more intensely in the fuel located around the cone of guide 11. In an alternative embodiment of the guide, the slits may be perpendicular to the vertical axis of the cone. Longitudinal slits 14 start from the base of the cone and are directed towards the tip of the cone-shaped guide and the rod fixing the guide.

[0023] Guide 11 attached to rod 12 can be rotated as necessary to mix the falling fuel, wherein falling charcoal particles pass the burning part of the burning chamber, the "fire ring" where oxidation or burning of fuel takes place at up to 1100 °C.

[0024] The cone of guide 11 attached to the invention prevents the sinking of fresh fuel into the burning zone and the lower narrowing 10 upon cold starting the gasifier, and also helps improve the quality of gas with changing loads. Therefore, the solution according to the invention is particularly suitable for gasifiers used in vehicles.

[0025] In regular solutions for free-fall gasifiers, there is a problem with fuel being compressed in the fuel silo and thereafter in the pyrolysis and burning zones of the gasifier, where the fuel burns in the immediate vicinity of burning air jets because there is little free space in compressed fuel for burning air provided by jets and for burning fuel. This, in turn, means that if the amount of input burning air decreases towards the centre of the gasifier's burning area, part of the fuel is not burned and falls down into the reduction zone and onto the ash grate located in the bottom part of the burning chamber. In regular solutions, this also results in a sufficiently large amount of pyrolysis by-products not being burned, including tar, the existence of which in generated gas is undesirable.

[0026] The free space underneath guide 11 is particularly important for igniting or cold start of the gasifier, because the charcoal created in fuel silo 3 in pyrolysis does not fall directly down into the burning zone, but moves there from the sides of the cone. Hence, there is free space for obtaining burning in the burning zone upon starting the gasifier due to free space underneath the guide.

[0027] The burning chamber 2 of the gasifier is also elongated with the guide 11 because the cone of guide 11 itself also heats up when fuel burns and therefore, the temperature necessary for pyrolysis is carried upwards in fuel located in fuel silo 3.

[0028] Burning chamber 2 is made with double walls, between which is free space for burning air input from the lower part of burning chamber 2 through the input aperture 15 for burning air. At the same time, burning air is heated in the space between walls of burning chamber 2 before being input in the burning zone through burning air jets 7. In the lower part of burning chamber 2 is the double bottom of the burning chamber, which is necessary for collecting ash created in generating gas and for removing it from the gasifier. Generated gas is removed from the centre of burning chamber 2 with generated gas output 16.

1 - fuel tank

2 - burning chamber

3 - fuel silo

4 - outer housing

5 - insulating material

6-lid

7 - burning air jets

8 - supports

9 - plate

10 - narrowing

11 - guide

12 - rod

13 - passage

14 - vertical and horizontal slits

15 - input of burning air

16 - output of generated gas

20 - screw conveyor

Claims

1. A co-current gasifier for generating gas, containing a fuel silo (3) of fuel tank (1) intended for gasified fuel, which is surrounded by insulating material (5) and the outer housing (4) of the fuel tank (1), and a double-walled burning chamber (2) attached underneath the fuel tank (1), which includes burning air jets (7) in the upper part for inputting burning air in the burning zone of the gasifier, input aperture (15) for burning air in the outer wall of the lower part, and output passage (16) for generated gas in the inner wall of the central part, characterised by that the lower part of fuel silo (3) of the fuel tank (1) above burning air jets (7) of burning chamber (2) contains a cone-shaped guide (11) with the bottom of cone facing downward, wherein the tip of the cone of cone-shaped guide (11) is attached to rod (12), the other end of which reaches out of the top of fuel tank (1), and because there is a throat narrowing downwards between the cone-shaped guide and the wall of the fuel silo.

2. The co-current gasifier according to claim 1, characterised by that the cone-shaped guide (11) is a bottomless cone narrowing upwards, wherein solid by-products created in the pyrolysis zone of fuel silo (3) upon pyrolysis of gasified fuel slide down the cone surface of guide (11) into the burning zone of the gasifier.

3. The co-current gasifier according to claim 1, characterised by that the surface of the bottom of the cone of cone-shaped guide (11) coincides with the surface of lower side of the fuel silo (3).

4. The co-current gasifier according to claim 1, characterised by that the rod (15) reaching out of the top part of fuel silo (1) is attached to the top of fuel tank in a way to prevent the rod falling down into the burning chamber together with the attached guide (11), and wherein a means for rotating the rod is attached to the top of the rod to enable mixing the gasified fuel in the fuel silo and improve its fall into the burning zone of the gasifier.

5. The co-current gasifier according to claims 2 or 3, characterised by that slits (17) have been added to guide (11) to direct burning heat from the burning zone through the cone-shaped guide to the pyrolysis zone of the gasifier to intensify the reactions therein.

6. The co-current gasifier according to claim 1, characterised by that the fuel tank (1) is made with a screw conveyor (20) for inputting fuel in the fuel silo, the mouth of which is in the top part of the fuel silo.

Drawing