A fluidized bed gasifier system with freeboard tar removal

Abstract

 There is provided a fluidized bed gasifier system 100 comprising a main chamber 101, which has a lower space region 101a, and an upper space region 101c. The system 100 further comprises a fuel feed inlet 102 for providing fuel to the main chamber, a dense fluidized bed 104 arranged at the lower space region for producing a product gas from the fuel, and a product gas outlet 105 arranged at the upper space region 101c. The system further comprises a first reformation device 110 arranged inside the main chamber above the dense fluidized bed.

Description

FIELD OF THE INVENTION

[0001] The present invention relates generally to the field of gasification of carbonaceous material, and more particularly to a fluidized bed gasifier system arranged for reducing impurity products formed under production of synthesis gas.

BACKGROUND OF THE INVENTION

[0002] Synthesis gas, or syngas, is a fuel gas mixture consisting primarily of hydrogen, H₂, carbon monoxide, CO, and typically some carbon dioxide, CO₂. Syngas can be produced via gasification of Biofuels (carbonaceous materials). A 1st generation of Biofuels for transportation is no longer encouraged as it is usually difficult to meet criteria of greenhouse gas (GHG) saving when replacing fossil fuels. On the other hand, the 2nd generation of Biofuels from lignocellulosic biomass has been more and more attractive for development and commercialization. Transport Biofuels as well as chemicals can be produced from high-quality syngas (mainly hydrogen and carbon monoxide) via biomass gasification.

[0003] When syngas is used for synthesis, a high CO + H₂ concentration (>80%) with a high H₂/CO ratio in the syngas is required to ensure smooth downstream synthesis. In addition to H₂ + CO, the raw syngas from biomass gasifiers contains CH₄, trace amounts of higher hydrocarbons (tars), possible inert gases from biomass and gasification agent, and various contaminants. There are many years of experience in gas cleaning related to engine and turbine applications, but product gas for synthesis normally has a much stricter specification of impurities than these applications. Syngas can be conditioned to different degree depending on a balance of economic cost against technical specification for downstream synthesis. The downstream syngas cleaning usually accounts for up to 38% of the transport fuel production cost. The major challenge in the production of high quality syngas through biomass fluidised-bed gasification is the reforming of tars and methane (except for methanation application) to a minimum allowable limit.

[0004] Reduction of tars and methane (CH4) to an acceptable low level is usually achieved by high temperature thermal cracking, low temperature catalytic cracking, or physical tar treatment like water scrubbing + sedimentation and oil scrubbing + combustion or combinations. Catalytic cracking efficiency can be 90-95 % at reaction temperatures about 800 - 900°C, whereas thermal cracking requires temperatures above 1200°C to reach the same efficiency at expense of energy losses and big investments on high temperature materials.

[0005] The catalysts can be used as the secondary method, in downstream catalytic reactors, such as catalytic beds, monoliths and filters, or as the primary method, e.g. added directly in the fluidised bed gasifier as the bed material. The use of catalytically active bed materials promotes char gasification, water-gas-shift (WGS) and steam reforming reactions, which can enhance tar/CH₄ reforming and increase the H₂ content in the syngas. The primary method is more cost-effective attributed to lower thermal losses, less downstream reactors and lower investment cost. Ni-supported olivine is highly effective in reduction of tars and CH₄, but an important drawback is the toxicity of nickel and the volatiles particles that occurs in fluidised bed gasifiers. The catalyst can be deactivated due to carbon deposition, chloride, sulphur poisoning, oxidation, and sintering. However, the lifetime of the catalyst can be prolonged by the oxygen balance in a dual fluidised bed gasifier (DFBG).

[0006] One common catalytic bed-material used in DFBGs is olivine ((Mg, Fe)₂ SiO₄), a natural mineral containing magnesium, iron oxide and silica. Catalytic activity of olivine in cracking and reforming of tars and enhanced steam and dry reforming of hydrocarbons are reported in a number of articles. Olivine has been a more and more attractive bed material used in DFBGs due to good attrition resistance comparable to silica sand, low price, and good catalytic effect comparable to dolomite. However, the tar/CH₄ reforming performance by the olivine or Fe doped olivine catalytic bed materials is still limited. The performance might be improved by more intensive contact between volatile gas and catalytic bed material at a higher temperature zone in the gasifier, above the dense bed where the hot bed material returning from the combustor.

[0007] Fluidized bed gasifiers have been employed for many years to produce syngas from biomass raw material. A fluidized bed gasifier typically comprises a reactor chamber in which a so called fluidized bed is created at a lower space region of the reactor chamber by arranging solid particles as bed material and blowing air through the bed of solid particles at a sufficient velocity to keep these in a state of suspension. The bed is heated and when a sufficiently high temperature is reached, fuel particles, i.e. biomass raw material, are introduced at the bottom of the reactor chamber, very quickly mixed with the bed material, and almost instantaneously heated up to the bed temperature. During continuous operation a part of the fuel is oxidized (burned) to produce sufficient heat to maintain the pyrolysis /gasification process. Alternatively, heat is provided by a separate combustor in fluid connection with the reactor chamber. As a result of this treatment the fuel is almost instantly pyrolysed, resulting in a component mix with a relatively large amount of gaseous materials, syngas or product gas. Further gasification and tar-conversion reactions occur in the gas phase. Typically the fluidized bed systems are equipped with a cyclone in order to minimize particle and char blow-out as much as possible. The product gas typically has to be purified further, to allow processing to form more advanced Biofuels or chemicals. One of the major challenges in production of high quality syngas thru biomass fluidized-bed gasification is the reforming of tars and methane (CH₄) to a minimum allowable limit.

[0008] EP 0700868 B1 discloses a first stage fluidized bed reactor for producing syngas connected to a downstream second stage in-line reactor for reforming the produced syngas. The process in the first stage fluidized bed reactor is performed at temperatures ranging from 815°C to 1038°C. The second stage in-line reactor is a fixed bed of catalytic metal solids. The process in the second stage fluidized bed reactor is performed at temperatures ranging from 871°C to 982°C.

[0009] The system described above is generally effective in accomplishing a sufficient reformation of syngas. However, there is a need for a less complex, less costly, more efficient fluidized bed gasifier system with efficient reformation of the syngas to reduce impurities and unwanted byproducts under production of syngas.

SUMMARY OF THE INVENTION

[0010] It is an object of the present invention to at least provide an improved fluidized bed gasifier system. It would be advantageous to achieve an efficient fluidized bed gasifier system with efficient in-situ reformation of the product gas to reduce impurities and byproducts such as tars and methane within the produced syngas.

[0011] According to a first aspect of the invention, there is provided a fluidized bed gasifier system comprising a main chamber, which has a lower space region, an intermediate space region, and an upper space region. The system further comprises a fuel feed inlet for providing fuel to the main chamber, a dense fluidized bed arranged at the lower space region for producing a product gas from the fuel, and a product gas outlet arranged at the upper space region. The system further comprises a first reformation device arranged inside the main chamber above the dense fluidized bed.

[0012] Thereby a fluidized bed gasifier system is provided in which a reformation device, i.e. a catalytic device, is arranged inside the main chamber between the dense fluidized bed and the product gas outlet. With this arrangement the reformation of the product gas produced from fuels like biomass raw material, solid fuels, slurries, cellulose, hemicelluloses, lignin or coal, takes place downstream from the dense fluidized bed but before exiting the main chamber via the product gas outlet, which preferably is arranged at a top portion of the main chamber. Gas-solids interaction in the main chamber is increased due to a prolonged space time of the product gas in denser areas of catalytic reformation device material. Since the reformation device is placed within the main chamber the high temperature within the main chamber can be directly utilized in the reformation process, and there is less need for an external reformation reactor which requires its own internal heating- and control system to provide reformation of the product gas. The advantages above decreases the initial investment cost of the system, and the energy cost during operation of the system. Further, also the space required for the gasification system is decreased. The present inventive concept is advantageously applicable for fluidized bed gasifier being one of a Dual Fluidized Bed gasifier, DFB gasifier, a Bubbling Fluidized Bed gasifier, BFB gasifier, and a Circulating Fluidized Bed gasifier, CFB gasifier.

[0013] According to an embodiment of the system, the first reformation device is arranged at a heat input arranged in the main chamber. The heat input advantageously provides a high temperature to form an active zone. This active zone is spread out in the substantially the whole cross sectional area of the main chamber where the reformation device is placed and typically has the same height as the reformation device.

[0014] According to an embodiment of the system, it further comprises a second reformation device arranged above (i.e. downstream from) the first reformation device. The second reformation device can have the same catalytic properties as the first reformation device, thereby providing an even longer space time in denser areas with better gas solids interaction if only one catalytic type is used.

[0015] According to an embodiment of the system, the second reformation device comprises or comprises other types of catalytic materials than the first reformation device, which materials in combination with the first reformation device give unique functionalities. As an example, such a combination enables reformation or "catching" of substances in the catalytic means of the first reformation device, which are harmful (poisonous) to the catalytic means of the second reformation device thus enabling the use of more precious catalysts in this subsequent reformation step. This "in series" catalytic reforming will provide superior functionalities compared to a single reformation device. The first and second reformation device can each be selected to provide reforming of different individual properties in the produced gas, i.e. the product gas that normally is addressed in separate external downstream reactors.

[0016] According to an embodiment of the system, the second reformation device is arranged above the heat input. This advantageously allows for use of catalytic material with less wear resistance than for the first reformation device since there is less or no transport of bed material in the space region above the heat input (for DFB gasifier systems), which reduces the need for wear resistance. Thereby it is possible to use more porous catalytic materials providing increased active surface area in the second reformation device/step inside the main chamber.

[0017] According to an embodiment of the system, each of the first reformation device and the second reformation device is selected from a group of reformation devices being one of a catalytic monolith (single monolith), and a catalytic solid bed (catalytic pellets or small monoliths), a catalytic fluidized bed (catalytic particles), and catalytic candle filter.

[0018] According to an embodiment of the system, the first and second reformation devices are arranged having one of the same-, complementary-, and different properties. Different physical properties applied in the first and second reformation devices, respectively, provide the possibilities to combine e.g. an allowed high wear resistance in the first reformation device with a high specific surface area in the second reformation device.

[0019] According to an embodiment of the system, applying different physical properties in the first and second reformation device provide means to model the pressure drop, i.e. provide a predetermined pressure drop, in different parts or in the overall length of (extension along) the gasifier. Further, applying different physical properties in the first and second reformation devices provides filtration possibilities close to the exit but still inside the main chamber/ the gasifier. In this embodiment, the second reformation device is preferably arranged with a filtration function, or is arranged like a filtration device, and thus provides a hot gas filter inside the main chamber which is advantageous. Gas filtration above 600°C is typically difficult to achieve, and when applying an external filtering process the product gas is typically cooled below 500°C. Here the second reformation device provides an intrinsic physical filtering effect due to the fact that the second reformation device can be selected to have both filtering and catalytic properties such as filter candles with an active surface.

[0020] In the latter embodiment, where the second reformation device functionality is at least partly filtrating, the need for recirculation of fly ash in the case of fluid bed gasifier, e.g. a DFB gasifier, is partly eliminated (decreased) and the need of external downstream gas filtration is decreased.

[0021] By applying different catalytic properties in the first and second catalytic reformation device respectively, different combined catalytic properties that normally are placed externally in separate downstream reactors, can be utilized inside the gasification vessel, i.e. inside the main chamber at different preselected locations. These individual catalytic properties may normally not be possible to combine in the same vessel or in/on the same support material. According to the invention, the first and second reformation devices are operated at different sites along the gas stream inside the gasification vessel, and these multiple catalytic functions can co-operate sufficiently as long as the temperature, pressure and gas atmosphere is within an accepted range.

[0022] According to an embodiment of the system, the properties for the first and/or second reformation device are selected to provide regeneration of (catalytic) material of the dense fluidized bed material. In the case of a DFB gasifier and when utilizing bed material which has the capability to carry oxygen between the oxidizing vessel, i.e. the riser, and the reducing vessel, i.e. the main chamber, by oxides on/in the particles, the oxides introduced by these particles to the first or second catalytic device, i.e. the first and second reformation device, will alter the oxygen balance promoting regeneration of the catalytic properties by un-blocking blocked sites due to oxidizing of blocking substances such as sulfur, S, chloride, Cl, and carbon, C.

[0023] According to an embodiment of the system, the properties for the first reformation device are selected to facilitate regeneration/cleaning from substances such as sulfur, S, and carbon, C, due to abrasion from the inflowing (feedback) bed material in the case of a DFB gasifier.

[0024] According to embodiments of the system, the first reformation device and the second reformation device if present comprise separate active reforming catalytic materials, such as dolomite, Ca, Fe, C, Ni, Rh, Ru, Pd, Pt, Re, or Co or compounds comprising the active reforming catalytic materials.

[0025] According to a second aspect of the invention, there is provided a method for operating a fluidized bed system, like for instance a Dual Fluidized Bed gasifier, DFB gasifier, a Bubbling Fluidized Bed gasifier, BFB gasifier, and a Circulating Fluidized Bed gasifier, CFB gasifier, which comprises a main chamber having a fuel inlet and a product gas outlet, the method involving the steps of

• forming a fluidized bed in a lower space region of the main chamber for producing product gas by at least partly gasifying the fuel; and
• providing a first reformation step arranged to reform the product gas inside the main chamber.

[0026] The method has similar advantages as described above for the corresponding system. Preferably, a product gas outlet is provided above the first reformation step such that product gas generated in the fluidized bed is reformed/filtered in the reformation device before exiting the main chamber

[0027] According to an embodiment of the method, the method further comprises:

providing a second reformation step after the first reformation step inside said main chamber. Thereby, product gas generated in the fluidized bed is reformed/filtered in the reformation device before exiting the main chamber.

[0028] According to an embodiment of the method, the method further comprises:

• providing heat to said first reformation step.

[0029] According to an embodiment of the method, the method further comprises:

• arranging the first reformation step and said second reformation step to have the same, complementary-, or different catalytic and/or filtering properties.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The invention will now be described in more detail and with reference to the appended drawings in which:

Figs. 1a and 1b, are schematic cross-sectional side views of embodiments of a fluidized bed gasifier system according to the present invention which comprises a BFB gasifier;

Figs. 2a and 2b, are schematic cross-sectional side views of embodiments of a fluidized bed gasifier system according to the present invention which comprises a CFB gasifier;

Figs. 3a and 3b are schematic cross-sectional side views of embodiments of a fluidized bed gasifier system according to the present invention which comprises a DFB gasifier; and

Figs. 4 to 8 illustrate main gas components as a function of gasification temperature for comparison of two cases, with or without Ni-catalytic pellets filled in an in-situ reformer, i.e. reformation device according to an embodiment of a fluidized bed gasifier system according to the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0031] The present invention will now be described more fully hereinafter with reference to the accompanying drawings. The below embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

[0032] Referring now to Fig. 1a, a schematic illustration of an embodiment of a fluidized bed gasifier system 100 according to the present invention which is arranged for providing a Bubbling Fluidized Bed, BFB, is shown. The fluidized bed gasifier system 100 comprises a reactor chamber, main chamber 101, in which a bed material to form a dense fluidized bed 104 is pre-installed at a lower space region 101a thereof. The fluidized bed 104 comprises solid particles which are set into a fluidized state during operation of the system. A gas inlet 106 is arranged at the lower space region 101a for creating the dense fluidized bed by applying gas at a velocity suitable for causing the particles of the dense bed 104 to be effectively retained in the fluidized state in the dense fluidized bed 104 during operation of the fluidized bed gasifier system 100. Further, the main chamber 101 is arranged having a fuel feed inlet 102 for providing fuels such as solid fuels, slurries, coal, cellulose, hemicellulouce, lignin, or biomass raw material to the fluidized bed 104. The fuel, which here is biomass raw material, is fed to the main chamber 101 from a silo or storage 50 by means of a fuel feeder, e.g. screw feeder 51. At a top portion of the main chamber 101, in upper space region 101c, a product gas outlet 105 is arranged in fluid connection with a subsequently arranged cyclone separator 52 (optional). The cyclone particle separator 52 is arranged for separating particle from the product gas which is then discharged from the fluidized bed gasifier system 100 via a syngas outlet 107.

[0033] Further, inside the main chamber 101, in line with and above the dense fluidized bed 104, a first reformation device 110 is arranged. The first reformation device 110 is here provided as an obstacle through which the hot product gas formed by the pyrolysis process in the dense fluidized bed 104 is passed. The obstacle, i.e. the first reformation device 110, is in the form of a catalytic means comprising for instance single monoliths, a packed bed of small monolith beads, a catalytic active candle filter, or a fluidized bed of catalytic active bed particles. This catalytic means has the ability to use the catalytic active property at a suitable high temperature to crack open bindings between molecules in the produced gas, thereby forming lighter compounds which are beneficial for the overall process and efficiency, before the product gas exits the main chamber 101 via the product gas outlet 105. The material of the first reformation device is preferably made of, or coated with Nickel, Ni, or a Ni-compound material. However, other materials such as dolomite, Ca, Fe, C, Rh, Ru, Pd, Pt, Re, or Co are applicable.

[0034] With reference now to Fig. 2a, which is a schematic illustration of an embodiment of a fluidized bed gasifier system 200 according to the present invention, the shown fluidized bed gasifier system 200 is arranged for providing a Circulating Fluidized Bed, CFB. Overall the fluidized bed gasifier system 200 has some similar components as the BFB-system described above with reference to Fig. 1a: it comprises a main chamber 101 in which a bed material to form a dense fluidized bed 104 is arranged at a lower space region 101a thereof. The fluidized bed 104 comprises solid particles which are set into a fluidized state during operation of the system. A gas inlet 106 is arranged at the lower space region 101a for creating the dense fluidized bed by applying gas at a velocity suitable for causing the particles of the dense bed 104 to be effectively retained in the fluidized and in addition a transporting state in the fluidized bed during operation of the fluidized bed gasifier system 200. Some examples of bed materials include silica sand, and different types of natural minerals, such as various olivines. Further, the main chamber 101 is arranged having a fuel feed inlet 102 for providing fuels such as solid fuels, slurries, coal, cellulose, hemicellulouce, lignin, or biomass raw material to the fluidized bed 104. The fuel, e.g. biomass raw material, is here fed to the main chamber 101 from a silo or storage 50 by means of a fuel feeder, e.g. screw feeder 51. At a top portion of the main chamber 101, in upper space region 101c a product gas outlet 105 is arranged and in fluid connection with a subsequently arranged cyclone separator 52 which via a feedback coupling 201 returns particles, that are separated from product gas exiting the main chamber 101 via the product gas outlet 105, to the lower space region 101a and the fluidized bed 104 inside the main chamber 101.

[0035] Further, inside the main chamber 101, in line with and above the dense fluidized bed 104, a first reformation device 110 is arranged. Here the first reformation device 110, which has the form of a catalytic means comprising for instance single monoliths, or a packed bed of small monolith beads, is arranged in an intermediate space region of the main chamber 101b.

[0036] In Fig. 3a an embodiment of a system according to the present invention, a Dual Fluidized Bed, FDB, system 300 is schematically illustrated in a cross sectional side view. The shown fluidized bed gasifier system 300 comprises a gasifier, i.e. main chamber 101 in which a bed material to form a dense fluidized bed 104 is installed at a lower space region 101a thereof. The fluidized bed 104 comprises solid particles which are set into a fluidized state during operation of the system. A gas inlet 106 is arranged at the lower space region 101a for creating the dense fluidized bed by applying gas, e.g. steam, at a velocity suitable for causing the particles of the dense fluidized bed 104 to be effectively retained in the fluidized state in the dense fluidized bed during operation of the fluidized bed gasifier system 300. Some examples of bed materials are silica sand, and different types of natural minerals, such as various olivines. As in the previous example embodiments, the main chamber 101 is arranged having a fuel feed inlet 102 for providing fuels such as solid fuels, slurries, coal cellulose, hemicellulouce, lignin, or biomass raw material to the fluidized bed 104 from a silo or storage 50 by means of a fuel feeder, e.g. screw feeder 51. At a top portion of the main chamber 101, in upper space region 101c, a product gas outlet 105 is arranged.

[0037] The dual fluidized bed gasifier system 300 has an additional reactor chamber, a combustor, which is arranged in fluid connection with the gasifier 101 forming a feedback loop circuit for heating a portion of the bed material of the fluidized bed 104 thereby providing indirect heating of the bed material of the dense fluidized bed 104.

[0038] The combustor, which herein after is referred to as riser 302, is arranged in fluid connection with the main chamber 101 via a downwards inclined transport channel 301, through which a limited amount of the bed material from the dense fluidized bed 104 in the main chamber 101 and char is transported to the riser 302 (the fluid connection between the main chamber and the riser being governed by a lower pressure lock 313). Air or air in combination with other gases is injected in the riser 302 at a gas inlet 306 arranged at the bottom of the riser together with additional fuel from fuel feeder 312 to maintain the desired gasification temperature such that a second fluidized bed 311 of heated bed material is formed inside the riser 302. At a top portion of the riser a particle separator 308 in fluid connection with the riser 302 is arranged to separate particles from flue gas of the riser 302, which flue gas is then discharged via a flue gas outlet 307, while heated bed material, i.e. the separated particles, is guided back to the main chamber 101 under the control of an upper pressure lock 303. The heated bed material enters the main chamber 101 at a heat inlet, feedback inlet 304 of the riser loop circuit, which provides a high temperature zone, which is herein after referred to as active zone 310. The active zone 310 is spread out in the total cross sectional area of the part where the first reformation device 110 is placed and typically has the same height as the reformation device. The heated bed material from the feedback loop circuit typically has a temperature of approximately 800-1000 °C.

[0039] The type of reformation device is preferably selected based on the specific raw material feed (fuel), the temperature in the active zone, the target properties for the product gas and available pressure inside the main chamber. Different types of catalytic devices that are suitable to use as first reformation device (or second reformation device as described below) are: single monoliths, packed beds of small monolith beads, fluidized beds of catalytic active bed particles, and catalytic filter candles.

[0040] As is illustrated in Fig. 3a, inside the main chamber 101, in line with and above the dense fluidized bed 104, a first reformation device 110 is arranged. The first reformation device 110 is arranged below the heat inlet, feedback inlet 304, such that the first reformation device 110 is placed in the active, high temperature zone 310. The first reformation device 110 is in this exemplifying embodiment a single monolith arranged on a carrier device. The single monolith forms an obstacle through which the hot product gas formed by the pyrolysis process in the dense fluidized bed 104 is passing under interaction with the catalytic active material in the obstacle (catalytic means). This catalytic means has the ability to use its catalytic active properties together with suitable high temperature to crack open bindings between molecules in the produced gas forming lighter compound beneficial for the overall process and efficiency before the product gas exits the main chamber 101 via the product gas outlet 105. The high temperature in the active zone 310 and the positioning of the first reformation device 110 in the active zone 310 below the feedback inlet 304 provides for a highest possible temperature provided by the feedback inlet of bed material. The temperature is essential for the function of the catalytic means. That is, if the catalytic means has a high temperature, the temperature in the dense region, i.e. the fluidized bed 104, can be lower providing efficiency gains. The flow of bed material in the feedback loop circuit provides intensive interaction between gas and solids, i.e. the bed material, but also intensive interaction between bed particles and catalytic material. This in turn provides a mechanical stress on the catalytic material that advantageously can be used to clean the surface of the catalytic active material from deposits such as sulfur, S, or carbon, C. Furthermore, in the shown DFB gasifier system, when utilizing bed material which has the capability to carry oxygen between the oxidizing vessel (the riser) and the reducing vessel ( main camber) by oxides on/in the bed particles, the oxides introduced to the first or second reformation device by these bed particles will alter the oxygen balance promoting regeneration of the catalytic properties by un-blocking blocked sites due to oxidizing of blocking substances such as sulfur, S, chloride, Cl, and carbon, C.

[0041] According to embodiments of the fluidized bed gasifier system of the present inventive concept, which are illustrated in Figs. 1b, 2b and 3b, the system comprises a second reformation device. In the case of a dual fluidized bed gasifier system 300 of the present invention which is illustrated in Fig. 3b, which has a similar constitution as the system 300 described with reference to and illustrated in Fig. 3a, the system is arranged having a second reformation device 120 arranged above the first reformation device 110. Further, in this illustrative example, the second reformation device 120 is arranged above the feedback inlet 304. Utilizing a first and a second reformation device 120 in line with the first reformation device 110 inside the system 100, 200 is also applicable in BFB- and CFB-gasifier systems, respectively, as illustrated in Fig. 1b and Fig. 2b. However, for CFB systems the second reformation device 120 has to be placed in, or downstream of, a subsequently arranged cyclone separator 52 if a filtering function is desired. The first reformation device 110 and the second reformation device 120 are arranged having one of the same-, complementary-, and different properties for instance as described above, see also Summary.

Experimental Setup

[0042] One gasifier used in the experiments on which the application is based, is a DFBG (corresponding to Fig. 3a) and is herein after referred to as the MIUN (Mid Sweden University) gasifier. The MIUN gasifier consists of a bubbling fluidized bed (BFB) steam gasifier and a circulating fluidized bed (CFB) riser combustor, and has the biomass treatment capacity of 150 kWth, i.e. approx. 25 kg biomass feed per hour. The gasifier and the combustor have a height of 2.5 and 3.1 m, and inner diameters of 300 and 90 mm, respectively. The MIUN gasifier has been described in detail in a previous article 8 to which reference is made: Göransson, K.; Söderlind, U.; Zhang, W., Experimental test on a novel dual fluidised bed biomass gasifier for synthetic fuel production. Fuel 2011, 90, (4), 1340-1349.

[0043] The bed-material in these tests is olivine ((Mg, Fe)2 SiO4), a natural mineral containing magnesium, iron oxide and silica. The oxygen transport capacity of olivine can be 0.5wt%, see e.g. Lancee, R. J.; Dugulan, A. I.; Thüne, P. C.; Veringa, H. J.; Niemantsverdriet, J. W.; Fredriksson, H. O. A., Chemical looping capabilities of olivine, used as a catalyst in indirect biomass gasification. Applied Catalysis B: Environmental 2014, 145, (0), 216-222. Hence, the produced gas in the gasifier will be partially oxidized by oxygen input by the olivine in DFB operation. Reduction of bed material in the steam gasifier with a following oxidation in the air combustor achieves a catalyst recovery cycle, similar to the chemical looping combustion (CLC), see Pecho, J.; Schildhauer, T. J.; Sturzenegger, M.; Biollaz, S.; Wokaun, A., Reactive bed materials for improved biomass gasification in a circulating fluidised bed reactor. Chemical Engineering Science 2008, 63, (9), 2465-2476. The olivine is prepared by calcination inside the DFB reactor at 900°C in 10 hours, with air at slightly elevated pressure.

In-situ reformer

[0044] In general, the biomass gasification process occurs through three steps: 1) pyrolysis which devolatilises biomass into char and volatile matter including tars; 2) secondary reactions such as cracking and reforming of tars; 3) gasification reactions of the remaining carbonaceous residue with steam and carbon dioxide. The steps 1 and 3 take place in the dense bed of the fluidised bed gasifier, while the step 2 takes place in the freeboard of the fluidised bed. Thus, the reforming of tars and CH₄ in the freeboard is important for high quality syngas production, which is favoured by a good contact of volatile with catalytic bed material at a sufficiently high temperature. This might not be the case for the freeboard region of MIUN gasifier (where freeboard is corresponding to the space region above the dense fluidized bed), where the hot bed material returns next to the wall of the main chamber while the volatile passes through the centre of the main chamber. This insufficient gas-solids contact may be one reason that the tar content in the syngas in previous test of MIUN gasifier is not low enough, although Fe/olivine were used as the circulating catalytic bed material.

In-situ reformer with Ni-catalytic pellets

[0045] The in-situ reformer, first reformation device 110, can be combined with a second reformation device 120 coomprisng e.g. catalytic monolith, catalytic bed or catalytic filter candles, to procreate a better effect of tar/Methane reforming. In this test, the reformer, first reformation device, is filled with Ni-based catalytic pellets (see Table 1). Nickel oxide is the active component with alumina as support material. The catalyst has good stability and high mechanical strength, and can be used at 1500°C for a long time.

Table 1. Physical and chemical properties of the steam reforming catalytic pellets

Appearance	5 holes drums
Particle size (mm)	19-20
Pore diameter (mm)	3-5
Bulk density (kg/l)	0.90-0.95
Crushing strength (N/particle)	>300
NiO(%)	>14
Free silica (%)	0.2

Main gas components versus temperature

[0046] Figs. 4-7 show main gas components as a function of the gasification temperature for comparison of two cases, with or without Ni-catalytic pellets filled in the in-situ reformer, i.e. the first reformation device in a gasifier system as described above. It can be seen from the figures that higher temperature enhances the tar/CH₄ steam reforming reactions and results in higher content of H₂ and CO, while the CO₂ content slightly decreases since the exothermic shift reaction is favoured by low temperature. The contents in CO₂ and CH₄ are decreasing with temperature.

[0047] As seen in Table 2 and Figs 4 and 5, the CO+H₂ concentration clearly increases with temperature from 60% to 70% for the case without Ni-pellets, and from 55% to 74% for the case with Ni-pellets. The most significant change is H₂ concentration when Ni-pellets are added in the in-situ reformer, which increases from 24.8% at 750°C to 41.5% at 940°C and exceeds the CO concentration at 780°C. The Ni-pellets hardly change the CO concentration as shown in Table 2. These lead to a H₂/CO ratio under 1 for the reformer, reformation device. without Ni-pellets and above 1 for the reformer with Ni-pellets as seen in Table 2 and Fig. 6. The H₂/CO ratio varies from 0.9 to 1.0 for the reformer without Ni-pellets, and from 0.9 to 1.3 for the reformer with Ni-pellets. A clear trend of H₂ concentration increasing with temperature, suggests a strong steam reforming of hydrocarbons in the in-situ reformer by the Ni-catalyst.

[0048] Steam reforming of CH₄ is a strongly endothermic reaction:

         CH₄ + H₂O ↔ CO + 3H₂ ΔH°298 = +206 kJ/mol     (1)

[0049] Under the condition of the in-situ reformer, the moderately exothermic water-gas shift (WGS) reaction is extremely fast leading to the equilibrium state:

         CO + H₂O ↔ CO₂ + H₂ ΔH°298 = -41 kJ/mol     (2)

[0050] Steam reforming of hydrocarbons is favoured by high temperature; in contrast, the exothermic shift reaction is favoured by low temperature. The amount of steam will enhance the CH₄ conversion. The syngas composition is thus governed by the reactions (1) and (2) above, including reforming of other hydrocarbons. Fig. 7 shows the CH₄ concentration. CH₄ is the most recalcitrant hydrocarbon to reform, which very much depends on the temperature as also shown in Fig. 7. For the in-situ reformer without Ni-pellets, a decrease in CH₄ content from 11 to 9% is found at the higher temperatures. For the in-situ reformer with Ni-pellets, the CH₄ content is decreasing more clearly from 11 % to 6% . These results indicate that the in-situ reformer with catalytic pellets is active in the steam reforming of hydrocarbons.

Gravimetric tar content versus temperature

[0051] Fig. 8 shows that the tar content decreases with temperature as a general trend similar to CH₄. The reformer filled with Ni-catalytic pellets shows a higher reduction of tars than the unfilled reformer. By means of the in-situ reformer with Ni-pellets,

Table 2. Measurement results (mean values) of the test in the MIUN gasifier, (S/C=1.2).

Test:		1	2	3	4	5	6	7	8	9	10
	11	12	13
Temp.(°C):		750	800	850	900	940	750	800	850	900	909
	915	920	940

In-Situ Reformer:
	Without Ni-catalvtic pellets					With Ni-catalvtic pellets
Gas comp.(Vol.% db):
H2		29.8	28.7	31.8	35.4	34.4	24.8	28.8	34.2	38.1	35.5
40.4	40.7	41.5
CO			31.7	31.9	34.9	34.7	35.8	28.2	28.1	28.3	32.8
30.6	33.5	33.1	32.4
CH4		11.0	10.6	11.4	10.1	9.0	10.7	9.4	7.5	6.8	6.7
5.9	6.2	5.7
CO2		15.5	15.0	14.0	13.2	11.0	16.8	15.6	14.2	11.1	12.1
11.9	12.0	10.2
Ethene		4.1	4.0	4.1	3.2	2.5	3.4	3.1	2.4	1.5	1.8
1.6	1.2	0.6
Ethane		0.6	0.4	0.3	0.1	0.0	0.6	0.5	0.3	0.1	0.2
0.3	0.1	0.1
C3		0.2	0.1	0.1	0.0	0.0	0.3	0.2	0.1	0.0	0.0
0.0	0.0	0.0
C4		0.1	0.0	0.2	0.0	0.1	0.1	0.1	0.1	0.0	0.0
0.0	0.0	0.0
O2		0.8	0.7	0.4	0.9	0.9	0.7	0.8	1.5	N/A*	0.9
0.9	0.7	N/A*
N2*			12.3	15.0	8,0	9.0	12.1	14.7	12.7	12.6	3.7*
6.8	6.2	5.9	1.7*

H2+CO (Vol.% db):
		61.5	60.6	66.7	70.1	70.2	53.0	56.9	62.5	70.9	66.1
73.9	73.8	73.9
H2/CO		0.9	0.9	0.9	1.0	1.0	0.9	1.0	1.2	1.2	1.2
1.2	1.2	1.3

Grav. Tar (g/Nm3):
			23.2	13.3	26.0	12.5	16.3	23.7	14.5	10.6	6.3
	6.3	5.9	5.0	5.1.

*Upper pressure lock fluidised with Argon instead of air.

the gravimetric tars significantly decrease from about 25g/m³ at 750°C down to 5g/m³ at approx. 920°C. The relatively high tar yield of the tests with in-situ reformer filled with Ni-catalytic pellets, in comparison with other reported gasification tests with downstream Ni-catalyst reactor (tar yield <2 g/m³) , can be explained by a short gas residence time in the reformer and an insufficient specific surface area of the catalyst. The design of the in-situ reformer should be optimized to further reduce the tar content in the syngas.

[0052] So far, the measured tar content in the syngas is fairly independent of the experimental time in this study, which indicated no deactivation of Ni-catalyst. More information regarding the experimental setup and results can be found in the yet to be published paper "INTERNAL TAR/CH4 REFORMING IN A BIOMASS DUAL FLUIDISED BED GASIFIER", Kristina Göransson*, U1f Söderlind, Till Henschel, Per Engstrand and Wennan Zhang, FSCN-Fibre Science and Communication Network, Mid Sweden University,Sundsvall, SE-85170, Sweden *Corresponding author: kristina.goransson@miun.se (Kristina Göransson).

[0053] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A fluidized bed gasifier system(100) comprising

a main chamber (101) comprising a lower space region (101a), an intermediate space region (101b) and an upper space region (101c);

a fuel feed inlet (102) for providing fuel to said main chamber;

a dense fluidized bed (104) arranged at said lower space region for producing a product gas from said fuel; and

a product gas outlet (105) arranged at said upper space region;
characterized by:

further comprising a first reformation device arranged inside said main chamber above said dense fluidized bed.

2. A system according to claim 1, further comprising a heat input (304) arranged in said main chamber at which said first reformation device is arranged.

3. A system according to claim 2, wherein said heat input is arranged in said intermediate space region (101b).

4. A system according to any preceding claim, further comprising a second reformation device arranged above said first reformation device.

5. A system according to claim 4 when dependent on claim 2 or claim 3, wherein said second reformation device is arranged above said heat input (304).

6. A system according to any preceding claim, wherein each of said first reformation device and said second reformation device when present comprises one of a catalytic single monolith, a catalytic solid bed, a catalytic fluidized bed, and a catalytic candle.

7. A system according to any of claim 4 to claim 6, wherein said first and second reformation devices are arranged having one of the same-, complementary-, and different properties.

8. A system according to any of claim 4 to claim 6, wherein the properties for the first and/or second reformation device are selected to provide regeneration of material of at least one of said dense fluidized bed, said first reformation device and said second reformation device.

9. A system according to any preceding claim, wherein said first reformation device and second reformation device if present comprise separate active reforming catalytic materials, such as dolomite, Ca, Fe, C, Ni, Rh, Ru, Pd, Pt, Re, or Co or compounds comprising said active reforming catalytic materials.

10. A system according to any preceding claim, wherein the fluidized bed gasifier is one of a Dual Fluidized Bed gasifier, DFB gasifier, a Bubbling Fluidized Bed Gasifier, BFB gasifier, and a Circulating Fluidized Bed Gasifier, CFB gasifier.

11. A method for operating a fluidized bed system (100) comprising a main chamber (101) having a fuel inlet (102) and a product gas outlet (105), said method involving the steps of
forming a fluidized bed in a lower space region of said main chamber for producing product gas by at least partly gasifying said fuel; and
providing a first reformation step arranged to reform said product gas inside said main chamber.

12. A method according to claim 11, further comprising providing a second reformation step after said first reformation step inside said main chamber

13. A method according to claim 11 or 12, further comprising providing heat to said first reformation step.

14. A method according to any of claim 11 to claim 13, further comprising arranging the first reformation step and said second reformation step to have the same-, complementary-, or different catalytic and/or filtering properties.

Drawing