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Title:
PRODUCING LOW TAR GASES IN A MULTI-STAGE GASIFIER
Document Type and Number:
WIPO Patent Application WO/2011/159352
Kind Code:
A2
Abstract:
A system for gasifying solid matter uses multiple stages to produce low-tar combustible gas includes a first reactor having a fluidized bed to produce hydrogen containing gas, pyrolysis vapors, tars, and char particles at temperature less than the exit of the second reactor and a higher temperature partial oxidation combustor zones. A second reactor includes a higher temperature partial oxidation zone to activate hydrogen and cause cracking of aromatic ring compounds, a co-flow moving granular bed with a char gasification stage to catalyze tar reduction,and control char residence time, and a media screen comprising a parallel wire screen substantially vertically oriented supporting granular media.

Inventors:
PASKACH THOMAS J (US)
REARDON JOHN P (US)
EVANS PAUL (US)
SMEENK JEROD (US)
Application Number:
US2011/001080
Publication Date:
December 22, 2011
Filing Date:
June 16, 2011
Export Citation:
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Assignee:
FRONTLINE BIO ENERGY,LLC (1421 South Bell Avenue, Ames, IA, 50010, US)
International Classes:
C10J3/48; C10L3/00
Foreign References:
US20090090053A12009-04-09
US20090019770A12009-01-22
US5804066A1998-09-08
Attorney, Agent or Firm:
URBAN, Camille, L. (BrownWinick Law Firm, 666 Grand Avenue Suite 200, Des Moines IA, 50309-2506, US)
Download PDF:
Claims:
CLAIMS

The invention claimed is:

1. A multi-stage reaction system for producing low-tar combustible gas, the system comprising:

a fluidized bed reactor that includes a partial oxidation zone, in which a gas and a plurality of char particles are created in said partial oxidation zone; and

an entrained flow partial oxidation reactor positioned downstream from the fluidized bed reactor.

2. The system disclosed in claim 1 wherein said entrained flow partial oxidation reactor includes a moving granular bed.

3. The system of claim 1, wherein the fluidized bed reactor further comprises a freeboard, said freeboard operated at a velocity controlled to create a generally consistent char particle size feed.

4. The system of claim 2 wherein said plurality of char particles is of generally consistent char particle size and at least a portion of said plurality of char particles is provided to the entrained flow partial oxidation reactor.

5. The system of claim 3 wherein provision of said generally consistent char particle size comprises modulating a pressure of the fluidized bed reactor.

6. The system of claim 1, further comprising a sand recovery cyclone.

7. The system of claim 1 , wherein the entrained-flow partial oxidation reactor further includes a partial oxidation zone and means for injecting a stream of combined gas and char into said partial oxidation zone.

8. The system of claim 7, further comprising a cyclone for concentrating the plurality of char particles out of a fed gas stream prior to injection into said partial oxidation zone.

9. The system of claim 8, wherein said cyclone concentrates the plurality of char particles out of the fed gas stream prior to injection into said partial oxidation zone.

10. The system of claim 2, wherein the entrained-flow partial oxidation reactor includes a plurality of blast inlet ports configured around a periphery of a vessel enclosing the reactor.

11. The system of claim 10, wherein said plurality of blast inlet ports is arranged in an alternating pattern such that each of the plurality of blast inlet ports targets a tangent curve of a tangent circle.

12. The system of claim 10, wherein said plurality of blast inlet ports is arranged in an alternating pattern such that a first one of the plurality of blast inlet ports targets a first tangent curve of a first tangent circle and a second one of the plurality of blast inlet ports targets a second tangent curve of a second tangent circle, wherein the first and second tangent circles are located at the same elevation.

13. The system of claim 10, wherein said plurality of blast inlet ports is arranged in an alternating pattern such that a first one of the plurality of blast inlet ports targets a first tangent curve of a first tangent circle and a second one of the plurality of blast inlet ports targets a second tangent curve of a second tangent circle, wherein the first and second tangent circles are located at different elevations.

14. The system of claim 7, wherein the moving granular bed operates in co- flow with respect to the stream of combined gas and char to create a gas-char contacting zone.

15. The system of claim 14, wherein a gas-media disengagement screen is oriented at an angle that is steeper than an angle of repose of the combined media and char mixture.

16. The system of claim 15, wherein the gas-media disengagement screen is oriented substantially vertically.

17. The system of claim 15, wherein the gas-media disengagement screen includes a plurality of parallel wires extending between an upper frame edge and a lower frame edge.

18. The system of claim 17, wherein each of the plurality of wires includes a cross section partially defined by a first side that converges with a second side at a vertex in the direction of the disengaging gas flow.

19. The system of claim 18, wherein the cross section is wedge shaped..

20. The system of claim 2 wherein the entrained-flow partial oxidation reactor further includes a partial oxidation zone, means for injecting a stream of combined gas and char into said partial oxidation zone, and a plurality of blast inlet ports configured around a periphery of a vessel enclosing the reactor.

21. The system of claim 20 wherein the moving granular bed operates in co- flow with respect to the stream of combined gas and char to create a gas-char contacting zone.

22. The system of claim 2 wherein the entrained-flow partial oxidation reactor further includes a partial oxidation zone and means for injecting a stream of combined gas and char into said partial oxidation zone and said moving granular bed includes a gas-media disengagement screen oriented at an angle steeper than the angle of repose of the combined media and plurality of char particles.

23. A method for controlling an operating pressure of a two-stage gasification system, the method comprising:

performing a partial oxidation of a portion of biomass in a fluidized bed reactor, wherein the partial oxidation creates a gas and a plurality of char particles;

elutriating at least a portion of said plurality of char particles and gas from the fluidized bed reactor, wherein said elutriating includes removing a mixture of gas and char particles from the fluidized bed reactor;

receiving the mixture into an entrained flow reactor, wherein the entrained flow reactor includes a moving granular bed of filtering media; allowing the mixture to flow through the moving granular bed; and capturing a portion of the plurality of char particles in the filtering media.

24. The method of claim 23 further comprising screening a portion of the filtering media to remove captured char particles; and returning the screened filtering media to the entrained flow reactor.

25. A multi-stage reaction system for producing low-tar combustible gas, the system comprising:

a fluidized bed reactor that includes a partial oxidation zone in which a portion of the feedstock is partially oxidized, wherein said partial oxidation creates a gas and a plurality of char particles;

an entrained flow partial oxidation reactor situated downstream from the fluidized bed reactor, the entrained flow partial oxidation reactor including a moving granular bed;

a media screening device that screens media from the moving granular bed; and

a media recycle system that returns the screened media to the entrained flow partial oxidation reactor.

Description:
PRODUCING LOW TAR GASES IN A MULTI-STAGE GASIFIER

FIELD OF THE INVENTION

[0001] The present invention relates, in general, to gasifying materials such as biomass and waste to produce high quality gas.

BACKGROUND

[0002] "Tars are the Achilles heel of gasifiers, and many gasifier projects have failed because of insufficient attention to low tar production or efficient tar destruction"— Tom B. Reed (T. Milne 1998). The highly generic term "tar" was uniformly defined in 1998 (at the EU/IA/DOE conference in Brussels) as all organic contaminants of gasification that have a molecular weight larger than benzene. Several review articles have been published discussing the nature, formation and destruction of tar from biomass gasification. (Li 2009) (Han 2008) (T. Milne 1998).

[0003] A maturation process has been proposed for tar with temperature, progressing from mixed oxygenates (400°C), to phenolic ethers (500°C) , then alkyl phenolics (600°C), then heterocyclic ethers (700°C), then polycyclic aromatics (800°C), and then larger Polynuclear aromatic hydrocarbons (PAH), soot, and coke (900°C). Elliot, D.C. "Relation of reaction time and temperature to chemical composition of pyrolysis oils." Proceedings of the ACS Symposium Series 376, Pyrolysis Oils from Biomass. American Chemical Society, 1988. Polymerization and subsequent agglomeration of high molecular weight PAH is described as a homogeneous pathway to "soot" formation. Homann, K.H., Wagner, H.G.,. "Some new aspects of the mechanisms of carbon formation in premixed flames." Eleventh International Symposium on Combustion. Pittsburgh: The Combustion Institute, 1967. [0004] Several different classifications of tar have been established. These classifications are related to temperatures. Classification has been developed as follows: "primary tars" are vapors produced at lower temperatures and are the first evolved in thermal depolymerization of cellulose, hemicellulose, and lignin— these are mainly oxygenated compounds. Next, the secondary and tertiary reaction products of primary tars are termed "secondary tar" and "tertiary tar". Tertiary tars were sub-classified as tertiary-alkyl and tertiary- polynuclear aromatic hydrocarbons (PAH). It is hypothesized that once tertiary tars are formed these may require even higher temperatures and additional residence time for thermal destruction.

[0005] There are several approaches to achieve adequate reduction of tar after an initial stage of gasification including thermal cracking, partial oxidation, and catalytic cracking using mineral catalysts or reforming with metal catalysts. One such method is indirect heat thermal cracking. This method has been discussed in the open literature to reduce tars in raw product gas. In the absence of char, a temperature of 900°C is insufficient to achieve much tar destruction. Specifically, a slip stream was filtered at 450°C to remove all char dust, but no measureable difference was found (after a fluid bed gasifier (8000 mg/Nm 3 in feed gas from CFB operating at 825°C) was filtered at 450°C to remove all char dust). The application of a homogeneous phase reactor demonstrated only -25% reduction even with residence times as high as 12 seconds. Even at 1000°C with 12 second residence time, only 75% reduction was achieved (-2000 mg/Nm 3 in product). (Houben, M.P. Analysis of tar removal in a partial oxidation burner. PhD Dissertation, Eindhoven: Technical University Eindhoven (Netherlands), 2004). [0006] It is a common hypothesis that the minimal performance of the char-free thermal treatment at 1000°C as compared to the downdraft gasifier at the same temperature suggests a catalytic role for char in tar reduction. It is possible that the nature of the fed tars (refractory tertiary tars present in fluid bed gas compared to primary or secondary tars in lower temperature pyrolysis gases) may also play a role in determining the thermal requirement for cracking. Even so, non-catalytic (homogenous phase) tar conversion to below 200 mg tar per Nm of gas is possible, starting with tar at 8000 mg/Nm 3 by using ~1150°C for ~4 seconds. (Houben 2004). It is also notable that indirect heating only below 1100°C with short residence times (say 1075° for 2 seconds) initially increased the amount of 2+ ring polycyclic aromatics— quantifiable tars with two or more aromatic rings— but extended residence time mitigates this effect.

[0007] Partial Oxidation has been explored as an alternate method for achieving tar destruction. This method includes blast containing oxygen subsequently added to raw generated gas. The Energy Center of the Netherlands (ECN) performed experiments using an atmospheric circulating fluidized bed gasifier (operated at 850°C) where air was added subsequently to increase the product gas temperature to 1100° or more. (Zwart, R.W.R. Gas Cleaning, downstream of biomass gasification status report. Public Report, Energy Center of the Netherlands (ECN), SenterNovem, 2009.) To achieve 100 mg tar/Nm 3 , a temperature of 1150°C was required, resulting in a cold gas efficiency loss of 8%.

[0008] A custom low swirl number burner (swirl number less than 0.4) was employed by

Houben to partially combust a relatively cool (20° and 200°C) synthetic gas feed, and so the peak temperatures were also relatively low (less than 900°C). This experiment isolated (somewhat) the partial oxidation effect from thermal effect for tar destruction, and also included no effect of char. The optimum amount of blast addition of approximately 0.2 equivalence ratio, λ, relative to the fed gas was reported to avoid growth in the PAH number (number of aromatic rings). Further, adding no oxygen with indirect heat promoted tertiary tar formation, but so did adding too much oxygen, for example λ>0.4, in Partial Oxidation.

[0009] The presence of hydrogen also seems to play a key role in tar destruction. A PAH

"cracking" scheme described in Jess, A. "Mechanisms and kinetics of thermal reactions of aromatic hydrocarbons from pyrolysis of solid fuels." Fuel 75, no. 12 (1996): 1441-1448 describes the alternate pathways of PAH growth or PAH cracking (fewer aromatic rings and lower carbon numbers in tar compounds) that may occur with varying hydrogen concentration. Similarly, Houben (2004) found that if hydrogen concentration of the inlet gas were more than about 20% vol., tar reduction was optimized. Decreasing hydrogen at the inlet below this level dramatically increased tar concentration in the products for the same equivalence ratio, λ. Naphthalene and tertiary PAH (3+ ring) were totally eliminated with an inlet hydrogen content greater than 30%vol, but single ring aromatics, e.g. toluene and benzene were retained. Therefore, gasifier operations that increase the fed hydrogen concentration should result in beneficial tar reduction for the same POX condition.

[0010] Catalytic tar reduction by contacting the gas with char in temperatures in the range of 900 to 1000°C— notably lower than necessary for thermal destruction in the absence of char, but still elevated with respect to the typical biomass gasifier exit temperature (750 to 850°C)— have also been disclosed. (Chen 2009). The natural minerals in biomass ash (MgO, CaO, 2 0, etc.) are believed to contribute to the catalytic effect, but the state of prior preparation (temperature history, surface area or oxidative exposure) is also thought to impact performance. Using commercial biochar (active carbon) and laboratory produced biochars (using 500°C pyrolysis) blended with sand, it was reported that naphthalene conversion was 99.6% and 94.4% at 900°C with 0.3 seconds residence time (25 cm 3 catalyst bed, 2 cm bed height), starting with 90,000 mg tars/Nm 3 in fed gas, compared with the blank sand (2%), natural olivine and sand (55%), and dolomite and sand (61%).

[0011] Fixed carbon gasifies much more slowly (orders of magnitude more slowly) compared to the volatile matter fraction of a solid fuel at the same temperature when under non- oxidizing conditions. A portion of the initial fixed carbon feed is usually present as a residue of gasification. If an appropriate technology were available to capture this char and expose it to the flowing gas stream it could be employed as a catalyst.

[0012] Fixed char beds with direct blast addition help to achieve low tar by gaining elevated temperatures in the char bed and also by presenting the char to the gas for possible catalytic benefit, but this approach is prone to upsets such as high temperature excursions. On the other hand, by separating the partial oxidation zone to a location above the char bed, the hot gases can be exposed to the active catalytic properties of char without blast input to the delicate char bed. However, a mechanical grate supporting low density char dust requires low superficial velocities and this is also prone to its own possible solids flow upsets (bridging, chanelling ("rat holing"), local hot spots, etc.) due to the chaotic flow behavior of low density solids.

[0013] A partial oxidation zone that achieves higher temperatures (1150°C) can be used to help effectively convert tars with or without passing through a fixed bed of char. The presence of hydrogen in the fed gas is an important feature to achieve maximum POX performance where opening aromatic rings can be favored over PAH growth. It is thought that the type of tars produced may also impact their ability to be subsequently reformed on a bed of char, and may impact the cracking performance in the POX stage; however, this has remained an unproven possibility. [0014] The combination of these theories and principles (hydrogen rich gas production, followed by partial oxidation, exposure to the catalytic properties of char, and supported char bed) in a robust and scalable industrial design is not presently known to the state of the art. The classic fixed bed downdraft gasifier (and other techniques that employ a fixed bed of char alone) is not scalable over about 10 MW th due to the anisotropic shape and chaotic flow potentials in low density char beds. Blast addition directly into the fixed bed of char would not be sufficiently robust for commercial deployment and would not be scalable to industrial capacities (>10 MW th ). The fixed bed of char alone suffers from solids flow irregularities ("bridging") and other process upsets ("rat holes") that occur due its low bulk density and the anisotropic nature and non-uniform particle size of the produced char.

[0015] Generally known gasifiers are of several types. The downdraft gasifier having an integrated fixed bed is a classic technology that is well known to those skilled in the art for low- tar gas production (<300 mg/Nm 3 ). Increasing superficial velocity through the downdraft gasifier, even when there is no secondary air injection into the char bed, also results in an increase of peak temperatures in the char bed. Lowest tar yields are observed with high peak temperatures > 1000°C. (Reed 1999) Referring now to Fig. 3, separate addition of blast into the fixed bed of char is also known to improve performance— this two stage downdraft is known to produce the lowest tars (<100 mg/Nm 3 ). The lowest tar performance occurs when the secondary air (45) added to the char bed (44) is at its maximum and thus primary air at its minimum. Setting the secondary air flow such that it is slightly below the level where "smoke" puffs out the open top describes the relativity desired of primary and secondary air. Peak temperatures over 1000°C were achieved in the char zone (46). The first stage of the optimally operated two-stage downdraft gasifier functions as an indirectly heated devolatilization or pyrolysis stage (43) and is likely to produce simpler "primary" and "secondary" tar compounds. These primary and secondary tar compounds occur at relatively low temperatures (500 to 700°C) prior to encountering the hot char bed (47). The hot char bed is believed to provide high temperature thermal cracking opportunity as well as catalytic benefit from the biomass ash minerals.

[0016] An alternative downdraft gasifier having a separated POX zone is another possibility (See Fig. 4)._One of the challenges with the classical two-stage, fixed bed, downdraft gasifier is that injection of blast into a fixed bed of char can lead to difficult operational problems— slagging (temperatures well over the ash fusion point), clinkering (fused ash particles), chanelling ("rat holing"), fuel bridging and material degradation in the blast input tube.

[0017] A multi-stage gasifier system (Viking II) was developed by the Danish Technical

University (DTU) between 1980 and 1990 based on the principles of the downdraft gasifier, but separated the blast addition from the fixed bed to improve operability. The DTU gasifier incorporates a separate low temperature pyrolysis stage(52) (500 to 600°C) that is configured above a vortex flow partial oxidation section(55) operated to achieve peak temperatures ~ 1 150°C— this stage is the only zone of direct blast addition. This partial oxidation zone (505) is situated above a downdraft, dense "fixed" bed of char (57) supported on a mechanical grate (58) comprised of pivoting angle iron.

[0018] The DTU design suffers from limited scale-up potential (due to the fixed bed of char (57) and indirectly heated feed auger (51)). On the other hand, the DTU gasifier system proved to yield very low tars (<25 mg/Nm 3 ) and produced a rich gas with -25% hydrogen without steam addition, and -35% hydrogen with steam addition. The gas quality was greatly enhanced by the recuperative indirect heat stage that can include indirect drying (52). The main difficulty with the DTU system is that the gasifier system still relied on a fixed bed of char, which consists of low bulk density solids that are irregular in particle size and shape. A relatively low superficial velocity is believed to be required for achieving a char pile without disruption on the mechanical grate (58) (previously described)— which indicates a costly scale- up for this reaction stage. The low density bed of char exhibits chaotic solids flow properties that would be unmanageable in an industrial-scale system with commercial reliability requirements.

[0019] Moving granular beds have also been used in prior art to present char as a catalyst to produced gas but in a cross flow moving granular bed filter, see Fig. 1 (Van der Drift 2005). The Van der Drift article describes a laboratory experiment for validating the theory that char can perform as a tar reduction catalyst and only employed a slip stream from a larger gasifier. The cross-flow design was reported to achieve high filtration efficiency and about 75% reduction in tar at 900°C, being presented with gas from a fluid bed that was operated at 850°C. The media retention screen (18) at the dust laden gas inlet (16) of the moving granular bed of char was reported to have dust fouling problems, and the system also suffered from media agglomeration within the gas media retention screens (18) which made media movement difficult.

[0020] Another moving granular bed filter which is shown in Fig. 2 is disclosed in US

Pat. NO. 7,309,384 to Brown et al., and does not provide for disengagement screen scrubbing nor does it provide the opportunity for extended gas residence time in the presence of char. Instead, the gas residence time is shorter due to the rapid char and media disengagement in the counter flow design, where gas from the gas inlet (33) is admitted at the bottom of the media bed (35) and then travels upward following path (34) mostly through a bed of clean media which was admitted through the media inlet (31). Extended gas-char contact that would otherwise benefit catalytic tar reduction by char is therefore not provided. Further, although not shown in the patent drawing, the claimed system requires a gas barrier (downcomer) (39) for operation. The gas barrier is needed to retain the media in a column and to direct the gas flow upward through the downward moving media column.

[0021] The present invention differs from the above referenced inventions and others similar in that these prior devices do not provide features that can be readily scaled up to industrial operational levels. What was needed was a gasifier system able to meet the low tar requirements while producing high quality gases, and which is feasible and operable in an industrial setting.

SUMMARY

[0022] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used in isolation as an aid in determining the scope of the claimed subject matter. At a high level, embodiments of the invention relate to a gasification system for converting feedstocks such as biomass and waste to combustible gases with low tar levels.

[0023] Embodiments of the invention include a gasifier wherein the char bed can be scaled up while managing the low bulk density solids and the irregularities in operation caused by variations in superficial velocity. Some embodiments of the invention include a gasifier that provides a partial oxidation zone(s) to allow maximum advantage of the high temperatures required for lowest tar production. Additionally, embodiments of the invention provide a gasifier that fosters high quality gas production. Further embodiments of the invention include a gasifier constructed to provide disengagement screen scrubbing.

[0024] The utility of the present invention is to convert biomass and waste feedstock

(solids) into a combustible gas at elevated temperature and pressure with substantially reduced tar concentrations. There may be applicability of this invention to gasification of other higher volatile matter solid fuels, including for example, various low rank coals, brown coal, peat, and lignite. Achieving low tar gas is the key to unlocking quantitative gas conditioning needed for. advanced high efficiency gas-to-power systems (engines, combustion turbines, solid oxide fuel cells, etc.) and advanced synthesis technology for biofuels (ethanol, mixed alcohols, and Fischer- Tropsch liquids) and chemicals such as hydrogen and ammonia.

[0025] Embodiments of the invention utilize an entrained flow reactor coupled downstream of a fluidized bed reactor. An entrained flow reactor is a reactor in which the reactant feedstock and oxidant are fed into the top of the reactor so that the oxidant stream surrounds (e.g., "entrains") the feedstock and carries the feedstock through the reactor. A fluidized bed reactor is one in which a fluid is forced upward through a granular bed at velocities sufficient to cause the granular material to behave, in many respects, as a fluid. In certain embodiments, the entrained flow reactor incorporates a moving granular bed that captures and supports a catalytic char bed.

[0026] A first illustrative embodiment of the present invention relates to a multi-stage reaction system for producing low-tar combustible gas. In certain embodiments, the system includes a fluidized bed reactor that includes a partial oxidation zone, in which a portion of the solid feedstock is partially oxidized, thereby creating a gas and a plurality of char particles. The illustrative embodiment further includes an entrained flow partial oxidation reactor situated downstream from the fluidized bed reactor, and where the entrained flow partial oxidation reactor includes a moving granular bed.

[0027] A second illustrative embodiment of the present invention relates to a multi-stage reaction system for producing low-tar combustible gas. In certain embodiments, the system includes a fluidized bed reactor that includes a partial oxidation zone, in which a portion of the feedstock is partially oxidized thereby creating a gas and a plurality of char particles. The illustrative embodiment further includes an entrained flow partial oxidation reactor situated downstream from the fluidized bed reactor. The entrained flow partial oxidation reactor includes a moving granular bed. In certain embodiments, a media screening device screens media from the moving granular bed and a media recycle system returns the screened media to the entrained flow partial oxidation reactor.

[0028] A third illustrative embodiment of the present invention relates to a method for controlling an operating pressure of a two-stage gasification system. In certain embodiments, the method includes performing a partial oxidation of a portion of the feedstock in a fluidized bed reactor; elutriating the resulting plurality of char particles and the gas from the fluidized bed reactor as a mixture of gas and char; receiving the mixture into an entrained flow reactor that includes a moving granular bed of filtering media; and allowing the mixture to flow through the moving granular bed of char and media. As the mixture is pushed through the granular bed, embodiments of the method further include capturing a portion of the plurality of char particles in the filtering media; screening a portion of the filtering media to remove captured char particles; and returning the screened filtering media to the entrained flow reactor.

[0029] These and other aspects of the invention will become apparent to one of ordinary skill in the art upon a reading of the following description, drawings, and the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention is described in detail below with reference to the attached drawing figures, wherein:

[0031] FIG. 1 is a schematic drawing of tar reduction by tar reduction equipment in accordance with the prior art;

[0032] FIG. 2 is a schematic drawing of a counter-flow moving granular bed filter in accordance with the prior art;

[0033] FIG. 3 is a schematic drawing of a classical two-stage downdraft gasifier in accordance with the prior art;

[0034] FIG. 4 is a schematic drawing of a downdraft gasifier incorporating an indirect heat stage and separation of the partial oxidation zone and char fixed bed in accordance with the prior art;

[0035] FIG. 5 is a schematic drawing of a gasifier system in accordance with a first embodiment of the invention described herein;

[0036] FIG. 6 is a schematic drawing of a gasifier system in accordance with a second embodiment of the invention described herein;

[0037] FIG. 7 is a schematic drawing of a gasifier system in accordance with a third embodiment of the invention described herein;

[0038] FIG. 8 is a schematic drawing of a gasifier system in accordance with a fourth embodiment of the invention described herein;

[0039] FIGS. 9 A and 9B are top-plan diagrammatic views of nozzle placement and air flow;

[0040] FIG. 1 OA is a schematic drawing of a front view of a screen;

[0041] FIG. 10B is a schematic drawing of an end view of a screen [0042] FIG. 1 1 is a flow diagram depicting an illustrative method of the tar-reducing gasifier system in accordance with certain embodiments of the invention described herein;

DETAILED DESCRIPTION

[0043] The subject matter of embodiments of the invention disclosed herein is described with the specificity required to meet statutory requirements. However, the description itself is not intended to limit the scope of claims in this patent. Rather, the inventors have contemplated that the claimed subject matter might also be embodied in other ways, to include different features or steps, or combinations of features or steps, similar to the ones described in this document, in conjunction with other technologies. Moreover, although the term "step" is used herein to connote different elements of methods employed, the term should not be interpreted as implying any particular order among or between various steps herein disclosed unless and except when the order of individual steps is explicitly described.

[0044] Referring to the drawings, and particularly to FIG. 5, there is depicted an illustrative gasification system 100. The gasification system 100 includes a first reactor 101 and, situated downstream from the first reactor 101, a second reactor 102. As shown in FIG. 5, the gasification system 100 also includes a media screening device 103, a media recycle system 104, and a heat recovery device 105. It should be understood that the illustrative gasification system 100 is merely one example of a suitable gasification system and is not intended to express or suggest any particular limitations regarding implementations of aspects of embodiments of the invention.

[0045] For example, in some embodiments, the gasification system 100 can include any number of additional components such as, for example, those illustrated in FIGS. 6-8. In some embodiments, one or more of the components described herein can be integrated with one another and in other embodiments, one or more of the components described herein can be separated into any number of desired features, functions, and the like. According to various embodiments, for example, the first reactor 101 is a fluidized-bed reactor and the second reactor 102 is an entrained flow reactor. In some embodiments, the second reactor 102 can also include fluidized-bed technology, and in other embodiments, the first reactor 101 can include entrained flow technology. All of these various embodiments and implementation are considered to be within the ambit of the invention.

[0046] With continued reference to FIG. 5, the first reactor 101 includes an upper portion

106 and a lower portion 108. The upper portion 106 of the first reactor 101 includes a freeboard 110, which provides a partial oxidation zone 112. As shown in FIG. 5, the lower portion 108 of the first reactor 101 includes a fluidized bed 1 14 and a port 1 16 used for adding heat. The first reactor 101 also includes, as illustrated in FIG. 5, a number of blast inlets 1 18, a solid fuel port 120, and a blast/steam inlet 122. A fluidized-bed media discharge port 124 is situated at the bottom of the lower portion 108 of the first reactor 101. The fluidized-bed media discharge port 124 discharges media into a media discharge system 125, which can carry the discharged media to any number of various destinations such as, for example, a waste receptacle, a storage tank, a recycling system, and the like.

[0047] In operation, the first reactor 101 creates a hydrogen-rich partial oxidation zone

112 in its upper section 106 and preferably includes direct blast addition and/or indirect heat addition through the port 1 16. Embodiments of the invention allow for influence and control of the hydrogen concentration in the raw gas, thereby facilitating the subsequent cracking of tars, which occurs in the partial oxidation zone 112 of the first reactor 101 and/or in a partial oxidation zone 126 of the second reactor 102. [0048] With continued reference to FIG. 5, the second reactor 102 is a two-stage entrained flow gasifier that is operated in a non-slagging mode. The first stage is a partial oxidation stage and is accomplished in the partial oxidation zone 126 of the second reactor 102. As shown in FIG. 5, the partial oxidation zone 126 of the second reactor 102 is situated within an upper portion 128 of the second reactor 102. As illustrated, the partial oxidation zone 126 includes a low-swirl partial oxidation burner 136. A number of blast inlets 138 and 140 are located in the upper portion 128 of the second reactor 102 and will preferably include a multiple of blast nozzles 142 at each level, as needed to achieve localized "thermally intense zones," which will be described in more detail below, with reference to FIGS. 9 A and 9B. According to some embodiments, the first reactor 101 can also include a partial oxidation burner such as the burner 136. The second stage associated with the second reactor 102 is a "dense-bed" stage and is accomplished in a catalytic char-reduction zone 130 that is situated within a lower portion 132 of the second reactor 102. As shown in FIG. 5, the catalytic char-reduction zone 130 includes a moving granular bed 134 that facilitates operation of the second stage associated with the second reactor 102.

[0049] Embodiments of the invention can include a number of different options for configuring blast nozzles 142 around the periphery the first reactor 101 and/or the second reactor 102. The configuration of the blast nozzles 142 facilitates forming localized regions of oxidative thermal intensity (by virtue of the mixing pattern), rather than achieving more uniform mixing patterns achieved by typical approaches to designing gas burners for lean fuel conditions. Turning briefly to FIGS. 9A and 9B, top-view schematic drawings illustrate two different illustrative configuration options for placement of the blast nozzles 142, respectively. As illustrated in FIG. 9A, a vessel (e.g., reactor) 145 includes a number of inlet ports 147 and 149 having blast nozzles 150 and 151, respectively. The blast nozzles 150 and 151 are configured in an alternating pattern such that the blast nozzles 150 and 151 direct inputs toward tangent curves 152 and 154 associated with one or more target circles 1 3 and 156, the diameter of which can be varied according to various embodiments of the invention.

[0050] For example, as shown in FIG. 9A, the blast nozzle 150 targets the tangent 152 of a first target circle 153, which has a first diameter 157a. Similarly, the blast nozzle 151 targets a tangent curve 154 of a second target circle 156, which has a second diameter 157b. As shown, the first diameter 157a can be smaller in magnitude than the second diameter 157b. In other embodiments, the first diameter 157a can be larger in magnitude that the second diameter 157b. The targeting direction of each of any additional blast nozzles is configured to alternate between tangent curves of the first and second target circle 153 and 156. In the embodiment depicted in FIG. 9A, the blast nozzles 150 and 151 are oriented at the same elevation as one another, and therefore provide a coherent flow direction. Other flow patterns can be achieved, in other embodiments, by injection in a contrary flow direction at slightly different elevations.

[0051] Turning to FIG. 9B, an alternative configuration option for configuring blast nozzles to achieve desirable flow patterns in a blast zone 162 situated within a reactor vessel 160 is depicted. As shown, the vessel (e.g., reactor) 160 includes a number of inlet ports 163 and 165 having blast nozzles 166 and 168, respectively. The blast nozzles 166 and 168 are configured in an alternating pattern such that the blast nozzles 166 and 168 direct inputs toward tangent curves of target circles that are defined at different elevations. For example, the blast nozzle 166 targets the tangent curve 171 of a first target circle 169, which has a first diameter 173a. Similarly, the blast nozzle 168 targets a tangent curve 174 of a second target circle 170, which has a second diameter 173b. [0052] In the embodiment illustrated in FIG. 9B, the first target circle 169 and the second target circle 170 are situated at different elevations with respect to one another. That is, in certain embodiments, the first target circle 169 can be situated at a lower elevation than the second target circle 170, while in other embodiments, the second target circle 170 can be situated at a lower elevation than the first target circle 169. According to various embodiments of the invention, the first diameter 173a can be smaller in magnitude than the second diameter 173b. In other embodiments, the first diameter 173 a can be larger in magnitude that the second diameter 173b. In further embodiments, the first diameter 173a and the second diameter 173b can be substantially the same. The targeting direction of each of any additional blast nozzles is configured to alternate between tangent curves of the first and second target circle 169 and 170.

[0053] According to certain embodiments of the invention, one or more auxiliary blast zones will include multiple nozzles configured around the perimeter of the vessel so as to create at least two tangent target circles. In some embodiments, as depicted in FIG. 9A, the nozzles can be configured such that the inputs are injected coherent at the same elevation, while in other embodiments, the nozzles can be configured such that the inputs are injected convergent at slightly different elevations. These embodiments provide differing thermal intensity patterns and it should be understood that the configuration used in implementation can be selected to achieve the desired thermal intensity patterns.

[0054] Moreover, according to embodiments of the invention, mixing performance associated with the blast zones 146 and 162 can be optimized through computational fluid dynamics (CFD) calculations. For example, CFD software can be used to create 3-D patterns with thermally intense zones having various peak temperatures. In certain embodiments, mixing performance can be optimized by varying relative diameters of the target circles, adjusting swirl number (e.g., utilizing a swirl number less than 0.4), and by optimizing the equivalence ratio of the total auxiliary blast addition. The equivalence ratio, λ, is the blast to fuel ratio, relative to the stoichiometric blast to fuel required to just burn the fed gas and char. According to embodiments of the invention, the total auxiliary blast input is less than about 25% of the stoichiometric blast- to-fuel ratio calculated relative to the fed feedstock analysis. Additionally, in some embodiments, the total auxiliary blast can be about 50%, or more (and even up to 100%, particularly when indirect heat is supplied during the first stage), of the entire blast input to the reaction system.

[0055] For example, in one embodiment, the blast nozzle configuration is developed using CFD software to model at least one thermally intense zone having a peak temperature of ~1 150°C. The total auxiliary blast addition is controlled such that it has an equivalence ratio, λ, of approximately 0.2 (or less) in oxygen limited partial oxidation and incorporates a majority (>50%) of the total blast addition through auxiliary ports, configured to achieve localized zones of peak temperature of approximately 1 150°C. Configuring the blast nozzles accordingly can facilitate achieving desired performance objectives during operation.

[0056] A peak temperature of between about 1000°C and about 1200°C generally is sufficient for activating hydrogen molecules in the manner necessary for cracking aromatic ring compounds and providing the necessary termination to avoid ring polymerization. Too high a temperature in the bulk gas may cause melting of ash and slag formation that can interfere with operation. Accordingly, the partial oxidation zones are configured to include local thermally intense zones rather than high bulk gas temperatures. These localized thermally intense zones facilitate activation of hydrogen radicals that can subsequently initiate chemical reactions in the adjacent bulk gas. For example, hydrogen facilitates terminating the activated carbon atom in an aromatic ring that has been thermally cracked open, thereby providing for tar reduction rather than tar polymerization.

[0057] Returning to FIG. 5, a gas containing elutriated char 199, formed in the first reactor 101, and containing various natural catalytic minerals, escapes the first reactor 101 by an elutriation mechanism 200 and travels from the elutriation mechanism 200 through a gas conduit 202. The elutriated char 199 is delivered, via the gas conduit 202, to the second reactor 102 through a main gas inlet 204. The maximum size and delivery rate of the elutriated char 199 can be controlled, to a degree, by mamtaining the freeboard 1 10 superficial velocity through control of the operating pressure of the gasification system 100. The elutriated char particles 199 pass into the second reactor 102, either in a dispersed manner, through the main gas inlet 204, as shown in FIG. 1, or in a separated and concentrated form, through an auxiliary blast port 140 (e.g., see FIG. 7).

[0058] By controlling the operating pressure of the gasification system 100 for a given gas production rate, it is possible to control (to a degree) the maximum particle size and the rate of release of char 199, and the maximum particle size of the char 199, through the elutriation mechanism 200 associated with the first reactor 101. The particle size of the char 199 affects the catalytic performance of the char 199 for gas temperatures of less than 1000°C. In other words, a smaller particle size tends to produce more tar reduction for the same temperature, particularly if the temperature is less than 1000°C. For example, at 900° tar reduction in one study was 88% for one particle size range (1 to 2 mm) and 96% for another (0.1 to 0.15 mm). Accordingly, certain embodiments of the invention incorporate a method of operating the gasification system to control the char 1 19 particle size and elutriation rate. [0059] According to certain embodiments of the invention, the method includes, at least in part, maintaining a target velocity in the freeboard 1 10 of the first reactor 101 by modulating the pressure set point. It will be appreciated by individuals having skill in the relevant arts that pressure modulation can be accomplished in a number of ways such as, for example, modulating fuel and air inputs, modulating a downstream valve position (e.g., downstream from a particulate removal), and the like. For instance, as illustrated in FIG. 5, the gasification system 100 can include one or more modulating valves 210 that can be utilized to modulate downstream particulate removals, thereby providing some level of control over the operating pressure of the system 100.

[0060] Additionally, pressure control can be achieved by controlling the flow of char 199 through the second reactor 102. The gas 215 engaging the moving granular bed 134 in the second reactor 102 moves in co-flow direction with granular material 135. In certain embodiments, the granular material is input via the main gas inlet 204 of the second reactor 102. In operation, the moving granular bed 134 captures and dilutes char 199 in a matrix of granular solids 135 that has a higher specific gravity, thereby improving the solids' 135 flow properties. In this manner, a zone of gas-char 215 is created such that the gas-char 215 contacts, with sufficient residence time, the char 199 solids for catalytic tar-reduction-by-char. The moving granular bed 134 captures and mixes the low density char 199 (usually < 190 kg/m ) with other media (usually >1900 kg/m 3 ), thereby improving the char 199 flow properties. In this manner, the flow of char 199 can be positively managed by its association with the co-flowing media matrix 134.

[0061] With continued reference to FIG. 5, the concentration of char 199 in the granular bed 134 can be managed through a screening stage, accomplished by the media screening device 103. In one particular embodiment, for example, a portion of char 199 and media 135 is removed, via a media discharge port 220 and provided to the media screening device 103. As the char 199 and media 135 are passed through the media screening device 103, the char 199 is separated from the media 135. The media recycle system 104 is used to return the screened media 135 to the second reactor 102. The char 199 screened from the media 135 is discharged via a residue discharge system 221. According to various embodiments, the particle size of the moving granular bed 134 can be the same as the particle size of the fluidized bed 1 14 in the first reactor 101 (e.g., see FIG. 8). In other embodiments, particle size of the moving granular bed 134 can be much larger than the particle size of the fluidized bed 114 in the first reactor 101 (e.g., 10 times larger) to create a favorable pressure drop through the moving granular bed 134 in the second reactor 102.

[0062] Turning briefly to FIG. 11 , a flow diagram depicts an illustrative method 300 of controlling an operating pressure of a two-stage gasification system. At a first illustrative step, step 310, the illustrative method includes performing a partial oxidation of solid feedstock in a fluidized bed reactor. In certain embodiments, the fluidized bed reactor can be similar to, for example, the reactor 101 described above with reference to FIG. 5. Performing the partial oxidation in the fluidized bed reactor generates, among other things, gas and char. The char can be elutriated from the fluidized bed reactor as a gas/char mixture, as shown at step 312, using an elutriation device, or simply allowed to elutriate naturally without any additional device. At step 314, the mixture is received into an entrained flow reactor that has a moving granular bed. In certain embodiments, for example, the entrained flow reactor can be similar to the second reactor 102 described above with reference to FIG. 5. [0063] As illustrated at step 316, the mixture is allowed to flow through the moving granular bed and, as the mixture moves through the moving granular bed, char particles are captured in the media of the moving granular bed, as indicated at step 318. To control the concentration of char particles in the moving granular bed (and thereby, to facilitate control over the char flow rate and particle size), a portion of the media of the moving granular bed is screened to remove char particles, as shown at step 320. At a final illustrative step, step 322, the screened media is returned to the moving granular bed. According to certain embodiments, the illustrative method 300 can be used alone, or in conjunction with other methods, to affect control over the operating pressure of the gasification system by controlling the char flow rate in the entrained flow reactor.

[0064] Returning now to FIG. 5, it should be understood that embodiments of the moving granular bed 134 do not require an inlet screen for media retention at the gas engagement interface by virtue of the geometric down-flow design. In contrast, the media retention screen at the dust-laden gas inlet of the moving granular bed of the prior art illustrated in FIG. 1, for example, was reported to have dust-fouling problems in the gas engagement. To the contrary, as a result of employing co-flow bed and gas and the incorporation of a down-flow design along with various other features of the moving granular bed 134, embodiments of the present invention do not require any media retention screen at the gas engagement thereby providing an improved method of employing char as a catalyst. Additionally, whereas conventional moving granular beds are tuned (e.g., adjusted and controlled) to provide optimum filtration, the moving granular bed 134 of the present invention is tuned to provide an optimal char contacting zone.

[0065] The moving granular bed 134 is operated to capture char 199 as a physical barrier.

The media residence time is correlated with the char residence time (the period of time that the average char particle spends in the reactor), and this char residence time can be modulated in a controlled manner with the media screening and recycle subsystem (103/104). According to certain embodiments, the moving granular bed 134 also can be configured to provide a zone of narrow gas residence time distribution through the char bed 134 in a conceptually plug flow reactor that allows for maximum tar cracking. In certain embodiments, the gas residence time and char residence time can differ by several orders of magnitude; therefore, the differential velocity between the gas 215 and char 199 is very close to the local gas interstitial velocity through the bed 134. In certain embodiments, the char in the char bed 134 is continuously refreshed by the char 199 supply from the first reactor 101 thereby reducing or eliminating the need for high performance filtration, even though some small particles of char 199 may slip through the bed with the gas 215.

[0066] With continued reference to FIG. 5, the moving granular bed 134 includes a substantially vertical gas disengagement screen 222. Turning briefly to FIG. 10A, the disengagement screen 222 is comprised of a plurality of wires 224, oriented in a substantially parallel and vertical manner. The wires 224 are situated between an upper frame edge 222a and a lower frame edge 222b. As illustrated, the screen 222 can also include a pair of side frame edges 222c. The disengagement screen 222 includes a number of gaps 225, each gap 225 being defined between two adjacent wires 224. FIG. 10B depicts a bottom, partial view of the screen 222. As shown in FIG. 10B, each wire 224 may be made of commercially available triangular profile wire, or includes a wedge or V-cross section defined by a first side 230 and a second side 232 that meet at a vertex 234. The two sides 230 and 232 of the wire 224 converge (at the vertex 234) in the direction of gas flow. Preferably, the gaps 225 between the wires 224 are designed relative to the smaller cut size of the granular media. The substantially vertical orientation (which, at a minimum, is steeper than the angle of repose of the char-media matrix 135 of FIG. 5) of the gas disengagement screen 222 provides for scrubbing action with the moving bed 134 to maintain the gas disengagement screen 222, without plugging.

[0067] Embodiments of the moving granular bed 134 of the present invention include features that are not known to the art and that have been described above. These features include, for example, a co-flow design that is preferred for its gas-char contacting zone for enhancing catalytic tar-reduction-by-char performance rather than for its filter performance; the lack of a need for a media retention screen for media retention at the gas engagement interface; and a substantially vertically oriented gas disengagement screen (e.g., which is steeper than the angle of repose of the blended char and media matrix to scrub the disengagement screen keeping it free of dust clogging).

[0068] In contrast, for example, the prior art moving granular bed filter disclosed in US

Pat. No. 7,309,384 to Brown et al., and illustrated herein in FIG. 2, does not provide for disengagement screen scrubbing. The counter filter 304, 307 disclosed in the Brown et al. patent also does not provide the opportunity for extended gas residence time in the presence of char. Instead, the gas residence time is shorter due to the rapid char and media disengagement in the counter flow design which, in turn, shortens the gas-char contact and reduces the catalytic reduction of tar by char. To the contrary, embodiments of the present invention do not include, or require, the presence of a gas barrier for media retention whereas the Brown et al. invention will not work without such a barrier.

[0069] According to various embodiments of the invention the residence time (increased internal age distribution) of the trapped char particles is controlled by modulating the media flow that captures the char through an external recycle loop. With reference to FIG. 5, a first embodiment employs a bubbling fluid bed reactor 101 , the transport disengagement height of the freeboard 1 10 design, and the target operating velocity to achieve a mixture of gas 215 and char 199 delivered to the second reactor 102. As illustrated, the gasification system 100 of FIG. 5 includes an "external" active media recycle system 104 (which can be, for example, mechanical or pneumatic conveying). In certain embodiments, the fluid bed reactor 101 can include processing of the discharge stream 125 to remove foreign "tramp" materials entering with the feedstock, and can optionally be recirculated and reheated in a direct or indirect heating loop and returned to the first reactor 101 via the port 116.

[0070] Turning to FIG. 6, another embodiment of a gasification system 240 is illustrated.

As shown, the gasification system 240 includes a first reactor 241, which is a fluidized bed reactor, a second reactor 242 having a moving granular bed 243, a media screening device 244, a media recycle system 246, and a heat recovery device 248. This particular embodiment (illustrated in FIG. 6) is designed to enable a higher, more turbulent, velocity in the fluidized bed reactor 241 without excessive loss of fluid bed sand. In this case, a sand recovery roughing cyclone 250 is an elutriation device included between the first reactor 241 and the second reactor 242.

[0071] Turning now to FIG. 7, another embodiment of a gasification system 260 of the present invention is illustrated. As shown, the illustrative gasification system, according to this particular embodiment, includes a first (fluidized bed) reactor 261, a second (entrained flow) reactor 262 having a moving granular bed 263, a media screening device 264, a media recycle system 265, and a heat recovery device 266. In this embodiment (illustrated in FIG. 7), the sand recovery cyclone 268 and turbulent fluid bed 263 are both included, but a char-concentrating cyclone 270 is also included to give an opportunity for separate, controlled char injection into the partial oxidation zone 276 of the second reactor 262. The embodiment, illustrated in FIG. 7, includes the char fines cyclone 270 to create an opportunity for a majority of char to bypass an upper partial oxidation zone 277 in the second reactor 262. This configuration affords separate control of char injection using a steam motivated eductor 272 for delivery into the partial oxidation zone 277 through an auxiliary partial oxidation blast port 274. According to certain embodiments, the gasification system 260 can be optimized for char oxidation heat release by adding blast along with the char feed, therefore creating a hot zone through which the fed gas passes, in which case a lesser amount (or, in some implementations no amount) of blast gas is fed through an upper blast port 279.

[0072] Turning to FIG. 8, another embodiment of a gasification system 280 is illustrated.

The illustrated embodiment of FIG. 8 is a new form of a circulating fluidized bed reactor system

280. The illustrative gasification system 280 illustrated in FIG. 8 is quite different from the previously described embodiments herein in several respects. For example, this particular embodiment (shown in FIG. 8) requires no external media recycle system. Instead, the same media 283 is cycled between the first reactor 281 and the second reactor 282, and char concentration is modulated by adjusting the portion of discharged sand 290 that either returns to the first reactor 281 or that passes through the media screen 284 before recycling. There is no separate media recycle loop for the second reactor 282 in the embodiment depicted in FIG. 8. Circulated media 292 is the same particle size and same material used in the fluidized bed reactor

281. Bed material is circulated in a closed loop between the fluid bed reactor 281 and the second reactor 282. According to embodiments, the bed can have a ratio of superficial velocity relative to the minimum velocity required to fluidize (U Umf) of between 6 and 12 to cause increased sand elutriation. Dust-laden media discharging flow (indicated as 290) is split by gravity assist and/or pneumatic push to return a portion into the fluid bed 281a and the balance is processed to remove fines and dust by the media screening device 284 as needed, to produce a cleaned media stream 296. The media stream from the fluid bed 281a and the media screening device 284 combined 298 can optionally be used in a direct or indirect heating loop or cleaned of tramp materials and returned via the port 281b.

[0073] To recapitulate, embodiments of the invention include a gasification system having a fluidized bed reactor situated upstream from an entrained flow reactor. The entrained flow reactor includes a moving granular bed that holds up char and so presents catalytic properties of char to the gas for the purpose of tar cracking. In some embodiments, char concentration in the granular solids matrix is controlled with the media screening and recycle system (such as the media screening device 103 and the recycle system 104 illustrated in FIG. 5). Tests have shown that a gasification system having at least some of the features described herein performs as desired.

[0074] For example, tests were performed under various operating conditions in a laboratory-scale entrained flow reactor, configured according to embodiments of the invention, using yellow seed cord as a model feedstock. Air or oxygen was used as blast as indicated in Table. 1. The stoichiometric air/fuel requirement is 5.45 kg air/kg biomass (dry), or 1.26 kg oxygen/kg biomass (dry). Air blown gasification tests used 3.7 kg/hr biomass, and oxygen blown tests used 6 kg hr biomass with ~ 0.45 kg steam/kg biomass. Inert rock material and low grade iron ore (taconite) were used as media in the entrained flow reactor, sized to approximately 1/8" x 1/4" granules. The first stage (fluidized bed) gasifier was operated at various equivalence ratios, λ, (Air/Fuel relative to the stoichiometric Air/Fuel requirement): 0.1 1 , 0.14, and 0.18, as indicated in Table 1 , and achieved fluid bed temperatures from 600 to 700°C.

[0075] The entrained flow reactor consisted of a small partial oxidation burner that injected blast laterally through 6 small holes (having an internal diameter of 1.4 mm) with slight swirling action, in the configuration illustrated in FIG. 9A, with a tangent circle that is 13 mm diameter, inside of a 40 mm inside diameter pipe, that subsequently expanded into an 100 mm (inside diameter) pipe. Test results indicate that tars were converted with increasing blast (and increasing temperatures) up to a point, which correlated with delivering ~50% of the total blast into the secondary reactor. The lowest tar condition was ~560 mg/Nm 3 dry gas. The temperature in the partial oxidation zone was not measured, but the maximum measured temperature in the zone below was 980°C.

[0076] As another example, further tests were performed in which the same test conditions discussed above were analyzed for lower heating value ~ indicate that the heating value stabilized at ~ 5 MJ/Nm (dry) for air blown tests, and 10 MJ/Nm (dry) for oxygen blown tests, so long as the total equivalence ratio was less than 0.35, as reflected in Table 2, below.

[0077] A reactor, configured in accordance with embodiments of the invention, that combines a partial oxidation burner for tar reduction above a "pebble grate" (which is previously described as a bed of granular media supported by a vertical wire screen supporting the media at the gas disengagement) to support a bed of char has not heretofore been known to the art. The integration of a first reactor that operates at lower temperatures in sequence with a higher temperature partial oxidation stage (sub-stoichiometric combustion) with a subsequent heat recuperative device that transports thermal energy back to the first reactor to drive pyrolysis reactions is also not previously known. Because most moving granular beds are designed for filtration, the co-flow design of the present invention is also not known because it does not impart ideal filtration conditions but rather it imparts ideal gas-char contact conditions for tar cracking. Low density char— that otherwise has chaotic solids flow properties—is dispersed into a granular bed material that has approximately ten (10) times the bulk density, which imparts improved solids flow properties. This is an improvement over prior art and contrasts with any reactor that includes a fixed bed of char in downdraft type gasifiers (integrated or separated from partial oxidation zones) that have been known to experience upsets associated with poor solids flow, "solids bridging", and "rat hole" formations due to the chaotic movement and anisotropic nature of low density char beds.

[0078] The present invention has been described in relation to particular embodiments, which are intended in all respects to be illustrative rather than restrictive. Alternative embodiments will become apparent to those of ordinary skill in the art to which the present invention pertains without departing from its scope. For example, different contact times and variations in temperatures for certain zones may be employed. Connections between reactor vessels and return lines can vary in general position. It will be appreciated by individuals having skill in the relevant arts that certain optimizations will be necessary depending on the source of feedstock.

[0079] From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objects set forth above, together with other advantages, which are obvious and inherent to the system and method. It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.