Bubbling Fluidized Bed Reactor

Abstract

Various aspects provide for a multistage fluidized bed reactor, particularly comprising a volatilization stage and a combustion stage. The gas phases above the bed solids in the respective stages are separated by a wall. An opening (e.g., in the wall) provides for transport of the bed solids from the volatilization stage to the combustion stage. Active control of the gas pressure in the two stages may be used to control residence time. Various aspects provide for a fuel stream processing system having a pretreatment reactor, a combustion reactor, and optionally a condensation reactor. The condensation reactor receives a volatiles stream volatilized by the volatilization reactor. The combustion reactor receives a char stream resulting from the removal of the volatiles by the volatilization reactor.

Claims

1. A bubbling fluidized bed reactor (300, 400, 500, 600) configured to react a fuel in a fluidized bed of bed solids, the reactor comprising: a container (301) configured to hold the bed of bed solids; a wall (302) separating at least a gas phase above the bed in the container (301) into a volatilization stage (310) and a combustion stage (330), the volatilization stage (310) including: a fuel inlet (316) configured to receive the fuel; a LowOx gas inlet (314) disposed at a first portion of a bottom of the container; a LowOx gas supply (311) configured to supply an inert and/or less-oxidizing gas to the LowOx gas inlet (314) to fluidize the bed of bed solids to yield a first bubbling fluidized bed and volatilize the fuel to yield: a volatiles stream comprising a syngas (229); and a char stream; a volatiles stream outlet (318) configured to convey the volatiles stream out of the volatilization stage; a syngas outlet (229) coupled to the volatiles stream outlet (318) and configured to extract the syngas (229) from the reactor; and a volatiles pressure gauge (350) configured to measure pressure within the volatilization stage; the combustion stage (330) including: an oxidant inlet (334) disposed at a second portion of the bottom of the container; a HiOx gas supply (331) configured to supply the oxidant inlet (334) with a gas that is more oxidizing than that supplied by the LowOx gas supply (311), the HiOx gas supply and oxidant inlet configured to fluidize the bed of bed solids to yield a second bubbling fluidized bed and combust the char stream to yield an exhaust gas; an exhaust gas outlet (337) configured to convey the exhaust gas out of the combustion stage; and a combustion pressure gauge (352) configured to measure pressure within the combustion stage; an opening (304) through and/or below the wall (302) and below a surface of the at least one of the bubbling fluidized beds, the opening (304) configured to provide for a flow of the char stream and bed solids between the volatilization stage (310) and the combustion stage (330); and a controller (360) coupled to the pressure gauges (350, 352) and configured to control a pressure difference (P1?P2) between the stages (310, 330).

2. The reactor of claim 1, further comprising a heat exchanger (340) coupled to the exhaust gas outlet (337) and LowOx gas supply (311), the heat exchanger configured to transfer heat from the exhaust gas to the inert and/or less-oxidizing gas prior to the LowOx gas inlet (314).

3. The reactor of claim 1, wherein the controller is further configured to control a pressure drop (Pd1?Pd2) across at least one of the LowOx gas inlet and the oxidant inlet.

4. The reactor of claim 3, wherein the controller is further configured to control a pressure difference between a bottom of the fluidized bed proximate to the LowOx gas inlet and the pressure above the first fluidized bed (Pd2?P2).

5. The reactor of claim 1, wherein the controller is further configured to control at least one of: a pressure difference between a bottom of the first bubbling fluidized bed proximate to the LowOx gas inlet and the pressure above the first bubbling fluidized bed, (Pd2?P2); and a pressure difference between a bottom of the second bubbling fluidized bed proximate to the oxidant inlet and the pressure above the second bubbling fluidized bed.

6. The reactor of claim 1, wherein the bed solids comprise particles that are at least 0.4 mm.

7. The reactor of claim 6, wherein the bed solids comprise particles that are at least 0.6 mm.

8. The reactor of claim 1, further comprising a separation reactor (220) comprising the syngas outlet (229) and configured to separate out the syngas (229) from the volatiles stream.

9. The reactor of claim 8, wherein the separation reactor (220) is further configured to cool the volatiles stream.

10. The reactor of claim 9, wherein the separation reactor (220) comprises a scrubber.

11. The reactor of claim 9, wherein the controller is further configured to control: a pressure drop (Pd1?Pd2) across the LowOx gas inlet and the oxidant inlet; and a difference in pressure between a bottom of the fluidized bed proximate to the LowOx gas inlet and the pressure above the fluidized bed (Pd2?P2).

12. The reactor of claim 8, wherein the separation reactor (220) comprises a heat exchanger.

13. The reactor of claim 8, wherein the separation reactor (220) is further configured to separate a residual stream having a fuel value from the volatiles stream, and the reactor further comprises a residual stream outlet (228) configured to deliver the residual stream from the separation reactor (220) to the combustion stage to combust the residual stream having the fuel value.

14. The reactor of claim 8, wherein the separation reactor is further configured to separate a condensed species from a more volatile species.

15. The reactor of claim 1, wherein the wall (302) is disposed away from a transition between the LowOx gas inlet and the oxidant inlet by an extension length (440).

16. The reactor of claim 1, wherein the controller is further configured to control the pressure difference using closed-loop control.

17. A method comprising: providing reactor including a container (301) having: bed solids expected to yield a bubbling fluidized bed when fluidized by a gas; and a wall (302) configured to separate at least a gas phase above the bubbling fluidized bed to yield a volatilization stage (310) and a combustion stage (330); and an opening (304) through and/or below the wall (302) and below an expected height of the bubbling fluidized bed, the opening configured to provide for a flow of bed solids between the volatilization and combustion stages; delivering a fuel to the volatilization stage (310); fluidizing the bed solids within the volatilization stage to yield a first bubbling fluidized bed; reacting the fuel within the volatilization stage with a first gas to yield: a volatiles stream comprising a syngas (229); and a char stream having a fuel value; extracting the syngas (229) from the reactor; receiving the char stream into to the combustion stage (330); fluidizing the bed solids within the combustion stage (330) with a gas that is more oxidizing than the first gas to yield a second bubbling fluidized bed; oxidizing the char stream to yield an exhaust gas; and controlling a pressure difference (P1?P2) between the stages (310, 330).

18. The method of claim 17, further comprising controlling a pressure drop across at least one of: a first gas inlet configured to fluidize the first bubbling fluidized bed; and a second gas inlet configured to fluidize the second bubbling fluidized bed.

19. The method of claim 18, further comprising controlling at least one of: a pressure difference between a bottom of the first bubbling fluidized bed and an ambient pressure within the volatilization stage; and a pressure difference between a bottom of the second bubbling fluidized bed and an ambient pressure within the combustion stage.

20. A fuel stream processing system (200) comprising: a pretreatment reactor (210) including: a reaction zone (212) configured to react a fuel stream with an inlet gas; a LowOx gas inlet (214) configured to deliver an inert and/or less-oxidizing gas into the reaction zone; a fuel inlet (216) configured to receive a fuel supply and deliver the fuel supply to the reaction zone; a volatiles stream outlet (218) configured to convey a volatiles stream out of the reaction zone; and a char stream outlet (219) configured to convey a char stream out of the reaction zone; a separation reactor (220) comprising: a volatiles stream inlet (222) fluidically coupled to the volatiles stream outlet (318) and configured to receive the volatiles stream from the pretreatment reactor; a volatiles heat exchanger (224) configured to cool the volatiles stream into at least one condensed species and a residual stream; and a phase separator (225, 226) configured to separate the condensed species from the residual stream; and a residual stream outlet (228) configured to convey the residual stream out of the separation reactor; and a combustion reactor (230) comprising: a combustion zone (232); an oxidant inlet (234) configured to deliver a gas that is more oxidizing than that delivered by the LowOx gas inlet to the combustion zone; a char stream inlet (239) coupled to the char stream outlet of the pretreatment reactor and configured to convey the char stream into the combustion zone; a residual stream inlet (238) coupled to the residual stream outlet of the separation reactor and configured to deliver the residual stream into the combustion zone; and an exhaust outlet (237) configured to convey an exhaust from the combustion of the oxidant, char stream, residual stream out of the combustion zone.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0029] FIG. 1 is a schematic illustration of a typical fluidized bed boiler.

[0030] FIG. 2 is a schematic illustration of a fuel stream processing system, per some aspects.

[0031] FIG. 3 is a schematic illustration of a two-stage fluidized bed reactor, per some aspects.

[0032] FIG. 4 is a schematic illustration of a two-stage fluidized bed reactor, per some aspects.

[0033] FIG. 5 illustrates a three-stage reactor with an internal wall separating the gas phases of the fuel inlet and volatiles outlet, per some aspects.

[0034] FIG. 6 illustrates a three-stage reactor with an internal wall separating the gas phases of the fuel inlet and volatiles outlet, per some aspects.

DETAILED DESCRIPTION

[0035] The reduction, reuse, and recycling of waste streams is an increasingly important priority in many societies. Some waste streams are burned (e.g., for heat and/or electricity). While combustion might utilize the fuel value of a waste stream, the chemical properties of certain components of the fuel might be substantially more valuable if they were they utilized for chemical purposes, rather than as fuel. Some waste streams (municipal solid waste, dehydrated sewage) contain small quantities of chemicals that have very high value. Certain components of biomass (e.g., wood species) may have very high value.

[0036] Waste fuel streams such as municipal solid waste (MSW), sewage, and the like, and nonwaste fuel streams, such as petrochemicals, biomass and the like, comprise a wide range of molecules. Some of these molecules (or portions thereof) are valuable beyond their use as a fuel supply. Systems and methods described herein may be implemented to recover chemicals that might otherwise be combusted, enabling the subsequent use of these chemicals in higher-value applications.

[0037] A fuel stream processing system may comprise a pretreatment reactor (e.g., to pyrolyze/evaporate/volatilize/gasify/reform a fuel) and a combustion plant. A fuel stream flows into the pretreatment reactor to be reacted to form a volatiles stream and a char stream. The pretreatment reactor may pyrolyze/gasify/volatilize/precombust or otherwise react a solid or liquid fuel prior to its passage to the combustion plant, typically with an inert, reducing, or mildly oxidizing gas (e.g., N.sub.2, syngas, steam, and the like). The char stream flows into the combustion plant, where it is combusted. The pretreatment reactor may be retrofit to an existing combustion plant (e.g., with an additional fuel supply).

[0038] The volatiles stream may be used directly. For example, a fuel may be separated into a first fuel source (e.g., for a separate combustion process, such as an engine or turbine) and a residual char source (e.g., for combustion in a fluidized bed). A volatiles stream may flow to a separation reactor, which typically cools the volatiles stream to condense and separate out one or more (typically >5, including >10, including >100) chemical species from the volatiles stream. The separated chemical species may be subsequently processed and/or utilized. The chemical species may include syngas (H2+CO), gaseous hydrocarbons (including oxygenated hydrocarbons), liquid fuels (e.g., C4-C16) such as biofuels and/or biofuel precursors, volatile polymers, fuel gas, chemical compounds. fine chemicals, and the like. A residual stream (remaining, undesired chemicals which may have fuel value) may be routed to the combustion plant and combusted. A stream may be routed to a kiln, furnace, or other apparatus where it is combusted.

[0039] FIG. 2 is a schematic illustration of a fuel stream processing system, per some embodiments. A fuel stream processing system 200 may comprise a pretreatment reactor 210 fluidically coupled to a combustion reactor 230. The pretreatment reactor volatilizes an incoming fuel stream to form a volatiles stream. The volatilized stream typically includes useful chemical species 229, which are extracted via one or more chemicals outlets 229 (directly or after having been separated). Nonvolatilized fuel (char) is typically conveyed from the pretreatment reactor to a combustion reactor via a char stream, which burns the char stream to extract the heat value. The system may include a separation reactor 220 coupled to one or both of the reactors 210, 230. The pretreatment reactor may be retrofit to an existing combustion reactor (each reactor may have its own fuel supply).

[0040] Pretreatment reactor 210 receives the fuel stream via a fuel inlet 216, and pretreats (e.g., volatilizes/gasifies/pyrolyzes/reforms/reacts, herein: volatilizes) a portion of the received fuel to yield a volatiles stream and a char stream. Pretreatment/volatilization typically comprises treating the fuel in a reaction zone 212 with an inert and/or relatively less oxidizing gas than that used in the combustion reactor (e.g., N2, syngas, steam, CO2, and the like), delivered via gas inlet 214 from a gas supply 211. The pretreatment reactor outputs a volatiles stream via a volatiles stream outlet 218. The char stream is output via a char stream outlet 219 to a char stream inlet 239 of the combustion reactor 230, where it is combusted with a relatively more oxidizing gas (e.g., air, O2). The pretreatment reactor and combustion reactor may be discrete (e.g., with the char stream outlet/inlet coupled via a passage 299). The pretreatment reactor and combustion reactor may be integrated (e.g., with the char stream outlet/inlet forming an opening in a wall between the reactors). In some cases, to prevent undesired reactions (e.g., polymerization, decomposition, precipitation), the pretreatment reactor may include a fast pyrolysis reactor (e.g., that constrains volatiles to a residence time below 10 seconds, including below 3 seconds).

[0041] Combustion reactor 230 (e.g., a combined heat and power plant) includes a combustion zone 232 within which the char stream is reacted with an oxidant gas (e.g., air, oxygen, and the like). An oxidant supply 231 delivers oxidant via an oxidant inlet 234. In some embodiments, one or both of the inlets 214, 234 comprise diffuser plates (e.g., such that the respective reactors can function as fluidized beds). Combustion reactor 230 includes an exhaust 237, and may include an optional second fuel inlet 236 configured to deliver a fuel directly into the combustion reactor. Combustion of char may be augmented with fuel from the second fuel inlet 236 and corresponding supplementary fuel supply (not shown), which may be the main fuel supply to the combustion reactor (e.g., when retrofitting a pretreatment reactor to an existing combustion reactor).

[0042] The volatiles stream outlet of the pretreatment reactor may be coupled to a separation reactor 220 (e.g., a fast condensation/fractionation reactor, a cyclone, ESP, filter, scrubber, bath-quenching, and the like) via a volatiles stream inlet 222. Separation reactor 220 may extract and/or isolate desirable chemicals from the volatiles stream, outputting these species via chemicals outlet 229. A heat exchanger 224 (e.g., coupled to the separation reactor) may be used to remove heat from the volatiles stream, enhancing condensation. A heat exchanger 224 may be used to transfer heat from the volatiles stream to a fluidization gas delivered by a gas inlet. A separation reactor may include a heat exchanger 224, a cyclone 225, a phase separator 226 configured to separate condensed species from more volatile species (e.g., a filter, bag house, electrostatic precipitator, FIG. 3). A phase separator may comprise several phase separators. Water, ash, media, acids, and condensable fuels may be separated. For example, a first separator may remove ash, a second separator may remove condensable fuels (e.g., tar), and a third separator (e.g., an electrostatic precipitator) may remove particles, aerosols, and the like. A residual stream comprising CO, CO2, H2, and other permanent gases may be sent for combustion (e.g., in a lime kiln or other combustor).

[0043] A reactor may include an absorption loop that exposes a stream to a liquid that condenses/absorbs a species (e.g., a water-based scrubber or an amine CO2 scrubber). The liquid is circulated out, the species is removed, and the liquid is reexposed to the stream. In some cases, the liquid/species are removed and replaced with fresh scrubbing liquid. In some cases, separation reactor 220 outputs a residuals stream (e.g., comprising residual chemicals not extracted for other purposes) via residuals stream outlet 228. Residuals stream outlet 228 may be coupled to a corresponding residuals stream inlet 238 of the combustion reactor, providing for the combustion of the residuals stream.

[0044] A heat exchanger 340 may be coupled to the exhaust stream (e.g., via exhaust 237) of the combustion reactor 230 to preheat the pretreatment fluidization gas prior to its introduction into the pretreatment reactor via gas inlet 214.

[0045] A volatiles stream may have a range of uses (according to fuel source, pretreatment conditions, and the like) such as for raw gas, syngas, and the like. The volatiles stream may include syngas (e.g., for use in a subsequent chemical process) gaseous species (e.g., gaseous fuels), liquid fuels (e.g., biofuels and/or biofuel precursors), and the like.

[0046] A fuel stream processing system may comprise one or more fluidized bed reactors. For example, pretreatment reactor 210 may be configured as a volatilization stage of a fluidized bed reactor as described herein, and combustion reactor 230 may be configured as a combustion stage of a fluidized bed reactor as described herein. The reactors may share a fluidized bed of solids (e.g., separated by a wall) providing for a flow of char (and typically bed solids) from the pretreatment reactor to the combustion reactor. The system may be implemented as a standalone system and/or retrofit to an existing combustion reactor (e.g., an existing fluidized bed boiler). The fuel stream processing system need not incorporate a fluidized bed reactor.

[0047] FIG. 3 is a schematic illustration of a two-stage fluidized bed reactor, per some embodiments. A multistage fluidized bed reactor comprises an otherwise contiguous fluidized bed (e.g., one BFB) having at least a first (e.g., volatilization) and second (e.g., combustion) stages, each stage enabling a different chemical reaction. In this example, a first reaction zone 312 in a first portion of the fluidized bed and a second reaction zone 332 in a second portion of the fluidized bed provide for different reactions.

[0048] The first and second stages are separated, typically by a wall. The wall separates the gas phases above each stage, but allows the fluidized bed phases to communicate via an opening in the wall and/or a passage between beds of the stages. Thus, the fluidized bed phase (e.g., media and char stream) may flow between the stages, but the gas phase above the first stage is separated from the gas phase above the second stage. The fluidized beds may communicate via openings in the floor rather than the wall. The fuel residence time and/or transfer of fuel and bed material from the first to second stages is typically controlled via an increased/decreased gas pressure in the first stage vs. that in the second stage and/or the gas pressures supplied to the fluidization gas inlets. A controller coupled to pressure gauges within the stages may control these pressures (e.g., via a valve on the volatiles stream) to achieve a desired overpressure of the first stage vs. the second stage.

[0049] In exemplary FIG. 3, a fluidized bed reactor 300 comprises a container 301 (in this example, a single container) configured to hold a bed of bed solids. A wall 302 separates the container into a volatilization stage 310 and a combustion stage 330. Wall 302 may have an opening 304 through which bed solids and char may flow. Opening 304 may include char stream outlet 219, char stream inlet 239, and/or passage 299 (FIG. 2). Opening 304 may comprise openings in the floors of each stage, coupled by a passage. Wall 302 may include a plurality of walls. The media and char stream pass from the volatilization stage to the combustion stage, where the char is burned. The wall lets the media/char pass between stages, but prevents mixing of the gas phase in the volatilization stage with the oxidizing gas phase in the combustion stage.

[0050] The volatilization stage has a fuel inlet 316 configured to receive and deliver the fuel into the volatilization stage. The fuel inlet may include a lock hopper and/or other apparatus to transfer solid fuel while controlling gas flow/pressure. Fuel may be fed by gravity and/or auger. Fuel may be delivered to the lock hopper (e.g., via a feed screw) and a gas pressure within the lock hopper may be controlled to match that of the volatilization stage, such that fuel may be delivered to the volatilization stage at or above the pressure of the volatilization stage.

[0051] The bed solids are fluidized by a flow of gas from a LowOx gas supply 311 delivered via a gas inlet 314 (e.g., a diffuser plate/distributor plate having holes of any size and shape distributed across the plate to fluidize the bed) corresponding to the portion of the container (or the container) associated with the volatilization stage (e.g., first reaction zone 312). LowOx gas supply 311 supplies a (typically hot) gas chosen according to desired volatilization conditions (e.g., inert, reducing, mildly oxidizing), fuel source, desired composition of volatiles stream, and the like. The LowOx gas is typically mildly oxidizing (less oxidizing than that yielding complete combustion, e.g., steam, CO2, small amounts of oxygen, N2). The LowOx gas may, in some cases, be reducing (e.g., H2). Pressure drop across the distributor plate (Pd1?Pd2, FIG. 4) may be controlled (typically in concert with gas pressure at the top of the bed) to achieve a desired bubble size and/or bubble volume (within the bed), convection pattern, fuel residence time, bed temperature, and the like. Bed temperature and various reactions may be controlled via stage pressure (e.g., to control bed height, reaction rates, and/or residence times). A typical volatilization stage may have a lower temperature at the top of the bed than at the bottom (although in the absolute bottom of the bed (the first centimeters from the bottom) where the fluidization media enters the bed, the temperature is typically lower). A reduced bed height in the volatilization stage typically reduces residence time within.

[0052] A volatiles stream outlet 318 is configured to convey the volatiles stream out of the volatilization stage (e.g., to an optional separation reactor 220). A fuel processing system may comprise a separation reactor coupled to the volatilization stage and configured to separate out one or more chemical species from the volatiles stream. Useful species are typically extracted from the volatiles stream, yielding a residual stream, which may be sent to the combustion stage via a residuals line, where they are burned (FIG. 2). A volatiles pressure gauge 350 measures gas pressure in the volatilization stage, the volatiles stream outlet, and/or the corresponding volatiles line.

[0053] A reactor includes a means to control gas flow into and/or out of at least one stage, including multiple stages. Controlling this means in concert with pressure measurements, the controller may control the pressure difference between stages, typically via closed-loop (e.g., PID) control. In an embodiment, a volatiles outlet valve 370 (e.g., a butterfly valve) coupled to the volatilization stage outlet 318 is configured to control pressure in the volatilization stage and/or flow out of the volatiles stream outlet. FIG. 3 shows valve 370 upstream of separation reactor 220; it may be downstream.

[0054] Combustion stage 330 includes an oxidant inlet 334 (e.g., a diffuser plate) correspondingly disposed at the portion of the container associated with combustion (e.g., second reaction zone 332). An oxidant supply 331 coupled to the oxidant inlet delivers a relatively more oxidizing gas (typically air) at a flow rate and pressure sufficient to fluidize the bed solids in the combustion stage and combust the char from the volatilization stage. An exhaust gas outlet 337 removes combustion products power 337, chemicals 337, and/or heat 337 from the combustion stage, which may be subsequently harvested from the exhaust gas (e.g., via a heat exchanger, a turbine, and the like). A combustion pressure gauge 352 disposed in the combustion stage and/or exhaust measures pressure in the combustion stage. Reactor 300 illustrates an optional 2.sup.nd oxidant inlet 333 (e.g., to provide additional combustion air to supplement oxidant supplied via oxidant inlet 334). Additional gas and/or oxidant inlets may be included with the relevant stage. In this example, a fan 338 fluidically coupled to the exhaust 337 controllably extracts exhaust gas, which may be used to control pressure.

[0055] A controller 360 coupled to the pressure gauges (in this case, 350, 352) controls a pressure difference between the stages. In FIG. 3, controller 360 is coupled to the volatiles outlet valve 370, and controls pressure in the volatilization stage via throttling of the valve. During operation, controller 360 typically controls pressure of the volatilization stage to be different than that of the combustion stage. Lower pressure in the volatilization stage typically decreases fuel/char residence time; higher pressure typically reduces residence time. Pressures may be controlled via a valve on the flue gas line and/or relative flow rates of the fluidizing gas inlets. Pressure control of bed solids flow (and the resulting mass transfer rates) may be used to control residence time within the stages (e.g., in a pretreatment stage prior to a combustion stage).

[0056] A combustion stage may include a second fuel inlet 336 (e.g., to supplement the fuel value of the char), which may include a separate (or the same) fuel supply, typically with its own lock hopper. Second fuel inlet 336 may be the main fuel supply for the combustion stage, with a separate fuel supply implemented for the volatilization stage (e.g., as a retrofit to an existing combustion stage). A retrofit implementation may comprise a BFB volatilization stage retrofit into an existing BFB combustor to create a multistage BFB reactor.

[0057] The reactor may include a heat exchanger 340 configured to extract heat from the exhaust gas and transfer heat to the gas supplied to the volatilization stage (as shown) and/or the combustion stage (not shown), which may improve energy efficiency.

[0058] Increased gas pressure in the first stage may drive char and bed material into the second stage. In some cases, natural convection of the bed material recirculates at least some media back into the first stage from the second stage. FIG. 3 illustrates an implementation in which the floor heights of the two stages are the same; the floor heights may be different. FIG. 3 illustrates the volatilization stage coupled to an optional separation reactor 220 which, in this case, has a residual stream outlet 228 coupled to a corresponding residual stream inlet 238 of the combustion stage, such that the residual stream may be combusted. A residual stream may comprise syngas, raw gas, tar, and the like. A residual stream may comprise other gases, liquids, solids, and the like, and need not go to the combustion stage.

[0059] FIG. 4 illustrates a two-stage fluidized bed reactor, per some embodiments. FIG. 4 schematically illustrates an exemplary effect of overpressure in the volatilization stage on the difference in the surface heights of the beds in the two stages, and also illustrates different floor heights. A volatilization stage 310 may have a fuel inlet 316 and volatiles stream outlet 318 separated by an internal wall 402. In this example, an internal wall 402 separates at least a portion of the gas phases of the fuel inlet and volatiles outlet, so that fuel passes into the bed without interfering with the volatiles exiting the volatilization stage. In FIG. 4, wall 402 does not extend into the fluidized bed of the volatilization stage 310, allowing for some (indirect) gaseous communication between the fuel inlet and volatiles outlet without going through the bed. The volatiles outlet and fuel inlet are held at the same pressure in this example. FIG. 4 illustrates a slanted fuel inlet 316, which may enhance gravity assist. Other gravity-assisted mechanisms may be used. Insulation or thermally conductive material may be incorporated into wall 302 to reduce or increase heat transfer through wall 302. The wall 302 separating the volatilization and combustion stages may be slanted.

[0060] Wall 302 need not extend into the bed solids at the same location as the transition between the gas inlets 314 and 334. In FIG. 4, an extension length 440 defines a distance between the transition between gas inlets and the location of wall 302. In this example, wall 302 extends into the bed solids within the volatilization stage 310 (upstream of the transition between stages). Wall 302 may extend into the bed solids within the combustion stage 330 (downstream of the transition).

[0061] In some cases, the floor height of a stage is different than that of another stage, as shown in FIG. 4. A system may have a desired floor height difference 410 (typically controlled structurally/mechanically) and/or a desired bed surface height difference 420, typically controlled via pressure difference between the two beds. The extension distance of wall 302 into the bed, extension length 440, a distance 450 from the lower edge of the wall to the floor below, and/or the floor heights, may be used to define a transfer area 430 between the two beds. The transfer area may have a horizontal component (e.g., allowing for vertical bed flow) and/or a vertical component (e.g., allowing for horizontal bed flow), and is typically designed using Computational Fluid Design (CFD) tools to model bed flow and heat transfer between the stages. The transfer area is typically designed to achieve a desired heat and/or mass transfer between the beds (typically in concert with an expected pressure difference). Bed solids may be directed (e.g., horizontally) through a transfer area to enhance flow. For example, a reactor may include a splashgenerator (e.g., a high velocity gas jet) configured to impart a directed momentum to a local portion of bed solids (e.g., with a jet of high velocity gas), typically at least partially horizontally. For example, a splashgenerator may be used to increase circulation rates within a transfer area (directing flow into or out of a stage). Certain reactors include a stage having an adjustable floor height, which may provide independent pressure control (of the gas phases in the stages) and bed depths within each stage. Such control may be used to ensure both passage of the char stream from the first to second stage and recirculation of the bed media from the second to first stage.

[0062] For example, extraction of a combustible gas produced from a combustible solid or liquid may implement a single fluidized bed reactor having multiple stages. A combustion stage, where part of the cross section of the reactor vessel is fluidized with air, may be preceded by a volatilization stage, in which extraction and/or reaction is performed in a secondary reactor volume in which the fuel residence time is controlled by adjusting the pressure difference between the stages. A pressure difference between the stages (P.sub.1?P.sub.2, FIG. 4) and the pressure drop relationships across the distributor plate and the fluidized bed beneath the second reactor volume ((P.sub.d2?P.sub.2)/(P.sub.d1?P.sub.d2) FIG. 4) as well as the effective distance 450 (FIG. 4) between the distributor plate and the lower end wall 302 of the secondary reactor volume may be controlled. In some embodiments, an extracted volatiles stream has a lower heating value higher than, including at least two times higher than, the average heating value of the total gas volume leaving the volatilization and combustion stages.

[0063] FIG. 5 illustrates a three-stage reactor with an internal wall separating the gas phases of the fuel inlet and volatiles outlet, per some embodiments. In this example, internal wall 402 extends into the bed of the volatilization stage, separating this stage into an inlet stage 510 (in communication with the fuel inlet 316) and a reforming stage 610 (in communication with the volatiles outlet 318). Reforming stage 610 may be used for reforming reactions or other reactions. In descending below the surface of the bed, internal wall 402 forces all material (including gases) through the bed before volatiles may exit, and prevents gas-phase communication between the fuel inlet 316 and volatiles stream outlet 318.

[0064] The depth (into the bed) and thickness (in the flow direction) of the internal wall 402 may be chosen according to a desired residence time within the bed. FIG. 5 illustrates an additional pressure gauge 354 coupled to the controller, providing for separate pressure control over the inlet and reforming stages 510, 610 of the volatilization stage (e.g., via a separate valve 370 and/or gas inlet 316 providing for gas control into and/or out of inlet stage 510.

[0065] In this example, a second fuel inlet 336 provides additional fuel for the third (combustion) stage, and all three stages having the same floor height. This example schematically illustrates highest pressure in stage 510, lower pressure in stage 610, and lowest pressure in stage 330, resulting (in this case) in shorter distances between bed surface and floor. FIG. 5 illustrates differences 520, 520 between the surface heights of the beds of adjacent stages. The difference in heights of the bed surfaces may be controlled via corresponding pressure differences to achieve a desired flow rate (e.g., mass transfer equalization between fuel inlet 316, volatiles outlet 318, and exhaust 337. In this example, the stages have the same floor height (they may be different). In an embodiment, stages 510 and 610 have separate gas inlets and gas supplies (e.g., to deliver a different gas to the inlet stage than the reforming stage, which may be different than that delivered to the combustion stage. The distance from the lowermost edge of a wall to the bottom of a stage may be chosen according to a desired transfer area 430 (FIG. 4). In this example, a fan 338 is included to pump gas into or out of stage 510. FIG. 5 illustrates a single volatiles stream outlet 318 extracting volatiles from stage 610; and additional volatiles stream outlet may extract volatiles from stage 510. Stages 510 and 610 may have independent gas inlets (e.g., stage 510 is fluidized with exhaust gas recovered from exhaust 337 and stage 610 is fluidized with steam). Both stages may be fluidized with steam, N2, CO2, and the like.

[0066] FIG. 6 illustrates a three-stage reactor with an internal wall separating the gas phases of the fuel inlet and volatiles outlet, per some embodiments. In this example, wall 302 extends into the bed at the transition between the volatilization and combustion stages, and internal wall 402 separates the volatilization stage into an inlet stage 510 and a reforming stage 610.

[0067] FIG. 6 illustrates a baffle 620 (in this example, disposed at the current surface of the bed of the inlet stage 510. A baffle may be used to force non-gaseous fuel to pass through the bed for a certain amount of time. Baffle 620 typically extends sufficiently above the surface of the bed (e.g., above the bubble zone), such that fuel cannot pass over the baffle. Fuel must pass beneath the baffle to move from the portion of the bed in communication with the fuel inlet to the portion in communication with the volatiles outlet (and by extension, into the combustion stage). Baffle depth and thickness may be chosen according to a desired residence time in the bed. This example shows a constant floor height across the stages. A baffle may be used to segregate surface solids (e.g., incoming fuel), creating an internal dam (e.g., close to the fuel inlet) while keeping a portion of the bed open to the gas phase downstream of the baffle. A baffle may be disposed below the surface of the bed (e.g., at the bottom of the bed), including below a wall.

[0068] Internal upgrading of a combustible gas produced from a combustible solid or liquid is possible after extraction from a first fluidized bed reactor stage, where part of the cross section of the reactor vessel is fluidized with air and the extraction is achieved by the introduction of a secondary (upstream) reactor stage in which the fuel residence time is controlled by adjusting the pressure difference between the stages and the pressure drop relation between the pressure drop across the distributor plate and the hydrostatic pressure at the bottom of the fluidized bed(s), as well as lengths, distances and areas (450, 440, 430 FIG. 4) between and among the distributor plate(s) and the wall separating the stages. In some embodiments, the extracted gas has a lower heating value that is higher than, including at least two times higher than, the average heating value of the total gas volume leaving the primary (first zone) and secondary (second zone) reactor volumes, and where the upgrading of the extracted gas is achieved by the introduction of a third stage within the volatilization stage (with or without a baffle) to force all extracted gas to pass through a controlled height of bed material before the extraction of the volatiles.

[0069] Various features described herein may be implemented independently and/or in combination with each other. An explicit combination of features does not preclude the omission of any of these features from other embodiments. The above description is illustrative and not restrictive. Many variations of the invention will become apparent to those of skill in the art upon review of this disclosure. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.