Abstract: Apparatus for cooling hot particulate solids, especially shale solids, and reclaiming heat therefrom. The apparatus is constituted of an elongate housing divided into two compartments by a distributor plate sloped from 0.degree. to 15.degree. from horizontal, with jet openings therethrough declined downwardly from vertical at an angle between about 0.degree. to 45.degree.. The upper compartment contains a tube type heat exchanger and can be provided with a bed of solids. The lower compartment constitutes a plenum having a gas manifold with gas inlets for injection of gas into the manifold for release through the jets of the distributor plate. The gas is injected at velocities insufficient to fluidize a significant portion of the solids to maximize heat transfer between the solids and heat exchanger, and it contacts and expands the bed of solids, and assists in the downward movement of the solids along the distributor plate.

Abstract: A hydro-pressurized fluidized bed combustor having an uptanding shell and an entry at its bottom for admission of feedstock. The feedstock passes through a conduit surrounded by a heat exchanger. Inside the shell an entry conduit is outwardly flared in the upward direction to furnish a controlled expansion entry feeding into the fluidized bed. The entry conduit has a plurality of tuyeres in its peripheral wall. An injector pump feeds the feedstock into the entry. A weir above the entry conduit keeps the height of the bed constant within the combustion during operation.

Abstract: Exhaust gas treatment method and apparatus extract heat from an exhaust gas by operating in a water-condensing mode which allows more heat to be recovered, removes particulate matter and condensed acid from the exhaust gas, and washes heat exchange surfaces to keep them clean and wet to improve heat transfer. Systems for heating water, air, and both water and air are disclosed. Methods of constructing and assembling improved heat exchangers are disclosed.

Abstract: An apparatus for the cooling of hot fluidized solid particles.

Abstract: A fluidized bed combustion system for burning fuel particles, such as coal. The system includes a housing defining a first combustion region. An endless, flexible, perforate belt is shiftably mounted in the housing for supporting coal particles of relatively large size. A blower below the belt creates fluidized air which entrains smaller coal particles in a fluidized bed above the larger coal particles. The combustion gases arising due to combustion of the coal particles passes through a secondary combustion region in which coal fines are burned. The combustion gases continue upwardly through a scrubber in which limestone particles are entrained in the combustion gases to strip sulfides therefrom. The limestone particles are regenerated by a cyclone separator while the combustion gases travel through a passage containing boilers or other heat exchangers, whereby the heat from the combustion gases is transferred to fluids in the boilers.

Abstract: A reactor in which a plurality of vertical panels are disposed in a vessel and are constructed and arranged so as to form three combustion cells. Three of the panels each form a common wall between adjacent cells, and each cell is heated by a fluidized bed.

Abstract: A centrifugal spreader type feeder that supplies a mixture of particulate limestone and coal to the top of a fluidized bed reactor having a flow of air upward therethrough. Large particles of particulate matter are distributed over the upper surface of the bed to utilize the natural mixing within the bed, while fine particles are adapted to utilize an independent feeder that separates them from the large particles and injects them into the bed.

Abstract: A fluid bed combustor comprising a plurality of fluidized bed stages interconnected by downcomers providing controlled solids transfer from stage to stage. Each stage is formed from a number of heat transfer tubes carried by a multiapertured web which passes fluidizing air to upper stages. The combustor cross section is tapered inwardly from the middle towards the top and bottom ends. Sorbent materials, as well as non-volatile solid fuels, are added to the top stages of the combustor, and volatile solid fuels are added at an intermediate stage.

Abstract: Known vortex bed furnaces have a relatively high structural volume in relation to the firing performance. In addition, special devices are necessary for supplying the vortex bed with fuel and with sulphur-absorbing additives. Without subdividing the bed, a partial load can only be achieved with a vortex bed furnace which differs from the full load by only a small percentage. In order to solve these problems, it is proposed according to the invention that the fuel for the vortex bed should be blown with air via at least one dust burner, unsifted, into the combustion chamber, whereby the fine portion of the fuel conducted in is burnt in the dust flame and the coarse portion drops from the dust flame into the vortex bed. The dust burner serves on the one hand to load the vortex bed and on the other hand to increase the relative firing performance, and can be used to improve the suitability for partial load.

Abstract: The invention comprising a circulating fluidized bed firing system for a steam generator wherein the mass flow ratio for solid materials recirculated to hot gas flow employed to entrain and carry the recirculated solid materials to point/s of separation ranges from 6:1 to 2:1 at the furnace outlet and at rated conditions of the steam generator. Means are provided to cool the recirculated solids upstream and/or after separation of the recirculated solids from the gas stream. Conservative gas velocities for entrainment of solid particles in a range of from 16 to 25 ft./sec. at rated conditions of the steam generator minimize erosion of the coolant filled tubular heat exchange surface disposed in the gas stream upstream of the point of separation of solids from the gas stream.

Abstract: The total evaporator heating surface of a steam generator with circulating atmospheric or pressurized turbulent layer firing is distributed over several partial surfaces which are arranged in a turbulence-type combustion chamber (1) in a flow-bed cooler (7) or in a waste-heat steam generator (9). The partial surface through which flow takes place first, is dimensioned for the required low-load operation of the steam generator. The steam generator is so regulated that during increasing load of the steam generator the flow-bed cooler (7) receives an increasing quantity of solids, and during sinking load it receives a decreasing quantity of solids.

Abstract: The invention relates to a recovery method and installation for the heat contained in a solid substance, occurring in divided form and more especially in ash produced by a fluidized bed combustion furnace. According to the invention the coarsest ash is removed through a purging outlet from the fluidized bed, the finest ash is separated from the smoke and the ash is cooled in two apparatuses adapted to the granulometry, one to the finest ash and the other to the coarsest ash.

Abstract: A method for transferring heat between two fluids comprises (1) flowing the first fluid in an upright diamond shaped tube, and (2) flowing the second fluid therearound the tube over upper and lower surfaces of the diamond shaped tube formed at an angle to the horizon that is greater than the angle of repose of the second fluid therearound the tube for preventing accumulation of second fluid sediment on top and stagnant gases on the bottom of the tube. A novel heat exchanger tube is also disclosed.

Abstract: A heat exchanger is mounted in the upper portion of a fluidized combusting bed for controlling the temperature of the bed. The supported heat exchanger may be fed by or be a part of water-cooled tubes formed into support pillars extending up from the water-cooled plate by which the combusting bed is supported.

Abstract: A steam generator in which a main boiler is provided and at least one fluidized bed furnace is connected with the main boiler and is operated independently of the furnace of the main boiler. The fluidized bed furnace is connected with the main boiler underneath the boiler funnel. The tubes of the boiler funnel are partially fanned out and form flue gas passages, through which the flue gas of the fluidized bed furnace flows into the combustion chamber of the main boiler.

Abstract: A boiler is adapted for solid-fuel firing by connecting with an existing combustion chamber of the boiler. Apparatus comprising a bed of particles with means for feeding solid fuel and primary air to the bed. Secondary air is fed to the existing combustion chamber of the boiler with heated gases which leave the bed.

Abstract: The invention comprises a steam generator having a circulating fluidized bed combustion system whereby there is provision to admit air flow incrementally along the gas path to control combustion rate and firing temperature in a manner to maintain differential temperatures along the gas path. The initial portion of the gas path where combustion is initiated can be held in one temperature range as 1550.degree. F. which is optimum for sulphur retention and the final portion of the combustion zone can be elevated in temperature as to 1800.degree. F. to produce a greater degree of heat transfer through the gas to fluid heat exchange surface downstream of the combustion zone.

Abstract: An apparatus to serve as a valve to regulate the flow of particulate solids, from an upstream to a downstream location. The valve relies on pressure differential rather than moving mechanical parts. A plenum adjacent a chamber designed to accommodate a slumped mass of particulate solids receives fluid pressure and transmits the pressure to the slumped mass to move the particulate solids through an opening to a downstream location.

Abstract: A method of operating a fast fluidized bed reactor according to the invention comprises: (1) providing a fluidized bed reactor having an upper and a lower region, the upper region having a cylindrical shape; (2) feeding matter to be reacted into the lower region of the reactor; (3) supplying a first stream of pressurized air to the reactor in the lower region at a velocity to fluidize the granular material in the circulating regime, a portion of the granular material is continually entrained into the upper region; (4) tangentially supplying a second stream of pressurized air to the upper region wherein, at maximum operating capacity for the reactor, the second stream of air constitutes in excess of about 50% of the total pressurized air fed to the reactor; (5) maintaining a Swirl number of at least about 0.

Abstract: A fluidized bed combustor has its fluidizing chamber in thermal contact with a surrounding heat exchanger. A lined base portion of the chamber capable of containing the bulk of bed material while the bed is slumped is adapted to retard heat transfer from the bed. Thermostat linked devices in the bed and external load are arranged to switch the fuel and gas supplies to the bed so as to enable normal bed temperature to be attained without excessive heat removal to the heat exchanger.

Abstract: A shell boiler is disclosed having apparatus for feeding solid fuel to a furnace grate, contained within a furnace tube of the boiler, downwardly through the steam and/or water space of the boiler. The apparatus for feeding solid fuel to the furnace grate comprises a device for classifying and separating fine particles of fuel, having a particle size below a predetermined size, from the remainder of the fuel and feeding the fine particles into the furnace tube at a different location to that at which the remainder of the fuel is introduced into the furnace tube. The fine particles may be fed through a grit arrestor and fed into the furnace tube along with the grit separated by the grit arrestor.

Abstract: The invention comprises a dense pack heat exchanger for a steam generator having a circulating fluidized bed combustion system whereby a bed of solid particles comprising fuel and inert material is entrained in the furnace gas stream. Means are provided for collecting high temperature bed solid particles downstream of the furnace. The dense pack heat exchanger directs the hot collected particles down over heat transfer surface, such surface being a portion of the steam generator fluid circuits. Flow is induced by gravity means. The dense compaction of the solid particles around the fluid heat exchange circuits results in high heat transfer rates as the fluid cools the compacted solid material. The heat exchange surface is arranged to facilitate flow of the solid particles through the heat exchanger.

Abstract: The operation of gas turbines in combined cycle or cogeneration plants utilizing circulating fluidized beds is improved by increasing the temperature of the air supplied them. The temperature of bed solids circulating through an external heat exchanger is raised by combusting fuel in a combustion-augmenting zone through which the circulating solids pass. The gaseous products are combustion from that zone are introduced into the fluidized bed combustor. Thus the fluidized bed combustor operates at temperatures affording optimum sulfur removal by sulfur absorbing materials, the combustion-augmenting zone operates at an appreciably higher temperature to provide increased heat transfer to the compressed air for the gas turbine, and the off gases from the combustion-augmenting zone, which may be high in sulfur, are cooled in the combustor so as to bring about their desulfurization therein. Suitable apparatus is provided.

Abstract: A fluidized bed furnace (10) is provided having a perforate grate (9) within a housing which supports a bed of particulate material including some combustibles. The grate is divided into a plurality of segments (E2-E6, SH1-SH5, RH1-RH5), with the airflow to each segment being independently controlled. Some of the segments have evaporating surface imbedded in the particulate material above them, while other segments are below superheater surface or reheater surface. Some of the segments (E1, E7) have no surface above them, and there are ignitor combustors (32, 34) directed to fire into the segments, for fast startup of the furnace without causing damage to any heating surface.

Abstract: The invention comprises an integrated control means, and particularly at partial loads, for a steam generator having a circulating fluidized bed combustion system wherein gas recirculation means is used to supplement combustion air flow to maintain gas velocity in the circulation loop sufficient to entrain and sustain particle mass flow rate at a level required to limit furnace gas temperature to a predetermined value as 1550 F. and wherein gas recirculation mass flow apportions heat transfer from the gas and recirculated particles among the respective portions of the steam generator fluid heat absorption circuits, gas and circulating particle mass flow rates being controlled selectively in a coordinated manner to complement each other in the apportionment of heat transfer optimally among the fluid heat absorption circuits while maintaining furnace gas temperature at a predetermined set point.

Abstract: The invention comprises a drying and sorting apparatus which is integrated with a conventional steam generator for separating organically derived solid fuel from solid inert materials and for removal of moisture from the solid fuel prior to feeding such fuel to a combustor. Low level heat in the steam generator combustion gases, after heat exchange with the steam generator fluid circuits, provides the means for removing moisture from the solid fuel when hot air/gas (unsaturated with respect to moisture) is passed through a bed containing a mixture of solid fuel and waste inert material particles, fluidizing them. When in a fluidized state the lighter organically derived solid fuel particles separate from the heavier inert material particles.

Abstract: A fluidized bed boiler having a water-wall type construction has a steam-water natural circulation system for heat exchange. Vertical in-bed heat exchange tubes are provided and the steam drum of the boiler extends across the full length of the boiler combustion chamber and the convection heat exchange chamber. An air distributor grate is provided for introduction of fluidizing air into the combustion chamber and the air flow therefrom can be controlled to afford a flexible turn-down capability.

Abstract: Waste heat is recovered during the production of phosphorus pentoxide by a process comprising the combustion of phosphorus and the passing of the combustion gases through a fluid bed, wherein the solids making up the fluid bed are utilized to recover heat values derived from the process by contacting the same with water to produce steam.

Abstract: Tubing which contains crude oil being moved to the surface is surrounded by concentric sections of pipe at various depths along portions of the tubing. Said concentric sections of pipe contain a porous media incorporating an oxidizing catalyst in the annulus between said pipe and the tubing. A fuel and oxygen containing gas is passed down the tubing/casing annulus and passes through the catalyst bed causing the fuel to burn. The exhaust gas may be passed to the surface or it may enter the crude containing tubing to assist in gas lifting the crude to the surface. The crude is heated by the heated sections surrounding the tubing and by the hot exhaust gases thus reducing the crude viscosity and preventing the building up of wax within the tubing. The catalyst bed may alternatively comprise a single layer of catalyst supporting particles attached to the outer surface of the production tubing string or selected sections thereof.

Abstract: A fluidized bed heat exchanger in which a perforated plate is disposed within a housing for supporting a bed of particulate material which is introduced into the housing through an inlet. Air is passed through the plate to fluidize the particulate material and a drain pipe is provided for discharging the spent material from the bed. The flow rate of air introduced into the bed is increased in a direction across said bed from said inlet to said drain pipe to promote the circulation of the bed materials from the inlet to the drain pipe.

Abstract: A fluidized bed heat exchanger having a perforated support plate supporting relatively lightweight absorbent material particles and relatively heavy fuel ash particles includes a drain through which a flow of air defining a separating air screen retains the adsorbent material particles in the bed but allows the fuel ash particles to fall into the drain.

Abstract: A fluidized bed furnace is provided in which liquid fuel can be burned. Injectors extend up through an imperforate bed plate which properly mix the oil or other liquid fuel with the fluidizing air causing evaporation of the oil. This mixture is passed through restricted openings as it enters the fluidized bed, thus resulting in high velocity flow and fairly even fuel and combustion distribution throughout the cross-section of the fluidized bed.

Abstract: The fluidized bed is situated in a combustion chamber formed from evaporator tubes welded in seal-tight relationship and leading into a gas flue. The combustion chamber is connected to the gas flue via two inclined connecting wall surfaces. Heater tubes bent into an L-shape extend through the fluidized bed. Each shorter limb of the heater tubes extends substantially vertically while the other longer limb extends substantially horizontally. The horizontal limbs pass through a substantially vertical combustion chamber wall at the level of the fluidized bed and the vertical limbs pass through the free surface of the fluidized bed beneath the connecting wall surface. As a result of this arrangement of the heater tubes, the stresses therein due to uneven thermal expansion of the heater tubes remain within permissible limits.

Abstract: A heat exchanger system exhibits an improved coefficient of heat transfer over a conventional convection heat exchanger while maintaining the beneficial high temperature driving force of conventional convection heat exchanger. A plurality of heat extraction means are provided in heat flow communication with a plurality of shallow beds of particulate matter, which beds are fluidized by a heat-laden gas stream.A method for extracting heat from a heat-laden gas stream is also disclosed.

Abstract: The invention comprises a steam generator having a migrating fluidized bed combustor system. The bottom, head end of the bed incorporates a support floor system through which air is admitted tangential to the floor in a manner which causes the bed to migrate in a retraceable track. Tangential admission of air cools the floor and inhibits reverse flow down through the floor when the bed is slumped. Particle entrainment velocities are developed at mid-point in the bed. Tangential entrainment gas flow assures uniform distribution of combustibles and inert material throughout the lower bubbling bed and furnace area above the mid-point. Platens in the furnace zone straighten gas flow for gravity separation of particulate at the outlet of heat transfer surface above the furnace.

Abstract: The invention comprises a steam generator having a circulating fluidized bed firing system. Particles of fuel and solid inert material are recirculated in a furnace wherein gas velocities are maintained at levels sufficient to entrain the fuel and inert material particles in the gas stream. A plenum is provided at the furnace outlet wherein gas velocity drops below entrainment level and the particles are directed to a collection hopper for recycle. The gas is withdrawn from the plenum through ducting in a manner to assure uniform gas distribution through the plenum. High gas velocity through the ducting improves heat transfer in the fluid cooled enclosure surface where such surface is incorporated into the ducting. The ducting connect to the downstream gas path.

Abstract: The invention comprises a steam generator fluidized bed which recirculates through a major portion of the normal gas to fluid heat transfer circuits. Solid bed material is separated, collected and recirculated. Bed temperatures are limited by regulation of density of bed inert material to inhibit the radiant aspects of combustion. Gas recirculation is used to supplement air flow to achieve higher than entrainment bed gas velocity in the fuel ignition and reaction zone. Fuel ignition and reaction are controlled by limiting the amount of atmospheric air flow to the circulating fuel rich bed mixture to regulate extent of propagation of the ignition and reaction zone into the initial portion of the circulating bed loop, starting from the point of highest gas pressure.

Abstract: A fluidizing gas control apparatus for a fluidized-bed incinerator, in which a variation of the pressure loss of fluidizing gas flowing through a fluidized bed formed by a fluid-forming medium is measured, while progressively increasing the flow rate of fluidizing gas supplied to the incinerator in the starting stage, to determine the optimum value of the flow rate of fluidizing gas on the basis of the measured variation of the pressure loss, and the sum of the flow rate of fluidizing air and the flow rate of recirculated gases provided by recirculation of a portion of exhaust gases is controlled to be maintained at the optimum flow rate throughout the incinerating operation of the incinerator.

Abstract: A fluidized bed reactor in which a grate is disposed in a housing for receiving a single bed of particulate material. The interior of the housing below the grate is divided into a plurality of zones and air is selectively passed through portions of the grate to fluidize corresponding portions of the bed above the zones. A plurality of air distributors are provided in the bed for reducing the height of the particulate material accumulating in various portions of the bed.

Abstract: The specification describes a method and arrangements for operating fluidized bed combustors in particular boilers. In the described method and arrangements thermal energy carried away from the combustor by the flue-gas emitted therefrom is recuperated by passing the flue-gas through a scrubber in which it is scrubbed with water. The scrubbing water subsequently being used to pre-heat fluidizing gas fed to the fluidized bed in the combustor and/or working fluid fed to the boiler. Additional description is given of using a heat exchanger through which both flue-gases from the combustor and the working fluid fed to the combustor are fed such that the heat carried away from the combustor in the flue-gases is given directly to the working fluid fed to the combustor. In the described method and arrangements the fluidizing gas may be charged with water vapor and/or steam easing control of the bed.

Abstract: A low pollution method of burning a fuel comprises gasifying the fuel in a gasifier bed containing particles which are fluidized by a fluidizing gas containing substantially no inert components. The resulting combustible gas is burned with air diluted with nitrogen to reduce NO.sub.x formation. In addition, NO.sub.x production from the nitrogen content of the fuel is reduced as a result of the gasification of the fuel to combustible gas before combustion with air. Preferably the gasifier bed contains CaO to fix sulfur from the fuel as CaS. In one embodiment, the gasifier bed (51) contains CaSO.sub.4 and the fluidizing gas contains H.sub.2, inter alia, which mediates the transfer to the fuel of chemically-bound oxygen from the CaSO.sub.4 (which is thereby reduced to CaS). Particles containing CaS are passed to an oxidizer bed (72) wherein they are fluidized by air. The CaS is exothermically oxidized to CaSO.sub.4 by extracting oxygen from the air which is thereby heated and substantially exhausted of oxygen.

Abstract: A fluidized bed shell boiler for producing steam or hot water or a fluidized bed hot gas generator or incinerator in which the position at which bed material is deposited downstream of the bed is controlled. A baffle of firebrick with gas-flow passages extending through the baffle is positioned in the tube downstream of the bed.Gas velocities are distributed across the tube so that bed material is preferentially deposited in the combustion chamber downstream of the furnace tube.Deposition in the furnace tube is reduced to zero or to a negligible amount and deposition downstream of the combustion chamber is reduced.

Abstract: An improvement in a method of pyrolysis wherein an organic material, such as city waste, is pyrolyzed using a two-bed type pyrolysis system including a fluidized bed type pyrolysis reactor and a combustion reactor and wherein energy is recovered from burning the pyrolysis gases produced is disclosed. The improvement comprises recovering the heat of a combustion exhaust gas which is generated when the energy of the pyrolysis gas is recovered, heating a fluid medium with the recovered heat, and heating the organic material to be pyrolyzed with the heated fluid heat medium to dry the organic material before it is pyrolyzed.

Abstract: Only a part of the synthesis gas supply is passed through a first internally cooled catalytic reactor (1) and the hotter gas coming out of it is reunited with the remaining gas supply for passing through an adiabatic reactor (2) that is followed by a heat exchanger (3) on its way to a second internally cooled reactor (4) in which the methanization reaction is completed. Water is heated up to practically the saturated steam temperature in the cooling system of the last mentioned reactor and is converted to saturated steam in the cooling system of the first internally cooled reactor. The saturated steam is superheated in the above-mentioned heat exchanger. To make the process run more smoothly a steam drum is provided through which the hot water piping between the cooling systems of the two internally cooled reactors runs and the saturated steam is brought into the steam drum and from it to the heat exchanger before it is superheated.

Abstract: A bottom of a combustion chamber of a fluidized bed firing system is penetrated by coal nozzles for introducing a coal/air mixture, and by air nozzles for injecting combustion air into the fluidized bed. A plate provided with openings is arranged in spaced relationship above each coal nozzle for achieving an improved burn-up.

Abstract: A vapor generating system in which a furnace section is provided that is formed by four upright walls. A plurality of openings are formed in one of the walls, and a plurality of gasifiers extend adjacent said one wall and surround the openings so that the respective interiors of the gasifiers communicate with the openings. A bed of adsorbent material is supported in each gasifier for adsorbing the sulfur generated as a result of the gasification of fuel introduced into the gasifier, and air is passed through the bed of adsorbent material to fluidize said material so that, upon combustion of said fuel, a substantially sulfur-free product gas is produced which passes from the gasifier, through the openings and into the furnace section.

Abstract: A coal supply gun assembly for a fluidized bed combustor which includes heat exchange elements extending above the bed's distributor plate assembly and in which the gun's nozzles are disposed relative to the heat exchange elements to only discharge granular coal material between adjacent heat exchange elements and in a path which is substantially equidistant from adjacent heat exchange elements.

Abstract: A fluidizable bed combustion chamber comprises an intermediate partition (2,7) which divides the chamber into an upper combustion space (1a) and a lower plenum (1b) and which is provided with means (4,4a,8) for injecting fuel into the upper combustion space in which, during use of the combustion chamber, a bed of fluidized material (6) is created. The intermediate partition is composed of a plurality of nested modules (7), each of polygonal shape and having a substantially centrally positioned fuel supply member (8). Each corner surface (9) of each module is upwardly inclined in the direction away from the center of the module, and these corner surfaces are provided with openings (10) enabling air to be injected into the upper combustion space from the plenum chamber. Preferably, the modules are of regular polygonal shape, for example triangular, quadratic or hexagonal.

Abstract: Concentration of a liquid by evaporation is performed in a heat exchanger having riser tubes for the liquid and a granular mass fluidized by the liquid to occupy the tubes. At their upper and lower ends the tubes open into upper and lower chambers. A hot medium contacts the tubes to transfer heat to the liquid. In order to render this heat exchanger effective for evaporation concentration, means are provided for vapor collection and discharge from the upper chamber, the riser tubes extend above the base of the upper chamber. A return conduit for recirculation of the liquid and granular mass connects the upper chamber to the lower chamber, opening in each case at a lower level than the riser tubes. Supply and discharge connections for the liquid are at levels lower than the upper ends of the riser tubes.

Abstract: The invention provides a means for more effectively adapting fluidized bed combustors for retrofit of existing boilers for burning of low grade inexpensive solid fuels. The operating discharge gas from a fluidized bed combustor is substantially lower in temperature from what exists at the furnace gas outlet of a conventional steam generator. Thus, outlet gas from fluidized bed combustors needs to be placed in the downstream gas path differently from conventional practice. The external combustors of the present invention permit placement of hot gas in the steam generator gas path where it can be effectively utilized. The invention also teaches how new steam generators can be configured advantageously to accommodate multiple fluidized bed combustors particularly as pertains to larger capacity steam generators in the 200 MW electrical and larger range.