FLUIDISED BED REACTOR AND METHOD OF OPERATING SUCH A REACTOR

Abstract: A substantially enclosed circulating fluidised bed reactor (1) comprises a substantially upright reactor chamber (10) containing a fluidised bed (11) of granular material and a substantially upright and cylindrical cyclonic reactor vessel (20) adjacent to the chamber, the respective upper regions (16, 18) of the chamber and the vessel being connected via a conduit (14) and the respective lower regions of the chamber and the vessel being operatively connected. The vessel (20) has a cylindrically shaped exit throat (21) aligned substantially concentrically with it at its top. Operation of the reactor comprises feeding matter to be reacted into the chamber (10); supplying a first stream of pressurised air or other gas to the reactor through a plurality of openings (12) at the bottom of the chamber (10) at a sufficient velocity to fluidise the granular material and the matter in the circulating regime for reacting a minor portion of the matter in the chamber, whereby a substantial portion of the granular bed material, reaction product gases and unreacted matter are continually entrained out of the chamber and into the cyclonic reactor vessel (20) via the conduit (14); tangentially supplying a second stream of pressurised air into the vessel (20) through a plurality of openings (19) in the cylindrically shaped interior side wall of the vessel for cyclonic reaction of a major portion of the matter in the vessel, the second stream being supplied, and the vessel being constructed and operated, so as to produce a Swirl number of at least about 0.6 and a Reynolds number of at least about 18,000 within the vessel for creating a cyclone of turbulence therein having at least one internal reverse flow zone, thereby increasing the rate of combustion therein; permitting the reaction product gases generated in the reactor to exit from the reactor via the exit throat (21) while retaining substantially all of said granular material and unreacted matter within the reactor; collecting the granular bed material and any unreacted matter in the lower region of the vessel (20) and returning it to the lower region of the chamber (10) and controlling the reaction process in the reactor by controlling the flow of the first and second streams of air and by controlling the flow of granular bed material and matter to be reacted in the chamber and the vessel.

Description: The present invention relates to improved circulating, i.e., fast, fluidised bed reactors and to methods of operating such reactors. More particularly, the invention relates to a two stage circulating fluidised bed reactor in which the size of a fluidised bed reaction chamber and a cyclonic reaction vessel may be substantially reduced. The present invention has particular application, inter alia , to adiabatic fluidised bed combustors, fluidised bed boilers, compressed hot air generators and methods of operating them. As used herein, and in the accompanying Claims, "adiabatic combustor" denotes a fluidised bed combustor that does not contain internal cooling means, and "boiler" denotes a fluidised bed combustor that contains internal heat absorption means, in the form of boiler, superheater, evaporator, and/or economiser heat exchange surfaces. The temperature of adiabatic fluidised bed combustors is typically controlled by the use of pressurised air in substantial excess of the stoichiometric amount needed for combustion. On the other hand, fluidised bed boilers require very low excess air, so that heat absorption means are required in the fluidised bed. Fluidised bed gasifiers, in contrast, utilise less than stoichiometric amounts of air. The state of fluidization in a fluidized bed of solid particles is primarily dependent upon the diameter of the particles and the fluidizing gas velocity. At relatively low fluidizing gas velocities exceeding the minimum fluidizing velocity, the bed of particles is in what has been termed the "bubbling" regime. Historically, the term "fluidized bed" has denoted operation in the bubbling regime. This fluidization mode is generally characterized by a relatively dense bed having an essentially distinct upper bed surface, with little entrainment, or carryover, of the bed particles (solids) in the flue gas, so that recycling the solids is generally unnecessary. At higher fluidizing gas velocities, above those of the bubbling regime, the upper surface of the bed becomes progressively diffuse and carry-over of the solids increases, so that recirculation of solids using a particulate separator, e.g., a cyclone separator, becomes necessary in order to preserve a constant solids inventory in the bed. The amount of solids carry-over depends upon the fluidizing gas velocity and the distance above the bed at which the carry-over occurs. If this distance is above the transfer disengaging height, carry-over is maintained at a constant level, as if the fluidizing gas were "saturated" with solids. If the fluidizing gas velocity is increased above that of the bubbling regime, the bed then enters what has been termed the "turbulent" regime, and finally, the "fast," i.e., "circulating" regime. If a given solids inventory is maintained in the bed, and the fluidizing gas velocity is increased just above that of the turbulent regime, the bed density drops sharply over a narrow velocity range. Obviously, if a constant solids inventory is to be preserved in the bed, the recirculation, or return, of solids must equal the carry-over at "saturation." At fluidizing gas velocities below those associated with the aforementioned sharp drop in bed density, the effect upon bed density of returning solids to the fluidized bed at a rate well above the "saturation" carry-over is not marked. The addition of solids to a bed fluidized in either the bubbling or turbulent regime at a rate above the saturation carry-over will simply cause the vessel containing the fluidized bed to fill up continually, while the fluidized density will remain substantially constant. However, at the higher fluidizing gas velocities associated with the circulating regime, the fluidized density becomes a marked function of the solids recirculation rate. Circulating fluidized beds afford intimate contact between the high velocity fluidizing gas and a large inventory of solids surface per unit bed volume. Additionally, slip velocity ( i.e. , solids-fluidizing gas relative velocity) is relatively high in circulating fluidized beds, when compared with that in ordinary fluidized beds. Consequently, there is generally a very high level of particulate loading in the combustion gases exiting from circulating fluidized bed combustors. The combustion process which takes place in a circulating fluidized bed combustor is also generally more intense, having a higher combustion rate than that occurring in traditional fluidized bed combustors. Furthermore, as a result of the high solids recirculation rate in circulating fluidized beds, the temperature is essentially uniform over the entire height of such combustors. Conventional circulating fluidized bed combustors operate at gas superficial velocities many times higher than the terminal velocity of the fluidized bed mean particle. Consequently, there is a very high particulate loading in the combustion product gases exiting from the combustor and entering the downstream cyclone particle separator. Such conventional cyclone particle separators typically have a height which is roughly three times their diameter, so that separators having a large diameter designed to remove the entrained solids from circulating fluidized bed combustors are typically quite tall and bulky. Such large refractory coned cyclone particle separators constitute a significant portion of the total cost of conventional circulating fluidized bed combustor systems. Notwithstanding the many advantages offered by conventional circulating fluidized bed reactors, as enumerated above, the high cost of constructing and maintaining the extremely large cyclone particle (gas-solids) separators required for recirculation of the entrained solids at the rate necessary to maintain the bed in the circulating fluidization regime constitutes a severe economic impediment to widespread commercial utilization of such reactors. Prior art circulating fluidized bed combustor boilers are known which employ vertical heat exchanger tube-lined walls in the entrainment region of the combustor ( i.e. , parallel to the flow). Such combustors rely primarily on the transfer of heat from gases which typically are heavily laden with solids, and require an extremely large internal volume to accomodate the large heat transfer surface required. The tube-lined wall heat transfer surface installed in the free board region in conventional fluidized bed combustors necessarily possesses a significantly lower heat transfer coefficient than that of a heat transfer surface fully immersed in the fluidized bed. Furthermore, its heat transfer coefficient is dependent primarily on two parameters: (a) fluidizing gas velocity, and (b) particle concentration in the flue gases, i.e., particle loading. The latter parameter is, in turn, strongly dependent on the fluidizing gas velocity and the mean particle size of the fluidized bed material. The concentration of particles in the ascending gas flow in a conventional circulating fluidized bed combustor is directly proportional to the gas velocity to the 3.5-4.5 power, approximately, and inversely proportional to the fluidized bed mean particle diameter to the 3.0 power, approximately. The strong effect of, and careful attention to, these two parameters on the concentration of particles in the ascending gas flow helps to achieve a reasonable heat transfer coefficient for conventional tube-lined wall heat transfer surfaces in the free board region and facilitates the control of combustion temperature at nominal and reduced boiler capacity. Nevertheless, there is a need in the art for a fluidized bed combustor boiler having a reasonable heat transfer coefficient and permitting control of combustion temperature at nominal and reduced capacity without being so strongly dependent on fluidizing gas velocity and fluidized bed mean particle diameter. The height of the free board region of a conventional circulating fluidized bed combustor boiler having a tube-lined wall heat transfer surface as described above is directly proportional to the superficial gas velocity to the 0.5 power and inversely proportional to the surface's heat transfer coefficient. Also, it can be shown that the particle loading and heat transfer coefficient are directly proportional to any change in the superficial gas velocity. The latter fact means that, for instance, a reduction of the superficial gas velocity will require an incease in the free board height for such a conventional combustor of a given capacity. Similarly, it can be shown that in order to increase the capacity of such a combustor, the free board height must be increased, thereby significantly increasing the cost of constructing such a higher capacity combustor. In contrast to most conventional circulating fluidized bed combustors, the combustor disclosed in U.S. Patent No. 4,469,050 to Korenberg (assigned to a common assignee herewith) does not provide for transferring the entrained granular bed material, unburnt fuel, ash, gases, etc. directly into a cyclone particle separator. Rather, the entrained solids and gases are carried upward into a cylindrically shaped upper region of the combustor chamber, i.e., an extended free board region, where further combustion takes place. Vertical rows of tangential nozzles are built into and evenly spaced over this cylindrical upper free board region. This tangentially fed secondary air is supplied at a sufficient velocity, and the geometric characteristics of the cylindrical upper region are adapted, to provide a Swirl number (S) of at least about 0.6 and a Reynolds number (Re) of at least about l8,000 within such upper region, which are required to create a cyclone of turbulence. This cyclone of turbulence enables the combustor shown in U.S. Patent No. 4,469,050 to achieve specific heat releases higher than l.5 million Kcal per cubic meter per hour, thereby significantly increasing the rate of combustion. As a direct result, the "vessel" size of this combustor is significantly smaller than other prior art combustors. Essentially, compared to its downstream cyclone particle separator, the combustor vessel appears like a refractory-lined duct. The relatively large size of the cyclone particle separator compared to the combustor vessel produced an incentive for improving this system by eliminating the cyclone particle separator. This was achieved in the circulating fluidized bed combustor disclosed in U.S. Patent No. 4,457,289 to Korenberg (assigned to a common assignee herewith) by eliminating the entire external solids recirculation loop and utilizing "internal recirculation." To achieve this, a "throat" was inserted at the top of the cylindrical upper region of the combustor and the external cyclone separator was eliminated. The combustor disclosed in U.S. Patent No. 4,457,289 is significantly less expensive to construct than the combustor disclosed in U.S. Patent No. 4,469,050, and other prior art circulating fluidized bed combustors, since it does not require a separate cyclone particle separator. However, it has demonstrated a somewhat reduced particulate capturing efficiency compared to such other combustors, particularly when burning solid coal particles. Furthermore, the combustor disclosed in U.S. Patent No., 4,457,289 provides a residence time for solid coal particles and conventional sulfur absorbents which, in some cases, may be less than optimum for capturing any sulfur in the coal. In conventional, non-circulating and circulating fluidized bed reactors for combusting particulate material, the material to be combusted is fed in or over a bed of granular material, usually fuel ash, sulfur absorbents such as limestone, and/or sand. EP-A-0092622 discloses apparatus for carrying out a method of operating a circulating fluidised bed reactor, comprising providing a substantially enclosed reactor containing a fluidised bed of granular material, said reactor comprising a substantially upright chamber and a substantially upright and cylindrical vessel adjacent to said chamber, operatively connected to said chamber, said vessel having a cylindrically shaped exit throat aligned substantially concentrically with, and at the top of, said vessel; feeding matter to be reacted into said reactor; supplying a first stream of pressurised reaction-promoting gas to the reactor through a plurality of openings at the bottom of said chamber at a sufficient velocity to fluidise said granular material and said matter in the circulating regime for reacting a minor portion of said matter in said chamber, whereby a substantial portion of said granular bed material, reaction product gases and unreacted matter are continually entrained out of said chamber and into said vessel via said conduit; tangentially supplying a second stream of pressurised reaction-promoting gas into the reactor through a plurality of openings in the cylindrically shaped interior side wall of said vessel for reacting a major portion of said matter, said second stream being supplied, and said vessel being constructed and operated, so as to produce a Swirl number of at least about 0.6 and a Reynolds number of at least about 18,000 within said vessel for creating a cyclone of turbulence therein having at least one internal reverse flow zone, thereby increasing the rate of the reaction; permitting the reaction product gases generated in the reactor to exit from the reactor via said exit throat in said vessel, while retaining substantially all of said granular material and unreacted matter within the reactor; and maintaining the desired reaction in the reactor by controlling the flow of said first and second streams of reaction-promoting gas into said chamber and said vessel, respectively, and by controlling the flow of granular bed material and matter to be reacted in said chamber and in said vessel. In accordance with one aspect of the present invention, a method of operating a circulating fluidised bed reactor, is characterised in that the respective upper regions of said chamber and said vessel are connected via a conduit and the respective lower regions of said chamber and said vessel are operatively connected, and in that the granular bed material and any unreacted matter is collected in the lower region of said vessel and returned to the lower region of said chamber. In accordance with a second aspect of the present invention, a circulating fluidised bed reactor is characterised in that the respective upper regions of said chamber and said vessel are connected via a conduit and the respective lower regions of said chamber and said vessel are operatively connected; and in that the reactor further comprises means for collecting the granular bed material and any unreacted matter in the lower region of said vessel and returning it to the lower region of said chamber. The present invention, in a radical departure from the conventional circulating fluidized bed reators discussed above, has overcome the above-enumerated problems and disadvantages of the prior art by providing a two stage circulating fluidized bed reactor having a fluidized bed reaction (e.g. combustion) stage followed by a cyclonic reaction (e.g. cyclonic combustion) stage. A minor portion of the reaction gases (e.g. air) is supplied beneath the fluidized bed as fluidizing gases, while a major portion of the gases is supplied into the cyclonic reaction stage. Such major portion of the gases is fed tangentially into an upright cylindrically shaped cyclonic reaction vessel so as to create a cyclone of high turbulence, whereby the reaction takes place in both the fluidized bed and the cyclonic reaction vessel at a significantly increased rate. The solids entrained in the fluidized bed stage are carried over into the cyclonic reaction vessel where they are separated from the gases therein and recycled back into the fluidized bed. The invention provides a circulating fluidized bed reactor utilizing a cyclonic reaction stage which provides a cyclone of turbulent gases having a swirl number of at least about 0.6 and a Reynolds number of at least about 18,000 in a cylindrically shaped, refractory lined cyclonic reaction vessel downstream of the fluidized bed, thereby providing a significantly improved reaction rate and requiring a significantly lower volume of gases and solids circulating from the fluidized bed to the cyclonic reaction vessel. Consequently, the size of the reactor of the present invention is significantly smaller than prior art circulating fluidized bed reactors. Specifically, the height and internal diameter of the free board region of the fluidized bed and the height and internal diameter of the cyclonic reaction vessel of the present invention are significantly reduced, compared to the fluidized bed free board region and cyclone particle separator, respectively, of a conventional circulating fluidized bed reactor having the same reactor capacity. The invention provides a reactor having a shorter fluidizing gas residence time required to complete the reaction to the desired level. Specific heat releases in excess of about 1.5 million Kcal per cubic meter per hour are believed to be obtainable according to the present invention. The foregoing advantages will permit a significant reduction in the size and, thus, the cost of constructing the circulating fluidized bed reactor of the present invention. This will be true in adiabatic combustor and boiler applications of the invention. It is anticipated, for example, that several times less internal volume will be required for a combustor constructed in accordance with the present invention, and for boiler applications, at least about 3-5 times less heat transfer surface area will be needed for the combustion stage. An improved boiler system can be provided having a high turndown ratio and easier start-up than the prior art systems. In this regard the invention provides a separate cooling fluidized bed adjacent to the circulating fluidized bed for removing heat from the combustion stage by cooling the solids in the cooling fluidized bed and then recycling them back to the combustion stage. The cooling fluidized bed is preferably fluidized in the bubbling regime and contains evaporator, superheater and/or economizer coils immersed in the bubbling fluidized bed with the further objective of significantly reducing the heat exchanger surface area required for effective heat transfer. In such an overall system (circulating fluidized bed reactor with adjacent bubbling fluidized bed heat exchanger), the vertical heat exchanger tube-lined walls previously utilized in the upper region (vapor space) of prior art circulating fluidized bed reactors are eliminated, thereby considerably reducing the cost of constructing such a system. The method of the present invention may be performed in an adiabatic mode, in which the total pressurized air supplied is in excess of the stoichiometric amount needed for combustion; or in a non-adiabatic mode in which a heat exchanger surface is provided in the fluidized bed for removing heat from the bed. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and, together with the description, serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic vertical section view of an adiabatic circulating fluidized bed reactor constructed in accordance with the present invention. FIG. 2 is a diagrammatic vertical section view of a circulating fluidized bed reactor constructed in accordance with the invention. FIG. 3 is a diagrammatic plan cross sectional view A-B-C-D of the circulating fluidized bed reactor depicted in FIG. 2. FIG. 4 is a diagrammatic vertical section view of a circulating fluidized bed reactor according to a further embodiment of the invention. FIGS. 5, 6 and 7 are further diagrammatic vertical section views of the circulating fluidized bed reactor depicted in FIG. 4. FIG. 8 and 9 are diagrammatic front section and top section views, respectively, of an alternative heat exchanger tube arrangement suitable for use in the reactor shown in FIGS. 4-7. FIG. 10 is a diagrammatic vertical section view of a circulating fluidized bed reactor constructed in accordance with a further embodiment of the invention. FIGS. 11-13 are graphs plotting particulate loading vs. the fraction of air supplied as fluidizing air for three combustor embodiments of the invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. One preferred embodiment of the circulating fluidized bed reactor of the present invention is shown in FIG. 1. As shown, the reactor of the present invention may comprise, for example, a combustor, represented generally by the numeral 1. In accordance with this embodiment of the invention, the combustor 1 includes a fluidized bed combustion chamber 10 containing a fluidized bed of granular material in its lower region 11. The granular bed material is preferably fly ash, sand, fine particles of limestone and/or inert materials. The granular bed material is fluidized in the circulating fluidization regime with pressurized oxygen-containing gas, for example, air, which is supplied as a stream through a plurality of fluidization nozzles 12 extending through support surface 13. At maximum operating capacity for the combustor, the air supplied through openings 12 preferably constitutes less than about 50%, and still more preferably between about 15-35%, of the total air supplied to combustor 1, i.e. , the air required for the combustion process. As will be discussed in detail below, the significant reduction in the size of the combustor 1 relative to conventional circulating fluidized bed combustors, is achieved primarily by feeding significantly reduced levels of air to the combustor as fluidizing air, i.e., through nozzles 12. Thus, although amounts of air in excess of 50% the total air supplied to combustor 1 can be fed via fluidization nozzles 12 in accordance with the present invention, the extent to which the size of combustor 1 can be reduced will be increased proportionately by reducing the amount of air supplied to combustor 1 as fluidizing air. A source of pressurized air, e.g. , a blower (not shown), preferably feeds the air to a plenum chamber 15 beneath support surface 13 or as shown in Fig. 1. Chamber 15 supplies the air to nozzles 12. A separate conduit (not shown) extends through support surface 13 for removing refuse, such as tramp material and/or agglomerated ash, etc., if required, from combustion chamber 10. Combustor 1 further includes means for feeding combustible matter to the combustor, preferably to the lower region 11 of combustion chamber 10. As embodied herein, such means may comprise any suitable conventional mechanical or pneumatic feeding mechanism 17. The combustible matter which may comprise gases, liquids and/or solid particles, may be introduced into or above the bed in lower region ll of combustion chamber l0. The combustible matter undergoes partial combustion in lower ententent to an extent limited by the free oxygen available in the fluidizing gas. The unburnt fuel, any gaseous volatile matter, and a portion of the granular bed material are carried upward ( i.e. , entrained) by the fluidizing gas and the flue gases into an upper region l6 of combustion chamber l0, and exit from upper region l6 through conduit l4 tangentially into the upper region l8 of adjacent cyclonic combustor vessel 20. It is generally known that the quantity of particles transported by an ascending gas from a circulating fluidized bed is a function of the gas flow velocity to the third to fourth power. Thus, greater solids reaction surface can be achieved by: (a) maintaining maximum solids' saturation in the ascending gas flow, and (b) increasing the vertical velocity of the fluidizing gas to a desired level sufficient to provide the desired carry-over into upper region l8 of cyclonic combustor vessel 20. For any solid fuel having a given specific ash particle size distribution, this vertical gas velocity must be sufficiently high, as noted above, but must not be so high as to cause intensive erosion of the refractory liner in upper region l6 of combustion chamber l0, due to very high ash concentration in this region, as will be discussed below. The interior surface of upper region l8 is cylindrically shaped in order to achieve swirling flow in such upper region, as discussed more fully below. In accordance with the invention, means are provided for tangentially supplying a second stream of pressurized gas, e.g. , air, to the upper region l8 of cyclonic combustor vessel 20 through openings l9, and preferably at least two oppositely disposed openings l9. Still more preferably, a plurality of openings l9 are provided at several aggregate points in upper region l8. As shown in FIG. l, in one advantageous embodiment the plurality of oppositely disposed openings are vertically aligned and spaced apart throughout upper region l8. (The cross-sectional view shown in FIG. l necessarily depicts only one vertical row of openings.) As embodied herein, a source of pressurized air, e.g. , conventional blower (not shown) feeds the second stream of air to for example, a conventional vertical manifold (not shown). In one preferred embodiment of the invention, the second stream of air constitutes between about 65%-85% of the total air fed to combustor l, i.e. , the total air flow required for the combustion process, at maximum combustor capacity. In accordance with the invention, it is critical that the secondary air be supplied at a sufficient velocity, and that the geometric characteristics of the interior surface of upper region 18 of cyclonic combustor vessel 20 be adapted, to provide a Swirl number (S) of at least about 0.6 and a Reynolds number (Re) of at least about 18,000, which are required to create a cyclone of turbulence in upper region 18. Preferably, upper region 18 is constructed and operated in a manner adapted to yield these minimum values of Swirl number and Reynolds number when operating at maximum reactor capacity. On the other hand, the Swirl number and Reynolds number must not exceed values which would result in an unacceptable pressure drop through vessel 20. This cyclone of turbulence enables combustor 1 to achieve specific heat release values higher than about 1.5 million Kcal per cubic meter per hour, thereby significantly increasing the rate of combustion. As a result, the size of the chamber 10 and vessel 20 of the present invention can be significantly reduced, compared to the size of a conventional circulating fluidized bed combustor free board region and hot cyclone separator, respectively. Cyclonic combustor vessel 20 is provided with a cylindrically shaped exit throat 21 aligned substantially concentrically with the cylindrical interior surface of upper region 18. Exit throat 21 and the interior of the upper region 18 of vessel 20 must exhibit certain geometric characteristics, together with the applicable gas velocities, in order to provide the above-noted required Swirl number and Reynolds number. These features are explained below and are discussed generally in "Combustion in Swirling Flows: A Review," supra , and the references noted therein, which publications are hereby specifically incorporated herein by reference. The majority of the fuel combustion in combustor l preferably takes place in the cyclone of turbulence in upper region l8 of cyclonic combustor vessel 20 at a temperature below the fusion point, which provides a friable ash condition. The cyclone of turbulence in upper region l8, and the accompanying large internal reverse flow zones created therein, when the cross-sectional area and length of upper region l8, the cross-sectional area of tangential openings l9, and the diameter of cylindrical exit throat 2l are properly sized (see below), effectively prevent all but the smallest solids from exiting from upper region l8 through exit throat 2l. In the embodiment shown in FIG. l, the granular bed material ash and any unburnt fuel are collected in the lower region 22 of vessel 20 and allowed to descend under the force of gravity through port 23, returning to lower region ll of combustion chamber l0, thus constantly increasing the height of the bed in lower region ll, if a fuel having a sensible amount of ash is burned. As a result, it will be necessary to frequently discharge these solids. The solids collected and not fluidized in lower region 22 of vessel 20 descend as a gravity bed effectively precluding any gas flow through port 23. If the upper region l8 of vessel 20 is designed and operated so as to achieve a Swirl number of at least about 0.6 and a Reynolds number of at least about l8,000 therewithin, and the ratio of the diameter of the combustor exit throat 2l (De) to the diameter of upper region l8 (Do), i.e. , De/Do (defined herein as X), lies within the range of from about 0.4 to about 0.7, preferably about 0.5 to about 0.6, upper region l8 will, during operation, exhibit large internal reverse flow zones, with as many as three concentric toroidal recirculation zones being formed. Such recirculation zones are known generally in the field of conventional cyclone combustors ( i.e. , not involving fluidized beds), and reference is made to "Combustion in Swirling Flows: A Review", supra , and the references noted therein, for a general explanation of such phenomena. Such cyclonic flow and recirculation zones in upper region l8 act to separate the solids from the gases present in upper region l8. The very high level of turbulence in upper region l8 results in significantly improved combustion intensity and, as a result of improved solids-gas heat exchange, a substantially uniform temperature throughout cyclonic combustor vessel 20. As mentioned, vessel 20 should be constructed such that the value of the ratio X lies within the range of from about 0.4 to about 0.7. The greater the value of X, the lesser the pressure drop through vessel 20 and the greater the Swirl number; so that, generally, higher values of X are preferred. However, for values of X in excess of about 0.7, the internal reverse flow zones are not formed sufficiently to provide adequate gas-solids separation. Although the fluidized bed reactor of the present invention is fluidized in the "circulating" or "fast" fluidization regime, it differs fundamentally from prior art circulating fluidized bed reactors, in that: (a) it does not require the use of a large cyclone particle separator to separate the fluidized solids, e.g. , the granular bed material, unburnt fuel, ash, etc., from the flue gases, and (b) there is a significantly reduced gas flow through upper region l6 of combustion chamber l0 and into cyclonic combustor vessel 20 which, thus, can be of a smaller size. The elimination of the requirement for large cyclone separators and the reduced size of chamber l0 and vessel 20 will significantly reduce the size and the cost of reactor systems constructed in accordance with the present invention. In operation, the combustible matter is fed into combustion chamber l0. Optionally, for gaseous or liquid fuels, all or a portion of the combustible matter may be fed directly into cyclonic combustor vessel 20, preferably via tangential openings l9. The first stream of pressurized air is supplied to chamber l0 through fluidizing nozzles l2 at a sufficient velocity to fluidize the granular bed material and combustible matter in the circulating regime for combusting a portion of the combustible matter in chamber l0. A substantial portion of the granular bed material, combustion product gases and uncombusted matter are continually entrained out of chamber l0 and into cyclonic combustor vessel 20 via tangential conduit l4. The second stream of pressurized air is supplied tangentially to vessel 20 through openings l9 in the cylindrically shaped interior side wall of the upper region l8 of vessel 20 for cyclonic combustion of a major portion, for example, greater than about 50% and preferably between about 65% and 85%, of the uncombusted matter in vessel 20. The second stream of air is supplied, and vessel 20 is constructed and operated, so as to produce a Swirl number of at least about 0.6 and a Reynolds number of at least about l8,000 within vessel 20 for creating a cyclone of turbulence therein having at least one internal reverse flow zone, thereby increasing the rate of combustion in vessel 20. The combustion product gases generated in reactor l exit from the reactor via exit throat 2l in cyclonic combustor vessel. Substantially all of the granular bed material and uncombusted matter are separated from the combustion product gases and are retained within vessel 20, collected in lower region 22 and recycled to lower region ll of chamber l0, preferably under the force of gravity via port 23. Alternately, any conventional solids transfer mechanism capable of preventing flue gases from entering into vessel 20 from chamber l0 may be used to recycle the solids back to chamber l0. A key advantage of the fluidized bed combustor l of the present invention is that the cross-sectional areas of each of the upper region l6 of chamber l0 and the upper region l8 of vessel 20 are significantly smaller than the corresponding cross-sectional area of the upper region, i.e. , the free board region, and the cyclone particle separator, respectively, of a conventional circulating fluidized bed combustor of the same capacity. This results in a significant savings in construction costs for the fluidized bed combustor of the present invention. The above-described size reduction is accomplished by, for example, applying conventional circulating fluidized bed design criteria to size combustion chamber l0 and vessel 20 to operate at, for example, 25% of the desired capacity. That is, upper region l6 of chamber l0 and upper region l8 of vessel 20 may be sized to handle only, for example, 25% of the air flow associated with a conventional circulating fluidized bed combustor free board region and cyclone particle separator, respectively, of the desired capacity. This significant reduction in size is made possible by using vessel 20 as both a cyclone particle separator and a cyclonic combustor. Where, to continue the example, combustion chamber l0 and vessel 20 are reduced in size to handle only 25% of the conventional air flow, the remaining 75% of the conventional air flow is supplied as the second stream of air fed tangentially to cyclone combustor vessel 20 via openings l9 for cyclonic combustion of the major portion of the combustible matter in vessel 20. Thus, by selecting the relative amounts of air supplied to combustor l via fluidizing air nozzles l2 in combustion chamber l0 and via tangential openings l9 in cyclonic combustor vessel 20, it is possible, in accordance with the present invention, to reduce the volume of air flowing through chamber l0 and into vessel 20 via tangential conduit l4 and thereby proportionally reduce the cross-sectional areas of upper regions l6 and l8, compared to the corresponding cross-sectional areas of the free board region and the cyclone separator of a conventional circulating fluidized bed combustor. As shown, the embodiment depicted in FIG. l may comprise an adiabatic combustor for generation of hot combustion gases, i.e. , without any heat extraction from combustion chamber l0 or cyclonic combustor vessel 20. The hot gases may, for example, be used as process heat supply or supplied to heat a boiler, as known in the art. Such an adiabatic combustor operates at high excess air, with the level of excess air depending on the heating value of the fuel being burned. The combustion temperature in cyclonic combustor vessel 20 is controlled by controlling the fuel to air ratio. The desired temperature difference between chamber 10 and vessel 20, which will vary from case to case, is controlled by maintaining the proper mean particle size of the granular bed material and by controlling the fluidizing air superficial velocity in chamber 10 to provide a mean particle suspension density in chamber 10 and vessel 20 sufficient to sustain the desired temperature difference for the particular fuel being utilized. FIG. 11 is a graph showing the particulate loading (KG/M³) of fluidized bed granular material in upper region 16 of combustion chamber 10 and upper region 18 of cyclonic combustor vessel 20 for combustor 1 shown in FIG. 1 as a function of the fraction (η) of the total air flow into the combustor that is introduced as fluidizing air via nozzles 12 in the bottom of chamber 10 for temperature differences (ΔT) between chamber 10 and vessel 20 of 10°C (50°F) , 37.7°C (100°F), and 65.6°C (150°F). This graph was prepared based on calculations for Ohio bituminous coal having a low heating value (LHV) of 6371 KCAL/KG, an air stoichiometric coefficient (α) of 3.3 and assuming the temperature of the flue gases exiting from combustor 1 via exit throat 21 is 815.6°C (1500°F) for the adiabatic combustor of FIG. 1. As can be seen from FIG.11, for η = 0.25, a temperature difference of 37.7 °C (100°F) or 65.6°C (150°F) can be maintained between chamber 10 and vessel 20 by maintaining the particulate loading at about 3l KG/M³ and 2l KG/M³, respectively, using conventionally known techniques, for example, by controlling mean particle size and fluidizing air superficial velocity. The method of the present invention can also be used for boiler applications which, from an economic standpoint, require low excess air for combustion and, therefore, heat absorption in the fluidized bed. In one embodiment of the invention, such heat absorption is accomplished by installing a heat exchange surface in upper region l6 of combustion chamber l0. As shown, for example, in the dashed lines in FIG. l, the heat exchange surface may comprise a heat exchanger tube arrangement 25. The tube arrangement may be of any suitable size, shape and alignment, including a vertical tube wall, as is well known in the art. Preferably, heat exchanger tube arrangement 25 will be operatively connected to a process heat supply or to a conventional boiler drum (not shown) for boiler applications. The heat exchanger cooling media may comprise any suitable conventional liquid or gaseous media, such as, for example, water or air. In boiler applications, the exhaust gases exiting from combustor l (FIG. l) are preferably fed to the boiler convective tube bank in a conventionally known manner. In the embodiment of FIG. l, if heat exchanger tube arrangement 25 is provided in upper region l6 of chamber l0, the combustion temperature in cyclonic combustor vessel 20 is controlled by controlling the fluidizing air flow rate through plenum 15 at a given tangential air flow rate in upper region 18 of cyclonic combustor 20. This, in turn, controls the amount of solid particulate carryover from upper region 16 to upper region 18 via tangential conduit 14 and, consequently, the heat transfer coefficient of heat exchanger tube arrangement 25 is changed. In the embodiment shown in FIG. 1 utilizing optional heat exchanger tube arrangement 25, combustor capacities below 100% are achieved by sequentially reducing the tangential air flow in vessel 20 and then reducing the fluidizing air flow through nozzles 12 in chamber 10. FIG. 12 is a graph showing the temperature difference in degrees Celsius (ΔT) between vessel 20 (essentially the temperature of the flue gases exiting via throat 21) and chamber 10, (essentially the temperature in upper region 16) as a function of the particulate loading (KG/M³) of fluidized bed granular material in the flue gases in the upper region 16 of chamber 10, for the FIG. 1 embodiment utilizing heat exchanger tube arrangement 25. This graph was prepared based on calculations for Ohio bituminous coal having a LHV of 6371 KCAL/KG, an α of 1.25 and assuming the temperature of the flue gases exiting via exit throat 21 is 843.3°C (1550°F) for the combustor of FIG. 1 with heat exchanger tube arrangement 25 installed. As can be seen from FIG. 12, a very wide range of temperature differences between chamber 10 and vessel 20, 7.2°C (45°F) to 65.6°C (150°F), can be achieved if the particulate loading is varied between 50 KG/M³ and 15 KG/M³, respectively. Such temperature differences do not depend upon the value of η, the fraction of the total air flow that is introduced as fluidizing air (as described above), but rather, depend upon the particulate loading Z. Consequently, such a combustor can be designed with η ≦ 25% and a relatively low air superficial velocity in chamber 10.10, provided the particulate loading is maintained at least at 15 KG/M³, for example, a temperature difference (ΔT) limit of 65.6°C (150°F) for a given combustor design. Turning now to FIGS. 2 and 3, these figures illustrate an embodiment of the invention particularly suitable for use in boiler applications in which a high boiler turndown ratio is desired. Like reference numerals have been used in FIGS. 2 and 3 to identify elements identical, or substantially identical, to those depicted in FIG. 1, and only those structural and operational features which serve to distinguish the embodiment shown in FIGS. 2 and 3 from those shown in FIG. 1 will be described below. In particular, the embodiment shown in FIGS. 2 and 3 includes a cooling fluidized bed 40 (with a heat exchanger) situated immediately adjacent to region 11 of combustion chamber 10 and separated therefrom by a partition 30 having an opening 41 communicating with lower region 11. Cooling fluidized bed 40 comprises an ordinary ( i.e. , bubbling) fluidized bed of granular material, and includes a heat exchange surface, e.g. , shown here as heat exchanger tube arrangement 42, which contains water or another coolant fluid, such as, for example, steam, compressed air, or the like. The bed 40 is fluidized by tertiary pressurized air supplied from a plenum 43 through openings 44 in a support surface. As shown, these openings may take the form of nozzles. Fluidized bed 40 is comprised of the granular material and other solids flowing from lower region 11 into bed 40 through opening 41, as will be explained below by referring to both FIG. 2 and FIG. 3. Combustion also takes place in fluidized bed 40. Heat exchanger tube arrangement 42 functions as a cooling coil to cool fluidized bed 40. The cooled solids and combustion gases leave bed 40 through opening 46, in partition 30 which separates bed 40 from the circulating fluidized bed contained in lower region 11, and re-enter lower region 11 of reactor chamber 10. The solids are again fluidized therein. The fluid passing through tube arrangement 42 is preferably supplied from, for example, a conventional boiler drum (not shown) and after being heated and partially vaporized, is returned to the boiler drum. The fluid passing through tube arrangement 42 may also typically comprise steam for superheating or air for generation of compressed air. The movement of solids from the bubbling fluidized bed 40 to the circulating fluidized bed in lower region ll of combustion chamber l0 is preferably motivated by specially designed solids reinjection channel 47 (see FIG. 3) having a high solids reinjection rate capability for reinjection of solids back into lower region ll via port 48. Reinjection channel 47 has separately fed fluidizing nozzles (not shown) beneath it, with the solids reinjection rate being controlled by controlling the amount of air fed through these nozzles. Fluidized bed 40 may optionally consist of two or more separate beds which may be interconnected or not, as desired, with each having a separate tube arrangement. For a better understanding of how this boiler embodiment functions to improve the turndown ratio, a preferred procedure for initially placing it into operation from the cold condition to a full load and then turn it down to a desired level will be explained. An ignition burner (not shown), which may be located above or under the fluidized bed level in lower region ll, is turned on along with the first (fluidizing) air stream (nozzles l2), with the second air stream (nozzles l9), the cooling bed fluidizing air stream (nozzles 44) and the solids reinjection air stream being shut off. When the combustor's refractory in chamber l0 and its internal volume temperature exceed the solid fuel ignition temperature, the fuel is fed into combustion chamber l0. After the solid fuel is ignited and, consequently, the combustor's exit gas temperature has risen to the design level, the ignition burner is turned off, and from this moment an adiabatic fluidized bed combustor scheme is in operation at a high excess air and having a capacity lower than the minimum designed capacity. To reduce the high excess air to the design level, the fuel feed rate is increased, and to maintain the combustion temperature at a constant level, the cooling bed fluidizing air and the solids reinjection air flow through channel 47 are turned on and are kept at the required rate. From this moment the combustor is in operation at its minimum designed capacity with the corresponding design paramemeters. To increase the unit's capacity, at this time the air flow in the second stream (nozzles l9) is gradually increased, with a simultaneous increase in the solid fuel feed rate, and a corresponding increase in the solids reinjection air flow rate through channel 47 to maintain the combustion temperature constant. When the second stream flow rate achieves its maximum design level, the combustor can be considered as having its full load (l00% capacity). At this moment, if the gas exit temperature is at the desired, i.e. , design, level, the second stream air flow and fuel rate are not increased any further, and are then maintained in accordance with the fuel-air ratio required to obtain the most economical fuel combustion. The minimum capacity of the reactor, i.e. , desired turndown ratio, can be obtained if the sequence of operations outlined above is followed in reverse order, until the point where the ignition burner is shut off. Namely, while maintaining the desired fuel-air ratio, the second stream air flow (nozzles l9) is reduced until it is completely shut off. At the same time, the solids reinjection air is decreased proportionately to maintain the combustion temperature at a constant level. As a result, the solids' circulation through cooling fluidized bed 40 is reduced to a minimum corresponding to the combustor's minimum designed capacity, and likewise the heat exchange process between bed 40 and heat exchanger tubes 42 is reduced. In brief review, the key feature, in terms of obtaining a high turndown ratio according to the embodiment depicted in FIG. 2, is the fact that the cooling fluidized bed heat exchange surface 42 may be gradually pulled out (but not physically) from the combustion process so as to keep the fuel-air ratio and combustion temperature at the required levels. Furthermore, the above-desired boiler turndown ratio improvement has an additional advantage over known circulating fluidized bed boilers. Specifically, it requires less than one-half the heat exchange surface to absorb excessive heat from the circulating fluidized bed, due to the following: (a) the tubular surface 42 immersed in fluidized bed 40 is fully exposed to the heat exchange process, versus the vertical tube-lined walls in the upper region of the combustion chamber of prior art circulating fluidized bed boilers, in which only 50% of the tube surface is used in the heat exchange process; (b) the fluidized bed heat exchange coefficient in such a system is higher than that for gases, even heavily loaded with dust, and vertical tube-lined walls confining the combustion chamber of prior art circulating fluidized bed boilers. The latter results, in part, from the fact that it is possible, by using a separate fluidized bed 40, to utilize the optimum fluidization velocity therein, and the fact that fluidized bed 40 is comprised of small particles, for example, fine ash and limestone. FIG. l3 is a graph showing the particulate loading (KG/M³) of fluidized bed granular material in upper region l6 of combustion chamber l0 and upper region l8 of cyclonic combustor vessel 20 for combustor l shown in FIG. 2 as a function of the fraction η of the total air flow into the combustor that is introduced as fluidizing air via nozzles l2 and 44 in the bottom of chamber 10 for temperature differences between chamber 10 and vessel 20 of 7.2°C (45°F), 32.2°C (90°F) and 65.6°C (150°F). This graph was prepared based on calculations for Ohio bituminous coal having an LHV of 6371 KCAL/KG, an α of 1.25 and assuming the temperature of the flue gases exiting from combustor 1 via exit throat 21 is 843.3°C (45°F). As can be seen from FIG. 13, for η = 0.25, a temperature difference of 32.2°C (90°F) or 65.6°C (150°F) can be maintained between chamber 10 and vessel 20 by maintaining the particulate loading at about 75 KG/M³ and 44 KG/M³, respectively, using conventionally known techniques as described previously. In another embodiment of the invention, heat absorption from the fluidized bed is accomplished through the use of an adjacent cooling fluidized bed 40 (FIG. 2) and by additionally installing a heat exchange surface in upper region 16 of combustion chamber 10. As shown, for example, in the dashed lines of FIG. 2 (indicating its optional nature), the heat exchange surface may comprise a heat exchanger tube arrangement 25. The constructional and operational features of tube arrangement 25, as well as its interaction with the other features of combustor 1 are the same as discussed previously in connection with FIG. 1. FIGS. 4-7 illustrate a further embodiment of the present invention for achieving high capacity without requiring an excessively tall or otherwise large unit. This embodiment provides more heat transfer than the other embodiments discussed previously. Like reference numerals have been used to identify elements identical, or substantially identical, to those depicted in FIGS. 1 and 2. In this embodiment, combustion chamber 10 is constructed and functions virtually identically to chamber 10 in the other embodiments of the invention. Preferably, no heat exchange surface is present in chamber 10 and conduit 14 extends from upper region 16 into the top of a substantially upright, cooling chamber 50 containing a heat exchange surface. As shown, the heat exchange surface preferably comprises conventional heat exchanger tube lined walls 51A, 51B. Inlet headers 52 and outlet headers 54 are provided for tube lined walls 51A, 51B. Optionally, upper region 16 of chamber 10 may also contain similar heat exchanger tube lined walls (not shown). The combustion product gases and the granular bed material and unburnt combustible matter entrained therein exit chamber 10 through conduit 14 and descend along with the flue gases, through second chamber 50. At the bottom of chamber 50 is a fluidized bed 60 fluidized in the bubbling, i.e. , non-circulating, regime. Tube lined walls 80 preferably surround and serve to contain fluidized bed 60. As shown best in FIG. 4, fluidized bed 60 is in solids, but not in gas communication with the circulating fluidized bed in chamber l0 through the overflow opening (denoted by the arrow A in FIG. 4) between chamber l0 and chamber 50. By controlling the vertical height of fluidized bed 60, which is accomplished by controlling the fluidizing air flow through nozzles 9l beneath bed 90, varying amounts of bed material from bed 60 can be made to overflow wall 62 into lower region ll of chamber l0. As a result of the heat exchange that takes place as the combustion product gases, granular bed material and unburnt combustible matter pass through cooling chamber 50, the solids overflowing wall 62 into lower region ll will have a lower temperature than the solids in chamber l0. Consequently, the temperature in chamber l0 can be regulated in part by controlling the amount of solids overflowing wall 62 into chamber l0. Immediately adjacent to the cooling chamber 50 is a substantially upright second cooling chamber 70. Chambers 50 and 70 share a common, interior tube linedwall 5lA. Wall 5lA is preferable constructed as a tube sheet having fins extending between the tubes to render the tube sheet substantially impervious from its uppermost point downward to a height just above the top of fluidized bed 60 where there are no fins between the tubes, thus permitting passage of gases from the lower region of chamber 50 into the lower region of second cooling chamber 70. Thus, in the lower region of cooling chamber 50, above fluidized bed 60, the gases descending through chamber 50 effectively make a U-turn, entering second cooling chamber 70 above fluidized bed 60 at the bottom of chamber 70. In second cooling chamber 70, combustion product gases flow upward and then out from the upper region of chamber 70 via tangential conduit 7l into the upper region l8 of a cyclonic combustor vessel 20. Vessel 20 is constructed and functions virtually identically to vessel 20 in the other embodiments of the invention previously discussed, with the solids collected at the bottom of vessel 20 being recycled under the force of gravity through port 23 into the lower region ll of chamber l0 (see FIG. 7). Alternatively, any similar conventional device, such as, for example, a non-mechanical sluice, may also be used. An upflow channel 72 is created within or adjacent chamber 70. As embodied herein, channel 72 is formed by providing an inner wall 5lB (FIGS. 5 and 6), which preferably comprises a tube lined wall as shown. Wall 5lB is open at its upper end and contains a lower opening for permitting fluidized bed solids, including the granular bed material and unburnt combustible matter, to enter channel 72 (as shown by arrow B in FIG. 5). At the bottom of channel 72 are fluidization gas nozzles 73 for fluidizing in the pneumatic transport regime. The solids in channel 72 are thus entrained upwardly in the fluidization gases and exit from the open upper end of channel 72 into the upper region of chamber 70 (as shown by arrow C in FIG. 5). At this point, these elevated solids are entrained by the ascending gases in chamber 70 and are carried out of chamber 70 via conduit 7l. The velocity of the ascending gases must, thus, be sufficiently high to permit such carryover of the solids issuing from the top of channel 72. Preferably, such velocity is sufficiently high, and channel 72 is constructed and operated, so as to provide a rate of particulate solids entry into cyclonic combustor vessel 20 via tangential conduit 7l substantially equal to, or greater than, the rate of particulate solids exiting from combustion chamber l0 via conduit l4. The internal cross-sectional area of combustion chamber l0 can be significantly smaller than the free board region of a conventional circulating fluidized bed combustor; typically 4 to 5 times smaller, with respect to its cross-sectional area. In operation of the embodiment depicted in FIGS. 4-7, the superficial gas velocity is very high in chamber l0 for providing the desired particulate solids loading in the combustion product gases exiting via conduit l4. The downward superficial gas velocity in first cooling chamber 50, which is less than that in combustion chamber l0, is not high enough to cause damaging erosion of tube lined walls 5lA, 80 or any other heat transfer surface installed in cooling chamber 50. The same is true for the upward superficial gas velocity in second cooling chamber 70. The combustion product gases entering first cooling chamber 50 via conduit l4 are very heavily laden with solid particles (i.e., high particulate solids loading), thereby providing a high heat transfer coefficient in conjunction with tube lined walls 5lA, 80 despite the somewhat lower gas velocity than in combustion chamber l0. The combustion product gases flowing upward through second cooling chamber 70 have a sufficient velocity to provide the desired particulate solids loading for the gases entering cyclonic combustor vessel 20 via tangential conduit 7l, i.e. , loading selected to maintain the desired combustion temperature in vessel 20. Such loading is controlled by the velocity of upwardly flowing gases in chamber 70 and the amount of particulate solids exiting from the top of channel 72, as described previously. A portion of the solids carried by the gases in first and second cooling chambers 50, 70 will separate from the gases and fall into bubbling fluidized bed 60. Tramp material and ash building up in the bed is periodically removed via conduits 85 and l00 in a conventionally known manner. The fluidized bed material inventory in bed 60 is maintained at the desired levels by overflowing the bed material from bed 60 into the lower region ll of combustion chamber l0, as previously described. Combustion takes place in combustion chamber l0 and cyclonic combustor vessel 20 as described in connection with the embodiments of FIGS. l and 2, with the majority of the combustion taking place in vessel 20. For example, in one preferred embodiment, in excess of about 70% of the total air fed to combustor l is fed via tangential air inlets l9 in vessel 20. The capacity of the combustor shown in FIGS. 4-7 can be turned down from l00% capacity, and vice-versa, in substantially the same manner as described previously in connection with the embodiments of FIGS. l and 2. As explained above, in the embodiment shown in FIGS. 4-7, the velocity of the combustion product gases in first cooling chamber 50 is less than the gas superficial velocity in combustion chamber l0. However, the gas velocity in chamber 50 is not high enough to create an erosion problem with any internal heat transfer surface. In an alternative embodiment of the invention shown in FIGS. 8 and 9, the heat transfer surface in first cooling chamber 50 comprises both heat exchanger tube-lined walls 80 and serpentine-like tubular heat exchanger coils 8l installed inside the chamber. This embodiment permits the height of first cooling chamber to be reduced and utilizes a more compact heat transfer surface. Combustion gases heavily laden with the particulates entrained out of combustion chamber l0 via conduit l4 flow downward between the serpentine coils 8l which are preferably inclined at l2°-l5° for natural water circulation. This heat exchanger coil arrangement provides minimum obstruction to gas flow and does not require any practical increase in the chamber's cross-sectional area at a given gas velocity, compared with an arrangement in which the heat exchanger coils are aligned horizontally. Moreover, such a horizontal tube alignment does not provide natural water circulation. On the other hand, a strictly vertical arrangement of coils 8l would require a multiplicity of tubes and very large headers. FIG. l0 depicts a further embodiment of the invention having enhanced particle separation efficiency in the cyclonic combustor vessel. Except where noted below, the structure and operation of combustor l are virtually identical to those shown in FIG. l, and like reference numerals have been used to identify elements identical, or substantially identical, to those depicted in FIG. l. As discussed previously, cyclonic combustor vessel 20 also performs a gas-solids separation function. In particular, the lower region 22 of vesel 20 has a downwardly converging shape (e.g., as a hopper) for collecting the particulate solids separated from the gases by the spinning flow in upper region l8. The solids slide down the interior surface of vessel 20 as a mass of bulk material which is discharged via port 23 back into the fluidized bed in lower region ll of combustion chamber l0. It is known in the art of cyclone separation that the effective operation of a conventional cyclone particle separator can be destroyed by gas (air) leakage upward into the separator through the particle collection hopper at the bottom of the separator. Such gas leakage into the bottom of the cyclone separator can, if large enough, provide an upwardly moving gas stream in the separator which can reduce the cyclone particle separation efficiency to zero. In the combustor of the present invention, such undesirable gas leakage can also reduce the particle separation efficiency of cyclonic combustor vessel 20. The most destructive effect on separation efficiency is produced by leaked gases which pass upwardly through vessel 20 in the central core region of the vessel. To combat the passage of any leaked gases upward through the central core region, the embodiment shown in FIG. l0 is equipped with a substantially centrally located, vertically aligned, refractory column 82 having a diameter approximately equal to or somewhat less than that of exit throat 2l. Column 82 functions to divert any gases which may leak into the bottom of vessel 20 away from the central region of the vessel. Column 82 preferably has a top portion which is frusto-conically shaped. Gas diverter column 82 may obviously be utilized in any of the embodiments of the invention disclosed here. For example, it may be installed in cyclonic combustor vessel 20 of the embodiment depicted in FIGS. 4-7. Although the invention has been described in the field of fluidized bed combustors, the invention can be used for other applications in which fluidized bed reactors are used, such as, for example, various chemical and metallurgical processes.

Claims: A method of operating a circulating fluidised bed reactor, comprising providing a substantially enclosed reactor (1) containing a fluidised bed (11) of granular material, said reactor comprising a substantially upright chamber (10) and a substantially upright and cylindrical vessel (20) adjacent to said chamber, operatively connected to said chamber, said vessel having a cylindrically shaped exit throat (21) aligned substantially concentrically with, and at the top of, said vessel; feeding matter to be reacted into said reactor; supplying a first stream of pressurised reaction-promoting gas to the reactor through a plurality of openings (12) at the bottom of said chamber at a sufficient velocity to fluidise said granular material and said matter in the circulating regime for reacting a minor portion of said matter in said chamber, whereby a substantial portion of said granular bed material, reaction product gases and unreacted matter are continually entrained out of said chamber and into said vessel via said conduit; tangentially supplying a second stream of pressurised reaction-promoting gas into the reactor through a plurality of openings (19) in the cylindrically shaped interior side wall of said vessel for reacting a major portion of said matter, said second stream being supplied, and said vessel being constructed and operated, so as to produce a Swirl number of at least about 0.6 and a Reynolds number of at least about 18,000 within said vessel for creating a cyclone of turbulence therein having at least one internal reverse flow zone, thereby increasing the rate of the reaction; permitting the reaction product gases generated in the reactor to exit from the reactor via said exit throat in said vessel, while retaining substantially all of said granular material and unreacted matter within the reactor; and maintaining the desired reaction in the reactor by controlling the flow of said first and second streams of reaction-promoting gas into said chamber and said vessel, respectively, and by controlling the flow of granular bed material and matter to be reacted in said chamber and in said vessel, characterised in that the respective upper regions (16, 18) of said chamber and said vessel are connected via a conduit (14) and the respective lower regions of said chamber and said vessel are operatively connected, and in that the granular bed material and any unreacted matter is collected in the lower region of said vessel and returned to the lower region of said chamber. A method according to claim 1, wherein the reactor comprises a fluidised bed combustion reactor, the method comprising controlling the combustion process in the reactor by controlling the flow of said first and second streams of air into said combustion chamber and said cyclonic combustor vessel, respectively, and by controlling the flow of granular bed material and matter to be combusted in said chamber and said vessel. A method as claimed in Claim 1 or Claim 2, wherein said second stream of air or other gas comprises between about 65% and about 85% of the total air or other gas fed to the reactor. A method as claimed in Claim 2 or Claim 3, wherein said matter to be combusted includes solid combustible material. A method as claimed in Claim 4, wherein the total pressurised air supplied to the reactor is in excess of the stoichiometric amount needed for combustion. A method as claimed in any one of Claims 2 to 5, wherein said matter to be combusted includes liquid combustible material. A method as claimed in any one of Claims 2 to 5, wherein said matter to be combusted includes gaseous combustible material. A method as claimed in Claim 6 or Claim 7, wherein said liquid or gaseous material is fed directly into said cyclonic combustor vessel. A method as claimed in any one of Claims 2 to 8, further comprising the step of providing a heat exchange surface in the upper region of said combustion chamber for removing heat from said upper region. A method as claimed in any one of Claims 1 to 9, wherein said plurality of openings for supplying said second stream of pressurised air or other gas are substantially vertically aligned and spaced apart along said side wall of said vessel. A method as claimed in any one of Claims 1 to 10, further comprising the steps of providing a separate second fluidised bed (40) situated within the reactor and adjacent to the lower region of said combustion chamber, said second fluidised bed being separated from the fluidised bed (11) in said combustion chamber by a substantially vertically extending partition (30) and being fluidised in the bubbling regime; permitting the fluidised granular material to flow from said combustion chamber into said second fluidised bed via a first opening in said partition; permitting the fluidised granular material to flow from said second fluidised bed into the fluidised bed in said combustion chamber via a second opening in said partition; and providing a heat exchange surface immersed in said second fluidised bed for removing heat therefrom. A method as claimed in Claim 11, including the step of supplying the heat removed from said second fluidised bed to a boiler or process heat supply. A method as claimed in any one of the preceding Claims, wherein the interior surfaces of the reactor are refractory lined. A method as claimed in Claim 1 or Claim 2, wherein said second stream of air or other gas comprises in excess of about 50% of the total reaction-promoting gas fed to the reactor. A method as claimed in any one of the preceding Claims, further comprising the step of providing a vertically extending substantially cylindrical diverter column (82) extending from the bottom of said cyclonic vessel to a height sufficient to divert any gases entering said vessel from said lower region of said chamber away from the central axis of said vessel, said column having a diameter substantially equal to or somewhat less than the interior diameter of said exit throat. A method according to at least claim 2, wherein the substantially enclosed combustion reactor further comprises a first cooling chamber adjacent to said combustion chamber and having a first heat exchange surface, and a second cooling chamber having a second heat exchange surface, said first and second cooling chambers having a common bubbling fluidised bed in their bottom regions, the method further comprising passing said product gases and entrained solids downward through said first cooling chamber and removing heat therefrom via said first heat exchange surface, and permitting said entrained solids to enter said bubbling fluidised bed; then passing said gases from said first cooling chamber to said second cooling chamber and permitting said gases to ascend through said second cooling chamber while removing heat therefrom via said second heat exchange surface; and entraining the solids containing said uncombusted matter in the ascending gases in said second cooling chamber and passing said gases and entrained solids out of said second cooling chamber and into the upper region of said cyclonic combustor vessel. A circulating fluidised bed reactor comprising (a) a substantially enclosed reactor (1) containing a fluidised bed (11) of granular material, said reactor comprising a substantially upright chamber (10) and a substantially upright and cylindrical vessel (20) adjacent to said chamber, operatively connected to said chamber, (b) means (17) for feeding matter to be reacted into said reactor; (c) means (15) for supplying a first stream of pressurised reaction-promoting gas to the reactor through a plurality of openings (12) at the bottom of said chamber at a sufficient velocity to fluidise said granular material and said matter in the circulating regime for reacting a minor portion of said matter in said chamber, whereby a substantial portion of said granular bed material, reaction product gases and unreacted matter are continually entrained out of said chamber and into said vessel via said conduit; (d) means for tangentially supplying a second stream of pressurised reaction-promoting gas into the reactor through a plurality of openings (19) in the cylindrically shaped interior side wall of said vessel for reacting a major portion of said matter, said second stream being supplied, and said vessel being constructed and operated, so as to produce a Swirl number of at least about 0.6 and a Reynolds number of at least about 18,000 within said vessel for creating a cyclone of turbulence therein having at least one internal reverse flow zone, thereby increasing the rate of the reaction; and (e) a cylindrically shaped exit throat (21) aligned substantially concentrically with, and at the top of said vessel for permitting the reaction product gases generated in the reactor to exit from the reactor, while retaining substantially all of said granular material and unreacted matter within the reactor; characterised in that the respective upper regions (16, 18) of said chamber and said vessel are connected via a conduit (14) and the respective lower regions of said chamber and said vessel are operatively connected; and in that the reactor further comprises (f) means for collecting the granular bed material and any unreacted matter in the lower region of said vessel and returning it to the lower region of said chamber. A reactor as claimed in Claim 17, wherein said means for collecting the granular bed material and uncombusted matter and returning it to the lower region of said combustion chamber comprises a hopper (22) having an opening (23) communicating with a port in the lower region of said combustion chamber. A reactor as claimed in Claims 17 or 18, further comprising a heat exchange surface (25) in the upper region of said chamber for removing heat from said upper region. A reactor as claimed in any one of Claims 17 to 19, wherein said plurality of openings for supplying said second stream of pressurised air are substantially vertically aligned and spaced apart along said side wall of said vessel. A reactor as claimed in any one of Claims 17, to 20, further comprising: a separate second fluidised bed (40) situated within the reactor and adjacent to the lower region of said chamber, said second fluidised bed being separated from the fluidised bed in said chamber by a substantially vertically extending partition (30) and being fluidised in the bubbling regime; means for permitting the fluidised granular material to flow from said combustion chamber into said fluidised bed via a first opening (41) in said partition; means for permitting the fluidised granular material to flow from said second fluidised bed into the fluidised bed in said chamber via a second opening (46) in said partition; and, a heat exchange surface (42) immersed in said second fluidised bed for removing heat therefrom. A fluidised bed reactor as claimed in any one of Claims 19 to 21, further comprising boiler means operatively connected to said heat exchange surface. A fluidised bed reactor as claimed in any one of Claims 17 to 22, further comprising a vertically extending substantially cylindrical diverter column (82) extending from the bottom of said cyclonic combustor vessel to a height sufficient to divert any gases entering said vessel from said lower region of said combustion chamber away from the central axis of said vessel, said column having a diameter substantially equal to or somewhat less than the interior diameter of said exit throat. A fluidised bed reactor as claimed in Claim 23, wherein the top portion of said diverter column is frusto-conically shaped. A reactor according to any of claims 17 to 24, wherein the reator comprises a circulating fluidised bed combustion reactor. A reactor according to claim 25, further comprising: a substantially upright first cooling chamber (50) adjacent to said combustion chamber and having a first heat exchange surface (51a); and a substantially upright second cooling chamber adjacent to said first cooling chamber (70) and having a second heat exchange surface (51b), said first and second cooling chambers having a common bubbling fluidised bed in their bottom regions; wherein the respective upper regions (16, 80) of said combustion chamber and said first cooling chamber are connected via a conduit (14) and the respective lower regions of said combustion chamber and said first cooling chamber are in solids communication, the respective bottom regions of said first cooling chamber and said second cooling chamber being in open solids and gas communication, and the respective upper regions of said second cooling chamber and said combustor vessel being connected via a port (71); means for permitting solids from said bubbling fluidised bed to flow into said circulating fluidised bed in said combustion chamber for controlling the temperature of the latter bed; means for entraining the solids containing said uncombusted matter in the ascending gases in said second cooling chamber and passing said gases and entrained solids out of said second cooling chamber and into the upper region of said cyclonic combustor vessel via said port; and means for controlling the combustion process in the reactor by controlling the flow of said first and second streams of air into said combustion chamber and said cyclonic combustor vessel, respectively, and by controlling the flow of granular bed material and matter to be combusted in said combustion chamber, said first and second cooling chambers, and said vessel.

Inventors: KORENBERG, JACOB
Applicants: DONLEE TECHNOLOGIES INC.
Application year: 1987
Main classification: F23C11
IPC codes: F23C6, F22B31, F23C10