FLUIDIZED BEDS HAVING MEMBRANE WALLS AND METHODS OF FLUIDIZING

DESCRIPTION

Heading

BACKGROUND OF THE INVENTION [Para 1] 1. Field of the Invention

[Para 2] The present invention relates to fluidized beds, and methods of fluidizing. In another aspect, the present invention relates to fluidized bed reactors and to methods of gasification. In even another aspect, the present invention relates to fluidized bed reactors having membrane walls, and to methods of gasification. In even another aspect, the present invention relates to fluidized bed coal gasification and to methods of coal gasification.

[Para 3] 2. Description of the Related Art

[Para 4] Fluidization is commonly defined as an operation by which particulate fine solids are transformed into a fluid-like state through contact with a gas or liquid. Fluidized beds are known for their high heat and mass transfer coefficients, due to the high surface area-to-volume ratio of fine particles. Fluidized beds are used in a wide variety of industrial processes such reaction, drying, mixing, granulation, coating, heating and cooling.

[Para 5] In many industrial applications, a fluidized bed consists of a vertically- oriented column filled with granular material, and a fluid (gas or liquid) is pumped upward through a distributor at the bottom of the bed. When the drag force of flowing fluid exceeds gravity, particles are lifted and fluidization occurs.

[Para 6] In a reaction process, a fluidized bed suspends solid fuels on upward- blowing jets of air. The result is a turbulent mixing of gas and solids. The tumbling action, much like a bubbling fluid, provides more effective chemical reactions and heat transfer.

[Para 7] Fluidized bed technology is utilized in coal gasification. There are a number of patent applications which are directed toward fluidized beds and/or coal gasification.

[Para 8] A coal gasification reactor of the type wherein agglomerated coal ash is withdrawn from a fluid reaction bed of finely divided coal without the removal of the finely divided coal particles is disclosed in Jequier et al, U.S. Pat. No.

2 ,906,608 and Matthews et al, U.S. Pat. No. 3,935 ,825. These patents are incorporated herewith by reference. [Para 9] In a coal to gas conversion process of the type referenced, a vessel is provided for a fluidized bed. A gas distribution grid is usually positioned in the vessel and defines the bottom surface of the fluidized bed. The central portion of the grid may be conical or cylindrical in shape and comprises a passage. At the bottom of the passage, a constriction is provided having a fixed opening defining a venturi of fixed throat size to provide a uniform upward gas velocity into the vessel and thus into the fluidized bed. Directing a stream of high velocity gas through the venturi or passage into the reaction vessel causes ash particles in the vessel to agglomerate and eventually discharge through the passage and venturi throat.

[Para 1 0] U. S. Patent No. 4,023 ,280, issued May 1 7, 1 977, to Schora et al., discloses a fluidized bed of material retained in a vessel receives a high velocity gas stream through a venturi orifice and passage to assist in the agglomeration of ash particles. The particles form a semi-fixed bed within the passage upstream from the venturi orifice. The particular dimensions of the semi-fixed bed are dependent, in part, upon the orifice size of the venturi. An iris valve defining the orifice permits adjustment of the cross-sectional area of the orifice thereby controls the velocity of the gas stream through the venturi.

[Para 1 1 ] U. S. Patent No. 4,435 ,364, issued March 6, 1 984, to Vorres, discloses an apparatus for withdrawing agglomerated solids, e.g. ash, from a fluidized bed of finely divided solid hydrocarbonaceous material, e.g. coal, is described. Agglomeration is effected by a high temperature reaction between the inorganic constituents of the hydrocarbonaceous material in the fluidized bed

environment. A venturi is utilized to serve as a passage for withdrawing the agglomerated solids from the fluidized bed. Spiral or other descending ridges are positioned on the interior surface of the constricted cylindrical opening of the venturi to permit variable and increased rates of agglomerate discharge with improved separation and classification of the solid materials.

[Para 1 2] U. S. Patent No. 4,453 ,495 , issued, June 1 2 , 1 984, to Strohmeyer, Jr., discloses an integrated control for a steam generator circulating fluidized bed firing system. The system includes 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 1 550 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 temperatu re at a predetermined set point.

[Para 1 3] U . S. Patent No. 4,453 ,498, issued June 1 2 , 1 984, to Juhasz, d iscloses a gas- or oil-burning warm water, hot water or steam boilers, main ly for the supply of households, communal institutions, and industrial plants, the surfaces of which su rround ing the furnace are formed as membrane wal ls having annular passageways con nected by thin plates, the passageways receiving the heat carrying agent.

[Para 1 4] U . S. Patent No. 4,454,838, issued June 1 9, 1 984, to Strohmeyer, Jr. , d iscloses a dense pack heat exchanger for a steam generator havi ng a circulating fluid ized bed combustion system whereby a bed of solid particles com prising fuel and inert material is entrai ned in the furnace gas stream .

Means are provided for collecting hig h 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 flu id circuits. Flow is induced by gravity means. The dense compaction of the solid particles around the fluid heat exchange circuits results in hig h heat transfer rates as the flu id cools the compacted solid material. The heat exchange surface is arranged to facilitate flow of the solid particles throug h the heat exchanger. [Para 1 5] U. S. Patent No. 4,462 ,341 , issued July 31 , 1 984, Strohmeyer, Jr. discloses 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 1 550F which is optimum for sulphur retention and the final portion of the combustion zone can be elevated in temperature as to 1 800F to produce a greater degree of heat transfer through the gas to fluid heat exchange surface downstream of the combustion zone.

[Para 1 6] U. S. Patent No. 4,745 ,884, May 24, 1 988, Coulthard, discloses a fluidized bed steam generating system includes an upstanding combustion vessel, a gas/solids separator, a convection pass boiler and a heat exchanger positioned directly below the boiler and all of the above elements except the gas/solids separator are enclosed within a waterwall structure having outside waterwalls and a central waterwall common to the reactor vessel on one hand and the convection pass boiler and heat exchanger on the other hand. The close proximity of the components of the system eliminate numerous problems present in conventional multi-solid fluidized bed steam generators.

[Para 1 7] U. S. Patent No. 5,277, 1 51 , issued January 1 1 , 1 994, to Paulhamus, discloses an integral water-cooled circulating fluidized bed steam generation system having a particle separator which is formed by the membrane walls of the reactor chamber. The particle separator has a serpentine configuration which includes a first turn which is capable of causing the solid particles in the flue gas to move toward the rear membrane wall and a second turn which is capable of causing smaller sized solid particles and the flue gas to be disposed between the front membrane wall and the larger sized solid particles wherein the flue gas passes through the solid particles to a discharge conduit which is disposed within the rear membrane wall and wherein the smaller sized solid particles are retained between the front membrane wall and the larger sized solid particles. The particle separator also includes a means for recycling the solid particles from the particle separator to the reactor chamber.

[Para 1 8] U. S. Patent No. 5,391 ,21 1 , issued February 21 , 1 995, to Alliston discloses an integral cylindrical cyclone and loopseal. The cyclone separator for a solids-laden process gas from a reactor also provides a pressure seal for the reactor. The cyclone includes a main housing with a longitudinal axis. The housing is made of a membrane wall construction having a plurality of tubes arranged around the axis and encased within membrane wall panels. A portion of the tubes are bent outwardly to form an inlet which communicates with the main housing for receiving the solids-laden process gas from the boiler. Solids are separated from the solids-laden process gas as they swirl together in the main housing of the cyclone separator. A partition wall is disposed at the lower section of the main housing around the longitudinal axis for defining an outer chamber and an inner chamber adjacent to the outer chamber. Gas is provided to the outer and inner chambers for creating fluidized beds of the solids in the outer and inner chambers. Solids are passed from the inner chamber to the outer chamber through an underflow port in the partition wall. Solids exit the main housing from an overflow port which communicates with the reactor.

[Para 1 9] U. S. Patent No. 5,393 ,31 5 , issued February 28, 1 995, to Alliston, et al., discloses an immersed heat exchanger in an integral cylindrical cyclone and loopseal. The cyclone separator for a solids-laden process gas from a fluidized bed boiler or reactor also provides a pressure seal and heat exchanger surfaces for the reactor or boiler. The cyclone includes a cylindrical main housing with a longitudinal axis. The housing is made of membrane wall construction. A portion of the tubes are bent outwardly to form an inlet which communicates with the main housing for receiving the solids-laden process gas from the boiler or reactor. Solids are separated from the solids-laden process gas as they swirl together in the main housing of the cyclone separator. A partition wall is disposed at the lower section of the main housing around the

longitudinal axis for defining an outer chamber and an inner chamber adjacent the outer chamber. Gas is provided to the outer and inner chambers for creating fluidized beds of the solids in the outer and inner chambers. Solids are passed from the inner chamber to the outer chamber through an underflow port in the partition wall. Solids exit the main housing from an overflow port which communicates with the reactor. Immersed heat exchanger surfaces are provided in the outer chamber for removing heat therefrom.

[Para 20] SUMMARY OF THE INVENTION

[Para 21] According to one non-limiting embodiment of the present invention, there is provided a fluidized bed apparatus. The apparatus includes a vessel having a top and bottom, and defining a fluidized bed region. The vessel further comprises a membrane wall.

[Para 22] According to another non-limiting embodiment of the present invention, there is provided a method of fluidizing. The method includes fluidizing while heat is being provided through a membrane wall of the fluidizing vessel.

[Para 23] According to even another non-limiting embodiment of the present invention, there is provided a method of fluidizing. The method includes introducing particles into a fluidizing bed region of a vessel. The method further includes providing heating through a membrane wall of the fluidizing vessel. H ead i ng

BRIEF DESCRIPTION OF THE DRAWINGS

[Para 24] FIG. 1 is a schematic representation of one non-limiting example of a fluidized bed of the present invention.

[Para 25] FIG. 2 is a cutaway side view of a portion of vessel 1 0 of FIG. 1 , showing wall 1 1 0 and grid 1 8 as comprising tubes 202 arranged to from membrane walls 200.

H ead i ng

DETAILED DESCRIPTION OF THE INVENTION

[Para 26] A non-limiting embodiment of a fluidized bed of the present invention is shown in FIG. 1 , which shows a schematic drawing of a fluidized bed gasifying apparatus or device 1 00 that includes means for agglomerating ash or particulate in the fluidized bed. Such a device has been described in Jequier et al U.S. Pat. No. 2,906,608 and Matthews et al U.S. Pat. No. 3 ,935 ,825, both herein incoprporated by reference. [Para 27] Briefly, device 1 00 includes a vessel 1 0 within which a fluidized bed 1 2 is retained. Vessel 1 00 further comprises outer wall 1 1 0. Pulverized fresh feed coal enters via line 1 4 and is contained within the bottom portion of the vessel or reactor 1 0 as a fluid bed 1 2 having a bed density of about 1 5 to 30 pounds per cubic foot. The coal within bed 1 0 is converted by reaction with steam and air to gaseous fuel components. These gaseous fuel components pass from the vessel 1 0 through a discharge line 1 6.

[Para 28] A shaped sloped grid 1 8 is provided within vessel 1 0 at the bottom of bed 1 2. Air and steam enter through a line 20 and pass through ports in grid 1 8 to assist in maintenance of bed 1 2 in a fluidized state. The ash contained in the feed coal within bed 1 2 generally settles near the bottom of fluid bed 1 2 due to its greater density. Thus, the ash particles flow down the sides of the generally conical grid 1 8 and pass into or enter a withdrawal chamber or particle exit passage 22 that is formed as part of the grid 1 8.

[Para 29] Referring additionally to FIG. 2 there is shown cutaway side view of a portion of vessel 1 0 of FIG. 1 , showing wall 1 1 0 and grid 1 8 as comprising tubes 202 arranged to from membrane walls 200. The tubes of the membrane wall form a spiral flow path for the heat transfer fluid. [Para 30] The membrane walls comprise tubes that are generally arranged in large panels or banks of parallel tu bes wh ich are connected together with a metal mem brane or web continuously interposed between each pair of adjacent tubes in the bank to form a tube wall. It shou ld be understood, that the d imensions for the membrane wall may be any suitable dimensions as desired and appropriate. It should also be u nderstood that the membrane walls may be made of any suitable material by any suitable method .

[Para 31 ] As a non-limiti ng example, the tubes may generally have an outer d iameter which can range from about 1 inch up to about 3 inches, with a wall thickness which can be u p to about 0.5 inch. The web or membrane connecting adjacent tubes to each other general ly has a thickness about equal to the wall thickness of the tubes, with the width of the webbing generally rang ing from about 0.25 inch to about 0.75 inch . The webs or membranes can be welded to the outer walls of adjacent tubes to form the tube banks; however, the tube and connecting membranes can be, and preferably are, formed together in a single casting operation.

[Para 32] It should be understood that any part or all of device 1 00 may com prise one or more membrane wal ls. As non-limiting examples, part or all of wall 1 1 0 may comprise one or more membrane walls, and/or part or all of grid 1 8 may comprise one or more membrane walls. [Para 33] Referring additionally to FIG.3, there is shown a schematic of membrane wall 210 as forming wall 110 and grid 18. In the non-limiting embodiment as shown, membrane wall 210 comprises ports 211 and 212 for circulation of a heat transfer fluid.

[Para 34] Referring additionally to FIG.4, there is shown a schematic of membrane wall 220 as forming grid 18. In the non-limiting embodiment as shown, membrane wall 220 comprises ports 221 and 222 for circulation of a heat transfer fluid.

[Para 35] Referring additionally to FIG. 5, there is shown a schematic of membrane walls 230, 240, 250 and 260 as forming wall 110 and grid 18. In the non-limiting embodiment as shown, each of membrane walls 230, 240, 250 and 260 comprise ports 231 and 232 for circulation of a heat transfer fluid. It should be understood that membrane walls 230, 240, 250 and 260 may be operated independently to provide different heating/cooling zones as desired.

[Para 36]While not shown, it should be understood that any single circulation loop may be provided with more than just a pair of ports, and may be provided with any suitable number of ports to vary/control the circulation as desired.

[Para 37] While not shown, it should be understood that membrane walls may be utilized for other parts of system 100 other than just for wall 110 and grid 1 8. As non-limiting examples, one or more membrane walls may be utilized to form part or all of coal inlet stream 1 4, part or all of inlet stream 20, and/or part or all of inlet stream 28. Use of membrane walls at these streams may assist in preheating any reactants. A membrane wall could also be utilized to cool outlet streams 1 6 and 30, or even to recover heat from outlet streams 1 6 and 30.

[Para 38] Various methods of the present invention for fluidizing particles include providing heating/cooling to the particles by circulating heat transfer fluid through one or more membrane walls.

[Para 39] A non-limiting example of a method of fluidizing is as follows. It should be understood that velocities, percentages, diameters, flow rates, temperatures, reactant compositions, output gas, and any other operating parameter, may be varied according to the operation desired. The following operating conditions are merely specific to this non-limiting example, and are not meant to limit the claimed invention in any way, shape or form.

[Para 40] The ash particles are contacted within passage 22 by a high velocity air-steam stream having a velocity in the range of about 50 to about 200 feet per second. This high velocity air-steam stream enters the chamber or passage 22 by passing from line 28 and through the narrow throat or orifice 24 of the passage or venturi tube 22. The ash particles may be admixed with a considerable amount of finely divided coal particles and form a semi-fixed bed in the passage 22. Depend ing upon the type of coal utilized , particle size, and other factors, this semi-fixed bed may have a density generally in the range of about 40 to about 60 pounds per cubic foot.

[Para 41 ] The semi-fixed bed within the passage 22 protects the sides of the passage 22 from abrasive effects created by the high velocity stream th rough the throat or orifice 24 and additionally protects the walls of the vessel from localized high temperatu res. Also, the air-steam stream entering the throat 24 via an inlet line 28 reacts with coal particles that enter the reg ion of the passage 22 resulting in tem peratu res of about 1 OOF to about 200F higher than the temperatu re mai ntai ned in the fluid bed 1 2.

[Para 42] The air-steam stream represented by input throug h passage 22 may constitute in the range of approximately 20-40% of the total ai r and steam to the bed 1 2. The remainder enters by way of line 20 and grid 1 8. Typically, the flu id bed has a temperature of 1 800F-2000F and the temperature in the region of the passage is about 2000F-2200F.

[Para 43] The localized higher temperatu res in the region of passage 22 cause the ash particles withi n the passage 22 to become sticky. As a consequence, the ash particles as they stri ke each other g radually agglomerate. When they reach a sufficient size and weight, the velocity of air-steam stream entering through the venturi orifice 24 is insufficient to keep the agglomerated particles in a fluid or suspended state. They pass downwardly through the orifice 24 into withdrawal line 30.

[Para 44] The velocity of the inlet gases through the venturi throat 24 may be high compared to the gas velocity at distribution grid 1 8. This high velocity stream, as mentioned previously, forms a jet or a spout giving rise to a violent and rapid circulation of solids in the zone of the passage 22. The gases passing through the orifice 24 may also contain a higher percentage of the oxident than those gases passing through the distribution grid 1 8. Thereby, as previously explained, a higher temperature is generated in the zone of the passage 22 and in the middle, but not entirely through the fluidized bed 1 2.

[Para 45] The present invention has been described mainly by reference to coal gasification. It should be appreciated, that the present invention is not limited to coal gasification, but rather, finds utility in many applications in which fluidizing of particles is desired.