Device and process for converting coal particles to a fuel gas

Description

[0001] The present invention relates to a device for converting carbonaceous particles such as crushed coal to a fuel gas comprising an upstanding elongated reactor having an upstanding reactor wall and a supporting member for supporting a fluidized bed and for distributing gases in the bottom portion of the reactor a discharge duct for withdrawing ash from the bottom portion and means for forming a mixture of gas and carbonaceous particles and for introducing said mixture via at least one duct into the bottom portion of the reactor at a predetermined velocity.

[0002] In the gasification of coal, it is well known that certain coals, particularly bituminous coal, become plastic and sticky under certain temperature conditions. In this plastic state, the coal particles can cake or agglomerate. This caking or agglomeration interferes with gasification and consequently must be substantially reduced or eliminated for an efficient gasification process.

[0003] Various methods to reduce agglomeration are known. As disclosed in United States Patent 2,805,189, the coal particles can be mildly oxidized with a gas containing oxygen, such as air. This method has the disadvantages of generating large amounts of heat that are difficult to recover and converting a portion of , the carbon value of the coal to carbon dioxide. In addition, the gaseous byproducts of the pretreatment step contain valuable hydrocarbon liquids which are lost, unless separately treated, from the product gases. This, however, substantially increases the capital expenditure for the gasifier unit.

[0004] Another method of pretreating coal is illustrated in United States Patent 2,582,712. A single volume of raw pulverized feed coal is admixed with 15 to 30 volumes of hot circulating residue recovered from the gasification reaction. This rapidly preheats the coal to gasification temperatures and, therefore, substantially avoids coal agglomeration. However, the circulation of high volumes of abrasive solid particulate matter has the obvious disadvantages of equipment wear and expense.

[0005] A method of introducing coal directly into a fluidized bed is illustrated in U.S. Patent 3,927,996. In this method, coal is entrained in a carrier gas and, injected at a superficial gas velocity of 5-300 meter per second at an acute angle down into the upper or cooler portion of the fluid bed. The velocity of the carrier gas is adjusted in response to the amount of fines carried overheat to control fines loss. This adjustment of carrier gas velocity and the preferred introduction of the coal into the upper portion of the bed at a high velocity are not conductive to the efficient conversion of coal to a fuel gas and the maintenance of a stable fluidized bed in the reactor.

[0006] Finally, there is illustrated in U.S. Patent 2,577,632 a method for introducing coal particles into a fluidized bed from a single injection point directly into the center of a fluidized bed at a slow velocity. This method of introduction does not include high velocity injection and, as a result, increases the tendency for the coal to agglomerate in the fluidized bed.

[0007] According the invention the supporting and gas distribution member includes a plurality of portions sloping downwardly to a plurality of venturi-type ash withdrawal throats uniformly positioned in said supporting and gas distribution member and associated with said sloping portions, and a plurality of inlet duct equally spaced around the perimeter of the reactor adjacent the bottom of the fluid bed in the supporting and gas distribution member or the sidewalls of the reactor for high velocity introduction of a mixture of carbonaceous particles in a gas stream.

[0008] The present invention provides an improved apparatus and method for feeding carbonaceous particles, such as coal, to a fluidized bed gasifier, particularly a single stage fluid bed gasifier maintained in an elongated reactor for the conversion of the material, i.e. coal to a fuel gas. Specifically, the present invention substantially eliminates the necessity of pretreatment of the carbonaceous particles into the fluidized bed, to avoid agglomeration therein.

[0009] The invention relates also to a process for converting carbonaceous particles into a fuel gas utilizing an upstanding elongated reactor having a reactor wall, a fluidized bed in the bottom portion thereof maintained at conditions to convert said carbonaceous particles to fuel gas and means for withdrawing ash from the bottom portion of the reactor, in which a gas stream in admixture with said carbonaceous particles is introduced into the bottom of said fluidized bed, whereby that gas stream in admixture with said carbonaceous particles is introduced into said bed at a predetermined high velocity at a plurality of spaced-apart around the perimeter of the reactor and a substantial distance away from said withdrawal means, and said fluidized bed is operated at a temperature within the range of about 1260-1370⁰K. Thereby the carbonaceous particles are shock heated to a temperature sufficient to render the carbonaceous particles non-caking within the bed. This effectively "pre- treats" the coal particles and obviates the need for a separate or external pretreatment zone. More particularly, the high velocity gas stream in admixture with said carbonaceous particles is passed either substantially directly upwards into the bottom of the fluidized bed or passed directly into the bottom of said fluidized bed in a plane normal to the vertical axis of the elongated reactor. Either of these methods of introduction rapidly and effectively shock heats the coal while maintaining a stable fluidized bed having a relatively uniform residue time distributions therein.

[0010] Various objects, features and advantages of the present invention are apparent from the following description of a preferred embodiment.

[0011] A preferred embodiment of the present invention will be described in detail with reference to the attached drawings.

FIGURE 1 is a schematic diagram of a fluidized bed gasification system incorporating a preferred embodiment of the present invention;

FIGURE 2 is a top view of the gas distribution grid shown in Figure 1.

FIGURE 3 is an enlarged cross-sectional view of the bottom portion of the gasifier shown in Figure 1; and Figure 4 is an enlarged partial cross-sectional view of the bottom portion of a fluidized bed reactor incorporating a second preferred embodiment of the present invention.

[0012] Referring to Figure 1, a device 1 for the conversion of caking coal particles in a single stage into a fuel gas is schematically illustrated. The device 1 includes an elongated gasification reactor 12 having a vertical reactor wall 14 and a fluidized bed 16 of coal particles in the lower portion thereof. The bulk of the fluidized bed 16 is non-caking, charred material.

[0013] The device 1 also includes as a preferred embodiment of the present invention, a coal feed system 17, a gas injection system 18, an ash withdrawal system 20 and a fuel gas withdrawal system 22. The coal feed system 17 delivers freshly crushed coal particles to the reactor 12 which is maintained under predetermined conventional gasification conditions. The coal particles are gasified within reactor 12 to produce gas which evolves from the fluidized bed 16 into the upper, free portion of the gasification reactor 12.

[0014] The gasification reactor 12 preferably operates at a pressure of about 350 to 2750 k Pa and a fluidized bed temperature of about 1260 to 1370°K. A preferred specific pressure and temperature are 2400 k Pa and 1310° K. The fuel gas produced therein has a heating value of about 3700 to 11200 k J/nm³,

[0015] Referring now to Figures 1-3 the reactor 12 has positioned in the bottom, lower portion thereof a substantially horizontal gas distribution grid 24 to support the fluidized bed 16. Grid 24 is positioned substantially normal to the axis of the reactor. The fluidization and reactant gases, preferably steam and an oxygen-containing gas, such as air, enter reactor 12 through openings, selectively shown and designated as openings 26, in the gas distribution grid 24, via the gas injection system 18.

[0016] The ash withdrawal apparatus 20 includes a series of venturi-type throats 28, uniformly positioned on the gas distribution grid 24 in the center of the reactor to service equal cross-sectional areas of the reactor 12. The number of venturi-type throats 28 depends primarily upon the size of the reactor 12 and the coal being treated. The three throat system illustrated is simply illustrative.

[0017] The gas distribution grid 24 slopes toward the venturi-type throats 28. As shown, each . venturi-type throat 28 is associated with four sloping portions, selectively designated 30, of the gas distribution grid 24. Preferably, the gas distribution grid 24 defines substantially conical sections, tapered towards each venturi-type throat 28. The ash withdrawal apparatus 20 is fully described in United States Letters Patents Nos. 2,906,608 and 3,935,825, the teachings of which are incorporated herein by reference. As disclosed therein, coal ash is separated from the fluidized bed 16 with a minimum of carbon loss and fluidizing gases enter the reactor 12 through the venturi-type throats 28.

[0018] The fuel gas withdrawal apparatus 22 includes a pair of cyclones 32A, 32B for withdrawal of the fuel gas from the reactor 12 and separation of finely divided coal and dust particles. The coal and dust particles are recycled to the fluidized bed 16 via the venturi-type throats 28 to recover the carbon value therein. This system in combination with the position of the coal inlets at the bottom of the fluidized bed provides efficient recovery of fines and obviates the need to specifically control the velocity of the incoming coal particles to minimize the loss of coal fines. The raw gaseous fuel is removed from the cyclone 32B via a conduit 34 for processing well known in the art.

[0019] The coal feed apparatus 17 includes a gaseous stream generator 38, a coal hopper 40 for receipt and pressurization of coal particles, and an inlet 42 to the reactor 12. The gaseous stream generator 38 produces a gaseous stream, having predetermined high velocity, in a carrier vessel 44. Preferably, the predetermined high velocity is 15 to 90 meters per second. In this embodiment of the present invention, the gaseous stream contains steam and air or oxygen.

[0020] From the lock hopper 40, the coal particles are dropped through a valve 46 into the carrier vessel 44 and entrained in the gaseous stream to produce a gas particulate mixture. In the preferred embodiment shown in Figures 1-3, the gaseous stream in the carrier vessel 44 transports the coal particles to the inlet 42 for injection into the bottom of the fluidized bed 16, at the predetermined high velocity.

[0021] That is, the coal particles are admixed with the gaseous stream, preferably a steam-oxygen stream, and the resulting gas particulate mixture is pneumatically injected upwardly into the fluidized bed 16. Preferably, one to twenty pounds of coal are admixed per pound of gas in the stream. As shown in Figure 2, there are two inlets 42 associated with each venturi-type throat 28 to provide six points of introduction of the coal particles into the bed around the inside perimeter of the reactor. The exact number of the introduction points around the inside of the reactor is a function of reactor diameter. In a typical commercial embodiment, at least three introduction points are provided.

[0022] Once injected, the carrier gases, i.e. steam and air or oxygen and the fresh coal, are distributed in the fluidized bed 16 without substantially altering the stability of or the residence time distribution of the bed and to become part of the total gasifying agent in the reactor 12. The quantity of oxygen in the carrier gas is limited, preferably 3 to 10 parts oxygen per 100 parts steam, to substantially avoid preignition of the coal particles in the vicinity of the gasifier 12. The small quantity of oxygen facilitates oxidation of the coal particles.

[0023] Referring again to Figure 3, the inlet 42 includes a port 50 and a transport pipe 52, which communicates with the carrier vessel 44. The port 50 widens preferably conically in the direction of gas flow, such that inadvertent agglomeration of coal particles in the bed will not block the inlet 42.

[0024] To further avoid preheating and agglomeration, the coal feed apparatus 17 includes a water jacket for maintaining a sufficiently low coal particle temperature prior to entry into the reactor 12. As best shown in Figure 3, the water jacket 54 substantially insulates the portion of the coal feed apparatus 17 within the wall 14, i.e. the transport pipe 52. The water jacket 54 substantially avoids premature heating due to conduction or radiation from the fluidized bed 16. The water jacket 54 preferably maintains the coal particle temperature below approximately 600° K.

[0025] The inlets 42 are positioned in close proximity to or near the reactor wall 14 and substantially away from the associated venturi-type throat 28 of the ash withdrawal apparatus 20 to facilitate mixing of the coal particles within the fluidized bed 16 without altering the stability of the bed and the residence time distribution of the coal in the bed. Preferably, the inlets 42 are spaced as far as possible from the throats 28. In this preferred embodiment, i.e. an ash agglomerating reactor 12, the solids in the fluidized bed 16 generally move downwardly along the reactor wall 14 and upwardly above the venturi-type throats 28. The flow or control between the fluidized bed 16 against the fresh coal feed results in rapid mixing thereof. This placement of the inlets 42 also substantially avoids interference with the operation of the ash withdrawal apparatus 20 by the injected gas particulate mixture.

[0026] Referring to Figure 4, a second preferred embodiment of the present invention is shown wherein the gas particulate mixture is injected through the reactor wall 14 substantially tangentially into the side of the fluidized bed 16 at the bottom thereof. As shown, the inlets 42 are preferably positioned substantially tangentially to the reactor wall 14 to provide a plane substantially normal to the axis of the reactor, such that the gas particulate mixture is injected along the interior surface thereof. The respective flow directions of the fluidized bed 16 and gas particulate mixture are, in this embodiment, substantially perpendicular to facilitate mixing thereof. Injection in this embodiment also occurs substantially away from the ash withdrawal apparatus 20 to avoid interference therewith.

[0027] Injection of coal particles in accordance with the present invention substantially avoids agglomeration and maintains the stability of the fluidized bed. Entering the fluidized bed 16 at the predetermined high velocity of 15 to 90 meters per second, the coal particles are shock heated to a temperature above the plastic temperature range. That is, the coal particles pass rapidly through the plastic, caking state to a charred non-caking state. Further, the particles mix rapidly with the non-caking fluidized bed 16 and the resulting dilution separates the coal particles during the short transition period.

[0028] Heating the coal particles under the fluidized bed conditions of high temperature present in the bottom of the bed and a gaseous environment causes the release of volatile matter, including tars and oils. The rapid mixing of the fresh coal particles and charred material of the fluidized bed 16 maintains the volatile matter in the fluidized bed 16, such that thermal cracking occurs. That is, the tars and oils are reduced to carbon and low molecular weight gas, substantially eliminating the tars and oils from the gas effluent of the fluidized bed 16. For this reason, it is important that the coal be injected as close as possible to the bottom of the fluidized bed to maximize the production of fuel gas.

[0029] The shock heating of the coal particles also produces fines due to the explosion of the coal particles in a "popcorn" fashion. The fines are captured by the upper portion of the bed, and those particles which are carried out of the bed with product gas are captured by cyclones 32A, 328 and recycled to the fluidized bed 16 through the venturi-type throats 28. There the fines are rapidly gasified, adhering to the denser ash agglomerates which are withdrawn by the ash withdrawal apparatus 20.

[0030] Preferred embodiments of the present invention have been disclosed and described herein. It is to be understood, however, that various changes and modifications can be made without departing from the true scope and spirit of the invention, as set forth and defined in the following claims.

Claims

1. A device for converting carbonaceous particles such as crushed coal to a fuel gas comprising an upstanding elongated reactor having an upstanding reactor wall and a supporting member for supporting a fluidized bed and for distributing gases in the bottom portion of the reactor, a discharge duct for withdrawing ash from the bottom portion and means for forming a mixture of gas and carbonaceous particles and for introducing said mixture via at least one duct into the bottom portion of the reactor at a predetermined velocity, characterised in, that the supporting and gas distribution member includes a plurality of portions sloping downwardly to a plurality of venturi-type ash withdrawal throats uniformly positioned in said supporting and gas distribution member and associated with said sloping portions, and a plurality of inlet ducts equally spaced around the perimeter of the reactor adjacent the bottom of the fluid bed in the supporting and gas distribution member or the sidewalls of the reactor for high velocity introduction of a mixture of carbonaceous particles in a gas stream.

2. A device as claimed in claim 1, characterised in, that said inlet ducts are positioned to direct said particulate mixture through said supporting member for supporting the fluidized bed.

3. A device as claimed in claim 1 or 2, characterised in, that said inlet ducts direct said particulate mixture along the interior surface of said reactor wall in a plane normal to the vertical axis of the elongated reactor.

4. A reactor as claimed in any of the preceding claims, characterised in, that at least three inlet ducts have been provided around the perimeter of the reactor.

5. Process for converting carbonaceous particles into a fuel gas utilizing an upstanding elongated reactor having a reactor wall, a fluidized bed in the bottom portion thereof maintained at conditions to convert said carbonaceous particles to fuel gas and means for withdrawing ash from the bottom portion of the reactor, in which a gas stream in admixture with said carbonaceous particles is introduced into the bottom of said fluidized bed, characterised in, that said gas stream in admixture with said carbonaceous particles is introduced into said bed at a predetermined high velocity at a plurality of spaced-apart points around the perimeter of the reactor and a substantial distance away from said withdrawal means, and said fluidized bed is operated at a temperature within the range of about 1260-1370⁰K.

6. Process according to claim 5, characterised in, that the high velocity gas stream in admixture with said carbonaceous particles is passed substantially directly upwards into the bottom of said fluidized bed.

7. Process according to claim 5, characterised in, that the high velocity gas stream in admixture with said carbonaceous particles is passed directly into the bottom of said fluidized bed in a plane normal to the vertical axis of the elongated reactor.

8. Process according to any of claims 5-7, characterised in, that said high velocity gas stream in admixture with said carbonaceous particles is introduced into said bed in at least three spaced-apart points.

9. Process according to any of claims 5-8, characterised in, that said high velocity gas stream in admixture with said carbonaceous particles is introduced at a velocity of 15 to 90 m/s.

Revendications

1. Dispositif pour convertir des particules charbonneuses, par exemple, charbon broyé en carburant gazeux comprenant un réactor allongé en haut avec une paroi d'aplomb et un organe de support pour supporter un lit fluidisé et pour distribuer des gaz dans la partie inférieure du réactor, et comprenant un conduit de décharge pour retirer les cendres de la partie inférieure et des moyens pour former un mélange de gaz et particules charbonneuses et pour introduire ce mélange à travers, au moins, un conduit dans la partie inférieure du réactor à une vélocité prédéterminée caractérisé en ce que l'organe de support et de distribution du gaz comporte un nombre de secteurs inclinés en bas vers un nombre de gorges en forme de venturis pour retirer les cendres uniformément disposées dans le dit organe de support et de distribution du gaz et associées aux dits secteurs inclinés et en ce qu'un nombre de conduits d'introduction sont prévus à distances égales autour le périmètre du réactor auprès du fond du lit fluidisé dans l'organe de support et de distribution du gaz ou dans la paroi latérale du réactor pour l'introduction à haute vélocité d'un mélange de particules charbonneuses dans le courant de gaz.

2. Dispositif selon la revendication 1 caractérisé en ce que ces conduits d'entrée sont disposés à diriger le mélange de particules à travers l'organe de support pour supporter le lit fluidisé.

3. Dispositif selon la revendication 1 ou 2 caractérisé en ce que les conduits d'entrée dirigent le mélange de particules le long de la face intérieure de la paroi du réactor dans un plan à angle droit à l'axe vertical du réactor allongé.

4. Réactor selon l'une quelconque des revendications précédentes caractérisé en ce qu'au moins trois conduits d'entrée sont prévus autour du périmètre du réactor.

5. Procédé de conversion de particules charbonneuses en un carburant gazeux utilisant un réactor allongé étant debout et ayant une paroi de réactor et un lit fluidisé dans une partie de fond du réactor maintenu dans des conditions adaptées à convertir les particules charbonneuses en un carburant gazeux et moyens pour retirer des cendres de la partie de fond du réactor, un courant de gaz mélangé avec les particules charbonneuses étant introduit dans le fond du lit fluidisé caractérisé en ce que le courant de gaz mélangé avec les particules charbonneuses est introduit dans le lit à une vélocité prédéterminée à un nombre de points écartés autour du périmètre du réactor et à une distance appréciable des moyens à retirer les cendres et en ce que le lit fluidisé est opéré à une température comprise entre environ 1260 et 1370° K.

6. Procédé selon la revendication 5 caractérisé en ce que le courant de gaz à haute vélocité mélangé avec les particules charbonneuses est passé pratiquement verticalement au fond du lit fluidisé.

7. Procédé selon la revendication 5 caractérisé en ce que le courant de gaz à haute vélocité mélangé avec les particules charbonneuses est directement passé au fond du lit fluidisé dans un plan à angle droit à l'axe vertical du réactor allongé.

8. Procédé selon l'une quelconque des revendications 5 à 7 caractérisé en ce que le courant de gaz à haute vélocité mélangé avec les particules charbonneuses est introduit dans le lit à, au moins, trois points à distance l'un de l'autre.

9. Procédé selon l'une quelconque des revendications 5 à 8 caractérisé en ce que le courant de gaz à haute vélocité mélangé avec les particules charbonneuses est introduit à une vélocité de 15 à 90 m/s.

Ansprüche

1. Vorrichtung zur Umwandlung kohlenstoffhaltiger Teilchen z.B. zerkleinerter Kohle in Brennstoffgas mit einem aufrechtstehenden, langgestreckten Reaktor mit einer aufrechtstehenden Reaktorwand und einem Stützorgan zum abstützen eines Wirbelbetts und zum Verteilen von Gasen im Bodenteil des Reaktors, mit einer Entlastungskeitung zum Wegziehen von Asche aus dem Bodenteil und mit Mitteln zur Bildung eines Gemisches aus Gas und Kohlenstoffteilchen und zum Einführen dieses Gemisches durch mindestens eine Leitung in den Bodenteil des Reaktors mit einer vorherbestimmten Geschwindigkeit dadurch gekennzeichnet dass das Stütz- und Gasverteilungsorgan eine Anzahl van Sektionen enthält, die schräg nach unten in Richtung auf eine Anzahl venturiartiger Aschenentziehungskehlen verlaufen, die gleichmässig im Stütz- und Gasverteilungsorgan untergebracht sind und den schräg verlaufenden Sektionen zugehören, wobei eine Anzahl von Einlassleitungen gleichmässig verteilt um den Umfang des Reaktors nahe dem Boden des Wirbelbetts im Stütz- und Gasverteilungsorgan oder den Seitenwänden des Reaktors vorgesehen sind für die Einführung eines Gemisches aus Kohlenstoffhaltigen Teilchen in eine Gasströmung mit hoher Geschwindigkeit.

2. Vorrichtung nach Anspruch 1 dadurch gekennzeichnet, dass die Einlassleitungen angeordnet sind, um das Teilchengemisch durch das Stützorgan zum Abstützen des Wirbelbetts zu richten.

3. Vorrichtung nach Anspruch 1 oder 2 dadurch gekennzeichnet, dass die Einlassleitungen das Teilchengemisch längs der Innenwand der Reaktorwand in einer zur veritkalen Achse des langgestrecken Reaktors senkrechten Ebene führen.

4. Reaktor nach einem der vorhergehenden Ansprüche dadurch gekennzeichnet, dass mindestens drei Einlassleitungen um den Umfang des Reaktors vorgesehen sind.

5. Verfahren zur Umwandlung kohlenstoffhaltiger Teilchen in ein Brennstoffgas durch Verwendung eines aufrechtstehenden, langgestreckten Reaktors mit einer Reaktorwand, einem Wirbelbett im Bodenteil dessen Fähigkeit zur Umwandlung der kohlenstoffhaltigen Teilchen in Brennstoffgas aufrechterhalten wird, und Mitteln zum Wegziehen von Asche aus dem Bodenteil des Reaktors, wobei eine mit den kohlenstoffhaltigen Teilchen gemischte Gasströmung in den boden des Wirbelbetts eingefürht wird, dadurch gekennzeichnet, dass die mit den kohlenstoffhaltigen Teilchen gemischte Gasströmung in das Bett mit einer vorherbestimmten, hohen Geschwindigkeit an einer Zahl voneinander entfernter Stellen um den Umfang des Reaktors und in einem grossen Abstand van den Wegziehmitteln eingeführt wird und dass das Wirbelbett bei einer Temperatur von etwa 1260 bis 1370° K wirksam ist.

6. Verfahren nach Anspruch 5 dadurch gekennzeichnet, dass die mit den kohlenstoffhaltigen Teilchen gemischte Gasströmung hoher Geschwindigkeit nahezu unmittelbar aufwärts in den Boden des Wirbelbetts geführt wird.

7. Verfahren nach Anspruch 5 dadurch gekennzeichnet, dass die mit den kohlenstoffhaltigen Teilchen gemischte Gasströmung hoher Geschwindigkeit unmittelbar in den Boden des Wirbelbetts in einer zur vertikalen Achse des langgestreckten Reaktors senkrechten Ebene geführt wird.

8. Verfahren nach einem der Ansprüche 5 bis 7 dadurch gekennzeichnet, dass die mit den kohlenstoffhaltigen Teilchen gemischte Gasströmung hoher Geschwindigkeit an mindestens drei voneinander entfernten Stellen in das Bett eingeführt wird.

9. Verfahren nach einem der Ansprüche 5 bis 8 dadurch gekennzeichnet, dass die mit den kohlenstoffhaltigen Teilchen gemischte Gasströmung hoher Geschwindigkeit mit einer Geschwindigkeit von 15 bis 90 m/s eingeführt wird.

Drawing