METHOD AND APPARATUS FOR GASIFYING CARBONACEOUS MATERIAL

Abstract: Method of gasifying carbonaceous material in two phases in a circulating fluidized bed reactor. Carbonaceous material is supplied to the first zone (2) of a gasifying reactor (1) and is gasified there by means of a gasifying agent and hot particles separated from the gas exhausted from the reactor. The non-gasified material carried by the gas from the first zone is arranged to contact the gasifying agent (14) by supplying it to a layer of solids running down in a spouting type fluidized bed in the second zone of the gasifying reactor, in which zone a higher temperature is maintained than in the first zone.

Description: METHOD AND APPARATUS FOR GASIFYING CARBONACEOUS MATERIAL Technical field: The present invention relates to a method for gasification of carbonaceous material in two phases in a circulating fluidized bed reactor in which solid particles contained in gases exhausted from the reactor are separated and recycled to the reactor. The invention also relates to an apparatus for carrying out the method. It is an object of the invention to provide a method and an apparatus for producing gas of low tar content by utilizing fluidized bed technology for gasification of a carbonaceous material such as coal, brown coal or peat. Prior art: Two-staged gasification is . known technology. The so called HT gasifier (Hochtemperatur-Winkler) could be mentioned as an example. In an apparatus of this kind the gasifying agent of the second phase is, however, supplied "unselected" directly to the gasified mixture which, in addition to coal and tarry substances, contains gases (hydrogen, carbon monoxide, methane) which are the desired end products of the gasification process. Oxygen then reacts primarily with these gaseous substances although a reaction with the coal would be advantagous for the product of the gasification. Contact of the coal and the supplied aqueous steam also decreases which results in an incomplete coal conversion and low grade gas. British patent specification number 1506729 discloses a method of gasifying carbonaceous material in a circulating fluidized bed reactor which is devided into two parts and in which the carbonaceous material is supplied to the upper part of a gasification reactor. When the first stage of the gasification, for example pyrolyses of the volatiles, during which pyrolysis for example tarry substances build up, takes place in the upper part of the reactor, the tarry substances remain in the product gas. The amount of these tarry substances depends on the gasified material and the gasification temperature and it may, e.g. in case of coal, be small. The object of this prior method does not primarily seem to be to produce gas of low tar content either but to achieve an as good a coal coversion as possible. The primary object of the present invention, on the other hand, is to produce gas containing as little tar as possible. Thus the upper part of the reactor is used for removing tar by raising the temperature. An essential feature is that the temperature is increased by combusting coal and not gaseous components. To achieve this, a spouting type fluidized bed is used. Finnish patent specification number 62554 discloses a two- staged gasification method, in which the beginning of . the gasification process is carried out in the upper part of the reactor, as in the method of GB 1506729 mentioned above, and the tarry substances remain in the product σas. Disclosure of invention: The present invention is characterized in that gaseous material is supplied to a first zone of a gasifying reactor and is there gasified by a gasifying agent and hot particles separated from the gas, and that the remaining non-gasified material carried by the gas from the first zone is arranged to contact the gasifying agent by supplying the remaining non- gasified material to the solids running down in the spouting type fluidized bed of a second zone, the temperature of which is maintained higher than the temperature of the first zone. A "spouting type" reactor typically has an upward flow in the center and a downward flow of solid material at the periphery. An apparatus for carrying out the method of the present invention is characterized in that the inlet of the particles to be recycled to the reactor and the inlet of the carbonaceous material are located in the lower reactor; that the upper reactor comprises an upward widening portion; and that the inlet/inlets of the gasifying agent of the upper reactor is/are located close to the surface formed by the upward widening portion. In the method of the present invention the lower reactor is primarily used as a pyrolysis reactor for gasification of volatile particles. Gasification of the remaining coal and tar removal are carried out in a spouting type lower portion of the upper reactor in which lower portion the gas, which contains oxygen and is required for a raise of temperature and the gasification process, and aqueous steam are arranged to contact primarily coal by supplying them to the coal and other circulating material running down in the conical part of the zone. Breif Description of the Drawing: The invention is described further, by way of example, with reference to the attached drawing which is a schematic illustration of a fluidized bed reactor. Best Mode of Carrying out the Invention: The method of the present invention is based on the use of a reactor (1) of the type wherein solids circulate. The reactor is divided in two regions or zones which are herein referred to as a lower reactor 2 and an upper reactor 3. Between the reactor zones (2, 3) there is a throttle 4 in which the flow velocity of the gas increases thus preventing the circulating material from running from the upper reactor 3 to the lower reactor 2. A bottom portion 5 of the upper reactor is desiσr.ec " to create a fluidized bed of so called spouting type. This is realized by the widening of the cross section area of the reactor which decreases the velocity of the vertical flow. A bottom portion 6 of the widened portion is conical with an inclination of between 20 and 60 relative the horizontal. The cross sectional area in the upper portion of the upper reactor 3 is reduced to be equal to the cross sectional area of the lower reactor 2. The circulating materials carried by the gas (ash, residual coal, etc.) are separated from the gas in a cyclone separator 7 arranged downstream in the process after the upper reactor 3. From the separator 7 the separated material is returned through a return duct 8 and an inlet 9 down to the lower reactor. Carbonaceous material 10 to be gasified is supplied through an inlet 11 to the lower reactor 2 in which it is gasified at a low temperature, preferably 700 to 900 C, by means of the hot particles separated from the gas and by means of gasifying agent 13 supplied to the reactor through orifices 12 in a bottom plate. Oxygen-containing gas, such as air, and possibly steam is - used as the gasifying agent. The temperature of the gas is chosen so as to produce a low coal conversion in the gasification and gas of rather a high tar content. The amount of coal in the lower reactor is regulated by supplying, if required, steam with the oxygen-containing gas and by changing the gasifying temperature. The primary function of the lower reactor is to serve as a pyrolysis reactor for the gasifying substances contained in the carbonaceous material supplied to the reactor. Further, partial oxidation of the fuel to be gasified can also be carried out in the lower reactor. A mixture of fuel containing coal and tarry substances flows from the lower reactor through the throttle 4 to the upper reactor. The purpose of using a spouting type fluidized bed is to raise the reaction temperature to 900 to 1100 C by adding oxygen-containing gas and steam so as to cause the oxygen-containing gas and thesteam to react primarily with the coal and not with the gas. Thus a zone is created in the upper reactor in which zone the coal concentration of the gas is remarkably higher than the average. This kind of a fluidized bed typically has an upward flow in the center and a downward flow of solid material at the periphery. A layer of downwardly running solids builds up in the conical portion 6 at the bottom of the upper reactor. This layer is rich in coal. Oxygen-containing gas and steam 14 are supplied through inlets 15 to this layer of solid material running down along surface 16, whereby the gas and the steam react with the coal contained in the layer and thus raise the temperature as desired. The supply of steam causes an endothermic reaction which reduces the temperature and this must be compensated for by supplying the oxygen-containing gas. The use of steam, on the other hand, improves the gasification of coal. Removal of tar is based on the rise in temperature, i.e. thermal dis¬ integration. The following conditions are appropriate for the operation of the method and apparatus according to the invention. Flow velocity range of the gasifier: - lower reactor 3 to 10 m/s - throttle between the lower and the upper reactor 10 to 15 m/s - spouting portion of the upper reactor 1 to 4 m/s - upper portion of the upper reactor 4 to 12 m/s Pressure in the gasifier (absolute) 1 to 6 bar The invention is not to be limited to the embodiments described here but it can be modified and applied within the scope of protection defined by the appended claims.

Claims: Claims : 1. A method of gasifying carbonaceous material in two stages in a fluidized bed reactor, in which particles contained in gases exhausted from the reactor are separated and recycled to the reactor, characterized in that the carbonaceous material is supplied to a first zone of the gasifying fluidized bed reactor and is gasified there by means of a gasifying agent and hot particles previously separated from the exhausted gases; and that the remaining non-gasified material carried by gas from the first zone is caused to contact a gasifying agent by supplying it to the downwardly-running solids in a spouting type fluidized bed of a second zone in the gasifying reactor, in which zone a higher temperature is maintained than in the first zone. 2. A method as claimed .in claim 1, characterized in that the temperature in the first zone is 700 to 900 C. 3. A method as claimed in claim 1 or 2, characterized in that the temperature in the second zone is 900 to 1100 C. 4. A method as claimed in claim 1, 2 or 3, characterized in that the gasifying agent comprises oxygenous gas and aqueous steam. 5. A method as claimed in any of claims 1 to 4, characterized in that the velocity of the gas flowing from the first zone to the second zone is maintained high enough to prevent the solid material from running from the second zone to the first zone. 6. A method as claimed in any of claims 1 to 5, characterized in that the velocity of the gas in the first zone is 3 to 10 m/s. 7. A method as claimed in any of claims 1 to 6 , characterized in that the velocity of the gas in the spouting portion of the second zone is 1 to 4 m/s. 8. A method as claimed in claim 7, characterized in that the velocity of the gas in the inlet of the second zone is 10 to 15 m/s. 9. A fluidized bed reactor for gasifying carbonaceous material, comprising means (7) for separating particles entrained by the gas exhausted from the reactor; means (8) for recycling the separated particles to the reactor; a lower reactor (2) and an upper reactor (3) and means (inlets 11, 15) for inlet of gasifying agent into said reactors (2, 3) , characterized in that the inlets (9, 11) for the particles to be recycled to the reactor and for the carbonaceous material are located in the lower reactor (2) ; and in that the upper reactor (3) comprises a portion (6) which widens or increases in cross-section in an upward direction; and that the inlet/ inlets (15) for the gasifying agent in the upper reactor are located close to the surface (16) provided by the upwardly widening portion. 10. A fluidized bed reactor as claimed in claim 9, characterized in that the bottom (6) of the upper reactor (3) is conical. 11. A fluidized bed reactor as claimed in claim 10, characterized in that the inclination of the bottom (6) in relation to a horizontal level is between 20 and 60 . 12. A fluidized bed reactor as claimed in claim 9, characterized in that the inlet/inlets (15) for the gasifying agent in the upper reactor (3) are arranged to supply oxidizing gas downwards in the direction of the surface (16) of the upwards widening portion. 13. A fluidized bed reactor as claimed in any of claims 8 to 12, characterized in that the cross sectional area of the portion (4) connecting the upper reactor (3) to the lower reactor (2) is smaller than the cross sectional area of the lower reactor (2) . 14. A fluidized bed reactor as claimed in any of claims 1 to 13, characterized in in that the cross sectional area of the widened portion (5) of the. upper reactor (3) is larger than the cross sectional area of the lower reactor (2) .

Inventors: NIEMINEN JORMA, NIEMINEN, JORMA
Applicants: AHLSTROEM OY, A. AHLSTROM CORPORATION
Application year: 1987
Main classification: C10J3
IPC codes: C10J3