Apparatus and methods for gasification

Abstract

The invention relates to a circulating fluidized bed (CFB) reactor for thermal processing of added carbonaceous material, the carbonaceous material normally comprises organic material or organic material mixed with inorganic material such as in straw or other vegetable waste, manure, household rubbish, dried wastewater, dried animal remains or other dried carbonaceous waste products. The invention also relates to a process for manufacturing a combustible product gas having a heating value around 4-8 MJ/Nm3 from such a carbonaceous material by subjecting the carbonaceous material to pyrolysis in one process step and oxidation in two subsequent process steps. A circulating fluidized bed (CFB) reactor according to the invention comprises a primary char gasification chamber ( 5 ) and an intermediate char gasification chamber ( 9 ) typically provided with a fluidized bed wherein the height (h 10 ) of the second fluidized bed ( 10 ) in the intermediate char gasification chamber is larger than the height (hn) of the first fluidized bed ( 11 ) in the primary char gasification chamber ( 5 ).

1 . A circulating fluidized bed (CFB) reactor for thermal processing of added carbonaceous material, comprising:
 a first pyrolysis reaction chamber ( 1 ) wherein added carbonaceous material is pyrolysed due to contact with hot recirculating particles, which first reaction chamber ( 1 ) has an inlet ( 1   a ) for carbonaceous material, an inlet ( 1   c ) for fluidizing gas, and an outlet ( 1   b ) for product gas in the upper part of the first reaction chamber ( 1 ) which product gas carries carbon containing char particles and recirculating inert particles,   one or more separators ( 4 ) having an inlet ( 4   a ) through which the product gas carrying particles from the first reaction chamber ( 1 ) is received, and an outlet ( 4   b ) through which the particles leave each separator and enter into a primary char gasification chamber ( 5 ) via one or more conduits ( 14 ),   said primary char gasification chamber ( 5 ) comprising an inlet ( 5   a ) for pyrolysed and recirculating particles, an inlet ( 5   b ) for fluidizing gas ( 6 ) in the lower part of the primary char gasification chamber ( 5 ), an outlet ( 5   d ) in the upper part of the primary char gasification chamber ( 5 ) for produced gas and an outlet ( 5   c ) for particles in the lower part of the primary char gasification chamber ( 5 ) opening into a particle return conduit ( 7 ) which particle return conduit ( 7 ) opens into an intermediate char gasification chamber ( 9 ), and   said intermediate char gasification chamber ( 9 ) comprising an inlet ( 9   a ) for particles from the primary char gasification chamber ( 5 ) and an inlet ( 9   b ) for a fluidizing gas e.g. gas containing O 2 /H 2 O in the lower part of the reactor ( 9 ), and further comprising an outlet ( 9   c ) for produced gas carrying particles from the upper part of the chamber ( 9 ) which outlet ( 9   c ) opens into a conduit ( 8 ) having at least one outlet to the lower part of the first reaction chamber ( 1 ) and which provides fluidizing gas to the first reaction chamber ( 1 ).   
     
     
         2 . A CFB reactor according to  claim 1 , wherein the inlet ( 1   c ) for fluidizing gas from the intermediate char gasification chamber ( 9 ) is positioned below i.e. upstream the inlet ( 1   d ) for gas from the fluidized bed primary char gasification chamber ( 5 ). 
     
     
         3 . A CFB reactor according to  claim 1 , wherein an outlet for ashes is provided in one or more of the separators ( 4 ) and/or in the bottom of the intermediate char gasification chamber ( 9 ). 
     
     
         4 . A CFB reactor according to  claim 1 , wherein the cross-sectional area of the intermediate char gasification reactor is at least 50% smaller than the cross-sectional area of the primary char gasification chamber ( 5 ). 
     
     
         5 . A CFB reactor according to  claim 1 , wherein the inlet ( 1   c ) for fluidizing gas from the intermediate char gasification chamber ( 9 ) is positioned below i.e. upstream all inlets ( 1   a ) for carbonaceous material into the pyrolysis reaction chamber ( 1 ). 
     
     
         6 . A CFB reactor according to  claim 1 , wherein the reactor is configured such that the top of the intermediate char gasification chamber is placed at a level that is intermediate between the levels of the top and bottom of the primary char gasification chamber. 
     
     
         7 . A CFB reactor according to  claim 1  wherein the reactor is configured such that the top of the intermediate char gasification chamber ( 9 ) is placed at a level that is higher than that level of the primary char gasification chamber ( 5 ) at which the majority of fluidizing gas is introduced. 
     
     
         8 . A CFB reactor according to  claim 1 , wherein the reactor is configured such that greater than 50% of the volume of the intermediate char gasification chamber is placed at a level beneath the bottom of the primary char gasification chamber and beneath the bottom of the pyrolysis chamber. 
     
     
         9 . A CFB reactor according to  claim 1 , wherein during operation a first fluidized bed ( 11 ) of particles is provided in the primary char gasification chamber ( 5 ), the volume of said first fluidized bed ( 11 ) is defined as the volume present above the level of adding the fluidizing gas at the bottom of the fluidized bed and up to the surface of the same fluidized bed, above the volume of the first fluidized bed ( 11 ) is a lower density freeboard volume ( 13 ) containing gas and entrained fine particles, 
     
     
         10 . A CFB reactor according to  claim 1 , wherein during operation particles are transported through the intermediate char gasification chamber ( 9 ) forming a second fluidized bed ( 10 ) of particles where the volume of said second fluidized bed ( 10 ) is defined as the volume above the level of adding the fluidizing gas at the bottom of the fluidized bed and up to the center of the outlet ( 9   c ) for produced gas and particles in the upper part of the intermediate char gasification chamber wherein the height (h 10 ) of the second fluidized bed ( 10 ) in the intermediate char gasification chamber ( 9 ) is larger than the height (h 11 ) of the first fluidized bed ( 11 ) in the primary char gasification chamber ( 5 ). 
     
     
         11 . A CFB reactor according to  claim 1 , wherein during operation particles are transported through the intermediate char gasification chamber ( 9 ) forming a second fluidized bed ( 10 ) of particles where the volume of said second fluidized bed ( 10 ) is defined as the volume above the level of adding the fluidizing gas at the bottom of the fluidized bed and up to the center of the outlet ( 9   c ) for produced gas and particles in the upper part of the intermediate char gasification chamber wherein the pressure difference between the bottom and top of the primary char gasification chamber ( 5 ) is smaller than between the bottom and top of the intermediate char gasification chamber ( 9 ). 
     
     
         12 . A CFB reactor according to  claim 1  further comprising nozzles through which fluidizing gas may be introduced located within the bottom 15% of the pyrolysis chamber. 
     
     
         13 . A process for manufacturing a product gas having a desirable heating value from a carbonaceous material, comprising
 a first process step where the carbonaceous material is introduced into a first pyrolysis reaction chamber in which are flowing a fluidization gas having a low O 2  content and hot inert recirculating particles, and in which the temperature T 1  is between 400 and 850° C., producing a product gas which carries partly converted particles i.e. char and recirculating bed particles out of the first process step,   a second process step where the product gas from the first step is separated from the recirculating and partly converted char particles, where the product gas exits the process while the separated char particles and bed particles enter a third process step   a third process step, conducted in a primary char reactor, where carbonaceous material remaining in the separated char is subjected to a decomposing oxidation treatment in a fluidized bed at a temperature T 2  between 600 and 850° C., producing a product gas which is withdrawn from the upper part of the primary char reactor and which product gas enters the first process step, together with a fraction of fine entrained particles, while bed particles from the lower part of the primary char reactor are transferred to a fourth process step, and   a fourth process step, where remaining char is subjected to a second decomposing oxidation treatment in a fluidized bed at a temperature T 3  between 600 and 850° C., producing a product gas which, together with recirculating particles, exits the fourth step and enters the first process step as a fluidization gas,   
       wherein the gas retention time (t 10 ) in the fluidized bed in the fourth process step is larger than the gas retention time (t 11 ) in the fluidized bed of the third process step (t 10 >t 11 ). 
     
     
         14 . A process according to  claim 13 , wherein t 10 >1.2t 11 , and preferably >1.5t 11 . 
     
     
         15 . A process according to  claim 13 , wherein the temperature T 2  of the third process step and the temperature T 3  of the fourth process step differs with less than 10° C., i.e. T 3 −T 2 <10° C., normally T 3 −T 2 <5° C. 
     
     
         16 . A process according to  claim 13 , wherein the temperature T 1  is between 400 and 800° C., normally between 625 and 775° C. 
     
     
         17 . A process according to  claim 13 , wherein the temperature T 2  is between 650 and 800° C., normally between 700 and 800° C. 
     
     
         18 . A process according to  claim 13 , wherein the temperature in the first process step is controlled by regulating the flow of fluidization gas into the fourth process step which determines the flow of fluidization gas and recirculating particles into the first process step. 
     
     
         19 . A process according to  claim 13 , wherein at least 95 wt % of the bed material in the third process step is inert particle material while less than 5 wt % of the material is remaining carbonaceous material. 
     
     
         20 . A process according to  claim 13 , wherein the carbonaceous material comprises any one or more of cereal straw, rice straw, related grain cleaning waste streams; residues from crops including sugar cane, sorghum, beets, maize, potato, nuts, tea, cotton, wine, olive and oil palms; Algaes—eg. including sea weed; energy crops including grasses, including eg. Miscantus; residues from short rotation forest crops based on fast growing wood including Willow and Poplar; Crops having an elevated content of salt due to e.g. growth in proximity with salty water or having other contact with salty water; residues from meat production industry including meat and bone meal; animal manure including dewatered manure slurry; Municipal and industrial organic waste, including organic fractions derived from such streams; sewage sludge; or energy containing residues such as fiber and lignin products from processing wood and raw organic products. 
     
     
         21 . A process according to  claim 13 , wherein during operation the pressure difference between the bottom and top of the primary char gasification chamber ( 5 ) is smaller than between the bottom and top of the intermediate char gasification chamber ( 9 ).