Treatment of granular solids in a fluidized bed with microwaves

Abstract

This invention relates to a method for the thermal treatment of granular solids in a fluidized bed ( 3, 3 a ) which is located in a fluidized-bed reactor ( 1, 1 a ), wherein microwave radiation is fed into the fluidized-bed reactor ( 1, 1 a ) through at least one wave guide ( 5 ), and to a corresponding plant. To improve the efficiency of the microwave irradiation, the irradiation angle of the microwaves is inclined by an angle of 10° to 50°, in particular 10° to 20°, with respect to the principal axis ( 11 ) of the fluidized-bed reactor ( 1, 1 a ).

1 . A method for thermal treating granular solids in a fluidized bed which is located in a fluidized-bed reactor, comprising feeding microwave radiation into the fluidized-bed reactor through at least one wave guide, inclining microwaves by an irradiation angle of 10° to 50° with respect to a principal axis of the fluidized-bed reactor.  
     
     
         2 . The method as claimed in  claim 1 , further comprising feeding a gas stream into the fluidized-bed reactor through the at least one wave guide.  
     
     
         3 . The method as claimed in  claim 2 , wherein the gas stream introduced through the at least one wave guide contains gases which react with the fluidized bed.  
     
     
         4 . The method as claimed in  claim 2  wherein the gas stream introduced through the at least one wave guide is additionally utilized for a fluidization of the fluidized bed.  
     
     
         5 . The method as claimed in  claim 2  wherein heat is additionally supplied to the fluidized bed by the introduced gas stream.  
     
     
         6 . The method as claimed in  claim 2  wherein the fluidized bed is cooled by the introduced gas stream.  
     
     
         7 . The method as claimed in  claim 2 , wherein by of introducing the gas stream into the at least one wave guide, solid deposits in the at least one wave guide are avoided.  
     
     
         8 . The method as claimed in  claim 2 , wherein the reactor comprises at least two fluidized-bed reactors, which are separated from each other by weirs or partitions such that solids can move as migrating fluidized-bed from one fluidized-bed reactor into the adjacent fluidized-bed reactor.  
     
     
         9 . The method as claimed in  claim 2 , comprising combining a microwave source with a secondary gassing of a ring conduit and that the at least one wave guide is simultaneously used for secondary gassing.  
     
     
         10 . The method as claimed in  claim 2 , wherein the microwave radiation has a frequency between 300 MHz and 30 GHz.  
     
     
         11 . The method as claimed in  claim 2 , wherein the fluidized bed has a temperature between 150° C. and 1200° C.  
     
     
         12 . The method as claimed in  claim 2 , wherein the at least one wave guide has a Particle-Froude-Number (Fr p ) between 0.1 and 100.  
     
     
         13 . A plant for thermal treating granular solids in a fluidized bed as claimed in  claim 1 , comprising a fluidized-bed reactor, a microwave source disposed outside the fluidized-bed reactor and a wave guide for feeding the microwave radiation into the fluidized-bed reactor, wherein the wave guide is inclined by an angle of 10° to 50° with respect to a principal axis of the fluidized-bed reactor.  
     
     
         14 . The plant as claimed in  claim 13 , wherein the wave guide has a rectangular or round cross-section, which is adjustable to the used frequency of the microwave radiation.  
     
     
         15 . The plant as claimed in  claim 13 , wherein the wave guide has a length of 0.1 m to 10 m.  
     
     
         16 . The method as claimed in  claim 10 , wherein the frequency is 435 MHz, 915 MHz, or 2.45 GHz.  
     
     
         17 . The method as claimed in  claim 12 , wherein the Particle-Froude-Number is between 2 and 30.  
     
     
         18 . The plant as claimed in  claim 13 , wherein the angle is between 10° and 20°.