Fluidized bed without a distributor

Abstract

A fluidized chamber with a coarse layer of refractory particles and a fine layer of refractory particles along with a fluidizing gas inlet connected to a fluidizing gas supply. The fluidizing bed does not have a distributor and fluidizing gas is passed through the fluidized bed at a flow rate to fluidize the fine layer particles but not to fluidize the coarse layer. Preferably, the fluidized bed is a heat treating furnace, the fluidizing gas is combustible and objects to be heat treated are fed through the fluidizing chamber on a continuous basis. A method of operating a fluidized bed is also provided.

1 . A fluidized bed comprising:
 (a) a fluidizing chamber having a fluidizing inlet therein;   (b) a coarse layer of refractory particles of sufficiently large size so as to remain unfluidized when said bed is operating, the coarse layer being located in the chamber above the inlet;   (c) a fine layer of refractory particles of sufficiently small size so as to be fluidized when said bed is operating, said fine layer being located in the chamber immediately above said coarse layer;   (d) said particles of said fine layer being located in a fluidized zone above said coarse layer when said bed is operating;   (e) the gas inlet being connected to a supply of fluidizing gas;   (f) a blower to cause the fluidizing gas to flow through the fluidizing gas inlet and through the coarse layer and fine layer without passing through a distributor at a flow rate to fluidize the fine layer but not the coarse layer; and   (g) an access to an interior of the chamber.   
     
     
         2 . A fluidized bed as claimed in  claim 1  wherein the fluidizing gas is a premixed air/gas mixture. 
     
     
         3 . A fluidized bed as claimed in  claim 2  wherein the premixed air/gas mixture is combustible and the fluidized bed is a heat treating furnace. 
     
     
         4 . A fluidized bed as claimed in  claim 3  wherein the bed has an igniter to ignite the air/gas mixture as the mixture exits the coarse layer, a spacing between the particles of the coarse layer being sufficiently small to prevent combustion from occurring within the coarse layer. 
     
     
         5 . A fluidized bed as claimed in  claim 4  wherein a size of the particles in the coarse layer is chosen to be less than the quenching distance of the air/gas mixture. 
     
     
         6 . A fluidized bed as claimed in  claim 5  wherein the fine layer is comprised of fine particles of sand and the coarse layer is comprised of coarse particles of sand. 
     
     
         7 . A fluidized bed as claimed in  claim 6  wherein the coarse layer is coarse grit sand. 
     
     
         8 . A fluidized bed as claimed in  claim 7  wherein the material of the coarse layer is the same material as the material of the fine layer with a different particle size. 
     
     
         9 . A fluidized bed as claimed in  claim 4  wherein the access is several aligned openings in walls of the fluidizing chamber with each pair of openings on opposing walls being sized to receive wires to be heat treated. 
     
     
         10 . A fluidized bed heat treating furnace comprising:
 (a) a fluidizing chamber having a premixed air/gas inlet therein;   (b) a coarse layer of refractory particles of sufficiently large size so as to remain unfluidized when said bed is operating, the coarse layer being located in the chamber above the inlet;   (c) a fine layer of refractory particles of sufficiently small size so as to be fluidized when said bed is operating, said fine layer being located in the chamber immediately above said coarse layer;   (d) said particles of said fine layer being located in a fluidized zone above said coarse layer when said bed is operating;   (e) the premixed air/gas inlet being connected to a supply of premixed air/gas mixture, the mixture being combustible;   (f) a blower to cause the air/gas mixture to flow through the premixed air/gas inlet and through the coarse layer and fine layer at a flow rate to fluidize the fine layer but not the coarse layer;   (g) an igniter to ignite the air/gas mixture as the mixture exits the coarse layer, a spacing between the particles of the coarse layer being sufficiently small to prevent combustion from occurring within the coarse layer;   (h) at least one retainer to support objects to be heat treated within the fluidized zone of the chamber; and   (i) the chamber having an access to an interior thereof.   
     
     
         11 . A fluidized bed as claimed in  claim 9  wherein the furnace is constructed so that the premixed air/gas mixture does not pass through a distributor. 
     
     
         12 . A method of operating a fluidized bed, said bed having a fluidizing chamber with a fluidizing gas inlet and a bottom thereof, the method comprising:
 (a) locating a layer of coarse refractory particles of sufficient size so as to remain unfluidized when said bed is operating, the coarse layer being located in a bottom of the chamber above the inlet;   (b) locating a fine layer of refractory particles of a size so as to be fluidized above the coarse layer when said bed is operating, said fine layer being located immediately above said coarse layer when said bed is not operating;   (c) connecting the fluidizing gas inlet to a supply of fluidizing gas;   (d) connecting a blower to pass the fluidizing gas through the fluidizing gas inlet and through the coarse layer and the fine layer without passing through a distributor at a velocity to fluidize the fine layer but not to fluidize the coarse layer;   (e) choosing the particles of the coarse layer so that a spacing between the particles is sufficiently small that combustion does not occur in the coarse layer; and   (f) operating the fluidized bed at a temperature, flow rate and duration to achieve a desired result.   
     
     
         13 . A method of operating a fluidized bed as claimed in  claim 12  including the step of choosing a size of the particles in the coarse layer to be less than the quenching distance of the air/gas mixture. 
     
     
         14 . A method of operating a fluidized bed as claimed in  claim 12  including the step of choosing the fine layer to be comprised of fine particles of sand in choosing the coarse layer of sand to be comprised of coarse particles of sand. 
     
     
         15 . A method of operating a fluidized bed as claimed in  claim 14  including the step of choosing the coarse layer to be coarse grit sand. 
     
     
         16 . A method of operating a fluidized bed as claimed in  claim 12  including the step of choosing the material of the coarse layer to be the same material as the material of the fine layer with a different particle size between the coarse layers and the fine layer. 
     
     
         17 . A method of operating a fluidize bed as claimed in  claim 12  including the step of having the access have several aligned openings in walls of the fluidizing chamber with each pair of openings on the opposing walls being sized to receive wires to be heat treated. 
     
     
         18 . A method of operating a fluidized bed heat treating furnace to heat objects, said furnace having a fluidizing chamber with a premixed air/gas inlet in a bottom thereof, said method comprising:
 (a) locating a layer of coarse refractory particles of sufficient size so as to remain unfluidized when said bed is operating, the coarse layer being located in a bottom of the chamber above the inlet;   (b) locating a fine layer of refractory particles of a size so as to be fluidized above the coarse layer when said bed is operating, said fine layer being located immediately above said coarse layer when said bed is not operating;   (c) connecting the premixed air/gas inlet to a supply of combustible gas and to a source of air, premixing the air and gas to form a premixed air/gas mixture that is combustible;   (d) locating objects to be heat treated within said chamber to be within said fluidizing zone when said bed is operating;   (e) connecting a blower to pass the air/gas mixture through the premixed air/gas inlet and through said coarse layer and said fine layer at a velocity to fluidize said fine layer, but not to fluidize said coarse layer;   (f) choosing the particles of said coarse layer so that a spacing between the particles is sufficiently small so that the combustion does not occur in the coarse layer;   (g) igniting the air/gas mixture as the mixture exits from said coarse layer; and   (h) operating the fluidized bed at a temperature, flow-rate and duration to heat treat the objects.   
     
     
         19 . A method as claimed in  claim 18  wherein said objects to be heat treated are passed through said access on a continuous basis.