Method and apparatus for promoting biaxially uniform particle size distribution in an airstream containing coal particles of mixed sizes

Abstract

An apparatus for promoting biaxially uniform distribution of coal particle size in an airstream supplying combustible mixture to a firebox by way of a header having a quadrangular arrangement of feed pipes. A conduit or duct which receives the coal air mix from a bowl mill pulverizer uses first and second single axis mixer elements in series, the operating or mixing axes of the two elements being disposed orthogonal to one another and at right angles to the air flow direction in the vicinity of the mixer elements. Deflector bars are disposed immediately upstream of the mixer elements.

What is claimed is:  
     
         1 . Apparatus for promoting biaxially uniform particle size distribution in an airstream containing particles of mixed sizes comprising: 
 an air-flow duct having an inlet and an outlet and defining an air-flow direction;    a first mixer element disposed in the duct at a first location between the inlet and outlet for mixing particles which are size distributed along a first axis extending across the air-flow; and    a second mixer element disposed in the duct at a second location downstream of the first mixer element for mixing particles which are size distributed along a second axis extending across the air-flow direction; 
 the first cross-axis being orthogonal to the second cross-axis whereby the particle size distribution at the outlet is more uniform than the particle size distribution at the inlet of the duct.  
   
     
     
         2 . Apparatus as defined in  claim 1  wherein the first mixer element comprises a plurality of stacked parallel flow channels which collect air and particles across flow channel inlets extending fully across the duct and parallel to the first cross-axis, said stacked flow channels being arranged to alternately oppositely direct the collective air and particles to opposite sides of the duct measured along the first cross-axis.  
     
     
         3 . Apparatus as defined in  claim 1  wherein the second mixer element comprises a plurality of stacked parallel flow channels which collect air and particles across flow channel inlets extending fully across the duct and parallel to the second cross-axis, said stacked flow channels alternately oppositely directing the collective air and particles to opposite sides of the duct measured along the second cross-axis.  
     
     
         4 . Apparatus as defined in  claim 1  further including a deflector bar disposed in the duct upstream of the first mixer element and having a longitudinal axis which is orthogonal to the first cross-axis.  
     
     
         5 . Apparatus as defined in  claim 4  wherein the deflector bar is angularly adjustable in position.  
     
     
         6 . Apparatus as defined in  claim 5  wherein the deflector bar has teeth formed thereon.  
     
     
         7 . Apparatus as defined in  claim 4  further comprising its second deflector bar disposed in the duct between the first and second mixer elements and having a longitudinal axis which is orthogonal to the second cross-axis.  
     
     
         8 . Apparatus as defined in  claim 7  wherein the second deflector bar is angularly adjustable about the longitudinal axis thereof.  
     
     
         9 . Apparatus as defined in  claim 8  wherein the second deflector bar has teeth formed thereon.  
     
     
         10 . Apparatus as defined in  claim 1  further comprising a header means attached to the outlet of the duct for receiving air and particles flowing therefrom. Said header means comprising four quadrangularly arranged outlet pipes adapted to convey a coal particle/air mixture to a combustion chamber.  
     
     
         11 . A method of promoting biaxially uniform particle size distribution in a coal particle/air stream wherein the coal particles are of mixed sizes comprising the steps of: 
 a. causing the coal particle/air mix to enter a duct;    b. mixing the particle sizes across a first axis extending across the air flow direction;    c. thereafter mixing the particle/airstream across a second axis extending across the air-flow direction wherein the second cross-axis is orthogonal to the first cross-axis; and    d. thereafter directing the twice-mixed coal particle/air mixture to a combustion chamber.    
     
     
         12 . The method of  claim 11  wherein the step of directing the twice-mixed mixture is carried out using a header structure with four quadrangularly arranged feed pipe outlets.