Catalyst ash protector

Abstract

A combustion apparatus includes: a combustion device operable to produce flue gas having large particulate ash entrained therein; an outlet duct coupled in flow communication with the combustion device so as to receive the flue gas; a screen positioned at least partially in the outlet duct downstream of the combustion device, the screen effective to trap large particulate ash while permitting flow of the flue gas therethrough; and apparatus operable to remove large particulate ash from the screen while at least a portion of the screen remains inside the duct.

1 . A combustion apparatus comprising:
 a combustion device operable to produce flue gas having large particulate ash entrained therein,   a outlet duct coupled in flow communication with the combustion device so as to receive the flue gas;   a screen positioned at least partially in the outlet duct downstream of the combustion device, the screen effective to trap large particulate ash while permitting flow of the flue gas therethrough; and   apparatus operable to remove large particulate ash from the screen while at least a portion of the screen remains inside the duct.   
     
     
         2 . The apparatus of  claim 1  wherein the screen is in the form of a belt extending across the outlet duct and wrapped around a pair of spaced-apart rollers. 
     
     
         3 . The apparatus of  claim 2  further comprising an electric motor arranged to drive one or more of the rollers. 
     
     
         4 . The apparatus of  claim 1  wherein a portion of the screen is positioned above or within a hopper positioned outside the outlet duct. 
     
     
         5 . The apparatus of  claim 4  wherein the hopper contains a liquid wash solution. 
     
     
         6 . The apparatus of  claim 1  wherein the screen comprises a barrier having a plurality of holes formed therein, the holes having a diameter of about 0.1 mm to about 10 mm. 
     
     
         7 . The apparatus of  claim 1  further comprising an injector operable to inject alkaline material having a particulate size greater than about 0.1 mm into the outlet duct, upstream of the screen. 
     
     
         8 . A method of removing large particulate ash from a gas stream, comprising:
 passing a combustion gas stream having large particulate ash entrained therein through a duct,   collecting large particulate ash on a screen positioned at least partially in the duct, while permitting flow of the flue gas therethrough; and   removing the ash from the screen at a location external to the duct while at least a portion of the screen remains inside the duct.   
     
     
         9 . The method of  claim 8  further comprising passing the gas stream to a selective catalyst reduction unit downstream of the screen. 
     
     
         10 . The method of  claim 8  wherein large particulate ash is removed from the screen by:
 moving a portion of the screen outside the duct; and 
 removing large particulate ash from the portion of the screen which is outside the duct; and 
 returning the portion of the screen to the duct. 
 
     
     
         11 . The method of  claim 10  wherein the screen is in the form of a belt extending across the duct and wrapped around a pair of spaced-apart rollers, and the screen is moved by rotating the rollers. 
     
     
         12 . The method of  claim 8  further comprising passing a portion of the screen above or within a hopper positioned outside the duct and depositing large particulate ash removed from the screen in the hopper. 
     
     
         13 . The method of  claim 12  wherein the hopper contains a liquid wash solution. 
     
     
         14 . The method of  claim 8  wherein the screen comprises a barrier having a plurality of holes formed therein, the holes having a diameter of about 1 mm to about 8 mm. 
     
     
         15 . The method of  claim 8  further comprising:
 injecting alkaline material effective to absorb vapor phase contaminants and having a particulate size equal or larger to large particulate ash into the outlet duct upstream of the screen; 
 collecting the alkaline material on the screen; and 
 removing the alkaline material from the screen at a location external to the duct while at least a portion of the screen remains inside the duct.