Systems and methods for catalyst screens in selective catalytic reduction reactors

Abstract

A system for use in selective catalytic reduction reactor is disclosed. The system may include a catalyst bed and a screen located close to the catalyst bed in a manner so that flow of flue gas to the catalyst bed contacts the screen before it contacts the catalyst bed. The screen may be adapted to support a weight of at least 400 pounds above the catalyst bed so that the weight is not imposed on the catalyst. The screen may have a plurality of holes across its surface in a manner so that the screen is adapted to change the velocity distribution of the flue gas as it flows through the screen.

What is claimed is: 
     
         1 . A system for use in a selective catalytic reduction reactor, the system comprising:
 a catalyst bed; and   a plate screen located at a distance in a range of 1 in. to 12 ft. above the catalyst bed so that flow of flue gas to the catalyst bed contacts the plate screen or passes through the plate screen before the flow of flue gas contacts the catalyst bed or passes through the catalyst bed, the plate screen adapted to support a weight of at least 400 pounds above the catalyst bed so that the weight is not imposed on the catalyst bed, the plate screen having a plurality of holes across its surface.   
     
     
         2 . The system of  claim 1 , wherein the plate screen is adapted to change velocity distribution of the flue gas as it flows through the plate screen, wherein the change in velocity distribution as a result of the plate screen comprises a 3 to 6% decrease in Root Mean Square (RMS) of overall velocity distribution of the flue gas. 
     
     
         3 . The system of  claim 1  further comprising:
 a duct adapted to channel the flue gas that emanates from a boiler to the selective catalytic reduction reactor. 
 
     
     
         4 . The system of  claim 1 , further comprising:
 a LPA separator for separating LPA from the flue gas prior to the flue gas contacting the plate screen.   
     
     
         5 . The system of  claim 1 , wherein the plate screen comprises a perforated metal plate. 
     
     
         6 . The system of  claim 1 , wherein the plurality of holes comprises holes of different sizes. 
     
     
         7 . The system of  claim 1 , wherein the plurality of holes comprises holes of different sizes are arranged so that holes nearer to the perimeter of the plate screen are smaller than holes further from the perimeter of the plate screen. 
     
     
         8 . The system of  claim 1 , wherein the plate screen comprises a surface having a Ra of 20 μm. 
     
     
         9 . The system of  claim 1 , wherein the plate screen is adapted to normalize flue gas flow that has different velocities so that the plate screen increases the velocity of a section of the flue gas flowing to the plate screen at a velocity lower than the flue gas's average velocity and decreases the velocity of a section of the flue gas flowing to the plate screen with a velocity higher than the flue gas's average velocity. 
     
     
         10 . The system of  claim 1  wherein the ratio of area of holes/area of screen surface is in a range of 45% to 65%. 
     
     
         11 . The system of  claim 1 , wherein the holes are shaped as a selection from the list consisting of: hexagon, circle, square, rectangular, triangle, pentagon, and combinations thereof. 
     
     
         12 . The system of  claim 1 , wherein the plate screen comprises 12 gauge carbon steel. 
     
     
         13 . The system of  claim 1 , wherein the plate screen comprises an elliptical shape extending from one end of the plate screen to another end of the plate screen, the elliptical shape defined in a plane perpendicular to the flow of flue gas. 
     
     
         14 . A method for protecting a catalyst bed in a selective catalytic reduction reactor, the method comprising:
 disposing a plate screen at a distance in a range of 1 in. to 12 ft. above the catalyst bed so that flow of flue gas to the catalyst bed contacts the plate screen or passes through the plate screen before the flow of flue gas contacts the catalyst bed or passes through the catalyst bed, the plate screen adapted to withstand a weight of at least 400 pounds without that weight being imposed on the catalyst bed, the plate screen having a plurality of holes across its surface; and   flowing the flue gas through the plate screen.   
     
     
         15 . The method of  claim 14 , further comprising:
 changing velocity distribution of the flue gas as it flows through the plate screen, wherein the change in velocity distribution as a result of the plate screen comprises 3 to 6% decrease in Root Mean Square (RMS) of overall velocity distribution of the flue gas   
     
     
         16 . The method of  claim 14 , wherein the plate screen comprises a perforated metal plate. 
     
     
         17 . The method of  claim 14 , wherein the plate screen comprises a surface having a Ra of 20 μm. 
     
     
         18 . The method of  claim 14 , wherein, when the flue gas flow has different velocities, normalizing the flue gas flow comprises increasing the velocity of a section of the flue gas flowing to the plate screen at a velocity lower than the flue gas's average velocity and decreasing the velocity of a section of the flue gas flowing to the plate screen with a velocity higher than the flue gas's average velocity. 
     
     
         19 . The method of  claim 14 , wherein the ratio of area of holes/area of screen surface is in range of 45% to 65%. 
     
     
         20 . The method of  claim 14 , wherein the holes are shaped as a selection from the list consisting of: hexagon, circle, square, rectangular, triangle, pentagon, and combinations thereof. 
     
     
         21 . The method of  claim 14 , wherein the plate screen comprises 12 gauge carbon steel. 
     
     
         22 . The method of  claim 14 , wherein the plate screen comprises an elliptical shape extending from one end of the plate screen to another end of the plate screen, the elliptical shape defined in a plane perpendicular to the flow of flue gas.