Wear resistant screen

Abstract

A method of manufacturing a screen used to block the passage of particulate material in a gas flow path is disclosed. A screen substrate, typically comprising a steel mesh, grate or perforated plate, is coated by thermal spraying to apply a coating comprising a relatively soft metallic base material and a hard phase in the base material. Various feedstock materials for the thermal spraying process are disclosed. Preferably, the coating is applied by providing a number of spray heads, each of which is inclined relative to the plane of the screen at an angle between 15 and 45 degrees, so that a greater than 180 degree coating of each portion of the screen is achieved. The resulting screens have application in exhaust systems of fossil fuel fired plants, upstream of a selective catalytic reduction (SCR) system.

1 . A method of manufacturing a screen used to block the passage of particulate material in a gas flow path, the method comprising: 
 providing a substrate of suitable material defining a screen structure; and    applying a wear resistant coating to the substrate by thermal spraying, the coating comprising a relatively soft metallic base material and a hard phase in the base material.    
   
   
       2 . A method according to  claim 1  wherein the material of the substrate is metallic.  
   
   
       3 . A method according to  claim 2  wherein the material comprises steel.  
   
   
       4 . A method according to  claim 2  wherein the substrate comprises a mesh of woven wire, a perforated plate, a grid or a grate.  
   
   
       5 . A method according to  claim 1  wherein the screen structure of the substrate defines apertures having a size selected to be within a predetermined range after application of the wear resistant coating in the substrate.  
   
   
       6 . A method according to  claim 5  wherein the apertures are rectangular, round or polygonal in shape.  
   
   
       7 . A method according to  claim 5  wherein the range of size of the apertures is selected to be suitable for use upstream of a Selective Catalytic Reduction (SCR) system in an exhaust conduit of a fossil fuel fired plant.  
   
   
       8 . A method according to  claim 1  wherein the wear resistant coating comprises agglomerated metal/carbide powders applied with an oxygen/fuel thermal spray system.  
   
   
       9 . A method according to  claim 1  wherein the wear resistant coating comprises blended metal/carbide materials applied with an oxygen/fuel thermal spray system.  
   
   
       10 . A method according to  claim 1  wherein the wear resistant coating comprises wear resistant metal alloys with hard phase precipitates in the form of wires or in the form of powders, applied with Arc and Hybrid Arc spray systems in oxygen/fuel thermal spray systems.  
   
   
       11 . A method according to  claim 1  wherein the wear resistant coating comprises powder cored feedstock wires applied with either Arc/Hybrid Arc or oxygen/fuel thermal spray systems.  
   
   
       12 . A method according to  claim 1  wherein the wear resistant coating is applied to at least one side of a generally planar substrate.  
   
   
       13 . A method according to  claim 12  wherein the coating is applied to the substrate at a predefined angle relative to a plane defined by the substrate, to ensure uniform coating of the substrate with a desired extent of coating of individual elements of the substrate.  
   
   
       14 . A method according to  claim 12  wherein the coating is applied by a plurality of spray heads.  
   
   
       15 . A method according to  claim 14  wherein the spray heads are inclined relative to the plane of the screen at an angle of between 15 and 45 degrees.  
   
   
       16 . A method according to  claim 15  wherein the spray heads are inclined at an angle of approximately 30 degrees.  
   
   
       17 . A method according to  claim 14  wherein said plurality of spray heads are arranged in a predetermined relationship, each being inclined relative to the screen and being aimed at a common point on the screen.  
   
   
       18 . A method according to  claim 17  wherein four spray heads are mounted in a spaced apart relationship so as to lie at intervals of 90 degrees on a circle adjacent and parallel to the plane of the screen, with each spray head being inclined at an angle relative to the plane of the screen and aimed at a common point on the screen.  
   
   
       19 . A method according to  claim 13  wherein the wear resistant coating is applied to the opposite side of the screen to allow for increased lateral coverage on the sides of individual elements of the screen.  
   
   
       20 . A method according to  claim 14  wherein multiple passes of the spray heads are made over the screen to attain the coating thickness required.