Method For Reducing Pressure Drop Through Filters, And Filter Exhibiting Reduced Pressure Drop

Abstract

Methods for generating and applying coatings to filters with porous material in order to reduce large pressure drop increases as material accumulates in a filter, as well as the filter exhibiting reduced and/or more uniform pressure drop. The filter can be a diesel particulate trap for removing particulate matter such as soot from the exhaust of a diesel engine. Porous material such as ash is loaded on the surface of the substrate or filter walls, such as by coating, depositing, distributing or layering the porous material along the channel walls of the filter in an amount effective for minimizing or preventing depth filtration during use of the filter. Efficient filtration at acceptable flow rates is achieved.

1 . A filter for removing particulate matter from a fluid stream, comprising at least one porous wall having a plurality of pores defined by pore walls, said plurality of pores normally allowing fluid flow through said at least one wall while restraining said particulate matter from passing completely through said at least one wall, wherein an accumulation of porous material is present along said at least one porous wall in an amount sufficient to inhibit depth filtration in said filter. 
     
     
         2 . The filter of  claim 1 , wherein said fluid stream is the exhaust gas discharged from a diesel engine. 
     
     
         3 . The filter of  claim 2 , wherein said filter comprises a ceramic material. 
     
     
         4 . The filter of  claim 1 , wherein said porous material comprises inorganic material. 
     
     
         5 . The filter of  claim 4 , wherein said inorganic material comprises a catalyst effective for promoting soot oxidation or reducing levels of gaseous exhaust components. 
     
     
         6 . A filter for separating particulate matter from a fluid stream, comprising a plurality of channels defined by porous channel walls, said plurality of channels being closed at alternate ends thereby defining a fluid flow path through said porous channel walls, said porous channel walls being coated with inorganic material in an amount effective for inhibiting depth filtration of said particulate matter by said porous channel walls. 
     
     
         7 . The filter of  claim 6 , wherein said fluid stream is the exhaust gas discharged from a diesel engine. 
     
     
         8 . The filter of  claim 6 , wherein said particulate matter is separated from said fluid stream by formation of a particulate matter containing cake on said walls, and wherein said filter is regenerated by combustion of said cake. 
     
     
         9 . A method of generating and applying a porous coating to the walls of a filter comprising: providing a filter downstream of a combustion chamber; combusting hydrocarbons in said chamber; forcing the resulting combustion products into said downstream filter, and allowing said combustion products to accumulate on said walls of said filter in a predetermined amount. 
     
     
         10 . The method of  claim 9 , wherein said hydrocarbons comprise diesel engine oil. 
     
     
         11 . The method of  claim 9 , wherein the combustion products comprise ash. 
     
     
         12 . The method of  claim 9 , wherein said predetermined amount is an amount sufficient to prevent depth filtration. 
     
     
         13 . A method of inhibiting, in a filter having a plurality of longitudinal passageways extending from an inlet end face to an outlet end face and defined by porous walls, depth filtration of particulate matter entrained in a fluid stream, said method comprising loading said porous walls with a porous material in an amount sufficient to substantially prevent said particulate matter from entering said pores, thereby causing said particulate matter to form a filter cake on the surfaces of said walls. 
     
     
         14 . The method of  claim 13 , wherein said porous material comprises synthetically produced ash. 
     
     
         15 . The method of  claim 14 , wherein said ash is generated by combusting soot. 
     
     
         16 . The method of  claim 15 , wherein said soot is generated by combusting diesel engine oil. 
     
     
         17 . The method of  claim 13 , wherein said porous walls are loaded by driving said porous material into said passageways. 
     
     
         18 . The method of  claim 17 , wherein said porous material is driven with a blower or pump. 
     
     
         19 . The method of  claim 13 , wherein said porous walls are loaded by contacting them with a solution or slurry containing said porous material. 
     
     
         20 . The method of  claim 13 , further comprising removing said filter cake by combusting said particulate matter, thereby regenerating said filter. 
     
     
         21 . The method of  claim 13 , further comprising applying a layer of porous material to the pores of said porous walls prior to said step of loading said porous walls with said porous material, by allowing soot to accumulate in said pores, and combusting said soot to form a layer of incombustible material in said pores. 
     
     
         22 . A method of generating and loading a filter having a plurality of channels, defined by porous channel walls, with a porous material, comprising combusting soot and allowing the products of that combustion to load onto said channel walls; combusting a composition comprising inorganic material and allowing said inorganic material to load onto said channel walls; and oxidizing the products of said soot combustion. 
     
     
         23 . The method of  claim 22 , further comprising, after said oxidation of said products of said soot combustion, applying additional inorganic material to said channel walls. 
     
     
         24 . The method of  claim 23 , wherein said step of combusting soot is carried out below the oxidation temperature of said soot. 
     
     
         25 . The method of  claim 23 , wherein said inorganic material comprises zinc.