Treatment of particulate filters
A method and apparatus for applying a dry powder to a porous substrate ( 10 ) comprising: a) locating the porous substrate ( 10 ) in a holder ( 2 ) such that an inlet face ( 11 ) is in communication with an inlet chamber ( 15 ) and an outlet face ( 12 ) is in communication with a vacuum generator; b) establishing a primary gas flow through the porous substrate ( 10 ) using the vacuum generator to apply a pressure reduction to the outlet face ( 12 ); c) spraying the dry powder into or within the inlet chamber ( 15 ) such that dry powder is entrained in the primary gas flow and passes through the inlet face ( 11 ) of the porous substrate ( 10 ) to contact a porous structure ( 13 ) of the porous substrate ( 10 ); d) during the spraying of the dry powder directing a secondary gas flow onto and/or across the inlet face of the porous substrate ( 10 ); and e) using a pressure and/or a flow rate of the secondary gas flow to control an axial distribution of the dry powder that is deposited in the porous structure ( 13 ) of the porous substrate ( 10 ).
1 . A method of applying a dry powder to a porous substrate, the porous substrate having an inlet face at an inlet end and an outlet face at an outlet end with the inlet face and the outlet face being separated by a porous structure, the method comprising the steps of:
a) locating the porous substrate in a holder such that the inlet face is in communication with an inlet chamber and the outlet face is in communication with a vacuum generator;
b) establishing a primary gas flow through the porous substrate from the inlet face to the outlet face by using the vacuum generator to apply a pressure reduction to the outlet face of the porous substrate;
c) spraying the dry powder into or within the inlet chamber such that dry powder is entrained in the primary gas flow and passes through the inlet face of the porous substrate to contact the porous structure;
d) during the spraying of the dry powder directing a secondary gas flow onto and/or across the inlet face of the porous substrate; and
e) using a pressure and/or a flow rate of the secondary gas flow to control an axial distribution of the dry powder that is deposited in the porous structure of the porous substrate.
2 . The method of claim 1 , wherein controlling the axial distribution of the dry powder comprises:
selecting a relatively high pressure and/or flow rate of the secondary gas flow to skew the axial distribution of the dry powder that is deposited in the porous structure towards the inlet end of the porous substrate;
selecting a relatively low pressure and/or flow rate of the secondary gas flow or deactivating the secondary gas flow to skew the axial distribution of the dry powder that is deposited in the porous structure towards the outlet end of the porous substrate; and
selecting a relatively intermediate pressure and/or flow rate of the secondary gas flow to obtain an intermediate axial distribution of the dry powder that is deposited in the porous structure.
3 . The method of claim 1 , wherein the secondary gas flow is active for:
an entire duration of the spraying of the dry powder; or
a portion of the duration of the spraying of the dry powder.
4 . The method of claim 1 , wherein the secondary gas flow remains active or is activated after the spraying of the dry powder has ceased in order to blow off dry powder accumulated on the inlet face of the porous substrate.
5 . The method of claim 4 , wherein the vacuum generator remains active during activation of the secondary gas flow after cessation of spraying of the dry powder such that the dry powder blown off the inlet face is entrained in the primary gas flow and passes through the inlet face of the porous substrate.
6 . The method of claim 1 , wherein the secondary gas flow is configured to be a 360° or substantially 360° flow of gas.
7 . The method of claim 1 , wherein the secondary gas flow is configured to be directed at a downwards angle onto the inlet face.
8 . The method of claim 1 , further comprising using a ring air blade to generate the secondary gas flow.
9 . The method of claim 1 , wherein the dry powder is sprayed into or within the inlet chamber using a spray nozzle, and when using the pressure and/or the flow rate of the secondary gas flow to control the axial distribution of the dry powder, a spatial separation of the spray nozzle from the inlet face remains fixed.
10 . The method of claim 1 , further comprising applying dry powder successively to a plurality of porous substrates, wherein for each of the plurality of porous substrates the pressure and/or flow rate of the secondary gas flow is selected in order to control the axial distribution of the dry powder that is deposited in the porous structure of that porous substrate.
11 . The method of claim 10 , wherein a spatial separation of a spray nozzle for spraying the dry powder and the inlet face of the plurality of porous substrates remains fixed.