Treatment of particulate filters

Abstract

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).

Claims

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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Aspects and embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic illustration of an apparatus according to the present disclosure;

(3) FIG. 2 is a schematic illustration from above of a ring air blade of the apparatus of FIG. 1 and an inlet face of a porous substrate;

(4) FIG. 3 is a schematic illustration from the side of the ring air blade and porous substrate of FIG. 2;

(5) FIG. 4 is a graph showing the relative mass of dry powder deposited against distance from the inlet face for an example porous substrate;

(6) FIG. 5 is a graph showing a powder deposition ratio against secondary gas flow pressure;

(7) FIG. 6 is a photograph of an inlet face of a porous substrate after spraying of a dry powder; and

(8) FIG. 7 is a photograph of the porous substrate of FIG. 6 after operation of a ring air blade.

DETAILED DESCRIPTION

(9) The skilled reader will recognise that one or more features of one aspect or embodiment of the present disclosure may be combined with one or more features of any other aspect or embodiment of the present disclosure unless the immediate context teaches otherwise.

(10) An example of an apparatus in accordance with the present disclosure will now be described with reference to FIG. 1 which shows a schematic diagram of an apparatus 1 for treating a porous substrate 10 for filtering particulate matter from exhaust gas. The porous substrate 10 is of a type having an inlet face 11 and an outlet face 12, the inlet face 11 and the outlet face 12 being separated by a porous structure 13.

(11) The apparatus 1 comprises a holder 2 for holding the porous substrate 10, an inlet chamber 15 in communication with the inlet face 11, a vacuum generator in communication with the outlet face 12 for establishing a primary gas flow through the porous substrate 10 from the inlet face 11 to the outlet face 12, a spray device for spraying dry powder into or within the inlet chamber 15 and a secondary gas source for producing a secondary gas flow, shown by way of example in the form of a ring air blade 30.

(12) The holder 2 may comprise means for holding securely the porous substrate 10. The holder 2 may comprise an upper inflatable collar 3 supplied by inflation line 5 and a lower inflatable collar 4 supplied by inflation line 6.

(13) The vacuum generator may comprise a vacuum cone 17 connected via a line 16 to, for example, a regenerative blower.

(14) The spray device may comprise a spray nozzle 20 supplied with dry powder along a powder supply line 21, for example by gravity feed. A gas feed line 22 may supply compressed gas, e.g. compressed air, to the spray nozzle 20 for entraining, mobilising and spraying the dry powder out of the spray nozzle 20. The spray nozzle 20 may be located within the inlet chamber 15 as shown in FIG. 1 or alternatively located outside the inlet chamber 15 but orientated to spray the dry powder into the inlet chamber 15.

(15) The spray device may be located at a distance, h, of 100 cm or more from the inlet face 11, optionally at a distance of 150 cm or more, optionally at a distance of 200 cm or more. The distance, h, may be fixed for a particular apparatus 1.

(16) The inlet chamber 15 may comprise a tube 15 having, optionally, an open upper end. The tube 15 may have a shape conformal to the shape of the inlet face 11 and a size that is equal to or large than the inlet face 11.

(17) The secondary gas source, e.g. ring air blade 30, may be located within the inlet chamber 15 as shown in FIG. 1 or may be arranged in series with one or more portions of the inlet chamber 15 or located between the inlet chamber 15 and the inlet face 11. A gas supply 31 feeds pressurised gas, for example air, to the ring air blade 30.

(18) A controller may be provided for selecting a pressure and/or a flow rate of the secondary gas flow generated by the secondary gas source. For example the controller may be an electronic and/or software control operatively connected to a valve and or pump. Alternatively, the controller may be a manual control for setting the pressure and/or flow rate of the secondary gas flow, e.g. by manually adjusting a valve or pump setting thereby controlling the pressure and/or flow rate of the secondary gas flow, for example the flow of gas emitted by the ring air blade 30.

(19) As shown in FIGS. 2 and 3, the ring air blade 30 may comprise two semi-circular elements 32, 33 that together form a ring shape that extends 360 around the inlet face 11 of the porous substrate 10. Each semi-circular element 32, 33 may have its own gas inlet 31a, 31b that may be supplied from a common gas supply 31.

(20) The ring air blade 30 may have a gas outlet 35 that extends around the inner circumferential wall of each semi-circular element 32, 33 and is orientated generally radially inwards as shown in FIG. 3. Thus, as shown by the arrows in FIG. 2, gas entering each semi-circular element 32, 33 is guided around its element 32, 33 and exits generally radially so that gas is emitted around all or substantially all 360 of the ring air blade 30.

(21) A lower surface 36 of the gas outlet 35 may be rounded to deflect, due to the Coanda effect, gas exiting the gas outlet 35 downwards towards the inlet face 11 as shown in FIG. 3. Thus, a generally conical flow of air may be obtained.

(22) The plane of the gas outlet 35 of the ring air blade 30 may be positioned between 1 and 10 cm above the plane of the inlet face 11 as shown schematically in FIG. 3 using the reference d.

(23) In use, the porous substrate 10 is first located in the holder 2 such that the inlet face 11 is in communication with the inlet chamber 15 and the outlet face 12 is in communication with the vacuum generator, e.g. the vacuum cone 17. The upper and lower inflatable collars 3, 4 may be inflated to secure the porous substrate 10.

(24) Next, a primary gas flow is established through the porous substrate 10 from the inlet face 11 to the outlet face 12 by using the vacuum generator to apply a pressure reduction to the outlet face 12 of the porous substrate 10.

(25) In addition, the ring air blade 30 is activated to generate the secondary gas flow downwards onto the inlet face 11 with the pressure and/or flow rate of the secondary gas flow having been set to a desired level.

(26) The pressure and/or flow rate of the secondary gas flow may be fixed throughout the treatment of a particular porous substrate 10 or may be varied during the treatment of a particular porous substrate 10.

(27) Dry powder is sprayed into or within the inlet chamber 15, e.g. using the spay nozzle 20, such that dry powder is entrained in the primary gas flow, passes along the inlet chamber 15, through the turbulent zone generated by the secondary gas flow, and then passes through the inlet face 11 of the porous substrate 10 to contact the porous structure.

(28) The secondary gas flow may be 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.

(29) While in the above examples the secondary air flow has been described as generated by a ring air blade 30, it is within the scope of the present disclosure to use alternative arrangements for generating the secondary air flow onto or across the inlet face 11 to generate a turbulent zone at or above the inlet face 11.

Examples

(30) FIG. 4 shows a graph plotting the relative mass of dry powder deposited against distance from the inlet face for samples of a porous substrate.

(31) The porous substrate was an Aluminium Titanate filter substrate supplied by Corning. Diameter=171.9 mm, Length=152.4 mm.

(32) A washcoat was applied to the filter substrate. The washcoat comprised Cu exchanged zeolite (CHA, SAR=18.5, supplied by Tosoh, Cu loading=3.3 wt %) and stabilised gamma alumina (supplied by PIDC) with a 9:1 ratio suspended in water. The washcoat had a d90 of 4-5 m. The surface of the zeolite was modified using an aminosilane (see US11192793B2).

(33) The washcoat application was according to EP3122458. Washcoat was applied to the outlet end of filter substrate to coat 80% of the filter volume, with a calcined loading of 1.58 g.Math.in.sup.3 wrt to the filter volume. Additional washcoat was applied to the inlet end of the filter substrate to coat 35% of the filter volume, with a calcined loading of 0.52 g.Math.in.sup.3 wrt to the filter volume. The filter substrate was calcined at 500 C. for 1 hour.

(34) The dry powder was a mixture of Zeolite (a chabazite zeolite with a d90 of 4 m and SAR of 23, available from Tosoh) and a Silres MK powder (a methyl silicone resin with a d90 of 9 m, available from Wacker) and was prepared at a 3:1 Zeolite:Silicone resin ratio. The resulting mixed powder was sprayed onto the washcoated filter substrate from the inlet end under a constant flow of air. The air flow forming the primary gas flow was at 300 m.sup.3/hr. The coated part was then calcined to 500 C. for 1 hour.

(35) The particle size measurements necessary to obtain d90 of solid particles (e.g., a zeolite or a Silres MK powder) can be obtained by Laser Diffraction Particle Size Analysis using a Malvern Mastersizer 3000, which is a volume-based technique (i.e. d90 may also be referred to as d(v,0.90)) and applies a mathematical Mie theory model to determine a particle size distribution. The laser diffraction system works by determining diameters for the particles based on a spherical approximation. For the particle size measurements by Laser Diffraction Particle Size Analysis, diluted samples were prepared by sonication in distilled water without surfactant for 30 seconds at 35 watts.

(36) A ring air blade 30 was used as the source for the secondary gas flow. The spray nozzle height, h, was fixed at 200 cm throughout. Samples of the filter substrate were treated with the secondary gas flow switched off (marked None on FIG. 4), and with the secondary gas flow at a pressure of 2 bar, 3.5 bar and at 5 bar (the 3.5 bar result is omitted from FIG. 4 merely for clarity).

(37) FIG. 4 is a graph showing the relative mass of dry powder deposited against distance from the inlet face of the filter substrate. The results were obtained by performing an X-ray scan of the filter substrate before and after application of the dry powder. In each scan a measurement of the radial average x-ray absorption was taken every 0.5 mm along the axis of the filter substrate. The pre-application measurements were then subtracted from the post-application measurements and the results then normalised.

(38) As can be seen from FIG. 4, with the secondary gas flow switched off the deposition of the dry powder shows a skew to the outlet end of the filter substrate with a peak around 120 cm from the inlet face. With the secondary gas flow set to 2 bar the otherwise same treatment conditions resulted in an intermediate distribution of the dry powder along the length of the filter structure. With the secondary gas flow set to 5 bar the otherwise same treatment conditions resulted in a deposition of the dry powder showing a skew to the inlet end of the filter substrate with a peak around 5 cm from the inlet face and a secondary peal around 55 cm.

(39) FIG. 5 shows a graph of a powder deposition ratio against secondary gas flow pressure for the filter substrates tested as described above at 0, 2, 3.5 and 5 bar pressure for the secondary gas flow pressure. The powder deposition ratio was calculated as the normalised absorption value at 60 mm from the inlet face divided by the normalised absorption value at 120 mm from the inlet face.

(40) As can be seen from FIG. 5, a strong linear relationship was shown between the pressure of the secondary gas flow and the powder deposition ratio showing that use of the secondary gas flow pressure provides a reliable and controllable means for controlling the location of the deposition of the dry powder within the porous substrate.

(41) As shown in FIG. 6, treating the porous substrate 10 with dry powder can result in a build-up of the dry powder on the inlet face 11, in particular on the ends of the walls separating the inlet channels and/or on any channels having their inlet end plugged.

(42) Therefore the ring air blade 30 may be activated to direct a gas flow downwards onto the inlet face 11 to blow off the dry powder accumulated on the inlet face 11 of the porous substrate 10. The vacuum generator may remain active during activation of the ring air blade 30 such that the dry powder blown off the inlet face 11 is entrained in the gas flow and passes through the inlet face 11 of the porous substrate 10.

(43) As shown in FIG. 7, the result is that the inlet face 11 may be effectively cleaned of the build-up of dry powder.

(44) The ring air blade 30 may be activated to blow off the dry powder after the spraying of the dry powder into or within the inlet chamber 15 has ceased (but while the vacuum generator is still running). Additionally or alternatively, the ring air blade 30 may be activated during the spraying of the dry powder into or within the inlet chamber 15.