Combined Soot Filter and Urea Hydrolysis

Abstract

A monolith filter unit for exhaust gas cleaning combines urea hydrolysis with particle filtering.

Claims

1. A catalyst impregnated exhaust gas particulate filter unit for vehicle exhaust gas, the unit comprises at least one monolith comprising a plurality of channels open at one end and closed at the other end, a first open end, and a second open end, wherein the at least one monolith is divided in two sections, a first section which is not coated or which is coated with a first type of catalyst and a second section which is coated with a second type of catalyst.

2. The catalyst impregnated exhaust gas particulate filter unit according to claim 1, wherein the first type of catalyst is a urea hydrolysis catalyst.

3. The catalyst impregnated exhaust gas particulate filter unit according to claim 2, wherein the urea hydrolysis catalyst is at least one of ZrO2, TiO2, Al2O3, H-ZSM-5 or SiO2.

4. The catalyst impregnated exhaust gas particulate filter unit according to claim 1, wherein the second type of catalyst is a diesel oxidation catalyst.

5. The catalyst impregnated exhaust gas particulate filter unit according to claim 4, wherein the diesel oxidation catalyst is at least one of Pt/Al2O3; (Pt, Pd)/Al2O3; Pt/TiO2; (Pt, Pd)/TiO2; 0-50 g/ft3 or precious metals.

6. The catalyst impregnated exhaust gas particulate filter unit according to claim 1, wherein the filter unit has a cylindrical shape and the first section has the shape of a sector of a circle when seen in a cross sectional view of the filter unit.

7. The catalyst impregnated exhaust gas particulate filter unit according to claim 1, wherein the filter unit has a cylindrical shape and the first section has the shape of a segment of a circle when seen in a cross sectional view of the filter unit.

8. The catalyst impregnated exhaust gas particulate filter unit according to claim 1, wherein the first section has the shape of a circle when seen in a cross sectional view of the filter unit.

9. The catalyst impregnated exhaust gas particulate filter unit according to claim 1, wherein the unit further comprises a flow guide upstream the first section adapted to guide a part of the exhaust gas stream only to the first section and isolate this part of the exhaust gas stream from the rest of the exhaust gas stream.

10. The catalyst impregnated exhaust gas particulate filter unit according to claim 1, wherein the filter unit further comprises a mixer arranged downstream the first and second section adapted to mix the exhaust gas stream from the first section with the exhaust gas stream from the second section.

11. A process for vehicle exhaust gas cleaning comprising the steps of providing a catalyst impregnated exhaust gas particulate filter unit for vehicle exhaust gas comprising at least one monolith comprising a plurality of channels open at one end and closed at the other end, a first open end, a second open end, at least one wall adapted to fit around said at least one monolith, wherein the at least one monolith is divided in two sections, a first section which is not coated or which is coated with a first type of catalyst and a second section which is coated with a second type of catalyst, providing a vehicle exhaust gas upstream the first open end of the unit, and injecting urea into a partial stream of the vehicle exhaust gas, upstream the first section of the at least one monolith.

12. The process according to claim 11, further including the step of providing a fluid guide upstream the first section of the at least one monolith for the partial stream, adapted to guide the partial stream to the first section of the at least one monolith.

13. The process according to claim 11, further including the step of providing a mixer downstream the filter unit and mixing the flow of fluids comprising NO2 and NH3 exiting the first and the second section of the filter unit.

14. The process according to claim 11, further including the step of providing an SCR unit downstream the filter unit.

Description

[0029] A more detailed description of the invention will be apparent from the following description of a specific embodiment with reference to the drawings in which—

[0030] FIG. 1 shows an isometric view of the filter unit upstream an SCR catalyst unit, and

[0031] FIG. 2 shows a graph of the performance of the invention.

POSITION NUMBERS

[0032] 01. Filter unit. [0033] 02. SCR catalyst unit [0034] 03. First section (UDPF) of the monolith(s). [0035] 04. Second section (CDPF) of the monolith(s).

[0036] Referring to FIG. 1, a filter unit 01 according to an embodiment of the invention is shown with the monolith inside it. The filter unit of this embodiment has one cylindrical cassette wall not shown adapted to enclose the sides of the monolith to be mounted inside it and to fix the monolith against movement relative to the wall. When the monolith is mounted within the wall, it is adapted to receive an exhaust gas to be cleaned in the monolith. The monolith is separated in two sections. In the first section 03 a sector of the cross sectional area of the cylindrical monolith is the UDPF. In the second section 04, the rest of the monolith is the CDPF. The exhaust gas enters the filter unit through the first open end. One stream of exhaust gas with urea injected enters the first section and another stream of exhaust gas comprising NO enters the second section. The gas streams flows into the monolith which comprises a plurality of channels with a closed end, hence, the gas streams flows through the filter sides of the monolith to exit through the second open end of the filter unit in a gas stream comprising ammonia and NO2. To homogenize the gas exiting the filter unit before it enters the SCR, a mixer (not shown) may be employed downstream the filter unit and upstream the SCR.

[0037] FIG. 2 shows how experiments have shown a higher NOX conversion when the urea is injected into the exhaust gas stream before the (U)DPF as according to the present invention than if the urea is injected into the exhaust gas stream before the SCR (downstream the UDPF).