Title:
SILOXANE FILTER IN AN EXHAUST AFTERTREATMENT SYSTEM
Kind Code:
A1


Abstract:
An exhaust aftertreatment system for an engine is provided. The exhaust aftertreatment system includes an exhaust duct, at least one of a diesel particulate filter and a diesel oxidation catalyst, a selective catalytic reduction (SCR) catalyst, and at least one siloxane filter. The at least one siloxane filter is positioned upstream of the exhaust aftertreatment system. The at least one siloxane filter is configured to filter siloxanes from exhaust gases and is structured to create a uniform distribution of siloxanes throughout the at least one siloxane filter.



Inventors:
Clayton Jr., Robert D. (Peoria, IL, US)
Application Number:
14/510138
Publication Date:
01/22/2015
Filing Date:
10/09/2014
Assignee:
Caterpillar Inc. (Peoria, IL, US)
Primary Class:
International Classes:
F01N3/035
View Patent Images:
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Primary Examiner:
DUONG, THANH P
Attorney, Agent or Firm:
Caterpillar Inc. (PEORIA, IL, US)
Claims:
What is claimed is:

1. An exhaust aftertreatment system for an engine, the exhaust aftertreatment system including an exhaust duct, and at least one of a diesel particulate filter, a diesel oxidation catalyst, and a selective catalytic reduction (SCR) catalyst, wherein the exhaust aftertreatment system comprises: at least one siloxane filter positioned upstream of the exhaust aftertreatment system, the at least one siloxane filter configured to filter siloxanes from exhaust gases and structured to create a uniform distribution of siloxanes throughout the at least one siloxane filter.

Description:

TECHNICAL FIELD

The present disclosure generally relates to exhaust aftertreatment systems. More particularly, the present disclosure relates to a siloxane filter in an exhaust aftertreatment system.

BACKGROUND

Landfill operations are a major part of waste management. During landfill operations, waste may be delivered to landfill sites via waste collection vehicles. After the waste is unloaded on a surface area of the landfill site, machines, such as compactors or bulldozers, may be used to spread and compact the waste over the surface area. The waste may include certain domestic products that may be composed of siloxanes. The siloxanes are non-toxic silicon-bearing organic compounds that may be added to many domestic products. Due to the widespread use of the domestic products, siloxane concentration may gradually increase in the landfill sites. Siloxanes are volatile compounds that evaporate and migrate out into the ambient air. The machines that operate in the landfill sites may be exposed to the siloxanes in the ambient air. Siloxanes may be combusted harmlessly or harmfully inside internal combustion equipment. The siloxanes may be introduced into an engine of the machine via air intake and may combust to form a solid, fine silica. The silica may stick to hot surfaces inside the engine and an exhaust aftertreatment system of the engine. Also, these components may get plugged, or restrict the exhaust flow, which increases the backpressure and regeneration frequency. Additionally, sensors can be coated or plugged, causing inaccurate readings or delayed response. Therefore, high concentrations of siloxanes in the ambient air may severely affect the maintenance intervals of the engine or machine. There may be much more downtime and many more parts to replace.

U.S. Pat. No. 6,365,108 discloses a siloxane filter system to protect an oxygen probe in an internal combustion engine fueled by biogases. The filter system includes a stainless fiber filter, which is disposed in fluid communication with an exhaust duct such that exhaust gases flow through the filter. Hence, the siloxane in the exhaust gases is deposited on the stainless fibers of the filter and essentially siloxane-free gases pass over the oxygen probe. However, the filter in the referenced patent may clog within a short period of time and hence may require frequent replacement. This may increase the operational cost of the machines engaged in landfill operations.

SUMMARY OF THE INVENTION

The present disclosure is related to an exhaust aftertreatment system for an engine.

In accordance with the present disclosure, the exhaust aftertreatment system includes an exhaust duct, at least one of a diesel particulate filter and a diesel oxidation catalyst, a selective catalytic reduction (SCR) catalyst, and at least one siloxane filter. The at least one siloxane filter is positioned upstream of the exhaust aftertreatment system. The at least one siloxane filter is configured to filter siloxanes from exhaust gases and is structured to create a uniform distribution of siloxanes throughout the at least one siloxane filter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of an embodiment of an engine system that includes an exhaust aftertreatment system, in accordance with the concepts of the present disclosure;

FIG. 2 is a schematic of an embodiment of a siloxane filter of the exhaust aftertreatment system of FIG. 1, in accordance with the concepts of the present disclosure;

FIG. 3 illustrates a schematic of another embodiment of a siloxane filter of the exhaust aftertreatment system of FIG. 1, in accordance with the concepts of the present disclosure; and

FIG. 4 illustrates a schematic of yet another embodiment of a siloxane filter of the exhaust aftertreatment system of FIG. 1, in accordance with the concepts of the present disclosure.

DETAILED DESCRIPTION

Referring to FIG. 1, there is shown an engine system 100. The engine system 100 includes an engine 102, a turbine 104, a compressor 106, and an exhaust aftertreatment system 108. The engine 102 may be of any conventional type, such as a spark-ignited or compression-ignited engine. The engine 102 may be used for any conventional application, such as for vehicular motive power, energy generation, or driving other mechanical equipment. The engine 102 includes combustion chambers (not shown) and is fluidly coupled to the turbine 104. The turbine 104 is operably connected to the compressor 106 by way of a common rotatable shaft 110. The turbine 104 and the compressor 106 may be of any conventional design, such as the axial or centrifugal-flow type. The turbine 104 may be fluidly coupled to an exhaust manifold (not shown) of the engine 102, via an exhaust duct 112.

The exhaust gas is delivered to the turbine 104 via the exhaust duct 112. However, a portion of the exhaust gas may be navigated to the compressor 106. The remaining portion of the exhaust gas delivered to the turbine 104 is navigated to the exhaust aftertreatment system 108. The exhaust aftertreatment system 108 includes one or more siloxane filters 114, a diesel oxidation catalyst (DOC) 116, a mixing chamber 118, and a selective catalytic reduction (SCR) catalyst 120. In the FIG. 1, the siloxane filter 114 is positioned upstream of the DOC 116. However, the siloxane filter 114 may be positioned upstream of at least one of the turbine 104, the DOC 116, the mixing chamber 118, and the SCR catalyst 120. In an embodiment, the siloxane filter 114 may be positioned downstream of at least one of the DOC 116, and the SCR catalyst 120. The siloxane filter 114 is structured to filter and remove siloxane from the exhaust gases before the siloxane-containing exhaust gases flow to the exhaust aftertreatment system 108.

Further, the siloxane filter 114 is in fluid communication with the DOC 116, therefore the filtered exhaust gas from the siloxane filter 114 flows to the DOC 116. The DOC 116 is in fluid communication with the mixing chamber 118, where the exhaust gas is mixed with a reductant. The exhaust gas then flows to the SCR catalyst 120 for catalytic reduction. In an embodiment, the exhaust aftertreatment system 108 may include the one or more siloxane filters 114. The one or more siloxane filters 114 may be installed anywhere in the exhaust aftertreatment system 108. Positioning of the one or more siloxane filters 114 depends on what exhaust aftertreatment components have the potential to fail due to the siloxane deposits. The one or more siloxane filters 114 may be positioned upstream and/or downstream to a variety of emissions treatment components, including, but not limited to, regeneration devices, heat sources, oxidation catalysts, lean NOx traps (LNTs), thermocouples, pressure transducers, sensors (such as oxygen sensors, NOx sensors, ammonia sensors, soot sensors) and/or mufflers.

Referring to FIG. 2, there is shown a schematic of the siloxane filter 114. The siloxane filter 114 may be composed of material, such as silicon carbide, stainless steel, polypropylene, cordierite, aluminum titanate, mild steel, fiber, or other metallic compound known in the art. The composition material of the siloxane filter 114 is selected based on material qualities required to withstand engine-out exhaust temperatures and exhaust gas composition. The siloxane filter 114 may be constructed of woven material, non-woven material, monolithic structures, pleated material, mesh, porous supports, foams, arrays of cells, honeycombs, or combinations thereof. Further, the siloxane filter 114 may be bare or coated with a high surface area catalyst support, such as alumina The siloxane filter 114 is structured to cause siloxane in the exhaust gases to be deposited uniformly on the siloxane filter 114.

The siloxane filter 114 may include a plurality of channels (not shown). The channels (not shown) may be of square, triangular, hexagonal, sinusoidal, or other shapes known in the art. The channel (not shown) may have an axial geometry, which may be uniform or tapered. However, the shape, size, and geometry of the channels (not shown) do not limit the disclosed idea. The siloxane filter 114 may be adapted to have varied permeability, pore size, porosity, and cells per square inch (cpsi).

The siloxane filter 114 may include a first section 200, a second section 202, and a third section 204. The first section 200 may be referred to as a coarse zone. The first section 200 acts as an inlet section for an exhaust gas flow 206 to enter the siloxane filter 114. The first section 200 may be removably coupled to the second section 202. The second section 202 is positioned downstream of the first section 200 and upstream from the third section 204. The second section 202 may be referred to as a medium zone (filters finer particles than the first section 200). The second section 202 may be removably coupled to the third section 204. The third section 204 acts as an outlet section for the filtered exhaust gas flow, which is then navigated to the exhaust aftertreatment system 108. The third section 204 may be referred to as a fine zone. Each of the coarse zone, the medium zone, and the fine zone refers to pore size, porosity, permeability, or cpsi of the corresponding section of the siloxane filter 114. Hence, each of the first section 200, the second section 202, and the third section 204 exhibit a defined porosity. The porosity of the siloxane filter 114 decreases from the first section 200 to the third section 204. This implies that the first section 200 (the coarse zone) has the highest porosity and the third section 204 (the fine zone) has the lowest porosity. The porosity of the second section 202 (the medium zone) lies between the porosity of the first section 200 and the third section 204. In an embodiment, the siloxane filter 114 may include one or more sections positioned downstream from the third section 204 and may exhibit the porosity finer or higher than the third section 204. The increasingly fine porosity of the siloxane filter 114 is one way to achieve uniform siloxane distribution. Hence, the siloxane filter 114 may be equipped with more sections or less sections, which continuously vary from coarse porosity to fine porosity. In another embodiment, the first section 200, the second section 202, and the third section 204 may form a single unit, instead of being removably attached. Alternatively, the porosity of the siloxane filter 114 may continuously and uniformly transition from coarse porosity to fine porosity.

Referring to FIG. 3, there is shown another embodiment of a siloxane filter 300, which exhibits a tapered geometry. The siloxane filter 300 may include a plurality of channels (not shown) similar to the siloxane filter 114 (shown in FIG. 2). Further, the composition and structure of the siloxane filter 300 may be similar to that of the siloxane filter 114 (shown in FIG. 2). The siloxane filter 300 is also structured to achieve uniform siloxane distribution. The siloxane filter 300 includes an inlet 302 and an outlet 304. The inlet 302 has a larger cross-sectional area that tapers to a smaller area at the outlet 304. The exhaust gas flow 206 enters through the inlet 302, is filtered of the siloxanes, and exits through the outlet 304.

Referring to FIG. 4, there is shown the siloxane filter 400. The siloxane filter 400 may also include a plurality of channels (not shown) similar to the siloxane filter 114 (shown in FIG. 2) and the siloxane filter 114 (shown in FIG. 3). Further, the composition and structure of the siloxane filter 400 is similar to that of the siloxane filter 114 (shown in FIG. 2) and the siloxane filter 300 (shown in FIG. 3). The siloxane filter 400 includes at least one mixer 402 and a substrate 404. The mixer 402 is positioned upstream from the substrate 404. The mixer 402 is adapted to create turbulence in the exhaust gas flow 206, which enter the siloxane filter 400. The mixer 402 agitates the exhaust gas flow 206, when the exhaust gases pass through the substrate 404. The exhaust gases are filtered across the substrate 404 and flow to the exhaust aftertreatment system 108. In an embodiment, the siloxane filter 400 may be equipped with more than one mixer 402 positioned upstream from the substrate 404.

INDUSTRIAL APPLICABILITY

In operation, the siloxane filter 114, 300, or 400 is positioned upstream of the components of the exhaust aftertreatment system 108, to protect them from siloxane derived deposition damage. The siloxane filter 114, 300, or 400 is structured to provide uniform distribution of siloxanes throughout the length of the channels (not shown), to minimize back-pressure increase. The exhaust gases exit the engine 102 and flow towards the exhaust aftertreatment system 108. Prior to entrance into the exhaust aftertreatment system 108, the exhaust gases pass through the siloxane filter 114, 300, or 400, in which siloxanes are removed. In addition, the siloxane filter 114, 300, or 400 is functional to achieve a uniform distribution of siloxanes, which increases the time between siloxane filter 114, changes. Further, the siloxane filter 114, 300, or 400 may be configured for removal and replacement of either the entire filter or filter elements. The disclosed idea provides increased maintenance intervals as compared to current siloxane filters. Current filter systems clog quickly and require short maintenance intervals. The disclosed idea may be beneficial for landfill gas engines, turbines and/or boilers, which are required to run full time, and at full capacity.

Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein.

One skilled in the art will realize the disclosure may be embodied in other specific forms without departing from the disclosure or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting of the disclosure described herein. Scope of the invention is thus indicated by the appended claims, rather than the foregoing description, and all changes that come within the meaning and range of equivalence of the claims are therefore intended to be embraced therein.