Composite catalytic converter

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

The present invention relates to a contact converter for converting gaseous contaminants in an exhaust stream into harmless and / or environmentally acceptable gaseous components. These contact converters consist of electrically heatable contact converters (EHCs) and non-electrically heatable ceramic contact converters that are in a strengthening relationship and are in a common housing.

【0002】

[Background of Invention and Conventional Technology]

The purpose of the contact converter is to convert pollutants in engine or turbine exhaust, such as carbon monoxide, unburned hydrocarbons, nitrogen oxides, etc., into carbon dioxide, nitrogen and water. Conventional contact converters use a square straight hole or chamber, a ceramic honeycam monolith with catalyst-coated alumina beads, or a thin metal leaf honeycam monolith with a catalyst supported or supported on the surface. The catalyst is generally a noble metal, such as platinum, palladium, rhodium or ruthenium, or a mixture of two or more of these noble metals. The catalyst promotes chemical reactions, oxidation, reduction, or both, thereby converting contaminants into harmless by-products, which are then sent to the atmosphere through the exhaust system. However, this conversion is less efficient when the exhaust and converter are initially relatively cold. To be effective at high conversion rates, the catalyst and converter surfaces leading to contact with the exhaust must be at a minimum high temperature, eg, 390 ° F to carbon monoxide, volatile organic compounds (VOCs). On the other hand, it should be 570 ° F and 1000 ° F for ethane or natural gas. Otherwise, the conversion to harmless by-products is inadequate and the air pollution level at low temperature start is high. When the exhaust system reaches its operating temperature, the contact converter becomes most effective. Thus, it is necessary to bring the relatively cold exhaust into contact with the hot catalyst in order to achieve perfect conversion at engine start. Both compression point (diesel) and spark ignition engines require it.

【0003】

To achieve catalyst heating, an electrically heatable contact converter consisting of a corrugated thin metal leaf monolith connected to a power source, eg, a 12 volt or 24 volt car battery, is provided, preferably pre-starting and During start-up, an electric current is applied to raise and maintain the temperature of the catalyst to at least 650 ° F. For this, refer to Co-Application Patent Application No. 587,219 filed on September 24, 1990, which discloses the disclosure of this patent application for the effective heating of electroheatable contact converter cores and metal monoliths. It is incorporated here as a reference for details about the electric power system.

【0004】

There is a problem with thin metal leaf contact converters that are spirally or S-shaped and have a corrugated shape, and the present invention solves this problem. A rigorous compression test shall be performed on the thin corrugated metal monolith score and the device shall pass the test. Such compression can result in the destruction of electrically heated contact converters. This test consists of vibrating (100-200 Hz and 28-60 G) the device in a vertical position at high temperature (700-950 ° C) while allowing exhaust from an operating internal combustion engine to pass through the device. The device shall be disqualified from the test if the wound core device compresses or breaks in the direction of the airflow after a predetermined time, for example 5 to 200 hours. Normally, if a device is disqualified, it will be disqualified within 5 hours.

【0005】

An object of the present invention is to provide a device that has passed the above tests and is therefore reliable under extreme conditions of use.

【0006】

Here we should refer to U.S. Pat. No. 3,768,982 to Kittsner dated October 30, 1973. In this patent, the catalyst is heated to the optimum operating temperature by transferring the heat from the centrally located electric heater through conduction through the catalyst support of the monolith. In addition, the US Patent No. 3 to Kittsner dated October 30, 1973, which discloses a central electrothermal core in a ceramic monolith that is heated by heat transfer to a catalyst contained in the hole of the ceramic monolith. See also No. 3,770,389. The heating core consists of two types of metal sheets, coated with alumina and also carrying a catalyst, one corrugated and the other flat. The metal core is electrically heated by its own electrical resistance. Conductive heating takes too long to solve the problem of air pollution at start-up. Moreover, the thin metal cores of the present invention do not require flat metal sheets that alternate with corrugated metal sheets. Flat metal sheet adds about 20-30% extra weight to the device and requires a relatively long heating time or a relatively large amount of power.

【0007】

For details on the method for producing a corrugated thin metal leaf having a refractory metal oxide coating and a noble metal catalyst deposited on the oxide surface, dated December 8, 1987. See also US Pat. No. 4,711,009 to Cornelison et al. By folding this foil into an accordion shape or winding it in a spiral shape, the electroheatable monolith of the present invention can be formed. This patent will be incorporated here as a reference.

【0008】

International PCT Publication No. WO / 10471, filed November 2, 1989, should also be referred to, but this document discloses a conductive honeycam catalyst support device useful in automobiles. In order to obtain a suitable electrical insulation of 0.03 to 2 ohms, the honeycam body is cross-sectioned by a gap and / or an electrically insulating intermediate layer or coating so that a current path having at least one desired resistance is obtained. And / or axially, electrically classify. Heating is controlled by a time delay. One or more separate converters in the exhaust system that can be electrically heated but are otherwise common are disclosed. The basic apparatus shown in WO 89/10470 of this application and its accompanying application of November 2, 1989 can be used in the present invention. Spiral or S-wound cores are exposed to the same problems with compression under the rigorous tests described above.

【0009】

In the following description, there is a description of "ferritic" stainless steel. A suitable composition for this material is described in US Pat. No. 4,414,023 dated November 8, 1983 to Egens et al. Specific ferrite stainless steels useful in the present invention contain 20% chromium, 5% aluminum, 0.002 to 0.05% at least one rare earth metal selected from cerium, lanthanum, neodymium, yttrium and praseodymium, with the balance being iron and steelmaking impurities. Is.

【0010】

In the following description, there is also a description of fibrous ceramic mat or felt. For the composition and manufacture of ceramic fibers useful in the present invention, reference to US Pat. No. 3,795,524 dated March 5, 1974 to Bowman. Such materials are currently marketed by 3M under the trade name "Intellam".

【0011】

In addition, some patent applications, namely serial numbers 524,284 and 587,219, filed April 16, 1990, should also be referred to. Both of these patent applications are owned by the applicant and are incorporated here with reference to their disclosure.

【0012】

Simply put, the present invention can electrically heat a housing, a multi-compartment of thin corrugated stainless steel having a refractory metal oxide with a supported noble metal catalyst on at least one surface in the housing. Electricity from the catalyst monolith and the conventional multi-compartment ceramic catalyst monolith in parallel or physically adjacent to the catalyst monolith that can be electrically heated in the housing, as well as from a voltage source. It consists of means for heating a catalytic monolith that can be heated. In a preferred embodiment, the electrically heatable catalytic monolith is in contact with or embedded in the upstream surface of a conventional ceramic catalytic monolith. Alternatively, an electrically heatable catalytic monolith may be placed between two normal monolith moieties, such that at least one of the normal monoliths contains a noble metal catalyst placed in that compartment. Can be done.

【0013】

Conventional ceramic catalytic monoliths offer several advantages. First, it is relatively easy to modify existing contact converters. Second, ceramics provide good heat storage, and the main catalyst device more quickly removes contaminants, for example, with less energy loss in corrugated thin metal monoliths that heat non-electrically. It makes it possible to detoxify. Finally, ceramic monoliths appear to provide even better catalyst protection than metallic, non-electrically heated catalytic monoliths.

【0014】

The present invention may be better understood by reference to the drawings illustrating preferred embodiments of the present invention.

【0015】

As mentioned above, the present invention relates specifically to composite contact converters for use in movable or fixed compression or spark ignition internal combustion engines. This composite contact converter uses a single housing for the EHC and at least one conventional contact converter. Common contact converters are ceramic monoliths, such as cordierite or barium / titanate ceramics. For example, most modern automobiles have a ceramic monolith in a contact converter. In particular, the present invention modifies a common ceramic contact converter with a contact converter (EHC) that can electrically heat it so that the catalyst is at a temperature lower than the temperature required for optimal conversion of contaminants. Provided is a means for improving the efficiency of a device for removing contaminants generally coming out of an exhaust pipe during start-up or cold operation.

【0016】

Then, more specifically with reference to FIG. 1, this figure shows a cross section of a portion of a composite contact converter according to the present invention. The complex 10 includes a conventional multi-segment ceramic monolith 12 of the type commonly used in automobiles. These monoliths are known and their cross section can be circular or oval. Such monoliths are porous. They are formed by extrusion of refractory compositions and have straightening compartments, usually with a number of compartments of about 100-400 per square inch. These compartments can have a circular, square or triangular cross section, and of a noble metal catalyst, such as platinum or palladium, or rhodium, or ruthenium, or these metals deposited in the pores of a ceramic monolith. It has two or more mixtures.

【0017】

The ceramic core 12 is preferably supported by the packaging of the fibrous ceramic insulator 14 in the steel housing 16. For fibrous ceramic insulating formulations, see, for example, US Pat. No. 3,795,524 dated March 5, 1974 to Bowman. The steel house jig 16 is a normal housing for such a ceramic monolith, similar to that shown in FIG. However, in FIG. 1, the front end, or upstream end, of the housing is in contact with the upstream surface of a normal monolith to allow an insert that includes an electrically heatable contact conversion device 18, such as that shown in FIG. It has been carefully cut. The front end of the ceramic core 12 is hollowed out to provide a recess 20 having a depth equal to the width of the thin metal foil forming the EHC 18 to accommodate the electrically heatable device 18. Within the recess 20, there is also an inner recess 21 for receiving the protruding end of a conductive rod or pin with each corrugated metal strip folded over it. The indentation 21 is not required when using a barbed rod or tube that has a length equal to the axial dimension of the EHC and the folded ends of the strip are tightly welded. EHC is formed as described in Japanese Patent Application No. 587,219 above, for which particular reference should be made to FIGS. 2, 2a and 5 of the patent application. No inner core insulation or separate flat thin metal strips are used in the EHC cores of the present invention. U.S. Pat. No. 4,711, As noted in No. 009, the thin metal leaf strips are first corrugated, preferably in a arrowhead or chevron pattern, and then on at least one surface a refractory metal oxide, eg, preferably 1-5% up to 30 After coating with gamma alumina including the portion of ceria up to%, firing is performed to fix the coating. After that, an aqueous solution of the noble metal catalyst is applied to the surface of the refractory metal oxide, and the catalyst-coated metal foil strip is heated to a sufficient temperature to reduce the water-soluble catalyst salt to a catalytically active metal. .. Alternatively, the waveform may be straight but not nested, as noted in US Pat. No. 4,810,588 dated March 7, 1989 to Baroque et al. These manufacturing stages are as described in US Pat. No. 4,711,009. Strips carrying the coated catalyst are then folded and welded onto a wire rod as detailed in Japanese Patent Application No. 587,219, and their core elements are collected at the protruding wire ends and then spirally formed. Wrap it tightly. The pins form a central core through which power is supplied to the catalytic core. As noted in Japanese Patent Application No. 587,219, the free end of the folded corrugated strip provides an electrical connection means for finally connecting to one of the poles of the DC power supply. The corrugated metal folding strip without any rod is spot welded directly to the rod or tube core as described above to connect the tube or rod to one side of the power supply. As noted in No. 219, the free end of the folded corrugated strip is finally equipped with an electrical connection means for connecting to one of the poles of the DC power supply. Corrugated metal folding strips without any rods are spot welded directly to the rods or tube cores as described above to connect the tubes or rods to one side of the power supply. As noted in No. 219, the free end of the folded corrugated strip is finally equipped with an electrical connection means for connecting to one of the poles of the DC power supply. The corrugated metal folding strip without any rod is spot welded directly to the rod or tube core as described above to connect the tube or rod to one side of the power supply.

【0018】

Figure 2 shows an EHC that does not have protruding pins and juxtaposes the upstream surface of a normal ceramic catalyst core. Normally, EHC has a smaller cross-sectional area than a normal ceramic core, and therefore in the upstream surface of the ceramic core so that the pressure drop across the surface of the gas blocking surface can be kept approximately the same. It is desirable to retract the EHC at least partially. If the cross-sectional area of the EHC is equal to or approximately equal to the cross-sectional area of the ceramic core, the EHC can be positioned in contact with the upstream surface of the ceramic core as shown in FIG.

【0019】

The spirally wound core is then held in a steel band. FIG. 4 shows a semi-processed piece 22 generally made of stainless steel, for example ferritic stainless steel, with a width of about 0.75 . At the center of one edge 24 of the semi-processed piece 22, there is a protrusion 26 integrated with the band. It is desirable that the width of the tip 28 of the protrusion 26 is 0.75 , and the protrusion 26 extends approximately 0.75 outward. This protrusion is for attaching a power terminal later as described later. The edge 30 is at an angle of about 135 degrees with respect to the edge line 24. As shown in FIG. 5, the blank of FIG. 4 is rolled into a circle having the same diameter as the tightly compressed spiral core. This circle does not close initially, leaving a gap 32 of about 0.12 to allow compression of the spirally wound core after insertion into the band 22. Weld to the free end of the spiral core as noted in the patent application of serial number 587,219 to provide good electrical communication between the band 22 and the core 18.

【0020】

FIG. 3 shows the side elevations of the EHC assembly before insertion into the ceramic core 12. The central terminal 34 protruding from the spirally wound core 18 on both sides is a point for attaching the opposite pole of the DC power supply.

【0021】

6 and 7 show the transition end cap 38, which allows the contact converter to be connected to the exhaust pipe of the engine, or formed to fit between the adapter 38 and the body of the contact converter housing 16. The extension portion 36 is shown. The extension portion 36 has an oval or circular shape depending on the cross-sectional shape of the contact converter housing or container. The extension 36 includes an oval or circular band 40 and a ground rod 42. The ground rod 42 is preferably made of nickel or a nickel alloy. It extends along the minor or circular extension of the oval extension.

【0022】

The ground rod 42 extends through the extension portion 36 and is welded at the bottom 48 and the head 46 as shown in FIG. The protrusion 44 from the head is extended and threaded to accommodate cable terminals and retaining nuts not shown in the figure. A hole 50 is provided through the wall of the extension 36 to allow the thermocouple to be inserted into the corrugated thin metal core 18. Details on the structure of the thermocouple lead-in are given in Japanese Patent Application No. 587,219. The thermocouple connection points are placed in a compartment in a corrugated metal monolith and the conductors are insulated over their entire length and where it passes through the extension 36.

【0023】

The positive terminal 52 also generally extends through the extension 36 with the appropriate insulating means shown in 51. A metal bush 54 welded to the collar 56 is provided, while the collar 56 is welded to the extension 36. The terminal 52 is placed in an insulating sleeve 54 to isolate it from electrical contact with the inner end of the terminal rod 52. The inner end 58 is then welded to the protrusion 26 of the tightening band 22, while the band 22 is welded to the free end of the corrugated thin metal folding strip forming the multi-partition core 18 as described above. Thus, the anode of the DC power supply is electrically connected to the voltage source.

【0024】

Grounding, that is, connecting the cathode of the DC power supply to the protruding end 44 of the grounding rod 42. The ground rod 42, then upon attachment to the downstream end of the converter housing 16 of the extension 36, consists of a number of protruding rods with thin corrugated metal strips folded around and welded together. Weld to the center rod 34. These operations are described in detail in Japanese Patent Application No. 587,219. If desired, the anode and cathode can be reversed.

【0025】

After inserting the EHC18 together with the extension part 36 into the recess 20 of the ceramic converter body 12, the transition part 38 (Fig. 8) is welded to the outer free end of the extension part 36 to complete the refurbished composite contact converter. Then reattach the entire assembly to the exhaust pipe 60.

【0026】

As mentioned above, the EHC has multiple compartments like a normal catalyst unit. EHC monoliths have a partition density of 100-700 compartments per square inch, preferably 150-300 compartments per square inch, and conventional contact converter units, typically made of ceramic, have a compartment density of 100-400 compartments per square inch. have. If the EHC must be separated from the ceramic converter unit for any reason, it will be accompanied by a catalyst deposited between the upstream surface of the normal contact converter unit and the downstream surface of the EHC, preferably in the compartment. A ceramic block with an axial length of about 2 inches and a partition density of 16-36 compartments per square inch may be inserted.

【0027】

Thus, when delivering 1500-5000 watts of power from a power source, such as a 12 volt car battery, to terminals 44 and 52, that power is supplied to the corrugated thin metal core 18 by the resistance of the thin metal strip portion. Heating of a contact converter, which can be electrically heated, can be achieved very quickly, up to a conversion temperature of at least about 650 ° F in 2-30 seconds.

【0028】

The embodiments shown in FIGS. 1-9 withstand harsh test conditions for at least 5 hours without being compressed by the EHC core.

【0029】

FIG. 9 shows another embodiment of the invention, in which the EHC is placed coaxially between the two parts of the ceramic monolith in contact with them. The oval or circular housing 70 shown in this figure has transition end caps 72 and 74 welded to it for adaptation to a standard exhaust pipe 60, as in FIG. A pair of axially spaced ceramic catalyst monoliths 78 and 80 are centrally located in the housing. They are inserted into the housing using a ceramic mat cushion 82. In the case of ceramic monoliths 78 and 80, the mat 82 helps reduce the likelihood that the monolith units 78 and 80 will be damaged by vibration.

【0030】

The ceramic mat 82 also suppresses the axial movement of the ceramic monoliths 78 and 80, thereby also helping to hold the core of the EHC against axial movement or compression, especially in the downstream direction.

【0031】

Similar to the electrically heatable catalyst unit 18 shown in FIG. 1 except that the band 86 does not need to have protrusions 26 (FIGS. 4 and 5) between and in contact with the monolith units 78 and 80. A contact converter 84 that can be electrically heated is located. Band 86 encloses a bundle 88 of spirally wound folded corrugated thin metal strips, similar to those shown in Japanese Patent Application No. 587,219, FIGS. 1, 2, 2a, 3, 4 and 5. I'm out. A bundle of steel rods 34 (FIG. 3) protrudes from both sides of the spirally wound core 18 and the corresponding indentations 90 and 92 accept the protruding ends 98 and 100 as shown in FIG. It is provided in. A hole 92 in the downstream monolith 80 communicates with a shaft hole 102 for receiving a conductive rod 104, while the rod 104 is welded to a radially extending rod 106 at its inner end 108. The tip of the rod 106 is welded to it as it exits the housing 70 and accepts support nuts and tightening nuts (not shown) to hold the cable terminals from the grounding electrode of the power supply 112 conceptually shown. , 110 can have a screw. The positive terminal 113 is a suitable type of insulated feedthrough (eg, Patent Application No. 587, Insert through the insulated feedthrough) shown in 74 and 76 in Figure 4 of No. 219. The terminal 113 is welded to the band 86 that surrounds and holds the bundle 84 at its inner end 116. Terminal 113 is threaded at its cutting edge 118 to receive and hold the cable from power supply 112. The monoliths 78 and 80 have 16-400 compartments per square inch, preferably consisting of extruded ceramics with axial dimensions of 1 to 3 , preferably 2 , and a noble metal catalyst. It is carried. The upstream portion 78, i.e. the monolith 78, can be omitted in some cases. The monoliths 78 and 80 are pressed firmly against the EHC unit 84. The fit between the ceramic mat 82 and the housing 70 must be tight to prevent downstream slippage and compression of the EHC core 84. The outer diameter of the ceramic unit may be the same as or different from the outer diameter of the EHC. A thermocouple 119 is used. Within the EHC84 is a junction 121 located with a lead and a plug 12 extending through the housing by feedthrough 123.

【0032】

FIG. 10 shows a cross section of another embodiment of the present invention. In this case, the EHC 120 has a diameter smaller than the diameter of the ceramic portions 122 and 124. The upstream portion 122 has a suitable hole 126 and a recess 128. The downstream portion 124 has a suitable hole 130 and a recess 132. These recesses 128 and 132 correspond to the extensions 134 and 136 of the core rod 138. The downstream recess 132 is truncated at a hole 140 to receive the current-carrying shaft rod 142, and the rod 142 is welded to the radiant current-carrying rod 146 extending through the housing 148 at its downstream tip 144. .. The extension through the housing is totally insulated from the housing 148 by the appropriate feedthrough shown in 150. See Figure 3 of Japanese Patent Application No. 587,219 for more information on proper feedthrough. The facing surfaces 152 and 154 of the ceramic portions 122 and 124 have an axial spacing of about 0.5 to fit one or more radiating current transfer rods 156 and 158. The medial ends of the rods 156 and 158 are respectively welded to a holding band 160 that joins a number of folded corrugated thin metal leaf strips forming the core 120 of the EHC as described above. It is convenient to weld the outer ends of the rods 156 and 158 to the housing 148. Rods 156 or 158 may be extended and threaded at the tip to accommodate cable mounting projections not shown in the figure.

【0033】

FIG. 10 shows, for example, having a thermocouple that passes through the EHC 120 and exits the housing 148 through a suitable feedthrough 162, as shown in FIG. 3 of Japanese Patent Application No. 587,219. The ceramic monoliths 122 and 124 are properly held within the housing by the surrounding ceramic mat 164 compressed in the space between the housing 148 and the ceramic block or portion 122 and 124.

【0034】

The close juxtaposition of the ceramic block or portion 124 with respect to the downstream end of the core 120 prevents compression in the downstream direction of the core 120.

【0035】

In this way, by forming a composite contact converter consisting of one part that is an EHC and the other part that is a normal contact converter, an electrically thin metal with a spiral or S-shaped corrugation is formed. It has been possible to provide a means for improving the performance of a contact converter that can be heated. Both parts are placed in parallel by fitting the EHC partially or completely into a conventional contact converter. Combined converters, which can be either modified devices as shown in Figures 1-8 or OEM devices as shown in Figures 9 and 10, are suitable for installation in a normal exhaust system and are by the manufacturer. It is durable enough to withstand rigorous testing and is therefore recognized to withstand harsh conditions of use. The device of the present invention can be contained in a single can or housing located in the exhaust line under the floor of the vehicle or in contact with the engine exhaust manifold.

[Simple explanation of drawings]

[Figure 1]

A cross section of a composite contact converter according to the invention, showing a thin corrugated metal contact converter that is fitted into the upstream surface of a normal ceramic contact converter that cannot be electrically heated and can be electrically heated. It is a figure.

[Figure 2]

It is sectional drawing of the composite contact converter according to this invention which shows the contact converter which can be electrically heated juxtaposed with the upstream surface of the ordinary ceramic contact converter which cannot be heated electrically.

[Fig. 3]

It is a side elevation view of EHC before insertion into a hole in the plane of a normal ceramic contact converter.

[Fig. 4]

A semi-processed piece with a developed current transfer band for EHC.

[Fig. 5]

It is a front view of the band of FIG. 3 when it is wound to surround the thin metal catalyst core having a spirally wound waveform shown in FIG.

[Fig. 6]

A front view of an extension for insertion into the housing of a conventional contact converter to accommodate a core capable of electrically heating, powering the EHC. Also shown is an electrical connecting rod for.

[Fig. 7]

It is a terminal view of the extension part shown in FIG.

[Fig. 8]

It is a side view of the modified housing containing the composite contact converter according to this invention.

[Fig. 9]

Sectional view of another composite contact converter according to the invention, in which at least one is placed on the inner surface of the compartment between two multi-compartment ceramic portions containing the catalyst in physical contact with them. , Shows a thin corrugated metal contact converter that is coaxial with them and can be electrically heated.

[Fig. 10]

FIG. 5 is a cross-sectional view of yet another composite contact converter according to the present invention, showing an EHC partially fitted in the facing planes of two ceramic multi-partition contact converter portions.