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    • 专利摘要:
    SYSTEM FOR TREATING EXHAUST GASES CONTAINING NOx FROM AN ENGINE, AND, METHOD FOR TREATING A CHAIN OF EXHAUST GAS CONTAINING NOx AND SOUL A system for treating exhaust gases from a combustion engine and a method for using the same one that results greater conversion of NOx during engine start-up. The system includes a compact SCR throughflow monolith (20) installed upstream of a compactly coupled SCR wall flow filter (22), in which the compact SCR throughflow monolith can be extruded or made from a thin-walled substrate, such that the SCR through-flow monolith has a smaller volume with less thermal capacity and greater catalyst loading compared to the SCR wall-flow filter.
    公开号:BR112015008400B1
    申请号:R112015008400-1
    申请日:2013-10-17
    公开日:2021-01-19
    发明作者:Paul Richard Phillips；James Alexander Wylie
    申请人:Johnson Matthey Public Limited Company；
    IPC主号:
    专利说明:

    FIELD OF THE INVENTION
    [001] This invention relates to the purification of exhaust gases from combustion engines. BACKGROUND OF THE INVENTION
    [002] One of the most troublesome components of vehicle exhaust gas is NOx, which includes nitric oxide (NO), nitrogen dioxide (NO2), and nitrous oxide (N2O). NOx production is particularly problematic for low-burn engines, such as diesel engines. To mitigate the environmental impact of NOx in the exhaust gas, it is desirable to eliminate these undesirable components, preferably by a process that does not generate other harmful or toxic substances.
    [003] In addition to the production of NOx gases, poorly burning combustion engines, due to their combustion characteristics, have the disadvantage of generating particulate matter, or soot, in which a variety of organic substances can be absorbed, including non-hydrocarbons. burning and sulfuric acid produced by the oxidation of sulfur dioxide derived from sulfur species present in fuel or lubricants. Exhaust gas from diesel engines tends to have more soot compared to gasoline engines.
    [004] Because exhaust gases from poorly combustion engines contribute to air pollution, treatment systems are critical to minimize the polluting effects of operating a poorly combustion engine.
    [005] Two methods are commonly used to reduce pollutants in the exhaust gases of combustion engines with poor combustion. The first method converts NOx into a diesel exhaust gas into more benign substances, also known as selective catalytic reduction (SCR). An SCR process involves converting NOx, in the presence of a catalyst and reducing agent, typically anhydrous ammonia, aqueous ammonia, or urea, to elemental nitrogen (N2) and water. The second method reduces soot emissions by passing the soot-containing exhaust gas through a particulate filter. However, the accumulation of soot particles in the filter can cause an undesirable increase in exhaust system back pressure during operation, thereby decreasing efficiency. To regenerate the filter, the accumulated carbon-based soot has to be removed from the filter, for example, periodically burning the soot by passive or active oxidation at high temperatures.
    [006] It is known from WO 99/39809 to combine numerous separate individual components in an exhaust system, including an SCR catalyst, to treat, among others, particulate matter and nitrogen oxides. For example, an exhaust gas stream from an engine combined with a reducing agent can first flow through a through-flow monolith incorporating the SCR catalyst to reduce NOx and then the gases are additionally treated downstream to remove particulate matter, passing through a particulate matter filter. The drawback of such designs is that the increase in the number of components after treatment of the exhaust gas increases the overall cost of the exhaust system, and also increases the total volume and weight of the system, which is particularly disadvantageous for vehicles. The heavier a general vehicle exhaust system, the more fuel the vehicle needs to transport it.
    [007] To overcome the above noted inconveniences, exhaust systems with a single component capable of reducing NOx and particulate matter were designed. US patent publication 2010/0180580 discloses a system of combining an SCR catalyst with a wall flow filter. Wall flow filters contain multiple adjacent parallel channels, which are capped at one end, where capping occurs at opposite ends of adjacent channels in an alternating pattern. Capping of alternating channel ends prevents gas entering the filter inlet from flowing directly through the channel and out of that channel. Instead, the exhaust gas enters the front of the substrate and travels in approximately halfway through the channels where it is forced through the channel walls before exiting through the outlet face of the substrate. The catalyst is typically applied to the walls of the wall flow filter in the form of an aqueous mixture, or reactive coating composition, and then calcined to adhere to the surface of the walls.
    [008] The disadvantage of certain SCR wall flow filters is that a limited amount of catalyst can be applied to its surface. A thick reactive coating composition will narrow the channels and, in some cases, the pores, and prevent the gas flow from contributing to the back pressure and negatively affecting the efficiency of the system. A known method for reducing back pressure involves limiting the volume of the applied reactive coating composition. Less reactive coating composition results in less catalyst and the ability of the filter to convert NOx. Finally, coating the SCR catalyst on the surface of a wall flow filter increases the overall weight of the filter. Greater mass will require more time and energy to heat the wall flow filter to the temperatures required to activate the catalyst, which is a considerable disadvantage in starting when the engine has not yet reached its normal steady state operating temperatures. To increase the heating rate of an SCR wall flow filter, the filter can be arranged close to the engine.
    [009] A known method for overcoming the disadvantages associated with an SCR wall flow filter is to place an SCR throughflow monolith upstream of the wall flow filter. Cross-flow monoliths with a so-called honeycomb geometry comprise multiple adjacent parallel channels that are open at both ends and generally extend from the entrance face to the exit face of the substrate. Each channel typically has a square, round, hexagonal or triangular cross section. Catalytic material is applied to the substrate typically as a reactive coating composition or other paste that can be incorporated onto and / or into the substrate walls. SUMMARY OF THE INVENTION
    [0010] The claimants have discovered a system to treat the exhaust gas of a low-combustion combustion engine that reduces NOx and soot. The system comprises a compact SCR throughflow monolith which is located upstream of a compactly coupled SCR wall flow filter.
    [0011] In the form used here, the expression "compactly coupled" refers to a position of the component in an engine exhaust gas treatment system that is less than about 1 meter downstream of the gas collector. exhaust or turbocharger of the engine, preferably about 0.05 to about 0.5 meter. When starting or operating an engine under heavy load, components in a compactly coupled position are typically exposed to higher exhaust gas temperatures, compared to further downstream components. It has been found that the combination of a compact SCR throughflow monolith and a compactly coupled SCR wall flow filter separately has a synergistic effect that is not seen in combinations of SCR throughflow monoliths and SCR filters. SCR wall flow downstream or larger SCR wall flow filter that are not coupled close to the engine. Furthermore, this effect is not observed in a single SCR wall flow filter with a volume and catalyst loading equivalent to the SCR through-flow monolith and SCR wall flow filter of the present invention combined. In particular, the synergistic combination of SCR components produces a soot combustion efficiency that is greater than that of conventional SCR through-flow monolith and SCR wall flow filter combinations. In addition, the synergistic combination of components produces greater NOx conversion compared to a single SCR wall flow filter compactly coupled with a volume and catalyst loading comparable to the synergistic combination of components. That is, the synergistic combination of components of the present invention improves the overall NOx conversion efficiency of an SCR / soot filtration system without the need for an additional catalyst, thus reducing the cost of the system, while also providing stability at high temperature of the wall flow filter to favor consistent filter regeneration.
    [0012] The compact SCR throughflow monolith is characterized in that it has a lower thermal capacity compared to the SCR wall flow filter downstream. The lower thermal capacity may result from a SCR direct flow material with a lower specific thermal capacity and / or a lower volume or mass compared to the SCR wall flow filter.
    [0013] In this way, an aspect of the invention provides a system for treating exhaust gases containing NOx from an engine, said system comprising (a) a through-flow monolith with a first catalytic composition for selective catalytic reduction of NOx and with a first volume; (b) a particulate matter filter compactly coupled with a second catalytic composition for reducing particulate matter and selective catalytic reduction of NOx and with a second volume; and (c) a volume ratio of the first volume to the second volume of less than about 1: 2; wherein said through-flow monolith is in fluid communication with said particulate matter filter, and incorporated upstream of it.
    [0014] In accordance with another aspect of the invention, a method is provided for treating an engine exhaust gas stream containing NOx and soot comprising: putting said exhaust gas stream, in the presence of a reducing agent, in contact with a through-flow monolith with a first charge of the SCR catalytic composition and a first volume to produce an intermediate gas stream, wherein a first portion of said NOx has been converted to N2 and O2; placing said intermediate gas stream in contact with a compactly coupled catalytic particulate filter with a second loading of the SCR catalytic composition and a second volume, wherein said second volume is at least about twice the first volume, to trap a portion of the soot and produce a clean gas stream, in which a second portion of said NOx has been converted to N2 and O2; oxidizing said soot portion at a soot oxidation temperature to regenerate the catalytic particulate filter; heating said compactly coupled catalytic through-flow monolith to an activation temperature of the SCR catalyst before heating said catalytic particulate matter filter to an activation temperature of the SCR catalyst; and maintaining, and, low load conditions, said soot oxidation temperature of the catalytic particulate matter filter for a longer period of time, compared to a catalytic particulate matter filter with a volume equal to said first and second combined volumes. BRIEF DESCRIPTION OF THE DRAWINGS
    [0015] Figure 1 is a schematic representation of an embodiment of an engine exhaust gas treatment system according to the present invention; and Figure 2 graphically illustrates the total NOx mass converted at engine start by a system including only an SCR wall flow filter and a system according to the present invention. DETAILED DESCRIPTION OF THE INVENTION
    [0016] This invention provides an unprecedented system for treating the exhaust gas of a low-combustion combustion engine comprising a series of temperature-stabilized SCR catalysts to produce better NOx conversion and greater soot combustion efficiency. In particular, the invention involves a system for reducing soot and treating NOx in an exhaust gas comprising a compact SCR throughflow monolith located upstream of a compactly coupled SCR wall flow filter. The invention is believed to have particular application in exhaust gases from heavy-duty diesel engines, especially vehicle engines, for example, truck or bus engines, but should not be considered limited to this. Other applications can be LDD (light duty diesel), GDI (direct gasoline injection), CNG (compressed natural gas) engines, ships or stationary sources. For simplicity, however, most of this description refers to such vehicle engines.
    [0017] Because the SCR wall flow filter is compactly coupled, the overall length of the compact SCR throughflow monolith used in the present invention must be less than the space provided between the SCR wall flow filter SCR and the engine outlet to also accommodate other exhaust system components, such as the reducing agent injection point or an oxidation catalyst. The compact SCR throughflow monolith must also be light in order to warm up quickly to the catalyst activation temperature during engine start. Prior to the present invention, the structural integrity of a light compact through-flow monolith such as this was questionable.
    [0018] The compact monolith assists in the reduction of NOx, particularly when starting the engine. The heavier SCR wall flow filter, upon heating to the activation temperature of its SCR catalyst (ie, catalyst activation temperature) during steady-state engine operating temperatures, will then convert a larger portion of NOx into the gases exhaust after departure. Because the SCR wall flow filter is heavier and compactly coupled to the engine, it will take longer to cool and therefore maintain NOx conversion while the engine is operating in low load conditions or is running thus improving its soot oxidation efficiency.
    [0019] Because the compact SCR throughflow monolith of the present invention is small and therefore has limited surface area in which a catalyst can be applied, it is preferable to provide conditions for the monolith to be heavily charged with catalyst per unit volume of monolith. It is also preferable that the compact SCR throughflow monolith has a catalyst load per unit volume which is greater than the catalyst load per unit volume of substrate in the SCR wall flow filter used in the present inventive system. The compact monolith has a preferred catalyst loading range of about 182.94 to about 914.7 kg / m3 (about 3 to about 15 g / in3), more preferably about 243.92 to about 609 , 8 kg / m3 (about 4 to about 10 g / in3). In comparison, the SCR wall flow filter preferably has a catalyst loading range of about 60.98 to about 170.74 kg / m3 (about 1 to about 2.8 g / in3), for example example, 91.47 to 152.45 kg / m3 (1.5 to 2.5 g / in3). Thus, in certain embodiments, the SCR catalyst loading rate per unit volume on the compact monolith compared to the particulate wall flow filter is about 15: 1 to about 1.5: 1, for example, about from 4: 1 to about 2: 1. The SCR catalyst in the throughflow monolith and the SCR catalyst in the wall flow filter can be the same catalyst, or a different catalyst. In certain embodiments, the SCR catalyst in the upstream through-flow monolith is an iron-promoted zeolite and the SCR catalyst in the downstream wall-flow filter is a copper-promoted zeolite.
    [0020] The dimensions of the compact monolith are also selected, in part, based on the desired thermal capacity per unit of volume for the compact monolith. The "volume" in the form used here is determined by the external dimensions, for example, length and diameter, of the monolith or filter. As previously mentioned, the compact size and weight of the SCR through-flow monolith allows it to warm up quickly during engine start to the catalyst activation temperature and provides an exhaust gas treatment system with better NOx conversion. desired values of the compact monolith can be expressed in relation to the size of the SCR wall flow filter downstream. The volume of the compact monolith of the present invention is preferably about 10% to about 75% of the volume of the SCR wall flow filter, more preferably about 15% to about 50%, more preferably about 15% to about 40%, and above all preferably about 20% to about 25%. Preferably, the volume ratio of the throughflow monolith to the volume of the wall flow filter is less than about 1: 2, for example, about 1:10 to about 1: 2, or about 1: 6 about 1: 4.
    [0021] In addition to selecting the dimensions of the compact monolith, the types of material used to produce the compact monolith are selected based on the desired thermal capacity per unit volume of the compact monolith because the thermal capacity depends on the material properties of the object to be heated. Similar to volume, the desired thermal capacity per volume unit (i.e., specific thermal capacity) of the compact monolith can be expressed in relation to the specific thermal capacity of the wall flow filter. The specific thermal capacity of the compact throughflow monolith is preferably about 20% to 80% of the specific thermal capacity of the wall flow filter, more preferably 25% to 75%, above all preferably 35% to 65%.
    [0022] In a first preferred embodiment, the compact monolith used in the present invention is extruded. The extruded monolith is manufactured by first combining starting materials including a catalyst, a binder, and optionally inorganic fibers to form a suspension. The suspension is further processed by mixing and / or further kneading in an aqueous acidic or alkaline mixture. An organic reagent is added to the aqueous mixture to produce a composition suitable for extrusion. After extruding the composition in the form of a monolith, it is dried and calcined. The result is that the monolith has sufficient mechanical stability and effective activity for long-term application.
    [0023] By extruding a catalyst composition in the form of a monolith, the need for a substrate coated with a catalyst is eliminated and replaced with the catalyst body with the catalyst material throughout the body. Therefore, extruded monoliths typically contain more catalyst per unit volume than inert substrates to which a reactive coating composition containing a catalytic component is applied. An extruded catalytic monolith can be compact and lightweight, allowing it to be placed upstream of an SCR wall flow filter in the present inventive system.
    [0024] In a second preferred embodiment, the compact monolith used in the present invention is manufactured first by preparing an aqueous mixture including a catalytic component and optionally a binder, and applying the aqueous mixture to an inert substrate in the form of a monolith which is then dried and calcined. Because a light monolith is desired, a material must be selected that will provide thin walls to allow an effective amount of the catalyst to be applied to its surface without sacrificing the mechanical stability of the monolith for long-term application in the present invention.
    [0025] The flow-through monolith is preferably a hive with a plurality of channels that are opened at both ends and pass through the monolith in an approximately parallel direction. The cross-sectional shape of the channels is not particularly limited and can be, for example, square, circular, oval, rectangular, triangular, hexagonal, or the like. Preferably, the through-flow monolith (both extruded catalyst and inert substrate) contains about 150 to about 800 channels per square inch (cpsi) (1 in2 = 6.45 cm2), and more preferably about 300 to about 400 cpsi (1 in2 = 6.45 cm2) or about 600 to about 800 cpsi (1 in2 = 6.45 cm2). In certain embodiments, the through-flow monolith (both extruded catalyst and inert substrate) may have walls with an average wall thickness of less than about 0.30 mm, less than about 0.25 mm, less than about 0 , 22 mm, or less than about 0.20 mm. In certain embodiments, the cell walls will have an average thickness of about 0.30 mm to about 0.25 mm, about 0.25 mm to about 0.22 mm, or about 0.22 mm to about 0.20 mm.
    [0026] The throughflow monolith is preferably constructed of one or more materials which include, as a predominant phase, ceramics, cermet, metal, oxides, and combinations thereof. Combinations mean physical or chemical combinations, for example, mixtures, compounds, or composites. Some materials that are especially suitable for the practice of the present invention are those made of cordierite, mullite, clay, talc, zirconium, zirconia, spinel, alumina, silica, borides, lithium aluminosilicates, silica alumina, feldspar, titania, pyrogenic silica, nitrides, borides, carbides, for example, silicon carbide, silicon nitride or mixtures thereof. A particularly preferred material is silicon carbide.
    [0027] In accordance with the present invention, the system includes an SCR wall flow filter that is downstream of the compact SCR throughflow monolith, but compactly coupled to the engine. Such SCR wall flow filters are known in the art and can include catalysts equal to or different from the compact direct flow filter used in the present inventive system. The catalyst is incorporated into the wall flow filter by applying a reactive coating composition of the catalyst to a substrate before calcination. A vacuum is commonly used to extract the reactive coating composition through the filter walls. Conventional diesel wall flow filter substrates typically have several parallel channels and contain about 250 to 800 cpsi (1 in2 = 6.45 cm2), for example about 250 to 350 cpsi (1 in2 = 6.45 cm2 ), and are provided in the form of both a ceramic and metallic hive. The channels are defined by porous walls and each channel has a lid on both the inlet and outlet faces of the substrate. Wall flow filter substrates for use in vehicle exhaust systems such as these are commercially available from a variety of sources and can have any form suitable for use in an exhaust system.
    [0028] The walls of the wall flow filter have a porosity and pore size that can make it gas permeable, but allow it to trap a larger portion of particulate matter, such as soot, from the exhaust gas as it it passes through the wall. The substrate can be constructed of a porous material with a porosity of at least about 35%, more preferably about 45 to 55%. The average pore size of the porous substrate is also important for filtration. The average pore size can be determined by any acceptable means, including mercury porosimetry. The average pore size of the porous substrate must be high enough to promote low back pressure, still providing adequate efficiency both for the PER SE substrate, for promoting a layer of soot cake on the substrate surface, and for a combination of both. . Preferred porous substrates have an average pore size of about 10 to about 40 μm, for example, about 20 to about 30 μm, about 10 to about 25 μm, about 10 to about 20 μm, about 20 to about 25 μm, about 10 to about 15 μm, and about 15 to about 20 μm.
    [0029] Preferred wall flow substrates are high-efficiency filters. Efficiency is determined by the percentage by weight of particulate matter with a specific size removed from the untreated exhaust gas when passing through a wall flow substrate. Therefore, efficiency is relative to soot and other similarly sized particles and particulate concentrations typically found in conventional diesel exhaust gas. Particulate in diesel exhaust can vary in size from 0.05 micron to 2.5 microns. Thus, efficiency is based on this range. Wall flow filters for use with the present invention preferably have an efficiency of at least 70%, at least about 75%, at least about 80%, or at least about 90%. In certain embodiments, the efficiency will preferably be about 75 to about 99%, about 75 to about 90%, about 80 to about 90%, or about 85 to about 95%.
    [0030] Catalysts for use in accordance with the present invention include any suitable catalyst that is capable of reducing nitrogen oxides in the presence of a reducing agent. Catalysts include support materials loaded with metal. Suitable catalysts include vanadium, titania, tungsten, or combinations thereof, and also metal, particularly molecular sieves promoted from base metal, including, but not limited to, aluminosilicates and silicoaluminophosphates promoted by copper and / or iron. A particularly preferred metal is Cu. In one embodiment, the transition metal loading is about 0.1 to about 10% by weight of the molecular sieve, for example, from about 0.5% by weight to about 5% by weight, from about 0.5 to about 1% by weight, and from about 2 to about 5% by weight. The type and concentration of the transition metal may vary according to the host molecular sieve and the application. Preferable aluminosilicates have a silica to alumina (SAR) ratio of about 15 to about 50, for example, about 20 to about 40 or about 25 to about 30.
    [0031] Molecular sieves have a suitable structure for SCR processes, including, but not limited to, Beta, CHA, AEI, LEV, MFI, ERI, and mixtures or intergrowths thereof.
    [0032] It is highly preferred that the SCR catalyst present in both the through-flow monolith and the wall-flow filter is arranged in a way that minimizes any restriction of the exhaust gas flow through the component. More than one catalyst can be layered on top of each other. The catalyst material can also be arranged so as to form one or more concentration gradients along the channel walls or through the channels between the upstream side and the downstream side of the wall. A different catalyst can be loaded along the channel walls or on the upstream side and correspondingly downstream side of the walls in a wall flow filter.
    [0033] The system of the present invention can also include a source of reducing agent. The reducing agent (also known as a reducing agent) for SCR processes in general means any compound that promotes the reduction of NOx in an exhaust gas. Examples of suitable reducing agents in the present invention include ammonia, hydrazine, or any suitable ammonia precursor, such as urea ((NH2) 2CO), ammonium carbonate, ammonium carbamate, ammonium hydrogen carbonate or ammonium formate, and hydrocarbons such such as diesel fuel, and the like. Particularly preferred reducing agents are nitrogen-based, with ammonia being particularly preferred. Other reducing agents include hydrocarbons, such as propylene and diesel fuel.
    [0034] The source of the reducing agent fluid can use existing technology to inject fluid into the gas stream. For example, a mass controller can control the supply of compressed NH3, which can be injected through an annular injector ring mounted on a discharge pipe. The injector ring can have a plurality of injection holes arranged around its periphery. Conventional diesel fuel injection systems include pumps and nozzles to inject urea. A stream of compressed air can also be injected around the nozzle to provide good mixing and cooling. In a preferred embodiment of the invention, the injection point of reducing agent is located upstream of the compact SCR throughflow monolith. A second injection point can optionally be included between the compact monolith and the SCR wall flow filter.
    [0035] A difficulty in the treatment of NOx from mobile source applications is that the amount of NOx present in the exhaust gas is transient, that is, it varies with the driving conditions, such as acceleration, deceleration and cruising at various speeds. The transient nature of the NOx component in the mobile exhaust gas presents numerous technical challenges, including correct dosage of nitrogen reducing agent to reduce enough NOx without waste or nitrogen reducing agent emission into the atmosphere.
    [0036] In practice, SCR catalysts can preferably adsorb (or store) nitrogenous reducing agent, thus providing a buffer for the appropriate supply of available reducing agent. Technologists use this phenomenon to calibrate the injection of the appropriate nitrogen reducing agent into the exhaust gas. Low storage capacity will require more frequent injections of reducing agent into the system during operation. An SCR catalyst has a desirable NH3 storage capacity at a given temperature (to ensure that any excess NH3 does not "slip" beyond the catalyst and to allow conversion to continue if NH3 is not present in the feed) and high fraction-independent activity of the NH3 loading level (loading level is defined in relation to a saturated NH3 storage capacity). The NH3 loading level can be expressed as the amount of NH3 (for example, in grams) present in the complete catalyst (for example, in liters) in relation to a maximum loading level under a given set of conditions. It may be desirable to incorporate an ammonia leak catalyst downstream of the SCR wall flow filter, to remove any NH3 or derivatives thereof that could pass through unreacted products or as by-products. Ammonia leakage catalyst can include a double layer catalyst with a reducing component layer, such as a metal-promoted zeolite, and an oxidative component layer, such as platinum or palladium.
    [0037] The current inventive exhaust gas treatment system can also optionally include an oxidation catalyst upstream of the compact SCR through-flow monolith. In one embodiment, the oxidation catalyst is adapted to produce a gas stream that enters the SCR zeolite catalyst with a NO to NO2 ratio of about 4: 1 to about 1: 3 by volume, for example, at an exhaust gas temperature at the inlet of the oxidation catalyst from 250 ° C to 450 ° C. The oxidation catalyst can include at least one metal of the platinum group (or some combination thereof), such as platinum, palladium, or rhodium, coated on a through-flow monolith substrate. In one embodiment, at least one metal of the platinum group is platinum, palladium or a combination of both platinum and palladium. The platinum group metal can be supported in a high surface area reactive coating composition component such as alumina, a zeolite such as an aluminosilicate zeolite, silica, silica, non-zeolite alumina, ceria, zirconia, titania or a mixed oxide or composite containing both ceria and zirconia.
    [0038] In an additional aspect, an engine combined with an exhaust system according to the present invention is provided. The engine can be a diesel engine, a low-burn gasoline engine, or an engine powered by liquefied petroleum gas or natural gas. As seen in Fig. 1, a poorly combustion engine (10) is shown and has an exhaust manifold (12) and optional turbocharger (14) of which an exhaust gas stream from the poorly combustion engine ( 10) moves towards (30) first to an optional oxidation catalyst (28), then to a compact SCR throughflow monolith (20) and then to a compactly coupled SCR wall flow filter (22) . Mounted near and upstream of the compact monolith (20) is an injection point for a reducing agent (24), such as ammonia or urea. A second and optional injection point (26) for a reducing agent is located between the compact monolith (20) and the wall flow filter (22). The gas stream leaving the SCR wall flow filter (22) is treated in such a way that the concentration of NOx gases and particulate matter has been reduced, compared to the exhaust gas that leaves the engine. The location of the SCR wall flow filter (22) in relation to the collector (12) or optional turbocharger (14) is such that the exhaust gas displaces less than 0.5 meters, or even less than 0.3 meter, between the outlet of the collector or turbocharger and the outlet of the wall flow filter. The flow distance of the exhaust gas between the inlet of the compact monolith (20) and the outlet of the collector (12) or turbocharger (14) should not be particularly limited, and is preferably minimized to allow injection and mixing of the optional oxidation catalyst (28) and suitable reducing agent. The flow distance of the exhaust gas between the inlet of the wall flow filter (22) and the outlet of the compact monolith (20) is not particularly limited, as long as at least a certain distance separates the two components. Examples of suitable distances include 0.05 meter, 0.1 meter and 0.2 meter. Components 20, 22, 24, 26 and 28 are all in fluid communication with each other via an exhaust gas conduit or other engine exhaust gas conduit through the treatment system.
    [0039] According to another aspect of the invention, a method is provided for reducing NOx in an exhaust gas stream of a combustion engine, which comprises introducing a reducing agent into the exhaust stream, conducting the gas stream exhaust through a compact SCR throughflow monolith and, finally, conduct the gas that leaves the compact throughflow monolith through a compactly coupled SCR wall flow filter. Particulate matter in the exhaust gas is simultaneously trapped in the SCR wall flow filter. In one embodiment, the temperature of the exhaust gas stream at the inlet of the compactly coupled SCR wall flow filter under heavy load is at least 600 ° C.
    [0040] The method may also include the step of regenerating the SCR wall flow filter. During normal operation of the exhaust system, soot and other particulates accumulate on the entrance sides of the walls which lead to an increase in back pressure. To alleviate this increase in back pressure, the filter substrates are continuously or periodically regenerated by active or passive techniques including burning soot accumulated by known techniques including, for example, in the presence of nitrogen dioxide generated from an upstream oxidation catalyst. As mentioned here, the present inventive exhaust gas treatment system keeps the SCR wall flow filter in a close coupled position which, therefore, provides the advantage of being close to the heat source, providing easier thermal control and allowing regeneration of the filter.
    [0041] The presented method can be carried out on a gas derived from a combustion process, such as an internal combustion engine (either mobile or stationary), a gas turbine and coal or oil power plants. The method can also be used to treat gas from industrial processes such as refining, from heaters and boilers at refineries, ovens, from the chemical processing industry, coking plants, municipal waste plants and incinerators, etc. In a particular embodiment, the method is used to treat exhaust gas from a low-combustion vehicle internal combustion engine, such as a diesel engine, a low-burn gasoline engine, or an engine powered by liquefied petroleum or gas Natural.
    [0042] According to an additional aspect, the system may include a device, when in use, to control the dosage of nitrogen reducing agent in the exhaust gas in motion only when it is determined that the catalyst is capable of catalyzing NOx reduction to an efficiency or above it, such as above 100 ° C, above 150 ° C or above 175 ° C. The determination by the control device can be assisted by one or more suitable sensor inputs indicative of an engine condition selected from the group consisting of: exhaust gas temperature, catalyst bed temperature, accelerator position, gas mass flow exhaust system, collector vacuum, ignition timing, engine speed, exhaust gas lambda value, the amount of fuel injected into the engine, the position of the exhaust gas recirculation valve (EGR) and thereby amount of EGR and intensification pressure.
    [0043] In a particular embodiment, the dosage is controlled in response to the amount of nitrogen oxides in the exhaust gas determined either directly (using a suitable NOx sensor) or indirectly, such as using pre-correlated search tables or maps stored in the control device - correlating any one or more of the aforementioned inputs indicative of an engine condition with the predicted NOx content of the exhaust gas. The dosage of the nitrogen reducing agent can be arranged in such a way that 60% to 200% of theoretical ammonia are present in the exhaust gas that enters the SCR catalyst calculated at 1: 1 NH3 / NO and 4: 3 NH3 / NO2. The control device may comprise a pre-programmed processor such as an electronic control unit (ECU). EXAMPLE
    [0044] The conversion of total NOx at engine start to a system according to the present invention was compared with the conversion of total NOx from a system that includes only an SCR wall flow filter. The SCR wall flow filter comprised an inert silicon carbide substrate with a porosity of 52% and an average pore size of 20 microns. The volume of the wall flow filter was 2.5L. The volume of the compact monolith was 0.625 L. Before the test, the compact monolith and the SCR wall flow filter were aged at 800 ° C for 16 hours. Both systems were tested with a 1.9L engine in an automobile subjected to test conditions associated with the MVEG steering cycle with urea injected as the reducing agent at 180 ° C. The resulting NOx emissions for both systems and a control were plotted as a function of time.
    [0045] The NOx conversion potential provided by the present invention is demonstrated in figure 2, which shows a decrease in the total NOx output in the exhaust gases after passing through a system of the present invention compared to a system using a filter of SCR wall flow alone. Here, line 1 represents the cumulative NOx in the exhaust gas generated by the engine; line 2 represents the cumulative NOx using only an SCR wall flow filter, and line 3 represents the cumulative NOx using a system according to the present invention. Although both systems have significantly reduced total NOx emissions at engine start, the system according to the present invention has demonstrated a higher NOx conversion rate of about 15% to 20%.
    [0046] Although preferred embodiments of the invention have been shown and described here, it is to be understood that such modalities are provided by way of example only. Countless variations, changes and substitutions will occur to those skilled in the art without departing from the spirit of the invention. In this way, it is intended that the attached claims cover all such variations that fit the spirit and scope of the invention.
    权利要求:
    Claims (14)
    [0001]
    1. System for treating exhaust gases containing NOx from an engine, characterized by the fact that the system comprises: a through-flow monolith (20) with a first catalytic composition for selective catalytic reduction of NOx and with a first volume; a compactly coupled particulate filter (22) having a second catalytic composition for reducing particulate matter and selective catalytic reduction of NOx and having a second volume; and in which the through-flow monolith (20) is in fluid communication with the particulate matter filter, and incorporated upstream of it; wherein the through-flow monolith (20) has a volume that is about 15% to about 40% of the compactly coupled particulate filter (22); wherein the first catalytic composition is present in the throughflow monolith (20) in a first loading, the second catalytic composition is present in the particulate matter filter compactly coupled (22) in a second loading.
    [0002]
    System according to claim 1, characterized by the fact that the through-flow monolith (20) is an extruded catalyst block.
    [0003]
    System according to claim 2, characterized by the fact that the particulate filter compactly coupled (22) is an inert substrate coated and / or impregnated with the second catalytic composition.
    [0004]
    4. System according to claim 3, characterized by the fact that the substrate is basically made of both cordierite and metal.
    [0005]
    System according to claim 1, characterized by the fact that the through-flow monolith (20) has a specific thermal capacity that is about 35 to about 65% of the specific thermal capacity of the particulate matter filter.
    [0006]
    6. System according to claim 1, characterized in that the first and second catalytic compositions comprise an aluminosilicate or silioaluminophosphate molecular sieve promoted by base metal.
    [0007]
    7. System according to claim 6, characterized by the fact that the through-flow monolith (20) has a SCR catalyst loading of about 182.94 to 914.7 kg / m3 (about 3 to 15 g / in3).
    [0008]
    8. System according to claim 1, characterized in that the first and second catalytic compositions are different, provided that at least one of the first and second catalytic compositions comprise an aluminosilicate or silioaluminophosphate molecular sieve promoted by base metal.
    [0009]
    9. System according to claim 1, characterized by the fact that the second catalytic composition for selective catalytic reduction of NOx is coated and / or impregnated on one side downstream of the particulate matter filter.
    [0010]
    10. System according to claim 1, characterized by the fact that the second catalytic composition for selective catalytic reduction of NOx is coated and / or impregnated on one side upstream of the particulate matter filter compactly coupled (22).
    [0011]
    11. System according to claim 1, characterized by the fact that the particulate matter filter is about 0.01 to about 0.25 meters downstream of the through-flow monolith.
    [0012]
    System according to claim 11, characterized by the fact that it additionally comprises a source of injection of reducing agent, in fluid communication with and, disposed between, the throughflow monolith (20) and the particulate matter filter.
    [0013]
    13. Method for treating an engine exhaust gas stream containing NOx and soot, characterized by the fact that it comprises: contacting the exhaust gas stream, in the presence of a reducing agent, with a through-flow monolith (20 ) having a first charge of the SCR catalytic composition and a first volume to produce an intermediate gas stream, in which a first portion of NOx has been converted to N2 and O2; put the intermediate gas stream in contact with a compactly coupled catalytic particulate filter (22) having a second loading of the SCR catalytic composition and a second volume, to trap a portion of the soot and produce a clean gas stream in that a second portion of NOx has been converted to N2 and O2; oxidizing the soot portion at a soot oxidation temperature to regenerate the catalytic particulate filter; heating the compactly coupled catalytic through-flow monolith (22) to an activation temperature of the SCR catalyst before heating the catalytic particulate filter to an activation temperature of the SCR catalyst; and maintaining, under low load conditions, the soot oxidation temperature of the catalytic particulate matter filter for a longer period of time, compared to a catalytic particulate matter filter having a volume equal to the first and second combined volumes; wherein the throughflow monolith (20) has a volume that is about 15% to about 40% of the compactly coupled particulate filter (22).
    [0014]
    14. Method according to claim 13, characterized in that the steps of contacting the exhaust gas stream and contacting the intermediate gas stream have a greater conversion of NOx compared to a catalytic particulate filter having an equal volume the first and second combined volumes and an SCR catalyst load equal to the first and second loads.
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    法律状态:
    2018-11-21| B06F| Objections, documents and/or translations needed after an examination request according art. 34 industrial property law|
    2020-03-24| B06U| Preliminary requirement: requests with searches performed by other patent offices: suspension of the patent application procedure|
    2020-12-01| B09A| Decision: intention to grant|
    2021-01-19| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 17/10/2013, OBSERVADAS AS CONDICOES LEGAIS. |
    优先权:
    申请号 | 申请日 | 专利标题
    US201261715584P| true| 2012-10-18|2012-10-18|
    US61/715,584|2012-10-18|
    PCT/IB2013/059427|WO2014060987A1|2012-10-18|2013-10-17|Close-coupled scr system|
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