MXPA99009037A - REDUCING NOx - Google Patents

Abstract

A safe, reliable SCR system for reducing NOx emissions from a lean-burn internal combustion engine utilizes urea in aqueous solution. Overheating and hydrolysis of the solution are prevented by maintaining the temperature of the urea solution sufficiently low that it is not permitted sufficient time at elevated temperature to hydrolyze the urea to such an extent that solids precipitate. In a preferred embodiment, an injector system similar to those used for fuel injection provides a constant feed to injectors (32) and a return line (33). The feed and injection can be controlled to provide sufficient urea for NOx reduction and sufficient cooling capacity for the feed and injection system to avoid hydrolysis and deposits of hydrolysis products.

Description

REDUCTION OF NOx EMISSIONS FROM AN INTERNAL COMBUSTION ENGINE THROUGH THE UREA INJECTION CONTROLLED BY TEMPERATURE FOR SELECTIVE CATALYTIC REDUCTION TECHNICAL FIELD The invention relates to means and methods that allow the safe and reliable reduction of nitrogen oxide emissions (N0X) while allowing a diesel engine or other impoverished combustion engine to operate efficiently. Diesel and gasoline engines with depleted combustion provide advantages in fuel economy but produce both N0X and particulates during normal operation. When primary measures are taken (actions that affect the combustion process itself, eg, exhaust gas recirculation or evacuation and adjustments in engine timing) to reduce one of them, the other usually increases. In this way, the combustion conditions selected to reduce particulate pollution and to obtain good fuel economy tend to increase N0X. Current regulations and proposals impose on manufacturers the challenge of achieving a good economy in fuel and reducing P1563 / 99MX particles and N0X. Inefficient combustion engines will be necessary to achieve the goal of fuel economy, but the high concentrations of oxygen in the evacuation render the typical evacuation gas catalyst systems ineffective to reduce N0X. For the reduction of N0X, SCR (Selective Catalytic Reduction) has been available for some years in some contexts. However, to date, the SCR has relied on the use of ammonia, which has safety problems associated with its transportation and storage. Urea is safer but has not been practical for many SCR applications - particularly, mobile sources of NOx. Due to the difficulty to convert it from a solid form or from an aqueous form to its active gaseous species, normally the NHi and HNCO radicals. There is then a current need for a safe, economical and effective response to the problems associated with SCR, particularly for diesel engines and other impoverished combustion engines.

BACKGROUND OF THE INVENTION When SCR catalysts are used to limit NOx emissions from diesel engines, it has to be treated with either the hazards P1563 / 99I1X of ammonia or with the risk of vitiated catalysts in most conditions. In this regard, see R. J. Hulterman; A Selective Catalytic Reduction Of N0X from Diesel Engines Using Injection Of Urea; doctoral thesis. September 1995. Hulterman describes several technical challenges that include the clogging of atomizers, decomposition problems and system dynamics. Similarly, in SAE No. 970185, entitled "Transient Performance of a Urea DeNOx Catalyst for Emissions Heavy Duty Diesel Engines", it is indicated that the injection nozzles should be protected against excessive heat. Limited attempts to use the SCR with urea for diesel engines have required the use of large pyrolyzing chambers or other devices after the urea introduction point in the evacuation, as disclosed in U.S. Patent No. 5,431,893, to Hug, et al. The team of this type highlights the known problems with urea. Once introduced into the diesel evacuation, the urea requires time to decompose and can cause the nozzle to clog as it is conventionally introduced and as is still proposed in this description. To protect the catalyst against the vitiated, Hug, et al. They propose a bulky team. In addition, this revelation highlights the need to maintain P1563 / 99MX urea solution at a temperature below 100 ° C to prevent decomposition before passing it through the nozzle. They propose the use of moderate urea pressures when the urea is fed and consider it necessary to have an alternative means to introduce high pressure air into the feed line when it is covered. The nozzles used by Hug, et al. they apparently have the ability to produce moderately fine dews whose dispersion is aided by auxiliary air, but the droplets are still large enough to require a large pyrolization channel. See also WO 97/01387 and European Patent Application 487,886 Al. Each of the precautionary points in these references about the difficulties of using urea with SCR systems, especially for mobile sources, point to the problem that the technique has had. and still have. The technique is waiting for the development of a process and an apparatus that allows the use of urea in an SCR process in a simple, reliable, economical and safe way.

SUMMARY OF THE INVENTION It is an object of the invention to provide a safe and reliable SCR system for reducing N0X emissions from an engine of P1563 / 99MX internal combustion. Another object of the invention is to eliminate the security problems associated with the storage and handling of ammonia for mobile uses. It is another object of the invention to enable the use of urea for the reduction of N0X by SCR without the plugging of the feed lines due to the hydrolysis of urea. Another object of the invention is to enable the use of urea for SCR which prevents wetting of the catalyst or deposition of solids thereon. Another object, more specific, of one aspect of the invention is to provide a simple and robust SCR system having the capacity of a fast response time in order to meet the transient conditions prevailing in diesel engines. It is another additional and more specific object of the invention to enable the use of urea in an SCR system that allows the treatment of the exit gas at temperatures between 180 and 650 ° C. It is another additional and more specific object of the invention to enable the use of urea in an SCR system that allows integration with an engine management system (EMS), thus avoiding the need for an additional controller.

P1563 / 99MX Another specific object of the invention is to provide a simple mechanical device for achieving the above objects and, preferably, to enable close coupling of the reagent injection means and the SCR catalyst. These and other objects are achieved by the present invention, which provides an improved method and apparatus for the reduction of N0X. The method of the invention reduces N0X emissions from an impoverished combustion engine having associated thereto an evacuation system having an evacuation passage to transport the exhaust gases containing N0X to an effective reactor for selective catalytic reduction of NOx and, in one embodiment, comprises: feeding an aqueous solution of urea from a storage vessel through a line to an injector; return the urea solution from the injector to the storage container, the feed and return rates will be sufficient to supply the urea as necessary to the exhaust gases for the reduction of NOx and to maintain the temperature of the urea solution sufficiently low such that sufficient time is not allowed at elevated temperature which can hydrolyze the urea to a degree where the solids precipitate (eg, below about 140 ° C); inject the urea solution P1563 / 99MX in the exhaust gases at a sufficient exhaust gas temperature for the SCR and pass the evacuation gas through an SCR reactor. In another mode, the return or return is not used or it is not the only means for maintaining the temperature of the urea solution. In this embodiment, a heat exchange fluid, such as air or a motor coolant, can be passed into contact for thl exchange with the injector. In this embodiment, the temperature of the urea solution can be allowed to rise above 100 ° C, as long as the urea solution is maintained at a pressure above the saturation vapor pressure at the temperature. Among the preferred aspects of the method are the use of concentrated urea solutions, for example, containing at least about 25% by weight of urea. Preferably, the urea is injected when the temperature of the exhaust gases is within the range of from about 180 to about 650 ° C. In one embodiment the apparatus comprises: means for feeding an aqueous urea solution from a storage vessel through a line to an injector; a means to return or return the urea solution from the injector to the storage container, the feeding and return regimes will be sufficient to P1563 / 99MX supply the urea when necessary to the exhaust gases for the reduction of the N0X and to keep the temperature of the urea solution sufficiently low, so that sufficient time is not allowed at high temperature that can hydrolyze the urea to a degree such that the solids precipitate (e.g., below about 140 ° C); an injector means for injecting the urea solution into the evacuation gases at an effective evacuation gas temperature for the SCR; and an evacuation passage means leading from the injector means to an SCR reactor. A preferred embodiment of the apparatus further includes: means for detecting the temperature of the evacuation gas; means for generating a signal representative of the detected temperature of the evacuation gases; a means to detect the load of the motor; means for generating a signal representative of the detected load of the motor; a means for detecting the temperature of the urea solution; means for generating a signal representative of the detected temperature of the urea solution; and a means for comparing the generated signals with reference values and for generating control signals to control the feeding, injection and return of the urea.

P1563 / 99MX BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood and its advantages will be more apparent from the following detailed description, especially when read in light of the accompanying drawing, wherein: Figure 1 is a flow chart showing the main components of one embodiment of the invention.

DETAILED DESCRIPTION OF A PREFERRED MODALITY In this description, the term "impoverished combustion engine" is intended to include engines that can be operated with an input oxygen concentration greater than the amount required for the stoichiometric (or chemically correct) combustion of a hydrocarbon fuel, for example, an oxygen excess of at least 1% by weight. The term "engine", in a broad sense, includes all the combusers that effect the combustion of hydrocarbon fuels to supply heat, for example, for direct or indirect conversion into mechanical or electrical energy. Internal combustion engines of the Otto, Diesel and turbine types, as well as burners and ovens, are included and may benefit from the invention. However, since the problems and advantages of the successful achievement of a reliable NOx reduction in diesel engines are so pronounced, P1563 / 99MX the diesel engine is used throughout this description for example purposes. Stationary and mobile motors are contemplated. With the term "diesel engine or diesel engine" we want to include all compression ignition engines, both for mobile (including marine) power plants and stationary and two-cycle power plants, four times per cycle and the rotary type. The term "hydrocarbon fuel" includes all those fuels prepared from "distilled fuels" or "petroleum fuels". They include gasoline, turbosine, diesel fuel and various other distillate fuels. The term "distillate fuel" refers to all those products prepared by the distillation of petroleum or petroleum fractions and residues. With the term "petroleum" in its normal sense, all those materials are included without considering the source, normally included within the meaning of the term, and include hydrocarbon materials, without considering the viscosity, which are recovered from fossil fuels. The term "diesel fuel" means "distillate fuels" that include diesel fuels that meet the ASTM definition for diesel fuels or for others even when not fully comprised by distillates and may P1563 / 99MX understand alcohols, ethers, organonitro compounds and the like (for example, methanol, ethanol, diethyl ether, methyl ethyl ether, nitromethanes). Emulsions and liquid fuels derived from vegetable or mineral sources, such as corn, alfalfa, shale and coal, are also within the scope of this invention. These fuels may also contain other additives known to those skilled in the art, including dyes, cetane improvers, antioxidants such as 2,6-di-tertiary butyl-4-methylphenol, corrosion inhibitors, oxidation inhibitors. , such as alkylated succinic acids and anhydrides, bacteriostatic agents, gum inhibitors, metal deactivators, upper cylinder lubricants, antifreeze agents and the like. With the term "urea" is meant to cover urea in all its commercial forms, including those that contain: amelide; ameline; ammonium carbonate; ammonium bicarbonate; ammonium carbamate; ammonium cyanate; ammonium salts of organic acids including, sulfuric acid and phosphoric acid; ammonium salts of organic acids including formic and acetic acid; biuret; cyanuric acid; Isocyanic acid; melanin and tricianourea. Normally, the commercial form of urea will consist essentially of urea, which contains 95% or more of urea P1563 / 99MX or an aqueous solution containing urea of this purity. Aqueous solutions of urea can be used up to their solubility limits .. Normally, "the aqueous solution will contain from about 2 to about 65% of the reagent based on the weight of the solution." This is an advantage of the invention that allows you to use concentrated urea solutions The prior art has taught that diluted urea solutions are necessary to avoid problems with the precipitation of the decomposition products The invention allows to use urea to the maximum advantage without the usual problems of ammonia or plugging problems The concentrated solutions are preferred, because they limit the amount of water that must be stored, transported, vaporized and protected against freezing in winter.The typical concentrations of urea are in the range of from about 25 up to about 50%, for example, about 35%. A can be stored in the form of a solution or dried in a can. When stored dry, the water is made to come in contact with the urea as needed to prepare a solution. In this way, the concentration of the solution can be varied from almost saturation (to reduce P1563 / 99MX minimum storage and use of water) or at any suitable concentration for a vehicle or a stationary installation. It is desired, in some circumstances, to provide heaters for the water and / or storage of the urea solution to prevent freezing or to reduce the time for gasification. In the same way, it can be useful to use antifreeze materials. Reference will be made to Figure 1, which illustrates schematically, one embodiment of the invention. Briefly, the diesel engine 10 is fed with fuel through the lines 12 and the injectors 13. The engine produces exhaust gases containing NOx which are passed through the evacuation tube 20. The urea solution is fed from the vessel 30 to the evacuation line 12 by one or more injectors, such as 32. The evacuation gases are then passed through the unit 344 of the SCR reactor. The process is preferably controlled by means of a controller 40, which can be integrated into an engine management system (EMS), thus avoiding the need for an additional controller. In a mode not shown, the urea solution is introduced into the evacuation between the evacuation valves of the engine and a turbocharger evacuation turbine. The invention allows the use of P1563 / 99MX aqueous solutions of urea in place of ammonia for SCR reduction of N0X in a way that prevents plugging of the solution injector feed system with urea hydrolysis product reservoirs or catalyst wetting or formation of solid deposits on the catalyst. The advantages associated with avoiding deposits in the reagent supply system are achieved by ensuring that hydrolysis does not occur in the feed system. The advantage of avoiding deposits on the catalyst is achieved by promoting the rapid decomposition of the urea after the solution is introduced into the evacuation gases. The fact that the invention does not depend on the low concentration of urea to avoid decomposition in the feed lines, increases the decomposition rate of the urea in the evacuation. In addition, the invention does not require the use of air to cool a dilute urea solution to less than 100 ° C - these low temperatures, especially when achieved by the use of large volumes of cold air introduced into the exhaust gases, can retard the decomposition of urea by the evacuation gases. The Figure shows a reagent injector system using a feed line, for example, a common rail 31, with the return to the P1563 / 99MX supply through the spill line 33. This system maintains a continuous flow of reagent between the storage container 30 and the injector 32. The term injector, is used herein to describe any device capable of controlling the flow from the urea solution from rail 31 to the evacuation gases. The injector can be either a high pressure device or a low pressure device. Among the low pressure devices is any of the available means of low pressure liquid distribution, such as a mechanical atomizer of the type used in spray paints, a sonic atomizer, a simple valve that extends into a tube with a dispersion device comprising a plurality of holes to provide a fine spray, a central pivot-controlled nozzle capable of adjustable spray patterns or the like. Air-driven nozzles can be used but it is preferred to operate them with a minimum of air to reduce the cost of the equipment and the effect that the air has on the cooling of the evacuation. In circumstances where neither the air supply nor the cooling effect are unacceptable design compromises, air can be used to cool the injector and / or assist in the injection of the urea solution.

P1563 / 99MX High pressure injectors include injection devices of the type used for fuel injection, which open abruptly from 1000 to 10,000 psig and have peak dynamic injection pressures up to approximately 50,000 psig. The central pivot-type injectors operate with the above-mentioned pressure ranges and can provide the added advantage of the self-cleaning characteristic by scraping to minimize the deposits in the injector at the outlet of the nozzle. Other injectors can also be used, without considering the operating pressure, for example, some operate at pressures of the order of 30 psig. Preferably, an in-line mixing medium is used to ensure good distribution of the urea solution within the exhaust gases, especially when using low pressure injectors. The distribution is important, because high concentrations of the urea solution can cause localized cooling and this can result in droplets of water or in urea particles or in pyrolysis products that survive and then impact the SCR catalyst. A suitable device is shown as the propellant 46. Alternatively, a foraminate body, a mist eliminator, a static mixer, a particulate trap or a P1563 / 99MX similar device that has mixing capacity. The Figure also shows that the bend 21 in the evacuation tube 20 acts as a guard against the contact of the liquid or solid urea or the residues of the urea with the catalyst in the SCR reactor 34. The mode illustrated in the Figure includes a rail pressure sensor 35 and a pressure regulating valve 36. The pressure within the rail and the return lines by the valve 36 and the pump 37, in response control the signals supplied by the controller 40. It will be noted that the pressurized lines 31, 31 '31"are shown in the darkest figure. that the non-pressurized return lines 33 and 33 '. Optionally, a heat exchanger 50 can be used in line 33 to cool the urea solution in case of overheating: Lines 38 and 38' between pump 37 and container 30 provide agitation as needed to the urea solution The controller 40 is preferably integrated to the EMS of the motor 10 to avoid the need for several different controllers and to use the existing wire harness and detectors as much as possible. diverse, detectors and operate to detect the various operating parameters and to generate operating signals representative of the P1563 / 99MX parameters detected. The operation signals are then sent to the controller, the controller compares them with the reference values, calculates one or more control signals and sends the control signals to one or more of the devices that will be controlled. The Figure shows the detector 41 for the motor, the detector 42 for the temperature of the exhaust gases, the detector 43 for the level of the urea in the container 30 and the detector 44 for the temperature of the urea solution in the line return 33. Motor loading, as represented by one or more suitable parameters, such as fuel flow, engine speed, choke position or injection system settings, are important parameters and one of these or as a factor can be monitored to determine the amount of N0x that is being generated and the need to feed reagent to the heating unit or its hydrolysis products fed to the evacuation gases. Optional detectors, such as detector 45 for residual NOx concentrations, can be used for feedback control to the extent that this is practical. The figure also shows in dotted lines the operation signals that will be sent to the controller and the control signals that will be sent to the controlled devices. The temperature of the urea solution in P1563 / 99MX the entire system is kept at a sufficiently low value so that sufficient time is not allowed at the elevated temperature that the urea can hydrolyze to such an extent that the solids precipitate (eg, below about 140 ° C. ). The injector 32 will tend to heat up as the temperature of the exhaust gases increases after startup to within a range of from about 300 ° to about 650 ° C at high load for some engines. Unless precautions are taken, the high temperature will cause urea hydrolysis before injection - causing the hydrolysis products to precipitate due to their lower solubility compared to that of urea. The invention continuously circulates the urea solution of vessel 30 through lines 31 and 33 (and associated lines, as controlled) to provide cooling to the injector. It is practical with the appropriate controls to let the temperature of the solution rise to between 105 ° C and 130 ° C when the system is pressurized to the saturated vapor pressure for the temperatures involved. Because the residence time in the spill line is short, the urea solution can be allowed to reach higher temperatures without reaching the solubility limit of the hydrolysis products. An auxiliary heating medium P1563 / 99MX (not shown) can be used in the container 30 or on some other side of the feed or return system to obtain the desired temperature. It is a distinct advantage of the invention that no air is required to obtain the control temperature - saving on equipment cost and avoiding reduced efficiency due to the effect of air cooling on the exhaust gases. It is also an advantage of the invention that the high pressure injector equipment having a return line can be designed for sufficiently high operating pressures to effect atomization, preferably with at least some gasification of the urea solution with the release of pressure . This feature allows the close coupling of the injector to the SCR reactor 34 to be better. However, in another embodiment, the return lines 33 and 33 'are not used or are not the only means to maintain the temperature. In this embodiment, the heat exchange fluid, such as air or engine coolant, may be passed in heat exchange contact with the injector. In an allowable manner, in this mode, the temperature of the urea solution can be allowed to rise above 100 ° C as long as the urea solution is maintained at a pressure above the saturation vapor pressure at the P1563 / 99MX temperature. It is possible to provide a catalyst that promotes hydrolysis and / or pyrolysis of the urea as a coating on one or more of the component parts of the evacuation system or as a separate element. For example, it could be coated on the evacuation tube 20, especially in the fold 21. It could also be used in the mixing device 46. Coatings of this type have the double advantage of keeping the operating system clean and improving the gasification of the urea. Suitable hydrolysis catalysts include those which comprise a material selected from the group consisting of phosphoric acid and acidic phosphates, alkali metal hydroxides and carbonates, such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, silicates of alkali metals, hydroxides and oxides of alkaline earth metals, aluminum hydroxide and oxides and mixtures of two or more of these. See also U.S. Patent No. 4,997,631 to Hofmann, et al., PCT Application WO 92/02291 to von Harpe, et al., U.S. Patent No. 5,139,754, Hofmann, Sun and Luftglass, U.S. Pat. U.S. Patent No. 5,281,403 to Jones and JP HEI 2-191,528 to Ebina for an additional listing of catalysts and techniques. See also, EP 615,777, which reveals a P1563 / 99MX mixed oxide catalyst of Al203-Ti02-Si? 2-Zr? 2, which has the ability to decompose to urea in diesel evacuation. The SCR catalyst used is one that has the ability to reduce the concentration of nitrogen oxide in the effluent in the presence of ammonia. These include, for example, activated carbon, coal or coke, zeolites, vanadium oxide, tungsten oxide, titanium oxide, iron oxide, copper oxide, manganese oxide, chromium oxide, noble metals, such as metals of the platinum group, such as platinum, palladium, rhodium and iridium and mixtures of these. Other SCR catalyst materials conventional in the art and familiar to the experienced can also be used. These SCR catalyst materials are normally mounted on a support such as a metal, a ceramic compound, zeolite or a homogeneous monolith, although they can also be other supports known in the art may be used. Among the useful SCR catalysts are those representative of the processes of the prior art described below. Selective catalytic reduction processes to reduce NOx are well known and use a variety of catalytic agents. For example, in European Patent Application WO 210,392, Eichholtz and Weiler analyze the catalytic removal of the oxides P1563 / 99MX nitrogen using activated carbon or activated coke, with the addition of ammonia, as a catalyst. Kato et al. in U.S. Patent No. 4,138,469 and Henke in U.S. Patent No. 4,393,031, disclose the catalytic reduction of N0X using metals from the platinum group and / or other metals such as titanium, copper, molybdenum, vanadium, tungsten or oxides thereof with addition of ammonia to achieve the desired catalytic reduction. See also EP 487,886, which specifies a V205 / W03 / Ti02 catalyst with a working range of 220 to 280 ° C. Other platinum-based catalysts may have even lower operating temperatures, for example, up to about 180 ° C. Another process of catalytic reduction is disclosed in Canadian Patent 1,100,292 by Knight, which relates to the use of a metal catalyst of the platinum, gold and / or silver group deposited on a refractory oxide, Mori et al., In the United States No. 4,107,272, analyzes the catalytic reduction of N0X, using vanadium oxysulfide, sulfate or sulphite compounds, chromium, manganese, iron, copper and nickel with the addition of gaseous amoiiaco. In a multi-phase catalytic system, Ginger, in U.S. Patent No. 4,268,488, discloses the exposure of an effluent that P1563 / 99MX contains nitrogen oxides to a first catalyst containing a copper compound such as copper sulfate and a second catalyst comprising metal combinations such as iron and vanadium sulfates or tungsten and iron in a carrier in the presence of ammonia. The effluent to which the urea has been introduced is preferably passed over the SCR catalyst while the effluent is at a suitably high temperature, usually between about 180 ° C and about 650 ° C, for example, at least about 300 ° C. In this way, the active species present in the effluent, due to the hydrolysis and the gasification of the urea solution, facilitate more effectively the catalytic reduction of nitrogen oxides. The effluent will contain an excess of oxygen. The use of the present invention with any of the above SCR catalysts (the disclosure of which is specifically incorporated by reference) reduces or eliminates the requirement to transport, store and handle large amounts of ammonia or ammonium water. Because the invention is compatible with other emission reduction and fuel economy technologies, several hybrid processes are available to the engine designer, the vehicle producer and the fuel market.

P1563 / 99MX update. For example, the fuel can be catalyzed with a suitable metal additive of the platinum group and / or an auxiliary catalytic composition selected from the group consisting of compounds of sodium, lithium, potassium, calcium, magnesium, graphene, iron, copper, manganese and mixtures . Among the compounds are any of the disclosed, for example, in the above-mentioned US Patents Nos. 4,892,562 and 4,891,050 to Bo ers and Sprague, 5,034,020 to Epperly and Sprague, 5,215,652 to Epperly, Sprague, Kelso and Bowers and 5,266,083 to Peter-Hoblyn, Epperly, Kelso and Sprague, WO 90/07561 to Epperly, Sprague, Kelso and Bowers and U.S. Patent Application Serial Number 08 / 597,517 filed January 31, 1996 to Peter -Hoblyn, Valentine and Sprague, incorporated herein as references. Where the application allows, a mixture of these compounds can be used with one or more other metal compounds of the platinum group, such as soaps, acetyl acetonates, alcolates, β-diketonates and sulfonates, for example, of the type to be described in more detail later. The metal catalyst of the platinum group and / or other catalyst may be added in some effective manner for its intended purpose, such as, for example, by adding it to the fuel in the P1563 / 99MX storage in bulk, to fuel in a tank associated with the engine or by continuous or intermittent addition, for example by means of a suitable metering device in, for example: the fuel line leading to the engine or in the form of a vapor , gas or aerosol in the air intake, the exhaust gases before the trap, the exhaust gases after the trap but before the recirculation to the engine or a mixing chamber or an equivalent means, where the exhaust gases mix with the incoming air. When used, particularly in combination with particle traps, the metal catalyst compositions of the platinum group are preferably used at concentrations of less than 2 parts by weight of the metal of the platinum group in parts per million by volume of fuel (ppm). For the purposes of this description, all figures in "parts per million" are based on weight to volume, that is, grams / million cubic centimeters (which can also be expressed as milligrams / liter) and percentages are given by weight, unless otherwise indicated. Auxiliary catalysts are used at effective levels for their intended purpose, preferably at levels of from 1 to 100 ppm of the fuel used, for example, from 10 to 60 ppm.

P1563 / 99MX The foregoing description is intended to teach persons of ordinary skill in the art the manner in which the present invention is practiced and is not intended to detail all those obvious modifications and variations which will be apparent to the experienced after the reading of this description. However, it is intended that all such obvious modifications and variations be included within the scope of the present invention, which is defined by the following claims. The claims cover the components and steps indicated in all arrangements and sequences that are effective to meet the intended objectives of the invention, unless the context specifically indicates otherwise.

P1563 / 99MX

Claims (14)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following CLAIMS is claimed as property; 1. A method to reduce N0X emissions from an impoverished combustion engine that has an evacuation system associated with it, the system has an evacuation passage to transport the N0X-containing evacuation gases to an effective reactor for the reduction selective catalyst of the N0X, the method comprises: feeding an aqueous solution of urea from a storage container and through a line to an injector; return the urea solution from the injector to the storage container, the feed and return rates will be sufficient to supply the urea as necessary to the exhaust gases for the reduction of the N0X and to maintain the temperature of the urea solution sufficiently low, so that it is not left for a sufficient time at high temperature that it can hydrolyze the urea to such an extent that the solids precipitate; injecting the urea solution into the exhaust gases at a temperature of the exhaust gases sufficient for the SCR; Y P1563 / 99MX pass evacuation gases through an SCR reactor.
2. 2. A method according to claim 1, wherein the urea solution contains at least about 25% by weight of urea.
3. 3. A method according to claim 1, wherein the temperature of the evacuation gases is within the range of from about 180 to about 650 ° C.
4. 4. A method according to claim 1, wherein the urea solution is maintained at a temperature below about 140 ° C.
5. 5. A method according to claim 1, wherein the urea solution is injected into the evacuation gases at a pressure of at least about 30 psi.
6. 6. A method according to claim 1, wherein the urea solution is fully or partially heated by an auxiliary heating means.
7. 7. A method according to claim 1, wherein the urea solution is fully or partially heated by heat transfer from the evacuation. A method according to claim 1, wherein the urea solution is introduced into the evacuation between the evacuation valves of the engine and the evacuation turbine of the turbo charger. P1563 / 99MX 9. A method according to claim 1, wherein the urea is introduced into the evacuation in a close coupling relationship with the SCR catalyst. 10. A method according to claim 1, wherein the introduction of the urea in the evacuation is controlled by a controller integrated into the engine management or administration system. 11. A method to reduce NOx emissions from an impoverished combustion engine associated with it has an evacuation system that has an evacuation passage to transport the exhaust gases containing the NOx to an effective reactor for catalytic reduction selective of NOx; the method comprises: feeding an aqueous solution of urea from a storage vessel through a line to an injector; to pass a heat exchange fluid in heat exchange contact with the line and / or the injector, the feed rates of the urea solution and the passage of the heat exchange fluid will be sufficient to supply the urea to the exhaust gases according to is necessary for the reduction of the N0X and to maintain the temperature of the urea solution sufficiently low, so that it is not left for a sufficient time at high temperature that it can hydrolyze the urea in P1563 / 99MX such a degree that the solids precipitate; injecting the urea solution into the exhaust gases at a sufficient exhaust gas temperature for the SCR; and passing the evacuation gases through an SCR reactor. 12. A method according to claim 11, where the temperature of the urea solution is allowed to rise above 100 ° C and the solution is maintained at a pressure above the vapor saturation pressure at the temperature of the solution. 13. An apparatus for reducing N0X emissions from an impoverished combustion engine that has an evacuation system associated with it, the system has an evacuation passage that leads to an effective SCR reactor for the selective catalytic reduction of NOx. , which comprises: a means for feeding an aqueous solution of urea from a storage container, through a line to an injector; a means to return the urea solution from the injector to the storage container, the feed and return rates are sufficient to supply the urea, as necessary, to the exhaust gases for the reduction of NOx and to maintain the temperature of the urea solution sufficiently low, so that it does not leave for a sufficient time at temperature P1563 / 99MX high that can hydrolyze the urea to such an extent that the solids precipitate; an injector means for injecting the urea solution into the exhaust gases at a temperature of the exhaust gases sufficient for the SCR; and an evacuation passage means leading from the injector means to an SCR reactor. 14. An apparatus according to claim 13, further including: means for detecting the temperature of the evacuation gas; means for generating a signal representative of the detected temperature of the evacuation gases; a means to detect the load of the motor; means for generating a signal representative of the detected load of the motor; a means for detecting the temperature of the urea solution; means for generating a signal representative of the detected temperature of the urea solution; and a means for comparing the generated signals with the reference values and for generating control signals to control the feeding, injection and return of the urea. P1563 / 99MX