Patent Application
20060277897
1. Field of the Invention
The present invention relates to a system and method for reducing noxious oxides from an exhaust gas of an internal combustion engine, and, more particularly, to such a system and method using a catalytic process.
2. Description of the Related Art
Noxious oxides (NOx) has been the subject of air pollution regulations and control efforts for over 30 years. These efforts began in southern California, but under the direction of the U.S. Environmental Protection Agency (EPA), NOx control efforts are spreading throughout the U.S. and to many major cities worldwide. Increasingly stringent control efforts continue to be mandated by regulatory bodies, both domestically and internationally. In southern California and other areas of the U.S. (representing over 60% of the population) that have not attained EPA's ambient air quality standards, an active trading market exists for NOx “credits”, which have economic value and can be created when controls are installed whose performance exceeds regulatory requirements.
Emission standards in the U.S. will require reduction of diesel emissions for transportation vehicles (light and heavy-duty diesel powered trucks and buses) by as much as 90% from current levels in the 2005-2010 time frame. In addition, emissions levels for boilers-electric generators (especially coal fired boilers) and internal combustion (IC) engine (gas and diesel) powered electric generators are required to meet even more stringent NOx emissions levels. Achieving these levels with acceptable costs and durability will be very difficult for these industries.
NOx reduction approaches presently being developed may present problems and difficulties. Catalyst poisoning, thermal cycling and supplying a practical reductant make the performance and life of NOx adsorbers and lean NOx catalysts problematic. Selective Catalytic Reduction (SCR) requires an external fluid be distributed and carried on commercial vehicles. Combustion control technologies such as Exhaust Gas Recirculation, high injection pressures, variable geometry turbines for air handing and other similar mechanisms used to control NOx emissions from diesel engines add complexity and cost.
What is needed in the art is a NOx reduction system and method which is simpler and does not require an additional fluid (reductant) source on board moving vehicles.
The present invention provides a system for reduction of noxious oxides including an additional reductant catalytic reactor providing a catalyzed reductant fuel to a NOx catalytic reactor.
The invention comprises, in one form thereof, a system for reduction of noxious oxides from an exhaust of an internal combustion engine. The internal combustion engine includes an engine exhaust. A NOx catalytic reactor has at least one inlet in communication with the engine exhaust. A reductant catalytic reactor includes an inlet in communication with a reductant fuel supply, and an outlet in communication with at least one inlet to the NOx catalytic reactor.
An advantage of the present invention is that a higher NOx reduction is effected (based on the chemical stability/sulfur resistance of the catalyst used) in the exhaust from a diesel engine burning high sulfur diesel fuel.
Another advantage is that one liquid can be used for fuel and to catalytically generate the NOx reductant.
Yet another advantage is that the system is thermally and chemically stable.
Still another advantage is that the system uses only about 3% of the system total fuel for NOx reduction.
A further advantage is that the NOx catalyst, constituting the bulk of the system's catalysts, does not use precious metal catalysts.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner.
Referring now to the drawings, and more particularly to
Reductant fuel supply 18 contains diesel fuel, gasoline and/or one or more other hydrocarbons. In one embodiment, reductant fuel supply 18 is the same fuel tank which supplies fuel to IC engine 14, and thus reductant fuel 22 within reductant fuel supply 18 is also the same as the fuel supplied to IC engine 14 (e.g., diesel fuel). Configured as such, it will be appreciated that a separate supply line leads from reductant fuel supply 18 to IC engine 14. Although the present invention is described and shown herein with reference to a diesel engine, it should be understood that the present invention is applicable to any hydrocarbon combustion source (e.g., diesel, natural gas, gasoline, coal, alcohols, etc.).
NOx catalytic reactor 16 has an inlet 24 in communication with engine exhaust 12, and an outlet 26 in communication with the ambient environment, and optionally in communication with analyzers for determining a NOx level within the exhaust.
In one embodiment, NOx catalytic reactor 16 includes a ceramic catalyst material comprised of Al2O3, doped with (either integrated into the crystal structure of the Al2O3 or impregnated with) with an alkaline earth element (Na, Li, K or CS), Zr, Ti, V, Ce or La. In another embodiment, NOx catalytic reactor 16 includes a ceramic catalyst material comprised of Y zeolites, doped with (either integrated into the crystal structure of the zeolite or impregnated with) an alkaline earth element (Na, Li, K, or CS), Zr, Ti, V or La or Beta zeolites doped with Fe.
Reductant catalytic reactor 20 includes an inlet 28 in fluid communication with reductant fuel supply 18, and an outlet 30 in communication with inlet 24 to NOx catalytic reactor 16. More particularly, outlet 30 is coupled with branch exhaust 32 upstream from inlet 24 to NOx catalytic reactor 16. Gases transported from outlet 30 of reductant catalytic reactor 20 therefore mix with engine exhaust gases from exhaust 12, prior to entering NOx catalytic reactor 16 at inlet 24.
Pump 34 and coil heater 36 are disposed in a series arrangement between reductant fuel supply 18 and reductant catalytic reactor 20. Regulator 38 controls the volumetric fluid flow through pump 34, and ultimately to reductant catalytic reactor 20. Heater 36 heats the reductant fuel outputted from pump 34 to a temperature of between approximately 450-600° F., which is necessary to maintain a minimum temperature required to drive the reforming/cracking process of the reductant fuel within reductant catalytic reactor 20.
Reductant catalytic reactor 20 includes a cracking and/or reforming catalyst used for reductant formation. In one embodiment, the cracking and/or reforming catalyst is comprised of zeolites, silica aluminas, precious metals wash coated on Al203 wash coated onto extruded corrigated monolith cylinders and/or Al2O3 or a combination of these compounds (needed to produce the desired combination of reductants to optimize NOx reduction at a given exhaust condition). The zeolites are preferably of ZSM5 configuration with a SiO2 to Al2O3 ratio of from 5-1000. These zeolites may be used in the pure form or doped with (impregnated or integrated into the crystal structure) Mo, Ti, Fe. The Silica Aluminas are solid solutions of SiO2 and Al2O3 oxides that are doped with Mo, Ti, and/or Fe.
During use, diesel fuel, gasoline or other hydrocarbons are catalytically cracked and/or reformed to produce H2, CO and/or short chain hydrocarbons (oxidized and partially unsaturated) to act as reductants for NOx when passed over NOx catalytic reactor 16 in conjunction with the NOx from exhaust 12 originating from IC engine 14. The cracked and/or reformed reductant fuel is mixed with the engine exhaust in branch exhaust 32 and transported to inlet 24 of NOx catalytic reactor 16. The equation for the reductant reaction in NOx catalytic reactor 16 is:
HC, CO and/or H2 (one or all)+NOx=>N2+CO2+H20 (dependent upon the reductant mix).
Unlike three-way catalysts used on automobiles for NOx reduction, system 10 reduces NOx in the presence of high concentrations of O2 (less than 1%) and sulfur oxides (less than 15 ppm) normally found in the exhaust of diesel and lean burn natural gas/gasoline engine powered vehicles as well as most coal and natural gas fired boilers.
System 10 uses a unique cracking/reforming catalyst to produce a tailored, very active reductant to activate a normally very thermally and chemically inactive ceramic catalyst to reduce NOx in the presence of high levels of sulfur oxide and oxygen. This unique combination of catalysts produces a NOx reduction after treatment system that is very sulfur tolerant and thermally stable and cost effective since the NOx catalyst (constituting the bulk of the system catalyst) does not use precious metals and is very efficient since it only involves a 2-3 fuel penalty. System 10 has demonstrated over 90% NOx reduction (
In contrast with conventional systems, the present invention catalytically and thermally produces, under controlled conditions, taylored reductants from commercially available hydrocarbons (such as diesel fuel and gasoline) that will cause materials that are not normally able to (or catalytically active for) effectively reduce the oxides of nitrogen from the exhausts of combustion sources. These normally inactive materials are preferably ceramics and are very stable thermally and chemically (are not poisoned by active compounds in the exhaust such as SOx) giving these materials the double benefit of being both very active for NOx but very stable thermally and chemically otherwise.
While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
