Patent Application
20100122521
The present disclosure is directed to a urea dosing system and, more particularly, to a method for purging a urea dosing system.
Urea dosing systems are typically used to reduce NOx emissions in large machines where space and weight considerations are not a concern, such as, for example, locomotives and engine-generators. Urea is a reductant that is typically mixed with water and stored in a tank that is located on the machine. As the machine operates and produces exhaust, the urea mixture is pumped from the tank into the exhaust system. The urea mixture may be mixed with air and sprayed into the exhaust system via a nozzle. The urea mixture may react with exhaust fumes at high temperatures, affecting a selective catalytic reduction (SCR) reaction that may reduce NOx emissions of the machine. A shortcoming of dosing systems relates to the relatively high ambient temperatures at which urea mixtures freeze, such as about −11° C. (about 12° F.). The urea mixture may freeze and expand within the dosing system, causing damage to intricate components such as injector nozzles. Additionally, when heated to intermediate temperatures between about 100° and 250° C., urea may decompose into a urea byproduct that may clog dosing components and/or an exhaust system.
U.S. Patent Application Publication No. 2007/0180816 A1 (the '816 publication) by Masuda et al. discloses an exhaust emission purifying apparatus for an engine. The '816 publication discloses a urea storage tank that is connected to an exhaust system via a passage. Urea is injected into the exhaust system via a nozzle located on the passage. The '816 publication also discloses a discharge-forcing device that forcibly discharges urea gas, which collects in an upper portion of the storage tank, to the exhaust system.
Although the '816 publication may provide a method for discharging urea gas from the upper portion of a storage tank, it may fail to purge urea from a nozzle that sprays urea into an exhaust system and thereby fail to prevent damage from frozen urea. The system of the '816 publication may also fail to remove urea from dosing components and/or an exhaust system at temperatures between about 100° and 250° C., which may allow the urea to decompose into ammonia polymer and cause clogging.
The present disclosure is directed to overcoming one or more of the shortcomings set forth above and/or other deficiencies in the existing technology.
In accordance with one aspect, the present disclosure is directed toward a method for purging reductant from a reductant supply system. The method includes dispensing reductant into an exhaust system via a dispensing device. The method also includes purging the dispensing device by urging reductant from the dispensing device to a reductant source.
According to another aspect, the present disclosure is directed toward an emissions reduction system. The emissions reduction system includes a dispensing device configured to dispense reductant into an exhaust system. The emissions reduction system also includes a pressurized fluid source connected to the dispensing device and configured to urge the reductant from the dispensing device to a reductant source.
Exhaust system 12 may include an engine 13, an oxidation catalyst system 14, a mixer assembly 16, and an SCR assembly 17. Exhaust gas may be emitted from engine 13 and flow into oxidation catalyst system 14, where the exhaust gas may be initially treated. The exhaust gas may then flow to mixer assembly 16, where dosing system 10 may inject the reductant into the exhaust gas. The exhaust gas may then flow to SCR assembly 17, where SCR occurs.
Pumping system 15 transfers reductant toward exhaust system 12. Pumping system 15 may include a dosing pump 30, a reductant source 35, and a filter 40. Pump 30 may generate fluid flow within a passage 42, which may be fluidly connected to reductant source 35 and filter 40. Pump 30 may be a metering pump such as, for example, a diaphragm pump. Pump 30 may be driven independently of the engine such as, for example, by an electric motor. Reductant source 35 may be a low pressure tank for storing a reductant solution such as, for example, a urea solution. Reductant source 35 may be remotely located from housing 27 and may include a heating source for thawing the reductant solution. Filter 40 may be any suitable filter or strainer for removing ice crystals and debris from a reductant solution such as, for example, a plastic filter. As pump 30 pumps the reductant solution from reductant source 35 toward exhaust system 12, via passage 42, a portion of the reductant solution may be frozen. The frozen portion may be collected upstream of pump 30 via filter 40.
Spraying system 20 injects the reductant solution into exhaust system 12. Spraying system 20 may include a pressurized source 45, a pressure regulator 50, a control valve 55, a check valve 60, and a dispensing device 65. Pressurized source 45, pressure regulator 50, control valve 55, check valve 60, and dispensing device 65 may be fluidly connected via a passage 70. Pressurized source 45 may be remotely located from housing 27 and may include a pump and/or a pressurized container containing a pressurized gas such as, for example, air. Pressurized source 45 may pressurize air within passage 70 and may transfer the pressurized air toward dispensing device 65.
Pressure regulator 50 may mechanically regulate an air pressure within passage 70. Pressure regulator 50 may maintain an appropriate upstream pressure near pressurized source 45 so that, after pressure losses, an appropriate pressure is maintained within dispensing device 65 for reductant injection. Control valve 55 may be any suitable valve such as, for example, a solenoid-actuated and spring-biased control valve that is movable between a first position and a second position. Control valve 55 may selectively allow flow through passage 70 in a first position and may selectively block flow through passage 70 in a second position. Check valve 60 may ensure a unidirectional flow in passage 70, from pressurized source 45 toward dispensing device 65. Check valve 60 may be any suitable valve such as, for example, a ball check valve.
Dispensing device 65 introduces reductant into mixer assembly 16 of exhaust system 12. As illustrated in
Nozzle 85 may be disposed within mixer assembly 16 of exhaust system 12 and injects reductant into exhaust system 12. As illustrated in
Purging system 25 purges reductant from components of dosing system 10. Purging system 25 may include a sensor 115, a control valve 120, a control valve 125, a check valve 130, and a controller 135. Controller 135 may be any type of programmable logic controller known in the art for automating machine processes such as, for example, an engine control unit (ECU). Controller 135 may control an operation of pump 30 via an electrical line 137. Controller 135 may also be connected to other components of the machine such as, for example, the engine, an operator station, and the exhaust system. For example, controller 135 may be electrically connected to a temperature sensor disposed within exhaust system 12.
Sensor 115 may be disposed within passage 70 and may be any suitable sensor for measuring an air pressure. Sensor 115 may be electrically connected to controller 135 via an electrical line 140 and may provide values indicative of an air pressure in passage 70 to controller 135 as input. When sensor 115 reports air pressure values that are unsuitable for an operation of dosing system 10, controller 135 may control, via an electrical line 145, control valve 55 to move from the first position to the second position, thereby blocking air flow through passage 70.
Control valve 120 and check valve 130 may be fluidly connected via a passage 150 that may fluidly connect passage 70 and passage 42. Control valve 120 may be similar to control valve 55 and may selectively allow and block pressurized air flow through passage 150. Control valve 120 may be controlled by controller 135, via electrical line 155. Check valve 130 may be similar to check valve 60 and may ensure a unidirectional flow through passage 150, from pressurized source 45 toward an inlet of pump 30.
Control valve 125 may be similar to control valves 55 and 120 and may selectively allow and block flow through a passage 160. Control valve 125 may be controlled by controller 135, via electrical line 165. Passage 160 may fluidly connect an outlet of pump 30 and reductant source 35. Passage 160 may be sized larger than passage 42, so as to require less pressure for generating flow.
A passage 220 may be a bypass passage fluidly connecting the outlet of pump 30 to the inlet of pump 30. Control valve 205 may be similar to control valve 200 and may selectively allow and block flow through passage 220. Control valve 205 may be controlled by controller 135 via an electrical line 227.
The disclosed dosing system may be used in any system that delivers fluid to an exhaust system to reduce exhaust emissions such as, for example, a locomotive or a generator. The disclosed dosing system may be used to affect selective catalytic reduction within any machine having an exhaust system.
Dosing occurs in step 310. Dosing may occur when a temperature within exhaust system 12 exceeds a threshold temperature and selective catalytic reduction may be performed such as, for example, about 180° C. and above. When the exhaust temperature exceeds the threshold temperature, a temperature sensor disposed in the exhaust system signals controller 135. As illustrated in
Purging of reductant from dispensing device 65 and pump 30 occurs in step 315. Dosing may be stopped and purging may begin when a temperature within exhaust system 12, reported to controller 135 via the temperature sensor, falls below a threshold temperature such as, for example, between about 180° C. and about 250° C. For example, the threshold temperature may be about 180° C. The engine may remain on at this time and may be idling. Once the purging of step 315 begins, controller 135 may prevent the engine from being turned off until the purging process is complete. Alternatively, the engine may be fully shut down, and thereafter the purging of step 315 may be initiated.
As illustrated in
As illustrated in
As illustrated in the alternative dosing system 10 of
If the temperature within exhaust system 12 exceeds the threshold temperature, purging is stopped and dosing may begin again in step 320. The dosing of step 320 is similar to step 310. Steps 315 and 320 may be repeated as required, based on the temperature within exhaust system 12. The engine may be turned off by an operator and/or controller 135 in step 325. In step 330, dispensing device 65 and pump 30 may be purged in a manner similar to step 315.
Dosing system 10 may be used to purge reductant from dosing components to prevent damage and/or clogging. Dosing system 10 may purge reductant out of dispensing device 65 and toward reductant source 35. Reductant may thereby be removed to prevent damage to dosing components and/or the exhaust system from expansion of frozen reductant. Dosing system 10 may also purge reductant to avoid formation of polymer and the resulting clogging that may occur in nozzle 85 and exhaust system 12. Because dosing system 10 may purge reductant back to reductant source 35, instead of into exhaust system 12, release of the reductant into the environment may be substantially reduced. Release of offensive-smelling odor into the environment may thereby be significantly reduced.
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed dosing system. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed method and apparatus. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.
