Patent Application
20110138787
This invention relates to a reservoir for a fluid dosing system. More specifically, the invention relates to a reservoir for holding a reducing agent for introduction into a combustion exhaust gas.
The emission of nitrogen oxide (NOx) compounds in engine exhausts has long been the focus for health professionals and regulatory agencies worldwide. In many locations, regulations require stringent reductions of NOx levels in new equipments. NOx emissions may be found in a variety of systems such as internal combustion engines, gas turbine exhaust, lean burn engines, industrial boilers, process heaters or other process streams.
In order to reduce NOx emissions, it is known to use a selective catalytic reduction (SCR) device to treat an exhaust flow and to significantly reduce NOx emissions. In an SCR system a reducing agent, for example urea solution, is dosed into the exhaust gas flow upstream of an SCR catalyst. This reducing agent is then usually reacted in the presence of a catalyst downstream of the injection point in an SCR device. Within the SCR device NOx compounds are then reduced to nitrogen. WO2004111401 discloses such a device.
The general operation of an SCR device is shown in
The oxidation catalyst device 7 is a flow through device that consists of a canister containing a honeycomb-like structure or substrate. The substrate has a large surface area that is coated with an active catalyst layer. This layer contains a small, well dispersed amount of precious metals such as platinum or palladium. As the exhaust gases traverse the catalyst, carbon monoxide, gaseous hydrocarbons and liquid hydrocarbon particles (unburned fuel and oil) are oxidized, thereby reducing harmful emissions.
The SCR device 9 performs SCR treatment of NOx using ammonia derived from a source of urea as a chemical reductant. A slip catalyst 11 may be located downstream of the SCR device 9 to clean up any unreacted ammonia.
Urea for the SCR device 9 is stored in a tank 13 which is in fluid communication with the exhaust system 5. A pump 15 is provided to pump urea from the tank 13 to the exhaust system 5. The supply of urea is controlled by a control unit 17, for example the engine control unit, which receives engine speed and other engine parameters from the engine 1. An injection device 19 (also referred to herein as a fluid dosing device) is used to inject the urea into the exhaust flow.
As a 32.5% urea solution freezes at −11.5° C., urea delivery systems must be adapted for delivery of liquid urea to the vehicle exhaust system under conditions that would normally cause the liquid urea to freeze. One solution would be to simply heat the storage tank 13. However, this can require substantial quantities of energy to maintain the entire storage tank 13 in a liquid state and can take significant time to thaw if the tank has become completely frozen. An alternative arrangement is to place a smaller reservoir downstream of the storage tank that can be unfrozen quickly and/or maintained as liquid more efficiently since it contains a smaller amount of liquid urea. Such an arrangement is shown in
A liquid reductant dosing reservoir as shown in
According to the present invention, there is provided a liquid reductant dosing reservoir for a combustion exhaust treatment system comprising:
A method for assembling a liquid reductant dosing reservoir for a combustion exhaust treatment system is also provided comprising:
The invention provides effective electrical communication along a path free of liquid reductant between a bottom-affixed component and the outside of the reservoir that is easy to assemble and resists stresses that can be caused by relative motion of the top and bottom members of the reservoir due to thermal expansion and assembly/disassembly. These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
Referring now to the Figures, the invention will be described with reference to specific embodiments, without limiting same. Turning now to
Upper reservoir member 39 has affixed thereto a vertical rod heater 36 that extends downward therefrom toward the bottom of the reservoir. Electrical cable 32 provides power from outside of the reservoir through an opening in upper reservoir member 39 to the rod heater 36 to thaw frozen liquid reductant and/or to maintain liquid reductant in a liquid state. An exemplary rod heater useful as rod heater 36 is more fully described in the U.S. patent application filed on even date herewith entitled “Liquid Reductant Dosing Module with Heating Device”, the disclosure of which is incorporated herein in its entirety. Other types of heaters and configurations, e.g., PTC heaters, may also be used as is known in the art. Heat sink 31, which may be of any suitable conductive material that is compatible with the liquid reductant environment (e.g., aluminum with an anodized surface), is connected to the bottom area of rod heater 36 to enhance transfer of heat from rod heater 36 to the liquid reductant in the reservoir.
Pickup tube 34, which may be of any suitable material, e.g., stainless steel, is also affixed to upper reservoir member 39 and extends downward through an opening in upper reservoir member 39 to draw liquid reductant from near the bottom of the reservoir. In an exemplary embodiment, the pickup tube 34 is in contact with or is proximate to the rod heater 36 in order to limit any frozen blockages in the pickup tube. In one exemplary embodiment, the pickup tube 34 is inside a hollow rod heater 36. Associated with the bottom end of pickup tube 34 is an umbrella valve 35 that can open and close in response to fluid pressure changes, which serves to shield the open bottom end of pickup tube 34 from any ice that forms in the liquid reductant. A filter or screen element (not shown) may also be associated with the bottom end of pickup tube 34.
With continued reference to
According to the present invention, a flexible hollow plastic conduit 43 is connected at one end to an opening in upper reservoir member 39 and connected at the other end to level sensor 37. The conduit 43 may be made of any flexible plastic material that is impervious to the liquid reductant such as nylon 6 or other nylon resins such as Zytel®, polyoxymethylene resin, or polyphthalamides such as Amodel®. The flexibility of the conduit enables it to be routed around other components, such as the rod heater 36, and also enables it to be connected at each end prior to assembly of the upper reservoir member 39 to the lower reservoir member 40 while allowing the upper and lower reservoir members to be repositioned with respect to one another during the assembly process. Electric wires (not shown) inside conduit 43 connect the electrical output leads of sensor 37 to electrical connector 38 on the outside of upper reservoir member 39. The connections of conduit is 43 to the upper reservoir member 39 and the level sensor 37 are also sealed against penetration by the liquid reductant, such that a path free of liquid reductant is provided between the level sensor 37 and the opening in the upper reservoir member 39. One exemplary embodiment of such a seal is shown in
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description.
