Patent attributes
A multi-stage SCR system including a front reductant injecting device, a front mixer, a front SCR catalyst, a back reductant injecting device, a back mixer, a back SCR catalyst, and a DCU. The front and back reductant injecting devices receives reductant from an air-driven pump, which includes a liquid supply tank, a pressure tank, and solenoids control valves. Under pressure provided by a compress air source, reductant is pressed into the front and back reductant injecting devices from the air-driven pump. The front and back reductant devices also have flow-back paths fluidly connected to a reductant tank. And in purging or maintenance heating, the flow-back paths can be energized open. In the multi-stage SCR system, a DOC can be further positioned in between the two SCR devices for increasing the deNOx efficiency in the back SCR catalyst, so that the system is less sensitive to catalyst aging.
