SCR Systems: How the Nett BlueMAX™ SCR System Works
Nett's BlueMAX™ system is designed to control the emissions of oxides of nitrogen (NOx) from medium and heavy-duty diesel engines in on-road, non-road and stationary applications.
The system is a urea-SCR (Selective Catalytic Reduction) system. NOx is reduced over the SCR catalyst through chemical reactions with a reducing agent (urea). The urea solution is carried in an onboard tank and injected upstream of the SCR catalyst. The urea control strategy relies on a NOx concentration measurement by a sensor positioned upstream of the SCR converter. Based on the NOx sensor signal, in combination with an engine mass air flow sensor and temperature sensors, the necessary urea dosing rate is calculated by the control software.
The main components of the BlueMAX™ system include the SCR catalytic converter, the urea dosing system (UDS), and the urea tank (Figure 1).
The NOx sensor-based strategy makes the system very suitable for retrofit applications. No time-consuming calibration (such as through engine mapping) is necessary, and the system can be installed on a wide range of diesel engines, including mechanical engines.
Urea (in the form of a 32.5% water-based solution) is stored in the urea tank. From the tank, the necessary amount of urea is metered by a precise dosing pump. The urea solution is introduced to the exhaust pipe upstream of the SCR catalyst through an injection nozzle. Urea atomization is supported by compressed air supplied by a compressor.