The Wärtsilä NOx Reducer System is based on the Selective Catalytic Reduction technique for Nitrogen Oxide (NOx) reduction.
The main components are:
1. Reactor housing
2. Catalyst elements
3. Soot blowing unit
4. Urea injection and mixing unit
5. Urea dosing unit
6. Control and automation unit
7. Urea pumping unit
The reactor is a steel casing consisting of an inlet and an outlet cone, catalyst layers, a steel structure for supporting the catalyst layers and a soot blowing system. Compressed air connections for soot blowing are installed at each catalyst layer. The reactor is equipped with a differential pressure transmitter for monitoring the condition of the catalyst elements, and a temperature transmitter for monitoring the exhaust gas outlet temperature. One SCR Reactor is installed per engine and exhaust gas pipe.
The urea pump unit supplies urea to the dosing system and maintains a sufficient pressure in the urea lines. A suction filter protects the pump and the downstream equipment from impurities. Excess urea returns to the storage tank through an overflow line.
The dosing unit defines the correct urea dosing rate for the injection system and adjusts the urea flow accordingly by a control valve. The components in the unit are mounted on a frame, forming a compact module. One pump unit can be used for several SCR reactors while one dosing unit is installed for each SCR reactor.
The urea injector sprays reducing agent into the exhaust gas duct. After injection of the reducing agent, the exhaust gas flows through the mixing pipe to the reactor, where the catalytic reduction takes place. The reactor is equipped with a soot blowing system for keeping the catalyst elements clean.
Further reading: Wärtsilä Environmental Product Guide