Consumables

SCR (Selective Catalytic Reduction) is a common technology for the reduction of nitrogen oxides produced in various combustion processes such as coal-fired boilers, waste incinerators, gas turbines or diesel engines. The chemical process taking place on the surface of the SCR catalyst is selective, which means that preferentially nitrogen oxides are reduced while other unrequested side reactions are minimized.  The typical reactions taking place are:

beside other reactions. A reducing agent is required for this chemical reaction: NH3 = ammonia which needs to be injected into the exhaust gas before the SCR catalyst. Ammonia is difficult to handle so the preferred alternative is urea. Urea in the form of an aqueous solution (30 % to 40 % solution) is easy to handle and to store onboard a vessel. After the injection of the urea water into the exhaust gas a process named thermolysis takes place according to the following equation:

Aqueous urea solutions are widely used in trucks and cars. They are known under the name “AdBlue” (32,5 %).
Beside activating energy in the form of temperature the aqueous urea solution is the only consumable utilized in an SCR catalyst.