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Ammonia: Selective Catalytic Reduction (SCR)
Selective Catalytic Reduction (SCR) of NOx using an ammonia compound as reductant has been used for many years in stationary diesel engine applications, as well as for mobile applications. In the SCR process, NOx reacts with the ammonia, which is injected into the exhaust gas stream before a special SCR Catalyst. SCR is the only technology capable of reducing diesel NOx emissions to levels required by future emission standards.
Three forms of reductants can be used in SCR systems:
- pure anhydrous ammonia
- aqueous ammonia
- Urea.
The SCR process requires precise control of the ammonia injection rate. An insufficient injection may result in unacceptably low NOx conversions. An injection rate that is too high results in release of undesirable ammonia to the atmosphere. These ammonia emissions are known as ammonia slip. The ammonia slip increases at higher NH3/NOx ratios. The stoichiometric NH3/NOx ratio is about 1. DET’s NOxMaster© systems have been designed to perform at the optimum level eliminating the chances of ammonia slip from an engine. The prevention of ammonia slippage and a high NOx conversion rates is guarantied by the advanced Electronic Control Unit (ECU) and high-sensitivity engine and ambient parameter sensors.
SCR remains the only proven catalyst technology which is capable of reducing diesel NOx emissions to levels required by future emission regulations. |
