Exam Question
(a) How does the Selective Catalytic Reduction (SCR) system work? (10)
(b) If Selective Catalytic Reduction (SCR) has such an extremely high NOx reduction efficiency why is it so rare in marine applications? (10)
Class 4 (4th Engineer)
SSEP
📅 Apr 2024
Reference Answer
### (a) How does the Selective Catalytic Reduction (SCR) system work? (10 Marks)
#### 1. Principle of Operation
The Selective Catalytic Reduction (SCR) system is an after-treatment technology designed to reduce Nitrogen Oxides (NOx) emissions from diesel engine exhaust gas. The fundamental principle is to convert harmful NOx (primarily NO and NO2) into harmless diatomic nitrogen (N2) and water (H2O) by reacting it with a reducing agent, typically ammonia (NH3), in the presence of a catalyst.
As cited in the reference material, a urea-water solution (typically a 40% solution for marine applications) is used as the reducing agent. The process unfolds in several stages:
#### 1. Principle of Operation
The Selective Catalytic Reduction (SCR) system is an after-treatment technology designed to reduce Nitrogen Oxides (NOx) emissions from diesel engine exhaust gas. The fundamental principle is to convert harmful NOx (primarily NO and NO2) into harmless diatomic nitrogen (N2) and water (H2O) by reacting it with a reducing agent, typically ammonia (NH3), in the presence of a catalyst.
As cited in the reference material, a urea-water solution (typically a 40% solution for marine applications) is used as the reducing agent. The process unfolds in several stages:
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