Atmospheric emissions from a passenger ferry with selective catalytic reduction

Area of Science:

• Marine Engineering
• Environmental Science
• Chemical Engineering

Background:

• Staten Island Ferry's main propulsion engines (Caterpillar 3516A) were retrofitted with Selective Catalytic Reduction (SCR) technology.
• The goal was to reduce emissions of oxides of nitrogen (NOx) from ferry operations.
• Ferry operations were previously characterized into four modes: idle, acceleration, cruise, and maneuvering.

Purpose of the Study:

• To characterize pre- and post-aftertreatment emissions from the ferry's SCR system.
• To evaluate the effectiveness of the SCR system in reducing NOx emissions across different operating modes.
• To assess the impact of SCR on other emissions like carbon monoxide (CO) and particulate matter (PM).

Main Methods:

• Emissions were measured for both engines (NY and SI) during round trips between Manhattan and Staten Island.
• An analyzer system, data logger, and filter-based PM measurement system were utilized.
• NOx, CO, and CO2 measurements followed federal reference methods; SCR performance was assessed based on NOx reduction and ammonia slip.

Main Results:

• The SCR system achieved approximately 64% NOx reduction for engine NY and 36% for engine SI over a complete round trip.
• Cruise mode showed average NOx reductions of 75% (NY) and 47% (SI), with urea injection exceeding 94% reduction when active above 300°C.
• Oxidation catalyst reduced CO by 94% (NY) and 82% (SI); NOx emissions were predominantly produced during cruise mode (80%).

Conclusions:

• Initiating urea injection earlier in acceleration and cruise modes can significantly improve NOx reduction efficiency for both engines.
• The SCR system effectively reduced NOx and CO emissions, though PM impact was inconclusive.
• Optimizing SCR control strategy is key to maximizing emission reductions in marine applications.