Seawater/alkaline liquid cascade-scrubbing desulfurization performance for the exhaust gas of a 162-kW marine diesel engine

A cascade-scrubbing technology was developed for marine diesel engines to improve the current once-through desulfurization solutions. To confirm the seawater/alkaline liquid cascade-scrubbing advantages of higher efficiencies and lower lye consumption compared with current solutions, desulfurization experiments with different scrubbing models were performed for a 162-kW marine diesel engine. In the open-loop model with SO2 of 1,000-2,860 mg/Nm(3), desulfurization with the allowed liquid-gas ratios <= 8 L/Nm(3) for the packing tower failed to fully meet the ECA's requirements, despite the efficiency increasing with liquid-gas ratio, seawater alkalinity, and packing height and decreasing with SO2 concentration. In the closed-loop solution, to obligate the ECA's requirements with SO2 of 2,860 mg/Nm(3), a high liquid-gas ratio of 4.8 L/Nm(3) was necessitated at Na/S=2. In contrast, in the seawater/alkaline liquid cascade-scrubbing model under high-sulfur and low-alkalinity conditions (2,860 mg/Nm(3) and 0.84 mmol/L), the solution utilized 5-6 L/Nm(3) seawater in the main scrubbing section to scrub 80-90% SO2 and an extremely low alkaline-liquid dose below 1 L/Nm3 in the auxiliary scrubbing section to remove the residual SO2, finally allowing a high efficiency ahead of the open-loop model and meanwhile cutting down an 80-90% lye consumption compared with the closed-loop model.