Seawater/Seawater Cascade-Scrubbing Desulfurization Performance for Exhaust Gas of a 162-kW Marine Diesel Engine

Abstract

To confirm the higher-availability and lower-resistance superiority of a proposed seawater/seawater cascade-scrubbing solution meeting the emission control area (ECA) requirements under harsh high-sulfur and low-alkalinity conditions, desulfurization experiments for the exhaust gas of a 162-kW marine diesel engine were compared between the cascade-scrubbing model and currently used once-through, open-loop solution. With the once-through seawater to scrub SO2 levels of 1,000–2,860 mg/Nm3 (equal to about 1.8%–5% fuel-sulfur content), the desulfurization efficiency of the once-through system increased with the liquid-gas ratio and seawater alkalinity and decreased with SO2 concentration. At the harsh SO2 concentration of 2,860 mg/Nm3 where the once-through scrubbing thoroughly failed to meet the ECA’s requirements, an additional liquid-gas ratio increase above 8 L/Nm3 was confirmed to be infeasible because of the potential for liquid flooding. In contrast, with a total liquid-gas ratio ≥9 L/Nm3 (typically liquid-gas ratios of 7 and 2 L/Nm3 in the main and auxiliary scrubbing sections, respectively), the cascade-scrubbing model easily met the ECA’s desulfurization requirements under harsh high-sulfur and low-alkalinity conditions, along with its lower packing pressure-drop levels allowing for a further liquid-gas ratio increase. Aside from the above superiority compared with the once-through open-loop solution, the achievement of high-efficiency seawater desulfurization in this work suggests that the proposed seawater/seawater cascade-scrubbing solution should be more economical in comparison to the current closed-loop solution and hybrid system, which both necessitate costly NaOH usage.