Desulfurization performance comparison of a 162-kW marine diesel engine's exhaust gas based on two kinds of alkaline liquid scrubbing models

A cascade-scrubbing technology was proposed to improve the current once-through desulfurization solutions. Desulfurization experiments were performed for a 162-kW marine diesel engine's exhaust gas so as to confirm the alkali-lean/alkali-rich lye cascade-scrubbing advantages compared with the closed-loop solution. In the closed-loop scrubbing model, desulfurization efficiency presented multiple change patterns, such as initially decreasing but then increasing with the liquid-gas ratio, decreasing with SO2 concentration, and increasing with Na/S. At the high SO2 concentration of 2,860 mg/Nm(3) and Na/S = 2, desulfurization complying with emission control area's (ECA's) requirements necessitated a liquid-gas ratio above 4.5 L/Nm(3). Although raising Na/S could decrease the liquid-gas ratio requirement, the alkali-utilization efficiency dropped. In the alkali-lean/alkali-rich lye cascade-scrubbing model under the same SO2 and Na/S conditions, the auxiliary scrubbing section allowed a desulfurization capacity of 500-750 mg/Nm(3) with an alkali-rich liquid-gas ratio of 1-2 L/Nm(3). With the alkali-rich lye fed at liquid-gas ratios of 1, 1.5, and 2 L/Nm(3), the main scrubbing section's alkali-lean lye necessitated liquid-gas ratios of 2.8, 2.4, and 3.1 L/Nm(3) to comply with ECA's requirements, respectively. Two setups approaching the former two liquid-gas ratio assembles (i.e., a total liquid-gas ratio of 4 L/Nm(3) gaining a high alkali-utilization efficiency above 98%) thus confirmed that this cascade-scrubbing model was superior to the closed-loop solution in cutting the liquid-gas ratio requirement and alkali consumption, because of the latter necessitating a liquid-gas ratio of 4.5 L/Nm(3) at Na/S = 2 or 4 L/Nm(3) at Na/S = 2.16 but with the alkali-utilization efficiency dropping below 91%.