ASPEN PLUS desulfurization simulations for the scrubber of a large-scale marine diesel engine: main scrubbing section's desulfurization share optimization and superiority confirmation for the seawater/seawater cascade-scrubbing solution.

Aiming at perfecting the proposed three-stage cascade-scrubbing desulfurization technology, ASPEN PLUS simulations of seawater/seawater cascade-scrubbing desulfurization for an exhaust gas scrubber designed for a 10-MW large-scale marine diesel engine were performed to fix a reasonable desulfurization share for the main scrubbing section. Accordingly, three typical desulfurization share setups of 80%, 85%, and 90% were compared under various operational conditions by varying the fuel-sulfur content, liquid/gas ratio, and seawater alkalinity. In complying with the desulfurization requirements of emission control areas, 85% was obtained as the optimal desulfurization share among the three setups. Again, under the selected 85% setup, the cascade-scrubbing desulfurization was numerically compared with the conventional once-through open-loop solution, so as to confirm the seawater-saving advantage of the cascade-scrubbing desulfurization technology used for the exhaust gas of large-scale marine diesels. At relatively higher sulfur content above 3.5%, the open-loop solution solely achieved the desulfurization requirements of non-emission control areas by using higher liquid/gas ratio levels of 6.5-8.0 L/Nm, while fully failed to meet the much stricter requirements of emission control areas except the lowest 1.5% fuel-sulfur conditions. On the contrary, the cascade-scrubbing solution could meet the requirements of emission control areas under various fuel-sulfur content conditions and reduced the liquid/gas ratio by about 45%, in comparison to the open-loop solution.