Search

In the adaptability of a proposed cascade‐scrubbing technology used for ocean ships, ASPEN PLUS desulfurization simulations for a packing scrubber of a 10 000‐kW large‐scale marine diesel engine were performed to uncover effects of the scrubber's configurational parameters (i.e., scrubber diameter, spherical packing diameter, and packing thickness) and meanwhile confirm the selected parameters' availability. Desulfurization was evaluated not only under the once‐through open‐loop model with varying above scrubber's configurational parameters plus operational seawater temperature and scrubbing section's inlet gas temperature but also under the seawater/lye cascade‐scrubbing model for confirming its availability and superiority in saving both the seawater and lye consumption. Desulfurization exhibits increase, decrease, and slight increase trends with the packing thickness, packing diameter, and scrubber diameter, respectively. However, the packing‐layer pressure drop increases with the packing thickness and decreases initially but then varies little with the left two parameters. Any increase in these temperatures weakens desulfurization. A comprehensive consideration of multiple factors suggests that the selected packing diameter of 50 mm, total packing thickness of 3.5 m, and scrubber diameter of 2.8 m are reasonable and adaptable to the scrubber, which can comply with the required strict desulfurization standard by using the low‐alkalinity seawater (1.42 mmol/L) to scrub the high‐sulfur gas (fuel‐sulfur content of 3.5%) with a moderate liquid/gas ratio of about 6.5 L/Nm3. Under the same gas and seawater conditions, the seawater/lye cascade‐scrubbing model achieves about 38% and 90% reduction respectively in the seawater and alkali consumption as comparing with the once‐through open‐loop and closed‐loop models, respectively. [ABSTRACT FROM AUTHOR]

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/Nm3, 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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/Nm3, desulfurization with the allowed liquid–gas ratios ≤8 L/Nm3 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/Nm3, a high liquid–gas ratio of 4.8 L/Nm3 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/Nm3 and 0.84 mmol/L), the solution utilized 5–6 L/Nm3 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. [ABSTRACT FROM AUTHOR]

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/Nm3 and Na/S = 2, desulfurization complying with emission control area's (ECA's) requirements necessitated a liquid–gas ratio above 4.5 L/Nm3. 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/Nm3 with an alkali‐rich liquid–gas ratio of 1–2 L/Nm3. With the alkali‐rich lye fed at liquid–gas ratios of 1, 1.5, and 2 L/Nm3, the main scrubbing section's alkali‐lean lye necessitated liquid–gas ratios of 2.8, 2.4, and 3.1 L/Nm3 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/Nm3 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/Nm3 at Na/S = 2 or 4 L/Nm3 at Na/S = 2.16 but with the alkali‐utilization efficiency dropping below 91%. [ABSTRACT FROM AUTHOR]