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.

A cascade-arch-firing low-NO x and high-burnout configuration (CLHC) was proposed as a solution for the W-shaped flame furnace's incompatibility problem of strengthened low-NO x combustion and high burnout. Numerical simulations verified by industrial-size measurements of a 600 MW e W-shaped flame furnace were used to confirm the CLHC's low-NO x and high-burnout characteristics and evaluate its cascade-arch configuration effect on the gas/particle flow, coal combustion, and NO x formation. The furnace with the existing low-NO x combustion art showed NO x emissions of about 900 mg/m 3 at 6% O 2 and carbon in fly ash of about 5%. In applying CLHC as a replacement for the prior art, numerical simulations at typical cascade-arch configurations of C L = 1/5, 1/4, and 1/3 (C L signifying the ratio of the lower arch depth to the total arch depth) showed that as C L increased, both the flow field and combustion symmetry initially improved but then deteriorated. In conjunction with the improvement in both NO x emissions and burnout, the C L = 1/4 setting achieved the best furnace performance with NO x emissions 707 mg/m 3 at 6% O 2 and carbon in fly ash of 5.5%. In comparison with the prior low-NO x art, CLHC reduced further NO x emissions by 22% and almost maintains the burnout rate.

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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.