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

Abstract

A cascade-scrubbing technology was proposed to improve the current oncethrough 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 SO 2 concentration, and increasing with Na/S. At the high SO 2 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 SO 2 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 liquidgas 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%.

Seawater/alkaline liquid cascade‐scrubbing desulfurization performance for the exhaust gas of a 162‐kW marine diesel engine

“…This means that for a lye with pH = 13.1 at a liquid–gas ratio of 0.8 L/Nm 3 (Na/S = 2), raising the liquid–gas ratio elevates Na/S. Figure whose data are mainly from Wang et al show the desulfurization results regarding with various conditions, plus a picket line denoting the ECA's required limit of 98%. In Figure b showing results at Na/S > 2, the curve at Na/S = 2 (essentially given out previously in Figure a) is repeated for a convenient comparison.…”

“…The three models can be freely switched according to the surroundings (i.e., seawater alkalinity and temperature, local government's regulations, and emission limits). More detailed introductory material about the cascade‐scrubbing system can be viewed in the published work …”

“…In response to above limitations for these typical ship's scrubbing systems, a cascade‐scrubbing technology was proposed, with the scrubbing tower divided into the main and auxiliary scrubbing sections and allowing three kinds of cascade‐scrubbing models corresponding to different conditions (i.e., seawater/seawater, seawater/alkaline liquid, and alkaline liquid/alkaline liquid cascade‐scrubbing). Accordingly, by performing desulfurization experiments in a bench‐scale cascade‐scrubbing system for the exhaust gas of a 162‐kW marine diesel engine, our recently published work reported the desulfurization comparison of the once‐through seawater (i.e., the conventional open‐loop solution) and seawater/seawater cascade‐scrubbing models. The results found that the once‐through seawater scrubbing model failed to achieve the ECA's requirements under high‐sulfur and low‐alkalinity conditions, and on the contrary, the developed seawater/seawater cascade‐scrubbing model resolved this problem well with an easily increased liquid–gas ratio but without the flooding occurrence, thereby expanding the seawater scrubbing application in open ocean .…”

“…Accordingly, by performing desulfurization experiments in a bench‐scale cascade‐scrubbing system for the exhaust gas of a 162‐kW marine diesel engine, our recently published work reported the desulfurization comparison of the once‐through seawater (i.e., the conventional open‐loop solution) and seawater/seawater cascade‐scrubbing models. The results found that the once‐through seawater scrubbing model failed to achieve the ECA's requirements under high‐sulfur and low‐alkalinity conditions, and on the contrary, the developed seawater/seawater cascade‐scrubbing model resolved this problem well with an easily increased liquid–gas ratio but without the flooding occurrence, thereby expanding the seawater scrubbing application in open ocean . In this work, to confirm the seawater/alkaline liquid cascade‐scrubbing advantages of a higher desulfurization efficiency and far lower alkaline‐liquid consumption to overcome the aforementioned shortcomings of the open‐loop and closed‐loop solutions, a series of seawater/alkaline liquid cascade‐scrubbing desulfurization experiments were performed in the same bench‐scale cascade‐scrubbing system, plus the solely open‐loop and closed‐loop desulfurization experiments for comparison.…”

“…In this work, to confirm the seawater/alkaline liquid cascade‐scrubbing advantages of a higher desulfurization efficiency and far lower alkaline‐liquid consumption to overcome the aforementioned shortcomings of the open‐loop and closed‐loop solutions, a series of seawater/alkaline liquid cascade‐scrubbing desulfurization experiments were performed in the same bench‐scale cascade‐scrubbing system, plus the solely open‐loop and closed‐loop desulfurization experiments for comparison. The above differences in the research objectives and potential findings thus highlight the new contribution of this work compared with the recently published work . Findings in this work are intended to find a solution for the imperfect marine EGCS.…”