Mass transfer model of packed seawater scrubbers for marine exhaust gas cleaning

Abstract

Stricter limits on marine sulfur dioxide emissions have led to a need for action for ship operators. Installation or retrofit with exhaust gas scrubbers along with the continued use of sulfur-rich fuels is commonly deemed an economically attractive compliance choice. The development of adequate mass transfer models is therefore crucial for efficient scrubber design. In this work, a concise modeling approach for sulfur dioxide absorption in seawater scrubbers is presented. The model combines calculation methods for sulfur dioxide equilibrium molality in seawater with mass transfer properties (kGa and kLa) of the investigated packings. Packing kGa and kLa values are determined experimentally with standardized methodology using absorption and desorption test systems. The packed section is discretized for segment-wise calculation of sulfur dioxide molar flux. A pseudo Henry coefficient is used to jointly describe equilibrium molality of sulfur dioxide and its dissociation reaction products. The presented model is verified experimentally for five different structured packings through absorption measurements of sulfur dioxide in synthetic seawater. Model predictions for sulfur dioxide removal efficiency and effluent scrubbing liquid pH are in good agreement with experimental results over a range of operating conditions, especially for high separation efficiencies.