Trans RINA, Vol 161, Part A4, Intl J Maritime Eng, Oct-Dec 2019


CFD MODEL TO ANALYZE SO2 ABSORPTION IN A SEAWATER DROPLET (DOI No: 10.3940/rina.ijme.2019.a4.525a)


M I Lamas and C G Rodriguez, Universidade da Coruña, Spain SUMMARY


In the recent years, seawater scrubbers have become an interesting option to reduce SO2 emissions in marine engines. In this regard, this paper proposes a numerical model to analyze SO2 absorption in seawater. A single seawater droplet was analyzed, and the developed model was used to predict the influence of several parameters on the desulphurization efficiency, such as the droplet diameter, SO2 concentration, alkalinity and temperature. It was found that a droplet of 200 µm initial diameter can absorb up to 1.77∙10-14 mol of S for the parameters analyzed, and this reduction improves when the alkalinity and SO2 concentration are increased and diameter, seawater temperature and gas temperature are reduced. Differences up to of 21.5%, 19.8%, 2.2% and 16.3% in the S reduction were obtaining varying the SO2 initial concentration, alkaline initial concentration, initial liquid temperature and initial gas temperature respectively.


NOMENCLATURE A


Area (m2)


ΔG0 D ε


ϕ h k


Pr R


Re ρ σ ξ


T t


u υ 1.


Standard Gibbs free energy change (J/mol) Diameter (m or μm) Small quantity (m) Level set (m)


Heat transfer coefficient (W m-2 K) Henry’s constant (mol kg-1 atm-1) Prandtl number (-)


Universal gas constant (J mol-1 K-1) Reynolds number (-) Density (kg m-3)


Surface tension (N m-1) Artificial time (s) Temperature (K) Time (s)


Velocity (m s-1) Kinematic viscosity (N s m-2) INTRODUCTION


Although most combustion systems have achieved a significant reduction of their emissions during the last years, it is necessary to further reduce them due to the increasingly restrictive legislation. Particularly, in the marine field most medium and large marine engines operate on heavy fuel oil, which is a cheap combustible but contains an important


quantity of pollutant


substances, especially sulphur (S) (Lamas, et al, 2013). The oxidation of sulphur in the fuel forms sulphur oxides (SOx) in the exhaust gas, especially SO2 (Lamas, et al, 2015; Lamas & Rodriguez, 2017). SOx are the mayor source of acid rain (Lamas & Rodriguez, 2013), which causes breathing


difficulties, respiratory regulations illnesses,


acidification of lakes, agricultural crops, corrosion of materials, etc. In order to prevent these consequences, the International Maritime Organization (IMO) established a set of


to reduce emissions. Particularly,


Annex VI of MARPOL 73/78 regulates the SOx emissions by setting a maximum limiting value on the fuel sulphur content. This limit has been reduced from


©2019: The Royal Institution of Naval Architects


The most common method for flue gas desulphurization is scrubbing through an alkali absorbent like urea (Barbooti, et al, 2011), NaOH (Hikita, et al, 1977), limestone slurry (Lancia, et al, 1997; Puskar, et al, 2013), NaCl (Jeong & Kim, 1997), water (Bokotko, et al, 2005) and seawater, which is a promising solution in marine applications. The main advantages of seawater are the availability and the fact that the acidified effluent can be discharged directly


into the sea after a simple


neutralization process (Pyszko, et al, 2015; Ammar & Seddiek, 2017). There are some reports about seawater scrubbers available in the literature. For instance, Zhang


4.5% to 3.5% from 1 January 2012 and then from 3.5 to 0.5% w/w from 1 January 2020. Besides, sulphur emission control


areas there are (SECAs) with more


stringent requirements. The sulphur limits and implementation dates required by IMO are illustrated in Figure. 1. Instead of using low sulphur content fuels, other allowed solution is to employ exhaust gas cleaning/after-treatment systems. These have become a promising alternative due to the high price of low sulphur fuels such as Marine Diesel Oil and Marine Gas Oil (Seddiek & Elgohari, 2014).


Figure 1. Sulphur limits and implementation dates.


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