Study On Desulfurization Properties Of Seawater For Ship Exhaust Based On Jet Bubbling Reactor

Seawater desulfurization technology can be used to remove SO2 from ship exhaust with good prospect due to its advantages, such as low operation cost, abundant resources of desulfurizer and non-solid waste. However, the limitation of ship space and seawater alkalinity restrict the size and performance of desulfurization system, which cause low desulfurization efficiency of seawater for ship exhaust based on traditional spray tower and packed tower.In view of jet bubbling reactor with small occupied area and high desulfurization efficiency, the desulfurization properties of seawater in jet bubbling reactor was discussed, as well as reinforcement of various additives on seawater desulfurization. Firstly, mass transfer model about seawater desulfurization was built based on the principles of seawater desulfurization and characteristics of mass transfer between gas and liquid in jet bubbling reactor. Secondly, the parameters, such as gas flow, seawater temperature, immersion depth, seawater alkalinity, inlet concentration of SO2 and O2, influencing desulphurization efficiency in jet bubbling reactor were examined. Based on mass transfer model, the influence and mechanism of above parameters on desulfurization properties of seawater were analyzed from the perspective of reaction kinetics. Finally, the effect and its mechanism of various additives, including MgO, CaO, NaOH, Na2CO3, NaOH+CaO and NaOH+MgO, with different adding amount on desulfurization properties of seawater were studied in order to obtain the best scheme of seawater additive from the viewpoint of economic efficiency and reinforcing performance.Results showed that the absorption capacity of seawater scrubbing SO2 was up to 3.682 mmol/L about 3.92 times that of deionized water. Unlike deionized water, due to the existence of HCO3- in seawater, there was a buffer-descent stage in the change of pH value leading to high absorption capacity of seawater, which was the precondition of using seawater as desulfurizer in jet bubbling reactor.The experimental results of the effect of parameters on desulfurization properties showed that the desulfurization efficiency, which reduced linearly over desulfurization time, decreased with the increase in gas flow, seawater temperature and inlet SO2 concentration while it increased with increasing immersion depth, seawater alkalinity and inlet O2 concentration. Increasing gas flow and seawater temperature could increase total mass transfer coefficient of liquid phase. Compared to oxygen-free atmosphere, the concentration of SO42- was increased by 1.06-1.75 mmol/L in the presence of oxygen while concentration of SO32- decreased, which indicated that O2 promoted the oxidation of SO32-. The absorption capacity increased significantly with increasing inlet O2 concentration. It increased from 3.682 mmol/L to 7.463 mmol/L as the inlet O2 concentration increased from 0% to 12%.The experimental results of reinforcement of additives on seawater desulfurization showed that the abilities of seawater scrubbing SO2 were enhanced by adding MgO, CaO, NaOH, Na2CO3, NaOH+CaO and NaOH+MgO to seawater respectively. The absorption capacity increased with the increase in adding amount of additives while pH value was negatively correlated with adding amount of additives. The increment of absorption capacity of seawater showed downward trend when adding amount of CaO and MgO in unit volume of seawater was up to 6 mmol, which indicated that the reinforcing performance for seawater was limited by increasing the adding amount of CaO and MgO continually. Adding NaOH and Na2CO3 respectively to seawater leaded to increase the increment of absorption capacity while the decreasing degree of increment of absorption capacity was improved by using NaOH+CaO and NaOH+MgO as additives respectively. MgO was the optimal additive by taking economic efficiency and reinforcing performance into account. The absorption capacity of seawater by adding MgO was 2.169 times that of seawater without adding any additive when adding amount of MgO in unit volume of seawater was 8 mmol. The calculated values of absorption capacity obtained by fitting equation were in great agreement with the experimental value when the adding amount of MgO in unit volume of seawater was in the range of 0-8 mmol.