Experimental Research on the Decarbonization Performance in Ocean-Going Ship Exhaust Based on the Seawater–Sodium Hydroxide Method

Reducing CO2 emissions in the international shipping industry is crucial for mitigating global warming. International Maritime Organization (IMO) has set a decarbonization target of reducing CO2 emissions in the international shipping industry by at least 70% compared to the 2008 level by 2040. Ship-based carbon capture (SBCC) is an effective technology for reducing CO2 emissions from ocean-going ships. The core of SBCC is efficient and low-cost absorption solutions. In this paper, based on the exhaust emission characteristics of ocean-going ships, the seawater–sodium hydroxide method for decarbonization in ocean-going ships is developed for the first time. First, the decarbonization performance of the seawater–sodium hydroxide absorption solution is investigated, including the influence of NaOH concentration, absorption solution flow rate, and CO2 volume concentration on the decarbonization process. The results show that the seawater–sodium hydroxide absorption solution can efficiently capture CO2 from ship exhaust. For the ship exhaust with 9 vol % CO2, when the absorption solution flow rate is 0.75 L/h, the decarbonization rate reaches 51.80% using the seawater–sodium hydroxide absorption solution with 1.5 mol/L NaOH. When the NaOH concentration increases to 2.5 mol/L, the decarbonization rate increases to 83.38%. Furthermore, TiO2 nanoparticles are added to the absorption solution to investigate optimization schemes for decarbonization of the seawater–sodium hydroxide solution. The influence of nanoparticle mass concentration and size on decarbonization is studied, and the optimization parameters of the seawater–sodium hydroxide method are obtained. With 0.09 wt % of 30 nm TiO2 in seawater–sodium hydroxide absorption solution with 1.5 mol/L NaOH, the maximum enhancement factor (E) is 1.78, achieving the maximum decarbonization rate of 92.35% for ship exhaust containing 9 vol % CO2. The seawater–sodium hydroxide method is a feasible and cost-effective method to reduce CO2 emissions in ocean-going ships. The experimental results provide a valuable reference for the application of the seawater–sodium hydroxide method in ocean-going ship decarbonization and lay an important foundation for further research on SBCC technology.