Study on the effect of wet scrubbing technique on emissions in a dual fuel engine operating with diesel and hydrogen

Reducing emissions from internal combustion (IC) engines is a crucial goal, encompassing nitrogen oxide (NO), hydrocarbon (HC), carbon monoxide (CO), and smoke. To enhance both performance and emissions, contemporary IC engines have turned to alternative gases such as hydrogen (H2) and exhaust after-treatment systems. A promising method to effectively decrease exhaust emissions entails the application of the scrubber technique as an exhaust gas after-treatment. This study's objective is to explore two avenues for curtailing exhaust emissions. The first involves substituting traditional fuels in IC engines with hydrogen gas (H2) at a flow rate of 6 LPM. The second entails integrating a liquid chemical solution into the scrubber technique. Notably, the utilization of KMnO4 solutions exhibits an appreciable reduction in NO and CO emissions compared to solutions containing NaOH. The experimental process included two aspects: investigating hydrogen fuel (H2) as an alternative fuel for IC engines and incorporating a scrubber technique using both KMnO4 and NaOH solutions. These experiments were conducted using a single-cylinder engine with a power output of 5.2 kW, cooled by water. The engine underwent tests under various load conditions, spanning from minimal to maximal loads. The findings revealed that employing KMnO4 solutions within the scrubber technique led to reductions of 25% and 40% in NO and CO emissions, respectively, in contrast to the utilization of NaOH solutions. Similarly, introduction hydrogen gas also has a significant effect on emission reduction.

Characterization of scrubber water discharges from ships using comprehensive suspect screening strategies based on GC-APCI-HRMS

An extended suspect screening approach for the comprehensive chemical characterization of scrubber discharge waters from exhaust gas cleaning systems (EGCSs), used to reduce atmospheric shipping emissions of sulphur oxides, was developed. The suspect screening was based on gas chromatography coupled with high-resolution mass spectrometry (GC-HRMS) and focused on the identification of polycyclic aromatic hydrocarbons (PAHs) and their alkylated derivatives (alkyl-PAHs), which are among the most frequent and potentially toxic organic contaminants detected in these matrices. Although alkyl-PAHs can be even more abundant than parent compounds, information regarding their occurrence in scrubber waters is scarce. For compound identification, an in-house compound database was built, with 26 suspect groups, including 25 parent PAHs and 23 alkyl-PAH homologues. With this approach, 7 PAHs and 12 clusters of alkyl-PAHs were tentatively identified, whose occurrence was finally confirmed by target analysis using GC coupled with tandem mass spectrometry (GC-MS/MS). Finally, a retrospective analysis was performed to identify other relevant (poly)cyclic aromatic compounds (PACs) of potential concern in scrubber waters. According to it, 18 suspect groups were tentatively identified, including biphenyls, dibenzofurans, dibenzothiophenes and oxygenated PAHs derivatives. All these compounds could be used as relevant markers of scrubber water contamination in heavy traffic marine areas and be considered as potential stressors when evaluating scrubber water toxicity.

Membrane Separation Used as Treatment of Alkaline Wastewater from a Maritime Scrubber Unit

Since 1 January 2020, the sulfur content allowed in exhaust gas plume generated by marine vessels decreased to 0.5% m/m. To be compliant, a hybrid scrubber was installed on-board, working in closed loop and generating a high volume of alkaline wastewater. The alkaline water suspension was treated by a silicon carbide multitubular membrane to remove pollutants, and to allow the water discharge into the natural environment. In this paper, membrane filtration behavior was analyzed for the maritime scrubber wastewater. A range of operating parameters were obtained for several feedwater quality-respecting industrial constraints. The objective was an improvement of (I) the water recovery rate, (II) the filtration duration, and (III) the permeate quality. Thus, in high-fouling water, a low permeate flow (60 L h^-1 m^-2) with frequent backflushing (every 20 min) was used to maintain membrane performance over time. In terms of water quality, the suspended solids and heavy metals were retained at more than 99% and 90%, respectively. Other seawater discharge criteria in terms of suspended solids concentration, pH, and polyaromatic hydrocarbons were validated. The recommended operating conditions from laboratory study at semi-industrial scale were then implemented on a vessel in real navigation conditions with results in agreement with expectations.

Progress of ship exhaust gas control technology

Ship emissions problems caused by the rapid development of maritime trade can't be ignored. The NO_X, SO_X, CO₂, PM and other toxic substances contained in the exhaust gas are extremely harmful to the environment and human health. In order to cope with the adverse effects of ship emissions and the increasingly stringent emission regulations formulated by the IMO and governments, the shipping industry needs to adopt new clean energy and high-efficiency exhaust control technologies to reduce ship emissions. This paper provides a comprehensive review, including: (1) The impact of pollutants such as NO_X, SO_X, CO₂ and PM emitted by ships on the environment and human health; (2) New regulations about ship exhaust emissions; (3) Application of clean energy such as LNG, biodiesel, methanol, hydrogen and ammonia on ships; (4) After-treatment technology of ship exhaust gas such as SCR and EGR. And focusing on the principles, uses, characteristics, implementation obstacles and prospects of different energy and technologies, with a view to provide some help for the research on ship exhaust emissions control.

Selective Sulfur Dioxide Absorption from Simulated Flue Gas Using Various Aqueous Alkali Solutions in a Polypropylene Hollow Fiber Membrane Contactor: Removal Efficiency and Use of Sulfur Dioxide

Hollow fiber membrane contactors (HFMCs) provide a large specific surface area. Thus, their significantly reduced volume provides an advantage compared to the conventional gas–liquid contactor. In this study, the selective removal efficiency of flue gas, in which sulfur oxide (SO₂) and carbon dioxide (CO₂) coexist, was measured using a polypropylene (PP) HFMC with such advantages. To increase the selective removal efficiency of SO₂, experiments were conducted using various alkaline absorbents. As a result, with 0.05 M ammonia solution, the removal efficiency of 95% or more was exhibited with continuous operation for 100 h or more. We confirmed that the absorbent saturated by the once-through mode was aqueous ammonium sulfate ((NH₄)₂SO₄) solution and could be used as a fertilizer without additional processing.

Cost-Benefit Evaluation on Promising Strategies in Compliance with Low Sulfur Policy of IMO

According to the amendment of the “International Convention for the Marine Prevention of Pollution from Ships” (MARPOL), Annex VI stating that the sulfur content in marine fuel oil cannot exceed 0.5 wt. % came into effect in 2020. This study uses cost-benefit analysis method to evaluate the feasibility and implementation benefits of those strategies. A container ship serving on the ship route is selected as a representative. It is found that the very low-sulfur fuel oil (VLSFO) strategy has a higher total incremental cost than the scrubber strategy in the first 4.14 years, but then, the trend is reversed. After this container ship is equipped with a scrubber, the pollutant emission reduction is 5% higher than the condition of VLSFO only in the first year. The SOx and PM emission reduction rates of VLSFO strategy are higher than that of the scrubber strategy by 9% and 25%, respectively, within five years. In addition, during 3.3 years after the scrubber is installed, the cost-benefit ratio is higher than that of the VLSFO strategy. Hence, the scrubber for the ocean route container ships is merely a short-term compliance strategy within 3.3 years. In contrast, the low sulfur fuel oil strategy that less pollutant is emitted is a compliance strategy for periods longer than 3.3 years.