Meeting future emission regulation at sea by combining low-pressure EGR and seawater scrubbing

Abstract

In the current study, the environmental performance of the first full-scale combined low-pressure exhaust gas recirculation (EGR) and seawater scrubbing system was investigated thoroughly onboard an LPG carrier operated on high-sulfur HFO. Results clearly show that the chosen approach allows around 70% $$\hbox {NO}_x$$ reduction and simultaneous elimination (98% reduction) of $$\hbox {SO}_x$$ emissions. This would allow compliance both with $$\hbox {NO}_x$$ Tier III and future ECA sulfur regulations, although it would result in minor fuel penalty due to slightly deteriorated combustion (effect of EGR) and increased backpressure (effect of scrubber). The performed chemical analysis of the water samples revealed a fairly good performance of the wash water treatment plant with water samples identified as a good-quality water almost against all measured compounds. The values for pH, turbidity and nitrates were also far below the IMO requirements. However, in terms of certain metals (vanadium, nickel and zinc) and PAHs (fluoranthene and pyrene), the quality of discharge water was somewhat poorer. These compounds also appear to be the main drivers of risk of the environmental damage as was determined by the PEC/PNEC analysis. Here, the sufficient dilution with ambient seawater is essential to bring down the corresponding concentrations to the acceptable levels, although the measured excessive pollution of ambient water in terms of arsenic, copper and molybdenum should be kept in mind. Finally, different sampling procedures (IMO MARPOL and US EPA VGP rules) were practically evaluated providing some ideas for their further improvement, as with wrong sampling the obtained results can be very misleading.