Safety Debate: Exhaust Gas Scrubber’s Washwater

16/01/2020 06:45:31
pastingThe IMO 2020 Sulphur Cap requires the reduction of SOx emissions either by using compliant fuel oil or installing exhaust gas scrubbers. SOx reduction deadline was set to January 2020 and the ban on the carriage of non-compliant fuel is set to March 2020. There are still ongoing debates about the safety of scrubber washwater. In this article, we aim to shed some light on the environmental impact of scrubber washwater.



The Affirmative Speech: Exhaust Gas Scrubbing Is Economical
Exhaust gas cleaning or scrubbing is recognised to be more economical than using low sulphur fuel with payback time as low as less than a year for large ships especially with the current fuel price spread of over $300/MT between HFO and VLSFO (pricing of 6th January 2020). With Kamelia Cleantech scrubbers the payback period is even shorter as the scrubbers are designed to be commercial, compact and economical to install. Nevertheless, there have been debates concerning scrubbers as they are said to increase the CO2 footprint of the ship in the long run.¹ The well to wake emissions of using scrubbers with HFO can be lower than those of using MDO if the same speed is used for the vessels at sea. The increase in energy usage at the refinery for further refining to MDO / MGO is 5-10 %. 7 The well to wake emissions depend on how the ship and scrubbers are operated. Also, the lower combustion temperatures of HFO result in less NOx production at sea.5



The Argument: Is the Scrubber Washwater Safe?
Water-soluble components of exhaust gases are removed by dissolution into washwater. This washwater is then discharged by the ship into the vast oceans and seas. The question has been whether this discharge is safe or not and if it contains harmful substances. Chemical Oxygen Demand (COD) of washwater is also thought to have a potentially adverse impact on aquatic systems. Tests made in 2011 have also shown that washwater contain arsenic, copper, lead, nickel, zinc, cadmium, chromium, vanadium and selenium – all metals that are known to be toxic to aquatic life and humans, in higher concentrations.² This could potentially raise an issue regarding the wash water’s safety to the environment. Are these arguments substantial enough to opt-out of exhaust gas scrubbers? Let’s take a look at the science behind scrubbers.

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