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Thursday, February 20, 2020 

The Clean Shipping Alliance (CSA) 2020 held its Technical Conference on 20 February 2020 and among other sessions, the audience learned of a new proposal that could offer exhaust gas scrubbers as an alternative IMO decarbonisation strategy.

A panel discussion reiterated the relatively smooth transition for scrubber-equipped vessels to IMO 2020 sulphur regulations, while other presentations looked at corrosion issues and outlined the CE Delft study into scrubber washwater, which found that even with open loop scrubbers discharge and sediment were within limits for seawater quality in ports.

It was a presentation by Technical Consultant Dr Robert Allen, however, that caused a stir among the audience of ship operators, equipment suppliers and press. Dr Allen outlined a proposed application of alkaline water s a washing medium, which he said had the potential to remove not only Sox from exhaust gases, but cut emissions of NOx and CO2, possibly addressing the demands of IMO Tier III and the IMO 2030/2050 decarbonisation strategy.

The proposal harked back to a scrubber system developed by EcoSpec of Singapore which had claimed to cut emissions of NOx and CO2, but which failed to take off, little having been heard since 2014. Measurements taken by ABS at the time had proved it worked, but it was considered not to be commercially viable. Dr Allen believed the main difficulty was that the flow rate was uncertain and the power requirement for the electrolysis system was unfeasibly high. Additionally, the carbon removal methodology was controversial.

Dr Allen’s alternative works by producing hydroxyl radicals which react with acidic gases in the exhaust. The hydroxyl radicals in alkaline water are produced without chemicals, purely by electrolysis. He proposed a two-stage scrubber – the first stage follows conventional open-loop scrubber practice to remove the oxides of sulphur, with a second stage using alkaline water to react with NOx and CO2. Nitric and Carbonic acids are the by-products, but at far lower quantities than the sulphur discharge.

The system uses industrial tourmaline as electrolyte, a material that is produced in quantity in  China for various applications. Dr Allen’s small-scale laboratory trials show that the system can generate alkaline water at low power – virtually pump operating power alone. Scaling up, 20m3 of wash medium could be generated at a cost of less than US$10; with about US$7.5 for tourmaline crystals and beads. The actual cost will be dependent on volume of water and the amount of scrubbing needed.

Dr Allen says that more research is needed to prove if the system could work at a large scale – and he admits that is a ‘very big if’. He hopes that CSA2020 can help develop the system, and that funding could be provided by the industry’s research fund created to investigate new fuels and technologies, financed by a small surcharge on cargo rates.

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