Safer chemicals for scrubbers gaining industry traction

Scrubber. Credit: Yara Marine

In preparation for the IMO 2020 sulphur cap, operators have been fitting their ships with the industry standard for closed loop scrubbers, which use the chemical caustic soda to remove the sulphur content from the exhaust gas. The safety risks for crew handling this chemical can be many, however safer, cheaper alternatives, such as magnesium oxide are gaining traction. With the sulphur cap deadline looming, ship owners who have installed closed loop systems have opted for those that use the alkali, caustic soda to treat the washwater held in the washwater tank and neutralize the acidity of the sulphur, for the de-sulphurization process. This is the treatment process expected in a ‘wet’ scrubber.

However, despite caustic soda being the default alkali, the substance carries serious safety risks to not only the crew, but to the scrubber itself. Sophia Sloan, representative at Premier Magnesia, a manufacturer of magnesia products, speaking directly to SAS outlined the risks, “Caustic Soda is a highly corrosive chemical listed on the Special Health Hazard Substance List. On contact, it can burn the skin and the eyes, and cause permanent lung damage through inhalation.

“In contact with water, it can create enough heat to ignite combustibles and produce poisonous gases. In sum, mishandling caustic soda can have severe consequences.” She continued.
As such, companies such as Yara Marine and Premier Magnesia are turning towards the use of magnesium oxide instead in their scrubbers. “It is a completely harmless substance and the most common mineral found on earth, the price level has also been stable over the years unlike caustic soda which varies a lot … mostly we selected magnesium oxide because of safety and cost.” Commented Peter Strandberg, CEO of Yara Marine.

Strandberg went on to explain that despite the initial costs of caustic soda scrubbers being cheaper to install, the running costs make magnesium oxide the better candidate. A side by side comparison was provided with a vessel operating for 6 months in Alaska, continuously running closed loop scrubbers, they found that the chemical cost for the caustic soda system was USD1.9 million compared with magnesium oxide at USD400,000.

Sloan further commented that there is less chemical consumption 25-30% compared to caustic soda, plus magnesium oxide also requires less storage space onboard. However, it was noted that the maintenance costs for magnesium oxide are expensive but despite this, there will be less instances of corrosion in the scrubber. Caustic soda is a substance that causes severe corrosion and if this happens in the scrubber tower the plates will need to be changed. As scrubbers are also directly connected to the engine, if there is a malfunction the vessel will be put out of business until it is repaired. In both instances serious works would have to be carried out on the vessel, as opposed to more frequent but less invasive maintenance procedures.

However, Aakre Stian, general manager business development, Wartsila, provided reasoning behind why their standard is still caustic soda, stating it provides superior pH adjusting properties and the fact it is also completely soluble in water. The handling and thereby exposure risk is limited to the bunkering of the chemical. The dosing into the system is fully automatic.

Further, Wartsila sell predominantly open loop and hybrid systems, while Pacific Green Marine Technologies also share this customer demand. As commented by Khushroo Bhandari, marine operations director – Europe, Pacific Green, “most clients are either buying open loop or hybrid, the open loop can be easily modified to closed loop with add-ons when required”.

Bhandari also went on to remark that the reasoning behind this is the hope on behalf of ship-owners of a further relaxation of regulations on open loop scrubber bans, as seen earlier this year with Japan refusing to ban them outright.