In practical terms, to make an existing ship comply, you have to change to a low-sulfur MGO or low-sulfur HFO at 0.5 percent sulfur. All ships can do this without any modifications, or you can install an exhaust gas cleaning system (scrubber) which converts the sulfur in the fuel to sea salt.
The sulfur can also be removed from the HFO in the oil refinery by cracking, which leaves you with a low-sulfur diesel product. This is a very costly process and consumes 10-15 percent of the energy in the HFO.
This also requires large investment in the oil references and high opex. One of the residual products is petcoke, which contains the sulfur and the metal, mainly nickel and vanadium. Petcoke is normally used as fuel in power stations or metallurgical industry. This means that the nickel and vanadium will be released to the air or sea depending on the power station consuming petcoke, whether it has a scrubber or not.
Read more: Petroleum Coke | Oxbow
Read more: Petroleum coke | Wikipedia
Compliant 0.5 percent sulfur fuel can also be made by blending HFO with a high fraction and low-sulfur MGO. Then you need more crude oil, and we can add higher emissions of CO2 in the well-to-tank perspective.
Removing the sulfur from the exhaust with a sea water “FGD” Fluid Gas Desulfurisation process, also called Sea Water Scrubber, is the third alternative.
This technique is one of the preferred options for removing SOx from the exhaust in coal/oil-fired power stations and other industry located close to sea. The technique utilizes the alkanity (mainly calcium carbonate) in the seawater to neutralize the sulfur and the end product is calcium sulfate, one of the main ingredients in sea salt.
The present level is approximately 2.7 g/l, and if all vessels in the world utilize HFO for 150 years unrestricted, this number will rise to approximately 2.701 g/l. Which suggests that a seawater scrubber is a reactor which converts sulfur to seasalt.
The additional power consumed by the exhaust gas cleaning system makes up about 2-3 percent of the base total. This means that removing the sulfur emissions from the ship will increase the total CO2 emissions. Either in the oil refinery (10-15 percent) or on-board the vessel (2-3 percent).
Approximately 100 GW of FGD units are installed around the world, equivalent to 10,000 vessels with 10 MW installed power.
A seawater exhaust cleaning system normally has an efficiency rate of more than 98 percent, meaning that under normal operating conditions, the SOx emissions to the air equal << 0.1 percent sulfur. It also removes a considerable part of the soot and particles from the exhaust gas, depending on the technical system.