Stainless solution for greener ships
Emissions reduction is a collective agenda today. With countries around the world implementing regulations to prevent the release of greenhouse gases, companies like Valmet have stepped up with advanced air pollution control tools.
After an EU directive went into effect in 2015 that required ships operating in the EU to limit their sulphur concentration to below 0.1%, Valmet designed two flue-gas desulphurization units to be used in the Baltic and Northern Seas. Each unit weighs some 20 tonnes and is approximately 12 meters tall.
With these units, the harmful organic and inorganic substances that are created during combustion are no longer discharged into the atmosphere. Instead, with a flue-gas desulphurization unit, carbon dioxide, sulphur dioxide, dust and soot can be concentrated and deposited safely underground.
Several studies have been conducted to determine which material is best for use in such a harsh environment. Sulphuric acid condensation has been long recognized as a cause of corrosion in flue-gas desulphurization units. Sulphur, seawater and heat placed together require highly corrosion resistant materials.
A harsh environment
“The environment in the flue-gas desulphurization unit is harsh and varies depending on where ships are sailing. Sulphur, seawater and heat put together require highly corrosion resistant materials. Due to the presence of such demanding environments, we decided to use duplex stainless steel grades,” says Juha Laukka at Valmet.
For the two units, Outokumpu provided 40 tonnes in total, consisting of four high-alloyed stainless steel grades – Outokumpu Forta SDX 2507 super duplex stainless steel, Forta DX 2205 duplex stainless steel, Ultra 254 SMO austenitic stainless steel and Supra 316L/4404 austenitic stainless steel.
“We get good benefits of Outokumpu’s duplex grades in flue-gas cleaning, where material is under a lot of pressure. Duplex is an excellent material in this use,” says Laukka.