Mercury reduction at stainless steel EAF
Tornio, Finland
The challenge
Outokumpu Stainless Oy in Tornio Finland produces Stainless Steel (hot rolled and cold), using ferrochrome from the nearby Kemi mine and mainly imported scrap metal. The steel smelting shops have a production capacity of 1.6 million tons per year.
The primary source of mercury is the scrap metal imported to the Tornio plant from worldwide suppliers.
The mercury emissions at Tornio plant were often a challenge, as high peaks made it difficult to respect the future emission limits of 50 µg/Nm3 (8 h average) and > 170 µg per ton of steel produced. The high level of Mercury in the off gases ultimately had the consequence that annual production rate had to be reduced.
EAF #2 exhaust was identified as the main source of Hg emissions and continuous measurement showed mercury concentrations at around 30 g/heat and mercury peaks of > 1000 µg/Nm3 .
The target was < 10 g Hg/heat.
The Lhoist solution
The Lhoist solution was to set up a full-scale sorbent injection trial at the EAF #2 Bag house Filter, injecting the Activated Carbon based, non ATEX classified blend, Sorbacal® Micro 2135. Immediately after initializing the trial, the Hg emissions were decreased significantly.
Adjustable dosing rate of 25-350 kg/h controlled by the in-house continuous Mercury analyzer enabled Hg reductions of up to 70-90%. Technical support from Lhoist was present throughout the entire project to ensure the best possible benefits for Outokumpu.
Based on the successful trial results, Outokumpu decided to invest in a permanent storage and dosing system for Sorbacal Micro 2135.
The benefits
The use of the Sorbacal® Micro sorbent ensured compliance with the new regulation. Activated carbon is a part of the blend together with a nonflammable component and because its content is kept below a defined limit, the mixture is no longer considered as explosive.
This means that transport, storage and dosing can be done using normal non-ATEX installations.