Treatment of materials soiled by fuel because of Erika’s sinking
Clients : Total / Brézillon
December 12 th 1999, oil tanker called Erika went down off the French coasts, spreading around 20 000 tons of fuel in the ocean. When this oil slick reached the shore, coast was soiled, creating a huge amount of wastes (around 270 000 tons) composed of sand, water, seaweeds and fuel. Costs predicted in those days: 1000 to 1500 francs per ton representing in global 200 to 300 million. TotalFina, which handled project ownership, sent an international call for bids and more than 100 companies expressed themselves to treat either a part or the totality of these wastes.
Technical commitments were many: mass of wastes (around 300 000 tons) and heterogeneity of materials. They were composed of slick of oil (40 to 50% of fuel) and soiled sands (1 to 2% of fuel). Technical commitments were also connected to environmental impact: 100% of wastes had to be recycled, no rejection in natural environment, low water and electricity consumption, no industrial risks and pollution hazard.
Chosen after the call for bids, Brézillon Company proposed a physical-chemistry washing solution including sands treatment, able to treat these mixed materials with high rate.
MS, thanks to its experience in complicated problematics, drove trades with Brézillon team and proposed this innovative concept: design/manufacture/install a washing solution which enable to clean up wastes with a rate of 100 T/h, a solution to treat and recycle soiled waters, and a solution to press slurry. MS also committed itself to trained machine-operators.
Physical-chemistry treatment flowsheet for wastes from Erika.
Treatment of soiled sands
Washing step is the key element in the whole process to treat the 300 000 tons of wastes. Constraints were many: heterogeneity of collected materials, 100% of valorization and low consumption of water. In a first phase, the mixing of “water + wastes + diluent” was sent to a washing trommel, then to a screening phase which allows to separate macro-wastes (wood, plastics, and stones).
A part of this mixing “water + wastes + diluent” was transported to a dewaterer, screened under water, then washed through two cycloning/dewatering units MS 200x60 HYD, including a hydro-separator with adaptable overflowing from 0 to 2 m³/h which allows to eliminate undesirable materials such as seaweeds. Performances of cycloning/dewatering units are 200 m³/h of treated materials, 60T/h of dewatering sand with adaptable cut from 50 to 100 µm.
Another part of the mixing “water + wastes + diluent” was sent to an MS thickener DR9,5 in order to collect thanks to sedimentation, sand in the bottom of the thickener (which supplied then a cycloning/dewatering unit MS 300x60), and in the top water + fuel (which supplied oil-separator tanks). All these washing phases were necessary in order to avoid clogging of oil-separator tanks and to product 0/4mm concrete sand. Entirely modular, this installation was designed to be plug-in easily in the whole process of wastes treatment.
Treatment of process waters
W ashing phase of sands soiled by fuel is possible thanks to a mixing of water and diluent. These process waters from cycloning/dewatering units and oil-separator tanks had to be treated, recycled and sent back into the process because of constraints on water consumption and rejection in natural environment. Brézillon chose again MS to supply a water treatment plant to clarified process waters. After a phase of tests in its laboratory, MS designed a thickener DR16 (16m of diameter), with 400 m³/h of throughput, automatic management of coagulant and floculant. 400 m³/h of clarified water were sent back in the washing process allowing to reduce needing of make-up water.
Then, flocculated slurries from thickener were stocked into 3 silos which allows to regulate feeding of filter presses.
Treatment of slurry
In order to recycle even more process water and to reduce wastes volumes, slurries were sent to a pressing equipment. After a phase of tests in its laboratory, MS suggested a slurry treatment through lime addition to improve dry content and filterability of slurry. Precisely, MS designed upstream a slurry preparation plant entirely automatic with lime addition. Then, slurries were sent to three compact filter presses (FP12) with plates and pneumatic cylinders for cakes release system. Performances of each filter press were 3,1T/h of dry materials corresponding to 4,3 T/h of cakes with 30% of moisture. These three filter presses treated 120 Tons of dry materials every 14 hours thanks to theirs automatic programs. Cakes of slurry were used as fuel in ovens of cement industries in Belgium. Filtrates still had a low quantity of oil, and consequently had to be treated through oil-separator tanks and then sent back in the washing process.
This extraordinary device allowed to treat and recycle 300 000 tons of wastes from Erika within 19 months. Nowadays this installation is uninstalled, however it underlined the know-how of MS and its capacity to answer to complicated issues. Extent of this work site, its technical constraints and innovative aspects gave it back as a flagship project by MS and a world preview.