Slovakian oil refinery company Slovnaft announced last Tuesday (17 October) that it has launched a new ethylene storage tank.
The investment of almost 70 million euros is expected to reduce the need for regular shutdown of the LDPE4 polyethylene production unit by half. In addition, this is estimated to reduce the volume of carbon emissions and electricity consumption, Slovnaft said in a press release.
“While until now we needed to shut down the production unit in the petrochemical part of the refinery (LDPE4) an average of 24 times a year due to the raw material balance, by increasing the storage capacity of ethylene, which is the basic raw material for the production of polyethylene, the need to shut down LDPE4 will gradually decrease to 12 times a year by the end of the year,” said Ondrej Zákutný, Head of Investments at Slovnaft, noting that flaring, that is burning of raw material on flare stacks, is an important safety feature when shutting down petrochemical production units.
The new ethylene storage tank is designed for the storage of liquefied ethylene. The non-pressurised double-walled cylindrical vessel with an outer diameter of 30 metres and a height of 26.7 metres can hold 6,000 tonnes (10,000 m3) of liquid ethylene. It is stored there at a temperature of -103 degrees celsius and an overpressure of 8 kPa(g).
“The new ethylene storage tank will allow for smoother operation of LDPE4, while reducing the risk of forced shutdown of the Ethylene Unit where ethylene is produced. The total CO2 savings amount to 2558 tonnes per year,” said Mr Zákutný.
The BAT (Best Available Technology) principle was used in the construction of the ethylene storage tank. The main contractor was OT Industries, which, like Slovnaft, belongs to the MOL Group. The storage tank itself was made by Italian company Paresa, the compressor packages were supplied by Howden ČKD, NEAD and Aerzen. Two cryogenic submersible pumps from American company Ebara are installed in the tank, while the evaporation of ethylene is carried out by an exchanger from Linde.
“The roof of the storage tank was built inside and then was pushed on top of it by air. The roof itself weighs more than 100 tonnes and its construction, as well as the shell itself, was manufactured with millimetre precision in order to realise this lift,“ explained Mr Zákutný.
Another operation was the drilling and plugging of a DN1000 diameter exhaust pipe at a 45-degree angle using a “T.D. Williamson method”. Such a specific connection method has never been implemented anywhere in the world before and was specially developed for Slovnaft by SEPS.