The Sandvik Group’s expertise in sulphur solidification has been well established over many decades and its Rotoform system has now been installed at most of the world’s major refineries. On example is Hellenic Petroleum’s Elefsis refinery near Athens.
Hellenic Petroleum, one of the largest commercial and industrial groups in Greece, is currently modernizing its Elefsis refinery, to produce fuels which meet the latest European and international specifications. The project includes a flexicoker, a high-pressure hydrocracker, and a sulfur recovery unit. Environmental investment accounts for 25 percent of the total cost of the project, and Hellenic Petroleum aims to cut local pollutants by up to 85 percent as a result.
Front end engineering design (FEED) was carried out by Foster Wheeler Italiana. The engineering, procurement and construction management (EPCM) and project management contractor (PMC) roles are being undertaken by Tecnicas Reunidas in Madrid.
In January 2009, Sandvik was selected to supply the equipment required for the solidification, storage and ship loading of sulfur recovered by the refinery. The relationship between Sandvik and Hellenic Petroleum began in 1986 with the installation of sulfur granulation lines at the Aspropyrgos refinery.
The equipment will be delivered by two divisions of the Sandvik Group: Sandvik Process Systems, Germany, is manufacturing and installing the solidification package, while Finland-based Sandvik Mining and Construction will provide the solid sulfur handling facilities. Construction of the sulfur plant began in March 2010 and commissioning is due for the end of 2010 or the beginning of 2011.
Sandvik has developed an efficient and environmentally friendly process for cooling and solidifying molten sulfur. The process begins when liquid sulfur is pumped from the refinery’s sulfur recovery units to a liquid sulfur storage tank. From here it is transferred to a sulfur preconditioning system, via a heated pipeline and a double filter. The preconditioner accepts liquid sulfur at temperatures of up to 150 °C and cools it to a constant 125 °C.
The pastillation system is based on a Sandvik Rotoform feeder which deposits droplets of liquid sulfur onto a continuously running stainless steel belt. Water is sprayed against the underside of the belt, cooling the droplets into solid pastilles. The Rotoform itself has a heated, cylindrical stator around which a perforated shell revolves, depositing sulfur drops across the width of the steel belt. The circumferential speed of the Rotoform is synchronized with the speed of the belt, ensuring that drops are deposited accurately, consistently and without deformation.
The Rotoform produces the pastilles mechanically: subsequent grinding or crushing is not required, so the associated costs, noise and dust are eliminated. This combination of simplicity, efficiency, product quality and low environmental impact is the key to the success of the Rotoform system, which now boasts more than 1,400 installations across a wide range of applications.
Good pastilles require a number of characteristics:
- uniform size, low friability and high impact abrasion resistance;
- good flow characteristics;
- low moisture content;
- stable properties over time;
- consistent quality; and
- high bulk density and angle of repose.
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