Stamicarbon strives to improve the urea process constantly, and has now introduced the Rotoform process designed by Sandvik Process Systems as a very useful alternative or addition to the traditional finishing techniques of prilling and granulation.
The Rotoform process has been successfully employed in the petrochemical, chemical, food and fertilizer industries since the early 1980s and there are currently more than 1400 Rotoform units in operation worldwide.
The Rotoformer principle brings together the specially designed drop-former with the outstanding features of the Sandvik steel belt cooler. This technology is ideal for removing bottlenecks, for upgrading the prill tower or granulation section, or for the production of specialty urea products (UAS S-urea, micro nutrients). Premium-quality pastilles can be produced at low investment costs, low operating costs and with minimum emissions.
The Rotoform process offers the following advantages:
- Very low dust emissions.
- Simple solution to realize very low ammonia emissions.
- Very low power consumption figure.
- More uniform product.
- Good crushing strength even without adding formaldehyde.
- Flexible production by switching on/off rotoformer lines.
- Lower investment costs.
- Possibility of producing controlled-release urea and mixed fertilize.
Mechanically, a single Rotoform unit for urea pastillation consists of a continuously moving steel belt, typically 1.5m wide and 15-20m long (for a 125 ton/day unit), with a drop-former feeding device at one end of the moving belt and a scraper at the discharge end. The feed to the Rotoform is urea melt with a concentration of 99.6wt% and typically branched off from the urea evaporation section downstream from the urea melt pumps.
Urea is introduced under pressure (3 bar) in molten form to the drop former. The Sandvik Rotoform High Speed Drop Former consists of a heated stator and a perforated rotating shell, which turns concentrically around the stator to deposit drops of urea across the full width of the belt. The circumferential speed of the Rotoformer is synchronized with the speed of the steel belt cooler ensuring that the drops are deposited on the belt without deformation and, after solidification; result in regular pastilles with an optimum shape. The rotating shell contains rows of small holes which are sized to deliver the required product size. The heat released during crystallization and cooling is transferred by the stainless-steel belt to the cooling water. The cooling water is sprayed against the belt underside, absorbs the heat and is collected in pans, cooled in a cooling system (cooling tower) and returned to the Rotoform units. Under no circumstances can the cooling water come into contact with the urea product.
After solidification, the pastilles are smoothly released from the steel belt via an oscillating scraper. The product then falls directly onto a conveyor belt for transfer to storage. The section above the moving steel belt is enclosed with a hood and vented to an existing vent system. There is no visible urea dust emission, only some ammonia vapors which can be easily removed from the very small air flow by means of a normal atmospheric absorber. Several Rotoform units can be installed in parallel in order to achieve higher capacities.
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