A granulation installation for a melt produced in a metallurgical plant having a water injection device for quenching and granulating the melt and a granulation tank for collecting water and granulates. The installation includes a steam condensation tower located above the granulation tank for collecting steam generated therein, where the tower has a steam condensing system. The system includes a water-spraying device disposed above a water-collecting device. The tower further includes a stack extending into the tower and configured for selectively evacuating excessive steam to the atmosphere. The stack has an inlet communicating with the lower zone of the tower and an outlet arranged to evacuate steam to the atmosphere above the tower. The stack is equipped with an obturator device for selective evacuation of steam through the stack. The installation may process an increase of 60% of slag without any risk of steam backflow in the granulation area.