Solidification: prill cooling
During the prilling process, the prills need to have sufficient cooling time to solidify. This is achieved by spraying droplets in a counter-current stream of cooling medium in the Kreber Prilling Tower. As for the height of the prilling tower, it can be up to 100m in height and 30m in diameter. At Kreber we prefer to keep the design of the tower as compact as possible.
Our prill tower is usually constructed in stainless steel or aluminium and designed according to ASME VIII. Fabrication and erection can either be done at our location near the Rotterdam harbour in The Netherlands or on-site anywhere worldwide.
Air inlet filtration
In the prilling tower process, air is sucked in by fan(s). To avoid contamination of the prilled product with dust from the atmosphere, it is possible to install air filters around the lower circumference of the tower. This is often applied in the chemical industry, such as the Urea prilling tower design for a prilling tower in a Urea plant. The cooling air which is sucked from outside passes through these air filters. The air inlet filters are fitted in the lower part of the side wall of the tower. The fitting housings are based on a module system, designed specifically for use with cassette filters.
As an extension, we offer accessories to optimize production or to ensure a safe working enviroment.
The utilizing air fans of the prill tower are of a special design to cope with the working conditions, such as hot air and dust. The prilling fan and de-dust unit system will be located at ground level, immediately downstream and next to the prilling tower. The variable speed induced draft fan will draw the required amount of air through the tower and the de-dust unit, discharging the filtered air to the atmosphere.
Filter bags are cleaned by an automatic pulse-jet type blowback system. Blowback will be controlled by a timer with the frequency adjusted based on differential pressure for maximum bag life. Bag cleaning will be done with instrument air. Level detection and sonic horns will also be provided to prevent build-up of dust on the de-dusting unit hopper walls. The design is such that filter elements can be changed during operation.
The towers are usually gas cooled, preferably with ambient air, and can be executed with open or closed loop systems. Optionally Kreber supplies an anti-icing system that can be used to preheat ambient air flowing towards the tower filters. The system works with regenerated waste heat from outlet stack and helps to control the prilling temperature in the tower.
Explosion suppression system
During normal operation, the risk of dust explosion in the prilling tower is extremely low due to the high air to dust ratio. To assure that the dust concentration in the prilling tower remains below the critical level during startup and normal operation, a pressure transmitter with a low-air pressure shutdown switch will be provided.
To prevent potential dust explosion in the de-dust unit, which could happen especially during the bag cleaning cycle, an automatic dust explosion detection and explosion-suppression system will be installed. Isolation extinguishers will also be installed on the de-dusting unit inlet duct to isolate the prilling tower from the de-dusting unit in case of explosion.
In case of a dust explosion, both the pressure rise and rate of pressure rise will be detected by the explosion-suppression system. High rate discharge extinguishers mounted on the de-dusting unit will be automatically activated and rapidly discharge chemical suppressant in an effort to quench the fire before the maximum de-dust unit design pressure is reached. The explosion suppression system will also automatically activate high rate discharge extinguishers mounted at the de-dusting unit inlet ducts. The extinguishers will discharge chemical suppressant to isolate the prilling tower from the de-dusting unit.