Process description

The feed solution, typically a 96% urea solution, is dispensed to the injection heads and finely atomized upwards into the bed of moving particles. This spraying is assisted by air.

Fluidization air, delivered by a fan under the perforated plate, flows through the product layer and is exhausted at the granulator top.

Granular urea flows out of the granulator at a controlled rate to a fluid bed cooler. After cooling, the granules are lifted by means of a bucket elevator to the screening section.

The fines fraction is recycled directly to the granulator whereas the coarse material is first crushed and thereafter sent to the granulator as seeding particles.

The on-size product is sent to the warehouse after final cooling, if needed by the required storage temperature. The cooling of urea to a constant and sufficiently low storage temperature is one of the most significant parameters to avoid caking.

The solids recycle ratio is stable 0.5 only, so there is no need for large over design in the solid recycle loop equipment. The low recycle ration is acceptable because it only plays a minor role in the granulation heat balance mechanism.

The air from the granulator and coolers contains some urea dust which is easy to catch in standard scrubbing equipment. With industrially proven scrubbers, efficiencies of more than 99.5% are easily obtained.
Therefore dust outlet concentrations of less than 0.1 kg per ton of urea produced can be achieved.

In UFT's process, the granulation mode is accretion. This means that particles grow by solidification of tiny droplets onto seed material. The result is a very hard granule, far superior in quality than granules produced according to the layering or agglomeration based processes.

Only this slow accretion process allows for continuous and thorough stripping of the water present in the urea solution, while still achieving a remarkable low moisture content in the end product.

Indeed, the bulk of the crystallization heat, released at urea solidification, is removed by means of evaporation of the water present in the urea solution. By means of this mode of heat release the amount of fluidized air can be limited. This evaporation is most efficient because it takes right on the spot i.e. the granule surface itself.

Operation of the fluid bed granulation plant is simple and very reliable, guaranteeing a high on-stream factor. The granulator itself contains no moving parts, and its design is optimized to limit down time for cleaning to a strict minimum.