Fluid-bed Granulation

Today, the most commonly used finishing technology is fluid-bed granulation, which was commercialized by Stamicarbon in response to changing market needs. Our patented fluid-bed urea technology is used in several urea plants and offers:

Large reductions in formaldehyde content compared to other fluid-bed granulation technologies.
Unprecedented uninterrupted run times, which can exceed 100 days before washing is required.
Excellent product quality (round and uniform, with a smooth surface).
More stable operation conditions.
Low urea dust formation, resulting in a lower recycle of urea solution to the urea synthesis plant.
Low opacity at outlet granulation vent stack.
Substantial savings on operational costs when compared to other fluid-bed granulation technologies.
Excellent properties for downstream coating (for specialty fertilizers).

In just five years, Stamicarbon's fluid-bed granulation technology has been licensed over 10 times for commercial scale plants, including capacities exceeding 3500 mtpd. The plants using this technology are operating at or above their original design capacity, producing superior-quality products that meet all required product quality standards.

Stamicarbon's fluid-bed granulation process works as follows: A urea melt stream with a urea concentration of 98.5wt% is introduced into the fluid-bed granulator through the injection headers, which are connected to the urea melt line and the secondary air system. Each injection header comprises vertically placed risers fitted with spray nozzles that spray the urea melt onto the seed particles. The secondary air, required to transport the granules through the urea melt film, is provided by a secondary air blower. Urea formaldehyde is added to the urea melt as a granulation additive and anti-caking agent. This also improves the granule crushing strength.

The granulator is divided into a granulation section and a cooling/conditioning section. In both sections, fluidization air is evenly distributed to fluidize and cool the granules. Seed (recycled) material is introduced into the first chamber of the granulation section. The urea melt is then sprayed onto this seed material. As the granules move through the granulation section, their size is steadily increased by layering, until they reach the required granule diameter.

At this point, the product finally flows out of the granulator. The granules flow from the granulation section to the cooling section (without spray nozzles), where they cool down and harden. Fluidization air and secondary air are exhausted from the top of the granulator by means of an off-gas fan in the off-gas line of the granulator scrubbers. In the scrubbers, the air is cleaned using a scrubbing solution, and the cleaned air is exhausted into the atmosphere. The scrubbing solution (a diluted urea solution) is partly recycled to the scrubber as a scrubbing solution. A purge stream is also pumped to the urea-dissolving vessel and recycled to the urea melt plant.

The product from the granulator flows through a screen to prevent any lumps from reaching the granulate cooler. The fluidization/cooling air, which contains some dust, is exhausted from the top of the granulate cooler and is combined with the air from the product cooler and the de-dusting air. This combined stream is cleaned in the cooler scrubber system.

A bucket elevator lifts the cooled urea granules onto screens, where they are sorted according to size. Fine product is recycled to the granulator. Coarse product is crushed to a smaller size and then recycled to the granulator. On-size product is transported to the product cooler, where it is air-cooled in a fluidized bed cooler or a bulk-flow heat exchanger.