Urea Granulation (Spout Fluid Bed Granulation Process)

Summary

TOYO started the establishment of a urea granulation process based on a Spout Bed type urea granulator and expanded its own Technical range to provide a variety of urea fertilizer products since late 1970’s in addition to the conventional Urea Prill Product and Urea Solution Product. In 1980's, TOYO further improved its design of the granulator by applying the Spout-Fluid Beds for the granulator, which is a combination of the spouted beds and fluidizing beds and reduces energy requirements and improves the quality of the product granules.

Feature

Toyo’s Spout Fluid Bed Granulation Process has following features.

1.	High Energy Efficiency (Low Power Consumption) No requirement of compressed atomizing air for granulator Seed circulation at moderately high temperature minimizes cooling air requirement and heat removal in the process Optimal bed depth minimizes pressure loss in the granulator Uniquely designed low pressure drop dust scrubber
2.	High Product Quality Rapid cooling of granules in the granulator with minimum residence time reduces biuret formation to negligibly small Efficient drying in the granulator reduces granule moisture low enough to increase product hardness Optimal combination of spouted bed and fluidized bed produces round and uniform granules
3.	Low Emission Optimal spouted bed air velocity minimizes dust formation in the granulator Uniquely designed (Packed Bed type) low pressure-loss dust scrubber reduces urea dust to less than 30 mg/Nm³

Conceptual Chart of Spout Fluid Bed Granulation

Process Flow Diagram of Granulation Process

The urea solution or molten urea is fed on the spouting urea seeds through the multi spray nozzles to enlarge the recycle particles (seeds) in the granulator. The water in the feed urea solution is evaporated by spouting air on the spouted beds in the granulator to produce the urea granules. The enlarged granules are cooled to a suitable temperature by fluidizing air on the internal fluidized beds in the granulator.Coarse urea granules produced in the granulator are screened to separate the product size granules from over and under size granules through the double deck screen. Small sized granules are recycled back to the granulator as the seed and over sized granules are crushed through the double roller type crusher and recycled back to the granulator together with the under sized granules as the seeds. Exhaust air from the granulator and cooler is scrubbed in the wet type dust scrubber to recover the urea dusts in the exhaust air. Recovered urea dusts through the dust scrubber are recycled back to the urea plant for the recovery.

Process Flow Diagram of Granulation Process

Product Qualities

Total Nitrogen	46.3 wt.%
Biuret	0.8 wt.%
Moisture	0.2 wt.%
Formaldehyde	0.45 wt.%
Size 2 - 4 mm	95 wt.%
Hardness	3.5kg/granule for 3 mm

*Typical Standard Figure depends on design condition of each plant.

Utility Consumption

Steam	0.01 MT/MT *1)
Power	23 kWh/MT *2)
CoolingWater	Nil

*1)	Typical standard figure depend on atmospheric condition, utility and concentration of urea solution.
*2)	Typical standard figure in case of fluidizing product cooler. In case of bulk flow cooler by cooling water, power consumption becomes19ｋW/MT. Depend on production capacity, atmospheric condition, utility and concentration of urea solution.

Clean Emission

Urea dust in the exhaust air from the granulator and the product cooler is a major concern of air pollution in a urea plant. Optimal air velocity for spouted bed and through free board area of granulator minimizes the dust formation in the granulator. And the Uniquely designed (Packed Bed type) low pressure-loss dust scrubber reduces urea dust to less than 30 mg/Nm³.