CRG: the next generation
The CRG process using the driving force of the exhaust air fan
The next generation of the CRG process, the CRG applied in a configuration where the suction force of the exhaust air fan is the driving force for the fluidization of the bed, has been successfully commissioned in plants of various capacities, and in each case the same principles of the CRG process were adopted, but then applied under the principles of making use of the suction power of the exhaust air fan.
The improvement in the CRG process implies that the Fluid Bed Granulator and the Fluid Bed Cooler are operated at a negative pressure of ca -500mmWC, suggesting a pulling force rather than a pushing force on the airflow through the system.
The urea Granulation plant was designed with 2 exhaust fans linked to the Green Granulation "Double Temperature" scrubbing technology. A small, dedicated fluidization air fan was provided for the chilled compartment of the Fluid bed Cooler and a relatively small main fluidization air fan, which only requires the capacity of delivering 300mmWC pressure.
With or without the main fluidization air fan, the system is operated under a vacuum of ca -500mmWC in the upper casings of Granulator and Cooler.
Adavantages of the improved technology
The advantages of the improvements on the CRG process can mainly be found in the better evaporation of water in the spray area inside the fluidized bed and in the fact that through installing a big exhaust air fan and relatively small inlet blower, the mass of the heat generation from the blowers is shifted to downstream the Granulator and Cooler. This means that for the same amount of fluidization air, a more effective cooling is realized on the Fluid bed Cooler and less air is required in the Granulator as vehicle to remove heat from the bed. The Heat Balance of the process is optimized and it speaks for itself that this is also causing a saving in electric power consumption.
There are however conditions to be met for this technology to be economically feasible and beneficial. For the larges part this comes down to a reduction of the pressure drop over the system as much as possible so that the exhaust fan(s) can be limited in size and power. Practically, Green Granulation realizes this by minimizing the pressure drop over the fluid bed by operating at a low bed level of ca 450mm, both in the Granulator as in the fluid bed Cooler. This is made possible by the “Optimized Dynamics” principle in the fluidized bed, which refers to a patented technology that embodies the arrangement of the air-assisted urea spray nozzles in such a way that banks of open spaces are formed between the rows of sprayers to enable a rolling motion inside the fluidized bed layer. Furthermore, Green Granulation applies its "Double Temperature" scrubbing technology that uses BlueFil® demister pads that generate hardly any pressure drop. This solution combines high performance air treatment with very low total pressure drop.
This combination of essential factors makes it possible and opportune to realize the improved CRG technology in an industrial environment. Data collected confirmed that the Green Granulation urea distribution system, combined with the low effective atomization air pressure and flow on the air nozzle that the Green Granulation sprayer requires, is resulting in a recycle back to the urea synthesis as low as 2,5%, calculated on end-product capacity. This means an important relief for the urea synthesis plant without any compromise on product quality or plant reliability.
Other possible applications
The Green Granulation CRG process can, given minor adjustments, be made suitable for applications other than production of pure nitrogen based granules. It can also be adapted to enable production of urea enriched with ammonium sulfate or urea with Sulphur addition. Sulphur and ammonium sulfate are often byproducts of other industrial processes and are of lower economic value, although they can prove to be of great importance for a well-balanced fertilization of the soil.