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The most prominent factors on normal operation of the Granulator in Granular Urea Fertilizer plants are ambient temperature and humidity, urea solution composition, the Granule section flushing/start-up procedure, abnormal process condition in the urea Melt section and Urea-Formaldehyde injection quantity and quality. In the present investigation, the effect of capacity reduction procedure of the urea Melt section (regarding the amount of reduction as well as its duration) on some important parameters that could affect the Granulator normal operational period, is discussed. The less decrease in synthesis capacity for fewer hours while the Granulator is being washed, apparently, causes in rapid increment in liquid level of the Urea Storage Tank. Higher liquid level of this tank leads to longer residence time for urea solution when it is time to be consumed again in the Granulator. Based on actual data of laboratory analysis, Biuret content of urea solution, particularly for the last hours of storage tank depletion, rapidly raises to 0.49 wt.% while its allowable value is <0.40 wt.%. This disturbance in urea solution composition which mostly may occur after 72 hours, would alter the LP Recirculation section of urea plant either. Keeping constant almost all other parameters but the procedure of capacity reduction of the urea Melt section for comparing the Granulator normal operational duration, it was revealed that increase in liquid level of Urea Storage Tank from 55% to 75% which leads to increase in total depletion time of this tank from 83 hours to 117 hours, could decrease the Granulator normal operational duration over 40%. On the other hand, keeping synthesis capacity at 95% for 5 hours instead of lowering it to 80% for the same duration, appeared to save about 50% of annual reduction in Urea production which can provide extra income for the company. The final result of this investigation, therefore, suggested an optimized capacity reduction procedure considering these three important factors: higher annual Urea production, safe zone for liquid level of the Urea Storage Tank and longer Granulator operational duration.

This paper was presented at the Nitrogen & Syngas Conference 2019 in Berlin, Germany.