Energy-Saving and Environmental-Protection Potentialities of the Falling-Curtain Process for Granulation of Urea

摘要

A new process for production of granular urea from urea melt has been developed by TVA through the pilot-plant stage, and a demonstration-scale plant of 330-ton-per-day (300 metric tons/day) capacity now is under construction. This process offers attractive potentialities for lower investment costs, lower energy consumption, and less generation of dust. There are promising indications that incorporation of formaldehyde in the granules, a practice now used widely to harden granules, reduce dusting, and prevent caking, may not be required in this process. An essential feature of the process is a rotating granulation drum with specially designed internal flights and baffles that direct the in-process urea particles into the form of a dense falling curtain onto which urea melt is sprayed through high-pressure atomizing nozzles. Granules grow to product size by successive surface layering and solidification of melt. Design of the baffles in the drum is such that long drops of the in-process granules, with resultant dust generation, are avoided. Nozzle placement is close to the falling curtain, which promotes efficient layering of melt. A significant portion of the heat released by the solidification of melt and cooling of granules is removed from the grenulator drum by evaporative cooling. With this method of cooling, required airflow per unit of product is relatively low and a relatively small granulation drum is sufficient. (ERA citation 07:054265)