20110229394 | UREA GRANULATION PROCESS WITH AN ACIDIC SCRUBBING SYSTEM AND THE SUBSEQUENT INTEGRATION OF AMMONIUM SALT INTO UREA GRANULES - A process for the granulation of urea with a scrubbing system includes several waste streams for removal of dust and ammonia from the off-gas of a urea granulation unit. A urea granulator, a granulator scrubber dust stage, a granulator scrubber acid stage, product coolers, a product cooler scrubber dust stage, an evaporation unit, and a condenser unit are included in the system. A first stream of fresh air is sent into the urea granulator, whereby dust- and ammonia-laden air is drawn off from the granulator and conveyed into a granulator scrubber dust stage, followed by a granulator scrubber acid stage and ammonia is scrubbed from that air by the generation of an ammonium salt. A second stream of fresh air is used for cooling the product drawn off from the urea granulator in product coolers. The cooling air is thus heated up and conveyed to a product cooler scrubber dust stage. The clean off-gas drawn off from the granulator scrubber acid stage, and the clean off-gas drawn off from the product cooler scrubber dust stage, are released into the atmosphere. The scrubbing system is a complete closed system, and totally decoupled from urea synthesis. The ammonium salt solution stream from the granulator scrubber acid stage, is fed into the product cooler scrubber dust stage, whereby the ammonia of the dust-laden air stream exiting the product coolers is removed, and the released liquor from the product cooler scrubber dust stage and the released liquor from the granulator scrubber dust stage is sent to the evaporation unit. The vapour stream from the evaporation unit, which contains ammonia is sent to the condenser unit, which releases a liquid process condensate which is sent into the granulator scrubber acid stage, and the concentrated liquid stream from the evaporation unit, containing urea and ammonium salt, and a urea melt from a synthesis unit are conveyed into the urea granulator, separately. Thereby the ammonium salt contained in the concentrated liquor stream is integrated into the granulated urea product. | 09-22-2011 |