| 摘要 |
Urea granulation process with scrubbing system including several waste streams for removal of dust and ammonia from the off-gas of a urea granulation unit comprising a urea granulator (1), a granulator scrubber dust stage (2), a granulator scrubber acid stage (3), product coolers (5), a product cooler scrubber dust stage (4), an evaporation unit (6), and a condenser unit (7). Thereby a first stream of fresh air (8), running through a first sequence of process steps, is send into the urea granulator (1), whereby dust- and ammonia-laden air (9) is drawn off from the granulator (1) and conveyed into a granulator scrubber dust stage (2), followed by a granulator scrubber acid stage (3), in which stage the ammonia-laden air (12) is contacted with an acid in liquid (22) phase and ammonia is scrubbed from that air by the generation of an ammonium salt. A second stream of fresh air (15), running through a second sequence of process steps, is used for cooling the product drawn off from the urea granulator (1), whereby said cooling is performed in product coolers (5), thereby said air is heated up, and afterwards is conveyed to a product cooler scrubber dust stage (4). The clean off-gas (13) drawn off from the granulator scrubber acid stage (3), and the clean off-gas (18) drawn off from the product cooler scrubber dust stage (4), are released into the atmosphere (19). Hereby the scrubbing system is passed, which in itself is a complete closed system, and totally decoupled from urea synthesis, whereby the ammonium salt solution stream (23) from the granulator scrubber acid stage (3), is fed into said product cooler scrubber dust stage (4), whereby the ammonia of the dust-laden air stream (17) exiting the product coolers (5) is removed, and the released liquor (24) from the product cooler scrubber dust stage(4) and the released liquor (11) from the granulator scrubber dust stage (2) is send to the evaporation unit (6). The vapour stream (29) from the evaporation unit (6), which contains ammonia is given into the condenser unit (7), which releases a liquid process condensate (30), and said liquid process condensate (30) is given into the granulator scrubber acid stage (3), and the concentrated liquor stream (28) from the evaporation unit (6), containing urea and ammonium salt, and a urea melt (26) from a synthesis unit (27) are conveyed into the urea granulator (1), separately. Thereby the ammonium salt contained in the concentrated liquor stream (28) is integrated into the granulated urea product. |
