Advantages of three-stage concentration in the evaporation section over two-stage concentration
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The original designed production capacity of the urea plant in this workshop was 170,000 tons; after renovation, its current production capacity can reach 240,000 tons. However, the original granulation tower finds it difficult to cool the urea particles at the current production volume. Later, four fans were reluctantly installed at the top of the granulation tower to facilitate forced ventilation and maintain production; although production targets could barely be met, the quality of the finished products was significantly reduced. The workshop is currently researching the construction of a new granulation tower; however, since the height of the new tower differs significantly from that of the original one, this increases the residence time of the urine inside it, which in turn raises the content of biuret in that urine. To solve this problem, the research team plans to transform the original evaporation section from a two-stage dual-system design to a three-stage single-system design. We would appreciate it if experts could offer more suggestions, and we look forward to discussing this matter together. This post was last edited by lxq700918 on 2009-4-9 21:30.]
By three-stage concentration, do you mean flash evaporation, first evaporation, and second evaporation? This is our process. Flash urine concentration: 70; first distillation: 93; second distillation: 99 (full circulation of aqueous solution)
What the poster is referring to regarding substandard urea levels is likely an excess amount of biuret. Firstly, an excessive content has nothing to do with the granulation tower; increasing the length of the urine pipeline has little effect on the residence time. On the contrary, an increase in production leads to a higher flow rate, which can reduce the residence time； Furthermore, if the granulation tower can meet the current load after modification, there is no need to rebuild it. The formation of biuret occurs mainly during the evaporation and concentration stage. An increase in production leads to a greater evaporation load; if the equipment is not upgraded, raising the evaporation temperature of the urine is necessary to achieve the same concentration. This increase in temperature results in an excess level of biuret, so the evaporation system needs to be modified.
I agree with the view from the 3rd floor: when the system is upgraded, the heaters and separators in the evaporation system should also be enlarged accordingly. Otherwise, if the evaporation capacity is insufficient, one can only rely on increasing the temperature, which will lead to an increase in dicyandiamide. An increase in the height of the newly constructed granulation tower will have no impact on the quality of urea; on the contrary, it will improve its quality.