In general, urea solution is vaporized isothermally. The concentration of the urea solution increases gradually while water is continuously vaporized and expelled during evaporation. In the No. 1 Urea Plant of Ningxia Petrochemical Company in the People’s Republic of China, urea solution evaporation is divided into two stages. Pressures of the first-stage and second-stage evaporations are 0.30~0.35 MPa (a) and 0.034 MPa (a) respectively. The Concentration is increased from 75 wt% to 99.7 wt%, meeting prilling requirements. However, to reach vacuum pressure in the evaporation system during startup or normal production often fails, or the vacuum degree in the evaporation system is too low, thus seriously affecting the startup progress or the quality of finished urea product.
Because many factors affect the vacuum of the evaporation section, corresponding measures should be taken to effectively solve problems like failure of vacuum pressure, low vacuum degree, etc. of the evaporation section which occur during startup or production, in order to ensure smooth startup of the evaporation system, and all urea products are up to standard quality.

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