Mechanism And Prevention Of The Caking And Pulverization Of Urea

With increasing capacity of urea fertilizer production, enlarging import and lowering growth of farm requirement, fertilizer urea is meeting great challenges in domestic market of China. Urea producers must pay more attention on the qualities of urea in order to keep their market share. Beside the chemical composition, the appearance qualities, such as, caking properties and dust content, are very important for the vendition of urea product.Based on the analysis of successful experience over the world and progress of Jianfeng Plant in the prevention of caking and pulverization of urea, it was found that the control of moisture, dust and mechanic strength is the key for the prevention of caking and pulverization of urea. The effects of sprayer structure on the mechanic properties of granulated urea were studied. Two potential sprayers were tested. The results show that different sprayers should be switched in different seasons.The influence of adding formaldehyde on the granule strength of urea was investigated. An optimal adding amount of formaldehyde was recommended for the SNAM urea production process. Furthermore, the affecting mechanism of crystal seeds on the granule urea was discussed. A new granulation process with crystal seeds was proposed. Considering the moisture controlling in storage of urea, a new anti-caking additive was used. It obviously lowered the moisture adsorption in the storage period.A temperature sensor was fixed inside the sprayer. It was used to detect the melted urea level inside the sprayer. The temperature detected was back fed to theDCS to control the rotation speed of sprayer. It ensures the spraying urea is distributed uniformly inside the tower. The moisture content of granule urea is an important factor for the mechanic properties of urea granule. To control the moisture content in granule, a formula was developed to calculate the granule temperature at the outlet of granulation tower according to different climate condition. The model was used to be an objective function for the control of air velocity in the tower. A systematic model for controlling blinds of air stream was built up for the 600 kt/a urea device in Jianfeng Plant and automatic regulation was realized.