Issues with urea addition in sprayed sulfur-based compound fertilizers
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Dear sea friends, in the production process of sprayed sulfur-based compound fertilizers, urea is often added. One method involves dissolving urea in the neutralizing slurry, while the other involves spraying molten urea on the finished product. What are the advantages and disadvantages of each of these two methods? Will peeling occur if it is sprayed on the outside of the finished product?
Adding urea to the slurry is a method that is currently used by many factories; it is an early-developed and highly mature technique. Due to the limitations of the spray granulation production process, the nitrogen content in the resulting products remains below 12%. When producing 15-15-15 type products, this nitrogen content is clearly insufficient, and therefore nitrogen supplementation is necessary. There are two ways to carry out this supplementation: adding urea during the neutralization of the slurry or applying urea slurry externally. Many consider internal supplementation to be the more reliable approach, as it results in a more stable and consistent distribution of nitrogen, as well as higher efficiency in nitrogen supplementation. With external supplementation, improper handling may lead to poor adhesion of the urea, resulting in shell shedding. However, it is said that the external supplementation method is more flexible nowadays, and with proper operation, it is possible to achieve products with higher nitrogen content. Internal supplementation has limitations in terms of the extent to which nitrogen content can be increased. In both cases, urea slurry needs to be prepared; therefore, it is important to pay close attention to controlling the temperature of the urea slurry in order to avoid nitrogen loss and an increase in biuret levels.