Production process of sulfur-based NPK compound fertilizer

Thread Content

Process selection: Depending on the raw materials, types, and methods used in the production of compound fertilizers, there are numerous process technologies and routes for producing sulfur-based nitrogen-phosphorus-potassium fertilizers, each with its own advantages, making it difficult to determine which is superior. Therefore, no comparisons with other processes will be made in this chapter; instead, only the process technology plan intended for this project will be described. This project adopts the tower-type melt spray granulation process to produce sulfur-based NPK compound fertilizers. This technology is the most advanced among similar domestic devices known to date. Tower-type melt spray granulation is the melt granulation technology first introduced in the world by the Norwegian company Norsk Hydro; it represents a typical process for producing UAP/UAPK urea-based compound fertilizers, using molten urine – obtained directly from the urea production system – along with ammonium dihydrogen phosphate melt and powdered potassium chloride as the base materials. A 99% concentrated molten urine solution and an ammonium phosphate melt produced in a tubular reactor are each pumped to a mixer at the top of the granulation tower, where they are mixed with preheated fine potassium chloride powder. From there, the mixture is sprayed into the tower through a rotating porous nozzle equipped with a scraper at the bottom, resulting in a fan-shaped distribution pattern. During the descent driven by its own weight, it is cooled and solidified by the rising air currents, and the compound fertilizer is collected at the bottom of the tower. Process overview (see the process flow diagram for details): The semi-finished urea melt produced in urea plants or solid urea is heated first; thereafter, urea, diammonium phosphate, potassium sulfate, and fillers are mixed in a ratio of 1.5:(0–1.0):(0–1.0):(0–1.0):(0–1.0), with the nitrogen and phosphorus fertilizers as well as the potassium fertilizer not both being zero. The mixture is then heated and melted at a temperature of 100°C–145°C. The molten slurry is dispersed into small droplets by a granulation device, and then falls under the action of gravity into an air cooling tower where it cools and solidifies to form compound fertilizer. Product performance parameters: Total content 45%, N:P2O5:K2O=15:15:15 (adjustable), C-=90%. The percentage of water-soluble phosphorus in total available phosphorus is >=70. Sulfur-based nitrogen-phosphorus-potassium compound fertilizer, potassium sulfate, ammonium phosphate