Water control of drum granulator during granulation
In chemical processing industry, rotary drum granulator is widely used in organic fertilizer production line and NPK fertilizer production line. In the granulation process of the drum granulator, the coarsening in the pellet is mainly in the form of cladding, so the material circulation volume should be larger, so as to provide a coarser core for the cladding process, and the water injection volume should be smaller, so as to reduce the water absorption of the core. When pelletizing by bonding or "gathering", the materials are smaller, because the materials in the drum are mainly composed of fresh materials with small particle size and mutual bonding. The liquid ratio required for bonding should be large, because the space between the fine powder particles to be bonded with each other should be filled with water.
The main structure of the rotary drum granulator is an inclined rotary cylinder, and the drive can be constant speed or variable speed. When the liquid content of the feed powder is appropriate, agglomeration occurs and rolls in the drum. The drum has a certain slope, and the included angle between its axis and the horizontal is below 10 °, which can help the material roll along the long direction of the drum. The feed end is often equipped with a retaining ring to prevent the material from flowing back. A retaining ring can also be installed at the discharge end to increase the thickness of the material layer and extend the retention time in the main drum. In other occasions, the spiral discharge ring is often used to convey the boring to the screen at the back of the drum. Sometimes, the cylindrical screen and the rotary drum are integrated to form a product discharge port. The feed consists of fresh material and circulating material, and the feeding system can adopt belt conveyor, chute pipe or other similar equipment. The bonding liquid is injected either before the solid material enters the rotating cylinder or immediately after the solid enters the rotating cylinder.
Different from the roller granulator, the inner surface structure of the drum plays an important role in whether the material can react well in the drum. The inner part of the steel rotary drum is usually made of hot expanding metal. The function of various internal scrapers is to keep a certain thickness of the material on the inner surface of the rotary drum, so that the material layer is uniform, so that the material can roll and turn normally in the rotary drum. Rubber baffles and linings as well as external vibrators are used to prevent the accumulation of fertilizer during granulation.