VRM Air-tighten Feeder
Grinding is one of the critical processes in cement production. Vertical roller mills (VRM) nowadays play an important part thanks to higher efficiency and more power saving performance compared to traditional ball mills. According to the design, the inlet and outlet of VRM are both in the upper part of the equipment. After the raw meals or clinkers are ground, they would be induced out by high negative pressure through the outlet. Due to this design, an issue has harassed many cement plants: how to prevent air leakage when raw meals and clinkers are delivered to the VRM.
If this air-tighten issue could not be resolved, three problems will occur:
1) Energy consumption stays at a high level due to ID fan load increase.
2) VRM output stays at a lower level
3) Waste gas has a higher content of oxygen
At present, in China, rotary feeder is applied in most of the VRMs for air seal purpose. However, there are always some problems. In this system, the gaps between the metal parts are designed for air seal. However, during operation, with the wearing of the metal, the gap is enlarged, which will result in air leakage, materials jamming & choking problems. Consequently, lower mill output, higher ID fan power consumption and out-of-limit oxygen content in exhaust would occur. In some cases, the heavy choking may even lead to unsteady feeding and excessive vibration, which may cause damage to the VRM bearings.
In addition, the variations of raw materials in particle size, moisture, viscosity, and temperature make it difficult for the rotary feeder to seal the air. Choking and jamming problems frequently occur.