The rotary feed sluice is an essential part of the ATOX raw mill installation. Its main functions are to ensure:
– Uniform flow of feed to the mill for stable mill operation
– Low ingress of false air to decrease fan kW usage and cost
The sluice handles all new feed and material coming from the external circulation system. For normal raw mills this material flow accounts for 115-150% of the new feed rate; for bigger mills it can represent more than 1,000 t/h.
Compared to other types of feed sluices, the rotary sluice ensures a uniform feed of material to the feed table. This is crucial for stable mill operation, since lack of feed will lead to reduced grinding bed thickness and to a corresponding increase in vibration level. Therefore, the uniform feed rate keeps the grinding bed stable and the vibrations low, ensuring steady operation and high availability withoutrisk of mill stop.
The rotary sluice also minimises the amount of false air entering the mill. Due to the high underpressure in the range 40-70 mbar inside the raw mill, even small gaps at the inlet will cause a considerable flow of cold air into the mill. As the gas flow to the mill inlet must be constant independent of the amount of false air, every percentage in false air savings through the sluice results in a considerable cost savings, due to less gas flow sucked out of the mill and through the mill fan.
The FLSmidth rotary sluice delivers:
– Sturdy design and low speed
– Alignment with feed belt
– Split sluice for normal materials
– Heated sluice for very sticky materials
– Friction coupling, preventing overload of sluice
– Easy adjustment of sealing plates
– Easy access and easy replacement
of wear parts
For trouble-free operation and long life, the feed sluice’s design is based on a low-speed rotor. The low speed, ability to feed big lumps and high rate of feed material have resulted in relatively big rotary sluices. Sluices for ATOX raw mills are in the range Ø800 to Ø2200 mm.
To ensure proper filling and distribution inside the rotary feed sluice, the sluice and the incoming feed belt are aligned. The circular bottom flange of the sluice and feed chute to the mill enables proper connection, independent of the direction of the feeding belt relative to the ATOX mill.
In case extraordinary foreign bodies such as big wood blocks, timber or similar materials enter and block the rotor in the feed sluice, friction coupling ensures that the sluice parts are not damaged. A speed monitor stops the material belt and prevents overfilling of the sluice.
Large inspection doors enable the sluice to be easily cleaned and restarted. For normal raw materials, the standard split sluice with steel-lined rotor and lined housing is the optimum solution for steady operation and long life. The split design of the housing enables easy access and inspection of the interior of the sluice. When one side is opened, rotor lining replacement is a quick and easy job. The condition of the housing lining should be checked and replaced whenever required.
To limit false air ingress, replaceable sealing plates at the tips of the rotor vanes can be adjusted to obtain a small gap between the rotor and housing. The heated rotary sluice is also the right solution for sticky mill feed. Hot gas from the mill inlet is guided through the rotor, thus preventing the sticky material from caking onto the rotor. Due to the change in rotor design, hardfacing is used for this version.