Considering the different pipe’s features, each system has three sizes of centrifugal fans with different powers (11 – 30 and 45 kW). This solution allows us to use the most suitable fan according to the diameter type of the pipe in the works. The 11 kW centrifugal fan can extract the mill scale in a range between 400 m3/h and 1,300 m3/h and it is useful for small size pipes; the 30 kW one can extract the mill scale in a range between 1,300 and 4,800 m3/h and it is useful for medium size pipes; eventually, the 45 kW one can extract the mill scale in a range between 4,500 and 9,500 m3/h and it is useful for higher diameter size pipes. The group of fans is placed in a soundproofing booth, in order to reduce their noise.
The air flow sucked by the pipe is conveyed within the cartridges filter, where it is treated before its emission in the atmosphere. The discharge system under the filter includes a double air shutter, which allows the mill scale to be discharged ceaselessly.