Crossflow ventilation

The application of very high-permeability dryer fabrics in the paper industry made it possible to introduce air through the fabrics. Therefore, the above-mentioned blowing rolls and the hot air ducts below (or above) the felt rolls between the cylinders became very popular. These systems provide better crossflow ventilation, which in turn results in more uniform and higher mass-transfer rates. 

Crossflow ventilation is a technology that has been designed into the cellhouse structure in the past to reduce acid mist. Amplats Rustenberg plant in South Africa applied a cross flow principle first and this was applied on a larger scale at the zinc EW cellhouses in Canada (Cominco Trail in early 1980 s) and Kidd Creek. From the mid 1990 s until the more commonplace application of cell hoods, the large tankhouses in Chile typically used combinations of positive crossflow ventilation, balls and foams. The DESOM crossflow ventilation configuration, which became common practice in Chile, was first applied to the El Teniente SX-EW operation in 1985. Cerro Colorado, Quebrada Blanca, Chuqui SBL, Quebrada M and Escondida Coloso followed in 1994. 

In general, the air from the production area enters the front of the LAF cabinet in a controlled way, passes at first a set of pre-filters in the cabinet that separates coarse dust. Sometimes more HEPA filters placed in series after the pre-filters act as supplementary pre-filters (in certain types of safety cabinets). After pre-filtration the air is forced via a ventilator box through a set of framed HEPA filters and finally enters the aseptic process area as sterile filtered air in a unidirectional flow. The speed of the unidirectional flow is kept between limits. Finally the exhaust air re-enters the room (crossflow LAF units), or can be exhausted to the outside with or without extra HEPA filtration (safety cabinets). 

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