Opening the Nutch Filter


Nutch filters are often being opened while a solvent wet substance is still in the filter. Results of a simulation performed with Computational Fluid Dynamics (CFD) (taking into account both flow of the fluid and diffusion) show that 'the rule of thumb zoning' (with zone 1 merely in the immediate vicinity of the filter) is completely inappropriate even if the room where the filter is situated is adequately ventilated (the simulation below allows for the air extraction opening in the corner of the room to complete five air exchanges per hour).

The simulation shows vapour spreading after the filter was opened. The filter contains substance wet with acetone at room temperature. The light blue isosurface shows the concentration level of a quarter of LEL which normally requires zone 1 classification. The video is time-lapsed.


Simulations with CFD also help define appropriate measures for actual prevention of unnecessary large emissions of flammable vapour. The following video shows the same procedure as above but with appropriate local exhaust ventilation installed under the filter. Local exhaust ventilation can be extremely efficient if its geometry is properly designed and if sufficient exhaust capacity is provided. Considerations about design and the necessary capacity are of course best aided with CFD simulations.

 

Same data as above, but with well designed local exhaust ventilation.