Solution: Dust Extraction System
Client: GKN Aerospace, Luton
MECHON was commissioned to design and project manage a dust extraction system to control explosive dusts generated by a CNC Milling process. The materials being machined by the Client are temperature sensitive, so MECHON paid particular attention to the design approach used for the capture, containment and control of dust emissions.
Traditional LEV dust extraction capture methods such as articulated arms were considered but not employed in this design due to feasibility. Exposure benchmarking suggested that a fully enclosed system would be most effective control measure. The CNC machine enclosure was placed under negative pressure with a total extraction rate of 1,270m3/hr.
A system of air-bleeds were introduced to give the operator some limited control over the introduction of ambient air into the enclosure, whilst maintaining the correct conveying velocities in the ductwork system (required under the CoSHH regulations outlined in HSG 258).
A reverse jet (pulse jet) filtration unit was utilised to remove the dust particles from the airstream before recirculating the clean air back into the room (for energy recovery). A pulse of compressed air is introduced to the filter elements, allowing automated cleaning of the cartridges whilst the dust extraction system is still in operation. The dust collector unit is complete with high efficiency, carbon impregnated cartridge filter media, designed to remove 99.99% of dust particles at 0.5 micron (by weight). A single hopper system with sealed bin lift mechanism (designed by Mechon) was installed to safely collect the dust, allowing sufficient collection for a continuous 24 hour operation.
In accordance with the ATEX Directive and DSEAR (2002) regulations, the system design incorporated explosion protection suitable for a dust with a KST value < 200bar.m.s-1. An explosion relief panel was fitted to the dust filtration unit. The panels are non-reusable and designed to burst in the early development stages in of an explosion. The main force of an explosion is thus dissipated into a designated safe venting area, preventing deformation or rupture of the dust collector itself.
An explosion isolation valve was also installed within ductwork system, between the pulse jet filter unit and the inlet hood. This mechanical valve is designed to shut in the event of an explosion, preventing the pressure wave and flame from entering the workplace. All ductwork between the valve and filter is strengthened and certified to handle the force of the explosion.