Dust extraction: Benefits all round

Whether handling or processing powdered or granular material, cutting, forming, machining or finishing products, or indeed packing and marshalling finished products, dust may be released into the atmosphere. Gus Bishop, for Nederman, outlines a solution and explains the benefits it brings - not just in terms of health and safety

While an employer is obliged by law to provide a healthy atmosphere for the workforce, the opportunity should be taken to make the most of the several other benefits available.

For example, general maintenance requirements will be reduced; product quality may (and probably will) be improved; absenteeism of employees may well be reduced and also turnover of staff.

Employees who feel that their environment and welfare are uppermost in the minds of their employer are more likely to be committed and remain loyal, bringing a further bonus of reduced cost in recruiting and training new operatives. The plant will be more attractive to visiting customers and prospective customers, so that good dust control even becomes a 'hidden' salesman.

Clearly what may be considered at first to be just a costly necessity can be turned into an integral part of a progressive enterprise.

So, where does good engineering come into the equation? If dust control is to be achieved by local exhaust ventilation (LEV), commonly called dust extraction, then the dust collection devices or hoods should be designed to extract all the dust effectively, with the minimum airflow quantity, but not impeding the operator or process - and they should be easily accessible for maintenance.

Moving air requires costly energy, so care should be taken to design the whole ducting system aerodynamically to reduce resistance.

On a dust collection system serving a number of dust extraction points the main extractor fan motor could be the biggest single motor on site, operating continuously, but with its energy cost not separately monitored.Maximising the efficiency of this drive could save literally thousands of pounds per year.

Duct routing and sizing should be carefully engineered. Higher than needed duct air speeds could increase the energy requirements by a factor of six, as well as create unnecessary noise that could impair the effectiveness of employees. It could also fall foul of the Noise Regulations, where continuous levels above 80dB(A) will require attention. If possible the duct routing should be considered within the general layout of the production facility, allowing for 'slow' bends and progressive duct diameters to maintain a minimum critical air speed. This should be determined as the minimum speed at which the particular dusts remain buoyant.

The dust collector itself is critical to the overall efficiency of the system. The variety of designs and technologies is huge.

However, there is a place for each kind, depending upon the characteristics and quantity of dust to be removed, whether the dust is simply waste, or able to be reprocessed for further use or resale, how much space is actually available to site the unit, whether there is one centralised unit or several smaller satellite units and so on.

A supplier such as Nederman, who also manufactures the key elements of the installation and who can offer a range of technologies, is worth considering, as there will be no bias towards a particular type of unit that could result in an inappropriate or inefficient installation. A careful site survey should always be conducted, in close liaison with the prospective user, and a proposal from the dust extraction supplier should indicate particular reasons for their selection of equipment. Space may be limited, either horizontally or vertically. Therefore a conventional rectangular dust collector with a hopper may not fit. An alternative may be a cylindrical cyclonic filter that would occupy a much smaller footprint, if height is less of a problem. However, the relative dust collection capacities, resistance to wear from abrasion from aggressive materials, maintenance requirements and indeed initial costs should be considered. Similarly if the choice between flexible bag or cartridge element filters is relevant, then their relative merits and limitations should be studied. Of course, expertise to make such choices comes with accumulated experience and reference to comprehensive material data - something the supplier should demonstrate.

Finally, but important nonetheless, is the final installation, commissioning and handover process. Commissioning is a subject in itself and correct procedures and settings will prevent early failures, excessive operating costs and will ensure unobtrusive beneficial use over a long lifetime.