Safety in the Plant
Dust management strategy key to staff and plant safety
Dust explosions cause some of the most dangerous incidents in the process industries today, so dust management is a key consideration. Sean Ottewell reports.
Staubexplosionen verursachen heutzutage einige der gefährlichsten Unfälle in der Prozessindustrie, deshalb ist der Umgang mit Staub ein entscheidender Faktor. Sean Ottewell berichtet.
Les explosions de poussières provoquent certains des incidents les plus graves dans les industries de transformation à l’heure actuelle ; la gestion des poussières représente donc un élément clé. Selon Sean Ottewell.
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Fig. 1. Sandvik dust suppression systems are used in many materials handling situations.
enerally speaking, dust emissions can be treated using two different techniques - dust aspiration and wet dust suppression. The first can be costly and also inflexible if a
building needs modifying. The second can increase water consumption and also humidity - which in turn increases the risk of problems such as clogging. Cap Minerals uses the water spraying principle,
but with a very important difference: according to users’ needs and situations, the company can provide different processes which use either water alone, an ultra-fine air/water mixture, or a high- pressure solution. For example, in some situations the company
treats dust particles using decompression exhaust hoods. The design of these varies according to the type of material, its granulometry, the type of grinding-crushing mill used and the width of the conveyor belts being used. Such exhaust hoods allow limited dust zones and by their design slow down the dust flow caused by grinding chambers. Atomisation systems are integrated into the
exhaust hoods. This process consists of water micronisation which leads to fog sprayed over dust on the minerals. Atomisation is obtained by a regulated water and compressed air mixture forced through ultrasonic nozzles that split into millions of 15 micron-diameter micro-drops of water. According to Cap Minerals, the advantage of
atomisation is that it requires very little water (a maximum of five litres/h/nozzle) and thus avoids
risks of sludge and other build-up that could be linked to too much humidity on the materials. At the same time as atomisation, the company
also employs a complementary technique of micro pulverisation on different strategic points in the installation. Spraying is performed using hydraulic sprayers that work with water pressure and whose flow can be varied according to needs. Another technique involves spraying the primary
hopper. This technique prepares materials where permitted with a larger amount of water, such as on primary hoppers, grinding mill feeding and larger mats where minerals or materials will be stored on the ground. Unlike atomisation, micro-spraying does not need to be hooded as it is less impacted by the wind. The company’s processes are capable of
working in two different modes. The first is automatic, in which control enclosures are directly linked to and controlled by the user’s automation system. The second is manual. Here operators can turn treatment points off and on independently.
Customised solutions Sealpump Engineering offers complete solutions for the control of dust in all material handling processes, from its dry fog dust suppression systems to rain gun and sprinkler systems. The dry fog dust suppression systems control
airborne dust without wetting the product or site machinery, adding very little (usually less than 0.1 per cent) moisture. The systems are fully installed and integrated into all processes and suppress dust without the need for expensive extraction systems. Research in the development of the company’s
dry fog dust suppression systems showed that when water droplets are produced equal in size to that of dust particles, the airborne dust is suppressed through particle agglomeration. Sealpump’s engineers visit potential sites to carry out surveys and discuss individual needs to ensure that this process is as efficient as possible. For example, when it comes to conveyor transfer
points and conveyor belts, the placement of the dry fog nozzles is the most important aspect to achieving effective dust suppression and ensuring no wetting of material. So the dry fog spray should be generated and contained in well-designed shrouding, for example a conveyor chute, which eliminates dissipation due to wind. It also ensures the correct
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