Page 140 - Dust Explosions in the Process Industries

Dust Explosions: An Overview 1 13

The exhaust from the vacuum cleaner must be guided in such a way that it does not
hit dust deposits and generate dust clouds.
All electrically conducting parts of the equipment, including the hose and mouthpiece,
must be grounded with a resistance to earth of less than 1 Ma.
Vacuum cleaner housings must be constructed of materials that are practically non-
flammable. Aluminum and aluminum paints must not be used.
A clearly visible sign saying “No suction of ignition sources” should be fitted to the
housing of the vacuum cleaner.

Figure 1.130 shows an example of a large mobile vacuum cleaner for combustible dusts
in industry.

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Figure 1.1 30 Large mobile vacuum cleaner for explosible dusts in industry. The vessels and connecting
ducts are designed to withstand internal pressures of 9 bar@). The power requirement is 45-55 kW
(Courtesy of Edelhoff Polytechnik GmbH, Iserlohn, Germany).
Sometimes it can be useful to install stationary vacuum cleaning systems rather than
having mobile ones. Figure 1.13 1 is a schematic illustration of the main principle. A cen-
tral dust collecting station with a suction fan is connected to a permanent tube system
with a number of plug-in points for the vacuum cleaning hose at strategic locations.
The importance of good housekeeping is sometimes overlooked. Always remember
that clean workrooms exclude the possibility of extensive secondary explosions. Further,
cleanliness improves the quality of the working environment in general.

1.4.1 0
DUST CONTROL BY THE ADDITION OF LIQUID

As discussed in Chapter 3, adding liquids to dusts can give rise to particle enlargement
by the formation of agglomerates held together by liquid bridges or capillary forces.
Furthermore, if the main product is coarse, such as grains of wheat or oats, adding a suitable