Page 274 - Dust Explosions in the Process Industries

246 Dust Explosions in the Process industries

of the screw and optimizing its speed of rotation. However, to ensure proper dust dis-
persion, the dust output from the worm conveyor was fed into a swirl chamber driven
by a controlled airflow. A high level of turbulence shear created within this chamber by
the colliding whirlingjets produced cluster-free,uniform dust dispersion. For high dust
concentrations and especially for coal dust, a secondarydust dispersion source in the form
of a high-speed rotary disk was incorporated within the settling chamber. Thus, a uni-
form and finely dispersed dust cloud could be produced. This was gently drawn into the
explosion chamber by a small suction pump.

3.9.5
CONCLUSION

Provided the relatively large amounts of powder required and the relatively complicated
experimental apparatus can be justified, the open-circuit principle is the most satisfac-
tory alternativefor dust dispersion.However, as for the transientcloud systems,it is essen-
tial that the dust dispersion system be designed carefully, to ensure that the degree of
agglomeration of the particles in the cloud and the cloud turbulence corresponds with
the state actually wanted. Quite often, it is desirable or even necessary to keep the con-
sumption of dust or powder at a minimum. In such cases, the transient air blast technique
may, provided the limitations of the technique are borne in mind, offer the best solution.

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