Page 158 - Advanced Mine Ventilation

138 Advanced Mine Ventilation

1. Coal seams are infused with water and cut with very sharp bits to minimize dust generation
(discussed in Chapter 9).
2. Water mixed with surfactants is sprayed at high pressures to suppress the dust on site.
3. All cutting and drilling operations use a scrubber to collect the dust that became airborne.
4. Adequate ventilation air is provided to dilute the remaining airborne dust to keep its concen-
tration below the statutory limits.
5. For mine workers working in return airways, well-designed personal protective equipment,
such as air helmets, is provided.

10.1 Theory of Dust Suppression and Collection

To optimize the process of dust suppression by water sprays and dust collection by
scrubbers (filters), it is necessary to understand the theory behind them. We will first
discuss suppression/collection of a single dust particle by a single waterdrop. Next, the
collection of dust particles by a single strand of filter will be mathematically analyzed.
The dust suppression/collection efficiency for water droplets, E, is a function of the
following:
The radius of the water droplet, R
The radius of the dust particle, a
Velocity of water droplet, U
Density of dust particle, r 1
Density of water particle, r 2
Viscosity of water, h
Dimensional analysis of the independent variables yields a relationship given by
Walton and Woolcock [1] in Eq. (10.1).

Ur R Ur a a
2
1
E ¼ f ; ; (10.1)
h h R
It is easy to recognize the first two terms in Eq. (10.1) as water droplet and dust par-
Ur 2 R
ticle Reynolds numbers. In viscous flow, the term can be discarded, hence:
h
Ur a a

1
E ¼ f ; (10.2)
h R
E can thus be expressed as a function of k, where:
2
Ur a T
1
k ¼ ; (10.3)
Rh R
by multiplying the two dependent variables in Eq. (10.2).
Experimental data were plotted against k and are shown in Fig. 10.1.