Page 170 - Advanced Mine Ventilation

150 Advanced Mine Ventilation

oxideelike) sequences inserted to increase hydrophilic character of surfactant. All sur-
factants can be broadly classified as follows:
1. Anionic, such as, sulfates and phosphatesters.
2. Cationic, such as primary and secondary amines.
3. Zwitterionic, such as phospholipids.
4. Nonionic, such as fatty alcohol ethoxylates.
Mostly nonionic surfactants are used in coal mines. The details of Thakur’s study
[15] are presented in Table 10.5.
Another finding of this study was that surfactants helped create smaller size water
droplets in the 200 mm range. This may also have contributed to a better dust collection
efficiency.

10.9 Electrostatic Charging of Water Particles for
Improved Dust Collection

It was shown in Section 10.1 that dust collection efficiency can be increased by
reducing the water droplet size, and increasing the droplet velocity. This is generally
achieved by increasing the pressure at the spray inlet. In an experiment, Taylor and
Thakur [16] gradually increased the water pressure to 2000 to 4000 psi while adding
0.1% of ALFONIC 10e50 (the best of the bunch in Section 10.8) to water. This
created a positive electrostatic charge on the water particles. Most dust particles carry
a small negative charge. This improved the collection even further in general but
particularly in the under 2 mm range. The dust particles appear to adhere to larger water
particles and fall out of air.

10.9.1 Experimental Procedure
Laboratory tests to determine the effects of surfactants and high pressure sprays were
conducted on two occasions. During the first series of tests, the reduction in the respi-
rable dust levels and the charge enhancement of the water spray were investigated. The
experimental setup used to determine the dust reduction is shown in Fig. 10.7.
An Andersen Cascade Impactor was used to gravimetrically measure the respirable
dust concentration in five stages. The sprays were operated at 2900 psi and a flow rate
of 0.75 gpm. An intensifying pump was used to supply the high pressure water. The
experimental setup shown in Fig. 10.8 was used to determine the charge on the water
spray in both series of tests.
In the second series of tests, a small, triplex pump was used in place of the larger,
intensifier pump. The original nozzle was also replaced with a higher volume nozzle.
The water pressure and flow rates tested varied from 1000 psi and 0.87 gpm to
4000 psi and 1.65 gpm.
2
The screen shown is a 6.03 ft steel screen, suspended with rubber straps to prevent
grounding. A 1000 pF capacitor was used to permit a charge build-up for recording