Page 174 - Advanced Mine Ventilation

154 Advanced Mine Ventilation

Figure 10.11 Comparison of voltage induced in water sprays.

that would make such a significant difference in the charge. Results of the second se-
ries of tests are shown in Fig. 10.12. DC voltage created increased linearly with water
pressure from 1000 to 3000 psi.
Increasing the pressure from 3000 psi to 4000 psi resulted in only a slight increase
in the voltage. The voltage, measured by placing the screen in the water spray approx-
imately four feet from the nozzle, was higher for the surfactant solution than pure water
in every test conducted.
The results of these tests indicate that the use of ALFONIC 10e50 surfactant in-
creases the voltage present on a high pressure spray of the surfactant-water solution.
A series of tests conducted to determine the improvement in the dust collection effi-
ciency by adding a surfactant to high pressure sprays also showed a significant
improvement. The most pronounced increase in the collection efficiency was found
in the smallest size range ( 1.8 mm). The collection of particles in this size range is
of particular interest since particles in this size range cause the most lung damage.
The experimentation conducted shows a novel technology for suppressing respi-
rable coal dust. The experimental studies did not identify the actual reason for the
induced voltage, but the interacting effects of high pressure and the surfactant additive
apparently create the electrically charged water particles. They create an electrical
attraction for the dust particles, thereby causing agglomeration and consequent in-
crease in collection efficiency. It is assumed that the surfactant, by reducing the surface
tension of the water, allows the water to break up into very small droplets at the nozzle