Numerical method for determining air requirements for reverse air lift

This study defines analytically a method for determination of the air requirements necessary to establish and maintain adequate circulation rates for large-diameter shaft drilling. Two-phase flow analyses are compared with experimental data. Results indicate that fully developed 2-phase flow regimes are not encountered, in part, due to a relatively short injection string (generally no longer than 500 m) and, in part, due to diffuser design. A differential equation, establishing pressure gradients in reverse air-lift drilling, is presented. Due to lack of adequate experimental data, the degree of accuracy cannot be established. More experimental data are required to establish slip velocities, flow requirements, and mechanics of mixing in the air diffuser region. (12 refs.)