Patterns and laws of dilution and outflow of gaseous products from slot chambers

Abstract

A large proportion of nonferrous and rare metal deposits are of a small or medium thickness. These deposits are normally worked by open pit mining. The working spaces are chambers of different configurations filled continuously or periodically with toxic production materials. The types of chambers investigated in this study are slotlike workings with width and length greater by two orders of magnitude than their height; both by geometric parameters and by ventilation conditions, these workings differ significantly from the situations described in the literature and investigated by various authors [1][2][3][4].Our studies have shown that the process of equalization of concentration of gas products in chamberlike workings is protracted in time, i.e., the concentration leveling occurs both over the cross section and along the working length. The geometric parameters of a chamber change as the mineral is extracted, leading to altered aerodynamic conditions of advancing space and ratios of dilution and outflow of gas products, as well as altered concentration leveling times.When the working is advanced along the strike of the ore body (from the center to the flanks of a block), the ventilation of slotlike or flat chambers at the initial stage of the working of a block is conducted by a combined Jet, i.e., a free jet operates in the part of the chamber adjacent to the air supply opening while in the further portion (after it is opened up to the chamber boundaries), there develops a limited turbulent flow. As the working approaches the block boundaries, the ventilation of the chamber occurs by the action of vertically limited free Jets [5]. The process of ventilation of a flat chamber should therefore be considered in the dynamics of the progress of mining operation, i.e., with a gradual increase of the width of the chamber Bk.Without going into the aerodynamics of the stope spaces that had been analyzed earlier [5, 6], we will consider the diffusional distribution of impurities in turbulent flows.Figures la-c present the general results of all processes occurring in a chamber along the x and y axes as oscillograms of the impurity concentration variations in time. These results are aggregated for a large number of experiments (more than 20 for each situation). The process was recorded using a mirror-galvanometer oscillograph at the output from the hydraulic model (Fig. 2), using electrode sensors. The resultant variation curves of c f(T) are characterized by a certain effective turbulent dlffusivity.When activating the hydraulic model, the impurity, simulated by 1% NaCI solution, was instantly injected through a perforated pipe with openings of u -1 mm, oriented in the vertical plane, i.e., the injection process obeyed in time a 6-function (Fig. 3, curve I). Analysis of one of the unit oscillograms (Fig. 3, curve 2) showed that the original jet pulse brings out of the chamber (through the input channel) a portion of the impurity in a concentrated form, partly diluted through distension of the gas Jet (turbulent deformat...