Study On The Characteristic Of Air Lift System For Borehole Hydraulic Jet Mining

The rapid development of the world economy accelerates the growing demand for sourse of energy. However, high quality mineral resources are becoming less and less. Seeking new mineral resources has become one of the problems which must be solved currently. Right now, the potential mineral resources are located in deep sea and some spots with complex hydrogeological conditions. Those resources are well-known to be difficult to mine, and after mining, the ores are also very difficult to be lift up. This paper focuses on mineral ore lifting process, and tries to use air lifting method, a widely applied method in deep-sea mining and hydraulic-drilling, whose advantages include high lifting depth, simplicity, easy-to-maintenance, etc. To satisfy the purpose, several aspects have been studied as shown in following:①. Using the method of modularization system, affecting factors of lifting efficiency of air lifting system has been discussed.②. Based on the theory of minimum energy consumption and the multiphase flow pattern, it can be known that the annular flow pattern is in a relatively stable flow state. For annular flow, gas-liquid and gas-solid mathematical model of pressure drop has been used to derive gas-liquid-solid model of pressure drop.③. The feature of air lift system has been researched based on experiments and theoretical analysis which involves the theory of multiphase and shear layer;④. Based on the self-excited oscillation theory, the effective incentive conditions of double series self-excited oscillation chamber has been established, and the formation mechanism of jet has been analyzed;⑤. The network model of double series self-excited oscillation chamber has been established by using the theory of fluid network, and the computational expressions of the natural frequencies of nozzle has been obtained, and the effect of several factors, such as the structural parameters of nozzle, fluid parameters (pressure, flow) and the pump pressure oscillation, has been studied, and the design criteria of double self-excited oscillation chamber has been put forward.The theory and experimental study has led to the following important fruitful results, as listed in following, have been reached.①. Air lifting system is comprised of an air compressor, a gas pipeline network, a pipe system and an air lifting device. Therefore, the efficiency of the air lifting system is the arithmetic product of each sub-device. The efficiency of gas pipeline network and pipe system is mainly influenced by pipe length and local resistance losses. The efficiency of air raiser is decided by friction loss, local resistance losses, heat loss, slipping loss and immersion rate. For the knapper, its efficiency is influenced by its structure parameters and fluid parameters.②. The immersion rate has a significant effect on the characteristics of air lift. The higher the immersion rate, the higher the lift water quantity is, lift sand quantity and lift efficiency are. Except that, an optimum nozzle number exists. In this experiment, 3 nozzles have been used simultaneously. Air nozzle installation angle is also an important factor which affects the lift characteristics of air lift. When gas flow is less than 30m3 / h and air nozzle is tangent to the pipe wall, lift water quantity and lift sand quantity reach the maximum value. As gas flow is more than 37.5 m3 / h and air nozzle is not deflection, the maximum number has been gotten for lift water quantity and lift sand quantity. When gas flow is between 30m3 / h and 37.5 m3 / h, air nozzle angle has less influence on lift water quantity and lift sand quantity. Sometimes, whether installing knapper nozzle or not is a key factor affecting lift process. Though the installation of Knapper nozzle decreases the amount of lifting water, it increases the quantity of lift sand.③. Device structure and fluid parameters have to be considered during the structure parameter design process of double series self-excited oscillation chamber. Thus, the frequency of flow can be close to the natural frequency of the oscillation chamber.④. Experimental results have shown that, under the same conditions, double series self-excited oscillation chamber has stronger erosion effects than single chamber. The erosion depth impacted by double series self-excited oscillation chamber increased 47.53% and the eroding volume increased 65.43% comparing to single chamber.⑤. The frequency of double self-excited oscillation chamber is relatively low. The frequency of self-excited oscillation peak pressure decreases with the increasing of cavity length and the lumen diameter, and it increases with the increasing of pressure and velocity. There is an optimum cavity length ratio and lumen diameter ratio. Comparing with regular jet, the peak pressure of double series self-excited oscillation chamber increased about (25- 46)%, and the peak pressure of single self-excited oscillation chamber increased (15-35)%.The above results have prepared the theory and practice for air lifting application, and this paper has led to farther study for deep-sea mining and borehole hydraulic mining.