水下矿物浆料气力提升理论模型与流动特性实验研究

发布时间：2017-12-31 13:15

本文关键词：水下矿物浆料气力提升理论模型与流动特性实验研究　出处：《武汉大学》2016年博士论文　论文类型：学位论文

【摘要】：随着有利于浅层开采的矿产资源逐渐枯竭,着眼于深部与超深部资源的高效、无污染浆料提升技术己迫在眉睫。作为举升浆料的有效工具之一,气力提升系统不含运动部件,具有结构简单、体积小、成本低、污染少、不易堵塞和使用可靠等优点,特别适合应用于钻孔水力开采、深海采矿以及深水域库区疏浚等领域,对改善环境、解决自然能源供应紧张与经济高速发展之间的矛盾、倡导可持续性发展具有重要的经济战略意义。目前,因多相流的复杂性和不可预见性,针对于浆料气力提升技术的基础理论与实验研究尚不完善,特别是系统理论模型及其内部流动机制的研究极为缺乏。本文以获取精确、高效、通用性强的理论模型以及多相流动特性为目的,通过理论与实验研究揭示浆料气力提升系统的外部及内部特性。所开展的主要工作及其研究成果如下：(1)考虑气体沿管轴向的非线性变化特征,基于动量定理并结合相含率、压降与能量控制方程,建立了气力提升系统的理论模型,有效解决了传统模型中经验公式偏多及其受限于单一流型等弊端,计算得出了系统运行与结构参数对气力提升性能的作用规律,结果表明：液体表观流速、固体表观流速与提升效率随气体表观流速和管径增加均呈先升后降之趋势,而随浸入率和进气口高度增加则体现出单调性；气、液、固各相体积份数沿轴向在进气口位置出现突变,而在液-固两相中基本恒定不变,即使处于气-液-固三相段也仅发生细微变化；随气体表观流速与浸入率上升,两相段压降基本恒定不变,而三相段压降却受此作用极为明显。(2)以颗粒在液-固两相段中的临界模型为基础,结合气相含率控制方程建立了气-液-固三相段的临界模型,并通过与前者的比较判定颗粒得以提升的临界条件取决于液-固两相段。此外,考虑水底静压持效应,对上述两相段中的临界模型进行修正,其计算结果表明静压持效应极不利于颗粒的“启动”,甚至造成气力提升系统失效。(3)为验证理论模型的可靠性,搭建了总高度为3m的小型气力提升系统,并以中、小尺度球形麦饭石陶瓷颗粒为提升介质,同时利用压力传感器获取测点静压,实验分析了系统基本性能、压降特征与临界条件的影响因素及其内在联系,结果发现中等气体表观流速下实验值与模型结果吻合较好,而其值过低与过高均因各相滑移加大及流场结构的瞬变性、随机性等复杂因素增强引发模型预测失准,同时浸入率降低也会导致模型精确性降低。此外,对气力提升液体与固体颗粒的临界情况分别展开研究,发现前者对应临界气体表观流速不受颗粒影响,而后者却因其位置与尺度变化存在较大差异,且实验证实了水底静压持效应的确使得气力提升性能出现大幅恶化。(4)提出了一种兼有传统气举和射流泵双重功效的环喷式进气方式,使其固体表观流速与效率较径向式进气大幅升高,不过液体表观流速并未受此影响。对两种进气方式下的实验数据无量纲化处理还发现,两者分布规律基本服从于同一分布曲线,继而基于能量守恒首次推导了对应的无量纲理论模型,有效支撑了上述实验结论。另外,还通过引入水射流喷嘴研究其对气力提升性能的影响规律,结果表明水射流喷嘴不仅可解除水底压持效应,还使得颗粒易于跃过液-固两相段,从而大幅增强了气力提升性能,且喷嘴沿周向布置应适度“偏心”。(5)基于高速摄像技术对气-液-固三相流型进行划分,提出了泡状流,小弹状流,不规则弹状流,大弹状流(弹状流),搅拌流,细泡状流和环状流七种流型,并通过与固体表观流速峰值位置的比较判定细泡状流为气力提升性能对应的最佳流型,继而基于图像处理技术获得了各流型下的灰度直方图及概率图,从而通过提取其中统计特征值,获得了基于标准偏差的流型识别方法。通过利用高速摄像仪对混合流体及其中气泡与颗粒的分布和运动特性的分析发现,气泡与颗粒在提升性能增强过中逐渐渗入流道芯部,反之则向管壁靠拢并趋于离散,且气、液、固各相运动具有较强的周期性,从而使得混合流体呈振荡式上升运动规律。而且在固体颗粒的周期运动中发现其提升比极小,从而找出了长期以来气力提升性能一直偏弱的根本原因。鉴于此,利用高速摄像仪对环喷式进气方式作用下的混合流体实测,发现其中提升比显著升高。此外,气泡的塌陷式收缩还会引发邻近气泡与颗粒出现跳跃现象。(6)针对湖南省道县后江桥铁锰矿区的特有地质条件,提出了脉冲水射流和气力提升联合采矿方法,实现了国内特大型涌水矿床开采的先例。试验结果证实了气力提升技术在钻孔水力采矿中的优越性。
[Abstract]:With the help of shallow mining of mineral resources gradually exhausted, focusing on deep and ultra deep resource efficient, pollution-free pulp lifting technology is imminent. As one of the effective tools lifting slurry, pneumatic lift system has no moving parts, and has the advantages of simple structure, small volume, low cost, less pollution, no blockage reliable and use, especially suitable for hydraulic drilling, deep-sea mining and deepwater reservoir dredging and other fields, to improve the environment, to solve the contradiction between the tension and economic supply of natural energy of rapid development, has important strategic significance to promote economic sustainable development. At present, because of the complexity of multiphase flow and unpredictable and on the basis of theoretical and Experimental Research on slurry pneumatic lifting technology is still not perfect, especially the research of system model and its internal flow mechanism is extremely lacking. In this paper, in order to obtain Accurate, efficient, strong universal theoretical model and multiphase flow characteristics for the purpose, through theoretical and experimental studies reveal the slurry pneumatic lifting external and internal characteristics of the system. The main work and research results are as follows: (1) considering the nonlinear characteristics of gas along the axial tube, and the combination of momentum theorem based on the content, pressure drop and energy control equation, establishes the theoretical model of pneumatic lift system, effectively solve the traditional model in the empirical formula of partial and limited to single flow pattern defects, calculate the operation and structure parameters of the system on the role of the law. The results showed that the performance of pneumatic lifting liquid superficial velocity, solid apparent the velocity and efficiency with the superficial gas velocity and the increase of diameter first increased and then decreased, with the immersion rate and inlet height increase reflects the monotonicity of the gas, liquid and solid; the phase volume The number of copies in the inlet position along the axial direction of mutation, but not in liquid solid two phase constant, even in the gas liquid solid three-phase section only subtle changes occur; with the superficial gas velocity and immersion rate, two-phase pressure drop is basically constant, but the pressure drop and phase effect is extremely obvious. (2) with particles in liquid-solid two-phase critical model in section as the foundation, combined with the gas holdup control equation is established for the critical model of gas liquid solid three-phase section, and through the comparison with the former decision depends on the critical condition of the particles to improve the liquid-solid two-phase section. In addition, consider the bottom the static pressure hold effect on the critical period in the two-phase model was modified, the calculation results show cuttinghold effect is not conducive to the particle "start", even cause the failure of pneumatic lift system. (3) to check the reliability of theoretical model, built a total height of 3M small Type pneumatic lift system, and in small scale spherical stone ceramic particles to enhance the media, at the same time using pressure sensors to obtain the measured static pressure, the experimental analysis of the basic performance of the system, factors affecting the characteristics of pressure drop and the critical conditions and its internal relations were found to moderate the superficial gas velocity under the experimental values are in good agreement with the model results. While its value is too low and too high due to the phase slip flow structure and increase the transient, randomness and other complex factors lead to enhanced prediction model of misalignment, and the immersion rate will lead to decrease the accuracy of the model is reduced. In addition, the critical situation of pneumatic lifting of liquid and solid particles were studied and found apparent velocity the former is not affected by the particle effects of the corresponding critical gas, while the latter is due to the differences of location and scale change, and the experiments confirmed the static effect really makes the gas to the bottom of the lifting force Can a sharp deterioration. (4) proposed a method of cyclic type intake with traditional gas lift jet pump and double effect, the apparent solid velocity and efficiency significantly increased radial intake, but the liquid superficial velocity was not affected. The dimensionless treatment was also found on experimental data two inlet mode, distribution between the basic subject to the same distribution curve, and then based on the conservation of energy is derived for the first time the dimensionless corresponding theoretical model, effectively support the experimental results. In addition, through the introduction of water jet nozzle on the influence of air lift performance. The results show that water jet nozzle can not only remove the bottom cuttinghold effect, also makes the particles easily over the liquid-solid two-phase section, thus greatly enhance the performance of pneumatic lifting, and the nozzle arrangement along the circumferential direction should be "eccentric". (5) high speed camera technology for gas - liquid - based Solid pattern was divided, put forward small bubbly flow, slug flow, irregular slug flow, large slug flow (slug flow), mixing flow, fine bubble flow and annular flow of seven flow regimes, and by comparing the determined velocity peak position and the apparent solid fine bubble flow pneumatic lifting of optimal flow pattern corresponding to the image processing technology, and then obtained the gray histogram and the probability map of each flow based on which via extracting the statistical characteristic value, the flow pattern identification method based on standard deviation. By using a high-speed camera and the analysis of mixed fluid distribution and movement characteristics of bubbles and particles. Found that the bubbles and particles in the performance enhancement in the core flow gradually, and close to the tube and tend to be discrete, and gas, liquid, and solid phase movement has a strong cyclical, so that a mixed fluid oscillation type ascending motion rule Law. And periodic motion of solid particles in that it increase than the minimum, so as to find out the long lift root cause of performance has been weak. In view of this, the use of high speed camera measurement instrument on the effect of mixed fluid inlet ring jet mode, found promoted than significantly increased. In addition, the bubble collapse will shrink the cause of bubbles and particles near the jump phenomenon. (6) the special geological condition in Hunan province after the Daoxian County River Qiaotie manganese mine, put forward the pulse water jet and air lift combined mining method, realizes the large inflow of mining precedent. The experimental results confirm the superiority of pneumatic lifting technique in borehole hydraulic mining.

【学位授予单位】：武汉大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TD857

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