【作者】 廖寅飞；

【导师】 刘炯天；

【作者基本信息】 中国矿业大学 ， 矿物加工工程， 2014， 博士

【摘要】 浮选气泡行为及气体弥散状态直接影响着浮选的分选效果。由于对气泡运动行为缺乏认识以及气体弥散调控机制的缺失，导致经常出现气体弥散参数不稳定、调控滞后和浮选指标波动等问题。鉴于此，提出了浮选气体弥散及其调控研究，以期通过对气泡运动、系统辨识和模糊控制的研究，构建浮选过程当中的气体弥散调控机制、策略和模型，形成先进可靠的浮选气体弥散控制方法，为浮选设备和工艺的进步提供理论支撑。论文首先进行了三种起泡剂的性能比较及机理分析。开展了气流法和煤泥浮选试验，并利用滞留时间、动态起泡指数、泡沫衰变时间和浮选指标来比较起泡剂的性能；建立了气泡液膜厚度的光学测量系统，并从起泡剂的载水速率、分子吸附状态和气泡液膜厚度三个层面揭示了起泡剂性能差异的作用机理。研究表明：载水速率的增大使起泡剂的捕收性变好、选择性变差；在气-液界面上，正戊醇分子和MIBC分子以“斜躺”状态吸附，仲辛醇分子以“站立”状态吸附；含起泡剂的气泡液膜由内层结合水和外层自由水组成；结合水与起泡剂分子在气-液界面的吸附状态有关，“站立”状态吸附有利于形成较厚的结合水层；自由水靠水分子间的范德华力维系，厚度受起泡剂性质的影响较小。构建了以高速显微装置为核心的单气泡运动行为和气泡液膜流动观测系统，研究了单气泡运动过程和行为，并从气泡受力、气泡表面流动和上升终速模型三个层面探讨了其调控机理。研究表明：气泡上升过程中，气泡的速度和纵横比先升高至最大值，随后降低并围绕中心值振动；起泡剂能够抑制气泡的形变、抖动和振荡，缩短加速时间，降低气泡速度与纵横比的最大值、振动中心值和幅值，使气泡形状保持球形、运动轨迹保持直线。Marangoni作用力抑制了气泡在起泡剂溶液中上升时的形变，同时增加了气泡表面阻力，降低了气泡速度；气泡表面流动揭示了气泡表面的Marangoni效应，起泡剂使气泡表面更加粗糙、波纹更多；Clift终速模型证明了起泡剂性质和气泡表面流动对气泡速度的重要影响。基于高速摄像和图像处理技术建立了浮选气体弥散试验系统，分析了空间位置、表观气速、起泡剂种类和浓度对气体弥散参数的影响；对气含率与气泡尺寸、气泡间距、比表面积通量的交互关系进行了解耦，建立了气含率-比表面积通量模型、气泡间距-气泡面积百分率模型、气泡面积百分率-气泡体积百分率的均匀分散和随机分散模型。采用高速摄像和气泡识别跟踪手段，对气泡群运动过程进行了跟踪，捕捉和观测了气泡兼并与破裂现象，揭示了气泡群的运动行为和调控机理。研究表明：气泡群运动行为可以用气泡速度-尺寸曲线来表征，气泡速度-尺寸曲线受到空间位置、表观气速、气泡尺寸分布、起泡剂种类和浓度的影响；气泡间的相互作用使气泡群运动速度区别于单气泡运动速度，主导气泡尺寸级决定了气泡群运动速度；起泡剂降低了气泡群运动速度，使气泡群运动轨迹变直、变密集。气泡破裂以分裂成两个体积不相等气泡的形式发生；气泡兼并实为气泡接触碰撞、液膜排液至膜破裂的过程，起泡剂延长了气泡液膜的薄化时间，降低了气泡兼并概率；水中气泡碰撞弹回的缓冲时间长于起泡剂溶液，增加了由碰撞转变为兼并的概率；起泡剂主要通过抑制气泡兼并来控制气泡尺寸。研究了浮选气体弥散的边界条件和调控策略，得到了浮选气体弥散的状态区域图，并形成了以气含率和表观气速为测控核心，在线估计气泡尺寸和比表面积通量，实现气体弥散状态识别和报警的调控策略。利用阶跃信号和4级PRBS序列进行系统辨识，研究了气含率与表观气速和起泡剂浓度间的动态响应特性和传递函数，结果表明：平均气含率与表观气速和起泡剂浓度的动态响应过渡过程均为具有纯滞后的一阶惯性环节，两种辨识信号所得传递函数具有较好的一致性。采用机理法建模对传递函数进行了理论解析，结果表明：放大系数与溶液性质（起泡剂种类）有关，时间常数与液位高度成正比，纯滞后时间与管道长度以及管道内的流速相关，理论模型的计算结果与系统辨识试验结果相吻合。根据模糊控制理论，设计了气含率模糊控制器，分析了量化因子和比例因子对模糊控制器性能的影响并进行了优化，与常规PID控制的性能对比仿真试验表明：模糊控制在缩短过渡时间、降低超调量和抗干扰能力方面均具有优势，展现了更好的动态响应性能和鲁棒性，采用模糊控制器控制气含率将更加合理有效。提出了浮选气体弥散的模糊控制方法并对软硬件实现方案进行了设计，并采用DDC控制和MCGS组态软件相结合的方式构建了实验室系统，测试结果表明：通过运行该模糊控制方法，系统实现了对气体弥散参数的动态显示以及对气体弥散状态的识别和报警，完成了对气含率和表观气速的模糊控制以及对气泡尺寸和比表面积通量的间接调控。更多还原

【Abstract】 Bubble motion behavior and gas dispersion directly affect the flotationperformance. Due to the ignorance of bubble motion behavior and the lack ofregulation mechanisms, it always leads to the gas dispersion parameters instability,reguation lags and flotation indexes fluctuation. For the above reasons, the study offlotation gas dispersion and regulation was raised in this paper. The bubble motion,system identification and fuzzy control were studied in this paper in order toconstruct the mechanisms, strategies and models on gas dispersion regulation inflotation process and develop an advanced control method, which could providetheory supports for the development of flotation devices and process.The property difference of three typical frothers and its mechanism werestudied at the beginning of this paper. Air flow method and coal flotation tests werecarried out to compare the frother properties by use of retention time, dynamicfoamability index, collapse time and flotation indexes, and the mechanism ofproperty difference was revealed by water carrying rate, molecule adsorption statusand bubble film thickness with optical measurement system. Studies show that: thehigher water carrying rate, the better forther collecting capacity and the worseselectivity is, and Pentanol molecule and MIBC molecule recline on the thegas-liquid interface with Octanol molecule standing. Frother bubble film is a surfacewith an inner bound water layer surrounded by an outer free water layer. Boundwater layer is related with frother molecule adsorption status that standing status willbe thicker, while free water layer relies on van der Waals forces between watermolecules, less affected by frother.The single bubble motion and behavior were studied by single bubble behaviorand bubble surface motion observation system with core of high-speed digitalcamera and microscope, and the mechanism was discussed by stress analysis, surfacemotion and terminal velocity model. The results indicate that the bubble velocity andaspect ratio first increase to the maximum, then reduce and vibrate around the centralvalue. Frother can inhibit bubble deformation and oscillation, and shortenacceleration time, and reduce the maximum, vibration central value and amplitude ofbubble velocity and aspect ratio, so that bubbles tend to remain spherical, and therise paths tend to be rectilinear. Marangoni force suppresses bubble deformation andincreases bubble surface resistance reducing velocity. Bubble surface motion revealsthe Marangoni effect with the bubble surface rougher and more ripples by frother. Terminal velocity model by Clift proves an important influence of frother and bubblesurface motion on the bubble velocity.The effect of spatial location, superficial gas velocity and frother on gasdispersion parameters were analyzed by gas dispersion system based on high-speeddigital camera and image processing. The interaction between gas holdup, bubblesize, bubble distance and surface area flux were decoupled with the establishment ofbubble surface area flux-gas holdup model, bubble distance-area fraction model,bubble distance-volumetric fraction ideal and random dispersion model.The motion behavior and mechanism of bubble swarm were revealed withbubble swarm tracking and bubble coalescence and breakup observation. The bubbleswarm motion behavior can be characterized by the bubble velocity size-profile,which depends on spatial location, superficial gas velocity, bubble size distribution,frother type and concentration. Bubble swarm velocity is different from singlebubble velocity due to bubble interaction that the predominant bubble sizedetermines swarm velocity. Frother reduces bubble swarm velocity and makes thetrajectory become rectilinear and crowded. Bubble breakup occurs in the form ofsplitting into two bubbles of unequal volumes, and bubble coalescence is actually aprocess of bubble collision and film drainage to rupture. Frother lengthens bubblefilm thinning time reducing the coalescence probability, and the buffer time forbubble rebound process in water is longer than that in frother solutions increasingthe probability of collision to coalescence, so that frother controls bubble size mainlythrough preventing bubble coalescence.Boundary conditions and control strategies for gas dispersion were studied. Thegas dispersion status map was obtained, forming a regulation strategy that gasholdup and superficial gas velocity was the monitoring core with bubble size andsurface area flux online estimated to achieve status recognition and alarm for gasdispersion.Applying the step change signal and PRBS change signal respectively to systemidentification, the dynamic response properties and transfer functions between gasholdup, superficial gas velocity and frother concentration were studied. The resultsshow that the dynamic response transition processes between gas holdup, superficialgas velocity and frother concentration are one order inertial link with pure delays,and the transfer functions obtained by the two identification signal have a goodconsistency. By using the mechanism modeling method, the transfer functions wereanalyzed theoretically. It is indicated that the proportion parameter relies on thesolution properties (frother) with the time constant being proportional to level heightand pure delay time depending on pipe length and flow rate. The theoretical modelresults are consistent with that of system identification test.According to the fuzzy control theory, gas holdup fuzzy controller was designedand the effect of quantization factor and scale factor was analyzed and optimized.Simulation results compared to conventional PID control indicate that fuzzy controlhas an advantage in shortening transition time, reducing overshoot andanti-disturbance ability, which shows better dynamic performance and robustnessthat it is suitable for fuzzy controller to control gas holdup.The fuzzy control method of flotation gas dispersion was proposed and theimplementation scheme of software and hardware was also designed. CombiningDDC technology and MCGS configuration software, the laboratory control systemof flotation gas dispersion was developed. By running this fuzzy control method, it issuccessful to display parameters and recognize and alarm gas dispersion status withthe fuzzy control of gas holdup and superficial gas velocity and the indirect controlof bubble size and surface area flux.更多还原