Study On The Flotation Gas Dispersion And Regulation

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.