On-line analysis of the stability and other features of froths and foams by use of digital image processing

Ellis, Rene (2002-03)

Thesis (MScEng)--University of Stellenbosch, 2002.


ENGLISH ABSTRACT: The objective of this study is the assessment of the usefulness of an industrial machine vision system for laboratory studies of especially flotation froths and other foams. With this in mind it was attempted to meet three objectives. The first objective is the adjudication of the machine vision system's ability through image analysis to differentiate between characteristics of two-phase and three-phase systems. Secondly, through the use of image analysis the effect of varying surfactant concentration, as well as the addition of quartz particles on the foam/froth stability was quantified and thirdly it was attempted to define the nature of foam decay as stochastic or deterministic. While not as important in the industrial setting, the last objective is quite important when a laboratory system is concerned, even more so owing to the difficulty of quantifying the collapse or decay of foams and froths. Two experimental set-ups were used to attain above-mentioned objectives. A Leeds flotation cell was used for the flotation of the quartz with cetyltrimethylammonium bromide (CTAB) and octadecylamine (ODA) and as well as for the characterisation of the CTAB and ODA foam. A glass column was used to investigate the CTAB foam column decay. In both set-ups the foam/froth structures were monitored with an ELMO charged coupled device (CCD). The CCD was connected to a personal computer equipped with frame grabber, which captured and digitised the images. The following conclusions can be drawn from the experimental results: The machine vision system can differentiate accurately between surfactant groups of different concentration and thus groups with unique characteristics. 11 The stability of foam is highly correlated with all other foam variables extracted from the image analysis system. In particular, the movement of the foam/froth in the flotation cell has a substantial influence on the stability values obtained for the foam/froth. III As far as the experimental system was concerned, small quartz particles (- 75 urn) stabilised the froth, while coarser particles (75-106 urn, 106-150 urn and 150+ urn) destabilised the froth. IV Likewise, the decay of CTAB foam in a column was non-linear and deterministic. When observed manually, the decay of long life foams follow the same trend as short-life foams and short-life emulsions in that a specific decay constant can be calculated for a specific surfactant system. V The machine vision system is a viable alternative for current stability measurements. Firstly, no data processing need to be done to calculate a indirect stability parameter as it computes a direct stability parameter and secondly it also computes the bubble size distribution of the sample. The following recommendations are made: The experimental design of the system needs to be altered to minimise the effect the experimental environment has on results. The possibility of a different camera set-up must be investigated. The focus of the camera on the foam surface needs to be accurate as the computation of the stability value depends on the quality of the image obtained. Il The four factors that affect the stability of a flotation froth, namely solid concentration, particle size, particle type and particle hydrophobicity should be investigated in the same study. There exists many conflicting studies on this subject as many studies for different particles with a variety of sizes, hydrophobicity and concentration are performed. One study should be conducted where all four these factors are investigated under the same experimental conditions. III The method with which the image analysis system deal with fine froth need to be addressed. In laboratory systems a typical system investigated will show a dense foam with small bubble distributions as in the case of CTAB. The extent to which the grouping of fine froth as one bubble influence the instability values obtained needs to be investigated .

AFRIKAANSE OPSOMMING: Die doelwit van hierdie studie is die evaluering van die toepassing van 'n industriële masjienvisiesisteem in 'n laboratorium studie van hoofsaaklik flottasie skuim. Die doel van hierdie toepassing is drie-ledig. Die eerste doelwit is om die onderskeidingsvermoë van die masjienvisiesisteem tussen groepe met verskillende eienskappe te evalueer deur intydse beeld verwerking. Tweedens is die invloed van oppervlakmiddelkonsentrasie veranderinge asook die byvoeging van kwarts partikels op die stabiliteit van die skuim ondersoek. Derdens is die aard van die skuim verval ondersoek om vas te stelof die proses deterministies of stochasties is. Alhoewel laasgenoemde doelwit nie so belangrik is in die industriële toepassing nie, is dit van uiterse belang in die laboratorium studies, veral as gevolg van die probleme wat ondervind word in die kwantifisering van skuimverval. Twee eksperimentele opstellings is gebruik om bogenoemde doelwitte te bereik. 'n Leeds flottasiesel is gebruik vir die flottasie van kwarts met CTAB en ODA asook vir die karakterisering van CTAB en ODA skuimeienskappe. 'n Glaskolom is gebruik vir die ondersoek van die aard van skuimverval. In beide opstellings is die beelde gemonitor deur 'n ELMO CCD. Die CCD is verbind met 'n rekenaar wat toegerus is met 'n raam-vanger wat die beelde vang en digitiseer. Die volgende gevolgtrekkings kan uit die eksperimentele resultate gemaak word: Die masjienvisiesisteem differensieer akkuraat tussen oppervlakmiddel groepe van verskillende konsentrasies en dus ook tussen groepe met unieke eienskappe. 11 Die skuim stabiliteit korreleer met die ander skuim eienskappe naamlik gemiddelde area, gemiddelde omtrek, aantal borrels, fynheid van die beeld (SNE), beweging van die skuim en kleur van die skuim. Veral die beweging van die skuim in die flottasiesel het 'n beduidende invloed op die skuimstabiliteit. 111 In die genoemde eksperimentele sisteem IS gevind dat klein kwartspartikels (-75 urn) skuim stabiliseer terwyl groter partikels (75-106 urn, 106-150 urn en 150+ urn) skuim destabiliseer. IV Die verval van CTAB skuim in 'n kolom is nie-lineêr en deterministies. In die geval waar die verval van die CTAB met die hand gemeet is, is gevind dat die verval van 'n lang-lewe skuim dieselfde tendens as kort-lewe skuim en kort-lewe emulsies volg. 'n Spesifieke verval konstante kan bereken word vir 'n spesifieke oppervlakmiddel sisteem. v Die masjienvisiesisteem IS 'n werkbare alternatief in die meting van skuimstabiliteit. Anders as in bestaande stabiliteitsmetings waar 'n indirekte stabiliteitsparameter bereken moet word, bereken die sisteem 'n direkte stabiliteitsparameter asook die borrelverspreiding van die skuim monster. Die volgende aanbevelings kan gemaak word: Die eksperimentele ontwerp van die sisteem moet aangepas word om sodoende die invloed van eksperimentele kondisies op die resultate te verminder. Die moontlikheid van 'n alternatiewe kamera opstelling moet ook ondersoek word, aangesien die verkrygde stabiliteitswaardes afhanklik is van die kwaliteit van die skuimbeelde. 11 Daar is talle teenstrydige studies ten opsigte van die vier faktore wat die stabiliteit van flotasie skuim beinvloed naamlik erts tipe, partikel grootte, partikel hidrofobisiteit en vastestof konsentrasie. Hierdie faktore moet gelyktydig in 'n studie ondersoek word onder dieselfde eksperimentele kondisies. 111 Die masjienvisiesisteem groepeer fyn skuim gedeeltes saam as een borrel. Hierdie wyse van fyn skuim hantering moet aangespreek word aangesien 'n tipiese oppervlakmiddel sisteem in die laboratorium, soos in die geval van CTAB, digte skuim met 'n fyn borrelverspreiding toon. Die mate waarin die onvermoë van die sisteem om fyn borrels te herken die stabiliteitswaardes beïnvloed, moet ondersoek word.

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