Precipitation predicting

Silverman, D. and J.A. Draoup Artificial neural networks and long-range precipitation prediction in California, J. Appl Meteorol 39 (2000) 57-66. 

Predicting a Precipitate Predict whether a precipitate of PbCQ will form if 100 ml of 0.01 OOM NaCI is added to 100 ml of 0.0200M Pb(N03)2. 

From the solubiUty product data the thermodynamic tendency of a metal hydroxide to precipitate as a function of pH can be deterrnined. The actual solubihties on complex samples must be deterrnined empirically however, general predictions can be made regarding metal—metal separations by hydrolysis. 

Calcium Carbonate Protective Scale. The LangeHer saturation index (LSI) is a useful tool for predicting the tendency of a water to deposit or dissolve calcium carbonate. Work pubHshed in 1936 deals with the conditions at which a water is in equiHbrium with calcium carbonate. An equation developed by LangeHer makes it possible to predict the tendency of calcium carbonate either to precipitate or to dissolve under varying conditions. The equation expresses the relationship of pH, calcium, total alkalinity, dissolved soHds, and temperature as they relate to the solubiHty of calcium carbonate in waters with a pH of 6.5—9.5 ... 

Zauner and Jones (2000b) presented a computationai metiiodoiogy for predicting precipitate particie properties and mean size based on a hybrid SFM coupied with the popuiation baiance that can simuitaneousiy account for micro-, meso- and macromixing effects, and by way of iiiustration wiii be described here in detaii. 

The model is able to predict the influence of mixing on particle properties and kinetic rates on different scales for a continuously operated reactor and a semibatch reactor with different types of impellers and under a wide range of operational conditions. From laboratory-scale experiments, the precipitation kinetics for nucleation, growth, agglomeration and disruption have to be determined (Zauner and Jones, 2000a). The fluid dynamic parameters, i.e. the local specific energy dissipation around the feed point, can be obtained either from CFD or from FDA measurements. In the compartmental SFM, the population balance is solved and the particle properties of the final product are predicted. As the model contains only physical and no phenomenological parameters, it can be used for scale-up. 

Figure 8.14 Predicted (a) concentration profiles in the film region, and (h) mean particle sizes during gas-liquid precipitation of CaC03 (Wachi and Jones, 1991a). Ga.s-liquid precipitation cell...

The data plotted in the figure clearly support the predicted positive dependence of crystal size on agitation rate. Precipitation in the crystal film both enhances mass transfer and depletes bulk solute concentration. Thus, in the clear film model plotted by broken lines, bulk crystal sizes are initially slightly smaller than those predicted by the crystal film model but quickly become much larger due to increased yield. Taken together, these data imply that while the initial mean crystal growth rate and mixing rate dependence of size are... 

The significance of this novel attempt lies in the inclusion of both the additional particle co-ordinate and in a mechanism of particle disruption by primary particle attrition in the population balance. This formulation permits prediction of secondary particle characteristics, e.g. specific surface area expressed as surface area per unit volume or mass of crystal solid (i.e. m /m or m /kg). It can also account for the formation of bimodal particle size distributions, as are observed in many precipitation processes, for which special forms of size-dependent aggregation kernels have been proposed previously. 

Figure 8.24 Predicted transient particle size distribution during the hatch precipitation of calcium carbonate crystals (Wachi and Jones, 1992)...

The reaction engineering model links the penetration theory to a population balance that includes particle formation and growth with the aim of predicting the average particle size. The model was then applied to the precipitation of CaC03 via CO2 absorption into Ca(OH)2aq in a draft tube bubble column and draws insight into the phenomena underlying the crystal size evolution. 

Schreiner etal. (2001) modelled the precipitation process of CaC03 in the SFTR via direct solution of the coupled mass and population balances and CFD in order to predict flow regimes, induction times and powder quality. The fluid dynamic conditions in the mixer-segmenter were predicted using CFX 4.3 (Flarwell, UK). 

David, R. and Marcant, B., 1994. Prediction of micromixing effects in precipitation Case of double-jet precipitators. American Institution of Chemical Engineers Journal, 40, 424M32. 

Marcant, B., 1996. Prediction of mixing effects in precipitation from laser sheet visualisation. Industrial Crystallization 1996, Toulouse (Rugby Institution of Chemical Engineers), pp. 531-538. 

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