Simple float systems

Air flotation is simply the production of microscopic air bubbles, which enhance the natural tendency of some materials to float by carrying wastewater contaminants to the surface of the tank for removal by mechanical skimming. Many commercially available units are packaged rectangular steel tank flotation systems shipped completely assembled and ready for simple piping and wiring on site. 

Ferric hydroxide coprecipitation techniques are lengthy, two days being needed for a complete precipitation. To speed up this analysis, Tzeng and Zeitlin [595] studied the applicability of an intrinsically rapid technique, namely adsorption colloid flotation. This separation procedure uses a surfactant-collector-inert gas system, in which a charged surface-inactive species is adsorbed on a hydrophobic colloid collector of opposite charge. The colloid with the adsorbed species is floated to the surface with a suitable surfactant and inert gas, and the foam layer is removed manually for analysis by a methylene blue spectrometric procedure. The advantages of the method include a rapid separation, simple equipment, and excellent recoveries. Tzeng and Zeitlin [595] used the floation unit that was devised by Kim and Zeitlin [517]. 

The choice of a filler depends on the number of bottle sizes being considered for use on it. For example, if 3 1 PET bottles are to be filled, a 126 mm pitch between filling valves is required. If only small bottles up to 500 ml are to be filled, then a 70 mm pitch will suffice. This has a direct effect on the size of the filler and its footprint on the factory floor. Unless the filler bowl level is kept within tightly controlled limits, pressure head variations will affect the rate of flow into containers. Systems such as that shown in Figure 7.15 need to be employed. Wherever possible there should be minimal contact between any instrumentation and the product. Conventional float valves should be avoided and simple capacitance probes, which are easily cleanable but small and very effective, should be used. It is not uncommon in older fillers to only have one float valve. This often gives rise to filler bowl flooding, which may lead to inconsistent fill level and poor counter-pressurisation of the container pre-filling. 

The pressure of the vapor present at equilibrium is called the equilibrium vapor pressure, or, more commonly, the vapor pressure of the liquid. A simple barometer can measure the vapor pressure of a liquid, as shown in Fig. L6.46. The liquid is injected at the bottom of the tube of mercury and floats to the surface because the mercury is so dense. A portion of the liquid evaporates at the top of the column, producing a vapor whose pressure pushes some mercury out of the tube. When the system reaches equilibrium, the va-... 

For basic studies, model experiments have to be carried out and analyzed. We shall mostly consider liquid (L) drops on horizontal solids (S) in a vapour phase (G), because in such a system hysteresis is most manifest. A simple set-up is sketched in fig. 5.29. The droplet on a tilting plate (fig. 5.32) is an alternative. In fluid-fluid systems (LjLjG), say an oil drop floating on water, or a water droplet on mercury, hysteresis may be absent, but then the interpretation is more complex because the vertical component of the surface tension ly sin a) has also to be considered because the liquid substrate cannot support a vertical stress. In other words, analysis requires Neumann s triangle (5.1.3] rather than Young s law [5.1.2]. 

---