Greasy and oily water coming from a variety of sources need to be purified in industrial applications. Apart from the technical reasons behind this, there is also an environmental issue that has negative effects and can damage the flora and fauna. In order to separate correctly oily substances and water industrial plants have three main approaches: Chemical, Mechanical and Thermal separation.
- Chemicals are commonly used for treatment of oily wastewater and are used to enhance mechanical treatment and separation. In resolving emulsions, stabilizing factors must be neutralized to allows emulsified droplets to coalesce. Electrostatic charges on emulsified droplets are neutralized by introducing an oppositely charged chemical (see theory of emulsions). Emulsion breakers provide this opposite charge and are most often combined with mechanical and thermal treatments to achieve the best separation . Oil in water emulsions are typically treated using cationic coagulants (es. Starch based coagulants, iron or aluminium based coagulants etc.).
- Mechanical treatment is used to separate the oily substances (generally constituted by hydrocarbons and sometimes even from edible fats) from the water. A simple mechanical separation based on the difference in specific weight between the two phases of the water-oil system can be used. Gravity separation of wastewater from refineries takes place in basins A.P.I. American Petroleum Institute (separator) In the case of oily emulsions difficult to break, the gravity separation must be preceded by chemical treatments, studied case by case. In this case, however, it requires large tanks and large surfaces that are not always available. Other industries therefore make use of coalescing filters, where the oil droplets coalesce to form larger drops and therefore easier to separate by gravity. A fairly common technique for oil-water separation is that of the “dissolved air flotation” (DAF – dissolved air flotation). The liquid is injected into the flotation tank after being saturated, fully or partially, with air under pressure. In the tank, at atmospheric pressure, it is released so tiny air bubbles, (with an average diameter close to 50 microns), which adhere to oily particles dragging upwards. On the same principle is based the “flotation by bubbling” (IAF: induced air flotation): in this case the air is introduced directly into the tub through speakers in plastic material or porous ceramic, which however produce bubbles of a diameter of several hundreds of microns . Another widely used technique is the ‘ultrafiltration, where the water is filtered through the membranes obtained by casting of special plastic materials on a resistant glass fiber support. The so obtained membranes are permeable to small molecules, such as those of the water and retain the larger molecules such as those of the oils or fats.
- Thermal treatment of emulsions has a two fold purpose. First, increase in temperature reduce viscosity of the mixture, allowing faster film flowing and separation of water from oil. Secondly , increase in temperature allows for better chemical mixing and neutralization of the stabilizing factors of the emulsion .
This is where CFD can help companies in the stage of the design of an Oil Water Separator, saving costs and increasing drastically the efficiency of the system. MFX can reproduce accurately and with short time the process of oil separation via a mechanical system, as shown in the picture below.
Designing of the geometry is done with the help of CAD tools with the specifications from the client, or geometries can be imported directly if the client has already their own.