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The basic principle of difference in gravity between the phases (liquid – liquid or solid – liquid) is employed in an OWS in separation of the two phases. This phenomenon is defined as “Gravity Separation”. It is therefore apparent that the phase with high density will settle and with lower density float to the surface of fluid. In an OWS, the effectiveness of this technique is subjected to various factors such as difference in the density, viscosity, factors of the medium, temperature, turbulence, and also the nature of impurity etc. In some cases chemical coagulation and flocculation is needed for removal of the impurity by making them heavier or lighter.
In separation technique while considering the above referred factors, which affects the separation of impurities, an overflow rate (m3/m2/day) or settling velocity (m/hr) is arrived at. This factor determines the surface area required for the gravity separation in an OWS. Incidentally it proves the fact that it is independent of the depth of basin. In Oily water treatment, tilted (placed in predetermined angles) plate packs are used in CPI/ TPI separators to improve the size and economy of the separator system. As corrugated plate pack are predominantly used, the tilted plate pack type separators are widely known as Corrugated plate interceptor or simply as CPI separators. However, a TPI (Tilted plate interceptor) may use a corrugated type plate pack or simply plain parallel plate pack. Hence, TPI separator is a generic terminology used in such type of separators. The separator when used in separation of liquid – liquid phases (predominantly removal of free oil in oily water treatment) are called a TPI (Tilted plate interceptor) or a CPI separator. Any separation of suspended solids in oily water treatment by use of CPI (Corrugated plate interceptor)/ TPI (Tilted plate interceptor) separator is incidental due to difference in gravity between the effluent’s liquid phase and the solid phase. The Tilted plate pack (CPI) separator offered by Paramount with technology acquired from M/s. PWT, Holland provides an extensive reduction in surface area requirement of a separator by introducing multi layer separation wherein area required is reduced considerably depending upon number of such layers. It is feasible to achieve almost complete removal of all the particles which would not have normally be achieved by a single large surface separator. This is possible because of considerable increase in the surface area of the unit, within the same depth. In most of the cases the plates are installed at an angle of 45°deg. or more and thus the separated material can be collected and removed by gravity. Principle of a TPI/ CPI separator in Oil – water separation (Oily water treatment)Highly efficient oil removal systems are required to recover maximum quantity of hydrocarbons for oily water treatment as well as to make effluent amicable for further treatment & also to meet the pollution control requirements. The existing API type units need vast extensions of the surface area to take care of oil globules of smaller size so as to meet these requirements.
An enlarged separating surface in a CPI/ TPI separator, as discussed earlier can be achieved by placing various smaller planes on the top of each other in a tank. If these planes are subsequently inclined in a fitted position, the oil/solids separated between the plates can be removed by gravity. This principle has been realized in the counter current TPI (tilted plate interceptor) or CPI (Corrugated plate interceptor) separator unit. The objective is not to disturb the particle size distribution of the separated phase. This system is preferably fed by gravity. However, separators are also successful in operation where in the influent flow is pumped from other locations by locating a buffer tank before the influent pass through the separator. The oily water flows into the interceptor through various components and oil gets separated as described below:
PWT was the first manufacturer to succeed in launching the CPI (corrugated plate interceptor)/ TPI (Tilted plate interceptor) separator in a commercial and technically attractive construction. Hundreds of complete advanced wastewater treatment plants have since been put into operation throughout the world. The compact design and the high separating efficiency (of the TPI/ CPI separator) which are so characteristic, for this gravitational system have unmistakably proven their value in practice in the course of the time.
The corrugated plate pack in a TPI/ CPI separator, used in Oily water treatment for removal of free oil, is the heart of our various purification systems consisting of number of parallel corrugated plates. A Plate pack is a housing of flat plastic plates (strengthened by resins) and stiffened by a frame made from plastic material (strengthened by resins) and/or stainless steel. The number of plates in a Plate pack is determined by in-house developed calculations, based on the long experience acquired by supply of the separators to various industrial applications. The number of plates per Plate pack is also factored to a certain extent on economy of size of the separator. The number of Plate packs per TPI/ CPI separator is calculated based on the effluent flow and its characteristics to the unit The liquid to be treated flows through the spaces between the Corrugated Plates in each Plate pack. Ideal condition for separation is achieved in the TPI (Tilted plate interceptor)/ CPI (Corrugated plate interceptor) separator by simulating a laminar flow condition through the plate pack. Much attention is also being given on the profile of the corrugated plates in the Paramount (PL) designed TPI/ CPI separator. The specific profile has been chosen by Paramount (PL) so that a smooth transfer and compaction of the separated particles is effected in the TPI/ CPI separator. In order to reduce the frictional resistance between the separated material and the corrugated plates to a minimum, particular attention is paid to the smoothness and hardness of the plate surface. The Corrugated Plates as well as the casing of the Plate Pack of TPI/ CPI separator are made from glass fiber reinforced polyester resin. This material is resistant to the most frequently used chemical additives and temperature. Paramount has specialized in design of TPI/ CPI separator installation in both RCC (Reinforced cement concrete) and steel basins. The selection of the basin of the TPI/ CPI separator is advised to client based on the basic requirement, adaptability, time and economy criteria envisaged in the Oily water treatment process installed.
Comparison of TPI vs API Oil Separator
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