FLASH DISTILLATION
PRINCIPLE
It is a special operation in distillation where a liquid mixture is heated & fed with a constant flow into a distillation equipment. This is a one-step operation where a liquid is partially vaporized, the vapours are in equilibrium with the residual liquid. The resulting vapor and liquid phases enter a phase separator – an equilibrium chamber – & the resulting vapours & liquid are separated & are drained separately. During the operation, the total pressure and temperature of the system, as well as the compositions of the two phases in equilibrium remain constant over time.
APPARATUS
The apparatus consist of pump which is used to force feed into a heating chamber. As a result feed gets heated. The other end of pipe is attached to vapour separator through pressure reducing valve. There is also provision for vapor outlet at the top & liquid outlet at the bottom. At the end of the process, the vapor will be in equilibrium with liquid.
WORKING
Due to pressure drop, the hot liquid flashes. The sudden vaporisation causes cooling. The individual vapor phase molecules of high boiling fraction gets condensed & low boiling fraction stay as vapour. After some vapour & liquid phase separate & achieve equilibrium. The vapour then escaped from vapour outlet & concentrated liquid from liquid outlet.
The mixture to be separated is fed from the feed tank (1) by a pump (2) through a heat exchanger (3) at pressure P3. Here, it is heated above the boiling point it would have at P5, the pressure inside the phase separator (5). The pressure of the mixture is then decreased by flowing it through a valve (4), so that it partially evaporates and yields a vapor and liquid phase with equilibrium compositions.
USES
It is used for components with large relative volatility.
It is most commonly used in petroleum refining industries.
ADVANTAGE
It is a continuous process.
DISADVANTAGE
Not suitable when nearly pure component is required.
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