Condensation Process

Phase-change operations play an important part in major industrial chemical process, which material is transferred from one phase (gas, liquid or solid) into another. Some of the examples of phase-change operations are freezing, melting, evaporation and condensation. Condensation is a physical process whereby a substance changes its state from gas or vapour state to liquid state. Condensation usually can be achieved by lowering the temperature or compressing the gas. When the gas has condensed, the liquid product is referred as the condensate. Condensation appears everywhere around us, such as the formation of clouds, fog, mist, dew or frost, which depend upon the physical conditions of the atmosphere.

Condensation process is important in industrial operation due to several reasons. It involves transfer of heat during the process, which is applied in the operation of refrigeration systems. During condensation, the latent heat of vaporization of the substance will be released. Besides that, condensation is also an important component of all distillation processes, which is used in laboratories, as well as large-scale distillation operations. Some of the examples are those in chemical plants, petroleum refineries, and alcohol distilleries. It is used to separate substances within a mixture from one another.

There are two main categories of condenser used in industry, which are total condenser and partial condenser. They are differentiated by the extent of condensation. In a total condenser, the vapor inlet is entirely condenser. The composition of the liquid condensate leaving the condenser is same as the input vapor composition. There will be no separation achieved in this process. Therefore, a total condensation is not counted as a separation process. In a partial condenser, the inlet vapor is only partially condensed. The compositions of the three streams (feed, vapor outlet and liquid outlet) are different. Normally, uncondensed gases will be in equilibrium with liquid condensate. Therefore, a partial condenser is usually used as a vapor-liquid separation device for gaseous mixtures. It can only be used if the difference in boiling points of the substances is large enough to make only one of them to be condensed into a liquid essentially under suitable conditions, i.e. the system contains single condensable species.

In practice, both the temperature and pressure of a condenser can be adjusted to suit different composition of products desired. Atmospheric pressure is usually chosen as the operation condition since it is more cost-effective. However, if the two conditions are fixed, cooling requirements of the condenser will be another way to adjust the compositions of products.

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