The temperature - composition diagram is used for isobaric conditions. X-Y Diagram for Constant Pressure. X-Y Diagram for Constant Temperature. The process involves heating a feed stream and then allowing it to expand into a vessel maintained at low pressure. The above diagrams represent classical simple laboratory distillation, attributed to Rayleigh, 1903.
Heat is applied to vapourise some of the solution.
Now in a small time increment dt, vapour of m.v.c. composition y is given off. The amount of vapour given off is V kmol. The system typically adopted for continuous fractionation is shown below. A single stage of the continuous fractionation column is now considered for comparison. Consider a fractionating column of N plates, where the condenser and reboiler are counted as 'plates'.