A binary distillation column is to be designed using McCabe Thiele met...
It is evident from above figure that the operating line for the enriching section, corresponding to the minimum reflux ratio, passes through the point of intersection the equilibrium curve and qline.
View all questions of this test
A binary distillation column is to be designed using McCabe Thiele met...
Given Data:
- Distillate composition: 90 mol% of the more volatile component
- Point of intersection of the q-line with the equilibrium curve: (0.5, 0.7)
Explanation:
McCabe Thiele Method:
- McCabe Thiele method is used for the design of binary distillation columns.
- It involves constructing the operating line and equilibrium curve on a graphical representation of the mixture composition.
- The intersection of the operating line and equilibrium curve determines the number of equilibrium stages required for the separation.
Construction of Operating Line:
1. Draw a q-line from the feed composition on the diagonal.
2. The q-line represents the composition of the liquid and vapor leaving each stage.
3. The slope of the q-line is given by the equation: L/D = (y-x) / (x-α)
- L/D is the liquid to distillate ratio (L/D = (1-D)/D)
- y is the vapor composition
- x is the liquid composition
- α is the point of intersection of the q-line with the equilibrium curve
Equilibrium Curve:
- The equilibrium curve represents the relationship between the vapor and liquid compositions at equilibrium for a given pressure and temperature.
- It is obtained from experimental data or thermodynamic models.
Minimum Reflux Ratio:
- The minimum reflux ratio is the minimum amount of liquid that needs to be returned to the column to achieve the desired separation.
- It is determined by the point of intersection of the q-line with the equilibrium curve.
- The minimum reflux ratio occurs when the operating line is tangent to the equilibrium curve.
- At the point of tangency, the liquid and vapor compositions are the same (x = y).
- Therefore, the minimum reflux ratio occurs when the point of intersection of the q-line with the equilibrium curve is at (x, x).
Given Information:
- Point of intersection of the q-line with the equilibrium curve: (0.5, 0.7)
Calculating the Minimum Reflux Ratio:
- Since the point of intersection is (0.5, 0.7), the liquid and vapor compositions are the same.
- Therefore, the minimum reflux ratio is given by: L/D = (y-x) / (x-α) = (0.7 - 0.5) / (0.5 - 0.5) = 0.2 / 0 = ∞
Conclusion:
- The minimum reflux ratio is ∞, which means that an infinite amount of liquid needs to be returned to the column to achieve the desired separation.
- However, in practical distillation operations, a finite reflux ratio is used to ensure efficient separation.
- The closest finite reflux ratio to ∞ is 1. Therefore, the minimum reflux ratio for this operation is 1.