Table of Contents
What does minimum reflux ratio in a distillation column results in?
The Minimum Reflux Ratio (R min) is the lowest value of reflux at which separation can be achieved even with an infinite number of plates. It is possible to achieve a separation at any reflux ratio above the minimum reflux ratio. As the reflux ratio increases, the number of theoretical plates required decreases.
How does reflux ratio affect reboiler duty?
On increasing the reflux ratio up to 5.5, the heat load on reboiler duty increases upto 2600000 kW. If the reflux ratio is further increased then there is no significant effect of the reflux on reboiler duty is seen. At reflux ratio of 7, the purity of the bottom product increases up to 90\%.
How does reflux ratio affect condenser duty?
9.9. The higher the reboiler duty, the higher the overhead condenser duty. This gives a higher reflux ratio and thus a smaller column with fewer trays. The lower the reboiler duty, the lower the reflux ratio will be and thus the tower must have more trays.
How do you choose reflux ratio?
The total cost, which is the sum of fixed cost and operating cost, must therefore passes through a minimum. The reflux ratio at this minimum total cost is the optimum (or economical) reflux ratio. Typically the optimum reflux ratio is approximately 1.2 to 1.5 times Rmin.
What is reflux ratio at total reflux?
The Reflux ratio is the ratio between the boil up rate and the take-off rate. Or in other words, it is the ratio between the amount of reflux that goes back down the distillation column and the amount of reflux that is collected in the receiver (distillate). Instead we call this “total reflux” or equilibration.
How is reboiler and condenser duty calculated?
Then you can calculate heat duty by the following equation.
- For cooling or heating or for no phase change, heat duty is calculated by:- Q=m*Cp*∆T.
- For condensation with subcooling, heat duty is calculated by :- Q= m*λ + (m*Cp*∆T)
- For reboiler ,heat duty is calculated by:- Q=(m* λ)*1.05 (considering 5\% heat loss)
How can we reduce reboiler duty for a distillation column?
Installing a feed preheater is a very common process option to minimise reboiler heat duty. If the feed preheater can be integrated with other valuable process streams (as a heating medium), overall energy efficiency of the distillation system can be improved further.
What are the minimum and maximum reflux ratio?
The reflux ratio at this minimum total cost is the optimum (or economical) reflux ratio. Typically the optimum reflux ratio is approximately 1.2 to 1.5 times Rmin.
How does reflux improve distillation?
Reflux in industrial distillation Inside the column, the downflowing reflux liquid provides cooling and condensation of the upflowing vapors thereby increasing the efficiency of the distillation column.
Can minimum reflux ratio be less than 1?
In the case where all the reflux is collected as distillate the reflux ratio would be 0:1. If no distillate is collected then a reflux ratio is not assigned. So higher reflux ratios usually mean higher purity of the distillate. It also means that the collection rate for the distillate will be slower.
What is a good reflux ratio for distillation?
In practice, values of 110-150 per cent of the minimum reflux ratio are used although higher values are sometimes employed particularly in vacuum distillation.
What is the optimum reflux ratio (R0)?
The Optimum Reflux Ratio (R 0) is that at which the total cost of the distillation is a minimum, taking into account the capital cost of the column (which depends on the number of theoretical plates) and running cost, which depends on the reflux ratio. Note that the capital costs of the reboiler and condenser also depend on the reflux ratio.
What is the relationship between reflux ratio and number of plates?
As the reflux ratio is reduced (by taking off product), the number of plates required increases. The Minimum Reflux Ratio (R min) is the lowest value of reflux at which separation can be achieved even with an infinite number of plates. It is possible to achieve a separation at any reflux ratio above the minimum reflux ratio.
How does the reflux ratio affect the capital and operating costs?
Increasing the reflux ratio from Rm therefore affects the capital and operating costs of a column as follows: (a) The operating costs rise and are approximately proportional to (R + 1). (b) The capital cost initially falls since the number of plates falls off rapidly at this stage.