Page 317 - Process Equipment and Plant Design Principles and Practices by Subhabrata Ray Gargi Das

11.5 Design illustration e fractionator 319

Based on heat of vaporisation and specific heat of components, estimated
Enthalpy of distillate vapour at 98 C ¼ 67,022 kJ/kg mol.

Enthalpy of distillate liquid at 90 C ¼ 12,227 kJ/kg mol.

Q c ¼ðR þ 1Þ D Enthalpy difference
¼ð2:336 þ 1Þ 521:9 ð67022 12227Þ¼ 95401295 kJ=hr ¼ 26500 kW

Reboiler load,
Q reb ¼ Q c þ Enthalpy leaving with D þ Enthalpy leaving with B Enthalpy entering with F

¼ 26916 kW
Note: Individual enthalpies are calculated based on the problem data.
Table 11.8 is worked out for various values of R/R m and it summarises the effect of R on the number
of trays. Corresponding condenser and reboiler loads can be arrived at from the base value at
R/R m ¼ 1.2, i.e., R ¼ 2.3359. The basic relationship is

; and
Q c ¼ðQ c Þ base case ðR þ 1Þ=ðR þ 1Þ base case Q reb ¼ Q c þðQ reb Q c Þ base case

Table 11.8 Effect of variation of reflux ratio.
Number of actual trays ðh [ 0:7Þ)
Total number of trays
considering one
additional tray for feed
R/R m R Rectification section Stripping section section
1.05 2.0439 7 3 11
1.10 2.1413 6 3 10
1.15 2.2386 6 3 10
1.20 2.3359 5 2 8
1.25 2.4333 5 2 8
1.30 2.5306 5 2 8
1.35 2.6279 5 2 8
1.40 2.7253 5 2 8
1.45 2.8226 4 2 7
1.50 2.9199 4 2 7
1.55 3.0173 4 2 7