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Optimization of the reflux ratio for methanol–water stage distillation column

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Abstract

In this paper, the enthalpy-concentration method was applied in order to model a steady-state continuous methanol–water mixture distillation column. This work includes three steps; first, to develop a code in MATLAB v.7.6 to apply to the mathematical model of the column. The second step is to simulate the column using HYSIS v.3.2. While the third is the calculation of the optimized reflux ratio to minimize the operating cost. For a distillation tower such as the methanol–water splitter in this study, there are relatively few degrees of freedom that can be manipulated in order to minimize operating costs; the reflux ratio can influence the steady-state operating point and therefore the daily costs. In this paper, we have discussed the trade-offs between reflux ratios and operating costs. A correlation is derived to define the optimum value of the reflux ratio as an exponential function of a certain economic parameter of energy prices and depreciation costs. We demonstrate that, at low energy prices or high equipment depreciation costs, the optimum reflux factor is high.

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Abbreviations

C P :

Heat capacity at constant pressure (J g−1)

D :

Distillate rate (kmol h−1)

F :

Feed rate (kmol h−1)

G :

Vapor rate in enriching section (kmol h−1)

\( \bar{G} \) :

Vapor rate in stripping section (kmol h−1)

H :

Molar enthalpy (J mol−1)

L :

Liquid rate in enriching section (kmol h−1)

\( \bar{L} \) :

Liquid rate in stripping section (kmol h−1)

L 0 :

External reflux rate (kmol h−1)

M :

Molecular weight (g mol−1)

N act :

Actual number of trays

N min :

Minimum number of trays

Q B :

Heat added in the reboiler (kJ h−1)

Q C :

Heat removed in the condenser (kJ h−1)

Q tot :

Total duty (kJ h−1)

R :

Reflux ratio

R m :

Minimum reflux ratio

T :

Solution temperature (K)

W :

Residue rate (kmol h−1)

x :

Mole fraction of more volatile component in the liquid

y :

Mole fraction of more volatile component in the vapor

z :

Average mole fraction of more volatile component in the mixture of liquid and vapor phases

β :

Reflux factor

β opt :

Optimum reflux factor

λ :

Latent heat of vaporization (J g−1)

ϕ :

Economic parameter

Φ:

Operating cost parameter ($ h−1)

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Correspondence to Bahador Abolpour.

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Abolpour, B., Abolpour, R., Shamseddini, A. et al. Optimization of the reflux ratio for methanol–water stage distillation column. Res Chem Intermed 39, 681–692 (2013). https://doi.org/10.1007/s11164-012-0589-7

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  • DOI: https://doi.org/10.1007/s11164-012-0589-7

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