Rigorous methods for multicomponent

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Rigorous methods for multicomponent distillation
process
General representation of an equilibrium stage as
a thermodynamic system
Stage j
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Rigorous methods for multicomponent distillation
process
1. M Material balance equations
- There should be C equations for each stage
2. E Equilibrium relations
- There should be C equations for each stage
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Rigorous methods for multicomponent distillation
process
1. S Summation equations
- There should be 2 equations for each stage
2. H Enthalpy H balance
- There should be 1 equation for each stage
MESH equations
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Rigorous methods for multicomponent distillation
process
Degrees of freedom analysis
Total number of equations N (2C3) Unknowns
3C
10
N(3C10)1
N itself
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Rigorous methods for multicomponent distillation
process
Thermodynamics relations
(Once we know temperature, pressure and
composition of a stream we can calculate
thermodynamic properties of the stream using
P-v-T equation of states and activity
coefficients models)
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Rigorous methods for multicomponent distillation
process
Design specifications
C
N(2C3)
Remaining unknowns
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Rigorous methods for multicomponent distillation
process
General solution strategy The idea is to
rewrite the first 3 of MESH equations so to
eliminate y and L
where
Note that these equations now contain only V and
x as unknowns
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Rigorous methods for multicomponent distillation
process
General solution strategy In matrix form
Given V and T values for each stage we can solve
this matrix for each component to obtain mole
fraction of component i in liquid phase at each
stage j (xi,j)
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Rigorous methods for multicomponent distillation
process
General solution strategy In a similar way we
can compose another set of equations using the
enthalpy balance
where
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Rigorous methods for multicomponent distillation
process
General solution strategy In a similar way we
can compose another set of equations using the
enthalpy balance
Given T, (xi,j), (yi,j) values for each stage we
can solve this matrix for each stage to
calculate vapour flow rate for the stage Vj
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Rigorous methods for multicomponent distillation
process
Complete design strategy
Specify
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Stage efficiency analysis
Step 1 Thermodynamics data and methods to
predict equilibrium phase
compositions Step 2 Design of equilibrium stage
separation Step 3 Develop an actual design by
applying the stage efficiency analysis
to equilibrium stage design