第十讲 平衡级分离过程

Degrees-of-Freedom Analysis (3)
Therefore,
V = CP 2 C P 4 P CP +6
E =P +CP 1 C 1 P CP +1 (4-4)
F V E =C 5
For example, if variables (zi, TF, PF, F, T, P) are specified, all the remaining variables can be calculated from the equations.
in which V is the number of variables, E
the number of independent equations. It should be pointed out that V does not count the thermodynamic functions which can be calculated from the intensive variables.
The calculations of single stage separation are made by combining material balance and energy balance with phase equilibria relations.
Degrees of Freedom
Gibbs Phase Rule
For a system at physical equilibrium,
the number of independent intensive
variables to describe its thermodynamic
state is given by Gibbs phase rule as
The variables to describe the physical equilibrium of a system are classified as intensive variables, which are independent of the size of the system, and extensive variables, which depend on system size.
Only a few of the variables are independent to determine the state of system. The number of the independent variables is called the degrees of freedom.
A,B
KA KB
yA yB
xA xB
1
yA yA
xA 1 xA
(4-4)
Binary Vapor-Liquid Systems (2)
While P has been specified,
T and zi can
change freely in single phase
regions but xi
F CP 2
(4-1)
in which C is the number of components,
P the number of phases.
For the vapor-liquid equilibrium of a
ternary system,
F 322 3
Degrees-of-Freedom Analysis (1)
For a system with feed streams and extensive variables, the phase rule should be extended by an general analysis of degrees of freedom as follows
F V E
additional variables (zi, TF, PF, F, Q, V, L) to describe the process state. And there should be independent equations for P molar normalizations, C(P -1) K-values, C component material balances and 1 energy balance.
Degrees-of-Freedom Analysis (2)
For a single equilibrium stage shown in the right figure, there are ຫໍສະໝຸດ BaiduCP +2) intensive variables to determine the phase equilibrium, and (C +P +4)
Binary Vapor-Liquid Systems (1)
For binary vapor-liquid systems, Gibbs phase rule gives
F CP 2 222 2
Then if T and P are specified, the phase
compositions (xi , yi) should be completely determined. And the relative volatility A,B (separation factor) is also determined .
全日制专Fi业rs硕t p士a研ge究生学位课程
传递过程 与
分离技术
面向应用的 专业基础课程
第十讲—平衡级分离过程
i10.1 单级分离过程
and
Flash Calculation
Introduction
The separation process by single equilibrium stage is one in which two phase in contact are brought to physical equilibrium and followed by phase separation.