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大家都知道aspen模拟i的关键在过程参数的选择上
关于热力学方程的选取，很关键。希望对学生朋友有用。因为我们没什么工程经验
When modeling mass transfer equipment, there are two key points to remember:
(1) thermodynamics is important; and (2) convergence is difficult.
The key decisions you must make are (1) what model to use for
the vapor phase activity coefficient and (2) what model to use for the liquid phase activity
coefficient.
The options for the vapor phase are relatively easy. Some of them are used in Chapters
2 and 3, because once you choose an equation of state, the vapor phase activity coefficient
can be determined. The options for the activity coefficient of the gaseous phase are: ideal
gas, Redlich–Kwong or Redlich–Kwong–Soave, Peng–Robinson, plus a few specialized
ones (i.e., HF hexamerization and Hayden–O’Connell).
In the liquid phase, the simplest option is an ideal liquid, with an activity coefficient
equal to 1.0. That choice leads to Raoult’s law, which may suffice for similar chemicals.
Other models include regular solution theory using solubility parameters (although not in
Aspen Plus), NRTL, Electrolyte NRTL, UNIFAC, UNIQUAC, Van Laar, and Wilson.
Characteristics of the models are:
. The Electrolyte NRTL is especially suited for acid gas adsorption, which includes the
removal of carbon dioxide and hydrogen sulfide from a gas stream. Refineries routinely
use this process when making hydrogen. This is also one way of capturing
carbon dioxide from a power plant to capture and sequester it.
. The UNIFAC model is a group contribution method that allows the model parameters
to be estimated using the molecular structure of each chemical. When experimental
data is not available, this is the only method that can be used.
. The UNIQUAC model uses binary parameters, which must be determined from
experimental data. Once found, however, the same parameters can be used in multicomponent
mixtures of three or more chemicals.
. Both UNIFAC and UNIQUAC can be used when two liquid phases or azeotropes are
present.
. The Van Laar options are less recommended in Aspen Plus; they are simpler to use
than the others, but less successful in general. In Aspen Plus the ease of use is immaterial
since someone else has created the program.
. The Wilson equation is an option if there is only one liquid phase, and it does handle
azeotropes.
Chapter 6 of the Aspen Plus manual gives a flow chart to help you pick the model to use
for your system. The decisions you have to make are
Polar or nonpolar?
Electrolyte or nonelectrolyte?
74 SIMULATION OF MASS TRANSFER EQUIPMENT
Real or pseudocomponents?
Pressure less than 10 bar or greater than 10 bar?
Interaction parameters available?
One or two liquid phases?
Vapor phase association?
Degree of polymerization?
This sounds pretty daunting, and it is. Fortunately, the Aspen Plus manual does give some
hints on useful choices for particular applications, some of which have been developed
especially for the application. A few of them are:
Oil and Gas Production (OIL GAS) – Peng–Robinson with Boston–Mathias a
function (PR-BM) or Redlich–Kwong–Soave with Boston–Mathias a function
(RKS-BM).
Refinery, medium pressure (Refinery) – Chao–Seader, Grayson, Peng–Robinson,
Redlich–Kwong–Soave.
Refinery, hydrogen-rich applications (Refinery) – Grayson, Peng–Robinson, Redlich–
Kwong–Soave.
Gas processing, hydrocarbon separations (GASPROC) – Peng–Robinson with
Boston–Mathias a function (PR-BM), Redlich–Kwong–Soave with Boston–
Mathias a function (RKS-BM), Peng–Robinson, Redlich–Kwong–Soave.
Gas Processing, acid gas absorption (Chemical and Electrol) – electrolyte NRTL.
Petrochemicals, aromatics and ether production (Petchem) – Wilson, NRTL,
UNIQUAC.
Chemicals, phenol plants (Chemical) – Wilson, NRTL, UNIQUAC.
Chemicals, ammonia plant (Chemical) – Peng–Robinson, Redlich–Kwong–Soave,
SR-Polar (Schwartzentruber–Renon).
Chemicals, inorganic chemicals (Chemical and Electrol) – electrolyte NRTL.
Coal processing, combustion (Coalproc) – Peng–Robinson with Boston–Mathias a
function (PR-BM), Redlich–Kwong–Soave with Boston–Mathias a function
(RKS-BM), or the combustion databank.
We have to compare your thermodynamic predictions with experimental data.but we are students.what shall we do? |
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发表于 2009-8-29 10:25:42
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