Title: Modeling and Simulation of a Distillation Unit.
Author : Ahmed Yehia Ibrahim Abd El-Kader
Collection : M.Sc. Chemical
Abstract:
The
methanol production process is a petrochemical industry that uses
distillation process in the purification of the crude Methanol.
Emethanex is a Company located in Damietta produces Methanol with 99.9%
purity using the distillation as the end process for the methanol
production. it consist of three towers : the Topping column separates
light ends as carbon dioxide and Methane from the crude Methanol to be
used in the process fuel, the Refining column produces about 50% of the
Metahnol production, the remain quantity is produced in the third tower
named the Recovery column.
A
mathematical model on the Recovery column based on some assumptions is
developed to calculate some parameters like the liquid flow rates across
the tower. The column consists of 74 stages, the reboiler is stage
number 1 and the condenser is stage number 74 named NT. Methanol is the
light component from the top of the tower, and is separated as product.
Water is the heavy component. It is separated at the bottom to be used
in other unit of the process.
The
comparing between the plant data and the Matlab calculated values shows
a deviation less than 10% for the liquid flow rates across the tower.
The model takes into consideration the dynamic equations.
A
simulation is done by HYSYS for the three towers in the steady state
mode and the dynamic mode. the steady state simulation shows the severe
effect of the changing in the rebolier duty in the composition of the
streams, for example: increasing of the reboiler duty from 1.900E+07 to
2.460E+07 increases the mole fraction of the Methanol in top from 0.5251
to 0.7645 in the Topping column, also the increasing of the reboiler
duty from 2.574E+08 to 2.974E+08 decreases the mole fraction of the
methanol in product from 0.9896to 0.6410 in the Refining column. This
means that the product is out of specifications. Also the steady state
simulation shows the great effect of the reflux rate on the product
purity; the decreasing of the reflux rate of the refining column from
2.500E+05 kg/h to 2.200E+05 kg/h decreases the mole fraction of the
product methanol from 0.9372 to 0.6347.
The
dynamic mode shows that the severe change in the process parameters in
controllers makes a big disturbance in the process, for example Changing
the set point of the TICRecovery controller that adjusts the Recovery
bottom temperature suddenly from 118 °C to 145 °C makes a big trouble
shooting and disturbance in the process, the controller returns to the
normal operation after 67 min, this is unacceptable in the real process,
the dynamic mode shows also the controllers response in normal
operation, some studies are created in the dynamic mode, for example the
increasing of the bottom temperature of the Topping from 85oC to 90 oC
increases mole fraction of the top methanol from 0.591642 to 0.7449,
this means that we lose product in the first tower. Other studies are
done on the dynamic mode.
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