(605a) Heat Transfer Investigation and Dynamic Simulation of Internally Heat-Integrated Distillation Column

Heat Transfer
Investigation and Dynamic Simulation of Internally Heat-integrated Distillation
Column

Li Chunli, Fang Jing, Qi
Junjie, Su weiyi, Li Hao

School of Chemical Engineering
and Technology, Hebei University of Technology, Tianjin 300130, China

Distillation is
the most widely applied process of separation in various chemical industries.
But it is quite energy intensive and accounts for 3% of the total industrial
energy consumption. The overall thermodynamic efficiency of this process is
found to be as low as 5-20%. Therefore several methods have been developed to
improve the thermal efficiency, such as heat pump-assisted distillation,
multi-effect distillation, vapor recompression distillation, and dividing-wall
distillation. Heat-integrated distillation column (HIDiC) is another attractive
distillation scheme, which has received considerable attention due to the high
energy saving potential by means of improving thermodynamic efficiency.
Compared with the conventional distillation column, the energy consumption
saving of HIDiC could be up to 30%-60%.

In
a HIDiC, the rectifying section and the stripping section are set as two
independent columns for a clear perspective, between which heat coupling could
happen. Specifically a compressor is used to increase the pressure of the vapor
from the top of the stripping section, which is then fed to the bottom of the
rectifying section. The liquid leaving the bottom of the rectifying section is
fed to the top of the stripping section after the pressure is reduced by a
throttling valve. Thus the rectifying section is operated under higher pressure
and temperature than the stripping section. A certain amount of heat is
exchanged between the two sections, and it provides the necessary internal
liquid flow for the rectifying section and internal vapor flow for the
stripping section. As a consequence, the heat duties of the bottom reboiler and
top condenser are reduced, and a considerable amount of energy is saved.

In this paper, the
heat transfer between rectifying and stripping section of a pilot-plant
concentric structured internal heat-integrated distillation column (HIDiC) was
investigated experimentally. The equation of heat transfer coefficient (U)
changing with the pressure ratio was regressed. The result shows that the
values of U decreased with the increase of pressure ratio. In addition,
a dynamic simulation was developed upon the HIDiC. The control scheme with
larger gain and smaller period was chosen to operate the HIDiC equipment. It
can be found that the HIDiC system can rapidly return to steady state when feed
disturbances occurred. In the process of continuous operation, good stability
and operability were observed.