ie502516y_si_001.pdf (1.13 MB)
Operation of Dividing-Wall Distillation Columns. 3. A Simplified Double Temperature Difference Control Scheme
journal contribution
posted on 2014-10-15, 00:00 authored by Yang Yuan, Kejin HuangAlthough
the double temperature difference control (DTDC) scheme
outperforms the temperature difference control (TDC) scheme in controlling
dividing-wall distillation columns (DWDCs), four additional temperature
measurements are required and result in a more expensive and complicated
control structure. In order to overcome its drawbacks and still keep
its advantages, we proposed a simplified DTDC (SDTDC) scheme, which
includes two temperature control (TC) and two DTDC loops. While the
two TC loops are designed, respectively, to regulate the top and bottom
products, the two DTDC loops are designed to control tightly the prefractionator
and intermediate product. The design strategy makes deliberately use
of the operating characteristics of the DWDC and can consequently
facilitate its product control and robustness to the operating condition
changes. The control of a DWDC, fractionating a benzene/toluene/o-xylene mixture, is studied to compare the SDTDC scheme
against the TDC and DTDC schemes. Although sharing an equal number
of temperature measurements, the SDTDC scheme is superior to the TDC
scheme with comparable or even reduced static offsets in the three
products and enhanced capability of handling feed composition disturbances.
The SDTDC scheme leaves slightly greater static offsets than the DTDC
scheme, but its reduced cost and alleviated complication justify it
to be a competitive alternative for the operation of the DWDC. The
SDTDC scheme can be further reinforced through the formation of TDC
loops in the rectifying and/or stripping sections with the available
temperature measurements in the two sections along the dividing wall,
and this increases the diversity of the proposed control strategy.
A systematic approach is given to search for the tight control scheme
for the DWDC with as a small number of temperature measurements as
possible.