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Reducing Energy Usage in Extractive Distillation
Abstract
Butadiene 1:3 is separated from other C4-hydrocarbons
by extractive distillation in a
sieve plate tower. Prior to the development
work to be described, the pressure in the
extraction tower was controlled at a fixed
value. The tower pressure-boilup control loop
did not behave satisfactorily in the presence of
non-condensables which entered with the feed.
The capacity of the flooded reflux drum
condenser for the tower was limiting production
during summer months.
The tower pressure control loop was put on
manual. The pressure was allowed to drop to its
lowest attainable value for the existing
conditions of boilup and condenser cooling
capability. This manner of operation is known
as floating pressure control. By taking
advantage of the higher relative volatility at
the lower tower pressure, energy usage was
reduced and there was an increase in production
capacity. The tower operation at a lower
temperature reduced tower and reboiler fouling.
Substantial savings have resulted from these
improvements. The annual energy consumption has
been reduced by 25% and maximum productive
capacity is higher by 15%. The rate of tower
and reboiler fouling has not been fully
quantified but is greatly reduced. A more
stable tower operation has also contributed to
higher productivity and reduced energy usage.
Venting of non-condensables does not affect
tower stability and the operators have adapted
well to the new control strategy.
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Citation
Saxena, A. C.; Bhandari, V. A. (1985). Reducing Energy Usage in Extractive Distillation. Energy Systems Laboratory (http://esl.tamu.edu). Available electronically from https : / /hdl .handle .net /1969 .1 /93107.