Evaporator Start-up
The trend (left) shows solids levels
from the final effect of the evaporator,
with multiple starts overlaid on the
same trend. Despite the operator
running the plant cautiously, some
of the start-ups overshoot, recording
solids levels that are too high and
which will give rise to increased fouling
and compromised efficiency. When
the same evaporator is started with
advanced control (right), overshoot is
minimised and the time taken to reach
stable, on-spec operation is reduced by
as much as 40%. As well as improved
efficiency throughout the run, the
faster start permits much more agile
manufacturing with shorter turnaround
and less wasteful grade or product
changes.
Dryer Start-up
In this example, exhaust air
temperature gives an excellent
indication of the variability observed
during different dryer starts. Again,
the trend on the left is plotted from
multiple separate production runs and
exhibits a wide spread of control.
One of the main advantages conferred
by Advanced Control (right) is
greater consistency of operation – a
higher level of repeatability between
production runs, even when other
process disturbances are present.
For the dryer, MPC delivers a 50%
reduction in the time required to
achieve stabilised operation, defined
as temperatures and production rate at
setpoint, with expected product quality
being achieved. In addition, the time
to bring all six nozzles on line was
reduced by 16%. Again, this provides
far greater agility for dryers with a high
number of product changes in their
schedule, and more reliable, efficient
operation for dryers with longer run
times between CIP.
Perceptive Engineering Limited, Vanguard House,
Keckwick Lane, Daresbury Sci-Tech, Cheshire WA4 4AB, UK
www.PerceptiveAPC.com / [email protected] / +44 1925 607150
Issue 18 PECM
93