Model-Free Adaptive Control
of Batch Reactors
|• Automatically controls reactor temperature
during all batch stages, process dynamics changes,
||• Safer and smoother operations, higher
quality and yield, and less intensive labor.
|• Robust MFA controller protects reactor
temperature from running too high or too low during
||• Enables automatic control of reaction
tempera-ture with user defined temp boundaries.
|• SISO MFA adapts between heating and cooling
||• No controller manual tuning is required.
Left: Cascaded MFA control system
with a Robust MFA as C1 to control reactor temp and
MFA as C2 to control the steam and cooling
water flow using the control output split-range design.
Right: Configuration menu of Robust
MFA. Users can define the Upper and Lower
bounds for reactor temp with related gain ratio to protect
the temp from running too high or too low.
Chemical Batch Reactor Automatic Control Solution
Batch Reactor: Chemical
batch reactors are critical operating units and automatic
control of the reaction temperature is desirable. Due
to its complex nature, a large percentage of batch reactors
running today cannot keep the temp in auto-matic control
throughout its entire operating period. This results
in lower efficiency, wasted manpower and materials,
and poor product quality.
Batch Stages: An exothermal batch reactor
has 4 operating stages:
1. Startup Stage: ramps up the reactor
temperature by use of steam to a pre-defined reaction
2. Reaction and Holding Stage: holds the temperature
by use of cooling water while chemical reaction is taking
place and heat is being generated;
3. No-reaction and Holding Stage: holds the temp by
use of steam after main chemical reaction is complete
and heat is not being generated;
4. Ending Stage: ramps down the reactor temp for discharging
Problems: During the transition period
from Stage 2 to 3, the reactor can change its nature
rapidly from heat-generation to heat-consumption. It
happens without any triggering signal because the chemical
reaction can end at any time depending on the types
of chemicals, their concentration, catalyst, and reaction
temperature. Within a very short period of time, the
reactor temperature can drop significantly.
Objectives: The control system must
react quickly to cut-off the cooling water and send
in a proper amount of steam to drive the temperature
back to normal. PID cannot control the temp during this
transition if it is tuned to control the process for
Stages 1 and 2. Typically, reactors are switched to
manual control and rely on well-trained operators during
Solution: To avoid or ease this tedious
task and improve product quality and yield, a Robust
MFA and a SISO
MFA based cascade control system provides
an effective solution.
Split-Range Control: Since steam and
cooling water are used to maintain the reaction temperature
during different heating and cooling stages, split-range
control is used. Because this can cause large process
gain changes, a SISO
MFA is well suited to control this loop
and requires no manual tuning.
Plant Safety: Since an exothermal reactor
can be a run-away process, great caution has to be taken
in using an automatic control system. All plant safety
procedures including manual override, safety shutdown,
watchdog flags, safety alarms, backup valves, onsite
operator monitoring, and redundant control sys-tems
and I/Os are still critical.