Model-Free Adaptive Control
|•Manipulates inflow and outflow simultaneously.
||•Improves density control by at least 50%
reduction in variability.
|•Reduces over-drying the slurry.
||•Steam consumption is reduced.
to be started and maintained in automatic control.
||•Allows flexible production and reduces
load disturbances on the steam generation system.
|•Reduces product density variation.
and production efficiency is improved.
|•Improves efficiency & productivity.
||•Full investment is returned in months if
A multivariable MFA controller in CyboCon
software quickly and tightly controls
density and level by manipulating inflow
and outflow simultaneously. An MFA constraint controller
protects the evaporator level from running too high
or too low.
Model-Free Adaptive (MFA) Control Tames Zero-Discharge
at Tri-Valley Growers, Madera, CA, reported in Control
Tri-Valley is a zero discharge plant,
and processes its wastewater through a three-effect
evaporator to concentrate solids. In the first effect,
the water starts to evaporate. The second effect achieves
high density. The third effect produces a sludge solid,
evaporating water so it can be reused.
The two main variables to be controlled are outlet water
density, which controls density of the solid, and the
wastewater level in the evaporator. The two manipulated
variables are the inlet and discharge water flow rates.
Both affect water density and level. The process is,
by its nature, a multi-input, multi-output (MIMO)
The old system, using three PID controllers, was difficult
to start up and maintain in automatic control, and the
density loop frequently oscillated.
"The MFA contro ller is well-suited to this type
of application since it does not require a process model,
and can perform both adaptive and multivariable control,"
says Steve Smialkowski, process control engineer. "It
enables complex processes to be controlled without quantitative
process knowledge and identification, and eliminates
the need for controller design and complicated manual
Smialkowski reports that a new multivariable control
system using MFA improves evaporator control. Unlike
traditional self-tuning or model-reference adaptive
control systems, MFA is as simple as a basic feedback
control system. There is no model or identification
mechanism in the MFA system. For configuration, only
qualitative information such as the process acting type
and pro cess time constant are required. The system
allows operators to switch between PID auto, manual,
and MFA control modes with bumpless transfer. If a PC
goes down, the PLC assumes control.
"By implementing MFA, Tri-Valley Growers has achieved
much better evaporator control performance," Smialkowski
says. "Commis sioning was completed in one eighthour
The MFA controllers took over the control without any
bumps to the system. The evaporator can now be started
and maintained in automatic control mode, and the process
variables reach their setpoints quickly with little
overshoot. Smialkowski says, "The system stability
margin has been significantly increased, and variation
in product density has decreased more than 50%."