Hydrocarbon Processing - November 2021 - 27

Special Focus Process Control, Instrumentation
and Automation
A. KERN, APC Performance LLC, Red Lodge, Montana
The path forward for process automation:
Multivariable control as core competency
In process automation, multivariable
control has always been considered an
area of specialization and a luxury for
those companies with sufficient scale and
resources to justify its high costs of ownership.
However, one of the key insights to
emerge from the past few decades is that
multivariable control is not a specialization.
It is, instead, a fundamental aspect
of virtually every process operation-ask
any operator or process engineer.
The question is not whether or not
a process has multivariable control, but
whether it is carried out manually (by the
operating team) or automatically (by a
method of automated multivariable control).
Moreover, multivariable control can
be more easily understood and readily
mastered by observing traditional manual
multivariable control principles and practices
throughout industry, rather than by
struggling with the conventional, highly
specialized multivariable control paradigm.
In the coming two decades, the domiactivity
will
nant
process
automation
most likely be multivariable control. Industry
has already undergone several decades
of multivariable control activity, but
the conventional paradigm (model-based
multivariable control and real-time optimization,
or MPC) has never evolved into
the core competency needed to meet industry's
widespread scalable needs. Much
work remains to be done, and more agile
tools are needed to do it.1
With traditional
manual multivariable control as a guide,
automated multivariable control
competency will finally emerge.
What is multivariable control? When
console operators make setpoint and output
adjustments to single-loop controllers
in the course of process operation, that is
FIG. 1. The basic method operating teams have always used for manual multivariable control,
which notably does not require process models or real-time optimizers. This method can be
automated to provide a less fragile and more readily mastered multivariable control tool.
Hydrocarbon Processing | NOVEMBER 2021 27
core
manual multivariable control. Operators
typically make multiple controller adjustments
in concert, with multiple constraint
limits and optimization goals in mind.
This is the most practical and intuitive
way to understand the role of multivariable
control in process operation-the
coordinated adjustment of groups of
related controllers for constraint management
and process optimization purposes-whether
carried out manually by
operators or with the aid of automated
multivariable control technology.
Operators make controller adjustments
based on many considerations,
including their training and experience,
feedback from process alarms, input from
process engineers and supervision, and
operating orders that typically flow down
the chain of command from daily sitewide
production planning and optimization
(PP&O) meetings. The entire operating
team works together in this way to
meet production and optimization goals,
while safeguarding reliable process operation.
This inherent activity can be found
in place on virtually every process operation
in industry because the multivariable
nature of most processes demands it, and
because it is actually the most natural,
effective, state-of-the-art way to manage
and operate complex industrial processes.
In this light, manual multivariable control
has always been a core competency of
the process industries, and each site's level
of success is dependent upon its ability to
master it. To take process operation, automation
and optimization to the next level,
automated multivariable control must also
become an industry core competency.
Model-based control and real-time
optimization. Model-based control and
real-time optimization are double-edged
swords. While powerful in concept, they
have proven to be too complex and frag

Hydrocarbon Processing - November 2021

Table of Contents for the Digital Edition of Hydrocarbon Processing - November 2021