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As part of this general trend to use APC in various reduces process variance, plant operation can move
industries, there is an increased focus in implementing operating point to improve production margins while
APC to Industrial Powerhouses. Real time operation of considering all relevant constraints.
an Industrial Powerhouse with traditional technology The key to this technology is the use of a dynamic
requires management of many single-loop controllers. model of the process, used in real-time computing, to
How to handle all them to increase efficiency and estimate future trends.
effectiveness of production is not always easy to The calculation algorithm considers the process model
understand. A modern APC-based architecture, with and a structured set of targets like, as an example,
direct objectives set in terms of Powerhouse efficiency production and physical constraints and is able to
objectives is capable of optimizing production in all determine the optimal moves for the underlying single
conditions and, at the same time, reduce operator loop controllers.
workload. Over the years, APC technology has evolved from an
approach based on a matrix linking input and outputs
APC Technology dynamics, to a state space formulation, using a state
vector X to estimate future values for model outputs
As discussed earlier, the purpose of APC technology is to through the well-known equations:
manage the production process in a more structured and
efficient way, using multiple actuators in order to pursue a Where it is:
set of coordinated production targets. In practice APC • u inputs vector
systems do not operate directly on the actuators, but • y outputs vector
instead they interact with single control loops set point. • x state vector
This allows retaining benefits associated with the use of
the control loops on the DCS/PLC, like linearization of
actuator, fast response to disturbances etc.
ABB multivariable process control software, OptimizeIT
Predict & Control, uses state-space models to
implement real-time APC control in industrial process
plants.
Further details on the APC technology, its evolution and
benefits from state-space formulation can be found in
articles [2, 3, 4].
Fig. 1 - How APC A modern APC system uses an explicit model of the APC applied to Powerhouses
improves process process to estimate future behavior. Its ability to predict
control process future values (at least in the short term) allows As briefly mentioned, multiple, key technical points
handling of multiple targets and constraints explicitly. As favor use of APC technology in Powerhouses and
a result, application of this technology brings a reduction Industrial Power Plants. Among them are:
in the variability of key process variables compared to a • multiple process objectives, very often conflicting
traditional control strategy.
A reduction in process variability has an associated or partially conflicting;
value in itself but, even more interesting, we can use • configuration with multiple equipment in parallel
this to increase the profitability of production, for
example, by increasing production throughput or e.g. boilers, turbines, steam headers, very often
reducing production costs. with different efficiency;
We can summarize this concept is the figure 1: as APC • presence of multiple degrees of freedom;
• large values/costs at stake;
• different dynamics playing a role – from very fast to
slow ones.
APC on Powerhouses is nowadays a mature technology,
thanks to hundreds of installations in recent years.
Articles [5, 6] provides insight on a few APC
implementations on Power plants and Powerhouses.
Let us consider the case of an APC application at a
Sugar Beet refining plant. The refining process, where
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