- August 25, 2014
By Bill Lydon, Editor
They say, ‚ÄúWhat goes around comes around.‚Äù I think this is happening with Advanced Process Control (APC) and Model Predictive Control (MPC). There seems to be a renewed interest in APC, and the systems, while not trivial, seem to be easier to use and lower cost.
By Bill Lydon, Editor
They say, “What goes around comes around.” I think this is happening with Advanced Process Control (APC) and Model Predictive Control (MPC). A number of years ago there was a great deal of excitement around expert systems and APC. The excitement was fueled by technology and a great deal of hype. This is a common situation with technology. Applying APC and MPC solutions was very costly and required a great deal of expertise. There seems to be a renewed interest in APC, and the systems, while not trivial, seem to be easier to use and lower cost. These APC systems are optimized by calculating the ideal operating points to achieve a certain level of cost efficiency or performance. Multiple constraints are considered, and the goal is to maximize desired factors and minimize undesired ones.
Rio Tinto Alcan Experience
Terry Snow, Manager of Advanced Process Control at Rio Tinto Alcan in Queensland, Australia, presented on APC at the Honeywell User Group 2014. They replaced an early, advanced, real-time expert system with the Honeywell Profit Controller on top of an existing Bailey control system. Rio Tinto Alcan realized a positive return on investment and better production efficiency.
Profit Controller is a component of Honeywell’s Profit Suite for Advanced Control and Optimization and includes tools to design, implement, and maintain multiple input/multiple-output (MIMO) advanced process control applications. Profit Controller utilizes a dynamic process control model to predict future process behavior while minimizing manipulated variable movement to bring variables within limits or to set points. Honeywell’s Profit Suite is a collection of advanced process control and optimization products for managing control and optimization. Application examples range from improving regulatory loop control to globally optimizing an entire process plant.
Snow described their centralized APC group, which includes a steering committee with the general manager. He stressed that a successful APC program needs management support and ongoing efforts. Another important key related to management support is that large APC projects require significant additional field automation to be successful.
More powerful controllers allow more functionality and capabilities to be embedded. Siemens offers advanced process control functions blocks that come as part of PCS 7. They describe this as “democratizing Advanced Process Control,” by providing function blocks that allow users to flexibly design advanced control to meet unique needs. Siemens has an impressive set of lean and easy-to-use function blocks that reside in controllers. The function block library includes gain scheduling, Butterworth low-pass filter, lead-lag, feed-forward, PID tuning, Smith predictor, Fuzzy control and soft sensor/neural networks, and 4 x 4 MPC function block. At the 2014 Siemens Automation Summit, Siemens introduced the faster PCS 7 CPU 410-5H controller. It boasts a cycle time of up to 10 milliseconds/9 process tasks and floating-point operation at 0.135 µs. Making use of this power, a new 10 x 10 x 4 MPC function block was added with improved configuration software using fill-in-the blank screens.
Thoughts & Observations
Advanced control methods have followed a typical technology adoption cycle. Users had great expectations, but in many cases, desired results could not be achieved. A big issue with new technologies is they are initially difficult to use and require special training. Over time, they become refined and easier to use. A commercial example is DOS compared to Windows. I believe APC has become significantly refined and is easier to apply. As a result, users should consider it more often as a tool to increase efficiency. PLC-oriented vendors are approaching APC differently by providing building blocks for users to build more customized solutions. The good news is users are getting more cost-effective solutions that are easier to implement.
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