Time-Synchronized Digital Closed Loop Control

by | Sep 22, 2014 | Asset Management

Jim Cahill

Chief Blogger, Editor

The October 6-10 Emerson Exchange conference in Orlando, Florida is rapidly approaching. If you have, but are not taking full advantage of some of the digital field devices in your facility and will be joining us at the conference, you may want this session. Emerson’s Jonas Berge posted this thread [hyperlinks added] in the Refining track of the Emerson Exchange 365 community.

Jonas Berge Director, Applied Technology

Jonas Berge
Director, Applied Technology

I would like to draw your attention to the workshop “Petrochemical Plant Achieves World Class Performance using Time-Synchronized Digital Closed Loop Control” at Emerson Exchange.

HMC Polymer’s propane dehydrogenation (PDH) plant in Thailand started operation in 2011. The DeltaV control system was specially engineered with FOUNDATION fieldbus [FF] to meet the process licensor’s exacting demands for dynamic performance of control loops by using time-synchronized control-in-the-field for high performance. The session will explain the control architecture and approach taken to meet and exceed the performance requirements cost effectively. Also covered is how the same architecture is used for intelligent device management with the AMS system. Lastly, results and experience is shared.

The process licensor requires pressure and flow loops with a 250 ms control response period from input to output, not just in the controller itself, for tight control and to avoid heat damage. This is costly to achieve using 4-20 mA as an asynch controller must run much faster. Several fast loops are complex. Health, calibration, and configuration of hundreds of instruments must also be managed.

DeltaV with FOUNDATION fieldbus is used with control in the field devices for fast loops, digital and time-synchronized end-to-end from sensor to actuator; fast devices with powerful function blocks, bifurcation of cascade loops, control in the H1 interface card, and optimized communication for the complex loops. AMS Device Manager is used for instrument diagnostic alert management for all devices.

True 250 ms control response period was achieved resulting in tight control of heat and mass transfer equipment realizing high-quality propylene production with low operating cost enabled by low feedstock consumption and low energy usage. Project results included reduced wiring and plenty of I/O spare capacity. The run & maintain organization also enjoy efficiencies from device diagnostics.

For pressure and flow FF loops performs 10-15% better than a loop using 4-20 mA signals. It is most beneficial at slow [1 second] controller cycle time. This is significant if loops are run slow to decrease controller load. This in turn enables more loops per controller.

Session ID for this workshop is 5-2016.

We hope to see you in Orlando!

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The opinions expressed here are the personal opinions of the authors. Content published here is not read or approved by Emerson before it is posted and does not necessarily represent the views and opinions of Emerson.