Distributed Control

DCS brings power to optimize unit operations

GE's Nexus control system is a fully configurable DCS that improves overall unit availability and provides simplified expansion capabilities for steam turbines and balance of plant equipment.

CG1506 ProdEx GEAcross North America, thousands of turbine power plants, paper mills and other unit operations are still controlled by antiquated systems that prevent them from improving efficiency, avoiding downtime and meeting regulatory requirements.

"There's a large installed base of turbines that may be using mechanical controls and need the opportunity to do optimization," says John Emery, product line leader, Control Solutions, GE Measurement and Control. "Some are 50-year-old mechanical controls; some are Mark I or Mark II systems from the 1960s and 1970s; some are old analog systems where it's hard to find spare parts.

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"In the United States, state and federal regulators are raising demands for emissions and efficiency. The old systems can't do it."

So GE's Measurement & Control business, a division of GE Oil & Gas, is now making the company's Nexus control system available in North America. Nexus is a fully configurable DCS that improves overall unit availability and provides simplified expansion capabilities for steam turbines and balance of plant equipment in power generation, renewable generation and pulp & paper, among other processing industries.

Built on GE's 50 years of control system experience using proven technology currently in more than 4,700 installed control systems worldwide, Nexus is already running many plants in the Middle East, Europe and Asia. "Now we're bringing it to North America," says Nate Martin, product line manager, Distributed Control Systems, GE Measurement & Control. "We realized customers wanted control systems that are more affordable, reliable and easy to configure on-site for DCS and steam turbine applications. Nexus replaces a lot of different products that are over-engineered."

The system includes flexible configuration and integrated software tools designed to provide centralized unit control, increased asset availability and reduced operational costs. "We've developed software modules and code around specific applications, with the toolsets and features to give value in the market," says Emery.

Engineered with special attention to diagnostic and redundancy features, the Nexus control system provides seamless integration of control and optimization solutions to improve communication speed and reliability; reduce forced and unplanned outages; extend the maintenance cycle; and minimize installation, training and overall operation costs.

"Flexible logic configuration can be done online to avoid excess system outage or shutdown," says Martin. "It's an adapted-for-purpose controller, with easy to drag-and-drop new functions. Logic can be configured online, with no need for shutdowns, which saves time."

I/O communication and power are distributed individually, enabling independent replacement of modules without a complete system shutdown. "Using a ring topography for communication and power allows I/O to be removed and replaced without shutdown," says Martin. "An embedded sequence-of-events module on the ring topology eliminates the need for a separate module and significantly improves the ability to track events."

The historian can be expanded without additional equipment, saving cost and allowing for more analytical capability. "The OptimumC HMI has an embedded historian so there's no need to buy that separately," says Emery.

A three-level system network provides real-time performance with high-speed data exchange between the controller and HMI. Non-critical information, such as data backups, is handled on a separate data highway.

The distributed architecture reduces impact from loss of system components so the loss of any one component does not affect the rest of the system. It also allows for optimization of available space by distributing control, I/O and HMI functions to different areas of a plant, eliminating the need to allocate a large, central area for installation. Each operator station further supports control, monitoring and configuration of the entire system. Additionally, the Nexus Control System provides a suite of integrated control solutions to customize the system to any site's needs.

System hardware and software are proven and robust. "The remote I/O works at -20 to 70 °C without losing any performance," says Emery. "It meets all the criticality requirements of NRC CIP 5. Cybersecurity is already considered; the modules are ready to meet it."

The system is new to North America, but globally, "It's already in 2,900 thermal applications," says Martin, "In 1,500 steam turbines and 1,200 DCS systems."

The company has wide experience with Nexus control system with other companies' turbines. "We've done more of those than of GE turbines," says Emery.

"Industrial and process industries rely on continued uptime and transparency in an increasingly competitive and digital market environment," says Terry Knight, general manager of control solutions, GE Measurement and Control. "With the Nexus control system, GE extends its expertise built into the Mark VIe to support balance of plant facilities for an advanced, reliable and cost-effective unit control system that gives operators a full view of system health."

For more information, visit www.gemeasurement.com

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