CONTROL SYSTEM RETROFITS

OEMS AND INDEPENDENTS HAVE THEIR SIGHTS SET ON AGING UNITS THAT ARE NEARING OR EXCEEDING INITIAL SERVICE CONTACTS

The retrofit market for gas turbine (GT) and compressor control systems is poised for a major boom. Systems sold during the GT bubble of the nineties and early 2000s are ready for an upgrade, not to mention even older systems equipped with analog controls or electromechanical governors.

“The average life cycle of many OEM controls are in a 10- to-15-year time frame,” said Clark Weaver, Manager of New Product Introduction, Wood Group GTS. “Some sites are one failure away from being down indefinitely and are not aware of it.”

The battle to serve this burgeoning market is being waged by OEMs, such as GE and Siemens, looking to persuade users to upgrade their original control systems, and independent suppliers, such as Wood Group GTS, Invensys, Tri-Sen, Young & Franklin and Emerson, offering users the option of switching to open architectures and newly manufactured replacements.

OEMs are urging users to stay with their controls for the life of the turbine or compressor. The basic logic is that the hardware and controls are designed to work in harmony. As turbine and control engineers work together, OEMs say that their controls can be counted on to work best on their own machines.

Independents, on the other hand, argue that users of OEM systems may be deprived of software logic, have no alternative to expensive spares and support, and may be forced to comply with programmed life cycle management. Whereas, the open philosophy lets them support their units as they desire.

They also claim to provide users with functionality and upgrade options that the OEM either resists, charges more for, or doesn’t provide. Users can modify control functionality, they say, particularly as it relates to operations criteria or auxiliary controls to improve flexibility or deal with sitespecific issues that are hindering operations. This, they claim, can be achieved without jeopardizing turbine safety or critical control and protection logic.

Wood Group GTS, for example, has released a control system upgrade for the GE LM6000. The market potential is significant: More than 1,000 LM6000s have been shipped since the unit was introduced in 1991. The Wood Group GTS system can replace the original LM6000 hardware and software whether it employs NetCon, Micronet, GE Mark V or GE Mark VI platforms.

Wood Group GTS uses the Rockwell PlantPAx process automation system, which has been installed in over 500 installations. It operates in a similar fashion to a PLC-based system and can be expanded to plant-wide controls.

Similarly, ABB’s Symphony controls system is being used to upgrade Pratt & Whitney FT8 TwinPac turbines located at Iberdrola’s Klamath Cogeneration Facility. The retrofit included the design and implementation of enhanced control logic and graphics, development of the advanced surge protection module, startup and commissioning.

Wear and tear

When an original control system is configured and tuned properly, turbine performance and starting reliability are good, said Laurence O’Toole, Director of Turbine Business Development for Emerson Process Management’s Power & Water Solutions. “Over time, though, performance can degrade due to equipment wear and tear and changes in plant operating parameters,”

When that happens on a turbine using an older, OEM control system, said O’Toole, it can be difficult to see exactly what the control system is doing, and to adjust its operation. “The calibration of a fuel system, for instance, may involve a complex set of steps requiring detailed technical training,” he said.

Upgrading to a modern controls platform with integrated predictive diagnostics can give users a clear window into their turbine generator operations, allowing them to analyze and modify control strategies, added O’Toole. For example, owners today may wish to switch from base load to faster starts, yet older systems may not have the programming logic to implement these improvements.

“Many OEM control systems lack the flexibility to allow the user to add a new function or expand performance,” said Daren Zahabizadeh, senior turbomachinery engineer, Invensys Operations Management. “Users should compare features of platforms and select the best platform based on that comparison and on an assessment by the engineers who will implement it.”

The Invensys Triconex platform is OEMindependent; the same controller can be used on different turbines and compressors regardless of size or brand. The user has one platform to deal with for all turbines. Invensys believes that non-OEM control retrofits are generally more capable of handling system complexity, having a greater capability to tightly coordinate and integrate the many interactive plant subsystems.

An example is a control retrofit and upgrade for an extraction steam turbine-driven generator. By exchanging control set points, control measurements, and control output positions, it can coordinate with other generator controls and electrical distribution controls, enabling the user to put as much of the low-pressure flow as possible through the extraction steam turbine.

In the event of a generator trip, the turbine control can instantly feed forward the steam flow demands to the appropriate pressure- reducing valves and boiler controls without waiting for the process to move away from the control target levels.

“The general rule for defining the scope of the control upgrade project is to keep to a minimum what has to be changed to achieve objectives without replacing or trying to fix anything that is not broken,” said David Brown, Consulting Application Engineer at Invensys Operations Management.

Better parts

One difference between the controls systems of today compared with those of the last millennium is better parts, due in large measure to improved manufacturing. This, combined with improved internal diagnostics, has lead to higher availability for users. Another area where controls systems have improved is in the rate at which they are able to update and assimilate process data. This opportunity to “see” the process and react in real time allows users to more comfortably run closer to the limits of their machinery.

Higher processor speeds also provide much higher resolution for data acquisition. And high-resolution data acquisition provides the ability to reconstruct machinery or process problems to determine the root cause.

“Newer controls have more high-bandwidth communications, allowing more complete integration of the machine control and information with the plant control system,” said Jim Jacoby, Vice President, Tri-Sen. “Many OEM’s are looking outside their organization for controls since this is not their core business.”

While turbine efficiency is determined by the mechanical condition of the turbine, maximizing output (operation exactly at temperature limit), minimizing combustor dynamics, and ensuring availability and reliability are closely tied to the control system.

Another take

OEMs have a different perspective, recommending users stay with their controls for the life of their turbine or compressor. “Our turbine and controls engineers work side-byside to build power generation solutions that perform best as a single system,” said James Van Wormer, GE Power & Water Controls Product Management. “GE controls are specifically built to run and improve the performance of GE equipment and plants.”

Van Wormer points out that the GE Mark VIe Control System is configured as a modular technology solution, to facilitate the upgrade process on a component-by-component basis. It is a control system developed for power generation applications and integrated across unit, plant, power conversion and safety controls.

This allows the user to take advantage of the full potential of their equipment over the life cycle, he said, incorporating ongoing improvements that GE makes in turbine and control technology. These improvements increase output and efficiency of the equipment, improve reliability and reduce maintenance costs over the life of the asset.

“The ‘one system’ approach to plant control makes it simpler to install, operate and maintain,” said Van Wormer. “The operator’s productivity and operational awareness is increased with a common interface to operating data, advanced diagnostics and asset management tools.”

Siemens, on the other hand, utilizes the DCS-based SPPA-T3000 for turbine controls. It can be scaled for an industrial turbine island or control an entire plant. This system is said to be applicable for any turbine, any size, from any manufacturer, including gas, steam and hydro machines.

The SPPA-T3000 uses Siemens hardware and software components. At its core lie Embedded Component Services, which package all process-relevant data into every relevant component. This componentembedded approach allows all data to be available for operation, engineering and diagnostics. The SPPA-T3000 can run application software for turbomachinery on a classic PLC (S7400H) as well as on industrial PCbased controllers.

DCS Flexibility

“A dedicated turbomachinery controller had been necessary in the past to provide the required functionality combined with low costs, but it never provided the flexibility of a DCS for turbine controls,” said Jürgen Pernegger, Head of Turbine Controls Product Management, Siemens Energy. “SPPA-T3000 is a scalable DCS suitable for small applications, such as turbomachinery controllers, to large power plants."

The latest controls from Siemens can provide a simple 1-to-1 functional replacement of the old controls, he said, but they are also the basis for integrated solutions beyond turbine controls and protection, such as diagnosis, process optimization, simulation of turbomachinery and plants, as well as management.

“Siemens SPPA-T3000 is a system which will never become obsolete and can be easily migrated from previous Siemens turbine control systems,” said Pernegger. “We recommend our customers take advantage of a turbine manufacturer's expertise when it comes to turbine controls modernization.”

Pernegger expects control systems to move past the basics of governor controls and become a hybrid of a control and information system. Functionality, such as extended monitoring and diagnostic packages, which, in the past, was exclusively available for large DCS systems, will be available for industrial turbine islands as well.

Vanes and actuators

The retrofit market is also open to non-OEM vanes and actuators. Young & Franklin (Y&F) fuel control valves and inlet guide vane actuators provide turbine owners with as-new overhauls or newly manufactured replacements to facilitate upgrades to digital control systems at minimum cost, said Paul Boeckerman, Y&F Sales Engineer.

“Many turbine owners find upgraded control systems start-up more easily and automatically, provide more useful diagnostics to guide repairs and maintenance, and require less operator knowledge for central control rooms operating many unit processes,” said Boeckerman.

But he cautions users not to be dismissive of the latest OEM control system upgrades. “It’s a myth that upgrading the legacy OEM control system with a modern OEM control system is always a mistake.”

“Turbine owners should instead take extra care to consider the complicated tradeoffs between higher OEM costs and the benefits of third-party ownership. Many turbine owners have noticed that smaller third-party suppliers don’t have the deep pockets that ensure decades-long sustainability.”

“OEMs will be forced to abandon their exclusively proprietary hardware platforms,” said Boeckerman. “They won’t be able to withstand the price and performance pressure from generic off-the-shelf, hardware-based control platforms which are continually falling in costs, while increasing in speed, capability and programming flexibility.”

Looking ahead

When it comes time to upgrade, users should consider their plans for future maintenance of the control system, in-house support needs, the opportunity to reduce costs associated with spare parts and training, and compliance with requirements, said Emerson’s O’Toole. “Migrating the entire power block to a single control system, covering balance of plant as well as steam and gas turbines can simplify maintenance, training and security of cyber assets and drive improved plant reliability.”

He also sees the adoption of smart devices and digital bus technology as a way to pave the way for increased automation and predictive maintenance in power plants, along with greater usage of wireless technology.

In the future, a new population of operators that have grown up with laptop computers and personal electronic devices will run the power plants, said GE’s Van Wormer. “They will have less mechanical experience but much more savvy at using digital tools and software. This will drive new requirements for the interface between control system and operator, and tools associated with operation and maintenance.”

Correction: Our Nov/Dec cover story on controls said: “Woodward controllers … deceleration every 100 ms and perform a CPU …” It should have read “100 microseconds.”