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November 2009

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Modern turbines

Paper packaging upgrade meets turbine control challenges

By Zbigniew Lemieszko and Jerry Kopczynski

Saturn Management Swiecie in Poland is an industrial power outsourcing company responsible for the management of electricity and heat generation assets to cover energy demand of the Swiecie paper manufacturing plant. Since 2002, the company has been responsible for the upgrade of facilities, operation of the district heating plant, and supply of steam, electricity, and heat to the paper mill. But when an outage threatened production, they went into modernization mode with a whole new steam turbine, meeting stringent requirements for operators.

Mondi Packaging Paper Swiecie S.A. is a Poland-based paper producer with more than 90 production facilities in 30 countries and 16,000 employees. The company produces paper-oriented products from ordinary paper to card paper and paper bags, as well as operates as a packaging specialist for containerboard, corrugated packaging solutions, craft paper, industrial bags, extrusion coating, release liners, and consumer flexible solutions. The company concentrates on producing paper seeing use for cardboard production, covering Kraft liner, test liner, extra top liner, semi-chemical fluting, fluting fresco, and waste-based fluting paper, as well as bag paper including standard, half-stretch and stretch bag paper.

Power plant goes modern

During an outage at the district heating power plant at the mill in Swiecie, plans to modernize included a new steam turbine and replacement of the originally installed turbine mechanical control system with a modern electro-hydraulic system.

During the outage, the district heating power plant replaced the turbine-generator and upgraded the obsolete turbine control system and the generator’s automatic voltage regulator.

The electronic scope included a redundant turbine controller, 3-channel turbine protection system, non-redundant turbine auxiliaries’ controller, two operator stations, and a redundant link to the plant DCS. The main components of the hydraulic scope included new inlet and extraction steam stop, steam flow and temperature control valves, and 3-channel turbine trip block.

Tall turbo-generator task

The main task of the turbo generator (TG1) was to supply process steam to the paper mill. The technological demand, variable steam flow, and temperature required developing complex algorithms for the turbine control system.

The installed system at the Mondi paper mill supports:

• Bumpless switching from active to back-up processors and back
• Deterministic, redundant data highway data bus
• Possibility of replacing online components of the system
• Possibility of program and parameters modification online
• Remote troubleshooting support through a high-speed Internet connection, allowing service engineers to immediately remedy problems without the delay of traveling

The TG1 turbine is not a typical steam turbine because of the stringent requirements of the paper mill. Its design was based on a standard reaction, single casing, backpressure, and double extraction machine. Live steam from the 870 psi header feeds the turbine through one main stop valve and three control valves. The extraction’s steam pressure reduction and cooling station feeds the 188 psi collector. Turbine exhaust supplies steam to the 87 psi collector.

The new TG1 turbine design included backpressure turbine only; 100% of steam feeds the 87 psi collector, and the extraction butterfly valve is closed. With the extraction/backpressure turbine, extraction steam feeds the 188 psi collector, and extraction supplies steam to the 87 psi collector.

Modes of turbine operation

• Parallel operation of the steam turbines TG1 and TG2 or TG4. Turbine TG1 provides controlled reduced pressure steam from the chemical recovery boiler. Turbine TG2 or TG4 maintains steam pressure in the 188 psi and 87 psi collectors. TG1 turbine does not participate in maintaining steam pressure in either collector.
• The leading turbines TG2 or TG4 are not operating. Only the TG1 turbine feeds both steam collectors and maintains steam pressure in the 870 psi header, but it does not control steam pressure in the 188 psi and 87 psi collectors.

Several years ago, the turbine manufacturer developed standard software packages for particular types of turbines and specific controls functions. These packages were defined as the standard process function plans (PFUPs), and they are available now from the matrix. The vendor’s engineers in Poland selected the standard PFUPs, modified them as necessary to fulfill the paper mill process requirements, and discussed with the mill process engineers. Then the vendor’s electronic engineers coded them to the function plans, which were loaded to the system’s processors. Finally, the fully assembled electronic control system was connected to the process simulator tested and tuned.

Electronic turbine control system

The installed steam turbine control system is a modular and open architecture turbine control platform designed around industry standard PLC hardware. The turbine controller is offered in simplex and redundant configurations and is coupled with a human-machine-interface platform.

The design of the electronic system keeps in mind the needs of today’s steam turbine operators. With an aging fleet of turbines, and an obsolescent fleet of control systems, the selected system was the ideal solution for turbine control retrofits. The controller technology and a standardized system design make it the preferred choice for the power plant control systems requirements.

The 32-bit digital control system processor is based on industry standard PLC products, readily available worldwide. The system input/output (I/O) is built up in standard 19-in rac-mounted modules, or optionally as modular blocks of configurable remote I/O.

Redundancy is built into the system at the processor level. A standby processor runs the same logic and application code as the primary processor and is synchronized with the primary processor’s memory during operation. This configuration allows for bumpless transfer to the standby processor at any time in the case of a failure in the primary system. They connect to both processors through a redundant control bus.

This system is designed for 3-channel turbine protection (a fault-tolerant system preferred and standard with today’s control systems). The advantages of the 3-channel protection system are increased reliability, improved equipment maintenance flexibility, online replacement of components, and online protection system testing.

Programming, engineering station

Programming of the processor and hardware configuration is accomplished through a software application running on the engineering station (Windows-based personal computer). The programming language is developed in ladder diagram logic with customized functionality applied as C-Program blocks and parameterized sub-routines. This flexible and user-friendly programming environment allows for online debugging, tuning of parameters, and processor source code editing.

The human machine interface (HMI) package coupled with the turbine control system is a Windows-based application with true distributed client/server architecture. Applications range from small stand-alone systems to large networked configurations for a complete power plant. The use of industry standard technology means the HMI application is an open, expandable system easy to develop and maintain. The HMI software has extensive flexibility for alarms, data management, and reporting. This allows full customization of the HMI to the site-specific needs.

The following functions are part of the installed HMI application:

• Supervisory control: Rapid process monitoring allows quick response to plant issues
• Advanced alarming: Reliable, flexible, and easy-to-use system, with unlimited alarm areas, exception-based alarms, alarm priorities, and remote management of alarms
• Data management: Ability to collect and manage data, store historical data, and export data to common databases
• Historical data: Automatic and long-term means of sampling, storing, and displaying process data
• Reporting: Client/server architecture and plug-and-solve capabilities allow for multiple reporting options

The back-up LCD touch-up panel provides operator’s access to the control system in case of the primary operator station’s failure. The LCD touch-up panel can see use as a second operator station.

ABOUT THE AUTHORS

Jerry A. Kopczynski (jerry.kopczynski@power.alstom.com) is a product line manager at Alstom Power in Midlothian, Va. Zbigniew Lemieszko (teresabejgier@pepsa.com.pl) works at Saturn Management, in Swiecie, Poland.

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