GE’s New Control System Hits the Mark
Plant-wide control system yields multiple benefits at new power station in South Africa
South Africa, which weathered a severe power shortage last year, continues to face heavy demand on its energy infrastructure. A new power plant owned and operated by South African oil and Gas Company Sasol, will enable the company to increase its own on-site power generation capacity, thereby helping to reduce electricity demand on the country’s grid. The project supports Sasol’s commitment to energy self-sufficiency for South Africa.
Scheduled to enter commercial service by the end of 2009, the new 280 MW gas-fired plant is located at the site of Sasol’s synthetic fuels facility in Secunda, South Africa. It will provide power for the production of synfuels, with excess electricity sold to the grid. The Secunda project marks the first installation of GE Energy’s Frame 9E gas turbine technology in South Africa. GE has also signed a 15-year service agreement designed to provide long-term plant reliability, which in turn will enable Sasol to fulfill the conditions of its power purchase agreement and ensure a steady revenue stream. In addition to all maintenance activities, the service agreement includes around-the-clock monitoring and diagnostics of the gas turbines.
The gas turbines are designed to meet South Africa’s new reduction standards for industrial emissions. Initially, natural gas will be the fuel for the gas turbines, but future plans call for the use of low-flare gas for a reduction in emissions for the Secunda facility as a whole. Recent trends in the power industry call for reduced project execution cycles along with improved operability and maintainability of the power plant.
A key aspect of the Sasol project is the installation of a single control platform for unit and plant control, featuring GE’s newest control technology, theMark VIe control. According to the company, the single control platform improves integration, reduces system complexity, reduces start-up problems, reduces project cycle time and risk. With the tight coupling of the equipment, enabled by the control system, GE has indicated that they can provide operational benefits such as better fuel flexibility, faster start-up, improved turndown capability and enhanced grid response.
The integrated plant control system includes: main control room operator interfaces, engineering workstation and plant historian, turbine-generator control and protection system, plant distributed control system (DCS) cabinets, I/O cabinets and network switches. Having common control system hardware throughout the plant reduces spare parts and training costs, however, added value is found in the level of system integration achieved by having a single control system for all plant equipment. Operator productivity and operational awareness are increased through a common interface provided by a single hardware and software platform.
This allows the operator, from a single operator station, to access and perform critical operations for all systems of the plant, including balance of plant (BOP), electrical and gas turbines. Problems can be identified more quickly and resolved sooner with all of the process data, alarms, events and trend data in a single time-coherent database that is coupled with advanced system tools. The single database with time-coherent data in an integrated platform contributes to simplified life-cycle maintenance.
The ease of use and the time to identify and resolve issues are critical to proper operation. The common look and feel of operator screens, total plant access and advanced operation tools are enabling technologies for the plant operator. Integrated alarm management, diagnostic messaging and sequence of events (SOE) data contribute to the enabling technologies. The single time-coherent database adds to the richness of data and its associated management. Traditional integration of disparate plant and unit level controls is eliminated. This reduces system complexity, startup problems, commissioning time and project risk. The complete control system will have an integrated factory acceptance test to improve the quality of the delivered system and reduce the time and risk of installation. Maintenance and operations personnel become more knowledgeable in a single system than in a system requiring separate expertise of two distinct control systems. All of these features contribute to simplified life-cycle maintenance and training for the plant equipment and personnel.
The GE Mark VIe control is a flexible control platform. The Mark VIe control serves as a control and protection system for gas turbines, steam turbines and plant equipment. Its distributed architecture allows control equipment to be installed throughout the plant, interconnected with 100 MB Ethernet. The control and I/O can be provided with different levels of redundancy, simplex, dual or triple redundant configurations as needed for an application. The control system has a common time-coherent database.
Having a common database simplifies system configuration and provides quality data for operations and diagnostics analysis of the complete system. High-speed data recording is available to view system-wide operations. An operator can use a common trend to view signals from the gas turbine and BOP equipment. These advanced engineering and operation tools, based on a single database, are made available in a common toolset with access from each operator interface.
Implementing the Mark VIe control platform across the gas turbine and plant equipment improves the coordination of unit and plant controls. The advanced capabilities of the Mark VIe control coupled with advanced modeling capabilities of turbine and plant equipment allow for the implementation of advanced model-based algorithms. These algorithms provide better control within operating envelopes, which provide reduced operating cost and improved plant performance, reduced start-up times and emissions.