Power plant owners are seeking ways to deliver higher levels of performance, availability, and reliability while reducing installation costs and meeting increasingly rigorous environmental criteria. GE and its EPC partners are therefore focusing on developing plant designs and installation packages that reduce construction times and building size, while helping operational and economic objectives to be met. One such design is GE’s new 109FB Block 2 combined cycle power plant, an improved design with a reduced centreline height (from 8 m to 5.5 m) and reduced span, with a 5.5 m reduction in length. This reduced building size contributes to significant cost reduction. The new standard plant design also features a single plant-wide GE control system

Building on F experience

The new plant uses the 9FB gas turbine, building on extensive experience with F-class machines. With more than 1000 F-class gas turbines shipped and numerous F-class combined cycle power plants in operation worldwide, GE has applied a systems level perspective to the design of the new 109FB combined cycle power plant. GE and its EPC partners have integrated operating experience, emerging trends, and owner’s insights into development plans for the new plant design.

GE brought the very first F-class advanced air-cooled technology gas turbine into operation in 1988 at Virginia Power’s Chesterfield station, in a combined cycle configuration. The first 50 Hz F gas turbine, the 9F, went into commercial operation in 1992 at EDF’s Gennevilliers power station. Since this time, no OEM has installed more F-class combined cycle plants – greater than 400 sites globally – and no OEM has more combined cycle operating experience. GE’s total installed fleet of F-class gas turbines has surpassed 30 million hours of commercial operation; 16 GE F units have each exceeded 100 000 hours of operation.

The 109FB standard plant employs lessons learned from this extensive operating experience, as well as those from leading EPC companies.

GE’s 9FA is a mature product, with over 240 units sold, and 180 in commercial operation in over 25 countries. Collectively, there have been 7.9 million fired hours and 80 000 starts. The 9FB represents the latest evolution of the 9F platform, with 49 9FB gas turbines sold since its introduction.

GE’s F platform has the largest experience base across all operational profiles while yielding industry leading reliability, availability and flexibility in operation. Insights gained by millions of hours of experience have been successfully incorporated and demonstrated in current fleet operations as well as future designs’ reliability and availability. Simply stated, the 9F platform’s reliability and availability translates into more operational time and starting flexibility.

GE’s F-class availability and reliability advantage can be monetised into real financial benefit. A simplified rule of thumb is that 1 percentage point of availability benefit equates to $1-2 million per year operator value. On an NPV basis, this represents in excess of $10 million of benefit for a 109FB achieving 1 percentage point of availability benefit over the life of the plant.

While there are many measurement definitions for reliability and availability, as well as various claims for demonstrated levels, GE’s preference is to reference independent, third party published metrics. As reported by independent third party data source ORAP*, GE’s 9F was better than the industry average (to 3Q08) in terms of reliability, availability and starting reliability.

The 9FB is the latest evolutionary step in the development of GE’s proven F series of air-cooled gas turbines. Taking F technology to a new level of output and efficiency, we have applied cutting-edge technology, including materials developed for the H system and GE’s aircraft engines. The 9FB gas turbine represents the latest advancement in air-cooled technology from GE, with a growing fleet that includes 48 units in operation, installation, or on order. Building upon more than 32 million hours of F-class experience, the 9FB has current fleet experience of more than 195 000 fired hours and 3200 starts.

In developing the 9FB, GE followed a specific course that significantly improves the key driver of overall combined cycle plant efficiency – firing temperature. The FB firing temperature is more than 100°F higher than GE’s 9FA technology, driving a combined cycle efficiency increase in excess of 1 percentage point.

Economic uncertainties and industry dynamics have placed greater pressure on the operation of gas turbines. Higher fuel prices have driven greater cyclic operation; and increasingly stringent emissions requirements are pressuring the amount of time a turbine may operate. GE has taken several proactive steps in the 9FB design to address these dynamics and provide an operationally flexible gas turbine product.

In addition to providing lower NOx and CO emissions, the 9FB’s DLN 2.6+ combustion system provides increased operational flexibility for reduced cost of operation. This enhanced product builds upon decades of experience at the forefront of gas turbine combustion technology. The DLN 2.6+ combustion system combines leading-edge technology with design innovations to deliver sub 30 mg/Nm3 NOx (15 ppm) and 13 mg/Nm3 CO (10 ppm). The key feature of the DLN2.6+ configuration is the addition of a sixth burner, located in the centre of the five existing burners. The presence of the centre nozzle enables the DLN 2.6+ to extend its turndown well beyond the five-nozzle design.

Aerodynamically equivalent to the 9FA compressor, the 9FB compressor utilises the latest technology enhancements to provide greater tolerance for a broader range of operating environments. Building upon F-class operational experience, the 9FB compressor has increased stress margins, reduced wear characteristics, and greater damage tolerance, which lead to improvements in both system reliability and availability.

Improved steam turbine design

A main contributor to the reduction in building size achieved in the 109FB Block 2 combined cycle power plant (centreline height reduced from 8 m to 5.5 m and length by 5.5 m, as already noted) is the improved steam turbine design.

The 109A block two steam turbine features include a proven three bearing design and elimination of the low pressure diffuser.

It is an evolution of GE’s HEAT® steam turbine, introduced in 2002, with launch units having over 20 000 hours of commercial operation and the fleet over 100 000 hours.

The block two steam turbine is available in eight centreline designs, for both single-shaft and multi-shaft configurations and offers 42in and 48in last stage buckets. In conjunction with the 109FB block 2 standard plant, the first of the 109A block 2 steam turbines shipped in October 2009.

Plant level controls

The initial design of plant equipment and distributed control system (DCS) is a critical phase in the typical combined cycle project life cycle. Decisions made at this stage have a significant impact on the final implementation and overall schedule of the project. A standardised design and collaborative engineering environment are very beneficial.

System integration starts in the design phase, where it is important to define a plant control philosophy that reduces multiple systems and simplifies the design. A single control platform for plant and unit level control improves integration, minimises system complexity, and lessens start up problems and commissioning times, reducing project cycle time and risk. Tight coupling of equipment via the control system provides operational benefits such as better fuel flexibility, faster start-up, improved turn-down capability, and enhanced grid response.

The new 109FB plant design employs a single hardware and software control system, the Mark* VIe, across the gas turbine, steam turbine, generator, heat recovery steam generator, mechanical equipment, and electrical equipment.

The flexibility of the Mark* VIe system allows different levels of redundancy, depending on the system being controlled and protected, ranging from TMR (triple module redundant) for turbine control and emergency shutdown systems to dual control for balance of plant equipment. Simplification of the plant control system design involves the elimination of interfaces and third party control equipment.

Operator productivity and operational awareness is increased through a common interface provided by a single hardware and software platform. This allows the operator, from one single operator station, to access and perform critical operations for all systems of the plant, including balance of plant, electrical, gas and steam turbines. Problems can be identified more quickly and resolved sooner with all of the process data, alarms, and events and trend data in a single time coherent database that is coupled with advanced system tools. Having a single database with time coherent data in an integrated platform contributes to simplified life-cycle maintenance.

The combination of an advanced control platform, design knowledge of the gas and steam turbines, and plant design expertise, leads to improved power plant performance and operability, with a systems solution approach achieving improvements such as extended turndown or faster start-up.

Codes and standards

GE has a dedicated compliance and certification team ensuring that operators around the world have a timely solution for meeting the latest industry code requirements. As well as complying with all major codes and standards, the current production of the 109FB standard plant has options for SIL (safety integrity level) compliance when required.

GE’s SIL compliant products include the Mark* VIeS safety controller and the Bently Nevada 3500 hazgas monitor. GE is also advancing to the next tier of SIL compliance by working to acquire both type and process SIL certifications, meaning that the products and the processes used in manufacture both meet SIL standards and requirements.

GE Energy strives to address the power plant operator’s safety issues before they become operational risks and, as each project has its own unique requirements, aims to be in on the ground floor of project planning to ensure compliance is achieved.

Standardisation delivers improvements all round

Summarising, in response to market requirements from the power industry, GE, along with its EPC partners, has developed a standard combined cycle plant design incorporating a single plant-wide GE control system. This structure includes a pre-designed power island, collaborative engineering, structured control libraries, and field proven lessons learned. The result is a project with a shorter cycle time, reduced project risk, and better cost containment. Operations and engineering also benefit over the life span of the power plant. By combining OEM plant design knowledge, a single plant control system philosophy, and advanced controls, plant operability is also improved.