Made to measure?

Using operational experience from Baglan Bay, GE Energy has uprated the H System from 480 to 520 MW. The technology is commercial and proven, but can it measure up in the competitive global GT market?

Siàƒ¢n Green

At Power-Gen Europe in Milan in June 2005, GE Energy announced that it has uprated its 109H technology from 480 MW to 520 MW. Taking operational experience and lessons learned from operation of the first 9H System at Baglan Bay in Wales, the company has included a number of key enhancements to its most advanced gas turbine offering.

The changes to the H System design mean a more optimized product that will benefit plant owners, according to GE. “The uprated 9H will further improve the economies of scale provided by large gas turbine combined cycle power plants by enabling plants with fewer gas turbines to generate larger blocks of power,” said Brian Ray, general manager of the H System product line at GE Energy.

The key enhancements made include the introduction of fuel moisturization, improved clearance control, and a number of improvements to cooling and sealing. The net result is improved performance and higher output.

Validated design

The H System was originally announced in 1995 and was developed as part of the US Department of Energy’s Advanced Turbine Systems programme. It uses a combination of closed-loop steam cooling and advanced coating materials to achieve firing temperatures in the 1400à‚°C range. It is the most powerful single-shaft combined cycle system in the world, and the first platform capable of achieving a thermal efficiency of 60 per cent.

In December 2000, a 50 Hz, 480 MW 109H was shipped to Baglan Bay, which has served as the commercial demonstration site for the H System. Field testing of the H System at Baglan Bay began in November 2002, and the unit entered commercial operation in September 2003. The H System is the most thoroughly tested industrial gas turbine technology in GE’s history.


Figure 1. Operational experience and data from the Baglan Bay site has enabled GE to uprate the H System
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The 9H unit at Baglan Bay has now completed over 9500 operating hours, and, with the exception of a three-month outage at the plant in mid-2004 caused by insufficient cooling on some of the buckets, the plant is meeting GE’s expectations. However, site conditions mean that GE Energy has not been able to demonstrate the H System’s ability to achieve 60 per cent thermal efficiency.

“The [Baglan Bay] site was never designed to achieve 60 per cent thermal efficiency, but to test the gas turbine unit and closed loop steam cooling,” explained Don Hoffmann, H System product line manager at GE Energy. “You need the right site conditions in order to achieve 60 per cent efficiency and it’s not possible at Baglan Bay. GE intends to guarantee 60 per cent thermal efficiency at ISO conditions for all future deliveries of the H, provided that site conditions are suitable.”

The extensive testing at Baglan Bay validated the H System design – in particular the closed loop steam cooling system – and the unit has generated up to 530 MW at ambient temperatures of 6.7à‚°C. The data and experience gathered has enabled GE to optimize the design of the H in three key areas. The majority of the uprated design will enter service for the first time in 2007 at the Baglan Bay power station.

Fine-tuning

A fuel moisturization system has been added to the H System to increase mass flow through the turbine and reduce NOx emissions. This equipment consists of a saturator which sprays heated water over the fuel. Water vapour equivalent to approximately 20 per cent of the fuel becomes part of the gas stream, thereby increasing mass flow and reducing the peak flame temperature in the combustor. The effect is a 1-2 per cent net increase in output (approximately 5 MW for the H System) and a 4-6 mg/Nm3 reduction in NOx emissions.

GE Energy patented this technology with the intention of putting it into service in the first 60 Hz 7H unit. It will be tested on a scaled test rig at the company’s Greenville, SC, facility, and full scale testing will be carried out when the first 7H unit enters operation at the Inland Empire site in California – GE’s chosen launch site for the 7H – in 2008.

The H System features an active clearance control system based on technology used in GE’s aircraft engine designs. This system increases clearances during start-up and other transients by heating up the air between the inner and outer turbine shell. This prevents casing rubs in the aft stages of the compressor and the first two turbine stages. Based on test data at Baglan Bay, GE has been able to configure the active clearance control to achieve more optimal clearances for the first two turbine stages and therefore improve overall performance. Further improvements are possible, says Hoffmann, and clearance control optimization is an on-going project.


Figure 2. The H Systems destined for Japan and California will start shipping in 2006 ready for operation in 2008
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In addition to fuel moisturization and optimization of clearance control, a number of small adjustments have been made to the cooling and sealing of the H System. “For example, we have improved air flow going to cool the stage two buckets, and improved the cooling holes on the transition piece of the combustor,” says Hoffmann. GE engineers have examined actual operating temperatures and adjusted the cooling design as required for each component of the gas turbine. Although firing temperature will remain 1400à‚°C class, it will be adjusted to take advantage of a lower-than-expected temperature drop across the first stage nozzles.

“Small improvements have also been made to the seals,” says Hoffmann. “For example, the turbine shell is a half-shell with a bolted arrangement; GE is putting a groove in the shell with a compression seal.” These small adjustments have been made from information gathered at Baglan Bay, and together have a positive impact on performance.

Large vs small

Key markets for the H System are Europe, the USA and Asia, says Hoffmann. However, such an advanced, large-scale machine may have a hard time competing against other large industrial gas turbines as well as IGCC and clean coal technologies.

Nevertheless, demand for gas turbine equipment is on the rise in all three of the major regions at which the H is aimed. According to recent market analysis by Frost & Sullivan, demand for gas turbine-based power plants in Europe is once again rising, driven mainly by demand in Central and Eastern Europe, Spain, Italy and Turkey. Market forces driving this demand include rising electricity demand, decommissioning of ageing conventional and nuclear power plants, deregulation and growing competition and environmental/climate change imperatives. According to Frost & Sullivan, a total of 46 640 MW of gas turbines is expected to be added to the European electricity sector between 2005 and 2010, generating total revenues of $11 billion. It has forecast the addition of a further 40 GW in 2011-2015 and 43 GW in 2016-2020.

Although over half of the capacity additions in the 2005-2010 period are expected to be in the >180 MW unit size category, Frost & Sullivan’s analysis states that deregulation and a focus on distributed generation will boost the small gas turbine sector. Overall, however, the medium range turbine segment will continue to be the favourite output segment.


Figure 3. GE has enhanced cooling, sealing and clearance control on the H gas turbine, and has also added a fuel moisturization system
Click here to enlarge image

So where does this leave large-scale, advanced gas turbines? In competitive markets such as those in Europe, technology with high efficiency, high availability and the flexibility to operate as either baseload or peak-shaving operations are highly valued, and the H System can fulfil these requirements, says Hoffmann: “In a competitive market, an H System-based power plant will be able to operate for more hours at a lower variable cost due to its high efficiency. The H System is a strong baseload technology, but has been designed for flexibility.”

According to Hoffmann, the design requirements given to GE’s engineers designing the H System were the same as those for the F fleet of gas turbines. “GE’s F fleet has now achieved over 13 million operating hours and is a cyclic leader for gas turbines,” says Hoffmann. “At one site in Korea, FA units have been started and stopped on average every 17 hours, and the H System, too, has been designed for daily start-stop cycles. Tepco has specified that the H units at its Futtsu site be able to perform daily start-stop cycles, a requirement in the Japanese market.”

H System in Asia

The three 109H combined cycle systems for Tepco’s Futtsu site are due to start shipping in early 2006, with the first unit scheduled to start commercial operation in mid-2008. These units will be the first application of H technology in Asia, and combined output of the three systems will be 1520 MW.

At the Inland Empire site in Riverside County, California, construction has just started on the 775 MW plant that will consist of two 7H combined cycle systems. The California Energy Commission awarded the license for the plant and GE Energy has acquired the site from Calpine. GE expects the plant to be on-line in mid-2008 – in time to help offset forecast energy shortfalls in southern California.

Hoffmann points out that the Inland Empire project shows the environmental capabilities of the H System. At Baglan Bay, GE is required to achieve NOx emissions not exceeding 50 mg/Nm3, and has consistently achieved 20-30 mg/Nm3. At Inland Empire, however, NOx emission requirements are much more stringent – 6 mg/Nm3 – and require the use of an SCR system. “The Inland Empire project was originally designed for two FB units with a total output of around 650 MW,” says Hoffmann. “However, it will now consist of two H units with a total output of 775 MW, but will still meet the required NOx emission limits.

“In other words, the site will have 15 per cent more output than planned, with no increase in NOx.”

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