Baglan Bay: an H showcase
In 1995, GE Power Systems launched a programme to develop its H class gas turbine combined cycle power generation system. Four years on, the first H system unit is being prepared for shipment to the UK for installation at the Baglan Bay Energy Park.
Baglan Bay, near Swansea in south Wales, will become the first site in the world to demonstrate this advanced, high efficiency technology. A 500 MWe combined cycle power plant based on the H system will be constructed by GE at the site, entering commercial service in 2002.
The $500 million power plant is being developed by GE and BP Amoco, owner of the Baglan Bay site. It will supply electricity and heat to industrial and commercial consumers at the energy park, and will also export power to the south Wales grid. The plant will be the first combined cycle power station in the world to demonstrate the capability of 60 per cent thermal efficiency.
GE and BP-Amoco received final approval for the power plant in July 1999 after the government announced in April that it would not oppose its construction. This decision was somewhat controversial as it appeared to contravene government policy on the development of new natural gas fired capacity, the so-called `gas moratorium`. An earlier application by BP Amoco to construct a 1100 MW power plant at the site based on F technology met consent application problems, as did a proposal by GE to build a 1000 MW H technology demonstration plant in Lancashire.
BP Amoco therefore revised its plans for a power plant at Baglan Bay, and began talks with GE for incorporating H technology at the site. The result was the 500 MW H technology combined cycle cogeneration plant. In April therefore, the government stated that certain factors in the revised application allowed a policy exception to be made. These factors included the demonstration of leading-edge gas turbine technology, the supply of low-cost electricity, and the plant`s potential to support economic development in the area through the Baglan Energy Park scheme.
The Baglan Bay Energy Park is a joint development between BP-Amoco, the Welsh Development Agency (WDA) and the Neath Port Talbot County Borough Council. The site has more than 1000 developable acres (405 ha) and aims to attract industrial development in the area. The first two phases of the development, comprising around 200 acres (81 ha), could support up to 600 jobs alone.
The Neath-Port Talbot area suffers high unemployment due to dependence on fast-disappearing manufacturing and other heavy industries. BP Amoco and the site`s other developers see the scheme as an innovative way to capitalize on the existence of a skilled work force, attract inward investment and help economic `regeneration`.
The Baglan Bay power plant is essential to the fulfilment of these objectives for several reasons. An existing 100 MW oil-fired power plant at the site would not be able to support such a development. BP Amoco and GE have stated that energy consumers at the Baglan site will be able to enjoy savings of 30 per cent on their electricity bills compared with retail prices – an attractive prospect for any energy-intensive business.
The H technology plant at Baglan will also achieve low emissions due to its use of natural gas, its steam-cooled technology, and the high efficiency that it will reach. Compared with data for existing UK CCGT facilities, Baglan will have 80 per cent lower NOx emissions and 16 per cent lower CO2 emissions. With the planned closure of the 30-year old oil-fired plant, overall site emissions of CO2 will be reduced by 66 per cent, NOx by 88 per cent and SOx by 99 per cent.
The plant will have black start capability, improving security of supply in south Wales where there is currently a supply deficit of 300 MW. After accounting for demand at the Energy Park, Baglan will export up to 300 MWe to the Welsh grid. Baglan will supply steam to BP`s isopropanol facility and other Energy Park users, and will also provide steam to the proposed Neath Port Talbot district heating scheme. Total heat capacity of the plant will be 185 MWth.
The power plant therefore forms the `heart` of the energy park development. It will be constructed by GE at a cost of around $500 million and will create up to 500 temporary construction jobs. Construction will begin this year and will take two years. Commercial operation will start in 2002 after several months of testing.
GE is responsible for the supply of all the equipment to the power plant, which will be equipped with a single H system unit – a gas turbine, steam turbine, one generator, control system and a heat recovery steam generator (HRSG) with chp capability. GE will also supply the steam supply systems with additional heat recovery, as well as auxiliaries.
The H system is part of the US Department of Energy`s (DOE) Advanced Turbine System (ATS) programme, and is a product of the drive towards higher efficiencies for power generation technology.
Deregulation and the introduction of competition to the world-wide power industry has driven a growing need for cost reduction in power plant equipment, and has prompted a move towards high power densities and high efficiency machines to help reduce fuel costs. As fuel represents the largest single cost of running a power plant, an increase in a single percentage point in thermal efficiency can reduce operating costs by as much as $20 million over the life of a typical gas fired combined cycle power plant of 400 to 500 MW.
These factors, and the need to reduce emissions, prompted the DOE to implement its ATS programme to develop low-cost, high efficiency gas turbine systems with superior environmental performance. Specifically, it aims to help manufacturers to develop systems with efficiencies of 60 per cent or more (LHV), NOx emissions of less than 9 ppm, and with busbar energy costs ten per cent lower than current commercial advanced turbine systems.
GE Power Systems embarked its H programme in mid-1995 after signing an agreement with the DOE, and began detailed design and component testing activities. The centrepiece of H technology is its advanced closed-loop steam cooling system in the gas turbine which permits higher firing temperatures while keeping combustion temperatures low – an essential combination for increasing efficiency while keeping NOx emissions low.
GE says that this advanced design has resulted from the integration of technologies from its Aircraft Engine and Power Generation business units and its Corporate Research and Development Centre. Its experience in the aircraft industry has played a significant part in the development of the H system, according to Ed Lowe, GE`s H system programme manager. “We are much more in the high-technology aircraft engine type of philosophy,” said Lowe.
According to Lowe, most turbine manufacturers aim to get a full-sized unit out in the field for testing as soon as possible when developing a new unit. GE`s philosophy is different however, and is more like that seen in the aircraft industry where extensive material, component and subsystem testing is carried out before a full-sized unit is tested and then installed in the field. “We end up having a much higher degree of confidence that the unit we put out there is going to operate exactly as we anticipated,” commented Lowe.
This philosophy has been demonstrated over the past four years by GE`s extensive testing on the H system components, culminating in a full speed no load (FSNL) test carried out earlier this year on the 9H gas turbine-compressor unit that will be installed at Baglan.
The 9H unit, with an ISO rating of 480 MW, consists of an 18-stage compressor, a can-annular dry low-NOx (DLN) combustion system similar to those in other GE gas turbines, and a four-stage turbine. The compressor provides a 23:1 pressure ratio with an airflow of 1510 lbs/s (684.9 kg/s). It is scaled up from GE`s high-pressure compressor used in the CF6-80C2 aircraft engine and in the LM6000 industrial gas turbine. Turbine inlet temperature is 1426 degreesC (2600 degreesF), approximately 100 degreesC above GE`s other gas turbine models.
The turbine uses closed-loop steam-cooling for the first and second stage nozzles and buckets plus the stage one shroud. Steam is extracted from the high pressure (HP) steam turbine exhaust and is introduced to the turbine components to provide cooling. The steam is then returned to the combined cycle section, joining the reheated steam from the HRSG before entering the intermediate pressure (IP) section of the steam turbine and expanding through the bottoming cycle. Air cooling is used for the third stage nozzles and buckets and the fourth stage is uncooled.
Closed-loop steam cooling uses the superior heat transfer characteristics of steam compared to air, allowing the higher firing temperatures that are needed, to be used. It also allows better integration between the gas turbine and steam turbine cycles, and means that GE can only offer H technology as a complete combined cycle unit.
The steam turbine to be installed at Baglan will be a GE unit with a combined HP/IP section and a double-flow low pressure (LP) section. Other than its integration with the gas turbine, there is nothing unique in the design of the steam turbine. The exhaust temperature and pressure of the HP section will match the conditions required to achieve optimum operation of the gas turbine, and according to Lowe, these are typical of steam turbines in similarly sized CCGT power plants. Typical inlet pressures and temperatures will also be seen on the IP section.
GE is in the process of finalizing the supply contract for the HRSG for Baglan. The HRSG will be a three pressure unit similar in design to HRSGs installed in GE F technology-based CCGTs. The one distinguishing feature of the HRSG will be its reheat section, which will be smaller compared to other units because the steam-cooled stages of the gas turbine act as a reheat section.
Tried and tested
GE has carried out four years of extensive design data and validation test programmes on the H system to ensure that the first unit meets the reliability, availability and maintainability levels required. In 1995, the company carried out a `baseline` compressor test to validate the fundamental compressor design approach, and followed this up in 1996 with a 9H compressor test. These were carried out on CF6-80C2-sized units at GE`s aircraft engine compressor development test facility in Lynn, MA.
More than 1300 pieces of instrumentation were used on the 9H compressor test to measure the aerodynamic, aeromechanic and thermal characteristics of the compressor. The results showed that parameters such as airflow and vibratory stresses were within design limits.
In 1997, GE successfully tested prototype full-size, steam-cooled first-stage turbine vanes at H thermal conditions in a component rig at a GE aircraft engine test facility in Cincinnati, OH. This nozzle cascade test was designed to validate heat transfer, material capability and steam cooling effects, and the test results were incorporated into detailed aero, thermal and stress models to show that the H stage 1 nozzle meets life requirements. The stage 1 nozzle has also undergone successful extensive heat transfer tests, materials testing in steam, thermal barrier coating testing and steam purity tests.
Testing of the H system design culminated in May 1998 with FSNL testing on the full-sized 9H gas turbine compressor unit to be installed at Baglan. The tests were carried out over a 30-day period at GE`s Greenville, South Carolina facility, and encompassed five test runs. They were designed to test and confirm rotor dynamics, vibration levels, compressor airfoil aeromechanics, airflow, efficiency, running clearances and the scale-up from the CF6-80C2-sized units previously tested. The Mark VI control system, which controls the whole power train, was also tested. Thermal barrier coatings, steam cooling and environmental performance parameters were not tested by the FSNL testing as the test was carried out at no-load operating temperatures.
The FSNL tests were successful, and results were “outstanding,” according to GE, with all of the performance values derived from the models and previous tests validated and confirmed. “All of our components were extremely successful,” said Lowe. “We had outstanding results and everything was within predicted values.”
After the FSNL test, GE took the unit apart and examined all of the components for signs of stress. “All of the hardware was in excellent condition,” said Lowe. GE has now reassembled the unit in the Greenville test cell where it will undergo pre-shipment testing before being shipped to the UK in the fourth quarter of 1999.
The challenge ahead
The extensive testing carried out on the H system to date has enabled GE to confirm that the technology is now ready to go out into the field. However, there are still likely to be challenges in integrating a complete unit, including component life and thermal barrier coating performance. The closed-loop steam cooling system is also a concern, with issues such as steam quality of particular interest.
The H system at Baglan will undergo full load characterization testing over eight months in 2001. During these tests, thermodynamics, performance and analysis tools will be confirmed together with the combustor rig tests. The rotor and structure steady state temperatures and airfoil temperatures will be validated, and the control system and system operability will be confirmed. Following this, the unit will undergo a one-year demonstration to further confirm operability under full commercial operating conditions.
Figure 3. Site plan for Baglan Bay. 1: turbine building; 2: switchyard; 3: LM2500+; 4: cooling tower; 5: administration building; 6: main power transformer