The world's largest coal-fired pressurised fluidised bed combined-cycle power plant is under commissioning in Japan. The 360 MWe Karita unit, designed to burn a wide range of imported coals, is the latest example of the application of this modern clean coal technology. The combined cycle unit recently achieved the nameplate rating for the gas turbine and will very shortly reach full plant load. After completing its commissioning programme the plant will be ready for commercial operation in the middle of next year. Dirk Veenhuizen, ABB Stal, Finspong, Sweden
Kyushu Electric Power Company (KyEPCO), one of Japan’s leading utilities, with an installed capacity of about 15 700 MWe, decided in 1991 to build the world’s first 360 MWe pressurised fluidised bed combined-cycle (PFBC) plant.
The contract for the engineering, manufacturing, erection and commissioning of the plant was placed with Ishikawajima-Harima Heavy Industries Co Ltd (IHI) under licence from ABB Carbon, a unit within ABB Stal, an ABB Alstom Power company in Sweden.
This is a similar business arrangement to that used for introducing the first PFBC plant in Japan, a 71 MWe plant built for EPDC at the Wakamatsu power station, in 1994.
The Karita PFBC plant is built around the ABB Stal GT140P gas turbine, which provides the air for fluidisation and combustion at about 16 bar in the pressurised fluidised bed boiler. The GT140P gas turbine was specially developed in Finspong for this type of combined cycle operation.
The boiler is used for generating steam at supercritical conditions (242 bar/566°C/593 °C) for the 290 MWe reheat steam turbine and at the same time acts as combustion chamber for the gas turbine. The generated flue gas is used for driving the gas turbine, producing power for the compressors as well as for the 75 MWe gas turbine generator. Downstream of the gas turbine, exhaust economisers are used for condensate and feedwater preheating, further enhancing the combined cycle efficiency.
The plant is designed to burn a wide range of imported coals. Emission control is primarily performed within the fluidised bed process, with inherently low NOX production and sulphur retention in the limestone added to the fuel. Further NOX reduction is accomplished by the use of a dry ammonia SCR unit in the exhaust system, where an ESP is applied for final reduction of particulate emissions.
The design of the plant is based on the experience from a number of smaller PFBC plants, built by ABB Stal and its licensees in Europe, the United States and Japan, which have been in operation since 1990.
In early 1997 the first foundations at the Karita power plant site in Fukuoka Prefecture were completed. In parallel, the complete PFBC combustor, a pressure vessel containing the fluidised bed boiler, the hot gas cyclone separators and parts of the ash handling systems, was assembled at the IHI Aioi works in Hyogo Prefecture.
In November 1997, the 3600 t vessel, towering 52 m high, was shipped by barge the 400 km to the site. There it was lifted by Asia’s largest 4100 ton capacity marine crane onto 26 special unit heavy load carriers for the 600 m transport to the foundation.
The pressure vessel, resting on its unit carriers, was then very slowly rolled along the specially constructed transport route to the installation site, taking two and a half hours. The carriers were operated as a single unit by computer-controlled monitoring. The total transport platform was 51 m long and 25 m wide, with a weight ratio of 7 t/m2, and a swing radius of 37 m.
The complete GT140P gas turbine was tested in the ABB Stal workshop in Sweden from December 1996 until April 1998. The workshop test was performed to verify the general function, main performance characteristics and mechanical integrity of the machine.
During the test programme, the GT140P was run on liquid fuel, using a GT11N silo combustor. After completion of the test programme, the gas turbine was dismantled and thoroughly inspected. It was then shipped to the site, arriving in sections on Japanese soil on 10 September 1998. A month later the complete gas turbine was installed on its foundation. Erection of the steam turbine, supplied by Toshiba, was performed in parallel.
Commissioning of the Karita plant began early this year, with cold testing from January to May, and hot testing from May onwards. First coal firing was performed early in July and first synchronisation of the steam turbine generator to the grid was on 2 August. Commissioning has continued throughout the summer, with verification runs at loads of 35 per cent, 50 per cent and 75 per cent. Two months later the plant produced 350 MWe of electricity, of which 275 MWe was generated by the steam turbine and 75 MWe by the gas turbine. This means that the GT140P, the first gas turbine of its kind, successfully achieved 100 per cent of its name plate rating. At time of writing preparations are being made for the 100 per cent plant load test.
The entire commissioning period has progressed smoothly and successfully, incorporating some minor modifications and verifications, but moving surely towards its goal. Customer take-over of the plant is planned for 1 July 2000, following thorough testing of the entire plant.
The progress of the project proves PFBC technology can fulfil its promise.