Increasing competition in power generation is bringing new life to ageing steam power plants, including the assets of non-commissioned or to-be-decommissioned nuclear power plants.

Due to this transformation of the market, utilities are becoming increasingly involved in the field of re-engineering their steam turbine plants. Since steam power plants can remain operational for many decades, it is a very attractive proposition for older plants to be repowered to drastically improve their efficiency and produce higher levels of power with increased operating flexibility. It is not uncommon for a 30-year-old plant to remain operational for an additional 20 to 30 years as part of a modern combined cycle plant.

In a number of cases, it is impractical to meet increasing demand by building an additional plant. There is often insufficient funding to construct a new plant, or insufficient space because the best site for a new plant has already been occupied by an existing plant. Lengthy permitting processes and occasionally social or political reasons can also slow the process.

PowerSenoko repowers

PowerSenoko, a subsidiary of Singapore Power and the largest power generation company in Singapore, operates the 201 MWe Pasir Panjang power station (two gas turbines for peaking and black-start) as well as the 2460 MWe Senoko plant, which supplies nearly half of Singapore’s electricity needs.

At Senoko there is currently 1610 MWe of steam plant and 850 MWe of combined cycle plant – encompassing the most efficient units in the system as well as some of the oldest.

The thermal plants at Senoko were developed in three stages, entering commercial service between 1976 and 1983. Capacity at the site was further increased in 1990-91 when four Siemens V94.2 gas turbines were installed. Subsequently these were converted to two combined cycle blocks (425 MWe each), the first being completed in July 1996 and the second in November 1996.

These combined cycle units, with net efficiencies of 45.9 per cent, are among the most advanced in the country. At the other end of spectrum, the three units of the oil-fired Senoko Stage I steam plant were commissioned some 22 years ago and are approaching the end of their useful physical and economic life. PowerSenoko has therefore decided to repower the facility and a contract has been signed with ABB Alstom Power, who, as main supplier, will provide overall project management for the engineering, procurement and construction of the facility.

The project will be carried out in two phases. In the first phase, the first of the three units of Stage I will be repowered. The total project cost of this phase will be around $180 million and will add about 240 MWe. The second phase, repowering of the second and third units, is optional. Should the second phase go through to completion the total increase in power generation capacity would be around 720 MWe and the existing 3 x 120 MWe of low merit, low efficiency oil-fired steam plant comprising Stage I of Senoko will have been transformed into 3 x 360 MWe of highly efficient natural gas fired combined cycle plant, with significantly reduced emissions. The estimated total project cost for both phases is around $670 million.

” We consider the investment timely as we are confident that the economy will eventually recover from the current setback,” says Peter Seah, Chairman of PowerSenoko. When repowered, the plant will boast a net efficiency of 56 per cent, some 40 per cent higher than the present level, thereby helping to improve the competitiveness of PowerSenoko in the deregulated Singaporean power market.

“The bottom line is cost savings for our customers”, adds Lau Khoon Chor, Managing Director of PowerSenoko. “By using the existing site and retaining the civil infrastructure, the construction cost is lowered by 10 per cent as compared with new construction on a green-field site. Furthermore, higher plant efficiency and operational productivity will eventually lead to a lower cost for the electricity generated.”

To minimize interruption to the operation of Stage I and electricity supply to consumers, a phased construction programme will be adopted. Most of the existing civil structure and equipment will be re-used, albeit with some modification and refurbishment.

The repowering concept involves replacement of the existing oil-fired boiler with a new GT26 gas turbine and heat recovery steam generator (HRSG). The gas turbine will fire natural gas, with diesel oil No 2 as back- up.The waste heat from the hot exhaust of the gas turbine will be used to generate steam in the triple pressure reheat HRSG to drive the existing steam turbine-generator, which will be modernized.

The repowering concept will be the first of its kind in Singapore as well as in this region. For Phase 1, as well as the gas turbine and its associated generator and transformer, ABB will also supply the new steam turbine components. CMI is expected to be the HRSG supplier.

The contractor took possession of the site in July 1999 and the shutdown of unit 1 of Stage I for rehabilitation is scheduled for April 2000. The first repowered unit is expected to come into commercial operation in the first quarter of 2001.

In Phase 1 of the Stage I repowering project, the gas turbine and associated equipment, eg the HRSG, will be installed in new buildings where the store/workshop was originally located. The existing steam turbine will be fitted with a complete new HP/IP section and the LP section will be equipped with new rotating and stationary parts. To achieve increased efficiency the steam data has been modified and new blading installed. Fetaures will include welded rotors and high efficiency reaction type blading.

The new steam turbine equipment will be designed to minimize changes to existing foundation works. The existing steam turbine generator and transformer will also be re-used. The steam turbine exhaust steam will enter the existing condenser, which will be used without any modifications, except for the introduction of new steam turbine bypass stations.

The new combined cycle plant will use the existing cooling water system, which will be thoroughly refurbished and equipped with new cooling water circulating pumps and other components.

A particular challenge of the project is the very compact space available to house the combined cycle plant and limited space for building works as well as the tight project schedule. The entire worksite is within the boundary of the existing station.

Phase 2 of the Stage I repowering project will require substantial demolition work, including removal of the existing 180 m high chimney, which will need to be done before the installation work can be started.

Among the recent project highlights:


Three stages of Senoko
Repowering projects using ABB gas turbines (GT)

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