Dangjin 3
Dangjin 3 heralds in a new era of efficiency for CCPPs, not only in South Korea but also Asia
Credit: Siemens

South Korea’s Dangjin 3 plant incorporates some of the most advanced features available today in combined-cycle technology, producing over 400 MW on one shaft. The plant is capable of a net efficiency of over 60 per cent, marking a new level of efficiency in Asia, writes Dr. Heather Johnstone.

Contrary to many other OECD countries, the Republic of Korea, more commonly known as South Korea, recovered quickly from the 2008 global crisis. According to the OECD (Organisation for Economic Co-operation and Development), it is the fourth largest economy in Asia, with a growth forecast of 4-5 per cent for next year.

The total population was recorded last year at 50 million, representing a doubling in the last 50 years (i.e. 25 million in 1960). Currently, South Korea has the third-youngest population in the OECD, but like many other countries it faces a rapid ageing of its population – by 2050 it is forecast to have the second oldest.

With a growing economy and population it is therefore not surprising that South Korea’s consumption of electricity has steadily risen over the last decade, and in December of last year, peak power demand hit an all-time record of just under 76,000 MW.

Over the same ten-year period, however, the addition of new capacity has not kept pace, and its reserve margin has been in sharp decline – from 17 per cent in 2003 down to a worringly low 5.5 per cent in 2012.

Thankfully South Korea has responded to reverse this trend and several measures have been introduced to increase the reserve margin to 22 per cent by 2027. Further, between 2011 and 2012 construction of 9 GW of gas-fired power plants was started, plus in January of this year, the government issued an ambitious plan that includes the construction of 15,800 MW of thermal power plants, fuelled by coal and liquefied natural gas (LNG) by 2027.

However, like its neighbour Japan, South Korea possesses few natural energy resources, so it has to import huge quantities of energy products. According to the EIA (Energy Information Administration), South Korea is one of the top energy importers in the world – in 2011, it was the second-largest importer of LNG, the third-largest importer of coal and the fifth-largest importer of crude oil.

Natural gas dominates the country’s power generation mix and is expected to continue as the fuel of choice for power plant operators. This means South Korea is highly dependent on LNG imports, which are brought in by tankers, and therefore is at the mercy of the global gas market, where wholesale prices remain stubbornly high. Thus, the ability to generate electricity in the most fuel efficient manner is topping the agendas of all South Korean power producers.

Korea Electric Power Corporation (KEPCO), which is responsible for generation, transmission, distribution and retail, continues to dominate the sector. However, independent power producers (IPPs) have started to play an increasingly important role on the power generation side.

One of the country’s most active IPPs is GS Electric Power & Services Limited (GS EPS), which was founded in 1996. The IPP currently operates two LNG-fired combined-cycle power plants (CCPPs) – 538 MW and 550 MW – and in late August of this year took possession of a new 415 MW CCPP, called Dangjin 3.

What is especially interesting about Dangjin 3 is that it not only represents the first installation in Asia of Siemens Energy’s high-efficiency SGT6-8000H gas turbine and its corresponding combined-cycle technology in a single-shaft arrangement (SCC6-8000H 1S), but also with a net efficiency in excess of 60 per cent (LHV) it is widely regarded as the most efficient CCPP in the region.

Furthermore, Dangjin 3’s plant design, Siemens says, also provides high operational flexibility, enabling cycling and frequent and quick start-stops – it is able to hot start in under 30 minutes (hot start ‘on the fly’ conditions).

Long-standing relationship

Siemens has a long history with South Korea that dates back to 1991, and an almost equally long one with GS EPS. In October 1997, GS EPS awarded the contract for its first project to Siemens for a new CCPP to be located in the city of Dangjin, about 100 km south of Seoul.

This CCPP, now known as Dangjin 1, is recognised as a pioneering project in the development of the country’s electricity sector because it was one of the first power plants in South Korea to feature F-class technology and the first to use the SGT6-4000F gas turbine. At the time of its commissioning in 2000, Dangjin 1 was reportedly the most efficient power plant in the country.

In 2006, GS EPS awarded a follow-up order for an extension to the Dangjin site, the Dangjin 2 CCPP project. The unit, which once again features the SGT6-4000F gas turbine, was supplied on a turnkey basis with GS E&C as a consortium partner.

The installation and commissioning were completed one month ahead of schedule in February 2008, after a construction period of 26 months. Dangjin 2 features a ‘2×1’ multi-shaft arrangement and a net efficiency of 58.6 per cent, topping Dangjin 1 in the efficiency stakes.

Subsequently, GS EPS and Siemens partnered for a third time on a project that the German OEM describes as “bringing the latest technology to Korea”. GS EPS took the decision to move away from the F-class technology to the new high-efficiency H-class in an effort to reduce fuel consumption, as well as NOx emissions.

In collaboration with GS E&C, Siemens supplied a complete turnkey H-class single-shaft CCPP for Dangjin 3. Interestingly, the project marks the introduction of the LNG-fired single-shaft plant concept to the Korean market. The contract was signed in January 2011, with the ground-breaking ceremony for the new project held the following April. Interestingly, the same team that had been involved in building Dangjin 2 was brought onboard for the Dangjin 3 project.

The 415 MW-rated (gross) CCPP went into commercial operation in August 2013 – a construction period of 30 months and again ahead of schedule, reports Siemens. According to Kihwan Cho, team leader and project manager of Dangjin 3 at GS EPS, the total project investment was in the region of 460 billion won ($420 million).

SGT6-8000H at its heart

SGT6-8000H
The SGT6-8000H was manufactured and tested at Siemens’ facility in Berlin
Credit: Siemens

As mentioned above, Dangjin 3 was a joint project, with Siemens responsible for the manufacture, supply and commissioning of the main power block, and GS E&C overseeing the design, construction and supply of the plant’s auxiliary equipment.

The power block features the 60 Hz version of the H-class gas turbine, which is said to be a direct aerodynamic scaling from the 50 Hz version. The fully air-cooled SGT6-8000H, like the original SGT5-8000H, is a single-shaft machine with a single casing design.

The basic design of the SGT6-8000H, adopted from previous gas turbine models, includes the following features: disc-type rotor with central tie bolt and radial serrations; two journal bearings and one thrust bearing; generator drive at the compressor intake end; and axial exhaust diffuser. Further, the combustion system consists of 12 low-NOx burners and baskets with air-cooled transitions, and its annular arrangement provides good exhaust gas temperature field uniformity.

The steam turbine is a SST6-5000, with a laterally installed condenser (seawater cooling), which is coupled to the generator by a synchro-self-shifting (SSS) clutch. It comprises one combined HP/IP turbine casing and one double-flow lLP casing, with all components being standardised modules.

A major feature of the SST6-5000 is the compact design of the HP/IP turbine. The hot steam conditions are confined to the middle of the casing, while the glands at the casing ends are under relatively cool steam conditions. Temperature decay is much slower compared with a design with individual turbine casings, and as a result, says Siemens, the start-up time is significantly shorter, saving precious fuel.

A triple-pressure reheat heat recovery steam generator (HRSG) is located downstream of the gas turbine diffuser and produces steam in three pressure stages. The HP steam generator is of the Benson® type, with a once-through evaporator in the HP section and natural-circulation drum-type evaporators in the IP and LP sections.

It features advanced steam conditions, with 150 bar and 585 °C in the HP stage at the steam turbine nozzle, which increases the efficiency of the CCPP.

The generator is a two-pole SGen6-2000H with direct radial hydrogen cooling for the rotor winding and indirect hydrogen cooling for the stator winding. The hydrogen-filled generator casing has a pressure-resistant and gas-tight construction and is equipped with two end shields. The hydrogen cooler is divided into four sections, with two positioned at each generator end.

The three-phase winding inserted in the stator core slots has a two-layer transposed-bar design. The winding is vacuum-pressure impregnated with the stator core and the high-voltage insulation employs a proven proprietary epoxy-mica system.

The generator rotor shaft is a vacuum-cast forging and has two end-shield sleeve bearings. The hydrogen is circulated in the generator interior in a closed circuit by axial-flow fans arranged on the rotor shaft journals.

turbine-generator package
The simple arrangement of the turbine-generator package can be clearly seen
Credit: Siemens

Finally, Siemens also provided a SPPA-T3000 plant control system with an operator station integrated into the Dangjin site’s existing control room.

This system uses a continuous information flow, consistent data management and storage, flexible instrumentation and control concepts, and uniform human-machine interface (HMI) platforms to perform the required automation, operational control, and data monitoring for the plant.

The SPPA-T3000 control system has a hierarchical structure and possesses design features such as a plant-oriented process control structure that provides operational functions, combined with monitoring and diagnostic capabilities and an open local area network structure for interfacing to other systems and external computer networks.

Dangjin 3 timeline

As mentioned above the Dangjin 3 project took 30 months to build, with excavation work commencing in June 2011.

In April of the following year, the generator was delivered and its installation started.

Also in the same month, the installation of the HRSG commenced, along with the delivery of both the steam turbine and gas turbine. At the end of April, the construction of the turbine building was also completed.

The following December saw the completion of the installation of the power block, i.e. the gas turbine, steam turbine, HRSG and generator.

A landmark in the project was reached on 21 March of this year, with ignition and first fire of the SGT6-8000H. A week later, synchronisation took place.

The all-important performance testing was conducted between late July and early August, immediately followed by reliability testing, and finally, on 19 August Siemens handed over Dangjin 3 to GS EPS and the CCPP entered commercial operation.

Achieving the goals

According to Thomas Hagedorn, Siemens Energy’s vice president, Gas Turbine Power Plant Solutions APAC: “On an annual basis Dangjin 3 will save more than 3 per cent of its natural gas fuel per kWh compared to the Dangjin 2 plant. Assuming operation at baseload, this will result in savings of up to 20,000 m3 of natural gas per year.

Hagedorn puts this saving into perspective: “A typical LNG tanker carries four to five tanks of LNG of approximately 35,000 m3. This means Dangjin 3 will save one tank every two years, one complete LNG tanker load every eight years or three LNG tanker loads over its projected 25-year economic lifespan.” At today’s LNG prices this saving is clearly significant.

In terms of NOx emissions, during baseload operation they are kept well below 20 ppm – straight from the gas turbine, i.e. not controlled via a SCR. Hagedron also says that “Dangjin 3 CCPP is currently the fossil power plant with the lowest carbon emissions in Korea”, estimating an additional annual saving of 20,000 tonnes of CO2, compared with Dangjin 2 for the same amount of electricity output. South Korea is clearly proving a fertile ground for Siemens and all the signs are this will continue.

In 2012 and 2013, Siemens sold a further seven units in the country – KOSCO Company Limited’s Andong – 1 x SCC6-8000H 1S (single-shaft configuration), POSCO’s Ansan -1 x SCC6-8000H 2×1 (multi-shaft configuration), POSCO Energy’s 7, 8 and 9 units – 3 x SCC6-8000H1S (single-shaft configuration) and Lotte Engineering & Construction’s Daegu City – 1 x SCC6-8000H 1S (single-shaft configuration, but with a CHP application).

Furthermore, in October, the German OEM opened a new regional headquarters for its Energy Solutions business in the capital Seoul. Known as Siemens Energy Solutions Limited, Korea, it is headed up by Rochus Bergmann, a Siemens veteran of 20 years.

Clearly the future is looking bright in South Korea for Siemens and its ground-breaking SGT6-8000H gas turbine.

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