With Turkey’s economy booming, power generating company Enerjisa has taken an early lead in the race to provide the country with the electricity it urgently needs, with the award earlier this year of the contract for the 919 MW Bandirma combined-cycle power plant.

Franz Binder & Nicolas Perl, A-TEC Power Plant Systems, Austria

Energy consumption in Turkey is currently increasing at between eight and ten per cent per year. To cope with this challenge, state influence in electricity generation and distribution has been steadily declining, making it easier for private companies to invest in power generation.

Combined-cycle technology offers a way of coping with this increasing demand, due to its high efficiency and relatively low investment costs, as well as the short lead time required for designing and building these power plants. The technology is approved worldwide and combines flexible operation (rapid start-ups and load changes) with high operational reliability.


Location of Bandirma CCPP
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In September 2007, power generation company Enerjisa chose a consortium consisting of A-TEC Power Plant Systems (A-TEC PPS) and Mitsubishi Heavy Industries as preferred bidder in negotiations for an engineering, procurement and construction (EPC) contract to build a 919 MW combined-cycle power plant (CCPP) near Bandirma in Turkey. In January 2008, the contract was finally signed.

The power plant will be erected on a greenfield site directly on the Sea of Marmara coast so that seawater can be used for once-through open-loop water cooling. This together with the site’s proximity to a gas pipeline makes this a perfect location for an efficient, high-output CCPP.

The EPC contract includes the delivery of a complete plant on a turnkey basis, designed for base load operation. The core elements of the CCPP are new Mitsubishi M701F4 gas turbines, their exhaust gas will be used to fire two heat recovery steam generators supplied by Nooter-Eriksen, USA. The produced steam will be fed to a condensing reheat steam turbine, also provided by Mitsubishi (see Table 1 for more details).

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The selection of high-quality components, which fit together perfectly, will result in a guaranteed net power output of 919 MW at a net electrical efficiency of 59 per cent under ISO conditions.

These impressive figures will make Bandirma CCPP Turkey’s first next-generation power plant. With this project, Enerjisa will enter a new era of energy production in Turkey.

New turbine

The core components that will enable Bandirma CCPP to reach its high efficiency and performance targets are two new Mitsubishi M701F4 gas turbines.

The M701F4 gas turbine consists of a 17-stage, high-efficiency axial compressor combustion chamber equipped with 20 combustors, arranged in a circular array around the engine, and a four-stage reaction type turbine. The gas turbine is directly coupled to the generator at the compressor end. Ambient air is drawn through the inlet manifold and inlet casing into the compressor. It is pressurized to approximately 18 atmospheres and fed into the combustors, where it is mixed with fuel and ignited, raising the temperature of the mixture of air and combustion products.

All engine casings are horizontally split to facilitate maintenance with the rotor in place. Individual inner casings (blade rings) are used for each turbine stationary stage. These can be readily replaced or serviced with the rotor in place.

The M701F4 gas turbine has a single rotor and is supported by two tilting-pad bearings. The thrust bearing is a double-action multi-pad type thrust bearing using leading-edge groove lubrication.

The 17-stage axial flow compressor, with its 18:1 pressure ratio, is based on the highly successful M501F compressor. The flow and pressure coefficients of the M701F compressor have been kept similar to those of the M501F compressor by increasing the mean diameter of the stages to accommodate the 50 per cent (approximately) increase in flow. The rear stages of the new compressor have one additional stage to accommodate the increased pressure ratio.

The combustion system consists of 20 combustion chambers, fuel nozzles, an ignition system and flame detectors. Each combustion chamber is comprised of two main units: the combustor basket and the combustor transition piece.

With gas firing, the combustor can achieve low NOx emissions without water injection. The dry, low-NOx combustor features a three-stage burner assembly and a bypass valve.

The design of the M701F4 turbine maintains moderate aerodynamic loading despite the increased inlet temperature by using a four-stage turbine. The first and second stages on the turbine rotor blades are of the freestanding type. The third and fourth stages use integral Z-tip shrouds.

Optimal design

While Mitsubishi is providing the two gas turbines and the steam turbine, A-TEC PPS, as consortium leader, will engineer, procure and erect all the other components of the plant. It is also A-TEC PPS’ responsibility to calculate and utilize the water/steam cycle for optimum performance and efficiency.

The design of the gas turbine generators is based on a hydrogen-cooled stator winding, core and rotor winding. The design also incorporates static excitation and vacuum-treating hydrogen sealing. The generators are horizontally mounted, rotating-field cylindrical rotors that are explosion proof and suitable for indoor installation. The three main generator transformers are provided by Hyundai, each with a 420 MVA capacity and tap changing on load. An oil-directed, air-forced system is used for cooling.


Design layout of Bandirma CCPP
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The overall dimensions of each transformer are 19.6 m x 9.5 m x 8.5 m. Their combined weight is 499 tonnes. The two heat recovery steam generators are designed with triple pressure systems and reheat sections.

The horizontal steam generators are drum-type generators with natural circulation. The CCPP incorporates the water/steam cycle and the gas turbine cycle by establishing fuel gas preheating systems and rotor air-cooling systems.


HRSG with horizontal design
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The Mitsubishi steam turbine includes a three-casing, four-flow exhaust system with 40.5-inch last-stage buckets and a design output of 325 MW. It is intended that a once-through direct cooling system using water from the Sea of Marmara will provide the main cooling system.

Tough challenge

The power plant is being erected directly on a steeply inclined seashore approximately 30 m above sea level. One of the most challenging construction projects is the erection of the intake structure for the main cooling water system. Approximately 200 m offshore and 20 m deep, this structure is essential for water withdrawal. The pump house onshore features three main cooling water pumps, which are designed to bridge the 30 m elevation difference up to the power plant. Each pump will consume 4 MW of power each.


M701F4 gas turbine by Mitsubishi
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The site is situated in a major earthquake zone, which places great demands on all construction and civil engineering, especially as turbines are intolerant of movement. Detailed soil investigations were carried out to assess the risk of landslides in the event of an earthquake.

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KEY PLAYERS

 

Enerjisa

Enerjisa Power Generating Company was established in 1996 with the aim of providing reliable energy for its customers and evaluating future business opportunities in the energy sector. Since May 2007, Enerjisa has been jointly owned and controlled by Sabanci Holding and Österreichische Elektrizitätswirtschafts-Aktiengesellschaft (Verbund), after the two partners teamed up to become the leading player in the Turkish electricity sector.

Enerjisa plans to generate 5000 MW of output by the end of 2015, as well as purchase electricity distribution capacity during the grid privatization process. The decision to step up its efforts to bring forward its schedule for the implementation of its first large-scale gas fired power plant has been taken by Enerjisa against the background of the acute power needs of the booming Turkish economy. The company aims to consolidate its position as a leading player in the emerging Turkish energy market and take advantage of first-mover position.

A-TEC PPS

A-TEC PPS was established with the aim of becoming a major player in the European combined-cycle power plant market. A-TEC PPS can provide an excellent combination of single components available on the market to deliver optimal turnkey combined-cycle power plants according to customer requirements.

A-TEC PPS benefits from the global network and long experience in the energy sector of A-TEC Industries AG, an international industrial group with a thriving business in plant construction, drive technologies and mechanical engineering.

The Consortium

The collaboration between A-TEC PPS and Mitsubishi Heavy Industries began in 2006, with the aim of expanding the two companies’ combined-cycle power plant businesses.

Enerjisa’s Turkish combined-cycle power plant project is the consortium’s first marketing success. The consortium’s design for a power plant that precisely met Enerjisa’s requirements led to the awarding of the contract.