In August last year Hitachi Power Europe and GE Energy signed a contract to build what has been described as one of the world’s most modern cogeneration plants. The CHP power plant, which will be located in Malmö, Sweden, will supply the Nordic electricity system with an annual output of 3 TWh of electricity and 1 TWh of thermal heat for district heating.

Olaf Lipinski, Hitachi Power Europe, Germany

In August 2006 a consortium comprising Hitachi Power Europe GmbH (HPE) and GE Energy signed an agreement with Eon Gasturbiner Sverige to build a turnkey combined heat and power (CHP) plant in the Swedish town of Malmö. Incorporating state-of-the-art technology, the new CHP Öresundsverket power plant promises to be one of the most modern cogeneration plants in the world. The new plant will replace old coal and oil fired boilers for electricity and heat production.

The power plant has been designed for more than 7000 hours of annual operation, with an electrical capacity of approximatley 440 MW, and more than 250 MW of thermal heat generation. Under combined operations it will have a maximum gross fuel utilization of over 89 per cent, which will make this combined-cycle power plant one of the most efficient CHP plants in the world.

At the time of signing a very tight project time schedule was agreed upon, with the construction time for the CHP plant being 28 months, and a commercial operation date of the beginning of 2009.

Power train design

The CHP power train will consist of one GE gas turbine type 9 FB, one condensing-extracting steam turbine and one vertical heat recovery steam generator (HRSG), which will be located behind the gas turbine. The main components will be arranged in a multi-shaft arrangement, with each turbine having its own generator. The main equipment will be erected in-line.

The fuel for the gas turbine is a high caloric natural gas, with a light fuel oil, available from huge storage tanks on site, serving as back up fuel.

During condensing operation mode the power plant will have a net electrical power output of 447 MW, of which the gas turbine will generate 293 MW, and a heat consumption of 767 MJ/s, resulting in a top net electrical efficiency of 58.3 per cent.

An artist’s impression of the new CHP Öresundverket power plant under construction in Malmö, Sweden
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The hot flue gas leaving the gas turbine is used to generate steam in the HRSG, which will produce 310 t/h of live steam. The steam will be used to operate the steam turbine, generating a maximum electrical power output of 161 MW.

Approximately 5000 hours of district heating per year is required, so the steam turbine can be operated in extraction mode to generate 250 MW of thermal heat.

To get the maximum flexibility from the CHP plant, and to avoid the start-up of other heat production units in the district heating system, it will be possible to produce 408 MW of thermal heat for peak load operation by shutting down the steam turbine and feeding the district heating heat exchanger directly with steam from the HRSG.

The CHP is expected to generate approximately 3 TWh of electricity and around 1 TWh of thermal heat per year.

Project rationale

The main reason behind Eon Gasturbiner Sverige decision to commission a new power plant is to be able to supply the electrical grid with additional electricity generation for the southern part of Sweden. In combination with this, to be able to supply heat for Malmö city in an efficient and economic way with a state-of-the-art CHP plant.

Challenges faced

The biggest challenge of the project is that the CHP plant is to be installed within an existing building, and that components and equipment located outside of the existing building are to be kept to a minimum.

The original Öresundsverket power plant was built in three stages between 1953 and 1964, and used coal and oil fired boilers for electricity and heat production. The plant is located in an industrial and harbour area in Malmö.

To be able to build a power plant within an existing building special attention needs to be made to the layout of the CHP during the design phase. This is to ensure the best possible use of the building’s existing structure with respect to space and arrangements for erection, daily operation, maintenance and overhaul. In particular, the columns supporting the roof or different floors cannot be touched, which clearly makes the erection of the equipment more difficult.

Furthermore, because of the columns and their given distance, the appropriate arrangement of new gates for erection and maintenance is very important. To gain more precise information about the dimensions and location of existing structures such as columns, platforms, walls, a laser beam scanning process was carried out.

Furthermore, it is important that the sequence of the installation of the main equipment is settled at the very beginning of the project phase. To put the large main components (e.g. steam turbine, gas turbine and the two generators) in their locations inside the building they have to be brought in successively. Therefore, it is necessary to have an accurate scheduling and shipment of the equipment, especially with regard to the short construction period.

Plant technology

To be able to reach the required power output and efficiency it is necessary to build the power plant using high quality and highly efficiency equipment. The main component of the power plant is the GE gas turbine type 9FB.

The 9 FB gas turbine is the latest evolution in GE’s proven F series, which has accumulated more than 13 million hours of commercial service around the world. The 9 FB is the 50 Hz version of the 60 Hz, 7 FB gas turbine, which was introduced in 1999.

The compressor is based closely on the FA compressor and consists of 18 stages with variable inlet guide vanes to maintain high part-load efficiency and low emissions over a wide operating range. The variable vanes also improve low-speed surge characteristics, make start-ups easier, and provide good part-load performance in combined-cycle applications. Closing the vanes keeps exhaust temperatures up at reduced loads, thus retaining steam-raising capabilities if the gas turbine is running at less than 100 per cent load. The 9 FB machine runs at a compressor pressure ratio of 18.5 to 1.

The CHP plant’s power train will consist of a GE Energy 9FB 50Hz gas turbine
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The three-stage turbine of the 9 FB was redesigned because of the requirement for a higher firing temperature. Within the 18 combustors (with a dry low NOx (DLN) 2.6+ combustion system) the firing temperature is greater than 1370 °C.

The FB firing temperature was increased by more than 38°C compared to GE’s FA technology, resulting in combined-cycle efficiency rating improvements of more than one per cent. Output improvements in excess of five per sent were also achieved.

The use of advanced turbine materials, such as single crystal first-stage buckets ensures that components can stand up to the higher firing temperatures of the FB without increasing maintenance requirements.

Behind the gas turbine is a triple pressure HRSG with reheat in a vertical arrangement and its stack on top. Supplementary firing is not available.

To fulfil the strict emission regulations of 15 mg/MJ fuel for NOx operating on natural gas, the HRSG is equipped with a selective catalytic reduction system, working on aqueous ammonia. The necessary auxiliary equipment, like truck unloading station and ammonia storage tanks, are located close to the HRSG. An auxiliary boiler supplies steam for start-up.

The steam turbine is a three casing condensing-extracting turbine consisting of a high-pressure/intermediate-pressure part and a double flow low-pressure part connected with a “one-pass” condenser with titanium tubes because the cooling medium is sea water. The sea water intake is approximately two km away from the CHP plant, so the cooling water will be piped to and from the site.

Becasue of a gas turbine power output of more than 281 MW during ISO-conditions the gas turbine generator is hydrogen-water cooled. For the steam turbine power output an air/water cooled generator is sufficient.

To provide the necessary demineralized water, a water treatment plant will be supplied. Two lines of 100 per cent capacity will refill the 1200 m3 demineralized water tank to feed the water/steam cycle and the gas turbine during operation on liquid fuel oil.

A second water treatment plant will be erected to compensate for any losses in the district heating system of Malmö city. In order to maintain the pressure of the district heating system, a pressure control system will be provided.

The CHP plant’s distributed control system (DCS) is located in the control room. It handles the overall plant control functions (via start-up, shutdown and emergency operation signals), monitors the field instrumentation and controls the auxiliary systems. Due to the high automation standard only one operator is necessary to control the entire CHP plant via the DCS.

The gas turbine and its generator will be controlled and monitored by a GE Mk VI control and monitoring system which is linked to the DCS. The control and monitoring system of the steam turbine and its generator will be similarly likewise.

Project status

HPE is the consortium leader and has responsibility for the overall design of the CHP plant. In addition, the company will execute the civil works, the installation, the commissioning and supply the balance of plant and electrical equipment. GE Energy will supply the gas turbine and steam turbine generator set, as well as the HRSG and the DCS.

Because of the project’s tight timeframe it is of prime importance that the components arrive at site as scheduled. However, before the new equipment can be installed, some civil works needs to be finalized, consisting of some demolition works, new piling inside the building and new foundations.

In 22 months the gas turbine will have its “first fire”, starting the hot commissioning phase for the CHP plant and ending in a trial run with a performance test to demonstrate that the cogeneration plant fulfils the agreed operating characteristics and performance.