Case Studies

1. Wartsila

8 MWe Gas Engine CHP. Ringkøbing Fjernvarmeværk District Heating, Denmark


Project Description

Ringkøbing is a town in Denmark. Its CHP district heating project plays a central role in the town’s heat and electricity supply, and the wider Danish CHP development.

The system consists of a Wärtsilä 20V34SG spark-ignition lean-burn gas engine, air-compressor and gas regulator auxiliaries, an exhaust-gas boiler, and 5,200 m3 heat storage tank. With an installed capacity of 8 MWe and 9.6 MWth, it is the largest such engine of its kind, and Wärtsilä’s first commercial 20-cylinder gas engine. It replaced an existing gas turbine at the site.

The gas engine produces 14.7 kg/s of exhaust gas at 390ºC. This is used to heat water to 75ºC for district heating of the local community. The water is returned at 35ºC to 45ºC for re-heating in the heat recovery system.

The cogeneration plant is connected to the town’s district heating network and local electricity grid.

Operational Conditions

The Ringkøbing plant operates around 15 hours a day in summer and 24 hours a day in winter, responding to the local heat demand. It delivers heat to 3,500 local people. Its electricity output is sold to the local utility company RAH through the grid. The limited operation time in summer favours the use of gas-engines as they are flexible and responsive for regular starting and stopping. Furthermore, the power-to-heat ratio of the Wartsila engines is favourable, increasing the value of the electrical output.

Project Development Process

The plant was established in the early 1990s during the height of the Danish government’s programme to promote CHP and when the town was also connected to the piped natural gas network. Ringkøbing Fjernvarmeværk, the district heating company, originally chose to install a gas turbine at the Rindum substation.

This was the most appropriate technology to meet the government’s requirement at the time that 90% of the heat output was from CHP. In today’s market the electrical output from the plant contributes more to the system’s payback, so it became attractive to install a gas engine with a suitable power-to-heat ratio in 2002. It has also helped to meet the strict Danish standards on pollution emissions from power stations. The system was operational three months after it arrived on site.

Project Performance

Table 1. Project Performance Data

Total electricity production

~ 56,000 MWh / year

 

Pre-2002 system

Wärtsilä engine

Electrical efficiency

27.2%

44%

Thermal efficiency

64.8%

52.3%

Total operational efficiency

92%

96.3%

Power-to-heat ratio

0.42

0.84

Maintenance

<8 days per year

Outages (first 2,300 h operation)

None

NOx emissions (5% O2)

500 mg/m3

The gas engine system has enabled the plant to adapt successfully to its new circumstances. The power output of the system has almost doubled, while the heat output has decreased by less than 1%. The overall efficiency of the system has increased because the gas engine’s exhaust gas contains less oxygen so that more heat can be recovered. Furthermore, the system has both low-temperature and high-temperature cooling circuits, improving heat-recovery. The maintenance requirements are unchanged, and the system’s reliability is high, with no outages in the first 4 months of operation.

Project Operational Arrangements

The CHP system is owned and operated by Ringkøbing Fjernvarmeværk which has responsibility for supplying heat and power to the local networks. With the installation of the engine in 2002, the company signed a 63,000 hour maintenance and service contract with Wärtsilä to replace the servicing arrangements for the old system. This was the most convenient and cost-effective option, as Wärtsilä has a well-established network in Denmark.

Project Financing

Table 2: Project financing data

Generator installed costs

$625 to $690 per kW

Total installed costs

$5.3 million (€4.2 million)

O&M costs

20% lower

Fuel costs (natural gas)

$75 to $80 per MWh

Project lifetime (y)

20 years

Payback period (y)

Not available

The total investment for the installation of the gas engines was high, but since the previous system was due for overhaul, the marginal cost was reduced. The extra investment is paid back through the 20% reduction in heat production costs, the increased electricity output increased and lower O&M costs.

Further Developments

CHP applications for district heating are very common in Denmark, as they were actively promoted by the government in the 1980s and 1990s. Various technologies and fuel-types are used, including a large number of gas engines based on their operational flexibility and power-to-heat ratio. Wartsila has 170 MW of installed gas engines in the country at 26 district heating plants.

2. Solar Turbines

4,600 kWe Gas Turbine CCHP. Shanghai Pudong International Airport

Project Description

This CCHP project at Shanghai Pudong International Airport generates combined electricity, heating and cooling for the airport’s terminals at peak demand times. It is fuelled by natural gas from offshore in the East China Sea.

The system consists of a Centaur 50 gas turbine supplied by Solar Turbines, an unfired Heat Recovery Steam Generator (HRSG) and steam-fired absorption chillers. The electrical capacity is 4,600 kW.

The gas engine exhaust is used by the HRSG at a rate of 11 t/hr, producing 8 barg saturated steam at 185ºC. The steam is used by the absorption chillers to cool water to 7ºC/12ºC. The project is connected to the electricity network at a 10.5 kV level, but does not export electricity, as all power is used on-site.

Operational Conditions

The system operates 16 hours per day to offset peak energy costs for the airport. It therefore does not aim to provide a complete energy solution, but rather to decrease the dependence of the airport on the network, and to save energy costs.

The energy use of the airport is substantial, with electricity demand around 28 MW and heat demand between 20 and 65 t/hr. The CCHP system meets 20% to 30% of the airport’s electricity demand and 15% to 50% of its heat demand, depending on the season.

Project Development Process

The aim of installing the CCHP system at Shanghai Pudong International Airport was to provide the terminals with a secure and reliable energy supply, while reducing the energy costs for the owner.

The CCHP project at Shanghai airport became operational in 1999, but the planning process was started several years before that. Technologically there were no problems in the development and installation process, as CCHP is an established technology, and Solar Turbines has strong experience.

The main obstacle during project development was securing approval to connect to the electricity network. The system would not export electricity to the grid, but there were concerns about the impact on network loads when the system would start operating. As a result the approval process took two years, and only after two years of operation could the system reach full capacity.

Project Performance

Table 3. Project performance data

Total energy production

19,200 MWh

Electrical efficiency


29%

Thermal efficiency


45%

Total operational efficiency


74%

Maintenance

< 10 days per year

Outages

< 5 days per year

Table 4. Environmental performance

NOx (ppm)

5 to 25

Noise level (dBA)

60

The CCHP system has been successful during the seven years operational life. The gas turbines have proven a reliable power source for the airport, and the achieved costs savings have repaid the investment.

Natural gas price fluctuations have been affecting the project. The airport therefore installed a fuel gas compressor, so that gas could be stored more easily, so gas can be bought when prices are favourable.

Tables 3 and 4 above show the technical and environmental performance of the system.

Project Operational Arrangements

The project is fully owned by Shanghai Pudong International Airport, but Solar Turbines provided the project management during the development process. System operation and maintenance has been provided by Shanghai Mariso Gas Turbine Services Co. since 2001. This outsourcing of O&M allows the project to run the system for longer hours, thereby increasing the financial benefits of the project.

Project Financing

Table 5: Project cost data

Installed costs

$5,400 per kW

O&M costs

< $3.00 per MWh

Fuel costs (natural gas)

$8.5 per MWh (power only)

Project lifetime (y)

25 years

Payback period (y)

< 6 years

Table 5 shows the project financial performance. Shanghai Pudong International Airport provided the full investment costs for the project. The up-front investment for the system was substantial, but it has been very successful in achieving costs savings, so it has had a real positive cash flow since 2001, and the payback is less than 6 years. Fluctuating natural gas prices remain the only uncertain factor in the economic performance of the project.

Further Developments

After commissioning the gas turbine system at the airport, Solar Turbines has been successful in securing further CCHP orders in China. Similar installations are now planned for Beijing Zhongguancun Software Park (1.2 MWe CCHP), Beijing Zhongguancun International Mall (2X4.6 MWe CCHP), Chengdu Century International Exhibit Centre (10.6 MWe CCHP), and a further 10 projects are under negotiation.

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