The Geothermal Power Plant at Nesjavellir, Iceland

Abstract

The third stage of the Nesjavellir combined power plant was commissioned in late 1998 after a record construction period of only 22 months. Two 30 MW turbine generator units were installed and considerable modifications of the thermal power plant were made. The nominal capacity of the plant is now 60 MWe electric and 200 MWt thermal power. Geothermal steam and water from 10 production wells are gathered in a central separator station, supplying up to 132 kg/s of steam and 240 kg/s of water. Electricity is generated in two condensing steam turbine units. The exhaust steam from the turbines is used to preheat fresh water in the condensers. The separated geothermal water is used in heat exchangers to heat the preheated water up to the required temperature. Finally, the water is treated in de-aerators to suit the requirements of the distribution system. Thus, the steam and the separated geothermal water are utilised, in the most economical way possible, for co-generation of electric and thermal power, which is also good for the environment as less heat is released to the atmosphere than in conventional geothermal plants. The paper gives a general overview of the process, the design and the layout of the Nesjavellir plant. The main features of the equipment used are described, as well as the planned operation with load variations during summer and winter seasons to achieve an optimal use of the geothermal source.