The Nesjavellir geothermal field is a high-enthalpy geothermal system within the Hengill area of SW-Iceland. Construction of the geothermal power plant began in 1987 and the first stage of the thermal plant was commissioned in 1990, following an intensive drilling and testing phase in the 1980s. The last 30 MWe turbine generator unit was commissioned in 2005.
Nesjavellir Geothermal Power Plant details:
- Flash steam, combined cycle geothermal plant
- 120 MWe, developed in three phases
- 300 MWth, or 1,800 liters/second of hot water at approximately 83° C
- 25 boreholes were drilled, from 1,000-2,200 meters
- Project management
- Overall plant design
- Environmental impact assessment and report
- Detailed mechanical design of the plant
- Detailed design of HVAC systems
- Bid preparations and tender evaluations
- Site supervision
- Acceptance test
- Training of operators
- Groundwater modelling
- Pre-feasibility study
- Feasibility study
The Nesjavellir power plant is a combined heat and power plant (CHP) wherein it produces electricity and hot water for district heating. The plant itself is a combined cycle plant, wherein a mixture of steam and geothermal brine is transported from the wells to a central separation station at 200° C and 14 bars.
From there the fluid (steam and liquid) goes into a steam separator and the two phases are separated. Moisture is removed from the steam, which is then sent through the turbine after which it is condensed in a condenser. Within the condenser fresh water is preheated. The preheated fresh water is then run through a system of heat exchangers, which utilize the heat from the liquid part of the brine after the steam separator. The fresh water is heated to the required temperature and sent through deareators, which remove the bulk of the oxygen. Then finally a small amount of geothermal steam containing acidic gases (hydrogen sulfide) is injected into the water to remove any remaining oxygen, thereby preventing corrosion and scaling.
This hot water is then pumped to a large storage tank at an elevation of 406 meters. From there, the hot water flows by gravity to two smaller storage tanks on the outskirts of Reykjavik to be used for heating and hot tap water.