The Kárahnjúkar project is the largest individual hydropower project developed in Iceland and is located in East Iceland. The gross head is 600 m. The project harnesses two glacial rivers, impounded by the Kárahnjúkar dam and two saddle dams. Headrace tunnels are a dominant feature of the Kárahnjúkar hydroelectric project. The powerhouse and appurtenant structures are located mostly underground in the Fljótsdalur valley.
The Kárahnjúkar supplies all generated electricity to an aluminium smelter operated by Alcoa. Therefore, operational reliability was a key issue in all design of the hydroelectric project.
The project harnesses two glacial rivers. The larger one, Jökulsá á Dal, is impounded by the concrete faced Kárahnjúkar dam and two saddle dams forming the Hálslón reservoir. The dams are rock-earthfill dams. The smaller one, Jökulsá í Fljótsdal, feeds into the Ufsarlón pond. Further diversions from the area east of Jökulsá í Fljótsdal add to the project. An overflow spillway and a bottom outlet in the Hálslón reservoir convey water back into Jökulsá á Dal and the Hálslón tunnel intake is equipped with trashracks, bulkhead and wheel gates.
From Hálslón reservoir and Ufsarlón pond water is conveyed by an extensive interconnected headrace tunnel system under the Fljótsdalsheiði plateau. Three tunnel boring machines were used to excavate 90% of the 40 km long headrace tunnel. The headrace tunnel feeds two vertical, steel lined pressure shafts leading to six Francis units located in the underground powerhouse. The transformers are located in a transformer cavern adjacent to the powerhouse. A one km long cable tunnel, with 220 kV cable connections, leads to the substation. Water from the turbines empties into a tailrace tunnel which opens into a tailrace canal, ending in the river Jökulsá í Fljótsdal. The surge facilities consist of the mildly sloping Miðfell surge tunnel and the vertical Hólsufs surge shaft.
Verkís provided complete engineering services including project planning, feasibility studies, tender documents, economic study, technical study, civil work design, mechanical design, electrical systems design, design review, environmental impact assessment and supervision.
The Challenge
Reykjavík Energy owns the Hellisheidi geothermal power plant, a combined heat and power plant located about 20 km from Reykjavík in south-west Iceland. The area is one of Iceland’s most active high enthalpy areas. A new area, at Gráuhnúkar, is being investigated for steam and fluid extraction. The purpose of the plants is to meet increased demand for electricity for industrial and domestic use and for hot water for heating. The 303 MWe geothermal power plant in Hellisheiði, Iceland, was commissioned in 5 stages during the years 2006-2011. The first stage was completed in 2006 with two high pressure geothermal turbines of 45 MWe capacity each. The second stage was completed in 2007 with one low pressure geothermal turbine of 33 MWe capacity. The third stage was completed in 2008 with two additional high pressure geothermal turbines, 45 MWe each.
In 2010 a heating plant for hot water generation was added to the plant, intended for district heating. The heat output of the first stage is 133 MWth and two further 133 MWth stages are to follow later. At the same time the Hellisheiði hot water main was put into service. The main is a 19,5 km long pipeline, 0,9-1,0 m in diameter, that carries hot water to Reykjavík. In 2011 the 5th stage of the plant was finished, which includes two new 45 MWe high pressure geothermal turbines, similar to the former turbines, situated in a new power house in Sleggjubeinsdalur.
The plant utilizes 500 kg/s of 180°C geothermal steam for electrical generation. The hot fluid is extracted from 30 wells, 2.000 – 3.000 m deep, and is led through steam and mist separators before entering the turbines. The high pressure steam gathering system operates at 9 bara pressure. The low pressure steam is generated with flashing of brine water from the steam separators at a pressure of 2 bara. The generating units are of single flow, single flash type with axial exhaust. Cooling is achieved through wet cooling towers of the counter flow type.
The main components of the electrical system for each unit consist of a 50 MVA generator, 50 MVA step-up transformer to 220 kV transmission voltage, an 11/11 kV transformer for connection to the 11 kV station service system and two 11/0,4 kV transformers for station service. The generating units, as well as the 11 kV and 0,4 kV distribution boards, are monitored and controlled by the state of the art control- and protection equipment.
Our Solution
Reykjavík Energy owns the Hellisheidi geothermal power plant, a combined heat and power plant located about 20 km from Reykjavík in south-west Iceland. The area is one of Iceland’s most active high enthalpy areas. A new area, at Gráuhnúkar, is being investigated for steam and fluid extraction. The purpose of the plants is to meet increased demand for electricity for industrial and domestic use and for hot water for heating. The 303 MWe geothermal power plant in Hellisheiði, Iceland, was commissioned in 5 stages during the years 2006-2011. The first stage was completed in 2006 with two high pressure geothermal turbines of 45 MWe capacity each. The second stage was completed in 2007 with one low pressure geothermal turbine of 33 MWe capacity. The third stage was completed in 2008 with two additional high pressure geothermal turbines, 45 MWe each.
In 2010 a heating plant for hot water generation was added to the plant, intended for district heating. The heat output of the first stage is 133 MWth and two further 133 MWth stages are to follow later. At the same time the Hellisheiði hot water main was put into service. The main is a 19,5 km long pipeline, 0,9-1,0 m in diameter, that carries hot water to Reykjavík. In 2011 the 5th stage of the plant was finished, which includes two new 45 MWe high pressure geothermal turbines, similar to the former turbines, situated in a new power house in Sleggjubeinsdalur.
The plant utilizes 500 kg/s of 180°C geothermal steam for electrical generation. The hot fluid is extracted from 30 wells, 2.000 – 3.000 m deep, and is led through steam and mist separators before entering the turbines. The high pressure steam gathering system operates at 9 bara pressure. The low pressure steam is generated with flashing of brine water from the steam separators at a pressure of 2 bara. The generating units are of single flow, single flash type with axial exhaust. Cooling is achieved through wet cooling towers of the counter flow type.
The main components of the electrical system for each unit consist of a 50 MVA generator, 50 MVA step-up transformer to 220 kV transmission voltage, an 11/11 kV transformer for connection to the 11 kV station service system and two 11/0,4 kV transformers for station service. The generating units, as well as the 11 kV and 0,4 kV distribution boards, are monitored and controlled by the state of the art control- and protection equipment.
The Result
Reykjavík Energy owns the Hellisheidi geothermal power plant, a combined heat and power plant located about 20 km from Reykjavík in south-west Iceland. The area is one of Iceland’s most active high enthalpy areas. A new area, at Gráuhnúkar, is being investigated for steam and fluid extraction. The purpose of the plants is to meet increased demand for electricity for industrial and domestic use and for hot water for heating. The 303 MWe geothermal power plant in Hellisheiði, Iceland, was commissioned in 5 stages during the years 2006-2011. The first stage was completed in 2006 with two high pressure geothermal turbines of 45 MWe capacity each. The second stage was completed in 2007 with one low pressure geothermal turbine of 33 MWe capacity. The third stage was completed in 2008 with two additional high pressure geothermal turbines, 45 MWe each.
In 2010 a heating plant for hot water generation was added to the plant, intended for district heating. The heat output of the first stage is 133 MWth and two further 133 MWth stages are to follow later. At the same time the Hellisheiði hot water main was put into service. The main is a 19,5 km long pipeline, 0,9-1,0 m in diameter, that carries hot water to Reykjavík. In 2011 the 5th stage of the plant was finished, which includes two new 45 MWe high pressure geothermal turbines, similar to the former turbines, situated in a new power house in Sleggjubeinsdalur.
The plant utilizes 500 kg/s of 180°C geothermal steam for electrical generation. The hot fluid is extracted from 30 wells, 2.000 – 3.000 m deep, and is led through steam and mist separators before entering the turbines. The high pressure steam gathering system operates at 9 bara pressure. The low pressure steam is generated with flashing of brine water from the steam separators at a pressure of 2 bara. The generating units are of single flow, single flash type with axial exhaust. Cooling is achieved through wet cooling towers of the counter flow type.
The main components of the electrical system for each unit consist of a 50 MVA generator, 50 MVA step-up transformer to 220 kV transmission voltage, an 11/11 kV transformer for connection to the 11 kV station service system and two 11/0,4 kV transformers for station service. The generating units, as well as the 11 kV and 0,4 kV distribution boards, are monitored and controlled by the state of the art control- and protection equipment.
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