Planning started already in 1947 and was continued for two years in this
50 km˛ High Temperature Area, one of at least 27 such resources, which
are directly connected with the most volcanic regions of the country.
A few experimental boreholes were drilled for the evaluation of
the exploitable power and the chemical composition of the steam.
After a rather long
intermission exploration and research continued with shorter intervals
from 1965 to 1986. The construction of the Geothermal Power station was
commenced in 1987 and continued incessantly until the cornerstone was
laid on May the 13th 1990. It
was officially started on September 29th the same year.
The Hengill Area is
amongst the largest High Temperature Areas of the country.
The geothermal activity is closely connected to three active
volcanic systems in the region. The
source of the natural- and artificial (boreholes) thermal activity in
and in the vicinity of the horticultural village Hveragerdi to the south
of the mountain range is an extinct central volcano, called 'The
Grenjadalur System'. North
of it is still another one, called 'The Hromundartindur System', which
was last active about 10.000 years ago.
The westernmost of the three systems, The Hengill System, has
erupted several times during Holocene and every now and then we are
reminded of the natural forces at large by tremors and earthquakes.
The Nesjahraun Lava
field was created during a fissure eruption of the Kyrdalur Fissure near
the Power station 2000 years ago and at the same time the largest island
of the lake came into being.
Results of extended
research have shown that the precipitation in the mountains north of the
geothermal areas percolates deep down into the earth and then flows
through subterranean faults and fissures to lower regions.
On its way the water is heated by the hot rock and resurfaces as
boiling water or steam through fissures extending to the surface or can
be reached by boreholes where there is no obvious thermal activity on
the surface. According to
the scientists, the hot water travels at a depth of only 3 km on the
average, but in places it comes as close as 1 km to the surface.
Because of extended
recent volcanic activity in the area, the rock strata are relatively
young. The uppermost 500 m
consist of hyaloclastites but beyond that are differently thick layers
of basaltic lavas. Dykes
become more frequent at greater depths and at 1400 - 1600 m they are
prevailing. Water veins are
common at the margins of the dykes, especially if they are acidulous.
The geothermal gradient
of the 'Kyrdalssprunga Volcanic Fissure' is the greatest in the area.
At sea level the temperature is 100°C and at 2000 m it exceeds
Since 1972 the
boreholes drilled have been fitted for future exploitation.
The results have been extremely good.
The average hole yields up to 60 mw. of exploitable power on the
average, sufficient for the central heating of a habitation of 7500
All together 23 holes
have been sunk, thereof 13 exploitable.
Four of them were connected at the first stage.
Their total output equals 140 mw.
At the end of the second stage additional 100 mw. will be
exploited, of which 50 were pipelined to the power station in 1991.
The remaining 50 MW will be activated this year (1994) bringing
the total output of the station up to at least 200 mw. The power station is designed for a maximum output of 400 mw.
in the year 2010 and according to estimates the present area can be
exploited economically with an average 300 mw. output for at least 30
exploitation of the excess steam for electrical production is ideal.
Then the steam is pipelined through turbines.
Some of the holes deliver almost clean steam for that purpose and
are estimated to suffice for up to 80 mw.
The pumps of the geothermal power station use 14 mw. of
electricity at it's maximum output (400 mw.).
A mixture of water and
steam is pipelined from the boreholes to the station through separators.
The steam continues to the heaters and the turbines. Exhaust chimneys are used for the excess steam.
In the heaters the steam condenses and the boiling water is
pumped to condense heaters where it heats up cold ground water.
The condense water cools of to about 20°C
The separated water
from the bore holes containing various minerals, which are deposited on
the inner surface of the heater. To
remove these deposits, steel balls are placed in the current to
pulverize them continuously.
The cold ground water
is supplied through boreholes in the lava field close to the lake and
pumped to containers by the station.
From there it continues to the separator heaters or condense- and
steam heaters, where it is heated to 85°C or 90°C.
The cold water is
saturated with oxygen, which causes corrosion after heating.
To eliminate the oxygen and other gasses the water is boiled at a
lower pressure level. This
process cools the water to 82-85°C.
Eventually a minute quantity of acid steam is added to the water
to eliminate the remnants of oxygen and reduce the ph of the water to
prevent deposits in the pipes. This
tiny quantity of sulphuric acid also prevents oxygen to reaccumulate in
the supply tanks of the capital and lends the funny smell to the water
when we turn on the tabs at home.
The natural discharge
from the Nesjavellir Thermal Area has for centuries been carried to the
lake. The increased
discharge from the power station might affect the organic life.
Therefore constant research and observations are carried out to
spot any changes immediately. Experiments
with pumping the discharge back into the ground are also continued, as
it has become a known fact, that the circulation of the water can be
overexploited if we are not careful.
The main buildings of
the power station are at an elevation of 177 m above mean sea level.
From there the hot water is pumped through a pipeline, 90 cm in
diameter in the beginning but narrowing to 80 cm for most of the 27,2 km
distance to the capital. The
pumps have only to be used to conquer the uphill gradient through the
mountains to the 406 m level and after that it free flows downhill to
Reykjavík. The pipeline carries a maximum of1870 l of 100°C hot water
per second. It is
thoroughly insulated and the heat loss never exceeds 2°C, the greater
the quantity of water running through, the less the heat loss.
Snow never melts on the pipeline in winter, which goes to show
how well it is insulated.
The steel pipeline to
the surge tank has a diameter of 900 mm and a wall thickness of 12 mm.
It is designed to carry water up to 96°C hot with a maximum
transport capacity of 1870 litres per second.
From the surge tank the water flows by gravity to storage tanks
on Reynisvatnsheidi and Grafarholt from where it is distributed to
Reykjavik and the nearby communities.
Those tanks are at an elevation of 150 m above sea level.
The steel pipeline from the surge tanks has a diameter of 800 mm
and a wall thickness of 8 to 10 mm, depending on the maximum inside
pressure. The steel pipe is
laid mostly above ground and rests on concrete pillars.
It is insulated with rock wool and covered with plastic and
aluminium sheets. Five
kilometres of the pipe is an underground-preinsulated pipeline with
polyurethane insulation and about 17 mm thick polyethylene plastic
cover. From Nesjavellir to
Grafarholt the transmission pipe measures about 27 km in length.
For design, material,
and manufacturing specifications the AD-Merkblâtter and DOM standards
were used. Testing
requirements were chosen according to the same Merkblâtter, but for
pressure testing of the steam collecting lines the ANSI B 31,1 standard
was used. Due to the
mountain slope the elevation difference between the highest and lowest
wellheads is 140 metres. By
using steam for pressure test, this elevation difference had not to be
taken into account, when choosing the pipe wall thickness.
Quality control is based on different control levels, which
includes approval of welders and weld inspectors, and welding
All welders had to have
a welding certificate according to DIN 8560, R 2-m to be accepted at the
site. All welds were marked
by initials to keep good record of each welder.
For the steam supply and the piping inside the powerhouse, the
quality standard for the welding and testing were based on the German
AD-Merkblâtter HP series. Contractors were required to keep record of all welds tested
and to hand over these reports to the inspectors at the end of each job.
In the steam supply system welding requirements were according to
the DIN standard 8563, part 3, quality class BS.
The wellheads are prefabricated and welded in a workshop.
Each wellhead is 100% X-rayed and visually inspected on both the
outside and as much as possible on the inside.
The welding method mostly used is manual metal arc welding.
pipelines have a diameter range from DN 250 to DN 1000.
The pipes are mostly spiral welded and came in random lengths of
about 12 metres. The steel quality was St-37.0 according to DIN 1626, with
certificates according to DIN 50049, 3.1.B.
All welding seams of the pipes were 100% inspected by ultrasonic
testing during the manufacturing process and the pipes were pressure
tested. All pipes on site
were welded with manual metal arc welding method.
25% of each weld were ultrasonic inspected.
Some radiographs were taken to compare the result to the
ultrasonic inspection. The
pipelines had to be laid through lava fields and down steep hills with
an inclination up to 45°. Overall
welding quality was very high, only small defects were found, mostly
porosity, slag and misalignment in large diameters.
Most of the cold water pipes are ductile iron with sockets, which
do not require welding.
Inside the powerhouse,
most of the pipes are made of stainless steel with a diameter range from
DN 100 to DN 800. These
stainless steel pipes are thin walled and have longitudinal welds.
The manufacturing process test requirement is similar to the
steam collecting pipes. The
most used welding method was TIG welding.
For few weldings, where the back gas shielding was difficult to
achieve, manual metal arc welding was used.
The welding quality control was 25% X-Ray supported by dye
penetrant testing. Only few
minor defects were detected.
transmission pipe design was based on spiral-welded pipes according to
steel quality St 37-3, DIN 17100. Pipes
made from steel quality St 52-3 were offered at the same price as those
made of steel St 37-3. The
St 52-3 pipe material was chosen and due to the stronger steel, a lower
welding factor was required, allowing a reduced welding control.
The total length (27 km) of the transmission line was divided
into three sections. Erection
time was chosen two years to enable Icelandic firms to carry out the
work. Three Icelandic
companies built the pipeline and a forth company made and erected the
concrete fundaments. The
welding method was MMA. The
welds were carried out inside tents, which was obligatory, because of
windy weather and often heavy rain.
Most of the welders preheated the joints to 50-100°C before
welding. The welding rods
were kept in heating boxes on site.
The welding quality required was according to the DIN standard
8563/3, quality class BS. All
welds were inspected visually from the outside and the inside.
Some times the inspectors requested minor repairs, mostly due to
undercuts or incomplete penetration.
After the visual
inspection the inspectors chose the welds to be X-Rayed.
Due to the close visual inspection on the outside and the inside,
an X-Ray inspection amount of only about 2% of the total weld length was
required, unless there was a quality problem with a new welder.
The result from the X-Ray inspection was very good.
Only minor defects were found, like porosity. Ultrasonic testing was also performed at random places.
The result was also very good.
Each new welder was under strict inspection during the first
weeks. That way the
inspectors noticed very quickly if a welder had problems with fulfilling
the quality requirements. Two
or three welders gave up welding after a short time even though they had
passed the welders test. At
the end of the project a weld report was published.
A part of this project was to dismantle two storage tanks at
Oskjuhlid in Reykjavik and to erect them again at Reynisvatnsheidi.
These storage tanks were built in the year 1968 and all parts
were visually inspected. Some
plates had to be rejected due to deep pitting corrosion and the material
was replaced by a new on. The
inspectors performed the same quality control and inspection as on the
This project is one of
the biggest welding and welding quality control projects in Iceland to
this date. The welding quality control was a part of the task of the
construction supervision team. This
brought the extension of the quality control directly to the Owners
decision. The co-operation
between the welding quality control and the welders was good and no
claims were blamed on the execution of the quality control.
Due to this close co-operation between all involved parties,
quality control was achieved at minimum cost.
The plant and transmission line have been in operation since
1990. No weld failures have
occurred showing so far that the weld quality is satisfying.
14 boreholes inLaugarnes.
17 boreholes in the capital.
boreholes in the capital.
13 holes sunk in Ellidaar Valley; 8 exploited in 1993
10 holes exploited in the capital.
77 boreholes sunk.
39 boreholes sunk.
34 boreholes exploited.