Oil shale in Estonia
Oil shale in Estonia is an important resource for the national economy. Estonia's oil shale deposits account for just 17% of total deposits in the European Union but the country generates 90% of its power from this source. The oil shale industry in Estonia employs 7,500 people—about one percent of the national work force—and accounts for four percent of its gross domestic product.
There are two kinds of oil shale in Estonia – Dictyonema argillite (claystone) and kukersite. The first attempt to establish an open-cast oil shale pit and to start oil production was undertaken in 1838. Modern utilization of oil shale commenced in 1916. Production began in 1921 and the generation of power from oil shale in 1924.
In 2005 Estonia was the leading producer of shale oil in the world. Of all the power plants fired by oil shale, the largest was in this country. As of 2007, six mines (open cast or underground) were extracting oil shale in Estonia.
There are two oil shale types in Estonia–Dictyonema argillite (claystone) and kukersite.
Dictyonema argillite 
The marine-type Estonian Dictyonema argillite (also known as Dictyonema oil shale, Dictyonema shale or alum shale) of an Early Ordovician age is a brown lithified claystone belonging to the formation of black shales of sapropelic origin. It occurs in most of northern Estonia on an area of about 11,000 square kilometres (4,000 sq mi). The thickness of the Dictyonema argillite layer varies from less than 0.5 metres (1.6 ft) to 8 metres (26 ft) and lays at a depth of 10 to 90 metres (30 to 300 ft). Geological reserves of Dictyonema argillite in Estonia were estimated approximately to 70 billion tonnes. Although reserves of the Dictyonema argillite surpass those of kukersite, its quality is poor as a source for the energy production. The heating value of the Dictyonema argillite is 5–8 MJ/kg, and the Fischer Assay oil yield is 3–5%. The organic content of the Dictyonema argillite of north-western Estonia varies from 10 to 20%, and it contains up to 9% pyrite. It also contains a small scale of heavy metals, such as uranium (up to 300 g/t), molybdenum (up to 600 g/t), and vanadium up to 1200 g/t. The argillite of north-western Estonia has sulfur content of 2–4 %; it contains fewer metals and up to 17% of organic matter.
Kukersite is a light-brown marine-type oil shale of the lowest Upper Ordovician formation, named after the Kukruse settlement in Estonia. Kukersite lies near the surface and dips to the south, so that deposits are found at depths from 7 to 170 metres (20 to 560 ft). It occurs as an often calcareous layer of 2.5 to 3 metres (8.2 to 9.8 ft) thickness. There are a total of 50 oil shale layers. Kukersite was deposited in a shallow marine basin, forming a part of the Baltic oil shale basin with a total area about 3,000 square kilometres (1,200 sq mi) to 5,000 square kilometres (1,900 sq mi). The main kukersite deposits in Estonia are the Estonian deposit and the Tapa deposit.
Estonian kukersite deposits are one of the world's highest-grade deposits with more than 40% organic content and 66% conversion ratio into shale oil and oil shale gas. Fischer Assay oil yield is 30 to 47%. The principal organic component of kukersite is telalginite, derived from the fossil green alga, Gloeocapsomorpha prisca, which has affinities with the modern cyanobacterium, Entophysalis major, an extant species that forms algal mats in inter-tidal to very shallow subtidal waters. Matrix minerals dominantly include low-magnesium calcite, dolomite, and siliciclastic minerals. They are not rich in heavy metals.
Early history 
The first written information about oil shale in Estonia were made by August Wilhelm Hupel in 1777. According to Peter Simon Pallas, the occurrence of burning rock on the southern coast of the Gulf of Finland occurs in the travel notes of the 18th century naturalist and explorer Johann Anton Güldenstädt. According to Paul Kogerman, Estonia's former Minister of Education and the founder of the oil shale chemistry, Estonian oil shale was discovered by a professor of University of Tartu Otto Moritz Ludwig von Engelhardt.
The first scientific research on the oil yield of Estonian oil shale was carried out at the St. Petersburg Imperial Academy of Sciences in 1791 by a German chemist Johann Gottlieb Georgi. The paper was based on the samples collected on the territory of Kohala Manor near Rakvere. In 1838—1839, a Baltic German geologist Gregor von Helmersen described in detail the Vanamõisa oil shale deposit. In 1838, he undertook the first attempt to establish an open-cast pit in the vicinity of Rakvere and attempted to obtain oil from the Vanamõisa oil shale deposit by distillation. Although the attempt of shale oil distillation failed, oil shale was used as a low-grade fuel. In the nineteenth century, the geology and chemistry of oil shale were also studied in the University of Tartu by Georg Paul Alexander Petzholdt, Alexander Gustav von Schrenk, Carl Ernst Heinrich Schmidt, Carl Friedrich Schmidt, and others.
Studies of Estonian oil shale resources and mining possibilities intensified in the beginning of 20th century because of industrial development of Saint Petersburg and a shortage of fuel resources in the region. In 1910, there was a plan of construction of a large-scale shale oil plant in Estonia. The coming of World War I, coupled with a serious fuel crisis, accelerated these studies and in 1916, a group of geologists led by Nikolay Pogrebov were sent to Estonia to organize the mining of oil shale and its transportation to St. Petersburg. In June 1916, the first tonnes of oil shale were mined in Pavandu and were delivered to the Saint Petersburg Polytechnical Institute for large-scale experiments. Oil shale was utilized at gasworks and was also burned in boiler houses. For large-scale oil shale utilization, construction of oil shale-fired power plants and shale oil thermal processing factories was planned. However, Germany occupied Estonia and the following Estonian War of Independence caused their cancellation. At the same time, experiments on the uses of oil shale started in Estonia.
The year 1916 is considered the beginning of the Estonian oil shale industry. In 1917, Russian paleobotanist Mikhail Zalessky named kukersite oil shale after the Kukruse settlement. Continuous mining activities started shortly after. In February 1918, the oil shale basin in North-East Estonia was occupied by German troops and mining activities were carried out by Internationales Baukonsortium. However, before the end of the occupation at the same year, only a trainload of oil shale was mined and sent to Germany for investigation and experimenting with a retort constructed by Julius Pintsch A.G. (Pintsch's generator).
On 24 November 1918, the Estonian State Oil Shale Industry (Riigi Põlevkivitööstus, predecessor of nowadays Viru Keemia Grupp) as department of the Ministry for Trade and Industry was established and it took over all existing open-pit mines. New open-pit mines were opened at Vanamõisa in 1919 and underground mines at Kukruse and Käva in 1920 and 1924 respectively. At the same time, several foreign investors started their oil shale activities in Estonia. Underground mines were opened at Kiviõli (1922), Küttejõu (1925), Ubja (1926), Viivikonna (1936), and Kohtla (1937). Initially, oil shale was used primarily in the cement industry, for firing in locomotive furnaces, and as a household fuel. The first large industrial consumer of oil shale were the Port Kunda cement factory (now Kunda Nordic Cement), which transferred its rotary kilns for cement production to oil shale firing in 1921, and the Asserin portland cement factory Aseri. Tallinn pulp factory (Põhja paberi- ja puupapivabrik) opened its own oil shale mine in 1923. As of 1925, all locomotives in Estonia were powered by oil shale. Systematic research of oil shale and its products began in Estonia in 1925, initiated by professor Paul Kogerman.
Shale oil production started in Estonia in 1921, when the National Oil Shale Industry built the first experimental oil shale processing retorts in Kohtla-Järve. These retorts used vertical retort technology, the forerunner of current Kiviter processing technology. In 1924, an oil plant using horizontal retort (fusion retort) technology was opened in Vanamõisa. The German-owned company Eesti Kiviõli (predecessor of Kiviõli Keemiatööstus) built four tunnel kilns between 1927 and 1938. Swedish owned Eestimaa Õlikontsortsium (Estonian Oil Consortium), founded in 1928 and operating in Sillamäe, used originally internally heated retorts, but switch to tunnel kilns in 1935. In 1931, Consolidated Gold Fields of the United Kingdom built an oil factory at Kohtla-Nõmme equipped with eight rotating retorts (Davidson's retorts). This facility was closed in 1961.
The oil shale-fired power industry started in 1924, when the Tallinn Power Plant switched to oil shale. Afterward oil shale-fired power plants were built in Püssi, Kohtla, Kunda, and Kiviõli. At the beginning of World War II, the total capacity of oil shale power plants was 32.5 MW. These power plants used mainly furnaces with a movable-bar sloping grate (Krull-Lomshakov or Ilmarine-type).
After beginning of the Soviet occupation in 1940, all oil-shale industry was nationalized and subordinated to the Mining Office and later to the General Directorate of Mining and Fuel Industry of the Peoples' Commissariat for Light Industry. In 1941, the industry was largely destroyed by the retreating Soviet forces. During the German occupation, the industry was merged into a company named Baltische Öl GmbH – Berlin, which was subordinated to Kontinentale Öl, an affiliate of IG Farben. The main purpose of the industry was oil production for the German Army. In 1942, 592,102 cubic metres (20,909,900 cu ft) of shale oil was transported to Germany. When the Soviet troops advance into Estonia in 1944, about 200 Estonian oil shale specialists were evacuated to Schömberg, Germany to work at the oil shale industry planned as a part of the Operation Desert (Unternehmen Wüste).
Post World War II 
After World War II, the shale oil industry was developed at Kohtla-Järve and Kiviõli. Between 1946 and 1951, 13 Kiviter-type retorts were built in Kohtla-Järve with an additional three retorts built between 1981 and 1987. In addition, between 1956 and 1968 two tunnel kilns were in operation. From 1953 to 1963, eight Kiviter-type retorts were in use at Kiviõli. The first Galoter-type retorts with a solid heat carrier were built at Kiviõli in 1953 and 1963 (closed in 1963 and 1981 respectively) and the Narva Oil Plant with two Galoter-type retorts was commissioned in 1980 near the Eesti Power Plant.
From 1948, after commissioning of the shale gas plant in Kohtla-Järve, Estonian-produced oil shale gas was used in Leningrad and in northern Estonian cities as a substitute for natural gas. 276 gas generators were operational until 1987. During 1946–1952, Dictyonema argillite was used for uranium production at Sillamäe Processing Plant.
In 1949, the Kohtla-Järve Power Plant – the first power plant in the world using pulverized oil shale at an industrial scale – was commissioned with capacity of 48 MW, followed by the Ahtme Power Plant in 1951 with capacity of 72.5 MW. The world's two largest oil shale-fired power stations – Balti Power Plant and Eesti Power Plant (known as the Narva Power Plants) – were opened in 1965 and in 1973. Because of the success of oil shale-based power generation, Estonian oil shale production peaked in 1980 at 31.35 million tonnes. In 2004, two power units with circulating fluidized bed combustion (CFBC) boilers were put into operation at Narva Power Plant.
In 1984, the scientific-technical journal Oil Shale was founded in Estonia.
As of May 2007, Estonia has been actively engaged in exploiting oil shale on a significant scale and accounts for 70% of the world's processed oil shale. In 2005, Estonia mined 14.8 million tonnes of oil shale. During the same period, mining permits were issued for almost 24 million tonnes, with applications for mining an additional 26 million tonnes. Estonia has adopted the "National Development Plan for the Use of Oil Shale 2008-2015", which limits the annual mining of oil shale to 20 million tonnes. Companies involved in oil shale mining are Eesti Põlevkivi, Viru Keemia Grupp, Kiviõli Keemiatööstus and Kunda Nordic Cement.
As of 2007, six oil shale underground mines and open-cast mines were in operation and one mine was in preparation phase in Estonia. The historical ratio of underground mining to open-cast mining is approximately fifty-fifty, although it is tending to move away from open-cast production as bed depths increase.
The Aidu and Narva opencast mines, operated by Eesti Põlevkivi, uses surface mining technology of stripping with relatively big bucket (10–35 cubic meters) excavators. Both the overburden and the bed are at first broken up by blasting. Stripping is done with smaller excavators in opencasts with thin overburden using front end loaders and hydraulic excavators. The Aidu opencast mine uses bulk extraction of all beds, while the Narva opencast mine and the Põhja-Kiviõli opencast mine, operated by Kiviõli keemiatööstus, use highly selective extraction in three layers of seams. Exhausted open-cast areas are gradually being regenerated through land recultivation and reforestation.
Underground mines exploit room and pillar method. Longwall mining, used earlier, was abandoned in 1990s. The largest oil shale mine in the world is the Estonia Mine, opened in 1972. It is operated by Eesti Energia Kaevandused.
Shale oil extraction 
In 2005, Estonia was the largest shale oil producer in the world although it is expected that as of 2007, China has taken that position. In 2005, Estonia produced 345,000 tonnes of shale oil, of which 222,000 tonnes were exported, 8,000 tonnes were utilised for electricity generation and 98,000 tonnes for heat generation. There are three shale oil producers in Estonia: VKG Oil (a subsidiary of Viru Keemia Grupp), Narva Oil Plant (a subsidiary of Eesti Energia) and Kiviõli Keemiatööstus.
Electricity generation 
The Estonian energy company Eesti Energia owns the largest oil shale-fuelled power plants (Narva Power Plants) in the world. In Estonia, more than 90% of electricity is generated from oil shale.
Cement production 
The spent shale (semi-coke) is used for portland cement production at the Kunda Nordic Cement factory. In 2002, 10,013 tonnes of semi-coke were used for cement production. As well, the Viru Keemia Grupp is planning to construct a cement factory for utilizing spent oil.
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