Oil shale in Estonia

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A brownish-grey wall of kukersite is shown with a blue-handled pick axe somewhat to the right of its centre. Fragments of other rocks are visible; most are a little wider than the pick axe handle.
Outcrop of Ordovician kukersite oil shale, northern Estonia

Oil shale in Estonia is defined by a national development plan as a strategic energy resource. It can be processed to produce an oil or directly burnt as a fuel. There are two kinds of oil shale in Estonia, both of which are sedimentary rocks laid down during the Ordovician era.[1] Graptolitic argillite (claystone) is the larger resource, but its organic matter content is relatively low and therefore it is not in industrial use. Kukersite has been mined for almost one hundred years. Its deposits in Estonia account for 1.1% of global oil shale deposits.

The first attempts to establish a surface oil shale mine and to start shale oil production were undertaken in 1838.[2] Modern industrial use commenced in 1916. Shale oil production began in 1921 and oil shale was first used to generate electrical power in 1924.[3] Systematic research into oil shale and its products began shortly afterwards and a department of mining was established at Tallinn Technical University in 1938. After World War II several new oil shale mines were opened. Estonian oil shale gas was used in Leningrad and in northern Estonian cities as a substitute for natural gas. Large oil shale-fired power stations were built and extraction peaked in 1980. Subsequently, the power supply from nuclear power stations that had come on line in Russia reduced demand and production.

The oil shale industry in Estonia employs 6,500 people—about one percent of the national workforce—and accounts for four percent of its gross domestic product. Most mined oil shale is used for electricity generation; about 85% of Estonia's electricity is generated by oil shale. Of all the power stations fired by oil shale, the largest was in this country.[4][5] Estonia is the second largest shale oil producer in the world. In addition, oil shale and its products are used for heating and as a feedstock for the cement industry.

The industry has serious past and present environmental impacts. It produces about 70% of Estonia's ordinary waste and 82% of hazardous waste and more than 70% of greenhouse gas emissions. It has also altered the groundwater regime and water quality. Former and current oil shale mines cover about one percent of Estonia's territory.

Resource[edit]

Graptolitic argillite[edit]

A specimen of Estonian graptolite argillite. The shiny portions are pyrite.
A specimen of graptolite argillite containing pyrite (FeS2) from the Türisalu cliff, a part of the Türisalu Formation
An isopach map of the Ordovician graptolitic argillite deposits in northern Estonia, indicating thickness in meters

Estonian graptolitic argillite (also known as Dictyonema argillite, Dictyonema oil shale, Dictyonema shale or alum shale) was laid down during the Early Ordovician age under a marine environment. It is a brown, lithified claystone of the Türisalu Formation belonging to the group of black shales of sapropelic origin.[6][7] In mainland Estonia, it occurs at the foot of the North-Estonia Klint, ranging from the Pakri Peninsula to Narva in an area covering about 11,000 square kilometres (4,200 sq mi).[8][9] When findings in the western Estonian islands are included, its extent increases to about 12,200 square kilometres (4,700 sq mi).[7] The thickness of the layer varies from less than 0.5 metres (1 ft 8 in) to a maximum of 8 metres (26 ft) in western Estonia, as does its subsurface depth, which ranges from 10 to 90 metres (33 to 295 ft).[8][10] It formed some 480 million years ago.[9]

Geological reserves of this rock in Estonia have been estimated at 60–70 billion tonnes.[6][9] Although reserves of graptolitic argillite surpass those of kukersite, it is a poor source of energy. Its calorific value is 5–8 megajoules per kilogram (MJ/kg) and its Fischer Assay oil yield is 3–5%.[8] The organic content of graptolitic argillite found in northwestern Estonia ranges from 10 to 20%. It contains up to 9% pyrite (generally between 2.4 and 6%) and various heavy metals, such as uranium (up to 1,200 parts per million (ppm) or 300 grammes per tonne (g/t)), molybdenum (up to 1,000 ppm or 600 g/t), vanadium (up to 1,600 ppm or 1,200 g/t), and nickel.[1][7] Other minerals include K-feldspars, quartz, clay minerals, light-brown phosphatic ooids, and accessory amounts of zircon, tourmaline, garnet, rutile, chalcopyrite, and glauconite.[7]

The composition of graptolitic argillite varies by location within Estonia. Western deposits contain corundum, amphiboles, and disthene and more clay minerals than are present in the east.[7] Analyses of northwestern Estonian deposits show a sulphur content of 2–4%; it contains fewer metals and up to 17% of the rock is organic matter.[1] In northeastern Estonia its carbon-to-hydrogen atomic ratio is about nine.[7]

Although the name Dictyonema argillite is widely used instead of graptolitic argillite, this name is a misnomer as the fossils in the rock are not graptolites from the genus Dictyonema but from the genus Rhabdinopora.[9]

Kukersite[edit]

Main article: Kukersite
A map of kukersite deposits in northern Estonia and Russia. The upper, northern third of the map shows the bordering water bodies. The Baltic Sea lies to the left of centre and the Gulf of Finland to the right.
Location of kukersite deposits within the Baltic Oil Shale Basin in northern Estonia and Russia

Kukersite is a light-brown marine-type oil shale of the lowest Upper Ordovician formation, formed some 460 million years ago.[11] Its name reflects the German language rendition of Kukruse Manor in northeastern Estonia.[12][13][14]

Estonian kukersite deposits are one of the world's highest-grade deposits with organic content varying from 15% to 55%, averaging over 40%. Its conversion ratio into usable energy (shale oil and oil shale gas) is between 65 and 67%[15][16] and its Fischer Assay oil yield is 30 to 47%.[17] Its organic matter has an atomic ratio of hydrogen to carbon of 1.51 and its mean calorific value is 3,600 kilocalories per kilogram.[15]

The principal organic component of kukersite is telalginite, derived from the fossil green alga Gloeocapsomorpha prisca. This species has affinities with the extant modern cyanobacterium, Entophysalis major, which forms algal mats in inter-tidal to very shallow subtidal waters.[17] Matrix minerals dominantly include low-magnesium calcite, dolomite, and siliciclastic minerals. Its heavy metal content is low in comparison with other oil shales in Estonia and Sweden.[10]

A photograph of northern Estonian kukersite. The rock is chocolate brown and the apparently abstract white branching figures are fossils.
Fossils in northern Estonian kukersite

Kukersite was deposited in a shallow marine basin. It lays at depths of 7 to 170 metres (23 to 558 ft).[8][16] The rock occurs within the Kukruse and Uhaku stages of the Viivikonna and Kõrgekallas formations, as an often calcareous layer.[16][17][18] The most significant kukersite deposits in Estonia—the Estonian deposit and the Tapa deposit—cover about 3,000 to 5,000 square kilometres (1,200 to 1,900 sq mi)[8][19][20] and together with the Leningrad deposit, which is an extension of the Estonian deposit, form the Baltic Oil Shale Basin.[18][21] The Estonian deposit, which covers about 2,000 square kilometres (770 sq mi), is used industrially. The Tapa deposit is not considered a reserve due to its lower calorific value, which makes its extraction economically inexpedient.[22][23] In northern Estonia there are 50 layers of kukersite; the six lowest of these form a 2.5-to-3-metre (8 ft 2 in to 9 ft 10 in) thick mineable bed.[1] In this area kukersite lies near the surface. To the south and west it lies deeper and its thickness and quality decrease.[22]

Estonia's kukersite represents about 1.1% of global and 17% of European oil shale resources.[24] The total kukersite resources in Estonia are estimated to be about 4.8 billion tonnes, including about 1 billion tonnes economically proven reserve, 0.3 billion tonnes economic probable reserve and about 3.5 billion tonnes uneconomical proven and probable reserve.[25][26] Economically proven and probable reserves forms active resource, which is defined as mineable deposits with energy ratings of at least 35 gigajoules per square metre and calorific values of at least 8 MJ/kg, located in areas without environmental restrictions.[22][25][27] Energy rating of the oil shale mining block is calculated as the sum of the products of thickness, calorific values and densities of all oil shale layers and limestone interlayers.[27] Up to 50% of active resources are designated as recoverable.[26]

History[edit]

Early history[edit]

The earliest documented description of oil shale in Estonia, authored by August Wilhelm Hupel, dates to 1777.[23] According to Peter Simon Pallas, the travel notes of the 18th-century naturalist and explorer Johann Anton Güldenstädt mention burning rock on the southern coast of the Gulf of Finland.[23][28] According to Paul Kogerman, a foundational figure in oil shale chemistry who later became Estonia's Minister of Education, Estonian oil shale was discovered by Otto Moritz Ludwig von Engelhardt, a professor at the University of Tartu.[14]

The first scientific research into the rock's oil yield was carried out at the St. Petersburg Imperial Academy of Sciences in 1791 by the German chemist Johann Gottlieb Georgi. His paper was based on samples collected on the territory of Kohala Manor near Rakvere.[23] In 1838 and 1839, the Baltic German geologist Gregor von Helmersen described the Vanamõisa oil shale deposit in detail. In 1838 he undertook the first attempt to establish a surface mine in the vicinity of Rakvere and sought to distil oil from the Vanamõisa oil shale deposit.[2][29] Although the distillation effort failed, oil shale was used as a low-grade fuel.[30] Other analyses of oil shale geology and chemistry were conducted during the nineteenth century at the University of Tartu. The analysts included Georg Paul Alexander Petzholdt, Alexander Gustav von Schrenk, Carl Ernst Heinrich Schmidt, and Carl Friedrich Schmidt, among others.[23][28]

Beginning of oil-shale industry[edit]

A monument commemorating the beginning of the oil shale industry, consisting of a grey concrete block about 1.5 metres wide and three-quarters of a metre deep. The block is topped by a black metal hopper filled with rocks. A blue plaque with white Estonian-language lettering just above the block explains its significance.
Historical monument at the location where the first tonnes of oil shale were mined

Analysis of Estonian oil shale resources and mining possibilities intensified during the early 20th century while Estonia was part of the Russian Empire. Industrial development was under way in Saint Petersburg, but regional fuel resources were in short supply. A large shale oil extraction plant in Estonia was proposed in 1910. The outbreak of World War I, coupled with a fuel supply crisis, accelerated the pace of the research.[28] In 1916, a group of geologists, led by Nikolay Pogrebov, was sent to Estonia to organise the mining of oil shale and its transportation to Saint Petersburg (then known as Petrograd). In June 1916, the first tonnes of oil shale were mined at Pavandu and delivered to Saint Petersburg Polytechnical University for large-scale experiments.[31] This is considered the beginning of the Estonian oil shale industry.[32] Oil shale was used in Saint Petersburg at gasworks and was also burned in boiler houses. For large-scale oil shale utilisation, the construction of oil shale-fired power stations and oil shale thermal processing facilities was planned. However, Germany occupied Estonia and the following Estonian War of Independence disrupted these plans.[3] At the same time, experiments on other uses of oil shale started in Estonia. Surface mines were opened at Kukruse by Böckel & Co. and at Järve by Mutschnik & Co.[33][34]

In 1917, Russian paleobotanist Mikhail Zalessky named kukersite[13][23] and the state enterprise Kütuse Erinõupidamise volinik põlevkivi kokkuostu ja varumise alal (English: Special Commissioner on oil shale purchase and stockpiling) began preparing an oil shale mine at Pavandu.[34] In February 1918, the area surrounding the oil shale basin in northeast Estonia was occupied by German troops and mining activities were carried out by Internationales Baukonsortium (English: International Construction Consortium). The occupation ended in late 1918, by which time no more than a single trainload of oil shale had been mined and sent to Germany for investigation and experimentation. This work used a retort constructed by Julius Pintsch AG (Pintsch generator).[35]

Development during Estonia's independence[edit]

 black-and-white photograph, dated 1924, of rail cars approaching a shale oil extraction facility. Small dark squares on the lower right indicate its path under a bridge.
Entrance to the Kukruse oil shale mine (1920s)
A black-and-white photograph of an open-pit shale mine dated to 1933. The upper half of the photo is occupied by a partly cloudy sky. The darker lower half shows a rail line, below ground level, with workers and hoppers full of materials.
Open-pit oil shale mine in Estonia (1933)
A black-and-white photo of the shale oil processing facility at Kohtla-Järve, dated to 1924. A rail line is shown in the lower third of the photo.
Kohtla-Järve shale oil extraction plant (Riigi Põlevkivitööstus, 1924)
A black-and-white photo of a shale oil extraction plant at Kohtla operated by New Consolidated Gold Fields Limited
Kohtla shale oil extraction plant (New Consolidated Gold Fields Ltd.)
A black-and-white photo of the Püssi power station, dated to 1937
Püssi power station (1937)

On 24 November 1918, Riigi Põlevkivitööstus (English: Estonian State Oil Shale Industry, later: Esimene Eesti Põlevkivitööstus (English: First Estonian Oil Shale Industry), the predecessor of nowadays Viru Keemia Grupp), was established as a department of the Ministry for Trade and Industry. It took over all existing open-pit mines.[35] 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 investors from abroad initiated oil shale enterprises in Estonia. Underground mines were opened at Kohtla (1937), and open-pit mines were opened at Kiviõli (1922; since 1930 underground mine) Küttejõu (1925), Ubja (1926) and Viivikonna (1936).[3] Initially, oil shale was used primarily in the cement industry, for firing locomotive furnaces, and as a household fuel. The first major industrial consumers of oil shale were the Port Kunda cement factory (now Kunda Nordic Tsement) in Kunda, which as an owner of the Ubja open-pit mine transferred its rotary kilns for cement production to oil shale firing in 1921, and the Asserin portland cement factory in Aseri.[3][36] In 1925, the Tallinn pulp factory Põhja paberi- ja puupapivabrik (English: Nordic Paper and Woodboard Mill) acquired the mining company Eesti Küttejõud (English: Estonian Heating Power), which had been established in 1922 by the Union of Estonian Industrialists as the first private oil shale mining company. As of 1925, all locomotives in Estonia were powered by oil shale.[37]

Shale oil production started in Estonia in 1921, when Riigi Põlevkivitööstus built 14 experimental oil shale processing retorts in Kohtla-Järve.[3][38] These vertical retorts used the method developed by Julius Pintsch AG that would later evolve into the current Kiviter processing technology. Each retort processed 40 tonnes of oil shale per day and produced an oil yield of 18%.[38] Along with the shale oil extraction plant, an oil shale research laboratory was founded in 1921.[33] In 1924, the British investor-owned Estonian Oil Development Syndicate Ltd. (later Vanamõisa Oilfields Ltd.) purchased an open-pit mine in Vanamõisa and opened a shale oil extraction plant which used horizontal retort (fusion retort) technology.[1][38][39] Each of the plant's two retorts was capable of retorting 15 tonnes of shale per day; however, technical problems arose and the plant was abandoned in 1931.[38][39] The German-owned company Eesti Kiviõli (German: Estländische Steinöl, English: Estonian Stone Oil, predecessor of nowadays Kiviõli Keemiatööstus), affiliated with G. Scheel & Co. and Mendelssohn & Co., was established in 1922.[40][41] After unsuccessful tests with the moving grate kiln, the company built four tunnel kilns between 1927 and 1938.[3][41] The Swedish–Norwegian consortium Eestimaa Õlikonsortsium (Swedish: Estländska Oljeskifferkonsortiet; English: Estonian Oil Consortium), controlled by Marcus Wallenberg, was founded in 1926 to build a shale oil extraction plant in Sillamäe.[39][42] The consortium built a tunnel oven in 1928. However, due to recession, production halted in 1930 and was not restarted until 1936.[38][43] A second tunnel oven was added in 1938.[44] In 1936, it produced 15,000 tonnes of oil, including 2,400 tonnes of gasoline.[38] New Consolidated Gold Fields Ltd. of the United Kingdom built a shale oil extraction plant at Kohtla-Nõmme in 1931 that was equipped with eight rotating retorts (Davidson retorts).[3][38] Each of these retorts was capable of processing 15 tonnes of oil shale per day.[38] This facility continued to operate until 1961.[3]

In 1939 Estonia mined 1.453 million tonnes of oil shale and produced 181,000 tonnes of shale oil, including 22,500 tonnes of oil that were suitable gasoline equivalents. The largest shale oil producer was Eesti Kiviõli (70,000 tonnes) followed by Esimene Eesti Põlevkivitööstus (61,000 tonnes). The mining and oil industry employed 6,150 persons.[40] Shale oil and gasoline produced from shale oil were exported to Germany, Czechoslovakia, Finland, Sweden, Norway, Latvia and Lithuania. In 1934, Eesti Kiviõli and New Consolidated Gold Fields established the service station chain Trustivapaa Bensiini (now: Teboil) in Finland. During 1940 this chain sold more shale-oil-derived gasoline in Finland than the entire conventional gasoline market in Estonia did.[45] In 1935, Eesti Kiviõli concluded a contract with the German Kriegsmarine to supply shale oil as a ship fuel.[40][46] Esimene Eesti Põlevkivitööstus and Eestimaa Õlikonsortsium signed similar contracts later.[46] In 1938, 45% of Estonian shale oil was exported exceeding import value of other fuels. It accounted for 8% of Estonia's total export.[47] Although the price of oil shale-based gasoline was at least triple that of global gasoline prices, high production and bilateral agreements supported its export.[45]

The oil shale-fired electrical power industry started in 1924, when the Tallinn Power Station switched to oil shale.[19] In 1933, it reached a capacity of 22 megawatts (MW). Other oil shale-fired power stations were built in Püssi (3.7 MW), Kohtla (3.7 MW), Kunda (2.3 MW), and Kiviõli (0.8 MW). At the beginning of World War II, the total capacity of oil shale-fired power stations was 32.5 MW. These power stations used mainly furnaces with a movable-bar sloping grate (Krull-Lomshakov or Ilmarine-type).[3]

On 9 May 1922 the first international discussion of Estonian kukersite took place at the 64th meeting of the Institution of Petroleum Technologists.[48] Systematic research into oil shale and its products began at Tartu University's Oil Shale Research Laboratory in 1925, initiated by professor Paul Kogerman.[29][49] In 1937, the Ministry of Economical Affairs established the Geological Committee. The Institute of Natural Resources was founded at the same year. A department of mining was established at Tallinn Technical University in 1938.[48] Estonian oil shale industries conducted tests of oil shales from Australia, Bulgaria, Germany and South Africa.[50]

German occupation[edit]

Soon after the Soviet occupation in 1940, the entire oil shale industry was nationalised and subordinated to the Mining Office and later to the General Directorate of Mining and Fuel Industry of the Peoples' Commissariat for Light Industry.[51] Germany invaded the Soviet Union in 1941 and the industry's infrastructure was largely destroyed by retreating Soviet forces.[40] During the subsequent German occupation, the industry was merged into a company named Baltische Öl GmbH. This entity was subordinated to Kontinentale Öl, a company that had exclusive rights to oil production in German-occupied territories.[40][51] Baltische Öl was divided into five units (Kiviõli, Küttejõu, Kohtla-Järve, Sillamäe, and Kohtla). Each consisted of an oil shale mine and shale oil extraction plant, except Küttejõu, which did not have an associated shale oil extraction plant. The shale oil extraction industry was partially restored and in 1943 it processed 201,600 tonnes of oil shale. Prisoners of war made up about two-thirds of the work force.[40]

The primary purpose of these industries was production of oil for the German Army. In 1942, 592,102 cubic metres (20,909,900 cu ft) of shale oil was transported to Germany.[51] Baltische Öl started construction of new mines and shale oil extraction plants; however, none of them became operational.[40]

While Soviet troops were advancing into Estonia during 1944, about 200 Estonian oil shale specialists were evacuated to Schömberg, Germany to work at an oil shale industry there, planned by the Operation Desert (Unternehmen Wüste).[49][51] Shale oil extraction plants in Estonia were destroyed and mines were ignited or inundated.[40][52] Existing oil shale-fired power stations in Püssi and Kohtla-Järve were also destroyed.[52]

Restoration of the industry after World War II[edit]

A colour photograph of the shale oil facility in Kohtla-Järve. The lower third of the photo is occupied by a curving driveway and the cars parked along it.
Old shale oil extraction plant in Kohtla-Järve
A black-and-white photograph of an underground oil shale mine, dated to 1970. The worker on the far right is steering a machine to the left of the photo.
Oil shale mining in a sub-surface mine in Estonia (1970)

In 1946 the mining industry was merged into Eesti Põlevkivi (Russian: Эстонсланец, English: Estonian Oil Shale, now Eesti Energia Kaevandused) under Glavslanets. Shale oil extraction, with the exception of the Kiviõli and Kohtla-Nõmme plants, was merged into the Kohtla-Järve shale oil combinate (Russian: Сланцехим, now Viru Keemia Grupp) under Glavgaztopprom. Both organisations were directed from Moscow.[53] New mines were opened near Ahtme (1948), Jõhvi (Mine No. 2, 1949), Sompa (1949), Tammiku (1951) and in the area between Käva and Sompa (Mine No. 4, 1953).[23] The Küttejõu open-pit mine was closed in 1947 and the Küttejõu underground mine was merged with the Kiviõli mine in 1951.[54]

The shale oil industry at Kohtla-Järve and Kiviõli was redeveloped. In 1945, the first tunnel kiln was restored and by the end of the 1940s four tunnel kilns located in Kiviõli and Kohtla-Nõmme had been restored. German prisoners of war contributed most of the labour.[55] Between 1946 and 1951, 13 Kiviter-type retorts were built in Kohtla-Järve. An additional three retorts were constructed between 1981 and 1987. In addition, between 1956 and 1968 two tunnel kilns were in operation at Kohtla-Järve. Eight Kiviter-type retorts were in use at Kiviõli between 1953 and 1963.[3]

In 1947, a pilot Galoter retort unit was built in Tallinn, capable of processing 2.5 tonnes of oil shale per day.[56][57] The first Galoter-type commercial scale pilot retorts were built at Kiviõli in 1953 and 1963 with respective capacities of 200 and 500 tonnes of oil shale per day. The first of these retorts closed in 1963 and the second in 1981.[3][56][58][59] During the 1950s, unsuccessful tests of oil shale underground gasification were conducted at Kiviõli.[1][60][61]

In 1948 an oil shale gas plant in Kohtla-Järve began production and for several decades the gas was used as a substitute for natural gas in Saint Petersburg (then known as Leningrad) and in northern Estonian cities.[47][62][63][64] It was the first time in history when synthetic gas from oil shale was used in households.[62] To enable its delivery, a 200-kilometre (120 mi) pipeline from Kohtla-Järve to Saint Peterburg was built, followed by a 150-kilometre (93 mi) pipeline from Kohtla-Järve to Tallinn.[62] In 1962 and 1963, converting oil shale gas into ammonium was tested; however, for industrial production oil shale gas was replaced with natural gas.[65] Oil shale gas production peaked in 1976 at 597.4 million cubic metres (21.10×10^9 cu ft).[66] Although this gas had become uneconomical by 1958, 276 gas generators operated until 1987.[3][67]

Between 1946 and 1952, uranium compounds were extracted from graptolitic argillite at the Sillamäe Processing Plant (now: Silmet).[10][68][69] More than 60 tonnes of uranium compounds (corresponding to 22.5 tonnes of elemental uranium) were produced from 271,575 tonnes of shale which was mined at the 15-metre (49 ft) deep underground mine.[7][9]

In 1949, the 48 MW Kohtla-Järve Power Station—the first power station in the world to use pulverised oil shale at an industrial scale—was commissioned, followed by the 72.5 MW Ahtme Power Station in 1951.[3]

An oil shale research institute (now a department within Tallinn University of Technology) was founded at Kohtla-Järve in 1958.[70] Preliminary research into oil shale-based chemical production began the same year. These investigations explored its potential uses in bitumen, synthetic construction materials, detergents, synthetic leathers, synthetic fibres, plastics, paints, soaps, glues, and pesticides.[71] Between 1959 and 1985, 5.275 billion cubic metres (186.3×10^9 cu ft) of mineral wool was produced from oil shale coke.[72]

Peak of production[edit]

A colour photograph of the Balti Power Station, highlighting its towers against a partly cloudy sky
The Balti Power Station
A black-and-white photograph of open-pit mining, dated to 1970, showing the silhouettes of bare hills and extraction machinery
Oil shale open pit mining in Estonia (1970)

In 1965, 510 million cubic metres (18×10^9 cu ft) of oil shale gas were produced and 16.5 million tonnes of oil shale were mined.[73] During the 1960s and 1970s the world's two largest oil shale-fired power stations (the Narva Power Stations) were built. Both burned pulverised oil shale. The Balti Power Station was built between 1959 and 1971 and the Eesti Power Station was built between 1969 and 1973.[22] This increased the demand for oil shale and consequently new mines were constructed: the underground mines Viru (1965) and Estonia (1973) along with the open-pit mines Sirgala (1963), Narva (1970) and Oktoobri (1974; later named Aidu).[23] The Estonia Mine became the largest oil shale mine in the world.[74] At the same time mines No.2, No.4, Kukruse, and Käva were closed.[23]

Because of the success of oil shale-based power generation, Estonian oil shale mining peaked in 1980 at 31.35 million tonnes and power generation peaked at the same year at 18.9 TWh.[2][22][75] The industry declined during the two decades that followed this peak. Demand for locally produced electrical power was reduced by construction of nuclear power stations in the Soviet Union, particularly Leningrad Nuclear Power Station.[2] In 1988, Moscow-based authorities planned a third oil shale-fired power station in Narva with a capacity of 2,500 MW. The concept met local opposition and was never implemented.[76]

The Narva Oil Plant, annexed to the Eesti Power Station and operating two Galoter-type 3,000-tonnes-per day retorts, was commissioned in 1980 and has since been updated.[3][59][77] These retorts were designed by Atomenergoproect and developed in cooperation with the Krzhizhanovsky Institute.[57][59] Started as a pilot plant, the process of converting it to a commercial-scale plant took about 20 years. Eesti Energia, an owner of the shale oil extraction plant, has modernised more than 70% of the equipment that was part of its original design.[58]

The intense pace of exploitation at the time was accompanied by growth in research. In 1968, a branch of the Skochinsky Institute of Mining was established in Kohtla-Järve,[48] and in 1984 the scientific-technical journal Oil Shale was founded in Estonia.[29]

Developments after regaining independence[edit]

A colour photograph of a train with open cars carrying oil shale near Ahtme, dated to June 2007. The locomotive is on the left.
Oil shale cargo train near Ahtme (20 June 2007)

The Tammiku and Sompa mines were closed in 1999 and the mines at Kohtla and Ahtme were closed in 2001.[78] In 2000, the open-pit mines at Viivikonna, Sirgala and Narva were merged into the singular Narva open-pit mine.[79] The Aidu open-pit mine was closed in 2012 and the Viru underground mine in 2013.[80][81] New mines were opened by Kiviõli Keemiatööstus (Põhja-Kiviõli open-pit mine; 2003), Kunda Nordic Tsement (Ubja open-pit mine; 2005) and Viru Keemia Grupp (Ojamaa open-pit mine; 2006).[1] In 2006, 90 years after major mining had begun, one billion tonnes were mined.[32][82]

In 2004, two power units with circulating fluidised bed combustion boilers were put into operation at the Narva Power Stations.[83] Construction of the new 300 MW Auvere Power Station, located next to the existing Eesti Power Station, began in 2012.[84] At the end of 2012, the Ahtme Power Station was closed.

In 2008, Eesti Energia established a joint venture, Enefit Outotec Technology, with the Finnish technology company Outotec. The venture sought to develop and commercialise a modified Galoter process–the Enefit process–that would enhance the existing technology by using circulating fluidised beds.[85] In 2013, Enefit Outotec Technology opened an Enefit testing plant in Frankfurt.[86][87]

VKG Oil opened a new Galoter-type retort called Petroter in December 2009.[88][89] Two firms participated in its engineering - the retort work was performed by Atomenergoproect and the condensation and distillation plant work was done by Rintekno of Finland.[90] The company started construction of a second Petroter plant in 2012 and plans to build a third plant.[91][92] Eesti Energia opened a new generation Galoter-type plant using Enefit 280 technology in 2012.[93]

Economic impact[edit]

A colour photograph of the Ojamaa oil shale mine near Kohtla-Järve, dated to 2007. Machinery and supporting devices are visible in the lower half and a stream of water traverses the centre of the photo. A cliff on the left is topped with trees; the low hills on the right are bare.
Ojamaa oil shale mine near Kohtla-Järve (July 2007)
Dragline excavator in the Narva open-pit mine (26 April 2005)

The "National Development Plan for the Utilisation of Oil Shale 2008–2015" defines oil shale as a strategic energy resource.[94] Estonia is the only country in the world that uses oil shale as its primary energy source.[95] In 2012, it supplied 70% of Estonia's total primary energy[24] and accounted for 4% of Estonia's gross domestic product.[26] About 6,500 people (1.1% of the workforce in Estonia) are directly employed in the oil shale industry.[96] In 2011, about one-third of Estonian public research, development and demonstration expenditures (€3.1 million) went to the oil shale sector.[24] A new development plan for 2016–2030 is at a preparatory stage.[26]

Mining[edit]

Estonia has adopted the national development plan, which limits the annual mining of oil shale to 20 million tonnes.[94] In 2012, Estonia mined 15.86 million tonnes of oil shale.[24] As of 2014, five oil shale mines are in operation. Four of these are open-pit mines and one is underground. The historical ratio of underground mining to open-pit mining has been approximately equal, but since usable deposits close to the surface have become scarcer, underground mining will probably increase.[97]

The Narva open-pit mine, operated by Eesti Energia Kaevandused, uses technology of stripping the rock with relatively large-bucket (10–35 cubic metres or 350–1,240 cubic feet) excavators. Both the overburden and the bed are first broken up by blasting. At open-pit mines with thin overburdens, stripping is done with smaller excavators using front end loaders and hydraulic excavators. The Narva mine and the Põhja-Kiviõli open-pit mine, operated by Kiviõli keemiatööstus, use highly selective extraction in three layers of seams.[1] Other open-pit mines are located at Ojamaa (operated by Viru Keemia Grupp) and Ubja (operated by Kunda Nordic Tsement).[1]

Oil shale mined at Ojamaa is transported to the processing plant by a unique 13-kilometre (8.1 mi) belt conveyor. Although there are similar conveyors in operation in other countries, the conveyor at Ojamaa is an unusually challenging installation, since its path contains many curves and sharp turns.[98]

The only underground mine—Estonia mine—exploits the room and pillar method. Longwall mining, used earlier, was abandoned during the 1990s.[1] This mine, which opened in 1972, is the largest oil shale mine in the world.[74] It is operated by Eesti Energia Kaevandused.

Electricity and heat generation[edit]

Eesti Power Station

National policy, as codified in a 2009 document, prioritises oil shale as a resource for ensuring Estonia's electricity supply.[99] Although the national development plan of the Estonian electricity sector until 2018 describes the extensive environmental impact of oil shale fired power stations and very high share of oil shale in electricity production as threats,[100] and although the oil shale-based share of electrical generation will decrease, the plan supports the industry as part of a national energy security strategy.[101]

In 2012, over 85% of mined oil shale in Estonia was used for power generation and about 85% of Estonia's electricity was generated from oil shale.[24][102] Eesti Energia owns the largest oil shale-fuelled power stationss (Narva Power Stations) in the world.[4][5] In addition, a new 300 MW station, which will use circulating fluidised bed boiler technology, is under construction in Auvere.[103]

In 2010, 11.4% of the heat supply in Estonia was generated by direct combustion of oil shale and 5.88% by combustion of shale oil. Shale oil was used as a fuel by 9.36% of all boiler houses in Estonia.[104] Heat produced by co-generation at the Balti Power Station is used for district heating of Narva, the third largest city in Estonia with 58,700 inhabitants (2013).[105] The co-generation plants in Kohtla-Järve, Sillamäe, and Kiviõli burn oil shale to produce electrical power and supply district heating to nearby towns.[94] In addition to oil shale, the Kohtla-Järve Power Station uses oil shale gas, a by-product of shale oil production, for the same purposes.[104]

Shale oil extraction[edit]

See also: Narva Oil Plant

In 2008, Estonia was the second largest shale oil producer in the world after China.[106] Production accounted 536,903 tonnes of shale oil in 2010.[104] 85% of produced shale oil is exported; most of the remainder is used for heating.[95]

There are three shale-oil producers in Estonia: VKG Oil (a subsidiary of Viru Keemia Grupp), Eesti Energia Õlitööstus (a subsidiary of Eesti Energia) and Kiviõli Keemiatööstus (a subsidiary of Alexela Energia).[104][107] Two processes—Kiviter process and Galoter process—are in use for shale oil extraction.[1][61]

Cement production[edit]

Spent shale (also known as semi-coke) is used for portland cement production at the Kunda Nordic Tsement factory. In 2002, 10,013 tonnes of semi-coke were used for cement production.[72] VKG Plokk, a subsidiary of Viru Keemia Grupp, produces building blocks by using oil-shale ash and spent shale, and plans to construct a cement factory.[108][109] The mined waste rock is used for road construction.[1]

Environmental impact[edit]

A colour photograph of the un-rehabilitated Aidu open-pit mine. The lower two-thirds of the photo shows hilly land that is mostly brownish-grey. Some small, green trees are growing within this section.
Unrehabilitated land at the Aidu open-pit mine (May 2007)
A colour photograph of an old semi-coke heap in Kiviõli, dated to 2005, with a large tree in the foreground. The heap is green.
An old semi-coke heap in Kiviõli (July 2005)

Annually, the oil shale industry produces 70% of Estonia's ordinary waste and 82% of hazardous waste.[26] Losses during mining amount to about four million tonnes per year; together with losses during the enrichment process, more than 30% of the resource is lost.[26][110] Former and current oil shale mines occupy about 1% of Estonia's territory.[15] About 500 square kilometres (190 sq mi) or 15% of Ida-Viru County's territory is out of use due to open-pit mines and waste landfills; an additional 150 square kilometres (58 sq mi) has sunk or become unstable due to underground mining.[111] Approximately 73 million tonnes of graptolitic argillite as overlying deposit was mined and piled in waste heaps in the process of phosphorite–ore mining near Maardu in 1964–1991.[7]

The mining and processing of about one billion tonnes of oil shale in Estonia has created about 360-370 million tonnes of solid waste. Combustion ashes are the largest component (200 million tonnes), followed by mining waste (90 million tonnes) and semi-coke (70–80 million tonnes).[72][112] As of 2006, semi-coke heaps near Kohtla-Järve and Kiviõli covered 180–200 hectares (440–490 acres) and ash heaps near Narva covered 210 hectares (520 acres).[112] The oil shale waste heaps pose a spontaneous ignition risk, due to their remaining organic content.[110] The waste material, particularly semi-coke, may contain pollutants including sulphates, heavy metals, and polycyclic aromatic hydrocarbons (PAHs), some of which are toxic and carcinogenic.[113][114] A 220 square kilometres (85 sq mi) underground water body that holds over 170 million cubic metres (140,000 acre·ft) has formed under eight abandoned mines—Ahtme, Kohtla, Kukruse, Käva, Sompa, Tammiku, No.2 and No.4.[78][115][116]

For each cubic meter of oil shale mined in Estonia, 25 cubic metres (880 cu ft) of water must be pumped from the mine area.[4] This alters the groundwater regime and its quality, lowering groundwater levels and releasing mine water into surface water bodies. Mining activities have contributed to lower water levels in 24 lakes out of 39 in the Kurtna Lake District.[110] The pumping process introduces oxygen via aeration and thereby oxidises the rock's pyrite. Pyrite contains sulphur and one consequence of its oxidation is an influx of significant amounts of sulphates into mining water.[110][116] In some of the Kurtna Lakes, sulphate levels have increased tens of times compared to the pre-mining period. Suspended mineral matter in the mine water pumped into these lakes has changed the composition of the lakes' sediments. This disturbance diminishes over time; studies show that sulphates and iron in mining water decrease to levels that meet drinking water quality standards about five years after mine closure.[116]

The process waters and waste waters used in shale oil extraction contain phenols, tar, and several other environmentally toxic products.[112][113] Power stations use water for oil shale ash removal and hydraulic transportation to the ash heaps, which then become highly alkaline. The total volume of alkaline water is 19 million cubic metres (670×10^6 cu ft).[117]

The use of oil shale releases more carbon dioxide than any other primary fuel. Its combustion is the chief source of CO
2
and other greenhouse gas emissions in Estonia, accounting for more than 70% of all such emissions.[24][26] Annually, the industry emits about 200,000 tonnes of fly-ash, which includes heavy metals, carbonates, alkaline oxides, and harmful organic substances, into the atmosphere. About 30% of the fly-ash is calcium oxide; a portion is neutralised by atmospheric carbon dioxide.[110]

Various efforts have reduced the industry's environmental impact. Fluidised bed combustion generates fewer PAHs than the earlier, dominant technologies that burnt pulverised oil shale.[117] Since the 1970s, reclamation and reforestation of exhausted mining areas have been implemented.[118] In 2010–2013, a €38 million project was implemented for environmentally safe closing of 86 hectares (210 acres) of semi-coke and ash heaps.[111] In accordance with a European Union waste framework directive, the heaps were covered with waterproof material, new topsoil, and sod.[119] In Kiviõli, a 90-metre (300 ft) semi-coke heap, the highest artificial hill in the Baltic countries, was converted into a ski centre.[120] The former Aidu open-pit was converted into a rowing course.[121]

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