Thanks to its qualities and use in diverse industrial sectors, hard coal remains a strategic resource for the future. Experts estimate that worldwide hard coal reserves amount to approximately 479,000 million tonnes. Coal mining is expected to continue for another 200 to 300 years with efficient, economic and profitable processes sustained by the dynamic modernisation of mining technologies.
How and where is hard coal mined in the Czech Republic?
In the past, there were several operating hard coalfields in the Czech Republic (Pilsen-Manětín, Kladno-Slaný and others). Following the winding up of coal mining operations in these fields during the 1990s, the only remaining hard coal mining district in the country is Ostrava-Karviná in the southern part of the Upper Silesian coalfield. The major part (approximately 80%) is situated in Poland. The district yields quality hard coal with a low sulphur content and high carbon content, which is sourced from four mines operated by NWR subsidiary, OKD, a.s.
Mining in the Ostrava area was terminated in the 1990s, with the remaining operating mines located in the Karviná and Frýdek-Místek districts of the Moravian-Silesian Region. In 2010, OKD produced approximately 11.4 million tonnes of coal at these mines.
In simple terms, it can be said that two types of coal are obtained from the mines: thermal coal, used as fuel with a high heating power, and coking coal, used in the production of coke. Another NWR subsidiary, OKK Koksovny, a.s., is the largest European producer of foundry coke.
Specific features of the Ostrava-Karviná hard coal district
Implementation of an ambitious investment project, the Productivity Optimisation Programme 2010 (POP 2010), saw the equipping of NWR mines with the most up-to-date mining and longwall technology. This technology ensures continuous access to coal reserves at greater depths and under conditions that would have made it impossible to exploit the reserves due to efficiency, safety and technological constraints.
The Ostrava-Karviná hard coal district ranks among the world’s most demanding to exploit. This is mainly due to geological conditions with frequent tectonic faults crossing the coal strata at depths where the coal is extracted. The average depth of mining in the Ostrava-Karviná district is 930 metres below ground. The deepest pit, Doubrava III at the Karviná Mine, is 1,177 metres deep, while the deepest operated level, in the Paskov Mine, has an absolute depth of 1,120 metres below ground.
Coal mining in the vicinities of Ostrava and Karviná has a tradition reaching back several hundred years. Systematic mining in the district began in the mid-18th century, and developed into regular mining operations in the 19th century with the growth of ironworks and the evolution of the railroad network.
The Ostrava-Karviná district holds 90% of all hard coal reserves in the Czech Republic.
From stating an intention to actual mining
There is a long and complicated journey that winds between the initial intention to mine for coal and gas (traditionally linked to coal deposits) at any given site and the arrival of the first tonne at the surface. How is hard coal mined and what precedes the actual mining?
In order to locate a deposit of hard coal and make a qualified judgement as to the extent and quality of the deposit, it is first necessary to create a geological survey bore that is drilled from the surface. The survey helps to define what the deposit contains, facilitates calculations on the extent of the reserves and determines the mining area. The survey from the surface is then supplemented with an additional underground exploration, which specifies the extent of the reserves in the mining area.
In line with valid legislation, a mining area is delimited for each mine where hard coal and possibly carboniferous natural gas can be exploited. The opening of a mine must be preceded by the meeting of stringent legal requirements pertaining to relationships and circumstances of the exploration and mining that must be agreed with local government, residents and authorities that administer the area of environmental protection.
An application for a mining permit must be preceded by a demonstration that any exploration and mining activity will not cause significant negative effects that impact on the local residents and the natural environment, and that the mining entity is capable of eliminating such possible negative effects. The law therefore requires the development of an Environmental Impact Assessment, typically referred to as an EIA.
Coal strata are mostly located horizontally in the Ostrava-Karviná district. The height of the strata ranges from 1 metre to 6.5 metres, with seams exploited at greater depths, at the Staříč site and in the Lazy Mine, found in strata with heights from 0.8 metres to 1.3 metres.
NWR mines for coal in nine mining areas spanning territory of 121 km2. The coal reserves in NWR mines were approximately 206 million tonnes at the end of 2010.
Mining for coal
Following the satisfactory resolution to all the legislative requirements related to the possible commencement of mining at a given site, two pits are excavated in the most suitable locations in accordance with information on the deposit. The first pit is used to transport the mining crews and material, while the second serves for the removal of excavated material. The design of the pits is of fundamental importance for the ventilation inside the mine. One of the pits therefore acts as the downcast airshaft, bringing fresh air underground, with the other utilised as the upcast airshaft. The latter is fitted with a heavy-duty ventilator. This arrangement is essential for safety in the mine especially with respect to the mine gas (also called firedamp) and air conditioning within the mine.
When a mine is opened for exploitation, the deposit is split into horizontal levels, with the excavation commencing between the first and second levels from the top downwards and from the mining area boundary towards the pit. The levels are divided by cross-cuts made in rock and passing across the seams to ensure their stability. The cross-cuts also divide the space from the mining area boundary to the pit. An air slit is also opened between the levels to ensure correct ventilation. Mining galleries are then interconnected with the subsequent installation of longwall technology. After the completion of one longwall, new galleries are cut and a new longwall is started.
Technological revolution in NWR’s mines
Coal in the Ostrava-Karviná district is most often exploited using longwall complexes, with coal ploughs used in strata of the Ostrava type. Over the past three years, NWR has invested nearly CZK 10 billion in purchasing the most up-to-date mining and longwall technology. The company acquired 12 longwall complexes manufactured by Bucyrus, 13 mining complexes with a comprehensive support system made by Sandvik and 12 traditional tunnelling sets comprising a cutting machine and a loader manufactured by Deilmann Haniel. Mechanised supports are used to fortify the longwalls.
The Ostrava-Karviná hard coal district is also distinct in that it operates an average of five longwalls per mine, while the usual concept practiced around the world is “one mine, one longwall”.
For a better understanding: the new longwalls achieved an average daily production of 2,800 to 3,000 tonnes of coal per longwall in 2010. Some longwalls accomplished peak daily production of up to 10,000 tonnes, while the average daily production per longwall in NWR mines, combining old and new technology, has increased by 15% to 1,743 tonnes. The introduction of new technologies has clearly had a positive impact on the performance of the mines.
Longwall mining
Longwall mining takes place from the border of the mining area towards the pit. The mined space is subsequently filled with the use of a controlled cave-in, which is the reason why underground mining sometimes manifests itself on the surface. This why the commencement of mining at any specific location is preceded by the drawing up of a “subsidence map” specifying the locations of likely subsidence. Mining operations are also preceded by the purchasing of land and premises where the negative effects of mining are expected to materialise.
The excavated coal is transported by conveyors to a storage space through the mine works. The coal is then transported by a mine train or a conveyor to a skip pocket near the upcast airshaft. Skip buckets, carrying approximately 20 to 30 tonnes, are then used to transport the coal to the surface and unload it into a skip plant on the surface.
Coal mining is inevitably linked to seismic shocks, resulting from the release of energy accumulated in the rock massif due to changing stresses caused by mining activities. Seismic phenomena have been part and parcel of mining since its very beginnings. They result from excavated spaces created by mining performed over more than a century, as well as the depths reached by mining and the solid rock material in the exploited strata of the active parts of the mining district. The frequency and degree of seismic activity is monitored over the long term and evaluated for the purposes of adopting corresponding shock-prevention measures during mining and tunnelling.
Coal processing
Raw coal is transported from the skip plant via a conveyor to the processing plant. Here, coal is passed over separation screens and is sorted according to size in a heavy fluid and in washboxes or in cyclone separators. This process separates coal from rock residues. Wet coal is then drained in centrifugal separators and filters, or in a drying plant, where it is dried with hot air.
At the processing plant, coal is separated from tailings. Tailings are partly used in the construction industry. For example, the Paskov Mine sold nearly one million tonnes of tailings for construction purposes last year. Tailings are also used in reclamation projects designed to rectify the effects of previous mining activities.
Modern processing plants do not produce sludge; on the contrary, reserves of middlings from outdoor tanks are utilised as a resource available mainly for the energy sector.
Technical closure of a mine
The completion of mining at a mine is followed by the technical closure of the site. This process requires an emphasis on safety in relation to other active mines. Mining areas in the Karviná region are adjacent to one another. It is therefore imperative that interferences, such as flooding, are prevented. When a mine is being closed, all environmentally hazardous equipment is removed from the mine. The main mine works – the pit – is filled with rock or a cement and fly ash mixture.
Following the termination of mining operations, mines spontaneously flood with groundwater, usually of high salinity. Measures are therefore implemented to prevent the seepage of firedamp to the surface, in order to protect surface structures and other assets.
Firedamp
Firedamp is a byproduct of coal mining and manifests a different composition to the natural gas that comes with crude oil. Firedamp, also called “carboniferous natural gas”, comprises more than 90% methane, which offers an exceptional heating value. During mining, the gas seeps from the rock in which it is bound. A proportion of the gas, diluted by ventilation in the mine, is released naturally from the mine via the upcast airshaft. Firedamp and air mixture, with concentrations from 5% to 15% of firedamp, is highly explosive. A proportion of the firedamp is extracted via degassing bores and degassing pipes in the upcast airshaft to a degassing station on the surface, where the gas is purified and supplied to the network for subsequent utilisation.
Hard coal as a strategic resource for the future
With respect to the diminishing oil reserves, hard coal is considered a resource for the future, with a broad range of industrial applications. Attention is especially focused on the efficient utilisation of coal energy in advanced combustion in power plants. Experts are also seeking methods to convert coal into environmentally acceptable quality fuel for vehicles. Coal may also be required in the future to replace oil in the chemical industry as well as in other sectors.