Aerial view of the Mělník power plant
Electricity and heat from the town of the Bohemian queens
The royal dowry town of Mělník is the only one that spreads on the banks of the biggest Bohemian rivers, which form a confluence here. The castle above the confluence of the Elbe and Vltava from about the year 1000 was given as a dowry to the Bohemian princesses and queens. This custom later spread to the entire adjacent settlement, which started growing rapidly. Today, this town that is also famous for its viticulture has a population about 20,000.
The nearby Mělník Power Plant is a significant point on the energy map of the Czech Republic. It generates electricity and supplies heat. It produces both commodities in a common, so-called, combined cycle, which results in substantially higher utilisation of fuel and, hence, in energy savings with a positive environmental impact.
Its advantageous location (30 kilometres from Prague) gives this energy plant the privilege of serving as a significant source of heat for the capital city. More than a quarter of a million households are heated by energy from this locality.
The Mělník Power Plant comprises three technological units - Teplárna Energotrans, a. s., (EMĚ 1), Elektrárna Mělník 2 (EMĚ 2) and Elektrárna Mělník 3 (EMĚ 3).
See how a coal power plant works.
Flight through Bohemian history
The aerial view of Mělník and its surroundings is also a flight through Bohemian history. To the North-West near the D8 Motorway rises the unmistakable silhouette of the mythical Říp Mountain (456 metres above sea level) with the Rotunda of St. George on its peak. In the background rise the conical hills of the Bohemian Central Mountains. From the times of forefather Čech, when we look north-east, we quickly jump to the twin peak of Bezděz (604 metres above sea level) with a castle. This castle was built in the second half of the 13th century for Přemysl Otakar II. While Štětí and Roudnice nad Labem spread toward the north, to the south the landscape drops toward the Prague basins. To the south-east we see the flat landscape of the approaching Elbe.
The Mělník Coal Power Plant or Did you know that…
- The Mělník Power Plant is the ČEZ power plant that is closest to Prague? It lies about thirteen kilometres downstream of the confluence of the Elbe and Vltava.
- the furthest heat appliance lies at a distance of 74.5 km from the heating plant of Energotrans, a.s.?
- water for Prague is transported via a pipe of diameter 1.2 metres to a distance of more than 34 km at a pressure of up to 2.5 MPa?
- the hot water feeder Mělník – Prague runs over two pipeline bridges over the Vltava and four times over a railway track?
- The Mělník 3 Power Plant with the 500 MW block is the largest coal block in the Czech Republic?
- in Mělník at peak output one wagon of coal is incinerated within 12 minutes?
- the gypsum board produced by desulphurisation of the Mělník 2 and 3 power plants is further processed as a full energy by-product in the adjacent Rigips plant for production of plasterboard?
- a smaller hydro power plant with an installed output of 490 kW, which transforms the energy of the residual cooling water from the Mělník Power Plant to electricity, lies in the premises of the Mělník Power Plant?
- the heat is supplied to Prague via a unique hot water feeder, heat is transferred using hot pressured water, and heat according to the season of the year is in the range 90 to 140°C. On the consumer side (in Prague or Neratovice) the water cools (transfers heat) and returns at a temperature in the range 60 to 70°C?
- the water in the hot water feeder travels at a speed of more than two metres per second?
- the hot water travels to Prague on average in 6 - 8 hours and in this period its temperature drops by about 1°C, but the losses usually do not exceed 4 % (it depends on the season of the year)?
- production and supply of heat runs continuously 24 hours per day all year round with the exception of one week during the summer holidays when scheduled maintenance of the feeder is done?
- maintenance of the production equipment may be done also in operating conditions and supply of heat thanks to the back-up system and parallel co-operation between the turbines and boilers? Thanks to the heat plant hot-water connection between EMĚ 1 and EMĚ 2, the system for heat back-up has significantly improved.
- construction started between the end of the sixties and end of the seventies as a complex of condensation power plants burning brown coal supplied by rail from the North Bohemian and West Bohemian mines.
Energotrans, a.s. (EMĚ 1) (4x60MW)
Teplárna Energotrans, a. s., (EMĚ 1) has an installed output of 240 MWel. Its construction started in 1956 and it was put into operation in 1960. From 1993, it was operated by Energotrans, a.s. In June 2012, the Office for Protection of Competition permitted the merger of ČEZ, a.s. and Energotrans, a.s.
At the turn of the 1980s and 1990s, reconstruction of EMĚ 1 was done and a hot water feeder was installed for supply of heat to the Prague hot water network.
In EMĚ 1 the production is realised by means of four turbo generators (2 x back-pressure, 2 x condensation extraction) - each with an installed output of 60 MWel., six granulation boilers (steam output 6 x 250 t/h).
Supply of heat to Prague dates back to 1995, and supply of heat to Neratovice is from 2003.
| Basic technical parameters: | |
|---|---|
| Installed output: | 4 x 60 MW |
| Commissioning year: | 1960 |
| Installation and desulphurisation: | 1998 |
Supply of heat to Prague
In the period 1988-1995, the exchanger station for the heat feeder to Prague was built. The heat carrier is hot water, which is fed to Prague via a 34 km long hot water pipeline.
Teplárna Energotrans, a. s., (EMĚ 1) is the largest heat generation plant in the Czech Republic with a maximum heat output of 650 MWt in the heating season. The annual heat supply is 10,000,000 GJ/year.
The heating of the water for the hot water line is done in three heating stages.
Supply of heat to Prague is realised on the European scale by means of a unique structure, which is the hot water feeder of diameter DN1200 (1.2 metres). Before the water reaches Prague, it travels a total distance of 34 km. At maximum flow rate, which is 8,200 tons of water per hour, the journey takes almost 5 hours.
The hot water that flows through the system, depending on the season, has a temperature ranging from 90 °C to 140 °C at a pressure of up to 2.5 MPa. The entire system also has a backup gas boiler plant on the outskirts of Prague, in Třeboradice, such that half the population of the capital city, but also the population of Mělník or Neratovice need not fear that they will be deprived of heat in case of extraordinary production failure at the Mělník Plant.
In the course of 2014, a heat connection was built between EMĚ 1 and EMĚ 2.
EMĚ 1 can backup production of heat for Mělník and Horní Počaply; EMĚ 2 for Prague and Neratovice.
In the summer, EMĚ 2 can cover the entire supply of heat for the Prague and Mělník hot water lines and supply of technological steam. In winter and in the interim period, EMĚ 2 is a backup and auxiliary source of heat to EMĚ 1.
See the video on modernisation of the heat facilities for supply of heat to Prague!
Power Plant Mělník 2 (EMĚ 2) (2 x 110 MW)
The original four blocks of EMĚ 2 were commissioned in November 1971. The period of 1971 - 1976 was characterised by gradual optimisation of the major technological equipment. In subsequent years, the technological equipment was modernised.
Within the framework of this programme for dampening of ČEZ resources, it was decided to operate only two blocks after the new environmental legislation came into force (from 1 January 1999). These were then subjected to the ČEZ ecological modernisation programme.
Two new turbines were installed with a possibility for future off-take of heat both in the form of steam as well as hot water. The modern Westinghouse WPDF II control system was also installed. Radical renovation of the boilers was also done (membrane linings, modification of the combustion modes - primary measures for reduction of NOx, modification of additional surfaces). The desulphurisation equipment using the wet lime scrubbing method was also commissioned in the second half of 1998. The remaining two non-renovated blocks were finally shut-down in as at 31 December 1998.
Since the year 2000, EMĚ 2 has supplied heat to the regional heat feeder to Mělník and the nearby communities of Horní Počaply and Dolní Beřkovice.
Production in EMĚ 2 is done using two 110 MWel blocks (2 x steam turbine – condensation extraction type with an installed output of 110 MWel, 2 x granulation boiler with a steam output of 2 x 350 t/h).
| Production unit - Mělník 2 | |
|---|---|
| Installed electric capacity | 2 x 110 MW |
| Year of commissioning | 1971 |
| Desulphurisation since | 1998 (2 x 110 MW) |
Power Plant Mělník 3 (EMĚ 3) (1 x 500 MW)
EMĚ 3 with the 500 MW block was commissioned in 1981. This block is the largest coal block in the Czech Republic. The new control technology was first used on this block - flexibly programmable sequential automatons and computer information and control system. Thanks to its technical concept, it became one of the most economical coal power plant blocks. In time, it underwent greater modernisation and renovations.
The target of the investment intensive period of 1994-1998 was to extend the service life of EMĚ for a minimum additional period of 20 years. At the same time, it was necessary to achieve not only competitiveness in terms of the operational and economic parameters of production, but also environmentally friendly operations. Reconstruction of the VT body of the turbine was done. After this intervention, the block safety achieves its initial design output of 500 MW. Within the scope of the overhaul, so-called primary measures were also applied to the boilers to reduce NOx emissions. At end of 1998, the desulphurisation of flue gases was commissioned just as applied to EMĚ 2.
Production in EMĚ 3 is done using one 500 MWel production block (1 x steam turbine – condensation extraction type with a rated output of 500 MWel, 1 x granulation boiler with a steam output of 1 x 1600 t/h).
The gypsum board produced by desulphurisation of the EMĚ 2 and EMĚ 3 is further processed as a full energy by-product in the adjacent Rigips plant for production of plasterboard. The combustion products, such as ash and coal clinker are modified into certified building materials for building construction industry and recultivation.
| Production unit - Mělník 3 | |
|---|---|
| Installed electric capacity | 1 x 500 MW |
| Year of commissioning | 1981 |
| Desulphurisation since | 1998 |
Watch the animation describing how a coal power plant works!
Pump and exchanger station for the Prague hot water feeder
The pump and exchanger station has basic pumps for circulation of the water in the hot water line. It was built gradually in the period of 1993-1995. We find five class C1 pumps and five class C2 pumps here, which can also operate in series or in parallel. Other similar pumps, so-called C3, are found at Třeboradice near Prague. The pumps ensure the transportation of the water in the entire hot water line; the water is pumped from here further into the EMĚ 1 technology for 1st stage heating - turbo generator 1 (TG1) and turbo generator 2 (TG2), subsequently also 2nd stage TG3 and TG4, or interconnection with EMĚ 2. The heated water subsequently returns to the pumping station and 3rd stage heating. From here, it is fed to Třeboradice where it is taken over by Pražská teplárenská, a.s. A maximum of 8 200 3 / h of water flows through here.
3rd heating stage
The pumping and exchanger station has 3rd stage heating with an input of hot steam of temperature 535 °C and pressure 9.3 MPa for the separators. From here the steam is fed to the individual peak heaters. This is the same steam that is also supplied to turbo generators TG1 – TG4. Third stage heating is used only as a backup in case of shut-down of first or second stage heating.
Overall View of the Generator Room
In the machine room of Energotrans, a. s., we find two back-pressure turbines TG1, TG2, which are used as heating stage 1 for water to Prague. Water is heated in them to 120 °C. Further, two extraction turbines TG3, TG4, that are used for stage 2 heating for water for Prague and heat the water to 140 °C. The four turbines in the machine room are driven by steam from six boilers, which are transported via a double common steam collector. The steam comes from all the boilers and goes to all the turbines. The turbines are used according to the quantity of heat that Prague needs. The first two are primarily used in the heating season, the other two can also be used in condenser mode to generate only electricity without steam for the hot water line to Prague. The turbines were initially of condenser type. They were renovated and modified to the current state just to meet the requirements of the hot water line to Prague.
The condensers of the extraction turbines TG 3 and 4 are cooled using raw water from the River Elbe. The rest of the water for cooling the operating equipment or water for production of steam is jointly treated in the chemical treatment plant for the entire EMĚ premises.
Boiler plant
The six boilers are installed at a height of 35 m. At a temperature of 1,400 °C in the fire core, each of them produces 250 tons of steam with a temperature of 535 °C and pressure of 9.3 MPa. The steam is fed to the steam collector which may at a single moment contain up to 1,500 tons of steam, from where it is consumed by the four steam turbines.
The two phase drum granulation boilers (brown coal) with four hammer mills consume 1.4 million tons of coal per year. Boiler build-up to full operating state with connection to the common steam collector takes about 2.5 to 3 hours. After burning the coal, the clinker falls from the boiler into the lower section, from where it is washed using water to the machine drain building. The flue gases leaving the boiler carry fly ash, which is subsequently trapped by the electrostatic precipitator technology.
Common control room of EMĚ 1
The common control room is used to control all the six boilers and other boiler plant accessories, including DeNOx equipment, four turbo generators for production of electricity and heat at heating stages I and II, operation of the pumping and exchanger station of heating stage III for the hot water line to Prague and both desulphurisation units for desulphurisation of the flue gases from all boilers.
Under full operational conditions, this work is done by only 6 operators (3 x boiler plant, 2 x machine room, 1 x desulphurisation) under the strict supervision of an executive.
R 110 kV substation
Used for transformation and transfer of electric power from the individual turbine generators via outlet transformers to the distribution system lines and block transformers for own power supply to EGT – EMĚ 1. At the same time, power supply from this substation is ensured via various connections to the appliances of the power plant when the production equipment is shut-down or in case of failure states. The substation is further connected to the R 110kV ČEZ EMĚ 2 external substation.
Area of the pipe for supply of raw cooling water and hot water pipes to EMĚ 1 and EMĚ 2
In the area of the cooling water supply, the water is distributed to the individual appliances of the turbines and further to the filter station for chemical treatment of the water. The hot water line for transport of heat to Prague runs in the direction of EMĚ 2.
The yellow structure that runs to the pumping and exchanger station is a pipeline bridge which brings steam from the common steam collector of all the four heaters in the exchanger station. The cable space and condensate return pipes for stage III heating also run through here to the steam system. In front of us is the pipe separator of water from the hot water line for the individual turbines. Each turbine of the first and second heating stage has two heaters. Then there is a pipe connection to the heaters of EMĚ 2, which supplies heat together with EMĚ 1 to the Prague hot water line.
Back-pressure TG - stage I heating - height 0 m
The primary heaters of the back-pressure turbines used as stage one heating for the Prague hot water line take up the largest space. Here, the temperature of the heating water rises from 60-70 °C to 120 °C. This heating is done by means of steam from the turbo generator and this steam is also used to heat the water in the hot water line instead of uneconomical cooling in the condenser of the condensation turbines. This heating water is subsequently transported to stage II heating at TG3 and TG4 or by pipe connection to EMĚ 2. Here, we also see other auxiliary equipment necessary for the operation of the turbo generator and boilers: expander, electro feeding, drainage systems, and steam pipes.
Electrostatic precipitators, desulphurisation, coal handling
Electrostatic precipitators – are used to expel ash from the flue gases of the individual boilers. The detailed picture shows the pneumatic transport of ash from the discharge chute of the electrostatic precipitator.
Desulphurisation – used to separate sulphur from the flue gases. For this purpose, two desulphurisation lines exist here (each for three boilers). Desulphurisation is done by means of wet lime scrubbing. The detailed picture shows the circulation pumps for transport and circulation of the lime suspension.
Coal handling – coal is transported by rail. At the unloading point the coal is discharged from the wagons via a grille into the underground storage containers and is further transported by belt conveyor to the boiler plant for direct consumption by the individual boilers or to the fuel dump. At the dump a supply of coal is created to cover higher consumption in winter, i.e. in the heating season. The hall at the dump is handled using bulldozers.
Hot water heaters OTV 1 and OTV 2 in EMĚ 2
The hot water heaters are mounted on a steel structure in the EMĚ 2 machine room. Both exchangers are identical in terms of design and material. They are of vertical design, the heat surface comprises U-shaped pipes at both ends rolled into the tube plate. The water chamber is welded to the housing and has a partition inside, which creates two water draughts. The condensate collects in the lower part of the housing and the level sensors are also installed here to control the level in the heater. The steam and water chamber of the heater have discharge and air relief valves. The maximum heat output is 120 MWt from each block.
Heat connection was built between EMĚ 1 and EMĚ 2
In the course of 2014, a heat connection was built between EMĚ 1 and EMĚ 2. EMĚ 1 can backup production of heat for Mělník and Horní Počaply, EMĚ 2 for Prague and Neratovice.
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