Aerial view of the Hodonín power plant

The Hodonín power plant is an organic part of the town of Hodonín, the birthplace of T. G. Masaryk, the first President of Czechoslovakia. The power plant is situated in its south-western part, making the two power plant stacks an integral part of the townscape.

The whole aerial view is dominated by the power plant site with its main building, conveyors, fuel storage areas and a siding of the Břeclav-Otrokovice-Přerov trunk line.

The northern direction offers a clear view of the town of Hodonín as well as the distant peaks of the Ždánice Forest and the Chřiby.

The eastern azimuth takes the eye of a keen observer across the Hodonín system of ponds fed by the Kyjovka. The remote horizons are bordered by the Pavlov Hills and the landscape around the Nové Mlýny reservoir.

The southwest and the south and southeast offer an excursion across the national border. The first view takes us to Lower Austria’s Danube plains towards Vienna. The other option shows us a portion of westernmost Slovakia – the area of Holíč and Záhorie.

Eastward, behind the town of Skalica, you can see the frontier mountain range of the White Carpathians.

On the roof of the main building

The Hodonín power plant was built in two stages in 1951 - 1957. The choice of the location for its construction was based on local conditions, the vicinity of a lignite mine and the Morava River. Its first two boilers with a 50MW turbine were put into operation in 1954 and its last two boilers with a 55MW turbine in 1958. With its capacity of 205 MW the Hodonín power plant was the largest source of electricity in Czechoslovakia at the time. All the turbines there were condensing, with once-through cooling. The first major reconstruction of the power plant increased the boiler capacity from 125 tonnes of steam per hr to 135 tonnes of steam per hr. In 1980, turbine unit TG4 was replaced with a machine with controlled steam extraction of up to 180 t/hr with suppressed condensation. A similar method was used in 1996 to rebuild turbine TG3, which now has two controlled heating steam extraction systems. Heat generation for district heating then began to prevail in the plant’s production. The Hodonín power plant is also unique in Europe for its cross-border heat delivery. Tens of thousands of GJ of heat are regularly supplied from it to Holíč, Slovakia.

Two fluidized bed boilers, with a steam capacity of 170 t/hr each, were built in 1992–1997. The installation of the new fluidized bed technology completed the desulphurization and ecologization of the power plant. The electrostatic precipitators were replaced in 1995 and 1996 and currently capture fly ash with up to 99.5% efficiency. Operations noise was reduced by additional insulation. The power plant currently has an installed electrical capacity of 105 MW. Its annual heat supplies are 700,000 GJ.

Since the supplies of lignite were increasingly unreliable, it was decided to convert some of the production to a renewable energy source – biomass. Starting from 31 December 2009, one unit of the Hodonín power plant with boiler FK2 is designed solely to combust pure biomass.. The unit has an electrical capacity of up to 35 MW and requires up to 1,000 tonnes of biomass every day (mostly forest chips and other products of wood processing). The Hodonín power plant generates about 400 million kWh of electricity per year. More than 200 million kWh of electricity is generated from biomass, covering the annual consumption of more than 60,000 households in Southern Moravia.

The view from the roof of the main building shows some interesting places in the northern part of the power plant site and gives insight into the production processes. Besides a side view of the production building, the prominent features are, once again two electrostatic precipitators including two 100-metre stacks. We can see the entire siding site with a train that is just being unloaded. Coal and biomass are transported by covered belt conveyors from the stockyard to the boilers where they are combusted. The set of three ochre-painted silos up to 32.6 m high contains ash materials used to produce certified materials (power plant byproducts) and the white-painted silo is used to store limestone neededfor flue gas desulphurization (FGD).

The power plant is organized into “units”. A power plant unit means an independent unit consisting of a boiler, a turbine and its accessories, a generator, electrostatic fly ash precipitators and a unit transformer. Equipment shared by both units includes a fuel stockyard, coal handling systems, water management systems (intake, cooling water feeders, pumps and chemical treatment plant), FGD limestone dosing equipment, fly ash transport equipment and an ash material mixing centre. The power plant does not have any cooling towers. It uses once-through cooling by river water from the Morava River, with water running through the intake structure and feeder to the turbine unit condensers and returning to the Morava.

Since the nature and processes of biomass combustion are similar to those of conventional electricity and heat generation from coal, in the next sections we are offering selected specific operations of the Hodonín power plants with focus on biomass operations.

Power output

A 110 kV substation and a 22 kV substation are used for delivering power from the power plant. Electricity generated in the turbine generator is supplied to the unit transformer, where the required voltage of 110 kV is achieved. A portion of electric output is lowered to 22 kV in another transformer and delivered to the 22kV substation. Electricity from both substations is delivered to the distribution grid of E.On Distribuce.

Control room

The central control facility of the whole power plant is the central control room collecting information from all parts of the power plant. CEZ shift engineers use monitors and control panels to check and control all operated equipment including live indicators and values related to electricity and heat generation and supply to customers off-site.

Main hall with turbines

The principle of electricity and heat generation from biomass is the same as in a coal-fired plant. Chemical energy bound in biomass is converted first into thermal energy in the common process of combustion in a fluidized bed boiler. Thermal energy is then converted into the kinetic energy of steam, which is converted into mechanical energy of rotation and that into electrical energy. The heat carrier is common water steam generated in a boiler. Steam is delivered to a turbine, which is mechanically connected by a common shaft with an electric generator. Mechanical energy of rotation is thus further converted by the generator into electrical energy, which is supplied to the grid.

Electricity and heat are generated with greater efficiency by a process called “combined heat and power” (CHP). In practice this means that a portion of the steam that enters the turbine is released, after carrying out mechanical work, at a certain point from the turbine to a steam distribution system or used to heat circulating water in a hot-water system used to supply heat.

The default view of the main hall shows the generator of the biomass unit with noise insulation. You can see pressure gauges and other generator gauges in the front.

In the opposite direction, you can see piping of the water-steam circuit in the main hall (green and grey paint).

Boiler house – fluidized bed boiler

The Hodonín power plant is currently fitted with two circulating fluidized bed boilers (CFBB) with hot cyclones between the combustion chamber and secondary air.

A modification to one of the fluidized bed boilers, completed in 2009 and costing CZK 120 million, subsequently allowed burning pure biomass up to 75 % of the boiler rated capacity. The maximum capacity of newly installed transport lines is 50 t of biomass per hour in total. New operating biomass hoppers were installed in the fluidized bed boiler house as part of the project. The two square steel hoppers with a capacity of 60 t each are located in a bunker structure in place of original coal bunkers, now demolished. Fuel is transported to the boiler combustion chamber by two transport lines. The biomass transport line consists of a system of biomass conveying screws that are connected to the original coal transport line. Screw speeds are controlled by frequency converters.

Vegetable biomass is not predried in any way. Its temperature is measured continually; the hoppers are equipped with an extinguishing system in case of ignition. The hoppers have enough capacity for about 2 hours of operation.

Since 2011, the biomass combustion equipment has included two compressed air-based transport lines for pelleted biomass. The entire boiler control system was modified as well.

Biomass screener

Reliable operation of the equipment for transporting biomass into the boiler is guaranteed by a stationary screener. The unattended star screener is integrated into the coaling bridge building and its screening bed consists of a set of several sections fitted with rotating rubber stars that biomass has to pass through. Biomass of the required grade falls through as the undersize. The oversize, i.e. oversized pieces of biomass and foreign bodies more than 50 mm in size fall over at the end of the sorting surface through a collector to a belt conveyor system and are transported back to the yard. The screener throughput is about 100 t/hr depending on the current biomass moisture content.
The fuel (biomass) is transported by a belt conveyor system from the screener through a consumed biomass sampler and magnetic separators to the fluidized bed boiler hoppers.

Consumed biomass sampler

A modern automatic biomass sampler allows the Hodonín power plant to document the quality and amount of biofuels burnt and the volume of electricity generated from biofuels as accurately as possible. It also helps improve the bio-unit control efficiency. The unique functional prototype developed under the Futur/E/motion, Science & Research programme can sample various types of biofuels to be consumed from the belt conveyor. The device also includes technology for sample conditioning for processing in a lab. The sampler can process more than 1,200 samples monthly. The sampler has been certified as a commercial measuring instrument.

Biomass sampler – 1st storey

The sampling device collects the desired sample from the biomass conveyor. The sampler then crushes, transports and divides the sample. The sample is put in a container and delivered to the lab for examination.

Main biomass stockyard

Building a paved area in one half of the coal stockyard was necessary to:

create a handling area for unloading delivered biomass,
create an operative stock of biomass, and
allow handling the biomass when loading it into the FK2 boiler hoppers.

Two high-capacity wheeled loaders are used to handle biomass. This solution allows keeping noise low when handling biomass and reducing the operating cost of diesel fuel in comparison with bulldozers.

An elevated, roofed hopper with vertical walls and screw conveyors for dispensing biomass has been built at the fuel stockyard. The biomass loading equipment includes a biomass screener, a fuel sampler and magnetic separators.

Sample room

This room is equipped with a large table and two drying kilns. A sample of biomass (either freshly delivered or to be consumed) is transported here in a hermetically sealed container. Here the sample is quartered and placed in a drying kiln to determine its gross water content.

Milling plant

The dried sample is then processed by batteries of FRITSCH Pulverissete cutting mills to analytical size.

Biomass lab

Another step in making the Hodonín power plant one of the very best biomass plants in the Czech Republic was equipping its lab, which focuses on preparing samples and analysing biomass. The transition to full analysis of each biomass delivery required investing in all equipment encountered during a visit to all three parts: theSample Room, the Milling Plant and the Biomass Lab itself. These involved especially drying kilns for biomass samples, lab scales, abattery of FRITSCH Pulverisette cutting lab mills, LECO AC-600 calorimeters, LECO TGA-701 thermogravimetric analysers and a control PC.

The aim was to introduce a sampling and analysis system that would allow determining the calorific power and amount of biofuel consumed with predefined accuracy as a basis for billing and the power plant's heat balance. The power plant is also able to precisely document the quality and amount of biofuel burnt from the obtained data.

The full analysis of each sample includes:

Total water determination
Ash content determination
Analytical water determination
Determination of the contents of C, H, N, S
Determination of gross calorific value
Calculation of net calorific value

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