Innovative FGD at Matra

The lignite-fired Matra power station, located about 120 km east of Budapest, started life as the Gagarin plant in 1969/73. It has five blocks, two of 100 MWe and three of 200 MWe.

The 3 x 200 MWe units have been upgraded by Matra Kraftwerke AG over the period 1998-2000, with installation of flue gas desulphurisation (FGD). The FGD system uses two wet absorbers with limestone as neutralising agent producing commercial grade gypsum. It is the first FGD in Hungary. Without it the power station would have to be permanently shut down in 2004 due to environmental regulations.

In the modified plant the raw flue gas from each unit passes through electrostatic precipitators and then to two absorbers. A unique feature of the FGD system is that each of these absorbers is placed inside one of station’s dry cooling towers, which combine the functions of housing and stack.

Advantages

Locating the absorbers inside the towers does not influence the cooling capacity of the towers, but does have a number of advantages. In particular, it means that temperatures at the absorber surface are always moderate to high (about 20°C higher than outside the cooling tower), there is no wind and the climate is dry. This results in big savings in steel construction, while the need for stack and reheater is eliminated. On the negative side, maintenance (especially in summer) is more demanding because of the higher ambient temperatures, all the electronics have to be equipped with a special cooling system, and the top of the cooling tower has to be protected against possible contact with wet flue gas in case of strong winds. However the benefits outweigh the disadvantages.

The wet clean gas (at 66°C) is exhausted without reheating into the atmosphere through the dry cooling tower and complies with the German emission laws.

The absorbers operate as countercurrent flow spray systems, with the following main process steps:

absorption of pollutant gas into the washing slurry;

neutralisation of slurry by means of limestone (CaCO3);

oxidation of intermediate products into gypsum (CaSO4);

crystallisation of the gypsum (CaSO4•2 H2O);

separation of washing slurry and treated flue gas.

Use of advanced materials engineering and flow dynamics has led to a smaller but more efficient scrubber through optimisation of nozzle type and spacing in an “intersecting spray system” configuration. The new mist eliminator system achieves an even lower pressure drop than the previous technology. It also has a low tendency to incrustation, and high efficiency droplet separation.

Overall, the FGD has significantly reduced energy demand and the combination of new nozzles, oxidation air distribution by stirrer and an optimised flushing programme for mist eliminators is expected to lead to a total FGD availability of about 100 per cent.

In an emergency, bypass operation is possible (full-load or part-load), allowing all the units to stay in operation. The bypass is situated between the new flue gas fans and the existing stack. In addition, the FGD is designed such that one FGD line can handle 90 per cent of the flue gas of 2 blocks (120 per cent of FGD volume flow).

Where necessary, redundancy is provided to achieve maximum power plant availability.

Implementation

Babcock Borsig Power Environment GmbH (Gummersbach, Germany) and its partner EGI Engineering and Contracting Co (Budapest, Hungary) provided the FGD system on a turnkey basis, including flue gas ducts, fans, gypsum dewatering, storage and rail loading/unloading facilities, rail unloading and storage facilities for the limestone, electrical equipment, instrumentation and control, civil works, erection and commissioning, over a period of 21 months.

In May and June this year, flue gas was run through the two absorber lines and they have performed without significant problems. Hot commissioning is currently underway.