Steam power plantsDry lignite achieves more

In lignite-fired power plants, the combustion of pre-dried lignite provides the most important means for further increasing the efficiency. Hot flue gas from the boiler is suitable for the drying, as depicted on the left. However, that requires the use of more high quality fuel. It is therefore more efficient to draw off steam from the turbines and to use this waste heat (approximately 100 °C). The water vapour that evaporates from the coal therefore also contains heat. This can be recovered by preheating the storage water or air for the boiler. This increases the efficiency in dry lignite-fired power plants by up to 5 per cent. In Niederaussem (BoA1), this technology dries around a quarter of the raw lignite using a WTA plant (fluidised bed drying plant with internal heat recovery), which is the world’s first prototype.