Thanks to fluidised bed drying with internal waste heat utilisation (WTA), the water content of raw lignite can be reduced from 55% to just 12%. This in-house development by RWE offers a major advantage – in contrast to the previous drying process, which used flue gas heated to 1,000 °C, the WTA drying process operates at a temperature of 110 °C, making it both much more energetically efficient and also more environmentally friendly. The heat used to dry the coal is now also largely recovered and recycled. By comparison, to achieve a similar effect for the environment, almost 500,000 medium-sized cars would have to stay in the garage permanently.
CO2 reduction of up to one million tonnes per year
Fluidised bed drying has already been successfully tested at a small facility in Frechen since 1993. In 2009, a commercial prototype facility commenced operations in the RWE Innovation Centre. This prototype facility can generate up to 110 tonnes of dry lignite per hour, which corresponds to up to 30 % of the entire coal requirement of the block lignite power station with optimised equipment technology (BoA) in Niederaussem. Thanks to WTA, the efficiency of future lignite power plants could be increased by 10 % to over 47 %. This would mean that a plant with 1,000 MW output could generate the same amount of electricity but with a reduction in CO2 emissions of up to one million tonnes per year – a very impressive figure.
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Why is fluidised bed drying so efficient in terms of resources and therefore so environmentally friendly? The answer is simple: raw lignite has a naturally high water content of up to 60 %. This stored water makes it harder to burn the coal, which is why it must be subject to drying before any industrial use in order to remove as much water as possible from the coal. However, the evaporation heat used to dry the coal is lost in the processing chain. This wastes a relatively high amount of energy, of course, which is then not available for power generation. As a consequence, more coal has to be burned overall, which also results in higher CO2 emissions.