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Jänschwalde power plant: With greater flexibility it is intended to cover the residual load better, new dry lignite burners with plasma ignition help at it.
© Jörg Friebe, www.lausitz-bild.de
Augmenting existing power plants
Projektinfo 07/2016

The fuel passes together with the conveying air into the burner and flows around the plasma ignition lance at its end. At the ignition, two secondary air supply nozzles ensure an adequate air supply that enables complete combustion.
© Vattenfall Europe
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Dry lignite increases flexibility

Shoulder to shoulder with the energy transition: Coal plants are becoming more flexible to enable more energy from renewable sources to be used to supply the electricity grid. The output from renewable sources is currently not enough to meet the entire energy demand in Germany at all times. But their share is growing. This is transforming the role of conventional power plants: instead of providing constant base loads, they now have to cover fluctuating residual loads. To achieve this, pilot burners with integrated plasma ignition are being used for the first time in the world at a power plant in Jänschwalde in Brandenburg. These are using dry lignite as the fuel.

Coal-fired power plants will only be able to support the grid system in the coming years if they have considerable load flexibility. There are several reasons for this. Grid operators are giving priority to feeding renewable energy into the grid. However this power is not sufficient to meet the electricity demand at all times. The remaining demand, the so-called residual load, is met by fossil power plants. The construction of new wind and solar power generators, and the associated fluctuating feed-in into the grid, are increasing the level of flexibility needed by power plants.

The decentralised feed-in in sparsely populated areas also requires that the electricity is transported to the urban and industrial areas. This is increasing the risk of transmission line overloads in the grid. If a bottleneck occurs, it is necessary to act fast: on the one side the generated power is throttled, and on the other side increased. The result: Less electricity is transported via the overloaded transmission line. This intervention in the operational plan of power plants is known as re-dispatching. In recent years, these measures have increased in the German transmission grid from 1,588 hours in 2010 to 8,435 hours in 2014. This value was already exceeded during the first three quarters of 2015; the figures for the fourth quarter were not available on time of going to press.

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New fuel: Dry lignite instead of oil

In order to operate existing power plants more flexibly, Vattenfall has replaced ignition burners in the Jänschwalde power plant as part of a research project. The new models use dry lignite instead of heavy heating oil as the fuel. The aim is to operate them as both start-up and auxiliary burners. The auxiliary combustion enables the unit‘s minimum load to be reduced from 36 to 26 per cent. This therefore enables power plants to contribute to the system stability of the electricity grid even with a high proportion of renewable energy.

The new auxiliary burners in Boiler F2 have an electrical direct ignition. This produces a microwave-induced plasma on the ignition lance. The finely-ground coal enters the burner via an airflow. At the end it flows around the plasma and ignites.

The necessary underlying principles and experimental tests for this process are based on the findings made at the research facility in Schwarze Pumpe near Jänschwalde. There, the burners were prepared for use on an industrial scale. Jänschwalde is the first power plant in the world to use pre-dried lignite burners for auxiliary and start-up firing with plasma ignition.

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Addresses

Project management
Vattenfall Europe AG

Scientific support
BTU Cottbus

Scientific support
TU Hamburg-Harburg, TT

Scientific support
Hochschule Zittau/Görlitz