The increasing percentage of electricity supplied from renewable energy sources into the power grid poses a great challenge to today's hard coal and lignite power plants. The power plants designed for continuous load operation must react more flexible to the natural fluctuations in solar and wind energy as well as to the varying energy demand. In addition, there are more and more shutdowns because the minimum load of a power plant often exceeds the requested power. This leads to an increased number of hot, warm and cold starts, for which expensive conventional starting fuels such as oil or gas are required. Moreover, since such start-up procedures take a very long time, this results in lower efficiency and higher costs for power generation.
The aim of this project is the use of a purely electric plasma ignition system, which on the one hand enables the use of solid primary fuels (lignite, hard coal, biomass) as starting fuels and on the other hand to further reduce the minimum load by stabilizing the coal flame with the help of the plasma. Overall, this should increase the flexibility and efficiency of coal-fired power plants and reduce their emissions.
Here, DC plasma torches are used as plasma ignition systems. In this case, a DC arc is generated between two electrodes and blown out of a nozzle as a hot jet. The plasma typically has a temperature around 10000 K and is therefore in principle hot enough to ignite the air/coal dust mixture flowing around it.
However, the ignition process and the flame stability depend on many factors, such as coal type, water content, grain size distribution, air/coal mixing ratio, gas flow in the burner or positioning of the plasma ignition system in the burner. Therefore, in order to better understand the interaction of plasma and coal, basic laboratory scale experiments are performed by optical emission spectroscopy (OES) and a high speed camera.
The ignition behavior and the flame stability are further investigated under realistic conditions in a small-scale incinerator (KSVA) of the Institute of Combustion and Power Plant Technology (IFK, University of Stuttgart) with up to 300 kW of thermal power and variation of the various parameters. The findings will eventually be used to test for ignition at 3 MW in a real coal-fired power plant.