Our power stations all over the country are equipped with flue gas purification systems. With that, E.ON Kraftwerke is making an essential contribution towards the reduction of emissions. Flue gas purification primarily aims at minimising the emission of sulphur dioxide (SO₂), nitrogen oxides (NO_x) and soot particles.

Not only since yesterday

As early as the seventies, E.ON Kraftwerke started developing flue gas purification methods. In 1975 the time had come. We were able to install the first flue gas purification system at the coal fired power station Wilhelmshaven. This was a first for Germany and a true innovation in terms of process engineering. The technology is constantly being refined. Thus today, pollutants at E.ON Kraftwerke hardly have a chance to escape to the environment.

This is how flue gas purification works:

In three stages, nitrogen, dust and sulphur are removed from the power stations’ flue gas.

1. For the removal of nitrogen, a distinction is made between primary and secondary methods. The use of special burners at the steam generator firstly achieves that only low amounts of nitrogen oxides are generated (primary method). The secondary methods are used accordingly downstream of combustion in hard coal fired power stations. At the same time, the so-called SCR method (selective catalytical reduction) is the most widespread. Through the addition of a reduction agent (e.g. ammonia) and under the influence of a catalyst, the nitrogen oxides are converted to pure nitrogen, such as it occurs in air and water. In many modern power stations, the SCR plant is used as first purification stage and achieves NO_X separation efficiencies of 95 percent.

2. As a rule, this is followed by the dedusting stage using an electrostatic precipitator. For this, the dust particles are polarised negatively with a spray electrode. When they pass through an electric field, the particles are attracted by a positively charged precipitation electrode and thus removed from the flue gas. This method achieves a separation efficiency of more than 99 percent of differently sized dusts. Together with the residual ash from the steam generator, this fly ash is used as concrete additive or in road construction.

3. The last purification stage to follow is the flue gas desulphurisation plant. Today, we are able to achieve a degree of desulphurisation in excess of 95 percent. For this purpose, the flue gases are sprayed with an aqueous lime solution. The result of this is gypsum that can be virtually completely reused.