ENVIRONMENT :Concerns about nitrogen oxide

Against the resistance of Germany, the EU lowers the upper limit for nitrogen oxide emissions from brown coal power plants.

The Weisweiler brown coal power station is one of the industrial plants with the highest pollutant emissions throughout Europe. (Photo: panthermedia.net/Werner Nick)

For more than 3,000 smaller and larger combustion plants, the EU is now redefining the state of the art.Experts from the Member States, the European Commission, as well as industrial and environmental associations had been struggling to achieve the best available technologies (BAT).

The EU reference number now largely agreed with the BAT reference document, albeit with minor changes. The emission of particulate matter, sulfur dioxide, nitrogen oxides (NOx) and mercury will be stricter in four years.

"The German-led brown coal lobbies were overruled", reveals Christian Schaible from the European Environment Bureau (EEB). This lobby also included Bulgaria, Finland, Poland, Romania, Slovakia, the Czech Republic and Hungary.
"The vote was very short," adds Schaible. A qualified majority of 65% was necessary. These reached 20 EU countries with a voting weight of 65.14% so grade. Before this, Greece was agreed with the package with a vote weight of 2.11%, after it was decided that the new BAT requirements for the use of heavy fuel in diesel engines on islands would only apply from 2030 onwards (by comparison, Germany's weight of votes) 16.06%).
The reference document was controversial. Thus, the Federal Government interfered with the values ​​for NOx emissions from brown coal power plants (300 MW heat output). In normal operation, an upper limit of 200 mg NOx / m³ was used in annual mean. In the future, there should be a range of 85 mg to 175 mg NOx / m³.
However, the Federal Government considers the upper limit value to be not appropriate and instead proposed 190 mg / m³. "We have relied on the scientific assessment of the Federal Environmental Agency," says Stephan Gabriel Haufe, spokesman for the Federal Environment Ministry.
The reference document recognizes several measures to reduce NOx emissions as BAT, according to the UBA. To regulate air supply in the boiler, for example, so that little nitrogen is oxidized. Or to remove the flue gas afterwards.Selective non-catalytic reduction (SNCR) and more effective but more expensive selective catalytic reduction (SCR) are offered here.
But a combination of measures is not prescribed, emphasizes UBA specialist Rolf Beckers. "The application of only combustion technology measures is also regarded as BAT". A recent UBA survey in the federal states in which lignite-fired power plants are operated showed that the annual power plants release between 160 mg and 195 mg NOx / m³ with firing technology optimization.
"Only four of 28 German lignite blocks reliably emit 175 mg / m³," says Beckers. There are two in each case at the locations Lippendorf in Saxony and Schwarze Pumpe in Brandenburg. But also brown coal power plants in Greece have been emitting less than 175 mg / m³ since 2010, Schaible adds. He considers the derivation of the 175 mg value to be appropriate. And he has no objection to a combination of measures.
"The 175 mg can be safely met with SNCR technology," said Bernd von der Heide, Managing Director of the Essen company Mehldau & Steinfath Umwelttechnik, as well as Wolfgang Schüttenhelm, responsible for business development and technology at ERC Technik in Buchholz.Both companies are using this technology in waste incineration and biomass plants as well as in Eastern European lignite and brown coal power plants. The NOx emissions can thus be reduced by 30% to 50%, in addition to measures in terms of combustion technology.
For example, ERC has retrofitted Block 3 of the world's largest brown coal power plant in Bełchatóv in Poland with an SNCR facility in 2016. "Since then, the valid NOx limit value of 200 mg / m³ has fallen below 50 mg / m³," emphasizes Schüttenhelm.
SNCR is not a marvel, says Anlagenbauer von der Heide: "We arrange several lances around the furnace in the boiler, through which we can reduce the amount of NOx in the flue-reducing agent." These are chemicals which, under the action of heat, ammonia (NH3) Which reacts with NOx to form nitrogen and water vapor.

Important is the temperature, supplemented by the heath. The reaction of NH3 with NOx proceeds favorably between 950 ° C and 1030 ° C. If, however, it becomes hotter than 1200 ° C in the furnace, the reducing agent itself burns into nitrogen oxides. This can happen in many power stations at full load. "We then cool the flue gas by selectively sucking in the lance."
But the political discussion is not yet finished. The tussle continues. Now, exceptions and the upcoming revision of the large combustion plant regulation are being disputed.
"In the interests of proper implementation, licensing authorities may grant exemptions in individual cases", Haufe explains. They may permit slightly higher annual emissions if the 175 mg upper limit can only be met with disproportionate expenditure.
However, the UBA expects only minor improvements in air quality. "In the brown coal power plant, the NOx emissions would drop by an average of 10 mg / m³," says Beckers. This corresponds to a reduction in the annual freight by 5% - and thus by a good 4500 t. The total NOx cargo of 1.22 million tonnes from all sources would thus drop by less than 0.4%. The load with nitrogen dioxide (NO2) in inner cities would not drop measurably.
However, the release of nitric oxides would decline significantly, the Federal Government did not follow the 175 mg target, but the technical possibilities, Schaible said. "We demand a NOx annual limit of max. 85 mg / m³ for power stations that will still run until 2027. "To do this, the plants would have to catalyze their flue gas catalytically - as is already the case today with coal-fired power plants. "If a power plant block goes off the grid by 2024, Schaible would accept an upper limit of 150 mg / m³, which is achievable with the cheaper SNCR variant.
In addition, Schaible considers the retrofitting with SNCR or SCR as justifiable. "Both economically worthwhile in just a few years." He points to figures from the European Environment Agency in Copenhagen: every ton of saved NOx emissions reduces health costs and damage to the environment of up to € 19,000.
Article: VDI