Just add bromine
March 23, 2012
Mercury is highly volatile and a neurotoxin. Coal power stations are responsible for the highest amount of mercury emissions in Germany, the US and worldwide. They emit the poisonous metal, also known as quicksilver, into the atmosphere and it can eventually make its way into the food chain.
“The mercury problem can only be solved if coal power stations lower their emissions,” Rolf Beckers from the German Federal Environment Agency (UBA) told DW.
Mercury is only found in coal in small amounts, but coal is burned around the world and in large quantities. The United Nations Environment Program estimates that internationally coal power plants emit some 500 tons of mercury a year - Germany is responsible for more than five tons, the US for almost 50 tons and China for more than 100 tons.
Some countries have limited mercury emissions from coal power plants by law. The EU limits emissions to 50 micrograms of mercury per cubic meter per day; Germany has an even stricter limit of 30 micrograms.
Doable goals
The US has set new standards. In late 2011, US President Barack Obama announced the strictest mercury emission limits worldwide. From 2016 onwards, the monthly average emission of mercury per cubic meter must not exceed 1.5 micrograms in any coal power plant.
Experts says this is a realistic goal. Some 12 percent of US power plants already fall below this mark.
It's never the entire amount of mercury contained in the coal that ends up in the air. Modern coal power plants use flue gas treatment to remove particulates and carbon dioxide. Three quarters of mercury is extracted in this process. That's a welcome side effect, according to UBA expert Beckers. But it's the maximum of what can be done with traditional flue gas treatment in terms of limiting mercury emissions. That's because part of the metal becomes insoluble in water in the burning process, making it impossible to extract it. “That's the part that goes into the atmosphere,” Beckers explained.
Bonding with bromine
Twelve years ago, process engineer Bernhard Vosteen and his team at the Leverkusen-based chemical company Bayer came up with a possible solution. When studying the methods of burning industrial waste in a special waste burning facility, Vosteen noticed that the exhaust fumes hardly contained any mercury whenever there was a trace of bromine present.
"The salts contained in bromine turn the elementary mercury in the hot flue gas into mercury bromide,“ he said. And that's a chemical element that can be extracted from the flue gas.
Vosteen turned this realization into a method to cut mercury emissions. His company is now selling it around the globe. More than ten coal power plants in the US already use bromide to limit mercury emissions to a maximum of one microgram per cubic meter. This allows them to emit considerable less of the poisonous metal per cubic meter of flue gas than German coal power plants.
Berlin considers stricter limits
Based on the move by the US to cut mercury emissions, Germany's UBA is now also trying to lower the limit in Germany considerably. From 2016 onwards, German coal power plants are only allowed a maximum of three micrograms of mercury per cubic meter a day. From 2019 on that limit drops to just one microgram.
"The three-microgram-limit would reduce mercury emissions from power plants by some 40 percent, if you reduced it further to one microgram, emissions would be reduced by almost 80 percent,” said Beckers. These proposals are currently being debated by the German government.
Author: Ralph Heinrich Ahrens / nh
Editor: Holly Fox