Scientists at the Naval Research Laboratory are exploring the use of electron beam to reduce the amount of nitric acid and nitrogen dioxide (NOx) emitted by coal-burning power plants. They have already shown that zapping NOx in the presence of nitrogen breaks apart the nitrogen and oxygen of the NOx and it reforms into pure nitrogen and oxygen. It takes about four electron volts (eV) to break the bonds in an NOx molecule. They are now testing the technique on actual flue gas using a KrF laser fired at five pulses per second. Firing in pulses rather than a steady beam lets the laser operate work continually without overheating.
This approach could prove useful and economical when the EPA comes out with tighter NOx emission restrictions. Current regulations restrict powerplant emissions to less than 100 ppm. New regulations are expected to restrict it further to less than 30 ppm. The current method of reducing NOx emissions is selective catalytic reduction, which uses scrubbers, an expensive solution. It also consumes up to 15% of the plant’s generated electricity to run the scrubbers. And they create ammonium nitrate, an explosive byproduct that requires disposal. The new approach of firing lasers into the gas, on the other hand, uses only 10 to 20% of the cost of scrubbers for the energy and there are no byproducts.