Nitrous Oxide Emissions Control by Afterburning: Laboratory Experiments

Nitrous oxide (N20) can be the primary oxide of nitrogen emitted from coal-fired fluidized bed combustors. This is of concern because N20 is both a greenhouse gas and an ozone depleting gas. In this paper laboratory results are presented on N20 removal by the afterburning (i. e., reburning) method. The laboratory combustion reactor simulates the conditions of the fluidized bed combustor flue gas and afterburning zone. The reactor has two chambers: a primary chamber in which products of combustion are generated, followed by the afterburning chamber in which the nitrous oxide, products of primary combustion, and the afterburning fuel are reacted. The level of nitrous oxide doped into the primary combustion products is 200 to 340 ppmv. The temperature level of the primary combustion products is varied between 1080 and 1370K, and the oxygen level of these gases is varied between 3.3 and 4.8%. Several afterburning fuels are tested. The rank order of after burning effectiveness is H2 > CH4 > C2H4 and C2H6 > CO. Tests are also performed with the primary combustor operated fuel rich. Without any afterburning fuel added, large removals of N20 are obtained when the fuel-air equivalence ratio of the primary combustion is about 1.1. The experimental results are presented, discussed, and compared to chemical kinetic modeling.