Reduction of nitrogen oxides in flue gases

In recent years there has been an unprecedented growth and development in flue gas control technologies capable of reducing NOx emissions to the low levels required by current legislation. Major post-combustion technologies include selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR). The current status of these technologies is summarised, and the advantages and disadvantages of both methods are reviewed. SCR offers the advantage of greater NOx reduction and has therefore been widely adopted in industrialised countries with stringent emission limits, while SNCR requires lower capital costs and is increasingly being applied by industries in developing countries. Other techniques, such as hydrocarbon-selective catalytic reduction (HC-SCR) and direct catalytic decomposition of NOx, although showing some promise in laboratory experiments, are still not commercially viable.