NOx control for high-ash coal-fired power plants in India

Many countries have strict emission limits for nitrogen oxides (NOx); thus NOx control systems are widely deployed. India has recently introduced NOx emission limits, which require that pollution control technologies must be installed on most coal-fired plants. However, operational experience with NOx control systems in India is limited to primary measures only. Additionally, Indian coals have a high level of inherent ash, which is also highly erosive and can influence the behaviour of some NOx control systems and thus affect the selection process. Primary measures for NOx control from coal-fired power plants include low NOx burners (LNBs), overfire air systems (OFA), fuel reburning, flue gas recirculation, fuel biasing, low excess air and combustion optimization. Secondary NOx control includes selective catalytic reduction, selective non-catalytic reduction and multi-pollutant control systems. Retrofit of primary measures (LNBs and OFA) in India has been recommended to take place during next-scheduled plant outages; for many plants this could occur by 2019. However, control strategies for individual plants will be needed to ascertain the appropriateness of installing post-combustion technologies or various combinations of NOx control measures. Hence installation of secondary NOx controls is not expected before test results from secondary controls on selected Indian power plants units are known.