Explain selective non-catalytic reduction (SNR) for NOx control. A 500MW coal-fired plant is designed to burn coal at a firing rate of 500000lb/hr. Flue gas flow rate in the plant is 2 million scfm and it contains 1000ppm of NO and 100ppm of NO2, as it exits the boiler. Calculate the overall percentage reduction of NOX required to meet the NSPS (new source performance standards). Assume NSPS for NOx as 2lb/MWh of gross energy output. If a combination of low NOX burners and overfire air is estimated to reduce the formation of NOx by 50%, what removal efficiency is required for the SCR (selective catalytic reduction) system that is being designed? [5+6+4=15]