Non-catalytic NO_x removal from gas turbine exhaust with cyanuric acid in a recirculating reactor; small scale evaluation and industrial application

A novel SNC technique to remove oxides of nitrogen (NO_x) from stationary gas turbine exhaust has been investigated and applied. The technique employs the use of cyanuric acid (CYA), a non-toxic, dry powder, combined with the injection of auxiliary turbine fuel and recirculation. During the initial investigation, exhaust, generated by a 150 kW gas turbine, was treated in an insulated recirculation reactor, with a mean residence time of 0.65 to 0.71 seconds and a pressure drop of 660 Pa. In the reactor, autoignition of injected auxiliary gas turbine fuel raises the fuel gas temperature to between 700 and 800 ºC. CYA slurry is injected. Temperature rise and NO_x reduction occur simultaneously. Load following has been achieved. At all temperatures, signifcant NO_x reduction from initial concentrations of 106 to 124 ppm to as low as 18 ppm at 15% O₂ have been observed. However, The process generates N₂O emissions, which vary from 45 to 163 ppm, increasing with increasing CYA/NO_x ratio. The ratio of N₂O formed to NO removed was found to be between 1 to 1.5 to 1. The performance of CYA ((HNCO)₃) is compared to that of ammonia (NH₃) and urea ((NH₂)₂CO). A numerical model, which combines a detailed chemical kinetic mechanism with recirculation, has been developed. The model captures all observed trends well and is an invaluable guide to improved understanding of the interactive NO_x removal process. The process was then successfully scaled up and applied to a variety of industrial 3.7 MW gas turbines and similarly significant NO_x reduction has been achieved.