An Experimental Study on N₂O Reduction Over Circulating Ashes of CFB Boilers

An experimental study on nitrous oxide (N₂O) reduction with circulating ashes of circulating fluidized bed (CFB) boilers was conducted for the development of an effective and economical technology to reduce the N₂O emission from CFB boilers. The experiments were conducted with three kinds of circulating ashes, by using a fixed bed reactor with a diameter of 25mm, under various conditions of different operational temperatures, initial N₂O concentrations, NH₃ additions and O₂ concentrations. The effects on N₂O reduction were compared that with quartz sand. The experimental results showed that circulating ashes may possess remarkable catalytic effect on N₂O reduction and the intensity of the catalytic effect strongly depends on operational parameters such as reaction temperature and O₂ concentration. It was also found nitric oxide (NO) was produced during the process of N₂O reduction and its concentration also strongly affected by reaction temperature and O₂ concentration. The mechanisms of N₂O reduction were discussed. The study confirmed the feasibility of injecting NH₃ at the cyclone entrance of CFB boiler to form a selective catalytic reduction (SCR) process for N₂O emission without using extra catalyst and provided some guidance to choose the operational parameters for N₂O reduction with circulating ashes.