Reduction of NO emissions from a coal-fired fluidized bed combustor by addition of NH 3 through a water-cooled injector

Abstract

To reduce NO emissions, ammonia was injected into a coal-fired fluidized bed combustor having a diameter and expanded bed height of 30 cm and a freeboard height of 100 cm. The injector consisted of a water-cooled stainless steel tube that could be moved axially to adjust the injection height. Experiments were performed to investigate the optimal position for NH 3 addition, and the influence of coal type and operating conditions, such as the fluidization number ( u u mf ), the NH 3:NO molar ratio β, the excess air level and the temperature. A distinct optimal position in the axial coordinate was always found, and depends on the fluidization number and coal type. The amount of NO reduction increases with β, with maximal reduction levels of 70% at β = 2 and a temperature of 850°C. The amount of excess air was also found to have an important influence on the NO reduction: optimal results were obtained at about 5% O 2 in the flue gas. The rather low temperature level at which the reaction proceeds, and the weak temperature dependence seem to indicate that the NONH 3O 2 reaction is influenced by heterogeneous reaction steps in the environment of the fluidized bed combustor.