Use of SNCR to control emissions of oxides of nitrogen from cement plants

As air pollution environmental requirements for Portland cement manufacturing facilities become ever more demanding, and opportunities for controlling emissions of oxides of nitrogen are restricted by other emission limitations (e.g., for carbon monoxide and sulfur oxides), the cement manufacturer is faced with the need to control NO_x, while continuing to control the other pollutants. There are a number of methods that may be adopted by plants to achieve these mutually competing goals. One of these is implementation of low-NO_x calciners, which cause a portion of the calciner fuel to be burned under sub-stoichiometric (low oxygen) conditions - this method causes combustion under conditions which will suppress generation of fuel NO _x from the calciner, and may also cause decomposition of some of the NO_x (thermal and fuel) produced in the rotary kiln. Another method is selective non-catalytic reduction (SNCR) of NO_x using ammonia or urea. This latter method, when injected in the proper range of temperature, excess oxygen, and possibly carbon monoxide, has the advantage of compatibility with oxidizing conditions in the calciner, which will often minimize or avoid buildup difficulties associated with movement of sulfur as SO₂ within the preheater. The most efficacious combination of one or both of these methods may be one of the best approaches available to control NO_x emissions for new and existing kiln systems, while simultaneously avoiding excessive emissions of CO or SO₂ and reducing the process problems associated with sulfur cycles