New approach into NOx removal from flue gas by carbohydrazide

Abstract

Selective non-catalytic reduction (SNCR) is a proven technique to reduce nitrogen oxide (NOx) emissions from stationary sources. The process utilizes NH3 or urea as a reducing agent, which is only effective in a narrow and high temperature range with the maximum NOx abatement falling with the increase of the O2 content. In large industrial boilers, the effectiveness of the deNOx process may be decreased with boiler load variations and excess O2. This study investigated carbohydrazide as a reagent to improve SNCR performance. NO reduction by carbohydrazide was experimentally investigated in a pilot-scale flow reactor. The effect of reaction temperature, molar ratio of NH2 to NO (normalized stoichiometric ratio, NSR) on the NO reduction was determined. Moreover, the promotion effect of carbohydrazide on the reactivity of NH3 and urea was also investigated. The experimental results indicated that NO reduction by carbohydrazide occurred in a relatively low temperature range of 650–850 °C, and the optimum reaction temperature was about 730 °C at NSR of 2.0, the O2 content of 11.5%–16.6% and the initial NOx concentration of 635 mg/m3. After adding a small amount of carbohydrazide to an NH3 or urea solution, the data showed that carbohydrazide could shift the temperature window of NH3 to the left, but had no positive effect on urea deNOx and the NO conversion efficiencies of NH3 deNOx. Consequently, carbohydrazide is a potential reducing agent for NOx, but was not adapted to improve the deNOx performance with NH3 and urea.