Numerical Simulation of Urea Based SNCR Process in a Trinal-Sprayed Precalciner

Abstract

In order to study the combustion characteristics, NOx emission and NH3 slip in a new trinal-sprayed precalciner, the simulations of combustion and aqueous urea solution based selective non-catalytic reduction (SNCR) process were conducted by computational fluid dynamics in this precalciner, the effects of different injection heights, different injection flow rates and stratified injection under different flow rates on SNCR process were studied. The results showed that the flow field was symmetrically distributed in the precalciner, and the flue gas from the rotary kiln formed the recirculation region on both sides of the cone body, which increased the residence time of the solid particles. The temperature was mainly between 1100 K and 1250 K in the middle and upper column of the precalciner, which met the demand of the pulverized coal combustion and raw material decomposition. The concentration of NO at the outlet of the precalciner was 559 ppm, moreover, different injection heights and different injection flow rates had a strong influence on NOX removal efficiency and NH3 slip. The aqueous urea solution should be injected at SNCR-1 to prolong the residence time of NH3, and injection flow rate had an optimal flow rate but not the higher the better. When the injection flow rate under stratified injection was 0.019 kg/s, which could play a better optimization role on NO removal efficiency on the basic of the injection flow rate. In consideration of cost effective, a stratified injection with an injection flow rate of 0.019 kg/s and an injection height of 20 m, 25 m and 30 m was suggested as a compromise of a satisfactory NOx reduction rates and reasonable NH3 slip. Under this condition, numerical simulation result showed that NOx concentration at the outlet of precalciner was 297.27 mg/Nm3 and NH3 slip was 4.67 mg/Nm3, meeting emission standard.