Development of a Selective Noncatalytic Reduction (SNCR) System for
Stationary NOx Emission Control, 01-R8213
Inclusive Dates: 04/01/11 04/01/12
Background — Nitric oxides (NOx), including nitric oxide (NO) and nitrogen dioxide (NO2), are toxic pollutants formed during combustion processes. Regulations on nitrogen oxides (NOx) emission from stationary sources are increasingly more stringent. The selective noncatalytic reduction (SNCR) does not have a catalyst, and has been used for NOx emission control from stationary sources. It has the potential of solving the problems inherent with selective catalytic reduction (SCR) technology, e.g., high catalyst cost, high maintenance cost and sensitivity to impurities in flue gas. However, one of the disadvantages of SNCR technology is the low NOx removal efficiency comparing to the SCR technology.
Approach — The objective of this project is to investigate the feasibility of increasing the NOx removal efficiency of SNCR technology by optimizing the temperature distribution and increasing residence time. The project was focused on developing structured materials to tolerate high temperature with low pressure drop to achieve the objective. Computational fluid dynamics (CFD) modeling was applied to simulate the temperature and flow distributions in the SNCR reactor and calculate the pressure drops with different structured packing materials under different operating conditions.
Accomplishments — A prototype SNCR system was developed, as shown in Figure 1. NOx concentration was measured with ASTM D5504 method (chemiluminescence GC analysis), such that NOx reduction efficiency was calculated. CFD modeling simulated the temperature and flow distributions in the SNCR reactor and calculated the pressure drop with different packing materials under a wide range of operating conditions. Pressure drop for different packing materials was measured and compared with the CFD modeling results. The system was tested on simulated flue gas with NOx concentrations in the range of 300 to 500 ppm and temperature from 800°C to 1,000°C. SNCR tests for different NOx concentrations at 300 ppm, 400 ppm and 500 ppm with NH3/NOx = 2/1 showed that the percentage of NOx removal was increased more than 10 percent with better temperature distribution created by the packing materials, and the ammonia slip was below 2 ppm. Hydrocarbons were also tested to be a very good reducing agent for NOx removal. The effect of temperature on NOx removal was also studied.