Papers by Keyword: Ammonia Slip

Abstract: The selective non-catalytic reduction (SNCR) process of a 480tžh^-1 CFB boiler was simulated with the Reynolds Stress Model (RSM) model. The effects of injection position, normalized stoichiometric ratio (NSR) and reaction temperature on the NO_x removal process were studied with urea and ammonia as reducing agents. While three spray guns were set at the outside of the separator entrance and two spray guns at the up side, the system can reach the highest NO_x removal efficiency. The NO_x reduction efficiency of ammonia is about 20%-25% higher than that of urea, but the ammonia slip is also higher. The NO_x reduction efficiency and ammonia slip both increases with the increase of NSR. Raising the inlet gas temperature of cyclone separator can significantly improve the NO_x removal efficiency and reduce ammonia slip. At the temperature of 925 C, the ammonia slip of the two reducing agents are both less than 10μl/l. Simulation results are comparatively consistent with the experiment datas cited form authoritative journals.

Abstract: _{Subscript text}The kinetic model for simulating the mechanism of the promoted effect of methanol on the NOxOUT process has been established and it mainly includes the optimal sub-mechanisms respectively for the NOxOUT process and the chemical reaction of methanol. The oxygen concentration does not obviously influence the maximum NO reduction efficiency in the range of 1-6 %, but the temperature window is overall shifted to lower temperature zone with oxygen concentration increased. Meanwhile, the mole ratio of urea to nitric oxide by a factor of 2 should be maintained between 1.5 and 2 from both the efficiency and running cost view. Also, ample residence time of 300/T-400/T s must be guaranteed for the reduction occurring thoroughly. Methanol does not compromise the maximum NO reduction efficiency and broadens the temperature window towards low temperature zone. The promoted mechanism of methanol on the NO_xOUT process is the abundant OH formation through the methanol regenerative reaction of CH₂OH/CH₃O+H2O=CH₃OH+OH and methanol should be maintained at 50-100 ppm for an obvious promoted effect. During the co-injection of methanol and urea, the “ammonia slip” is depressed, especially at 1173 K where the promoted effect on NO reduction is obvious, but emission of nitrous oxide is also markedly increased at this temperature.

Abstract: Nowadays, due to the stringent engine emission norms, an efficient technique is required to reduce oxides of nitrogen (NOX) from automobiles especially from the lean burn engines. Although Urea Selective Catalytic Reduction (SCR) is capable of satisfying these norms, the ammonia slip nullifies its advantages. Ammonia slip is mainly due to the lack of uniformity of ammonia at the monolith entrance. The uniformity of ammonia distribution mainly depends upon the flow parameters of exhaust gas and the injection parameters of urea water solution. The current study addresses the effect of flow parameters, temperature and flow rate of exhaust gas on the injection pressure. The results obtained reveals useful guidelines for enhancing the uniformity of ammonia in Urea-SCR.

Abstract: This paper presents the experimental studies on an SCR system for a mobile heavy-duty diesel engine to reduce NO_x emission below Euro V emission limits. The test results obtained by one engine serving in China show that NO_x emission was reduced to 1.81 g/kWh with ESC and 1.66 g/kWh with ETC, the reduction efficiency of NO_x was reduced by about 80%, while the average NH₃ slip is kept below 6 ppm.