Simulation and experiment on improving NOX conversion efficiency of ship selective catalytic reduction system

Selective catalytic reduction (SCR) technology is the main means of reducing NOX emissions. Urea injection structure parameters (i.e., the hole number in a nozzle, spray angle, the distance between the nozzle and the front section of the catalyst) and operating parameters (i.e., exhaust gas temperature, gas hourly space velocity, ammonia-to-nitrogen ratio (ANR)) of the SCR systems have a significant impact on denitrification efficiency (deNOX). A three-dimensional simulation model is developed to investigate the impact of diverse parameters on deNOX. The influence of temperature, ANR and space velocity on the deNOX of SCR system is studied by using the control variable method. The simulation model is modified according to the SCR catalyst gas distribution test results. A diesel bench experiment is conducted to test the deNOX of the SCR system of D2 cycle and two additional operating points to verify the accuracy of the numerical simulation model. Based on this model, the influence of key factors on the deNOX of SCR system is studied. In SCR system, the optimal urea injection angle is about 75°, the optimal number of nozzle holes is 4, the distance between the optimal urea injection point and the front section of the catalyst is 8 times of the pipe diameter, and the optimal operating temperature is 300 ∼ 420℃. The influence trend of ANR on deNOX at different temperatures is obtained. This provides a theoretical support for the realization of SCR system in the future.