船舶柴油机Urea-SCR系统催化反应动力学分析

Kinetics analysis of catalytic processes for marine diesel Urea-SCR system

针对Urea-SCR系统的工作特点,利用计算流体动力学耦合化学反应动力学的方法,对某型船舶柴油机Urea-SCR系统的高负荷性能进行了计算,得到了脱硝率(DeNOx率)、NH3逃逸率和尿素消耗量的关系,探讨了快速SCR反应对脱硝率和NH3逃逸率的影响,分析了催化过程中各组分质量分数的空间分布.结果表明:假定尿素溶液均匀混合在废气中,当(NH2)2CO与NOx摩尔比为0.475时,即NH3与NOx摩尔比为0.95,脱硝率和NH3逃逸率的匹配最佳,且脱硝率的计算值与试验值的误差保持在5%以内;高负荷时,快速SCR反应可使系统脱硝率进一步提高,并可以明显降低系统NH3逃逸率,避免造成二次污染.

According to the characteristics of Urea-SCR system,kinetics analysis of catalytic processes for marine diesel Urea-SCR system was carried out by computational fluid dynamics（CFD） coupled with chemical reaction kinetics.Based on 3-dimensional transient model,DeNOx rates and NH3-slips under different urea solution consumption rates,effects of fast SCR reaction on the catalytic processes and distributions of different specie concentrations were discussed.The results show that high DeNOx rate and low NH3-slip are obtained at optimal（NH2）2CO/NOx ratio of 0.475 for high load of marine diesel.The experimental DeNOx rate is consistent with calculated value with error less than 5%.DeNOx rate at high load can be further enhanced by increasing NO2/NO ratio to 1 ∶1 with obvious decrease of NH3-slip.