Abstract
The most effective de-NOx technology in marine diesel applications is the urea-based selective catalytic reduction (SCR) system. The urea-SCR system works by injecting a urea solution into exhaust gas and converting this to NH3 and CO2. The injection, mixing, and NH3 conversion reaction behavior of the urea-water solution all have a decisive effect on the performance of the system. To improve de-NOx efficiency, it is important to provide enough time and distance for NH3 conversion and uniform distribution prior to the solution entering the catalyst. In this study, therefore, the characteristics of gas flow, NH3 conversion, and its distribution are investigated with a static mixer by means of numerical methods, providing a special advantage to ship manufacturing companies through the optimization of the urea-SCR system. The results show that the inclusion of the mixer induces strong turbulence and promotes the NH3 conversion reaction across a wider region compared to the case without the mixer. The mean temperature is 10 °C lower due to the activated endothermic urea-NH3 conversion reaction and the NH3 concentration is 80 PPM higher at 1D than those without the mixer. Moreover, the uniformity of NH3 distribution improved by 25% with the mixer, meaning that the de-NOx reaction can take place across all aspects of the catalyst thus maximizing performance. In other words, ship manufacturing companies have degrees of freedom in designing post-processing solutions for emissions by minimizing the use of the reduction agent or the size of the SCR system.
Highlights
Environmental pollution caused by marine ships has recently emerged as an international issue and as a result since 1 January 2016 the International Maritime Organization (IMO) has applied Tier 3 regulations for diesel engines keel laying at the NOx emission control area (NECA) [1]
The results show that the mixer generates strong turbulence at the mixing area and reduces the axial velocity of the fluid, whereas the flow is almost laminar without the mixer
Since the recirculating flow has a significant impact on the velocity uniformity index (UI) and the disruption urea droplets gases decreases, and the biased reductantto lowers de-NOx of the steadyand andexhaust stable supply of NH3 to thehence catalyst, it is important minimize the efficiency by restricting evaporation and the thermolysis reaction
Summary
Environmental pollution caused by marine ships has recently emerged as an international issue and as a result since 1 January 2016 the International Maritime Organization (IMO) has applied Tier 3 regulations for diesel engines keel laying at the NOx emission control area (NECA) [1]. Johnson et al studied de-NOx characteristics in marine diesel systems [5] They investigated correlations between system parameters and NOx rates, as well as NH3 slip. Sung et al analyzed the effect of swirltype mixers and mixing chambers on NOx conversion efficiency in a marine system for an optimized compact design [10]. They evaluated flow characteristics and parameters of de-NOx conversion for each case. This group analyzed the synergistic effects of mixers and a mixing chamber on flow mixing and NOx reduction for a marine urea-SCR system [11]. We can distribute the design data for the optimization of the urea-SCR system to researchers working in related industrial fields
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