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Outline
Urea deposits in a selective catalytic reduction(SCR) system can be effectively suppressed by adjusting injector parameters, adding mixers, and coating catalysts on the pipe wall. Based on samples of urea deposits in a marine SCR system, V2O5-WO3/TiO2 catalyst and pure urea(CH4N2O), etc., the urea catalytic decomposition characteristics and the chemical composition of samples were firstly analyzed using characterization techniques such as thermogravimetric analysis(TGA) and Fourier transform infrared spectroscopy(FT-IR). Secondly, based on density functional theory(DFT), a detailed urea decomposition mechanism was proposed, which complemented the formation and decomposition path of cyanuric acid(C3H3N3O3) and its homologue. Finally, a non-catalytic and catalytic coupled kinetic model of urea was developed using TGA experimental data and chemical reaction kinetics methods. The results showed that the main chemical components of urea deposits in marine SCR system are cyanuric acid and its homologue, and ammelide(C3H4N4O2). Increasing the quantity of catalyst can accelerate urea decomposition, thereby blocking the conversion of urea and biuret(C2H5N3O2) to cyanuric acid. However, as the decomposition temperature of the by-products increases, a greater amount of catalyst is required.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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