Influence of non-uniform distribution of catalysts on the characteristics of ship SCR system
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摘要:
选择性催化还原（SCR）系统常用于降低柴油发动机尾气排放出的氮氧化物（NOx）。为进一步提高其脱硝性能，首先建立三维数值模拟模型，通过改变SCR转换器中孔隙率来实现催化剂的非均匀分布，从而研究在不同发动机负荷下的催化剂非均匀分布对SCR系统中的流动、传质和传热等性能的影响；其次，与催化剂的均匀分布进行对比，重点考察催化剂非均匀分布时对SCR系统性能的影响；最后，基于场协同原理分析SCR系统中的速度场和温度场对传热过程的影响。结果表明：催化剂的非均匀分布可以提高SCR系统的性能。在发动机25%的负荷下，与均匀分布相比，案例P-R5的压力损失降低165 Pa，脱硝率提高了0.8%，氨的逸出量减少了7 mg/L；案例P-R5的温度梯度高于均匀孔隙率催化剂温度梯度的最大峰值，这表明向外部传递的能量较少，催化剂非均匀分布的结构可以保持催化区域的温度，提高催化剂的活性，有利于脱硝反应。
Abstract:Selective catalytic reduction (SCR) systems are typically used to reduce nitrogen oxides (NOx) emitted from diesel engine exhaust emissions. To further improve its de-NOx performance, firstly, a three-dimensional numerical simulation model was established. The non-uniform distribution of the catalyst was achieved by changing the porosity in the SCR converter, and the impact of the non-uniform distribution of the catalyst under different engine loads on the flow, mass transfer, and heat transfer performance of the SCR system was investigated. Secondly, the impact of the non-uniform distribution of the catalyst on the performance of the SCR system was examined and compared with that of the uniform distribution. Finally, based on the principle of field synergy, the influence of velocity and temperature fields on the heat transfer process in the SCR system was analyzed. The results indicate that the non-uniform distribution of catalysts can improve the performance of SCR systems. At 25% engine load, compared to a uniform distribution, the pressure drop of Case P-R5 is reduced by 165 Pa, the conversion efficiency of NOx is increased by 0.8%, and the escape of ammonia is reduced by 7 mg/L. In addition, the temperature gradient of Case P-R5 is higher than the maximum peak of the temperature gradient of the catalyst with uniform porosity, indicating that there is less energy transferred to the outside. The non-uniform distribution of the catalyst structure can maintain the temperature of the catalytic region, improve the catalyst activity, and facilitate de-NOx reactions.
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图 2 不同发动机负荷下的仿真模拟结果与试验值的比较
Figure 2. Comparison of simulation results and experimental values under different engine loads
图 4 不同案例在50%发动机负荷下的压力分布云图
Figure 4. Pressure distribution cloud map of different cases at 50% engine load
图 5 50%发动机负荷条件下SCR系统中心线温度分布
Figure 5. SCR system centerline temperature distribution at 50% engine load
图 6 发动机负荷为50%时案例的温度分布
Figure 6. Temperature distribution of the cases at 50% engine load
图 7 不同发动机负荷下案例的脱硝率
Figure 7. NOx conversion efficiency of the cases under different engine loads
图 8 50%和100%发动机负荷下案例的中心平面NO含量的分布
Figure 8. Distribution of NO mass fraction in the central plane of the cases at 50% and 100% engine loads
图 9 不同发动机负荷下SCR系统出口氨的逸出量
Figure 9. Ammonia escape at the SCR system outlet under different engine loads
图 10 不同案例在50%和100%发动机负荷下氨的逸出量分布
Figure 10. Ammonia escape in different cases under 50% and 100% engine loads
图 11 不同发动机负荷下案例的轴向温度梯度峰值的变化
Figure 11. Variation in peak axial temperature gradient under different engine loads
图 12 不同发动机负荷下催化转化器前部的平均速度和均匀性系数
Figure 12. Average speed and uniformity coefficient in front of catalytic converter under different engine loads
表 1 SCR系统物理模型参数
Table 1. SCR system physical model parameters
入口和出口
截面直径
（d2）/mm入口或出口
段长度
（L1)/mm膨胀角度
（α）/（°）催化反应
段直径
（d1）/mm催化反应
段长度
（L2)/mm120 60 90 240 320 
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表 2 不同负荷下船用柴油机的催化转化器的边界条件
Table 2. Boundary conditions for catalytic converters of marine diesel engines under different loads
柴油机负荷/% 质量流量/（kg/s） 尾气压力/MPa 尾气温度/℃ NOx含量/（mg/L） H2O含量/% O2含量/% CO2含量/% 理论氨氮比 25 0.56 0.16 255 1 218 3.13 16.16 3.60 0.821 50 1.08 0.228 320 1 131 3.12 15.06 4.38 0.797 75 1.52 0.318 350 1 054 3.11 14.56 4.75 0.731 100 1.84 0.392 400 1 124 3.11 13.69 5.37 0.693
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表 3 案例设置
Table 3. Cases setting
案例 催化剂的分布 区域半径/mm 孔隙率 区域1（R1） 区域2（R2） 区域1（ε1） 区域2（ε2） P-R1 催化剂非均匀
分布40 80 0.41 0.75 P-R2 20 80 0.41 0.75 P-R3 40 100 0.41 0.75 P-R4 40 80 0.75 0.75 P-R5 40 80 0.41 0.41 P0 催化剂均匀分布 整个区域的孔隙率为0.65，半径为120 mm
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表 4 网格独立性
Table 4. Research on grid independence
网格类型 网格数量/个 出口处NO浓度/（mg/L） 粗网格 59 904 227 中网格 449 280 203 细网格 3 669 850 200
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[1] 屠星月, 邵社刚, 张潇天, 等. 基于时空数据挖掘的大气重污染传输过程时空规律分析[J]. 环境工程技术学报,2023,13(3):940-948. doi: 10.12153/j.issn.1674-991X.20220696TU X Y, SHAO S G, ZHANG X T, et al. Analysis of spatiotemporal laws in the transmission process of atmospheric heavy pollution based on spatiotemporal data mining[J]. Journal of Environmental Engineering Technology,2023,13(3):940-948. doi: 10.12153/j.issn.1674-991X.20220696 [2] 胡杰, 张磊, 李敏, 等. SCR催化器热失活数值仿真[J]. 内燃机学报,2015,33(5):72-78.HU J, ZHANG L, LI M, et al. Numerical simulation on SCR catalyst thermal inactivation[J]. Transactions of CSICE,2015,33(5):72-78. [3] 钟超. 柴油机微粒捕集器再生对选择性催化还原性能影响研究[D]. 长沙: 湖南大学, 2020. [4] CHEN L, LIAO Y F, XIN S R, et al. Simultaneous removal of NO and volatile organic compounds (VOCs) by Ce/Mo doping-modified selective catalytic reduction (SCR) catalysts in denitrification zone of coal-fired flue gas[J]. Fuel,2020,262:116485. doi: 10.1016/j.fuel.2019.116485 [5] ZHANG Z Q, TIAN J, LI J T, et al. Effects of different mixture ratios of methanol-diesel on the performance enhancement and emission reduction for a diesel engine[J]. Processes,2021,9(8):1366. doi: 10.3390/pr9081366 [6] 张文强. 柴油机尿素SCR系统反应特性的研究[D]. 长沙: 湖南大学, 2011. [7] ZHANG G W, YAN H Y, LI T H, et al. Relation analysis on emission control and economic cost of SCR system for marine diesels[J]. Science of the Total Environment,2021,788:147856. doi: 10.1016/j.scitotenv.2021.147856 [8] LEI Z G, WEN C P, CHEN B H. Optimization of internals for selective catalytic reduction (SCR) for NO removal[J]. Environmental Science & Technology,2011,45(8):3437-3444. [9] YE J D, LV J S, TAN D L, et al. Numerical analysis on enhancing spray performance of SCR mixer device and heat transfer performance based on field synergy principle[J]. Processes,2021,9(5):786. doi: 10.3390/pr9050786 [10] PENG Q G, E J, CHEN J W, et al. Investigation on the effects of wall thickness and porous media on the thermal performance of a non-premixed hydrogen fueled cylindrical micro combustor[J]. Energy Conversion and Management,2018,155:276-286. doi: 10.1016/j.enconman.2017.10.095 [11] YU Y S, LI Y, LU H F, et al. Performance improvement for chemical absorption of CO2 by global field synergy optimization[J]. International Journal of Greenhouse Gas Control,2011,5(4):649-658. doi: 10.1016/j.ijggc.2011.03.008 [12] ZHU Y, XIA C, SHREKA M, et al. Combustion and emission characteristics for a marine low-speed diesel engine with high-pressure SCR system[J]. Environmental Science and Pollution Research,2020,27:12851-12865. [13] CHOI C, SUNG Y, CHOI G M, et al. Numerical analysis of NO x reduction for compact design in marine urea-SCR system[J]. International Journal of Naval Architecture and Ocean Engineering,2015,7(6):1020-1034. doi: 10.1515/ijnaoe-2015-0071 [14] ZHU Y Q, ZHANG R P, ZHOU S, et al. Performance optimization of high-pressure SCR system in a marine diesel. part Ⅱ: catalytic reduction and process[J]. Topics in Catalysis,2019,62(1):40-48. [15] TAN L G, GUO Y G, LIU Z, et al. An investigation on the catalytic characteristic of NO x reduction in SCR systems[J]. Journal of the Taiwan Institute of Chemical Engineers,2019,99:53-59. doi: 10.1016/j.jtice.2019.02.020 [16] 叶杰栋. 船用柴油机SCR系统喷射雾化及催化转化性能研究[D]. 钦州: 北部湾大学, 2021. [17] ZHANG Q L, ZHANG Y Q, ZHANG T X, et al. Influence of preparation methods on iron-tungsten composite catalyst for NH3-SCR of NO: the active sites and reaction mechanism[J]. Applied Surface Science,2020,503:144190. doi: 10.1016/j.apsusc.2019.144190 [18] XU H X, LUO J B, PAN Y J, et al. Effect and optimization of radial non-uniform porosity catalyst on SCR characteristics based on response surface method[J]. Journal of Environmental Chemical Engineering,2023,11(5):110771. doi: 10.1016/j.jece.2023.110771 [19] 马修元, 孙尊强. 燃煤机组电除尘器入口烟道流场优化数值模拟研究[J]. 环境工程技术学报,2023,13(3):965-972. doi: 10.12153/j.issn.1674-991X.20220019MA X Y, SUN Z Q. Numerical simulation study on flow field optimization of electrostatic precipitator inlet flue duct in coal-fired units[J]. Journal of Environmental Engineering Technology,2023,13(3):965-972. doi: 10.12153/j.issn.1674-991X.20220019 [20] 赵鸿华, 宋双文, 王志凯, 等. 小弯管冲击冷却结构流场和温度场的场协同分析[J]. 推进技术,2023,44(4):1-7.ZHAO H H, SONG S W, WANG Z K, et al. Field synergy between flow field and temperature field in concave wall impingement cooling structure[J]. Journal of Propulsion Technology,2023,44(4):1-7. [21] 胡娅萍, 吉洪湖. 平壁气膜冷却流场与温度场的协同分析[J]. 工程热物理学报,2004,25(1):94-96. doi: 10.3321/j.issn:0253-231X.2004.01.027HU Y P, JI H H. Synergetic analysis of velocity and temperature fields of flat plate film cooling[J]. Journal of Engineering Thermophysics,2004,25(1):94-96. doi: 10.3321/j.issn:0253-231X.2004.01.027 [22] ZHANG Z Q, YE J D, LV J S, et al. Investigation on the effects of non-uniform porosity catalyst on SCR characteristic based on the field synergy analysis[J]. Journal of Environmental Chemical Engineering,2022,10(1):107056. doi: 10.1016/j.jece.2021.107056 [23] LUO J B, XU H X, WANG J, et al. The research on dynamic performance of single channel selective catalytic reduction system with different shapes[J]. Journal of Environmental Chemical Engineering,2022,10(5):108530. □ doi: 10.1016/j.jece.2022.108530 -
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