-
选择性催化还原 (selective catalytic reduction, SCR) 脱硝技术因其效率高、成本低和选择性高等优势而被广泛应用于烟气脱硝[1-3]。尽管该技术解决了电力行业中高温烟气 (300 ℃以上) 脱硝的问题,但由于SCR催化剂活性温度较高、抗毒性能较差,无法处理非电力行业大量低温烟气 (120~300 ℃以下) 中的NOx[4-5]。因此,低温烟气SCR脱硝技术的研究热点为具有低活性温度和抗毒性能强的催化剂[2, 6-7]。尽管SCR催化剂的活性温度已低于120 ℃[8-9],但受成本、工艺等制约,相关催化剂难以在实际工业低温烟气脱硝工程中应用。目前,在工业上实际运行的低温SCR催化剂操作温度约为200 ℃[10-12],故反应温度是控制NOx转化率的首要因素。在SCR催化剂的活性温度区间内,催化剂的活性与反应温度成正比[13-15]。非电力行业的低温烟气脱硝反应器一般设置于烟气处理末端,即设置于脱硫除尘之后,烟气温度通常在100 ℃以下 (湿法脱硫可低于60 ℃) ,烟气温度远低于目前工业化SCR催化剂的活性温度区间。因此,脱硝反应器前会加装预热器,使烟气温度达到催化剂的活性温度区间。预热烟气进入反应器后会先将热量传递给催化剂,只有催化剂整体达到高活性温度,脱硝反应才会高效进行。
YANG等[16]采用将粉状活性金属组分涂覆在空白单体载体表面制备NH3-SCR蜂窝催化剂,并在250~350 ℃的温度下进行实验。结果表明,SCR脱硝反应主要在催化剂表面的微界面进行。因此,理论上讲,只要使SCR催化剂反应界面温度在其活性温度区间即可保证NOx高转化率,而无需将烟气整体温度升高。基于此,以催化剂颗粒为循环热载体,并利用旋流循环流化反应器可在无需整体加热的情况下实现NOx在催化界面的反应,从而达到降低能耗以去除NOx的目标。旋流流化反应器应用于气态污染物治理中。马良等[17-18]开发了新型旋流流化床反应器,用于活性炭吸附挥发性有机化合物,反应器在120 Pa压降下的吸附效率接近100%。同时,增加颗粒自旋转速度可在一定程度上提高吸附效率[19]。
基于以上原理,本课题组设计了一种低温SCR旋流循环流化反应器,以开发高温催化剂为循环热载体的低温烟气脱硝工艺。采用计算流体力学 (computational fluid dynamics, CFD) 与离散元方法 (discrete element method, DEM) 耦合的数值模拟方法[20-22],研究低温烟气与高温催化剂在反应器中的传热特性及脱硝可行性,以期为低温烟气脱硝提供参考。
低温烟气脱硝旋流流化反应器的传热特性
Heat transfer characteristics of low-temperature flue gas denitrification swirl fluidization reactor
-
摘要: 现行工业低温烟气脱硝技术需对烟气及整个反应系统进行整体加热以达到催化剂高效反应的温度,存在能耗高的问题。由于脱硝反应仅在高温催化颗粒的微界面上进行,提出以高温催化剂颗粒为循环热载体,利用旋流流化反应器使其与低温烟气中的氮氧化物快速接触,发生脱硝反应的新方法。通过CFD和DEM耦合计算,模拟研究了旋流流化反应器中高温催化剂颗粒和低温烟气间的传热特性。调控因素主要包括进口气速、进料速率、进口烟气温度。结果表明,在催化剂进料速率为25 g·s−1、进口气速为7.5 m·s−1 (空速81 000 h−1) 时,反应器出口催化剂平均温度可达200 ℃以上 (催化剂高效活性温度区间为200~300 ℃) ,对比直接加热低温烟气的方式,不考虑加热与传热过程热量损失,可直接节约能耗28.36 %。本研究对比低温烟气脱硝中整体加热烟气的方式,可为低温烟气脱硝技术的优化提供参考。Abstract: At present, for industrial low-temperature flue gas denitrification, the flue gas and the whole reaction system is heated to achieve the efficient reaction temperature of the catalyst, the overall energy consumption of whihc is high. Based on the denitrification reaction on the face of high-temperature catalytic particles, a new method for rapid reaction with nitrogen oxides in low-temperature flue gas in a cyclone fluidization reactor using high-temperature catalyst particles as the circulating heat carrier was proposed. Through the coupling calculation of CFD and DEM, the heat transfer characteristics between high-temperature catalyst particles and low-temperature flue gas in the cyclone fluidization reactor were simulated and studied, and the regulatory factors mainly included inlet gas velocity, feed rate and inlet flue gas temperature. The results showed that when the catalyst feed rate was 25 g·s−1 and the inlet gas velocity was 7.5 m·s−1 (airspeed 81 000 h−1), the average temperature of the catalyst outlet of the reactor could reach more than 200 °C (the efficient active interval of the catalyst was 200~300 °C). Compared with the direct heating of low-temperature flue gas, the direct energy consumption saving reached 28.36% without considering the heat loss in the heating and heat transfer process.
-
表 1 旋流流化反应器结构参数
Table 1. Geometric parameters of the cyclone
圆柱直径D/mm 柱高H/D 进口宽度a/D 进口高度b/D 芯棒直径De/D 芯棒高度S/H 25 41.6 0.4 0.6 0.32 0.5 表 2 EDEM中颗粒相与壁面参数
Table 2. Parameters of particle phase and wall in EDEM
物理位置 泊松比 密度/ (kg·m−3) 杨氏模量/Pa 恢复系数 静摩擦 动摩擦 颗粒相 0.45 2 760 1 108$ \times $ 0.4 0.55 0.08 壁面 0.3 7 800 7 1010$ \times $ 0.25 0.3 0.04 -
[1] ZHANG J, LI X C, CHEN P G, et al. Research status and prospect on vanadium-based catalysts for NH3-SCR denitration[J]. Materials (Basel), 2018, 11(9): 2-15. [2] LIU H Z, TAN Q, JIANG X, et al. Comprehensive evaluation of flue gas desulfurization and denitrification technologies of six typical enterprises in Chengdu, China[J]. Environmental Science and Pollution Research, 2020, 27(36): 45824-45835. doi: 10.1007/s11356-020-10460-5 [3] XIONG S C, CHEN J J, LIU H, et al. Advances in the treatment of multi-pollutant flue gas in China's building materials industry[J]. Journal of Environmental Science (China), 2023, 123(01): 400-416. [4] ANTHONSAMY S B I, AFANDI S B, KHAVARIAN M, et al. A review of carbon-based and non-carbon-based catalyst supports for the selective catalytic reduction of nitric oxide[J]. Beilstein Journal of Nanotechnol, 2018, 9(1): 740-761. [5] WU Y, HU Z, ZHOU J-l, et al. Improvement in the resistance to KCl and PbCl2 synergistic poisoning of the commercial SCR catalyst by Ce(SO4)2 modification: A combined experimental and spin-polarized DFT study[J]. Journal of Environmental Chemical Engineering, 2023, 11(3): 2-11. [6] TAN W, WANG J, CAI Y, et al. Molybdenum oxide as an efficient promoter to enhance the NH3-SCR performance of CeO2-SiO2 catalyst for NO removal[J]. Catalysis Today, 2022, 397-399(01): 475-483. [7] HAN Q, JIN S, WANG J, et al. Insights to sulfur-resistant mechanisms of reduced graphene oxide supported MnOx-CeOy catalysts for low-temperature NH3-SCR[J]. Journal of Physics and Chemistry of Solids, 2022, 167(01): 2-17. [8] WU Z, JIN R, LIU Y, et al. Ceria modified MnOx/TiO2 as a superior catalyst for NO reduction with NH3 at low-temperature[J]. Catalysis Communications, 2008, 9(13): 2217-2220. doi: 10.1016/j.catcom.2008.05.001 [9] LAGUNA O H, ROMERO S F, CENTENO M A, et al. Gold supported on metal-doped ceria catalysts (M=Zr, Zn and Fe) for the preferential oxidation of CO (PROX)[J]. Journal of Catalysis, 2010, 276(2): 360-370. doi: 10.1016/j.jcat.2010.09.027 [10] 熊天龙, 李艳松, 刘琪琪, 等. 焦化行业烟气低温SCR脱硝中试研究[J]. 四川化工, 2016, 19(1): 52-55. doi: 10.3969/j.issn.1672-4887.2016.01.015 [11] 冀岗, 董卫杰, 李强, 等. 太钢烧结烟气氮氧化物超低排放技术研究[J]. 烧结球团, 2018, 43(2): 28-34. doi: 10.13403/j.sjqt.2018.02.031 [12] CHEN C, CAO Y, LIU S, et al. Review on the latest developments in modified vanadium-titanium-based SCR catalysts[J]. Chinese Journal of Catalysis, 2018, 39(8): 1347-1365. doi: 10.1016/S1872-2067(18)63090-6 [13] GAO X, LIU S, ZHANG Y, et al. Physicochemical properties of metal-doped activated carbons and relationship with their performance in the removal of SO2 and NO[J]. Journal of Hazard Materials, 2011, 188(1-3): 58-66. doi: 10.1016/j.jhazmat.2011.01.065 [14] GAO X, LIU S, ZHANG Y, et al. Low temperature selective catalytic reduction of NO and NO2 with NH3 over activated carbon-supported vanadium oxide catalyst[J]. Catalysis Today, 2011, 175(1): 164-170. doi: 10.1016/j.cattod.2011.03.058 [15] JIANG B Q, LIU Y, WU Z B. Low-temperature selective catalytic reduction of NO on MnOx/TiO2 prepared by different methods[J]. Journal of Hazard Materials, 2009, 162(2-3): 1249-54. doi: 10.1016/j.jhazmat.2008.06.013 [16] YANG J, MA H, YAMAMOTO Y, et al. SCR catalyst coated on low-cost monolith support for flue gas denitration of industrial furnaces[J]. Chemical Engineering Journal, 2013, 230(1): 513-521. [17] MA L, HE M Y, FU P B, et al. Adsorption of volatile organic compounds on modified spherical activated carbon in a new cyclonic fluidized bed[J]. Separation and Purification Technology, 2020, 235(1): 2-11. [18] MA L, SHEN Q S, LI J P, et al. Efficient gas-liquid cyclone device for recycled hydrogen in a hydrogenation unit[J]. Chemical Engineering & Technology, 2014, 37(6): 1072-1078. [19] MA L, XIANG G L, HUANG Y, et al. Effects of spherical adsorbent fluidization and self-rotation on removal of VOCs in a cyclonic fluidized bed[J]. Journal of Industrial and Engineering Chemistry, 2020, 85(01): 181-189. [20] CHU K W, WANG B, YU A B, et al. CFD-DEM modelling of multiphase flow in dense medium cyclones[J]. Powder Technology, 2009, 193(3): 235-247. doi: 10.1016/j.powtec.2009.03.015 [21] CHU K W, WANG B, XU D L, et al. CFD–DEM simulation of the gas–solid flow in a cyclone separator[J]. Chemical Engineering Science, 2011, 66(5): 834-847. doi: 10.1016/j.ces.2010.11.026 [22] FU P B, ZHU J Y, LI Q Q, et al. DPM simulation of particle revolution and high-speed self-rotation in different pre-self-rotation cyclones[J]. Powder Technology, 2021, 394(01): 290-299. [23] TIAN J Y, NI L, SONG T, et al. CFD simulation of hydrocyclone-separation performance influenced by reflux device and different vortex-finder lengths[J]. Separation and Purification Technology, 2020, 233(1): 2-15. [24] ZHANG Y, LIU Y, QIAN P, et al. Experimental investigation of a minihydrocyclone[J]. Chemical Engineering & Technology, 2009, 32(8): 1274-1279. [25] ZHANG Y, LIU P, GE J, et al. Simulation analysis on the separation performance of spiral inlet hydrocyclone[J]. International Journal of Coal Preparation and Utilization, 2021, 41(7): 474-490. doi: 10.1080/19392699.2021.1934828 [26] VAKAMALLA T R, MANGADODDY N. Numerical simulation of industrial hydrocyclones performance: Role of turbulence modelling[J]. Separation and Purification Technology, 2017, 176(1): 23-39. [27] RAZMI H, SOLTANI G A, MOHEBBI A. CFD simulation of an industrial hydrocyclone based on multiphase particle in cell (MPPIC) method[J]. Separation and Purification Technology, 2019, 209(1): 851-862. [28] 赵国智, 孔凡让, 占惊春, 等. 基于SIMPLE算法的湍流场数值模拟[J]. 水电能源科学, 2007, 25(3): 100-102. [29] BASSE N T. Turbulence intensity and the friction factor for smooth- and rough-wall pipe flow[J]. Fluids, 2017, 2(2): 2-13.