Numerical Simulation of Fly Ash Deposition Characteristics and Flow Field Optimization for SCR External Flue

doi:10.12096/j.2096-4528.pgt.23014

Abstract

Abstract:

Objectives Selective catalytic reduction (SCR) denitrification is widely used in denitrification of boiler flue gas due to its high denitrification efficiency and reliable operation. However, under high-ash arrangements, the denitrification flue gas has not yet been de-treated, and fly ash in the flue gas will block the catalyst and cause wear on it. In order to reduce the wear and clogging of fly ash particles on SCR catalysts, an SCR external flue is designed and studied to trap and separate fly ash particles in flue gas. Methods Based on simulation software and its user defined function, numerical simulation of fly ash deposition characteristics and flow field optimization for SCR external flue is carried out. Results When the flue gas flow rate increases from 1 to 2 m/s, the fly ash deposition rate decreases from 24.0% to 1.88%. Therefore, as the increase of flow rate, the fly ash deposition rate decreases rapidly. It is difficult to trap fly ash particles below 50 μm. However, with the increase of the fly ash particle size, the fly ash deposition rate increases rapidly, and the fly ash is trapped by the SCR external flue. The flow velocity distribution at the inlet of the denitrification reactor is extremely uneven. Based on the flow field analysis, an optimization plan for the flow field at the inlet of the denitrification reactor is proposed. The flow field distribution is improved through the optimized design of the guide plate, and the velocity unevenness coefficient at the inlet of the denitrification reactor is reduced from 93.7% to 14.7%. Conclusions The research results may provide reliable theoretical guidance for the field operation of SCR external flue.

Key words: coal-fired power plants, boiler flue gas, selective catalytic reduction (SCR), fly ash deposition, flow field optimization, numerical simulation

CLC Number:

TK 223

Kai LI, Pingheng ZHANG, Zhihao MENG, Yunning CAO, Yao XU, Li LIU, Lianming LI. Numerical Simulation of Fly Ash Deposition Characteristics and Flow Field Optimization for SCR External Flue[J]. Power Generation Technology, 2025, 46(1): 145-153.

Figures/Tables 13

Fig. 1 Schematic diagram of the original SCR catalyst layout

Fig. 2 Schematic diagram of SCR external flue

Tab. 1 Parameters of flue gas and fly ash particles

参数	数值
烟气流速/(m/s)	1~2
烟气密度/(kg/m³)	0.617
烟气粘度/(Pa⋅s)	2.82×10^-5
飞灰颗粒粒径/μm	50~250
飞灰密度/(kg/m³)	1 840
飞灰质量流量/(kg/s)	4.4×10^-3

Fig. 3 Comparison of numerical calculation results and literature results

Fig. 4 Effect of flue gas velocity on deposition rate of fly ash

Fig. 5 Velocity contours of initial design flue section and inlet section of denitration reactor

Fig. 6 Velocity distribution of reactor section center in initial design

Fig. 7 Effect of particle size on fly ash deposition rate

Fig. 8 Optimal arrangement scheme of bending guide plate

Tab. 2 Optimization scheme of guide plate size

部位	方案
部位	1	2	3	4	5	6
U	800	650	600	550	520	490
V	800	750	900	750	880	910
W	800	900	700	900	950	1 000
X	900	1 050	1 200	1 100	1 000	950
Y	700	650	600	700	650	650

Fig. 9 Velocity inhomogeneity coefficient of SCR catalyst inlet under case 1-6

Fig. 10 Velocity contours of flue section and reactor inlet section after guide plate optimization

Fig. 11 Velocity distribution of reactor section center after guide plate optimization

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