Optimization Simulation of Ammonia Injection in SCR DeNO x System of Coal-Fired Power Plant

doi:10.12141/j.issn.1000-565X.220446

Abstract

Abstract:

To improve the uniformity of NO _x mass concentration distribution at the outlet of SCR (selective catalytic reduction) denitration reactor of a 660 MW unit, this paper proposed an optimal ammonia injection strategy based on the kinetic model with the objective of minimizing the relative standard deviation of NO _x mass concentration distribution at the outlet of SCR. The on-site measured data was used as the inlet boundary condition, and CFD numerical simulation calculations were conducted by coupling turbulent flow, component transport, and chemical reactions in the reactor. The ammonia flow characteristics was visually analyzed, and the flow influence coefficient of the ammonia injection grid partition/nozzle was defined. The optimal controllable ammonia injection flow of different partitions or nozzles of the ammonia injection grid can be obtained by directly solving the optimization matrix equation, and combining the mathematical relationship between the outlet NO _x concentration distribution and the inlet NH₃ concentration, which is based on the SCR reaction kinetics model. The simulation results show that under the uniform ammonia injection mode, the mixing matching degree of ammonia nitrogen concentration in different zones is not high, the relative standard deviation of NO _x mass concentration at the outlet of SCR reactor reaches 40.1%, and the uniformity of NO _x mass concentration distribution at the outlet is poor. After the optimization of ammonia injection according to the method proposed in the paper, the relative standard deviation of NO _x mass concentration at the outlet decreases to 6.8%, and the uniformity of the outlet is greatly improved. This can not only realize the pressure line emission of NO _x to meet environmental requirements but also avoid areas with high and low denitrification efficiency. The flow field was visualized through numerical simulation in the article, and ammonia injection optimization was carried out by quantitatively solving the ammonia injection volume of each valve. This can provide theoretical reference for actual ammonia injection optimization debugging in power plants and reduce the blindness of adjustment.

Key words: SCR DeNO _x reaction, numerical simulation, ammonia spraying optimization, NO _x concentration field, kinetic model

CLC Number:

X799.3

LU Zhimin, LI Bohang, TANG Wen, et al. Optimization Simulation of Ammonia Injection in SCR DeNO _x System of Coal-Fired Power Plant[J]. Journal of South China University of Technology(Natural Science Edition), 2023, 51(8): 62-70.

Figures/Tables 13

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区域	分区1	分区2	分区3	分区4	分区5
C11	0.18	0.06	0.00	0.00	0.00
C12	0.21	0.02	0.00	0.00	0.00
C13	0.22	0.01	0.00	0.00	0.00
C21	0.05	0.17	0.05	0.00	0.00
C22	0.08	0.16	0.02	0.00	0.00
C23	0.16	0.10	0.00	0.23	0.00
C31	0.00	0.07	0.18	0.06	0.00
C32	0.01	0.12	0.17	0.02	0.00
C33	0.07	0.14	0.07	0.01	0.00
C41	0.00	0.00	0.08	0.17	0.03
C42	0.00	0.02	0.13	0.15	0.01
C43	0.00	0.11	0.14	0.06	0.00
C51	0.00	0.00	0.00	0.10	0.16
C52	0.00	0.00	0.02	0.15	0.11
C53	0.00	0.02	0.12	0.14	0.04
C61	0.00	0.00	0.00	0.01	0.25
C62	0.00	0.00	0.00	0.02	0.24
C63	0.00	0.00	0.01	0.09	0.16

参数	模拟值	实测值^［13］	相对误差/%
入口截面速度/（m·s^-1）	11.99	11.82	1.44
入口截面温度/K	644.19	644.35	0.03
入口截面NO _x 质量浓度/（mg·Nm^-³）	334.93	329.19	1.79
催化剂上游氨氮比	0.91	0.88	3.41
脱硝率/%	87.55	85.54	2.35

喷嘴编号	喷氨量		喷氨量		喷氨量
AIG1-1	0.044 7	AIG5-3	0.035 3	AIG10-2	0.046 8
AIG1-2	0.050 4	AIG6-1	0.048 2	AIG10-3	0.045 0
AIG1-3	0.044 3	AIG6-2	0.050 6	AIG11-1	0.050 2
AIG2-1	0.045 1	AIG6-3	0.036 6	AIG11-2	0.043 0
AIG2-2	0.047 3	AIG7-1	0.048 1	AIG11-3	0.047 2
AIG2-3	0.039 5	AIG7-2	0.051 8	AIG12-1	0.045 6
AIG3-1	0.046 7	AIG7-3	0.038 0	AIG12-2	0.044 1
AIG3-2	0.046 2	AIG8-1	0.049 2	AIG12-3	0.048 4
AIG3-3	0.036 1	AIG8-2	0.052 9	AIG13-1	0.048 0
AIG4-1	0.047 8	AIG8-3	0.039 2	AIG13-2	0.048 3
AIG4-2	0.046 7	AIG9-1	0.051 4	AIG13-3	0.050 4
AIG4-3	0.034 3	AIG9-2	0.050 6	AIG14-1	0.055 2
AIG5-1	0.048 1	AIG9-3	0.042 2	AIG14-2	0.052 6
AIG5-2	0.049 2	AIG10-1	0.053 4	AIG14-3	0.050 4

优化方法	出口NO _x 质量浓度均值/（mg·Nm^-3）	出口NO _x 质量浓度相对标准偏差/%	出口氨逃逸率/（μL·L^-1）	出口氨逃逸率相对标准偏差/%
均匀喷氨	41.7	40.1	3.20	7.6
5个分区喷氨	41.4	33.0	3.18	5.5
42个喷嘴喷氨	39.9	6.8	3.17	2.5

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