CFD numerical simulation of wet flue gas desulfurization:performance improvement based on gas-liquid mass transfer enhancement

doi:10.11949/0438-1157.20231100

Abstract

Abstract:

In view of the desulfurization problem of flue gas containing high SO₂ concentration resulting from burning high sulfur coal in flue gas desulfurization process of coal-fired power plants, the research on the high-efficient SO₂ removal based onlimestone was carried out by computational fluid dynamics (CFD), and the enhancement method for SO₂ removal by installing sieve plate and optimizing the spray system in the absorption tower simultaneously was proposed. A coupled model of SO₂ multiform absorption including spray absorption and bubbling absorption was established at the scale of macro scale. Based on the model, the variation laws of pH and SO₂ absorption rate during slurry droplets falling were obtained, and the gas-liquid flow, mass transfer and chemical reaction processes in the absorption tower are analyzed. The strengthening mechanism of sieve plate on the desulfurization efficiency is explored, and the optimization for the arrangement of sieve plate and spray system is carried out further. It was found that by optimizing the sieve plate components and the spray system in the tower, the SO₂ removal efficiency of the desulfurization tower can be increased by 3%—8% under different working conditions.

Key words: absorption, CFD, optimal design, gas-liquid mass transfer enhancement, SO₂ removal

摘要：

针对燃煤电厂烟气脱硫过程中，高硫煤燃烧产生的高含硫烟气高效脱硫难题，通过计算流体力学（CFD）开展了钙法烟气SO₂高效脱除研究，提出了基于塔内筛板构件及喷淋系统优化的多手段耦合增效方法。建立了宏观脱硫塔尺度下涵盖喷淋吸收-筛板鼓泡吸收的SO₂多形式吸收脱除耦合模型，获得了浆液下落过程中的pH及SO₂吸收速率变化规律，并研究了湍流构件对脱硫塔内的气液混合流动、相内相间传质、浆液内部化学反应等过程的影响机制。探究了筛板对于脱硫塔脱除效率的强化机制，并进一步开展了筛板布置位置优化设计研究。同时，针对脱硫塔喷淋系统开展了优化设计研究，通过对比研究获得了喷淋系统优化后布置方案。基于所提出的脱硫塔多手段耦合增效方法，研究了包括液气比、浆液粒径及入口烟气SO₂浓度等不同参数影响下的脱硫塔SO₂脱除性能，发现通过塔内筛板构件及喷淋系统优化多手段协同增效后，可实现不同工况下脱硫塔SO₂脱除效率提升3%~8%。

关键词: 吸收, 计算流体力学, 优化设计, 气-液传质强化, SO₂脱除

CLC Number:

TK 09

Wenjun LI, Zhongyang ZHAO, Zhen NI, Can ZHOU, Chenghang ZHENG, Xiang GAO. CFD numerical simulation of wet flue gas desulfurization:performance improvement based on gas-liquid mass transfer enhancement[J]. CIESC Journal, 2024, 75(2): 505-519.

李文俊, 赵中阳, 倪震, 周灿, 郑成航, 高翔. 基于气-液传质强化的湿法烟气脱硫CFD模拟研究[J]. 化工学报, 2024, 75(2): 505-519.

Figures/Tables 22

Fig.1 Chemical reaction system in slurry

Fig.2 Logic diagram for solution

Fig.3 Wet flue gas desulfurization tower

Table 1 The structure parameters of desulfurization tower

参数	数值
塔高/m	33.7
吸收塔塔径/m	16
气液分布环数量/个	3
喷淋层数量/层	4
喷淋层高度/m	11.4,13.9,16.4,18.9
筛板安装高度/m	9.7
喷嘴数量/个	4×180
喷嘴喷淋角度/(°)	120

Table 2 The parameters settings of model

参数	数值
烟气流量/(m³/h)	2779200
烟气入口温度/K	373.15
烟气SO₂浓度/(mg/m³)	1680
浆液流量/(m³/h)	33750
浆液粒径/mm	1.5
浆液初始pH	5.5

Table 3 The boundary conditions of model

项目	边界条件
连续相
脱硫塔入口	速度入口
脱硫塔出口	压力出口
离散相
脱硫塔壁面	捕捉
脱硫塔出口及入口	逃离
除雾器	捕捉
气液分配环	反射

Table 4 Test desulfurization efficiency under different conditions

工况	负荷/MW	入口SO₂浓度/(mg/m³)	出口SO₂浓度/(mg/m³)	浆液pH	脱硫效率/%
1	667	1927.22	20.26	4.62	92.43
2	664	1838.49	20.55	4.91	94.28
3	663	1918.39	20.77	4.67	93.18
4	650	1865.04	23.02	4.97	95.13
5	618	1870.65	19.85	5.34	97.04
6	612	1831.43	24.18	5.26	98.38
7	597	1650.07	19.79	5.29	98.80
8	584	1426.23	13.56	5.35	99.05
9	576	1405.45	14.07	5.33	99.00
10	547	1749.27	14.31	5.36	99.18
11	534	1494.17	13.50	5.33	99.40
12	512	1552.55	17.24	5.28	98.89

Fig.4 Accuracy validation of model

Fig.5 Gas flow pattern in desulfurization tower

Fig.6 SO2 absorption characteristics of slurry in tower

Fig.7 The effect of sieve tray on SO2 removal in tower

Fig.8 The SO2 distribution under different installment heights of sieve tray

Table 5 Comparison of removal efficiency with different installation heights of sieve plate

筛板安装高度

H/m

Fig.9 The scheme diagram for different spray arrangements

Fig.10 Comparison of slurry distribution in tower under different schemes

Fig.11 The effect of different schemes on slurry distribution and its residence time in tower

Fig.12 The variation of SO2 concentration in tower under different schemes

Fig.13 Slurry distribution in tower with different droplet diameters

Fig.14 The effect of droplet diameter on residence time and desulfurization efficiency

Fig.15 The effect of liquid-gas ratio on liquid holding height of sieve plate and removal efficiency

Fig.16 The effect of inlet SO2 concentration on desulfurization efficiency

Fig.17 The variation of desulfurization efficiency under different flue gas flow rates

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