Simulation and experimental analysis on dehumidification and white smoke removal of coal-fired flue gas in falling-film plate used in WESP

doi:10.11949/0438-1157.20200935

Abstract

Abstract:

To save space and improve the integration of equipments, a novel process combining the liquid dehumidification and wet electrostatic precipitator (WESP) is proposed in this paper for both dehumidification and dust removal of flue gas. Through the numerical simulation and experiment of the falling film dehumidification process of the wet electric flat plate, the influence of the flue gas and solution parameters on the water heat recovery performance is explored. The results show that the model can agree with the process quite well and the highest water and thermal efficiency is 37.5% and 35% respectively. Most of the latent heat is transferred to the solution. The dehumidification process has almost no effect on dust removal of WESP. Through the analysis of psychrometric chart and visual comparison, it is proved that the falling-film dehumidification in WESP can reduce even eliminate white smoke.

Key words: coal-fired flue gas, water and heat recovery, solution dehumidification, numerical simulation, white smoke

摘要：

为了节省电厂空间，提高设备集成应用，提出了一种溶液除湿与湿电相结合的工艺，使用除湿溶液在阳极板布膜，同时实现除尘与除湿功能。通过湿电平板降膜除湿过程的数值模拟与试验，探究了烟气及溶液参数对水热回收性能的影响。结果显示数学模型能够较好地反映该过程，试验工况下湿电平板降膜最高水、热回收率分别可达37.5%和35%，水蒸气所释放的汽化潜热大部分转移到溶液。除湿过程对于湿电除尘效果几乎没有影响，通过焓湿图分析及可视化比较证明，湿电平板降膜除湿可以实现白烟的削弱甚至完全消除。

关键词: 燃煤烟气, 水热回收, 溶液除湿, 数值模拟, 白烟

CLC Number:

TK 124

ZHANG Hao, DONG Yong, LAI Yanhua, CUI Lin, YANG Xiao. Simulation and experimental analysis on dehumidification and white smoke removal of coal-fired flue gas in falling-film plate used in WESP[J]. CIESC Journal, 2021, 72(4): 2249-2257.

张昊, 董勇, 赖艳华, 崔琳, 杨潇. 用于燃煤烟气除湿消白的湿电平板降膜模拟及试验研究[J]. 化工学报, 2021, 72(4): 2249-2257.

Figures/Tables 15

Fig.1 Schematic diagram of dehumidification process of falling-film plate in WESP

Table 1 Structural parameters of WESP

Shell parameters		Anode plates parameters		Operating parameters
length/m	1.5	length/m	1	voltage/kV	4—6
width/m	3	width/m	0.1	water pressure/MPa	0.4
height/m	6.8	height/m	4

Fig.2 Schematic diagram of dehumidification system of falling-film plate in WESP

Table 2 The composition of flue gas in dehumidification system of falling-film plate in WESP (t=50℃, RH=100%)

The composition of flue gas	Volume fraction/%	The composition of flue gas	Mass concentration/ (mg/m³)
O₂	6	SO₂	9.8
CO₂	12.3	NO_x	15.2
H₂O	12.5	particles	55

Table 3 Specification of different measuring devices in dehumidification system

Device	Type	Accuracy	Range
thermometers	thermocouple K	±0.1℃	-40—120℃
temperature & humidity ensor	Rotronic HC2A-S	±0.1℃/±0.8%RH	-50—100℃/0—100%
densitometer	—	±0.5 kg/m³	1200—1400 kg/m³
flue gas flow meter	Testo 425	±0.03 m/s	0—20 m/s
solution flow meter	LDG-MK	±0.5%	0—10 m³/h

Fig.3 Comparison between simulated and experimental water recovery efficiency

Fig.4 Effect of the inlet flue gas temperature and Re on water recovery efficiency

Fig.5 Effect of the inlet flue gas temperature and Re on thermal recovery efficiency

Fig.6 Effect of the solution temperature and concentration on water recovery efficiency

Fig.7 Effect of the solution temperature and concentration on thermal recovery efficiency

Fig.8 Effect of the different parameters on heat variation

Table 5 Dust removal efficiency of falling-film plate dehumidification in WESP

No.	Inlet flue gas temperature/℃	Inlet particles concentration/(mg/m³)	Outlet flue gas temperature/℃	Outlet particles concentration/(mg/m³)	Particles removal efficiency/%
1	50.2	55	42.5	4.5	91.8
2	45.2	57.5	43.5	4.8	91.6
3	50.1	53.2	45.2	4.5	91.5
4	40.2	55.8	40.6	4.8	91
5	49.8	50.2	46.3	5	90

Fig.9 Representation of outlet flue gas status on enthalpy wet figure

Fig.10 The visualization of white smoke under different working conditions

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