Study of removal characteristics of particulate matters within flue gas by spray tower for waste-heat recovery

doi:10.11949/0438-1157.20221646

Abstract

Abstract:

The low-temperature water sprayed by the spray tower can recover the waste heat of the flue gas and purify the flue gas. In the study, the models evaluating the heat and mass exchange between flue gas and water drops, the size growth of particulate matters (PMs) caused by heterogeneous condensation and the removal of PMs in the spray tower were developed to explore the mechanisms of removing PMs within coal-fired flue gas coupled with waste heat recovery. The removal characteristics of PMs in the flue gas were also investigated under various working conditions of the spray tower. The results show that the capture mechanisms of sub-micrometer PMs in the lower part of the spray tower are mainly thermophoresis and diffusiophoresis while the capture mechanism of sub-micrometer PMs in the upper part of the spray tower is inertial collision due to water vapor condensed on the sub-micrometer PMs at the flue gas inlet temperature of 50℃, the flue gas inlet relative humidity of 100%, the water- gas ratio of 2 L/m³, the cold water temperature of 20℃, and the spray water droplet size of 550 μm. For the spray tower, the removal efficiency of PMs can be improved under the conditions of higher water-gas ratios, lower spray water temperatures, lower water droplet sizes, and higher temperature differences between flue gas and water droplets, or higher water vapor saturation levels. The spray tower has the better removal performance of PMs at the condition of water-gas ratio of 2.5 L/m³ and spray water temperatures of 10—15℃.

Key words: spray tower, particulate matter, condensation, flue gas, capture

摘要：

喷淋塔喷淋低温水可回收烟气余热和净化烟气。以喷淋塔为研究对象，建立喷淋塔内气-液热质交换、颗粒物异质凝结增长与脱除模型，探究余热回收喷淋塔内烟气颗粒物脱除机理，研究不同工况下颗粒物脱除特性。结果表明：当烟气入口温度50℃、入口相对湿度100%、水气比2 L/m³、喷淋水温20℃、喷淋水滴粒径550 μm时，在喷淋塔下半部区域，水滴主要靠热泳与扩散泳捕集亚微米级颗粒物；随着水蒸气在亚微米级颗粒物表面凝结，在喷淋塔上部区域，惯性碰撞为水滴捕集亚微米级颗粒物的主要机制。提高水气比、降低喷淋水温、减小液滴粒径、增大气液两相温差及水汽饱和度均可提高喷淋塔内颗粒物脱除效率，其中水气比为2.5 L/m³，喷淋水温为10~15℃，可实现较好的颗粒物脱除效果。

关键词: 喷淋塔, 颗粒物, 凝结, 烟道气, 捕集

CLC Number:

X 51

Guohua SHI, Linshen HE, Xiling ZHAO, Shigang ZHANG. Study of removal characteristics of particulate matters within flue gas by spray tower for waste-heat recovery[J]. CIESC Journal, 2023, 74(4): 1735-1745.

时国华, 何林珅, 赵玺灵, 张世钢. 余热回收喷淋塔的烟气颗粒物脱除特性研究[J]. 化工学报, 2023, 74(4): 1735-1745.

Figures/Tables 14

Fig.1 Schematic diagrams of spray tower for waste-heat recovery and corresponding state change of flue gas

Fig.2 Microelement section of heat and mass transfer in the spray tower

Fig.3 Flow chart of solution of flue gas waste heat recovery and PMs removal model

Table 1 Comparison of simulation results and experimental data

工况条件			颗粒物脱除效率
喷淋水温/℃	烟气入口温度/℃	水气比/(L/m³)	实验值/%	计算值/%	偏差/%
10	48.0	1	85.2	81.5	4.3
10	48.2	1.5	98.5	95.4	3.1
10	48.4	2	98.7	97.2	1.5
10	49.2	3	99.2	99.1	0.1
20	48.2	1	76.6	73.6	3.9
20	47.8	1.5	89.2	86.6	2.9
20	47.7	2	97.0	93.6	3.5
20	47.8	3	98.1	97.2	0.9

Table 2 Values of parameters used in numerical simulation

参数	数值
烟气参数
烟气入口温度/℃	50
烟气入口相对湿度/%	100
塔内烟气流速/(m/s)	1
喷淋参数
喷淋水温/℃	20
喷淋量/(t/h)	22.6
水气比/(L/m³)	2
喷淋水滴Sauter平均粒径/μm	550
喷淋塔参数
喷淋塔半径/m	1
喷淋塔有效喷淋高度/m	4
喷嘴数/个	45

Fig.4 Distribution of PMs sizes in flue gas after desulfurization tower

Fig.5 Variation of PMs sizes and water vapor saturation along the tower height

Fig.6 Variation of capture efficiency by single droplet for dp= 0.15 μm PM along the tower height

Fig.7 Removal efficiency for PMs with different sizes by the flue-gas spray tower

Fig.8 Effect of liquid-gas ratio on PMs’ removal efficiency

Fig.9 Effect of spray water temperature on PMs removal efficiency

Fig.10 Effect of particle spray droplet’s size on PMs removal efficiency

Fig.11 Effect of flue gas inlet temperature on PMs removal efficiency

Fig.12 Effect of relative humidity at flue gas inlet on PMs removal efficiency

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