超细飞灰对烟气酸露点与酸凝结的影响研究

doi:10.11949/0438-1157.20200022

摘要/Abstract

摘要：

准确预测燃煤锅炉尾部烟气的酸露点和酸凝结对深度降低排烟温度、保障尾部换热设备的安全高效运行十分重要。尾部烟气中存在的飞灰颗粒对酸露点和酸凝结液滴的发生有很大影响，不可忽略。考虑烟气中超细飞灰颗粒对酸露点和酸凝结的影响，提出了飞灰粒径对考虑局部凝结质量传输效果的酸露点和酸凝结迭代计算方法，实现了酸露点和壁面温度下酸凝结的准确预测。当飞灰粒径低于中肯半径（r_ash<r₀）时，飞灰粒径对凝结率有显著影响；随着飞灰粒径的降低，硫酸蒸气、水蒸气以及酸液凝结率明显增加，尤其是硫酸蒸气凝结率；飞灰粒径越小，凝结越易发生。然而，过冷度超过30℃时，烟气中超细飞灰颗粒对低温壁面酸凝结的影响可以忽略不计。烟气携带而不被低温壁面捕获的凝结酸液量较少，烟气中超细飞灰颗粒对烟气酸蒸气的降低作用可以忽略不计。理论计算方法为分析现场酸-灰作用积灰层提供理论依据，对于优化燃煤锅炉尾部烟道的安全高效运行有重大指导意义。

关键词: 烟道气, 飞灰, 酸露点, 凝结, 算法, 燃煤锅炉

Abstract:

Accurate prediction of acid dew point(ADP) and acid condensation is the key to deeply reduce the flue gas temperature and to ensure the safe and efficient operation of the heat exchange equipment in coal-fired power plants. The ash particles in the flue gas have great influence on the occurrence of ADP and acid condensation droplets. The iterative calculation method of ADP and acid condensation considering the effect of fly ash particle radius on local condensation mass transfer were proposed for the first time in this paper. When the fine ash particles radiuses are smaller than the critical radius (r_ash<r₀), with the reduction of fine ash particle radius, the condensation rate around fine ash particles, especially acid condensation rate, is markedly increased at ADP. And the acid condensation is easier to occur with the smaller ash particle radius. However, when the supercooling degree exceeds 30℃, the effect of ultrafine ash particles on the acid condensation of heating surface can be ignored. The amount of acid solution condensed around fine fly ash particles, which can not be caught on the heating surface, is small, and the reduction effect of the fly ash particles on the acid vapor of flue gas can be negligible. The theoretical calculation method in this paper provides a theoretical basis for the analysis of acid-ash fouling layer on the field experiments, and useful guiding significance for the safe and efficient operation of the heat exchange equipment in the coal-fired boiler.

Key words: flue gas, fly ash, acid dew point, condensation, algorithm, coal-fired boiler

中图分类号:

TK 16

魏伟, 李秀财, 孙奉仲. 超细飞灰对烟气酸露点与酸凝结的影响研究[J]. 化工学报, 2020, 71(7): 3258-3265.

Wei WEI, Xiucai LI, Fengzhong SUN. Research on effect of ultrafine ash particles on acid dew point and acid condensation for coal-fired boilers[J]. CIESC Journal, 2020, 71(7): 3258-3265.

图/表 9

图1 考虑超细飞灰颗粒（rash<r0）的迭代计算模型图Pwaterwall,i、Pacidwall,i分别为气液平衡界面水蒸气和酸蒸气的饱和分压力；Pwaterg、Pacidg分别为烟气中的水蒸气和酸蒸气的饱和分压力

Fig.1 Flow chart of acid condensation calculation with account of fine ash particle (rash<r0)

图2 酸露点估算结果与实验值对比

Fig.2 Comparison between the predicted values in this work and experimental data in previous research

图3 烟气成分对热力学酸露点中肯半径的影响规律

Fig.3 Effect of flue gas components on ADP and initial condensation concentration

图4 酸露点下飞灰粒径对凝结率的影响规律

Fig.4 Effect of fine ash radius on acid condensation rate covering fine ash particles at ADP

图5 80℃壁面温度下飞灰粒径对凝结率的影响规律

Fig.5 Effect of fine ash radius on acid condensation rate covering heating surface at 80℃

表1 不同过冷度下酸液凝结率涨幅的汇总表

Table 1 Summary of acid condensation rate increment under different degree of supercooling

过冷度/℃	酸液凝结率增加量/(g/(m²?s))	涨幅/%
5	357.18×10^－6	124.57
10	221.77×10^－6	46.87
15	134.68×10^－6	22.78
20	79.75×10^－6	12
25	45.98×10^－6	6.49
30	25.68×10^－6	3.5
35	13.83×10^－6	1.84
40	7.11×10^－6	0.94

表2 超细颗粒质量比对降低烟气酸蒸气含量的汇总表

Table 2 Effect of fine ash particles mass ratio on reducing gas compositions

超细颗粒质量比/%	反应后烟气含酸量/ (μl/L)	反应后烟气含水量 /%
1	19.782	9.995
2	19.564	9.989
3	19.346	9.984
4	19.128	9.979
5	18.91	9.974

表3 反应时间对降低烟气酸蒸气含量的汇总表

Table 3 Effect of reaction time on reducing gas compositions

反应时间/s	反应后烟气含酸量/(μl/L)	反应后烟气含水量/%
1	19.978	9.999
5	19.891	9.997
10	19.782	9.995
20	19.564	9.989
30	19.346	9.984

表4 烟气温度对降低烟气酸蒸气含量的汇总表

Table 4 Effect of gas temperature on reducing gas compositions

烟气温度/℃	反应后烟气含酸量/(μl/L)	反应后烟气含水量/%
120	19.778	9.996
110	19.776	9.995
100	19.782	9.995
90	19.791	9.994
80	19.801	9.993

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