Abstract:

Viscose ash deposition and dewpoint corrosion in an industrial coal-fired boiler were investigated by field study of temperature-controlled mild steel 20^# test probes under different wall temperatures of 90℃, 80℃, 70℃, 60℃, 50℃ and 40℃. Ash deposits and metal samples were analyzed by X-ray fluorescence (XRF), X-ray diffraction (XRD) and scanning electron microscope with energy dispersive X-ray spectroscopy (SEM-EDS). The results showed that when wall temperature fell to 70℃, viscose deposits and dewpoint corrosion began to form on probes due to condensation of H₂SO₄ on wall surface. The deposit accumulation and corrosion depth increased with the decrease of wall temperature, when wall temperature was lower than 80℃. At wall temperature of 40℃, HCl started condesing on wall surface which further enhanced ash deposition and corrosion. The coupling mechanism of viscose ash depostion and dewpoint corrosion was discussed and it was proposed that fly ash in flue gas could absorb and react with acid condensation to reduce viscose ash deposit and corrossion. Therefore, in order to avoid or reduce deposition and corrosion, it is recommended that low-temperature heating surface in industrial coal-fired boilers should be maintained above 70℃.

Key words: coal combustion, industrial boiler, acid condensation, deposition, corrosion, flue gas cooling

摘要：

通过现场实验研究了燃煤工业锅炉的黏性积灰和露点腐蚀耦合机理，在现场测试了不同壁面温度（90、80、70、60、50和40℃）下20^#碳钢实验段的积灰和腐蚀特性，然后利用XRF、XRD和SEM-EDS对灰样和金属试样进行了系统理化分析。结果表明，当壁面温度低至70℃时，H₂SO₄开始在壁面上冷凝并沉积，引起黏性积灰和露点腐蚀。随着壁面温度的降低，实验段上的积灰量和腐蚀层厚度不断增加。当壁面温度降至40℃时，HCl开始在壁面上冷凝并加重积灰和腐蚀。烟气中的飞灰可以通过吸附冷凝的酸液并与其反应来减少壁面的黏性积灰和露点腐蚀。燃煤工业锅炉的低温受热面宜控制壁面温度在70℃以上，以减少酸液冷凝造成的黏性积灰和露点腐蚀。

关键词: 煤燃烧, 工业锅炉, 酸冷凝, 沉积物, 腐蚀, 烟气冷却