Removal of fireside deposits from the heat transfer tubes in kraft recovery boilers is carried out by sootblowing and occasionally "chill-and- blow" practices. During chill-and-blow, black liquor flow is reduced to rapidly cool the deposits.Thermal stresses generated in the deposit as a result of thermal shock can effectively weaken the deposit, facilitating its cleaning. For this study, we investigated the mechanical weakening effect of thermal stresses generated by the transient temperature gradients. We quantified the mechanical weakening effect due to thermal shock by measuring the decrease in biaxial flexure strength of a preheated sodium chloride disk at various quenching times and surface heat transfer coefficients. We observed that the mechanical weakening occured by transient thermal stresses as well as crack propagation. Approximately 35% loss in biaxial flexure strength could be achieved at heat transfer coefficients above 3.3·103 W/m 2K, and at quenching durations above 40 s.
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机译：清除牛皮纸回收锅炉传热管中的炉边沉积物是通过吹灰和偶尔的“冷吹”做法进行的。在冷吹过程中，黑液流量减少以快速冷却沉积物。由于热冲击而在沉积物中产生的热应力可以有效地削弱沉积物，从而有利于清洁。对于这项研究，我们研究了瞬态温度梯度产生的热应力的机械减弱作用。我们通过测量在各种淬火时间和表面传热系数下预热的氯化钠圆盘的双轴弯曲强度的降低，来量化由于热冲击引起的机械减弱效果。我们观察到，机械强度的下降是由瞬态热应力以及裂纹扩展引起的。当传热系数大于3.3·103 W / m 2K且淬火持续时间大于40 s时，双轴弯曲强度大约可降低35％。
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