Abstract
The slag deposited on the wall tubes of furnaces/boilers seriously reduces the heat transfer from the furnace to tubes and degrades the tubes by corrosion. During boiler operation, slag deposits are removed by sootblowers that blast the deposits with steam or air jets. In this study, we develop a novel numerical model using the cohesive zone method (CZM) and coupled Eulerian—Lagrangian (CEL) analysis to investigate the dynamics and mechanism of deposit fracture during sootblowing. Cohesive elements subject to the softening traction—separation relationship and evolution laws are embedded into the deposit model to describe crack formation during deposit breaking. The deposit cracking status is evaluated by extracting the scalar stiffness degradation variable from damaged cohesive elements. The dynamic process and mechanism of deposit fracture are analyzed and revealed in detail, particularly in terms of the destructive degree and fracture rate of the deposit model. The effects of the sootblowing steam pressure (0.9–1.8 MPa) on slag breaking, wall tube stress, and steam consumption are also investigated. Sootblowing steam pressures over 1.2 MPa do not further benefit the sootblowing effect but adversely affect the wall tube lifetime.
目 的
蒸汽吹灰是锅炉运行中常见的破坏水冷壁渣层的方法。本文通过建立三维吹灰模型, 模拟不同压力下吹灰过程中蒸汽射流和渣层破坏的动态变化过程, 研究在渣层破坏过程中应力波的传播变化, 得出条件合适的吹灰参数。
创新点
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1.
通过内聚力单元法和耦合欧拉-拉格朗日法建立吹灰流程的三维数值模型, 详细揭示渣层破坏的动力学过程, 并对蒸汽射流的扩散和应力波在渣层中的传播进行全过程分析;
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2.
通过建立三维数值模拟, 研究吹灰蒸汽压力对渣层破坏、 管壁应力和蒸汽消耗的影响, 并通过模拟结果探讨合适的吹灰参数。
方 法
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1.
对渣层模型采用内聚力单元法进行建模;
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2.
对蒸汽射流和渣层的流固耦合现象采用 ABAQUS 中的耦合欧拉-拉格朗日法进行分析。
结 论
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1.
越高的吹灰压力会导致渣层被破坏得越快并最终完全脱离水冷壁; 综合考虑渣层破坏效率、 水冷壁管应力和蒸汽消耗的影响, 1.2 MPa 是最合适和经济的吹灰压力参数。
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2.
蒸汽射流带来的切向应力是引起渣层破坏的主要因素, 射流对渣层的直接冲击是切向应力的来源, 并且是渣层破坏的次要因素。
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Project supported by the 2017 Science & Technology Innovation Project Along the Yellow River of China and the Major Project of Key R&D Programs of the Ningxia Hui Autonomous Region, China (No. 2018BCE01004)
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Shao, Lt., Kuang, Jp., Yang, Wj. et al. Simulation analysis of fracture process of slag deposits surrounding wall tubes during steam sootblowing. J. Zhejiang Univ. Sci. A 20, 447–457 (2019). https://doi.org/10.1631/jzus.A1900030
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DOI: https://doi.org/10.1631/jzus.A1900030