Abstract

Flow accelerated corrosion (FAC) is considered one of the major causes of damage to heat-recovery steam generators (HRSG) of combined-cycle units. In the last few decades, a great number of papers devoted to this problem have been published in many countries around the world. The results of investigations were analyzed as a rule, on the basis of the flow-averaged thermochemical parameters of the flow, while the features of the near-wall liquid film determining the FAC rate were not taken into account. The indicators in the near-wall region depends on the heat-and-mass transfer conditions, flow hydrodynamics, and the specific of chemicals used to correct the water chemistry (WC). For ammonia and oxygen water treatment chemistries, an equilibrium model is proposed and its validity for HRSG evaporators is substantiated. The rate of the exchange of gas reagents between steam and water is determined by the distribution coefficient K_d. To simplify calculations, simple approximating correlations of K_d for ammonia and oxygen is recommended. For the water chemistry with solid reagents, a diffusion model has been developed to calculate mass transfer on the basis of data on heat transfer in steam-generating tubes. The concentration of reagents near the wall is determined by both the turbulent transport of the liquid between the flow core and the near-wall layer and the coefficient of reagent distribution between the phases. Simple approximating correlations of distribution coefficients for Na₃PO₄, NaOH, and 90H Turb helamine are proposed. An approximate correlation between the hydraulic resistance coefficient K_h and the geometric parameter K_с of the FAC process has been established. The hydrodynamic fundamentals of the standard HRSG structural members have been studied in more detail than FAC. To estimate K_с, one can use the known value of K_h and the correlation between them. However, this correlation should be used with care since it has been obtained for certain conditions of unambiguity (i.e., specific construction material, water chemistry, flow history, etc.). Under other conditions, this correlation will change somewhat; therefore, it can only be used for rough estimation.

中文翻译：

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热力传递和流动流体动力学对联合循环机组余热蒸汽发生器蒸发器中流动加速腐蚀速率的影响

摘要

流动加速腐蚀（FAC）被认为是损坏联合循环机组热回收蒸汽发生器（HRSG）的主要原因之一。在过去的几十年中，有关此问题的大量论文已在世界许多国家发表。通常根据流量的平均流量热化学参数来分析调查结果，而没有考虑确定FAC速率的近壁液膜特性。近壁区域中的指示器取决于热质传递条件，流动流体动力学以及用于校正水化学（WC）的化学物质的特定性。对于氨和氧气水处理化学品，提出了一种平衡模型，并证明了其对HRSG蒸发器的有效性。ķ _d。为了简化计算，建议对氨和氧气的K _d进行简单的近似相关。对于使用固体试剂的水化学，已经开发了一种扩散模型，用于基于蒸汽发生管中传热的数据来计算传质。壁附近试剂的浓度由流动芯和近壁层之间液体的湍流传输以及各相之间试剂分布的系数决定。提出了Na ₃ PO ₄，NaOH和90H Turb helamine分布系数的简单近似相关性。水力阻力系数K _h之间的近似关系和几何参数ķ _с的FAC过程已经建立。标准HRSG结构构件的流体力学基础比FAC进行了更详细的研究。为了估计ķ _с，人们可以使用的已知值ķ _ħ以及它们之间的相关性。但是，应谨慎使用此关联，因为已针对某些明确条件（即特定的建筑材料，水化学，流动历史等）获得了关联。在其他条件下，这种相关性将有所变化。因此，它只能用于粗略估计。