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Erosion of heat exchanger tubes in the convective section of an industrial boiler by products of coal combustion.

机译：工业锅炉对流段中的换热管受燃煤腐蚀。

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摘要

Uncertain supply of petroleum-derived fuels makes it attractive to convert oil-designed boilers to coal firing. Among the questions to be addressed when considering such a conversion is the effect of ash and unburned char particles on performance of convective heat exchangers. Two candidate fuels, coal-water fuel and micronized coal (pulverized coal, finely ground), were burned in an oil-designed industrial boiler at Penn State's Energy and Fuels Research Center. Erosion of carbon steel by ash and unburned char particles was measured in the convective section of the boiler. The rate of erosion was enhanced by directing a small jet of clean gas (nitrogen, 3% oxygen in nitrogen, air, or oxygen) to accelerate the particles toward the surface of a test coupon. Each sample was exposed to the effects of the jet and particles for 2 hours with metal temperature at 450, 550, or 650 K.; A model for simultaneous erosion and oxidation of carbon steel provided the basis for determination of erosion rate coefficients from the experimental observations. In the model, metal undergoes ductile erosion, increasing with increasing temperature, while oxide exhibits brittle erosion, at a rate independent of temperature. Oxide and metal are removed in series, their proportions depending upon their relative resistance to erosion and the steady average thickness of the scale. Over most of the range of temperature investigated, oxide scale was more resistant to erosion than the carbon steel substrate.; Four parameters were adjusted to fit the model to the measurements: (1) Erosivity of the particles toward the metal; (2) Erosivity of the particles toward the metal oxide; (3) Effective order of the metal oxidation process with respect to oxygen; (4) Average area of scale removed by a single impact. Using the values for these parameters which fit the accelerated erosion measurements, the gas velocity dependence of the erosion rate was calculated for typical convection section conditions, corresponding to the coal-water fuel combustion and micronized coal combustion conditions investigated.; Under steady conditions the average thickness of oxide scale is that at which its rates of formation by oxidation and removal by erosion are equal. At low velocities, where material loss is slow, the oxide layer is thick and erosion behavior is that characteristic of oxide. As velocity is increased the steady thickness of oxide layer decreases. The onset of the transition from oxide- to metal-controlled erosion, where the rate of metal loss begins to increase rapidly, was predicted to occur at the following velocities: 12 m/s for coal-water fuel and 16 m/s for micronized coal at an impaction angle of {dollar}90spcirc{dollar} (on the upstream stagnation line of the tube); and 21 m/s for coal-water fuel and 25 m/s for micronized coal at an impaction angle of {dollar}30spcirc.{dollar} Erosion on the stagnation line was expected to be slower than 0.05 {dollar}murm m/h{dollar} at gas velocities less than approximately 8 m/s for coal-water fuel and 9.4 m/s for micronized coal, under respective conditions of particle size, particle composition, particle loading, metal temperature, and gas composition at which the measurements were made. (Abstract shortened by UMI.)
机译：石油来源的燃料供应不确定，因此将石油设计的锅炉转换为燃煤的吸引力很大。考虑这种转换时要解决的问题之一是灰分和未燃烧的炭颗粒对对流热交换器的性能。宾州州立能源与燃料研究中心在由石油设计的工业锅炉中燃烧了两种候选燃料，即水煤燃料和微粉煤（粉状煤，细磨）。在锅炉的对流区测量了灰烬和未燃烧的炭颗粒对碳钢的侵蚀。通过引导一小束清洁气体（氮气，氮气，空气或氧气中的3％氧气）将颗粒加速朝向测试试样的表面，可以提高腐蚀速率。在金属温度为450、550或650 K的条件下，将每个样品暴露在射流和颗粒的作用下2个小时。碳钢同时腐蚀和氧化的模型为根据实验观察确定腐蚀速率系数提供了基础。在该模型中，金属遭受延性侵蚀，并随温度的升高而增加，而氧化物则呈现脆性侵蚀，其速率与温度无关。依次去除氧化物和金属，其比例取决于其相对的抗腐蚀能力和水垢的稳定平均厚度。在研究的大部分温度范围内，氧化皮比碳钢基材更耐腐蚀。调整了四个参数以使模型适合测量：（1）颗粒对金属的侵蚀性； （2）颗粒对金属氧化物的侵蚀性； （3）金属相对于氧气的氧化过程的有效顺序； （4）一次撞击消除的平均水垢面积。使用适合加速腐蚀测量的这些参数的值，计算出典型对流截面条件下腐蚀速率与气体速度的相关性，对应于研究的煤-水燃料燃烧和微粉化煤燃烧条件。在稳定条件下，氧化皮的平均厚度等于其氧化形成速率和腐蚀去除速率相等。在低速下，材料损失缓慢，氧化物层很厚，腐蚀行为是氧化物的特征。随着速度增加，氧化物层的稳定厚度减小。从氧化物控制的侵蚀过渡到金属控制的侵蚀开始发生，其中金属损失的速率开始迅速增加，预计将以以下速度发生：煤-水燃料为12 m / s，微粉化为16 m / s撞击角为90spcirc {dollar}（在管子的上游停滞线上）的煤；撞击角为30spcirc时，煤-水燃料的速度为21 m / s，微粉煤的速度为25 m / s。美元的停滞线上侵蚀预计比0.05 {dollar} murm m / h慢。 {美元}在煤，水燃料的气体速度小于约8 m / s，微粉化的煤的气体速度小于9.4 m / s的条件下，分别进行粒径，颗粒组成，颗粒负载，金属温度和气体组成的测量条件被制造。 （摘要由UMI缩短。）

著录项

  • 作者

    Xie, Jianyang.;

  • 作者单位

    The Pennsylvania State University.;

  • 授予单位 The Pennsylvania State University.;
  • 学科 Applied Mechanics.; Engineering Mechanical.; Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 1995
  • 页码 127 p.
  • 总页数 127
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 应用力学;机械、仪表工业;工程材料学;
  • 关键词

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