旋轉窰冷卻段爐管破裂原因探討

Investigation on Cracking of Rotary Kiln Cooling Section

本文針對一旋轉窰式磁粉煅燒爐冷卻段爐管破損、斷裂之原因進行探討。首先針對破損爐管進行外觀觀察、取樣進行成分與腐蝕生成物分析，破損爐管內壁表面與破斷面進行金相分析；同時針對運轉中之冷卻段爐管進行溫度分布量測，以研判腐蝕之形成原因。由分析結果顯示：在煅燒爐高溫段會逸散出HCl蒸氣，所逸散出HCl蒸氣又會在煅燒爐冷卻低溫段（約在50 ~ 60℃的冷卻段爐管內壁表面上）冷凝下來，進而發生鹽酸露點腐蝕；此時旋轉窰冷卻段爐管內壁表面因不斷受到磁粉粒的磨擦與沖擊，在腐蝕與沖蝕雙重作用下，更加速爐管內壁局部侵蝕、減薄。被侵蝕、減薄的冷卻段爐管內壁形成蝕孔，持續擴大後會形成裂縫；當裂縫進一步延伸後，冷卻段爐管在持續承受扭轉力下被扭斷。

This study is to analyze the fracture of a cooling pipe, which had been used in the cooling section of the ferric oxides rotary kiln calcinations. The experimental methods included visual observation, first, sampling and composition analysis, corrosion product analysis, metal texture analysis of the fractured pipe inside surfaces and fractured surface observation, meanwhile, the temperature measurement was conducted while the cooling pipe was running with ferric oxides in the rotary kiln calcinations before conclusion had reached. The results revealed that HCl vapor was emitted from the ferric oxides in the high temperature zone of rotary kiln, which had condensed at chilled wall of rotary kiln, there was corroded and pitted by HCl condensation. Meanwhile, the wall of rotary kiln was eroded by ferric oxides inside while rotating. At the synergistic effect of corrosion and erosion, the wall thickness reduced quickly, where the wall became thinner and thinner, a crack was induced at the pit tips by the rotated driven forces finally, when the crack grown up, the cooling pipe was broken eventually.