Study on Abnormal Vibration Cause and Blade Damage Fractal of Induced Draft Fan Burning Low-quality Coal

Abstract

With increasingly fierce competition in the electricity market and the gradual recovery of coal prices, the co-firing of low-quality coal is becoming increasingly popular among large-capacity thermal power units as a means to reduce fuel costs and improve economic efficiency. This study first conducted an abnormal vibration analysis of the induced draft fan blades in a thermal power plant that follows the principles of low-quality coal blending. The results are as follows: By recording vibration data inside the bearing housing during operation, it was found that severe bearing looseness caused excessive vibration. Upon disassembling the induced draft fan and inspecting its condition, it was discovered that, due to the high silicon and sulfur content in the low-quality coal, a significant amount of ammonium bisulfate crystals had formed on the hub. Additionally, the blades exhibited severe corrosion and wear, ultimately leading to dynamic imbalance and resulting vibration. Next, fractal theory was applied. Threshold segmentation was performed using ImageJ software to identify areas of pitting, wear, and microcracks in the segmented images. Fractal dimensions were calculated at different locations on the blades to determine their specific damage states and priority maintenance areas. Finally, corresponding measures to prevent excessive induced draft fan vibration were proposed for operating and maintenance personnel at power plants burning low-quality coal.