Ash wear of boiler heating surfaces

Abstract

The study is aimed at analysing the causes of ash wear leading to failure of boiler unit equipment, as well as reviewing existing approaches to increasing the service life of boiler convective heat transfer surfaces. An analytical forecasting procedure was applied, including the calculation of abrasive wear depending on the type of burned coal fuel and the method of pipe surface diagnostics performed by low-frequency electromagnetic fields without special preparation. The implementation of pipe surface diagnostics was proceeded using the "Heating surface condition" software combined with Autodesk AutoCAD 3D models. Together with analytical forecasting of the ash wear, the application of the scanning-based convective surface diagnostics was demonstrated to provide the systematic monitoring of the surface condition of boiler heating units. The following approaches to reducing the abrasive wear intensity during the operation of boiler units are proposed: reduced quantity of coal fuel having abrasiveness of >63%; reducing the fineness of coal dust to the value of 30-35% by grinding; installation of protective metal devices on heat exchanger pipes; control of the gas flow rate (for low- and high-abrasive coal, the flow rate was limited by 10-12 and 6-8 m/s, respectively); regular diagnostics of the pipe surface (every 50,000 hours of operation and every 25,000 hours in the case of pipes reduced in thickness by 0.5 mm or more). The proposed measures ensure an increase in the service life of boiler heating surfaces by 2-3 times. The necessity of using non-destructive methods for monitoring the condition of pipe surfaces in combination with adjustment of the gas flow rate in the gas duct, as well as selecting the optimal grinding for the fineness of coal dust depending on the coal type, is demonstrated to be an effective means of avoiding unplanned shutdowns of boilers.