Among all kinds of accidents of boiler and its accessories, the leakage and blasting of heating surface (economizer, water wall, superheater, reheater) are the most common, about 30% of the total number of accidents. Once the boiler heating surface leaks or bursts, most of them have to be shut down before they can be dealt with. The economic losses caused by this will be enormous. When the heating surface blasts, the smoke temperature on the blasting side will be significantly reduced due to the large amount of steam and water injection which will disturb the operation of the boiler, which will increase the deviation of the smoke temperature on both sides of the boiler and bring difficulties to control and adjust the parameters. When the water wall bursts, it also affects the combustion stability of the boiler, and even causes the boiler to shut down. When the heating surface leaks or blasts, if not treat it on time, it will easily cause the wall of adjacent heating surface blown, and bring adverse effects on air preheater, electrostatic precipitator, I.D fan and other equipment. Therefore, after the loss of heating surface accident, we should find out the causes and formulate preventive measures to minimize the occurrence of leakage or explosion accidents.
- Main Causes of Boiler Heating Surface Damage
Generally speaking, there are the following reasons for leakage or explosion of boiler heating surface:
- The reasons of manufacturing quality. The material of heating surface is not good, the material of design is improper or the manufacturing, installation and welding process is not qualified.
- Design or installation reasons. The bearing or position of heating area is unreasonable, causes tube panels waggles or free expansion unevenly, relative displacement and friction between the tubes or screens damaged the tubes, and the incorrect position of the sootblower nozzle caused the damage of the tubes.
- Reasons for material change. The feed water quality is unqualified for long time or excessive local heat load result in serious scaling in tube, corrosion under scaling or high temperature corrosion, which reduces the strength of pipes. Due to thermal deviation or uneven distribution of working fluid flow, the local pipe wall is over-heated for a long time and the strength decreases. Leakage and tube burst accidents caused by fly ash wear the tube wall of heating surface to thin or long years running of equipment, aging of pipe materials are the common faults. In addition, for once-through boilers, large changes in working fluid flow or feed water temperature in the tube will also cause displacement of the phase change zone in the boiler, which will lead to the wall temperature of phase change zone changes greatly, leading to the fatigue damage of the pipe wall.
- Operation and other reasons. There are many reasons for leaking or blasting of furnace tubes, including equipment and operation problems. For example, the blown pipe wall damaged by excessive control of soot blowing pressure or incomplete hydrophobicity, or caused by flame scouring screen and falling of large coke residue due to poor combustion, etc. In addition, scaling or foreign matter blocking at the throttle control valve or throttle ring at the inlet of the heating surface tube or water wall tube panel makes part of the pipe flow significantly reduced, and equipment damage accidents caused by the wall superheater are also common in operation.