After operating for a long time, boilers are prone to scale and rust buildup. This is mainly due to the presence of hardness components in the water. Under high temperature and pressure conditions, these minerals evaporate and concentrate inside the boiler, leading to a series of physical and chemical reactions that ultimately form hard, dense scale on the heated surfaces. Scale is one of the primary causes of boiler failures and can lead to serious accidents. Its negative effects include:
First, it leads to significant fuel waste. The thermal conductivity of scale is only a fraction of that of steel. When the heat transfer surface becomes fouled, heat transfer is hindered. To maintain the boiler's output, the temperature on the fire side must be increased, resulting in greater heat loss through radiation and flue gas emissions. The amount of fuel wasted depends on the thickness and type of scale, which varies with the boiler's working pressure. According to tests and calculations, there is a direct relationship between scale thickness and fuel loss: when the scale thickness (S) is ≥1 mm, fuel loss ranges from 5% to 13%; at ≥2 mm, it increases to 13%–18%; and at ≥3 mm, it can reach 18%–26%.
Second, scale can cause overheating and damage to steel plates and pipelines. After scaling, the boiler must maintain its pressure and evaporation, which requires higher temperatures on the fire side. As the scale thickens, the thermal resistance increases, causing the fire-side temperature to rise further. Normally, the fire-side temperature is around 900°C, while the water-side temperature is about 190°C. Without scale, the metal sheet temperature is approximately 230°C. However, with just 1 mm of scale, the metal temperature can increase by around 140°C. At 315°C, the metal begins to lose its ductility, and at 450°C, it may start to creep or deform due to overheating. Therefore, scale buildup significantly increases the risk of metal failure and potential boiler explosions.
Third, scale increases maintenance costs and shortens the boiler’s lifespan. Many boiler accidents are caused by scale-related issues, and this trend is on the rise. These incidents not only damage equipment but also pose serious safety risks. Even with good water quality, strict adherence to national standards during boiler operation is essential. Preventing scale formation during operation and promptly removing it once it occurs is crucial. Controlling water quality is an effective way to reduce such problems. The most scientifically sound method today involves using high-performance cleaning agents, regular maintenance, and descaling procedures to ensure safe and efficient boiler operation.
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