How the scale generated in boilers?
Boiler is the heat-exchange device.The medium is water.A thick layer of scale will be covered where flue and water connects. For two hundred years, people have analysised the cause and type of scale and find various technique to avoid it. But the scale can not be completely solved. Cleaning technique is adopted to keep transfering heat .
Then, how the scale generated in boiler? There are there main factors.
1. Impurities in the feed water is evaporated and concentrated continuously in the boiler. And the salt concentration increases continuously to saturated or supersaturated level. Then, sediments are formed on the surface of the metal.
2. The solubilities of some salt decrease with increased water tempreature. The scale is formed.
3.Interaction or thermal decomposition of different salts produce compounds difficult to dissolve.
The salts constantly concentrated when water is heated to steam, fimally discharged out of the boiler. When the salinity level of boiler feed water saturated or supersaturated in a continuous process of continuous evaporation, the pure water into steam sent from the boiler. When the salinity level of boiler feed water saturated or supersaturated, salts will generate solid precipitate. Some adhere to the heating surface with large heat load and form soft or hard scale. Others in boiler flue with the boiler water.
When the water cycle of the heating surface is bad or is slow. lower flow rate, then substances on the heated surface form secondary scale, or deposit in the boiler drum, the lower header in the form of dirt.
Therefore, The generation of scale is related to the running status of boiler to a large extent besides the impurities contents of feed water. The higher intensity of the evaporation of water, the higher circulation rate. It is easier to generate loose precipitate easily broken by water circulation. This reduces the number of scale on the boiler evaporation surface. In contrast, low evaporation intensity and the lower circulation rate make it easy to form scale on the evaporation surface of boiler.
Whatever it is steam generator,hot water boiler, vacuum boiler, you should pay attention to the thickness of scale during the operation and arrange reasonable sewage.
