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Causes and Harm of Scale Formation in Biomass Boilers

15 Feb, 2022

Causes of Scale Formation in Biomass Boilers

  1) Scale is formed by thermal decomposition of bicarbonates of calcium and magnesium. In the process of heating and evaporating water, magnesium and calcium bicarbonate in water are decomposed by heat to form calcium carbonate and magnesium hydroxide which are insoluble in water.

  2) After the water in the boiler is heated and boiled, it continuously evaporates to produce water vapor, but the salt contained in it still remains in the pot water, so the salt content in the pot water continues to increase. After the concentration of the species reaches the saturation concentration, it will be precipitated from the pot water to form a precipitate.

  3) The solubility of some salts (such as calcium sulfate, calcium silicate, magnesium hydroxide, etc.) decreases with the increase of water temperature. When the solubility is reduced to the saturated concentration, if the water temperature continues to rise, then calcium, magnesium The salt will precipitate out of the pot water to form a precipitate.

  The reason why the precipitates in the biomass boiler water can adhere to the heating surface is that the surface of the heating surface is rough and uneven, and there are many tiny raised hills. These hillocks can become the core of the product when the solid is precipitated from the solution. In addition, because the heating surface of the metal is often covered with a layer of oxide, this oxide has a considerable adsorption capacity and can become the bonding layer between the metal wall and the precipitate from the solution. The salts precipitated from the water may become scale or water slag. This depends not only on their chemical composition and the state of the final product, but also on the conditions of precipitation. For example, in economizers and water supply pipes, the calcium carbonate precipitated in the water often forms hard scales. In the heating surface of the boiler body, if the alkalinity of the boiler water is strong and it is in a violent boiling state, the precipitated calcium carbonate often forms a sponge-like soft water slag.

Biomass Boilers

Formation and harm of biomass boiler scale:

  When the water quality of the boiler is not good, after running for a period of time, a layer of solid deposits adheres to the drum and tube wall, which is called water scaling. These attachments are usually composed of a mixture of many compounds. It is called scale (commonly known as water alkali), such as carbonic acid scale, sulfate scale, silicate scale, mixed scale, oily scale, mud scale, etc.

  During the operation of the boiler, some solid substances precipitated from the boiler water under certain conditions are relatively loose and suspended; for water slag. Among them, the water slag in the state of sedimentation, if not removed in time, participates in the water cycle and will be converted into secondary scale after being baked at high temperature on the heating surface.

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