What are boiler scales and how they are removed?
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What are boiler scales and how they are removed?
Scale is too hard to mechanically remove, and therefore is normally removed by acid cleaning. For one type of scale that is composed singly of hardness, it is practiced to take a method of dissolving and removing deposited scale by adding hydrochloric acid and heating.
Where do boiler scales form?
Scales are formed out of salts. These salts come inside the boiler through water in form of soluble solids and are precipitated when the concentration level increases because of evaporation. Scales are basically crystalline and more difficult to remove.
What is the disadvantage of boiler scale?
Disadvantages of Scale formation (1) Wastage of fuel : Scales have a poor thermal conductivity so the rate of heat transfer from boiler to inside water is greatly reduced. This causes distortion of boiler tube and also makes the boiler unsafe to bear the pressure of the steam, especially in high-pressure boilers.
What causes scale buildup in boilers?
Boiler scale is caused by impurities being precipitated out of the water directly on heat transfer surfaces or by suspended matter in water settling out on the metal and becoming hard and adherent. Common feed water contaminants that can form boiler deposits include calcium, magnesium, iron, aluminum, and silica.
Does scale cause corrosion?
Scaling occurs when water has high levels of minerals like calcium carbonate, which can build-up on surfaces. Slight scaling can be considered beneficial in that the inside surfaces of metal pipes become coated with harmless minerals that act as a barrier to corrosion.
What causes scale in a boiler?
Which boiler trouble occurs due to hardness?
Two main problems occur due to the insulative effect of the scale material: under deposit corrosion and overheating of the boiler tube metal (creating “hot spots”), leading to water tubes failure and stress corrosion cracking, pushing up operational costs.
What causes scales on boiler?
What are the disadvantages of scale formation?
Disadvantages of Scale formation (1) Wastage of fuel : Scales have a poor thermal conductivity so the rate of heat transfer from boiler to inside water is greatly reduced. (ii) Lowering of boiler safety : Due to scale formation, over-heating of boiler is done in order to maintain a’ steady supply of steam.
Why scales are more harmful than sludge?
Sludges are poor conductor of heat, so they tend to waste a portion of heat generated. If sludges are formed along with scales, then former gets entrapped in the latter and both get deposited as scales. Excessive sludge formation disturbs the working of the boiler.
What causes scale in boilers?
How does scale impact boiler performance?
In addition to the overheating and eventual failure of the boiler tubes due to scale, efficiency is also decreased in the short-term because of the scale’s insulating effect on the heat transfer surfaces. A layer of scale just 1/8 inch thick can cause as much as 20-25 percent loss in efficiency – heat lost up the boiler stack.
How is scale detrimental to boilers?
When scale precipitates and forms within the boiler system, it can cause an isolating effect, which increases temperature variations. These increased variations can result in leaks in a boiler tube, or in extreme cases, boiler tube rupture . Another effect of scale formation is seen in heat transfer efficiency.
What is scale formation in case of a boiler?
(1) Carbonate and sulfate scale.
How sludge and scales are formed in boiler?
Scale and sludge formation in boilers In boilers, water evaporates continuously and the concentration of the dissolved salts increases progressively. When their concentrations reach saturation point , they are thrown out of water in the form of precipitates on the inner walls of the boiler.