【Weekly Topic】20150817 What are the main hazards of scale to boiler operation? (Participation rewards available)
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What are the main hazards of scale to boiler operation? Users who actively participate in the discussions can receive a wealth reward of 2–8 points, while those who submit excellent responses will get 1 red flower plus a wealth reward of 8–15 points! All sailors are welcome to participate actively!
1. Due to the poor thermal conductivity of scale, it reduces the amount of heat absorbed by the water in the pot, thereby wasting fuel. 2. It is prone to causing accidents; once scaling occurs on the heating surfaces, the wall temperature of these surfaces increases, their strength decreases, and explosions are likely to occur. 3. Scale contains a certain amount of calcium carbonate, which causes corrosion beneath the scale and shortens the boiler’s lifespan. 4. When scaling occurs on the inner surface of the boiler’s heating surfaces, it not only reduces the flow cross-section within the boiler tubes, but also, due to the uneven distribution of scaling and the high roughness, it increases the flow resistance. This has an impact on the flow of water or steam inside the boiler; in severe cases, it can cause the hydrodynamic characteristics to deviate significantly from those designed, potentially leading to accidents.
Scale deteriorates the heat transfer in the heating surfaces, raises the flue gas temperature, reduces efficiency, and increases fuel consumption. It also exacerbates electrochemical corrosion, facilitating \"under-scale corrosion\" and accelerating the damage to the heating surfaces.
Boiler scaling can cause the following hazards:
1. Fuel waste: After scaling occurs in a boiler, the heat transfer efficiency of the heating surfaces decreases. The heat generated by fuel combustion cannot be transferred to the boiler water in a timely manner, and a large amount of heat is carried away by the flue gases. This results in excessively high flue gas temperatures, increased exhaust losses, and reduced thermal efficiency of the boiler. To maintain the boiler’s rated parameters, more fuel must be used, leading to fuel waste. Approximately 1 millimeter of scale results in a 10% increase in fuel consumption.
2. Damage to heating surfaces: In boilers with scale, the reduced heat transfer efficiency prevents the heat from fuel combustion from being quickly transferred to the boiler water, causing the temperature in the furnace and flue gases to rise. As a result, the temperature difference across the heating surfaces increases, the temperature of the metal walls rises, and their strength decreases. Under the pressure inside the boiler, bulging or even rupture of the walls can occur.
3. Reduced boiler output: Due to the reduced heat transfer efficiency caused by scaling, more fuel is required to achieve the rated evaporation rate. However, as the scale thickness increases, the volume of the furnace remains constant, limiting fuel consumption. Consequently, the boiler’s output decreases.
4. Corrosion:
4.1 Metal damage: Oxygen, acidic, and alkaline substances present in water can corrode the metal surfaces of boilers, causing the wall thickness to decrease, creating indentations, or even leading to perforations. This reduces the strength of the boiler and severely affects its safe operation. This problem is especially severe in hot water boilers, where the large volume of circulating water accelerates corrosion.
4.2 Under-scale corrosion: Scale containing ferric ions can cause corrosion of the metal in contact with it. Moreover, the corrosion products of iron tend to re-form scale. This creates a vicious cycle that can rapidly lead to damage to boiler components. The effects of metal corrosion products are particularly severe in fuel-fired boilers.
5. Foaming: In addition to improper operation, foaming can occur when the boiler water contains large amounts of sodium chloride, sodium phosphate, oils, and silicates. Or when organic substances and alkalis in the water react to form soaps, foam appears on the surface of the boiling water, resulting in foaming.
6. Disruption of water circulation: Boilers operate either through natural circulation or forced circulation. The flow rate of water in these systems must remain balanced. Both the rising and falling tubes require sufficient cross-sectional area. When scale forms on the inner walls of the tubes, the cross-sectional area inside the tubes decreases, increasing the resistance to water flow and disrupting the normal water circulation. This leads to an increase in the temperature of the metal heating surfaces. If the tubes become blocked by scale, water circulation stops, and local overheating or tube rupture may occur, posing a threat to the boiler’s normal operation. Once scaling occurs in a boiler, it must be removed to ensure its safe and efficient operation. Currently, chemical descaling methods are commonly used to remove scale, involving acid cleaning. The thicker the scale, the more chemicals are needed, which requires more labor and resources, and ultimately shortens the boiler’s lifespan.
1. Fuel waste: After scaling occurs in a boiler, the heat transfer efficiency of the heating surfaces decreases. The heat generated by fuel combustion cannot be transferred to the boiler water in a timely manner, and a large amount of heat is carried away by the flue gases. This results in excessively high flue gas temperatures, increased exhaust losses, and reduced thermal efficiency of the boiler. To maintain the boiler’s rated parameters, more fuel must be used, leading to fuel waste. Approximately 1 millimeter of scale results in a 10% increase in fuel consumption.
2. Damage to heating surfaces: In boilers with scale, the reduced heat transfer efficiency prevents the heat from fuel combustion from being quickly transferred to the boiler water, causing the temperature in the furnace and flue gases to rise. As a result, the temperature difference across the heating surfaces increases, the temperature of the metal walls rises, and their strength decreases. Under the pressure inside the boiler, bulging or even rupture of the walls can occur.
3. Reduced boiler output: Due to the reduced heat transfer efficiency caused by scaling, more fuel is required to achieve the rated evaporation rate. However, as the scale thickness increases, the volume of the furnace remains constant, limiting fuel consumption. Consequently, the boiler’s output decreases.
4. Corrosion:
4.1 Metal damage: Oxygen, acidic, and alkaline substances present in water can corrode the metal surfaces of boilers, causing the wall thickness to decrease, creating indentations, or even leading to perforations. This reduces the strength of the boiler and severely affects its safe operation. This problem is especially severe in hot water boilers, where the large volume of circulating water accelerates corrosion.
4.2 Under-scale corrosion: Scale containing ferric ions can cause corrosion of the metal in contact with it. Moreover, the corrosion products of iron tend to re-form scale. This creates a vicious cycle that can rapidly lead to damage to boiler components. The effects of metal corrosion products are particularly severe in fuel-fired boilers.
5. Foaming: In addition to improper operation, foaming can occur when the boiler water contains large amounts of sodium chloride, sodium phosphate, oils, and silicates. Or when organic substances and alkalis in the water react to form soaps, foam appears on the surface of the boiling water, resulting in foaming.
6. Disruption of water circulation: Boilers operate either through natural circulation or forced circulation. The flow rate of water in these systems must remain balanced. Both the rising and falling tubes require sufficient cross-sectional area. When scale forms on the inner walls of the tubes, the cross-sectional area inside the tubes decreases, increasing the resistance to water flow and disrupting the normal water circulation. This leads to an increase in the temperature of the metal heating surfaces. If the tubes become blocked by scale, water circulation stops, and local overheating or tube rupture may occur, posing a threat to the boiler’s normal operation. Once scaling occurs in a boiler, it must be removed to ensure its safe and efficient operation. Currently, chemical descaling methods are commonly used to remove scale, involving acid cleaning. The thicker the scale, the more chemicals are needed, which requires more labor and resources, and ultimately shortens the boiler’s lifespan.
Scale is very harmful to boilers; it is a poor conductor that adheres to the boiler walls, hindering heat exchange. The furnace walls should be burned out. Coal consumption increases. Therefore, scale poses a serious threat to the safe operation of boilers. An increase in coal consumption leads to higher economic costs; it also causes thermal imbalances, which in turn result in thermal stresses that reduce the boiler’s pressure-bearing capacity and create safety hazards. Due to the poor thermal conductivity of scale, heat transfer from the heating surface to the working fluid is hindered, resulting in less heat absorbed by the working fluid. This leads to an increase in the boiler’s exhaust temperature and greater heat losses. 2 Due to the poor thermal conductivity of scale, it hinders the transfer of heat from the heated surface to the working fluid, causing the operating temperature of the heated surface to rise; in severe cases, this can lead to tube failure or bulging in the superheater. 3 Corrosion: Natural water is an aqueous solution of electrolytes, and it readily causes electrochemical corrosion when in contact with metals. 4 If scale deposits at the valves of the steam system, it may cause the valves to malfunction and leak. Scale poses a direct threat to the safety of the boiler installation as well as its service life, due to its very low thermal conductivity. The thermal conductivity of water is several hundred times lower than that of metals. Therefore, even if a not-too-thick scale forms on the heated surface, the high thermal resistance resulting therefrom reduces its heat conduction efficiency, leading to heat loss and fuel waste. Practice has shown that 1 millimeter of scale on the heating surfaces of boilers can increase coal consumption by about 1.5 to 2%. Scale formation on the heated surface can cause localized overheating of the metal tube walls. When the wall temperature exceeds the allowable operating limit, the tube may bulge; in severe cases, this can lead to tube rupture in the boiler, posing a threat to human safety. Scale is a complex salt that contains halide ions, and it is corrosive to iron at high temperatures. Analysis of iron-based scale shows that its iron content is around 20–30%. Scale erosion of metal makes the inner walls of the boiler brittle and continues to corrode deeper into the boiler.
Boiler scaling can cause the following hazards:
1. Fuel waste: When a boiler is scaled, its heat transfer efficiency decreases. The heat generated by fuel combustion cannot be transferred to the boiler water in a timely manner, and a large amount of heat is carried away by the flue gases. This results in excessively high flue gas temperatures, increased exhaust losses, and reduced thermal efficiency of the boiler. To maintain the boiler’s rated parameters, more fuel must be used, leading to fuel waste. Approximately 1 millimeter of scale results in a 10% increase in fuel consumption.
2. Damage to heat transfer surfaces: In boilers with scale, the reduced heat transfer efficiency prevents the heat from fuel combustion from being quickly transferred to the boiler water, causing the temperature in the furnace and flue gases to rise. As a result, the temperature difference across the heat transfer surfaces increases, the temperature of the metal walls rises, and their strength decreases. Under the pressure inside the boiler, bulging or even rupture of these walls can occur.
3. Reduced boiler output: Due to the poor heat transfer efficiency caused by scaling, more fuel is required to achieve the rated evaporation rate. However, as the scale thickness increases, the volume of the furnace remains constant, limiting fuel consumption. Consequently, the boiler’s output decreases.
4. Corrosion:
4.1 Metal damage: Oxygen, acidic, and alkaline substances present in water can corrode the metal surfaces of boilers, causing them to thin out, become dented, or even develop holes. This reduces the strength of the boiler and poses a serious threat to its safe operation. This problem is especially severe in hot water boilers, where the large volume of circulating water accelerates corrosion.
4.2 Under-scale corrosion: Scale containing iron ions can cause corrosion of the metals in contact with it. Moreover, the corrosion products of iron tend to re-form scale, creating a vicious cycle that rapidly leads to damage to boiler components. The effects of metal corrosion products are particularly severe in fuel-fired boilers.
5. Boiling overflow: In addition to improper operation, boiling overflow can occur when the boiler water contains large amounts of sodium chloride, sodium phosphate, oils, and silicates. Or when organic substances and alkalis in the water react to form soaps, foam appears on the surface of the boiling water, leading to boiling overflow.
6. Disruption of water circulation: Boilers operate either through natural circulation or forced circulation. The flow rate of water in these systems must remain balanced. Both the rising and falling tubes require sufficient cross-sectional area. When scale forms on the inner walls of the tubes, this reduces the cross-sectional area, increasing the resistance to water flow and disrupting the normal water circulation. This leads to an increase in the temperature of the metal walls exposed to heat. If the tubes are blocked by scale, water circulation stops, and some tubes may overheat or even burst, posing a direct threat to the boiler’s normal operation.
Once scaling occurs in a boiler, it must be removed to ensure its safe and efficient operation. Currently, chemical descaling methods are commonly used to remove scale, involving the use of acids for cleaning. The thicker the scale, the more chemicals are needed, which in turn requires more labor and cost, thereby shortening the boiler’s lifespan.
1. Fuel waste: When a boiler is scaled, its heat transfer efficiency decreases. The heat generated by fuel combustion cannot be transferred to the boiler water in a timely manner, and a large amount of heat is carried away by the flue gases. This results in excessively high flue gas temperatures, increased exhaust losses, and reduced thermal efficiency of the boiler. To maintain the boiler’s rated parameters, more fuel must be used, leading to fuel waste. Approximately 1 millimeter of scale results in a 10% increase in fuel consumption.
2. Damage to heat transfer surfaces: In boilers with scale, the reduced heat transfer efficiency prevents the heat from fuel combustion from being quickly transferred to the boiler water, causing the temperature in the furnace and flue gases to rise. As a result, the temperature difference across the heat transfer surfaces increases, the temperature of the metal walls rises, and their strength decreases. Under the pressure inside the boiler, bulging or even rupture of these walls can occur.
3. Reduced boiler output: Due to the poor heat transfer efficiency caused by scaling, more fuel is required to achieve the rated evaporation rate. However, as the scale thickness increases, the volume of the furnace remains constant, limiting fuel consumption. Consequently, the boiler’s output decreases.
4. Corrosion:
4.1 Metal damage: Oxygen, acidic, and alkaline substances present in water can corrode the metal surfaces of boilers, causing them to thin out, become dented, or even develop holes. This reduces the strength of the boiler and poses a serious threat to its safe operation. This problem is especially severe in hot water boilers, where the large volume of circulating water accelerates corrosion.
4.2 Under-scale corrosion: Scale containing iron ions can cause corrosion of the metals in contact with it. Moreover, the corrosion products of iron tend to re-form scale, creating a vicious cycle that rapidly leads to damage to boiler components. The effects of metal corrosion products are particularly severe in fuel-fired boilers.
5. Boiling overflow: In addition to improper operation, boiling overflow can occur when the boiler water contains large amounts of sodium chloride, sodium phosphate, oils, and silicates. Or when organic substances and alkalis in the water react to form soaps, foam appears on the surface of the boiling water, leading to boiling overflow.
6. Disruption of water circulation: Boilers operate either through natural circulation or forced circulation. The flow rate of water in these systems must remain balanced. Both the rising and falling tubes require sufficient cross-sectional area. When scale forms on the inner walls of the tubes, this reduces the cross-sectional area, increasing the resistance to water flow and disrupting the normal water circulation. This leads to an increase in the temperature of the metal walls exposed to heat. If the tubes are blocked by scale, water circulation stops, and some tubes may overheat or even burst, posing a direct threat to the boiler’s normal operation.
Once scaling occurs in a boiler, it must be removed to ensure its safe and efficient operation. Currently, chemical descaling methods are commonly used to remove scale, involving the use of acids for cleaning. The thicker the scale, the more chemicals are needed, which in turn requires more labor and cost, thereby shortening the boiler’s lifespan.
What are the main hazards of scale to boiler operation? 1 Due to the poor thermal conductivity of scale, which hinders the transfer of heat from the heated surface to the working fluid, the amount of heat absorbed by the working fluid decreases, the flue gas temperature of the boiler rises, and heat losses increase. 2 Due to the poor thermal conductivity of scale, it hinders the transfer of heat from the heating surface to the working fluid, causing the operating temperature of the heating surface to rise; in severe cases, this can lead to tube rupture or bulging in the superheater. 3 Corrosion: Natural water is an aqueous solution of electrolytes, and it readily causes electrochemical corrosion when in contact with metals. 4 If scale deposits at the steam valves, it may cause malfunctioning of the valves as well as leakage
Answer: 1. Fuel waste: When a boiler is scaled, its heat transfer efficiency deteriorates. The heat generated by fuel combustion cannot be transferred to the boiler water in a timely manner, and a large amount of heat is carried away by the flue gases, resulting in excessively high exhaust temperatures. Increased exhaust losses lead to reduced boiler thermal efficiency. To maintain the boiler’s rated parameters, more fuel must be used, thus causing fuel waste. Approximately 1 millimeter of scale results in a 10% increase in fuel consumption. 2. Damage to heat transfer surfaces: In boilers with scaled heat transfer surfaces, the reduced heat transfer efficiency prevents the heat from fuel combustion from being quickly transferred to the boiler water, leading to higher temperatures in the furnace and flue gases. As a result, the temperature difference across the heat transfer surfaces increases, the temperature of the metal walls rises, and their strength decreases. Under the pressure inside the boiler, bulging or even explosion can occur. 3. Reduced boiler output: After scaling, the poor heat transfer efficiency means that more fuel is required to achieve the rated evaporation rate. However, as the scale thickness increases, the volume of the furnace remains constant, limiting fuel consumption. Consequently, the boiler’s output decreases. 4. Corrosion: 4.1 Metal damage: Oxygen, acidic, and alkaline substances present in water can corrode the metal surfaces of boilers, causing them to thin out, become dented, or even develop holes. This reduces the strength of the boiler and seriously affects its safe operation. This is especially true for hot water boilers, where the large volume of circulating water leads to more severe corrosion. 4.2 Under-scale corrosion: Scale containing ferric ions can cause corrosion of the metals in contact with it. Moreover, the corrosion products of iron tend to re-form into scale. This creates a vicious cycle that can rapidly lead to damage to boiler components. The effects of metal corrosion products are particularly severe in fuel boilers. 5. Foaming: In addition to improper operation, foaming can occur when the boiler water contains large amounts of sodium chloride, sodium phosphate, oils, and silicates. Or when organic substances and alkalis in the water react to form soaps, foam appears on the surface of the boiling water, resulting in foaming. 6. Disruption of the water circulation
What are the main hazards of scale to boiler operation? It affects heat transfer; scale results in a low heat transfer coefficient, leading to increased consumption under the same conditions and wasted resources. As scale prevents heat from being transferred to the water in a timely manner, it causes the temperature of the boiler walls to rise, which can easily lead to structural damage to the boiler. .
1. It reduces the thermal efficiency of the boiler, resulting in significant fuel waste. When scale forms on the boiler, the heat transfer efficiency of the heating surfaces decreases. The heat released during fuel combustion cannot be transferred quickly to the boiler water, as a result of which a large amount of heat is carried away by the flue gases. This leads to an increase in the flue gas temperature, greater heat losses through the exhaust gases, and a reduction in the boiler’s thermal efficiency. 2. It causes metal overheating, reduces strength, and endangers safety. The steel used for the heating surfaces of boilers is generally carbon steel, and during operation, the metal wall temperature is allowed to be below 450°C. During normal operation of the boiler, the temperature of the metal wall is generally below 280°C. When the heating surfaces of the boiler are free of scale, the metal can transfer heat to the water quickly once heated, with a temperature difference between the two around 30°C at this time. However, if scale forms on the heated surface, the situation is quite different. 3. Disrupt the water cycle. There are two forms of boiler water circulation: natural water circulation and forced water circulation. The former is a water circulation driven by the pressure difference resulting from the different specific gravities of steam and water in the rising pipe and the descending pipe. The latter is primarily forced to circulate by the mechanical power of the water pump. Regardless of the type of circulation pattern, it is designed and calculated to ensure that there is sufficient flow cross-sectional area. When scale forms on the inner wall of the furnace tubes, it reduces the flow cross-sectional area within the tubes, increases flow resistance, disrupts the normal water circulation, and causes the temperature of the metal walls exposed to the flame to rise. When the safety of the pipeline is compromised by scale buildup, water circulation comes to a complete stop, and the temperature of the metal walls rises. Over time, this can lead to pipe failure due to overheating. The water wall tubes are evenly arranged within the furnace, absorbing radiant heat. In the high-temperature area on the fireward side, about 400 millimeters away from the heat exchanger box, if scale forms, accidents such as bulging, leakage, bending, and explosion are most likely to occur. 4. Increased maintenance work leads to significant financial waste. Once a boiler becomes scaled, it must be cleaned to ensure its safe and economical operation. Therefore, chemical agents such as acids and bases must be used to remove scale. The thicker the scale buildup, the more chemicals are required, and thus the greater the investment needed. 5. Shortens the service life of the boiler.
Corrosion, heat transfer efficiency, steam quality, etc