Sulfur Recovery Daily Question 2019.1.12

(1) Scaling. (2) Massive waste of fuel. (3) Reduce yield and quality. (4) Increase the amount of boiler maintenance.  (5 Endangers safety.

1: The scaled water evaporates when heated in the boiler, which not only provides chemical reaction conditions for the impurities in the water but also causes the boiler water to become increasingly concentrated. When these impurities reach saturation in the boiler water, solid substances precipitate out. The solid substances that precipitate, if they remain suspended in the boiler water, are called sludge ； If it deposits on the heated surface, it is called scale. The thermal conductivity of scale is dozens to hundreds of times lower than that of steel. Therefore, when scale forms on the boiler, it deteriorates the heat transfer performance of the heating surfaces; the heat released by fuel combustion cannot be transferred quickly into the boiler water, and a large amount of heat is carried away by the flue gases. This results in an increase in the flue gas temperature, higher heat losses through the flue gases, and a reduced thermal efficiency of the boiler. It wastes fuel, damages the heating surfaces, reduces the boiler’s output, and scaling shortens the boiler’s service life. Hazard 2: Corrosion – The water-cooled walls, convective tube banks, and drum of the boiler can all suffer from corrosion due to poor water quality. As a result, these metal components become thinner and dented, or even perforated. More severe corrosion can damage the internal structure of the metal. The strength of corroded metal is significantly reduced. Therefore, it severely affects the safe operation of the boiler, shortens its service life, and results in economic losses. After metal corrosion products are carried by the boiler water to the heating surfaces of the boiler, they tend to combine with other impurities to form scale. Scale containing high-valent iron can easily cause corrosion of the iron metals in contact with it. And the corrosion products of iron tend to re-form into scale. It is a vicious cycle that will rapidly lead to damage to the boiler components. Hazard 3: Foaming in the boiler water. When the boiler water contains large amounts of sodium chloride, sodium phosphate, oils, and silicates, or when the organic substances in the water react with alkalis to form soaps, foam will appear on the surface of the liquid during the boiling and evaporation process. After the foam film ruptures, many water droplets are separated out; these highly saline droplets are continuously carried away by steam, resulting in a phenomenon of sparging. Foaming in the boiler can cause: severe contamination of the steam ； Severe salt deposition in the superheater tubes and steam flow pipes can cause these pipes to become blocked ； Reduce the temperature of the superheated steam ； Bubbles are present inside the level gauge, resulting in an unclear reading of the liquid level ； It causes water hammer effects, which can easily lead to damage at the connections in the steam system ； It can easily cause corrosion in steam valves, return bends, and within the superheater. Boiler water treatment refers to the process of treating water through techniques such as filtration and decomposition in order to remove impurities and purify it. Its purpose is to reduce undesirable phenomena such as boiler scaling, corrosion, and foaming, to extend the service life of the boiler, to save fuel, and to ensure the safe and economical operation of the boiler. It can generally be divided into external boiler water treatment and internal boiler water treatment. Water treatment in the boiler: A certain amount of chemical is added to the boiler to convert the scaling substances present in the boiler feed water into sludge, which is then removed through blowdown, thereby preventing scaling in the boiler

The adverse quality of water used in boilers can cause the following problems for them: ① Formation of scale in the boiler； ②Causes boiler corrosion ； ③It affects steam quality.

(1) Fuel waste. When a boiler becomes scaled, its heat transfer efficiency declines; to maintain the boiler’s rated parameters, more fuel must be used, resulting in fuel waste. (2) Damage to the heat transfer surfaces. In boilers with scale, the temperature difference across the heat transfer surfaces increases, raising the temperature of the metal walls and reducing their strength. Under the pressure inside the boiler, bulging may occur, or even serious accidents such as tube rupture can happen. (3) Reduction in the boiler’s output. After scaling occurs, the scale also reduces the flow area within the heat transfer tubes, increasing the resistance to water circulation inside them. In severe cases, the tubes can become completely blocked. This disrupts the normal water circulation in the boiler, hinders heat transfer within it, and reduces the boiler’s evaporation capacity. As a result, the boiler’s output is reduced. Corrosion.

①Boiler scaling occurs； ②Causes boiler corrosion ； ③It affects steam quality.

It causes boiler scaling, leads to boiler corrosion, and affects steam quality

1: The scaled water evaporates when heated in the boiler, which not only provides chemical reaction conditions for the impurities in the water but also causes the boiler water to become increasingly concentrated. When these impurities reach saturation in the boiler water, solid substances precipitate out. The solid substances that precipitate, if they remain suspended in the boiler water, are called sludge ； If it deposits on the heated surface, it is called scale. The thermal conductivity of scale is dozens to hundreds of times lower than that of steel. Therefore, when scale forms on the boiler, it deteriorates the heat transfer performance of the heating surfaces; the heat released by fuel combustion cannot be transferred quickly into the boiler water, and a large amount of heat is carried away by the flue gases. This results in an increase in the flue gas temperature, higher heat losses through the flue gases, and a reduced thermal efficiency of the boiler. It wastes fuel, damages the heating surfaces, reduces the boiler’s output, and scaling shortens the boiler’s service life. Hazard 2: Corrosion – The water-cooled walls, convective tube banks, and drum of the boiler can all suffer from corrosion due to poor water quality. As a result, these metal components become thinner and dented, or even perforated. More severe corrosion can damage the internal structure of the metal. The strength of corroded metal is significantly reduced. Therefore, it severely affects the safe operation of the boiler, shortens its service life, and results in economic losses. After metal corrosion products are carried by the boiler water to the heating surfaces of the boiler, they tend to combine with other impurities to form scale. Scale containing high-valent iron can easily cause corrosion of the iron metals in contact with it. And the corrosion products of iron tend to re-form into scale. It is a vicious cycle that will rapidly lead to damage to the boiler components. Hazard 3: Foaming in the boiler water. When the boiler water contains large amounts of sodium chloride, sodium phosphate, oils, and silicates, or when the organic substances in the water react with alkalis to form soaps, foam will appear on the surface of the liquid during the boiling and evaporation process. After the foam film ruptures, many water droplets are separated out; these highly saline droplets are continuously carried away by steam, resulting in a phenomenon of sparging. Foaming in the boiler can cause: severe contamination of the steam ； Severe salt deposition in the superheater tubes and steam flow pipes can cause these pipes to become blocked ； Reduce the temperature of the superheated steam ； Bubbles are present inside the level gauge, resulting in an unclear reading of the liquid level ； It causes water hammer effects, which can easily lead to damage at the connections in the steam system ； It can easily cause corrosion in steam valves, return bends, and within the superheater. Boiler water treatment refers to the process of treating water through techniques such as filtration and decomposition in order to remove impurities and purify it. Its purpose is to reduce undesirable phenomena such as boiler scaling, corrosion, and foaming, to extend the service life of the boiler, to save fuel, and to ensure the safe and economical operation of the boiler. It can generally be divided into external boiler water treatment and internal boiler water treatment. Water treatment in the boiler: A certain amount of chemical is added to the boiler to convert the scaling substances present in the boiler feed water into sludge, which is then removed through blowdown, thereby preventing scaling in the boiler

It easily causes scale formation in boilers, reduces thermal efficiency, increases the frequency of chemical cleaning, and corrodes boiler components. Excess salt content in boiler water can lead to azeotrope formation between steam and water, thereby deteriorating the quality of the steam; in severe cases, this can result in safety accidents.