One Question per Day (March 13)

Answer: During the cooling process after shutdown, the drum has a thick insulating layer, which results in little heat loss to the surroundings; therefore its cooling rate is slow, and its wall temperature as well as the temperature of the water inside it remain at the saturated temperature for an extended period of time. Furthermore, since the heat released by steam condensing on the drum wall is greater than that released by water on the drum wall, the upper part of the drum retains the stored heat for an extended period of time. In this way, the wall temperature of the upper half of the steam drum will be higher than that of the lower half. If the drum cools too quickly, the temperature difference will reach very high values, thereby causing excessive thermal stress on the drum. Therefore, after the boiler is shut down, to ensure the safety of the drum, it is absolutely necessary not to cool the drum rapidly.

Due to its thick walls and large water volume, the drum has a high heat capacity; coupled with good insulation, its cooling rate is relatively slow. Its cooling depends mainly on the decrease in the temperature of the boiler water. 1# zgj2405

Due to its thick walls and large water volume, the drum has a high heat capacity. Coupled with good insulation, its cooling rate is relatively slow; its cooling depends mainly on the decrease in the temperature of the boiler water.

Continue to inject demineralized water, gradually reducing temperature and pressure

Due to its thick walls and large water volume, the drum has a high heat capacity; coupled with good insulation, its cooling rate is relatively slow. Its cooling depends mainly on the decrease in the temperature of the boiler water.

Due to their thick walls (#1 boiler’s drum has a wall thickness of 112 mm and weighs 123 tons; #2 boiler’s drum has a wall thickness of 95 mm and weighs 122.2 tons), these drums have a large water capacity (#1 boiler: 45.23 m3; #2 boiler: 44 m3). As a result, they possess a high heat capacity. Coupled with good insulation, their cooling rate is relatively slow; their cooling depends mainly on the decrease in the temperature of the boiler water.

Due to its thick walls and large water volume, the drum has a high heat capacity; coupled with good insulation, its cooling rate is relatively slow. Its cooling depends mainly on the decrease in the temperature of the boiler water. After the boiler is shut down, as the pressure decreases, the saturation temperature of the boiler water also drops. The metal temperature remains relatively high, and the drum releases heat to both the boiler water and the steam. The upper part of the drum contains steam while the lower part contains water. Since the heat transfer coefficient of water is relatively high, heat transfer occurs more rapidly in the areas in contact with water; as a result, the wall temperature is close to that of the boiler water. On the other hand, the heat transfer coefficient of steam is much lower, so heat transfer in the upper part in contact with steam is slower, which leads to a temperature difference between the upper and lower walls.

After the boiler is shut down, as the pressure decreases, the saturation temperature of the boiler water also drops. The metal temperature remains relatively high, and the drum releases heat to both the boiler water and the steam. The upper part of the drum contains steam while the lower part contains water. Since the heat transfer coefficient of water is relatively high, heat transfer occurs more rapidly in the areas in contact with water; as a result, the wall temperature is close to that of the boiler water. On the other hand, the heat transfer coefficient of steam is much lower, so heat transfer in the upper part in contact with steam is slower, which leads to a temperature difference between the upper and lower walls. Therefore, to prevent a temperature difference between the upper and lower walls of the steam drum, the drum must be filled with water after shutdown; in this way, the entire inner wall of the drum is submerged in boiler water, the heat dissipation conditions on the upper and lower walls are essentially the same, and thus their temperatures remain fairly close to each other. Due to the thick wall of the drum, its large water volume and high heat capacity, coupled with good insulation, the cooling rate is relatively slow; its cooling depends mainly on the decrease in the temperature of the boiler water.

During the shutdown cooling process, due to its thick insulation layer, the steam drum loses little heat to its surroundings, resulting in a slow cooling rate; its wall temperature and the water inside it remain at the saturated temperature for an extended period of time. Furthermore, since the heat released by steam condensing on the drum wall is greater than that released by water on the drum wall, the upper part of the drum retains the stored heat for an extended period of time. In this way, the wall temperature of the upper half of the steam drum will be higher than that of the lower half. If the drum cools too quickly, the temperature difference will reach very high values, thereby causing excessive thermal stress on the drum. Therefore, after the boiler is shut down, to ensure the safety of the drum, it is absolutely necessary not to cool the drum rapidly. 1# zgj2405

Due to its thick walls and large water volume, the drum has a high heat capacity; coupled with good insulation, its cooling rate is slow. Its cooling depends primarily on the decrease in the temperature of the boiler water.