【Daily Question】In-depth Processing 20161026 Quiz: What are the reasons for supercooling of condensate water?

1. The amount of circulating cooling water is too high, or the back pressure setting of the air-cooled unit is too low. 2. Air leaks into the condenser, or the vacuum pump is not functioning properly. 3. Circulating cooling water leaks into the condensate water. 4. The level of condensate water is too high. 5. The impact of make-up water added to the condenser

Reason: 1. The cooling water volume and temperature remain unchanged, while the turbine load decreases； 2. The inlet temperature of the cooling water has dropped significantly ； 3. The cooling water pressure increases, the flow rate increases, and so on

Reason: Air has accumulated in the condenser. The presence of air in the condenser reduces the partial pressure of steam, which in turn lowers the temperature of the condensed water, thereby significantly increasing the degree of subcooling.

①Since the vapor partial pressure on the outer surface of the cooling water tubes is lower than the average vapor partial pressure between the tube bundles, the condensation temperature of the vapor is lower than the temperature of the mixed vapor stream between the tube bundles, resulting in supercooling. ②Due to the vapor resistance present in the condenser, steam encounters resistance as it flows from the exhaust port toward the lower section, resulting in a lower steam pressure in the lower area compared to the upper area. Consequently, the temperature of the condensate water in the lower section is lower than that in the upper section, leading to supercooling. ③When steam is cooled into droplets, it flows between the cooling water tubes in the condenser and is cooled by the circulating water inside those tubes. Since the temperature of the droplets is higher than that of the tube walls, the condensate cools down below its saturation temperature, resulting in supercooling. ④Due to the accumulation of air on the steam side of the condenser, the partial pressure of air increases while the partial pressure of steam decreases. The steam continues to condense under its own partial pressure, resulting in a condensate temperature that is lower than the exhaust steam temperature, thereby causing supercooling. ⑤There are defects in the design of the condenser; the arrangement of the cooling water tubes is improper, which causes a water film to form outside these tubes. When this water film thickens and hangs down in the form of droplets, the temperature of those droplets – as well as the average temperature of the inner and outer layers of the film – is lower than the saturated temperature at the outer surface of the film, resulting in supercooling. ⑥If too much air leaks into the condenser or if the extractor is not functioning properly, the air cannot be removed in time; as a result, the partial pressure of air increases, leading to an increase in subcooling. ⑦The water level in the hot water well is above the normal range, causing some of the copper tubes in the condenser to be submerged. As a result, the circulating water in these submerged tubes takes away some of the heat from the condensate, leading to supercooling. ⑧Too low a circulating water temperature and an excessive amount of circulating water cause the condensate to be over-cooled, increasing the degree of subcooling. ⑨The copper tubes of the condenser broke, allowing circulating water to leak into the condensate, which reduced the temperature of the condensate and increased its subcooling.

Air is leaking into the condenser, or the extractor is not functioning properly. During operation of the unit, if there are any leaks in components such as the turbine exhaust cylinder, condenser, and low-pressure feedwater heating system, which are under vacuum conditions, air can leak in. On the other hand, if the exhaust pump does not function properly, it is unable to remove the air that has leaked into the condenser in a timely manner.

Reason: 1. Air is accumulated in the condenser. 2 The condenser water level is high. 3 The water circulation volume is large. 4 The cooling water pipes of the condenser are arranged too closely.

Since the vapor partial pressure on the outer surface of the cooling water tubes is lower than the average vapor partial pressure between the tube bundles, the condensation temperature of the vapor is lower than the temperature of the mixed vapor stream between the tube bundles, resulting in supercooling.

Answer: The main reasons for supercooling of condensate water are: 1) Air accumulation on the condenser side； 2) Excessively high condensate water level during operation ； 3) Poor arrangement or excessive density of the condenser cooling water pipes ； 4) Excessive circulating water volume.