Frequent flushing of the deaerator seal

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Hello, colleagues. In my plant, the 5 boilers with a capacity of 20T each are equipped with two atmospheric-type thermal deaerators (equipped with deaeration heads). These deaerators have been modified; as a result, the condensed water recovered from the boiler pipes is filtered of iron before being mixed with water from the soft water tank and then fed directly into the deaerators. The condensed steam recovered is also fed directly into the deaerators after flashing. The deaeration process parameters in my plant are as follows: the deaeration temperature ranges from 102 to 104 degrees, while the deaeration pressure is 0.2 MPA. This pressure comes from the boiler’s pressure vessel and is reduced to 0.4 MPA after passing through a pressure relief valve. Neither the amount of condensed steam nor the amount of condensed water fed into the deaerators is controlled by any actuators, which means there are no limits on these amounts. The temperature of the water in the soft water tank, after being heated by the condensed water, is around 70 degrees, and this water is used as the direct feed for the deaerators. During operation of the deaerators, it was observed that the water seals were frequently flushed, and the external pipes of the deaerators were often damaged. As a result, the recovery of flashed condensed steam was stopped, and only condensed water was recovered. Nevertheless, several interesting phenomena were observed – the water seals continued to be flushed. First: Our current deoxygenation water level is set at 800 centimeters, but the actual value is often around 1000–1200. Once condensate water is recovered, this level rises above 1600, triggering a red alarm on the deoxygenation control screen. In such a state, the temperature shown on the screen remains at 102 degrees, while the pressure stays between 0.2 and 0.3, resulting in a flooding seal. The second scenario: after the boiler is drained, the water level in the deaerator does not change much, and the deaeration temperature remains at 102 degrees without any variation. However, the deaeration pressure gradually increases, though not rapidly, which leads to the occurrence of a flush seal issue. Third: When the steam flow rate from the boiler decreases suddenly (it’s the instant of this change, not a gradual decrease from a high level to a low level), the deaeration pressure also increases gradually. At this time, the deaeration temperature and liquid level remain unchanged, resulting in a flushing seal. The fourth scenario: when the steam flow rate from the boiler is low, even if the deaeration pressure and temperature rise steadily to above 0.35 MPa and 105 degrees respectively, the deaerator will not initiate a flushing process to restore the water seal. Another situation occurs when, after all flushing actions are carried out to re-establish the water seal balance, if the boiler’s steam flow rate is so low that there is no significant change in the water supply to the boiler (for example, due to blowdown, the boiler’s water level may rise from 45% of the set level to 70% of that set level), then the deaeration temperature remains below 100 degrees, the same temperature as after the flushing process. Even if the deaeration pressure stays between 0.2 and 0.3 MPa, the deaeration temperature shows no tendency to increase over several hours. Only by performing boiler blowdown can the deaerator temperature rise in a short time. Finally, the maximum make-up water flow rate of the boiler feed water pump between our boiler and deaerator is 25 T/H. When the set water level in the boiler is reached, the feed water pump shuts off quickly; the slope on the trend graph of the boiler feed water flow rate is very unstable. I would appreciate it if experts could help me analyze what the cause is and how to resolve this issue.