When the boiler is overfilled, it's common to observe that the water level in the gauge glass appears dark or non-existent, which is a key indicator distinguishing full water from low water conditions. In an overfilled state, the high water level alarm will typically activate, and the temperature of the superheated steam may drop significantly. Additionally, the feedwater flow rate often becomes abnormally higher than the steam flow. In severe cases, boiler water can enter the steam piping and superheater, leading to water hammer and fouling of the superheater. As a result, the primary danger of overfilling is the degradation of steam quality, which can ultimately damage the superheater and other downstream components.
Common causes of boiler flooding include operator negligence, such as failing to monitor the water level properly or misinterpreting instrument readings. This might involve leaving the control panel unattended or not paying enough attention to critical indicators. Another cause is a malfunctioning water level gauge, which can create a false reading, leading the operator to believe the water level is normal when it's actually too high. Additionally, if the water level alarm or the automatic feedwater control system fails without being detected in time, it can also lead to overfilling.
Once a boiler is found to be overfilled, the first step is to flush the water level indicator to check for any malfunctions. If the water level is confirmed to be high, the feedwater valve should be closed immediately, and water supply to the boiler should stop. The economizer recirculation line should be activated, the combustion reduced, and drain valves on the superheater and steam pipes should be opened. Once the water level returns to normal, these drain valves should be closed again. The root cause of the incident must be identified and resolved, the water supply adjusted accordingly, and normal operation resumed.
If water hammer occurs during overfilling, it's essential to inspect the steam piping, valves, and supports after the water level has been restored to ensure no damage has occurred. Overfilling or underfilling of boilers is a frequent issue during operation, making it crucial for boiler operators to remain vigilant and take preventive measures to avoid such incidents. Proper training, regular maintenance, and continuous monitoring are essential to ensure safe and efficient boiler performance.
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