Troubleshooting of Vacuum Deaerator
2025-06-30 17:48:20
1. The vacuum degree cannot be drawn high
The higher the vacuum degree, the better the deoxygenation effect. Therefore, the deoxygenation head should maintain the highest vacuum degree as much as possible to achieve the best deoxygenation effect. The reason for the low vacuum degree may be:
(1) The water jet pump unit for vacuuming itself has problems
You can close the valve on the exhaust pipeline and start the water jet vacuum pump unit. At this time, the vacuum gauge reading at the pump suction port is the ultimate vacuum degree. If the unit is working normally, the ultimate vacuum should reach the saturation pressure corresponding to the circulating water temperature. For example, when the circulating water temperature is 25 ℃, the vacuum degree can be around 730mmHg. If it cannot be achieved, it indicates that there is a problem with the unit, which may be caused by centrifugal pump failure, pipeline or nozzle blockage in the centrifugal pump or jet pump, jet pump wear, etc. It should be checked or replaced one by one.
(2) There is air leakage in the vacuum system (including the exhaust pipeline and deaerator)
Open the valves on the exhaust pipeline, close all valves leading to the deaerator, and then start the water jet vacuum pump unit to extract air. Under normal circumstances, the vacuum degree displayed on the deaeration head should be basically the same as the vacuum degree at the suction port of the water jet vacuum pump. If the vacuum degree of the former is much lower than that of the latter, it indicates that there is a leak in the vacuum system, and a water pressure test should be conducted to find the leak and repair it.
(3) The inlet water temperature is too high
As mentioned above (1) and (2), there is no problem. However, after the deaerator is filled with water, the vacuum degree drops significantly. This is because the inlet water temperature is too high, exceeding the corresponding saturation temperature under the operating vacuum degree by too much, producing a large amount of low-temperature steam. The amount of gas (steam) in the deaeration head exceeds the pumping capacity of the jet pump, and the vacuum degree will decrease. Therefore, it is necessary to lower the inlet water temperature to keep it within the required range.
(4) Water accumulation in the exhaust pipeline
If there is no problem with both points (1) and (2) mentioned above, but there is a large difference in vacuum degree between the suction port of the water jet vacuum pump and the deoxygenation head, the reason may be that there is a blockage in the suction pipeline between the two. If the exhaust pipe is too long, the support span is too large, and the pipe has sag, there will be water accumulation inside the pipe. Therefore, it is necessary to maintain the slope of the exhaust pipe, increase the pipe support, and eliminate the water accumulation inside the pipe.
(5) Vacuum gauge inaccurate
The allowable error for a 1.5-level spring vacuum gauge is ± 1.5%, resulting in a difference of approximately ± 10mmHg in vacuum degree. If the vacuum gauge fails, the error will be even greater. Therefore, it is necessary to verify the vacuum gauge or apply a U-shaped mercury differential pressure gauge, which is both accurate and reliable.
2. The deaerator has a low inlet water volume, which cannot meet the outlet water requirements (i.e. unbalanced inlet and outlet water volume)
When this situation occurs, the liquid level rapidly drops and exceeds the minimum level, indicating that the inlet water volume of the deaerator is less than the outlet water volume. At this time, the outlet pressure of the softened water inlet pump must be higher than the normal value. If the inlet pressure of the deaerator is also higher than the normal value, it indicates that the nozzle inside the deaerator is blocked, causing a decrease in water intake. The deaerator head should be opened for inspection. During normal operation of the deaerator, due to the installation of valves, heaters, etc. in the pipeline between the inlet pump and the deaerator inlet, the inlet pressure of the deaerator is slightly lower than the outlet pressure of the inlet pump. If the pressure difference between the two increases, it indicates that there is a malfunction in the pipeline accessories, which should be checked one by one.
3. The water output of the diversion pump unit cannot meet the requirements of boiler feedwater
The maximum water output of the water intake pump unit is 120% of the rated output of the deaerator. If it cannot meet the boiler feedwater requirements, the working pressure of the water intake pump will drop to zero, and the sampler will not be able to extract water. The reason for this situation may be:
(1) Due to intermittent water intake into the boiler, the flow rate exceeds the maximum output of the water intake pump unit during water intake, and the boiler feed pump exhausts the water in the water intake pump unit, forming negative pressure. The water pump unit cannot work even if there is no water inside. Therefore, it is necessary to refill the water intake pump unit and adjust the inlet and outlet valves of the boiler feedwater pump, as well as the return valve between the inlet and outlet, so that the outlet pressure of the feedwater pump is slightly higher than the operating pressure of the boiler and the flow rate is lower than the maximum output of the water intake pump.
(2) If the inlet water temperature of the deaerator is too high for the water pump unit to discharge water, the inlet water temperature should be reduced to less than or equal to 50 ℃ according to regulations.
(3) There is a problem with the water intake pump unit itself
If there are no problems with (1) and (2) above, but the water pump unit cannot produce water or the water output does not meet the requirements during operation, it indicates that there is a malfunction in the water pump unit. The centrifugal pump and jet pump on the unit should be checked, and if there is wear, they should be replaced.
4. The residual oxygen level does not meet the standard
If the heating temperature of the deoxygenated water is 3-5 ℃ higher than the corresponding saturation temperature under operating vacuum, the residual oxygen content should be qualified. If a lower residual oxygen level is required, the deoxygenated water temperature can be slightly increased until the vacuum degree of the deaerator begins to decrease. If the residual oxygen level still does not meet the requirements, it may be:
(1) The vacuum degree inside the deoxygenation head is not high, as mentioned earlier;
(2) The sampling operation is too slow, and oxygen enters the sampling bottle;
The higher the vacuum degree, the better the deoxygenation effect. Therefore, the deoxygenation head should maintain the highest vacuum degree as much as possible to achieve the best deoxygenation effect. The reason for the low vacuum degree may be:
(1) The water jet pump unit for vacuuming itself has problems
You can close the valve on the exhaust pipeline and start the water jet vacuum pump unit. At this time, the vacuum gauge reading at the pump suction port is the ultimate vacuum degree. If the unit is working normally, the ultimate vacuum should reach the saturation pressure corresponding to the circulating water temperature. For example, when the circulating water temperature is 25 ℃, the vacuum degree can be around 730mmHg. If it cannot be achieved, it indicates that there is a problem with the unit, which may be caused by centrifugal pump failure, pipeline or nozzle blockage in the centrifugal pump or jet pump, jet pump wear, etc. It should be checked or replaced one by one.
(2) There is air leakage in the vacuum system (including the exhaust pipeline and deaerator)
Open the valves on the exhaust pipeline, close all valves leading to the deaerator, and then start the water jet vacuum pump unit to extract air. Under normal circumstances, the vacuum degree displayed on the deaeration head should be basically the same as the vacuum degree at the suction port of the water jet vacuum pump. If the vacuum degree of the former is much lower than that of the latter, it indicates that there is a leak in the vacuum system, and a water pressure test should be conducted to find the leak and repair it.
(3) The inlet water temperature is too high
As mentioned above (1) and (2), there is no problem. However, after the deaerator is filled with water, the vacuum degree drops significantly. This is because the inlet water temperature is too high, exceeding the corresponding saturation temperature under the operating vacuum degree by too much, producing a large amount of low-temperature steam. The amount of gas (steam) in the deaeration head exceeds the pumping capacity of the jet pump, and the vacuum degree will decrease. Therefore, it is necessary to lower the inlet water temperature to keep it within the required range.
(4) Water accumulation in the exhaust pipeline
If there is no problem with both points (1) and (2) mentioned above, but there is a large difference in vacuum degree between the suction port of the water jet vacuum pump and the deoxygenation head, the reason may be that there is a blockage in the suction pipeline between the two. If the exhaust pipe is too long, the support span is too large, and the pipe has sag, there will be water accumulation inside the pipe. Therefore, it is necessary to maintain the slope of the exhaust pipe, increase the pipe support, and eliminate the water accumulation inside the pipe.
(5) Vacuum gauge inaccurate
The allowable error for a 1.5-level spring vacuum gauge is ± 1.5%, resulting in a difference of approximately ± 10mmHg in vacuum degree. If the vacuum gauge fails, the error will be even greater. Therefore, it is necessary to verify the vacuum gauge or apply a U-shaped mercury differential pressure gauge, which is both accurate and reliable.
2. The deaerator has a low inlet water volume, which cannot meet the outlet water requirements (i.e. unbalanced inlet and outlet water volume)
When this situation occurs, the liquid level rapidly drops and exceeds the minimum level, indicating that the inlet water volume of the deaerator is less than the outlet water volume. At this time, the outlet pressure of the softened water inlet pump must be higher than the normal value. If the inlet pressure of the deaerator is also higher than the normal value, it indicates that the nozzle inside the deaerator is blocked, causing a decrease in water intake. The deaerator head should be opened for inspection. During normal operation of the deaerator, due to the installation of valves, heaters, etc. in the pipeline between the inlet pump and the deaerator inlet, the inlet pressure of the deaerator is slightly lower than the outlet pressure of the inlet pump. If the pressure difference between the two increases, it indicates that there is a malfunction in the pipeline accessories, which should be checked one by one.
3. The water output of the diversion pump unit cannot meet the requirements of boiler feedwater
The maximum water output of the water intake pump unit is 120% of the rated output of the deaerator. If it cannot meet the boiler feedwater requirements, the working pressure of the water intake pump will drop to zero, and the sampler will not be able to extract water. The reason for this situation may be:
(1) Due to intermittent water intake into the boiler, the flow rate exceeds the maximum output of the water intake pump unit during water intake, and the boiler feed pump exhausts the water in the water intake pump unit, forming negative pressure. The water pump unit cannot work even if there is no water inside. Therefore, it is necessary to refill the water intake pump unit and adjust the inlet and outlet valves of the boiler feedwater pump, as well as the return valve between the inlet and outlet, so that the outlet pressure of the feedwater pump is slightly higher than the operating pressure of the boiler and the flow rate is lower than the maximum output of the water intake pump.
(2) If the inlet water temperature of the deaerator is too high for the water pump unit to discharge water, the inlet water temperature should be reduced to less than or equal to 50 ℃ according to regulations.
(3) There is a problem with the water intake pump unit itself
If there are no problems with (1) and (2) above, but the water pump unit cannot produce water or the water output does not meet the requirements during operation, it indicates that there is a malfunction in the water pump unit. The centrifugal pump and jet pump on the unit should be checked, and if there is wear, they should be replaced.
4. The residual oxygen level does not meet the standard
If the heating temperature of the deoxygenated water is 3-5 ℃ higher than the corresponding saturation temperature under operating vacuum, the residual oxygen content should be qualified. If a lower residual oxygen level is required, the deoxygenated water temperature can be slightly increased until the vacuum degree of the deaerator begins to decrease. If the residual oxygen level still does not meet the requirements, it may be:
(1) The vacuum degree inside the deoxygenation head is not high, as mentioned earlier;
(2) The sampling operation is too slow, and oxygen enters the sampling bottle;
