Fluctuations in condensate tank level control
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The liquid level in the condensate tank of the low-pressure heat exchanger at the bottom of the plant’s regeneration tower keeps fluctuating significantly. There are no issues with the control valves or the level gauge; what could be the possible causes? The low-pressure steam flow rate is around 25 t/h; the pressure before the control valve is 0.4 MPa, and the temperature is around 140°C.
Is it a leak, or has the packing collapsed?
Try it manually; then you’ll know it’s not a problem with the control valve or the level gauge. Theoretically, it shouldn’t fluctuate too much
Manual operation doesn’t work either; the liquid level cannot be maintained. The steam flow is low; the liquid level can be stabilized, but it’s not operating at full capacity. Under normal circumstances, the flow rate shouldn’t be low.
What is the diameter/height of the tank? ““The steam flow is low, so the liquid level can be stabilized.” What is the flow rate at this time? What is the LV valve opening degree?
If there are no issues with the control valves and level gauges, it is likely that the pressure fluctuations in the condensate tank are to blame; the problem lies with the heat exchanger. At low flow rates, steam can undergo complete phase transformation, the function of the balance line operates normally (pressure is normal), and the pressure in the condensate tank is also normal； At high flow rates, the steam does not undergo complete phase transformation in a timely manner; as a result, pressure behind the steam control valve fluctuates, which causes fluctuations in the pressure on the balance line. Consequently, the pressure in the condensate tank also fluctuates, leading to variations in the liquid level. If it is a new heat exchanger, it indicates insufficient heat exchange capacity; if it occurs later on, it is likely due to scaling of the heat exchanger.
There is indeed some fluctuation in the pressure of the condensate tank. The heat exchanger shell is old, while the core has been replaced. It’s not just a problem with one set of devices; several sets have the same issue. If it were due to scaling, this problem wouldn’t occur across all of them at the same time.
What was the condition before the core was replaced? Has the core been modified? Are the cores in the other sets also newly replaced?
Are there large pressure fluctuations in the condensate tank?
In this control scheme, the flow control system FC is connected to the level control system LC; in other words, the adjustments made to FC affect LC； LC adjustments affect FC; if the correlation is strong, both control systems perform poorly.