Phenomenon of pressure surge due to liquid level failure in the catalytic reabsorption tower and its treatment
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I would like to ask about the phenomenon of pressure loss due to liquid level failure in the catalytic reabsorption tower and how to address it
Phenomena: 1 The most obvious issue is a sharp increase in reaction and distillation pressures; even opening the flare at the inlet of the atmospheric compressor fails to control these pressures. 2 The opening degree of the control valve for the liquid level at the bottom of the reabsorption tower is significantly higher than usual, sometimes even at full open. 3 The flow rate of dry gas leaving the tower decreases markedly. 4 The flow rate of the richly absorbed oil returning to the distillation tower experiences significant fluctuations.
Actions to take: 1 Close the control valve for the liquid level at the bottom of the tower. 2 Set the control valve to its normal opening degree, or adjust it accordingly based on the trend in the flow rate of the richly absorbed oil returning to the distillation tower. 3 Assign someone to monitor the liquid level using a glass gauge; it is essential to prevent the tank from becoming either completely full or empty, as well as to avoid situations where gas is mixed with liquid or the tank becomes under pressure again. 4 Contact the instrumentation team to calibrate the liquid level measurement. 5 If nothing else works, shut down the reabsorption tower
Actions to take: 1 Close the control valve for the liquid level at the bottom of the tower. 2 Set the control valve to its normal opening degree, or adjust it accordingly based on the trend in the flow rate of the richly absorbed oil returning to the distillation tower. 3 Assign someone to monitor the liquid level using a glass gauge; it is essential to prevent the tank from becoming either completely full or empty, as well as to avoid situations where gas is mixed with liquid or the tank becomes under pressure again. 4 Contact the instrumentation team to calibrate the liquid level measurement. 5 If nothing else works, shut down the reabsorption tower
Pressure surge due to liquid level failure in the reabsorption tower: 1. The reaction pressure rises rapidly； 2. The temperatures in the middle section of the distillation tower and at various points decrease rapidly ； 3. Reduced gas discharge flow rate ； 4. Pressure in the reabsorption tower decreases ； 5. The flow rate of the oil rich in absorbed substances returning to the tower increases. Solution: 1. Immediately close the liquid level control valve of the absorption tower to prevent dry gas from entering the distillation tower ； 2. Contact the instrument to calibrate the level ； 3. The operator on site shall communicate with the main operator using the level gauge to properly control the liquid level ； 4. If it cannot be repaired in a long time, the discharge and reabsorption system can be removed, and oil should be pressurized regularly using the on-site level gauge.
What was said upstairs is correct; our unit has never used a reabsorption tower from the very beginning. The pressure oil for the reabsorption tower is usually manually sent to V201 once the liquid level there is full, and the rich absorption oil line of the fractionation tower is not utilized. In fact, as long as the dry gas is of satisfactory quality, it doesn’t matter whether rich absorption oil is used or not.
It’s better to keep it running. Those upstairs said that it’s not necessary to shut it down as long as the dry gas is of good quality and there isn’t too much liquid present; it’s possible to proceed in this way when production is stable. . . But production is dynamic. . . So, a little bit of diesel can be added to help dissolve the heavier components of the dry gas into the diesel, thereby making the dry gas drier. . . :lol
If the flow rates of the absorbent oil and the rich absorbent oil are normal, keep the amount of rich absorbent oil being sent out unchanged; the amount of absorbent oil entering should be slightly less than usual. Pay attention to the pressure in the distillation tower – if there is an upward trend in distillation pressure despite no changes in the feed to the distillation unit or the heat at its lower section, immediately reduce the amount of rich absorbent oil being sent out. At the same time, check the instruments; if there are glass panels on site, keep in constant contact with those inside the facility.
(1) A malfunction in the liquid level sensor of the reabsorption tower, with the actual liquid level being too high, can result in liquid being carried along with the dry gas, affecting subsequent systems. (2) A malfunction in the liquid level sensor, with the actual liquid level being too low, may cause gas to flow into the distillation tower, leading to excessively high pressure in that tower; this in turn affects the pressure control in the reaction system, and in severe cases, overpressure can occur. (3) A malfunction in the liquid level sensor of the reabsorption tower can cause significant fluctuations in the flow rate of the absorbent oil, which in turn alters the load in the middle section of the distillation tower, having a substantial impact on both the dry point and flash point of diesel. (4) A malfunction in the liquid level sensor, with the liquid level being too high, can increase the gas pressure drop, leading to an increase in the pressure at the outlet of the compressor; in severe cases, surge phenomena can occur
I think the key is to disconnect the reabsorption tower in a timely manner and temporarily shut it down
The liquid level gauge in the absorber used by the original poster can be modified to have a dual-level design; together with the liquid level gauge on site, this greatly improves the accuracy of your operations!