In extraction processes in industries such as chemical engineering, hydrometallurgy, and pharmaceuticals, abnormal rises in the liquid level of the mixer settler are common but easily overlooked process faults. If not addressed promptly, they can lead to material overflow, phase entrainment, decreased separation efficiency, and even equipment damage. This article, using real-world case studies, systematically outlines the core causes of liquid level rises and provides rapid diagnostic methods to help operators quickly pinpoint the root cause of the problem.



I. Four Core Causes of Liquid Level Rise

1. Feed Flow Imbalance: Flowmeter Misjudgment or Valve Malfunction

Symptom: The liquid level rises rapidly within a short period, and the rate of rise is positively correlated with the feed flow rate.

Diagnostic Points:
Check if the feed flowmeter reading is abnormal (e.g., the displayed value is much higher than the actual value).
Confirm if the feed valve is stuck or if the control system is malfunctioning (e.g., PID parameter misalignment causing excessive valve opening).

2. Drainage System Failure: Pump Caustic or Pipeline Blockage

Symptom: The liquid level rises slowly, accompanied by abnormal vibration or noise in the drainage pipeline.

Diagnostic Points:
Check if the drainage pump current and outlet pressure have decreased (e.g., insufficient discharge due to pump impeller wear). Touch the temperature of the drain pipe (the temperature at the blockage point is significantly lower than other sections).

3. Abnormal Phase Separation: Emulsification or density difference changes.

Phenomenon: Liquid level rises accompanied by blurred interfaces and prolonged stratification time.

Diagnostic Points: Take samples to observe the two-phase separation effect (e.g., emulsion layer thickness exceeds 5mm).
Measure the density of the two phases (density difference < 0.05g/cm³ easily leads to flooding).

4. Equipment Structural Defects:Damaged weirs or displaced baffles.

Phenomenon:Localized rise in liquid level or wavy fluctuations.

Diagnostic Points: Check if the weir height in the extraction tank is consistent (tilted weirs can cause short circuits in the liquid flow).
Confirm whether the baffles are detached or deformed (affecting liquid residence time).



II. Quick Diagnosis "Four-Step Method"

Step 1: Observe the trend of liquid level changes.

• Rapid rise:Prioritize checking the feed system (flow meter, valves).
• Slow rise: Focus on checking the drain system (pump, pipes).
• Fluctuating rise:Pay attention to phase separation or equipment structural problems. 

Step 2: Check Key Instrument Data
Compare the readings of the feed flow meter and the drain flow meter (under normal operating conditions, they should be roughly balanced).
Monitor the extraction tank pressure (a sudden pressure increase may indicate a liquid seal due to poor drainage).

Step 3: On-site Sampling and Analysis
3.1 Take samples from different locations in the extraction tank and observe the two-phase separation effect:
3.2 If the upper organic phase is turbid, it may be due to emulsification;
3.3 If the lower aqueous phase contains organic phase, it may be due to entrainment or a weir problem.

Step 4: Equipment Structure Inspection
After shutdown, check the weir, baffles, agitator, and other components for damage.
Use a laser level to measure the weir height difference (allowable error ≤ 1mm).

III. Emergency Handling and Preventive Measures

• Emergency Handling
• Immediately close the feed valve to prevent the liquid level from rising continuously.
• Start the standby drain pump; if the main pump fails, switch to manual draining.
• Adjust the stirring speed (reducing the speed can reduce emulsification).
• Add a demulsifier (such as silicone oil or polyether, at a dosage of 0.1%-0.5% of the system volume). Preventive Measures: Install a liquid level interlock device: automatically cut off the feed when the liquid level rises to a high level.
• Regularly clean the drain pipes: flush the filter every shift to prevent scaling and clogging.
• Control process parameters: maintain a density difference between the two phases > 0.08 g/cm³, and keep the pH value stable within the process range.
• Equipment maintenance: check the tightness of the weir and baffle plates monthly, and replace worn parts.

Abnormal rise in the liquid level in the extraction tank is a "hidden killer" in industrial production, but by systematically analyzing the four key aspects of feeding, draining, separation, and equipment, combined with the four-step method of "observation-detection-sampling-inspection," the root cause of the problem can be quickly located. Mastering this skill can not only prevent production accidents but also significantly improve process stability and product qualification rate.

Whether in copper SX-EW plants, lithium battery recycling, other hydrometallurgy memtal extraction, or pharmaceutical solvent extraction processes, maintaining stable liquid levels is essential for achieving consistent and efficient operation.

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