Common faults and solutions of low-temperature evaporators

1. Insufficient vacuum degree leads to a decrease in evaporation capacity

Phenomenon: Negative pressure cannot reach the set value, evaporation temperature is too high, water production decreases, vacuum alarm reason: flange/mirror/sealing gasket aging and air leakage; Insufficient oil level and emulsified wear of the vacuum pump; Poor cooling effect of condenser; Instrument malfunction. Solution: Check for soap water leakage, tighten the flange, and replace the PTFE/fluororubber gasket; Inspect the vacuum pump and replace the vacuum oil; Clean the condenser and reduce the temperature of the cooling water; Calibrate or replace the vacuum pressure gauge.

2. Scaling of heat exchange tubes and continuous decrease in evaporation efficiency

Phenomenon: Under the same parameters, the water production decreases, the heating power increases, and the heat exchange temperature difference increases. Reason: Waste liquid calcium and magnesium ions, metal salts, and sludge adhere to the heat exchange surface; Long term failure to concentrate, resulting in high salinity of the concentrated solution. Solution: Shutdown using citric acid circulation cleaning; Regularly discharge concentrated high salt wastewater; Pre processing filtration is added to the front-end, and scale inhibitors can be added; Serious hard scale removal and cleaning of the heat exchanger.

3. Foaming and material leakage, and condensate water is polluted (foam entrainment)

Phenomenon: foam overflows into the condensate pipe, and the COD of condensate rises. The reason why the feed liquid is pumped out of the condenser is that cutting fluid, emulsion and cleaning wastewater contain surfactant; The liquid level is too high and the vacuum is pulled too quickly. Solution: Control the feed flow rate and chamber liquid level; Add suitable defoamers; Reduce the vacuum degree and temporarily eliminate bubbles; Install a foam removal net; Front end preprocessing to remove floating oil.

4. Pipeline/cavity crystallization blockage

Phenomenon: The pressure of the feed pump increases, the discharge is not smooth, the flow rate of the pipeline decreases, and the discharge port is blocked. Reason: The concentrated solution is supersaturated, and salt crystals precipitate; Shutdown without timely flushing. Solution: Shutdown hot water circulation flushing pipeline; Control the concentration ratio and avoid excessive concentration; Regular thickening; Add online flushing program for high salt working conditions.

5. Heat pump/heating system alarm, slow heating up

Phenomenon: Heating temperature cannot rise, compressor high/low pressure alarm reason: refrigerant leakage; Poor heat dissipation of condenser; Expansion valve blockage; Temperature sensor drift. Solution: Check the refrigerant pressure, check for leaks and replenish fluorine; Clean the heat pump condenser; Repair the expansion valve and filter; Calibrate the temperature sensor.

6. Abnormal fluctuation of liquid level, liquid level alarm

Phenomenon: The liquid level fluctuates rapidly, with frequent high and low liquid level alarms. Reason: The liquid level probe is scaled and wrapped in material; Unstable flow rate of feed pump; Foam interferes with liquid level detection. Solution: Remove and clean the liquid level sensor; Stabilize the variable frequency flow rate of the feed pump; When the foam is large, use non-contact liquid level detection.

7. Vacuum pump overload, abnormal noise, tripping

Phenomenon: The current of the vacuum pump is too high, the noise is loud, and the thermal protection shutdown is caused by water ingress and scaling in the pump chamber; The material steam enters the vacuum pump; Bearing wear; Voltage instability. Solution: Repair the vacuum pump and clean the scale in the pump chamber; Increase gas-liquid separation; Check the power supply; Replace parts for damaged bearings.

8. The condensate water quality does not meet the standard

Phenomenon: The condensate water detection exceeds the standard and cannot be reused. Reason: Waste liquid is carried by material leakage; Leakage of condenser; The volatile organic compounds of the material enter the condensation side. Solution: give priority to solving the problem of foam leakage; Check for perforations and leaks in the condenser; Increase pre-treatment of high VOC waste liquid.

9. Equipment corrosion

Phenomenon: Corrosion spots appear on the cavity, welds, and flanges. Leakage cause: waste liquid contains chloride ions, acid and alkali; The selection of sealing components is not corrosion-resistant. Solution: Choose 316L/titanium material according to the waste liquid material; Replace the corrosion-resistant gasket; Control pH and perform front-end neutralization pretreatment.

10. Frequent interlocking shutdown of the system

Phenomenon: There is no obvious pattern, and the equipment automatically stops and resets before giving an alarm for a short period of time. Reason: sensor drift; Poor contact of the circuit; The protection parameter settings are too tight; Pump and motor overload protection triggered. Solution: Calibrate pressure, temperature, and liquid level sensors one by one; Check the wiring terminals; Optimize interlocking protection threshold; Check the load on the pump body.

Simple operation and maintenance reminder

It is recommended to rinse the chamber and pipelines with clean water circulation during each shutdown to prevent crystallization and scaling;

Daily inspection focuses on: vacuum degree, temperature, liquid level, vacuum pump oil level, and condensate water quality;

Pre treatment is the most critical step in reducing malfunctions when dealing with high salt, oily, and foaming waste liquids.