A Professional, Practical, and Comprehensive Troubleshooting Guide for Industrial Evaporation Systems

 

Industrial evaporators—whether used for wastewater concentration, crystallization, MVR evaporation, or multi-effect evaporation—operate under high temperature, negative pressure, and long-duty cycles.

This makes them susceptible to a series of predictable and recurring faults.

 

 

This guide compiles the most common evaporator problems, their typical symptoms, engineering causes, and step-by-step troubleshooting methods used by experienced process engineers and maintenance teams.

 

Q1: The evaporator’s heat transfer efficiency drops sharply. What are the causes? How to troubleshoot it?

 

Typical Symptoms

 

• Significant reduction in evaporation rate
• Higher-than-normal steam consumption
• Abnormal temperature difference across effects
• Difficulty maintaining stable vacuum

 

Likely Causes

 

You already mentioned the major ones—here：

 

1. Scaling or fouling on heat exchange tubes（>60% of cases）

 

• Salt crystallization: CaCl₂, Na₂SO₄, CaCO₃
• Organic fouling from high-COD wastewater
• Silica scaling (the most difficult to remove)
• Oil/grease films from chemical or food industries

 

Severe scaling reduces the heat transfer coefficient by 50–80%.

 

2. Steam leakage / insufficient primary steam pressure

 

• Gasket aging
• Improper bolt torque
• Steam trap malfunction
• Condensate not being discharged on time

 

3. Circulation pump performance decline

 

• Cavitation
• Impeller erosion
• Bearing wear
• Reduced NPSH due to pipeline buildup

 

4. Insufficient vacuum

 

• Air ingress
• Condenser blockage
• Undersized vacuum pump
• Liquid ring pump fluid deterioration

 

5. Incorrect operating parameters

 

• Feed temperature too low
• Material viscosity increases at high concentration
• Operating pressure deviates from design

 

How to Troubleshoot (Professional Workflow)

 

Step 1 — Heat Transfer Diagnostics

 

• Conduct a heat balance test
• Compare actual vs. design U-value
• Check temperature profiles across effects

 

Step 2 — Mechanical Inspection

 

• Measure ΔP of pipelines
• Inspect pump performance curves
• Check impeller wear thickness

 

Step 3 — Vacuum System Assessment

 

• Use helium leak detection
• Validate condenser cooling water flow
• Measure vacuum pump discharge temperature

 

Step 4 — Tube Condition Inspection

 

• Insert an endoscope to observe scale
• Measure fouling thickness
• If silica scale: prepare alkaline + chelating cleaning formula

 

Additional Recommended Actions

 

• Install an online fouling monitor
• Add anti-scalant chemicals for high-hardness wastewater
• Optimize feed preheating to reduce viscosity

 

Q2: The circulation pump shows cavitation or abnormal vibration. How to solve it?

 

Typical Symptoms

 

• Loud crackling noise (“gravel sound”)
• Sudden pressure fluctuation
• Vibration amplitude > 0.1 mm
• Honeycomb pits on impeller

 

Causes

 

1. Inadequate inlet pressure

 

• Tank level too low
• Strainer clogged
• Suction line too long
• Poor piping design (90° elbows too close to pump inlet)

 

2. Gas entrainment

 

• Air leaks in seals
• Gas released from supersaturated solution
• Gas accumulation at high points in the pipeline

 

3. Mechanical installation errors

 

• Soft foundation
• Pump misalignment
• Unbalanced impeller

 

Solutions

 

1. Optimize NPSH

 

• Increase suction liquid height（≥1.5 m static head）
• Enlarge suction pipeline
• Avoid unnecessary valves before pump inlet

 

2. Remove gas from the system

 

• Install a cyclone degasser
• Add vacuum deaeration before feed tank
• Install automatic vent valves at pipeline high points

 

3. Strengthen pump maintenance

 

• Laser alignment (accuracy ±0.02 mm)
• Quarterly impeller wear measurement
• Replace bearings annually in heavy-duty systems

 

4. Process Parameter Optimization

 

• Reduce feed viscosity via preheating
• Maintain turbulence in evaporation chamber
• Avoid oversized pumps that cause low-flow cavitation

 

Q3: The evaporator’s vacuum system is unstable. How to troubleshoot?

 

Typical Symptoms

 

• Vacuum cannot reach design value
• Secondary steam cannot fully condense
• Large fluctuations in temperature & pressure
• Condensate with bubbles

 

Causes (Expanded)

 

1. Condenser problems

 

• Cooling water flow too low
• Heat exchange tubes fouled
• High cooling-water temperature (summer issue)
• Improper condenser design for new production loads

 

2. Vacuum pump failures

 

• Damaged rotor
• Worn vanes / worn impeller
• Contaminated working fluid
• Overheated vacuum pump

 

3. System leakage

 

• Gasket hardening
• Improper flange torque sequence
• Micro cracks at welds
• Aging sight glass seals

 

Troubleshooting Steps

 

Step 1 — Vacuum Leak Diagnosis

 

• Helium mass spectrometer
• Pressure decay test
• Soap test for quick diagnosis

 

Step 2 — Condenser Management

 

• Mechanical descaling (≥100 bar)
• Acid cleaning using 5% citric acid
• Increase cooling water flow

 

Install secondary condenser for energy-intensive systems

 

Step 3 — Vacuum Pump Maintenance

 

• Replace oil
• Clean water-ring pump working fluid
• Check vane-to-cylinder clearance (0.05–0.08 mm)
• Replace vanes every 6–12 months

 

Advanced Tip

 

• Install vacuum buffer tank to stabilize negative pressure during load fluctuations.

 

Q4: Crystal particle size is uneven. How to optimize evaporation parameters?

 

Key Parameters 

 

1. Supersaturation

 

• High supersaturation → fine particles
• Low supersaturation → large agglomerates

 

2. Circulation velocity

 

• <1.5 m/s → local crystallization
• 2.5 m/s → attrition (crystals break apart)

 

3. Residence time

 

• Too long → growth & agglomeration
• Too short → insufficient crystal growth

 

Effective Adjustments

 

1. Real-Time Monitoring

 

• Online brix, conductivity, density
• Feedback control of feed rate

 

2. Temperature Curve Optimization

 

• Avoid sudden cooling
• Use multi-stage cooling for crystallization

 

3. Seed Crystal Control

 

• Add 20–100 μm seed crystals
• Maintain 0.5–1% (w/w) addition
• Ensure uniform mixing

 

4. Mechanical/Structural Solutions

 

• Install internal baffles
• Modify circulation pump speed
• Use classification crystallizers for better size control

 

Q5: Frequent leaks at welds or flanges. How to eliminate the problem completely?

 

Common Leak Points

 

• Heating chamber welds
• Flange gaskets
• Sight glass seals
• Manhole covers
• Instrument ports

 

Root Causes

 

• Thermal stress fatigue
• Over-torque or uneven torque on flanges
• Corrosion due to chloride ions
• Vibration causing micro-movement
• Improper welding procedures

 

Solutions

 

1. Material Upgrades

 

• 316L stainless steel
• Titanium for high-chloride solutions
• Graphite/PTFE gaskets

 

2. Structural Optimization

 

• Double-side welding
• Radiographic inspection (RT)
• Expansion joints to absorb stress

 

3. Intelligent Monitoring

 

• Vibration sensors (10–1000 Hz)
• Thermal imaging for hot-spot detection
• Digital torque management for flanges

 

4. Preventive Maintenance

 

• Periodic gasket replacement
• Re-tightening after thermal cycles
• Annual weld inspection for high-temperature systems

 

Preventive Maintenance Schedule

 

Daily Checks

 

• Check steam inlet pressure
  
• Observe vacuum gauge stability
  
• Ensure cooling water flow & temperature are normal
  
• Confirm circulation pump noise/vibration
  
• Check for leaks in flanges & sight glass

 

Weekly Maintenance

 

• Clean strainers & filters
  
• Check pump shaft seal for leakage
  
• Record evaporation rate and compare trend
  
• Check condensate clarity & temperature
  
• Inspect drain valves and steam traps

 

Monthly Maintenance

 

• Vacuum pump fluid replacement (water/oil)
  
• Check inlet–outlet pressure difference
  
• Inspect motor alignment
  
• Check and clean condenser water side
  
• Lubricate pump bearings

 

Quarterly Maintenance

 

• Inspect impeller wear (≤2 mm allowed)
  
• Add fresh antifouling chemical if applicable
  
• Open sampling port to check scaling condition
  
• Tighten all flanges using torque sequence
  
• Inspect weld seams using dye penetrant

 

Annual Maintenance

 

• Full system descaling and cleaning
  
• Complete vacuum leak test using helium detector
  
• Replace all gaskets
  
• Conduct RT inspection of pressure-bearing welds
  
• Overhaul vacuum pump（replace vanes/seals/bearings）
• Evaluate overall energy consumption vs. design values

 

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