Troubleshooting / Evaporator

Evaporator Troubleshooting

The most common evaporator problems on the plant floor, with the likely causes and the fix for each. Part of the OEE Lab troubleshooting directory.

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Problems on this page:

Reduced capacity or poor heat transferProduct carryover or foamingVacuum or condenser problemsProduct burning on the heating surfaceConcentrate solids out of specVapour recompression losing performancePump seal failures under vacuumCleaning not removing the foulingCondensate backing up in the heater

Reduced capacity or poor heat transfer

Hits OEE: Performance

Symptoms: Lower evaporation rate, longer cycles, higher energy per kg.

Scaling/fouling on tubes
Clean (CIP/descale) the heating surfaces; manage fouling.
Non-condensables or vacuum loss
Purge non-condensables; fix vacuum/condenser issues.
Low steam or circulation
Check steam supply, traps and the circulation pump.

Prevention: Descaling/CIP schedule, vacuum integrity, utility checks.

Product carryover or foaming

Hits OEE: Quality

Symptoms: Product in the condensate, foaming, yield loss, contamination.

Level too high or surging
Control the level; stabilise feed; use a defoamer if allowed.
Separator/demister fault
Check the vapour separator and demister.
Boiling too vigorous
Tune the temperature/vacuum to control boiling.

Prevention: Level/feed control, separator upkeep, gentle boiling.

Vacuum or condenser problems

Hits OEE: Availability

Symptoms: Cannot hold vacuum, high boiling temperature, capacity loss.

Air in-leak
Find and seal in-leaks; test the system.
Condenser fouling or low cooling water
Clean the condenser; verify cooling-water flow/temperature.
Vacuum pump/ejector fault
Service the vacuum pump or steam ejector.

Prevention: Leak testing, condenser maintenance, vacuum-source upkeep.

Product burning on the heating surface

Hits OEE: Quality

Symptoms: Dark specks in the concentrate, burnt taste, faster fouling.

Too little product flowing over the surface
Check the circulation pump and the distribution.
Heating steam too hot
Lower the steam temperature.
Running partly dry at start-up or shutdown
Follow the start-up and shutdown sequence.

Prevention: Wetting and steam settings recorded per product.

Concentrate solids out of spec

Hits OEE: Quality

Symptoms: The concentrate leaves too thin or too thick.

Feed solids changed
Adjust for the new feed.
Steam supply unstable
Stabilise the steam pressure.
Density or solids instrument drifted
Calibrate the instrument.
Level control unstable
Tune the level control.

Prevention: Lab checks compared with the inline reading every shift.

Vapour recompression losing performance

Hits OEE: Performance

Symptoms: Less water evaporated for the same steam or power.

Thermocompressor motive steam pressure low
Check the steam supply to the thermocompressor.
Thermocompressor nozzle worn
Inspect and replace the nozzle.
Recompression fan fouled or out of balance
Clean and balance the fan.

Prevention: Steam per tonne of water evaporated tracked.

Pump seal failures under vacuum

Hits OEE: Availability

Symptoms: Leaking seals on circulation or extraction pumps, air drawn into the system.

Seal running dry
Check the seal flush or quench.
Product crystallising on the seal faces
Use a flush suited to the product.
Seal not suited to vacuum service
Use a seal arrangement rated for vacuum.

Prevention: Seal flush checks on the round.

Cleaning not removing the fouling

Hits OEE: Availability

Symptoms: Capacity does not recover after cleaning.

Cleaning solution too weak or too cool
Check concentration and temperature.
Cleaning flow too low
Check the cleaning pump and the flow.
Runs between cleanings too long
Clean before the fouling hardens.

Prevention: Capacity after cleaning tracked.

Condensate backing up in the heater

Hits OEE: Availability

Symptoms: Condensate builds up on the steam side and heating falls off.

Condensate pump losing suction under vacuum
Check the suction head and the pump seals.
Condensate level control or trap failed
Check the level control and the traps.
Condensate line blocked or too small
Check the line for blockages and size.
Non-condensable vents closed
Open the vents as the operating procedure describes.

Prevention: Steam side level and condensate flow checked on the round.

Guidance only. Always follow lockout/tagout and your site's safe-work procedures, and verify against OEM manuals before acting.

Related equipment guides: rotary dryer · spray dryer · steam boiler · industrial oven · distillation column · spiral freezer · plate freezer

Stop the same fault coming back

Recurring evaporator stops usually trace to a cause you cannot see by hand. The partner we recommend is Fabrico: it tracks OEE and downtime live from PLCs, IoT sensors or AI cameras; where cameras are fitted, the video of a stop sits next to its machine data so the cause can be reviewed; and a technician opens the work order from the stop in the same system. Data is hosted in the AWS EU region, and Fabrico and the company behind it hold ISO/IEC 27001, ISO/IEC 20000-1 and ISO 9001.

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Related tools: full troubleshooting directory · OEE calculator · downtime cost · MTBF / MTTR · glossary

Methods that cut recurring stops: the six big losses · root cause analysis · preventive vs predictive maintenance · TPM · SMED & changeover