Pulp Chest Level Measurement With Foam and Fiber Buildup

Pulp and stock chests contain water, fibres, air and process chemicals whose proportions change with grade and consistency. Agitators and recirculation prevent settling but create a moving surface, while foam and fibre deposits can obscure a nozzle. Reliable level measurement requires a representative location, maintainable connection and control logic that recognizes invalid signals.

Define stock conditions

Record fiber type, stock consistency, temperature, conductivity, additives, entrained air and foam range. Include furnish changes, broke, white water, washing and shutdown conditions. A low-consistency chest may behave very differently after a grade change or loss of dilution water.

Specify the level duty: pump protection, residence time, overflow prevention, blending control or inventory trend. State response time and independent reference for each critical alarm.

Map agitation and flow

Locate agitators, baffles, inlet jets, recirculation returns and suction outlets. Avoid the vortex centre and direct incoming stock. A surface near the wall may climb or carry persistent fibre mats, so confirm the measurement point while the chest is operating.

Check whether the agitator stops at low level and how that transition changes the surface. Control logic should account for the different signal behaviour instead of applying one damping value blindly.

Manage foam explicitly

Decide whether the required value is foam top or liquid-stock surface. Foam thickness and wetness change with chemistry, air entrainment and agitation. Radar may penetrate some foam and reflect from other foam, so representative testing is essential.

For overflow protection, determine whether foam carryover itself is hazardous to downstream equipment. A separate foam or point alarm may be appropriate when one continuous value cannot represent both duties.

Control fibre buildup

Keep the antenna clear of splash and avoid a long recessed nozzle where fibres can hang and dry. Follow projection and beam requirements. Provide safe cleaning access without adding a plate or spray assembly inside the beam.

Trend echo quality and save clean and coated curves. Investigate process causes such as cold surfaces, poor wash coverage or airborne fibre before shortening the maintenance interval.

Verify control and failure behaviour

Check local reading, output, PLC scaling, pump permissives, high and low alarms, historian and quality status. Include damping in the response-time test. A lost echo or held last value must be visibly invalid and must not continue enabling a pump indefinitely.

Use an independent level reference suitable for the chest geometry and stock condition. Hydrostatic comparison requires attention to density and aeration. Verify the approved fallback during communication loss and power recovery, including whether pumps restart automatically or require operator confirmation. Record the tested safe state and recovery sequence for operators and maintenance staff.

Commission across production states

Record low, normal and high points during filling, agitation and drawdown. Save stock consistency, grade, foam condition and echo curves with results. Test startup after cleaning and restart after settled stock.

Inspect early for fibre deposits, condensation and loose mounting. Reassess parameters after changes to furnish, chemistry, agitator or inlet routing.

Engineering checklist

• Record consistency, fibres, air and chemistry.
• Map agitator, inlet, return and suction flow.
• Define foam-top versus stock-surface duty.
• Prevent recessed fibre deposits.
• Test quality status, pumps and alarms.
• Commission across grades and operating states.

Frequently asked questions

Can radar always measure through pulp foam?

No. Foam structure and stock conditions determine which echo is returned; test representative production.

Can hydrostatic level verify the radar?

Only when stock density and entrained air effects are understood.

What should happen after lost echo?

The system should flag invalid quality and move pumps or alarms to the approved safe response.

Related measurement solutions

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