Heat Tracing for Pulp and Paper Mills
Pulp and paper mills move black liquor, green liquor, soap, tall oil and stock through long lines, many of which must stay above a minimum temperature. Heat tracing here protects process flow, not just pipes from freezing.
Lines that usually need tracing
- Black liquor lines: high solids, viscosity rises sharply as it cools.
- Green liquor and white liquor: crystallisation and scaling risk when cool.
- Soap and tall oil lines: high pour points.
- Stock lines in cold climates: frost protection during shutdowns.
- Chemical dosing lines: caustic, peroxide and other additives.
- Water and fire water: standard freeze protection.
Design points
1. Viscosity is the constraint, not freezing
Liquor becomes unpumpable well above 0 °C. Start from the viscosity-temperature curve and the pump's capability, then set the maintenance temperature accordingly.
2. Scaling and burn-on
Local overheating accelerates scaling on liquor lines. Uniform heating and correct sensor placement matter more than a high power density.
3. Corrosive and alkaline environment
Mills are wet and alkaline. Jackets, junction boxes and fixings must resist that environment; IP ratings and material selection often matter more than the certification level.
4. Long runs and steam tracing legacy
Many mills use steam tracing. When converting to electric, check existing steam line spacing and insulation condition — reusing poor insulation defeats the new system.
5. Shutdown and start-up
Cold starts with filled lines can require heat-up capacity. Decide whether the mill will drain lines or heat them up.
6. Maintenance reality
Pulp mills are congested and maintenance windows are short. Junction boxes must be accessible; documentation must be accurate, or repairs take twice as long.
Checklist
| Item | Confirm |
|---|---|
| Liquor type | Viscosity-temperature curve, solids |
| Pump requirement | Minimum pumpable temperature |
| Insulation | Condition and thickness; steam-line legacy |
| Environment | Alkaline, wet, washdown |
| Start-up | Drain or heat-up? |
| Control | Sensors, alarms, per-circuit monitoring |
Common mistakes
- Sizing by freezing point when viscosity is the real limit.
- High power density causing local burn-on and scaling.
- Reusing old steam-tracing insulation without checking it.
- Sensor on the cable instead of the pipe.
- Junction boxes placed where no one can reach them.
Pulp and paper project?
Send the liquor types, viscosity curves and line list. We size tracing for viscosity, not just frost.
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