26 months of lining life, then a 12-day reline: the Slep furnace maintenance calendar
Measured on four shaft furnaces running shell char at 850–900 °C. The failure mode is almost never the brick — it is the joint.
What 26 months actually means
Across four Slep furnaces running coconut and palm kernel shell char at 850–900 °C, the working lining reached replacement at 22–31 months, with a median of 26. The number is not a warranty figure; it is what the refractory schedule in the manual produces when the furnace is run as designed.
Two of those four furnaces were relined earlier than median, and both had the same cause: steam quality. Wet steam at the inlet erodes the joint between the combustion zone and the reaction zone, and once the joint opens, the brick behind it is gone within weeks.
The four things that shorten lining life
- Steam dryness below 0.95. Superheat another 20–30 °C or add a separator; this is the cheapest fix on the list.
- Thermal cycling. Every cold start below 200 °C/h of heating rate costs roughly two weeks of lining life. Three unnecessary shutdowns a year is a month.
- Ash with high alkali content. Potassium and sodium flux the brick surface. If your char ash is above 3%, expect the low end of the range.
- Brick joint thickness over 2 mm. Thin joints are not cosmetic; a thick joint is where penetration starts.
Reline schedule
| Stage | Days | Notes |
|---|---|---|
| Cool-down to ambient | 3 | Forced air below 300 °C, never water spray |
| Scaffold and demolition | 2 | Keep one course of the old lining as a reference |
| Shell inspection and repair | 1 | Weld any bulges before the new lining goes in |
| Brick and castable installation | 4 | Two masons per shift, 8 m² per shift each |
| Cure and controlled dry-out | 2 | 50 °C/h to 600 °C, hold 8 h |
| Total | 12 | 14 days if shell repair is needed |
Why the dry-out is not negotiable
Castable contains 8–12% water by weight. Heated too fast, that water turns to steam inside the material and spalls the surface off in sheets. The 2-day schedule exists because a 1-day dry-out will look fine and then fail in the first month of operation, usually at the expansion joint where nobody can see it.
The cost of doing it properly is two days of lost production. The cost of doing it fast is a second reline inside a year, plus the risk of a shell hot spot.
Signs it is time
A 15 °C rise in shell temperature at the same operating point, visible flame at a joint during the steam purge, or iron content in the product climbing above 150 ppm. Any one of these means schedule the reline, do not wait for the next shutdown window.
Other notes
Send the raw material, target tonnage and finished spec. You get a configuration, a utility schedule and a budget range — not a brochure.