Activation Furnace Start-up, Shutdown and First Baking Procedure
1. Three Days Saved on Baking Come Back at the First Relining
A new activation kiln is brought to temperature slowly before it sees feed. Baking drives out construction water, releases bound water, and lets the brickwork pass its inversion points without fighting itself.
The lining does not fear heat — mullite brick runs above 1200°C for years. It fears a temperature gradient: a 230 mm brick with an 800°C hot face and a 100°C back face carries 700°C through its thickness, so one metre of brickwork wants to grow 3–4 mm, all of it escaping through expansion joints and fireclay seams. Ramp too fast and the hot face finishes growing while the back is cold — the brick splits itself. Cooling shock is worse: the hot face crazes and spalls, and the turning bed grinds the loose brick away the same day.
2. The Baking Curve: Four Plateaus, Three Rate Limits
1. Ambient to 150°C: free water, ≤10°C per hour, hold 8–12 hours
Construction water flashes near 100°C with a thousand-fold expansion. Soak until the plume nearly vanishes.
2. 150–350°C: bound water, ≤15°C per hour, hold 6–8 hours
Castable releases bound water here with strong shrinkage; rush it and hairline cracks spall later.
3. 350–600°C: sintering and inversion, ≤20°C per hour, hold 4–6 hours
Quartz inverts near 573°C with a 0.5%–1% volume change, right where sintering begins. Add a 2–4 hour hold there.
4. 600°C to operating temperature: ≤30°C per hour, hold 4 hours
Hold 4 hours at 850–950°C to equalise the lining. A small kiln takes 5–7 days, a large one 10–14.
Rotate the shell from 200°C at 0.2–0.5 r/min; hot air or wood below 600°C, burner only above. Log every thermocouple every 30 minutes; a 30°C axial spread means stop.
3. Three Conditions Before First Feed
Even temperature — axial spread under 30°C. Sound lining — enter below 200°C, no through-cracks or steaming seams; hairline cracks are normal, anything over 2 mm is repaired. Zero moisture — off-gas humidity matches ambient.
Charge at 30%–50% of design load, then add 10% every eight hours to full load in 2–3 days. The classic mistake is answering low iodine with more steam: the kiln is not stable, the zone overcools, burn-off rises and yield falls.
4. Shutdown: Normal and Emergency Are Two Procedures
1. Normal shutdown: ≤30°C per hour
Stop feed, empty the kiln, cool at ≤30°C/h; 20°C/h through the 573°C inversion, natural below 400°C. Opening the door quenches the hot face by 200–300°C — manhole below 200°C, entry below 100°C. Keep the shell turning to 400°C or it bends.
2. Emergency shutdown: sequence
Cut reactants. Keep the ID fan running — residual CO must be drawn out or the next ignition meets an explosive atmosphere. Hold −20 to −50 Pa and purge to below 5% oxygen; keep the shell turning to 400°C, open nothing, log the trip.
3. Early signals
Shell at 80–120°C is normal; a section above 150°C means thin brick and 5%–10% more heat loss. Pale lumps over 5 mm are spalled lining. An activation zone 30°C cooler on the same fuel means lost insulation.
Frequently Asked Questions (FAQ)
Q: Can a new kiln be baked with the main burner from day one? A: Not below 600°C. Burner flames run 100–200°C above the reading and create hot spots.
Q: Can a seven-day curve be compressed to four? A: No. Hold times shrink, ramp rates cannot. Above 15°C/h below 350°C, cracking risk climbs and shows up months later.
Q: Does a hairline crack justify a shutdown? A: Within 2 mm, non-through and stable, no. Check width, penetration and rising shell temperature — any one means schedule a repair.
Q: How soon after an emergency trip can the kiln restart? A: Above 600°C, restart on the curve's second half at ≤30°C/h; below 400°C, 30–40°C/h straight up.
Keywords: furnace baking, start-up procedure, refractory lining, heating curve