10 TPH Calcium Bentonite Kiln — Furnace Backfire & Stack Emissions
Investigation of recurring furnace backfire at a 10 TPH calcium bentonite processing kiln in Karnataka. Diagnostic found undersized ductwork causing inadequate draft and excessive inlet velocities.
Key Results
--- title: 10 TPH Calcium Bentonite Kiln — Furnace Backfire & Stack Emissions category: Root Cause Analysis slug: kiln-bag-filter-rca description: Investigation of recurring furnace backfire at a 10 TPH calcium bentonite processing kiln in Karnataka. Diagnostic found undersized ductwork causing inadequate draft and excessive inlet velocities.
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10 TPH Kiln — Furnace Backfire RCA
[Diagnostic Chart: Problem Timeline → Investigation → Root Cause → Solution → Results]
The Problem
Symptoms — 2–3 furnace backfires per week, 30–60 min downtime each. Visible stack emissions. Burner replaced twice without solving issue. Operating at 60% capacity due to unreliability.
Root Cause — Ductwork severely undersized. Two 600mm ducts consuming 85% of induced-draft fan capacity, causing system imbalance and poor combustion.
Technical Diagnosis
Gas Volume Calculation:
- Feedstock: 2.5 m³/min
- Combustion products: 3.5 m³/min
- Moisture evaporation: 1.2 m³/min
- Total: 432 m³/hr needed
Ductwork Problem:
- Main duct: 400mm diameter (0.126 m² area)
- Face velocity: 57 m/s (should be 15–20 m/s)
- System pressure drop: 790 mm WC (fan rated for only 400 mm WC)
- Result: Induced draft pulling air through furnace at excessive speed → incomplete combustion → carbon buildup → backfire
The Solution
1. Enlarge ducts from 400mm to 1000–1200mm (reduces velocity to 12 m/s) 2. Install cyclone before baghouse for coarse dust separation 3. Upgrade fan to rated capacity with soft-start 4. Optimize pulse cleaning — trigger at 120–130 mm WC differential pressure 5. Reduce ID fan speed post-fix: 47 Hz → 25–32 Hz = 74% energy savings
Results
✓ Zero backfires in first 100 operating hours ✓ Stack emissions eliminated — 80% reduction visible ✓ Throughput recovered — 6 TPH → 9.8 TPH consistent ✓ Energy savings — 74% fan power reduction = ₹1,80,000/yr ✓ ROI — 8-month payback on ₹4,50,000 investment
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Key Lesson: Equipment failures are often system design problems, not component failures. Burner didn't fail—the system was forcing it outside design parameters.