Cement clinker rotary kilns operate at 1,450 C and burn multi-fuel (coal, petcoke, natural gas, RDF, tires). Flame failure with fuel accumulation can trigger furnace explosion. NFPA 85 (Boiler and Combustion Systems Hazards Code) defines purge, BMS (Burner Management System), flame detection and fuel cut-off rules.
Burner Management System (BMS)
- Class: SIL 3 (IEC 61511 process safety)
- Dual-redundant PLC: Siemens S7, Honeywell Safety Manager
- Logic: 1oo2 or 2oo3 vote
- Proof test: full functional every 12 months
Pre-Firing Purge
- Duration: 5 furnace volumes of air
- Flow: all induced/forced fans at max
- Minimum: 5 min (practically 15-30)
- CO monitor: <50 ppm during purge
- Interlock: no ignition until purge completes
Flame Detection
- Main flame: UV/IR scanner
- Pilot flame: ionization probe
- Loss-of-flame: 4 sec - fuel trip
- Dual fuel: separate flame scanner per fuel
- Scanner calibration: weekly self-check
Fuel Cut-Off Valves
- Double block + bleed: gas line
- Tight shut-off: ANSI Class VI
- Response: <1 sec closure
- Spring-return: fail-close
- PST: monthly partial-stroke test
Tire/Alternative Fuel (RDF)
- Pre-processing: magnetic metal removal, homogenization
- Feed control: belt scale, NFPA 664 wood-chip-like risk
- Suits clinker kiln: 1,450 C destroys toxics
- Tire chunks: caliper and steel wire - feed explosion risk
Kiln BMS with MEP Calc
MEP Calc sizes NFPA 85 kiln purge duration and flow, flame response time and fuel cut-off valve selection.
Download MEP Calc on the App Store
Sources & Further Reading
NFPA 85, NFPA 86, NFPA 54, IEC 61511, ASME B31.3, Cembureau Coprocessing Guidelines. NFPA 85 Boiler Hazards standard.