Kiln Burning Equipment: Complete Guide

The kiln burning equipment is the firing arsenal of the pyro line: the main burner that shapes the flame of the sintering zone, the auxiliary burners that start the kiln and hold it in the emergencies, the coal preparation and transport system that feeds the fuel at the exact fineness, and the burner management system that guards the safety: the burning equipment converts the chemical energy of the fuel into the heat of the clinker, and its condition, its settings and its safety philosophy decide both the production and the safety record of the plant: the burner is not a torch: it is an instrument of the process with the same precision requirements as the chemistry laboratory.

The Complete Cement Technical Package (931 files including the books, the courses, the Excel tools and the presentations: $249.99 one-time: instant download via the PayPal payment) includes this kiln burning equipment guide with the burner drawings, the firing system diagrams, the equipment selection tables and the safety checklists: the logarithm of the knowledge for the process engineers, the mechanical crews and the operation managers of the pyro line: this article walks the file: the main burner, the primary air system, the fuel preparation, the firing systems, the auxiliary burners, the flame safety and the maintenance: the reader leaves with the complete equipment map of the kiln firing in hand.

The burning equipment of a modern kiln line is a system of coordinated machines: the coal grinding mill prepares the fuel, the transport system carries it, the burner nozzle injects it with the primary air, and the flame detectors and the interlocks watch it: the failure of any link changes the flame and the flame changes the clinker: this page is organized so that the reader finds the equipment family by family, the operating figures with each machine, and the safety and the maintenance disciplines at the end: the file of the package follows the same order.

1. The Main Burner: The Instrument of the Flame

The main burner of the kiln delivers the fuel and the primary air into the burning zone and shapes the flame that sinters the clinker: the modern multichannel burner is a precision machine:

• The multichannel construction: the burner gathers the pulverized fuel in the central channel, the swirl air in the annular channel around it and the axial air in the outer channels: the swirl vanes of the inner channel rotate the air, the axial nozzles of the outer channels direct the stream: the flame shape is the product of the two;
• The fuel flexibility: the central channel carries the coal, the petcoke, the oil or the gas through the exchangeable nozzles: the modern burners switch the fuels without stopping the kiln: the fuel exchange is the daily reality of the plants with the alternative fuel programs;
• The momentum: the burner momentum, the product of the jet velocity and the mass flow, decides the flame penetration and the recirculation: the design momentum of 8 to 15 N per MW is the operating parameter that the operator tunes: the correct momentum gives the short intense flame with the internal recirculation;
• The flame shape control: the axial-swirl ratio moves the flame from the long narrow to the short wide: the operator adjusts the swirl vanes and the axial nozzle area from the control room or at the burner nose: the flame that touches the lining strips the coating, the flame that lies short leaves the meal unburned;
• The flame temperature: the peak flame temperature of 1700 to 2000 °C with the clinker at 1400 to 1500 °C: the radiation of the flame and the hot gas heat the bed: the burner position in the kiln nose and the flameness decide the heat transfer:

The burner is the single most important setting of the burning process: the same kiln with the same fuel produces different clinker, different NOx and different refractory wear under the different burner adjustments: the operator who masters the burner masters the kiln: the file documents the burner geometry, the setting procedures and the adjustment response tables.

2. The Primary Air System: The Pneumatics of the Flame

The primary air is the small fraction of the combustion air that the burner itself injects: its volume, its temperature and its velocity control the flame:

• The share of the air: the primary air is 8 to 12% of the total combustion air in the classic designs and 6 to 10% in the modern low-primary-air burners: the rest enters as the secondary air from the cooler hood through the kiln nose: the lower the primary air, the higher the flame temperature and the lower the NOx;
• The primary air fan: the dedicated blower delivers the air at 25 to 50 kPa to the burner channels: the fan capacity and the pressure define the nozzle velocities of 80 to 200 m/s: the multichannel burners use the single fan with the flow distribution to the channels;
• The air preheating: the primary air may be preheated from the cooler or the mill circuit to reduce the fuel consumption: the temperature of the primary air is limited by the burner material and the safety margins: the hot primary air is the free energy of the flame;
• The swirl adjustment: the swirl vanes rotate the inner air stream: the swirl number of the burner, defined by the vane angle and the channel geometry, sets the recirculation zone of the flame: the adjustment range of the vanes is the tuning knob of the flame;
• The instrumentation: the pressure taps and the flow meters of the channels feed the control system: the operator sees the channel flows and the pressures as the direct picture of the flame settings: the recorded settings of the good campaigns are the tuning references;

The primary air is the arm of the burner: the same nozzle with the wrong air velocity loses its efficiency: the fan filters, the duct leaks and the vane wear degrade the air delivery without the obvious alarm: the pneumatic tests of the burner system during the shutdowns verify the channel flows against the design: the file includes the test procedures and the nozzle selection tables.

3. The Coal Firing System: From the Mill to the Nozzle

The pulverized coal is the standard fuel of the cement industry, and its preparation equipment is part of the burning equipment: the coal must arrive at the burner at the right fineness, the right dryness and the right rate:

• The coal mill: the ball mills with the hot gas drying and the vertical roller mills grind the coal to the fineness of 2 to 5% residue on the 90 micron screen (for the kiln firing: the calciner accepts the coarser 5 to 10%): the grinding of the coal is a mill discipline of its own;
• The drying: the coal moisture is dried with the hot gas from the cooler or the auxiliary hot gas generator: the mill outlet temperature is controlled: the temperature and the flammability of the coal dust: the fire and the explosion protection of the coal grinding plant;
• The transport: the pulverized coal travels to the kiln burner and the calciner by the dense-phase or the lean-phase pneumatic conveying: the conveying air quantity is constant, the coal feed metered by the loss-in-weight feeders or the rotary feeders: the stable feeding of the coal is the precondition of the stable flame;
• The storage: the pulverized coal silos with the inert gases, the level measurement and the explosion venting: the retention of the fine coal is a fire risk: the silo management, the nitrogen purging and the temperature monitoring are the safety equipment of the storage;
• The feed metering: the weigh feeders deliver the setpoint rate with the accuracy of 1 to 2% : the coal rate is the primary manipulated variable of the burning zone control: the metering stability is measured in the coal flow signal, and the operators read it as carefully as the temperatures;

The coal system is the heart of the fuel logistics: the coal mill outage stops the kiln as surely as the burner failure: the plants keep the coal circuit redundancy, the standby mills and the alternative fuel capability: the coal quality, the moisture and the calorific value enter the burning calculation of every shift: the equipment of the coal firing is operated with the safety of the dust explosion constantly in mind.

4. The Firing Systems: Direct, Semi-Direct and Indirect

The connection between the coal mill and the burner defines the firing system of the plant, and the three classical arrangements have their operating characters:

The choice of the system follows the reliability requirements and the fuel strategy of the plant: the indirect systems protect the kiln from the mill outages and the air surges; the direct systems save the capital and are common with the stable fuel supplies: the firing system diagrams of the file show the air and the fuel flows of each arrangement with the control loops: the conveying air of the direct systems is an operating constraint, because it enters the primary air envelope and changes the flame settings with the mill load.

5. The Gas and Oil Firing Equipment: The Alternate Burners

Many kilns start on the natural gas or the fuel oil, and the plants with the gas infrastructure fire it as the main fuel: the liquid and the gaseous firing equipment differs in its details but shares the burner platform:

• The gas lance: the central gas tube with the radial or the axial injection nozzles inside the burner nozzle: the gas exits at 100 to 250 m/s: the gas flame is shorter than the coal flame, and the burner momentum for the gas needs the additional air momentum to reach the same flame length;
• The oil lance: the oil is atomized at the nozzle tip by the air or the steam at 6 to 12 bar: the oil lance slides inside the burner with the atomizer: the spray angle and the droplet size fix the oil flame shape: the atomization quality decides the combustion efficiency;
• The oil heating system: the heavy fuel oil is heated to 90 to 130 °C to reach the pumping viscosity: the fuel oil heaters, the filters and the recirculation loops form the oil circuit: the viscosity control at the nozzle is the primary oil setpoint;
• The dual fuel capability: the burners with the central gas passage and the surrounding oil channels switch the fuels while running: the changeover procedures are the drilling exercises of the control room: the ignition and the stabilization of the second fuel require the preplanned sequence;
• The atomization air or steam: the atomizing medium at the nozzle tip breaks the oil into the droplets of 30 to 100 microns: the air atomization suits the small burners, the steam atomization the large heavy-oil burners: the atomizing medium ratio is 0.1 to 0.5 kg per kg of oil;

The fuel switching capability is the strategic flexibility of the plant: the fuel price differences between the gas, the oil and the coal justify the multifuel burners in the markets with the volatile supplies: the firing equipment of the file covers the sizing of the lances, the atomizer selection and the changeover procedures for the three fuel families.

6. The Auxiliary Burners: The Start and the Insurance of the Kiln

Besides the main burner, the kiln firing equipment includes the auxiliary burners that operate in the defined windows of the kiln life:

• The startup burner: the small fuel-oil or gas burner installed at the kiln nose or through the hood for the kiln heat-up: it fires during the start curve and the refractory dry-out, then withdraws when the main burner takes over: the startup burner capacity is 5 to 15% of the full load;
• The kiln insurance burner: the fixed auxiliary burner that holds the kiln temperature during the short coal supply interruptions: the insurance burner prevents the cooling and the coating loss of the burning zone: the oil systems of the plants keep the insurance capability as the standard;
• The altemp (alternative fuel) burners: the separate lances for the liquid alternative fuels in the kiln and the calciner zones: the waste-derived liquids are burned at the side positions to protect the main burner passages from the corrosion and the blocking;
• The calciner burners: the firing devices of the calciner vessel, the lances and the injection units that receive the coal, the gas or the alternative fuels: the calciner burners run the rich-lower staged combustion of the LowNOx design: the calciner firing equipment serves 55 to 65% of the total fuel;

The auxiliary burners are the reserve team of the firing: they must be ready exactly when the main system stumbles: the monthly test firing, the atomizer inspection and the stored light-up procedures keep them alive: the insurance burner of a kiln that never tests its oil system is the insurance that does not exist: the file carries the auxiliary burner sizing and the test schedules.

7. The Flame Detection and the Burner Safety: The Management System

The burner is a controlled furnace: the burner management system decides when the fuel may flow and when it must stop, and its logic is the explosion prevention of the kiln:

• The flame scanner: the photoelectric detectors at the burner nose or the kiln hood watch the ultraviolet and the infrared signal of the flame: the scanner distinguishes the burner flame from the radiation of the hot kiln and the calciner flame: the flame failure signal closes the fuel valves within seconds;
• The fuel valve trains: the double block valves with the vent between them on the gas and the oil lines: the valve leakage tests and the limit switches: the valve train is the mechanical guarantee of the fuel shutoff: the purge to the safe location;
• The purge sequence: before the ignition the kiln is purged with the air for the predefined minutes at the predefined flow to sweep the accumulated fuel and the combustible gas: the purge is the mandatory first act of every light-up: the purge timers cannot be bypassed;
• The ignition interlocks: the fuel may flow only when the flame scanner confirms the ignition source and the draft is available: the interlock matrix reads the fan status, the damper positions and the scanner states: the bypass of the interlock is the forbidden act of the control room;
• The alarms and the trips: the flame loss, the high CO, the low draft and the fuel pressure anomalies trip the firing: the trip logic of the kiln burner differs from the mill burners: the trip responses are rehearsed: the firing safety of the kiln follows the same strict doctrine as the boilers of the power industry;

The burner management is the non-negotiable equipment of the firing: the fuel explosions of the kiln systems, although rare, have destroyed the hoods and injured the crews when the purge and the interlocks were defeated: the safety audits of the burning equipment verify the valve trains, the scanners and the logic annually: the safety of the firing is the first page of the operating manual, and the file of the package reproduces the complete safety documentation system.

8. The Burner Maintenance: The Nozzle, the Vanes and the Lance

The burner works in the hottest and the dirtiest corner of the kiln: its maintenance is the scheduled work of the shutdowns:

• The nozzle inspection: the nozzle channels erode from the coal abrasion and the heat: the channel diameters grow and the velocities fall: the nozzle inspection at every stop and the replacement on the wear criteria: the worn nozzle silently changes the flame shape;
• The vane and the swirler: the swirl vanes foul with the clinker dust and the ash: the vane angles and the freedom of the movement are checked: the stuck vanes freeze the flame shape at the wrong setting: the vane mechanism is the moving part that the maintenance must keep alive;
• The lance wear and the withdrawal: the burner lance slides from the kiln nose on the retract system: the lance supports, the seals and the damper must move freely: the stuck burner at the full load is the repair with the hood open and the kiln hot: the bowers and the retract strokes are tested at every opportunity;
• The refractory at the nose: the burner pipes pass through the nose ring refractory: the castable and the air seals around the burner are repaired with the firing equipment: the false air of the burner opening disturbs the secondary air and the flame;
• The primary air fan: the fan impeller, the filters and the silencers are on the annual maintenance list: the fan curve verified against the design after the overhauls: the channel pressures of the adjusted burner are recorded for the comparison of the campaigns;

The burner maintenance budget is small beside the kiln refractory, but its neglect costs the flame quality and the NOx and the clinker: the as-built records of the nozzle settings, the vane positions and the channel pressures belong to the quality system of the pyro line: the good burner maintenance is invisible and priceless.

9. The Operating Parameters of the Firing Equipment: The Control Envelope

The burning equipment delivers its setpoints through the control system, and the operating envelope of the firing is the daily contract between the operators and the equipment:

The envelope is the compromise of the combustion, the emissions and the refractory: the operators tune inside the band, and the deviations outside the band are the working hypotheses of the investigation: the firing equipment records from the control system, the scanner signals and the mill data form the complete diary of the flame.

10. The Alternative Fuel Burning Equipment: The Waste Economy

The alternative fuel programs have reshaped the burning equipment: the kilns fire the solid recovered fuels, the tire chips, the plastics, the solvents and the sludges, and each waste stream brings its own feeding machine:

• The solid fuel feed systems: the shredded and sieved solid recovered fuels are metered by the rotary feeders and the screw conveyors into the lime channels of the calciner or through the kiln feed lances: the particle size limit of the kiln feed is 10 to 30 mm, of the calciner feed up to 50 mm: the oversize material must be rejected before the metering;
• The whole-tire feeding: the tire chips or the whole tires are fed through the special feed gates in the kiln inlet or the calciner riser wall: the feed gates with the double flap valves maintain the gas seal: the tire feeding rate is limited by the combustion time and the local process conditions;
• The liquid waste burners: the hazardous liquid wastes, the solvents and the waste oils are atomized with the dedicated lances in the kiln nose: the liquid quality control, the heating and the filtration protect the atomizer: the waste burners carry their own flow meters and shut-off valves;
• The sludge co-processing: the dewatered sewage sludge is fed to the calciner or the kiln with the pipe systems: the sludge reduces the flame temperature and increases the water vapor: the feed rate limits protect the process stability and the emissions;
• The safety of the waste firing: the waste bins with the nitrogen blanketing, the fire detection and the explosion venting: the refuse-derived fuels are the fire risk of the storage areas: the feed interruption valves and the chute jam detectors: the waste handling is the new safety frontier of the burning equipment;

The alternative fuel equipment replaced a share of the fossil fuel burners in the plants with the strong waste programs: the thermal substitution rates of 30 to 80% exist across the industry bands, and the burning equipment of those lines includes the complete waste receiving, the storage, the dosing and the feeding systems: the file of the package documents the alternative fuel equipment selection, the feed point design and the emission monitoring of the co-processing lines.

11. The Equipment Sizing of the Burning System: The Design Logic

The burning equipment is sized from the fuel demand and the air balance of the line, and the design logic runs in the fixed steps:

• The heat demand: the clinker production times the specific heat consumption of 2900 to 3600 kJ per kg of clinker gives the total firing capacity: the fuel split to the kiln and the calciner follows the calcination chemistry: 35 to 45% to the main burner, 55 to 65% to the calciner;
• The fuel flow: the fuel rate is divided by the calorific value of the design fuel: the low-calorific alternative fuels multiply the mass flows: the transport and the metering equipment are sized for the highest-volume fuel of the strategy;
• The air balance: the combustion air of the burner and the calciner, the primary air share and the cooler air recovery close the air balance: the fans and the ducts are sized on the worst case of the fuel mix: the draft and the pressure losses of the firing path;
• The burner capacity margin: the main burner sized for 110 to 120% of the design fuel rate to cover the fuel quality swings and the partial load operation: the nozzle exchange range covers the gas, the oil and the coal without the burner replacement;
• The redundancy philosophy: the standby fuel pumps, the spare lances and the mill redundancy: the burning equipment availability is designed to match the kiln availability target: the weakest link of the firing chain sets the availability of the line;

The sizing documents of the file lead the engineer through the heat demand, the fuel flow, the air balance and the equipment selection tables: the plants that add the alternative fuels later recompute the same sizing for the new fuel portfolio: the burning system design is never frozen, because the fuel portfolio of the cement industry is still moving.

12. The Commissioning and the Performance Tests of the Burner

A new burner enters service through the commissioning sequence, and its performance is proven by the measurable tests, not by the impressions:

• The cold flow tests: the nozzle velocities, the channel flows and the swirl settings are measured before the ignition: the air distribution of the channels compared with the design: the cold tests catch the assembly errors at the cheap stage;
• The flame observation: the first light-ups observe the flame shape, the color and the stability through the viewing ports and the cameras: the flame length and the radiation are adjusted with the vane and the nozzle settings: the observations recorded on the standardized sheets;
• The performance indices: the specific heat consumption, the free lime of the clinker, the NOx and the CO of the emissions: the burner adjustment is optimized against the four: the tests at the defined load points build the operating map of the burner;
• The fuel changeover tests: the switch between the coal, the gas and the oil is rehearsed at the reduced load: the transient states of the flame and the temperatures are documented: the changeover procedures become the certified operating documents;
• The acceptance criteria: the commissioning report compares the measured figures with the design targets: the acceptance of the burner follows the documented evidence: the preparation of the report is the completion ritual of every firing project;

The performance test is the birth certificate of the burner setting: the recorded operating map guides the operators for the life of the equipment: the file of the package includes the test protocols, the observation sheets and the acceptance templates that the commissioning teams of the projects reuse on every kiln.

13. The Frequently Asked Questions

What is the difference between the primary and the secondary air?

The primary air is injected by the burner itself with the fuel: typically 6 to 12% of the total combustion air: the secondary air is the hot air drawn from the cooler through the hood around the burner: its share is 15 to 30%: the tertiary air goes separately to the calciner: the three streams form the air balance of the combustion.

Why do the modern burners use less primary air?

The low primary air raises the flame temperature because less cold air dilutes the combustion, and it reduces the NOx because the flame peak temperature is moderated by the recirculation instead of the dilution: the low primary air designs achieve the same flame control with the high momentum jets: the economy and the emissions both favor the low primary air.

How does the coal fineness affect the kiln firing?

The coarse coal falls out of the flame before the burn-out, settles on the clinker bed und burnt and raises the total carbon and the heat loss: the fine coal burns fast in the short flame: the kiln firing target of 2 to 5% residue on 90 micron balances the mill cost against the combustion quality: the calciner tolerates the coarser fractions.

What happens if the flame scanner fails during the operation?

The burner management system does not allow the fuel firing without the confirmed flame signal: the scanner failure trips the firing or demands the immediate shutdown of the fuel until the scanner is restored: the scanner maintenance is a safety task, and the spare scanners sit in the plant stock for the instant replacement.

Can one burner fire the gas, the oil and the coal at the same time?

The multichannel burners fire the combination of the fuels: the coal in the central channel with the gas or the oil through the auxiliary passages: the fuel ratios are controlled together and the changes are staged: the co-firing changes the flame, and the control system and the operators manage the transitions: the flexibility is the modern standard.

Does the package include the burner design tools?

The Complete Cement Technical Package includes the burner and the firing system documents: the multichannel burner sections, the firing system diagrams and the sizing spreadsheets: the engineers use the configuration tables and the performance checklists of the package: the 931 files of the package, the tools included.

14. Conclusion

The kiln burning equipment: the multichannel burner and its air, the coal preparation and the transport, the gas and the oil lances, the auxiliary burners and the burner management system: the firing arsenal of the pyro line converts the fuel into the flame and the flame into the clinker: the operator who knows the equipment knows the settings, and the engineer who maintains it keeps the flame true: the burning equipment, properly sized, tested and protected, is the quietest and the most profitable machine of the plant.

The Complete Cement Technical Package includes the kiln burning equipment guide with the burner drawings, the firing system diagrams, the selection tables and the safety checklists: the one-time 249.99: the instant download: the library of the cement: the firing file: the work of the professional: the cement knowledge, the measured: the burner of the package, the flame of the plant: the career of the engineer, fired right.

This file is part of the Complete Cement Technical Package (931 files) available from cementequipment.org. Respective rights holders; library copy for the licensed single user.