PYROPROCESS TECHNOLOGY COURSE

The basic cement kiln system comprises a preheater in which feed material is prepared by heat exchange with hot exhaust gas, a fired rotary kiln in which the clinkering reactions occur, and a cooler in which the hot clinker exchanges heat with ambient combustion air.

The kiln system has to be designed to cope with the chemical process requirements during which the kiln feed material is converted into cement clinker.

This process as a whole is endothermic and takes place at maximum material temperatures of 1450 °C. Receiving its thermal energy from hot gases of up to 2000 °C generated by combusting fuels is also referred to as pyroprocess.

Type of reaction and temperature development is compiled in “sequence of reactions occurring in a rotary kiln” (table 1) and graphically as the “quasi-qualitative variation of minerals with temperature.”

Kiln feed is subject to successive reactions as its temperature increases:

• 100 °C Evaporation of free water
• 500 °C Evolution of combined water
• 900 °CCaCO3 -> CaO + CO2
• 900 °C Reactions between CaO and Al2O3, Fe2O3 and SiO2
• 1200 °C Liquid formation
• 1280 °C Formation of C3S and the complete reaction of CaO   

The chemical process taking place in the kiln system where raw meal (input) is converted to cement clinker (output) can be subdivided into the following five steps:

1. Drying
2. Preheating
3. Calcining
4. Sintering
5. Cooling

Process and equipment have been developed and improved to perform these steps forever improved economy, which means:

• High availability
• Low heat consumption
• Low power consumption
• Higher unit capacity
• Stable kiln operation
• Good, uniform clinker quality

General Kiln Conditions

Description of Main Kiln System – Kiln Operation Priorities – Kiln System Stability – Main Parameters, Trends, and Absolute Values – Main Parameters to Control and Evaluate Kiln – Variables which the Operator Cannot Control – Variables which the Operator Can Control – Kiln Limitation Factor – Kiln Operation Target – Optimization of Kiln System – List of Most Frequent Factors when Kiln Operation Is not Satisfactory – List of Typical Kiln Operation Problems – What to Look for When Looking Inside a Kiln – Kiln Upsets – Kiln Cycling – How to Break a Cycle in a Kiln.

Kiln Emergency Conditions

Red Spot on Kiln Shell – Raw Unburned Feed-in Clinker Cooler – Large Ring Broken Loose in Kiln – Burning Zone Dangerously Hot – Sudden Sharp Rise in Back End Temperature – Black Smoke Emission from Kiln Stack – Distorted Flame Shape – Loss of Section of Refractory Lining – Cooler Drive or Clinker Conveyor Stopped – Red Clinker at Cooler Discharge – Rapid Rise of Temperature in Coal System – Power Failure – Heavy Rain or Thunder Storm – Sudden High Positive Pressure – Overheated Kiln Bearing – Kiln Hazardous Conditions.

Kiln Operation

Kiln Operation Techniques – Burning Zone Evaluation – Kiln Stable Temperature Profile – Target Set Point and Operation References – Back End Temperature Control – The Three Basic Variables – Target Range for the Three Variables – The Three Basic Conditions – The 27 Conditions (Kurt Peray) – Kiln Slow Down – Normal Operation Procedures on Shift – Plan of Action – Oxygen Level in Automatic Mode.

Kiln Start-Up and Shutdown Procedures

Light-up Flame Example (Gas) – Preheat or Drying of Refractory Lining – Heating to Reach Temperature Ready to put Feed On. – Feed On – Kiln Start-up Procedures after a Brick Job – Example of How to Re-start if Preheat is Required – Example of How to Re-start if No Preheat is Required – Kiln Shutdown General Information – Cooling Procedures – Kiln Rotation Schedule – Burner Pipe and Hood Protection – Emptying the Feed from the Kiln – Kiln Shutdown Procedures for Brick Job and Red Spot.

Cooler Section

Cooler Function – Cooler Operation – Cooler Controllers – Rule on Cooler Operation – Main Sensors to Control the Cooler Operation – Particle Size of Clinker – Operation of Cooler Fans – Clinker and Air Distribution.

Combustion

Flame – Rules on Flame – Combustion – Heat Transfer in Rotary Kiln – Burner Pipes and Nozzles – Fuels in Cement Industry – Solid Fuels – Drying, Grinding and Firing Solid Fuels – Comparison of the Three Major Fuels – Combustion Reaction – Non-Combustibles (Ash).

Basic Principles

Basic Principles, System of Units – Temperature Scale – Some Useful Conversion Factors – Basic Principles, Pressure, and Flows – Basic Principles, Heat, and Temperature – Basic Principles, Heat Exchange or Transfer