CEMENT CHEMISTRY AND CLINKER MICROSCOPY

A 4-week modular course designed to give the course attendee a solid understanding of the cement chemistry and clinker microscopy.

Cement microscopy is a valuable technique for examining clinker, cement, raw materials, raw feed, and coal. Every stage of the cement manufacturing process can be improved through the use of a microscope.

Most cement microscopy is done using a petrographic microscope. Usually, the specimen is a polished section of cement clinker examined using reflected light, although it may be a powder mount, or a thin section examined using transmitted light.

A scanning electron microscope (SEM) may also be used. The combination of SEM with X-ray microanalysis (=EDX, EDS, EDAX) is compelling as it enables the analysis of individual crystals or particles.

Important characteristics the microscopic examines include:

• Overall nodule microstructure – dense, porous, dense micronodules interconnected by tenuous ‘bridges.’ This gives a broad relative indication of burning conditions.
• Alite crystal size – coarse alite may indicate a slow heating rate, excessive burning, or coarse silica in the raw feed; silicate reactivity may be lower than it could be with improved burning conditions.
• Belite crystal size – larger belite crystals suggest a longer time in the burning zone.
• Aluminate and ferrite crystal size – coarse flux phases suggest slow cooling; finer, intergrown flux phases indicate faster cooling. Belite color also shows the cooling rate; fast-cooled crystals are clear, while slower cooling allows impurities to crystallize along lattice planes imparting a yellow color.
• Large clusters of belite or free lime – these may indicate coarse particles in the raw feed.
• The overall distribution of silicates – ideally, belite crystals will be dispersed evenly throughout each clinker nodule, either as individual crystals or in small clusters. If large clusters of belite are present, burnability is likely to be less good, and the clinker will be harder to grind.
• Performa a walk-around inspection of the pyro and other equipment areas.
• Observe the PH, kiln, and cooler, roll crusher, and coal mill operations.
• Intervene the system at various locations and collect field data, if needed.
• A baseline evaluation for the current Production and Specific Fuel Consumptions.
• Find the gap in the operations and explore the opportunity to improve the existing processes.
• Conduct a full-blown heat and mass balance, cooler balance, gas balance, volatile balance to benchmark the pyro process operation.
• Analyze the data and process and recommend solutions for improved operations.
• Collect the existing machinery and process design data.
• Perform the process analysis of the feed and product to help with fuel substitution and energy consumption.