2. Loading shovel
7. Blending and storage silos
8. Conditioning tower
9. Electrostatic precipitator
12. Coal silos
13. Clinker storage
15. Cement silos
16. Rotary bagging machines
17. Bagged-cement despatch
18. Bulk cement despatch
19. Palettisation (palettes or packet-packed - plastic packing)
After they are quarried the raw materials (limestone, marls, etc.) are first crushed and then move on to an initial blending stage (pre-blending).
These raw materials, possibly with several additives (sand, pyrite ash, limestone of high lime content, etc.) are simultaneously dried and crushed until a very fine powder is obtained, which is then batched and stored.
Various fuels are used in the cement industry, the most common being coal and pet-coke.
Both require preliminary grinding to allow their injection into and ignition in the kiln, providing an optimal thermal gradient.
Proper heat treatment transforms the powder into an intermediate product - clinker - in which the mineralogical constituents of cement can be found.
On leaving the blending silos the powder passes through a heat exchanger (cyclone tower), passing through the hot gases leaving the kiln and beginning the process of carbon removal.
Next, the burning (or clinkerisation) of the powder takes place in the cylindrical rotary kiln (a refractory-lined steel tube that slopes slightly to allow the powder to slip down), in which the temperature is higher than 1,500ºC, giving rise to the clinker. The clinker is then cooled quickly to stabilise its structure and to allow partial recovery of the heat.
Taking into account the way in which it is formed, clinker is an artificial igneous rock that is the main constituent of cement.
The dust is removed from the hot gases leaving the cyclone towers before dispersing into the atmosphere.
Very fine grinding of the clinker together with a binding regulator (gypsum) and perhaps other additives (limestone filler, fly-ash, steel-mill slag, etc,) gives rise to the various types of cement that meet the various standards.
Storage and Despatch
The cement is then pumped to storage silos and it may then be sold in bulk or packed in paper bags that are shipped out on pallets or packet-packed. Despatch can be by lorry, train or ship, as necessary.