Holcim (New Zealand) Ltd - How cement is made (dry process technology)

Limestone and silica-rich sand or rock is quarried and crushed, and transported to storage stockpiles near the kiln where pre-blending takes place.

The raw materials are dried, ground and mixed to form a fine, homogenous powder, with moisture content of less than one percent.

This powder is fed into the kiln where the heat promotes the necessary chemical reactions. The kiln exhaust gases are the main source of heat used to dry the raw materials.

This is known as 'dry process' technology (ie. no water is added to the ground raw materials) and is used by modern cement manufacturing plants.

Older cement kilns use a wet process, where the ground material is mixed with water to produce slurry, which is then fed to the kiln.

A modern 'dry process' plant uses approximately half the energy of a 'wet process' plant.