Precalciners

Precalciners are devices used in cement production to perform calcination of the raw meal before it enters the rotary kiln. By using heat from the kiln exhaust gases, precalciners decompose calcium carbonate into calcium oxide and carbon dioxide at temperatures around 900 to 980 degrees Celsius. This pre-calcination reduces the energy load and time required in the primary kiln, enabling higher throughput and more efficient fuel use.

Most modern precalciners are integrated with dry-process kilns and fall into two common designs. Cyclone precalciners, including multi-stage cyclone precalciners, use a series of cyclone separators and combustion zones to ensure the raw meal is thoroughly heated and calcined while contacting hot gases. A separate burner may provide additional heat and fuel gas to drive calcination. Vertical shaft precalciners, or shaft calciners, pass the raw meal downward through a tall shaft where it encounters rising hot gases, achieving calcination before the material reaches the main kiln.

Advantages of precalcination include lower heat requirements for the kiln, increased production capacity, improved raw mix diversion for better calcination control, and potentially reduced kiln dust emissions. However, precalciners entail higher capital and maintenance costs and add system complexity, requiring careful process control to maintain consistent calcination and material quality.

Precalciners are a hallmark of dry-process cement plants and are widely used to optimize energy efficiency and throughput in modern cement manufacturing.