Calcination of industrial products in general

Calcination in production

The term calcination is derived from the Latin word calx. The term refers to the decomposition of calcium carbonate (CaCO₃) and its conversion to calcium oxide (CaO) with the release of carbon dioxide (CO₂). The term calcination was once also used for other processes in which metal carbonates or metal hydroxides are decomposed by heat, metal oxides are formed and water vapor or CO₂ is released.

Today the term calcination is used in an even more general sense. The term is often equated with processes used to heat, decompose, dehydrate and decarbonize products. Calcination can thus be defined as all processes in which a solid is heated and thereby converted into another solid, accompanied by the release of gases. These gases mostly consist of H₂O, or CO₂. The most prominent examples of modern calcination processes are listed below:

• Calcination of lithium metal oxides from their carbonate or hydroxide components
• Calcination of inorganic color pigments (often based on Cd, Ti, Ni or Sb systems)
• Calcination of catalyst systems containing heavy metals

Our engineers also have the right solution for many other sophisticated calcination processes.

Basic conditions for successful calcination of your products

As calcination is an endothermic reaction, the solids must be supplied with thermal energy in order to be calcined. Reaction temperatures typically range from 400 to 1000 °C. The calcination temperature depends on the reaction’s enthalpy as well as the material’s crystal structure and bond strength.

The thermal energy required for calcination and the time required for diffusion can be calculated for a known particle size. The smaller the particles, the shorter the time required. Calcination can thus occur very quickly in case of fine powders that are continuously recirculated and in contact with the atmosphere. This is one reason why rotary kilns tend to be used for the rapid calcination of solid powders.

Sequence of different processes in production

A calcination process is often followed by other processes such as sintering, phase transformation or crystal growth. These processes normally require higher temperatures and the product should also not normally be recirculated. Rotary kilns are thus usually no longer suitable for such process combinations. For economic and ecological reasons, it nevertheless makes sense to carry out these processes one after the other in a single heat treatment step. That is why we at ONEJOON build customized roller kilns or pusher kilns that are ideally suited for the subsequent process.

As the material releases gases from its interior during calcination, the calcination must be performed on powdery substances. This is the only way to keep the paths for the diffusion of heat towards the center of the calcination material or powder bed and for the escaping gas to the exterior short. In contrast, large lumps cannot be fully calcined even after long heat treatments. That is why appropriate capsules or crucibles are often used to heat treat the powder.

ONEJOON has the technology and experience required to design and build various sizes of rotary kilns, roller kilns, pusher kilns and other special kilns. We develop, build and supply kiln systems customized to suit your requirements for both simple and combined calcination processes.