Calcium Carbonate Production from Limestone

The process under analysis comprises four major sections: (1) Calcination; (2) Carbonation; and (3) Finishing.

Calcination. Initially, the limestone from a quarry is stored in bins. It is assumed that the limestone extracted contains about 75 wt% calcium carbonate. The limestone is then crushed in a jaw crusher and calcined (burned) in a vertical shaft lime kiln at about 1,000 °C. The calcium carbonate present in the limestone is decomposed into calcium oxide (lime or quicklime) and carbon dioxide, which is captured and treated for further reuse in the process.

Carbonation. The lime formed is fed to a stirred slaker tank, where it is hydrated (slaked) with water, forming a calcium hydroxide slurry (slaked lime or slake). Before carbonation, the impurities (silica and other oxides) originating from the limestone are separated from the slake, producing a pure slaked lime. The pure slaked lime is then fed to a set of atmospheric stirred reactors, where it is diluted and subsequently reacted with the recovered carbon dioxide, generated in the lime kiln. The carbonation reaction is regulated by the equilibrium of the solution: as the calcium ions are converted to calcium carbonate and precipitated out, more calcium hydroxide dissolves to equalize calcium ions concentration.

Finishing. The slurry from the carbonators is sent to a filter press, which removes most of the water. Recovered water is recycled for further use in the slaking step. The Precipitated Calcium Carbonate (PCC) from the filter is dried with hot air, deagglomerated in grinders, packed and stored.