HOW TO CALCULATE
THE ENERGY EFFICIENCY OF YOUR
LIME BURNING PROCESS
Introduction
The practice of burning limestone to produce quicklime is, almost literally, as old as the hills.
In terms of basic chemistry and materials, the process involves the conversion of calcium
carbonate, CaCO3, to the more useful calcium oxide, CaO. Calcium oxide is a very reactive
substance. In fact, it is so 'lively' that it is usually hydrated (has water added) to form calcium
hydroxide, Ca(OH)2. Calcium hydroxide is commonly called hydrated or slaked lime, and
sometimes merely lime - which can be
confusing as powdered limestone is often
Types of limestone
referred to in the same way. Hydrated lime
is a more convenient material to handle
Calcite is a limestone which contains only
and use than quicklime. Quicklime and
hydrated lime have a very wide - and well
calcium carbonate, CaCO3. There are other
types of limestone which are of interest.
documented - variety of uses.
Dolomite has the chemical formula
This conversion of calcium carbonate to
CaCO3.MgCO3, i.e. it is a 'mixture' of
calcium and magnesium carbonates in the
calcium oxide is achieved by heating the
proportion 1:1 of their molecules. Dolomitic
limestone to a temperature high enough
limestones are those which contain some
(e.g. 1000ºC in a lime kiln) to 'drive off'
proportion of dolomite. Similarly, quicklime
carbon dioxide, CO2. The equation for this
process, with the approximate molecular
and hydrated lime may contain oxides and
hydroxides of magnesium as well as of
weights, is:
calcium.
100 CaCO3 + Heat <==> 56 CaO + 44 CO2
Continuing the approximation for hydration gives:
56 CaO + 18 H2O <==> 74 Ca(OH)2 + Heat
So, in simple terms, if the process were carried out with 1 tonne of limestone which was pure
calcium carbonate, it should produce 560 kg of quicklime. And if 180 kg (approximately 180
litres) of water were added to this quicklime, then 740 kg of calcium hydroxide should result.
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