Energy efficiency of lime brining
Some limestones are dolomitic, that is they contain
the mineral dolomite, CaCO3MgCO3, in addition to the
CaCO3 which is present as the mineral calcite.
Usually, pure calcitic limestones are preferable but
dolomite can be tolerated provided the quicklime is
well slaked before use.
Figure 1: A traditional lime kiln in
Sudan. Photo: Simon Croxton /
Efficiency of lime burning
Lime burners are generally seeking to produce the
highest quality quicklime possible from their stone
whilst keeping their production costs to a minimum. In
the majority of cases, a very major production cost will
be the fuel used. Thus, the efficiency of the burning
process (as opposed to the whole process of production
which will involve labour costs etc.) is judged by how
much fuel it takes to produce a quantity of quicklime.
For instance, a lime-burner may say “I produced X
tonnes of quicklime using Y tonnes of coal which cost
me Z dollars”. However, in order to compare different
types of kilns using various fuels and producing
quicklime of variable quality, it is necessary to develop
a more universal measure of efficiency.
Kiln or burning efficiency can be determined and
compared using the formula for thermal efficiency
proposed by Robert Boynton, former director of the
National Lime Association in the USA, in his book
‘Chemistry and Technology of Lime and Limestone’:
Figure 2: An improved vertical shaft kiln in
Zimbabwe. Photo: Kelvin Mason / Practical
Thermal efficiency (%) = theoretical heat requirement x available oxide content(%)
total heat requirement