HOW TO BUILD A
SMALL VERTICAL SHAFT LIME
KILN
AN EXAMPLE OF A CONTINUOUS PRODUCTION, MIXED FEED KILN
FROM ZIMBABWE
Introduction
In 1996 the Intermediate Technology
Development Group (Now known as
Practical Action) in partnership with
G&W Industrial Minerals Pvt. (Ltd)
built a continuous, mixed feed,
vertical shaft lime kiln at Chegutu in
Zimbabwe. Burning the calcitic
limestone from Chegutu, this kiln can
produce high-grade quicklime, which
is suitable for metal processing,
building, water purification and other
purposes. The kiln works well and
these notes give guidelines about how
to build it. The notes are a practical
guide to builders but naturally cannot
deal with every detail. Also, we can
only consider this particular size of
kiln. Anyone who wants to build a
bigger one should seek further
advice. Vertical shaft kilns (VSKs)
are not suitable for all types or sizes
of limestone. Soft material will crush
under the weight of stone in the
shaft, and fine material will not allow
enough air to flow through the kiln.
So, lime burners must consider
carefully before deciding if a VSK is
the right choice of technology for
them.
Design
The principle behind the design of
shaft kilns is that the height of the
Figure 1: The vertical shaft kiln built for Practical Action
in Chegutu, Zimbabwe. Photo: Kelvin Mason/ Practical
Action.
shaft should be at least six times the
diameter. The Chegutu kiln is designed for small-scale producers who want to start
continuous production of high-grade lime with the minimum investment cost. It uses
natural draught – there is no fan to ‘pump’ the air through the kiln. A chimney is used to
provide enough natural draught and to take smoke away from the loading area where
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