A small kiln for batch & continuous firing
Practical Action
In both batch and continuous operation the loading port and output port are sealed with bricks
and mud mortar during firing.
Capacity and output
A traditional box kiln would typically have a capacity of more than 15 cubic metres. The
experimental Dedza kiln has a capacity of only 3 cubic metres. This could be increased to 12
cubic metres if the sides of the internal shaft were doubled in length to 2 metres. When used
for batch burning the Dedza kiln would be suitable for rapid production of small quantities of
good quality lime. Fully charged it holds 1620 kilograms of limestone and about 1400
kilograms of dry pine firewood. So the output should be 900 kg of quicklime, giving around 1
190 kg of hydrated lime.
Efficiency and fuel use
The efficiency of traditional box kilns varies, but results obtained in Malawi suggest it is
typically less than 10%. As a batch kiln the experimental Dedza kiln has achieved 15%
efficiency producing much higher quality lime. In continuous operation the experimental kiln
has achieved similar efficiencies and product quality. Scaling up the design to 12 cubic
metres would be expected to improve performance. Interestingly, this research indicates the
way to further improve performance would be to develop small, continuous vertical shaft kilns
(VSKs).
Reference and further reading
• How to Calculate the Energy Efficiency of Lime Burning, Practical Action Technical
Brief.
• How to Build a Small Vertical Shaft Lime Kiln, Practical Action Technical Brief
• Lime Kiln Designs: Small & Medium Scale Oil Fired Lime Kilns Practical Action
Technical Brief
• A Small Lime Kiln for Batch and Continuous Firing Practical Action Technical Brief
• The Small Scale Vertical Shaft Lime Kiln: A practical guide to design, construction
and operation, Kelvin Mason, Practical Action Publishing, ISBN 9781853394652
• Small-scale Lime-burning: A Practical Introduction Michael Wingate, Practical Action
Publishing, ISBN 9780946688012
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