How to build a small vertical shaft lime kiln
Practical Action
Day 11:
Day 12:
Day 13:
Day 14:
Day 15–21:
Day 22–24:
Day 25–26:
Day 27–31:
Day 32:
Brick up to kiln floor slab.
Fix floor slab reinforcing mesh and starter bars for draw box sides. Cast
floor slab.
Fix reinforcing, shutter and cast sides to the draw box. Cure floor slab.
Shutter, fix reinforcing and cast roof of the draw box. Leave the side
shutters
in place. Cure floor slab and sides.
Cure floor slab, draw box sides and roof slab.
Build kiln shaft and outer casing, insert inspection pipes,
fill cavity with vermiculite concrete. Leave the draw box shutter in place
and prop the draw box roof slab.
Cast shaft ring beam. Shutter, fix reinforcing and cast platform slab.
Fix tension bands. Erect chimney and bolt in position. Plaster external
kiln face. Remove draw box props and remove the shutters.
Fix platform handrails. Complete infrastructure. Paint kiln metal work.
Operation
Once the kiln has been lit, limestone – broken into suitable size pieces – is fed into the top
with a measured amount of fuel: this process is called ‘mixed feed’. It is up to individual
lime burners to decide the best size for their particular limestone and the quantity of fuel
needed. The limestone travels down the shaft, burns and changes to quicklime. At regular
times, cool quicklime is taken out of the bottom of the kiln. Fresh limestone and fuel is
then loaded into the top.
Capacity and output
When it is full, the kiln will hold about one and three quarter tonnes of limestone and coal.
The daily output will be between 1 and 1 ½ tonnes of quicklime.
Efficiency and fuel use
The efficiency of any lime burning process can be calculated using a formula. 2 For the
Chegutu VSK it is possible to reach an efficiency of more than 40%.
As a brief practical guide, it has been found that the VSK in Chegutu produces good quality
lime when the limestone to coal ratio is about 7.5:1. That is, for every tonne of coal used
the kiln will burn about 7.5 tonnes of limestone. The stone used at Chegutu has a
diameter between 100 and 140mm. The kiln is operated with the shutter door one third
open. Lime burners will have to use their knowledge of their particular stone and
experiment to find out how much fuel they need to produce quicklime which is well enough
burned for their needs.
References and further reading
Lime - An Introduction Practical Action Technical Brief
Hydraulic Lime - An Introduction Practical Action Technical Brief
Methods for testing lime in the field Practical Action Technical Brief
How to calculate the Energy Efficiency of Lime Burning Practical Action Technical
Brief
Testing methods for pozzolanas 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
A Case Study in Lime Production No2 Improved Techniques at Chenkumbi,
Malawi. Practical Action Technical Brief
Lime and Alternative Binders in East Africa Elijah Agevi et al, Practical Action
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