Igloo type brick kilns in Zimbabwe
Practical Action
and Efficiency in Building Materials Production, by A. Russell, 1996). Net calorific value of coal
used was in the order of 30 MJ/kg.
Thermal efficiencies of the igloo kilns studied, on the basis of a theoretical energy input
requirement of 110 kJ/kg and specific heat capacity of clay of 1 kJ/kg °C (Ceramic Technology,
Volume 9), using formula would range from 15 to 25 %, which is definitely low by any
standards.
η = Theoretical energy input requ. x 100%
Total energy input
If the value of the theoretical energy requirement had been taken as 850 kJ/kg according to
Barringa, et al (1992), the efficiencies would be even lower.
The efficiency of these kilns is affected by the lack of adequate control of the air-to- fuel ratio, as
evidenced by dense masses of black smoke during fuel charging. The air-to-fuel ratio is always
lean, due to the fact that the high firebed resistance limits the supply of primary air, and limited
space above the fire bed denies access of secondary air.
The combustion gases emitted from the beehive kilns recorded the following aver-
age figures:
• Sulphur dioxide (S02) 0.42 ppm
• Carbon monoxide (CO) 230 ppm
• Carbon dioxide (C02) 2,215 ppm
• Nitrogen oxides (NOx) 0.153 ppm
Maintenance aspects
Igloo/beehive kilns require regular maintenance of buffer walls, which are often damaged during
the firing cycle. Flue channels would also require regular inspection to ensure that there are no
blockages.
This brief was originally prepared for the Building Advisory Service and Information Network
– BASIN by Peter Tawodzera of ITDG Zimbabwe (now Practical Action Southern Africa).
Practical Action
The Schumacher Centre
Bourton-on-Dunsmore, Rugby, CV23 9QZ, United Kingdom.
Tel: 44 (0) 1926 634400
Fax: 44 (0) 1926 634401
E-mail: infoserv@practicalaction.org.uk
Website: http://www.practicalaction.org
This Technical Brief is an output from a project funded by the UK Overseas Development Administration (ODA),
now called the Department for International Development (DFID) for the benefit of developing countries. The views
expressed are not necessarily those of the DFID. The Technical Brief was made available electronically with the
assistance of The Tony Bullard Trust.
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