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close this bookBoiling Point No. 20 - December 1989 (ITDG - ITDG, 1989, 40 p.)
View the document(introduction...)
View the documentAcknowledgements
View the documentNew Stoves For Old
View the documentKerosene and Gas Stoves in Nagercoil, South India
View the documentKerosene Wick Stoves
View the documentAn Investigation on the Colombian Kerosene Stove
View the documentTrials to Use Mineral Coal from Kiwira Coal Mines in the DUMA Wood Stoves
View the documentEnergy & The Environment in the Third World
View the documentUse Of Non Biomass Stoves In Sri Lanka
View the document''Simply Living''
View the documentLow-Wattage Cookers in Nepal
View the documentBiochar Briquetting & Burning
View the documentSTOVE PROFILE
View the document''Gourd Roots Make Good Fuel''
View the documentThe South Indian Clay Crusher
View the documentNEWS

Trials to Use Mineral Coal from Kiwira Coal Mines in the DUMA Wood Stoves

by Heinz-H Schneiders, CAMARTEC Stove Project, P O Box 764, Arusha, Tanzania, 15 August 1989


At the end of 1987 the Centre for Agricultural Mechanization and Rural Technology (CAMARTEC) and the Special Energy Programme (SEP) of the German Agency for Technical Cooperation (GTZ), initiated a joint project to develop, test, manufacture and disseminate improved wood and charcoal stoves.

By a letter from STAMICO, dated 21 April 1989, CAMARTEC has been requested to participate in a meeting on the increased utilization of mineral coal in Tanzania and discuss the role of different organizations in designing, testing and disseminating appropriate technologies to utilize mineral coal.

During the meeting it was decided, that the CAMARTEC Stove Project should concentrate on the fabrication of stoves which are suitable to utilize mineral coal and on manufacturing of strong and durable cooking pots.
Results of Combustion Trials

Combustion trials were carried out in June 1989 at CAMARTEC, Tengeru, by lighting mineral coal daily in a specially fabricated cast iron combustion chamber of a brick lined community woodstove with a 100 litres aluminium cooking pot which was filled with water.

The periods required to light the mineral coal were found to be rather long in comparison to lighting charcoal or wood. In the DUMA Wood Stoves, wood or charcoal reached an acceptable power output for cooking purposes after 20 minutes. With the Kiwira mineral coal, this lighting period took always more than 60 minutes, sometimes even 120 minutes.

The power output of the mineral coal was found to be significantly below the power output of wood or charcoal. While firing wood in the DUMA stoves it takes up the 30 minutes to boil 100 litres of water starting with a temperature of 20ºC. When Kiwira mineral coal was fired, this period took at least 100 minutes. In two out of five combustion trials with mineral coal, the boiling point was not even reached after 150 minutes.

Finally, it was discovered, that while firing the mineral coal, the combustion and the ash tray contained considerably larger quantities of ashes in comparison to firing of wood or charcoal. The poor performance of the Kiwira mineral coal led to the decision to send 4kg of coal for chemical analysis abroad. The results of this analysis are presented overleaf.

Results of the Chemical Analysis

Solid pieces of mineral coal were selected from various bags of the Kiwira coal up to a quanitity of 4kg coal dust, which is always contained in a coal delivery from STAMICO, was not included in the sample.

As a first step of coal analysis, the sample was separated in two baths of different densities to distinguish clean coal from impure pieces. In the following steps, the ash content, the amount of volatiles and sulphar and the heat values were established. The results of this analysis are presented over.







in g/cm


Content %



Value in kJ/kg

< 1.45












> 1.9






According to the results shown above, the Kiwiral mineral coal, as sold at present, contains only about 55% clean coal (ash content 15%) which is suited for combustion in stoves without ventilation. It contains around 26% of what may be called 'Grade II' (ash content 52%) which may be suited for combustion in ventilated stoves or furnaces only. Around 18% of the Kiwira mineral coal contains over 70% ash is therefore not suited for direct combustion.

Furthermore, the analysis revealed, that only 55% of the coal has a calorific value of more than 26,000kJ per kg which is comparable to the value of charcoal. Due to the high ash content, 45% of the coal has an impurity which slows down or prevents combustion. Therefore, the direct combustion of the presently offered Kiwira coal is rather wasteful and cannot be recommended.

The above results are likely to over estimate the amount of clean coal and under estimate the amount of impurity since only solid pieces without dust have been selected and sent for analysis. The share of dust in a delivery of Kiwira coal is presently estimated to be 15% to 20%.


The Kiwira coal should be cleaned (washed) at the site of the mine before it is sold to the customer. Continuation of the present sale of impure coal will endanger a further demand development and the future positive contribution of mineral coal in the preservation of forest reserves in Tanzania.