Cooking with Charcoal

What is Charcoal - Introduction

Charcoal is a solid biomass fuel obtained through the carbonization (also called pyrolysis) of wood. It has an average energy content of 30 MJ/kg. In comparison, firewood has an average energy content of 18 MJ/kg average. Just considering the energy content of firewood and charcoal, one might come to the conclusion, that charcoal is the more preferable cooking fuel. But the carbonization of firewood into charcoal also requires energy. Assuming an average kiln efficiency between 10% - 30%, the conversion of 1kg wood yields only 0.1 – 0.3 kg of charcoal. In other words, in order to produce 1 kg of charcoal with a specific energy content of 30 MJ/kg, 3.3 to 10 kg of firewood is required, which would otherwise have a total energy content of 60 to 180 MJ. Therefore, by using charcoal instead of firewood, one loses between two to six times the total amounts of energy contained in the original firewood.

Right after production charcoal has moisture content less than 1%. Charcoal absorbs quickly moisture from the air, which can lead to a moisture content between 5% – 10%. Rain or watering by charcoal dealers to raise the weight of the charcoal can increase the moisture content even higher. However, moisture content should be kept low to prevent the energy loss, which is required to evaporate the water while burning charcoal.

How is Charcoal Produced?

During the carbonization process high temperatures induce the absorption of heat which leads to the complete decomposition of the wood, separating it into volatile gases, vapors and solid char. At 400°C, the transformation of the wood into charcoal is practically complete. At this stage, however, the charcoal still contains a considerable amount of tar, of around 30%. In order to achieve a final carbon content of around 75%, which is desirable for good commercial quality, additional heating is required to drive off the tar and to increase the fixed carbon content. For the conversion of wood into charcoal the use of a “kiln” is necessary. The most common types of kilns are earth pits or mound kilns. Their efficiency ranges between 8% - 12%. Improved kilns with a higher efficiency between 25% - 40% are Casamance Kiln, Brick Kiln, Steel Kiln and the Adam Retort. For more information on kilns, see also the article on charcoal production.

The energy efficiency of the carbonization process as well as the quality of the charcoal is dependent on many factors, such as:

• the type of kiln (open pits, earthen kilns or steel cylinders – also called retorts),
• moisture content,
• wood species and wood stacking,
• production skills of the producer.

Global production of wood charcoal was estimated to be 47 million metric tonnes in 2011. Since 2003, global production of charcoal has increased by 11%. Charcoal demand is expected to continue to grow, especially in low-income countries, due to population growth combined with increasing urbanization. More than 80% of this wood-based energy is used for domestic purposes. In developing countries the charcoal market takes often place in the informal sector and the supply chain involves a number of various actors. There are generally two types of charcoal producers: the independent / occasional farm producers who are members of a community in which charcoal production takes place. And, the employed producers who are outsiders of this community. Community-based producers sell their goods to wholesalers, transporters on the roadside or directly to retailers. Employed producers outside of a community are contracted by wholesalers in exchange for monthly payments or for produced charcoal. Often a small group of transporters and wholesalers earn the highest profits.