How to Make Charcoal from Agricultural Waste

The Fuel from the Fields (FftF) team developed a method of producing charcoal from previously unused agricultural waste products. Charcoal provides significant advantages over raw biomass fuels because the process of carbonization reduces the particulate emissions, and reduces the risk of developing respiratory infections. Unlike LPG or kerosene, charcoal does not require people to purchase new stoves or change the way they cook.

Charcoal making is a traditional industry across the world – charcoal is an energy dense fuel that can easily be transported from rural to urban environments. Making charcoal requires three conditions:

  • A carbon-rich material (traditionally wood).
  • Heat.
  • Anaerobic conditions (i.e. it must burn without air present).

Traditionally, charcoal is made by cutting down a tree, setting fire to the trunk, and covering it
with soil. The tree carbonizes (turns into charcoal) over 1-3 weeks. The environmental impact is worsened because hardwood trees (those that grow most slowly) make the highest quality

The FftF technology involves filling a metal kiln with agricultural waste (the source of carbon.) This waste is ignited, and later sealed, to create anaerobic conditions. After two hours, charcoal is formed.

The Equipment

All materials are readily available in the developing world; the technology can be manufactured using
simple tools and welding equipment.

  • A 55-gallon steel oil drum. This forms the kiln in which the waste is burned to produce charcoal. A lid for the drum is also needed, which can be made out of scrap metal.
  • A briquette press. This is a small, cheap impact press used to make briquettes from carbonized powder.
  • A long, straight object like a stick – to create a central chimney in the oil drum; it should be taller than the oil drum, and as wide as a fist in diameter.
  • Three bricks or flat stones about the same size.
  • Rice bags or other large bags – to crush the charcoal powder in.
  • Grated cassava, or some other starch – to make strong briquettes, a small quantity of starch binder must be added to the charcoal powder. Grated cassava porridge is ideal, although any other starch (e.g. cornflour or cassava flour) can be used.
  • A basin – to mix the charcoal powder with the starch porridge.
  • Matches – to set fire to the agricultural waste.
  • Sand, mud or dirt – to help create an airtight seal around the drum.

Preparing the Equipment

a. The oil drum

The first time you make charcoal, the 55-gallon oil drum must be turned into a kiln. To do so, cut
one large hole in the top (this is a loading hole), and a number of small holes in the bottom (these
are air holes). The holes in the oil drum may be cut with either a hammer and chisel, or an angle grinder.

The loading hole in the top of the drum may be round or square. The edges of the loading hole should be at least 8cm from the edge of the drum, providing enough space for the lid to rest on. The empty drum will be easier to move if the edges of the loading hole are not rough and jagged so people can lift the drum more easily.

b. The cover

You need a lid, to cover the large loading hole in the top of the oil drum. The lid should be large enough to cover the loading hole in the oil drum, but small enough not to extend over the edges of the oil drum. An ideal lid is made from a piece of sheet metal. It is easier to place the lid on top of the hot kiln if a handle is welded onto the lid. If you can’t make a curved handle, a handle shaped like a short, flat ‘T’ has worked well. You can also use metal without a handle.

c. The briquette press

This is a small impact press used to make briquettes from the charcoal powder. The press can be
round or square and can be easily manufactured by any car mechanic or local blacksmith, if they
can weld metal. A round press can be manufactured using metal pipes; a square press, using
angle iron and sheet metal.

Making Charcoal

The process of charcoal production is as much an art as a science. It requires experience to produce high quality charcoal, and to get high yields of charcoal from an oil drum. The method must also be adapted slightly for different materials. Whilst this guide provides approximate details, the time required at each stage is variable; there is no substitute for experience.

a. Filling the drum

When filling the drum, it is necessary to allow air to flow through the drum so that the fire can burn hotly and evenly and produce high quality charcoal.

b. Lighting the fire

Once the biomass is fully on fire, it will make a large, billowing plume of white smoke. After about 10 minutes, the smoke starts to get a bit darker, thicker and yellower. As the drum gets hotter, volatile carbon gases begin to be formed. These can be ignited to make the fire burn more cleanly, giving
off carbon dioxide.

c. Sealing the drum

In order for the material to carbonize, rather than burning away, it is necessary to seal the drum, preventing oxygen from getting in. This step requires at least two and preferably three people.

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