Sneak preview of our new IP

by Kobus Venter

Well done to Troy Manufacturing for again being able to translate our drawings into workable solutions. Most components are laser-cut, but many add-ons are hand made. The quality of the welding is also top class. All components are in direct contact with fire so none will be painted. They all come together to form a single Biochar kiln to be used in the Vuthisa Biochar Initiative, sponsored by the Energy and Environment Partnership Southern and East Africa (EEP-S&EA) fund.

Visit for updates on the project.



The Vuthisa Biochar Initiative

By Kobus Venter

Welcome to the ‘Vuthisa Biochar Initiative’ blog page. On this page you will learn more about our project and what we hope to achieve. The project officially kicked off in December 2013.

The project actually has many outcomes, but the primary goals are:

Create Employment – Up to 30 workers will be employed in year one. Unemployment is rife (>50%) in the rural areas of KwaZulu-Natal especially with a minimum wage now being introduced for farm workers. The feedstock for the Biochar project will be secured by ‘Vuthisa Charcoal Projects’ through a contract signed with the Department of Environmental Affairs, Natural Resource Management Programme, that pays the wages of our workers.
Eradicate Invasive Alien Plant Species and restore the Natural Biodiversity of the land – We intend to clear over 300 hectares of Wattle in this area and restore the land back to virgin grassland. The main culprit being Acacia mearnsii (Black Wattle) and Acacia decurrens (Green Wattle). Unmanaged Wattles in KwaZulu-Natal has now reached more than 300,000 hectares in extent, according to the Agricultural Research Council (ARC) report commissioned by Water Affairs, 2010. Left untouched, this alien vegetation would spread at an average rate of one percent a year, threatening water and food security.  Concerted efforts are being made to prevent the further spread of these invasives especially in water catchment areas and it is estimated that R 34 Billion ($ 3.4 Billion) will have to be made available over the next 25 years to stop this spread.


Increase streamflows and reduce erosion – The Wattle trees spreads vigorously through the seed it puts out and these typically germinate in or near river systems, reducing filtration into underground aquafirs and streamflows. At the onset of the infestation when the trees are young, only 500 mm of water is preserved within a typical annual rainfall area of 1200 mm. As the invasives spread, after 24 years only 25% of the entire potential water yield namely 300 mm of water will become part of water supply into the local catchment.


Develop Emission Reducing Biochar Kilns and reduce greenhouse gas emissionsAcacia mearnsii is a hardwood species and makes excellent charcoal.  Conventional pyrolysing tecnologies in South Africa however are less than 20% efficient.  Our first goal is to achieve a minimum of 25% wood to biochar conversion efficiency. Using more efficient methods to produce charcoal (or Biochar) has the potential to save about 100 MtCO2 per year in Sub-Saharan Africa (See  CO2 production from Emission Reducing kilns has not been quantified, but a 5 to 10% reduction in GHG’s is expected. We plan to produce 150 tons of Biochar in the next two years and we expect that 20% of this will be bought indirectly by fertiliser companies which could result in at least 30 tons of carbon being sequestered back into the soil.


Develop Biochar Eco-fertilisersBiochar as a soil amendment will allow rural folk to improve their subsistence agriculture. Mixing biochar with soil or a good active organic compost before it goes in the soil will soak up its full compliment of water, nutrients and microbes so that it can make those available immediately to the plants as soon as it is added to the soil. Ultimate concentrations after some time of repeated applications of these eco-fertilisers (chemical free) will work up to about 8 to 10% biochar by weight of the soil content.

biochar trials

See this Google Earth map below of precise location of the clearing operation:

What is Biochar?Biochar is charcoal mixed with compost and applied to the soil as a soil amendment and has the same benefit to plants than chemical fertelizers. The act of burying the Biochar in the soil, removes carbon from the air (CO2) and sequesters carbon into the soil for thousands of years and prevents the release of Methane from harvested plant material into the atmosphere. Methane is a key fuel component to providing the heat into the retorts and in the Biochar forming process.  Venting un-burnt Methane into the atmosphere contributes 26 more times to the greenhouse effect than CO2 alone.  For more information on biochar, feel free to research the many references to Biochar on Google or read more on our Biochar web page:

Harvested IAPs ready to be charred


Biochar Retorts being primed for firing in Guatemala

Please donate to the project.

The Energy and Environment Partnership fund for Southern and East Africa (EEP-S&EA) have kindly stood up and agreed to fund 50% of the Project Management fees, Site Preparation, Tools and equipment and Administration fees. The EEP Programme in Southern and East Africa is jointly funded by the Ministry of Foreign Affairs of Finland (lead donor), The Austrian Development Agency (ADA) and the UK’s Department for International Development (DFID). For further information visit: or


To donate to the project please get in touch with us.  We offer branding opportunities on Hippo Water Rollers, send out T-shirts and give shout outs on Social Media. Contact us here to find out more.

We accept SWIFT payments whereby money is wired into our project bank account.  Please approach your local bank’s FOREX department and request the appropriate procedure and instructions to follow to expedite this type of payment.

Contact us here for our bank details.

Donate via PayPal (pay with a credit card):

Please Donate


Donate via EFT:






Please indicate in your bank reference which activity you wish to sponsor.

What will the money be used for?

We will have the following expenditures:

1 –  Water and Sanitation

Instead of purchasing large stationary water tanks to supply drinking water from rainwater harvesting, we thought it would be cool to use Hippo Water Rollers and collect water from the nearby fresh water vlei. Each water roller can hold 90 litres of water. This presents branding opportunities for companies out there, by having their name or logo printed on each Hippo Roller. Visit the website for Hippo Water Rollers here for more information: The cost of each Hippo Roller is R 1,500 ($ 136) including delivery to the site. We require a minimum of 4 Rollers and a total of R 6000 (± $ 544).

The cost of purchasing and delivering 2 x Portable toilets to the site is R 14,000 (± $ 1,272), and we’ll pay for the fortnightly servicing of the units.

[0%] of “Water and Sanitation” funded to date.

Reviewed on: 20 January, 2015

2 – Cooking Stoves

The cooking stoves we require are special portable wood- and charcoal fuel saving stoves and because we are re-sellers of this product we can provide them at cost to our workers. We require 8 of these stoves to offer the staff with a means to cook their food safely or to boil water. More information here:
The cost of delivering 8 stoves to the site is R 3,880 (± $ 352).

[0%] of “Cooking Stoves” funded to date.

Reviewed on: 20 January, 2015

3 – Protective Clothing

To ensure our workers are operating safely and are fully kitted out, we need to supply them with adequate protective clothing (PPE). These include Two-piece overalls, T-shirts, Rainsuits, Gloves, Chainsaw operator safety gear, Goggles and Masks. The most recent quotation revealed that we need R 22,560 (± $ 2,051).

[60%] of “Protective Clothing” funded to date.

Reviewed on: 20 January, 2015

4 – Tools & Equipment

The basic tools and equipment required for the project include Hatchets, Loppers, Knapsack sprayers, Combi-cans, First-aid kits, a Fire extinguisher and Spades. This will cost R 14,500 (± $ 1,318). We have already paid for 2 chainsaws worth R 11,300 (± $ 1,027).

[65%] of “Tools and Equipment” funded to date.

Reviewed on: 20 January, 2015

5 – Biochar Kilns

The specialized Biochar kilns have been developed over many years and are professionally constructed by a light engineering company in Mkondeni, Pietermaritzburg. The cost of each kiln ex-factory is R 9,000 (± $ 886) and we require 3 to start off with for a total of 27,000 ($ 2,658).

[18.5%] of “Biochar Kilns” funded to date.

Reviewed on: 20 January, 2015

6 – Environmental Impact Assessment consultancy cost

The planned activities for the biochar project and charcoal activities will require an Environmental Impact Assessment (EIA) and an Atmospheric Emission License (AEL).  The entire process is expected to take 11 months to complete.  Cost: R 329,543.22 ($ 32,954) including VAT.

[57%] of “EIA” funded to date.

Reviewed on: 20 January, 2015

When everything is tallied up we need R 87,940 (± $ 7,995) PLUS R 164,771.61 (± $ 14,979) for the EIA and AEL.  The EIA and AEL will be funded from biochar sales, but any donation towards this cost would be very much appreciated.

[33%] of “Vuthisa Biochar Initiative” funded to date.

Reviewed on: 20 January, 2015

In conclusion we would like to thank everyone for their support and that we will do everything in our power to meet the goals of the project.

Or for more information contact us here:


Vuthisa Biochar Trials Ivory Coast – Part 1

By Kobus Venter

Here we have Ivoire Consommation from Ivory Coast (Cote d’Ivoire) using the Vuthisa 3-Drum Biochar Retort. A concerted effort was made by Kouamé Bahfi (owner of Ivoire Consommation) to make Biochar and promote it as a soil amendment in his region. In this video Gmelina was carbonized (bought in), using twigs and bamboo as the fuel of choice to heat up the retorts. Later on however, it was found that bamboo placed inside the retorts made excellent Biochar and it worked out cheaper as well. I have it on good authority that he will be trying an Adam Retort, built from adobe bricks next. Watch this space…

Vuthisa Biochar Trials Guatemala – Part 1

Herewith Part 1 of the trials and tribulations of starting a Biochar project in Guatemala. Emphasis is on manufacturing Biochar from invasive alien species in the forests of Guatemala, without creating excessive air pollution. Using a retort system means that gaseous products that are normally vented unburnt are in fact now utilised to provide the heat back into the retorts, creating exothermic conditions, providing its own heat for carbonisation. Efficiencies are higher and the final conversion to Biochar (as opposed to making charcoal conventionally) should be around the 25% mark. The ‘3-Drum Retort’ system, whereby lower quality and smaller diameter feedstock is burned as fuel to provide the heat into the internal retorts is in the Beta phase and these types of testing will yield valuable lessons. There were many challenges in getting the kiln on to the farm in question. First it travelled by road on the back of a pickup truck and then by boat some 400 kilometres.


Then it had to be carried on foot to the burn site. Some innovative approaches are adopted, including the use of bamboo sticks to carry the pieces through the bush.

Other challenges we foresee would be to try to get hold of clay to seal the kiln off and this seems to be in short supply. The humidity is high and the first test burn resulted in creating torrefied wood only, so the burn will have to be extended to allow moisture to be driven off. We suggested placing wood piles close to the kiln to dry pre-dry the wood and to consider two subsequent burns: one burn to create the torrefied wood and a second to turn that into Biochar.

To be continued…

Charcoal from invasive alien tree species

By Vuthisa

We recently concluded a feasibility study into the viability of rolling out portable metal kilns to eradicate invasive alien tree species. The cattle farm in question is situated in Franklin, approximately 30 km North of Kokstad, KwaZulu-Natal, South Africa. To achieve this task we adapted the Portable Kiln system and made it into sections in order transport it up onto the mountain top where it was assembled, ready for use. This is a self-funded trial to determine if it is feasible to convert jungle Wattle plantations into charcoal in order to alleviate poverty and transfer skills and ultimately establish Community Based Organisations (CBO’s) …AND preserve our rich species biodiversity!PanoramicView

3-drum Biochar Retort

A single Trans-Portable kiln can process 550 kilogram feedstock into approximately 100 kg charcoal (un-sieved) or 50 kg sieved charcoal in a single 24-hour shift. We have since increased our daily yield by increasing the kiln diameter by 40% and adding conical lids and chimneys to increase yields and clean up emissions. The new retort dubbed the 3-drum Biochar Retort can also accept 3 perforated 55 Gal oil drums which is filled with smaller diameter feedstock in order the produce bona fide Biochar, obtained with a substantial reduction in emissions and a 25% yield. We processed a mix of exotic invaders from Australasia Acacia mearnsii (black wattle) and Acacia decurrens (green wattle) on the private farmers’ land and rehabilitated 6 hectares of this jungle back to pristine grassland. We had up to 8 kilns on the mountain. The felled timber was prepared and stacked in piles measuring 1 m (L) x 1 m (W) x 1 m (H) or approximately 280 kg (617 lb) per pile. We had a staff compliment of about twelve people, divided into clearfelling (and stacking) and burning teams. All of the bags (5 kg) produced were sold in Pietermaritzburg, Howick, Margate as well as Durban.

Overall we were quite happy with our feasibility study having been able to test the kilns for durability, conduct valuable market acceptance trials, gather cost breakdown per activity which is invaluable when project is finally scaled up.

Below are some late afternoon vistas of the farm following a thunderstorm, blessing the area with much needed precipitation. This is a very beautiful and picturesque farm and with the invasive wattle eventually removed it will be a polished diamond indeed, as seen through the eyes of the first inhabitants of the area.

For more information contact us.

The Vuthisa Team

(BEE rating: Level 4)

Biochar as a soil amendment and carbon sequestering tool

Photo courtesy http://2.bp.blogspot.comBy Vuthisa

It is surprising how many people cart away their yard waste (renewable biomass) to landfill sites or dispose thereof in open burns until only ash remains.  I say: Make your own biochar instead.

What is biochar and what is the difference between biochar and charcoal?

They are identical in many respects, but the telling difference is in how they are used.  Charcoal is used as a fuel.  Crushed charcoal mixed into soil as a soil amendment is biochar.

As a soil additive, biochar offers numerous potential benefits

Unlike fertilizers, biochar has an extremely long life in soils. Charcoal is carbon-rich and gives it the ability to persist in the soil indefinitely by not being susceptible to biological decay.  Biochar also attracts microbes and beneficial fungi, holds on to nutrients that are put into the soil. i.e. biochar works better the second and third year than it does the first.  One of the major challenges in agriculture is to make the nutrients in the soil available to the plant when the plant can benefit from them.  Fertilizers can often only be applied early in the growing season, before the crop canopy closes and field operations are no longer feasible.  Unfortunately, between the time the fertilizer is applied and the crop takes it up, fertilizers can be leached out of the soil by excess rainfall, consumed by weeds, or metabolized by microbial activity in the soil.  Biochar helps conserve plant nutrients by storing them within its matrix and making the nutrients available when the crop needs them.  This happens because of a property in biochar, certain clays, and soil organic matter known as Cation Exchange Capacity (CEC).  CEC is a measure of the capacity of biochar to retain ions, such as ammonium and potassium cations, in an exchangeable form that is available to plants.  CEC not only helps conserve the fertilizers added to the crop during the growing season, but also improves the ability of the soil to capture and retain nutrients from other sources available at other times.  For example at the end of the growing season crop residues are often left in fields to decompose.  When this organic matter decomposes, biochar captures some of the nutrients released, leaving those nutrients for the next growing season.

Biochar in soil also has the ability to hold moisture and save on irrigation costs.  Biochar modifies the soil’s performance by retaining moisture and making it available during periods of low precipitation and hot, dry soil conditions.  This is possible because biochars have very large internal surface areas – typically over 100 square metres per gram.  This internal surface area adsorbs moisture when water availability within the soil is high and releases it back into the soil when water availability is depressed.  Some may think that biochar being black in color would heat up in the sun, but biochar helps the soil stay moist even in full sunlight.  Biochar also has significant impacts on soil drainage.  Clay soils which are typically poorly aggregated are too tight and do not drain effectively.  Ineffective drainage results in extended periods of inadequate soil aeration.  Other soils, especially sandy soils may drain too efficiently.  Overly efficient drainage can shorten the benefit of periodic wetting.  In both cases, the addition of biochar compensates for the native soil deficiency in the following ways:

Clayey and poorly aggregated soils become less compacted and provide better aeration

Sandy soil acquire additional bulk moisture storage capacity

Biochar also makes a significant contribution to mycorrhiza by promoting microbe populations.  Mycorrhiza is a fungi that has a symbiotic relationship with plant roots and contribute to a healthy soil-plant nutrient exchange.  Biochar increases the availability of mycorrhiza by:

Detoxifying soil water by adsorbing compounds that inhibit microbe growth

Providing a  protective habitat for microbes

Improving soil moisture management in which mycorrhiza thrives


Biochar can mitigate climate change

By reducing consumption of fossil fuel and

Capturing CO2 and sequestering carbon in the soil

In a world dependent on fossil energy, it is easy to see the carbon capture benefits of biochar as offsets against current and future fossil fuel emissions.  Many scientists believe there is already an unsafe excess of carbon dioxide in the atmosphere, this obligates the nations that caused the excess to abate it.  It is notable that from the year 1850 to 2000, 34% of carbon dioxide emissions have been attributed to land clearing.  Therefore, in a sense, the first goal of biochar is to restore the carbon lost from the soil due to the past 150 years of agricultural practice.  After that, the particular durability of biochar will enable the build-up of more carbon in soils, with further fertility benefits as the existence of Terra preta soils have shown us.  Terra preta soils are fertile, black biochar-rich soil found in scattered tracts throughout the Amazon basin, also, the pre-Columbian civilization responsible for creating that soil, dating back to 450 to 8,000 B.C.  Charcoal has the potential to sequester gigatonnes of atmospheric carbon per annum, making it the most potent engine of atmospheric cleansing we possess.  Approximately 8 percent of all atmospheric CO2 is absorbed by plants each year. If just a small proportion of the carbon captured by plants can be pyrolysed and transformed into charcoal, humanity’s prospects will be much brighter, for this will buy us time as we struggle to make the transition to a low emissions economy.

How do you make biochar?

The production of charcoal and biochar has a common root.  Before fossil coal emerged during the Industrial Revolution (18th Century) the word coal meant charcoal – the black fuel made from wood.  The basis for all charcoal and biochar production is pyrolysis: essentially, breaking wood down into its chemical constituents by heat, with little or no oxygen.  We do not use the same archaic methods of yesteryear, with the development of cylindrical metal vessels and high temperature refractories.  Good biochar has high porosity, extensive micro-structure, and adsorption capacity that enable beneficial interactions between microbes, nutrients, and water in the soil.  The so-called 55/30, a simple closed retort, is popular with biochar enthusiasts.  In a typical configuration, the “55/30” consists of a 55-gallon (200 litre) outer drum containing the fire around a 30-gallon (100 litre) inner drum acting as the enclosed retort.  A 30-gallon barrel, open at one end standing with the open end down on flat surface, makes a simple and serviceable closed retort.  Click here for a collection of all types of biochar making kilns:

Vuthisa opted for the Portable Metal Kiln Method for biochar production, which differs from conventional open burn methods in five ways:

The steel plate is very thick and not only lasts longer than 55 gallon drums, but allows the contents of the kiln to “cook” in the absence of charcoal by means of a tight sealing lid

The drum can be made oval to fit in two sealable 55-gallon drums, yet also allow burning material to be added to heat the drums

Small sized feedstock, typically found in yard waste, such as twigs and branches are ideal for this system as it will not turn to ash, as with larger horizontal type kilns that can take up to 3 days to cool down, reducing small diameter feedstock to ash

Large quantities of biochar can be produced as opposed to the 55/30 type closed retort that produces small quantities

The kiln can be rolled long distances to adjacent feedstock piles without any difficulty, yet can still fit on the back of pickup trucks.  More information can be found here:

Resources The Biochar Revolution – Transforming Agriculture & Environment – Edited by Paul Taylor Make charcoal in your own backyard Biochar for Environmental Management: Science and Technology Edited By Johannes Lehmann and Stephen Joseph Mycorrhiza Biochar producing kilns Biochar discussion list website Improved Biomass Cooking Stoves

To obtain access to more URLs relating to the above subject matter (not for public viewing) send your request through to:

Make charcoal in your own backyard

…with a Portable Charcoal Kiln.

By Vuthisa

Herewith a step-by-step guide to making charcoal from yard waste in your own backyard. This specific design has been used extensively since 1996 to clear Namibian encroachment bush. Having tested this system recently we see no reason why this technique cannot be applied to clear yard waste or any other biomass, including corn cobs. For more information on how this charcoal can sequester CO2 back into the soil instead of being vented into the atmosphere visit our Biochar page. What’s great about this design is that it can be used for making charcoal for extended periods, due to its durable design AND its portability – you simply have to roll the drum to where the brush pile is located.  Even though this is a direct method of making charcoal, it does NOT require complicated opening and closing of air vents or chimneys, due to the vertical stack effect of the narrow drum. If you’re looking for a way to transform your yard waste into a fuel briquette (with or without charring), visit our Fuel briquettes page. **Update**  We secured a contract to remove invasive alien tree species and return the area back to pristine grassland and to increase streamflows. See more on that here. Due to the steepness of the terrain we decided to construct the kiln in sections to be assembled on site, but more on that later. See this new video slideshow outlining the production process: 

A single burn will produce between 120 kg to 160 kg (350 lb) of charcoal from 0.7 m3/1000 kg (25 ft3/2200 lb) of medium-sized hardwood, but yields are dependent on many variables, such as your geographic location, moisture content-; type-; size of material and the experience of the operator, to name a few. It is possible to char wet timber with this system, but we don’t advocate this due to the increased time it takes to vent the extra water vapor. Colder, wetter climates yield less charcoal. In the test described below we achieved a yield of 16% charcoal, a conversion ratio of approximately 6:1  (6 weeks air-dried).  By fine tuning your burn method and identifying the visual clues more accurately, yields closer to 30% can easily be obtained. Instead of increasing your carbon footprint by transporting large amounts of timber to the kiln (as with large industrial kilns) the kiln is simply rolled (by one person) to the already prepared and air-dried brush-piles. What you will need:

  • A kiln consisting of a cylindrical drum and lid
  • 120 kg of river grade sand (optional)
  • General purpose soft potters-clay
  • Industrial purpose gloves
  • Large polypropylene bags or paper charcoal bags
  • Small ladder
  • Wheelbarrow
  • Water or Fire extinguisher
  • Shovel (optional) and Spade
  • A few bricks
  • Garden fork
  • Tinder and matches
  • Axe and/or bow saw and/or chainsaw
  • A stockpile of yard waste, preferably within wheelbarrow distance of burn site
  • A Sieve constructed from 15 mm chicken wire or expanded metal sheets
  • Black plastic sheeting to prevent bags from getting wet
  • If you are on a small holding or farm you will need a truck and or trailer to transport polypropylene bags to the packaging area
  • In some cases it may be necessary to hire/purchase an Army type tent and small generator (for stitching machine) if you don’t have a shed
  • A stitching machine and extra cones (thread)

Kiln construction

You need to construct this kiln with the help of your local light engineering works. Expect to pay around $600 USD which includes the cost of labor, so get more than one quotation. It can be a D.I.Y. job if you have good welding and bending skills. Otherwise consider having the kiln built in three sections, which is simply bolted together, no welding required and it is easier to transport. We have dubbed the new system the “Trans-Portable Kiln“. The plans for both types of kilns are contained in our Trans-Portable Kiln Construction Plans and User Manual.

Click here to download the plans. Also included in the manual is the specification sheet of a wooden Sieve Chute to screen your own charcoal. Join our participatory discussion group called the Portable Kiln Google Group. Joining it is optional, and is exclusive to Portable Kiln Owners for sharing and discussing their experiences OR enter our DESIGN CHALLENGE to design a biochar producing kiln that emits less greenhouse gases. Just print out the plans and hand it over to your local engineering works.

DIY_Biochar_KitWe have also launched a new manual. This manual describes how to build our new Biochar kiln called the ‘3-drum Biochar Retort‘. The 3-drum Biochar Retort is more clean burning (with the added lid and chimney) and the burn is more controlled, and the user has an option to create either Biochar or conventional charcoal. Click here to view the development of this kiln and how the Design Challenge helped to draw in biochar experts around the world.

We are bound by a license agreement for use of the kiln in Southern Africa, so if you are from the southern part of Africa and wish to use the Portable Kiln commercially you’re required to pay a license fee.  For more information on licensing fees, made-to-order options or simply wanting to do backyard trials without paying the license fee, kindly visit our Order page.

The plans will outline the exact dimensions- and type of materials to use as well as the guidelines set out below.  The kiln basically consists of a:

a) Lid.  The lid sits loosely on top of a cylindrical drum. **Update** We have developed several new lids to suit different applications.

b) Open ended cylindrical drum/barrel.  A length of mild steel sheet, rolled into a drum shape and welded on the seam.  Please note: an ordinary 200 litre (55 gal) oil drum will not work – or last!  This drum has a 1400 litre (370 gal) capacity and weighs 37kg (81 lb).

Some garden waste!

The thickness of the branches or stems that you use need to be more than 30 mm (1-1/4 inch), but preferably not more than 120 mm (7-3/4 inch).  The larger pieces tend to not pyrolyze completely in the center.

Yard waste

Organize the waste into a separate pile.  The volume of waste is not important, although you have to try and fill the drum up with as much yard waste as possible, but typically one should have more than 1 m3 (35 ft3) of waste ready.  The kiln can accept 0.7 m3 (25 ft3) of carbonous brush.  The branches and stems must be cut in lengths not exceeding 1 m (3.2 ft) long with the use of an axe, bow-saw or chainsaw.

Site preparation

Before anything else, carefully decide on the location of the kiln.  Make sure there are no overhead hanging branches or power- or telephone wires nearby.  Have running water (preferably a hose pipe) available or if it’s in a remote area, bring a fire extinguisher along, in case of unforeseen emergencies.  The kiln is portable in the sense that it can be rolled into position.  Care has to be taken not to position the kiln near the brush pile.  Choose a level site and clear an area of approximately 3 x 3 metres (10 x 10 ft) of any flammable material.

If you don’t intend moving the kiln to other brush piles we recommend pouring river grade sand evenly over the site, but make sure it is at least 10 cm (4 inches) thick.  The sand insulates the ground, but also allows one to dig vent holes underneath the kiln.  If you find you don’t have sand or enough volume of sand, you can place 3 wooden pegs underneath the kiln, each approximately 100 mm (4 inches) in thickness, evenly spaced, to keep the kiln slightly elevated.  This will allow for enough ventilation or allow one to create the holes in the sand more easily.

Making charcoal

(Also see alternative method posted as a blog comment)

  • Burn “out of the fire season” and if you feel it necessary alert the neighbors if they are the jittery type – it is just common courtesy to respect other people’s rights.
  • Pick a clear morning or a quiet windless afternoon.  This is very important because in the first hour you are venting copious amounts of smoke and the neighbors will learn to hate you all over again!  Theoretically, strong winds can also cause tiny pieces of burning material/embers to start spot fires far away from the kiln.  I don’t believe this to be a serious possibility, but it’s always better to be on the safe side.
  • The burn site must be cleared of dry grass and any other flammable material.  A normal fire must be lit.

  • The kiln is then rolled into position over the fire.  If you’re using pegs – insert them now.  Make sure the drum is completely round, not oval, as the lid will not be able to close up the opening at the top.  Four air vents are then dug under the bottom of the kiln with the use of a spade.

  • The air holes will provide much-needed draft through the kiln.  Make sure holes are dug at least 30 cm (1 ft) across, even up to 50 cm (1.6 ft) to allow as much air in as possible.  The kiln is then fed with material until the burning slash-pile reaches the top.  The general rule is to keep adding timber until it no longer sags below the rim of the kiln.  Be careful not to have pieces hang over the edge.

  • Soon, all the wood/brushwood in the kiln will be ablaze and the smoke issuance will cease almost immediately.  The temperature in the kiln will consolidate  (and sometimes fluctuate) at between 380 to 400°C (716 to 752°F) anything from 1 hour to 1.5 hours after the last piece of timber has been loaded.

  • Once white ash is seen spilling out of the vent holes (four openings under kiln), they must be sealed, by simply kicking them closed with the surrounding sand or by removing the wooden pegs.  Blue/grey smoke will start appearing which means that the alcohols and phenols are burning off.  This phase is closely followed by the tar producing phase whereby yellow flames are now visible.  We advise that the lid be closed before the end of this phase as the tar given off assists in sealing off the lid against the drum.  This phase can last for up to 30 minutes.  Waiting too long before closing the lid can reduce the smaller sized wood to ash and closing the lid too quickly, won’t allow larger pieces of wood to pyrolyze completely on the inside.  One is usually left with a small proportion of semi-charred pieces, but these can simply be added to the next load waiting to be turned to charcoal.  Seal off the remaining openings with clay or strategically placed bricks, where one can see smoke spilling out.

  • Care must be taken against accidental skin burns when applying the clay, as temperatures inside the kiln can exceed 500°C (935°F).  Absolutely ALL the air supply to the kiln must be choked off, otherwise you’ll end up with too much ash.

  • No further oxygen is therefore allowed into the kilns and the cooling down period commences.  Under these conditions hydro-carbons are absorbed by the charcoal.  In larger horizontal type kilns, temperatures remain hot for almost 72 hours and larger pieces of timber (usually the trunks) are able to sufficiently “cook” during this period.  The same cannot be said for large pieces of wood contained in our kiln.  On the positive side that is why this kiln works so well with small sticks and twigs.  The kiln must only be opened once the metal sides are cool to the touch, usually the next morning (24 hours later).

  • Charcoal is then sieved and smaller pieces are separated from the larger pieces by use of a wire mesh screen or simple garden fork and placed into polypropylene bags.  In this exercise we produced 16 kg (35 lb) of charcoal which amounts to a conversion factor of 5.5 : 1.  Take care to store the charcoal in a dry environment as moisture can lower the calorific content (heating value) of charcoal.  The average heating value of charcoal is around 29 MJ/kg, almost twice that of wood.  We used logs with an average diameter of approximately 100 to 120 mm (4 to 4-3/4 inch) and as a result produced very little fines and ash.

The process – explained

Now that we know how to make charcoal, what thermodynamic reactions are actually taking place during the different stages of charcoal making?  Knowing this might help you to gauge your own operation and fine tune it.  It is a good idea to invest in an industrial purpose, digital thermometer and Type K thermocouple rod ±0.5 metres (1.6 ft) long.  This will cost approximately $200 (USD).

The pyrolysis of wood in such apparatus basically resolves itself into 3 different stages:

  1. Evaporation of the moisture present in the wood takes place as the initial phase, up to an average temperature of 170 °C (338°F). During this period scarcely any gas is produced.
  2. As the fire builds up inside the kiln, the temperature rises and at approximately 280 °C (536°F) the exothermic reaction begins to take place. Gas consisting almost entirely of carbon monoxide and dioxide is evolved and a certain amount of acetic acid is formed together with small quantities of wood-naphtha and tar.
  3. The exothermic reaction then continues during which concentration of carbon in the charcoal takes place. Large quantities of hydro-carbons, acetic acid and wood-naphtha and tar are produced while the temperatures rise to 380 to 400 °C (716 to 752°F).

What is charcoal generally used for?  The main use of charcoal in the households of the developing world is to heat water either to cook food or provide hot water for washing, but elsewhere charcoal also has many applications.  You could use the resultant charcoal and turn it into Biochar (also known as Terra Petra) as a soil amendment.  Charcoal can enhance plant growth, reduce fertilizer requirements, reduce the soil’s acidity and offer a host of other benefits as can be seen in this post: – OR – combine the char with a non-woody biomass fuel-briquette – OR – A good way to celebrate the fruits of your labor would be to test some charcoal in a barbecue, and since you reduced your carbon footprint by not buying commercially manufactured charcoal and converted waste biomass that would otherwise have decomposed at the landfill site, which would contribute to global warming – its eco-friendly too :-).