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Tag: retort

BLOG: Adventures in Charcoal: nothing ventured, nothing gained.

Steve Chamberlain southeast development officer

Late January I organised a training day focusing on charcoal production. The volunteers at Blaen Bran community woodland had been sorting out their yard and as a result had much waste wood.  I thought this would be an excellent opportunity to trial my new retort kiln prototype (ivor) that I have been tweaking since Lockdown #1 and then later in the year we will use the ring kiln with the volunteers and compare the advantages and disadvantages of kiln type in the production of charcoal. 

 Subzero temperatures were not anticipated but the sun was shining and the woodland had a wonderful winter atmosphere. It would seem the perfect time for charcoal production, however, that was not the case. Winter is the time of gathering materials for charcoal production and the summer months for creating it but we thought we would try anyway. We fired up the kiln and discussed all things charcoal whilst soaking up the heat being expelled from the kiln, potatoes hissing in their tins on the coals, what could go wrong?

It took 90 minutes to get the inner chamber up to 100 degrees. 300 degrees is the target –  as it is the point where the wood in the inner chamber releases gas that goes into the fire box and the wood starts ‘cooking’ itself. Four hours had now passed and still no gasification. We had only reached 230 degrees in the inner chamber despite piling in extra waste wood into the firebox. As nothing was progressing and the weather was desperately trying to snow we agreed we close the kiln down, by  and hope for the best.

This process could be viewed as a failure but as this was a test run and confirmed two important factors a failure it was not, so if knowledge was gained it should be deemed at least a partial success.

The first of the two learning factors was the quality of the wood being charred. This was cut and seasoned firewood which had been sat out in the elements for some ten years and had become light in weight, thinking this would have very little moisture if any, it may hold less wood gases also.

The second learning factor is the time of year or more accurately the temperature . The kiln is not insulated and could not get to the required temperature in sub zero conditions. We had considered this as a potential issue at the beginning of our trial but can confirm this now.

 Despite the lack of product at the close of play a good day was had by all, we all learned something new and we are looking forward to our next session in more clement weather. Charcoal and more importantly biochar is a great way for groups to learn important woodland heritage skills and generate an income from waste materials as well as trapping carbon and halting further climate change. Many groups already produce these products with traditional ring kilns but retort kilns are much more efficient and environmentally friendly so if you are interested in making the switch Llais y Goedwig would be glad to assist.

Have a look at the helpful glossary and links if you want to understand more about this process.


Retort Kiln – Wood is placed in a large steel cylinder (or “retort”). This has a tightly closed door, and some means to let tar and gases escape. The cylinder is heated from the outside. No air enters the barrel. When the wood in the cylinder has been heated to the right temperature, a chemical reaction (called carbonization) begins that gives off heat and by-products. Little additional outside heat is necessary.

Ring Kiln –  A ring kiln is a metal drum with chimneys and a lid that acts as an oven in just the same way as the soil once did.

Gasification – Gasification is a process that converts organic or fossil-based carbonaceous materials at high temperatures (>700°C).

Charcoal –  is a lightweight black carbon residue produced by strongly heating wood in minimal oxygen to remove all water and volatile constituents. without combustion, with a controlled amount of oxygen and/or steam into carbon monoxide, hydrogen, and carbon dioxide.

Biochar –  imore porous and has a larger surface area than charcoal — a few ounces of biochar can have an internal surface the size of a football! This porosity and surface area helps biochar improve soil structure and house beneficial microbes, resulting in healthy soil.




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