# @stem_antics on Instagram

- **Type:** Video
- **Original URL:** https://www.instagram.com/p/DdeQz2yBe6W
- **Gondola URL:** https://gondola.cc/posts/70577831-stem-antics-instagram
- **Thumbnail:** https://img.gondola.cc/tr:w-,h-,fo-auto/postThumbnails/dc4d562f50.jpg
- **Posted:** 2026-09-19T14:49:56.000+00:00
- **Account Owner:** Stem Antics (@stem_antics) — https://gondola.cc/stem_antics

## Caption

Charcoal is not burnt wood. It is wood that has been cooked to death in the deliberate absence of oxygen, and a large steel retort is the machine built to do that cooking with control rather than luck.

The process is pyrolysis, and it moves through distinct thermal regimes:

- Below 150C the charge simply dries. Free and bound moisture leaves, and every kilogram of water carried into the vessel steals roughly 2.6 MJ of energy that will never become product.
- Between 200C and 260C hemicellulose collapses first, shedding acetic acid, methanol and carbon dioxide.
- From 240C to 350C cellulose depolymerises through levoglucosan into permanent gases and condensable tars.
- Lignin decomposes lazily from 280C to 500C and supplies most of the fixed carbon skeleton that survives.

Near 280C the reaction turns exothermic. The charge begins heating itself, releasing on the order of 1 MJ per kilogram, and the operator stops feeding the firebox and starts managing the vessel instead.

A retort is a sealed steel chamber loaded with wood and heated externally, never internally. That distinction is the entire point. In an earth mound or a pit burn, part of the charge must be sacrificed as fuel and yields fall to 15 to 20 percent by dry mass. A properly run retort recovers the pyrolysis gases, pipes the carbon monoxide, hydrogen and methane back beneath the shell, and burns them to drive the next stage of its own reaction. Yields climb to 30 to 35 percent, and fixed carbon lands between 75 and 85 percent.

The steel itself is the hard engineering. Mild steel scales rapidly above 550C, so serious retorts use 309 or 310 stainless in the firebox skin, and every weld lives under thermal fatigue, carburisation and sulphidation attack. Lambiotte proved the continuous version in Belgium decades ago and the chemistry has not changed since.

Anyone can make fire. Making carbon takes a sealed vessel and patience.

#stemantics #pyrolysis #materialsscience #processengineering #carbonisation

## Stats

- **Views:** 21,085
- **Likes:** 265
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- **Comments:** 2

## Tags

processengineering, materialsscience, carbonisation, pyrolysis, stemantics

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