Biochar Production Equipment Compared: Burners, Kilns, Retorts & Screens
Compare biochar equipment: air curtain burners, pyrolysis kilns, retorts, and flame curtain kilns — plus the grinders and screens that feed and finish char.
Biochar production equipment compared: burners, kilns, retorts, and what feeds them
If you want to make biochar, the machine you pick should follow the job you actually have. A land-clearing crew sitting on burn piles has a different problem than an operation buying feedstock to run a dedicated char business. Below is how the main equipment types stack up — plus the grinders and screens that make any of them work.
The four ways to make char
Air curtain burners. These are disposal machines first, biochar makers second. The oxygen-starved char bed at the bottom of the box produces char as a byproduct while the unit's real job is reducing wood waste to a fraction of its volume. Best fit: land clearers and forestry crews already burning slash. Output runs from roughly 10–15 cubic yards a day with manual recovery up to a few hundred pounds an hour on automated systems like the CharBoss. Highly mobile, moderate capital cost, no feedstock chipping required — you can feed whole limbs and stumps.
Pyrolysis kilns. Sealed or semi-sealed chambers that heat biomass with limited oxygen and drive off syngas and bio-oil along with the char. Continuous-feed versions are built for dedicated facilities that want consistent, high-quality char. Yield is strong — commonly cited around 25–35 percent by weight — but you pay for it: high capital cost, stationary install, and chipped feedstock required.
Retorts. Batch vessels. You load feedstock, heat it externally, let it cool, then pull the char. Simpler and cheaper than a continuous kiln and a sensible way to test the char market before scaling. Yield lands around 20–30 percent by weight. The catch is throughput — every batch is a full heat-and-cool cycle, so daily output is limited.
Flame curtain kilns (Kon-Tiki). Open-top cone or trench designs where burning biomass at the surface forms a flame curtain that keeps oxygen out of the char forming below. Very low cost, minimal feedstock prep, yields in the low-to-mid 20s by weight. Best for small-scale and hobby production, not tonnage.
Quick comparison
| Factor | Air curtain burner | Pyrolysis kiln | Retort | Flame curtain kiln |
|---|---|---|---|---|
| Primary purpose | Waste disposal + char | Char production | Char production | Char production |
| Mobility | High | Low | Low–moderate | Moderate |
| Feedstock prep | None | Chipping required | Chipping required | Minimal |
| Relative output | Volume-driven | High, consistent | Batch-limited | Small scale |
| Capital cost | Moderate | High | Low–moderate | Very low |
The honest read: buy an air curtain burner if you're already managing wood waste and want char as extra revenue. Buy a kiln if biochar is the business and you have steady feedstock and a fixed site. Start with a retort if you're testing whether the char market is worth it in your region.
The machines nobody mentions: feedstock and finishing
Whatever burns or pyrolyzes the wood, two other machines usually decide whether the operation pencils out.
- Grinders (feedstock prep). Kilns and retorts want sized, uniform feedstock, and even burners run cleaner on consistent material. A horizontal grinder or tub grinder — Morbark, Diamond Z, Rotochopper, Peterson, CBI, Vermeer — turns stumps and slash into a feedable size class. Uniform feed means predictable char.
- Screens (finishing). Raw char and ash come off the bed as a mixed pile. A trommel screen or a vibrating/shaker screen grades it — separating fine ash, sized char, and oversize that needs another pass. Graded char sells; a bucket of char-and-ash mixed together does not. McCloskey, Powerscreen, Terex, and Doppstadt all build screens that handle this.
Get those two right and the char machine — whatever you chose — has a real product coming out the back end instead of a pile you still have to sort by hand.
Where RPG fits
RPG Equipment brokers the grinders and screens on both ends of a biochar setup, and we regularly move machines for operators changing direction — someone scaling up out of a tub grinder, someone offloading a screen after a job wraps. If you're building a burn-and-char line or sizing your first grinder, browse current listings, and if you've got a machine to move, consignment gets it in front of buyers nationwide.
Have questions about biochar production equipment? Contact RPG Equipment — we work with buyers and sellers across the US and Canada.
RPG Equipment is a heavy equipment brokerage based in Worcester, MA specializing in grinders, crushers, screeners, and material processing equipment. Contact us to buy or sell equipment, or browse more articles.