Pyrolyzer Safety


In the next post, we will show how to build a practical pyrolyzer to turn a pile of wood chips into useful fuel gas. But before we do, this post gives some safety tips for using this or any pyrolyzer.

On this site, we show people how to do things for education and entertainment, and invariably, someone is going to want to build a pyrolyzer for real. Keep in mind that pyrolyzers came about in wartime as a way of using locally available fuel to avoid starvation, so safety considerations weren’t really at the top of the requirements list.

Always wear leather gloves when building, operating or maintaining a pyrolyzer.

See that picture above? An unwary person could walk right into the flame shooting out to the left.

The most important thing to remember is that an operating pyrolyzer is full of hot, flammable fuel gas, so it already has two of the three fire triangle components. All that hot gas needs is air, and then it can easily ignite. If air were to unexpectedly enter the barrel during operation, the entire device could rupture, or shoot the chips back out of the stove pipe, blowing burning chips everywhere. We’re going to talk about several ways this can happen, but there are others.

During normal operation of our prototype, if the blower were to fall off the barrel or experience a power failure during a gust of wind, the normal draft would reverse, causing smoke to go up the stove pipe, sucking fresh air into the barrel, igniting the hot gas inside. Never remove the blower pipe from a hot pyrolyzer, or open the other port on the barrel to look inside. Imagine a hot flame jet to the face.

Too much air flow can also cause fresh air to be brought into the barrel past unburnt fuel. As the fuel begins to run out, you will hear a chugging sound as fresh air detonates inside the barrel past the fuel zone. Keeping the stove pipe full of fresh chips limits air flow, as does using a dimmer as we will show in a later video.

The barrel should also be on firm ground, keeping it from tipping over, which would also allow fresh air to enter in many ways. You should also only use barrels in good condition. Since the pyrolyzer is under suction, a rusty or damaged section could give way unexpectedly and let fresh air rush in.

Since chips and burning material can be ejected from the stove pipe with force during an accident, never look directly into the stove pipe after it is running. If you need to see what is going on, use a hand mirror instead or at least wear eye and face protection.

Similarly, you should never operate a pyrolyzer under a shelter or near flammable materials which could catch fire if burning material is ejected upward or scattered outward.

Keep one or more buckets of sand, dry dirt, or ash handy as a firefighting tool. Avoid using water since there is live AC power at the blower. Only use water after power has been killed, not just at the blower, but in the entire operating area. A wall safety switch installed by a qualified electrician, with circuit breakers and GFCI protection, is a must. Never approach a burning pyrolyzer until power has been removed. Practice your fire-fighting procedures and make sure everyone understands their roles in an emergency.

The wires to the blower can melt and short against each other or the metal of the barrel. Keep them away from the barrel with a brick or other nonflammable object. The design we have shown is only a prototype to demonstrate the operating principles and show that, in an emergency, practically anyone can make a pyrolyzer with simple tools. Later designs will locate the electrical components well away from heat sources.

One of the main fuel gasses in an operating pyrolyzer is carbon monoxide, which is poisonous. You should never operate a pyrolyzer indoors, or where the gasses can be blown indoors. Another possible gas product is methanol, or wood alcohol, which is also poisonous and can cause permanent eye damage if absorbed in sufficient quantities. Some resources advise drinking small amounts of ethanol, such as beer, wine or whiskey, to block absorption of wood alcohol, although operating a pyrolyzer while drunk would clearly be a bad idea.

When lighting a pyrolyzer, never use flammable liquids in any quantity. These will quickly meet fresh air in the barrel or downstream piping and can cause an explosion. Never add flammable liquids in any quantity to a running pyrolyzer as these could overwhelm the natural draft when they vaporize and also cause an explosion.

Also, never attempt to light the pyrolyzer without the blower running to pull the flames away from the operator. Otherwise, flames will climb back out of the stove pipe and endanger the operator.

When starting or stopping a pyrolyzer, the wood tends to produce large amounts of steam at lower temperatures instead of fuel gasses, which reduces the concentration of fuel gasses, preventing explosions. Blocking the stove pipe while leaving the blower running will allow the pyrolyzer to begin shutting itself down with steam as it cools. After the stove pipe is blocked to prevent a reverse draft, then turn off the blower and give the pyrolyzer several hours to cool down before opening anything.

Similarly, if the blower fails for any reason, immediately block the stove pipe. Never have so much fuel in the stove pipe that it is mounded above and cannot be easily blocked.

You can also shut down a pyrolyzer faster by spraying a mist of water into the stove pipe with a hand sprayer bottle, but remember that there is live AC power at the blower so never use a garden hose or bucket of water as this could create an electrical hazard. A small amount of water as a fine spray from a hand bottle into the stove pipe will often work well enough, but if you have to, quench it completely with your dry firefighting bucket, but only after killing power to the blower. Avoid using even a mist of water too often as this practice will rust the pyrolyzer faster, making it more prone to failure later. Letting the pyrolyzer cool naturally is best. So, don’t start your pyrolyzer unless you have free time to allow it to cool normally under supervision. Remember that any unburnt gasses at any time are dangerous to breathe.

While fueling your pyrolyzer, some wood will accumulate on the top of the barrel and can catch fire. Keep a wire brush and metal scoop handy to sweep any loose debris off the top of the barrel. Dump the sweepings into the stove pipe unless they are smouldering or burning, in which case you should dump them in your firefighting bucket and cover with dry material. Never let material accumulate on the barrel for any length of time.

A pyrolyzer should never be left unattended. Always have a responsible adult on hand and keeping things safe.

As you can tell, there are many ways that operating a pyrolyzer can be dangerous. You have to be responsible for your own safety.


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3 years 6 months ago

A pyrolyzer. Awesome!

How is it practically useful?