By Dan Hettinger, Biochar Facility Manager
Last month I wrote a little about the carbon impact of biochar production, and concluded with the assumption that going ‘carbon-negative’ is likely very possible with simple scale ‘backyard’ biochar technologies. Bob Wells’ immensely popular presentation on the Tin-Man shows an effective DIY method with a single 55 and 30 gallon steel drum. Lately, here at Living Web Farms, we’ve been taken by the TLUD (Top-Lit/Up-Draft) Gasifier as an alternate means of DIY biochar production. In fact, If you’ve followed us closely then you know that we’ve talked a little about TLUD gasifiers before.
I’ll be the first to admit this can be a hard thing for a lot of people to get excited about. That is, until you look closer at what’s possible with this technology.
What’s a Gasifier?
Chances are you’ve heard about coal gasification as one of the ‘clean coal’ technologies that’s been getting a lot of attention lately. The merits of this practice are debatable, and not within the scope of our work at all. Although the principles of the technology are very similar, when we talk about gasifiers, we’re generally talking about much smaller devices that convert biomass into gasses through the application of heat with a controlled amount of oxygen. Our gasifiers are low tech devices: think of them as vessels filled with biomass and lit with a torch, where just enough oxygen is applied to keep it lit. Pyrolysis ensues, biomass is reduced to carbon, and a myriad of gasses are released. The resulting mixture of Carbon Monoxide, Hydrogen and Carbon Dioxide is (often called Producer Gas, or Syngas) a fuel gas that can then mix with oxygen and burn at higher temperatures than ordinary smoke. Higher temperatures lend to a more complete burn that, when ultimately compared to an open burn, is a cleaner, more efficient process.
In the early part of the 20th century ‘town gas’ was produced as a coproduct of the coking process and distributed throughout nearby communities as a cooking fuel and illuminant. However, the discovery of cheap fossil fuels made this and the early chemical industry it supported irrelevant. Gasification of biomass saw renewed attention during the world wars where petroleum became so scarce that many European economies were forced to switch up to one million petroleum fueled motor vehicles to operate on syngas.
In 1989 FEMA published a manual on building simple down-draft gasifiers for powering motor vehicles during a petroleum shortages. Since then, wood gas gurus like Wayne Keith (driveonwood.com) have expanded on these plans to build reliable biomass trucks that are capable of continental travel on a surprisingly low amount of fuel. Today, there are many outlets for DIY and commercially offered wood gas electrical generators.
The LWF biochar crew built this passive charcoal gasifier to run a lawnmower we found on the side of the road! Charcoal as a fuel for gasification is a clean choice, as much of the tars have already been driven out, but it burns hot and can lead to different problems. Look closely and you’ll see how the engine exhaust doubles as the air intake to help make this run a little cooler.
Almost simultaneously in another part of the world, humanitarian engineers were developing small gasifying cookstoves for improved fuel efficiency and cleaner combustion. The World Health Organization has reported that ⅓ to ½ of the world’s population are still cooking their meals on an open fire, and, that annually, up to 4 million people prematurely die every year from indoor pollutants as a result of cooking indoors. There is a huge potential for positive global impact through the development of cleaner biomass combustion technology.
Top-Lit Up-Draft Gasifiers
Born out of years of development was the TLUD gasifying stove. These devices use chunky biomass (typically wood chips or pellets) as the fuel to produce both a clean flame for cooking or heat, and charcoal, to be used as biochar or sold as a value added commodity. Along with cooks in the developing world, conscious gardeners and homesteaders have made use of TLUD technology to make biochar from landscape wastes while providing heat for greenhouses, domestic water, canning, or even processing chickens.
The TLUD works on a natural draft of primary air through a column of smoldering biomass. The process starts when a small fire is started on top of the column. Primary air is then drawn in through holes underneath – enough to keep it hot, but not enough to create and open burn. Dense smoke(syngas) is generated, and, once a strong draft is established, secondary air is pulled in through holes towards the top of vessel. This secondary air mixes with the syngas in the combustion zone where it burns much cleaner than an ordinary campfire. Limited oxygen just below the flame facilitates preservation of charcoal. This line between the flame and charcoal is sometimes referred to as the pyrolysis front.
There are many ways to build a gasifier, with varying degrees of sophistication for different applications, and I encourage you to research further on your own. For the serious DIY small producer, I’d recommend starting with the champion style TLUD. With it’s preheated secondary air, it’s a little more involved that what I’ve demonstrated below, but worth the effort in achieving a cleaner, neighbor-friendly burn.
The LWF biochar crew built a few champion style TLUDs last fall (see below, end of slideshow for photos). Of note is the larger of the two, where we expanded on the champion design and offset the flue, so we could use this large flat plate as a heating surface for heating up large pots of water for canning. What we really wanted a robust stove with longer run times, that would also help move the canning chores (and all that heat and humidity) outside in the summertime. This device will heat 3 gallons of water from the well to boiling in about 45 minutes, it runs at full strength for about 2 hours and yields 2-3 gallons of crushed biochar.
It’s challenging to build a robust gasifier without some welding, though we realize welding can be intimidating (it’s easier than you think) and isn’t accessible to everyone. Below is a slideshow we put together to demonstrate a very simple and robust, large TLUD build from a salvaged 100 gallon propane tank and 2 sections of 6” flue pipe. You won’t need a welder to build this, but you will need to acquire an angle grinder with a few extra cut off wheels, some good eye and ear protection, gloves, a drill and a couple of self tapping screws. Locals can try the Asheville Tool Library if you don’t want to buy an angle grinder for just this one project.
You’ll know that a batch is done when the temperature drops, it smokes a little, and you smell that familiar charcoal scent. Be prepared, you’ll need to be nearby to quench the char in time. If you miss it, your precious biochar will be consumed in the presence of air. Quenching provides an opportunity to create microscopic fractures in the char that further enhance it’s value as a microbial substrate. Some biochar gurus will even add mineral amendments, such as SEA-90 or Azomite to the quenching water to help encourage microbes to move in. pH testing at our facility indicates that biochar made in a TLUD may be more alkaline than biochar made in the retort method. This is likely due the open-atmosphere nature of the technology that facilitates an increased ash content, especially if you don’t quench it in time. Use caution when applying TLUD char raw, it’s best to allow pH to neutralize by blending it with rich compost and allowing it to set for a few weeks prior to application in the garden.
Winter is a great time to make biochar at your homestead. This year, instead of making a burn pile in the yard, save your little stuff that doesn’t go in the wood stove. “Waste” wood like downed limbs and orchard trimmings that don’t compost easily are perfect feedstock for a manageable one person biochar operation. With its multitude of applications, ease of construction and availability of materials, these small gasifying and biochar producing devices are deserving of a place alongside the solar cell and bicycle as one of the bedrock appropriate technologies.
Send us an email if you’d like, we’re happy to help to get you started!