Baja Rob's Biochar Log

Big Kiln Burn

2010-07-31T13:07:00.001-07:00

Our large kiln, while not particularly grand by commercial standards, is plenty big enough. At 2M tall and 1.6M diameter, the kiln basket has a volume of around 4M3, a capacity to produce about 300 kg of biochar from a load of scrap wood. The hood portion has an integral water jacket and internal gutter for condensing and collecting wood vinegar (insecticide and plant growth stimulant). The kiln base serves as the primary fire chamber. A large gantry crane is required to lift of the lid and remove the kiln basket for loading and unloading.

When the kiln was originally fabricated the prior year by a shop near San Jose, a series of miscues and lack of qualified engineering oversight resulted in a number of defects and deficiencies. These were noted last August when Stephen Joseph was on hand to commission the kiln. Stepehen determined that further operation would rapidly result in degradation and eventual mechanical failure, so he left the Costa Rican engineers with a fix-it list. They prepared some engineering drawings, but a breakdown in communications between the NGO administering the project, the organization charged with building the unit, and their engineers and machine shops resulted in a stalemate. Six months later, the kiln was still in the same sorry state. When funding was approved for the 2010 season, we (Biocombustibles de Costa Rica--BCR) were given the nod as mechanical contractors, with on-site engineering oversight by the kiln's original designer, Nik Foidl of Austria. That's when we settled on the big TLUD to prime the kiln (see prior post).

When we took delivery of the kiln, a number of additional materials and mechanical faults were noted, and more still when Nik finally arrived. There was a flurry of work, with lots of improvisation to substitute for materials we were unable to track down, or specialty machine shop work that would have resulted in excessive delays. Throughout this period we experienced exceptionally high rainfall. Since the kiln and TLUD were out in the open, the rains significantly limited our testing time. In addition to abundant rains, here in the humid tropics the equilibrium moisture content percentage of seasoned wood hangs in the mid- to high-20's. Driving out all the water significantly increases the amount of time and fuel needed to prime and operate the kiln. It also adds so much water vapor to the exhaust stream that the combustible gases of pyrolysis can be impossible to ignite for much of the firing cycle, resulting in unacceptably high emissions. A drying oven--a converted shipping container powered by the waste exhaust from the kiln--had been designed into the facility, but this would be one of our last mechanical tasks once we were under cover.

So there we were, out in the mud, dodging rainstorms, cobbling together hardware and complaining about wet wood. We did one run with high moisture content wood, quite memorable for the quantity of smoke produced that day! After that, we used the exhaust from my diesel truck to pre-dry the sawdust, and a half-load of sawdust in the TLUD to pre-dry the kiln load--incredibly inefficient, but better than smothering the planet with smoke.

Finally, we had a load of dry sawdust in the TLUD, and a reasonably dry load of wood in the kiln basket. Ready to fire! The TLUD was connected to the kiln through three 10cm automotive steel flex tubes, wrapped with insulation, and connected to injection ports in the kiln base. Though we'd already run and tested the TLUD, optimizing heat transfer to the kiln proved tricky. At one point the bonnet of the TLUD got so hot that the automotive flex tubes failed, resulting in an all-hands-on-deck fire drill with welding gloves and baling wire. We eventually figured out that the TLUD temperature was less important than the delta T between TLUD and injection port, and maximum air mass transfer was key. Finally, the kiln load crept up to 300C and could sustain pyrolysis without the TLUD. We switched off the blower, sat back, and watched the show. Click here for an annotated online slide show of the big burn.

Next up, building a roof structure to house the kiln and TLUD, integrating the drying oven, building a new much larger BMC reactor to replace last years mechanical disaster, and a specialty cross-draft pyrolyzer for African oil palm waste (pending approval of funding).

My TLUD's Bigger 'n Yours

2010-07-31T13:07:00.000-07:00

The kiln load (Gmelina mill scrap) must get up to around 280C before it will produce enough combustible gas to "kick over" into pyrolysis mode, then gases will burn in the kiln's fire chamber and generate sufficient heat to sustain pyrolysis until the entire load has been carbonized. Our kiln was designed to have combustible gas from a different source injected into the fire chamber to "prime" the kiln until it could produce enough combustible gas to sustain the reaction on its own.

We opted for a biomass gasifier for this purpose. Nik Foidl designed a beast for us––a TLUD (top-lit updraft) sawdust gasifier a meter in diameter, capable of generating 200-350kW. That's a lot of hot! A blower injects air into a space in the base of the unit, and the perforated floor of the basket allows air to migrate upward through the sawdust. Squirt a bit of kerosene onto the surface of the sawdust and ignite to get it started. Then put down the hood and turn on the blower.

The flame front migrates downward, toward its oxygen source, producing a mess of smoke (mix of combustible gases). A pair of air ports in the hood of the TLUD introduce more air, causing the smoke to burst into flames, and the hot exhaust gases are injected into the kiln. The TLUD is powered by a single large blower regulated by butterfly valves. The primary butterfly controls the total air introduced into the system. A "Y" and pair of butterfly valves control the relative amount of primary air, which is injected into the base and blows through the sawdust; and secondary air, which is injected into the hood to ignite the gases.

Hot, hot hot!

Know of a bigger TLUD? We'd love to hear about it!

Nod to Nik

2010-06-07T17:06:00.001-07:00

Nikolaus Foidl, designer of the Costa Rica Biochar Project's large kiln, is a brilliant scientist & engineer with wide-ranging intellectual appetites and an unquenchable thirst for knowledge. He marked his birthday with us here on the Osa Peninsula. We celebrated with a BioChar-B-Que. Happy Birthday, Nik!

The Big Chill, and Fire!

2010-05-30T15:57:00.000-07:00

After making biochar in our kiln, we allow the retort drum to cool to ambient temperature, for ease of handling and to avoid the risk of the hot char self-igniting. Curiously, when we take the lid of the drum, the char cools abruptly. What's up with that?! We kicked it around and concluded that it's probably due to rapid evaporation of volatile compounds. On completion of pyrolysis the atmosphere in the retort is saturated with residual volatiles. When the lid is removed, these diffuse into the air, triggering evaporation from the manifold char surfaces as the system equilibrates to the new atmosphere. The coolness we're experiencing is the latent energy of evaporation (in the same way that rubbing alcohol feels cool on the skin, and then is gone).

Far more consequential is spontaneous combustion! We had just bagged some biochar (day-old and auto-chilled as above) and chucked it into the back of a station wagon for transport. Then we resumed work re-loading the kiln. Fortunately, one of our group noticed the smoke and we quickly removed the burning bags and quenched them with water. If you google "spontaneous combustion" (bypass the apocryphal tales of "Human Spontaneous Combustion"), you find sites insisting that spontaneous combustion of a bag of charcoal is the stuff of urban myths (I can assure you, it is NOT). The best explanation I found was here: http://www.madsci.org/posts/archives/2000-01/949094004.Ch.r.html. Crushing the char before stuffing it in the bag exposes heaps of surface area to fresh air; stir in the heat of friction from crushing, add a lick of water from humidity condensing on the char surfaces to catalyze oxidation reactions, and Voilá! Instant fire. Take care with handling fresh biochar!

Dr. TLUD and the Coffee Caper

2010-05-30T15:01:00.000-07:00

A couple weeks ago I took a break from my kiln work on the Osa to visit a very different sort of biochar undertaking in the coffee country of Costa Rica's Santos region: a women owned and run stove building workshop (APORTES/ Givers) for use by the families of coffee pickers.

The project originated when Arturo Seguro of Sol Colibrí coffees of Costa Rica, on a marketing mission in the Seattle area, happened upon an environmental fair where Art Donnelly of SeaChar (Seattle IBI chapter) was manning a table demonstrating a TLUD biochar-producing cook stove. Arturo saw in the stove a solution to a problem: Coffee pickers are mostly seasonal migrants from Nicaragua and Panama who live in tin-roof shacks, generally without electricity or running water, cooking on smoky open-hearth fires—a notorious source of upper respiratory health problems and driver of habitat destruction from overharvesting wood. This is a big problem, impacting the lives of 10's of thousands of agricultural workers.

After a couple of design iterations, and the capable guidance of Paul Anderson (aka Dr. TLUD), they had devised a stove based on a 5-gallon pail that would be efficient, smoke-free, and produce biochar in the bargain. Art and Paul were on hand to help Arturo and crew kick-off the workshop. The stoves will sell for around $30. I brought sample back to the Osa with me; judging from the reaction of my Costa Rican colleagues, the TLUD stove may enjoy a much wider reception. Although most area farm families have propane cook stoves, they still do a lot of cooking on wood as well, and the advantages of a high-efficiency smoke-free stove are obvious!

(Unfortunately, the trip was marred by a failed wheel bearing on my truck during our descent back to the coast. Ay caray!)

Rocket Retort Rocks!

2010-05-15T09:31:00.000-07:00

Yesterday was the christening of my new kiln, the Rocket Retort, a culmination of many months of research, design, contemplation; and a recent spate of hard work. Like so many others bit by the biochar bug, I wanted to create a kiln for my own use. I also recognized the potential that a practical, high-performance, "personal" biochar kiln could have in leveraging distributed production among home gardeners and other small stakeholders, and perhaps ultimately, subsistence farmers worldwide. My prior experience of small biochar kilns, gleaned from YouTube profiles and my own backyard pyrotechnics, had been of barely-contained conflagrations that produced an uncertain sort of biochar. My Rocket Retort design was informed by my work as hardware development manager for a philanthropic-funded biochar project in Costa Rica, involving a much larger kiln designed by Nikolaus Foidl and guided by Stephen Joseph, two of biochar's leading lights. Design criteria for my personal kiln include:

Low cost materials
Basic shop tools only
Low emissions
Efficient biomass conversion
Controlled firing profile
Recycle pyrolysis gases
Collect wood vinegar

The 55 gallon drum--durable, affordable, widely available, easily handled--is at the heart of the design. A removable-lid drum stuffed with wood mill scrap serves as the retort. To prime the kiln, I had been considering scaling up one of the newer innovative biomass stove designs, but felt stymied by the challenge of refueling and controlling output. On a suggestion from stover-friend Charlie Sellers, I looked into the Rocket Stove (www.rocketstove.org/), a versatile design that addressed my emissions, fuel feed, and control concerns. The rest of the hardware fell into place after a bit of "outside the drum" thinking: Create fire chamber and insulating jackets (two total) by cutting ends off drums, slitting open, and welding inserts cut from a third drum. The tricky bit was opening the slit drums evenly to maintain the roundness of the now-larger cylinders. The nesting Russian doll cylinders rest on staircase ledges in the modified rocket stove base. Each cylinder is topped by a shallow cone-shaped lid with a central exhaust vent made by cutting a sliver wedge out of a sheet metal disc and welding the cut edges together. The lids are secured by bolts welded to the inside rim of the cylinders.

The other design consideration was collecting wood vinegar (natural pesticide and plant growth stimulant) and recycling pyrolysis gases. A two-inch steel pipe was threaded onto the bung hole on the lid of the retort drum, exiting holes cut into the shallow cone lids, and elbowing down toward the stove's fuel feed opening. A "T" fitting and valves enable directing evolved gases toward either a condenser pipe leading away from the kiln to collect wood vinegar, or directly into the fuel chamber to fire the kiln. The fuel feed opening is divided horizontally by a stainless plate, with the lower portion intended for intake air. Being able to block the throat of the upper portion of the feed chamber enables greater range of control and can improve combustion efficiency by limiting excess air.

We were thrilled with our first firing! The rocket stove enables ramping up temperatures gradually, which could be a big advantage when working with high moisture content feedstocks. The cross-over from distillation to pyrolysis was fairly tender. Directing all of the gasses into the stove's fuel chamber resulted at first in an over-temperature condition, which was alleviated by diverting pyrolysis gasses out the vinegar condenser pipe--at one point flames were shooting out two meters (very dramatic!)--stimulating conversation on the various uses to which these surplus combustible gasses could be put.

For future firings the kiln will be fitted with thermocouples and a multi-station digital thermometer so we can approach pyrolysis temperatures a bit more gingerly, with the goal of achieving a longer soak at the lower end of the pyrolysis range to retain more organic compounds in the carbon matrix for a more plant-effective biochar. Separately, I'm working on a design for a rotisserie-style reactor for making biochar mineral complex (BMC)--a step up from garden variety biochar. Wood biochar, clay, chicken litter, and mineral nutrients (rock phosphate, calcium, etc.) will be blended and loaded into a 55 gallon drum mounted laterally over the rocket stove for tumble-heating at sub-pyrolysis temperatures, to create a substance resembling aged terra preta (based on the pioneering work of Stephen Joseph).

It is worth noting that labor was not among my design considerations. Although labor cost is crucial in commercial economic analysis, home gardeners are known to lavish lots of time on their gardens, heedless of return on their labors. Likewise, backyard biocharers generally do it for the benefit of their garden and for sport (the thrill of the burn). As for the ultimate target audience, subsistence farmers, the low-value of their labor is one of the snares of the poverty trap. Producing biochar, and improving the productivity of their agriculture, might just help them pick the lock.

For a captioned slideshow, go to: Rockin' Rocket Retort. We'll get a YouTube together soon.

What is Terra Preta?

2009-08-28T13:07:00.000-07:00

Biochar is widely associated with Terra Preta, the famously fertile and persistent anthropogenic "black soils" of Amazonia. I had understood Terra Preta soils to be the result of deliberate "slash and char" practices by native Amazonians, as opposed to the much more destructive "slash and burn" agriculture introduced by European settlers, which leaves soils degraded and depleted after only a few growing seasons.

As reported in Charles Mann's book 1491, an extraordinary account of civilizations in the New World prior to contact (everything they taught us in school was wrong!), native peoples lacked the steel tools that would have been required to slash much of anything. He even recounts an experiment wherein rainforest locals were hired to chop down trees using the relatively primitive tools that were known to have existed prior to contact. Slashing your way into burning a forest plot for a brief agricultural fling, without steel tools, just doesn't fit into anyone's energy budget, sustainable or otherwise!

When we look at the agricultural practices of the contemporary descendents of Terra Preta's creators, a different story emerges. An episode of the BBC documentary series Around the World in 80 Gardens tells of Terra Preta soils made by smolder-burning rotting wood and then mixing with ashes, shards of unfired clay pottery, spoiled food, and other organic wastes; as demonstrated in this six-minute video clip:

For a more extensive recounting of the Terra Preta phenomenon, check out the BBC special: The Secret of El Dorado. This more complex view of Terra Preta as a fertilizer that was deliberated produced from char, minerals, and organic debris is consistent with lab analysis of Terra Preta soil particles, which appear to be accretions of organo-mineral nutrients around a char core.

When you think about the way plants acquire nutrients from the soil, and the long timescale of human cultural evolution, it just makes sense that, once the benefits of char as a soil amendment were observed, it would be embellished and improved upon by astute gardeners whose very livelihoods depended on successful experimentation and innovation. The question now is, can we likewise improve on basic biochar by learning a lesson from this ancient agricultural wisdom; only do it on a much grander scale through the judicious application of technology?

Biochar Guru

2009-08-17T08:59:00.000-07:00

I had the pleasure of spending some time in the company of Stephen Joseph, co-founder of the International Biochar Initiative, and one of biochar's true pioneers. Stephen was visiting Costa Rica as a consultant to our project, a slight detour from his home in New South Wales, Australia en route to Boulder, CO to attend the North American Biochar Conference

Stephen is a scientific genius, brilliant engineer, and visionary. Drawing on clues from multiple disciplines, ranging from surveys of "fired biomass" agricultural traditions to analyses utilizing state-of-the-art laboratory research tools, he has deduced how Terra Preta soils were created (not simply "biochar", as widely believed) and postulated plausible mechanisms by which they derive their extraordinary fertility and persistence. Next, he reverse-engineered their structure and came up with a recipe for their synthesis. He then went on to perform field trials with this synthetic Terra Preta, and has demonstrated extraordinary plant response, exceeding both biochar and conventional fertilizer treatments. This is an important accomplishment, coming at a time when biochar field research shows generally promising but often inconclusive results, and the mechanisms of the biochar/soil/plant interaction are still subject to speculation.

While Stephen's work is recent and needs to be corroborated by further study, it has important implications for commercialization potential, carbon balance analyses, and future research directions. Following Stephen's lead (a hasty white board sketch and much fast talking and hand waving), we are building a reactor to create synthetic Terra Preta from biochar, soil minerals, and other ingredients. This synthetic Terra Preta will be evaluated in field and greenhouse studies by CATIE (tropical agriculture research institution) along with simple biochar and conventional fertilizer treatments .

Osa Biochar Project Kiln

2009-08-17T07:52:00.000-07:00

The kiln built for the Osa Biochar Project was designed by Nikolaus Foidl, through association

with the International Biochar Initiative (IBI). It is a moderate size retort kiln (4M3 capacity) with a removable lid and basket for loading/unloading by means of an overhead hoist. It's a clever design, with a central chimney that passes through the retort from the wood-fired primary combustion chamber below. Once pyrolysis is underway, secondary air inlets promote combustion around the sides of the retort as well, for more even heating.

A unique feature of this kiln design is a water jacket for condensing pyrolignous acids (wood vinegar) and lower temperature pyrolysis gases. Water is circulated through the jacket while temperatures climb through the 150-280C range, and the condensate is routed to an exit spout with a dip tube immersed in water to further condense the smoke. These "smoke chemicals" have been demonstrated to stimulate seed germination and promote plant growth, and are now considered the main actors in fire-response vegetation such as chaparral. (Back in the day when I was studying this stuff, heat of the fire was held to be the trigger that stimulated germination and sprouting.)

Once temperatures in the load have reached 300C, the reaction became self-sustaining (no more need to stoke the firebox with wood), and the chimney outlet holds a strong flame. A few hours later, pyrolysis burns out, and the load needs to cool before exposing to air. The char is then crushed and screened. First production from the new kiln is being used in plant growth field trials conducted by CATIE, the Costa Rican agricultural research institution.

The kiln will eventually be set up at the site of the Sustainable Agricultural Center at La Palma, where diverse feedstocks can be processed into biochar for local farmers. It may be fitted with additional apparatus to utilize waste heat for crop drying and pre-drying on-deck kiln loads. A specific need that has already been identified is powering a drying kiln for timber bamboo grown by the local "Amigos de Bamboo" agricultural cooperative--a key step in promoting commercialization of locally cultured bamboo as an alternative to harvesting rainforest trees for construction.

How Dry, and Why?

2009-08-02T10:58:00.000-07:00

Dryness matters, especially when you're working with wood waste, as we are. As discussed in a previous post, excessive moisture content (MC) in the feedstock hurts you on several fronts:

It takes more time and fuel to reach pyrolysis temperatures;
More fuel means more ash in the fire chamber that can interfere with thermal flows;
In a retort kiln pyrolysis of the load will be uneven, compromising the quality and yield of the char;
In a direct-burn kiln, the result is excessive polluting smoke and difficulty flaring-off waste gases.

A word about Moisture Content (MC) of wood and Relative Humidity (RH) of air. Both are percentages of water, which only serves to mislead, since they have about as much in common as apples and Frisbees. MC refers to the amount of water in the wood as a percentage of dry weight. Depending upon the wood species, freshly cut saturated wood will have an MC in the 30's. Relative Humidity is the percentage of the maximum potential water content of air at a given temperature. Here's the tricky bit: the maximum potential water content of air varies with temperature. A lot.

Under most terrestrial conditions, the equilibrium moisture content of wood (EMC) will be in the teens or drier. Wood waste that's allowed to air dry will approach the EMC as a function of surface/volume and how it's cut (end grain dries faster than other surfaces). Just age it a while, and you're good to go. But in the humid tropics, where temperatures are high and the relative humidity hangs in the 90's, typical EMCs will be in the 20's. Residents of the humid tropics are all too familiar with high EMC's; perfectly clean T-shirts get all moldy-smelling, not because they're dirty, but because the material is damp enough to support fungal growth (yuck!). EMC's in the 20's are high enough to complicate pyrolysis. Simple air drying is not dry enough.

The trick is to elevate the temperature and move air over the surface. Heating air from 30 to 60C takes the RH of the air from 100% to 25%. A given parcel of air that's been heated contains the same amount of water, but now its capacity to do the "work" of drying is much greater. Going from 30 to 60C is a piece of cake with a solar drying kiln. Making a drying kiln that's cheap and simple to use with unwieldy mounds of biomass is the design challenge. Stay tuned...

Melina Mill

2009-07-29T15:04:00.000-07:00

Our feedstock of choice is forestry waste from the Melina mill, just a stone's throw from the shop. Melina (Gmelina arborea) is a fast-growing tropical hardwood native to Asia, related to Teak, that's widely used as a utility timber (pallets, plywood, construction lumber, millwork, even furniture making). Our local mill cranks out pallet pieces which get carted off and assembled elsewhere. The waste comprises "flitches" (semi-rounds from squaring up the logs), trim scrap (mostly in the 2cm by 5-10cm range), and sawdust. We're focused first on the trim scrap, because of its abundance and the fact that it's easy to handle and dries relatively quickly.

Melina is widely grown in vast monoculture plantations and harvested after only 10-12 years. In our area it is cut into roughly 2M logs, dragged out by oxen, and loaded onto flatbeds. There are several Melina mills on the Osa, at least two in the greater Puerto Jimenez area (where our shop is). Once cut, the stumps sprout multiple shoots, and seedlings also sprout from the newly sunlit soil. If plantation sites are not cleaned after harvest, a dense impenetrable Melina thicket will grow up through the trim slash with little prospect of commercial utility.

Can-In-Can Kiln, Takes 2-20

2009-07-07T14:14:00.000-07:00

Moisture is the enemy. And waste biomass in Costa Rica's Osa Peninsula during the rainy season is nothing if not moist! To make matters worse, our feedstock of choice, Melina mill scrap, has a reputation in lumberman circles for persistent high moisture content. Moisture messes with you on several fronts: You have to drive it off before pyrolysis begins, so you consume more fuel wood (and time). We're using the same mill scrap for fuel wood, so the difficulty is compounded by smoky fires that are slow to get hot and require that much more wood to get the job done, resulting in that much more ash in the bottom of the fire chamber,

further confounding kiln performance. If that weren't enough, the volume of wood in the kiln retort (inner chamber that gets charred) is substantial enough so the outer portion (closest to the heat) has begun pyrolysis while the inner portion is still, quite literally, blowing off steam. The inevitable result is non-uniformity in the char, and frequently a high fraction that does not get charred at all.

We made a number of modifications to the kiln to improve its performance and accommodate the high-moisture fuel. These included more air intakes, a perforated kiln shelf to minimize ash blockage, corrugated roofing panels as thermal shields surrounding the kiln, and fitting the retort (inner drum) with a metal "diaper" to ease handling and minimize post-firing char burn. We also did our best to dry the scrap by sticker-stacking it and exposing it to the sun by day (running out in the middle of the night wearing nothing but our flip-flops to cover the stacks with plastic tarps if we get caught unawares by a tropical downpour!).

But the most important innovation we implemented was the afterburn. As described in my first can-can post, when pyrolysis begins, the fire really rips, promoting a positive feedback loop of heat-pyrolysis-combustion until (theoretically) all the pyrolysis gases have been driven off and you're left with nothing but char. Problem was, ours left us with a lot of wood, too. The inner portion of the load wasn't getting hot enough fast enough to "keep up" with the outer portion, because it had all that steam to blow off. So I implemented the afterburn:

After active pyrolysis winds down (no more roaring jet-engine-in-a-can), let it sit there being hot (driving off any remaining moisture) until the last embers in the bottom of the fire chamber have nearly burned out. Then re-load with fuel. This "second burning" takes a crack at the now-dry wood in the middle of the retort. You get a second coming of pyrolysis (jet-engine-in-a-can), though not quite as robust as the first. But when it's all done, you'll have nearly all char. (We never got 100% char, due to the fact that the "diaper" zone never sees the flame.)

We were ready to declare victory and proceed to a new kiln design when we were implored by the plant research group fraction in the project to make them some biochar for their field trials. A much larger kiln was under construction but was running behind schedule. Meanwhile, the plant research group had made commitments to graduate students from other institutions who were coming to Costa Rica for biochar thesis research. Plus, the growing season had begun and waiting longer could mess up an entire research season. So we made batch after batch of biochar using high-moisture-content Melina mill scrap in the inefficient can kiln.

How inefficient? An efficient kiln design should have a yield ratio of around 1:3; in other words you'll "sacrifice" (burn) about 1/3 of the wood volume as fuel for the 2/3 that gets turned to biochar. Given design limitations of the can-in-can kiln, at best it's probably a 1:1 proposition. With our high-moisture wood, we were running at 3:1 or worse, turning the yield ratio on its head. Not good. But they really needed biochar!

The English Kiln, Take 1

2009-07-06T11:33:00.000-07:00

That's not "English" as in country of origin; we named our kiln after a charcoal-making design that Alex English had experimented with while attending an appropriate technology conference in India some nine years ago (see English Kiln). Unlike our can-can kiln (previous post), this is a "direct" burn design, i.e. the feedstock is partially combusted directly and reduced to char, rather than being cooked "indirectly" from without. The knock on direct burn designs is the smoke they produce--including potent greenhouse gases. Alex added a chimney and afterburner to his, intending to flare-off the smoke, ideally reducing it to mostly heat, water vapor, and CO2.

(CO2?! Isn't that bad? Only if the "C" comes from burning fossil fuel.

The fate of most all living biomass is to wind up as CO2 in the atmosphere; quickly if it is burned, or more slowly as it gets metabolized through the lower reaches of the food chain. Since we're making biochar, we'll be carbon negative--reversing global warming--even if we spill a bit of "C" along the way.)

Our experiences with the can-can kiln told us that the high moisture content of the wood was problematic. We also observed that the board-like form of the Melina scrap often led to broad surface contact between pieces, effectively reducing the useful surface area. In the interests of improving our chances for a decent burn the first time out, we cut the wood into smaller chunks to increase surface area and reduce contact between pieces.

Still concerned about moisture content, we decided to fill the kiln with our little wood chunks and build a small fire underneath to drive off moisture before formally igniting it from the top, as intended. We thought we were pretty clever as we watched a cloud of steam wafting out the top. When the cloud became denser, hotter, and tainted with a brownish color and creosote odor, we started feeling less clever. Wood just doesn't conduct heat very well, and things got a bit too toasty down in the bottom. We had unwittingly initiated pyrolysis in the load.

Of course, pyrolysis is what it's all about; but the design calls for initiating pyrolysis in the top and controlling intake air so the pyrolysis front will move slowly downward through the load. By initiating pyrolysis in the bottom with our external drying fire, we were faced with the prospect of the entire load going off at once. Sort of a green-biofuel version of the "China Syndrome". Not good.

We tried to suffocate the load it by collaring the intake vents, and put on the lid and chimney stack in an attempt to shunt smoke away from the building. But the damned thing had the bit in its mouth and was making a break for it. Dense smoke was pouring out with no sign of abating.

Reluctantly, we decided to abort the mission and overturn the load.

Can-In-Can Kiln, Take 1

2009-07-01T12:35:00.000-07:00

My capable collaborator for pyrolysis pursuits in the Osa Peninsula has been Jason (a.k.a. "Pollo Loco"), proprietor of one of Costa Rica's leading renewable energy companies. I'd been introduced to Jason the season before when, while blathering on with another local expat about the unalloyed goodness of biochar, I was told, "You've got to talk to Pollo." Jason was already into pyrolysis; his interest was more on biomass gasification for powering generators--perfectly compatible with my own biochar fixation.

Jason got us queued onto a nascent biochar project coming to the Osa that was funded by a philanthropic organization, with Costa Rica's tropical agricultural research institution and the quasi-governmental "clean production center" as primary participants. We inserted ourselves into the group's circle of communications. Their mission was to create a biochar pilot plant and investigate biochar application rates and plant response. As production scaled up, surplus biochar would be used for local habitat restoration work. Target biomass waste streams included bamboo, residue from African palm oil pressings (a major regional crop), and Melina mill waste (a fast-growing, plantation-grown utility wood species used in pallets, plywood, etc.).

The bamboo and palm oil operations were some distance away, but the Melina mill was just a stone's throw from Jason's shop. So we got a pick-up load (which they were only too happy to load into my truck; mill waste was choking the site, and they regularly had to haul the stuff off to dump it out in the forest--nasty business). First impression: This stuff is WET. So we sticker-stacked it to dry in the sun. Now we needed a kiln.

Designs for pyrolysis kilns are all over the map, from traditional charcoal pits to simple can-based affairs for the independent-minded backyard barbecue-er. If you google "making charcoal", you'll find heaps of links, including lots of YouTube videos. There are two basic approaches; direct, and indirect. Direct method kilns smolder-burn the feedstock by restricting airflow (producing lots of smoke). Indirect method kilns enclose the feedstock in a container and fire it from the outside, using the escaping combustible gases to feed the flames. I found an indirect design based on a 1-gal. can inside a 5-gal. can. I scaled up the design to incorporate a 22 gal. drum inside a 55 gal. drum. Jason made the necessary modification with his cutting torch, and a kiln was born.

We cut the Melina to fit the inner drum (known as the "retort") and stuffed it full. With some awkward gyrations we managed to center it open-face-down on the bottom of the 55 gal. drum. We filled the space between the drums with wood, piled more on top, and lit it. With holes cut around the lower rim of the outer drum, flames were drawn downward toward the incoming air. After a while, combustible gases escaping from the bottom rim of the inner drum fed the flames; it really roared.

After the pyrotechnics burned out and cooled, we overturned the whole affair to see what we got. There was a bit of char, but mostly some slightly blackened wood. This was not to be as simple as advertised on the YouTubes!

The Pyrolysis Arts

2009-06-30T15:27:00.000-07:00

Just as "biochar" sounds like something you don't want to have happen to your steak; "pyrolysis" sounds like something you don't want to catch. The connotations are unfortunate. Because "pyrolysis" of biomass is how "biochar" is made.

Pyrolysis is defined as thermal degradation in a restricted-oxygen atmosphere. When you pyrolyze biomass, you wind up with a mix of combustible gases, volatiles, and solid residue. The nature and relative proportion of these co-products depends on the pyrolysis environment and the type of biomass you started out with.

(There isn't yet universally accepted terminology in this field, so here's my take: The generic solid residue of pyrolysis can be referred to as "char". When this char is burned as fuel, as it has been for millennia, call it "charcoal". When we apply it as a carbon-sequestering soil amendment, call it "biochar". OK?)

The biomass, or "feedstock", is typically crop residue or agroforestry waste; but just about anything that was once living or derived from living material can be pyrolyzed, including sorted municipal waste and de-wetted sewage. As for the pyrolysis environment, that's all over the map--maximum temperature reached, heating rate, dwell time at different levels, presence of small amounts of oxygen, suffusing with certain gases, size of the biomass particle, etc. Larger scale engineered plants operate more like refineries, and the pyrolysis environment can be manipulated to maximize the yield of particular products; bio-oil for processing into biodiesel, combustible gases for resale or direct power production, and other commercially valuable products. Alchemy comes to mind. Given the huge range of inputs and variables and possible co-products, referring to the "Pyrolysis Arts" seems well justified.

Our interest is the solid stuff, the lowest common denominator. In the most basic char-making kilns, the gases and volatile compounds produced are consumed in the process, with the excess either released to the atmosphere or burned. Since many of these compounds can be potent greenhouse gases, atmospheric release is a no-no; if nothing else, we'll want to flare them off. Better still would be to capture some of the heat and use it (for drying more biomass, for example).

Many future posts will be devoted to experimentation with and optimization of char-making kilns.

Birth of an obsession

2009-06-29T16:24:00.001-07:00

It was April 30, 2008. I know because it's stamped in my passport. Diane and I were driving back to Costa Rica's Osa Peninsula from the cool coffee highlands of Boquete, Panama where we'd gone on a "visa vacation" (non-residents are required to leave the country every 90 days). We took advantage of the hotel's high-speed internet for downloading and were plowing through a pile of Science Friday podcasts on the drive back, when Ira Flato's guest spoke of something he called "biochar", which he described as fertilizer made from pulverized charcoal. Whoa! Hang on a sec! We both had MS degrees in Botany. We know what fertilizer is; charcoal is NOT. Who was this crackpot, and how'd he get to be on this highly respected, nationally syndicated science program?!

Curious, I googled "biochar". What I learned blew me away. As a soil amendment, biochar is not only a potential source of plant nutrients, but it also improves water retention, reduces acidity, and changes soil surface properties to improve nutrient availability. It persists in the soil, so you only need to add it once. It reduces reliance on petrochemical fertilizers, improves groundwater quality, and reduces emissions of greenhouse gases common with traditional agricultural. As if that weren't enough, a co-product of making biochar in specially designed processing plants can be biofuel or electric power. And it's made from agricultural waste or timber slash, solving a waste disposal problem. Best of all, biochar persists in the soil for hundreds to thousands of years, sequestering CO2 and reversing the effects of global warming.

Is this possible? A potent and permanent soil amendment that improves environmental quality, is a non-fossil fuel energy source, solves waste disposal problems, and reverses global warming? Why didn't I know about this? Why doesn't everyone know about this?!

It's not even new. Turns out, there are areas in the Amazon basin know as Terra Preta (dark soil) where native peoples appear to have been practicing "char agriculture" for millennia. It was described in the soil science literature back in the '60s, but for some reason languished in relative obscurity until very recently. And while charcoal making is among the most ancient of the industrial arts, even modern "high tech" methods of simultaneously producing both char and power date back to WWII. Yet, despite its huge range of benefits and technical feasibility, nobody I talked to had even heard of biochar, and hardly anyone was actually practicing it.

Biochar embraces a constellation of disciplines that mirrors my personal interests, experiences, education, and aspirations; a "perfect storm" of environmental activism, plant science, technology development, sustainable agriculture; a chance to contribute, learn and grow. Plus, burning stuff is fun! Unbound by work or other hard commitments, and already dedicated to the principles of sustainable living, I decided to up the ante by making the advancement of biochar my personal mission.