Here’s a story from some fellows in Amphoe Prao trying to do something about smoke from agricultural field waste and hoping to get carbon for soil improvement rather than ash :
This shows a film of a makeshift biochar kiln in action:
https://www.youtube.com/watch?v=iQCxu4_Yo-w&feature=youtu.be
What is happening? Well, I saw a farmer burning a fallow field that he had strimmed, and racked into piles. Dylan was the first to see the fires, and we then went and took a look, and started talking to the farmer. It was obvious to me that each pile needed more air. This was near Warm Heart and I suggested to the farmer that i would like to see if I could make something to burn the biomass without as much smoke. He said fine, help yourself.
I put mind into gear, and went shopping for bits in Phrao. I found some 5ft. long roofing sheets, several 6m. lengths of angle iron and some self-tapping screws, and made a five ft. cube, open at the bottom and with a large hole in the top with an even larger chimney, suspended six inches above the hole in the top. Dylan was convinced it needed much more air, so I put a 6″ gap in the middle of each of the four sides. I borrowed one of Warm Heart’s trucks and collected some biomass from the farmer’s field, but there wasn’t much left, but I thought enough. It was a bad thought. This prototype was called the Star Ship by the kids.
Dylan and I tried a burn, but it was not a real success. Small amount of smoke, but lots of black ash sent up. It caused anger among their neighbours.
We all had a post-mortem, and decided to close the gaps in the side and fill it with something similar to rice straw, namely lemon grass leaves. I collected three truck loads, putting more on each trip. I can now hand you over to Michael Shafer of Warm Heart, and his email about the test which I couldn’t attend.
Gordon Hirst and Michael said:- That’s what my kid’s call Stuart’s shiny contraption in the middle of the football field.
One and all have been highly skeptical about the UFO’s potential. Today’s tests put all the skeptics to shame. The UFO performed wonderfully. Details below.
Before starting, I made a number of minor adjustments to the original design.
- I closed all of the side vents, leaving only an opening around the bottom for air inflow.
- I reduced the gap at the bottom to a single thin cinder block from the original two.
Gordon and I tried to create a test situation close to the anticipated field use. We stuffed the UFO full of dried lemon grass tops. It took 8-9 large bags of fuel, approximately two pickup loads to fill it completely. (Rough estimate of volume: 6 cu m) One of the kids jumped on top of the pile to compress it.
We top lit the pile.
The fire took immediately and burned very hot. For the first ten minutes we had a lot of flame and considerable smoke. During this time, we had flashes of burning gas bursting through the cracks between sheets of roofing metal. Toward the end of the 10 minutes,the fire had reached the bottom of the pile and began to creep out on the ground.
At this point – approximately the same time as with our regular TLUDs – the smoke stopped and the flames around the sides disappeared. Looking in the cracks around the top we could see a fairly chaotic pattern of orange flame floating above the pile. The chimney sucked the flames up. (Never saw the classic purple flame at all. So much space between the ultimate top of the pile and the chimney perhaps the orange was the inevitable consequence of cooling).
At one point we began to get a lot of smoke. When I investigated, I found that part of the pile had collapsed against the side of the UFO, cutting off the upward flow of air from the ground level “vent.” When I adjusted the pile and pushed stuff around some to recreate a flow, the smoke stopped.
We decided to quench the pile after an hour to see what was happening.
We poured a huge amount of water on the pile and even so it reignited an hour later.
When poked open, the pile revealed that pyrolysis had gone in about 6-9 inches on average. (Much more in some areas. Interior airflow was very chaotic and the burn varied all over the place). Within the pile, the lemon grass was entirely untouched.
The outer layer was GREAT biochar. Even wet, it “clinked” when crushed in your hand. Perfect carbonization of the stalks preserving every detail, brittle, essentially no ash on the surface of the pile.
Lessons learned:
- KISS: keep it simple, stupid.
- The simple sheet steel was entirely unaffected by the process. No burn holes, little discolorization, no warping, sagging or whatever.
- The frame was totally unaffected.
- The “box” kiln (with plenty of leaks, drafts, etc.) produced a very chaotic burn, but pyrolysis preceded without trouble.
- Filling the container to the max made a huge difference. The mini-piles used previously simply allowed way too much air to give a good test of the kiln.
- Quenching is as big a problem as we have always thought it was.
- Burn time is as big a problem as we have always thought it was.
What next:
Given these lessons, Gordon and I have decided to make some big changes in our plans.
- We have decided to abandon the pyramid model as unnecessarily difficult to make and maintain, and wasteful of materials (all those wasted little triangles). We plan to try with a modified box design that is perfectly cubical to minimize material wastage.
- We have decided to keep the interior chimney/outside airway concept from the Vietnamese design but to modify it.
- On the one hand, we believe that the ability to add oxygen to the interior of the pile is critically important to speed the burn process and
- On the other, we believe that the ability to inject water into the interior of the pile is critically important to speed the quenching process. (I am really hung up about the quenching issue. We poured water onto this pile to very little effect. The problem is that even pyrolyzed, the straw in arrayed in such as way as to sluice the water off, thus keeping it from penetrating. Also, the heat instantly turns the water into steams which explodes outward, thus not touching the burning areas below. I really think that the way to go is going to be to force water up into the inside of the pile. Here it will cool, etc., but more important, when it flashes to steam, it will escape outward through the still pyrolyzing straw, cooling and killing the oxygen. In fields where there is no easy access to water, this is the only way I think that we will be able to quench without busting our springs toting water by truck!)
Tomorrow, Wed., I will test various thicknesses of a “cement board” to see how it stands up to heat. Because it comes in 4×8 sheets, it lends itself to the extremely easy construction of modular wall and top pieces for a cubical kiln in which the board can be easily and quickly replaced if broken or burnt through.
If with testing it turns out that cost/burnout rate make the cement board solution impractical, a second option is to use the corrugated roofing steel Stuart used. Because it comes in much smaller and less convenient sizes, however, it will require much more work in the construction of the frames, and from a practical point of view seems to be a second choice at this point. That said, tomorrow I will test the sheet steel and cement board at the same time to see if I can establish use-life comparisons between them.
Michael
I then proposed building the same basic box at the School of Renewable Energy to its Director Dr. Natthawud Dussacee. He gave me the go ahead. It’s built and is ready for a trial early this coming week. I’ll keep you in the loop.
Stuart
Ricky,
Thanks for getting the discussion of biochar out into the open, especially as it regards agricultural field waste. It is true that Chiang Mai and the North in general suffer a great deal of smoke pollution as a result of forest fires. What often goes undiscussed is the huge amount of smoke generated by burning rice straw and corn stover. Generally speaking, for every ton of rice or corn produced, at least an equal amount of straw and stover is produced. Around here, this is burned in the field. The piles are very tightly packed and so burn very slowly and at very low temperatures. The result is a smoke column that contains a huge amount of particulate matter, as well as a huge amount of NOX and other smog precursors, dioxins and furons.
The government routinely claims that it is going to solve this problem by, for example, collecting all of the field waste to compost or some such. The waste’s very low density, however, means that transportation costs far exceed any possible value for the waste as a fertilizer feed stock and doom such notions. The result is that farmers, with no better options,burn the stuff.
There is no need to do so. In fact, for farmers doing so is the equivalent of burning money.
As you note in the post above, at Warm Heart we are working on a simple, light weight, transportable, easy to manufacture, cheap, in-field pyrolyzer that any farmer can use to turn his field waste into high quality biochar. The process should be entirely smokeless and should produce virtually no noxious emissions. The resulting biochar will be approximately 15-20% of the volume of the original waste pile and will weigh approximately 25% as much. With such a reduction in density and increase in value added, the biochar can now profitably be moved to market or to a fertilizer manufacturing facility. A smart farmer, however, will mix his biochar with manure, maybe a little dolomite, clay, rice husk ash (if he is growing rice), etc. and make a high quality fertilizer that will permanently improve the quality of his soil.
For the farmer, the immediate benefit is that this relatively slight effort can within a year or two begin to reduce the need for expensive synthetic fertilizers, increasing net income. Even if you don’t believe the claims that biochar can produce 50-200% yield increases by itself, there is substantial evidence that in fields that were once doused with synthetic fertilizers, biochar can produce yields that are at least 80% of those produced with chemicals. Given the huge cost savings from not buying chemicals, an 80% yield results in a large net income increase.
From an environmental point of view, the immediate benefit is an end to smoke pollution caused by crop burning. But the long-term benefits are much more important. Biochar production for fertilizer use is perhaps the only carbon negative activity around. For every ton of biochar produced, three tons of CO2 are removed from the atmosphere – permanently – and sequestered in the soil. Given that tiny Phrao, which is largely forest, produces at minimum 150,000 tonnes of agricultural waste annually, the potential benefits are not insignificant. If the government were to enforce anti-burning regulations in Phrao and force farmers to use in-field pyrolyzers, a minimum of 50,000 tons of CO2 would be sequestered annually. Replicated on any scale in Chiang Mai Province, the climate change benefits are potentially huge.
Just a thought.
If you or any of your readers are interested, we will be testing the first prototype of the transportable in-field pyrolyzer during the week or so after SongKran. I suppose people can get in touch with you if they would like to come and I can provide dates, details and directions.
Michael and Ricky – I’m very interested in learning more about your work on bio-char. Michael – Can you go ahead and provide more details on your upcoming tests, or a contact e-mail address/phone number where you can be reached? Much obliged.