Perhaps, Time, Temperature, Turbulence is too easy to remember?
“TTT” is elegant shorthand for how to achieve clean combustion and perhaps other factors are too obvious to mention?
At the same time, leaving out other clean burning factors confuses me.
Metering the right amount of woodgas into the combustion zone is important, too. Too much woodgas makes smoke right away.
Air Rich has to be included. Starving a fire can even put it out.
Yes, high Temperatures are very important.
Air, woodgas and fire need to be well Mixed.
High temperatures reduce needed residence Time.
MART MixT is a lot more clumsy…
https://aprovecho.org/wp-content/uploads/2021/12/12-29-harris-mixers.jpg458580Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2024-10-04 17:28:332024-10-04 17:29:41Expanding the Three T’s (Again)
ARC is working on three types of Zero Green Premium biomass heating stoves designed to protect health and climate. “Zero Green Premium” means that the new product costs the same as the dirty one it replaces. As a rough estimate, ARC uses 0.5 grams per hour of PM2.5 at <5% Black Carbon ratio to define the performance and emissions that protect urban health and climate.
Sixty percent of electricity in the US is generated by burning natural gas (40%) and coal (20%). Utilities are wondering how to meet increasing demand while replacing fossil fuels. Help is very welcome!
When renewably harvested biomass is burned cleanly enough, could it join solar, wind, and hydro as another useful energy resource? Heating a home with wood is ~ 80% efficient. Making biomass into alcohol is ~ 1/5th as efficient. (Energy Primer, 1976)
Is there enough biomass? In 2023, the DOE estimated that the US produces more than 1 billion tons of renewable biomass per year. Providing the needed ~3 tons of biomass per US home (currently heated by burning fossil fuels) requires 420 million tons, a drop in the bucket.
Six steps: Clean burning of biomass
Optimize heat transfer efficiency
Control the rate of reactions
Achieve molecular mixing in the combustion zone
Maintain temperatures above 850C
For a minimum of 0.5 seconds
In an air rich environment.
https://aprovecho.org/wp-content/uploads/2024/09/zero-green.jpeg450400Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2024-09-27 16:13:422024-09-27 16:32:33Working Towards “Zero Green Premium” Stoves
Small sticks make higher temperature gases, better for heat transfer efficiency, but more smoke
Monitoring many fires seems to show that along with density, moisture, etc., the diameter of sticks has a large effect on both heat transfer and combustion efficiency.
In a Rocket stove without a closing door, there is obviously a lot of cold excess air entering the fire. How do we raise Temperatures without limiting primary air?
Our observations seem to indicate that burning smaller diameter sticks results in more flame/higher temperatures. However, burning smaller diameter sticks also tends to make more smoke. For this reason, it may be that burning small sticks increases thermal efficiency but decreases combustion efficiency.
Conversely big sticks seem to burn slower making less flame, resulting in lower temperatures while making less smoke. Since flame from wood makes smoke, when the wood becomes charcoal, much less PM2.5 is emitted.
The Jet-Flame can burn 2” by 2” sticks and testing shows that PM2.5 gets lower with bigger diameter sticks. The jets of air make the made charcoal very hot and even big sticks stay lit. In a normal Rocket stove without a Jet-Flame, especially with wet wood, only smaller sticks will keep burning.
The goal is to create as-hot-as-possible gases flowing next to the heat exchanger (pot) while controlling emissions. The size of the sticks does seem to have a significant influence on thermal and combustion efficiency.
Sunken pot, 50% thermal efficiency cook stove with chimney
When (oh, when!) will PM2.5 be included in carbon offset methodologies?
Who can blame stove manufacturers for selling high thermal efficiency/low combustion efficiency stoves when protecting health is not financially rewarded?
Factories can only sell what the market demands even when they manufacture better stoves. Manufacturers, like SSM, already have slightly more expensive, much cleaner burning stoves ready to go.
Including PM2.5 in carbon revenue might go a long way to help projects pay for higher combustion efficiency stoves.
PM 2.5 needs to be reduced by ~ 90% to protect health in kitchens with 15 air exchanges per hour. The needed % reduction is halved when air exchange rates are doubled. This may be the most cost effective way to protect health? Cooking outdoors with an estimated 60 air exchange rates per hour is very effective in reducing exposure.When cooking inside, perhaps a durable stove with improved combustion efficiency and a chimney would help the large percentage of cooks who, for many reasons, continue to cook with biomass?
https://aprovecho.org/wp-content/uploads/2024/09/sunken-pot-cad.jpg630438Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2024-09-06 15:46:042024-09-06 16:04:40Increased Air Exchange Rate Protects Health
Wow, heat transfer efficiency is easy to understand!
Read on…
Raising the Temperature of gases flowing next to the heat exchanger (the pot in a cook stove) is probably the most effective technique in a Rocket stove to increase heat transfer efficiency (use less wood for cooking).
Doubling the Temperature of gases doubles heat transfer efficiency.
Doubling the Area exposes to the gases doubles heat transfer efficiency.
Doubling the Velocity of gases ~doubles heat transfer efficiency.
Doubling Radiation increases heat transfer efficiency to the 4th power.
Increasing the view factor helps, too! That’s the proportion of the radiation strikes the bottom surface of the pot.
A 6mm to 7mm channel gap pot skirt increases heat transfer efficiency by ~ 25%.
Simmering at the needed low firepower can save a lot of fuel, too.
https://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.png00Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2024-08-30 14:27:352024-08-30 14:27:36Heat Transfer Efficiency!
New SSM Health/Climate Biomass Heating Stove Buildings
Here is a video I made last week, introducing some of the the new things I saw on my visit to Shengzhou Stove Manufacturer (SSM). I keep on saying in the video (Sorry!) how much I admire Mr. and Mrs. Shen. Mr. Shen is a great engineer who has built the new buildings, installed the machines, and taken the ideas that Dr. Winiarski brought to him and manufactured over five million durable, affordable Rocket stoves. Mrs. Shen runs the business, does HR, sells the stoves, etc.
An amazing combination! Daughter, Kristina and nephew Chenkai, are being trained to assist the business. You’ll meet the younger generation in the video. Kristina went to the University of Oregon and is now a Vice President at SSM. Chenkai leads a team selling stoves out of his offices in Shenzen.
I walked around new buildings, tested clean burning stoves (including the Jet-Flame and forced draft TLUD) and saw a new wing being built (above) with huge machines to make health/climate biomass heating stoves, a new venture. Since 1976, Aprovecho has helped approximately one hundred stove projects, with SSM becoming the most commercially successful, rolling profits into expanding capacity.
I just returned to the Oregon lab from a two-week visit to Shengzhou Stove Manufacturer. The next few newsletters will be about SSM and progress made. There’s a lot to talk about! SSM has sold over 5 million stoves and the factory is a wonderful place to visit.
SSM started testing stoves for durability twenty-four hours a day (three eight hour shifts at a nearby farming community) three years ago. The farmers keep fires going in eight SSM stoves and the tests continue for one year of each stove. That’s 8, 860 hours.
It’s great that SSM has been doing long term, real life testing of their stoves. Previously, tests in a kiln with wet, salted pieces of metal resulted in confusing estimates of durability. In 2017, M.P. Brady and T.J. Theiss shocked the stove world by showing that in a wet, salty, hot kiln even very expensive metals were not long lasting. (Energy for Sustainable Development 37 (2017) 20–32, “Alloy Corrosion Considerations in Low-Cost, Clean Biomass Cookstoves for the Developing World”, Michael P. Brady, et al.).
The SSM testing is being written up. It seems to show much longer durability of various combustion chamber metals when real fires are used. Full details to follow.
https://aprovecho.org/wp-content/uploads/2024/08/PHOTO-2024-08-11-00-06-57.jpg8101080Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2024-08-16 15:29:022024-08-16 15:29:42Durability Testing at SSM
Using the ISO testing protocols, Champion (2021)* reported energy emission factors (g/MJ) from the Three Stone Fire, a forced draft Pellet Stove, a forced draft Wood Fan stove, a natural draft Rocket stove and a charcoal stove. ARC added results from a Jet-Flame stove. Using the estimates of global warming potential from the Gold Standard 2017 Methodology** we started to develop a feeling for how various stoves might address climate change.
The calculations suggest that the Three Stone Fire could be a lot worse for climate when Black Carbon and short-term climate forcers are included in offset calculations. At the same time, forced draft stoves appear to have the potential to generate increased emissions reductions (and higher carbon revenues).
*Champion, Wyatt M., et al. “Cookstove Emissions and Performance Evaluation Using a New ISO Protocol and Comparison of Results with Previous Test Protocols.” Environmental Science & Technology, 2021, 55, (22), 15333-15342. DOI: 10.1021/acs.est.1c03390
Community organizers often say that to be successful the solution has to come from the folks with the problem. Another important factor is to appreciate the culture and long evolved expertise in their technical and social solutions. The women at Rancho San Nicolas, where I lived for eight years, were incredibly skillful at cooking on an open fire and were understandably proud of their abilities when cooking perfect tortillas, fish, beans, soup, etc. At a fish camp, guys who were not cooking every day, had a lot of trouble making anything close to a succulent home cooked meal.
Along with the hundreds of technical skills that made ranching fun, culture made life easier and more beautiful. Ranch culture was at least half of competency and expertise. Laughing at life’s problems made overcoming them much more likely. Religion, nature, the beauty of living outdoors and liking the slow pace were strengths in my friends that I grew to envy and attempted to emulate.
Bringing innovations started with lots of failure. The first Rocket stoves became flowerpots. The first solar cookers became toilet seats and windows. Eventually, ARC appropriate technologists made prototypes that were simply put on public display. Of our many attempts to introduce ‘helpful’ technology, cement rat proof boxes were the biggest success.
We learned a lot more than we taught, starting with listening to our expert hosts. The shorter and higher firepower Rocket stove that has gone viral was created by women in 18 villages in Southern India. Dr. Winiarski had the idea and the cooks made it practical.
https://aprovecho.org/wp-content/uploads/2022/07/7.11.22-Batil-Camp-SuperPot.jpg591725Kim Stillhttps://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2024-07-26 16:14:342024-07-26 16:34:21Appreciating Local Expertise
Catching up to changing stove expectations reminds me of human maturation. Babies may only need to laugh to keep parents happy, but as kids grow up the stages of development result in further complications. Happily, meeting the expanding goals of protecting deforestation, health and climate can make stoves increase their abilities without changing an essential character that continues to please the cook.
Designed to protect forests, the initial stove featured increased thermal efficiency.
The health-protecting stove added burning up carbon monoxide (CO) and particulate matter (smoke, especially PM2.5).
Protecting climate matures the same stove as harmful climate forcers are combusted as well (NOx, Black Carbon, VOCs, Methane, etc.). Importantly, attempting to burn 100% renewable biomass can zero out the warming effect of Carbon dioxide (CO2).
In simple terms, a stove loved by cooks can be changed to cook using as little wood as possible, then CO and PM2.5 are combusted and then the previously uncounted gasses and black component in smoke are burned up, too. The biomass fuel should be as renewable as possible to decrease adding CO2 to climate.
The same stove does better and better making stakeholders proud.
