“The concept of black boxes has been around since the early days of systems theory though some attribute the first use to the field of electrical engineering.
It is a simple concept and has a straightforward definition: we know the inputs and subsequent outputs to a system but the internal workings of the system are not visible to us.
Black boxes approaches focus on input and output rather than the details of how inputs are transformed into outputs”.
The results of experiments guide the subsequent experiments. For instance, adding secondary air jets into flame is shown to decrease PM2.5. Guided by the result, further investigation in a prototype under the emission hood determines the most successful application by varying parameters.
Random Experimental Design
In a Black Box (where the situation is complex and not understood) randomized approaches to experimental design can be effective and efficient.
http://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.png00Kim Stillhttp://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2023-11-30 17:25:332023-11-30 18:02:16Iterative Development of Stoves and Black Box Theory
Following the COP26 international climate conference, Senator Susan Collins (R-ME) and Senator Dick Durbin (D-IL), have introduced a bill to accelerate access to clean cooking. Here is the opening text of the section defining the activities directed in the bill. H.R.6316 has been referred to the Subcommittee on Energy:
SEC. 5. CLEAN COOKING PROGRAM.
(a) Department Of State; United States Agency For International Development.—The Secretary of State and the Administrator of the United States Agency for International Development shall work with the Clean Cooking Alliance, founded in 2010—
(1) to engage in a wide range of diplomatic activities, including with countries across the globe and with United States embassies abroad, to support activities of the Clean Cooking Alliance and the clean cookstoves and fuels sector;
(2) to continue the clean cooking initiatives supported by the Climate and Clean Air Coalition, an intergovernmental organization formed in 2012, to reduce emissions of climate pollutants;
(3) to advance programs that support the adoption of affordable cookstoves that require less fuel to meet household energy needs and release fewer pollutants, as a means to improve health, reduce environmental degradation, mitigate climate change, foster economic growth, and empower women; and
(4) to carry out other activities authorized under this Act.
(b) Department Of Energy.—The Secretary of Energy shall work with the Clean Cooking Alliance—
(1) to conduct research to spur development of low-cost, low-emission, high-efficiency cookstoves through research in areas such as combustion, heat transfer, and materials development;
(2) to conduct research to spur development of low-emission, high-efficiency energy sources;
(3) to support innovative small businesses in the United States that are developing advanced cookstoves and improved cookstove assessment devices; and
(4) to carry out other activities authorized under this Act.
The bill continues on in sections (c) through (f) to direct the National Institutes of Health, Centers for Disease Control and Prevention, Environmental Protection Agency and other federal agencies to engage in supportive activities. You can read the full text of the bill at https://www.congress.gov/bill/117th-congress/house-bill/6316/text
It’s great to start making stoves and testing ideas with tincanium (cut up tin cans). Making new prototypes from tin cans is a quick, inexpensive way to start the design process but tin cans only last for a limited amount of time, depending on the temperature of the combustion chamber. At 1000C in fire, a tin can burns out in an hour or so!
One of the most challenging components in a cookstove is the combustion chamber, which can operate at high temperatures (often ≥600 °C) in wet and salty conditions. Wood can be salty and water vapor is produced when wood is burned.
In 2017, M.P. Brady and T.J. Theiss shocked the stove world by showing that in their tests even expensive metals could not be estimated to be 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.).
“Corrosion evaluation under cookstove-relevant conditions was studied by two methods: 1) lab furnace testing and 2) in-situ exposure in an operating cookstove. The lab furnace testing was conducted in air with 10 volume percent of H2O to simulate water vapor release from burning biomass, and direct deposition of salt onto the test samples to simulate the burning of highly corrosive biomass feedstocks. In particular, relatively high levels of salt species are encountered in many types of biomass and can lead to significantly accelerated alloy corrosion rates (Antunes and de Oliveira, 2013; Baxter et al., 1998; Saidur et al., 2011; Okoro et al., 2015). The in-situ cookstove testing was conducted using wood fuel that was pre-soaked in a salt water solution to yield accelerated, highly corrosive conditions.”
“Each day of testing, cookstoves were burned continuously for an average of ~6 h. The average fuel consumption rate was 570 g/h. To determine the range of temperatures that the alloy test samples would experience, a thermocouple was placed inside the chimney of each stove at the same height as the coupon fixture. Typical combustion chamber temperature profiles for the cookstoves, where test coupons were placed, are shown in Fig. 2. The average gas temperature range during steady state in-situ testing was 663 °C ± 85 °C”
“Much faster corrosion rates were observed in the 800 °C lab furnace testing where evaluation of most alloys stopped after 500 h of exposure due to excessive corrosion. Of the alloys tested to 1000 h, only the FeCrSi and pure Ni samples exhibited good corrosion resistance. The FeCrAlY and 310S alloy samples were consumed through-thickness in some crosssection locations.”
“Type 201 stainless steel, type 316 L stainless steel, and the 12 and 20Ni AFA alloys all exhibited relatively poor corrosion resistance in the in-situ cookstove testing, with metal losses in excess of −200 μm after only 500 h of exposure, consistent with the lab furnace trends. The types 310S and 446 stainless steels exhibited moderately worse corrosion resistance, with metal loss values of −190 μm and -230 μm after 1000 h. Despite exhibiting the best corrosion resistance in the lab furnace testing, the pure Ni suffered from −300 μm metal loss after only 500 h in the in-situ cookstove testing.”
What could stove companies do? Attempts were made to reduce temperatures in combustion chambers. Insulation was removed and external air was directed to cool the external surfaces of the metal.
Refractory Ceramic, A Viable Alternative
When Dr. Winiarski insulated the combustion chamber in his Rocket stoves, it became all too obvious that available metals were short lived. Unfortunately the alternative – heavy ceramic materials that were free and available – absorbed heat which lowers temperatures, resulting in reduced thermal efficiency and higher emissions.
More than 20 years ago, the quest began for an inexpensive, refractory metal and/or a durable, low mass, abrasion resistant refractory ceramic material. In Central America, Don O’Neal and Dr. Winiarski found a locally manufactured, inexpensive, thin walled refractory tile called a baldosa that can last for about seven years in a plancha stove and is now in use in hundreds of thousands of stoves.
The wisdom of using refractory ceramic was confirmed in 2011. Metallurgy experts at a DOE Biomass Cookstoves Technical Meeting pointed out that only refractory ceramic seemed to meet the requirements of being affordable with a prolonged longevity. Unfortunately, making lightweight, abrasion resistant refractory ceramic has proven to be difficult.
Shengzhou Stove Manufacturer has for years manufactured low mass, abrasion resistant refractory ceramic combustion materials in China. Since 1407AD, potters in eastern China have used rare local clays to make and sell these combustion chambers to East Africa. In 2023, SSM sells ceramic combustion chambers in Rocket stoves globally.
Though not necessarily refractory, simple earthen ceramic stoves continue to to be the most popular models in many countries. These stoves are locally produced, inexpensive and are replaced relatively frequently as needed. These heavy bucket shaped stoves can save fuel when used with a pot skirt.
The Importance of Durability
Durability has became more important as carbon credits, which currently support most large-scale stove projects, are generated only when the stove is in use. Carbon credits are based on improvements in fuel use while emissions of CO and PM2.5 are not counted. The ‘perfect’ carbon credit stove is least cost, long lived, and as fuel efficient as possible. When ARC is asked to develop a cookstove for a carbon project we usually aim for cost under $20, over 40% thermal efficiency, with a minimum 5 year durability.
The ARC carbon credit stove is dependent on a tight fitting pot skirt (close to optimal heat transfer efficiency) coupled with as cool as possible temperatures in metal parts, resulting in improved lifespan. Shengzhou Stove Manufacturer sells millions of carbon credit stoves with their light weight, abrasion resistant combustion chambers.
ARC tries to add mixing in the combustion chamber and a chimney whenever possible. Cooking outside/increasing the air exchange rate in houses is also effective in reducing exposure. The Jet-Flame is moving into greater use and has been field tested in Africa. Carbon revenue is moving better stoves into homes as humanitarian oriented partners like C-Quest Capital replace older stoves with better stoves. Progress has picked up in the last five years.
http://aprovecho.org/wp-content/uploads/2023/07/5753694404_2a26665ef0_c.jpg800600Kim Stillhttp://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2023-07-27 16:18:542023-07-27 16:18:56A Short History of Cookstove Durability
Transitioning to carbon neutral electric generation would replace a big climate problem in the U.S., since about 60% of its electricity comes from burning natural gas.
The World Energy Forum forecasts that around 40% of electricity could be from wind and solar doing most of the heavy lifting by 2040, enabling a net zero global future.
Today hydropower provides about 16% of the world’s electricity, generating power in all but two U.S. states. 80% to 90% of our electricity at the lab comes from the wonderful Columbia River.
ARC is working to clean up combustion so renewable biomass (domestic switch grass, for example) could cook food and heat homes when fossil fuels are no longer available.
Reading a book at night in a warm house is a wonderful thing. Somebody is playing the piano… Dinner was great.
http://aprovecho.org/wp-content/uploads/2023/05/image-1-e1683852943480.png574900Kim Stillhttp://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2023-05-18 12:43:332023-05-18 12:43:35Electricity: Planning for Net Zero by 2040
If renewable switch grass, for example, was burned cleanly enough biomass could join solar, wind, hydro, and thermal energy as sustainable energy replacements in the post fossil fuel era. ARC estimates that an emissions rate of 0.3 grams/hour of PM2.5 would protect air quality in cities and meet the Paris Agreements when replacing natural gas.
Not all that hard to do…
“Earth is likely to cross a critical threshold for global warming within the next decade, and nations will need to make an immediate and drastic shift away from fossil fuels to prevent the planet from overheating dangerously beyond that level, according to a recent report from the Intergovernmental Panel on Climate Change.
… It says that global average temperatures are estimated to rise 1.5 degrees Celsius (2.7 degrees Fahrenheit) above preindustrial levels sometime around ‘the first half of the 2030s,’ as humans continue to burn coal, oil and natural gas.
…Under the 2015 Paris climate agreement, virtually every nation agreed to ‘pursue efforts’ to hold global warming to 1.5 degrees Celsius. Beyond that point, scientists say, the impacts of catastrophic heat waves, flooding, drought, crop failures and species extinction become significantly harder for humanity to handle.” –Brad Plumer reporting in the New York Times, 4/21/23
On the other hand, transitioning to renewability accomplishes an almost universal dream of humanity.
http://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.png00Kim Stillhttp://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2023-04-28 16:42:352023-04-28 16:42:37Earth Day 2023: The Future Can Be Fun!
Since 1976, ARC has been investigating how to improve heat transfer and combustion efficiency in Low Middle Income Countries’ wood burning cook stoves. Emissions of Particulate Matter have been shown to kill millions of people annually. PM concentrations are frighteningly high in homes without chimneys but emissions into outdoor air are an increasing health/climate concern. Incomplete combustion in cooking and heating stoves is an obvious problem especially when compared to the very clean combustion in more mature technologies like automobiles.
The EPA biomass heating standard allowing two grams per hour of PM to pollute the environment is very lenient. National standards in Europe also allow biomass stoves to endanger health/climate. Cook stoves are forced to burn much more cleanly by stricter WHO standards and ISO benchmarks.
The Guardian’s Environment Editor Damian Carrington reported in 2021, “Despite their severe impacts on air pollution and human health, domestic heating emissions are under-regulated in the EU, especially when compared to other sources such as traffic. Neither the EU EcoDesign requirements nor the more ambitious Nordic ecolabel succeed to keep particle emissions from new stoves within acceptable levels. In 2022 a new EcoDesign stove will be allowed to emit 60 times as much particulate matter as an old truck from 2006, and 750 times as much as a newer truck from 2014.”
http://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.png00Kim Stillhttp://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2023-04-28 16:40:222023-04-28 16:40:24Clean Burning Also Necessary for Biomass Home Heating
Depending on the size of the home, winter heating with a pellet burning stove uses from 2 to 6 tons of wood pellets per year. If the average house burned 3 tons per year, 3,729,400 homes could be heated with pellets currently manufactured in the USA. There are 142,153,010 residences in the USA. biomassmagazine.com/plants/listplants/pellet/US/
Bill Gates has written that the climate crisis can be solved by developing least cost, renewable technologies to replace fossil fuels. (“How to Avoid a Climate Crisis”, 2021)
Fuel switching from natural gas to renewably harvested wood pellets or split logs or dried wood chips (only if they can be burned cleanly enough to meet the Paris Agreements) seems to include a relatively small Green Premium. Replacing LPG/Propane, electricity, and Fuel Oil #2 with wood pellets seems like a good deal.
The Jet-Flame pushes jets of primary air into the fire to aid combustion.
When a wooden stick is burned a lot of smoke is produced but the made charcoal at the tip of the wooden stick does not make much smoke. Rocket Stove: Push the sticks in slowly so the charcoal at the tip is burning. TLUD: Charcoal covers the slowly burning fresh wood.
If the stove begins smoking, the solid wood is being turned into gas too quickly, too much wood gas is being produced and un-combusted fuel is escaping. Rocket Stove: Pull the sticks back until just the tips are burning. TLUD: Reduce the primary air.
Mixing the smoke, gases, flame, and air reduces emissions. Rocket Stove and TLUD: Cut up the laminar flames with static mixing devices or jets of primary or secondary air. Aim the jets of secondary air into the flame and adjust the velocity of the jets to completely cover the burning fuel. Primary air jets can also achieve close to complete combustion. Excess velocity in primary or secondary jets is detrimental when it reduces the combustion temperature.
For close to complete combustion the temperature in the combustion zone needs to be 850C or above. The woodgas and air and flame have to be thoroughly mixed. The residence time needs to be 0.2 seconds or more. Reduce the amount of woodgas entering the combustion zone until close to complete combustion is achieved. Biomass fuels with 15% or lower moisture content are easier to burn.
It is necessary to tune the stove under an emissions hood to achieve close to complete combustion. Change one variable at a time and test until significance is achieved.
http://aprovecho.org/wp-content/uploads/2020/12/12.30.burning3.png578898Kim Stillhttp://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2023-02-24 17:27:292023-02-24 17:27:31How To Achieve Close To Complete Combustion of Biomass
The ARC lab is located in the Oregon woods where “hippies” and “rednecks” live on small farms in approximately equal numbers and share numerous points of view. I learned about these overlapping values when I accompanied my Dad, a Christian community organizer, to pot-luck meetings at nearby Granges, members of a farmers’ association organized in 1867. The one hundred and sixty two Granges in Oregon sponsor social activities, community services, and political lobbying.
My Dad was taught community organizing by Saul Alinsky in Chicago. He reminded his students to “Never go outside the expertise of your people.” https://www.goodreads.com/book/show/102748.Rules_for_Radicals The people who have a problem have to be the ones to generate the solution. Mahatma Gandhi and E.F. Schumacher agreed. I watched my Dad as he listened and I admired his ability to help folks become aware that their constituency was a rainbow coalition.
Americans are a rich people but we often feel that life in the USA is getting worse and that this trend is out of control. Both “hippies” and “rednecks” can feel that nature is not being respected, that God has been forgotten, and that fighting for more money – being selfish – is largely responsible for the downward spiral. When many sorts of rural Oregonians visit our lab, they are happy that we are working to make renewably harvested biomass burn without making smoke.
Improving technologies can become a middle path that wins a rainbow coalition of friends.
http://aprovecho.org/wp-content/uploads/2022/12/12.29.22-middle-path.jpg7191280Kim Stillhttp://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2022-12-29 18:28:202022-12-29 18:28:21Win a Rainbow Coalition of Friends
The direct burning of biomass seems to be dramatically more efficient compared to ethanol for applications such as home heating, cooking, heating water, or drying clothes. It makes sense that not having to create alcohol from biomass would save energy. When the use of natural gas is decreased (due to climate change), burning biomass for heating seems like a fuel-efficient option that could reduce the extra burdens on electricity.
One of my favorite reference books is “The Energy Primer” published in 1974. It has comprehensive review articles on solar, wind, water, and biomass energy. The following chart comes from a great article on biomass written by Richard Merrill. It shows that when renewable biomass is combusted, the efficiencies are much higher compared to making alcohol from biomass and then burning it.
The very clean burning of biomass allows efficient heating applications.
http://aprovecho.org/wp-content/uploads/2022/01/1.5.22-chart.jpg10411160Kim Stillhttp://aprovecho.org/wp-content/uploads/2015/11/Aprovecho-Logo.pngKim Still2022-12-16 17:16:142022-12-16 17:16:15Ethanol or Direct Burning for Heating Applications?
