Cleaner Burning Biomass Stoves: In Homes!

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The British Petroleum clean burning Oorja FD-TLUD stove from India

If protecting health and climate are important in stove projects, why not monetize the reductions of health/climate pollutants in carbon-offset projects?

Only the reduction in fuel use earns carbon income now!

With equal heat transfer efficiency, dirty burning stoves earn as much as clean burning stoves.

Dirty burning stoves are less expensive. “Market demand” reinforces the use of biomass stoves with low combustion efficiency.

Why not add income from reductions in CO, PM2.5 and Black Carbon, etc. to carbon projects to get cleaner burning stoves into use?

The approved 2017 Gold Standard Methodology already exists to do this! See: www.goldstandard.org/articles/black-carbon-and-other-short-lived-climate-pollutants

Moving Forward: Thanks to Jim Jetter’s EPA Lab!

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Champion (2021) average energy emission factors (g/MJ) from ISO high, medium, and low tests. 

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

Lab testing can quickly compare emissions from stoves. The EPA and ARC labs now measure the climate emission factors, not just PM2.5 and CO. It has been proven that only field tests show real world performance. Together, lab and field tests help to move stoves forward as we get closer to market driven stoves that please cooks, successfully cook food, use a lot less fuel, and protect health/climate.

The above chart contains a lot of information. Some takeaways are:

  1. Wow! The Three Stone Fire (TSF) was pretty bad! 943g/MJ for PM2.5, 15.5 g/MJ for CO.
  2. Charcoal made ~90% less PM2.5.
  3. The Carbon Monoxide (CO) from charcoal was only a bit higher than the Three Stone Fire (19.2g/MJ).
  4. LPG did so well! (Too bad that we are entering the end of the fossil fuel era).
  5. The forced draft pellet stove looked great, as well. (PM2.5: 30g/MJ, 2.2g/MJ CO)
  6. Black Carbon (EC) is much worse than CO2 for climate change. Many of the stoves, except the Rocket stove, successfully reduced Black Carbon. 
  7.  In this recent lab test, as in the previous MacCarthy study (2008), the Rocket stove emitted a lot of Black Carbon.  www.sciencedirect.com/science/article/abs/pii/S0973082608604299
  8. R&D has shown that the Rocket stove requires successful forced draft mixing at high temperatures to decrease emissions of Black Carbon and potentially address climate. 

When the emissions factors are summed and converted to global warming potential the forced draft stoves have the potential to generate large amounts of carbon offsets. 

Clean Burning with Metering and Mixing

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Primary air usually controls the rate of reactions: How fast the solid biomass changes into wood gas.

Jets of primary air into the charcoal beneath the biomass add mixing while raising temperatures.

Secondary air jets into the side of the flame can also supply needed mixing but tend to lower temperatures.

Metering the gas supply into the tuned combustion chamber is important!

Too much wood gas can easily overcome the ability of even a well-tuned combustion chamber to achieve close-to-complete combustion. 

You can’t pour too much gas into a carburetor!

Pot Skirts – basic theory

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Dr. Sam Baldwin describes the use of a pot skirt in his book “Biomass Stoves: Engineering Design, Development, and Dissemination (1987).” Changes in the length and diameter of the channel gap (between the pot and the interior of the skirt) result in dramatic changes in heat transfer efficiency.

“In fact, the channel efficiency, defined as the fraction of the energy in the hot gas entering the channel that is transferred to the pot, is extremely sensitive to changes in the channel gap. For a 10cm long channel, the channel efficiency drops from 46% for an 8mm gap to 26% for a 10cm gap. Thus the stove and pot dimensions must be very precisely controlled.” (pg. 45)

If stoves are to be compared, these types of variables must be controlled. The use of a standard pot, or pots, without pot skirts will result in performance scores that are significantly reduced. If a pot skirt is used on testing pots it should be identical in all aspects. Again, the use of a standard pot(s) seems to be required.


Happy Holidays, 2023!

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That the days are shorter is easy to attest to here at Blue Mountain. Our campus is wedged between parallel rows of 100-foot tall Fir trees. Yesterday, the rare sun fell down below the celestial horizon at 2PM.  We envy the valley farmers whose day lasts until around five. On the other hand, being surrounded by the forest up here makes the air sweet and clean. But only when the wood burning heating and cooking stoves that we are developing and testing are protecting health and climate.

It can be so terrible when traditional stoves are belching smoke! I have had pneumonia three times and get nervous when my throat gets sore. Clean burning makes me a lot happier. 

HEALTH: Can biomass be burned cleanly enough to protect air quality when warming houses and cooking food? 

CLIMATE: Can the Global Warming Potential of burned biomass meet the Paris Agreements and join solar, hydro and wind as a renewable energy source? 

Sure, we do both every day.  

Celebrating life and scientific endeavor in the forest becomes pleasant and comforting when we are toasty warm, and the smoke disappears. 

Feels downright civilized.

Iterative Development of Stoves and Black Box Theory

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“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”.

-John M. Green, The Application of Black Box Theory to System Development

Data Driven Hypothesis Generation

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.

Updating a 9-year-old “Clean Combustion” YouTube Video

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The great and upsetting thing about YouTube videos is that they don’t go away! A lot of this old video now seems incomplete:

Our understanding of how to come closer to complete combustion has changed and includes details missing before. The following describes a hopefully less wrong set of design principles. David Evitt is currently deep diving into clean combustion and who knows what details will be added in the next few years?

Nine years ago, we thought that close to complete combustion could be achieved by forcing all gases and smoke into flame for a sufficiently long amount of time.

  1. Today we add that the air/fuel ratio in the combustion zone needs to be air rich.
  2. We add that the flame/gas/smoke/air mixture needs to be thoroughly mixed. 
  3. We add that the temperature in the combustion zone needs to be above 850°C to allow short residence times to become effective.
  4. We add that at a minimum of 850°C the residence time needs to be more than 0.2 seconds. Longer is better.
  5. Wet wood, un-preheated air jets, and mass tend to reduce temperatures to below 850°C.
  6. Optimized heat transfer efficiency helps to reduce harmful emissions since less fuel accomplishes tasks.

Aprovecho Announced as a Winner of the Wood Heater Design Challenge

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The U.S. Department of Energy (DOE) Bioenergy Technologies Office (BETO), in collaboration with Brookhaven National Laboratory (BNL), Lawrence Berkeley National Laboratory (LBNL), and the Alliance for Green Heat, today announced the winning teams for the Wood Heater Design Challenge (WHDC). 

Aprovecho Research Center, from Cottage Grove, Oregon, came in second place and won $25,000 with a novel burn pot, airflow configuration, and sensor package for pellet heaters. Davidon Industries from Warwick, Rhode Island was awarded first place for their mechanically automated, combustion-air control technology for cordwood heaters. Kleiss Engineering from Cloverdale, Indiana, won the third-place prize with a smart wood stove heater.

“Embracing innovation allows us to challenge existing norms, push boundaries, and discover new solutions that can reshape the entire industry,” said Dr. Valerie Sarisky-Reed, Director of BETO. “Wood stove research is part of DOE’s overall strategy to develop affordable bioenergy technologies and convert our nation’s renewable resources into fuels, power, products and in this case, more efficient wood stoves for homeowners.”

Aprovecho, Davidon, and Kleiss were selected from nine teams competing at the Wood Heater Technology Slam in September 2022. Teams pitched new wood stove ideas to retailers, the public, and experts, who assessed which stoves were the most innovative, efficient, and offered the greatest market potential. The three finalist teams moved forward to the testing phase of the competition, which was held this past spring at BNL in Upton, New York.

Read the full press release on the DOE Website. Learn more about the BETO-funded Wood Heater Design Challenge.

Biochar Goals

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A few years ago, on another series of hot summer days, Aprovecho hosted a seminar on biochar. About twenty enthusiasts from all over the US joined us for a biochar summer camp, lighting a lot of stoves and scaring the safety advisors.

We needed more spark screens.

At the closing event, we created a list of three goals for biochar production:

  1. The biomass should be renewable
  2. The generated heat should be used for a purpose
  3. The total package of emissions, including buried biochar, should be carbon negative (-CO2e). By weight, smoke is ~ 700 times worse for climate than CO2. Methane is ~ 25 times worse than CO2, etc. 

Since most of the biochar production at the seminar resulted in a lot of smoke and the heat was lost into the sky, it was appreciated that R&D was needed to perfect our efforts. 

Having goals is a first step.

H.R.6316 – Clean Cooking Support Act

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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