Fred & Lise Colgan, founders of InStove
Fred & Lise Colgan, from InStove

Fred and Lise Colgan created InStove, manufacturing and distributing institutional stoves initially designed by Dr. Larry Winiarski. They developed and sold large Rocket stoves that cooked food, sterilized medical equipment, and pasteurized water.

The autoclave, sold by Wisconsin Aluminum Foundry, works like a big pressure cooker and sterilizes quickly using steam and pressure. The unit fits into a Rocket stove that delivers the heat using less wood compared to traditional stoves. A chimney removes smoke from the room. The system can sterilize about 7 gallons of surgical instruments, dressings, and other medical supplies at a time, making them safe for either reuse or hygienic disposal.

These larger Rocket stoves combine the same strategies that are used in smaller versions. A pot skirt cylinder surrounds the sterilizer creating a narrow channel gap that is especially effective in transferring heat, in part because the pot is larger. Big pots have more surface area so increased percentages of heat pass into the water. When a chimney is attached to the stove, the hot gases are forced to flow down another channel on the outside of the pot skirt. In this way, adding a chimney to the stove does not diminish the fuel efficiency. A lot of the heat has already scraped against the pot and been absorbed before it exits out of the chimney. The light weight bricks used in a larger Rocket stove combustion chamber can be thicker and larger than bricks used in a smaller stove. The Institutional Stove described in the Institutional Rocket Stove pdf on the Publications page can handle pots from 50 to 300 liters. The downloadable Excel worksheet Institutional Stove Gap Calculator can help you determine the measurements of an institutional stove designed to fit the large pot you have available for use.

It can be challenging to find the time to read a book so here’s a ten-minute video introduction to “Clean Burning Biomass Cookstoves” (2020), our recent updating of the 2015 edition. Download the book for free on the publications page. We spent a significant part of last year rewriting most of the book trying to put in one place pretty much everything that ARC has learned in the last five years. The plan is to do the same in 2025.

The summary includes:

  • The energy ladder and renewable biomass
  • Fire is investigated in the lab
  • Stoves are designed by cooks in the field
  • Factories tell us how to help them
  • Chimneys and air exchange rates protect health
  • A new outside air model helps to predict PM2.5
  • Increasing heat transfer efficiency! No problem
  • Residence time is shorter than previously imagined
  • Metering and mixing get us most of the way to cleaner combustion
  • There are great new stoves!
  • Let’s move faster

Aprovecho Research Center is pleased to announce that it has just been awarded a $50,000 grant from The Osprey Foundation in support of expanding research into the connection between biomass combustion and climate change.

To date, a handful of lab and field studies have resulted in relatively little information on how stove/fuel interventions could impact emissions. The Gates funded GH Labs has partnered with us in this project because information is vitally needed to make sure that stove interventions are most productive.

Research has identified renewable biomass as carbon neutral but only when burned without making climate forcing emissions.  Aprovecho manufactures and sells the Laboratory Emissions Monitoring System (LEMS) as a tool to characterize cook stove performance. The LEMS enables ARC to develop stoves addressing climate, health, and effectiveness. It has become the centerpiece of more than 60 cookstove laboratories worldwide.

The LEMS measures thermal efficiency and the emissions rates of PM2.5, CO, CO2, and Black Carbon. Minimizing those emissions is important for addressing climate change and protecting human health. The effectiveness of the stoves is assured when cooks are deeply involved in designing them.

Non-methane hydrocarbons (NMHC) and methane contribute to a significant fraction of the global warming potential, especially from charcoal burning stoves, but to date have not been measurable with the LEMS.

The Osprey Foundation sponsored project goals are:

  • Adding the measurement of methane and NMHC to the LEMS.
  • Surveying the global warming potential of wood burning stoves and charcoal stoves and creating market driven designs that address climate/health/effectiveness.
  • Widely distributing open source information (including CAD drawings) describing how to minimize climate forcers in biomass stoves.

At the Leaders Summit on Climate hosted by President Biden, the U.S. government pledged to help countries achieve their climate ambitions through expanding access to clean cooking. We feel very lucky to be investigating how to manufacture improved biomass stoves that cook well, are affordable, and protect personal and planetary health. Thank you, Osprey Foundation!

Photo from the BURN Newsletter, May 2021
Photo from the BURN Newsletter, May 2021
Photo from the BURN Newsletter, May 2021

In a recent BURN newsletter it was announced that the natural draft Kuniokoa stove with a new pot skirt achieved 51.3 % thermal efficiency. That’s Tier 5, the highest score on the voluntary tiers of performance. Achieving great thermal efficiency involves improving heat transfer efficiency which is summarized in the acronym TARP-V: Increase Temperature, Area, and Radiation, use narrow channel gaps to achieve Proximity, and increase the Velocity of the gases flowing past the pot without decreasing the temperature.

Making a clean burning fire does not help very much to increase thermal efficiency. Even 97% combustion efficiency is very smoky.

How can your stove get around 50% thermal efficiency?

  1. The BURN stove is very light weight, weighing in at around 3 kilos. Thermal mass in the stove body absorbs heat from the fire lowering the temperature of the gases trying to heat the water in the pot. MAKE THE GASES AS HOT AS POSSIBLE!  Hotter gases in narrow channels flowing past the bottom and sides of the pot thin the boundary layer of still air next to the pot and result in better heat transfer efficiency. The insulation in the BURN stove is 15mm of trapped air – a cylinder surrounds the riser in the Rocket combustion chamber.
  2. The channel gaps on the bottom and sides of the pot can be 6mm. 10cm or higher pot skirts are better. It’s great if the pot skirt is as high as the water level in the pot.
  3. Small, kiln dried sticks make a lot of flame (and smoke). Small sticks (we used 1cm by 2cm in a recent test) create hotter fires and gases, using less fuel compared to burning larger sticks. The hotter gas temperatures get a higher percentage of the heat into the pot.
  4. A big pot has more surface area and can be a better heat exchanger. Dr. H. S. Makunda found that larger pots (32cm in diameter) could score in the 50% range, while smaller pots (25cm) tended to get around 40% thermal efficiency. (H. S. Mukunda, CURRENT SCIENCE, VOL. 98, NO. 5, 10 MARCH 2010). 
  5. Don’t make a big fire. A moderate fire (3 to 5Kw) is better matched to family sized pots. (Prasad, Some studies on open fires, shielded fires and heavy stove, Eindhoven, 1981
  6. A hot start test usually adds something like 5% to the thermal efficiency. A cold start test transfers more of the heat from the fire into the stove body.

We built a Rocket stove that combined these characteristics. The stove top had 6mm high pot supports and the 6mm channel gap pot skirt was 10cm high. The pot had a diameter of 30cm. We used very light weight ceramic fiber insulation around the combustion chamber. The stove weighed 2.9 kilos and was 24cm high and 32cm wide. We tested it by burning five kiln dried 1cm by 2cm sticks in a hot, small fire that started quickly. The Rocket stove smoked like crazy at a firepower of around 4.5Kw, but the thermal efficiency from one high power, hot start test was 52.7%.

This week we will see what happens when we use the same Rocket stove/big pot with a Jet-Flame that should increase the Temperature of the gases and their Velocity.

Prices of carbon credits used by companies to offset their emissions are currently low, due to an excess of supply built up over several years.

According to recent research at the University of London, without the excess supply, prices would be around $15/tCO2e higher, compared to $3-5/tCO2e today. (tCO2e means tonnes of carbon dioxide equivalent, “carbon dioxide equivalent” being a standard unit for counting greenhouse gas (GHG) emissions.)

The paper predicts that the surplus will not last forever, with demand for carbon credits expected to increase five to ten-fold over the next decade as more companies adopt Net Zero climate commitments. This growth in demand should see carbon credit prices rise to $20-50/tCO2e by 2030, as more investment is required in projects that take carbon out of the atmosphere in the long-term. With a further increase in demand expected by 2040, carbon credit prices could rise in excess of $50/tCO2e.

Guy Turner, CEO of Trove Research and lead author of the study said “It is encouraging to see so many companies setting Net Zero and Carbon Neutral climate targets. What this new analysis shows is that these companies need to plan for substantially higher carbon credit prices and make informed trade-offs between reducing emissions internally and buying credits from outside the company’s value chain.”

Imagine the stoves that could be supported by a $20 price for an avoided tonne of carbon dioxide. Stoves with good thermal efficiency can save three tonnes or more per year making long lasting, super clean stoves with chimneys a great deal for carbon developers and investors.

And a great deal for consumers.

Report: https://trove-research.com/wp-content/uploads/2021/06/Trove-Research-Carbon-Credit-Demand-Supply-and-Prices-1-June-2021.pdf

When this sort of fire is maintained, a high mass Rocket stove can get close to Tier 3 for CO (less than 7.2g/MJd) and PM2.5 (less than 218mg/MJd).

Testing stoves means that many, many hours are spent watching the flames and pushing sticks of wood into the fire. We watch the real time emissions, water temperature, excess air, and temperatures in the combustion chamber on a computer screen as the testing continues. After hundreds of hours it becomes obvious that clean combustion has a certain “look.” For instance, when there is a lot of flame above the sticks the real time CO goes down on the computer screen. Without flame above the fuel, the gas rises up and is not combusted. That’s why charcoal can be dangerous, because burning charcoal does not create a lot of flame above the fuel.

When the wood sticks are changed into charcoal, the PM2.5 is dramatically reduced, as well. Pushing the unburned sticks into the fire creates smoke. Pushing the sticks in quickly makes a lot of smoke and pushing the sticks in slowly makes less smoke. Charcoal does not make much smoke and that’s one of the reasons that people like cooking with it. Feeding a fire is a compromise, as firepower and PM2.5 tend to rise together. A rocket stove can look OK as long as the sticks are fed slowly into the fire at less than about 2.5 kW. But at high power, Rockets start to smoke like crazy.

How can these two experiences be factored into a mathematical model of combustion? By using a video camera hooked up to a computer program? Residence time and temperature are easily measured, but the extent that turbulence occurs is not easily quantified. Engineers get past these sorts of problems by figuring out how to optimize mixing (using jets of air, for example), but a mathematical model is more easily filled in with numbers for other sorts of phenomena, such as the excess air ratio.

Both experiments and mathematical modeling shed light on how to make better stoves and hopefully complement each other. Arguments have been known to happen. I have been trying to figure out how to make clean burning biomass fires since 1989, and one thing has not changed since Dr. Winiarski started me on this path. I continue to be happier trying to answer questions that begin with the word “What” instead of “Why.”

Would any manufactured stove that you know of work well for this woman? Maybe not?

Working with local women to design cooking solutions is not hard when the team is located in the project area. It’s only natural to include the user in developing the product. But when wood stoves are created by foreigners, that invaluable input easily goes missing and the stove, although technically fine, usually misses other necessary attributes. That’s why ARC tries to develop stoves in the field, while learning how fire works in the lab.

Researchers associated with the Regional Testing and Knowledge Center in Accra, Ghana might agree with this strategy. They recently published a paper in which 20 biomass cook stoves available in Ghana were evaluated for high-power thermal efficiency, low power specific consumption rate, turn down ratio, high power CO emissions, high power PM2.5 emissions, low power CO emissions, low power PM2.5 emissions, affordability, fuel saving potential, operations and maintenance cost, time saving, indoor CO, and indoor PM2.5 emissions.

The authors concluded that none of the cook stoves satisfied the conditions of all of the performance indicators. The forced draft stoves were generally high performing on the technical and environmental attributes, but low performing on the economic and social/public health metrics like affordability, maintenance and operation costs, and fuel saving potential. The more traditional stoves did not perform very well technically and environmentally but ranked highest economically, being more affordable than the cleaner burning alternatives like forced draft stoves.

Available natural draft stoves were a better alternative considering the economic, technical, and environmental attributes.  The high cost of forced draft stoves (most are imported), their operation and maintenance cost, and the requirement of electricity resulted in adoption rates being low. The suitability to prepare Ghanaian staples, which require rigorous stirring, were also generally underestimated. Locally made natural draft stoves did not score well in terms of emissions but were much less expensive, did not require the preparation of fuel, and were made to prepare Ghanaian staple foods. 

The study highlights the need to consider all the performance criteria simultaneously in order to choose the “best performing” stove. 
The authors conclude with the hope that locally made stoves can be technically improved while maintaining the other necessary attributes. (Gloria Boafo-Mensah, et al., Biomass and Bioenergy 150, 2021).

It just so happens that our General Manager Sam Bentson is at the Regional Testing and Knowledge Center in Accra right now, working with Ms. Boafo-Mensah and the rest of the team on some exciting projects. We look forward to sharing Sam’s report about his trip when he returns!

Paul Anderson TCHAR stove

In 2011, Dr. Paul Anderson described how the made charcoal in a TLUD could drop into a charcoal stove base and then be used to cook food. The top of the TLUD stove was removed after the charcoal was made and the pot was placed on the lower base to continue cooking. ARC used the same idea in a TLUD stove that was tested by Jim Jetter, but the wood burning and subsequent charcoal burning happened in the same combustion chamber. The TLUD was shorter, so the lower firepower in the charcoal supplied enough energy to a covered pot with a tight skirt to keep simmering. The ARC TCHAR stove was clean burning and scored well in a series of tests. (Jetter, et al., 2012, Environmental Science & Technology 46(19):10827-34).

Dr. Anderson’s 2011 TCHAR stove. The top (silver) portion is removed after the fuel has become charcoal, and the pot is placed directly on the base for simmering.

Using the made charcoal to simmer food to completion increases thermal efficiency. In cities where biochar may be less desirable, a known amount of fuel can bring the food to boil (burning the wood) and then gently simmer the food until it’s done (burning the made charcoal) without much tending. To preserve the biochar for agricultural use the primary air that goes up into the batch of fuel is limited and the fire is extinguished. In a TCHAR more primary air helps to decrease the smoke made during the transition from wood to charcoal burning and helps the charcoal to completely combust.

The Turn Down Ratio in a 2021 ARC TCHAR is about 5 to 1, so the pot needs a lid and a tight skirt to keep boiling. Using 700 grams of biomass pellets the stove boiled five liters of water in 27 minutes and kept boiling for two hours (covered pot/tight skirt). The TCHAR is another TLUD variation and, who knows, may be useful somewhere?

Burning wood and then made charcoal results in a large turn down ratio.
Selling LPG in Rwanda

LPG (liquefied petroleum gas) is among the most important fuels for achieving clean cooking. Many countries are actively developing intervention programs. In a five year project starting in 2007, an Indonesian program converted over 50 million households cooking with kerosene to LPG. In 2016, India intensified their campaign providing free connections to LPG cylinders to “Below Poverty Line” homes. In China, gas and biomass fuels, the dominant energy fuels for cooking, are used by 44.8% and 32.1% of households, respectively. In 2014, 47.6% of rural cooks used biomass, whereas urban households were more likely to cook with gas (65.8%) (Applied Energy 2014, 136:692-703 Duan, et al.).

Even older LPG stoves burn cleanly. Five different LPG stoves were tested 89 times and described in a 2018 article. Two stoves were manufactured in China and obtained in a local market near Beijing. One was manufactured in Japan and purchased in Kampala, Uganda. Solgas Repsol Downstream Peru (an international LPG distributor) disseminated another stove. A worn-out appliance was obtained from a rural household in Cameroon  (Environ. Sci. Technol. 2018, 52, 904−915 Guofeng Shen, et al.).

  • The average thermal efficiency for the LPG cook stoves was 51 ± 6%.
  • Approximately 90% of the PM2.5 data was below the level of detection.
  • The other 10% of the stoves had an average PM2.5 score of 0.20 ± 0.16 mg/minute. (The WHO Emission Rate target is 0.23mg/minute).

However, in a country like Rwanda the switch from wood and charcoal to LPG is slow. In 2019, only 2% of cooks were using LPG in the cities. 64% used a charcoal or wood stove and in rural areas “the use of clean fuels is negligible” (The World Bank, 2019). 93% of rural households use wood, 6% of charcoal, and 0.2% of gas (National Institute of Statistics Rwanda, 2019).

The cost of LPG is a big factor. “Prices are much higher in rural areas and upcountry towns as retail traders factor in transport logistics. Rising prices for cooking gas in the country have sparked concerns of likely reversing gains made in the push for a clean cooking solution as more households turn to wood and charcoal.”  

Marie-Jeanne Uwanyiringira, a businesswoman who sells LPG, says that the fluctuation in prices has caused frustration among consumers. “When someone buys gas from me at RWF 3,500 and the next month I tell them that it is RWF 5,500, ($5 USD) they don’t seem to understand that it is not the seller’s fault.” (Rwanda Today, April 9, 2021).

In addition to the recent Tibbetts Award, ASAT has just received EPA recognition for our success. ASAT (the for-profit arm of ARC) was awarded a 2021 EPA Administrator’s Small Business Program Award for Outstanding Accomplishments by a Small Business Contractor. This award recognizes ASAT’s contributions in Fiscal Year 2020 and our efforts to promote EPA priorities of protecting human health and the environment.

ASAT Inc. staff pose with their Tibbetts Award. From left to right: Sam Bentson, David Evitt, Jill Allen, Dean Still, Kim Still, and Dr. Nordica MacCarty.

EPA SBIR funding enabled ASAT to research and develop commercially viable inventions. We developed the Integrated Stove (seen below) that includes stand-alone accessories including the Jet-Flame www.Jet-Flame.com, an air cooled thermoelectric generator, and an electrostatic precipitator that reduces emissions of smoke from chimneys.

The Integrated Stove with Air Cooled 20 Watt TEG Prototype.