Newsletters | Page 10 of 23

Charcoal Stoves: Ups and Downs!

August 18, 2021/0 Comments/in Testing Stoves

*Ryan Thompson and Sam Bentson spent a year exploring charcoal burning*

Ken Newcombe and C-Quest Capital have seen firsthand how charcoal production has wiped out forests in Africa. Making charcoal is a very energy inefficient process (Aprovecho Institute, 1984a). Burning off the volatile compounds in wood consumes and wastes between 50% and 80% of the energy! Ken recently observed that saving charcoal was not easy, and that field tests indicated that traditional stoves were as fuel efficient as more modern stoves. So I asked Ken if he had read Sam’s paper* on how to save fuel in charcoal stoves, and Sam sent it to him.

Busy people are out in the world accomplishing things. There’s a ton of information on the Internet and lots of it is conflicting. Publishing information in journals and books sometimes seems to be a fairly ineffective way to reach actively engaged stovers. That’s why we publish this weekly newsletter, trying to disseminate data driven information. Maybe you can pass it to on to your colleagues?

After testing many charcoal stoves, Sam concluded that:

“Using the minimum load to complete the WBT [water boiling test] results in similar performance between most charcoal stoves, while filling the combustion chamber with fuel results in large differences on the same measures. Based on these laboratory results, limiting the size of the combustion chamber so as to prevent excess fuel loading may be an effective technique for decreasing fuel consumption while cooking.” *

The loaded charcoal is used up, so loading only the amount needed for the cooking process is very important for saving fuel. At the same time, Sam and Ryan Thompson spent a year exploring charcoal burning and came up with an “all Tier 4” charcoal stove that was higher scoring than the other optimized wood burning stoves that ARC made for the US DOE.

CAD drawings and a chapter on charcoal describe what Sam and Ryan did and how to build the stove they invented. (Clean Burning Biomass Cookstoves, 2021, www.aprovecho.org/publications-3).

*(Energy for Sustainable Development, 2013, Bentson, Still, Thompson, Grabow)

Remembering Dr. Larry Winiarski

August 11, 2021/0 Comments/in News, Rocket Stoves, The Big Picture

Dr. Larry Winiarski, the Technical Director of Aprovecho Research Center (ARC), died this past week at the age of 81. In the 1980’s and 90’s, Dr. Sam Baldwin defined how to improve heat transfer efficiency in biomass cook stoves (pot skirts, etc.), Dr. Tom Reed created the TLUD, and Dr. Winiarski invented the Rocket stove. The saying “We stand on the shoulders of giants” certainly applies to the stove community.

Larry led teams from ARC around the world starting in Central America, where the plancha stove was evolved, after he found that a floor tile called a baldosa made a long lasting and relatively low mass combustion chamber that was surrounded by wood ash, a great natural source of refractory insulation. Larry discovered that Rocket type stoves, like plancha stoves, can be described by ten design principles and that these simple engineering principles could be taught to indigenous people, mostly women, who were the experts in using the stoves. My memories of Dr. Winiarski, who was born in Nicaragua, are often about him having a wonderful time speaking Spanish as stoves were constructed and flavorful food prepared.

It is not an exaggeration to say that Larry had a heart of gold. He picked up sick kids and walked from the city dump in Managua to a distant hospital. He slept on cement floors for months at a time in Haiti. Larry lived as others lived in Africa for years and because of his character was loved and respected in villages worldwide. His Rocket stove found a place in people’s homes in the same way that Larry was cared for, accepted, and loved by strangers. Larry is missed by thousands of friends and he was blessed with a life well lived.

There will be a Celebration of Larry’s Life on Saturday, August 28, 2021 at 1:30 PM, at Colgan’s Island, 79099 Hwy 99 N in Cottage Grove, Oregon.

Smoky kitchen with no chimney vs. kitchen with chimney and clear air

Lance MacCarty

Meeting the World Health Organization Emission Rate Targets

August 3, 2021/0 Comments/in Indoor Air Quality

In 2014, the World Health Organization (WHO) published intermediate and final indoor air guidelines for vented and unvented biomass cooking stoves. Their strong recommendation directed governments and implementers to advocate technologies and fuels that are proven to protect health. The WHO advises implementers that to protect health the cook stove intervention should not exceed the following air pollutant emission rates in actual use:

**WHO Intermediate Emission Rate Targets:**

*Unvented stove*	*Vented stove*
PM 2.5: 1.75 mg/min	PM 2.5: 7.15 mg/min
CO: 0.35 g/min	CO: 1.45 g/min

Many newer biomass cookstoves with chimneys meet the WHO Targets of 7mg/minute for PM2.5 and 1.45 g/minute for CO when tested in the laboratory. Adding chimneys to cook stoves makes them more costly, but ARC designers are relieved to have a “line drawn in the sand.” As seen in Sam and Shikhar’s video last week, experiments in the ARC Test Kitchen showed that a natural draft hood can also be a big help in protecting health.

Protecting outdoor air quality is equally important. Dr. Nordica MacCarty (Oregon State University) and Ken Newcombe (C-Quest Capital) will be investigating effects on indoor and outdoor air when the combination of a natural draft earthen hood and a CQC earthen stove with Jet-Flame is used in houses in Malawi. Ken and CQC are invested in protecting health and have funded the study.

Industrial technologies routinely achieve strict standards for combustion efficiency and further reduce emissions with post combustion techniques. Introducing these well-known applications into cook stoves seems a logical progression. Clean up combustion and, at the same time, clean up the indoor and outdoor air. We have been very successful doing this in the US and Europe, and China is now on the same path.

The WHO vented stove Emission Rate Targets are based on 75% of the smoke and gases being removed up the chimney and out of the house. In their review of field studies, an average of 25% of the smoke and gas remained in the kitchen. Almost none of the residential biomass heating stoves in the United States meet the WHO Targets for PM 2.5 but the chimney transports the smoke outside where it is diluted by clean outdoor air to safe levels of concentration.

Meeting emission targets is a necessary and ever present goal. At the same time, wood burning stoves can be improved in many other ways. Improving the smoky mud stove to use less fuel is not a complete cure but is very helpful, benefitting the user who either pays for the fuel or has to collect it. The functional chimney makes a tremendous difference by sending smoke and gas out of the kitchen, making it a more pleasant and healthy environment. Making the high mass stove safer results in fewer burns. The list of improvements goes on and on – making the stove better at cooking local foods, increasing the number of air exchanges per hour in the kitchen, moving the kitchen outdoors, etc.

In the real world, positive changes are hard to accomplish but are always great.

New Video: Test Kitchen 2021 Natural Draft Hood

July 28, 2021/0 Comments/in Indoor Air Quality, Videos

The old saying, “if you can’t handle the heat, get out of the kitchen,” is not lost on us when we are working in the test kitchen. It takes us a while to get the vertical and horizontal grid of Climate Solution Consulting’s HAPEx particulate matter monitors started and positioned. Then ARC’s PEMS-PC partial-capture based emissions sampler has to collect a zero point of the gasses in the atmosphere. Don’t forget the temperature sensors (where is that data?) and the wood. This is after reviewing yesterday’s work, discussing a plan for the day, and watering the garden. So, by the time the young scientist rolls into the test kitchen in the Oregon summer, currently home of America’s largest wildfire, it’s about 100°F and rising. But science must go on.

ARC’s four year old test kitchen is currently being used to test a natural draft hood of our design. Our experiment allows us to operate the fire without being exposed to the emissions from the fire. We used to use a vacuum cleaner as a positive pressure ventilator, but now we sit outside of the room and feed the fire through a glove box. After seeing that the hood was effective enough to reduce the concentration of PM_2.5 in the test kitchen to below 35 ug (averaged over 24 hr), we turned the hood around and made a video for you of us doing the water boiling test while enjoying a smoke free kitchen.

Enjoy the video (and know that those loud pumps and fans go with the bit about it being hot in the kitchen).

Please send your photos and stories of natural draft hoods! We don’t want to lose this beautiful technology.

-Sam Bentsen, Aprovecho Research Center General Manager

Product Development

July 21, 2021/0 Comments/in LEMS, Testing Stoves

*General Manager Sam Bentsen is happy about some LEMS test results.*

Why test a stove?

Most of the time, our lab uses testing for product development. If we did not test a stove prototype we would be guessing whether it met expectations. Testing in the lab gets us ready for the field testing of prototypes. Then, customers take the prototype and make it work. The factory and distributors frequently ask for design changes as the product gets closer to shelves. From initial design to market usually takes about a year of testing/iteration/development.

Recently, a factory in Africa asked us to design a $10 wholesale, pellet burning forced draft TLUD prototype that achieves Tier 4 for thermal efficiency, CO, and PM2.5. The stove has to last ten years with scheduled maintenance and require as low wattage as possible.

We had tested the Oorja several times during surveys of commercially available stoves. ARC published the results in books and papers trying to inform the public how stoves compare on various measures of performance. We were trying to make available a Consumer’s Report on stoves (see list below). We knew that the Oorja stove met the Tier rankings and that it used a high mass, low cost, durable combustion chamber. We tried a castable refractory in the lab and we also found several manufacturers that make inexpensive ceramic combustion chambers.

The factory wants a high-powered stove to meet the needs of cooks in their region. Protecting health is also a major concern. Delivering a design that can be made for $10 is also very important. All the interconnected partners in the business plan have to make a healthy profit to bring a “Tier 4” technology to the public. The designer is only the first step in a web of stakeholders.

After all of the necessary parts were combined in the lab, testing with the LEMS (Laboratory Emissions Monitoring System) started. Many iterations were needed to get close to optimal performance. Adjusting the primary and secondary air at high power took experimentation. In several weeks of daily testing, the prototype was repeatedly achieving best scores. A CAD drawing was made and the design was sent to the factory. The factory is making their version of the stove, we will test it here and make adjustments if needed, and then field testing of the prototypes will begin, including home trails and test sales in stores.

Does it sound like a lot of work? The payback to know, rather than guess, that the product can be successfully sold. It’s great to make data based decisions, and a careful approach attracts investment. Failing miserably with products we loved (and lost money on) has made ARC consider external input carefully, especially from field testing.

Cook Stove Performance Reports:

The Oorja Forced Draft TLUD: A Different Approach

July 15, 2021/0 Comments/in TLUDs

*Testing the Oorja Stove under the LEMS hood.*

There are many forced draft TLUDs that are quite similar to Dr. Tom Reed’s 2001 version, the WoodGas stove. The Oorja stove can be about as clean burning but has several obvious differences: a high mass refractory ceramic combustion chamber, much bigger secondary air holes, and high firepower. Like other forced draft TLUDs the turn down ratio, created by limiting the combustion air, is narrow. The Mimi-Moto had to turn to a smaller combustion chamber for simmering to achieve Tier 4 for low power metrics. It’s a problem for Forced Draft TLUDS.

I have been a fan of the Oorja stove since 1999. In 2003, when I was living in India, hundreds of thousands of British Petroleum Oorja stoves were in use, burning pellets made from field residue. It’s been fascinating recently to read Dr. H. S. Mukunda’s 2010 paper describing the development of the Oorja.* When his team tested the lifespan of a metal combustion chamber it was only about 12 months and cast iron was expected to last about twice as long. The team developed a ceramic combustion chamber to create a better, longer lasting stove. I’m testing an Oorja stove with ceramic combustion chamber that is 20 years old!

Mr. Prasad Kokil from the San Jay Group writes: “We had developed this Oorja stove for BP in our company. We developed the ceramic refractory for the Oorja at that time. Our Elegant Model (now for sale) has a ceramic refractory combustion and is a forced draft TLUD”.

*Large secondary air holes near the top of the combustion chamber.*

Dr. Mukunda and team decided that at a burn rate of 12 grams per minute the primary air should be 18 g/min, and the secondary air was set at 54 g/min. The 18 secondary air holes, just below the top of the combustion chamber, are larger than in other FD-TLUDs at 6.5 mm in diameter creating a velocity of 1.8 meters per second. Using larger holes means that a low wattage computer fan supplies air jets with sufficient volume and velocity. Emission measurements made by the development team, carried out at fuel consumption rates of 12 and 9 g/min, showed that the CO emissions were 1 and 1.3 g/MJ whereas particulate emissions were 10 and 6 mg/MJ for the high and low power levels. When burning the made charcoal, CO rose but did not exceed the Indian standards.

The Oorja stove has been tested at various times in our lab with impressive results. Learning from Dr. Mukunda and team how to make stoves that are super clean burning and last a really long time is an important development. Thanks for such a great stove!

* Gasifier stoves: Science, technology and field outreach H. S. Mukunda, et al., CURRENT SCIENCE, VOL. 98, NO. 5, 10 MARCH 2010

Rocket Stove Sterilization for Hospitals

July 7, 2021/0 Comments/in International Work, Rocket Stoves

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.

Video Overview of Clean Burning Biomass Cookstoves 2021

June 30, 2021/0 Comments/in ETHOS, The Big Picture, Videos

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

New Climate Change and Biomass Combustion Study Wins Osprey Foundation Support

June 23, 2021/0 Comments/in News, The Big Picture

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!

How to Achieve 50% Thermal Efficiency in a Rocket Stove

June 16, 2021/0 Comments/in Rocket Stoves, Testing Stoves

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?

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.
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.
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.
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).
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)
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.