Summary of Aprovecho’s Summer Stove Camp, 2006
By Dean Still and Nordica MacCarty, September 6, 2006

Aprovecho Camp 2006 02

Stove Camp 2006 was extremely interesting, especially because we had experts here who could help define what is known, figure out what needed to be done to expand the state of knowledge, and then, most importantly, have the tools to accomplish the experiments.

For Dean, the best moments happened around the table above when Chris Roden, Jonathan Lewis, the Aprovecho staff and everyone tried to get a general feeling for wood-burning stoves effect on global warming. Aprovecho’s recent tests at CSU of greenhouse gas emissions such as CO2, Methane, N2O, NOx, etc. helped to predict the gaseous emissions from the following stoves:
• Three stone fire
• Rocket stove
• Karve Gasifier stove
• Philips fan stove
• Charcoal Jiko stove
• Mayon rice hull burning stove

The gases, however, are only a part of the picture: particles also play an important role in the atmosphere. We learned that elemental (black) carbon particles produced in flames have a warming effect 1000 times greater than CO2 per gram, while organic carbon (white) particles produced by smoldering have a cooling effect 150-200 times stronger than CO2. Thankfully, Chris Roden had brought his and Dr. Tami Bond’s ARACHNE system which could measure the composition of the total PM to determine what percentage of black or white particles were produced by the stoves above. Chris, Damon and Nordica were at the lab till 11pm having a great time testing these stoves. Results should be available soon.

Doing this kind of research in a small lab in Creswell, Oregon for no money is what ETHOS stove camp is all about!

The publicized theme of this year’s camp was a competition to design the cleanest-burning fan stove. Two categories, side feed and top feed were awarded prizes. The top feed prize went to Dr. Paul van der Sluis for the Philips fan stove. The side feed Rocket stove with fan developed by Roger and Sule of Colorado State was the cleanest burning side feed stove. Congratulations to the winners!

WoodGas vs Wood Combustion
Tom Reed, Biomass Energy Foundation, April 2006

As a longtime proponent (since 1973) of biomass gasification and moderator of the gasification REPP group, let me define "gasification" a little more widely than the discussion below
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Coal pyrolysis produces typically 80% fixed carbon, 20% gas and volatiles. The principle step then for coal gasification is getting that carbon to be a gas with either oxygen, CO2 or water

2C + O2 ==> 2 CO
C + CO2 ==> 2 CO
C + H2O ==> CO + H2

The first reaction is exothermic, while the last two are endothermic.
So pass air/oxygen, CO2 and H2O through coal and you produce CO + H2.
Coal gasification was the principle form before 1940 and was practiced at a large scale because of the need to remove sulfur and ash. During WW II however, biomass was the fuel of choice for small gasifiers to run cars, trucks and buses.

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Biomass is typically 80% gas plus volatiles plus 20% fixed carbon. So the main problem is to convert the volatiles to CO + H2.

Pyrolysis typically occurs at 300-500C. Conventional bottom lit updraft gasifiers burn charcoal on a grate to produce hot CO-H2 which then pyrolyzes the incoming biomass to make VERY tarry gas. *(I call this a "char burning, tar making gasifier")*.

But if you pass air through a mass of biomass the temperature is 700-1000 C, and we call that "flaming pyrolysis". FP produces mostly CO
+ H2, CO2 and H2O and small amount of condensibles (tars). These then
pass through the remaining charcoal where most of the volatiles are destroyed. At the high end the condensibles are typically < 100 ppm.
At the low end, more like 2000. *(I call this a "tar burning, char making gasifier").
*
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I call the Flaming Pyrolysis process "PYROLYTIC GASIFICATION". It occurs at a continuum of temperatures from 700-1000C, depending on air/fuel ratio. At the low end, 700C, very little of the charcoal is gasified and the toplit updraft stoves produce 5-25% charcoal, depending on the moisture content of the fuel. At the high end up to 1000C the gas is VERY low tar and useful for operating engines for power and transportation and for synthesis of methanol and diesel. .

If secondary air is added to the gases after they are generated you have a very clean and hot flame. This is VERY different from direct combustion and I classify our WoodGas Campstove as a close coupled pyrolytic gasifier and combustor.

We now are selling WoodGas Campstoves at our website store along with our books on gasification (www.woodgas.com) and I recommend getting one and pondering the profound difference between the gasification and direct combustion of wood for cooking. While we have made the campstove, the principles can be applied at all scales for apartment and
field cooking around the world. We hope they will be.

Yours truly,

TOM REED
The Biomass Energy Foundation
tombreed@comcast.net

T. B. Reed and Ron Larson

*Presented at the "Developments in Thermochemical Biomass Conversion" Conference, Banff, Canada, 20-24 May, 1996.

Introduction -

A.The Problem

Since the beginning of civilization wood and biomass have been used for cooking. Over 2 billion people cook badly on inefficient wood stoves that waste wood, cause health problems and destroy the forest. Electricity, gas or liquid fuels are preferred for cooking - when they can be obtained, but they depend on having a suitable infrastructure and are often not available in developing countries. In the last few decades, many improved wood stoves have been developed (the Chula, the Hiko, the Maendeleo, the Kuni Mbili, etc.), but the new wood stoves are often more difficult to manufacture, often more heat goes to the stove than to the food, and they do not offer good control of cooking rate. They are not always accepted by the cooks for whom they are developed.[1] Because of the problems of wood cooking, people often cook over charcoal. However, charcoal manufacture is very wasteful of energy and very polluting, so the problems of the wood stove are externalized but not solved.

A.THE SOLUTION

Gas is preferred for cooking wherever it is available. Gas can be made from wood and biomass in gasifiers developed in this century, but these gasifiers are generally too big for home use. A downdraft stove for domestic cooking is now being manufactured in China.[2] We have developed a new "inverted downdraft gasifier" stove shown in Fig. 1. It operates using only natural convection. The rate of gas production and heating is controlled by the primary air supply to the gasifier. As an option, the gasifier can make charcoal with a 20-25% yield. The wood-gas stove consists of an "inverted downdraft gasifier" (shown in Fig. 2) plus a burner to mix air and gas and burn cleanly (Fig. 3). These sections are discussed below. The stove has been started and operated indoors with no exhaust fans and no odor of burning wood. However, we believe that there is still much work to be done in optimizing the stove for various fuels, adapting it to various cooking situations and developing other uses. For that reason we are publishing our preliminary results and hope that others will help adapt these principles to improve world cooking and wood conservation.