Principles

We are trying to (a) reduce the amount of emmisisons from charcoal production and (b) Condense and recover as much of the smoke into a usable product for your home/farm. Wood tar - the following is an explanation from the good folks at Food and Agriculture Organization of the United Nations (FAO) about what is going on in this process.
"The non-water component consists of wood tars, both water soluble and insoluble, acetic acid, methanol, acetone and other complex chemicals in small amounts. If left to stand, the proligneous acid separates into two layers comprising the water insoluble tar and a watery layer containing the remaining chemicals. Recovery of the water insoluble tar, often called wood or Stockholm tar, is simple - it is merely decanted from the water phase. This wood tar has uses as a veterinary antiseptic, a preservative for wood, a caulking agent, and as a substitute for road tar" http://www.fao.org/docrep/x5328e/x5328e0d.htm

For more pictures click here

File attachments: 

Dear Friends

This is very useful.

Save it!

y = 4-08x2 - 0.0036x + 99.996

X = your altitude in meters.
Y = the local boiling point (at standard air pressure)

If you know your altitude, it will give you the ‘standard’ boiling temperature.
If you know the local boiling point, you can work backwards to get the altitude where you are standing.

Excel cell contents:

=99.996-0.0036*Altitude+4*10^-8*Altitude

where ‘Altitude’ is the cell in which the altitude is located.

Regards
Crispin

Christa Roth's excellent report
Micro-gasification: Cooking with gas from dry biomass

has a new location:
https://energypedia.info/wiki/File:Micro_Gasification_Cooking_with_gas_f...

Her comprehensive survey of micro-gasification technology has great technical information and is well worth the read.

thanks to GiZ (the German people) for making it available to all of us.

Christa Roth, January, 2012

To the members of the list who don't know Energypedia yet: it is an online resource created as a Wiki by GIZ . After some years of development as company-interal resource, it was opened to the public energy community late last year. No registration needed to read.

Dr. N. Sai Bhaskar Reddy, CEO, GEO December, 2011
http://e-geo.org

See the attached pdf (about 150kb): Understanding Stoves
it is an excellent brief summary that highlights the important aspects of stoves design and testing. e.g. fuels, fuel preparation, stove design, materials, use and testing.

Crispin Pemberton‐Pigott October, 2008
Sustainable Energy Technology and Research Centre University of Johannesbrg 
Programme for Basic Energy Conservation GTZ/ProBEC a SADC Regional Project 

See the attached pdf: CERAMIC DEVELOPMENT FOR DOMESTIC STOVES 

Also take a look at Crispin's very good ceramic stove image galleries.

It is intended that this brief report describe in an accessible manner the results of some basic research into the performance of ceramic materials suitable for use to make modern, low‐cost improved charcoal stoves. The 
theatre of investigation is the area around Maputo, Moçambique. 

 The information and ideas are assembled from a large number of tests and reports. If studied carefully an understanding can be gained of the 
principle ingredients found in typical clays. It is hoped enough can also
 be learned about what the tests show so as to interest the ‘stover’ in a 
deeper study of this vast subject.  

Some reasons why clay stoves and stove components typically have such a 
short life are described and to a certain extent, what can be done about 
it.   

There is a great deal of material available on how to find, identify and 
process clays such as pottery books and the internet. It is not repeated 
here.  Unfortunately very little of the material available is geared to 
the design of low cost ceramics stoves which have problems not encountered
 in many industrial applications with far higher temperatures.  

Ceramics are complex mixtures of many minerals so it is not possible to 
give comprehensive explanations in such a brief text, however the novice 
reader should learn enough to be able to deal with a laboratory and 
understand some common terminology and the test results.  There have been
 many technological advances in recent years making accessible tests and 
analyses that were previously unaffordable to the ordinary potter.

Christa Roth, February, 2011

Dear all, find below the links to new publications by GIZ HERA poverty-oriented basic energy services, among them the manual on Micro-gasification: Cooking with gas from biomass. For queries please refer to the respective authors or Michael Blunck from HERA.

the HERA web site

Micro-gasification: Cooking with gas from biomass

- new link : https://energypedia.info/wiki/File:Micro_Gasification_Cooking_with_gas_f...

Micro-gasifiers: much more than „just another improved cook stove”. In this new HERA handbook, Christa Roth provides an introduction to the concept and the application of wood-gas burning technologies for cooking.

Modern Energy Services for Modern Agriculture. A Review for Smallholder Farming in Developing Countries.
http://www.gtz.de/de/dokumente/giz2011-en-energy-services-for-modern-agr...
This publication provides an overview on energy inputs required in different steps of the agricultural production chain, such as production, post-harvest and storage, processing, and commercialization.

Small-scale Electricity Generation from Biomass – Part III: Vegetable Oil
http://www.gtz.de/de/dokumente/giz2011-en-small-scale-electricity-genera...
In the third and final part of HERA’s paper series on power generation from biomass, GIZ and non-GIZ experience with electricity production from vegetable oils is compiled. While from a technology point-of-view, plant oils constitute a very viable option for off-grid power generation in developing countries, their sustainable application in daily operation for rural electrification projects still remains rare. The paper identifies remaining bottlenecks and provides recommendations for future electrification projects based on plant oil.

Carbon Markets for Improved Cooking Stoves – Revised Edition: January 2011
http://www.gtz.de/de/dokumente/giz2011-en-carbon-markets-for-improved-st...
After receiving a lot of positive feedback for the 2010 edition of the carbon market guidebook for cooking stove projects, HERA has come up with a major revision for 2011. Besides a large number of minor corrections and updates, a new chapter on “Implementing a Carbon-funded Cooking Stove Project” with information on how to practically design a carbon-funded stove project has been added. The chapter includes information on stakeholders’ roles and responsibilities, the CDM-PoA approach, recommendations on the use of carbon revenues as well as an overview on expected costs and revenues from a stove project on the carbon market.

Christa Roth and Christoph Messinger, August 2010

Existing Charcoal Stove

Existing Charcoal StoveImproved Charcoal Stove

Improved Charcoal Stove

Improving the Charcoal Stove for Haiti, Stove Camp 2010 (see the Stove Camp Summary for challenge details)

Main points mentioned at the end of the Stove Camp Workshop

  1. We need a high turn down ratio.

    To bring water and foods fast to the boil, we need high power in the heat-up phase.
    However, thereafter we commonly need low power for simmering. The stove
    therefore needs to offer the opportunity to turn down the power output drastically.
    Options:

    1. Regulation of primary air supply (e.g. closing door)
    2. The gap between pot and charcoal is increasing over cooking time (shape of char container provides more depth = increased gap to the char)
    3. c) The amount of char available at the end of cooking is reducing (conical shape of char container = less char over time available)
  2. We need to reduce heat losses to the bottom and to the side of the stove.

    A char container radiates heat to all sides – not just to the pot. To reduce the amount
    of char used, it is important to reduce the heat losses to the other directions.
    Options:

    1. Bottom of stove: rebounding plate (with holes) in between primary air supply
    2. intake and charcoal container. Thus primary air is channeled through the
    3. heated rebounding plate, taking some heat back into the char container.
    4. Side of the stove: double wall with air in between for insulation.
  3. We need to maximize heat harvest from a given amount of charcoal.

    Charcoal burning is mainly influenced by the amount of air available in the char
    container.
    Options:

    1. A vertical spacer in the center of the charcoal container (Lanny Henson’s pig tail”) seemed to increase the availability of air for charcoal combustion.
    2. Additional draft (e.g. forced air) may increase heat generation per time unit. However, this may also increase CO emissions and reduce efficiency of char use.
    3. Secondary air to burn off the CO in a gap between the charcoal and the pot may provide additional heat. However, for this to be beneficial it may not impact on the surface area available for direct radiation from the charcoal to the pot and should not cool down the air in the gap (well preheated secondary air).
  4. We need to maximise heat transfer to the pot.

    Generating as much heat as possible out of a given amount of charcoal is one step.
    But another important step is to make sure that most of this heat actually is
    transferred into the cooking pot.
    Options:

    1. “Sunken pot” concept seems to provide best results in terms of heat transfer (Henson stove). Unfortunately, in real life this might not be possible in many work environments.
    2. Best heat transfer is NOT achieved if the pot rests on the char. Optimum is about 1inch away from the char, not closer than that. For Simmer, this could increase to 2-3 inches.
    3. A skirt is highly important to shield the gap area between the pot and the char against the influence of wind. The gap between pot and skirt should bedetermined.

Christa’s Summary of the stove camp

Observation and necessary action Derived Design Principles
Charcoal radiates heat to all
sides: as much can radiate
towards the bottom of the stoves
as can radiate upwards towards
the pot.

Action:
Avoid loss of radiating and
conducting heat from charcoal
that is not directed towards the
pot.

  • Add space between the charcoal grate and other stove parts: Lift the charcoal grate slightly off the bottom of the stove and increase the space to the sides of the stove.
  • Limit the places where the hot grate can conduct heat to other stove parts.
  • Add a deflector plate between charcoal chamber and the stove bottom to radiate heat back upwards.
  • Insulate the stove bottom to prevent heat loss through the bottom.
  • Insulate sides of the stove.
  • Regain heat through air circulation (air cooling of stove) by passing air through heated stove parts thus preheating air entering the combustion system. This can be by passing primary air through the deflector plate below the grate and/or secondary air through a gap between double side walls of the stove.
Charcoal combusts in function of the available oxygen. Thus heat generation is a function of
air supply to the charcoal grate.

Action: get the right amount of air to the charcoal grate. To little will choke the combustion, too much will cool the flue gases.

If power of the stove is too low, increase air supply by

  • making more holes in the grate.
  • adding a ‘Henson pig-tail’ vertical air-pass through the charcoal bed.

Do not pile the charcoal up too high, as this will restrict air flow through the charcoal bed (this is influenced as well by the shape and particle size of the charcoal chunks).

The combustion of charcoal goes from oxidizing C to CO, then in
a subsequent step from CO to CO2.

CO is a toxic gas and has still considerable energy value. Ensuring a complete combustion
will increase energy output and reduce toxic emissions.
Action: avoid CO emissions.

Charcoal radiates heat but there is also considerable convection of hot flue gases.
Action:
Optimize transfer of created heat into the pot.
Avoid obstructions between the radiating charcoal bed and the bottom of the pot (increase
the view factor of the charcoal seeing the pot).

The stoves design and principles are explained with simple sketchs. Many stove designs are existing, but most common designs are presented here.

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