Difference between revisions of "Firewood Cookstoves"

From energypedia
***** (***** | *****)
***** (***** | *****)
m
 
(120 intermediate revisions by 15 users not shown)
Line 1: Line 1:
[[GIZ HERA Cooking Energy Compendium|--> Back to Overview GIZ HERA Cooking Energy Compendium]]
+
[[File:GIZ HERA Cooking Energy Compendium small.png|left|831px|GIZ HERA Cooking Energy Compendium|alt=GIZ HERA Cooking Energy Compendium small.png|link=GIZ HERA Cooking Energy Compendium]]<br/><br/><!--
 +
 
 +
-->{{#ifeq: {{#show: {{PAGENAME}} |?Hera category}} | Cooking Energy System |'''[[GIZ HERA Cooking Energy Compendium#Cooking Energy Technologies and Practices|Cooking Energy System]]''' {{!}} | [[GIZ HERA Cooking Energy Compendium#Cooking Energy Technologies and Practices|Cooking Energy System]] {{!}} | }} <!--
 +
 
 +
-->{{#ifeq: {{#show: {{PAGENAME}} |?Hera category}} | Basics |'''[[GIZ HERA Cooking Energy Compendium#Basics about Cooking Energy|Basics]]''' {{!}} | [[GIZ HERA Cooking Energy Compendium#Basics about Cooking Energy|Basics]] {{!}} | }} <!--
 +
 
 +
-->{{#ifeq: {{#show: {{PAGENAME}} |?Hera category}} | Policy Advice |'''[[GIZ HERA Cooking Energy Compendium#Policy Advice on Cooking Energy|Policy Advice]]''' {{!}} | [[GIZ HERA Cooking Energy Compendium#Policy Advice on Cooking Energy|Policy Advice]] {{!}} | }} <!--
 +
 
 +
-->{{#ifeq: {{#show: {{PAGENAME}} |?Hera category}} | Planning |'''[[GIZ HERA Cooking Energy Compendium#Planning Cooking Energy Interventions|Planning]]''' {{!}} | [[GIZ HERA Cooking Energy Compendium#Planning Cooking Energy Interventions|Planning]] {{!}} | }} <!--
 +
 
 +
-->{{#ifeq: {{#show: {{PAGENAME}} |?Hera category}} | ICS Supply |'''[[GIZ HERA Cooking Energy Compendium#Designing and Implementing Improved Cookstoves .28ICS.29 Supply Interventions|Designing and Implementing ICS Supply]]''' {{!}} | [[GIZ HERA Cooking Energy Compendium#Designing and Implementing Improved Cookstoves .28ICS.29 Supply Interventions|Designing and Implementing ICS Supply]] {{!}} | }} <!--
 +
 
 +
-->{{#ifeq: {{#show: {{PAGENAME}} |?Hera category}} | Woodfuel Supply |'''[[GIZ HERA Cooking Energy Compendium#Designing and Implementing Woodfuel Supply Interventions|Designing and Implementing Woodfuel Supply]]''' {{!}} | [[GIZ HERA Cooking Energy Compendium#Designing and Implementing Woodfuel Supply Interventions|Designing and Implementing Woodfuel Supply]] {{!}} | }} <!--
 +
 
 +
-->{{#ifeq: {{#show: {{PAGENAME}} |?Hera category}} | Climate Change |'''[[GIZ HERA Cooking Energy Compendium#Climate Change Related Issues|Climate Change]]''' | [[GIZ HERA Cooking Energy Compendium#Climate Change Related Issues|Climate Change]] {{!}} | }} <!--
 +
 
 +
-->{{#ifeq: {{#show: {{PAGENAME}} |?Hera category}} | Extra |'''[[GIZ HERA Cooking Energy Compendium#Climate Change Related Issues|Extra]]''' | [[GIZ HERA Cooking Energy Compendium#Climate Change Related Issues|Extra]] }}
 +
 
 +
<br/>
 +
 
 +
= Introduction<br/> =
 +
 
 +
Firewood is wood from logs, sticks or twigs. It has been used as a fuel since the beginning of mankind. In principle, it is renewable and relatively easy to produce, transport and store. However, the use of firewood for cooking is commonly associated with deforestation and health problems. This is not an inherent problem of the fuel, but is strongly influenced by the quality and quantity of its correct usage and can be overcome by improving the efficiency of the wood fuel usage.
 +
 
 +
Two major factors determine if firewood burns clean and efficient: its moisture content and the oxygen supply of the fire. While it depends on the user to make sure that the fuel is dry, the air-flow depends on the stove design. In a natural draught stove, the supply of air is created by the chimney or stack height of the fuel. However, there must be a difference in temperature between the stove and the top of the chimney to generate draught. Natural draught is likely to cause incomplete combustion with higher emissions and energy losses through the chimney. Moreover, it is also difficult to regulate.
 +
 
 +
<br/>
  
= Firewood<br/> =
+
<u>The burning of wood is a sequence of steps:</u>
  
Firewood is the first fuel used for cooking in human history. It is renewable and easy to produce, transport and store.
+
#Moisture is evaporated
 +
#Wood decomposes into combustible wood-gas and char
 +
#Char is converted into ash
  
The burning of wood is a sequence of steps determined by rising temperatures:
+
<br/>
  
*a) Moisture is evaporated
+
The main influencing agent for “a)” and “b)” is heat, whereas “c)is regulated by the supply of oxygen.
*b) Wood decomposes into combustible wood-gas and char
 
*c) Char is converted into ash
 
  
The main influencing agent for “a)” and “b)” is heat, whereas “c)” is regulated by the supply of oxygen. Find here more information and illustrating figures on pages 8-11 in the manual on micro-gasification ([http://www.gtz.de/de/dokumente/giz2011-en-micro-gasification.pdf http://www.gtz.de/de/dokumente/giz2011-en-micro-gasification.pdf])
+
Find here more information and illustrating figures on pages 14-15 in the "[[:File:Micro Gasification 2.0 Cooking with gas from dry biomass.pdf|Manual on Micro-gasification]]". For more information on the characteristics of firewood as a fuel see Cooking with Firewood.
  
 +
<br/>
  
 +
= The Wood-Fuel Cooking System =
  
[[File:GIZ-Feldmann-Malawi-3-stone-fire.jpg|600px|GIZ-Feldmann-Malawi-3-stone-fire.jpg]]
+
[[File:GIZ woodfuel cooking system 2011.jpg|thumb|left|300px|alt=GIZ woodfuel cooking system 2011.jpg]]As shown in the figure beside, in the wood-fuel cooking system, firewood is mixed with air in a reactor. After ignition, a chain reaction is triggered in which heat is generated. This heat is transferred through 3 processes:
  
Picture: Malawi-3-stone-fire (GIZ-Feldmann)
+
Convection: Hot gasses are passing a surface transferring heat into surrounding materials;<br/>Radiation: Red hot embers is radiating heat into surrounding materials;<br/>Conduction: Heat is conducted through materials. Metal is a good heat conductor, whereas air is a poor heat conductor.
  
 +
The reactor is emitting heat, but also light, gasses and particles. While the emission of heat is wanted, the emission of gasses, particles and light are rather unintended. Good stove designs can reduce the quantity of unwanted emissions in favor of additional heat generation. The heat does not enter automatically into a cooking pot. The design of the heat transfer unit has a big effect on the percentage of the heat transferred into the food to be cooked.
  
 +
<br/>
  
Firewood can be used for cooking even in the absence of a “stove”. Even to date, campfires are a popular leisure activity in developed countries. However, they are not favoured for daily cooking. Some disadvantages of the open fire are:
+
Overall there are two major dimensions for efficiency gains for firewood stoves:
  
*Smoke (= unburned fuel particles in the air):<br/>The combustion in an open fire tends to be incomplete as oxygen might not reach where it is needed. Low temperatures also contribute to the emission of unburned particles.
+
#Achieve complete combustion (=‘create more heat per unit of fuel used’)
 +
#Improve heat transfer (=‘get more heat actually into the pot’)
  
*Slow pace of cooking:<br/>Even if a lot of heat might be generated, the heat is not directed to the cooking pot, hence a lot of heat is lost to the environment. This problem is accelerated if there are windy conditions as the flames are not shielded. The cooking pot does not sit in the hottest part of the flames; hence less heat is transferred into the pot than theoretically possible.
+
<br/>
  
*Health risks:<br/>As the flames are not directed or shielded, the cook can easily catch fire when approaching the cooking pot. Sparks pose an additional risk when approaching the fire. Burns are a common effect of open fires. The smoke might cause eye infections.
+
<br/>
  
*High fuel consumption:<br/>The open fire consumes a lot of fuel as (a) not much heat is generated per unit of fuel, (b) only a small proportion of the heat is actually directed to the pot and (c) only a small fraction of the heat directed to the pot is actually transferred into the food.
+
= Three-stone Fires or Open Fires =
  
 +
[[File:GIZ-Feldmann-Malawi-3-stone-fire.jpg|thumb|right|300px|3-stone fire in Malawi]]Worldwide, millions of people cook on so-called 3-stone fires or open fires as this is the simplest and cheapest “stove” to create. Only three suitable stones of the same height are needed to balance a pot over a fire. However, the daily use of these 3-stone fires has the following disadvantages: &nbsp;
  
 +
High fuel consumption:<br/>The open fire consumes a lot of fuel as
  
On the other hand, some of these inefficiencies are also welcomed due to their positive side effects:
+
*(a) not much heat is generated per unit of fuel,
 +
*(b) only a small proportion of the heat is actually directed to the pot and
 +
*(c) only a small fraction of the heat that is directed to the pot is actually transferred into the food.
 +
*Slow pace of cooking:<br/>The cooking pot does not sit in the hottest part of the flames; hence less heat is transferred to the pot than theoretically possible. Even if a lot of heat is generated, the heat is not directed to the cooking pot and heat is lost to the environment. This problem is accelerated if there are windy conditions as the flames are not shielded.
 +
*Smoke:<br/>The combustion in an open fire tends to be incomplete as oxygen might not reach where it is needed. Low temperatures also contribute to the emission of smoke (= unburned particles).
 +
*Health risks:<br/>As the flames are not directed or shielded, the cook can easily catch fire when approaching the cooking pot. Sparks pose an additional risk when approaching the fire. Burns are a common effect of open fires. The smoke might also cause eye infections.
  
*Open fires are burning slow and do not require frequent attention. This is welcome if other household chores have to be done at the same time.
+
<br/>
*Smoke can chase away mosquitoes in malaria-infested areas;
 
*Smoke can be used to preserve food;
 
*Open flames are emitting light, which is welcome before sunrise or after sunset;
 
*Open fires are emitting heat, which is welcome in cold areas;
 
  
 +
On the other hand, users welcome some of these inefficiencies due to their positive side effects:
  
 +
*Open fires burn slow and do not require frequent attention. This is convenient if other household chores have to be done at the same time.
 +
*Smoke can chase away mosquitoes, which is especially beneficial in malaria-infested areas;
 +
*Smoke can be used to preserve food;
 +
*Open flames emit light, which is welcome before sunrise or after sunset;
 +
*Open fires emit heat, which is favorable in cold areas.
  
These observations on the open fire can be summarized as follows:
+
<br/>
  
{| border="1" cellpadding="1" cellspacing="1" width="100%"
+
<br/>
|-
 
! scope="col" | Parameter
 
! scope="col" | Advantages
 
! scope="col" | Disadvantages
 
|-
 
| Small proportion of heat is directed to the pot;<br/>Small proportion of heat is transfer into the food
 
| Slow cooking allows for other household work to be done at the same time
 
| Slow cooking, Inefficient cooking
 
|-
 
| Emission of smoke (unburned fuel particles)
 
| Repellant for mosquitoes, food preservation
 
| Health risk, Inefficient cooking
 
|-
 
| Emission of heat to the environment
 
| Warming of space in cold areas<br/>
 
| Inefficient cooking
 
|-
 
| Emission of light to the environment
 
| Good vision before dawn or after sunset<br/>
 
| Inefficient cooking
 
|}
 
  
 +
= Three-stone Fire versus Improved Cookstove =
  
 +
The development of improved cookstoves is facing a dilemma: the same characteristics are at the same time responsible for both users’ complaints and appreciations of the 3-stone fire. There is no solution which can satisfy all expectations. Any new stove will be a trade-off between different user needs. This dilemma is summarized in the table below. Furthermore, users are used to a specific cooking system and any change in cooking habits needs time.
  
The development of improved cook stoves is therefore facing a dilemma: the same characteristics which are at the same time responsible for complaints against and appreciation of the open fire. There is no solution which can satisfy all the expectations which are expressed in this table. Any new stove will be a trade-off between different user needs.
+
<br/>
  
{| border="1" cellpadding="1" cellspacing="1" width="100%"
+
{| style="width: 100%" cellspacing="1" cellpadding="1" border="1"
 
|-
 
|-
! scope="col" | Common changes of parameters in improved cook stoves
+
| '''Common changes of parameters in improved cook stoves'''
! scope="col" | Common expectation towards an improved stove<br/>
+
| '''Common expectations towards improved stoves'''
! scope="col" | "Disadvantages” for associated benefits of open fires<br/>
+
| '''"Disadvantages” for associated benefits of open fires'''
 
|-
 
|-
| Improve efficiency of heat production
+
|  
 +
Improve efficiency of heat production
 +
 
 
*More complete combustion = less emission of unburned fuel
 
*More complete combustion = less emission of unburned fuel
*Shelter the fire
+
*Shelter the fire against the wind;
 
*Direct flames to the pot
 
*Direct flames to the pot
  
Line 97: Line 120:
 
|-
 
|-
 
|  
 
|  
Improve heat transfer into the cooking pot
+
*Improve heat transfer into the cooking pot
 
+
*Position of the cooking pot at the hottest place of the flame;
*Position cooking pot at the hottest place of the flame;
 
 
*Hot gasses are passing close to the pot to maximize heat transfer;
 
*Hot gasses are passing close to the pot to maximize heat transfer;
  
Line 109: Line 131:
 
|  
 
|  
 
*Stove is sometimes higher than the open fire
 
*Stove is sometimes higher than the open fire
 +
*Some stoves don’t fit all pot sizes
  
 
|}
 
|}
  
 +
<br/>
  
 +
<br/>
  
 
Households have to prioritize their needs in order to come up with the decision if an improved cook stove is suitable for them. In areas with fuel scarcity, the need for reduced fuel consumption might be ranked higher than the need for space heating or lighting after dark.
 
Households have to prioritize their needs in order to come up with the decision if an improved cook stove is suitable for them. In areas with fuel scarcity, the need for reduced fuel consumption might be ranked higher than the need for space heating or lighting after dark.
  
Another strategy can be to provide additional solutions to complement the introduction of the improved cook stoves:
+
<u>A strategy can be to provide additional solutions to complement the introduction of the improved cook stoves:</u>
 
 
*an extra space heater for the cold season;
 
*a mosquito-repellent net,
 
*a solar lantern for lighting.
 
 
 
Stoves for firewood have been developed since 3000 years. Overviews on types and models have been developed from various entities, this is just a selection:
 
 
 
*UNESCO(1982): Consolidation of information. Cooking stoves Handbook [http://unesdoc.unesco.org/images/0005/000530/053052eb.pdf http://unesdoc.unesco.org/images/0005/000530/053052eb.pdf]
 
*GIZ (1995) by Westhoff/German 'Stove Images - a Documentation of Improved and Traditional Stoves in Africa, Asia and Latin America'. Also in French and Spanish on[http://www.gtz.de/en/themen/umwelt-infrastruktur/energie/32777.htm http://www.gtz.de/en/themen/umwelt-infrastruktur/energie/32777.htm] and [http://www.gtz.de/en/themen/umwelt-infrastruktur/energie/32777.htm http://www.gtz.de/en/themen/umwelt-infrastruktur/energie/32777.htm]]
 
 
 
The Aprovecho Institute in Oregon has analysed the design principles which can help to make firewood stoves more fuel-efficient. If all principles are applied, the result would be called a rocket stove, which was invented by Dr. Larry Winiarsky. For further details see [http://www.aprovecho.org www.aprovecho.org].
 
 
 
= The Rocket Stove Principle<br/> =
 
 
 
One of the most successful new concepts in stove design is the rocket stove principle.
 
 
 
*It has a tall combustion chamber which behaves a bit like a chimney; creating more draught than a standard stove. This assists in mixing the air, fuel particles and volatiles, resulting in a hot flame. The internal walls are insulated, reflecting all the heat back into the chamber rather than losing it to the stove body. The insulation keeps everything very hot so that the chemical reaction is more intense, whilst the tall chamber provides more time in which the gases and particles can be burnt completely, giving out all their heat and discharging mainly carbon dioxide and water vapour.
 
*These hot flue gases pass through a well defined gap between a ‘skirt’, and the pot, as shown in the illustrations given below, resulting in a large percentage of the heat being forced against the sides of the pot, and being transferred to the pot. Where various sizes of pot are used on the same stove, the skirt can be funnel-shaped to accommodate different pots, although some efficiency will be lost.
 
*An elbow-shaped combustion chamber, with a shelf for the fuel wood, supports the pre-drying of the firewood and allows a controlled, and sufficient, flow of primary air to be warmed as it passes under the wood to the burning wood tips.
 
 
 
 
 
 
 
{| border="1" cellpadding="1" cellspacing="1" width="100%"
 
|-
 
|
 
[[File:RocketStoveklein.JPG|none|RocketStoveklein.JPG]]
 
 
 
| The rocket stove principle. Source: Aprovecho
 
|}
 
 
 
 
 
 
 
Design principles, which can be used more generally include:
 
  
*Insulation around the fire and along the entire heat flow path using lightweight, heat resistant materials
+
*an extra space heater for the cold season
*A well-controlled, uniform draught in the burning chamber during the entire combustion process
+
*a mosquito-repellent net
*Use of a grate or a shelf under the firewood
+
*a solar lantern for lighting
*Heat transfer maximised by the insertion of the pot into the stove body or using a skirt around the pot.
 
  
{| border="1" cellpadding="1" cellspacing="1" width="100%"
+
<br/>
|-
 
|
 
[[File:Pic2.JPG|RTENOTITLE]]
 
  
|-
+
= Design Principles for Improved Cookstoves =
| A rocket-type stove in action, and showing insulation of the burning chamber, skirt around pot and support frame. Source: GIZ / Aprovecho Institute
 
|}
 
  
However, even all other improved firewood stoves do apply at least some of these principles.
+
All improved firewood stoves apply at least some of the aspects listed below geared toward increasing efficiency and improving heat transfer.<ref name="Aprovecho Research Center (2005): Design Principles for Wood Burning Cook Stoves. http://www.ewb-usa.org/files/2015/05/PrinciplesWoodBurningCookStoves.pdf">Aprovecho Research Center (2005): Design Principles for Wood Burning Cook Stoves. http://www.ewb-usa.org/files/2015/05/PrinciplesWoodBurningCookStoves.pdf</ref>
  
 
<br/>'''How can we improve the design of the stove to increase the combustion efficiency in a firewood stove?'''
 
<br/>'''How can we improve the design of the stove to increase the combustion efficiency in a firewood stove?'''
  
{| border="1" cellpadding="1" cellspacing="1" width="100%"
+
{| style="width: 100%" cellspacing="1" cellpadding="1" border="1"
 
|-
 
|-
! scope="col" | Principle
+
! style="text-align: left;  background-color: rgb(204, 204, 204)" scope="col" | Aspect<br/>
! scope="col" | Solutions
+
! style="text-align: left;  background-color: rgb(204, 204, 204)" scope="col" | How to achieve
 
|-
 
|-
 
| Increasing the temperature in the combustion chamber (as the burning process is temperature controlled)
 
| Increasing the temperature in the combustion chamber (as the burning process is temperature controlled)
 
|  
 
|  
 
*Shelter the fire against wind;
 
*Shelter the fire against wind;
*Use of isolative materials to reduce heat losses to the side and to the bottom;
+
*Use isolative materials to reduce heat losses to the side and to the bottom;
  
 
|-
 
|-
 
| Reduce the intake of firewood
 
| Reduce the intake of firewood
| By creating a small entrance for the firewood, only the required level of wood can be entered. Excess wood cannot be supplied to the reactor
+
|  
 +
*Create a small entrance for the firewood. Then only the required level of wood can be entered. Excess wood cannot be supplied to the reactor
 +
 
 
|-
 
|-
 
| Burn off all the volatiles
 
| Burn off all the volatiles
| Allow enough space in the combustion chamber (increasing the space between pot and fire)
+
|  
 +
*Allow enough space in the combustion chamber (increasing the space between pot and fire) since the hottest point of a fire is a bit above the end of the flame and for the volatiles to burn off high temperatures and enough air supply is needed.&nbsp;
 +
 
 
|-
 
|-
 
| Adequate air supply
 
| Adequate air supply
| Air and wood intake into the combustion chamber are regulated and correlated
+
|  
 +
*Regulate air and wood intake into the combustion chamber and ensure both the amount of air and wood intake are correlated.
 +
 
 
|-
 
|-
 
| Reduce the inflow of cold air
 
| Reduce the inflow of cold air
| Regulated air intake (door)<br/>
+
|  
 +
*Regulate air intake (door)<br/>
 +
 
 
|-
 
|-
 
| Intake of pre-heated air
 
| Intake of pre-heated air
| Air is used as an insulated between an inner and an outer wall of the stove. Air is channeled through this gap before entering the combustion chamber
+
|  
 +
*Use air as an insulation between an inner and an outer wall of the stove. Via a secondary air inlet, air is channeled through this gap and pre-heated before entering the combustion chamber.
 +
*Rest the wood on a shelf. The air passing under the shelf is preheated.
 +
 
 
|-
 
|-
 
| Increasing the draft
 
| Increasing the draft
 
|  
 
|  
*A vertical combustion chamber increases the natural draft in the stove;
+
*A vertical combustion chamber can increase the natural draft in the stove;
*A ventilator (battery, grid driven) is forcing the air through the stove
+
*A ventilator (battery, grid driven) can force the air through the stove
  
 
|-
 
|-
 
| Increase the surface of the wood that is in contact with air
 
| Increase the surface of the wood that is in contact with air
 
|  
 
|  
*Small door is only allowing smaller pieces of wood to be entered into the stove;
+
*Small door allows only smaller pieces of wood to be entered into the stove;
*Resting the wood on a shelf (wood and air entering the stove through the same entrance, the firewood above the air);
+
*Rest the wood on a shelf (wood and air enters the stove through the same entrance, the firewood above the air);
*Firewood and Air are entering the combustion chamber through different entrances; the tips of the firewood are hanging free in the chamber with the air being supplied from below.
+
*Firewood and air enter the combustion chamber through different entrances; the tips of the firewood hang free in the chamber with the air being supplied from below.
  
 
|}
 
|}
  
<br/>'''How can''''''we improve the design of the stove to improve the heat transfer in a firewood stove?'''
+
<br/>'''How can we improve the design of the stove to improve the heat transfer in a firewood stove?'''
  
{| border="1" cellpadding="1" cellspacing="1" width="100%"
+
{| style="width: 100%" cellspacing="1" cellpadding="1" border="1"
 
|-
 
|-
! scope="col" | Principles
+
! style="text-align: left;  background-color: rgb(204, 204, 204)" scope="col" | Aspect<br/>
! scope="col" | Solutions
+
! style="text-align: left;  background-color: rgb(204, 204, 204)" scope="col" | How to Achieve
 
|-
 
|-
 
| Raise the pot to the highest point of the flames
 
| Raise the pot to the highest point of the flames
Line 223: Line 220:
 
|-
 
|-
 
| Force the hot air to create turbulences on the surface of the cooking pot
 
| Force the hot air to create turbulences on the surface of the cooking pot
| Create a small gap between the cooking pot and the pot rest which is big enough not to choke the fire and small enough to mix the air close to the pot.
 
|-
 
| Increase the surface area for the heat transfer
 
| Create a skirt around the pot which is forcing the hot air to the walls of the pot. It creates turbulences in the air around the pot surface.
 
|}
 
 
&nbsp;&nbsp;
 
 
= Application of the principles<br/> =
 
 
== Clay stove (versus a 3-stone fire)<br/> ==
 
 
{| border="1" cellpadding="1" cellspacing="1" width="100%"
 
|-
 
| rowspan="2" | <span style="color: rgb(255, 0, 0)">[[File:Bernier Malawi Clay-stove.jpg|300px|Bernier Malawi Clay-stove.jpg]]</span><br/>
 
 
|  
 
|  
Increased combustion efficiency:
+
*Create a small gap between the cooking pot and the pot rest which is big enough not to choke the fire and small enough to mix the air close to the pot.
 
 
*Fire is shielded against the wind;
 
*Door is reducing the amount and size of wood used;
 
*More space to burn off the volatiles;
 
*Less intake of cold air;
 
  
 
|-
 
|-
 +
| Increase the surface area for the heat transfer
 
|  
 
|  
Improved heat transfer:
+
*Create a skirt around the pot which forces the hot air to the walls of the pot. This creates turbulences in the air around the pot surface.
 
+
*Insert the pot into the stove body.
*Pot sits higher above the flame;
 
*Most flue gasses have to pass the small gap between the potrest and the pot;
 
  
|}
 
 
 
 
There are quite a number of improved firewood stoves which – like this simple clay stove – adhere to some of these principles and deliver some improvement compared to the 3-stone fire. They are an entry point for households into the use of improved cook stoves as they are more affordable as compared to the sophisticated rocket stoves. Examples are:
 
 
*[[File:GTZ Malawi-Stove Fact Sheet Portable Clay 2008.pdf|Chitetezo Mbaula (Malawi)]], Chitetezo Mbaula (Malawi)
 
*Jiko Kisasa (Kenya),
 
*Tulipe (Benin)
 
*Anagi stove (Sri Lanka)
 
*VITA (Mauretanien)
 
 
 
 
{| border="1" cellpadding="1" cellspacing="1" width="100%"
 
|-
 
| &nbsp;[[File:Roth Malawi Institutional Rocket Stove 170-14 Comparison.jpg|600px|Roth Malawi Institutional Rocket Stove 170-14 Comparison.jpg]]
 
| Institutional Stove Compared to an open Fire: 40 instead of 170 kg of firewood
 
|}
 
 
<br/>The considerable savings have made institutional rocket stoves very popular among school feeding programmes in Malawi (see also Ashden Award video 2006, [http://www.ashdenawards.org/winners/aprovecho http://www.ashdenawards.org/winners/aprovecho http://www.ashdenawards.org/winners/aprovecho ttp://www.ashdenawards.org/winners/aprovecho])
 
 
 
 
{| border="1" cellpadding="1" cellspacing="1" width="100%"
 
 
|-
 
|-
 +
| Make sure that the heat is going into the pot instead of going into the stove body
 
|  
 
|  
[[File:GIZ Roth Malawi-probec-school feeding.jpg|RTENOTITLE]]
+
*Insulate the fire with lightweight, heat resistant materials.
  
 
 
| School feeding programme Mary`s Meals Blantyre, Malawi<br/>
 
 
|}
 
|}
  
 +
= <br/>The Rocket Stove Principle<br/> =
  
 +
One of the most successful concepts in stove design is the rocket stove principle, invented by Dr. Larry Winiarsky. Rocket stoves’ characteristics are:<ref name="http://www.ashden.org/files/Aprovecho2006.pdf">http://www.ashden.org/files/Aprovecho2006.pdf</ref>
  
== Fixed stoves from mud, brick or cement<br/> ==
+
*An elbow-shaped combustion chamber (1:1.5) with a shelf for the fuel wood, which supports the pre-drying of the firewood and allows a controlled, and sufficient, flow of primary air to be warmed as it passes under the wood to the burning wood tips.
 
+
*The tall combustion chamber behaves a bit like a chimney, creating more draught than a standard stove. This assists in mixing the air, fuel particles and volatiles, resulting in a hot flame.
Today most of the GIZ-promoted high-efficiency wood stoves follow this rocket stove principle (see fact sheets for the examples):
+
*The internal walls are insulated, reflecting all the heat back into the chamber rather than losing it to the stove body. The insulation keeps everything very hot so that the chemical reaction is more intense, whilst the tall chamber provides more time in which the gases and particles can be burnt completely, emitting all their heat and discharging mainly carbon dioxide and water vapor.
 
+
*These hot flue gases pass through a well-defined gap between a ‘skirt’, and the pot, resulting in a large percentage of the heat being forced against the sides of the pot, and being transferred to the pot. Where various sizes of pot are used on the same stove, the skirt can be funnel-shaped to accommodate different pots, although some efficiency will be lost.
=== One pot, mostly without chimney<br/> ===
 
 
 
{| style="width: 100%" border="1" cellpadding="1" cellspacing="1"
 
|-
 
|
 
'''One-Pot Shielded Fire Stove with air bypass''', Uganda (2011):
 
 
 
[[File:GIZ HERA 2011 Shielded-fire-stove-with-bypass-air-inlet Uganda.pdf|thumb|left|Add caption here]]
 
 
 
|-
 
|
 
'''Fixed One-Pot Rocket Mud Stove''', Benin, Uganda (2011)
 
 
 
[[File:GIZ HERA 2011 Rocket Fixe Benin-Uganda-Kenya.pdf|thumb|left|Add caption here]]
 
 
 
|-
 
|
 
'''Jiko Kisasa, '''Kenya (2011)
 
 
 
[[File:GIZ HERA 2011 Jiko kisasa Kenya.pdf|thumb|left|Jiko kisasa]]
 
 
 
|-
 
| Esperanza stove, Malawi<br/>
 
|-
 
|
 
'''Inkawasi Stoves''' in Peru (various models adapated for different regions and materials):
 
 
 
*Inkawasi UK for firewood and dung
 
*Inkawasi Tawa
 
*Inkawasi 3 hornillas
 
*Inkawasi Pichqa
 
*Inkawasi Sujta
 
*Inkawasi Plancha de Fierro
 
 
 
[[File:GIZ HERA 2011 Inkawasi-UK Peru.pdf|thumb|none|Add caption here]]&nbsp; [[File:GIZ HERA 2011 Inkawasi-Tres-Hornillas Peru.pdf|thumb|none|Add caption here]] [[File:GIZ HERA 2011 Inkawasi-TAWA Peru.pdf|thumb|none|Add caption here]]
 
 
 
 
 
  
 +
{| style="width:100%"
 
|-
 
|-
| MIRT stove for injeera baking Tikikil, Ehtiopia<br/>
+
| [[File:Rocket stove.JPG|thumb|left|200px|The rocket stove principle.|alt=Rocket stove.JPG]]<br/>
|-
+
| [[File:Pic2.JPG|thumb|left|300px|A rocket-type stove in action, and showing insulation of the burning chamber, skirt around pot and support frame|alt=Pic2.JPG]]<br/>
| rowspan="1" |
 
'''Rocket Brick Stove,''' Kenya (2011)
 
 
 
[[File:GIZ HERA 2011 Brick Rocket Stove Kenya.pdf|thumb|left|Brick Rocket Stove Kenya]]
 
 
 
GIZ PSDA Stoves Promotion<br/>Rocket Brick Stove: Builder’s Manual & User’s Guide
 
 
 
[[File:En-GIZ Kenya brick-rocket-stove-builder's-manual-2011.pdf|thumb|left|Add caption here]]
 
 
 
 
|}
 
|}
  
=== Multiple pots with chimney<br/> ===
+
<br/>Today, most of the GIZ-promoted wood stoves follow this rocket stove principle (see fact sheets below for examples). Besides household stoves also stoves for institutional or productive purposes can incorporate the rocket stove principle. For example in Malawi, the considerable savings have made institutional rocket stoves very popular among school feeding programs (see also [http://www.ashden.org/media/films/192/watch Ashden Award video 2006]).
  
{| style="width: 100%" border="1" cellpadding="1" cellspacing="1"
+
{|
 
|-
 
|-
|  
+
| [[File:Roth Malawi Institutional Rocket Stove 170-14 Comparison.jpg|thumb|left|350px|Institutional Stove Compared to an open Fire: 40 instead of 170 kg of firewood]]
'''Two pot mud-rocket Lorena with Air Bypass''', Uganda (2011)
+
| [[File:GIZ Roth Malawi-probec-school feeding.jpg|thumb|left|350px|School feeding program Mary`s Meals Blantyre, Malawi]]
 
 
[[File:GIZ HERA 2011 Rocket-Lorena-with-air-bypass Uganda.pdf|thumb|left|Add caption here]]
 
 
 
and construction guide from 2008 featuring air-bypass: [http://www.energyandminerals.go.ug/pdf/gtz/HOUSEHOLD%20Stoves%20Construction%20Manual%20August%202008.pdf http://www.energyandminerals.go.ug/pdf/gtz/HOUSEHOLD%20Stoves%20Construction%20Manual%20August%202008.pdf]), available in English and French
 
 
 
|-
 
|
 
'''Jiko Kisasa, '''Kenya, double pots (2011)
 
 
 
[[File:GIZ HERA 2011 Jiko kisasa Kenya.pdf|thumb|left|Jiko Kisasa]]
 
 
 
|-
 
|
 
'''Institutional Metal Rocket Stove''', Malawi (2008)
 
 
 
[[File:Final-inst metal rocket stove malawi-2008.pdf|RTENOTITLE]]
 
 
 
|-
 
|  
 
'''Malawi Institutional Brick Rocket Stove''', Malawi (2008)
 
 
 
[[File:Final inst brick rocket stove malawi 2008.pdf|Final-inst metal rocket stove malawi-2008.pdf]]
 
 
 
 
|}
 
|}
  
== Portable / movable rocket stoves<br/> ==
+
<br/>
 
 
{| border="1" cellpadding="1" cellspacing="1" width="100%"
 
|-
 
! scope="col" | '''One pot, mostly without chimney'''<br/>
 
|-
 
| '''Institutional Metal Rocket Stove''', Malawi (2008)<br/>
 
|-
 
|
 
Models developed by Stovetec: [http://www.stovetec.net/us/stove-models http://www.stovetec.net/us/stove-models]
 
 
 
Models developed by Envirofit: [http://www.envirofit.org/ http://www.envirofit.org/]
 
 
 
|-
 
|
 
'''Burkina Mixte''', Burkina Faso (2011)
 
 
 
[[File:GIZ HERA 2011 Burkina Mixte Burkina Faso.pdf|frame|left|Add caption here]]
 
 
 
|-
 
|
 
'''Jambar Stove, Firewood''', Benin, Kenya, Senegal (2011)
 
 
 
[[File:GIZ HERA 2011 Jambar Bois Senegal.pdf|frame|left|Add caption here]]
 
 
 
|-
 
|
 
'''Jambar Stove, Charcoal,''' Benin, Kenya, Senegal (2011)
 
 
 
[[File:GIZ HERA 2011 Jambar Charbon Senegal.pdf|frame|left|Add caption here]]
 
 
 
|-
 
|
 
'''Multimarmite Stove''', Burkina Faso (2011)
 
 
 
[[File:GIZ HERA 2011 Multimarmite Burkina Faso.pdf|frame|left|Add caption here]]
 
  
|-
+
<br/>
|
 
'''Ouaga Métallique''', Burkina Faso (2011)
 
  
[[File:GIZ HERA 2011 Ouaga M tallique Burkina Faso.pdf|frame|left|Add caption here]]
+
= Wood Fuel Stoves with Forced Convection<br/> =
  
|-
+
Instead of naturally ‘pulling’ air through a stove by stack height, fans or blowers are useful to ‘push’ air into the combustion chamber. This enhances a good air-fuel mix and thus, more complete combustion. Electricity is the most convenient power source to create a forced air-flow. It can be provided by batteries or, if available, through the grid. Forced convection can reduce emissions of stoves by up to 90&nbsp;%, thus alleviating Indoor Air Pollution (IAP) levels. See also the article on[[Gasifier Stoves|Micro-Gasifier Cookstoves]]. Recently, thermo-electric generators (TEG) have been developed to power fans in stoves. They use the temperature differences within the stove to generate electricity, thus eliminating the need for external power supply. TEGs also have great potential to provide power to other applications, such as LEDs or mobile phones. However, the unit makes a stove more expensive and can be destroyed easily, when getting too hot. Pico PV units could also easily provide that little electricity needed for mobile charging without burning firewood.<br/><br/><br/>
|
 
'''Sakkanal''', Senegal (2011)
 
  
[[File:GIZ HERA 2011 Sakkanal Senegal.pdf|frame|left|Add caption here]]
+
= Stove Factsheets and Manuals =
  
|-
+
The stove factsheets are a series of technical information sheets on different stoves promoted by GIZ. Wherever available, additional information such as construction manuals and user guidelines for the respective stoves is also provided.
|
 
'''Tulipe-Céramique''', Benin Burkina Faso (2011)
 
  
[[File:GIZ HERA 2011 Tulipe-C ramique Benin-Burkina Faso.pdf|frame|left|Add caption here]]
+
<br/>
  
|-
+
== Fixed Stoves<br/> ==
|
 
'''Nansu Unfired Clay Stove''', Benin (2011)
 
  
[[File:GIZ HERA 2011 Nansu C ramique Non Cuit Benin.pdf|frame|left|Add caption here]]
+
*[[:File:GIZ HERA 2012 Mirt stove.pdf|MIRT stove]] for injeera baking, Ethiopia; [[:File:Giz Trainning Manual Mirt stove 081211.pdf|Training Manual Mirt Stove]] in Amharic[LF2]&nbsp; (2011) and User Guideline [[:File:GIZ Mirt-User Manual-Page1.jpg|page 1]] and[[:File:GIZ Mirt-User Manual - Page 2.jpg|page 2in]] Amharic.
 +
*[[:File:GIZ HERA 2011 Jiko kisasa Kenya.pdf|Jiko Kisasa]], Kenya (2011)
 +
*[[:File:GIZ HERA 2011 Brick Rocket Stove Kenya.pdf|Brick Rocket Stove]], Kenya (2011); and [[:File:En-GIZ Kenya brick-rocket-stove-builder's-manual-2011.pdf|Rocket Brick Stove: Builder’s Manual & User’s Guide]]
 +
*[[:File:GIZ HERA 2011 Rocket-Lorena-with-air-bypass Uganda.pdf|Two pot mud-rocket Lorena with Air Bypass]], Uganda (2011); and [[:File:GTZ-HOUSEHOLD Stoves Construction Manual June 2008.pdf|Construction manual for household stoves]]. Guide from 2008 featuring air-bypass. --> Available also in French
 +
*[[:File:GIZ HERA 2012 Rocket Lorena with firewood shelf Uganda.pdf|Two pot mud-rocket Lorena with shelf]], Uganda (2012)
 +
*[[:File:GIZ HERA 2011 Rocket Fixe Benin-Uganda-Kenya.pdf|Fixed One-Pot Rocket Mud Stove]], Benin, Uganda (2011)
 +
*Esperanza stove, Malawi
 +
*[[:File:Final inst brick rocket stove malawi 2008.pdf|Malawi Institutional Brick Rocket Stove]], Malawi (2008)
 +
*Inkawasi Stoves in Peru (various models adapted for different regions and materials) (2011):
 +
**[[:File:GIZ HERA 2011 Inkawasi-UK Peru.pdf|Inkawasi UK for firewood and dung]][[:File:GIZ HERA 2011 Inkawasi-TAWA Peru.pdf|Inkawasi Tawa]]
 +
**[[:File:GIZ HERA 2011 Inkawasi-Tres-Hornillas Peru.pdf|Inkawasi Tres Hornillas]]
 +
**Inkawasi Pichqa
 +
**Inkawasi Sujta
 +
**Inkawasi Plancha de Fierro
  
|}
+
*[[:File:GIZ Honduras Manual UsoMantenimiento EcoEstufaJusta.pdf|Manual Uso y Mantenimiento de la Eco-Estufa Justa]], Honduras (2011)
 +
*[[:File:GIZ Honduras ManualConstrucción EcoEstufasJusta.pdf|Manual Construyendo la Eco-Estufa Justa 16 x 24]], Honduras (2011)
  
&nbsp;
+
<br/>
  
{| border="1" cellpadding="1" cellspacing="1" width="100%"
+
== Portable Stoves<br/> ==
|-
 
! scope="col" | '''Multiple pots with chimney'''<br/>
 
|-
 
! style="text-align: left" scope="col" |
 
Inkawasi portatil, Peru (2011)
 
  
|}
+
*[[:File:GIZ HERA 2012 Shielded fire stove with firewood shelf Uganda.pdf|One-Pot Shielded Fire Stove with shelf]], Uganda (2012)
 +
*[[:File:GIZ HERA 2011 Shielded-fire-stove-with-bypass-air-inlet Uganda.pdf|One-Pot Shielded Fire Stove with bypass air inlet]], Uganda (2011)
 +
*[[:File:GIZ HERA 2012 Tikikil Stove ET.pdf|Tikikil]], Ethiopia 2012; [[:File:GIZ Manual for Production of Tikikil Final Englisch.pdf|Production Manual]] (English); [[:File:GIZ Manual for Production of Tikiki Amharic.pdf|Production Manual]] (Amharic), [[:File:GIZ Tikikil stove user guide en.pdf|User guideline]] (English), [[:File:GIZ Tikikil stove user guide- Amharic.pdf|User guideline]] (Amharic)
 +
*[[:File:GIZ HERA 2012 IRS ET.pdf|Institutional Rocket Stove (IRS)]] Ethiopia (2012), [[:File:Giz CIRS Manual eng.pdf|Production manual]], [[:File:IRS user guide english.pdf|User guideline]]
 +
*[[:File:GIZ HERA 2011 Jambar Bois Senegal.pdf|Jambar Stove Firewood]], Benin, Kenya, Senegal (2011)
 +
*[[:File:GIZ HERA 2011 Tulipe-C ramique Benin-Burkina Faso.pdf|Tulipe-Céramique]], Benin, Burkina Faso (2011)
 +
*[[:File:GIZ HERA 2011 Burkina Mixte Burkina Faso.pdf|Burkina Mixte]], Burkina Faso (2011). Stove for firewood and charcoal.
 +
*[[:File:GIZ HERA 2011 Ouaga M tallique Burkina Faso.pdf|Ouaga Métallique]], Burkina Faso (2011)
 +
*[[:File:GIZ HERA 2011 Multimarmite Burkina Faso.pdf|Multimarmite Stove]], Burkina Faso (2011). Stove for firewood and charcoal. &nbsp;
 +
*[[:File:GIZ HERA 2011 Sakkanal Senegal.pdf|Sakkanal]], Senegal (2011). Stove for firewood and charcoal. &nbsp;&nbsp;
 +
*[[:File:GTZ Malawi-Stove Fact Sheet Portable Clay 2008.pdf|Chitetezo Mbaula]], Malawi (2008)
 +
*[[:File:Final-inst metal rocket stove malawi-2008.pdf|Institutional Metal Rocket Stove]], Malawi (2008)
 +
*[[:File:GIZ HERA 2011 Inkawasi-Port til Peru.pdf|Inkawasi portatil]], Peru (2011)
  
Efficient, smoke-free cooking with the Rocket Stove:
+
<br/>
  
<span style="color: rgb(255, 0, 0)">&nbsp;</span>[[File:En-Poster Rocket Stove-2007.pdf|RTENOTITLE]]
+
= Further Information<br/> =
  
= Additional information resources<br/> =
+
*<span style="color:#FF0000">Classification of Cookstoves</span>
 +
*[[Cooking with Firewood|Cooking with Firewood]], article on energypedia
 +
*[[Energy-Saving Cooking Equipment|Energy-Saving Cooking Equipment]]<br/>
 +
*[[Portal:Improved Cooking|Improved Cooking Portal]] on energypedia
 +
*[http://aprovecho.org/ Aprovecho Research Center]<br/>For almost 30 years, Aprovecho Research Center (ARC) consultants have been designing and implementing improved biomass cooking and heating technologies in more than 60 countries worldwide. Their website provides a wealth of useful information including construction materials.
 +
**[http://www.ewb-usa.org/files/2015/05/PrinciplesWoodBurningCookStoves.pdf Design Principles for Wood Burning Cook Stoves], by Aprovecho Research Center (2005).
 +
**[http://www.aprovecho.org/lab/rad/rl/stove-design/doc/19/raw 10 Design Principles for Wood Burning Stoves (Poster)], by Aprovecho Research Center (2005).
  
==== Aprovecho Research Center<br/> ====
+
*[http://www.rocketstove.org/ Design Tool for Constructing an Institutional Rocket Stove with Chimney]<br/>With funding from GIZ HERA, Rocket Stove.org and Prakti Design Lab have developed a new automated tool that allows users to build a customized institutional rocket stove. The tool can be used to design a brick or metal institutional rocket stove with or without chimney for any institutional pot (30 L + capacity).<br/>Depending on the availability of construction materials, components and production options, three stove options are available for this tool:
 +
**a fixed brick stove (w/out chimney)
 +
**a portable metal stove with square combustion chamber (w/out chimney)
 +
**a portable metal stove with circular combustion chamber (with chimney)
  
For almost 30 years, Aprovecho Research Center (ARC) consultants have been designing and implementing improved biomass cooking and heating technologies in more than 60 countries worldwide. Their website provides a wealth of useful information including construction materials. [http://www.aprovecho.org www.aprovecho.org]
+
*[https://vuthisa.files.wordpress.com/2011/03/rocketstoveanimation.gif Rocket Stove Principle]<br/>An animation showing the rocket stove principle.
 +
*[[:File:En-Poster Rocket Stove-2007.pdf|Efficient, smoke-free cooking with the Rocket Stove]]. Poster (2007)
 +
*[http://catalog.cleancookstoves.org/ Online Catalogue of Clean Cookstoves.] Compiled by the global Alliance for Clean Cookstove and its partners.
 +
*Stove Models Developed by other organizations and companies
 +
**[http://www.stovetec.net/us/stove-models Stovetec]
 +
**[http://www.envirofit.org/ Envirofit]
 +
**[http://www.biolitestove.com/Technology.html BioLite]
 +
**[http://www.burnstoves.com Burn]
 +
**[http://www.rocketworks.org/ Rocket Works]
  
==== Design Tool for Constructing an Institutional Rocket Stove with Chimney<br/> ====
+
*Stove Images - a Documentation of Improved and Traditional Stoves in Africa, Asia and Latin America. By Beatrix Westhoff and Dorsi German (1995). It is available in [[:File:Stove Images.pdf|English]], [[:File:Foyers en Images.pdf|French]] and [[:File:Estufas en Imágenes.pdf|Spanish]]. The publication provides a very comprehensive overview on global stove diversity.
 +
*UNESCO (1982): [http://unesdoc.unesco.org/images/0005/000530/053052eb.pdf Consolidation of Information. Cooking Stoves Handbook]
 +
*[http://www.bbc.co.uk/programmes/p038cs37?ocid=socialflow_facebook Changing Climate Change: Solutions]. BBC Documentary on portable ceramic cookstoves in Malawi used with a TEG.
  
With funding from GIZ HERA, Rocket Stove.org and Prakti Design Lab have developed a new automated tool that allows users to build a customized institutional rocket stove. The tool can be used to instantly design a brick or metal institutional rocket stove with or without chimney for any institutional pot (30 L + capacity).
+
&nbsp;<br/>
  
The stove options are:
+
<br/>
  
*fixed brick stove (w/out chimney)
+
= References<br/> =
*portable metal stove with square combustion chamber (w/out chimney)
 
*portable metal stove with circular combustion chamber (with chimney)
 
  
[http://www.rocketstove.org/ http://www.rocketstove.org/]
+
This article was originally published by [http://www.giz.de/fachexpertise/html/2769.html GIZ HERA]. It is basically based on experiences, lessons learned and information gathered by GIZ cook stove projects. You can find more information about the authors and experts of the original “Cooking Energy Compendium” in the [[Imprint - GIZ HERA Cooking Energy Compendium|Imprint]].
  
==== Rocket stove principle<br/> ====
+
<references />
  
An animation showing the rocket stove principle can be found here: [http://vuthisa.files.wordpress.com/2011/03/rocketstoveanimation.gif http://vuthisa.files.wordpress.com/2011/03/rocketstoveanimation.gif]
+
<br/>
  
==== New wood fuel stove designs<br/> ====
+
[[#Introduction|Top of the page]]
  
Two major factors determine if woodfuels burn clean and efficient: its dryness and sufficient ventilation, hence, the right amount of air on the right spot during the process to ensure a complete combustion.
+
<br/>
  
While it depends on the user to make sure that the fuel is dry, the air-flow depends on the stove design. In a natural draught stove, the movement of air is created by the chimney or stack height of the fuel. However, there must be a difference in temperature between the stove and the top of the chimney for generating draught. Natural draught is likely to cause incomplete combustion with higher emissions and energy losses through the chimney. Moreover, it is also difficult to regulate.
+
[[GIZ HERA Cooking Energy Compendium|--> Back to Overview GIZ HERA Cooking Energy Compendium]]
 
 
==== Wood fuel stoves with forced convection<br/> ====
 
 
 
Instead of naturally ‘pulling’ air through a stove by stack height, fans or blowers are useful to ‘push’ air into the combustion chamber. This enhances a good air-fuel mix and thus, more complete combustion. Electricity is the most convenient power source to create a forced air-flow. It can be provided by batteries or, if available, through the grid. Recently thermo-electric generators (TEG) are being developed to power fans in stoves. They use the temperature differences within the stove to generate electricity. Though TEGs have great potential to provide also power to other applications (LEDs, cell phone charging), they are still in their infancy. Forced convection can reduce emissions of stoves by up to 90&nbsp;% and thus alleviating IAP levels. More test results from more widespread use are expected soon.
 
 
 
= Additional information: BioLite<br/> =
 
  
BioLite: [http://www.biolitestove.com/Technology.html http://www.biolitestove.com/Technology.html]
+
<br/>
  
 +
{{#set: Hera category=Cooking Energy System}}
  
 
+
[[Category:Cooking_Energy]]
[[Cooking with firewood#Firewood|Top of the page]]
+
[[Category:Wood_Energy]]
 
+
[[Category:Cookstoves]]
[[GIZ HERA Cooking Energy Compendium|--> Back to Overview GIZ HERA Cooking Energy Compendium]]
+
[[Category:Improved_Cooking]]
 
+
[[Category:Rocket_Stove]]
[[Category:Cooking]]
+
[[Category:Cooking_Energy_Compendium_(GIZ_HERA)]]
[[Category:Cooking_Energy_Compendium]]
 
[[Category:GIZ_HERA]]
 

Latest revision as of 12:59, 30 April 2018

GIZ HERA Cooking Energy Compendium small.png



Cooking Energy System | Basics | Policy Advice | Planning | Designing and Implementing ICS Supply | Designing and Implementing Woodfuel Supply | Climate Change | Extra


Introduction

Firewood is wood from logs, sticks or twigs. It has been used as a fuel since the beginning of mankind. In principle, it is renewable and relatively easy to produce, transport and store. However, the use of firewood for cooking is commonly associated with deforestation and health problems. This is not an inherent problem of the fuel, but is strongly influenced by the quality and quantity of its correct usage and can be overcome by improving the efficiency of the wood fuel usage.

Two major factors determine if firewood burns clean and efficient: its moisture content and the oxygen supply of the fire. While it depends on the user to make sure that the fuel is dry, the air-flow depends on the stove design. In a natural draught stove, the supply of air is created by the chimney or stack height of the fuel. However, there must be a difference in temperature between the stove and the top of the chimney to generate draught. Natural draught is likely to cause incomplete combustion with higher emissions and energy losses through the chimney. Moreover, it is also difficult to regulate.


The burning of wood is a sequence of steps:

  1. Moisture is evaporated
  2. Wood decomposes into combustible wood-gas and char
  3. Char is converted into ash


The main influencing agent for “a)” and “b)” is heat, whereas “c)” is regulated by the supply of oxygen.

Find here more information and illustrating figures on pages 14-15 in the "Manual on Micro-gasification". For more information on the characteristics of firewood as a fuel see Cooking with Firewood.


The Wood-Fuel Cooking System

GIZ woodfuel cooking system 2011.jpg

As shown in the figure beside, in the wood-fuel cooking system, firewood is mixed with air in a reactor. After ignition, a chain reaction is triggered in which heat is generated. This heat is transferred through 3 processes:

Convection: Hot gasses are passing a surface transferring heat into surrounding materials;
Radiation: Red hot embers is radiating heat into surrounding materials;
Conduction: Heat is conducted through materials. Metal is a good heat conductor, whereas air is a poor heat conductor.

The reactor is emitting heat, but also light, gasses and particles. While the emission of heat is wanted, the emission of gasses, particles and light are rather unintended. Good stove designs can reduce the quantity of unwanted emissions in favor of additional heat generation. The heat does not enter automatically into a cooking pot. The design of the heat transfer unit has a big effect on the percentage of the heat transferred into the food to be cooked.


Overall there are two major dimensions for efficiency gains for firewood stoves:

  1. Achieve complete combustion (=‘create more heat per unit of fuel used’)
  2. Improve heat transfer (=‘get more heat actually into the pot’)



Three-stone Fires or Open Fires

3-stone fire in Malawi

Worldwide, millions of people cook on so-called 3-stone fires or open fires as this is the simplest and cheapest “stove” to create. Only three suitable stones of the same height are needed to balance a pot over a fire. However, the daily use of these 3-stone fires has the following disadvantages:  

High fuel consumption:
The open fire consumes a lot of fuel as

  • (a) not much heat is generated per unit of fuel,
  • (b) only a small proportion of the heat is actually directed to the pot and
  • (c) only a small fraction of the heat that is directed to the pot is actually transferred into the food.
  • Slow pace of cooking:
    The cooking pot does not sit in the hottest part of the flames; hence less heat is transferred to the pot than theoretically possible. Even if a lot of heat is generated, the heat is not directed to the cooking pot and heat is lost to the environment. This problem is accelerated if there are windy conditions as the flames are not shielded.
  • Smoke:
    The combustion in an open fire tends to be incomplete as oxygen might not reach where it is needed. Low temperatures also contribute to the emission of smoke (= unburned particles).
  • Health risks:
    As the flames are not directed or shielded, the cook can easily catch fire when approaching the cooking pot. Sparks pose an additional risk when approaching the fire. Burns are a common effect of open fires. The smoke might also cause eye infections.


On the other hand, users welcome some of these inefficiencies due to their positive side effects:

  • Open fires burn slow and do not require frequent attention. This is convenient if other household chores have to be done at the same time.
  • Smoke can chase away mosquitoes, which is especially beneficial in malaria-infested areas;
  • Smoke can be used to preserve food;
  • Open flames emit light, which is welcome before sunrise or after sunset;
  • Open fires emit heat, which is favorable in cold areas.



Three-stone Fire versus Improved Cookstove

The development of improved cookstoves is facing a dilemma: the same characteristics are at the same time responsible for both users’ complaints and appreciations of the 3-stone fire. There is no solution which can satisfy all expectations. Any new stove will be a trade-off between different user needs. This dilemma is summarized in the table below. Furthermore, users are used to a specific cooking system and any change in cooking habits needs time.


Common changes of parameters in improved cook stoves Common expectations towards improved stoves "Disadvantages” for associated benefits of open fires

Improve efficiency of heat production

  • More complete combustion = less emission of unburned fuel
  • Shelter the fire against the wind;
  • Direct flames to the pot
  • Consume less fuel
  • Emit less smoke
  • Be safer
  • Cook faster
  • Faster and more efficient stoves require often more attention by the cook
  • No mosquito repellent, no food preservation
  • Less space heating
  • No lighting after dark
  • Improve heat transfer into the cooking pot
  • Position of the cooking pot at the hottest place of the flame;
  • Hot gasses are passing close to the pot to maximize heat transfer;
  • Consume less fuel
  • Cook faster
  • Be safer
  • Stove is sometimes higher than the open fire
  • Some stoves don’t fit all pot sizes



Households have to prioritize their needs in order to come up with the decision if an improved cook stove is suitable for them. In areas with fuel scarcity, the need for reduced fuel consumption might be ranked higher than the need for space heating or lighting after dark.

A strategy can be to provide additional solutions to complement the introduction of the improved cook stoves:

  • an extra space heater for the cold season
  • a mosquito-repellent net
  • a solar lantern for lighting


Design Principles for Improved Cookstoves

All improved firewood stoves apply at least some of the aspects listed below geared toward increasing efficiency and improving heat transfer.[1]


How can we improve the design of the stove to increase the combustion efficiency in a firewood stove?

Aspect
How to achieve
Increasing the temperature in the combustion chamber (as the burning process is temperature controlled)
  • Shelter the fire against wind;
  • Use isolative materials to reduce heat losses to the side and to the bottom;
Reduce the intake of firewood
  • Create a small entrance for the firewood. Then only the required level of wood can be entered. Excess wood cannot be supplied to the reactor
Burn off all the volatiles
  • Allow enough space in the combustion chamber (increasing the space between pot and fire) since the hottest point of a fire is a bit above the end of the flame and for the volatiles to burn off high temperatures and enough air supply is needed. 
Adequate air supply
  • Regulate air and wood intake into the combustion chamber and ensure both the amount of air and wood intake are correlated.
Reduce the inflow of cold air
  • Regulate air intake (door)
Intake of pre-heated air
  • Use air as an insulation between an inner and an outer wall of the stove. Via a secondary air inlet, air is channeled through this gap and pre-heated before entering the combustion chamber.
  • Rest the wood on a shelf. The air passing under the shelf is preheated.
Increasing the draft
  • A vertical combustion chamber can increase the natural draft in the stove;
  • A ventilator (battery, grid driven) can force the air through the stove
Increase the surface of the wood that is in contact with air
  • Small door allows only smaller pieces of wood to be entered into the stove;
  • Rest the wood on a shelf (wood and air enters the stove through the same entrance, the firewood above the air);
  • Firewood and air enter the combustion chamber through different entrances; the tips of the firewood hang free in the chamber with the air being supplied from below.


How can we improve the design of the stove to improve the heat transfer in a firewood stove?

Aspect
How to Achieve
Raise the pot to the highest point of the flames
  • Create a pot rest at the hottest point above the flames ;
  • Direct the hot flue gasses directly against the cooking pot (= pot sits ‘on top of a chimney’)
Force the hot air to create turbulences on the surface of the cooking pot
  • Create a small gap between the cooking pot and the pot rest which is big enough not to choke the fire and small enough to mix the air close to the pot.
Increase the surface area for the heat transfer
  • Create a skirt around the pot which forces the hot air to the walls of the pot. This creates turbulences in the air around the pot surface.
  • Insert the pot into the stove body.
Make sure that the heat is going into the pot instead of going into the stove body
  • Insulate the fire with lightweight, heat resistant materials.


The Rocket Stove Principle

One of the most successful concepts in stove design is the rocket stove principle, invented by Dr. Larry Winiarsky. Rocket stoves’ characteristics are:[2]

  • An elbow-shaped combustion chamber (1:1.5) with a shelf for the fuel wood, which supports the pre-drying of the firewood and allows a controlled, and sufficient, flow of primary air to be warmed as it passes under the wood to the burning wood tips.
  • The tall combustion chamber behaves a bit like a chimney, creating more draught than a standard stove. This assists in mixing the air, fuel particles and volatiles, resulting in a hot flame.
  • The internal walls are insulated, reflecting all the heat back into the chamber rather than losing it to the stove body. The insulation keeps everything very hot so that the chemical reaction is more intense, whilst the tall chamber provides more time in which the gases and particles can be burnt completely, emitting all their heat and discharging mainly carbon dioxide and water vapor.
  • These hot flue gases pass through a well-defined gap between a ‘skirt’, and the pot, resulting in a large percentage of the heat being forced against the sides of the pot, and being transferred to the pot. Where various sizes of pot are used on the same stove, the skirt can be funnel-shaped to accommodate different pots, although some efficiency will be lost.
Rocket stove.JPG
The rocket stove principle.

Pic2.JPG
A rocket-type stove in action, and showing insulation of the burning chamber, skirt around pot and support frame


Today, most of the GIZ-promoted wood stoves follow this rocket stove principle (see fact sheets below for examples). Besides household stoves also stoves for institutional or productive purposes can incorporate the rocket stove principle. For example in Malawi, the considerable savings have made institutional rocket stoves very popular among school feeding programs (see also Ashden Award video 2006).

Institutional Stove Compared to an open Fire: 40 instead of 170 kg of firewood
School feeding program Mary`s Meals Blantyre, Malawi



Wood Fuel Stoves with Forced Convection

Instead of naturally ‘pulling’ air through a stove by stack height, fans or blowers are useful to ‘push’ air into the combustion chamber. This enhances a good air-fuel mix and thus, more complete combustion. Electricity is the most convenient power source to create a forced air-flow. It can be provided by batteries or, if available, through the grid. Forced convection can reduce emissions of stoves by up to 90 %, thus alleviating Indoor Air Pollution (IAP) levels. See also the article onMicro-Gasifier Cookstoves. Recently, thermo-electric generators (TEG) have been developed to power fans in stoves. They use the temperature differences within the stove to generate electricity, thus eliminating the need for external power supply. TEGs also have great potential to provide power to other applications, such as LEDs or mobile phones. However, the unit makes a stove more expensive and can be destroyed easily, when getting too hot. Pico PV units could also easily provide that little electricity needed for mobile charging without burning firewood.


Stove Factsheets and Manuals

The stove factsheets are a series of technical information sheets on different stoves promoted by GIZ. Wherever available, additional information such as construction manuals and user guidelines for the respective stoves is also provided.


Fixed Stoves


Portable Stoves


Further Information

  • Design Tool for Constructing an Institutional Rocket Stove with Chimney
    With funding from GIZ HERA, Rocket Stove.org and Prakti Design Lab have developed a new automated tool that allows users to build a customized institutional rocket stove. The tool can be used to design a brick or metal institutional rocket stove with or without chimney for any institutional pot (30 L + capacity).
    Depending on the availability of construction materials, components and production options, three stove options are available for this tool:
    • a fixed brick stove (w/out chimney)
    • a portable metal stove with square combustion chamber (w/out chimney)
    • a portable metal stove with circular combustion chamber (with chimney)

 


References

This article was originally published by GIZ HERA. It is basically based on experiences, lessons learned and information gathered by GIZ cook stove projects. You can find more information about the authors and experts of the original “Cooking Energy Compendium” in the Imprint.

  1. Aprovecho Research Center (2005): Design Principles for Wood Burning Cook Stoves. http://www.ewb-usa.org/files/2015/05/PrinciplesWoodBurningCookStoves.pdf
  2. http://www.ashden.org/files/Aprovecho2006.pdf


Top of the page


--> Back to Overview GIZ HERA Cooking Energy Compendium