OPEN FIRE used for cooking in the millions of rural homes transfers heat to a pot poorly. As little as 10 percent of the heat goes to the cooking utensil; the rest is released to the environment.

Fuel-efficient cook stoves
The most immediate way to decrease the use of wood as cooking fuel is to introduce improved wood- and charcoal-burning cook stoves. Simple stove models already in use can halve the use of firewood. A concerted effort to develop more efficient models might reduce this figure to 1/3 or ¼, saving more forests than all of the replanting efforts planned for the rest of the century. Using simple hearths such as those used in India, Indonesia, Guatemala and elsewhere, one-third as much wood would provide the same service. These clay “cookers” are usually built on the spot with a closed hearth, holes in which to place the vessels to be heated, and a short chimney for the draught. Their energy yield varies, depending on the model, between approximately 15 and 25%. If these “cookers” were used throughout the Sahel, firewood consumption would be reduced by two-thirds: 0,2 m3 instead of 0,6 m3 per person per year. There are clear benefits of improved cook stoves to the individual family, the local community, the nation and the global community.  In brief, they include:
Less time spent gathering wood or less money spent on fuel, less smoke in the kitchen; lessening of respiratory problems associated with smoke inhalation, less manure used as fuel, releasing more fertilizer for agriculture,little initial cost compared to most other kinds of cookers,  improved hygiene with models that raise cooking off the floor,  safety: fewer burns from open flames; less chance of children falling into the fire or boiling pots; if pots are securely set into the stove, less chance of children pulling them down on themselves, cooking convenience: stoves (and be made to any height and can have work space on the surface,  the fire requires less attention, as stoves with damper control can be easier to tend.
Stove building may create new jobs, potential for using local materials and potential for local innovations, money and time saved can be invested elsewhere in the community.
Lowered rate of deforestation improves climate, wood supply and hydrology; decreases soil erosion, potential for reducing dependence on imported fuel.

COOKING WITH RETAINED HEAT
In regions where much of the daily cooking involves a long simmering period (required for many beans, grains, stews and soups) the amount of fuel needed to complete the cooking process can be greatly reduced by cooking with retained heat. This is a practice of ancient origin which is still used in some parts of the world today.
In some areas a pit is dug and lined with rocks previously heated in a fire. The food to be cooked is placed in the lined pit, often covered with leaves, and the whole is covered by a mound of earth. The heat from the rocks is retained by the earth insulation, and the food cooks slowly over time.
Another version of this method consists of digging a pit and lining it with hay or another good insulating material. A pot of food which has previously been heated up to a boil is placed in the pit, covered with more hay and then earth, and allowed to cook slowly with the retained heat.

THE HAYBOX COOKER
This latter method is the direct ancestor of the Haybox Cooker, which is simply a well insulated box lined with a reflective material into which a pot of food previously brought to a boil is placed. The food is cooked in 3 to 6 hours by the heat retained in the insulated box. The insulation greatly slows the loss of conductive heat, convective heat in the surrounding air is trapped inside the box, and the shiny lining reflects the radiant heat back into the pot.
Simple haybox style cookers could be introduced along with fuel-saving cook stoves in areas where slow cooking is practised. How these boxes should be made, and from what materials, is perhaps best left to people working in each region. Ideally, of course, they should be made of inexpensive, locally available materials and should fit standard pot sizes used in the area.

BUILDING INSTRUCTIONS
There are several principles which should be kept in mind in regard to the construction of a haybox cooker:
Insulation should cover an six sides of the box (especially the bottom and lid). If one or more sides are not insulated, heat will be lost by conduction through the uninsulated sides and much efficiency will be lost.
The box should be airtight. If it is not airtight, heat will be lost through warm air escaping by convection out of the box.
The inner surfaces of the box should be of a heat reflective material (such as aluminium foil) to reflect radiant heat from the pot back to it.

A simple, lightweight haybox can be made from a 60 by 120 cm sheet of rigid foil-faced insulation and aluminium tape. Haybox cookers can also be constructed as a box-in-a-box with the intervening space filled with any good insulating material. The required thickness of the insulation will vary with how efficient it is (see below).

Good Insulating Materials	Suggested Wall Thickness
Cork	5 cm
Polystyrene sheets/pellets/drinking cups	5 cm
Hay/straw/rushes	10 cm
Sawdust/wood shavings	10 cm
Wool/fur	10 cm
Fiberglas/glass wool	10 cm
Shredded newspaper/cardboard	10 cm
Rice hulls/nut shells	15 cm

The inner box should have a reflective interior: aluminium foil, shiny aluminium sheeting, old printing plates, other polished sheet metal’ or silver paint will all work. The box can be wooden, or a can-in-a-can, or cardboard, or any combination; a pair of cloth bags might also work. Be inventive. Always be sure the lid is air tight.

INSTRUCTIONS FOR USE
There are some adjustments involved in cooking with haybox cookers:
Less water should be used since it is not boiled away.
Less spicing is needed since the aroma is not boiled away.
Cooking must be started earlier to give the food enough time to cook at a lower temperature than over a stove.
Haybox cookers work best for large quantities (over 4 lifers) as small amounts of food have less thermal mass and cool faster than a larger quantity. Two or more smaller amounts of food may be placed in the box to cook simultaneously.
The food should boil for several minutes before being placed in the box. This ensures that all the food is at boiling temperature, not just the water.

The boxes perform best at low altitudes where boiling temperature is highest. They should not be expected to perform as well at high altitudes. One great advantage of haybox cookers is that the cook no longer has to keep up a fire or watch or stir the pot once it’s in the box. In fact, the box should not be opened during cooking as valuable heat is lost. And finally, food will never burn in a haybox.

SAND/CLAY STOVES: THE LORENA SYSTEM
The Lorena system involves building a solid sand/clay block, then carving out a firebox and flue tunnels. The block is an integral sand/clay mixture which, upon drying, has the strength of a weak concrete (without the cost). The mixture contains 2 to 5 parts of sand to 1 part of clay, though the proportions can differ widely.
Pure clay stoves crack badly because the clay shrinks as it dries and expands when it is heated. Sand/clay stoves are predominantly sand, with merely enough clay to glue the sand together. The mix should contain enough clay to bind the sand grains tightly together. The sand/clay mixture is strong in compression, but resists impact poorly. It is adequately strong in tension if thin walls are avoided. Unlike concrete, which works well as a thin shell, the sand/clay mixture relies upon mass for tensile strength.
Advantages:
Sand and clay are available in most places, and cheap.
The material is versatile; it can be used to build almost any size or shape of stove.
The tools required are simple.
Construction of the stoves requires simple skills.
Stoves are easy to repair or replace.

Disadvantages:
Construction relies on heavy materials that are not always available at the building site and are difficult to transport.
The stoves are not transportable.
Stove construction can require several days of hard work.
Efficiency of the stoves relies on the quality of the workmanship in their construction. Normally, they can be expected to work well for at least a year, after which they may need to be repaired.

KENYA STOVE
One of the most successful urban stove projects in the world is the Kenya Ceramic Jiko (KCJ) initiative. Over 500,000 stoves of this new improved design have been produced and disseminated in Kenya since the mid-1980s (Davidson and Karekezi, 1991). Known as the Kenya Ceramic Jiko, KCJ for short, the improved stove is made of ceramic and metal components and is produced and marketed through the local informal sector. One of the key characteristics of this project was its ability to utilize the existing cook stove production and distribution system to produce and market the KCJ. Thus, the improved stove is fabricated and distributed by the same people who manufacture and sell the traditional stove design.
Another important feature of the Kenya stove project is that the KCJ design is not a radical departure from the traditional stove. The KCJ is, in essence, an incremental development from the traditional all-metal stove. It uses materials that are locally available and can be produced locally. In addition, the KCJ is well adapted to the cooking patterns of a large majority of Kenya’s urban households. In many respects, the KCJ project provides an ideal case study of how an improved stove project should be initiated and implemented.
 

CERAMIC JIKO increases stove efficiency by addition of a ceramic insulating liner (the brown element), which enables 25 to 40 percent of the heat to be delivered to the pot. From 20 to 40 percent of the heat is absorbed by the stove walls or else escapes to the environment. In addition, 10 to 30 percent gets lost as flue gases, such as carbon dioxide.

The traditional metal stove that the ceramic Jiko replaces delivers only 10 to 20 percent of the heat generated to a pot, METAL STOVE , a traditional cooking implement, directs only 10 to 20 percent of the heat to a pot. From 50 to 70 percent of  the heat is lost through the stove's metal sides, and another 10 to 30 percent escapes as carbon monoxide, methane and other flue gases.

CHARCOAL PRODUCTION - PYROLYSIS
The production of charcoal spans a wide range of technologies from simple and rudimentary earth kilos to complex, large-capacity charcoal retorts. The various production techniques produce charcoal of varying quality. Improved charcoal production technologies are largely aimed at attaining increases in the net volume of charcoal produced as well as at enhancing the quality characteristics of charcoal.
Typical characteristics of good-quality charcoal:
Ash content : 5 per cent
Fixed carbon content : 75 per cent
Volatiles content : 20 per cent
Bulk density : 250-300 kg/m3
Physical characteristics : Moderately friable

Efforts to improve charcoal production are largely aimed at optimising the above characteristics at the lowest possible investment and labour cost while maintaining a high production volume and weight ratios with respect to the wood feedstock.
The production of charcoal consist of six major stages:
1. Preparation of wood
2. Drying - reduction of moisture content
3. Pre-carbonization - reduction of volatiles content
4. Carbonization - further reduction of volatiles content
5. End of carbonization - increasing the carbon content
6. Cooling and stabilization of charcoal

The first stage consists of collection and preparation of wood, the principal raw material. For small-scale and informal charcoal makers, charcoal production is an off-peak activity that is carried out intermittently to bring in extra cash. Consequently, for them, preparation of the wood for charcoal production consists of simply stacking odd branches and sticks either cleared from farms or collected from nearby woodlands. Little time is invested in the preparation of the wood. The stacking may, however, assist in drying the wood which reduces moisture content thus facilitating the carbonization process. More sophisticated charcoal production systems entail additional wood preparation, such as debarking the wood to reduce the ash content of the charcoal produced. It is estimated that wood which is not debarked produces charcoal with an ash content of almost 30 per cent. Debarking reduces the ash content to between 1 and 5 per cent which improves the combustion characteristics of the charcoal.
The second stage of charcoal production is carried out at temperatures ranging from 110 to 220 degrees Celsius. This stage consists mainly of reducing the water content by first removing the water stored in the wood pores then the water found in the cell walls of wood and finally chemically-bound water.
The third stage takes place at higher temperatures of about 170 to 300 degrees and is often called the pre-carbonization stage. In this stage pyroligneous liquids in the form of methanol and acetic acids are expelled and a small amount of carbon monoxide and carbon dioxide is emitted.
The fourth stage occurs at 200 to 300 degrees where a substantial proportion of the light tars and pyroligneous acids are produced. The end of this stage produces charcoal which is in essence the carbonized residue of wood.
The fifth stage takes place at temperatures between 300 degrees and a maximum of about 500 degrees. This stage drives off the remaining volatiles and increases the carbon content of the charcoal.
The sixth stage involves cooling of charcoal for at least 24 hours to enhance its stability and reduce the possibility of spontaneous combustion.
The final stage consists of removal of charcoal from the kiln, packing, transporting, bulk and retail sale to customers. The final stage is a vital component that affects the quality of the finally-delivered charcoal. Because of the fragility of charcoal, excessive handling and transporting over long distances can increase the amount of fines to about 40 per cent thus greatly reducing the value of the charcoal. Distribution in bags helps to limit the amount of fines produced in addition to providing a convenient measurable quantity for both retail and bulk sales.
 

ADVANTAGES OF CHARCOAL: Charcoal can be produced from nearly any kind of plant-derived biomass material.  Biomass can be converted to charcoal with conversion yields of 40% to 60% compared to current yields of 25% to 35%. High conversion efficiencies mean less feedstock is required to produce the same amount of charcoal, or conversely more charcoal is produced from the same amount of feedstock.  Charcoal can be produced in 1 to 2 hours compared to days with conventional systems.

Wood Gasification Basics
Wood gasification is also called producer gas generation and destructive distillation. The essence of the process is the production of flammable gas products from the heating of wood. Carbon monoxide, methyl gas, methane, hydrogen, hydrocarbon gases, and other assorted components, in different proportions, can be obtained by heating or burning wood products in an isolated or oxygen poor environment. This is done by burning wood in a burner which restricts combustion air intake so that the complete burning of the fuel cannot occur. A related process is the heating of wood in a closed vessel using an outside heat source. Each process produces different products. If wood were given all the oxygen it needs to burn cleanly the by-products of the combustion would be carbon dioxide, water,
some small amount of ash, (to account for the inorganic components of wood) and heat. This is the type of burning we strive for in wood stoves. Once burning begins though it is possible to restrict the air to the fuel and still have the combustion process continue. Lack of sufficient oxygen caused by restricted combustion air will cause partial combustion. In full combustion of a hydrocarbon (wood is basically a hydrocarbon) oxygen will combine with the carbon in the ratio of two atoms to each carbon atom. It combines with the hydrogen in the ratio of two atoms of hydrogen to one of oxygen. This produces CO2 (carbon dioxide) and H2O (water). Restrict the air to combustion and the heat will still allow combustion to continue, but imperfectly. In this restricted combustion one atom of oxygen will combine with one atom of carbon, while the hydrogen will sometimes combine with oxygen and sometimes not combine with anything. This produces carbon monoxide,  (the same gas as car exhaust and for the same reason) water, and hydrogen gas. It will also produce a lot of other compounds and elements such as carbon which is smoke. Combustion of wood is a bootstrap process. The heat from combustion breaks down the chemical bonds between the complex hydrocarbons found in wood (or any other hydrocarbon fuel) while the combination of the resultant carbon and hydrogen with oxygen-combustion-produces the heat. Thus the process drives itself. If the air is restricted to combustion the process will still produce enough heat to break down the wood but the products of this inhibited combustion will be carbon monoxide and hydrogen, fuel gases which have the potential to continue the combustion reaction and release heat since they are not completely burned yet. (The other products of incomplete combustion, predominately carbon dioxide and water, are products of complete combustion and can be carried no further.) Thus it is a simple technological step to produce a gaseous fuel from solid wood. Where wood is bulky to handle, a fuel like wood gas (producer gas) is convenient and can be burned in various existing devices, not the least of which is the internal combustion engine. A properly designed burner combining wood and air is one relatively safe way of doing this. so this water is available to play a part in the destructive distillation process. Wood also contains many other chemicals from alkaloid poisons to minerals. These also become part of the process.
As a general concept, destructive distillation of wood will produce methane gas, methyl gas, hydrogen, carbon dioxide, carbon monoxide, wood alcohol, carbon, water, and a lot of other things in small quantities. Methane gas might make up as much as 75% of such a mixture. Methane is a simple hydrocarbon gas which occurs in natural gas and can also be obtained from anaerobic bacterial decomposition as “bio-gas” or “swamp gas”. It has high heat value and is simple to handle. Methyl gas is very closely related to methyl alcohol (wood alcohol) and can be burned directly or converted into methyl alcohol (methanol), a high quality liquid fuel suitable for use in internal combustion engines with very small modification. It’s obvious that both of these routes to the production of wood gas, by incomplete combustion or by destructive distillation, will produce an easily handled fuel that can be used as a direct replacement for fossil fuel gases (natural gas or liquefied petroleum gases such as propane or butane). It can be handled by the same devices that regulate natural gas and it will work in burners or as a fuel for internal combustion engines with some very important cautions.

Producer Gas Generators
The simplest device is a tank shaped like an inverted cone (a funnel). A hole at the top which can be sealed allows the user to load sawdust into the tank. There is an outlet at the top to draw the wood gas off. At the bottom the point of the “funnel” is opened and this is where the burning takes place. Once loaded (the natural pack of the sawdust will keep it from falling out the bottom) the sawdust is lit from the bottom using a device such as a propane torch. The sawdust smoulders away. The combustion is maintained by a source of vacuum applied to the outlet at the top, such as a squirrel cage blower or an internal combustion engine. Smoke is drawn up through the porous sawdust, being partly filtered in the process, and exits the burner at the top where it goes on to be further conditioned and filtered. The vacuum also draws air in to support the fire. This burner is crude and uncontrollable, especially as combustion nears the top of the sawdust pile. This can happen rapidly since there is no control to assure that the sawdust burns evenly. “Leads” of fire can form in the sawdust reaching toward the top surface. Once the fire breaks through the top of the sawdust the vacuum applied to the burner will pull large amounts of air in supporting full combustion and leaning out the value of the producer gas as a fuel. This process depends on the poor porosity of the sawdust to control the combustion air so chunk wood cannot be used since its much greater porosity would allow too much air in and user would achieve full combustion at very high temperatures rather than the smouldering and the partial combustion needed. Such a burner is unsatisfactory for prolonged gas generation but it is cheap to build and it will work with a lot of fiddling. For prolonged trouble free operation of a wood gas generator the burner unit must have more complete control of the combustion air and the fuel feed. There are various ways to do this. For example, if the point of above mentioned original funnel shaped burner is completely enclosed then control over the air entering the burner can be achieved. This configuration will successfully burn much larger amount of wood.


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