Ben 2 and Ben 3 Firewood Stoves

The Ben 2 and Ben 3 Firewood Stoves, designed by Dieter Seifert, serve for cooking in pots up to 28 cm in diameter (Ben 2) or 28 cm to 32 cm or larger (Ben 3). Pans and woks can also be nested. Dry, thin sticks of firewood of any length are used as fuel.
The thermal efficiency of the cooker is over 40%. Compared to the traditional three-stone fire (with 10% efficiency), firewood consumption is reduced to less than a quarter (75% saving).
When the Heat-retention cooking is applied additionally (see: Imma and Dieter Seifert: ), the firewood consumption drops to about one-seventh. This small amount of wood can be provided by plantations, which can be harvested annually. Thus, the search of firewood and felling of trees is completely avoided.
If the use of charcoal from kilns is replaced, then the wood saving is even greater because multiples of wood is consumed for the traditional production of charcoal. At the same time, the disease burden by carbon monoxide and nitrogen oxides is inhibited.
For overcoming the firewood crisis it is important on the one hand that the demand for wood is reduced to about one-seventh (demand in a week, which was formerly the daily requirement) and that the remaining needs are covered by plantations, which can be harvested annually.
Simplicity, high efficiency and durability Construction of the stove is very simple. The stove consists of three parts which are placed into one another.
The operation of the stove is easy, both kindling, as well as the maintenance of the fire on the firewood grate. The stove weighs only about 3 kg; it is portable and can be produced with simple tools (optionally without any machine) of conventional mild steel. In the case of local production especially in developing countries the manufacturing costs are very low (in the order of $10 USD). Thus, the expense can often be saved already in a month. Due to the low costs and high savings, the household may install more than one cooker (or several stove shells), suitable to the pots and pans used.
Very little smoke is produced due to the effective supply of primary and secondary air. The thin steel sheets do not operate at a high temperature so that they have a long life.
The net power of the stove is 1.5 kW. Six liters of water can be brought to a boil in less than 25 minutes. For this operation, only about 400 g (1 lb) of small, dry wood sticks are required. With a daily consumption per household of 1.4 kg fuelwood, the annual demand is about 500 kg, instead of usual two to four tons of firewood (or more than 7 tons of wood, if charcoal is used).
The efficiency is high due to the proper combustion and the advantageous heat transfer to the pot, caused by the special firewood grate and the adapted stove shell. If solar technology is applied in addition (see e.g. Imma Seifert: Solar Cooking with the Parabolic Cooker), then the demand for wood can be reduced to less than one kg per day per household, even if additional tasks (boiling large quantities of water, conserving fruits, etc.) are carried out with the solar cooker.
==Advantages of these designs==
*Its operation can be learned in less than an hour, because it is probably easier to operate than a three stone fire (much easier to start and maintain the fire, due to effective primary air supply under the grate).
*Thin dry twigs are suitable, which do not harm the tree at harvest or which may be produced in short rotation plantations. Hence . 
*The stove can be easily produced without requiring special materials or tools because intentionally no insulation is provided and the unhindered primary and secondary air flow enables sufficient low temperature for the thin steel sheets.
*It was expected that therefore the efficiency is not particularly high, but the heat transfer of the Ben stove is obviously very good. Sometimes there is a misconception in efficiency discussions. We should consider that with an efficiency of 10% (= default value from UNFCCC for traditional three stone fire) there is a consumption of 10 kg firewood instead of theoretical 1 kg (at 100% efficiency), at 25% efficiency the consumption is 1 kg / 0.25 = 4 kg ( i.e., 6 kg savings), at 40% efficiency the consumption would be 1 kg / 0.4 = 2.5 kg (7.5 kg savings), and at about 66% efficiency the consumption is 1 kg / 0.666 = 1.5 kg (i.e. 8.5 kg savings). The diagram below shows that the major savings over the three stone fire occur at efficiencies up to 40%.
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*August 2019: Recently, the author received a note from Sri Lanka, which suggests a modified construction of the tripod. The tripod elements made of steel strip are fastened to the furnace shell by screws, so that no welding is necessary. The essential parts of the Ben-Stove are maintained. We will name it “Ben SL”. The parts of an example of Ben SL are described in the parts list and shown in the two drawings (Fig. 1 and 2, page 2) available in . Fig. 1 shows Ben-SL in section with a pot (left) and a pan. Fig. 2 is a top view. Shown are: the ash pan (1) with the built-in hairpin-shaped fire grate bars (2), the furnace shell (3), which is divided into two halves. The newly proposed tripod parts (4) are fastened to the furnace shell with two screws M6 x 15 (6) each. The bottom edge of the furnace shell (3) is 30 mm from the ground, so that the fire on the grate (2) is supplied with primary and secondary air unhindered. The diameter of the furnace shell results from the pot diameter D and the double gap width 2s. The gap width s is advantageously 7 to 10 mm. The most favorable distance of the pot from the furnace grid (2) depends on the fuel (especially on the flame length). Therefore, the furnace shell height H and the length L of the tripod have to be optimized experimentally. The contribution from Sri Lanka is a good example of the opportunities for cooperation with the open source principle for finding appropriate solutions. 
*April 2016: Dieter Seifert has a new design for the tripod for the Ben 2 and Ben 3 Firewood Stoves, which has several advantages. The tripod consists of three equal parts which are welded together. The parts are made of round steel with a diameter of 6 mm. 
*May 2015: Dieter Seifert writes: Today I have made tests with the Ben 2 and 3 Ben Firewood Stoves. It is almost unbelievable, but the efficiency is always higher than 40% and if one does not heat up too fast (i.e., the power under 1.5 kW is), the result is almost no smoke and approximately 350 g thin wooden sticks can bring 6 liters of water to a boil in 25 minutes. Of course cooking is much more convenient with a large parabolic solar cooker (We have used the AlSol 1.4 for many years.). The Ben ovens are so easy to prepare (2 sheets provided with holes and bending, drilling a ring and three legs and turn, turn 4 bars hairpin-shaped and assemble everything) that the cost in firewood crisis regions would be well below $10 USD. The combination of heat-retention cooking and with the solar cooker is ideal. The solar cooker can do much more than just cooking. It is a peace-creating technology that is so urgently needed.
==Efficiency==
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==Construction plans==
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==En español==
*Información detallada acerca de estos hornillos
==See also==
*October 2016:  - Dieter Seifert
*September 2016:  - Dieter Seifert
*June 2016: - Dieter Seifert
==Contact==
Category:Germany
Category:Improved combustion stoves