Alcohol Stoves
--> Back to Overview GIZ HERA Cooking Energy Compendium
What are liquid biomass fuels?
Liquid fuels derived from biomass are sometimes referred to as 'biofuel'. They can be divided into two main groups: alcohols and oils. The latter are also called 'plant' oil or ‘straight vegetable oil (SVO) to distinguish them from non-renewable fossil oils. Biofuels are generally bioadegrable and have lower sulfur content than liquid fossil fuels. Liquid biofuels are normally marketed by volume (liters, gallons), not by weight (kg, pounds). They are renewable sources of energy, if the biomass is harvested from sustainably managed sources.
Both alcohols and oils require considerable energy input during their production to convert the original feedstock into a liquid fuel: alcohols need to be distilled and oils need to be pressed.
Why deal with the use of liquid biomass as a fuel?
Projects promoting the use of liquid biomass fuels for cooking are often driven by this kind of vision:
|
“Instead of cutting down trees for firewood, the smallholder farmer grows crops with oil seeds which he can harvest every year. By pressing the oil, he is generating plant oil which he can either sell to the world market or use for his own cooking needs. Thus, he is protecting the environment, cooking on a powerful modern fuel and is improving his income situation”. |
Liquid fuels in general have a cutting-edge advantage over solid fuels when it comes to the use for transport. With solid fuels,the fuel container has to move with the engine. This is not the case in a cook-stove which remains in one place.
Also, alcohols and oils are more energy-dense than wood. For example, the alcohols methanol and ethanol have an energetic value of ca. 20-23 MJ/kg and 25-30 MJ/kg, respectively. Plant oils are even more energy dense and range between 39 and 50 MJ/kg. Kerosene has usually between 43 and 47 MJ/kg. Air-dry wood, on the other hand ranges around 16 MJ/kg. (Charcoal, however and can range between 27-30 MJ/kg).
The focus of this section of the compendium is on the domestic use of alcohol or plant oil for cooking.
With an appropriate burner that can regulate the mix of oxygen and the fuel, it is easy to burn liquid fuels cleaner than solid fuels as liquid biomass fuels generally have low emissions of particulate matter (soot). Liquid fuels can also be very convenient to use as the power output can be regulated 'by the turn of a knob'. They are clean to handle and easy transport in bulk or in small containers like recycled bottles.
While, in many cases, it is indeed convenient to use liquid biomass fuels for cooking, it needs to be assessed case-by-case what the comparative advantage of liquid biomass fuels is in relation to a solid fuel. for example, will the considerable extra effort needed to press oil out of oily seeds or to distill precious alcohol be outweighed by the advantages regarding convenience and clean burning of the liquid biofuel in a cookstove? This is relevant both for the economic viability of using liquid biomass fuels as well as the CO2-balance.
Production of liquid biomass fuels
As the production of alcohols and plant oils differs considerably, each is described separately below.
Production of Alcohols
Alcohols are commonly produced by energy-intensive distillation of fermented sugar-rich organic matter like sugar cane, maize, grain, cassava, sweet potato etc. These are often staple foods for human nutrition. Straw, grass and wood can also be used, though with less yield. The lightest, simplest alcohol with the lowest flash-point is methanol, followed by ethanol and butanol.
Methanol can also be produced from fossil natural gas at less cost compared to ethanol derived from biomass.
Ethanol can be further processed into gel-fuel, by adding a gelling agent and some more water. Studies in Malawi showed that the heating value of gelfuel was between 16 and 18 MJ/kg. This means that a kg of gelfuel contains approximately the same energy as a kg of dry firewood, or two thirds of charcoal. (why use gel fuel if less energy?)
Economic viability of the production of cooking-appropriate alcohol fuels depends on the scale and degree of purity that needs to be reached: the more water, the less power output when burning the fuel. Worldwide people produce ‘drinking alcohol’ in their backyards. But this alcohol produced at household level usually does not exceed 50% alcohol, the rest is water. It is not suitable as a cooking fuel. Even 70% rubbing alcohol that contains up to 30% water is not recommendable as a fuel, because of the low power output. Rectified ethanol between 90 and 96 % purity is good enough for use in a cookstove, yet difficult to obtain at household level. Fuel-grade ethanol for blending with transport fuel must contain less than 1% water. This last step of distillation is extremely energy intensive and requires sophisticated industrial-size technology and production skills.
Although alcohol can be distilled from a large variety of feedstock with rather simple means, it is rarely possible for a user to produce his or her own ethanol at household level for cooking, as this requires more sophisticated distilling equipment and skills than to produce ‘drinking alcohol’. In some countries, licensing issues also come into play. Small-scale alcohol production units have not yet taken root on a broader scale. If economically viable, they could contribute to local employment generation and ease fuel constraints. For the time being people have to purchase the industrially produced alcohol fuels on the market. Market prices of ethanol are often dictated by the petroleum import price due to the use of ethanol for blending with transport fuels.
For a user, it is a bad deal if he has to pay the same price for a litre of ethanol as for a liter of paraffin, because he gets a third less of the energy content. In places where kerosene or LPG are subsidized, this discrepancy becomes more severe and ethanol a less viable fuel for cooking.
Alcohol fuels are highly flammable. They vaporize and can be ignited at room temperature. The purified ethanol can be used either directly in a stove, or it can be thickened with a gelling agent. The downside of the gelled fuel is that another 15% of water is added, thus diluting the energy value of the gel. (This sounds random. And why only mention ethanol?)
Production of Oils
Plant oils are pressed from oil-rich parts of plants, usually seeds e.g. sunflower, rape, mustard, groundnut, cotton etc. or any nuts from trees like palms, pongamia, tung seeds etc. Seeds that are not suitable for human consumption include jatropha and castor seed.
Presses can range from simple hand-presses (RAM-type) and screw-presses to hydraulic presses requiring tri-phase electricity.
Once plant oils are pressed, they need to be cleaned, filtered and sometimes refined, before they can be used as fuel in a burner.
Other combustible oils can be processed from animal fats. These are usually refined into biodiesel and biokerosene for use as cooking fuel.
Competing uses: 'food' versus 'fuel' debate
In the view of the current food versus fuel debate, smallholder farmers have to make decisions on the use of their resources. As with any other cash crop, farmers have competing options:
- Food versus Fuel: the same crop can be consumed as food or used for fuel for cooking;
- Cash versus Fuel: the same crop can be used for cash income (e.g. soap making) or as fuel for cooking;
- Seed versus Fuel: a special form of “cash versus fuel” is the use of seeds for farmers own planting (or as a commodity sold for planting) rather than for producing oil. This is a particular problem in expansion phases where the value of seed used as planting material is considerably higher than compared to the value of the same seed as raw material for oil.
- Competition for land: the same piece of land can be used to grow a fuel crop or any other crop (e.g. food or cash crop)
- Competition for water: for irrigated production and limited access to water, the scarce resource can be applied to grow various products.
The mode of production of oil plants can accommodate some of the concerns above:
- Intercropping: e.g. jatropha trees are planted within the food producing fields with enough space between them to allow enough light for the food crops;
- Fieldside cropping: e.g. jatropha is planted as a hedge around fields or around the house.
- Use of degraded land: e.g. jatropha grown on land which is no longer suitable for crop production (with lower yields of crop)
- The processing of oil at smallholder level is another important area to be observed. It comprises both the pressing of the oil as well as the filtering of fiber out of the oil.
It is sometimes rational for a farmer NOT to use their liquid biomass as a fuel for cooking:
- Oil is often more valued for soap-making or as food, rather than as fuel.
- Ethanol fetches higher prices on the market for human consumption.
Cooking with Alcohol Fuels
A stove to burn alcohol fuels can be very simple. The main components of the burner are shown here:
Source: http://www.hedon.info/BP33_EthanolStovesForMauritius?bl=y
Cooking with Ethanol
Advantages of cooking with ethanol
- Very clean combustion without soot, can safely be used indoors
- Heat available instantly after ignition
Disadvantages of cooking with ethanol
- Low heating value, especially when further diluted with water to make gel-fuel
- Depending on the stove, cooking can take long
- High flammability, burns at low temperatures and might lead to accidents during transport and handling
Experiences of cooking with ethanol
At present, ethanol stoves seem to be more used when promotion is supported by a project. Market forces have not yet pushed ethanol to become a mainstream fuel for daily cooking. With more nations starting their own ethanol production, the uptake of ethanol as cooking fuel is expected to increase.
Ethanol and ethanol-based gel-fuel are quite common in niche applications, where clean combustion and convenience is required: e.g. in camp stoves, when little food has to be cooked or in warmers to keep food warm in restaurants. For day-to-day cooking, there are not many examples of ethanol as a main cooking fuel. Only in countries where ethanol is produced at large scale and is available at affordable prices, is cooking with ethanol more prevalent.
In specific circumstances like humanitarian interventions when large numbers of people need to be provided with fuel and stoves, ethanol stoves have a considerable success. Read reports from Ethiopia and Haiti on http://www.hedon.info/Project-Gaia-Jumpstarting-Emergency-Interventions-for-Sustainable-Development?bl=y
The most documented stove model is the CleanCook Stove promoted by Project Gaia:
CleanCook ethanol stove
The "CleanCook" Stove is available as a single burner or two-burner ethanol stove for households. It is a non-pressurized alcohol stove with a refillable fuel canister that contains a permanent, porous, refractory mass that absorbs and retains its liquid fuel in a manner that prevents spilling, leaking, fires and explosions. The power output per burner is rated at 1.5 kW. The ethanol and methanol (denatured to prevent ingestion) can be used as a mix in any proportions. The cost of the single-burner stove in 2010 was 65-70 USD (source http://www.hedon.info/View+Stove?itemId=8969)
In households studied in Ethiopia, the CleanCook became the stove of choice, except for baking the local staple food – injera.(contradictory..how stove of choice if dont make injera?) Pilot projects started in 2005, and since then the first commercial project have begun.
(http://www.bioenergylists.org/en/taxonomy/term/159 and www.projectgaia.com)
In Brazil, the stove was tested by 100 households, mainly in the vicinity of ethanol distilleries to assure continuous and convenient availability of the fuel. The main fuels used by the households before the study commenced were LPG and fuelwood. In general, the stove was well-received by the participants and they felt that, in terms of cooking time and cost, it was superior to LPG. Numerous families talked of being able to buy ethanol in small quantities, which suited their household economics better than saving for the refueling the LPG cylinder.
Cooking with Methanol
Methanol-use for cooking is still in its infancy. This is partially due to the fear of the potentially damaging health effects should the fuel be accidentally ingested. Project Gaia had a pilot study in Nigeria with Methanol (made from fossil flare gases): people were mainly satisfied with the stove, but complained that the fuel was not regularly available.
http://www.projectgaia.com/page.php?page=nigeria
Source: HEDON/Boiling Point
Additional information resources on ethanol
HEDON Household Energy Network
This network provides information on all aspect of ethanol as a household fuel. Visit http://www.hedon.info/ and type ‘Ethanol’ in the search box.
Cooking with Plant Oils
Plant oil fuels pose the challenge that they have a high viscosity and only ignite at temperatures above 200 ° Celsius. Depending on the oil type, simple wick-stoves are not suitable and sometimes preheating of the oil with another fuel that burns at lower temperatures is needed. Pressurizing enhances the performance and power-output, but adds more challenges and cost to the stove.
Plant oil differs from other liquids when used for cooking. Below are some advantages and disadvantages.
Advantages
- Safety: Plant oil is has a high viscosity and a higher flame point as compared to kerosene. For the user, this has the advantage of safety (it does not ignite spontaneously and is not so explosive when spilled).
- Smell: Most plant-oils also do not emit undesirable odours (it does not smell as intensive as kerosene).
- Fast cooking: Plant oil has a high energy content (only 5% less than kerosene). Hence it produces a powerful flame if used in a pressurized stove. Cooking large quantities can be done quickly.
Disadvantages
- Pre-heating: The advantages on safety and smell come at the expense that it usually needs to be preheated with another fuel (e.g. ethanol or methanol) in order to be ignited. This pre-heating is another cost factor and it consumes time.
- Simmering: The linked disadvantage is that it is difficult to simmer: in a pressurized regulating the plant-oil supply down for small heat poses a challenge.
- Cleaning: Plant-oils contain fiber, the amount of which depends on the kind of oil and the quality of the filter method applied. As the oil is burned as gas, the fiber remains behind and tends to clog the burner (depending on the type of stove). This requires regular cleaning of stove and nozzles.
- Noise: if burned in a pressurized system, cooking on plant oil can be quite noisy. It requires muffling of the sound.
Experiences of cooking with Plant Oil
During the last decades, projects have sought to design household appliances for cooking and heating that use plant oil. Until recently, none of them got beyond the test phase. Some of the reasons for the past failure of plant oil cookers are:
- Plant oil cookers have a rather complicated design which is not easy to construct;
- They may require ongoing maintenance;
- Production of plant oil is labour-intensive and expensive;
- The use of some plant oils as fuels competes with other uses, such as food crops, soap production etc., which are more profitable.
- In most cases, production of fuelwood is much easier and much cheaper than production of plant oil.
The PROTOS plant oil cooker
BSH (Bosch und Siemens Hausgeräte GmbH) designed a plant oil cooker named "Protos" that can use a variety of plant oils; even recycled and filtered oil previously used for frying. Field tests in the Philippines and in Tanzania have shown that households and small enterprises such as restaurants, that were previously cooking on 3-stone fires, can handle the Protos-stove. People stated that they enjoyed the comfort of cooking and said it was like cooking on gas, even if LPG was not available. Based on observations from the field tests, BSH has integrated improvements launched serial production as of May 2010 in Indonesia. Plans are to increase capacity and production in line with demand projections. The success will largely depend on the initial investment costs and the access and affordability of the fuel. Further information on the PROTOS on
http://www.plantoilcooker.com.
Additional information resources on plant oil
Reinhard K. Henning (2006): Jatropha curcas L. in Africa. Assessment of the impact of the dissemination of “the Jatropha System” on the ecology of the rural area and the social and economic situation of the rural population (target group) in selected countries in Africa
This paper gives a good overview on production of the Physic Nut in Africa and the variety of its use. Special attention is paid the use of plant oil as a fuel. An overview of existing cooker models is given including technical details.
http://www.underutilized-species.org/Documents/PUBLICATIONS/jatropha_curcas_africa.pdf
The Jatropha System - An Integrated Approach of Rural Development in Tropical & Subtropical Countries
The very comprehensive homepage provides a good overview of the role of Jatropha in different countries, technical aspects of oil extraction, different cooker models developed so far, a selection of projects working in the field of Jatropha use as well as a large amount of literature on the issue. http://www.jatropha.de/
