Alcohol Stoves

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What are liquid biomass fuels?

Liquid fuels derived from biomass are sometimes referred to as 'biofuel'. They are in general biodegradable, renewable, and have a low sulfur content. They can be divided into two main groups: alcohols and oils (normally referred to as 'plant' oil to distinguish them from the non-renewable fossil oils). They are normally marketed by volume, not by weight. Liquid biomass fuels are renewable sources of energy. Yet both groups require sometimes considerable energy input to convert the original feedstock into a liquid fuel, either by distillation in the case of alcohols, or by pressing (in the case of oils). If they can be considered carbon-neutral depends on the amount and type of energy invested in their production:

Production of liquid biomass fuels

Alcohols are commonly produced by energy-intensive distillation of fermented sugar-rich organic matter like sugar cane, maize, grain, cassava, sweet potato. 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 as ethanol derived from biomass.

Alcohols are less energy-dense than oils, which consist of longer-chain hydro-carbons that ignite at much higher temperatures. Methanol has an energetic value of ca. 20-23 MJ/kg, Ethanol between 25-30 MJ/kg, depending on the amount of water still contained. Plant oil, depending on the type, ranges between 39 and 50 MJ/kg, Kerosene has usually 47 MJ/kg.

Economic viability of the production of alcohol fuels for cooking depends on the scale and degree of purity that needs to be reached. Rubbing alcohol that contains up to 30% water is not recommendable as a fuel. Rectified ethanol between 90 and 96 % purity is good enough for use in a cookstove, whereas for blending with transport fuel fuel grade ethanol containing less than 1% water is required. This last step of distillation is very energy intensive and has a negative impact on the overall energy balance.

Although alcohol can be distilled from a large variety of feedstock with rather simple means, it is rarely viable for a user to produce his or her own ethanol at household level for cooking, so people have to purchase the fuel. 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 raw deal if he has to pay the same price for a litre of ethanol as for a litre of paraffin, but he gets a third less of the energy content. In places where kerosene or LPG are subsidised, this discrepancy becomes more severe.

Small-scale alcohol production units have not yet taken root on a broader scale. They could contribute to local employment generation and ease fuel constraints, if economically viable.

Alcohol fuels are highly flammable, they vaporise 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.

tabelle einfügen energy content, viscosity and flashpoints

Plant oils are pressed from oil-rich parts of plants, commonly seeds e.g. from sunflower, rape, mustard, groundnut, cotton etc. or any nuts from trees like palms, pongamia, tung etc. Seeds that are not suitable for human consumption are e.g. jatropha and castor seed.

Presses can range from simple hand-presses (RAM-type), 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.

Liquid fuels in general have a cutting-edge advantage over solid fuels when it comes to the use for transport, where the fuel container has to move with the engine. This is not the case in a cook-stove, which remains in one place.

 Where natural gas is available, it can be produced at a fraction of the cost of ethanol. To date, development of this fuel for household energy is still in its infancy.

Liquid biomass fuels 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. Liquid biomass fuels have generally low emissions of particulate matter (soot). Liquid fuels can be very convenient to use, the power output can be regulated normally 'by the turn of a knob'. They are normally clean to handle and easy transport in bulk or in small containers like recycled bottles.

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. Pressurising enhances performance and power-output, but adds more challenges and cost to the stove.

It needs to be assessed case-by-case what the comparative advantage of liquid biomass fuels is in relation to a solid fuel: will the considerable extra effort needed to press oil out of oily seeds or distilling precious alcohol outweigh the advantages regarding convenience and clean burn of the precious fuel in a cookstove?

Oil is often more valued for soap-making or as food, than as fuel. And ethanol fetches higher prices on the market for human consumption.

Cooking with Alcohol Fuels

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.

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 the warmers to keep food warm in restaurants. For the 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, cooking with ethanol is more prevalent.

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 on cooking with ethanol

CleanCook ethanol stove

The Gaia-Project has developed the “CleanCook-Stove”, a 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 ethanol and methanol (denatured to prevent ingestion) can be used as a mix in any proportions. When ethanol burns outside of its bounds, it burns lazily, taking on excess air. Both ethanol and methanol are safer than kerosene because they are miscible with water, and therefore easily extinguishable by water. 

In the households studied in Ethiopia, the CleanCook became the stove of choice, except for baking the local bread – injera. Pilot projects started in 2005, and it is hoped that the first commercial project will commence in 2008.
(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.
For further information see www.projectgaia.org

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

The production of plant oil

A broad variety of oil plants grow in the tropics and subtropics that can be used as renewable fuel sources. Examples of plants whose oils are suitable as fuels include; several species of castor oil plants - such as the physic nut (Jatropha), coconut, cotton seed, corn, and soy beans.
In the view of the current debate, smallholder farmers have to make decisions on the use of their resources based on their own knowledge and perception of opportunities and risks. As with any other cash crop, farmers perceive 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 e.g. Jatropha seed 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 as 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.

The use of plant oil for cooking

Plant oil differs from other liquids when used for cooking:

• Safety: Plant oil is has a high viscosity and a higher flamepoint 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 plantoils also do not emmit undesirable (it does not smell as intensive as kerosene).
• Pre-heating: This advantage comes to 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.
• Fast cooking: Plant oil has a high energy content (only 5% less than kerosene). Hence it produces a powerfull flame if used in a pressurised stove. Cooking large quantities can be managed fast. 
• Simmering: The linked disadvantage is that it is difficult to simmer as in a pressurised system it is difficult to regulate the plant-oil supply down to a small heat.
• Cleaning: Plant-oils contain – dependent on the kind of oil and the quality of the filter method applied – a certain amount of fibre. As the oil is burned as gas, the fibre remains behind and tends to cloque the burner (depending on the type of stove). The results into regular cleaning requirements.
• Noise: if burned in a pressurised system, cooking on plant oil can be quite noisy (like a vacuumcleaner next to your ear).

Experiences on 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.

BSH (Bosch und Siemens Hausgeräte GmbH) designed a plant oil cooker named "Protos" that can use a variety of vegetable oils; even oils that have been used for frying. The stove can be used by households and by small enterprises such as restaurants. It has been tested in the Philippines and in Tanzania and is now ready for market introduction. The Protos will be first produced in Indonesia. For further details and pictures see 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/

The Protos plant oil cooker. Additional information regarding this stove can be found at:
http://www.bsh-group.com/index.php?109906