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close this bookBoiling Point No. 20 - December 1989 (ITDG - ITDG, 1989, 40 p.)
View the document(introduction...)
View the documentAcknowledgements
View the documentNew Stoves For Old
View the documentKerosene and Gas Stoves in Nagercoil, South India
View the documentKerosene Wick Stoves
View the documentAn Investigation on the Colombian Kerosene Stove
View the documentTrials to Use Mineral Coal from Kiwira Coal Mines in the DUMA Wood Stoves
View the documentEnergy & The Environment in the Third World
View the documentUse Of Non Biomass Stoves In Sri Lanka
View the document''Simply Living''
View the documentLow-Wattage Cookers in Nepal
View the documentBiochar Briquetting & Burning
View the documentSTOVE PROFILE
View the document''Gourd Roots Make Good Fuel''
View the documentThe South Indian Clay Crusher
View the documentNEWS

''Gourd Roots Make Good Fuel''

The Rootfuel Alternative to Scarce Woodfuel in Third World Drylands: Combustion Tests and Socio-Economic Studies

by EB Shultz, Jr., Ph.D. Professor of Engineering and Applied Science, WG Bragg, Ph.D., Affiliate Prof. of Technology and International Development, D L Duke and B H Malkani, Graduate Research Assistants, Department of Engineering and Policy, Campus Box 1106, Washington University, St Louis, MO 63130, USA

Editorial Summary

Reforestation and high-efficiency cookstoves are unable to stem the tide of deforestation in the Third World for the provision of cooking fuel. An alternative to woodfuel is urgently needed. We have tested "rootfuel" (fast- growing non-woody sun-dried taproots of certain members of the Cucurbitaceae family such as wild dryland gourds and melons), in comparison with woodfuel in simple stoves commonly found in the Third World. The heating value of rootfuel is about 10 percent less than that of wood. Our experiments showed that rootfuel burns more slowly than wood. Transfer of heat to the cooking vessel is more efficient; the same boiled-meal cooking task was accomplished with about 0.7 as much rootfuel, by weight, in comparison with woodfuel, in almost the same time using a 3-stone fireplace. There is evidence in the literature that more dry biomass of this type than woody biomass can be grown per unit area of arid land.

The reactions of local cooks were encouraging in our on-site rootfuel acceptability tests conducted in rural Senegal, Niger, and Mexico on several types of meals. None of the cooks found objectionable flavours. Our paper also includes rootfuel characterizations and combustion-rate comparisons with woodfuels.

Overuse of Woodfuel

Deforestation and desertification are life-threatening problems in many Third World aridlands. The forests cannot naturally replenish themselves at the current rate of disappearance, and human efforts to replant trees are costly and have barely begun to address the problem Closely related to aridland deforestation is desertification; it is estimated that the world's deserts are adding to their area at the rate of 14 million acres per year. In addition, the dissemination of improved high-efficiency cookstoves that use less wood is happening very slowly . Efficient stoves, although helpful, cannot be made cheaply enough for the rural poor. In short, neither reforestation nor efficient stoves is meeting the need, as the problem worsens.

The Alternative Fuel Approach

In our opinion, the need for alternative cooking fuels in aridlands is great, and increasing rapidly. Appropriate alternative fuels would not only benefit the people now but would help to save their environment, preventing serious future adverse consequences of deforestation and erosion on the carrying- capacity of the land.

We suggest the following as a minimum set of criteria for an alternative solid fuel for aridlands: (a) it must be low in cost, (b) it must be culturally acceptable, (c) its production must not compete with food crops, (d) it must be producible at the village level, (e) its production must be sustainable, both socio-economically and environmentally, (f) its use must be ecologically sound, and (g) it must be producible in aridlands so it does not have to be imported from outside the nation or from other areas of the nation.

Rapidly-grown non-woody biomass offers an alternative to wood. The fast- growing taproots of certain species of cucurbitaceae (gourd, squash family) are one such non-woody fuel source. The roots can be sun-dried and burned as a hard, solid "rootfuel". An example of a wild New World aridlands cucurbit with fast-growing inedible carrot-shaped taproots and multiple-use potential is cucurbita foetidissima. H.B.K., DeVeaux and Shultz have published an interpretive review of the extensive literature of economic botany on this species through 1984.

Many cucurbits grow rapidly in aridlands without irrigation, and produce yields of dry biomass in the form of roots which may be similar to or even larger than yields of dry biomass from limbs of typical aridland trees. For example, cucurbita foetidissima has been grown by Nelson and co-workers as an annual in Arizona in high-density plantings over the summer season to maximize root yields. [J Amer. Soc. Hort. Sci. 108 (2): 198-201 (1984)]. Fresh root yields of as high as about 35 tonnes per hectare were reported, equivalent to about 11 tonnes of dry biomass per hectare. This is nearly twice the dry biomass yield reported by McKell et al. for unirrigated tree biomass cropping in the arid southwestern United States. (cited by Cushman and Ranney, in Proc. 6th Conf. on Energy from Biomass & Wastes, Institute of Gas Technology, Chicago).

The Present Work

The work to be described below includes laboratory analysis of fuel properties, combustion rate comparisons, tests of rootfuel-woodfuel equivalence, and on-site tests of cultural acceptability in Mexico, Senegal and Niger.

Characteristics Of Rootfuel And Woodfuel

Samples of local wood and locally-produced charcoal from Senegal, dried cucurbita foetidissima roots from Oklahoma, and dried wild melon roots from Niger were analysed for us by the Industrial Testing Laboratories, St. Louis, using standard methods. The heating value of the sun-dried Oklahoma roots was found to be 7645 Btu/lb; the value for the Nigerien roots was 7298 Btu/lb. The heating value of the Senegalese charcoal sample was nearly 1.7 times greater, and the average heating value of the woods was about 1.1 times that of the dried roots. Ash contents varied considerably for the wood samples, from 0.82 to 2.28 percent; ash content of the charcoal was 2.61 percent.

Both of the root samples had a high ash content, 3.86 percent for the US roots, and 6.63 percent for the Nigerien, a reflection to some extent of the difficulty in cleaning soil from root surfaces. The effect of high ash content is to increase ash-handling requirements, and the result of insufficient cleaning of the roots is to diminish ignitability.

Heat release rates (power ratings) can be calculated from the measured heating values and the weight-loss rates during combustion. The rootfuel released heat at the rate of 730 Btu/min, nearly four times as fast as the Senegalese charcoal, but only 48 percent as fast as one Senegalese wood ("haus"), and 81 percent as fast as the other ("raat").

In terms of heating value and rate of weight loss during combustion, rootfuel is more like wood than charcoal. However, the ignitability of rootfuel is similar to that of charcoal.

Rootfuel, then, is a fuel of much higher power than charcoal but significantly lower power than wood, assuming that size and shape of fuel pieces is similar. The power rating of a fuel will affect the way it is used; some cooking tasks require low power (low rate of energy release) as in the case of the slow simmering of grains, but other tasks may require a high- power fuel, e.g. frying. The power rating also affects the efficiency of capture of heat by the pot; more of the heat released by a more rapidly- burning fuel is likely to be lost to the surroundings in the form of hot gases.

On average, cooking with rootfuel required only about 7 percent more time to complete the task. The average amounts of the fuels consumed to complete a typical cooking task gave a rootfuel/woodfuel equivalence ratio of about 0.7 for a 3-stone fireplace.

Because less fuel in the form of dried roots would suffice, rootfuel should command a premium in the marketplace, in comparison with wood.

However, if women have to search for fresh roots to dig and carry home from distant sites, the advantage represented by the 0.7 rootfuel-woodfuel equivalence ratio would be lost; unlike wood, fresh roots are about two- thirds water. Therefore, carrying headloads or backloads of fresh roots for long distances is impractical. Perhaps twice as much fresh root as dry woodfuel, by weight, would have to be carried by the women, even when the 0.7 advantage is taken into account.

This is likely to foster the cultivation and drying of roots near home for home use, or the production of rootfuel for local marketplaces as a private or cooperative business. Therefore, not only would rootfuel help to take pressure off trees, but the long hours of carrying fuel by women might be lessened or perhaps even eliminated.

In addition to laboratory tests, cooking tests were carried out in Mexico, Senegal and Niger. In each case, we asked that a typical local meal be prepared by the cook's usual equipment and methods, but with rootfuel instead of the usual fuel. It was our intent to refrain from giving special instructions on the use of rootfuel and let the cooks decide how to use it. We noted any adjustments in technique made by the cooks due to the unusual nature of rootfuel.

These seven rootfuel tests involved women in five sites and two continents. They included a broad cross-section of society with both city and village women, both educated and peasant women. The roots were also tested in a variety of stoves; some were traditional and some were improved, energy-efficient stoves.

In Mexico, Claudia noted that rootfuel is slower to ignite than her usual fuels (animal dung cakes, crop residues, and dried maguey, a type of cactus), but within a few minutes the fire was burning briskly. She commented that the fire burned less rapidly than her other fuels.

The first cooking test in Senegal was performed at the home of Fatou Faye in N'gane, an outlying neighbourhood of Kaolack. One of us (DLD) chose to work with Fatou because she has known her for several years and feels that she has an honest relationship with her. Fatou speaks enough French and DLD enough Wolof and French that communication was no problem.

Fatou was chosen also because, although she technically lives in the city of Kaolack, her lifestyle is somewhere between that of a typical city woman and that of a typical village woman. She usually cooks with either wood or charcoal, depending on which is more readily available and cheaper. In the middle and upper class neighbourhoods of Kaolack, nearly all cooking is done with charcoal In the villages, most women cook with wood. Charcoal is preferred by city folk because it produces less smoke, some of the advantages thereof being that it does not irritate the eyes and lungs and does not blacken the cooking equipment. It also requires less tending.

At different times, Fatou cooks on a three-stone fire, a Malgache stove (the traditional West African metal stove), a mud stove and an improved charcoal stove, depending on availability. This again is like both the city and village women. Three-stone fires and mud stoves are predominant in the villages, whereas the Malgache and improved charcoal stoves are prevalent in the city.

Comparation of the Cooking Test

Since the cultural acceptability tests represented different socio-economic and cooking-skill levels, as well as different continents, cultures, foods, and stoves, the wide variation in results was not surprising. However, some generalizations can be made.

Quality of the meal. In all of the tests, the women succeeded in cooking an acceptable traditional meal. There were no complaints about the quality of the meal using rootfuels in any of the locations. We feel that this is a significant finding. A variety of meals was prepared: rice and tomatoes, eggs, tortillas, rice with vegetables and fish, and rice and beans. All were accepted by women, men and children, even by small children who might be considered too innocent to be polite. Even the quality of the xorn, (a crisp rice that sticks to the bottom of the pot) regarded as an indicator of cooking skill in Senegal, was judged to be excellent.

Ignitability. In four of the seven tests, the cooks found it difficult to ignite the roots. In the remaining three tests, the roots ignited rather easily. Several factors affect ignitability. First, ventilation (draft) is of major importance. Rootfuel seems to require at least as much ventilation as charcoal and perhaps more. The roots ignited easily in the well-built Multimarmite which is actually a charcoal stove. However, they did not ignite as easily in the cylindrical and M'Bow charcoal stoves. Both of these locally-crafted stoves probably would not have met ventilation standards set by improved stove designers. The roots burned well in the Nigerien Mau Sauki which is designed for wood and thus amply allows for draft.

Smoke. The second major complaint of the cooks concerned the thick white smoke present in every test, though not as abundantly in some as in others. Comments on the smoke seemed to depend on the standard against which the women made their comparisons. Women who are used to cooking with wood are accustomed to coping with smoke, whereas the city women of Kaolack, who cook with charcoal, are not. As would be expected, the former group was much more accepting of rootfuel smoke than was the latter.

All agreed that, qualitatively, the smoke was not a problem. They found it very similar in odour to smoke from wood. It seemed to only bother the cooks when it was more plentiful than they were accustomed to experiencing. In some cases, when the combustion was particularly poor, the smoke was profuse. Increased draft of air through the stove could alleviate much of the smoke problem, making the roots a viable alternative at least for the poorer women in the rural areas who typically accept fuels that smoke. City women who can afford charcoal will probably continue to prefer this premium fuel.

Summary of Cooking Test Results

· using rootfuel, one can cook a delicious meal that is altered neither in taste nor quality by the fuel
· rootfuel can be difficult to ignite, although with a little kerosene, well-dried, cleaned roots and adequate draft, ignition is not a serious problem.
· the smoke was not deemed to be a problem, qualitatively, but smoke can be abundant if good draft is not provided or if the rootfuel is not adequately dried.
· the roots were judged to require more tending than traditional fuels, because small roots were used in most tests, and small roots burn rapidly and require frequent replenishment. The importance of this varied from user to user and would probably be insignificant in areas where traditional fuels are scarce. Less tending is required if larger roots are used.
· a minority of testers felt that the roots did not produce adequate coals, but most were satisfied.
· cooking speeds for the rootfuels fell within ranges of traditional fuels. Wide variance demonstrated the overarching significance of the type of stove used.
· relatively affluent cooks who are accustomed to charcoal, such as many city dwellers, found rootfuel less acceptable.

If it is desirable to design a stove to accommodate rootfuel combustion characteristics, it is important that this be achieved without creating a high-priced stove that poor people cannot afford. Most of the woodfuel users are poor. Therefore, a special stove must be very simple in design and inexpensive. Provision for insulation to improve efficiency is desirable in principle, but tends to greatly increase the cost. A good stove should probably have the following characteristics, all related to providing ventilation for minimization of smoke production and improvement of ignitability:

· large door hole for ease of adding fuel and to aid in adequate ventilation
· closeable door for energy economy and regulation of ventilation
· high air-hole density in grate (about 30 percent)


Our principal finding is that rootfuel seems to be reasonably workable in a diversity of existing wood and charcoal stoves and three-stone fireplaces, in the cooking of a variety of meals under widely differing circumstances. A special stove is not mandatory, although it is clear that good draft is important. All of the local cooks who tried rootfuel for the first time were able to adapt their equipment and techniques to prepare acceptable meals without much effort, and with virtually no advice from us. Our main concern, that rootfuels might impart objectionable flavours to foods, did not materialize in any of our cultural acceptability tests.

The results of our studies in Mexico and West Africa suggested to us that rootfuels are probably going to be acceptable in many Third World aridland regions and cultures. Rootfuel may be most readily adopted where it is needed the most, in poverty-stricken deforested areas. It is women in the rural areas who are struggling to find fuel who will most likely see the value in a new, cheap, locally available combustible, in our view. These women will probably be tolerant of its main shortcomings (difficult as charcoal to ignite, smokiness unless the fire is well ventilated, frequent tending due to small size of typical roots that are one-season old), and willing to experiment with rootfuel to teach themselves how best to use it.

Ed Note: It is worth noting that the problem encountered with rootfuel acceptances are similar to those encountered with unpyrolised briquettes. We find that to achieve a minimum level of acceptance, benefits must be substantial.