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A New Stove for the Household Production of Palm Sugar

This paper describes part of the work of the Thai-French Farming Systems Research Project, in collaboration with the Faculty of Natural Resources, Prince of Songkla University, Autumn 1986, 9 pp. slightly abridged for 'Boiling Point'.

The research work has been carried out under the scientific assistance of Bernard GUERIN (FNSIA, 9130; MASSY, FRANCE) and Jose MUCHNIK (GRET, ALTERSIAL, 91305 MASSY, FRANCE) after a detailed analysis of the agrarian system in the concerned area.


In South East Asia, the palmyra palm, BORASSUS FLABELLIFER L., has been exploited for a very long time, mainly for its production of sweet sap which is fermented into alcoholic drinks or boiled to make sugar. In the peninsula of Sathing Phra, in the extreme south of Thailand, the poor farmers, who have no access to the land, obtain their principal income through this activity. Although the conditions surrounding their household commodities seem bad, (low labour productivity, dangerous work for the farmers, concurrence with the price of sugar cane...) the Production of alcohol and especially sugar has increased recently (VANDERGEEST, 1986; TREBUIL et al., 1983).

Palm sugar can be Produced all year round but its peak is between March and May. As 'he season approaches, the tappers prepare by building a stove, buying bamboo containers and a pan and collecting palm fronds for use as firewood. The juice isconcen'ratec into syrup or solid sugar cake in a single open-oar evaporator. Although sugar palm cultivation is increasing in "he Sathing Phra area, there are 2 important problems which threaten i's future. Firstly the lack of local firewood supplies and secondly the poor quality of the honey and solid sugar cake.

One of the most important problems is the concentration of the juice in open-pan evaporators. The traditional stove causes an inefficient use of wood and inferior quality of the final products. Farmers usually collect various parts of the palm tree and other kinds of wood as fuel but recent expansion in sugar cultivation has brought about a crisis in household supplies of fuel. Wood imports, especially of rubber wood, have increased over the last 10 years. The cost of fuel for boiling sap down to syrup is about 30-50% of the gross income from sugar production (TREBUIL et al., 1983; VANDERGEEST, 1986).

This research programme is concerned with improving the efficiency of the open-pan stove used to evaporate the water from palm sap. The primary objective is to reduce the cost of the fuel component. The first phase of the programme was a research phase during the 1985 sugar season, the second is the extension phase before and after the 1986 sugar season. (THAMRATWASIK and al., 1986).



The woodstove typically used in the Sathing Phra area is shown in figure 1. It is normally made from local and freely available materials: mud and clay and sometimes bamboo or rice straw for increasing the strength. The stove has one pan, made of iron, which can hold about 60 litres of fresh sap. It has no grate and no chimney and the fuel gases escape around the edges of the pan. This type or stove must be rebuilt every 2 or 3 years.

The improvement of Stoves for traditional sugar processing had -been studied all over the world.

The so-called Khandsari small factories in India (production of crystallized cane sugar) use improved stoves with 5open-pans and bagasse as fuel (BENNETT, 1981, KLAPLINKY, 1984).

If the theoretical ideas were given by university researchers, it is important to note that the ideas arose in the field with farmers from 2 different villages. The new stove is the result of these convergent factors. The investment means of the farmers, especially the climbers of Borassus, are too low for a vacuum concentrator which is the best and gives high quality sugar. In the Sathing Phra area, the climbers do not want to work together in groups of 2 or 3 households using each stove. A 3 or 4 pan stove is thus too big for them. Using palm petioles as fuelwood (a bulky material) imposes the need for a heavy stove with a big combustion chamber. In regard to theory, the main characteristics of the new stove are:

- The pan surface in contact with flames and ember radiations and the removal of flue gases has been increased in relation to the traditional one. The iron pans are the same as in the traditional stove for economic reasons. Then, to increase the heat transfer surface, the shape of the stove is adapted to the pan and the pan-fuelbed distance is reduced.

Fig. 1 Traditional Palm Sugar Stove

The combustion chamber and the chimney flue must be planned to extend the stay time of hot gases and to reduce the losses of heat through the chimney. The chimney allows air to be drawn into the combustion space but at the same time, a baffle prevents hot gases from escaping too cuickly. The chimney also means that the stove can be made smokeless.

- For complete combustion of the wood, the se. must have free access to the burning fuel. The fuelbed is on a grate so that air can pass through the charcoal (primary air) and the ash can be removed. Then, combustion and radiation transfer are improved.

Figure 2 shows an example of a 2-pan stove built by a farmer with some help from university researchers . The advantages of this type of stove are twofold: the materials that it employs are available almost everywhere (mud or clay) and only basic technical skills a-e needed to build it.


Tests of performance in similar conditions were set up to compare the new woodstoves alongside the traditional ones. The aim of these tests was to investigate the performance of the stoves in the field and to evaluate the fuelwood saving capabilities of the new stoves (De GAULMYN et al., 1986).

For each test the characteristics dealt with were the efficiency, evaporating time, specific consumption of wood and power output. The efficiency is the ratio between the output energy (heat used to raise the temperature of the sap plus heat used to evaporate water) and the input energy (heat released by the fire). The evaporating time is the time taken in minutes to evaporate one kilogramme of water. It is a measure Of the specific length of the evaporation. The specific consumption is the amount of wood per kilogramme of water evaporated. These 2 parameters are related to the amount of evaporated water because the main function of the process is to remove moisture from a solution. The power output is the average output of power during "he operating period, ie; the ratio of useful energy to total time. The table is a summary of the test results - 10 tests with a traditional, one pan stove and 12 with a new, 2- pan stove.

The results are significantly different between traditional and new stoves. They clearly confirm that a 2-pan stove has a better efficiency and a snorter evaporating time than the traditional one. It saves wood (25%) even though the power output is higher. (De GAULMYN et al., 1986)-.

After this comparative study of traditional and new stoves, a 2-pan model has been designed, built and improved. The extension work in the Sathing Phra area will be caried out with this final model . (The stave is made in the usual way -or mud stoves. The body is built up in layers, in a wood frame, using jars as inserts to leave pot holes and banana wood sticks for the passages and chimney hole. When set, it is carved out to the final form. The report shows the process in pictorial form Ed).

Figure 2 : Example of a two pan stove built during the research phase (in cm)

Table : Summary of Test Results


Before the 1986 sugar season, the extension phase for the new 2-pan stoves in the Sathing Phra area was set up. It was carried out by a committee in some target households. The aim was to introduce the idea of a 2-Dan stove into the peninsula and to build some examples for the farmers who might later want to build one for themselves.

The committee comprises 3 parts: representatives of the university, heads of the villages concerned (''Poo Yai Baan") and extension workers of each district "Kaset Tambon". This collaboration was set up to make contact with people of the area an-d to initiate relations between extension officers and university researchers.

The extension was carried out in a 2-day workshop. During the first day, lectures were given on the advantages and disadvantages of traditional and new stoves. Some slides and a small model of a 2-pan stove were shown. The second day, the technician of the university with help from all the farmers taking part demonstrated how to build a 2-pan stove. A model was built at a volunteer farmer's house in each village. Some simple techniques to test and improve the performance of the stove were given to the farmers. A cement tube -or the chimney and some bricks for the grate were given to the concerned farmers. The same extension procedure was repeated at the end of the 1986 sugar season with different villages.

A large number of farmers have already adopted the new 2-pan stove and more than 200 are now in use. But this process of Diagnosis-Research-Extension in the Sathing Phra area is not finished. An evaluation programme will be set up both for the technical aspects of the stove and the socio-economical aspects of the household.

The technical evaluation will emphasize the performance of the new stove and its durability. It will also be interesting to find out if the saving of wood (the new stove has been designed primarily to save wood) is the important characteristic for the climbers or if they prefer it for its shorter processing time, its greater capacity, its health and comfort aspects...

Preliminary results show that the saving of time is an important factor. Can the time saved provide additional opportunities for the farmers? Can the labour productivity of the household be high enough to compete with salaried employment in town? Is the adoption of a 2-pan stove sufficient for the survival of the household production of palm sugar, or is it necessary to introduce new ideas such as marketing cooperatives or small factories in the villages?


The research of the Thai-French Project is supported since 1982 by the French Embassy, Bangkok, Thailand.

We are grateful to the French Committee Against Hunger (Comite Francais Contre la Faim, 75015 Paris, France) for financial support for the extension phase.

Fig. 3