Charcoal Stove Testing at Dian Desa, lndonesia

Charcoal is a widely used and sold fuel in Java, the most populous island of Indonesia. It is usually made in the mountainous forest areas and then brought down to the main markets in the cities and towns. It is rarely used in rural areas. Most charcoal is sold by the kilogram, often packed in 1 kg plastic bags. The price in Yogyakarta in February 1983 was £0.10/kg (£1 = Rp1000). Kerosene, on the other hand, was only £0.075/kg in 1982, increasing to £0.125/kg in January 1983. The higher energy content of kerosene (44 MJ/kg vs 29 MJ/kg) and the higher efficiency of kerosene wick and pressure stoves, compared to charcoal stoves, make it cheaper to use than charcoal. For use in cooking however the bad smell of kerosene, the after taste it leaves, the heavier and more expensive stove it requires, and the inability to use it for grilling, means that there still is a large market for charcoal.

There are a few metal charcoal stoves produced but the vast majority are made of pottery. Charcoal pottery stoves 'anglos' are one of the major products of potters near Yogyakarta. The one piece anglos (Figure 1) sell for £0.075 in the potter's village and for up to £0.15 in a store, for the medium size stove. Under heavy daily use (eg. food vendors, and restaurants) they last less than two months.

In 1980 and 1981 Dian Desa made a number of new prototype charcoal stoves, but whilst they were faster than the traditional anglo they could not be made easily or cheaply by local artisans so no further work was done.

In 1983 Aryanto Soedjarwo and Bill Stewart began some new experiments with charcoal stoves. A simple prototype was made by lining a traditional anglo with cut pumice stone - the most easily available refractory insulation. m e pumice is mined in East Java and is widely available in hardware stores across Java. Its main use is for scrubbing stones, so the pumice available is in the form of 6-10 cm diameter balls. It costs £0.30/kg when purchased in small quantities. The balls were cut with a hacksaw and wedged into the stove to form a layer of insulation -about 5cm thick. The pieces were held in place by a cement mortar. The cement will crack under prolonged heat and a new production procedure is necessary to produce long lasting stoves. For the purpose of the testing this was not a problem. About 300 gm of pumice were used in the stove. Initial tests showed that there was not enough air flow through the grate because the insulation had blocked some of the holes. These holes were bored out to increase the air flow. The following table shows the grate areas for the three stoves tested.

STOVE	Hole Area	Total Grate Area	Holes
	sq cm	sq cm	%
Traditional Anglo	27	176	15
Pumice lined Anglo	23	133	17
Thai bucket	8	154	30

 

Test Procedure

me stoves were filled to capacity - 300 gm for the traditional anglo and Thai bucket, and 250 gm for the pumice lined anglo. A few pieces of charcoal were immersed in 10 gm of kerosene and placed back on the bed of charcoal and lit. Aluminium pots, 25 cm diameter, with lids were filled with 2 litres of water, brought to the boil, and boiled for 30 minutes (BP S30). None of the stoves had doors and all. The stoves were fanned to increase burning rates. Four tests were done on each stove. Results previously reported in Boiling Point No 4, for a traditional Kenyan charcoal stove and a Kenyan charcoal cement-vermiculite stove are shown for comparison (Table on following page).

FIGURE

 

Test Conclusions

1. The traditional Indonesian ceramic charcoal stove is 20X more thermally efficient than a traditional Kenyan metal charcoal stove. Apart from small differences due to the variations in test conditions, such as quality of charcoal, the improvement in thermal efficiency may be attributed to the higher charcoal bed temperature achieved as a result of the difference in stove wall material, ie metal v. insulating pottery.

2. The pumice-insulated stove consumed less fuel than the traditional ceramic stove. Overall it was 22% more thermally efficient.

3. The Thai bucket consumed slightly more fuel than the traditional ceramic stove, but the evaporation rate was significantly faster. Overall it was 19% more efficient.

4. Given the high cost of charcoal in relation to the stove cost (1.5 kg charcoal costs the same as one stove) a stove that gave significant savings in fuel should be potentially attractive to consumers.

 

FIGURE

FIGURE