|Boiling Point No. 33 - May 1994 Number 33 (ITDG - ITDG, 1994, 36 p.)|
by Allen Dong, I-Tech, PO Box 413, Veneta, OR 97478, USA, and Larry Fisher, Mark Kamiya, and Annie Souter, C.I.A.C., PO Box 2231, Davis, CA 95617, USA.
The typical woodstove used for cooking in Nicaragua, illustrated below, is a cement trough that contains an open fire, with metal straps suspended over the trough to support cooking pots. Since there is no chimney, most of the smoke exhausts into the kitchen. This type of cookstove can be improved by building a cover over the top of the cement trough using clay tiles and cement, and leaving round openings as seats for the cooking pots. The pot seats are strengthened by metal rings made from car-wheel rims, which also provide structural support for the surrounding cement and tiles.
We used a 14-inch (36cm) diameter wheel to make 1 3-inch (33cm) pot seats. The wheel rim was cut to make two 1.5 inch-wide rings, each measuring 14 inches (36cm) outside diameter. The rims can be cut with a hack saw, band saw, gas-cutting torch, or arc-cutting electrodes (see photo on page 19). These were placed on top of the trough where they were supported by the trough sides. The trough was covered with clay tiles, and the steel rings formed the pot seats. The tiles were used with the fire glazed surface down towards the fire box. Steel reinforcing rods supported the clay tiles over the trough. Cement was poured on top of the tiles and around the rings to hold them in place, and to seal and insulate the fire box.
If the cook stove is made with two or more pot seats, the first seat, nearest to the fuel door is heated directly by the fire. The next seat does not need direct fire heat. Instead, a brick baffle can be placed under the seat to cause turbulent gas flow. Hot gases flowing laterally from the first burner towards the smoke stack, are directed upwards to the pot on the second seat before entering the chimney. The baffle also slows the gas flow and allows more complete combustion. The distance between the bottom of the pot and the baffle should be 1 to 3 inches (2 to 8cm). The Lorena cookstove, which has a similar design, has up to four seats: the first is heated directly by the fire, and the remaining three are heated by turbulent hot gases flowing laterally from the fire, before going up the chimney. A damper or baffle is needed in the chimney to control the air-flow rate which, in turn, controls the rate at which the wood burns and heats the pots.
The traditional woodstoves can also be adapted, with steel pot seats and a chimney, to produce less smoke in the kitchen and use less wood for cooking. 5
1. Nijaguna, B.T. and S.B. Uppin (1989), 'Wood-burning cook stoves', RERIC International Energy Journal, Vol. II, No. 1, pp.35-60.
Technical assistance was provided by Roger J. Edberg, I-Tech, and Professor William Chancellor, University of California, Davis, California, USA.
When using a two-pot chimney stove, it is important that the second pot-seat is always closed with either a Pot or a cover.