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Research into cooking and heating applications of down-draught stoves
[top] [end]IntroductionTraditional stoves provide necessary heating in many situations where the temperature drops at night, in high altitude regions and/or during the winter. However, these stoves emit smoke inside the room and pollute the air, due to incomplete combustion.It is necessary to develop a cleaner burning stove with higher efficiency. The hot flue gases can be used directly for keeping the room warm without polluting the air inside. For sixteen years, the wood-burning stove group of Eindhoven University of Technology in the Netherlands and the Institute of Fuel Research and Development (BCSIR) in Bangladesh have been jointly pursuing research on the clean combustion of wood. The project has been sponsored by the EEC. In general, the combustion products of wood are carbon dioxide (CO2) water vapour, carbon monoxide (CO), particulates and polycyclic organic matter. The last three pollutants are very hazardous to human health. The yardstick for measurement of clean combustion is the CO/CO2 ratio in the combustion gases. For reasonably clean combustion this ratio must be less than 0.1%. The operating principle of the stove, in contrast to that of conventional designs, is that the flow of air is in the same direction as that of the combustion gases and fuel. By applying this principle, models have been developed for cooking and other heating purposes. These stoves emit very small amounts of carbon monoxide.
[top] [end]Types of down-draught stove suitable for domestic purposes[top] [end]Down-draught single mouth cooking stoveThe model consists of three main parts as in Figures 1a and 1b: a) Combustion chamberb) Pot hole c) Chimney [top] [end]a) Combustion chamberThe chamber is made of bricks covered with mud. At the bottom of the chamber, there is a grate. The grate is made by placing metal strips 3 mm (1/8 inch) thick, 10 mm apart. The distance between the grate and the top of the fire chamber is 152 mm (6 in). The chamber is connected with a pot hole through a 76 mm (3 in) diameter cylindrical hole passage from below the grate.[top] [end]b) Pot holeThe pot hole is placed between the fire chamber and the chimney and it has a mouth of 240 mm (10 in) diameter. The two longitudinal sides of the pot hole are made of bricks and covered with mud. Its bottom is made slanting downwards from the centre towards both sides along the direction of the flow of the combustion gases. This pot hole is then connected with the chimney through a 76 mm diameter cylindrical hole.
[top] [end]c) ChimneyA chimney 1 m (40 in) high and 76 mm (3 in) diameter is placed on a flat platform at a distance of 100 mm from the pot hole for creating necessary draught. This chimney leads the flue gases out of the stove.[top] [end]d) Type of potBoth round-bottomed and flat-bottomed vessels can be used in the down-draught stove, but there should not be any empty space between the pot and the stove. The stoves are suitable for cooking food for a family of 7-8 members.
[top] [end]Down-draught single-mouth cooking stove coupled with ovenThe main difference between this model and the previous one is the 'oven' which is fitted at the bottom of the chimney of the down-draught single mouth cooking stove (Figures 2a and 2b). The oven is kept warm by the spent flue gases which come out of the stove, The oven is double-walled. The flue gases pass between the walls and the oven gets heated, The maximum temperature attained in the oven is 200-250°C depending on feeding rate of fuel in the fire-box, when the cooking medium reaches its boiling point, the utensil containing the food is removed from the stove and kept in the hot box. The open mouth covered with another utensil containing fresh food items.The remaining cooking in the oven is completed simultaneously as the fresh food items cooked in the cooking mouth of the stove, The efficiency of the stove is 21.18%.
[top] [end]Down-draught double-mouth cooking stoveThis model is similar to a down-draught single-mouth cooking stove except that it has two pot holes side by side as in Figures 3a and 3b.
[top] [end]Combustion qualities
In this study, good combustion is characterized by a low CO concentration, no smoke formation, low concentrations of organic compounds in the flue gases and high temperatures near the fuel bed. High temperature at the fuel bed, accompanied by high temperature of the flue gases can be used in various applications such as drying, smoking, baking, tandur-making, passive space heating etc. [top] [end]Test resultsVariation in CO concentration in the flue-gases during the burning of fuelwood (cooking tests) for different kinds of down-draught stoves such as single-mouth, double-mouth with oven etc. are shown in Table 1. In this table, the CO concentration in the conventional improved cooking stove could not be measured as the values measured were more than 1% (beyond the range of measuring capacity of the equipment).The efficiency shown in Table 1 refers to the efficiency of heat transfer from the combustion gases to the cooking pot. It was measured by determining the rise in temperature and the amount of water evaporated from the cooking pot. The food cooked during the tests comprised: Chicken curry 1 kg Dal 0.25 kg Rice 0.8 kg [top] [end]Smoke output from down-draught stoveNo smoke was visible at the outlet of the chimney. A white paper was kept 60 mm above the outlet of the chimney; no blackening of the white paper was observed over a period of one minute. Keeping the paper in situ any longer lead to charring of the paper because of the high temperature of the flue gases. In the case of the improved stove, smoke was clearly visible during the pre-boiling period. During the simmering stage, smoke formation was considerably reduced, but it was never smoke free.[top] [end]Conclusions
Table 1: Cooking tests using different conventional and down-draught stoves Conventional stoves
Down-draught stoves
[top] [end]Contents: Boiling Point 40: Household energy and health
Categories: Boiling Point 40| Improved Stoves | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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02 August 2007; Last edited:
02 August 2007; Version: 0 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Pagename: ResearchIntoCookingAndHeatingApplicationsOfDown-draughtStoves @HEDON: YEGA | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
