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Highly efficient firewood-fuelled cooking stoves
Biomass 20 (1989) 125-128
Highly Efficient Firewood-Fuelled Cooking Stoves Cui Yuanbo Chinese Academy of Agricultural Engineering Research and Planning, Beijing, People's Republic of China
ABSTRACT
This paper discusses the development and benefits of the modem 'highly efficient'firewood-fuelled cooking stove in China. It introduces the highly efficient firewood stove, a highly efficient firewood stove incorporating a water-boiling device and NG-II type composite highly efficient firewood stove. The thermal efficiency of this type of stove can reach 25-30%. This type of stove is not only highly efficient but also hygienic. Key words: cooking stoves, highly efficient, firewood-fuelled, thermal efficiency, woodfuel.
Cooking stoves have a long history in China, stretching back several thousand years. Their development has passed through four basic stages: primitive stoves, old-style stoves, improved stoves and highly efficient stoves. The primitive stove consists of three stones supporting a pot over the fire. It is still used in remote areas and in field operations. The old-style stove consists of a framework of bricks, mud bricks or stones above which the pot is placed. The stove is open at one side for feeding in the firewood. Stoves of this type have a low thermal efficiency, generally 8-10%, and are very unhygienic. The improved stove is based on the old-style stove but is equipped with a grate and chimney which improves combustion and raises the thermal efficiency to 12-15%. It is also more hygienic in use. The highly efficient stove was developed during the 1980s and improves on the combustion and energy utilization of the improved stove. The thermal efficiency (the efficiency when taking water from room temperature to boiling point) of this type of stove can reach 25-30%. A typical modern wood-fuelled cooking stove is shown in Fig. 1. It consists of a grate, a combustion chamber, a firewood inlet, air inlet, fire 125 Biomass 0144-4565/89/S03.50 -- © 1989 Elsevier Science Publishers Ltd, England. Printed in Great Britain
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Fig. 1. Structureof the highlyefficientfirewood stove. 1, Chimney;2, smoke outlet; 3, fire fencingring;4, firebody;5, grate; 6, firewood inlet;7, air inlet. fencing ring, smoke outlet and chimney. Natural ventilation is used. The shape of the combustion chamber is usually either opening (spherical) or semi-opening (drum-shaped) and thermal insulation material is fitted closely around the chamber to reduce heat losses. To increase heat exchange between the flame, the smoke and the bottom of the cooking pot, the heat-absorbing surface of the cooking pot is placed in the hottest area of the flame. Usually the vertical distance between the bottom of the pot and the grate is about 14-16 cm. In addition, the fire fencing ring and smoke feedback channel above the combustion chamber contain the flame and hot smoke in order to prolong the period of contact with the cooking pot. This type of stove is not only highly efficient but is also hygienic. Further modifications have improved the heat recovery performance of these stoves. For example, provision for a second cooking pot or the installation of a water-boiling device (Fig. 2) can significantly increase the heat exchange efficiency. In recent years, composite materials have been introduced into the construction of stoves. Factories have developed stoves made partially or entirely from composite materials. This not only ensures stable performance but also simplifies building procedures and speeds up production, and is thus beneficial to the popularization of firewoodfuelled stoves. Figure 3 shows an NGII-type composite highly efficient firewood stove. In comparison with the improved stove, the highly efficient stove can save one-third to one-half of firewood. This has many benefits. Not only
Highly efficient firewood-fuelled cooking stoves
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Fig. 2.
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Highly efficient firewood stove incorporating a water-boiling device. 1, Water tank; 2, coiling pipe; 3, water outlet tap.
2-
JS
[////////, Fig. 3.
NG-II type composite highly efficient firewood stove. 1, Smoke outlet; 2, upper part of firebody; 3, lower part of firebody; 4, grate; 5, fuel feed entrance.
does it reduce fuel costs for the user, but it also saves firewood, grass and man-hours spent collecting firewood, making it possible to return crop residues and stalks to the fields, and freeing manpower to develop animal husbandry, weaving and knitting industries. The use of highly efficient firewood stoves also eases the energy shortage in rural areas, leading to decreased destruction of vegetation and forests and the promotion of an ecologically healthy cycle. With more vegetation saved by using firewood saving stoves a large portion of stalk will return to the field to refresh the soil with organic
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materials, which in turn will raise the fertility of the land. The extensive application of firewood saving stoves in Dafeng County of Jiangsu Province has allowed an annual return of 150 000 tonnes of stalk to the field, raising the organic content of the soil from 1% in 1973 to 1.21% in 1982; and the number of stock animals has increased 2-3 times. During its sixth 'Five Year Plan', China has spread highly efficient firewood stoves to 40 million households and plans to spread them further during the seventh 'Five Year Plan'. By the end of 1990 it is expected that 60% of rural households in China will use highly efficient firewood stoves.
Highly Efficient Firewood-Fuelled Cooking Stoves Cui Yuanbo Chinese Academy of Agricultural Engineering Research and Planning, Beijing, People's Republic of China
ABSTRACT
This paper discusses the development and benefits of the modem 'highly efficient'firewood-fuelled cooking stove in China. It introduces the highly efficient firewood stove, a highly efficient firewood stove incorporating a water-boiling device and NG-II type composite highly efficient firewood stove. The thermal efficiency of this type of stove can reach 25-30%. This type of stove is not only highly efficient but also hygienic. Key words: cooking stoves, highly efficient, firewood-fuelled, thermal efficiency, woodfuel.
Cooking stoves have a long history in China, stretching back several thousand years. Their development has passed through four basic stages: primitive stoves, old-style stoves, improved stoves and highly efficient stoves. The primitive stove consists of three stones supporting a pot over the fire. It is still used in remote areas and in field operations. The old-style stove consists of a framework of bricks, mud bricks or stones above which the pot is placed. The stove is open at one side for feeding in the firewood. Stoves of this type have a low thermal efficiency, generally 8-10%, and are very unhygienic. The improved stove is based on the old-style stove but is equipped with a grate and chimney which improves combustion and raises the thermal efficiency to 12-15%. It is also more hygienic in use. The highly efficient stove was developed during the 1980s and improves on the combustion and energy utilization of the improved stove. The thermal efficiency (the efficiency when taking water from room temperature to boiling point) of this type of stove can reach 25-30%. A typical modern wood-fuelled cooking stove is shown in Fig. 1. It consists of a grate, a combustion chamber, a firewood inlet, air inlet, fire 125 Biomass 0144-4565/89/S03.50 -- © 1989 Elsevier Science Publishers Ltd, England. Printed in Great Britain
126
Cui Yuanbo
Fig. 1. Structureof the highlyefficientfirewood stove. 1, Chimney;2, smoke outlet; 3, fire fencingring;4, firebody;5, grate; 6, firewood inlet;7, air inlet. fencing ring, smoke outlet and chimney. Natural ventilation is used. The shape of the combustion chamber is usually either opening (spherical) or semi-opening (drum-shaped) and thermal insulation material is fitted closely around the chamber to reduce heat losses. To increase heat exchange between the flame, the smoke and the bottom of the cooking pot, the heat-absorbing surface of the cooking pot is placed in the hottest area of the flame. Usually the vertical distance between the bottom of the pot and the grate is about 14-16 cm. In addition, the fire fencing ring and smoke feedback channel above the combustion chamber contain the flame and hot smoke in order to prolong the period of contact with the cooking pot. This type of stove is not only highly efficient but is also hygienic. Further modifications have improved the heat recovery performance of these stoves. For example, provision for a second cooking pot or the installation of a water-boiling device (Fig. 2) can significantly increase the heat exchange efficiency. In recent years, composite materials have been introduced into the construction of stoves. Factories have developed stoves made partially or entirely from composite materials. This not only ensures stable performance but also simplifies building procedures and speeds up production, and is thus beneficial to the popularization of firewoodfuelled stoves. Figure 3 shows an NGII-type composite highly efficient firewood stove. In comparison with the improved stove, the highly efficient stove can save one-third to one-half of firewood. This has many benefits. Not only
Highly efficient firewood-fuelled cooking stoves
127
/1
l ill
Fig. 2.
/ / I
t
Highly efficient firewood stove incorporating a water-boiling device. 1, Water tank; 2, coiling pipe; 3, water outlet tap.
2-
JS
[////////, Fig. 3.
NG-II type composite highly efficient firewood stove. 1, Smoke outlet; 2, upper part of firebody; 3, lower part of firebody; 4, grate; 5, fuel feed entrance.
does it reduce fuel costs for the user, but it also saves firewood, grass and man-hours spent collecting firewood, making it possible to return crop residues and stalks to the fields, and freeing manpower to develop animal husbandry, weaving and knitting industries. The use of highly efficient firewood stoves also eases the energy shortage in rural areas, leading to decreased destruction of vegetation and forests and the promotion of an ecologically healthy cycle. With more vegetation saved by using firewood saving stoves a large portion of stalk will return to the field to refresh the soil with organic
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Cui Yuanbo
materials, which in turn will raise the fertility of the land. The extensive application of firewood saving stoves in Dafeng County of Jiangsu Province has allowed an annual return of 150 000 tonnes of stalk to the field, raising the organic content of the soil from 1% in 1973 to 1.21% in 1982; and the number of stock animals has increased 2-3 times. During its sixth 'Five Year Plan', China has spread highly efficient firewood stoves to 40 million households and plans to spread them further during the seventh 'Five Year Plan'. By the end of 1990 it is expected that 60% of rural households in China will use highly efficient firewood stoves.