Modifications in traditional Indian cookstove and improved cookstove for efficient design Amit Ranjan Verma*, Rajendra Prasad, Risha Mal, Ratnesh Tiwari,V. K.Vijay Research Scholar Biomass cookstove Division Centre for Rural Development and Technology Indian Institute of Technology – New Delhi India

Energy Access- Present Status & Projections Present Global Scenario 1.3 billion people have no access to electricity and 2.7 billion people rely on biomass and traditional fuels for cooking; More than 95% of these peoples are either in Sub Saharan Africa or in Developing Asia and 84% are in rural areas. Developing Asia Over 1.9 billion people in developing Asia still rely on traditional use of biomass for cooking; More than 100 million each in Bangladesh, Indonesia, Pakistan and Myanmar without access to clean cooking facilities. Contd…

Indian Households Energy Scenario (Census 2011) Over 85% of households in rural areas depend on traditional fuels for cooking, with only 9% using LPG, Kerosene, biogas or electricity. In urban India on the other hand, 76% of households use LPG as the major fuel for cooking and only 18% use traditional biomass fuels for cooking. Between 2001-02 and 2009-10, the percentage of households in rural areas using traditional fuels remained at 85%. Nearly 500,000 premature deaths every year specially among women and children due to exposure to smoke and fumes from burning of biomass. Rural Households in million (%) Urban Households in million (%)

Improved Biomass Cookstove Cook-stoves with chimneys and closed combustion chambers are usually considered improved. Advantages of Improved Biomass Cookstoves Improved Biomass cookstoves can have efficiency ranging from 25-50%, give out very low level of emissions. It saves fuel and time of cooking Emits less CO and others Pollutants. Less harmful effects on human health. Classification of Biomass Cookstoves Open fire and shielded fire Portable and fixed cookstoves Single pot and multiple pot cookstoves Combustion and Gasifier cookstoves

The setup at IIT Delhi

The following tests are regularly conducted in the laboratory as per the Indian BIS for performance evaluation of the Biomass Cookstoves. Measurement of the Calorific value of the fuel . Measurement of the Moisture Content of the fuel . Measurement of Burning Capacity (Rate) of the stoves Thermal efficiency of a Cookstove using Water Boiling Tests Stove Emissions

Parameters or Factors affecting the Performance of cookstove Fuel type and size The size of wood considerably affects combustion. Large or thick piece of wood are difficult to burn and emit more smoke. Small pieces tend to give higher flames and burn for a shorter time than the same mass of bigger pieces. For this study Fuel type and size were fixed according to the BIS standards. Eucalyptus wood cut from the same log into size of 3 cm × 3 cm square cross-section and length of half the diameter of combustion chamber.  Moisture content of fuel All biomass contains some water which must be evaporated before the biomass can burn. Moisture content fixed of 5 (±1) % on wet bases to avoid variation in calorific value

Burning rate Burning rate define how much amount of fuel can be burn in given time period, in given cookstove. All stove have optimal burning rate on either side of which efficiency decreases. This optimal is not fixed, but depends on various factors such as size of grate, distance between grate and pot bottom, presence or absence or secondary air provision.

Support height or Gap It is height or gap between top plate of cookstove and pot bottom. Stove with small support height although have high efficiency, but they also reduce the amount of gas that can flow through the gap and thus limit the firepower. In case of larger fire either smoke will pour out the stove door, or else the fire will be choked and suffer poor combustion or simply not build up to desire power . Important to optimize the support height for each design of stove.

Primary, Secondary and Excess air Primary air is air provided at the bottom of the grate and from door of biomass cookstove. It helps in the burning of wood or charcoal on grate. A substantial proportion of volatiles escape unburnt or partially burnt along with the combustion product, resulting in a loss of the heating value of wood. Appropriate injection of secondary air in column of unburnt volatiles is expected to retrieve some of the heat. Although the role of primary and secondary air has been recognized, but incorporation of feature in design is not so simple. The optimum amount of each, the point of injection of secondary air, the effect of their temperature etc. are not yet very well understood.

Excess air is required to ensure proper burning of wood and volatiles. The amount of secondary air to be provided depends on the fraction of the oxygen in primary air left unused and combustion gases left unburnt. The theoretical amount of air required for stoichiometric combustion of wood can be calculated from its elemental analysis. To calculate the actual amount of air required, the theoretical amount is multiplied by excess air factor which is generally between 1.5 to 2.5. The amount of air required for stoichiometric combustion in excess of theoretical minimum is known as excess air. Excess air is required to ensure proper burning of wood and volatiles. The amount of excess air required depends on the degree of mixing or turbulence available in combustion chamber.   

Grate The use of grate in a stove is expected to facilitate the accessibility of air to a fuelbed. It promotes the combustion of charcoal that remains after the volatiles are driven out of wood. In general grate will generate higher power outputs from a given fuelbed area.

Modifications in traditional Indian cookstove

Traditional biomass cookstove in India are generally ‘U’ shaped with three side closed and front open. Traditional Indian cookstove simulated in lab Traditional Indian cookstove

Modification made in traditional Indian biomass cookstove Performance Evaluation of Traditional Indian cook stove S.No. Efficiency   CO(g/MJ) PM(mg/MJ) 1 23.50 10.67 553.28 Modification made in traditional Indian biomass cookstove Traditional Indian cookstove with grate

Traditional Indian cook stove with grate Experiments have been carried out and it has been found that traditional biomass cookstove with grate has 10% more thermal efficiency as compared to traditional biomass cookstove without grate. There is some reductions in the particulate matter generated but there did not appear any reduction in the CO emissions per unit of energy delivered to the cooking pot. S.No. Efficiency   CO(g/MJ) PM(mg/MJ) 1 27.065 10.38 447.005

Modifications in improved cookstove for Efficient design

Approaches to make modification in existing design Efficiency and emission performance of Improved biomass cookstove was tested in according to Indian BIS (As per Draft Revision Standard 2012), and the following results were obtained: Natural draft cookstove Thermal Efficiency was lower than BIS LIMITS. Hence it has been decided to modify existing design so that it could meet the Indian BIS requirement. Approaches to make modification in existing design Theoretical design procedure Results of parametric study S.No. Power output(KW) Thermal Efficiency PM(Mg/Mjd) CO(g/Mjd) 1 1.42 22.86 167.02 3.48 2 1.26 22.38 178.32 4.51 Average 1.34 22.49 172.67 3.995

Theoretical dimension(cm) Theoretical design procedure In this approach it has been decided to check the dimension of biomass cookstove according to theoretical design procedure given by K.K. Prasad (A woodstove compendium 1981). Conclusion from theoretical design S.no Parameters Theoretical dimension(cm) Actual dimension(cm) 1 Inner Diameter for combustion chamber 21.61 18 2 Vertical distance between grate and pan bottom(h) 10.52 20

Parametric study Theoretical dimensions of cookstove was not meeting with the actual dimensions. So it has been decided to follow parametric study results to make modification in existing model and hence different set of experiments have been concluded to modify existing design parameter like : Grate porosity Height of grate from base Decrease in the height between top plate and lid and Varying burning rate without changing the back bone of existing cook stove.  

S.No. Support Height(cm) Other Modification Power(KW) Efficiency CO(g/Mjd) P.M.(Mg/Mjd) 1 5 none 1.1 23.8 5.5 218 2 23.6 5.7 247 3 Decreased to 0.5 Fuel loading door half 23.5 12 385 4 1.4 29.9 9.1 509 Grate increased to 5.5 29.7 10 235 6 28.5 9.6 245 7 1.2 24.3 8.9 419 8 1.3 32.5 8.4 378 9 34.3 251 32.4 7.9 345 11 Grate at 3 31.9 7.7 381 Grate increased to 7 15 771 13 0.8 7.6 465 14 35.4 8.1 395 Decreased to 1 0.9 25.6 9.7 364

16 Decreased to 0.5 New Grate with large porosity 0.8 24.3 9.4 404 17 1.1 27.5 9.8 415 18 1st Grate with large porosity raised to 5.5 cm, 2nd original grate at 3 28 9.6 380 19 Grate increased to 7 1.4 35.8 6.6 389 20 1.6 32.5 14 878 21 1.2 5.4 377 22 36.6 5.9 423 23 34.1 6.2 413 24 Grate increased to 7, sec air holes present in base closed 1 28.6 8.2 741 25 New Grate height 7 less in diameter 28.3 12 459 26 Grate of vikram 6 used at increased height of 5.5 31.3 7.2 522 27 none 1.8 31.5 635 Grate of vik6 h= 3cm 30.5 6.4 409 29 Grate of vik6 h=7cm 7.6 515 30 Grate h = 8 33.6 6.7 31 Grate of vik 6 = 8cm 33 8.8 32 Grate h = 7cm, fuel loading door half 31.7 591

33 Decreased to 0.5 Grate height 7cm increased base height from ground 3 inches 1.2 33.8 5.6 435 34 Grate h = 3 with aluminum sheet 1.1 31 6.6 626 35 New grate with high porosity h=7 1 29.6 7.1 407 36 1st grate with large porosity raised to 8 cm, 2nd original grate at 5 cm 32 8.7 405 37 Decreased to 0.8 Original grate 8 cm 31.5 7.6 370 38 1.4 31.8 751 39 25.8 6.8 884 40 1.6 32.6 6.2 735 41 1.5 30.2 5.1 458 42 Original grate 3 cm 29.9 3.8 440 43 28.1 3.4 438 44 Decreased to 1.2 vik 6 grate 3 cm, 1.3 27.3 4.3 414 45 28.7 4.7 421 46 vik 6 grate 4 cm, 27.5 463 47 Vik 7 grate 5cm 1.34 27.92 5.21 353.43 48 1.31 27.25 6.31 400.73 49 1.23 25.49 5.01 358.66 50 1.36 28.22 3.74 364.47

Conclusion from parametric study Modification made in Existing Design Parametric study concluded that combination of different parameter with given modification can meet the Indian BIS standards. Modification made in Existing Design Modification in Grate height: Distance between base plate and grate is increased from 4 to 5 cm. Modification made in Support height: Distance between top plate of cookstove and pot is decreased from 5 to 1.2 cm.

Natural draft biomass cookstove Without any Modification With Modification

S.No. Power Output(KW) Thermal Efficiency PM(mg/MJd) CO(g/mJd) 1 1.34 27.92 353.43 5.21 2 1.23 25.49 358.66 5.01 3 1.36 28.22 364.47 3.74 Average 1.31 27.22 358.85 4.65

Conclusion Experimentally it has been concluded that modifications can be done in existing cook stoves for enhanced efficiency and low emissions by varying parameters such as Grate porosity, Height of grate from base, Height between top plate and lid and Burning rate without making major changes in the structure of existing cookstove such as diameter and secondary air inlet points.

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