Component-6 Improving Energy Efficiency and Emission ......Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Component-6 Improving Energy Efficiency and Emission Characteristics

Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6

Component-6

Improving Energy Efficiency and Emission Characteristics of Biomass Cooking Stoves by Incorporating Beneficial Aspects of Different Kilns

Principal Investigator

Md. Mominur Rahman

Assistant Professor Department of Chemical Engineering, BUET

Co-Investigator

Dr. Syeda Sultana Razia Professor

Department of Chemical Engineering, BUET

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TABLE OF CONTENTS

LIST OF TABLES ............................................................................................................... 6-iv

LIST OF FIGURES ............................................................................................................. 6-vi

ABSTRACT ......................................................................................................................... 6-vii

CHAPTER 1 BACKGROUND .......................................................................................... 6-1

CHAPTER 2 EXPERIMENTAL ...................................................................................... 6-6

2.1. Design philosophy ........................................................................................................ 6-6

2.1.1. Socio-economic and environmental consideration ................................................... 6-6

2.1.2. Technical consideration ................................................................................................... 6-6

2.2. Design Basis ................................................................................................................. 6-7

2.3. Construction features of the stoves .............................................................................. 6-8

2.3.1. Combustion chamber height ............................................................................................ 6-9

2.3.2. Pot mouth ......................................................................................................................... 6-9

2.3.3. Grate ................................................................................................................................ 6-9

2.3.4. Stack or Chimney ............................................................................................................ 6-9

2.3.5. Wall thickness of combustion chamber ......................................................................... 6-10

2.3.6. Inlet air (for combustion) hole diameter ........................................................................ 6-10

2.3.7. Stoke hole or secondary air inlet ................................................................................... 6-10

2.3.8. Double wall ................................................................................................................... 6-10

2.3.9. Ash pit and ash hole....................................................................................................... 6-10

2.4. Mud built stove construction procedure ..................................................................... 6-10

2.5. Cookstoves performance evaluation .......................................................................... 6-11

2.5.1. Water Boiling Test (WBT) ............................................................................................ 6-11

2.5.1.1. Time to boil (∆tc) ..................................................................................................... 6-12

2.5.1.2. Temperature corrected time to boil (∆tT) ................................................................. 6-12

2.5.1.3. Overall stove thermal efficiency ( ) ........................................................................ 6-12

2.5.1.4. Burning rate (rb) ....................................................................................................... 6-12

2.5.1.5. Specific fuel consumption (SC) ............................................................................... 6-13

2.5.1.6. Temperature corrected specific fuel consumption (SCT) ......................................... 6-13

2.5.1.7. Temperature corrected specific energy consumption (SET) .................................... 6-13

2.5.1.8. Firepower (FP) ......................................................................................................... 6-13

2.5.1.9. Useful/cooking power (FPuseful) ............................................................................... 6-14

2.5.1.10. Turndown ratio ...................................................................................................... 6-14

2.5.1.11. Environmental stove index (ESI)........................................................................... 6-14

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2.5.2. Controlled cooking test (CCT) ...................................................................................... 6-15

2.5.3. Emission measurements ................................................................................................ 6-15

2.5.4. Temperature profile ....................................................................................................... 6-15

CHAPTER 3 RESULTS AND DISCUSSIONS ............................................................. 6-24

3.1. Results and discussions on WBT performances ........................................................ 6-24

3.1.1. Temperature and draft profile of the stoves in WBT ..................................................... 6-24

3.1.2. Thermal performance of stoves in WBT ....................................................................... 6-26

3.1.3. Emission performances of stoves in WBT .................................................................... 6-30

3.1.4. Overall performances of the stoves in WBT ................................................................. 6-38

3.2. Results and discussions on CCT performances .......................................................... 6-39

3.2.1. Temperature and draft profile of stoves in CCT ............................................................ 6-39

3.2.2. Thermal performances of stoves in CCT ....................................................................... 6-40

3.2.3. Emission performances of stoves in CCT ..................................................................... 6-42

3.2.8. Benchmark emission of all stoves for cooking parboiled rice (gm/kg parboiled rice cooking) using rice straw as a fuel during CCT ..................................................................................... 6-46

3.2.9. Benchmark emission reduction by different stoves for cooking parboiled rice using rice straw as fuel during CCT considering Grameen Shakti-single pot concrete stove as reference. .......... 6-47

3.2.10. Benchmark emission reduction by different stoves for cooking parboiled rice using rice straw as fuel during CCT considering Grameen Shakti-double pot concrete stove as reference. ..... 6-48

CHAPTER 4 CONCLUSIONS ........................................................................................ 6-49

REFERENCES .................................................................................................................... 6-50

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LIST OF TABLES

Table 1.1. Traditional stove emissions (g/kg fuel) from laboratory tests using water-boiling test to determine emissions of biomass fuel types in Indian traditional cookstoves (Source: Venkataraman et al., 2010) ..................................................................... 6-2

Table 2.1. Design basis and calculated values of different parameters for single pot cookstove ............................................................................................................................... 6-7

Table 2.2. Design basis and calculated values of different parameters for multi pot cookstoves (double and triple pot stoves) ................................................................................ 6-8

Table 3.1.1. Temperature and draft profile of the stoves during WBT (cold and hot start in high power phase, and simmering in low power phase) ..................................... 6-25

Table 3.1.2. WBT performance parameters (boiling time, burning rate, specific fuel and energy consumption, firepower, cooking power, turn-down ratio, and overall thermal efficiency) of stoves ............................................................................... 6-28

Table 3.1.3. Benchmark fuel and energy consumption values of stoves for entire WBT (5 liter water) .................................................................................................................. 6-30

Table 3.1.4. Emission characteristic and combustion efficiency of stoves for WBT (cold and hot start-high power phase; simmering-low power phase). Compositions are given in wet basis. ......................................................................................................... 6-31

Table 3.1.5. Emission ratios of all stoves for WBT (cold and hot start-high power phase; simmering-low power phase) .............................................................................. 6-33

Table 3.1.6. Average emission ratios of all stoves for entire WBT ..................................... 6-34

Table 3.1.7. Emission factors by fuel mass on a pollutant mass basis (gm/kg D.F.) of the stoves during different power phases of WBT .................................................... 6-35

Table 3.1.11. Benchmark efficiency values and environmental stove index of all cookstoves for WBT .............................................................................................................. 6-39

Table 3.2.1.Temperature and draft profile of all stoves during CCT .................................. 6-40

Table 3.2.2. Fuel consumption and cooking time of all stoves during CCT (parboiled rice cooking) .............................................................................................................. 6-41

Table 3.2.3. Fuel and energy consumption per parboiled rice cooking and fuel/energy saving and cooking time saving of the stoves considering Grameen Shakti-single pot and double pot concrete stove as the comparison base separately............................. 6-41

Table 3.2.4. Emission characteristic and combustion efficiencies of different stoves during CCT (parboiled rice cooking) ............................................................................. 6-43

Table 3.2.5. Average emission ratios of the pollutants with respect to CO2 during CCT (parboiled rice cooking) ...................................................................................... 6-43

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Table 3.2.6. Average emission factors of CO2, CO, NO and CH4 by fuel mass basis (gm/kg D.F.) of all stoves using rice straw as fuel during CCT and WBT ..................... 6-44

Table 3.2.7. Average emission factors of CO2, CO, NO and CH4 mass by fuel energy content basis (gm/MJ) of all stoves using rice straw as fuel during CCT and WBT ....... 6-45

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LIST OF FIGURES Figure 2.1. Isometric, top and bottom view of BUET-single pot mud stove. ...................... 6-16

Figure 2.2. Isometric, top and bottom view of BUET-double pot mud stove (circular grate) 6-17

Figure 2.3. Isometric, top and bottom view of BUET-double pot mud stove (elliptical grate). ............................................................................................................................. 6-18

Figure 2.4. Isometric, top and bottom view, and front elevation of BUET-triple pot mud stove. ................................................................................................................... 6-19

Figure 2.5. Isometric view of Grameen Shakti-double pot concrete stove .......................... 6-20

Figure 2.6. Isometric view of Grameen Shakti-double pot concrete stove .......................... 6-20

Figure 2.7. Different phases (shaping, curing) of constructing BUET stove models .......... 6-21

Figure 2.8. Dimensions of the cooking pot that was used in WBT and CCT ...................... 6-22

Figure 2.9. WBT run on stove models of BUET and Grameen Shakti. In the figures: © means ‘circular grate’; (E) means ‘elliptical grate’ and GS means ‘Grameen Shakti’. . 6-22

Figure 2.10. CCT run on stove models of BUET and Grameen Shakti. In the figures: © means ‘circular grate’; (E) means ‘elliptical grate’ and GS means ‘Grameen Shakti’. ................................................................................................................ 6-23

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ABSTRACT

The objectives of this research work were to design and develop biomass based low cost energy efficient and low polluting household cookstoves targeting the poor who otherwise cannot afford to carry the overload of health cost due to indoor air pollution and purchasing or collecting excessive biomass fuel required for their existing traditional cookstove. Since climate change at present is a burning issue around the globe, this research work also focuses on reducing green house gas (GHG) emissions from the existing traditional household cookstoves through replacement with better designed stoves. Besides, with the goals in mind for conserving biomass fuel, reducing cooking time and reducing deforestation, four mud built stoves with double chimney were designed and developed to fit the average household size in context of Bangladesh. Developed stoves were named as: BUET-single pot mud stove, BUET-double pot mud stove (circular grate), BUET-double pot mud stove (elliptical grate), and BUET-triple pot mud stove. All the models were provided with preheating facility of combustion air to facilitate better combustion. Two other improved cookstove (ICS) models were brought from a leading NGO (Grameen Shakti) who is actively involved in disseminating ICSs in the local market. These models were named as Grameen Shakti-single pot concrete stove and Grameen Shakti-double pot concrete stove. Both stoves were single chimney concrete stoves and were claimed to be the most popular variant among the general households in Bangladesh. Standard water boiling test (WBT) and controlled cooking test (CCT) were performed on all the six stove models (four BUET models and two Grameen Shakti models) to compare thermal performance, emission performance, cooking time saving, fuel and energy saving, and also emission reduction potential. Within the group, i.e., single pot stoves and multi pot stoves, BUET-single pot mud stove showed superiority over Grameen Shakti-single pot concrete stove and BUET-double pot and BUET-triple pot mud stoves showed their superiority over Grameen Shakti-double pot concrete stove respectively both in WBT and CCT in every respect.

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CHAPTER 1 BACKGROUND

Bangladesh is the 9th most populous country in the world with an estimated population of 152.518 million and the 6th most densely populated country (1034 persons/square km) in the world. Around 50% of the entire country people lives below the international poverty line ($ 1.25 a day). With an average household size of 4.4 persons, there are about 32.173 million households in Bangladesh of which 31.863 million (99%) households are general type. About 72% of the entire population in Bangladesh lives in rural area. (GACC and USAID, 2012; BBS, 2011).

Only 40% of the total population and 30% of the rural people are connected to the electricity grid (Asaduzzaman et al., 2010). Merely 6% of the total population is covered through the natural gas supply networks in Bangladesh (LGED and FAO 2006). In Bangladesh the rural households mainly depend on biomass fuels, kerosene, electricity, candle, and liquefied petroleum gas (LPG) for their primary sources of energy supply (Asaduzzaman et al., 2010; Miah et al., 2010). In developing countries like Bangladesh, the rural household energy consumption constitutes over 70% to the national energy use (ADB, 1998; Koopmans, 2005). Biomass is the dominant fuel in Bangladesh, accounting for 99% of rural (crop residue: 45.6%, wood: 44.3%, dung: 9.4%, NG: 0.3%, LPG: 0.2% and other: 0.1%) and over 60% of urban (wood: 46.5%, NG: 34.8%, crop residue: 11%, dung: 3.6%, LPG: 3% and Kerosene: 0.4%) household fuel used (GACC and USAID, 2012). Around 89.6% of the total population in Bangladesh (99% of rural and 59.9% of urban population) uses biomass fuel for household cooking (WHO, 2007a). However, the contribution of biomass fuels to total primary energy supply in Bangladesh is about 60% (LGED and FAO, 2006; MoPEMR, 2008).

Around 24 million general households in rural area and 5.8 million general households in urban area in Bangladesh use biomass fuels for household cooking purpose (GACC and USAID, 2012). Almost all these households use traditional stoves for cooking and other heating purposes. A traditional stove is a mud built cylinder with three raised points on which cooking utensil rests. The stove may be built under or over ground (Hossain, 2003). The common biomasses used for cooking purpose are firewood, leaves, tree twigs, agricultural crop residues such as rice straw, rice husk, jute sticks, sugarcane bagasse, sawdust, cowdung etc. (Mamun et al., 2009; WB and BCAS 1998). The consumption of biomass fuels for household cooking with traditional cookstoves in Bangladesh is around 7 to 8 kg household-1 day-1 (Hassan et al., 2012; LGED and FAO, 2006; Rahman, 2007; Asaduzzaman and Latif 2005).

The energy efficiencies of these traditional stoves vary between 5 and 15 %. The poor thermal efficiency of the traditional stove is due to large distance between the fuel bed and utensils (30 to 60 cm), low draught that causes stagnant fluid film over the bottom surface of

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the utensils, inaccessibility and improper distribution of combustion air at the bottom of the stoves (Khan et al., 1995).

Therefore, with a poor thermal efficiency traditional cookstove has several disadvantages with respect to deforestation, biomass collection time, indoor air pollution and health impact, and climate change. In Bangladesh, most of the households cook their foods in traditional cookstoves using biomass fuels because of the unavailability of natural gas. Though large quantity of carbon dioxide (CO2), regarded as one of the potential greenhouse gas (GHG), are emitted from these stoves, the emission from this use of biomass is considered as GHG neutral if the biomass fuel cycle relies on renewable harvesting (Smith et al., 2000a).

Increased population growth, increased collection of fuel wood from forests and repeated fragmentation of the forests caused deforestation and the biomass fuel cycle unsustainable in Bangladesh (Streets and Waldhoff, 1999; Bhattacharya et al., 2002). Bangladesh’s forests have decreased by 50% since 1970. The country has rather small coverage of forest (about 11.1% of the total area of the country) whereas 25% of the land area of a country should be covered for a balanced ecology (GoB, 2005).

On average, each household in the villages and semi-urban areas spends about 200 hours per year collecting biomass fuel for their daily cooking (Asaduzzaman et al., 2010).

Design deficiency of the traditional cookstoves leads to incomplete and inefficient combustion which produces significant quantities of ‘products of incomplete combustion’ (PIC) importantly respirable particulates that have more global warming potential (GWP) than CO2 (Smith et al., 2000). Incomplete combustion of biomass in traditional cookstoves also releases carbon monoxide (CO), nitrous oxide (N2O), methane (CH4), polycyclic aromatic hydrocarbons (PAHs), particles composed of elementary or black carbon, and other organic compounds (Bhattacharya et al. 2000). Venkataraman et al. (2010) reported emission factors for traditional cookstoves using different biomasses which are shown in Table 1.1.

Table 1.1. Traditional stove emissions (g/kg fuel) from laboratory tests using water-boiling test to determine emissions of biomass fuel types in Indian traditional cookstoves (Source:

Venkataraman et al., 2010)

Fuel type

Pollutant emission factor (g/kg) Short-lived pollutant Long-lived pollutant CO NMVOC PM BC OM CO2 CH4 N2O

Wood 69±15 7.0±3.0 3.2±2.0 0.60±0.15 2.8±2.5 1358±43 5.0±4.0 0.09±0.09Agri. Res.

65.6 8.5 6.3±2.5 0.60±0.23 4.6±3.3 1302 7.6 0.050

Dung 39.9 24.2 3.0±1.9 0.12 2.5 1046 4.5 0.30

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In Bangladesh, women are the main cook in household cooking process and most of the households use traditional cookstoves for preparing their daily meals. It takes on an average 6.4 hours a day for effective cooking with this traditional cookstoves in Bangladesh (Asaduzzaman et al., 2010). This traditional stove usually lacks a chimney which releases the combustion products directly into the unventilated small kitchen as smoke. This indoor air pollution (IAP) poses a serious health impact on the women (Rahman, 2007). Study revealed a much higher concentration of PM2.5 in the countryside cooking area/kitchen. 24 hour average concentration of PM2.5 was found to be 340±344 µg/m3 in cooking areas/kitchens, whereas the mean level of PM2.5 in the cooking areas/kitchens was found to be 551±370 µg/m3 during cooking period. These levels of PM2.5 were several folds higher than the United States Environmental Protection Agency’s (USEPA) 2006 ambient air quality standard for 24 hours average (35 µg/m3) (USAID/WI 2009). Study conducted by the World Bank (Dasgupta et al., 2004a,b) provides a substantial amount of information on the levels and distribution of pollutants across a very large number of exposure configurations. Across households, 24-h average PM10 concentrations vary from 84 to 1165 µg/m3 for firewood, 60 to 755 µg/m3 for dung and 72 to 727 µg/m3 for jute stick. Women in all age groups and children under the age of 5 years of both sexes at homes that use biomass face the highest exposures compared to with men in the working age group. 24-h exposure concentrations of PM10 for women range from 209 to 264 µg/m3 and for children from 156 to 209 µg/m3 compared with 118 µg/m3 for men in the age group of 20-60 years.

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The health impacts of indoor biomass use in traditional cookstoves are now thoroughly understood as many of the researchers around the globe have published the ill effects in the international biomedical literature (Ezzati et al., 2004). Among the health impacts, blindness (Mishra et al., 1999), asthma (Schei et al., 2004), acute respiratory infections (Smith et al., 2000; Vinod et al., 2005), cancer (Bhargava et al., 2004), chronic obstructive pulmonary disease (Ekici et al., 2005), eye discomfort, headache, back pain (Diaz et al., 2007), reduced birth weight (Mishra et al., 2004), stillbirth (Mishra et al., 2005), and tuberculosis (Mishra et al., 1999) have been reported.

However, a recent review reveals that there is strong evidence for indoor air pollution as a cause of pneumonia and other acute lower respiratory infections (ALRI) among children under five years of age, and chronic obstructive pulmonary disease (COPD) and lung cancer (in relation to coal use) among adults. For the first time, the World Health Organization assessed the national burden of disease due to indoor air pollution (IAP) from biomass fuel use for the year 2002 and found the national health burden due to IAP in Bangladesh is one of the largest in the world. Total deaths attributable to biomass fuel use were 46,000 of which 32,330 were ALRI deaths (< 5 years age) and 13620 were COPD deaths (≥ 30 years age). Total Disability-Adjusted Life Years (DALYs) attributable to biomass fuel use were found to be 1,316,400 which was 3.6% of national burden of disease (WHO, 2007b). The Bangladesh Country Environmental Analysis revealed that reduced exposure to IAP could result in economic savings equivalent to 3.5% of GDP (WB, 2006).

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Several pollutants in the biomass smoke are climate active. The most important are nitrous oxide and methane, both well-understood greenhouse gases with much higher global warming potentials (GWPs) per tonne than CO2 (Smith et al., 2000b). CO and the entire mixture of non-methane volatile organic compounds (NMVOCs) in biomass smoke also act as indirect warming agents (Solomon et al., 2007).

The particles in biomass smoke are climate active, but the extent of warming depends on the ratio of black (warming particles) to organic (lighter-colored and cooling) particles in the smoke. The CO2 produced by biomass stoves in which the fuel is harvested renewably (crop residues, dung etc) does not contribute to global warming. The CO2 from burning of wood that is not harvested renewably (leading to deforestation) does contribute to global warming. Whether warming or cooling, the particles from biomass combustion contribute to regional air pollution (Nair et al., 2007). In addition, particle pollution over South Asia is responsible for significant blockage of sunlight, so-called “surface dimming”, which affects agricultural production (Chung et al., 2010). Heavy particle pollution in South Asia is thought by some observers to affect monsoon rainfall (Ramanathan et al., 2005). Finally, the deposition of black carbon particles onto snow and ice in the Himalayas may be associated with accelerated melting of glaciers that would eventually have significant hydrological impacts in the region (Ramanathan and Carmichael, 2008).

The methane, NMVOCs, and CO from household fuels are also contributors to the rise of regional tropospheric (ground-level) ozone levels. In addition to being a powerful greenhouse gas, ozone damages

human health, ecosystems, and agriculture (West et al., 2006). Cookstoves are not a small contributor to ozone levels — one estimate put their contribution of ozone precursors as one-sixth globally and perhaps one-quarter in South Asia and their contribution to carbon monoxide emissions as one-third globally (Unger et al., 2006).

Cookstoves with chimneys and closed combustion chambers are usually considered ‘improved’. An improved stove can be designed to improve energy efficiency, remove smoke from the indoor living space, or lessen the drudgery of cooking duties (WB, 2011).

The Institute of Fuel Research and Development (IFRD) of Bangladesh Council of Scientific and Industrial Research (BCSIR) started work in 1978 to develop ICSs in context of Bangladesh. IFRD developed several ICSs which include fixed and portable type, metal and clay, single and multiple pot, with chimney and without chimney, with grate and without grate, etc. (Sarkar et al., 2006). Among the developed models, improved single mouth cookstove (portable), improved single mouth cookstove (half underground), improved double mouth cookstove with chimney (on floor), improved double mouth cookstoves with chimney (half underground), improved single mouth cookstove with chimney (portable), improved

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double mouth cookstove coupled with single mouth cookstove having one common chimney, and improved double mouth cookstove with chimney for large scale cooking and semi industrial purposes are noteworthy. Thermal efficiency and fuel saving efficiency of those improved cookstoves were reported to be in the ranges of 21 to 31% and 45 to 60% respectively compared to the traditional cookstoves (VERC and WI, 2008).

IFRD completed two annual development program projects on dissemination of ICSs in the country jointly by BCSIR, Ansar-Village Defense Party (VDP) and Bangladesh Rural Development Board (BRDB) (Hossain, 2003). Besides, several Non Governmental Organizations (NGOs) in Bangladesh are actively involved in disseminating ICS technology among the community members in the rural areas (Sarkar et al., 2006). Current evidence shows there are only half a million of ICs in the market today and two NGOs, GIZ and Grameen Shakti, are the leading sellers of ICSs in the market (USAID and GACC, 2012).

Arif et al, (2011) conducted household kitchen performance tests on different ICSs (portable single pot with grate and without grate, double pot with chimney and with grate, and double pot with chimney and without chimney) and traditional single pot portable cookstove to compare thermal and fuel saving efficiency, cooking time and pollution level and found higher fuel consumption, lower thermal efficiency, longer cooking time and less pollution for double pot ICS with chimney compared to traditional cookstove whereas, lower fuel consumption, higher thermal efficiency, shorter cooking time and alike pollution level for portable single pot ICS without chimney compared to the traditional cookstove.

With the goals in mind for conserving biomass fuel, reducing smoke emissions in the cooking area and improving health conditions, reducing global warming potential, reducing deforestation, limiting the drudgery of women and children for biomass collection and reducing cooking time, and improving employment opportunities, this research work was endeavored to design and develop some mud built ICSs that will serve the several million poor households in villages and semi-urban areas in Bangladesh.

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CHAPTER 2 EXPERIMENTAL

The main objectives of this research work were to design and fabricate some mud built cookstoves to evaluate their performances and to compare them with the performances of the mostly disseminated ICSs in Bangladesh. Four types of mud built ICSs were designed and installed in the Department of Chemical Engineering, BUET. The designed stoves were: 1. BUET-Single-pot mud stove (circular grate), 2. BUET-Double-pot mud stove (circular grate), 3. BUET-Double-pot mud stove (elliptical grate), and 4. BUET-Triple-pot mud stove (circular grate). Two types of ICSs were brought from Grameen Shakti, a leading NGO involved in disseminating ICSs in Bangladesh, to compare their performances with the BUET designed stoves. The ICSs of Grameen Shakti were: 1. Single-pot concrete stove (circular grate) and 2. Double-pot concrete stove (circular grate). Stove models are shown in Figures 2.1 to 2.6.

2.1. Design philosophy 2.1.1. Socio-economic and environmental consideration

As the most of the people of the villages and semi-urban areas in Bangladesh use biomass cookstoves, much emphasis was given in design phase of the ICSs in this project. Materials of construction were so chosen that people can have easy access to those materials. Besides material selection, emphasis was also given to reduce IAP and health impact, to reduce global warming potential from the emission, to reduce fuel requirement for cooking of the designed ICSs.

2.1.2. Technical consideration

There are some basic design principles for an effective biomass cookstove. Any cookstove that possesses low energy loss to surrounding environment, good combustion and heat transfer efficiency is named as ICS. Insulation around the fire with light materials can resist heat from escaping. Wood ash was chosen for insulating material in this case as it is low cost waste material (Baldwin, 1986; Bryden et al., 2002).

Insulated chimney right above the fire can increase the draft inside the combustion chamber thus can induce proper combustion with less smoke and can increase convectional heat transfer to the pot. In convective heat transfer, the primary resistance to heat flow is in the ‘surface boundary layer’ of very slowly moving gas immediately adjacent to a wall. Within this region, heat transfer is primarily by conduction and the conductivity of gases is quite low. To improve the thermal efficiency of a stove, the thermal resistance of this boundary layer must be reduced by increasing the flow velocity of the hot gas over the surface of the pot. This was followed for all the ICS’s design (Baldwin, 1986; Bryden et al., 2002).

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Increasing of radiative heat transfer from firebed to pot is another option to increase heat transfer efficiency of the cookstove. To heat the pot more effectively by radiation directly from the fuelbed, the average fuelbed temperature could be increased (without increasing the fuel consumption) through proper air to fuel ratio. Alternatively, Radiative heat transfer canbe increased by lowering the pot closer to the firebed or the view factor could be increased by increasing the size of the pot relative to the firebed. In this project all the stoves were designed to maintain the above statement (Baldwin, 1986).

Waste heat utilization from flue gas is another option to increase the heat transfer efficiency of a stove. This phenomenon was also adopted to design multiport cookstoves in this project. Besides, a unique phenomenon, preheating of combustion air, which can raise the temperature of combustion chamber and provide relatively clean burning, was incorporated in each stove under this project. All the cookstoves were designed with double wall to prevent burn, which is one of the most important functions of an improved stove (Baldwin, 1986).

To mix the preheated combustion air with the fuel on firebed for better combustion, total estimated combustion air was distributed evenly through several circular ducts under the firebed (metal grate) (Baldwin, 1986).

Each of the stoves was fixed type and the base of the stove and floor surface were separated with insulating material (ordinary fired brick) to prevent excessive heat flow to floor materials. To lessen the excess heat load of the stove body, the height of all stoves was maintained a minimum providing the ash pit underground. Ash pit and ash hole on the floor surface were connected through an underground channel.

2.2. Design Basis

Before starting to design the cookstove structure, some calculations were performed to find the basis on which the dimensions of the design are to be selected. The design basis calculations were performed depending on a major parameter: amount of water to be vaporized at a certain time interval. Depending on this parameter all the calculations were performed and the values were used for construction of all the cookstoves. The values of design basis (assumed) and calculated values of different parameters based on design basis are listed in Table 2.1 and 2.2 for single pot and multi pot cookstoves.

Table 2.1. Design basis and calculated values of different parameters for single pot cookstove

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Parameters Unit Values Design Basis Heat loss due to conduction % 40 Fuel Required (air dried biomass) Kg/hr 0.80 (14% moisture content, wet

basis)

Air dried biomass composition Wt% Carbon 50 Water 14

Higher heating value (dry basis) MJ/kg 17 Combustion Air % excess 100 Flue gas temperature inside chimney oC 250 Calculated Value Mass of actual biomass (dry basis) gm 688 Fuel burning rate gm/minute 11.467 Heat produced Watts 3249 Actual combustion gas flow rate m3/hr 14.915 Stack Gas Velocity m/s 2.110 Draft of chimney Pascal 12.948 Chimney Height m 2.13 Chimney inner diameter mm 50

Table 2.2. Design basis and calculated values of different parameters for multi pot cookstoves

(double and triple pot stoves) Parameters Unit Values Design Basis Heat loss due to conduction % 40 Fuel Required (air dried biomass) Kg/hr 0.80 (14% moisture content, wet

basis)

Air dried biomass composition Wt% Carbon 50 Water 14

Higher heating value (dry basis) MJ/kg 17 Combustion Air % excess 100 Flue gas temperature inside chimney oC 200 Calculated Value Mass of actual biomass (dry basis) gm 688 Fuel burning rate gm/minute 11.467 Heat produced Watts 3249 Actual combustion gas flow rate m3/hr 13.489 Stack Gas Velocity m/s 1.9~2.0 Draft of chimney Pascal 11.445 Chimney Height m 2.13 Chimney inner diameter mm 50 2.3. Construction features of the stoves

Considering the cooking needs, shapes of cooking pots and types of biomass fuels, the four experimental cookstoves (fixed type) were designed. The stove models are: 1. BUET-Single-pot mud stove (circular grate), 2. BUET-Double-pot mud stove (circular grate), 3. BUET-Double-pot mud stove (elliptical grate), and 4. BUET-Triple-pot mud stove (circular grate).

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The stoves were constructed with locally available materials (ordinary fired brick, mud, metallic grate and ‘O’ ring, and concrete chimney). All the BUET designed models have two chimneys. The BUET models along with their dimensions are shown in Figures 2.1 to 2.4. All the BUET models contain features that would help in the effective burning of the fuel, good heat transfer to cooking pot and diminution of indoor air pollution.

Some common design rules were followed while sizing different dimensions of the stoves.

2.3.1. Combustion chamber height

This was calculated using the formula: H = A + P + L. Where, ‘A’ is the air hole height in cm, ‘P’ is the height from air hole to pot bottom which is 0.4 times pot diameter for cylindrical pots, which can be extended for spherical pots and ‘L’ is the distance between the pot bottom and the pot mouth (Baldwin, 1986). Considering all these, the height of combustion chamber of each stove was taken to be 11.8 inch (300 mm) from ground (floor) surface.

2.3.2. Pot mouth

Pot mouth of a cookstove is a hole where the utensil sits on. Pot mouth diameter for the BUET-Single pot and BUET-Double pot cookstoves (both circular and elliptical grate) was taken as 10 inch whereas, each pot mouth diameter for BUET-Triple pot stove was taken as 9 inch as these size of pots are usually used in general household in Bangladesh. A metallic ‘O’ ring of same diameter of pot mouth was placed on each of the pot mouths to prevent erosion of mud.

2.3.3. Grate

A metallic grate was used inside the combustion chamber of each type of stoves which was placed just above the primary combustion air inlet wholes. This grate acts as fuel bed and allows better mixing of combustion air and fuel. Rectangular slits were incorporated in the grate instead of circular slits for better combustion efficiency. This type of grate is also very useful for fuel wood, leaves and agricultural residues.

2.3.4. Stack or Chimney

Stack or chimney acts as an integral part of an improved biomass cookstove providing clean indoor environment. Each of the stove models has two chimneys. It is a standard rule to take chimney height same as roof top height 7-10 feet for not being exposed to smoke. Considering this along with the provision of draft ranging from 10-15 Pascals, the chimney height was taken as 7 feet. It is most beneficial for combustion to have a flue gas velocity of 2-3ms-1 within the chimney (Shaha, A.K., 1974). Considering this the internal diameter (ID) of the chimney was calculated to be 2 inch. For field application, ID of each stack was taken as 3 inch. 1 inch provision was provided for deposition of soot particles to avoid excessive pressure drop after long-run operation.

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2.3.5. Wall thickness of combustion chamber

For mud built cookstove, wall thickness should be in the range of 2-3 inch. In this case 2 inch wall thickness was chosen as design value (Baldwin, 1986).

2.3.6. Inlet air (for combustion) hole diameter

It is a good practice to maintain constant cross sectional area for combustion air inlet and combustion gas exit. That is why, along with the diameter of the chimney inlet, six air holes of 2 inches diameter were placed at the bottom of the combustion chamber wall.

2.3.7. Stoke hole or secondary air inlet

A stoke hole or secondary combustion air inlet was placed in each of the stove models above the gate or fire bed to provide stoke (fuel) in the combustion chamber and secondary combustion air to the diffusion flame zone for better combustion. This hole dimension was so chosen to keep the hole size minimum and to adopt with reasonable size of stokes.

2.3.8. Double wall

A second wall of two inch thick was provided outside the combustion chamber wall maintaining an annular space for each of the stove models to minimize heat loss to environment through convection, to minimize burn risk during cooking. The annular area of the double wall was also designed for preheating the primary combustion air to maximize waste heat utilization.

2.3.9. Ash pit and ash hole

In all stove models, a 6 inch deep ash pit was provided underground at the bottom of combustion chamber with a view to lessen the cookstove mass and excessive heat loss. Ash hole was provided to collect ash and it was connected to ash pit through underground channel. Ash hole remains closed during cooking.

2.4. Mud built stove construction procedure

First of all, all the initial structures were made with moulded sticky mud. Then structures were allowed to dry for 1-2 days in natural environment under the shade. After that a desired shape was given to the structures with knife and hands. Again the structures were allowed to dry completely by keeping them under the shade for another 5-7 days. During this drying process structures were rubbed with mud and water to fill up the cracks. It is customary to rub the structure with moulded sticky mud twice in a week. After several weeks of occasional firing and filling up the cracks with mud, no more new cracks were found and the stoves became strong like burnt fire bricks.

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Thus the stoves made with mud do not cost money except for grate and chimney, if one knows the technique of making the stoves. Different fabrication steps and curing are shown in Figure 2.7.

2.5. Cookstoves performance evaluation

All the cookstoves were fixed type and placed under a shed without any fence. Modified version of Water Boiling Test (WBT), version 4.1.2, (Bailis et al., 2009) was followed to evaluate the performances of the cookstoves designed by BUET and two other cookstoves manufactured by Grameen Shakti, a leading NGO in disseminating improved cookstoves (ICSs) in local market. WBT was carried out for cold and hot start in high power phase and simmering in low power phase. The cold start in high power phase began with the stove at ambient temperature and used a pre-weighed bundle of fuel to boil a measured quantity of water in aluminum pot. The hot start in high power phase followed immediately after the cold start in high power phase while the stove was hot. Simmering in low power phase started immediately after hot start in high power phase on the retained water in the pot and continued for 45 minutes and the temperature of the water in the primary pot was maintained average 3oC below the local boiling point of water. Real time in-stack measurements of emission from all the cookstoves were also done during different phases of the entire WBT. After completing WBT and emission measurements, Controlled Cooking Test (CCT) was also carried out by cooking a traditional food (parboiled rice) using all the cookstoves.

2.5.1. Water Boiling Test (WBT)

For WBT of different cookstoves, Aluminum made pots were used. Each of the pots was identical with respect to their dead weight, capacity and dimensions. Each pot had a dead weight of 350 gm and a thickness of 1.1 mm with a hemispherical bottom. Each of the pots was 116 mm high and the opening mouth diameter was 245 mm. The highest diameter of the pot was at the middle which was 290 mm. The dimensions of the pot are shown in Figure 2.8. For single pot, double pot and triple pot cookstoves, WBT required one, two and three pots respectively for single test run. For each test run, initially each pot was charged with exactly 4,150 ml of water. The cooking fuel used for WBT was locally available rice straw with measured moisture content: 6% (wet basis), gross calorific value (higher heating value) on dry basis: 14,400 kj/kg and a calculated net heating value on dry basis: 13,080 kj/kg. Higher heating value was determined in the laboratory using bomb calorimeter on wet basis. Net calorific value was calculated using the WBT, version 4.1.2 excels calculation sheet program developed for Shell Foundation’s-Household Energy and Health Programme (HEH) (Bailis et al., 2009). Nearly 160 kg of rice straw from a single lot was purchased from Gazipur. For multi-pot cookstoves, WBT was terminated with the boiling in the primary pot. No lid was used to cover the pot, so that evaporated water freely escapes from the pot. Fuel required heating up the known quantity of water to its local boiling point and the amount of evaporated water up to boiling point was recorded for each test run on all types of cookstoves. From WBT, time to boiling, burning rate, specific fuel consumption, specific energy consumption, firepower, cooking power, turndown ratio, and overall stove thermal

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efficiency were determined. Combustion efficiency was determined as percentage of airborne fuel carbon released as CO2 which is discussed under the section: Environmental Stove Index (ESI). Thereafter, heat transfer efficiency and environmental stove index were calculated. The stoking for entire WBT was carried by a several years experienced woman since stoking rate is highly person dependent. Photographs of WBT on different ICSs are shown in Figure 2.9.

2.5.1.1. Time to boil (∆tc) This is the time to boil water in the primary pot and it is simply a clock difference and expressed as: ∆t = tf – ti (i) Where, tf = Final clock time (min) ti = Initial clock time (min) 2.5.1.2. Temperature corrected time to boil (∆tT) This adjusts the time to boil to a standard 75oC temperature change (from 25oC to 100oC) to compensate different initial temperature and local boiling point. ∆tT = (tf – ti)×75/(Tf – Ti) (ii) Where, Tf = Local boiling temperature of water (oC) Ti = Initial temperature of water (oC) 2.5.1.3. Overall stove thermal efficiency ( ) This is a ratio of the work done by heating and evaporating water to the energy released by burning equivalent amount of dry wood and expressed as:

. ∑

(iii) Where, 4.186 j/goC = Specific heat of water P = Weight of empty pot (gm) Pi = Weight of pot with water before test (gm) Ti = Water temperature before test (oC) Tf = Water temperature after test (oC) fd = Equivalent dry fuel consumed (gm) Wv = Amount of water vaporized (gm) LHV = Lower heating value or net heating value of the fuel (kj/kg) 2.5.1.4. Burning rate (rb)

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The burning rate was calculated from the recorded initial and final weight of the fuel and time taken for completing WBT. It was calculated by dividing the equivalent dry fuel consumed during test run by the time required for the test, which is expressed as:

rb = (iv) Where, rb = burning rate (gm dry fuel/min) fd = Equivalent dry fuel consumed (gm) fd = fm × [1-(1.12 × m)] – 1.5 × ∆c ∆c = net change in char during test phase (gm) fm = Moist fuel consumed (gm); fm = fi - ff tf = Time at the end of test (min) ti = Time at the start of test (min) m = moisture content (%, wet basis) 2.5.1.5. Specific fuel consumption (SC)

It was measured as the amount of equivalent dry wood required producing one liter or one kilo of boiling water and is expressed as:

SC

∑ (v)

SC = Specific fuel consumption (gm fuel/gm water) P = Weight of empty pot (gm) Pf = Weight of pot with water after test (gm) Ti = Water temperature at the beginning of the test (oC) Tf = Water temperature after test (oC) Tb = Local boiling point of water (oC) 2.5.1.6. Temperature corrected specific fuel consumption (SCT)

This corrects the specific fuel consumption to account for differences in initial water temperatures. This correction accounts for a standard temperature change of 75oC (from 25 to 100oC). It is calculated as:

SC SC (vi) 2.5.1.7. Temperature corrected specific energy consumption (SET)

This was determined by multiplying SCT with the net calorific value of the fuel and the unit is kj/liter.

2.5.1.8. Firepower (FP)

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This is a ratio of the equivalent dry fuel energy consumed by the stove per unit time and the unit of the firepower is Watt. This parameter is useful for high and low power phase since turndown ratio of a cookstove can be found from high and low power phase firepower and expressed as:

FP

∆ (vii)

Where, fd = Equivalent dry fuel consumed (gm) LHV = Lower heating value (j/gm) ∆t = Duration of test run (min) 2.5.1.9. Useful/cooking power (FPuseful)

The useful/cooking power is the average rate of energy released from fuel combustion that is transferred to the pot over the duration of the test and the unit of the useful/cooking power is Watt. Cooking power was calculated for the cold start and hot start, but not for the simmer, because cooking power cannot be accurately measured during the simmer phase of the WBT, as discussed in the article. Cooking power is expressed as:

(viii)

2.5.1.10. Turndown ratio

It shows the operability of a stove with low power input and is the ratio of hot start firepower in high power phase to simmering firepower in low power phase.

2.5.1.11. Environmental stove index (ESI)

This is composed of two parameters. 1/(1-NCE) is a direct indicator of how much products of incomplete combustion (PIC) is released and indicates the amount of fuel used.

ESI = ln[ / (1-NCE)] (ix) Where, NCE (Nominal combustion efficiency) = 1/(K+1) and K = [(FC/CO2) – 1] (x) Fuel carbon (FC) = (Fuel consumed × carbon fraction) – (Ash produced × carbon fraction) CO2 = Carbon as carbon-di-oxide in flue gas (Smith et al. 2000b)

= Overall stove thermal efficiency and is expressed as:

NCE × NHE (xi)

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NCE (Nominal combustion efficiency): It is defined as the percentage of airborne fuel carbon released as CO2.

NHE (Nominal heat transfer efficiencies): It is defined as the percentage of heat released by combustion that is absorbed by the water in the pot. This was not measured directly in our experiments and was determined using Equation, since both NCE and are available from the tests.

2.5.2. Controlled cooking test (CCT)

In Bangladesh cooked rice is a traditional food and almost every general household cooks rice twice a day. Therefore, controlled cooking tests (CCT) were performed on every cookstove by cooking parboiled rice. A several years experienced household female cook was hired to cook the parboiled rice. The same pots (Figure 2.8) used in WBT were also used in CCT. A 40 kg bag of parboiled ‘miniket’ rice was purchased from local market to maintain the homogeneity in rice quality. To conduct CCT on single pot cookstove, 750 gm parboiled miniket rice and 3,900 gm water were taken into a single pot. For double and triple pot cookstoves, two and three pots of equal dimensions were used respectively each of which contained 750 gm miniket rice and 3900 gm water. Stoking rate and termination time for cooking rice were solely determined by the cook based on her experience. Each cookstove was tested thrice for cooking identical amount of parboiled rice with water. Pot lid was used for each CCT run to maximize heat utilization. During CCT on each cookstove, amount of fuel consumed and time required were estimated. Some mentionable photography of CCT are shown in Figure 2.10.

2.5.3. Emission measurements

For WBT and CCT, in-stack flue gas compositions for CO, NO, and stack temperature and draft were measured using a portable combustion analyzer (PCA-3, Bacharach Inc., USA). Besides, flue gas samples were collected from the chimney in Tedlar bags at an interval of two minutes during CCT and WBT for each type of cookstove. The samples were then analyzed for CO2, and CH4 using gas chromatography (FID-GC). Background ambient concentrations of all above mentioned parameters were also measured to find out the net emission compositions of flue gas from combustion. Flue gas and ambient air compositions were measured on wet basis.

2.5.4. Temperature profile

Stack temperature, flame zone temperature, fuel bed temperature, combustion air temperature were also measured using thermocouple with electronic reader during entire WBT for cold and hot start in high power phase, simmering in low power phase and CCT.

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Figure 2.1. Isometric, top and bottom view of BUET-single pot mud stove.

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Figure 2.2. Isometric, top and bottom view of BUET-double pot mud stove (circular grate)

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Figure 2.3. Isometric, top and bottom view of BUET-double pot mud stove (elliptical grate).

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Figure 2.4. Isometric, top and bottom view, and front elevation of BUET-triple pot mud stove.

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Figure 2.5. Isometric view of Grameen Shakti-double pot concrete stove

Figure 2.6. Isometric view of Grameen Shakti-double pot concrete stove

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Figure 2.7. Different phases (shaping, curing) of constructing BUET stove models

Shaping of BUET-single pot mud stove


Curing of BUET-single pot mud stove

Shaping of BUET-double pot mud stove


Shaping of BUET-double pot mudstove



Curing of BUET-double pot mud stove

Shaping of BUET-t pot mud stove


Curing of BUET-single pot mud stove

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Figure 2.8. Dimensions of the cooking pot that was used in WBT and CCT Figure 2.9. WBT run on stove models of BUET and Grameen Shakti. In the figures: © means

‘circular grate’; (E) means ‘elliptical grate’ and GS means ‘Grameen Shakti’.

WBT of BUET-single pot mud stove

WBT of BUET-double pot ©stove

WBT of BUET-single pot (E) stove

WBT of BUET-triple pot mud stove

WBT of GS-single pot concrete stove

WBT of GS-double pot concrete stove

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Figure 2.10. CCT run on stove models of BUET and Grameen Shakti. In the figures: © means ‘circular grate’; (E) means ‘elliptical grate’ and GS means ‘Grameen Shakti’.

CCT of BUET-single pot mud stove

CCT of BUET-double pot © stove

CCT of BUET-double pot (E) stove

CCT of BUET-triple pot mud stove

CCT of GS-single pot concrete stove

CCT of GS-double pot concrete stove

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CHAPTER 3 RESULTS AND DISCUSSIONS

3.1. Results and discussions on WBT performances 3.1.1. Temperature and draft profile of the stoves in WBT

Provision for preheating combustion air for BUET-single pot, double pot-circular grate, double pot-elliptical grate and triple pot mud stoves renders higher temperature of combustion air, fuel bed, and flame zone compared to Grameen Shakti-single and double pot concrete stoves. Combustion air temperatures of BUET-designed stoves varied from 63 to 74oC for high power phase and 52 to 59oC for low power phase. Whereas, combustion air temperatures of Grameen Shakti-single and double pot cookstoves were found to be the ambient temperature (30oC) for both power phases. This preheating phenomenon made a clear distinction between BUET-designed stoves and Grameen Shakti-designed ICSs with respect to fuel bed temperature, and flame zone temperature. Fuel bed temperature of BUET-designed stoves varied from 605 to 660oC in high power phase and 584 to 611oC in low power phase, whereas this temperature varied from 570 to 601oC in high power phase and 549 to 560oC in low power phase of Grameen Shakti-designed ICSs. Flame zone temperature of BUET-designed stoves varied from 710 to 762oC in high power phase and 685 to 698oC in low power phase, whereas this temperature varied from 667 to 683oC in high power phase and 644 to 648oC in low power phase of Grameen Shakti-designed ICSs. Stack flue gas temperatures of BUET-designed stoves were lower than those designed by Grameen Shakti in both high and low power phases that varied from 298 to 341oC in high power phase and 240 to 291oC in low power phase of BUET designed stoves, whereas these temperatures varied from 338 to 356oC in high power phase and 307 to 310oC in low power phase of Grameen Shakti-designed ICSs. These temperatures show a clear indication of better combustion and effective heat utilization in BUET designed stoves compared to Grameen Shakti designed ICSs. All BUET designed stoves have double chimney to compensate excess pressure drop due to annular flow of pre-heated combustion air. Draft in each chimney of BUET designed stoves varied from – 6.5 to – 7.5 pa for entire WBT test, whereas for single chimney of Grameen Shakti designed ICSs draft varied from – 6.8 to – 7.9 pa. Detail of the temperature and draft profiles during WBT of all the stoves is shown in table 3.1.1.

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Table 3.1.1. Temperature and draft profile of the stoves during WBT (cold and hot start in high power phase, and simmering in low power phase)

Parameters

Stove Type BUET-single pot mud stove Circular Grate

BUET-double pot mud stove Circular Grate

BUET-double pot mud stove Elliptical Grate

BUET-triple pot mud stove Circular Grate

Grameen Shakti-single pot concrete stove Circular Grate)

Grameen Shakti-double pot concrete stove Circular Grate

Mean.

Combustion air

temperature (oC)

Cold Run

63

64

66

64

30

30

Hot Run

69

72

74

71

30

30

Simmer -ing

52 57 59 56 30

30

Fuel bed temperature

(oC)

Cold Run

605

616

632

611

570

583

Hot Run

623

645

660

647

588

601

Simmer -ing

584 605 611 590 549 560

Flame zone temperature

(oC)

Cold Run

712

713

722

710

673

667

Hot Run

722

762

760

723

683

678

Simmer -ing

685 698 696 687 648 644

Stack flue gas

temperature (oC)

Cold Run

298

320

306

313

342

356

Hot Run

307

341

340

315

348

338

Simmer -ing

240 291 287 281 307 310

Draft inside chimney

(-Pa)

Cold Run

*7.4

*7.5

*7.5.

*7.4

7.9

7.5

Hot Run

*7.4

*7.5

*7.4

*7.5

7.8

7.6

Simmer -ing

*6.5 *6.7 *6.7 *6.6 6.9 6.8

*All BUET models have two chimneys. The draft reported here is the average draft per chimney.

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3.1.2. Thermal performance of stoves in WBT

WBT performance parameters (boiling time, burning rate, specific fuel and energy consumption, firepower, cooking power, turn-down ratio, and overall thermal efficiency) of all stoves are shown in table 3.1.2. Among the stoves, average boiling time (temperature corrected) was found to be the lowest for BUET-double pot mud stove (elliptical grate) which was 15.25 minutes to boil about 8.3 liter of water. Next higher boiling time was 18.85 minutes/8.3 liter of water that belonged to BUET-double pot mud stove (circular grate). BUET-single pot mud stove had the third lowest boiling time of 19.35 minutes/4.15 liter water. The fourth highest boiling time was found for BUET-triple pot mud stove which was 21.05 minutes/4.15 liter water. Grammen Shakti designed ICSs had the highest boiling time (21.4 minutes/4.15 liter water and 22.15 minutes/4.15 liter water for Grameen Shakti-single pot and double pot concrete stoves respectively). It is evident that all BUET designed stoves boil water faster than those designed by Grameen Shakti.

The highest fuel burning rate during high power phase was found in BUET-double pot mud stove but the burning rate of this cookstove in low power phase was lower than Grameen Shakti double pot cookstove. The burning rate of the rest three BUET designed stoves was lower than those designed by Grameen Shakti for both high and low power phases.

Specific fuel and energy consumptions (temperature corrected) of BUET designed stoves were lower than those designed by Grameen Shakti in both high and low power phases except BUET-single pot mud stove that consumed higher specific fuel and energy during simmering in low power phase compared to Grameen Shakti-double pot concrete stove. Specific fuel and energy consumptions were found to be the lowest for BUET-double pot mud stove (elliptical grate) during all power phases, whereas the highest specific fuel and energy consumptions were found for Grameen Shakti-single pot concrete stove in all power phases (table 3.1.2.).

Firepower is the output power of a stove and indicates how much energy a cookstove can produce per time. Average firepower of the stoves varied from 8,590 to 14,755 watt in high power phase and 4,195 to 6,702 watt in low power phase. Firepower was found to be the lowest for BUET-single pot mud stove in all power phases, whereas BUET-double pot mud stove (elliptical grate) was found to be the highest energy generator per time during high power phase. During simmering in low power phase, Grameen Shakti-double pot concrete stove showed the highest firepower (table 3.1.2.).

Cooking power is the fraction of the firepower that is eventually transferred to the cooking pot for boiling water. The ratio of cooking power to firepower indicates the fraction of firepower actually used for cooking. The larger the fraction, the larger will be the effective cooking power. The ratios of cooking power to firepower in high power phase were 0.18, 0.24, 0.25, 0.29, 0.10, 0.13 for BUET-single pot mud stove, BUET-double pot mud stove (circular grate), BUET-double pot mud stove (elliptical grate), Grameen Shakti-single pot concrete stove and Grameen Shakti-double pot concrete stove respectively. This ratio is in fact the overall thermal efficiency for a stove. Therefore, based on firepower utilization effectively, six stoves can be graded on ‘the best to the worst’ scale basis i.e., BUET-triple pot mud stove (the best) > BUET-double pot mud stove (elliptical grate) > BUET-double pot

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mud stove (circular grate) > BUET-single pot mud stove > Grameen Shakti-double pot concrete stove > Grameen Shakti-single pot concrete stove (the worst).

Turndown ratios of all the stoves were satisfactory and varied from 1.93 to 2.4. All the BUET models showed a turndown ratio above 2 which means BUET stoves were capable to simmer water with a 50% reduced burning rate compared to hot start in high power phase. Turndown ratio of Grameen Shakti-double pot concrete stove was somewhat below 2, whereas for Grameen Shakti-single pot concrete stove turndown ratio was above 2 (table 3.1.2.).

All BUET models showed higher thermal efficiency compared to Grameen Shakti models (table 3.1.2.). Overall thermal efficiencies of BUET-single pot, double pot (circular grate), double pot (elliptical grate), triple pot mud stoves and Grameen Shakti-single pot and double pot concrete stoves are 18%, 24%, 25%, 29%, and 10%, 13% respectively. The ranking of the stoves is similar to that for cooking power to firepower ratio scale, i.e., BUET-triple pot mud stove (the best) > BUET-double pot mud stove (elliptical grate) > BUET-double pot mud stove (circular grate) > BUET-single pot mud stove > Grameen Shakti-double pot concrete stove > Grameen Shakti-single pot concrete stove (the worst). It was shown experimentally for several biomass cookstoves using different biomass fuel that overall thermal efficiency ( of a biomass cookstove increases by moving up the energy ladder from dung cake to crop residue to wood. Nada Chulha, an improved double pot mud stove with chimney of India, very similar to Grameen Shakti-double pot concrete stove with chimney showed almost similar performance compared to the Grameen Shakti-double pot concrete stove using rice straw as fuel. Nada Chulha showed overall thermal performances of 10%, 10.9%, 13.5%, 19.7% and 23.5% using cow dung, rice straw, mustard residue, root fuel and wood (Acacia) as fuel respectively in WBT. Sugam Chulha, India is a version of Nada Chulha, India that used ceramic lining inside the fire boxes, flue gas passing line and inside chimney, showed much better overall thermal efficiency using rice straw as fuel. This Sugam chulha, India showed overall thermal efficiencies of 12.8%, 18.5%, and 29% using cow dung, mustard residue, and wood (Acacia) as fuel respectively in WBT (Smith et al. 2000b). In comparison with the Indial Nada Chulha, BUET models performed better, contrarily performance of Grameen Shakti models is very similar to Nada Chulha using rice straw as fuel.

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Table 3.1.2. WBT performance parameters (boiling time, burning rate, specific fuel and energy consumption, firepower, cooking power, turn-down ratio, and overall thermal

efficiency) of stoves

Parameters





Grameen Shakti-single pot concrete stove Circular Grate


Mean. Boiling time (corrected) (min)

Cold Start

20.5

20.4

16.3

22.5

22.3

23.6

Hot Start

18.2

17.3

14.2

19.6

20.5

20.7

Simmer -ing

na na na na na na

Burning rate (gm/min)

Cold Start

44.4

53.8

67.0

46.0

56.5

59.4

Hot Start

39.4

56.4

67.7

42.6

57.1

64.8

Simmer -ing

19.3 25.4 27.9 22.8 27.5 30.6

Sp. Fuel consumption (corrected) (gm/liter)

Cold Start

233.5

136.2 136.0 110.8 316.4

237.1

Hot Start

182

120.5

119.0

93.2

290.4

220.9

Simmer -ing

260.9 172.7 188.6 129.6 356.4 246.9

Sp. Energy consumption (corrected) (kj/liter)

Cold Start

3054

1781.9

1779.2

1449.2 4137.9

3100.7

Hot Start

2380.6

1576.4 1556.4

1219.2

3798.7

2889.2

Simmer -ing

3412.6 2258.7 2466.5 1695.1 4661.2 3229.6

Firepower (watt)

Cold Start

9,684

11,721

14,599

10,018

12,327

12,954

Hot Start

8,590

12,300

14,755

9,290

12,446

14,121

Simmer -ing

4,195 5,527 6,094 4,930 5,924 6,702

Turn down ratio

Simmer -ing

2.31 2.12 2.40 2.03 2.08 1.93

Cooking power (watt)

Cold Start

1,549 2,696 3,504 2,705 1,233 1,684

Hot Start

1,718 3,075 3,836 2,880 1,245 1,836

Simmer na na na na na na

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Parameters







Mean.-ing

Overall thermal efficiency (%)

Cold Start

16

23

24

27

10

13

Hot Start

20

25

26

31

10

13

Simmer -ing

na na na na na na

na: means not applicable for the said purpose

Benchmark fuel and energy requirements to boil 5 liter of water and then simmer it for 45 minutes of all stoves were calculated and are shown in table 3.1.3. It was found that the lowest and the highest fuel/energy consuming cookstoves were BUET-triple pot mud stove and Grameen Shakti-single pot concrete stove respectively. Fuel and energy consumptions per 5 liter water of BUET stoves varied from 1,158 to 2,343 gm and 15,147 to 30,650 kj respectively. The energy consumption standard to boil 5 liter water and then simmer it for 45 minutes of all types of biomass based ICSs with chimney set by Aprovecho Research Center for Shell Foundation should be below 1500 gm for wood or below 30,000 kj for using alternative biomass fuel (Still and MacCarty, 2006). On this basis energy consumptions of BUET-double pot mud stove (circular grate), BUET-double pot mud stove (elliptical grate) and BUET-triple pot mud stove (circular grate) were below the standard value. Energy consumption of BUET-single pot mud stove was slightly higher than the standard value. Energy consumptions of the cookstoves designed and marketed by Grameen Shakti were much higher than the standard energy consumption value set by Shell Foundation (table 3.1.3.). It was shown experimentally for several biomass cookstoves that overall thermal efficiency ( of a biomass cookstove increases by moving up the energy ladder from dung cake to crop residue to wood to kerosene to gas. (Smith et al. 2000b). Increasing thermal efficiency for a single cookstove with the biomass energy ladder (dung cake to crop residue to wood) means higher amount of effective energy utilization which in turn means less energy input. Therefore, there is every possibility for all non ICSs in this study to perform better with the biomass energy ladder (dung cake to crop residue to wood) and hence an opportunity to become true ICSs.

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Table 3.1.3. Benchmark fuel and energy consumption values of stoves for entire WBT (5 liter water)

Parameters





Grameen Shakti-

single pot concrete

stove Circular Grate


Mean Dry Fuel (rice straw) consumed benchmark value (gm/5 liter)

2,343 1,505 1,580 1,158 3,299 2,379

Energy consumed benchmark value (kj/5 liter)

30,650 19,689 20,671 15,147 43,147 31,123

*Aprovecho-Shell Foundation benchmark fuel/energy consumption for wood burning chimney stove to boil 5 liter water and then simmer it for 45 minutes

Less than 1.5 kg wood/5 liter water or less than 30,000 kj/5 liter water

*(Still, and MacCarty, 2006) 3.1.3. Emission performances of stoves in WBT

In-stack measurements of flue gases on wet basis was performed for CO2, CO, NO and CH4. Composition of the relevant gaseous components (vol%), and combustion efficiencies during cold and hot start in high power phase and simmering in low power phase are shown in table 3.1.4.

For entire WBT of all BUET and Grameen Shakti models, CO2 concentrations varied from 6.52 to 6.88 vol%, and 6.29 to 6.57 vol% respectively. CO concentrations of BUET and Grameen Shakti models varied from 0.325 to 0.381 vol% and 0.317 to 0.364 vol%

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respectively. NO concentrations of BUET and Grameen Shakti models varied from 0.0047 to 0.0072 vol% and 0.0027 to 0.007 vol% respectively. Basically, NO forms at high temperature. Since the combustion temperatures of all BUET models were higher than Grameen Shakti models, NO concentrations in flue gases were usually higher for BUET models than for Grameen Shakti models. CH4 concentrations of BUET and Grameen Shakti models varied from 0.061 to 0.091 vol% and 0.063 to 0.073 vol% respectively. Combustion efficiencies of all BUET models were found higher than Grameen Shakti models almost in all phases of WBT (table 3.1.4). This may be attributed to the preheating process of combustion air in all BUET models. Combustion efficiencies of all BUET and Grameen Shakti models for entire WBT varied from 80 to 85% and 77 to 81% respectively. However, Combustion efficiencies of all stoves in low power phase were lower than in high power phase. Since the fuel burning rate was lower in low power phase compared to high power phase, combustion temperature was lower in low power phase. Therefore, combustion efficiencies of all stoves in low power phase fell down compared to high power phase.

Table 3.1.4. Emission characteristic and combustion efficiency of stoves for WBT (cold and hot start-high power phase; simmering-low power phase). Compositions are given in wet

basis.

Parameters







Mean.

CO2 (vol%)

Cold Run

6.60 6.61 6.81 6.67 6.55 6.53

Hot Run

6.74

6.84

6.88

6.66

6.46

6.57

Simmer -ing

6.53 6.52 6.69 6.61 6.29 6.37

CO (vol%)

Cold Run

0.335 0.337

0.325

0.316

0.322

0.317

Hot Run

0.364

0.376

0.349

0.357

0.352

0.349

Simmer -ing

0.369 0.381 0.371 0.367 0.359 0.364

NO (vol%)

Cold Run

0.0055

0.0056

0.006

0.005

0.0027

0.0062

Hot Run

0.007

0.007

0.0072

0.0067

0.007

0.0064

Simmer 0.0051 0.0053 0.0056 0.0047 0.0051 0.0048

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Parameters







Mean. -ing

CH4 (vol%)

Cold Run

0.085

0.091

0.061

0.074

0.068

0.065

Hot Run

0.071

0.075

0.084

0.075

0.069

0.073

Simmer -ing

0.067 0.071 0.063 0.065 0.064 0.063

Combustion efficiency

Cold Run

81

81

84

82

80

80

Hot Run

84

84

85

83

80

81

Simmer -ing

80 80 82 81 77 78

It is customary to report the emission status as the concentration ratio of a pollutant with respect to CO2. As the ratio is dimensionless, it is very easy to compare the emission performance among the stoves. The emission ratios of all stoves in high and low power phase of WBT are shown in table 3.1.5. Table 3.1.6. shows the average emission ratios of all stoves for entire WBT. CO ratios of BUET and Grameen Shakti models in high and low power phases (table 3.1.5.) of WBT varied from 0.047 to 0.055 and 0.049 to 0.057 respectively, whereas the average emission ratios for entire WBT varied from 0.051 to 0.055 for BUET models and 0.053 to 0.054 for Grameen Shakti models. CO emission ratio of Indian Nada Chulha using rice straw as fuel varied from 0.0921 to 0.288 during the high and low power phases of WBT and the average CO emission ratio for entire WBT was found to be 0.1657 (Smith et al. 2000b) which is almost three folds higher than the emission ratios of all stove models of BUET and Grameen Shakti. NO ratios of BUET and Grameen Shakti models in different power phases of WBT varied from 0.00071 to 0.00104 and 0.00041 to 0.00108 respectively. The average NO emission ratios for entire WBT varied from 0.00082 to 0.00092 for BUET models and 0.00077 to 0.00090 for Grameen Shakti models. CH4 ratios of BUET and Grameen Shakti models in high and low power phases (table 3.1.5.) of WBT varied from 0.0089 to 0.0138 and 0.0099 to 0.0111 respectively, whereas the average emission ratios for entire WBT varied from 0.0102 to 0.0119 for BUET models and 0.0103 to 0.0104 for Grameen Shakti models (table 3.1.6.). CH4 emission ratio of Indian Nada Chulha using rice straw as fuel varied from 0.00916 to 0.0151 during the high and low power phases of WBT and the average CH4 emission ratio for entire WBT was found to be 0.0118 (Smith et al.

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2000b). CH4 emission ratios are almost similar among BUET, Grameen Shakti models and Indian Nada Chulha.

Table 3.1.5. Emission ratios of all stoves for WBT (cold and hot start-high power phase; simmering-low power phase)

Parameters







Mean.

CO/CO2 (vol.

ratio)

Cold Run

0.050 0.051

0.047

0.047

0.049

0.049

Hot Run

0.054

0.055

0.051

0.053

0.055

0.053

Simmer -ing

0.056 0.058 0.055 0.055 0.057 0.057

NO/CO2 (vol.

ratio)

Cold Run

0.00083

0.00085

0.00088

0.00075

0.00041

0.00095

Hot Run

0.00104

0.00102

0.00104

0.00100

0.00108

0.00100

Simmer -ing

0.00078 0.00081 0.00084 0.00071 0.00081 0.00075

CH4/CO2 (vol.

ratio)

Cold Run

0.0129

0.0138

0.0089

0.0111

0.0104

0.0100

Hot Run

0.0105

0.0109

0.0122

0.0112

0.0107

0.0111

Simmer -ing

0.0103 0.0109 0.0094 0.0098 0.0102 0.0099

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Table 3.1.6. Average emission ratios of all stoves for entire WBT

Parameters







Mean CO/CO2 (vol. ratio) 0.053 0.055 0.051 0.052 0.054 0.053

NO/CO2 (vol. ratio) 0.00088 0.00089 0.00092 0.00082 0.00077 0.00090

CH4/CO2 (vol. ratio) 0.0112 0.0119 0.0102 0.0107 0.0104 0.0103

Emission factors by fuel mass on pollutant mass basis of all the stoves during different power phases of WBT are shown in table 3.1.7 and average emission factors by fuel mass on pollutant basis of all stoves for entire WBT are shown in table 3.1.8. CO2 average emission factor (gm/kg) for BUET models varied from 979 to 1,003 and for Grameen Shakti models varied from 948 to 956. The upper limit of CO2 average emission factor for Grameen Shakti models is lesser than the lower limit of CO2 average emission factor for BUET models. Whereas, Smith et al (2000b) reported an average CO2 emission factor for Indian Nada Chulha of 983 gm/kg using rice straw as fuel. CO average emission factor (gm/kg) for BUET models varied from 32.63 to 34.11 and for Grameen Shakti models varied from 32.16 to 32.27. In comparison with the average CO emission factor of the Indian Nada Chulha (101 gm/kg), all the models of BUET and Grameen Shakti emit less CO per kg of fuel (rice straw). NO average emission factor (gm/kg) for BUET models varied from 0.550 to 0.630 and for Grameen Shakti models varied from 0.497 to 0.583. CH4 average emission factor (gm/kg) for BUET models varied from 3.55 to 4.22 and for Grameen Shakti model it was 3.59. Average emission factor of CH4 for Indian Nada Chulha was reported as 4.24 gm/kg using rice straw as fuel (Smith et al. 2000b), which is very similar to BUET models.

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Table 3.1.7. Emission factors by fuel mass on a pollutant mass basis (gm/kg D.F.) of the stoves during different power phases of WBT

Parameters







Mean

CO2 (gm/kg D.F.)

Cold Run 971.12 973.1 1007 983.10 959.13 961.12

Hot Run 1007 1008.2 1019 995.10 961.12 971.12

Simmer -ing 959.13 959.3 983.1 971.12 923.16 935.15

CO (gm/kg D.F.)

Cold Run 31.38 31.50 30.57 29.63 30.02 29.64

Hot Run 34.61 35.22 32.90 33.97 33.24 32.84

Simmer -ing 34.49 35.61 34.68 34.30 33.55 34

NO (gm/kg D.F.)

Cold Run 0.55 0.56 0.60 0.50 0.27 0.62

Hot Run 0.71 0.70 0.73 0.68 0.71 0.65

Simmer -ing 0.51 0.53 0.56 0.47 0.51 0.48

CH4 (gm/kg D.F.)

Cold Run 4.55 4.86 3.28 3.96 3.62 3.47

Hot Run 4.07 4.01 4.53 3.21 3.72 3.93

Simmer -ing 3.58 3.79 3.36 3.47 3.42 3.36

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Table 3.1.8. Average emission factors by fuel mass on a pollutant mass basis (gm/kg D.F.) of all stoves for entire WBT

Parameters







Mean

CO2(gm/kg D.F.)

979

980

1003

983

948

956

CO(gm/kg

D.F.) 33.49

34.11

32.72

32.63

32.27

32.16

NO(gm/kg

D.F.) 0.590

0.597

0.630

0.550

0.497

0.583

CH4(gm/kg

D.F.) 4.07

4.22

3.72

3.55

3.59

3.59

Average emission factors of pollutant mass by fuel energy content basis (gm/MJ) of all the stoves for entire WBT are shown in table 3.1.9. CO2 average emission factor (gm/MJ) for BUET models varied from 74.85 to 76.868, whereas this factor varied from 72.48 to 73.10 for Grameen Shakti models. CO average emission factor for BUET models varied from 2.50 to 2.61 gm/MJ, which was higher than CO emission factor for Grameen Shakti models that varied from 2.46 to 2.47 gm/MJ. NO average emission factor for BUET models varied from 0.042 to 0.048 gm/MJ which was higher than NO emission factor for Grameen Shakti models that varied from 0.038 to 0.044 gm/MJ. This was because of high combustion temperature in all BUET models than in Grameen Shakti models. CH4 emission factor (gm/MJ) for all BUET models were higher than Grameen Shakti models except for BUET-triple pot mud stove. CH4 average emission factor for BUET models varied from 0.271 to 0.323 gm/MJ, whereas, this emission factor for Grameen Shakti models was 0.274 gm/MJ. Smith et al (2000b) reported average emission factors of CO2, CO and CH4 to be 75.44, 7.751 and 0.3254 gm/MJ respectively for Indian Nada Chulha using rice straw as fuel.

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Table 3.1.9. Average emission factors of pollutant mass by fuel energy content basis (gm/MJ) of all stoves for entire WBT

Parameters







Mean CO2 (gm/MJ)

74.85

74.92

76.68

75.15

72.48

73.10

CO (gm/MJ)

2.56

2.61

2.50

2.50

2.47

2.46

NO (gm/MJ)

0.045

0.046

0.048

0.042

0.038

0.044

CH4 (gm/MJ)

0.311

0.323

0.284

0.271

0.274

0.274

Aggregated benchmark values of different polluting parameters (gm/5 liter water) for boiling 5 liter water and then simmering it for 45 minutes during entire WBT are shown in table 3.1.10. Total CO2 emission values for entire WBT for 5 liter water of all BUET models are lower than Grameen Shakti models except BUET-single pot mud stove. Total CO2 emission of BUET-single pot stove is somewhat higher than the Grameen Shakti double pot concrete stove. But in comparison with Grameen Shakti-single pot concrete stove, BUET-single pot mud stove emits much lower content of CO2 through the entire WBT for boiling 5 liter water and then simmering it for 45 minutes. The lowest CO2 emission can be attributed to BUET-triple pot mud stove whereas the second lowest CO2 emitter is BUET-double pot mud stove (circular grate). BUET-double pot mud stove (elliptical grate) is the third lowest CO2 emitter cookstove for entire WBT. The ranking of all the stoves in terms of CO emission for entire WBT (to boil 5 liter water and then to simmer it for 45 minutes) is similar to that in terms of CO2 emission. NO emission values of all BUET models were found to be lower for all BUET models compared to Grameen Shakti models for entire WBT. The lowest NO emission can be attributed to BUET-triple pot mud stove. In terms of CH4 emission for entire WBT, all the BUET models emit less CH4 compared to Grameen Shakti models except BUET-single pot mud stove that emits more CH4 compared to Grameen Shakti-double pot concrete stove for entire WBT. Based on CH4 emission, BUET-triple pot mud stove can be ranked as the lowest emitter, the second lowest emitter is the BUET-double pot mud stove (elliptical grate) and the third lowest emitter is the BUET-double pot mud stove (circular grate). Among all the stoves, BUET- triple pot mud stove emitted the lowest amount of each pollutant for entire WBT. The second and third lowest contributors to emission were BUET-double pot mud stove (circular grate) and BUET-double pot mud stove (elliptical grate) respectively.

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Table 3.1.10. Benchmark emission values of all stoves for entire WBT (5 liter water)

Parameters







Mean CO2 (gm/5 liter)

2,294

1,475

1,585

1,138

3,127

2,274

CO (gm/5 liter)

78.47

51.34

51.70

37.79

106.46

76.50

NO (gm/5 liter)

1.38

0.90

1.00

0.64

1.64

1.39

CH4 (gm/5 liter)

9.54

6.35

5.88

4.11

11.84

8.54

3.1.4. Overall performances of the stoves in WBT

Benchmark efficiencies (overall thermal efficiency, combustion efficiency and heat transfer efficiency) and environmental stove index (ESI) of all stoves for entire WBT using rice straw as fuel are shown in table 3.1.11. All the parameters for BUET models show higher values compared to Grameen Shakti models. Overall thermal efficiency, combustion efficiency, heat transfer efficiency and ESI of BUET –single pot mud stove and Grameen Shakti-single pot concrete stove were 18%, 82%, 22%, ln[1] and 10%, 79%, 13%, ln[0.48] respectively. If the BUET-double pot mud stoves are compared with the Grameen Shakti-double pot concrete stove, it can easily be seen that overall thermal efficiencies and heat transfer efficiencies of BUET-double pot mud stoves are almost double than Grameen Shakti-double pot concrete stove. Combustion efficiencies of BUET-double pot mud stoves are also higher than Grameen Shakti-double pot concrete stove. ESI of BUET-double pot mud stoves is also much better than Grameen Shakti-double pot mud stove. The highest overall thermal efficiency and heat transfer efficiency were found for BUET-triple pot mud stove. Most of the performance parameters of BUET models make them worthy to be ranked over the Grameen Shakti models. Superiority of the BUET models over Grameen Shakti models can be attributed to some unique design considerations of BUET models. Preheating provision for combustion air, high fuel bed and flame zone temperatures, high draft in double chimney to create turbulence inside combustion chamber, comparatively short distance between fuel bed and pot mouth to facilitate radiative heat transfer, comparatively low stack temperatures and even distributions of combustion air channels under the fuel grate make all the BUET models worthy to show their superiority over the Grameen Shakti models.

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Table 3.1.11. Benchmark efficiency values and environmental stove index of all cookstoves for WBT

Parameters







Mean Overall thermal

efficiency (%)

18 24 25 29 10 13

Combustion efficiency

(%) 82 82 84 82 79 80

Heat transfer efficiency

(%) 22 29 30 35 13 16

Environmental stove index

(ESI) ln[1.0] ln[1.33] ln[1.56] ln[1.61] ln[0.48] Ln[0.65]

3.2. Results and discussions on CCT performances 3.2.1. Temperature and draft profile of stoves in CCT

During controlled cooking test (CCT) of all the cookstoves, combustion air temperature, fuel bed temperature, stack flue gas temperature and the draft inside the chimney were measure which are shown in table 3.2.1. The values found are almost identical to those found during WBT. Combustion temperature, fuel bed temperature, flame zone temperature are higher for BUET models compared to Grameen Shakti models. Although in some cases the average temperatures of some BUET models were higher than Grameen Shakti-double pot concrete stove, temperature difference between stack and flame zone was much higher in BUET models compared to all Grameen Shakti models. Draft inside chimney of all BUET models shows higher value compared to Grameen Shakti models which means better relative turbulence in BUET models.

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Table 3.2.1.Temperature and draft profile of all stoves during CCT

Parameters







Mean Combustion

air temperature

(oC)

71

68

70

72

30

30

Fuel bed temperature

(oC)

633

628

638

645

602

606

Flame zone temperature

(oC)

731

726

726

724

690

683

Stack flue gas

temperature (oC)

297

332

327

331

336

330

Draft inside chimney (-

Pa)

*7.3

*7.5

*7.3

*7.4

7.2

7.1

*All BUET models have two chimneys. The draft reported here is the average draft per chimney. 3.2.2. Thermal performances of stoves in CCT Cooking menu of a traditional food (cooking of parboiled rice), average cooking time, average fuel requirement per cooking episode in CCT for each type of the stove model are shown in table 3.2.2. Normalized fuel and energy requirement per kg parboiled rice cooking following the same cooking menu for each type of the stove model, and therefore fuel and energy saving and cooking time saving taking the Grameen Shakti-single pot and Grameen Shakti double concrete stove as the reference stove separately are shown in table 3.2.3.

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Table 3.2.2. Fuel consumption and cooking time of all stoves during CCT (parboiled rice cooking)

Parameters







Mean. Cooking menu

Rice(gm) 750 1,500 1,500 2,250 750 1,500 Water(gm) 3,900 7,800 7,800 11,700 3,900 7,800

Cooking time (min) 22 27 19 34 24 30 Dry fuel consumed(gm)

1,128 1,739 1,316 2,350 1,400.6 2,068

It was found that BUET-double pot mud stove (elliptical grate) consumed the lowest fuel and energy per kg parboiled rice cooking (table 3.2.3). Table 3.2.3. Fuel and energy consumption per parboiled rice cooking and fuel/energy saving and cooking time saving of the stoves considering Grameen Shakti-single pot and double pot

concrete stove as the comparison base separately.

Parameters







Mean Fuel consumption (gm/kg parboiled rice cooking)

1504 1159.33 877.33 1044.44 1867.47 1378.67

Energy consumption (kj/kg parboiled rice cooking)

19,672.32 15,164 11,475.48 13,661.27 24,426.50 18,033

Fuel/energy saving

20% 38% 53% 44% Base 26%

Time saving 8% 44% 60% 53% Base 38% Fuel/energy saving

( � ) 9% 16% 36% 24% ( � ) 35% Base

Time saving ( � ) 47% 10% 37% 24% ( � ) 60% Base

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As per table 3.2.3 the rank order of the stoves (from the lowest to highest) based on the fuel and energy consumption for cooking 1 kg parboiled rice following the cooking menu (table 3.2.2.) is: BUET-double pot mud stove, elliptical grate (the lowest fuel and energy consumer) � BUET-triple pot mud stove � BUET-double pot mud stove, circular grate � Grameen Shakti-double pot concrete stove � BUET-single pot mud stove � Grameen Shakti-single pot concrete stove. Taking Grameen Shakti-single pot concrete stove as the base, BUET-double pot (elliptical grate), triple pot, double pot (circular grate), single pot mud stoves and Gramen Shakti-double pot concrete stove save fuel/energy consumption by 53%, 44%, 38%, 19.50% and 26% respectively and save cooking time by 60%, 53%, 44%, 8% and 38% respectively. Even if the BUET-double pot mud stoves are compared with the Grameen Shakti-double pot concrete stove taking this stove as a base BUET-double pot (elliptical grate) and double pot (circular grate) mud stoves can save fuel/energy consumption by 36.4% and 16% respectively and save cooking time by 36.67% and 10% respectively. Whereas, BUET triple pot mud stove can save about 24.24% of fuel/energy compared to Grameen Shakti-double pot concrete stove (table 3.2.3).

3.2.3. Emission performances of stoves in CCT

Pollutant concentrations (wet basis) of CO2, CO, NO and CH4 in flue gases and combustion efficiencies of all stoves during CCT are shown in table 3.2.4. Average emission ratios of CO, NO and CH4 in flue gases of all stoves during CCT with respect to CO2 are shown in table 3.2.5. It was noticed that the average emission ratios of CO of all the stoves during CCT (table 3.2.5) were less compared to average emission ratios of CO of all stoves during WBT (table 3.1.6). Average CO ratios of BUET models and Grameen Shakti models in CCT varied from 0.032 to 0.051 and 0.047 to 0.049 respectively (table 3.2.5). Average NO ratios of BUET models and Grameen Shakti models in CCT varied from 0.00076 to 0.00090 and 0.00077 to 0.00085 respectively (table 3.2.5). Whereas, average CH4 ratios of BUET models and Grameen Shakti models in CCT varied from 0.0104 to 0.0119 and 0.0106 to 0.0110 respectively (table 3.2.5).

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Table 3.2.4. Emission characteristic and combustion efficiencies of different stoves during CCT (parboiled rice cooking)

Parameters







Mean CO2 (vol%) 6.63

6.76

6.61

6.61

6.44

6.49

CO (vol%) 0.286

0.332

0.335

0.210

0.318

0.302

NO (vol%) 0.006

0.006

0.0054

0.005

0.0055

0.005

CH4 (vol%) 0.073

0.081

0.069

0.070

0.071

0.069

Combustion

efficiency 83

83

83

82

79

80

Table 3.2.5. Average emission ratios of the pollutants with respect to CO2 during CCT

(parboiled rice cooking)

Parameters







Mean CO/CO2 (vol. ratio)

0.043

0.049

0.051

0.032

0.049

0.047

NO/CO2 (vol. ratio)

0.00090

0.00089

0.00082

0.00076

0.00085

0.00077

CH4/CO2 (vol. ratio)

0.0110

0.0119

0.0104

0.0106

0.0110

0.0106

Average emission factors of the pollutants (CO2, CO, NO and CH4) by fuel mass basis (gm/kg D.F.) of all stoves during CCT and WBT are shown in table 3.2.6 for comparison. Also, average emission factors of the pollutants mass by fuel energy content basis (gm/MJ) of all stoves during CCT and WBT are shown in table 3.2.7 for comparison. It was found that the CO2 emission factors of all cookstoves increased during CCT compared to WBT with the exception of BUET-double pot mud stove (elliptical grate) and Grameen Shakti-single pot

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concrete stove both of which emitted less CO2 per kg of dry fuel. Average emission factors of CO of all stoves were found to be lower during CCT compared to WBT. Average emission factors of NO increased for BUET-single pot, double pot (circular grate) and Grameen Shakti-single pot concrete stoves during CCT compared to WBT, whereas, for the rest stoves this value decreased. Average emission factors of CH4 of all stoves increased during CCT compared to WBT with the exception of BUET-single pot mud stove wherein this emission factor decreased (table 3.2.6). During CCT, average CO2, CO, NO and CH4 emission factors varied from 983 to 998 (gm/kg D.F.), 19.88 to 31.10 (gm/kg D.F.), 0.50 to 0.61 (gm/kg D.F.) and 3.73 to 4.34 (gm/kg D.F.) respectively for BUET models and from 947 to 959 (gm/kg D.F.), 28.42 to 29.76 (gm/kg D.F.), 0.50 to 0.55 (gm/kg D.F.) and 3.71 to 3.80 (gm/kg D.F.) respectively for Grameen Shakti models.

Table 3.2.6. Average emission factors of CO2, CO, NO and CH4 by fuel mass basis (gm/kg D.F.) of all stoves using rice straw as fuel during CCT and WBT

Parameters







Mean CCT

WBT

CCT

WBT

CCT

WBT

CCT

WBT

CCT

WBT

CCT

WBT

CO2 (gm/kg D.F.)

995 979 998 980 983 1003

987 983 947 948 959 956

CO (gm/kg D.F.)

27.32

33.49

31.10

34.11

19.88

32.72

19.90

32.63

29.76

32.27

28.42

32.16

NO (gm/kg D.F.)

0.61 0.590

0.60 0.597

0.51 0.630

0.50 0.550

0.55 0.497

0.50 0.583

CH4 (gm/kg D.F.)

3.99 4.07 4.34 4.22 3.73 3.72 3.79 3.55 3.80 3.59 3.71 3.59

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Table 3.2.7. Average emission factors of CO2, CO, NO and CH4 mass by fuel energy content basis (gm/MJ) of all stoves using rice straw as fuel during CCT and WBT

Parameters







Mean CCT

WBT

CCT

WBT

CCT

WBT

CCT

WBT

CCT

WBT

CCT

WBT

CO2 (gm/MJ)

76 74.85

76.30

74.92

75.15

76.68

75.46

75.15

72.40

72.48

73.32

73.10

CO (gm/MJ)

2.09 2.56

2.38 2.61

1.52 2.50

1.52 2.50

2.28 2.47

2.17 2.46

NO (gm/MJ)

0.046

0.045

0.046

0.046

0.039

0.048

0.038

0.042

0.042

0.038

0.038

0.044

CH4 (gm/MJ)

0.305

0.311

0.332

0.323

0.285

0.284

0.290

0.271

0.290

0.274

0.284

0.274

Benchmark emission values of CO2, CO, NO and CH4 of all stoves for cooking one kg of parboiled rice using rice straw as fuel following the cooking menu (table 3.2.2) are shown in table 3.2.8. In context of emission values of all the four gases (CO2, CO, NO and CH4) during cooking one kg parboiled rice, BUET-double pot mud stove (elliptical grate) was found to be the lowest emitter. The 2nd, 3rd and 4th lowest emitter were the BUET-triple pot mud stove, BUET-double pot mud stove (circular grate) and Grameen Shakti-double pot concrete stove respectively. Grameen Shakti-single pot concrete stove was found to be the highest emitter in context of all the four pollutants. Therefore, these stoves can be ranked in context of emission performance during CCT as follows: BUET-double pot mud stove, elliptical grate (the lowest emitter) � BUET-triple pot mud stove � BUET-double pot mud stove, circular grate � Grameen Shakti-double pot concrete stove � BUET-single pot mud stove � Grameen Shakti-single pot concrete stove (the highest emitter).

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3.2.8. Benchmark emission of all stoves for cooking parboiled rice (gm/kg parboiled rice cooking) using rice straw as a fuel during CCT

Parameters







Mean CO2 (gm/kg parboiled rice cooking)

1,497 1,157 862 1,031 1,769 1322

CO (gm/kg parboiled rice cooking)

41.1 36.1 17.44 20.78 55.58 39.18

NO (gm/kg parboiled rice cooking)

0.92 0.70 0.45 0.52 1.03 0.69

CH4 (gm/kg parboiled rice cooking)

6.0 5.0 3.3 3.96 7.1 5.1

Benchmark emission reduction by different stoves under consideration for cooking parboiled rice following the cooking menu given in table 3.2.2 using rice straw as cooking fuel during CCT taking Grameen Shakti-single pot concrete stove as reference stove are shown in table 3.2.9. The highest pollution reduction was found in BUET-double pot mud stove (elliptical grate). The 2nd , 3rd , 4th and 5th highest emission reduction were found in BUET-triple pot mud stove, BUET-double pot mud stove (circular grate) and Grameen Shakti-double pot concrete stove and BUET-single pot mud stove respectively. Therefore, these stoves can be ranked in context of emission reduction performance during CCT as follows: BUET-double pot mud stove, elliptical grate (the highest emission reducer) > BUET-triple pot mud stove > BUET-double pot mud stove, circular grate > Grameen Shakti-double pot concrete stove > BUET-single pot mud stove (the 5th highest emission reducer). Tough the 5th highest emission reduction was found in BUET-single pot mud stove with respect to multiport cookstoves, it is better than Grameen Shakti-single pot concrete stove in context of emission reduction option.

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CO2, CO, NO and CH4 emission reductions of BUET models during CCT (considering Grameen Shakti-single pot concrete stove as reference stove) varied from 15 to 51%, 26-69%, 11 to 56% and 15 to 54% respectively whereas, these emission reductions were found to be 25%, 30%, 33% and 28% in Grameen Shakti-double pot concrete stove. Though the emission reductions of Grameen Shakti-double pot concrete stove are close to those of BUET-double pot mud stove (circular grate), the latter is better in context of pollution reduction option.

3.2.9. Benchmark emission reduction by different stoves for cooking parboiled rice using rice straw as fuel during CCT considering Grameen Shakti-single pot concrete stove as reference.

Parameters







Mean CO2 reduction 15% 35% 51% 42% Reference

stove 25%

CO reduction

26% 35% 69% 63% Reference stove

30%

NO reduction


33%

CH4 reduction


28%

Benchmark emission reduction by different stoves under consideration for cooking parboiled rice following the cooking menu given in table 3.2.2 using rice straw as cooking fuel during CCT taking Grameen Shakti-double pot concrete stove as reference stove are shown in table 3.2.10. It is obvious that BUET-double pot models and triple pot model take a ride on Grameen Shakti-double pot model in terms of emission reduction. However, BUET-double pot mud stove (elliptical grate) and BUET-triple pot mud stove are much better than Grameen Shakti-double pot concrete stove in context of emission reduction option. Negative sign in table 3.2.10 indicates that emission reductions of BUET-single pot mud stove and Grameen Shakti-single pot concrete stove are inferior compared to Grameen Shakti-double pot concrete stove.

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3.2.10. Benchmark emission reduction by different stoves for cooking parboiled rice using rice straw as fuel during CCT considering Grameen Shakti-double pot concrete stove as reference.

Parameters







Mean CO2 reduction

( � ) 13% 12% 35% 22% ( � ) 34% Reference stove

CO reduction

( � ) 4.9% 8% 55% 47% ( � ) 42% Reference stove

NO reduction

( � ) 33% ( � ) 1% 35% 25% ( � ) 49% Reference stove

CH4 reduction

( � ) 18% 2% 35% 22% ( � ) 39% Reference stove

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CHAPTER 4 CONCLUSIONS

All the BUET models were better designed stoves in context of combustion efficiency, heat transfer efficiency, overall thermal efficiency, and emission reduction. If one compares the performances of single pot stove between BUET and Grameen Shakti models, obviously BUET-single pot mud stove will be ascertained as the better option with respect to lesser amount of fuel requirement, lesser time requirement to cook, and lesser amount of pollutant emission. If one compares the performances of double pot stove between BUET and Grameen Shakti models, no doubt that BUET-double pot mud stoves will get ride on the Grameen Shakti-double pot concrete stove in context of reduced cooking time, reduced fuel consumption, and reduced emission. However, BUET-double pot mud stove with elliptical grate is the best engineered stove among the double pot stoves designed by BUET and Grameen Shakti from every nook of stove performances. BUET-triple pot mud stove can also be considered as one of the best models among the multi pot stove variant in context of reduced fuel consumption, cooking time and pollutant emission. Therefore, all the BUET models superseded the performances of Grameen Shakti models within their respective group i.e., single pot stove and multiport stove. This performance superiority of BUET models can be attributed to some basic concepts in engineering design of the stoves, i.e., preheating combustion air, better mixing of incoming combustion air with fuel and volatiles inside combustion chamber through evenly distributed multi channels under the fuel bed, increasing radiative heat transfer by shortening the distance between grate and pot mouth, and increasing convective heat transfer through maintaining high draft inside the chimneys.

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Documents

Component-6 Improving Energy Efficiency and Emission ......Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Component-6 Improving Energy Efficiency and Emission Characteristics