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© Applied Science Innovations Pvt. Ltd., India Carbon – Sci. Tech. 6/4(2014)15-22

ARTICLE Received : 18/12/2014; Accepted :25/12/2014 -----------------------------------------------------------------------------------------------------------------------------Efficiency enhancement of wood stove integrated with catalytic combustor and modified chimney

G. Murali (*), P. Goutham, I. Enamul Hasan, P. Anbarasan, G. Ashok

Department of Mechanical Engineering, Adhiyamaan College of Engineering, Hosur - 635109, Tamil Nadu, India.

Domestic wood combustion produces smoke that is harmful to human health and increases fine particle level in the atmosphere. Some necessary changes in the design are essential in the domestic wood stove in order to improve the performance and scale down the emission. In this work, an improved wood stove integrated with the catalytic combustor and modified chimney that uses wood as fuel has been experimentally evaluated. Water boiling test, cooking test and emission test have been conducted to evaluate the performance of the stove. It was observed that emission has been considerably controlled because of the incorporation of catalytic combustor. The heat losses through the walls of stove decresed by providing ceramic insulation. The thermal efficiency value of an improved wood stove obtained was 41.18% and this is 31.52% higher than traditional stove. The improved wood stove results better performance than a traditional wood stove.

Key words: Wood stove, Catalytic combustor, Emission, Cooking, Water boiling-----------------------------------------------------------------------------------------------------------------------------------------1. Introduction: Wood stove is widely used for cooking and room heating. Still more people in the rural and urban area uses firewood for cooking. Electric stoves and boiling rings have been rendered useless as a result of improper power supplies. Usage of wood stove causes discomfort owing to heavy smoke. According to the U.S. Environmental Protection Agency, the use of wood for residential heating contributes up to 50 percent of the polynuclear organic air pollutants, some of which may be carcinogenic. During winter, in areas where wood is the principal heating fuel, wood stoves produce as much as 80 percent of these kind of pollutants. Cooking over an open fire with solid fuels has been recognised as causing a serious health problem. Currently, most developed and developing countries are heavily dependent on fossil fuels. solid fuels are used for cooking particularly in rural areas.

Fossil based technology is the primary source in India to meet the energy requirement in small as well as large industrial applications. Still 2.5 billion people around the world do not have access to modern fuels [1]. Alphonse Nahayo et al. [2] evaluated that the thermal efficiencies of traditional stoves are relatively less. Yutana Sriudom [3] stated that thermal efficiency also decreases due to heat loss through walls, which encouraged to insulate the walls in this paper. The inverted siphon was used to draw the fire’s hot fumes up the front and down the back of the Franklin stove’s hollow baffle, in order to extract as much heat as possible from the fumes which made to redesign the chimney in this improved wood stove. Smoke from biomass combustion produces a large number of health-damaging air pollutants including respirable particulate matter, carbon monoxide (CO), nitrogen oxides, formaldehyde, benzene, 1,3 butadiene, polycyclic

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aromatic hydrocarbons (such as benzo[a]pyrene), and many other toxic organic compounds. West S et al. [4, 5] stated that annually about 2 million people become blind worldwide and cataract-related blindness accounts for half of these cases. Three epidemiological studies have provided some evidence of an association between cataract or blindness and exposure to indoor smoke from household use of solid biomass fuels, such as animal dung, wood, and crop residues [6-8]. Indoor air pollution (IAP) from traditional biomass burning contributes to serious health problems, particularly cancer and respiratory infections that cause an estimated 1.6 million premature deaths annually [9-11] which made to incorporate this improved wood stove with catalytic combustor.

Christoph schmidl et al. [12] designed a sampling device and compared the chemical profiles of fine particle emissions from wood stove combustion with various common woods. Murari Mohan Roy et al. [13] investigated the potential use of hay and switch grass briquettes and studied the combustion and emission of biomass briquettes and observed that CO emission has a strong correlation with excess air factor, the higher the excess air factor the lower the CO emissions. NOx and SO2 emissions are proportional to fuel N2 and S content respectively. Lars Kare Grimsby et al. [14] studied the fuelling of jatropha fruit coats in a sawdust stove with controlled water boiling test. E.Pieratti et al. [15] characterized the gaseous emission of spruce tree using two staged high efficiency-air gasifying woodstove. This experiment resulted in limitation of emission of unburned components. Julie F.Hart et al. [16] understood the reduction of particle count concentration and evaluated the effectiveness of an electrostatic filter portable air purifier. Emma Hedberg et al. [17] characterized the emissions of chemical compounds emitted from birch wood combustion in a wood stove. Komolafe [18] studied the design and fabrication of improved charcoal cooking stove and evaluated their performance under different test conditions. This paper discusses the observation of the study on an improved wood stove incorporated with catalytic combustor and evaluation done on their performance and efficiency.

2. Experimental Study: The wood stove consists of Combustion Chamber, Air Vent 1 & 2, Ash tray 1 & 2, Wood Holder, Chimney, Pot seat 1 and Pot seat 2. Combustion chamber is the place where wood is burnt to produce useful heat. Schematic diagram of wood stove with catalytic combustor and modified chimney are shown in Figure (1). The casing of the stove has three layers. The walls of the combustion chamber and remaining part of the stove is equipped with 50mm ceramic Insulation (Thermal conductivity is 1.06 W/mK). The Catalytic combustor is placed in between pot seat 2 and chimney. The inner and outer layer of the stove is made of mild steel and the chimney is made of galvanized iron pipe as shown in the photographic view figure (2). Ash tray is placed in stove which collects the burnt out wood ash. Chimney is designed in such a way that it restricts the flow of excess gas to the atmosphere so as to enhance the heat transfer to the both pots. Also two pots play a vital role in improving efficiency. One pot is used to absorb the energy from main source and another one is used to utilize the excess energy from the gases passing towards the chimney.

Keeping the air flowing correctly through a wood-burning stove is essential for safe and efficient operation of the stove. Fresh air needs to enter the wood compartment to provide oxygen fuel for the fire; as the fire burns, the smoke must be allowed to rise through the stove pipes, and exit through the chimney. To regulate air flow, there are damper devices built into the stove, flue, and stove pipes. By opening or closing the dampers, air flow can be increased or decreased, which can fan the fire in the wood compartment, or "dampen" it by restricting airflow and reducing the flames. The dampers can usually be accessed by turning a knob or a handle attached to the damper, found outside the stove or stovepipe. One of the uses of the dampers is to increase airflow into the wood compartment to raise flames and thus, the temperature of the stove, temporarily create a high heat for cooking. It is ash handling device in which burnt ash will be collected. After , it can be removed. It is a cavity provided inside the combustion chamber for placing the wood inside the combustion chamber.

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Figure (1): Schematic diagram of wood stove with catalytic combustor and Modified chimney

Figure (2) : Photographic view of wood stove with catalytic combustor and Modified chimney

2.1 Catalytic combustor and Modified chimney: Catalytic combustor is made of ceramic honey comb structure coated with reactants like platinum, palladium or rhodium. A typical catalytic combustor used in this improved wood stove is shown in Figure (3). Wood smoke gases coming in contact with the catalyst, causes chemical changes to take place. This will then allow the smoke to ignite at temperatures around 260o C. The catalytic combustor not only removes pollution from the exhaust, it also creates usable heat and a safer chimney. Wood smoke flows

through the honeycomb of the combustor, creating the catalytic reaction. Ash, particulates, and harmful gas exhausts are converted into water vapor and carbon dioxide, which safely exit chimney without polluting the atmospheric air. Significant heat is released as a result of chemical reaction occurred in the catalytic combustor. The advantage of maintaining combustor is extracting the excess heat that lost through the chimney. 'U' shaped chimney is used in the stove to slow down the flow gases, producing effective catalytic reaction. Also it decreases the wood consumptions with improved productivity. This chimney provides good ventilation and creates smooth flow to the flue gases from combustor.

Figure (3) : Catalytic combustor used in the improved stove

2.2 Water Boiling Test: The three trails of water boiling test were carried out to evaluate the improved cooking stove. The performance of the improved stove with catalytic combustor was evaluated and compared using wood as fuel material. The woods are dried such that to burn efficiently. The apparatus were two big size aluminium pots, a weighing balance, an infrared thermometer two mercury-in-glass thermometers, a stopwatch, water and matches. The stoves were tested in the open air with the atmosphere conditions being 28ºC dry bulb and relative humidity of 65%. These tests were carried out in such a way to match the cooking method commonly adopted in rural committees in India.

The improved wood stove was loaded with equal amounts of fuel (wood). In improved wood stove two pre-weighed aluminum pots designated as pot

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A and B were filled with the same quantity of water. The initial temperature of the water was recorded using a mercury-in-glass thermometer before the pots were placed on the stove. The wood was sprayed with 30 ml of kerosene and then ignited. The change in temperature up to the boiling point was recorded at two minutes intervals with the two thermometers permanently inserted in the two opened pots. At boiling temperature the pots were removed from the stoves and weighed. The temperature measurements of different locations of wood stove during the test are shown in figure (7). Also the fire was put out immediately and the remaining fuel was weighed. The traditional wood stove was loaded with equal amounts of fuel as of improved wood stove. In this stove, one pre-weighed aluminium pot filled with the same quantity of water was placed and other process were done as same as water boiling test done in improved wood stove.

2.3 Cooking test: One kg of rice with two litres of water was cooked using improved wood stove, as well as traditional stove. The cooking test results are shown in table (2).

2.4 Thermal efficiency: Efficiency, which is a measure of the proportion of the total energy which is usefully employed in a thermodynamic system. The burn rate and the net calorific value of the fuel were used in the calculation of this parameter as stated

Thermal Efficiency = ∑ of QU for all potsQa

Qa=W × C

where Qa = heat generated by the wood (dry weight)W = Weight of the wood burnt during the trailC = Calorific content of the wood is 17.39 kJ/g.

Qu=( W i−W f ) ×C v+(T f −T i ) ×W f ×C e

where,Qu= heat utilized (kJ),W initial= initial weight of water (g),W final= final weight of water (g),

C v = water vaporization heat (2.253 kJ/g),T initial= initial water temperature (oC )T final= final water temperature (oC)C e= water specific heat (0.00418 kJ/g/oC)

2.5 Emission Test: The emission test has been carried out using Crypton D 680 4 gas analyzer to measure CO & CO2 Indian Govt. Approved-ARAI Approved-TNPCB Approved). Test results are presented in table (2). Emission measurements were made on the both improved wood stove and the traditional wood stove. Concentrations of CO and CO2 were measured and emission factors were calculated.

3. Results and Discussion: The water boiling test results are specified in table (1) which gives the information about the data used for thermal efficiency calculation. Figure (4) illustrates time vide temperature history of both improved wood stove and traditional stove during water boiling test. It can be seen from the figure that water boils at pot A of improved wood stove within 19 minutes. But traditional wood stove takes 34 minutes to boil water. When water starts boiling in pot A, the temperature of water in pot B reaches 62oC, that is better than temperature of water in traditional stove. The unburned gases from pot A can be burnt due to the presence of catalytic combustor near by the pot B.

Figure (4): Time wide temperature variation during water boiling test

Figure (5) shows the fuel consumption of wood stoves to boil the water during the cooking test. It is absorbed from the figure that the improved

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wood stove save firewood more than traditional one. For cooking rice improved wood stove consumed low quantity of firewood 0.53 kg and the cooking time of 18 minutes but traditional firewood stove consumed high quantity of firewood like 2.43 kg and uses 37 minutes.

The performance of wood stoves by comparing the thermal efficiency is shown in figure (6). The efficiency obtained by improved and traditional stove is 40.18% and 8.66% respectively. The improved stove produces better efficiency because of the design and modification such as ceramic insulation of walls, incorporation of catalytic combustor and "U" bend of chimney, ceramic insulation. Ceramic insulation reduces the considerable heat loss to the surrounding. Catalytic combustor decreases the emission of CO and CO2. The emission test results has been listed in Table (3) for both stoves. The design modification of chimney slows down the exhaust gas flow in such a way that the catalytic combustor can burn the unburned gases. These things lead the improved performance of improved wood stove than traditional stove.

Table (1) Water boiling test results of both stoves

Parameter

Improved wood Stove

Traditional Stove

POT A

POT B

POTC

Initial mass of the water (Kg)

2 2 2

Water evaporated (Kg)

0.8 0.4 0.6

Initial water temperature (°C)

20 20 20

Final water temperature (ºC)

98 62 98

Latent heat of vaporization of water (J/kg)

2.25 x 106

Fire wood used (Kg)

0.5 0.5 1.1

Calorific value of fire wood (J/K) 1.68 x 107

Specific heat capacity of water (J/kg)

4.2 x 103

Table (2) Cooking Test Results of stoves.

No of test

Fire wood consumed (kg) Time (minutes)

Improved wood stove

Traditional stove

Improved wood stove

Traditional Stove

1 0.5 2.4 18 382 0.6 2.5 19 383 0.5 2.4 19 37Mean 0.53 2.43 18.66 37.66

Improved wood stove

Traditional stove0

0.5

1

1.5

2

2.5

3

Woo

d co

nsum

ptio

n (k

g)

Figure (5): Wood consumption for

cooking rice (Kg)

Improved wood stove

Traditional stove 05

1015202530354045

40.18

8.66

Effic

ienc

y (%

)

Figure (6): Efficiency comparison of improved wood stove with traditional stove

Table (3) Emission Test Results of stoves.

Name of the wood stove Emission factors(g/kg fuel used)CO CO2

Traditional wood stove 38.7 1607Improved wood stove 22.2 1584

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f

Figure (7): Temperature measurements at different locations of the wood stove during the

tests

4. Conclusion: The primary objective of the study was to assess how improved firewood stoves contribute to forest protection during the time that increasing the household’s income. The methodology used to test the improved wood stove and traditional stove was water boiling test, cooking test and emission test. The boiling time and firewood consumption have been determined. An improved wood stove was fabricated and compared with a traditional stove. The performances of the two stoves were evaluated. It is observed from the experimental study that the improved wood stove has an efficiency of 41.18% and the thermal efficiency of traditional firewood stove is 8.66%. Also the results that the improved stove yields less fire wood consumption, time consumption with controlled emission.

References:

[1] IEA, World Energy Outlook, Appendix 1, 2009.

[2] Alphonse Nahayo, Jean de Dieu Murindahabi, Jennifer Rono, ‘Assessing the contribution of improved stove to the household income and environmental protection in Musanze district, Rwanda’, New York Science Journal 5/11 (2012).

[3] Yutana Sriudom, ‘Thermal efficiency improvement and technology transfer of chimney stove for producing stove’, Amphoe Bo Kluea, Nan Province, Energy Procedia 9 (2011) 238 – 244.

[4] S. West, A. Sommer, ‘Prevention of blindness and priorities for the future’, Bull. World Health Organ. 79 (2001) 244 –248.

[5] J. C. Javitt, F. Wang, S. K. West, ‘Blindness due to cataract: epidemiology and prevention’, Annu. Rev. Public. Health 17 (1996) 159 – 177.

[6] M. Mohan, R. D. Sperduto, S. K. Angra et al., ‘India-US case-control study of age-related cataracts’, Arch Ophthalmol. 107 (1989) 670 – 676.

[7] V. K. Mishra, R. D. Retherford, K. Smith, ‘Biomass cooking fuels and prevalence of blindness in India’, J. Environ. Med. 1 (1999) 189 – 199.

[8] S. P. Zodpey, S. N. Ughade, ‘Exposure to cheaper cooking fuels and risk of age-related cataract in women’, Ind. J. Occupational Environ. Med. 3 (1999) 159–161.

[9] Naeher L.P. Brauer, M. Lipsett, M. Zelikoff, J. T. Simpson, C. D. Koenig, J. Q. Smith K. R, ‘Wood smoke health effects: A review’, Inhalation Toxicology 19 (2007) 67 – 106.

[10] K. R. Smith, ‘Health impacts of household fuel wood use in developing countries’, Unasylva 224/57 (2006) 41 – 44.

[11] WHO, Fuel for Life: Household Energy and Health. World Health Organization. Available at /http://www.who.int/indoorair/publications/fuelforlife/en/index.html (2006).

[12] Christoph Schmidla, Iain L. Marr, Alexandre Caseiro, Petra Kotianova, Axel Berner, Heidi Bauer, Anne Kasper-Giebl, Hans Puxbaum, ‘Chemical characterisation of fine particle emissions from woodstove combustion of common woods growing in

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mid-European Alpine regions’, Atmospheric Environment (2007).

[13] Murari Mohon Roy, Kenny, W. Corscadden, ‘An experimental study of combustion and emissions of biomass briquettes in a domestic wood stove’, Applied Energy 99 (2012) 206 – 212.

[14] E. Pieratti, D. Antolini, P. Baggio, M.negri, ‘Wood combustion process: Characterization of gaseous emissions of different parts of a Spruce tree by means of a Gasifying wood stove’, Venice 2010, Third International Symposium on Energy from Biomass and Waste.

[15] Emma Hedberga, Adam Kristenssonb, Michael Ohlssonc, Christer Johanssona et al., ‘Chemical and physical characterization of emissions from birch wood combustion in a wood stove’, Atmospheric Environment 36 (2002) 4823 – 4837.

[16] Julie F. Hart, Tony J. Ward, Terry M. Spear, Richard J. Rossi, Nicholas N. Holland, and Brodie G. Loushin, ‘Evaluating the Effectiveness of a Commercial Portable Air Purifier in Homes with Wood Burning Stoves: A Preliminary Study’, Journal of Environmental and Public Health Volume 2011, Article ID 324809, 7 pages.

[17] Lars Kare Grimsby, Erik Johan Langfeldt Borgenvik, ‘Fuelling sawdust stoves with jatropha fruit coats’, Sustainable Energy Technologies and Assessments 2 (2013) 12 – 18.

[18] C. A. Komolafe, O. Awogbemi, ‘Fabrication and Performance Evaluation of an Improved Charcoal Cooking Stove’, The Pacific Journal of Science and Technology Volume 11. Number 2. November 2010.

[19] Anne Jerneck, Lennart Olsson, ‘A smoke-free kitchen: initiating community based co-production for cleaner cooking and cuts in carbon emissions’, Journal of Cleaner Production 60 (2013) 208 - 215.

[20] Erick Boy, Nigel Bruce, Ruben Hernandez, ‘Fuel efficiency of an improved wood-burning stove in rural Guatemala: implications for health, environment and development’, Energy for Sustainable Development, Volume IV, No.-2l August 2000.

G.Murali is presently an Associate Professor in the Department of Mechanical Engineering, Adhiyamaan college of engineering, Hosur, Tamil Nadu, India. He has published 3 papers in the International Journals and presented 2 papers in the International Conferences

P.Goutham is currently an Under Graduate Scholar at the Department of Mechanical Engineering, Adhiyamaan College of Engineering, Hosur, Tamil Nadu, India.

I.Enamul Hasan is currently an Under Graduate Scholar at the Department of Mechanical Engineering, Adhiyamaan College of Engineering, Hosur, Tamil Nadu, India.

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P.Anbarasan is currently an Under Graduate Scholar at the Department of Mechanical Engineering, Adhiyamaan College of Engineering, Hosur, Tamil Nadu, India.

G. Ashok is currently an Under Graduate Scholar at the Department of Mechanical Engineering, Adhiyamaan College of Engineering, Hosur, Tamil Nadu, India.

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