Development and Evaluation of a Biomass Stove

Transcription

1 Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) (): 5-50 Scholarlink Research Institute Journals, 0 (ISSN: -70) jeteas.scholarlinkresearch.org Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) (): 5-50 (ISSN: -70) Development and Evaluation of a Biomass Stove V. I. Umogbai and J. G. Orkuma Department of Agricultural and Environmental Engineering, University of Agriculture, Makurdi, Nigeria. Corresponding Author: V. I. Umogbai Abstract Locally fabricated biomass stoves have become household items in igeria. The fabricated stoves are usually made by local artisans who have little or no knowledge of engineering principles and methods. A portable improved cookstove (ICS) that incorporates a cylindrical ceramic combustion chamber into a framed cylindrical metal casing for cladding and ease of handling was developed and tested in the Department of Agricultural and Environmental Engineering, University of Agriculture Makurdi. A modified University of California water boiling test (WBT) version. was used for testing of the stove. The results obtained from tests carried out on the improved cookstove were compared with the traditional -stone stove. The result of the cold start test indicates that the ICS used an average of g of wood to boil liter of water in about min (5 liters in min) as against g of wood to boil the same liter of water in about 5 min(5 liters in min) using the -stone stove. This indicates that the ICS is superior to the -stone stove in specific fuel consumption in the high power (cold start) phase. The average rate of wood consumption (burning rate) was higher for the - stone stove (0.g/min) than the ICS (.7 g/min) indicating better performance of over the -stone stove. Analysis showed that the performance of the ICS is statistically significant at t 5 but not at t against the -stone stove; (burning less wood per unit time to accomplish the same task). The thermal efficiency of the ICS (7%) was better than the -stone stove (%) and statistics at both t 5 and t showed a significant difference of such superiority of the ICS over the -stone stove for thermal efficiency. The firepower of the -stone fire stove (kw) was higher than the ICS (kw) which is in agreement with the burning rate as the -stone fire consumed more wood per unit time for the same task. The test results of the high power hot start phase showed that the average rate of wood consumption (burning rate) was higher for the -stone stove (0.g/min) than the ICS (. g/min). The firepower of the -stone stove (70kW) was lower than the ICS (77kW). The average thermal efficiency for this phase was % for the ICS and % for the -stone fire stove. In most aspects of stove performance the ICS was better than the -stone fire stove and thus it is recommended for use. Keywords: biomass, stove, design, construction, testing I TRODUCTIO Biomass fuel is the amount of fuel energy that can be derived directly or indirectly from biological sources. Biomass energy from wood, crop residues, and dung remains the primary source of energy for the poor in developing regions. (Microsoft encarta, 00). In a study of forty-five urban areas in developing countries, Barnes and Qian, () found that onethird of all household energy expenditures were on fuelwood or charcoal and that energy expenditure accounted for about one-tenth of all household expenditures. The urban poor sometimes spend as much as one-fifth of their cash income on energy, more than half of it on biomass fuels. Locally fabricated biomass stoves have become household items in Nigeria. The fabricated stoves are usually made by local artisans who have little or no knowledge of engineering principles and methods. These metal stoves deteriorate with time due to thermal fatigue and food spills and their efficiencies have not been ascertained using engineering procedures and techniques. The household sector is the largest energy consumer in Nigeria, accounting for about 0% of traditional fuels especially fuelwood (Adegbulugbe, 5). It is therefore necessary to develop and evaluate the performance of an improved cookstove using (ICS) established engineering principles. Improved cookstoves (ICS) can be of great significance to these people. Fuel savings can reduce cash outlays for purchasing wood or charcoal, shorten collection times, alleviate local pressure on wood resources, and diminish air pollution. The improved cookstove (ICS) pertains to the solid biomass fuel burning system in which heat is produced, by combustion, for immediate use in domestic cooking. ICS can also perform other tasks, depending on the design purpose arising from the user's needs. Such a stove may perhaps be termed an improved cookstove (ICS) which can be used for numerous applications, namely: cooking, food preservation/drying, domestic heating and other social and cultural activities. 5

2 Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) (): 5-50 (ISSN: -70) In Nigeria, biomass stove is essential not only for the poor but also for the middle class level as a result of the high cost of kerosene fuel (DPK). Also, electric power is mostly non-existence in rural communities; while in the urban areas its supply is poor and epileptic. Natural gas which is abundant in the Niger Delta region is flared off at source by the mineral oil producing companies, and the little that is tapped is made available to operate electric generating turbines and for use by major industrial outfits. Biogas and solar energy are still at the experimental stages in the country. Nigeria being a developing country, biomass stove would remain a major source of energy for a high percentage of her population. This elicits the need to develop and evaluate an improved stove based on engineering principles and techniques. Design Criteria A cookstove is best considered as a consumerspecific device. Both engineering and nonengineering parameters need to be taken into consideration in designing an appropriate ICS. This makes the exercise much more complex when compared with the design of other types of engineering equipment or of a kerosene burning stove. ICS design considerations can be classified into three major criteria, namely: social, engineering, and developmental & ecological. MATERIALS/CO STRUCTIO The materials used for the stove include clay and charcoal (which forms a ceramic composition) for the combustion chamber. A mm mild steel metal sheet for the stove casing; and an mm rod for grate. A flat metal bar clip was used for holding the combustion chamber to the casing. Combustion Chamber The combustion chamber was made from a claycharcoal mix. Raw un-briquetted charcoal was finely grinded using a grinder and the resulting powder was passed through #(.mm) screen. Clay was taken from a pond at Wurukum area of Makurdi, Benue State, Nigeria, and was allowed to dry at ambient temperature.,700g of the clay was mixed with water and then,500g of charcoal was added and the mixture was kneaded and molded by a local female potter into the cylindrical combustion chamber (Fig.). The chamber was allowed to dry for two days and then fired in a local kiln used for firing earthen pots. Design Calculations Equations used to determine the cross-sectional area of the cylindrical combustion chamber, and height of the chamber are those formulated by Brydem et al (005). Cross-sectional Area () Where is the area, =. and is the radius. Height of the combustion chamber () Bryden et al (005) recommended that for a family of five persons, using a pot size of 0cm diameter, the side opening of the combustion chamber should be cm and the cross-sectional area should be maintained throughout the body of the stove. Hence applying Eqn. the calculated cross-sectional area of the combustion chamber is:. According to Bryden et al (005), the height ( ) of the combustion chamber should be three times the diameter of the side opening. From Eqn. is: From the calculations the cross-sectional area of the combustion chamber is and runs through a height of. The Casing The casing is made from a mm metal sheet and framed cylindrical to encase the combustion chamber with its base sealed with the same material. A.cm round slot is made on one side of the casing as the side opening of the combustion chamber and tripod prongs 0cm long made from a metal bar were erected inside the base to accommodate the combustion chamber and hold it firmly in place (Fig.). The Grate The grate (Fig.) was made by framing mm rods into cm x0m rectangle, attached with rods to raise it 5cm high for the placement of fuel magazines in the combustion chamber to allow inflow of air beneath the burning woods in order to improve combustion. Bryden et al, (005) recommended a - 0cm height for grate or 5% of the side opening for combustion chambers of less than 0cm diameter. The Pot Stand A standard pot stand 7.5cm diameter rim with tapered baffle flaps for placement of different sizes of pots was bought from the local market in Makurdi as specified by Bryden et al (005) (Fig.) and place over the top of combustion chamber. Testing of Stove A modified University of California at Berkeley (UCB) water boiling test (WBT) version. by Bailis et al (00) was used for testing of this stove. This modified version of the well-known Water Boiling Test (WBT) is a rough simulation of the cooking process that is intended to help stove designers understand how well energy is transferred from the fuel to the cooking pot. It can be performed on most stoves throughout the world. In order to simulate the actual process of boiling in a cooking. 55

3 Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) (): 5-50 (ISSN: -70) Figure : The Assembled Stove process, which comprises cooking and simmering, the water boiling test has been modified. The WBT consists of three phases that immediately follow each other. In the modified method, the total test period is divided into two parts, namely, the high power phase (heating or cooking period) and the low power phase (simmering period). The rating of a cookstove is good according to this method if a certain mass of water can be quickly boiled during the high power phase and a small quantity of fuelwood is used during the low power phase. In the first phase,(the cold-start high-power test), the test begins with the stove at room temperature and uses a pre-weighed bundle of wood or other fuel to boil a measured quantity of water in a standard pot. After the water has boiled, then another quantity of fresh water is poured in the pot to replace the boiled water and to perform the second phase of the test. The second phase, (the hot-start high-power test), follows immediately after the first test while stove is still hot. Again, in the test, a pre-weighed bundle of fuel is used to boil a measured quantity of water in a standard pot. Repeating the test with a hot stove helps to identify differences in performance between a stove when it is cold and when it is hot (Bailis et al, 00). The third phase follows immediately from the second. Here, the tester determines the amount of wood required to simmer a measured amount of water at just below boiling for 5 minutes. This step simulates the long cooking of legumes or pulses common throughout much of the world. Figure : Ceramic Combustion Chamber Figure : Pot Stand placed on the ceramic combustion chamber This combination of tests measure some aspects of the stove s performance at both high and low power outputs, which are associated with the stove s ability to conserve fuel. However, rather than report a single number indicating the thermal efficiency of the stove, which is not necessarily a good predictor of stove performance (Bailis et al, 00), this test is designed to yield several quantitative outputs. Different stove designers may find different outputs more or less useful depending on the context of their stove program. The outputs are: time to boil (adjusted for starting temperature); burning rate (adjusted for starting temperature); specific fuel consumption (adjusted for starting temperature); Firepower turn-down ratio (ratio of the stove s high power output to its low power output); and thermal efficiency Before the testing the moisture content of the fuel wood (cm cm 0cm) was determined by gravimetric method and the average moisture content was found to be 0.%. 5

4 Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) (): 5-50 (ISSN: -70) A practice test was performed on ICS and the -stone fire stove in order to become familiar with the testing procedure and with the characteristics of the stove and the local boiling point of water was established as.5 o C. Three replicates were carried out for each phase and the control test. Microsoft Excel (00) was used for analysis of variance (ANOVA). Control Test The three-stone hearth was used as the control to evaluate the performance of the improved cookstove. The same sticks of wood were burned directly under the pot which was held cm above the testing surface by three bricks. The procedure described in section. was repeated three times for the control. A Water Boiling Test (WBT) version. excels calculation sheet program developed for Shell Foundation s- Household Energy and Health Programme (HEH) (Bailis et al, 00) was used to analyse the results obtained for the tests. Table is the result summary of the t-test between the ICS and the traditional stove high power (cold start) phase while table is the result summary of the t-test between the ICS and the -stone fire stove high power (hot start) phase and table is the result summary of the t-test between the ICS and the - stone fire stove low power (simmering). Fig - are the graphs of the; specific fuel consumption, burning rate, thermal efficiency and fire power against the time to boil for the two stoves. RESULTS A D DISCUSSIO Table : Summary of test results showing the effect of data variability on statistical confidence based on three tests of each stove (cold start) Stove- (ICS) Stove-(stone) Statistics Mean SD CoV Mean SD CoV Significant with 5% (Table Value=.0) Significant with % T-test (Table Value=.) to boil 5 liters of water (min) 5. 77%. % YES YES -. Thermal efficiency (%) 7 50% 5 % YES YES -. Rate of wood consumption (g/min) % 0..7 % YES NO.77 Specific fuel consumption (g/liter).. % 0 % YES YES -.5 Firepower (kw) % 5. % YES YES -.7 Table : Summary of test results showing the effect of data variability on statistical confidence based on three tests of each stove (hot start) Stove- (ICS) Stove-(stone) Statistics Mean SD CoV Mean SD CoV Significant with 5% (Table Value=.0) Significant with % (Table Value=.) T-test to boil 5 liters of water (min). %.. % YES YES -5.7 Thermal efficiency (%) 7 7% 5 % YES YES.5 Rate of wood consumption (g/min) 0..7 %.. % NO NO 0.7 Specific fuel consumption (g/liter) %. 0 % YES YES -7. Firepower (kw) 77 5 % 70 7 % YES YES. Table : Summary of test results showing the effect of data variability on statistical confidence based on three tests of each stove (simmering) Stove- (ICS) Stove- (stone) Statistics Mean SD CoV Mean SD CoV Significant with 5% (Table Value=.0) Significant with % (Table Value=.) T-test Thermal efficiency (%) 0% 5 % YES YES. Rate of wood consumption (g/min) % 5. % YES NO.7 Specific fuel consumption (g/liter). 77% 5 % YES NO -. Firepower (kw) % 7 % YES YES -.7 Turn down ration % % NO NO. 57

5 Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) (): 5-50 (ISSN: -70) Specific fuel consumption (kj/l) -stone ICS 0 to boil 5kg of water Thermal efficiency (%) IC to boil 5kg of water Energy to to Cold start Energy to to Hot start Thermal Cold Thermal Hot Fig : specific energy consumption and the time to boil 5kg of water for the two stove average of -test high power phases. Fig : Thermal efficiency and the time to boil 5kg of water for the two stove (average of -test) high power (cold start) Burning rate (g/min) ICS to boil 5kg of water Fire power (watts) IC to boil 5kg of water Burning Cold Burning Hot start Fig : Burning rate and the time to boil 5kg of water (average of -test) high power phases Fire power Cold Fire Fig : Firepower and the time to boil 5kg of water for the two stove average of -test high power phases Hot 5

6 Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) (): 5-50 (ISSN: -70) High Power (Cold Start) Phase Table is the summary of the three tests results at high power (cold start). The ICS used an average of g of wood to boil liter of water in about min (5 liters in min) as against g of wood to boil the same liter of water in about 5 min(5 liters in min). This is indicative of the fact that the ICS is superior to the -stone fire stove in specific fuel consumption in the high power (cold start) phase. Fig is the graph of the specific fuel consumption against the time to boil 5 liters of water for the two stoves. Statistics at both t 5 and t show significant difference of such superiority of the ICS over the - stone fire stove in specific fuel consumption. In Table, the average rate of wood consumption (burning rate) is high for the -stone fire stove (0.g/min) than the ICS (.7 g/min). Fig is the graph of the burning rate of the two stoves against the time to boil 5 liters of water. Also in this aspect of stove performance, the ICS was better and statistically significant at t 5 but not at t against the -stone fire stove; burning less wood per unit time to accomplish the same task. In table, the thermal efficiency of the ICS (7%) is better than the -stone fire stove (%). However, a direct calculation of thermal efficiency derived from the Water Boiling Test is not a good indicator of the stove s performance because it rewards the excess production of steam (Bailis et al, 00). Under normal cooking conditions, excess steam production wastes energy because it represents energy that is not transferred to the food. Temperatures within the cooking pot do not rise above the boiling point of water regardless of how much steam is produced. Thus, unless steam is required for the cooking process for example in the steaming of vegetables, excess steam production should not be used to infere indicators of stove performance (Bailis et al, 00). Fig is the graph of the thermal efficiency against the time to boil 5 liters of water for the two stoves. Statistics at both t 5 and t show significant difference of such superiority of the ICS over the -stone fire stove in thermal efficiency. Table shows that the firepower (i.e. the ratio of the wood energy consumed by the stove per unit time) for the -stone fire stove (kw) is higher than the ICS (kw) which is in agreement with the burning rate. Fig is the graph of the firepower against time to boil. Statistics at both t 5 and t show significant difference of higher firepower of the - stone fire stove over the ICS. In this aspect of stove performance also the ICS has a better indicator as the higher firepower indicated greater wood consumption over a longer duration. High Power (Hot Start) Phase Table is the summary of the three tests results at high power (hot start). This is indicative of the fact that the ICS is superior to the -stone fire stove in specific fuel consumption in the high power (hot start) phase. Fig is the graph of the specific fuel consumption against the time to boil 5 liters of water for the two stoves. Statistics at both t 5 and t show significant difference of such superiority of the ICS over the -stone fire stove in specific fuel consumption. In Table, the average rate of wood consumption (burning rate) is higher for the -stone fire stove (0.g/min) than the ICS (. g/min). Fig is the graph of the burning rate of the two stoves against the time to boil 5 liters of water. In this aspect of stove performance too, the ICS show lower average performance than the -stone fire stove but statistically not significant at t 5 and t against the - stone fire stove; burning more wood per unit time to accomplish the same task. Table shows that the firepower of the -stone fire stove (70kW) is lower than the ICS (77kW) Fig is the graph of the firepower against time to boil. Statistics at both t 5 and t show significant difference of higher firepower of the ICS over the - stone fire stove. In this aspect of stove performance the ICS has a lower indicator as the higher firepower indicate greater wood consumption over a longer duration. Low Power (Simmering) Phase In table, the average thermal efficiency of the ICS (%) is better than the -stone fire stove (%).. Statistics at both t 5 and t show significant difference of such superiority of the ICS over the - stone fire stove in thermal efficiency. Also in Table, the average rate of wood consumption (burning rate) is high for the -stone fire stove (5g/min) than the ICS (5. g/min). The ICS used an average of g of wood to simmer liter of water in about min as against the -stone fire stove s g of wood to boil the same liter of water in about min. The average turndown ratio of the ICS (%) is better than the -stone fire stove (0%) with no statistical difference at both t 5 and t. CO CLUSIO An improved cookstove (ICS) which incorporates a ceramic combustion chamber within a metal casing was constructed using available local materials. The performance was evaluated against a -stone fire stove (considered a traditional stove as a control) using the Water Boiling Test (WBT). The results of the three tests ( replicates) carried out on each stove shows that the thermal efficiency, the specific fuel consumption and firepower of the ICS were better than the -stone stove. It was also determined statistically that the turndown ratio, the efficiency, the specific fuel consumption and the fire power of the ICS was significant at t 5 5

7 Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) (): 5-50 (ISSN: -70) and t against the traditional -stone stove. Thus, the ICS showed superior attributes in most aspect of stove performance indicator than the -stone fire stove and is recommended for use. RECOMME DATIO S The following recommendations are made: It is desirable to conduct the Controlled Cooking Test (CCT) and the Kitchen Performance Test (KPT), which compares fuel consumption in households using the ICS to households using the -stone fire stove. The tests were conducted using an aluminum pot and thus the tests need to be conducted on other types of pots (clay, copper, brass, etc) to determine the performance of the tested parameters. Tests with other types of fuels (cereal stocks, hardwood etc) compatible with the stove should also be conducted to generate information on their performance. Where the requisite instruments are available, the smoke emission test should be conducted for the stove. REFERE CES Adegbulugbe K. 5, Urban Energy Use Pattern in Nigeria. Natural Resources Forum Vol.: pp5-. Bailis, R., Ogle, D., MacCarty, N., and Still, D., 00. The Water Boiling Test (WBT) version., Household Energy and Health Programme, Shell Foundation, 00, revised 00. Barnes D, and L. Qian.. Urban Interfuel Substitution, Energy Use, and Equity in Developing Countries: Some Preliminary Results. In James P. Dorian and Fereidun Fesharaki,eds., International Issues in Energy Policy, Development, and Economics. Boulder, Colo: Westview Press. Bryden, M., Still, D., Scott, P., Hoffa, G., Ogle, D., Bailis, R., and Goyer, K., 005. Design Principles for Wood Burning Cook Stoves, Aprovecho Research Center/Shell Foundation/Partnership for Clean Indoor Air, USEPA EPA-0-K-05_00. Microsoft Encarta, 00. "Biomass, Microsoft Student 00 [DVD]. Raymond, Microsoft Corporation, 007. Microsoft Excel,