Laboratory Evaluation of Improved Amfani Charcoal and Firewood Fired Cookstoves

Transcription

1 Nigerian Journal of Solar Energy, Vol. 27, Solar Energy Society of Nigeria (SESN) All rights reserved. Laboratory Evaluation of Improved Charcoal and wood d Cookstoves * 1 Garba, N. A. and 2 Anyanwu, C. N. 1 Sokoto Energy Research Centre, Usmanu Danfodiyo University, Sokoto 2 National Centre for Energy Research and Development, University of Nigeria, Nsukka Abstract - The performance of improved charcoal and firewood-fired cookstoves compared with the traditional three stone fire stove were evaluated in the laboratory using the water boiling test (WBT) method, which measured the fuel consumption and emissions as enumerated by the procedure of the Laboratory Emissions Measuring System (LEMS). The emissions measured were carbon monoxide (CO), carbon dioxide (CO 2 ) and particulate matter (PM). Results obtained showed that both the charcoal and firewood stoves have improved fuel efficiency (fuel consumption) and reduced pollutant emissions (CO, CO 2, and PM). Compared with the traditional three stone fire stove, the charcoal improved cookstove reduced fuel consumption, CO emission, and PM emission by -62.9%, 69.8%, and 99.0% respectively. The firewood improved cookstove reduced fuel consumption and CO emission by -19.6% and -25.4% respectively. The results also showed that the firewood improved cookstove produced more PM emissions (+15.4%). This study provides the performance of the improved cookstove, which can be used to improve the design of existing cookstoves as well as developing new ones. Keywords: Improved cookstoves, water boiling test, carbon monoxide, particulate matter, charcoal, firewood 1.0 INTRODUCTION All societies require energy to drive productive processes and to meet basic human needs such as cooking and lighting. One of the most common requirements for energy in Sub-Saharan Africa (SSA) households is cooking. Cooking is a vital need, since most of our nutrition comes from cooked food. In Nigeria, over 20 million households are dependent on the traditional use of firewood for their daily cooking. According to the Nigerian Alliance for Clean Cookstoves (NACC, 2015), smoke from cooking fire causes 95,300 deaths in Nigeria. Most families in the rural areas using three-stone fire spend much of the food budgets on buying wood and charcoal while others spend hours collecting wood. Inefficiency in the combustion of wood raises the cost of cooking for the poor and contributes to deforestation and global warming. However, in recent times, improving the efficiency and sustainability of traditional wood and charcoal cooking energy value chain through improved and clean, high efficiency stoves have shown promise for providing safe, sustainable and affordable cooking. According to Still et al. (2000), improved cookstoves are designed to optimize airflow through the stove and heat transfer to the pot improved in this context (both laboratory and field) indicates a combustion chamber constructed of lightweight refractory material and surrounded by insulation. *Corresponding author Tel: nasiranka@yahoo.com Improved cookstoves have the potential to reduce fuel consumption, cost, and may, if properly designed, contribute to significantly reduce carbon monoxide (CO), carbon dioxide (CO 2 ) and particulate matter (PM) emissions than the traditional cookstoves (Table 1). Improved wood stoves also reduce the negative impacts on the environment and human health (Roden et al., 2009; Roden et al., 2006). Table 1: Clean cookstove benchmark for fuel consumption and emissions associated with boiling 5L of water and keeping it simmers for 45 minutes Characteristics Three cook stove Benchmark n Fuel % consumption CO % PM % Source: Aprovecho (2013) While it is increasingly recognized that improved cookstoves reduce the indoor air concentration of CO and PM 2.5 generally by almost 50% (Chengapa et al., 2007; Masera et al., 2007), Smith et al. (2000) and Zhang et al. (2000) argued that improved cook stoves actually produces more PM emissions per mass of wood than traditional cook stoves. Testing is also required to develop technical standards for stove manufactured or imported into Nigeria. Laboratory testing of cook stoves 44

2 and certification services related to stove technical quality, indoor air pollution, and energy efficiency is extremely important in order to predict real-world cookstove performance. This paper assessed the performance of a charcoal and firewood fired improved cookstove to assist stove developers in improving stove design and construction methods. 2.0 MATERIALS AND METHODS A number of techniques such as the lab-based water boiling test (WBT) and controlled cooking test (CCT), and field-based kitchen performance test (KPT) have been developed for testing the performance of improved cookstoves. The most commonly used laboratory performance test is the WBT where a specified quantity of water (usually 5L) is brought to boil, and then simmered for 45 minutes, while total fuel consumption is recorded. Performance measures include time to boil, energy efficiency, and fuel usage; and emission data collected concurrently. This serves a useful purpose in assessing and comparing relative performance of different stoves. However, according to Bailis et al. (2007), WBT and CCT do not always translate to similar efficiencies in the field-based kitchen performance test (KPT). The WBT stove performance test protocol was used in the study. The test was conducted at the Clean Cook stoves Development and Testing Center, Afikpo, Nigeria, in April The Laboratory Emissions Measuring System (LEMS) was used for monitoring the CO, CO 2 and PM 2.5 emissions emanating from the stove during use. The carbon monoxide (CO) sensor used is an electrochemical cell. This cell has a reference terminal and requires a potentiostatic controller. The carbon dioxide (CO 2 ) sensor uses non-dispersive infrared (NDIR) to measure CO 2 concentration and outputs voltage. It is self - calibrating, with pure Nitrogen gas used for a zero reference. The LEMS has two particulate matter (PM) sensors: The scattering photometer equipped with both a laser and a light receiver. When smoke enters the sensing chamber, particles of smoke scatter the laser light into the receiver. More light reaching the receiver indicates more smoke in the chamber. The amount of scattered light was calibrated with a laboratory-standard nephelometer. The gravimetric system gives a direct measurement of total PM using filter-based sampling. A vacuum pump pulls a sample through the sample line and the critical orifice, which holds the flow at a steady 16.7 L/min. A cyclone particle separator is used so that all PM2.5 is collected on a glass fiber filter while the pump is on. The filter is weighed before and after the experiment to calculate the total PM2.5 mass. The flow is measured by a pressure pitot tube transducer which outputs a signal based on the pressure drop measured across the flow grid. Exhaust gas velocity, volume, and mass flow rate within the duct, are Garba, N. A. and Anyanwu, C. N. 45 calculated based on pressure drop recorded using the Magnesense pressure transducer. Analogue pressure measurement is provided by the Magnehelic sensor. Exhaust gas temperature was measured by a K-type thermocouple sensor in real-time. The data are required to calculate the density of exhaust air in order to calculate the mass flow of emissions. The thermocouple (TC) temperature sensor is used to record the water temperature of the pot. The thermocouple temperature output is linear and the thermocouple probe provided with the LEMS is rated for temperatures up to 250 C. 2.1 The Stove Tested Stove that was tested in this study is shown in Figure 1. The stove was designed for burning firewood and charcoal and the stove was tested with both charcoal and firewood in the study. The stove was made from clay. It has an opening on one side near the bottom of the stove for fuel (wood) to be inserted and for air to enter the combustion chamber. It also has opening at top for charcoal to be fed in. Draft is created by the large temperature difference between the air entering the bottom of the stove and the hot combustion gases exiting from the top of the vertical combustion chamber. Fig. 1: Stove tested: improved cookstove 2.2 Test System The Laboratory Emissions Measuring System (LEMS) was used to measure the total emissions produced during stove combustion. The stove was used to boil 5L of water under a hood (fume cupboard), which collects the emissions and air from the laboratory. The flow rate and exhaust temperature were measured in the exhaust tube. A fraction of the flow through the system was drawn by a suction pump through a sample line to the sensors in the sensor box, which includes the following: 1. PM Sensor. The PM sensor is a scattering photometer equipped with a laser and light receiver. 2. CO Sensor is an electrochemical cell. It functions on the basis that the electrical conductivity

3 Garba, N. A. and Anyanwu, C. N. between two electrodes is proportional to CO concentration. 3. CO 2 Sensor uses a Non Dispersive Infrared (NDIR) to measure CO 2 concentration. It is selfcalibrating. Fig. 2: The hood and ducting system of the LEMS Source: Aprovecho (2013) Separately, a thermocouple measurement was logged of the (water) pot temperature. A computer displays and records the temperatures, flow and concentrations in real-time. The data was then processed using the provided software and the performance of the stove was reported based on the mass of emissions measured. The test system (Figure 2) consists of a hood for collecting emissions from the stove, an air duct for sampling air pollutants, and a blower for drawing air through the hood and duct. water in a standard pot. The boiled water is then replaced with a fresh pot of ambient temperature water to perform the second phase. 2. The hot-start high-power phase is conducted immediately after the first phase while stove is still hot. Again the pre-weighted bundle of fuel is used to boil a measured quantity of water in a standard pot. This helps to identify differences in performance between a stove when it is cold and when it is hot. 3. The simmer phase, which begins immediately after the second phase with the stove, pot and hot water, provides the amount of fuel required to simmer a measured amount of water at just below boiling point for 45 minutes. For all three phases of the WBT protocol, measurements include the mass of fuel used, mass of charcoal produced or consumed, mass of water at the beginning and end of the test phase, temperature of the water, and time. Pollutants emissions were simultaneously measured during each phase of the WBT protocol. The stove was carefully operated throughout the test. Fuel wood (smaller pieces) was carefully and consistently fed into the fire by hand. The test was conducted for both charcoal (Figure 3) and firewood (Figure 4) based on the procedure described in the WBT Version protocol (Ballard-Tremeer and Jawurek, 1996; Brockmann, 1993; Roden et al., 2006; Zhang et al., 2000). Fig. 3: The stove being tested with charcoal in the 2.3 Test Protocol The WBT stove performance test protocol initially developed by VITA (Volunteers in Technical Assistance) and refined by the University of California- Berkeley, in collaboration with ARC and other stove researchers was used in the study (Jetter and Kariher, 2009). The WBT Version was used to measure performance and to simultaneously measure emissions during operation of the stove. The basic testing protocol includes optional instruction for measuring CO, CO 2 and PM concentrations in the stove s exhaust. The WBT protocol consists of three phases that immediately follow each other, which must be completed at least three times for each stove. 1. The Cold-start high-power phase begins with the stove at room temperature and uses fuel from a preweighed bundle of fuels to boil a measured quantity of hood system of the LEMS Fig. 4: The stove being tested with firewood in the hood system of the LEMS 3.0 RESULTS AND DISCUSSION Results from laboratory test were categorized by stove type charcoal and firewood and are summarized in 46

4 Garba, N. A. and Anyanwu, C. N. Tables 2 and 3. Table 4 provides the test results for charcoal and firewood stoves performance compared with the emission benchmark for improved cook stoves by the International Organization for Standardization (ISO). Similarly, Table 5 presents the results for charcoal and firewood stoves performance compared with the traditional three stone stove. Table 2: Performance of the charcoal and firewoodfired cookstoves Characteristics Units Charcoal wood High Power % Thermal Efficiency Low Power MJ/min/L Specific Consumption Rate High Power CO g/mj d Low Power CO g/min/l High Power mg/mj d PM Low Power PM mg/min/l Indoor Emission CO Indoor Emission PM g/min mg/min Table 2 showed that the firewood-fired stove had a higher efficiency of 24.5% than the charcoal cookstove that had an efficiency of 17.0%. Thermal efficiency is the ratio of the energy used for heating and evaporating water in the pot to the energy released by burning the fuel. However, results also indicated that charcoal stove had lower emissions throughout compared with firewood stove. Similarly, standard performance results of the WBT fuel consumption, CO emission, PM emission, energy to cook, time to boil and CO 2 emissions are shown in Table 3. Compared with charcoal stove, firewood stove took more time to boil. Fuel consumption, CO, CO 2, and PM emissions tended to be higher for firewood stove compared to charcoal stove. Table 3: The Performance Results of Cookstoves Units Charcoal cook stove wood cookstove Fuel to Cook 5L g CO to Cook 5L g PM to Cook 5L mg Energy to Cook 5L KJ Time to Boil min CO 2 to Cook 5L g Improved Cook stove versus Clean Cookstove Benchmark The performance measures results presented in Table 3 were compared with the universally accepted performance data for improved cookstoves. Table 4 presents charcoal improved cookstove fuel consumption, CO, and PM emissions compared with the benchmark data. As shown in Table 4, firewood cook stove was also compared with the benchmark data. Compared with the benchmark data, charcoal cookstove showed reduction in fuel consumption (- 12.7%) and PM emissions (-96.8%). However, CO emission was higher for charcoal stove (+33.8%) compared with the benchmark data. This means that charcoal cookstove emits less PM and consumes less fuel than the benchmark. For firewood cookstove, fuel consumption, CO emissions, and PM emissions were higher compared to the benchmark data. Table 4: Performance of the cook stoves compared to the benchmark Cooksto PM ve type charcoal firewoo d Benchma rk & n Benchma rk n Benchma rk n Fuel Consumpt ion C O , Improved Cookstove versus Three Stove Further comparison with traditional three stone fire stove performance data showed that fuel consumption,

5 CO emissions, and PM emissions for charcoal improved cookstove were reduced by -62.9%, -69.8%, and -99.0% respectively. Table 5 illustrates this comparison. Results for this study are in agreement with findings by Bhattacharya et al. (2002) and Zhang et al. (2000). However, for wood improved cookstove, comparison with traditional three stone fire stove performance data as presented in Table 5 showed that fuel consumption and CO emissions would be reduced by -19.6% and -25.4% respectively. The PM emission for improved cookstove was +15.4% higher that of the traditional three stone fire stove. This could be as a result of the kerosene used to kindle the firewood during the cold start of the test. Cookstove ignition and lighting both emit large quantities of PM, which are accompanied by increases in CO and CO 2 emissions. For instance, according to Butcher and Sorenon (1979), heating stoves during start-up produces the majority of the emissions. Studies have also shown that emission rates could be impacted by many factors such as kindling procedure, fuel type, fuel feeding practice, firewood size, stove type and design, and combustion temperature (Roden et al., 2009; Rau, 1989; Butcher and Ellenbecker, 1982). Table 5: improved cookstove versus three stone fires Cooksto PM ve Type Charcoal woo d Three & Reducti on Three Fuel Consumpti on Garba, N. A. and Anyanwu, C. N. C O Charcoal Three woo d Conclusion The performance of improved cookstove was tested in the laboratory with charcoal and firewood using the LEMS system based on typical WBT test protocol. Results revealed that both charcoal and firewood stoves 48 have improved fuel efficiency (fuel consumption) and reduced pollutant emissions (CO, CO 2, and PM) compared with traditional three stone fire stove performance data. Compared with the traditional three stone fire stove, charcoal improved cookstove would reduce fuel consumption, CO emission, and PM emission by -62.9%, 69.8%, and 99.0% respectively. On the other hand, firewood improved cookstove would reduce fuel consumption and CO emission by % and -25.4% compared with the traditional three stone fire stove, respectively. However, results also indicated that firewood improved cookstove would produce more PM emissions (+15.4%) compared with the traditional three stone fire stove. This study provides stove performance data to improved cookstove manufacturers and others disseminating stove information and may be used for improving the design of existing improved cookstoves as well as developing new designs. Laboratory tests serve a useful purpose in testing and analysing the performance of improved cookstoves. However, emission results from laboratory testing should not be considered representative of real world emission data. To promote better understanding of real world emissions, field-testing should also be carried out to identify the critical conditions and variables governing emissions. Acknowledgements The authors would like to thank the many training participants who took part in carrying out the test. Special thanks also goes to the International Centre for Energy, Environment and Development (ICEED), Nigeria, Nigerian Alliance for Clean Cookstoves and the improved cookstoves manufacturers from Cotonou, Benin Republic. References Aprovecho (2013). Water Boiling Test Protocol v , Aprovecho Research Centre, April 2013, [online], Bailis, R., Berrueta, V., Chengappa, C., Dutta, K., Edwards, R., Masera, O., Still, D., and Smith, K. R. (2007). Performance testing for monitoring improved biomass stove interventions: experiences of the household energy and health project. Energy for Sustainable Development XI, Ballard-Tremeer, G. and Jawurek, H. H. (1996). Comparison of five rural wood-burning cooking devices: efficiencies and emissions. Biomass and Bioenergy, 11(5), Battacharya, S. C., Albina, D. O. and Salam, P. A. (2002). Emissions factors of wood and charcoal fired cookstoves, Biomass and Bioenergy, 23:

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