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BIOMASS-BASED CLEAN COOKING

S.P. Parameswaran

A. Kumar

R. Sharma

Himanshu

S.K. Tyagi


Department of Energy Science and Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India

Biomass pellet-based cookstoves provide better thermal performance and emission characteristics compared to traditional cookstoves. The goal of this study was to provide a comparative analysis of pellet-based forced draft (FD), traditional, and liquefied petroleum gas (LPG) cookstoves in terms of thermal efficiency and carbon monoxide (CO) and particulate matter (PM2.5) emissions. This study also includes an analysis of ways to optimize the secondary airflow in the combustion chamber. Controlled secondary air flow plays a crucial role in emission reduction and thermal performance. The present analysis shows that the LPG cookstove has higher thermal efficiency, followed by the FD1.2, FD1.3, and FD1.1 cookstoves, while the traditional cookstove has the lowest thermal efficiency. Furthermore, the controlled air supply in the combustion chamber showed that PM2.5 emissions are the lowest in the FD1.2 cookstove and CO emissions are the lowest in the FD1.3 cookstove. Moreover, yearly fuel savings for FD cookstoves made in the laboratory ranged from 48.4% to 53.5% compared to traditional cookstoves, while the annual CO and PM2.5 emissions reduction potential ranged from 84% to 90.6% and 94% to 96.8%, respectively.

KEY WORDS: biomass, forced draft (FD), cookstoves, thermal efficiency, emission

1. INTRODUCTION

Biomass fuel is still used worldwide by more than 2.7 billion people for cooking, space heating, etc. Similar to wood, agricultural wastes, cow dung, and crop residues, biomass creates more emissions and has poor thermal efficiency when subjected to burning in open-fired traditional cookstoves. This is mainly due to the presence of unburnt fuel as a result of the poor structure of traditional cookstoves. In addition, biomass also releases a large number of pollutants such as carbon monoxide (CO) and particulate matter (PM) into the environment, causing air pollution and health issues (Pal et al., 2019). Moreover, traditional and three-stone fire biomass cookstoves emit huge amounts of harmful pollutants such as fine and ultrafine PM (PM2.5 and below) and CO, all of which have an adverse impact on the health of those exposed to them, and particularly on children under 5 years old.

The successful implementation of new cookstove programs depends on several factors. For example, a lack of awareness by people living in rural areas with respect to new technologies can lead to difficulties in implementing these programs. In addition, the successful implementation of new cookstove programs also depends on whether people’s expectations have been satisfied, acceptable budget allowances, and cultural factors. Gasifier stoves that are based on newly developed technologies have higher thermal efficiency and lower harmful emissions levels (Carter et al., 2014). Moreover, changing the feeding pattern from normal wood to pellets provides more thermal efficiency and results in lower polyaromatic hydrocarbon emissions (Du et al., 2021). Densification of biomass into pellets and briquettes provides good combustion characteristics. Experiments carried out using pellets as fuel have provided good results with respect to the emission characteristics and thermal performance. Controlling the air supply is an important factor in the gasifier setup. There are two ways of introducing air into cookstoves, which can be classified as primary and secondary air (Jetter et al., 2012). Primary air is helpful in the gasification process and secondary air is helpful in the complete combustion of the volatile components that are released during the gasification process. Pal et al. (2019) showed that secondary air has many other advantages and helps in the proper mixing of air and fuel. Secondary air also creates turbulence between the air and the volatile components released during combustion.

In this study, the emission characteristics and efficiency parameters of five different types of gasifier cookstoves—traditional, liquefied petroleum gas (LPG), and laboratory-made forced draft (FD) (FD 1.1, FD 1.2, and FD 1.3)—were analyzed. The main aim of this work was to optimize the flow of secondary air entering the combustion chamber. The locations and dimensions of secondary holes are necessary to maintain the flow condition inside the combustion chamber in order to provide a proper air–fuel mixing ratio and complete burning of the fuel with fewer emissions and high thermal performance.

2. MATERIALS AND METHOD

In this study, three FD cookstoves were developed in the laboratory: FD1.1, FD1.2, and FD1.3. The diameters of the secondary holes in the FD1.1, FD1.2, and FD1.3 cookstoves were 6, 4, and 3 mm, respectively, and the rest of the parameters were the same. These cookstoves were compared with traditional and LPG cookstoves. Biomass pellets, 6 mm in diameter, were used as fuel. The laboratory-made cookstoves had primary and secondary holes to supply primary and secondary air. The three FD cookstoves had different parameters in terms of the size and location of the secondary holes. The locations of the holes in each of the laboratory cookstove models are shown in Figs. 1 and 2.

Schematic diagram of the laboratory-made gasifier cookstove model, based on Himanshu et al. (2022) and Tyagi (2022)

Figure 1. Schematic diagram of the laboratory-made gasifier cookstove model, based on Himanshu et al. (2022) and Tyagi (2022)

Secondary holes of the different laboratory-made gasifier cookstoves based on Himanshu et al. (2022) and Tyagi (2022)

Figure 2. Secondary holes of the different laboratory-made gasifier cookstoves based on Himanshu et al. (2022) and Tyagi (2022)

An experimental investigation of the cookstove models was performed in the laboratory at Indian Institute of Technology Delhi (IITD). An analysis was also carried out to optimize the dimensions and correct locations of the holes. The size and location of the hole play a major role in the performance of cookstoves. The entire setup was made of mild steel with an annulus chamber through which the secondary air passed. The annulus chamber was insulated with glass wool to reduce the transfer of heat in ambient air. The provided annulus chamber helped to preheat the secondary air traveling from the bottom to the top and improved the efficiency of the cookstove. Furthermore, the primary air passed below the grate and assisted in the gasification process. The instruments used in the experimental investigation included a bomb calorimeter, hot wire anemometer, duct to collect flue gas, PM analyzer, gas analyzer, and vessels.

Following the Bureau of Indian Standards (BIS) guidelines, the water boiling test (WBT) was employed in the experimental procedure. Established methods were used in the WBT to analyze the thermal efficiency and emission data of the cookstoves. The emission test was carried out following the procedural instructions in the BIS standards. The PM2.5 data were obtained using a PM analyzer; however, the CO, carbon dioxide, sulphur dioxide, nitrogen oxide, and oxygen measurements were obtained using a gas analyzer. The thermal performance, calorific value of the fuel, and burning rate of the fuel per hour all have a significant impact on the power delivered from a cookstove.

The burning rate can be evaluated using the following equation (in kg/h):

\(\text{Burning rate}=2\left(M_{1} -M_{2} \right)\) (1)

The input heat rate can be calculated as follows (in kJ/h):

\(\text{Input heat rate}=2\times \left(M_{1} -M_{2} \right)\times \text{CV}\) (2)

The heat gained by the pot (\(Q_{\text{pot}}\)) can be determined by the following equation (BIS, 2013; Himanshu et al., 2022):

\(Q_{\text{pot}} =\left(M\times 0.896+m\times 4.186\right)\times \left[\left(n-1\right)\left(t_{2} -t_{1} \right)+\left(t_{3} -t_{1} \right)\right]\) (3)

The heat input to the cookstove can be evaluated as follows:

\(\text{Heat input}=\left[\left(W\times h_{1} \right)+\left(w\times \rho \times \dfrac{h_{2} }{1000} \right)\right]\) (4)

The thermal efficiency can be calculated as follows:

\(\eta_{\text{th}} =\dfrac{\text{Heat gained by the vessel}}{\text{Heat input}}\) (5)

The power output can be evaluated as follows (in kW):

\(\text{Power output}=\dfrac{W\times h_{1} \times \eta_{\text{th}} }{3600\times 100}\) (6)

where \({M}_{1}\) is the initial weight (kg); \({M}_{2}\) is the final weight (kg); CV is the calorific value (kJ/kg); \(M\) is the mass of the empty vessel and lid (kg); \(m\) is the amount of water filled in a vessel (kg); \(n\) is the total number of utilized vessels; \({t}_{1}\) is the initial water temperature (K); \({t}_{2}\) is the final water temperature before changing the vessel (kg); \({t}_{3}\) is the final water temperature in the last vessel (kg); \(W\) is the burning rate in the cookstove (kg/hr); \({h}_{1}\) is the net heating value of the fuel (kJ/kg); \(w\) is the amount of oil used (ml); \(\rho\) is the density of the oil (kg/cm3); and \({h}_{2}\) is the net heating value of the oil (kJ/kg).

The CO concentration in grams per megajoule energy delivered (MJD) can be estimated by the following relation (in mg/MJD) (BIS, 2013; Himanshu et al., 2022):

\(\text{CO}_{f} =3.411\times 10^{-4} \times \dfrac{cV}{tQ_{d}}\) (7)

where CO\({}_{f}\) is the quantity of carbon monoxide (g/MJD); \(V\) is the volume of exhaust gases (L); \(c\) is the CO concentration of diluted exhaust gas (parts per million); \(t\) is the absolute temperature of the sampled gas entering the analyzer; and \({Q}_{d}\) is the useful heat delivered to the vessel (MJD).

The particulate matter (PM2.5) can be determined using the following relation (in mg/MJD) (BIS, 2013; Himanshu et al., 2022):

\(\text{PM}_{2.5} =\dfrac{G\times q}{Q_{d}} \) (8)

\(G=\dfrac{R-S}{U}\) (9)

\(q=Q_{d} \times v\times 3600\times 1000\) (10)

where \({Q}_{d}\) is the total heat delivered to the vessel; \(G\) is the quantity of PM2.5 per liter of sample passed (mg/L); \(q\) is the volume of exhaust gases passing through the duct (L/h); \(R\) is the mass of the filter paper before deposition (mg); \(S\) is the mass of the filter paper after deposition (mg); and \(U\) is the total volume of gases passing through the sampler.

3. RESULTS AND DISCUSSION

A comparative analysis of the FD1.1, FD1.2, FD1.3, LPG, and traditional cookstoves was carried out to evaluate the thermal performance and levels of CO and PM2.5 emissions compared to 15 other cookstoves available in the market.

3.1 Thermal Efficiency

The FD1.2 pellet-based cookstove showed the highest thermal efficiency (42.03%) compared to the other 15 models available in the market that operate on solid fuels. The highest thermal efficiency in the FD1.2 model was due to its having better combustion and heat utilization compared to the other cookstoves. This better combustion was attributed to the proper mixing of air and volatiles through the secondary holes during the combustion process. Furthermore, the FD1.3 model had thermal efficiency of 40.62%, followed thermal efficiency of 37.87% in the FD1.1 model, while the traditional cookstove had the lowest thermal efficiency (16.8%). Moreover, the LPG cookstove showed thermal efficiency of 53.48%, which was the highest among all of the solid and gaseous-based cookstoves. The thermal efficiencies of the various cookstoves are shown in Fig. 3.

Comparison of thermal efficiency between different gasifier models and Ministry of New and Renewable Energy (MNRE) FD cookstove models [reprinted from Himanshu et al. (2022) with permission from Springer Nature, Copyright 2021]

Figure 3. Comparison of thermal efficiency between different gasifier models and Ministry of New and Renewable Energy (MNRE) FD cookstove models [reprinted from Himanshu et al. (2022) with permission from Springer Nature, Copyright 2021]

3.2 Carbon Monoxide and Particulate Matter Emissions

The CO emissions were found to be the lowest in the FD1.3 model, while the PM2.5 emissions were low in the FD1.2 model. The CO emission values for the FD cookstoves varied from 0.77 to 1.13 g/MJD, with the LPG cookstove had the lowest value of (0.69 g/MJD). The PM2.5 emissions from the FD1.2 model were lower by 32 times compared to the traditional cookstove. Furthermore, the PM2.5 emissions from the LPG cookstove were found to be lower by 1.5 times compared to the FD1.2 cookstove, indicating that the PM2.5 emissions from the LPG and FD1.2 cookstoves were in proximity to each other. Moreover, the ratio of the PM2.5 emissions between the LPG and traditional cookstoves was found to be 47, which was 31 times higher compared to the FD1.3 model. The CO and PM2.5 emissions are shown in Figs. 4(a) and 4(b).

Comparison of CO (a) and PM2.5 (b) emissions between different gasifier models and the Ministry of New and Renewable Energy (MNRE) FD cookstove models [reprinted from Himanshu et al. (2022) with permission from Springer Nature, Copyright 2021]
(a)

Comparison of CO (a) and PM2.5 (b) emissions between different gasifier models and the Ministry of New and Renewable Energy (MNRE) FD cookstove models [reprinted from Himanshu et al. (2022) with permission from Springer Nature, Copyright 2021]
(b)

Figure 4. Comparison of CO (a) and PM2.5 (b) emissions between different gasifier models and the Ministry of New and Renewable Energy (MNRE) FD cookstove models [reprinted from Himanshu et al. (2022) with permission from Springer Nature, Copyright 2021]

4. CONCLUSIONS

The comparative analysis showed that the FD1.2 cookstove had high thermal efficiency (42.03%), followed by the LPG cookstove (53.48%). The FD 1.3 and FD 1.1 models had thermal efficiencies of 40.62% and 37.87%, respectively. The traditional cookstove had the lowest thermal efficiency (16.8%) among all of the five cookstoves. The three laboratory-made cookstove models had low CO and PM emissions compared to the traditional cookstoves.

This experimental investigation provides a clear picture of how secondary air plays a predominant role in the performance of cookstoves and how it helps to lower emissions from biomass pellet-based fuel. According to the research findings, the flow of secondary air into the burning chamber should be carefully maintained since fast flow rates lead to lower combustion region temperatures, whereas slow airflow rates end in incomplete combustion of volatiles. A constant supply of secondary air into the burning chamber leads to complete burning of fuel and provides fewer emissions. The PM2.5 emissions were the lowest in the FD1.2 model, and at the same time the CO emissions were the lowest in the FD1.3 model. Furthermore, the yearly fuel savings for the laboratory-made FD cookstoves ranged from 48.4% to 53.5% when compared to traditional cookstoves, while the annual CO and PM2.5 emissions reduction potentials ranged from 84% to 90.6% and 94% to 96.8%, respectively.

ACKNOWLEDGMENTS

S.P.P. and R.S. thankfully acknowledge Swami Samarth Electronics Pvt. Ltd. for financial assistance; Nashik (Maharashtra) for providing funding for the research development and demonstration (RD&D) activities under Grant No. IITD/IRD/RP04288N/2022; and the IITD for support provided through Faculty Interdisciplinary Research Proposal (FIRP) Project No. IRD/MI02090/2019.

REFERENCES

Bureau of Indian Standards (BIS). (2013) Indian Standard on Portable Solid Biomass Cookstove (Chulha First Revision), BIS 13152 (Part 1).

Carter, E.M., Shan, M., Yang, X., Li, J., and Baumgartner, J. (2014) Pollutant Emissions and Energy Efficiency of Chinese Gasifier Cooking Stoves and Implications for Future Intervention Studies, Environ. Sci. Technol., 48(11): 6461–6467. DOI: 10.1021/es405723w

Du, W., Wang, J., Zhuo, S., Zhong, Q., Wang, W., Chen, Y., Wang, Z., Mao, K., Huang, Y., Shen, G., and Tao, S. (2021) Emissions of Particulate PAHs from Solid Fuel Combustion in Indoor Cookstoves, Sci. Total Environ., 771, 145411. DOI: 10.1016/j.scitotenv.2021.145411

Himanshu, Pal, K., Jain, S., and Tyagi, S.K. (2022) Energy and Exergy Analysis and Emission Reduction from Forced Draft Gasifier Cookstove Models: A Comparative Study, J. Therm. Anal. Calorim., 147(15): 8509–8521. DOI: 10.1007/s10973-021-11137-y

Jetter, J., Zhao, Y., Smith, K.R., Khan, B., Yelverton, T., DeCarlo, P., and Hays, M.D. (2012) Pollutant Emissions and Energy Efficiency under Controlled Conditions for Household Biomass Cookstoves and Implications for Metrics Useful in Setting International Test Standards, Environ. Sci. Technol., 46(19): 10827–10834. DOI: 10.1021/es301693f

Pal, K., Jha, M.K., Gera, P., and Tyagi, S.K. (2019) Energy and Exergy Analysis of a Natural-Draft Improved Biomass Cookstove with Varying Quantities of Different Biomass Feedstocks, Biofuels, 10(1): 121–130. DOI: 10.1080/17597269.2018.1475711

Tyagi, S.K. (2022) Biomass Pellet Based Combustion Devices, Indian Patent No. 397919, Ref. No. 201811019556/2018, Granted May 27, 2022.

Referências

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  3. Du, W., Wang, J., Zhuo, S., Zhong, Q., Wang, W., Chen, Y., Wang, Z., Mao, K., Huang, Y., Shen, G., and Tao, S. (2021) Emissions of Particulate PAHs from Solid Fuel Combustion in Indoor Cookstoves, Sci. Total Environ., 771, 145411. DOI: 10.1016/j.scitotenv.2021.145411
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  5. Jetter, J., Zhao, Y., Smith, K.R., Khan, B., Yelverton, T., DeCarlo, P., and Hays, M.D. (2012) Pollutant Emissions and Energy Efficiency under Controlled Conditions for Household Biomass Cookstoves and Implications for Metrics Useful in Setting International Test Standards, Environ. Sci. Technol., 46(19): 10827–10834. DOI: 10.1021/es301693f
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