1 Introduction

India is a developing country where 65–70% of the total population resides in the rural setup. Frequent power cut is a major problem of the rural areas, and the main cause for this is rapid increment in energy demand and shortage of power supply. Therefore, since many decades, it remained as a questionable mark against the reliable power supply system for the rural areas in the country [1]. The Indian Government started a program called “decentralized system” to secure and provide a reliable power supply to the people residing in the rural setup. Under this program, solar cooker and solar water heater are disseminating to fulfill the energy demands for cooking and water heating, which are two basic activities of the rural households [2]. Although the perennial sources of these systems are renewable, they are dependent on weather conditions and stop working in rainy season [3, 4]. In this condition, fuel wood will be a better option, which is renewable as well as abundantly available in the country [5, 6]. Presently, around 85% of the people in rural parts of the country are dependent upon fuel wood as a major source for cooking energy requirement because of the poverty, unemployment and due to the rising cost of the liquid fuels [7]. Raman et al. [8] also reported that of the total cooking and water heating energy demand, almost 75–95% energy was met by fire wood and charcoal only. Meanwhile, this fuel is burnt in a traditional cookstove to get the energy for cooking and water heating. Due to incomplete combustion of the fuel in same practice, cause emissions of high pollutant level inside the dwelling which leads to the health disorders. The traditional cookstove is also characterized by lower thermal efficiency of about 5–10%, where almost 90–95% energy is wasted [9]. As per the present situations and trend of the energy sources used by the rural people, the first objective of the research was to design and develop a “wood gas biomass improved cookstove” with improved efficiency and less emissions to fulfill the cooking energy demand.

Many researchers [10,11,12] have worked on either natural draft cookstove or forced draft to improve the overall efficiency, but due to the high upfront cost [13], 75% people in the rural India, whose monthly income is less than 77 US$, cannot afford. Hence, it remains a challenging task to design and develop a cookstove at an affordable price for the rural people with better efficiency. Therefore, the second objective of the research was to make it cost-effective so that people can use the cookstove in their daily lives.

The idea was also to develop such a cookstove, which will operate in forced draft mode, when electricity is available using charged battery and even during off-electricity hours, when battery is discharged, the cookstove can be operated in natural draft mode with better efficiency. The low cost with better thermal efficiency and reduced emissions makes it most adoptive.

2 Materials and method

2.1 Design of the cookstove

A portable biomass gasification-based cookstove was designed as per the methodology adopted by Belonio [14] for a family of six members. The per-capita energy consumption of the people living in the rural parts of the country was assessed from Ingole et al. [15]. Few assumptions taken from Rathore et al. [16] were taken initially for the cookstove sizing and are given in Table 1.

Table 1 Assumptions made for cookstove designing
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The size of the cookstove was estimated by computing the various design parameters [14], which are given below,

2.1.1 Energy required (Q n)

$$Q_{n} = {\text{no}} .\;{\text{of}}\;{\text{family}}\;{\text{members}} \times {\text{per}}\;{\text{capita}}\;{\text{energy}}\;{\text{required}}\;{\text{for}}\;{\text{cooking}}$$
(1)

2.1.2 Energy input (FCR)

$${\text{FCR}} = \frac{{Q_{n} }}{{{\text{CV}}_{\text{f}} \eta_{\text{g}} }}$$
(2)

2.1.3 Reactor diameter (D)

$$D = \sqrt {\frac{{1.27\;{\text{FCR}}}}{\text{SGR}}}$$
(3)

2.1.4 Height of the reactor (H)

$$H = \frac{{{\text{SGR}} \times t}}{{\rho_{\text{d}} }}$$
(4)

2.1.5 Amount of air needed for gasification (AFR)

$${\text{AFR}} = \frac{{\varepsilon \times {\text{FCR}} \times {\text{SA}}}}{{\rho_{\text{a}} }}$$
(5)

2.1.6 Area required for primary air passage (A)

$$A = \frac{\text{AFR}}{v}$$
(6)

2.1.7 Secondary air requirement

By examining the general composition of producer gas (H2—20%, CO—18%, and CH4—1%), the secondary air requirement (m3 h−1) for burning of producer gas is calculated [16]. The corresponding oxygen required for different combustion reactions is given below,

Combustion reactions for producer gas are as follows:

$$2{\text{H}}_{2} + {\text{O}}_{2} \to 2{\text{H}}_{2} {\text{O}}$$
(7)
$$2{\text{CO}} + {\text{O}}_{2} \to 2{\text{CO}}_{2}$$
(8)
$${\text{CH}}_{4} + 2{\text{O}}_{2} \to {\text{CO}}_{2} + 2{\text{H}}_{2} {\text{O}}$$
(9)

2.1.8 Stoichiometric air requirement for combustion

Stoichiometric air requirement for combustion was adopted as per the methodology suggested by Mukunda [17]. The stoichiometric air is around 6.1 kg air per kg biomass.

2.2 Cookstove description

The cookstove consisted of two co-centric cylinders made of 0.1-cm-thick MS sheet. The diameter and height of the outer cylinder are 24 cm and 30 cm, and the same for inner cylinder are 18 cm and 25 cm, respectively. The schematic diagram is shown in Fig. 1. To minimize the heat losses, combustion chamber was insulated using refractory cement of 3 cm thickness. The reactor height and diameter are 20 cm and 12 cm, respectively. The cross-sectional area required for the secondary air supply was estimated by calculating the volume of secondary air supply per second (m3/s) divided by velocity of air (m/s) at the secondary air holes. The numbers of holes were then calculated by area required for secondary air supply divided by area of single hole by taking 1 cm diameter of each hole. Eighteen numbers of holes were provided near the top of the combustion chamber of 1 cm diameter each for secondary air passage to burn producer gas. A 10-cm-diameter air opening at the bottom was given for the passage of primary air.

Fig. 1
figure 1

Cross-sectional view of the designed cookstove

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To cover the air opening, a manually operated circular-shaped cover plate of 11 cm diameter was fitted at the bottom so that air passage from the bottom can be restricted during forced draft mode. A blower (0.16 A, 12 V) was mounted at the middle of the outer body of the cookstove with a casing to provide primary air and secondary air required for combustion during forced draft mode. A rechargeable battery (12 V, 1800 mAh) was used to power the blower. The technical specification of the designed cookstove is presented in Table 2.

Table 2 Technical specifications of the cookstove
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2.3 Cookstove operation

The cookstove is working in the gasification principle. The fuel is fed from the top up to 3/4th of the height of reactor. During the forced draft convection mode, the primary air and secondary air is met through the blower. At the same time, the cover plate (11 cm) at the bottom remains closed. When the cookstove was tested in natural draft mode, the amount of air needed for combustion was met by the natural convection through the air opening (10 cm diameter) provided at the bottom only.

3 Instrumentation and measurements

The moisture present in the fuel was measured using a moisture analyzer (Make: Sartorius MA35M-000230V1). Flame temperature and surface temperature of the cookstove were recorded using digital temperature scanner (DTSC-3508, ADI Vadodara) coupled with NiCr-Ni thermocouple (Type-CR/AL, 1000 °C, IP 65). A digital Bomb calorimeter (Khera Instrument Pvt. Ltd., Delhi) was used to determine the calorific value of fuels. The CO and CO2 emissions during the operation were measured using a gas analyzer (HORIBA VA-3000), and total particulate matter (TPM) was measured using 2.5-μm filter paper through stack monitoring system (Model: PEM SMS4, Polltech, India).

4 Fuel collection and processing

The wood fuel (Acacia nilotica) and pellet (Arachis hypogaea) were collected from the local area of Udaipur, Rajasthan (India), at US$ 0.06 kg−1 and US$ 0.11 kg−1, respectively. The size and shape of the babul (Acacia nilotica) wood were taken as per the Bureau of Indian Standard (BIS-IS: 13152; Part-I), given in Table 3. Meanwhile, the shape and size of the groundnut (Arachis hypogaea) shell pellet were used as per the pellet manufacturer and are given in Table 4. The biomass fuel collected for performance evaluation was characterized by ASTM [18].

Table 3 Characteristics of babul (Acacia nilotica) wood
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Table 4 Characteristics of groundnut (Arachis hypogaea) shell pallet
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5 Performance evaluation

Performance evaluation of the cookstove was carried out as per the Bureau of Indian Standard (BIS-IS: 13152; Part-I) at the Biomass Cookstove Testing Centre (Ministry of New and Renewable Energy approved laboratory), College of Technology and Engineering (MPUAT), Udaipur, Rajasthan (India). Eighteen replications were taken to examine the performance. Thermal efficiency, power rating, CO and CO2 emissions and total particulate matter (TPM) were assessed with babul (Acacia nilotica) wood and groundnut (Arachis hypogaea) shell pellet.

5.1 Thermal efficiency

Thermal efficiency of the developed cookstove was assessed in the laboratory using water boiling test (WBT). The formula used for determining thermal efficiency is given below:

$$H_{\text{out}} = \left[ {\left( {n - 1} \right) \times \left( {W \times C_{\text{V}} + w \times C_{\text{w}} } \right) \times \left( {T_{2} - T_{1} )} \right] + } \right[\left( {W \times C_{\text{V}} + w \times C_{\text{w}} } \right) \times \left( {T_{3} - T_{1} } \right)]$$
(10)
$$H_{\text{in}} = \left( {{\text{FCR}} \times {\text{CV}}_{\text{f}} } \right) + \frac{{x \times C_{2} \times \rho_{\text{k}} }}{1000}$$
(11)
$$\eta_{\text{th}} = \frac{{H_{\text{out}} }}{{H_{\text{in}} }} \times 100$$
(12)

5.2 Power rating

The power rating was assessed using the following formula,

$$P_{\text{o}} = \frac{{{\text{FCR}} \times {\text{CV}}_{\text{f}} \times \eta_{\text{th}} }}{3600 \times 100}$$
(13)

5.3 Emissions and total particulate matter (TPM) measurement

The developed cookstove was tested for its emissions simultaneously along with the testing of thermal efficiency using stack monitoring system, a multi-component gas analyzer connected online for continuous measurement of CO and CO2.

6 Economic assessment

Economic assessment of the cookstove was evaluated as per methodology adopted by Panwar et al. [19]. The capital cost (Co), net present value (NPV), minimum number of feed to be cooked by cookstove to make economic (nm), and payback period (PP) were determined. Few assumptions were made to access the economic feasibility of the system and are given below:

  1. (a)

    Depreciation rate (dr), 10%

  2. (b)

    Repair and maintenance cost (α) at 5% of the capital cost of cookstove

  3. (c)

    Number of meals in a year (ny), 600 (twice in a day)

  4. (d)

    Life span of the cookstove (tc), 5 years

For economic feasibility, the cookstove was compared with a traditional cookstove of 10% thermal efficiency as reported by Mehetre et al. [9], kerosene stove of 53.08% [20] and LPG stove of 65% thermal efficiency [21] by considering the same energy input for a six-member family.

7 Result and discussion

7.1 Thermal efficiency

Average thermal efficiency of the system was found to be around 36.56% and 36.79% in forced draft air supply mode working on babul (Acacia nilotica) wood and groundnut (Arachis hypogaea) shell pellet, respectively, which is slightly higher than that of the cookstove tested by Panwar and Rathore [22]. In natural draft air supply mode with Acacia nilotica wood, the average thermal efficiency was found to be around 33.44%, which is also higher than the cookstove tested by Mehetre et al. [23] of 28.83% and Darfur cookstove recently tested by Suthar et al. [24] of 29%. Meanwhile, the thermal efficiency of various natural draft cookstoves approved by Ministry of New and Renewable Energy, Govt. of India [25], is also less than the developed stove.

7.2 Power rating

The average power output rating of the cookstove was found to be around 3.15 kW and 2.95 kW in forced draft mode with Acacia nilotica wood and Arachis hypogaea shell pellet, respectively, while in natural draft mode, it was about 2.5 kW with Acacia nilotica wood.

7.3 Emissions from cookstove

The average CO and CO2 emissions in forced draft mode operating with Acacia nilotica wood and Arachis hypogaea shell pellet were found to be 0.2 ppm and 10.4 ppm and 0.07 ppm and 12.9 ppm, respectively. In natural draft mode, using Acacia nilotica wood, the average CO and CO2 emissions were recorded at around 0.24 ppm and 8.8 ppm, whereas a cookstove tested on multi-fuel by Panwar [11] reported 17–25 ppm (CO2) and 3–6 ppm (CO). Therefore, the developed cookstove is working within the safe limit in both the air supply modes.

The average total particulate matters (TPM) emitted during operation of the cookstove in forced draft mode with Acacia nilotica wood and Arachis hypogaea shell pellet were recorded as 134.1 × 10−6 g kJ−1 and 132.73 × 10−6 g kJ−1, respectively. In natural draft mode, it was observed to be around 298.8 × 10−6 g kJ−1, which is much lower than the particulate matter emission limit set by the test protocol BIS: IS; 13152 (Part-I).

7.4 Economics of the cookstove

7.4.1 Capital cost

The capital cost of the cookstove is around 11 US$ (INR 70.54 US$−1), and the details are presented in Table 5.

Table 5 Cost paid against different items for cookstove fabrication
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7.4.2 Cost of cooking

The cost of cooking was calculated using data presented in Table 6. The CO2 emission equivalent was taken from the generalized approach as proposed by Emission Guidelines [26]. The prices of the fuels are taken as per local market cost (US$ kg−1). The cost reliability was checked with respect to the LPG and kerosene fuel. When compared with a conventional cooking liquefied petroleum gas (LPG) stove [21], it employs an annual saving of around 227.6 US$ and 161.1 US$ in forced draft mode on babul (Acacia nilotica) wood and groundnut (Arachis hypogaea) shell pellet, respectively. Meanwhile, in natural draft mode, 218.4 US$ could be saved with Acacia nilotica wood. Similarly, with respect to a pressurized kerosene stove [20], around 263.67 US$ and 197.2 US$ in forced draft mode and 254.48 US$ in natural draft mode could be saved, whereas in comparison with a traditional cookstove, around 206.2 US$ and 193.7 US$ could be saved in forced draft mode on Acacia nilotica wood and Arachis hypogaea shell pellet, respectively. In natural draft mode, it is in a position to save around 251 US$.

Table 6 Cost of the cooking and CO2 emissions equivalent
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7.4.3 Net present value, payback period and money value for fuel saved

The estimated economic parameters compared to a traditional stove are given in Table 7.

Table 7 Economic parameters of the designed cookstove
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8 Conclusions

In forced draft mode in comparison with a traditional stove of 10% thermal efficiency [9], the developed cookstove is enabled to save around 6.89 tons and 7.04 tons of CO2 annually with respect to the fuel used, whereas in natural draft mode, the stove working on Acacia nilotica wood is saving around 6.65 tons of CO2 annually. When the cookstove was compared with a traditional coal stove of around 28.2% thermal efficiency [27], it is enabled to save around 0.85 tons, 1.0 ton and 0.61 tons of CO2 annually. It was found quite interesting that the developed cookstove is working efficiently in dual draft mode and saving considerable amount of CO2 emission. The rural people can easily afford the developed cookstove. The cost spent for cookstove purchasing can only be recovered within 20–29 days, which makes a more attractive feature toward its adoption.