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Funnel Shape Biomass Gasifier for Community Cooking

In the context of growing renewable energy sources available, biomass has a good potential in Narmada district of Gujarat. Total forest area in Narmada District is 1,20,494 ha and out of that 74,238 ha forest area comes under Dediapada taluka only. Almost every rural household, small hotels, community cooking places (residential and non-residential schools), hospitals and many small-scale industries were used biomass base traditional appliances (chulhas) for community cooking and hot water generation. As it is proved that the direct burning of fuel wood is not an energy efficient process and large amount of heat is wasted into the atmosphere. The proper utilization of fuel wood in improved technology will not only increase the thermal efficiency but also liberate the flue gases at lower temperature in the atmosphere. Keeping this in view, a biomass based cooking system was developed for community cooking. 

Major components 

A new cooking system was developed based on the performance evaluation of traditional cooking system used in the tribal villages. The capacity of a proposed cook stove showed the energy needed for meeting the heat required to cook the meals per batch. The physical parameters of traditional cooking system, food habit and quantity, fuel type and its consumption rate, time required for cooking were considered while developing the cooking system.  

Funnel shape biomass gasifier 

Cook stove reactor of the funnel shape biomass gasifier is having the 0.3 m inner and 0.4 m outer diameter with 0.8 m height. Burner diameter is 0.3 m and height is 0.07 m. Hopper having 0.07 m diameter is provided for desire size fuel supply in stove. Area of 0.071 m² grate is placed at 0.1m height from bottom. The grate is used to provide the platform for fuel and ash fall in ash pit. Two numbers of primary air inlets with 0.05m dia. & 0.10 m length is provided to produce the draft inside the stove. Twenty numbers of secondary air inlets having 15mm size has been provided with burner for adequate air supply to complete combustion at top of stove. Ash chamber of 0.36 m dia. And 0.1 m height is provided to collect the ash formed in cook stove. Reactor chamber is placed for gasification of incomplete combustion of biomass. Sufficient insulation is provided to reduce heat loss from inner to outer body. As the weight of the gasifier is higher, four nos. of caster wheels are provided for easy transport and handling. The complete shape of the outer body is look like a funnel. By using this device, around fifty people meals can be prepared. Thus, this device is known as funnel shape biomass gasifier for community cooking/thermal application. The material used for fabrication of this device is IS standard only. Thus, Life of the gasifier is around 10 years without any major maintenance. Material cost and fabrication cost of improved cook stove are Rs. 5,800/- and Rs. 4,300/- respectively.  

Performance result of the improved gasifier 

The various operating parameters of cook stove were recorded to evaluate the performance of improved stove and it is shown in Table below. The improved cook stove was evaluated for thermal application. The thermal profile of the stove reactor at different height from grate and flame temperature was evaluated. The analysis of the feedstock was studied for the proximate analysis and calorific value estimation.  

Operating parameters 

Parameter 

 

methodology 

Star up time, min 

Time required for igniting the wood. 

Operating time, min 

Duration of flame start to end. 

Total operating time, min 

Duration of wood ignition to flame end. 

Total fuel consumption, (kg) 

Fuel occupy inside he cook stove entire run time. 

Fuel consumption Rate, kg/h 

Fuel consumed during total operating time. 

Sp. combustion Rate, kg/h.m2 

SGR=weight of fuel used (kg)reactor area(sq.m)×operating time (h)

 

Boiling time, min. 

Time taken by water to its boiling point. 

Combustion Zone Velocity, m/h 

CZR= length of reactor (cm)operating time (min)

 

Thermal efficiency, % 

th = SHw+SHu+LHwMfu×Hvf×100

 

Power Input, kW 

Pi= 0.0012 ×FCR ×HVF

 

Power Rating, kW 

Po = 0.0012×FCR ×HVF ×th

 

Ash produced (%) 

Char= mass of char (kg)mass of fuel used (kg)×100

 

Thermal profile of cook stove  

 

Zone wise temperature inside the reactor above grate at height of 16 cm (z4),17 cm(z3), 17 cm(z2)  and 17 cm(z1) was measured by using the K-type (Chromel-Alumel) digital thermometer at an interval of 5 minutes starting from the ignition of the fuel to the end of the test run 

Economic evaluation 

i)  Net present value ii) Benefit cost ratio iii) payback period 

 =              =                   

 Operational characteristics 

The performance evaluation of improved cook stove was carried out using the selected fuel Tectonia Grandis and Butea monosperma. The performance tests of the improved cook stove were carried out by loading the cook stove reactor with rated loadings capacity. The results obtained from the series of test runs for cook stove are shown in Table below. 

Operational characteristics of improved cook stove 

Parameter 

Butea monosperma 

Tectonia Grandis 

Avg. 

Fuel, kg 

8.00 

7.50 

7.75 

Star up time, min 

3.00 

2.50 

2.75 

Operating time, min 

110.0 

105.0 

107.5 

Total operating time, min 

115.0 

110.0 

112.5 

Fuel Consumption Rate, kg/h 

4.20 

4.10 

4.13 

Sp. combustion Rate, kg/h/m2 

59.10 

57.90 

58.49 

Combustion Zone Velocity, m/h 

0.37 

0.38 

0.37 

Wt. of utensil, kg 

3.2 

3.2 

3.2 

Sp. heat of utensil, kcal/kg °C 

0.2 

0.2 

0.2 

Weight of water, kg 

21 

21 

21 

Initial temp. of water, °C 

27.80 

28.50 

28.15 

Boiling temp. of water, °C 

100 

100 

100 

Boiling time, min. 

50 

40 

45 

Water evaporated, kg 

8.00 

7.50 

7.75 

Latent heat of water, kcal/kg °C 

540 

540 

540 

Sensible heat of utensil, kcal 

49.28 

48.64 

48.96 

Sensible heat of water, kcal 

1516.20 

1501.50 

1508.85 

Latent heat Evaporation of Water, kcal 

4320.0 

4050.0 

4185.0 

Heat Output, kcal 

5885.50 

5600.10 

5742.81 

Heat input, kcal 

28616.00 

28237.50 

28426.75 

Thermal efficiency, % 

20.50 

19.80 

20.19 

Power Input, kW 

17.90 

17.60 

17.76 

Power Rating, kW 

3.60 

3.50 

3.55 

Ash produced (%) 

2.8 

1.7 

2.3 

The average start-up time of improved cook stove was 2.5-3 min and that depends on the amount of fuel igniting material used. The average operating time of fully loaded improved cook stove was found to be 107.5 min with average total operating time was 112.50 min. The average total fuel consumed during the test was found to be 7.75 kg.  

Based on above results, the average specific combustion rate was determined as 58.49 kg/m/h. Based on fuel consumption and height of reactor, the average combustion zone rate was found to be 0.37 m/h. The average thermal efficiency of improved cook stove was found to be 20.19%. The average input in terms of heat energy was 28427 kcal. The average power input of open top gasifier was found to be 17.76 kW. The average power output of improved cook stove was found to be 3.55 kW. The final product of combustion i.e. ash produced was 2.3%. 

Thermal efficiency by water boiling test 

The water boiling test of improved cook stove was carried out to evaluate the thermal performance. The average thermal efficiency of improved cook stove was found to be 20.19 per cent. The higher thermal efficiency of improved cook stove than the traditional biomass cooking system revealed to scope for fuel saving. 

Thermal profile of combustion zone  

The variation of temperature at different height from the grate of stove reactor and flame temperature with respect to operating time of the reactor was measured. The temperature was measured at every 5 min interval from the ignition of stove upto the end of process.  The stove is of open top, the wood was lit-up from the top. Hence the hot bed moves from top to bottom of stove up to the grate into the reactor. During initial phase of time, the temperature was higher at the Zone-1 and go on decreasing up to the ambient at Zone-4. After 55 min the condition, changed and higher temperature was observed at Zone-4 and lower temperature observed at Zone-1. In the Zone-1, the gradually rise in temperature from 400ºC to 560ºC was observed during initial 30 min of operation. The gradual decrease in temperature upto 532ºC was observed in Zone-1 till 80 min of operation. The gradual decrease in temperature from upper zone during the operation of stove indicates the movement of char towards the grate. In Zone-2, the gradual rise in temperature from 53ºC to 733ºC was observed during initial 50 min of operation. It showed that the hot bed was moved from Zone-1 to Zone-2. The maximum temperature attend by the Zone-2 was 733ºC. The gradual decrease in temperature up to 588ºC was observed in 80 min of interval. The gradual decrease in temperature from Zone-2 during the stove indicates the movement of char towards the grate.  The Zone-3 remains in the range of 740ºC to 900ºC up to 115 min of operation and after that gradually fall of temperature was observed till the end of process. The Zone-4 remains in the range of 900ºC to 1100ºC up to 130 min. and after that temperature decreases gradually till the end of process. The outer body temperature of cook stove remains constant in the range of 150º to 225ºC till the end of the process. Outer body temperature of cook stove rise from ambient to 225ºC was achieved in 105 min of operation. It is observed that the maximum temperature attained by the flame was found to be 504ºC. Which revealed that adequate amount of heat is produced for cooking by improved cook stove. 

Comparison 

Comparison between developed cook stove and traditional system for fuel saving are summarised as shown in Table below. The average fuel consumption rate was found to be 4.13 kg/h in improved cook stove where as 8 kg/h was found in traditional cooking system. 

Comparison between developed cook stove and traditional system for fuel saving 

Parameters per batch 

Cook stove 

Chulha 

Avg. 

Avg. 

Start-up time (min.) 

2.75 

3.00 

Operating time (min.) 

108 

75 

Total operating time (min.) 

113 

79 

Total fuel consumed (kg) 

7.75 

10.10 

Fuel consumption rate (kg/h) 

4.13 

8.10 

Fuel saved in traditional system (kg/h) 

3.97 

Economic evaluation 

Economic evaluations were carried out on the basis of Cash inflow and outflow statement of developed cook stove. The present worth was observed as Rs.111165/- over a basic price of improved cook stove as Rs.10100/- in 10 year. It can be concluded that the improved cook stove is economical and there is considerable saving in wood of Rs.30876/- per annum as compared to the existing system. The benefit cost ratio was calculated by dividing present worth of benefit stream with the present worth of cost stream and found to be 2.5 for cooking using cook stove. The payback period of cooking system was found to be 4.36 months for the initial investment of cook stove. The pay-back period is less than one year it means developed cook stove economically feasible for cooking application. 

Conclusions 

Calorific value of Tectonia Grandis and Butea monosperma were found as 3765 kcal/kg and 3577/kg respectively. The average thermal efficiency using water boiling test of improved cook stove was found to be 20.19 % using teak and khakra wood with dimension 5 to 7 cm in diameter  and 30 to 35 cm long as feed stock for community cooking at PAED boys hostel. Average fuel saving was found to 3.97 kg/h by using improved cook stove over the traditional cooking system. Yearly net saving was found as rupees 30,876/- with utilization of improved cook stove over the traditional cooking system at PAED boys hostel. The economic evaluation of cook stove conclude that the net present worth (Rs.), benefit-cost ratio and payback period was found to be Rs.1,11,165/-, 2.5 and 4.36 months, respectively and revealed its economically feasible for cooking application. 

Acknowledgements 

Authors are highly thankful to the College of Agricultural Engineering and Technology, Dediapada for financial support to carry out the research work. 


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