Beehive Briquette – A Reliable Alternative Fuel

May 25, 2009

Presented by:

Dr. Krishna Raj Shrestha
Centre for Energy and Environment
Kathmandu, Nepal

Beehive briquette

Beehive briquette

Abstract: Biomass has been the prime source of fuel from time immemorial. About 85 percent of all energy consumed in Nepal at present is supplied by biomass. With the present crisis of fuel wood shortages, the rural population is depending more and more to the burning of loose agro-residues and cow dung for domestic cooking and other purposes. This is a highly polluting practice associated with health hazards. To solve the problem of fuel wood and associated deforestation, these agro-residues should be upgraded to convenient and smokeless fuels. In the present study a simple technology is developed for the production of beehive briquettes by the carbonization of the agro-forestry residues and mixing of the char with binders followed by briquetting. It provides smokeless domestic fuel easily ignitable with sustained uniform combustion. The test results and the tentative financial analysis are presented.

Keywords: Biomass, beehive briquette, agro-residues, briquetting, carbonization, char

1. INTRODUCTION

It has been reported that almost 43% of the energy used by the third world countries has been derived from biomass and over two billion people are totally reliant on biomass fuels for their Energy needs [1]. The present fuel wood consumption exceeds the sustainable wood fuel production of Nepal. In many areas of the country where the wood fuel resources are in deficit, people are increasingly relying on agricultural residues and animal wastes to meet their domestic energy needs.

The excessive and unregulated use of fuel wood for house hold cooking, space heating and wood based rural industries have led to the destruction of Nepal’s forests leading to serious ecological and environmental consequences.  Considering the above facts, it has become essential to reduce the consumption of fuel wood by substituting it with the efficient utilization of agro- residues and forestry wastes.  However, in most developing countries, huge quantities of agro – residues are used inefficiently causing extensive environmental pollution.  In addition to the problem of handling the loose biomass residues, their burning in conventional grates is associated with very low thermal efficiency and wide scale air pollution.  Hence it has been realized that there is an urgent need of a technology for the conversion of  these agro-forestry residues to a clean fuel which can be used without polluting the environment.

2. Technologies for the use of loose biomass residues

Loose agro-residues are inconvenient fuels and gives low thermal efficiencies and more pollutants directly in stoves compared to wood.  But this problem can be solved by adopting fuel preparation technologies. The agro-residues can be compacted to improve the handling characteristics and provide clean combustion. These technologies are direct briquetting and carbonization followed by briquetting of the char [2].

3.  Carbonization and briquetting of char

This technology involves partial carbonization of biomass residues, mixing of char with binders followed by briquetting. The char obtained is crushed and mixed with binders like bentonite clays or with inert materials like lime as an energy extender and then briquetted into cylindrical beehive briquettes. These beehive or the honeycomb briquettes are far superior to any other shape of briquettes. Only one briquette is needed for a stove and gives clean gaseous combustion like L.P.G. The nineteen holes in the briquette act like gasifiers and produce gases for uniform combustion. In addition to its convenience, these are delightful to watch and suitable both for cooking and space heating.

I. The Charring Drum or the Vertical Drum Kiln

The biomass material is charred in a Charring Drum or Vertical Drum Kiln. The drum can be made out of empty crude oil drum of 200 liter capacity. It is fitted with a conical shaped grate with fixed chimney and a top cover and water seal arrangements as shown in Fig 1. In remote areas where such drums are not available, a beehive kiln can be made out of locally available materials like bricks or stones.

II. Briquetting Mould
The briquetting mould is made up of mild steel. It consists of three parts a) the bottom plate with nineteen protruding rods each 13 mm f in diameter, b) outer cylindrical cover to fit the bottom plate and c) a perforated plate to slide down along the rods into the cylinder as shown in Fig. 2.

III. Charring Procedure
The charring of biomass materials in the drum kiln  is very simple. Even a layman can be trained in a day or two to produce char. In this unit depending upon the type of biomass, about 40-100 kg of biomass can be carbonized to give 25-35 % yield of charred material over a period of 2-3 hours.

During charring, a large amount of volatiles are released so it is advisable to use these drums in open spaces. Further these drums can be easily transported to the areas of biomass availability.

IV. Briquetting of Char
The biomass char is crushed to fine powdery form so that the maximum size is not more than 0.8 mm. It is mixed with 25% by its weight of bentonite clay or local potters clay, which acts as a binder as well as energy extender and a required quantity of water is added to the mixture.. Molasses or cooked starch may also be used as binders for briquetting.

For making beehive shaped briquettes from the char clay mixture, the mould set is filled compactly with the mixture and after filling up to the brim the top layer is leveled with a flat wooden piece. Now, holding the handles the mould is turned upside down on to a firm ground. The mould is removed and the briquette is allowed to dry in the sun for 2-3 days.

The briquette stove is a simple, cylindrical stove as shown in Fig. 3. It is made up of mild steel sheet. Towards the base there is a hole for air inlet and a grate made up of 5 mm iron rod placed about 50 mm above the base of the stove. The inside of the stove is lined with a mixture of clay, husk and dung. In the rural areas where the metal stove is not available, it can also be made out of locally available material like clay and cow dung,

4. RESULTS AND DISCUSSION

The proximate analysis and heating values of charcoal and beehive briquettes were done and are given in Table 1.

Table 1. Proximate Analyses and Heating values of Biomass Char and Beehive briquette

Proximate Analysis(%)
Heating Value
Material
Moisture Content
Volatile Matter
Fixed Carbon
Ash
Higher Heating Values (MJ/kg)
Biomass Char
8.86
17.97
69.72
12.31
26.04
Beehive Briquette
2.27
18.63
49.27
32.1
18.72

1. The Values of Volatile Matter, Fixed carbon and ash are given on dry basis.

Pollutant Emission Test on Beehive Briquette.

Pollutant emission test on beehive briquette was done by carrying out simple test determining the mean concentration of pollutants that were released to the atmosphere. Beehive briquette was ignited and the stove was kept inside the experimental hood . The purpose of the metallic flue gas enclosure was to ensure that a controlled amount of air enters the inlet of the briquette stove and all the exhaust gas would be collected and ducted out form the experimental system [3].

Apparatus

A gas chromatograph and a number of gas analyzers were used to monitor concentration of different gases.

Time (min) CO(%) CO2(%) CH4(ppm) NOx(ppm) NO (ppm)
0
0
0
0
0
0
5
0.1
0.5
100
2.99
1.95
10
0
0.5
100
0.34
0.6
15
0
0.5
100
0.41
0.42
20
0
0.5
100
0.5
0.46
25
0
0.4
200
0.55
0.56
30
0
0.4
100
0.6
0.6
35
0
0.4
100
0.63
0.64
40
0
0.4
100
0.64
0.65
45
0
0.4
100
0.65
0.66
50
0
0.3
100
0.66
0.68
55
0
0.3
100
3.22
1.87
60
0
0.2
100
3.01
2.88
65
0
0.1
100
2.96
2.79
70
0
0.1
100
2.58
1.75

The beehive briquette is easy to ignite. For igniting the briquette, it is placed on the grate inside the stove and ignited from the bottom end of the briquette. The heat thus generated can be used either for cooking meal or for space heating purposes. One briquette generally lasts for one to one and half hour. One briquette is usually enough for cooking a complete meal for a family of five to six persons. The calorific value of the briquette was determined by using a bomb calorimeter and was found to be 18.73 MJ/kg. The efficiency of the briquette stove was determined by the water-boiling test and was found to be 26 per cent. These beehive briquettes are most suitable for making barbecues. Barbecue stove using four to eight briquettes at a time were also designed and tested. For space heating requirements the length of the stove can also be increased to accommodate two briquettes at a time. Beehive briquetting technology has the potential to be propagated as an income generating activity. The major inputs required are only man power and biomass residues. It can be started as a family unit. A rural family with four charring drums and two hand moulds and other accessories costing US $ 602.73 and using manual labour can produce about 6500 pieces of beehive briquettes per month, weighing 400 grams each (approximately). By selling the briquettes at US $0.06 per piece an income of US $464.28 per month can be earned and a net profit of US $306.85 be made. A tentative financial analysis is presented in Table 3 by comparing it with kerosene oil.

Table 3.  Comparative financial performance of briquette with kerosene (Tentative)

S.N Cost Detail Amount US $
1 Fixed cost Equipment(Charring drum + Moulds + tools)

Life : 4 years

571.2
Annual depriciation(charring drum only) 114.28
Monthly depriciation 9.57
Interest on loan 8.57
2 Operation cost (Monthly*)
Energy input 27.85
Biomass 111.42
Labour (N Rs. 100/ Per day)
Total Monthly cost 157.42
Quantity of Briquettes Produced 2626 kg
No. of Briquettes Produced 6500 Pieces
Cost per kg of Briquettes US $ 0.064
Cost per piece of Briquette US $ 0.03
Cost per GJ of Briquette US $ 3.20/GJ
Cost per GJ of Kerosene US $ 16.54/GJ
Calorific value of Beehive Briquette 18.73 MJ/kg
Calorific Value of Kerosene 46.5 MJ/kg

5. CONCLUSION

The beehive briquetting technology is simple, pollution free and eco-friendly. It provides smokeless domestic fuel easily ignitable with sustained uniform combustion. The use of agro-forestry residues can replace fuel wood and wood charcoal. Being eco-friendly with high social relevance and having the potential to contribute forest conservation, this technology should be widely promoted throughout Nepal.

6. REFERENCES

[1]     Hall, D.O. and Overend, R.P. (Eds). (1987). Biomass Regenerable Energy, John Wiley & Sons.

[2]     Grover, P.D. (1995). Briquetting of Wood and Agro- Residues, Wood Energy News, Vol. 10. No.3.. pp 12- 14.1.

[3]        Shrestha, K.R. (2000). Design and Testing of Hybrid Solar /Biomass Energy Powered Drying System, Asian Institute of Technology, Bangkok, Thailand.

Advertisements

One Response to “Beehive Briquette – A Reliable Alternative Fuel”


  1. Thank you for your contribution! – Interesting!


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: