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close this bookBoiling Point No. 43 - Fuel Options for Household Energy (ITDG - ITDG, 1999, 44 p.)
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A compressing machine for briquetting biomass waste into usable fuel

by K. Marimuthu, S. Arumugam, S. Ramamurthy, E. Savarimuthu, Department of Physics, Gandhigram Rural Institute, Gandhigram - 624302, India.

Un ipement de compression innovateur pour la production de briquettes a partir des dets de biomasse.

Les briquettes de biomasse sont un bon substitut au bois. Cependant en raison de leur faible densitleur transformation en briquettes est indispensable. Les ipements disponibles sont chers et gralement non adaptes pour traiter de faibles quantit La machine dite dans cet article est peu coe, simple a construire et peut e utilispar un mge. Un foyer Chulha de conception assez simple est lement dit.

Introduction

Biomass is available in plenty as waste from certain industries such as saw mills, the coir industry and rice mills, and also in villages as agro-residues. But the utilization of these biomass residues in their natural form as a fuel is difficult because of their very low bulk density, low heat release and the excessive amounts of smoke they generate.

One of the ways of improving the thermal value of such biomass is to compress it into briquettes. The briquetting machines available in the market are costly and are intended for bulk production of briquettes and the users need certain skills in operating and maintaining them. This paper describes a simple low-cost household-level briquetting machine that has been developed. As briquettes cannot be used in standard firewood chulhas (stoves), a single-pot clay chulha in which these briquettes can be used as fuel has been developed.

Construction of briquetting machine

The briquettes were made in the form of hollow cylinders with an outer diameter of 16 cm and an inner diameter of 7 cm and length 18 cm, to fit into the chulha. Two 24 cm long cylindrical tubes were used, one of diameter 16 cm and the other with diameter 7 cm. The larger of these cylinders is formed from two 0.5 cm thick steel plates, shaped into 24 cm long half cylinders, flanged down their lengths. When clamped together, they form the 16 cm diameter outer cylinder. The half-cylinders can be separated to remove the briquettes easily after compression (see Figure 1). Holes at 2 cm and 22 cm along the flanges allow these plates to be bolted together.

A PVC tube of outer diameter 7 cm and length 24 cm serves as the inner tube. The outer steel tube fits between an open-topped rectangular frame (31 cm x 35 cm), to which it is welded, as shown in Figure 1. The top of the frame is 7 cm above the top of the iron tube. Two 1.5 cm diameter threaded holes are tapped into the frame at 11 cm from each edge. Through each hole passes a long threaded bolt of diameter 1.5 cm and length 30 cm. The bottom ends of the bolts are welded to an annular steel disc of inner diameter 7.0 cm and outer diameter 15.5 cm (Figure 2). To the top ends of the bolts are attached two 8 cm diameter discs which act as screw handles. By rotating these handles the steel compacting disc can be moved up and down the annular gap to compress the biomass or to remove the compressed fuel after it has been briquetted.

During combustion, to allow air to enter at the base of the stove, a hole of diameter 8.0 cm is punched symmetrically through the briquette. For this, a hole in one side of the outer tube is needed, the centre of which is 6.5 cm from the bottom of the tube. Into this is inserted a circular tube (such as a bottle) of the same diameter, which touches the inner cylindrical tube. A photograph of the entire briquetting machine is shown in Figure 3.


Figure 1:


Figure 2:

Briquetting method

In order to make biomass waste into fuel briquettes the following procedure is adopted. About 500 gm of biomass is mixed with 60 gm of paper pulp (which acts as a binder) and water is added until it binds together well. The compacting disc is raised to its topmost position. The two semi-cylindrical steel sections are bolted together to form the outer cylindrical tube, and the PVC tube is put down the middle. Another tube (or suitably sized bottle) of diameter 8 cm is inserted through the side hole of the outer tube until its closed end touches the inner tube.

The biomass with binder mixture is poured into the space between the inner and outer tubes. After pouring the maximum possible quantity of the mixture into the space, the compression disc is lowered and the fuel is compressed to form a briquette. If necessary, the compacting disc can be moved up, some additional mixture added, and the compaction done again. The compacting disc is raised, the machine is dismantled and the briquette removed. The wet briquette is kept in the sun for two or three days to dry before use. A briquette prepared in this way is shown in Figure 4.


Figure 3: Hand operated briquetting machine with compacted coir with fuel

Marimuthu

Single pot chulha

Conventional chulhas cannot be effectively used for the briquettes, so a single pot portable chulha, suitable for briquettes, has been developed (Figure 4). It is a cylindrical chulha of diameter 17.5 cm and height 19 cm. A circular opening of 8 cm diameter close to the base of the chulha allows air to reach the fire. The hole in the briquette is aligned with the opening in the chulha, About 70 gm of firewood, inserted into the chulha through the front opening, is needed to start the briquettes burning. The top of the chulha is curved (as shown in Figure 4) to provide a gap between the bottom of the vessel and the top of the chulha. This gap serves as an exit for the hot gases

Results and discussion

In the present study, briquetting of sawdust and coir-pith has been successfully achieved with waste paper pulp as a binder. The calorific value of each of the briquettes has been measured using an Advance bomb calorimeter and the values obtained are presented in Table 1. The estimated calorific values are close to those of commercial briquettes made with sophisticated machines (2). For comparison, the calorific values of commercially made AEN rice husk briquettes, and AGGNI biomass briquettes and Jaysree Industries coir pith briquettes are 3650 cal/gm, 4300 cal/gm and 3045 cal/gm respectively. This shows that the quality of the briquettes prepared using the simple household level briquetting machines is acceptable. Cooks could prepare the briquettes easily without drudgery with this machine, which could be made locally at a cost of about Rs800/-.

In order to determine the efficiency of the chulha, a water-boiling test was conducted (3). An aluminium vessel of mass 202 gm with water 1.5 kg was taken for the water-boiling test and the stove was lit as described above. The efficiency of the chulha was found using the briquettes prepared from selected biomass residues, the time taken for just boiling the water and the efficiency of the chulha are also shown in Table 1. The estimated efficiency of this chulha (20%) is comparable to the efficiency of several improved smokeless chulhas and low levels of smoke have been observed.


Figure 4: Single pot pottery chulha with compacted coir pith fuel

Marimuthu

Table 1: Calorific value of briquettes

Raw material

Calorific value
cals/gm

Time to reach boiling point
(mins)

Efficiency
(%)

Sawdust

3381

15

19

Coir pith

2300

19

21

References

1 Improved Smokeless Chulhas: A Guide to Trainees. N. Jeyabal Krishnan & K. R. Swaminathan, Technical back-up support unit, Bio-energy Department, Tamilnadu Agriculture University, Coimbatore

2 D.P. Grover (1995) Briquetting of wood and agro-residues; Wood Energy News 10(3); pp. 12-14

3 B.M.L. Garg and Paramjeet Singh Rajpal (1993). Regional Wood Development Programme in Asia:
Indian Improved Cookstove