Gliricida: Local Fuel to Local Power
Ray Wijewardena, Colombo, Sri Lanka, September 2005
1. Experimental fuel-wood-plots of Acacia (left) and Leucaena (right) growing between avenues of coconut palms.
2. Rows of Gliricidia sepium (our most sustainable and productive fuel-wood crop, so far, growing in twin rows in avenues between palms. The Gliricidia trees in this picture are already about 15 years old.. and will probably keep yielding for the next hundred .. bar some disaster! (storms or insects etc).
When we entered quantity-production we realised we had erred by not leaving an alternate avenue free of fuel-wood trees, for the priority (logistic) task of systematically plucking and collecting the coconuts... every two months. New plantings of fuel-wood crops now therefore reserve each alternate avenue for harvesting the nuts.
3. Harvesting (lopping) the branches of the Gliricidia trees(at about waist height) every four- to-six months. This system of pruning does not damage the tree... Only lops the branches... so the tree keeps on growing and producing wood and foliage under the year-round tropical sunshine and occasional monsoon rain...
Yields are about 6 kgs (dry) of wood and 5 kgs (wet) of foliage per tree per year. These trees are usually planted 1 metre apart (10,000 per ha) in the row and with row spacing from 1 metre to 2 metres to 10 metres, depending upon the logistics of harvesting and collecting the wood and foliage as well as the primary crop, - in our case, coconut.
Three bags (or 80 kgs wet-weight) of the foliage has, we find the 'N' equivalent of 800 gms of urea fertiliser... which is what a high-yielding (100 nuts per palm) palms needs annually,... plus K and Mg. according to how much of the crop is removed from the site.
4. The green foliage (here about 80 kgs) is laid in a trench around the palm,, together with any supplementary magnesium, phosphate and potassium (as annual soils- and leaf-analyses indicate is neccessary)... and turned in. This is an annual operation... performed for 10,000 palms on this little coconut small-holding... The application of the N, thus, organically, reduces costs for fertilising/green-manuring by half!.. This is the major item in COP to be managed!
5. The branches of fuel-wood are further lopped to about 4 cm lengths, which helps them dry very quickly, but no less than 20%..and then tipped into the hopper (orange, here) of the ANKUR gasifier. The operator is peering at the hot bed though one of the air intakes (someone called them tuyeres?) .. where the wood combines with limited air to form producer gas.
Earlier an air-blower (sucker?) was used to draw the air through the burning wood at the bottom of the hopper, but now we use a venturi (from bygone steam days) in conjunction with the spray of water for 'scrubbing' the gases, as we wished our ANKUR 4 kW gasifier-generator to be 'stand-alone' and not be dependent upon external power. Now an overhead (500 litre) tank supplies the initial flow of scrubbing water through the venturi to suck the air through the gasifier...
No external power needed! Perhaps the modern sophisticated gasifiers have electronic controls, pumps and blowers to achieve this...doubtless at additional cost. All these features are available on the newer ANKUR 9kW gasifiers which superceded this prototype.
We now have a 230-volt motor driven chopper which (with a 'rotating-tooth mechanism) chops the branches into the required 3-5 cm length as fast as the machine can be hand-fed. If such a machine is not available, the Gliricidia sticks/branches can be chopped by hand-labour quite economically. These are then very easy to dry from the 'green' state (of about 50%) to the ideal of about 20% moisture.
After scrubbing, the (now cooled) gasses pass through a primary cleaner containing saw-dust filter (on the right) and a secondary (cloth) filter to pass up and into the 'manual-carb-urettor' with two levers.. One to control the quantity of gas and the other to control (via the auto-type filter) the air. The mixture then feeds into the intake of the spark-ignition engine-generator (230 V, 50 cycle) shown in tne left fore-ground.
It is important to note the 2"-angle-iron stand on which the engine and gasifier are mounted, so that the natural vibration of the single-cylinder 1500 rpm engine provides the gassifier hopper with just the correct vibration for steady flow of the wood down and through the hopper. Such neat 'vibrators' are also fitted to the hoppers of the larger (e.g. 30 kW and over)ANKUR gasifiers to ensure smooth and steady flow of fuel through the hopper without 'bridging'.. thus also coping with a wide range of woods and materials for gasificiation.