Annual Generation of Biomass in India is more than thousand million tons. Part of this is residues from Agricultural Crops. Significant part of this is used as Animal Fodder, like Wheat Straw, Corn/Maize Straw and Bajra Straw. These are stored for off-season animal fodder.
Then there are Stalk/Straw, which are not used as Animal Fodder; like
- Mustard Husk/straw
- Soya Husk/straw
- Gwar/Till Straw/Cotton Stalk
- Soya Husk/Straw
- Cane Trash
- Coconut Leaves
Besides these, there are other types such as;
- Bagasse and Similar Waste
- Ground Nut Shell and husk of many others
Horticultural waste such as Leaves, Twigs, Branches, Bark, Lantana Camera & Sarkanda Grass etc. also form part of the biomass.
Most of these residues when harvested have very low bulk density and many times high moisture too. For gainful utilization of this biomass as Renewal Source of Energy, it should pass through pre-processing such as chopping, cutting, drying and grinding etc.
Different types of cutters and chippers are used for cutting/chopping the biomass to below 25 mm edge to edge size, diameter can be 10 mm.
Biomass requiring cutting/chopping are:
- Cotton Stalk/Arhar Stalk
- Mustard Stalk/Till Stalk
- Wood Waste/Bark etc
- Sarkanda/Lantana etc
These are chopped in wet condition, mostly has moisture of 25-30%. During storage, it dries up having 15-20% moisture and is good to go for further processing.
There are number of biomass which have high percentage of moisture, for example:
- Bagasse : 50%
- Saw Dust : 35-40%
- Press Mud : 50-70%
- Spent Wash/DGDS etc : 50-70%
These residues can be dried up to 20-25% moisture by passing them in hot air stream of 500-5500 C. In Flash dryer, these biomass become air born and are dried to desired moisture in very short time of 1.5 to 2 sec. While the wet air is discharged to atmosphere. This is the most economical method to dry the biomass having high moisture.
Loose Biomass has very low bulk density of about 40-60 Kg/m3 and size of edge to edge +25 mm and diameter +10 mm. To increase the bulk density by reducing the size, material is goes through grinding/shredding. Hammers moving at high speed of 50 meter/sec grind the material against grinding bars. Lighter materials get shredded during this process.Material is transported pneumatically and collected in cyclone. Dust laden air is discharged through dust suppression air filters.
Material after grinding/shredding have size less than 10 mm edge to edge and bulk density increases to around 140 Kgs/m3. During grinding/shredding, moisture also get reduce to 5% level.
DENSIFICATION BY BRIQUETTING:
Biomass having moisture of 10-12% and bulk density above 140 Kgs/m3 are put to Briquetting. Reciprocating ram forces the incoming biomass from vertical feeder to system to dies. A pressure of 1200 Kgs/cm2 is developed to extrude the material through split die. During high pressure compression, temperature of biomass rises to +3500 C and lignin comes out to surface. Compressed log at high temperature is cooled in split die to about 1000 C. Further cooling and toughening happen in cooling line.
Different types of Briquetting Presses are available in market;
- Briquetting Press (40-125) : 250 Kgs/hour
- Briquetting Press (50-150) : 500 Kgs/hour
- Briquetting Press (60-175) : 750 Kgs/hour
- Briquetting Press (65-200) : 1000 Kgs/hour
- Briquetting Press (70-200) : 1250 Kgs/hour
- Briquetting Press (90-200) : 2000 Kgs/hour
Bulk density of Briquettes is + 750 Kgs/m3
Specific Density is + 1250 Kgs/m3
Length of Briquettes can be 120-200 mm as desired. Process of binderless extrusion is pressing granular biomass into matrix of different dies. In each stroke biomass is forced into matrix of dies. In taper die, biomass gets compressed and gets heated up. As compressed log moves, it passes through split die of smaller cross section holes. Materials get extruded and lignin gets sprayed on the outer surface of compressed logs.
Compressed log gets cooled to 1000 C from 3000 C under pressure and lignin gets deposited on outer surface. Compressed and cooled log, i.e. briquettes, moves to cooling line for cooling and further strengthening.
At the end of cooling line, material can be cut to desire size of 120-200 mm. Temperature of briquettes at the end of cooling line is around 500 C. It is ready for packing and shipment.
For easy handling, briquettes are packed in HDPE or similar bags.
Director, Hi Tech Agro Energy Pvt. Ltd.
(Hi Tech Agro Energy is one of the leading companies providing Integrated Turn Key Solutions for setting up of such plants.)