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Need for Pelletizing

India with different agro climatic regimes does produce more than 250 million tons surplus Agro Residues annually. This is either not utilized at all or utilized sub optimally. Equal amount of other biomass gets wasted and results in severe environmental degradation.

Processing capacity of even 200 million tons of biomass in 10 years, will not only eliminate Import of coal but also cut down liquid fuel import substantially. Processing capacity of 100,000 ton requires an investment of about 2 – 3 Million USD and provides direct employment to around 50 people and indirect employment to 4 – 5 times the number, that too in rural areas. Total investment in processing facilities of 200 million tons will be around 5 billion USD and it is an insignificant amount compared to renewal fund planned by year 2020.

LACK OF DEVELOPMENT

pellets_1

India with more than 5000 Briquetting Presses is most advanced nation in the world in biomass densification. India produces about 5 million tons of briquettes. Addition of 10-million-ton capacity each year is a big task. Briquetting is simpler technology as compare to other technology but have severe limitations which will limit its growth.

  • Product is size specific and do not meet the requirement of user most of the time
  • Unit capacity is low as compared to other densification technology
  • Handling of briquette cannot be mechanized as per requirement
  • Due to above factors it is unlikely that briquetting facilities are going to increase significantly

 

IN CONTRAST TO ABOVE PELLETIZING HAS FOLLOWING ADVANTAGE

  • Large plant up to 100,000 tons annual output can be built with one line of 20,000 tons or more
  • Output size is not equipment specific and 8 – 25 mm diameter pellets can be produce from any press
  • It is possible to produce following pellet size
    • 8-10 mm diameter for Fluidized bed boiler (over bed fired)
    • 16-18 mm diameter for Stroker fired or traveling grate boiler
    • 22-25 mm diameter for Manually fired fixed grate boiler
  • Pellet handling can be mechanized
    • It can be stored in bunkers and unloaded in truck
    • It can be conveyed pneumatically
    • It can be fired mechanically in any boiler configuration

It is also possible to produce biomass granules having bulk density of 300-350 Kg/m3 and less than 6 mm size convenient to fire in under bed-fired fluidized bed boilers (pellet have bulk density of +650 Kg/m3)

 

PROBLEM IN PELLETIZING FIBROUS BIOMASS

Conventional pellet presses are of ring die type and are used for processing animal feed. Mostly materials are powdery and with high bulk density of agglomerate (input feed to pelletizer). Pelletizing is done at high speed of 7 – 8 meter/sec and pellet size is restricted to 6 mm diameter (quarter of an inch). These restrictions are real and cannot be relaxed. Since die thickness is 35 – 50 mm and it cannot make pellet of higher diameter than 10 mm. Speed cannot be less than this to enable lift of material against gravity.

These problems were solved to great extent in flat die presses where speed can be reduced and die thickness can be increased to the extent desired. However, moving die could not be accommodated easily when pellet sizes of more than 15 mm diameter were to be produced and this led to development of fixed flat die pelletizer. Fixed flat die pellet mills are sturdy and consume less power due to low rotating mass and are more suitable when higher diameter pellets are to be produced.

 

FLAT DIE PELLETIZER

Flat Die has following advantage over conventional ring die type:

  • Making the die is much simpler as compared to Ring die.
  • Replacement/Repair of die is easier.
  • Pellet press can work much longer time in one setting.
  • Low Density Fibrous Material can be pelletized with ease
  • Higher diameter pellets can be produced

 

ACHIEVEMENT SO FAR IN USE OF FLAT DIE PELLETIZER

Although it has been possible to develop high quality flat die pelletizer but use has not been wide spread due to following constraints:

  • Since pelletizing speed is much lower 2 – 3 meter/sec as compared to 7 – 8 meter/sec in Ring die, output is normally 1/3rd in flat die as compared to Ring die press and that makes it costly capacity wise.
  • There are few thousand Ring die pellet presses in production in India and introducing new and costly product is difficult.
  • Large capacity biomass pelletizing necessitates, collection pre-processing for size economy, but so far only small capacity plants are operated and emphasis on collection and pre-processing is lacking.

 

CONCLUSION

Based on the experience of few Pelletizing Plants that have been installed, it is expected that there will be exponential growth of Pellet Plants in India in next 10 years and this will far exceed the other technologies of densification. 

 

Amrit Khater

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.)

 

 

 

 

 

 

 

 

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