Biomass briquetting: The newest technology

Introduction

Many of the developing countries in the world produce huge quantities of agro residues but they are used inefficiently causing extensive pollution to the environment. The main residues are rice husk, coffee husk, coir pith, jute sticks, bagasse, groundnut shells, mustard stalks and cotton stalks. Sawdust, a milling residue is also available in huge quantity. The problems of transportation, handling, and storage are also there. Apart from these problems the direct burning of biomass in conventional grates is associated with very low thermal efficiency and widespread air pollution. The conversion efficiencies are as low as 40% with particulate emissions in the flue gases in excess of 3000 mg/Nm³ In addition, a large percentage of unburnt carbonaceous ash has to be disposed of. In the case of rice husk, this amounts to more than 40% of the feed burnt.

Taking a example of this problem: Ludhiana a city in Punjab generates 800 tonnes of rice husk ash everyday as a result of burning 2200 tonnes of rice husk. If we use these husks in making briquettes through briquetting plant than we could mitigate the problem of pollution while at the same time helping some industry to generate energy resource.

Briquetting technology is yet to get a strong foothold in many developing countries because of the technical constraints involved and the lack of knowledge to adapt the technology to suit local conditions. At present two main high pressure technologies: ram or piston press and screw extrusion machines, are used for briquetting. While the briquettes produced by a piston press are completely solid, screw press briquettes on the other hand have a concentric hole which gives better combustion characteristics due to a larger specific area.

With a view to improving the briquetting scene in India, the Indian Renewable Energy Development Agency (IREDA) - a finance granting agency - has financed many briquetting projects.