Science and technology aspects of bio-residue gasification

This paper addresses the use of loose biomass material like sawdust and other agro residues as fuel to generate electricity for captive power requirements using gasification system and a reciprocating engine. The development of open-top downdraft re-burn gasifiers at the Indian Institute of Science has made it capable of using agro residues after processing them into briquettes—a multi-fuel option. The inherent design feature that provides adequate residence times and establishes the right flux has made this possible. A typical closed-top design has a high superficial flux at the throat in the range of 2–2.5 kg m⁻² s⁻¹ as against the open-top design at 0.2–0.4 kg m⁻² s⁻¹ at the lowest cross section. This essentially prevents ash softening and fusion, an issue that needs to be addressed while using agro residues containing higher inorganic content. Further, captive power generation systems based on this design are installed in pencil manufacturing industries to use the sawdust generated. This paper addresses the performance of the gasification and engine system in the dual fuel mode. One industrial unit has operated for over 11,000 h in dual fuel mode in 2 years and generated about 400 MWh consuming about 400 tonnes of briquettes and about 35,000 l of diesel. The details of the system configuration, performance, and operations are reported here. Some of the critical issues that were addressed to ensure good industrial operations are highlighted.