6.2.3. Bio-power technologies
There are six major types of bio-power systems: direct-fired,
co-firing, gasification, pyrolysis, anaerobic digestion and small,
modular systems. Most of the bio-power plants use direct-fired
systems. In addition, gas and liquid fuels can be produced from
biomass through pyrolysis. In pyrolysis biomass is heated in the
absence of oxygen. The biomass then turns into a liquid called
pyrolysis oil, which burns like petroleum to generate electricity.
Several bio-power technologies can be installed in small, modular
systems which can generate electricity at a capacity of 5 MW or
less [62]. Bridgwater et al. [60] presented a comparison of pyrolysis,
gasification and direct combustion for electricity generation from
wood chip feedstock and concluded that fast pyrolysis system has
great potential to generate electricity at a profit in the long term,
and at a lower cost than any other biomass to electricity system
at small scale. A lot of studies have been made by researchers for
the environmental and economic feasibilities of RE from biomass
for different countries. Recently, Buragohain et al. [63] highlighted
the technical and economical issues related to decentralized power
generation in India using biomass gasification and present their
analysis for both fixed bed and fluidized bed gasification with preand
post-process treatment. The study suggests that the downdraft
gasifier design, being well developed and demonstrated, is
the most feasible technology for wood biomass to energy conversion
[61]. Formerly Lora and Andrade [64] demonstrated available
technologies for electricity generation out of biomass for different
power ranges and concluded that biomass energy technologies
having the high and medium technological maturity and economic
feasibility are the steam cycle, gasification with internal combustion
and stirling engine and biodiesel/internal combustion engines.
For small power systems (5–200 kW) the situation is critical as they
are not available technologies with high technological maturity and
economical feasibility. Extensive research is still needed to find
optimal biomass to energy conversion flow sheet with minimum
waste generation and valuable by-products.