Biomass gasification is a thermo-chemical conversion
process, which utilizes oxidizing agents (air, oxygen, steam or
amix of them), to produce a fuel gas (syngas) rich in hydrogen,
carbon monoxide, methane; carbon dioxide, steam and nitrogen,
in addition organic (tar) and inorganic (H2S, HCl, NH3,
alkali metals) impurities and particulate are also obtained [17].
Conventional small-to-medium scale gasification technologies
utilize fixed bed reactors and air as gasification medium.
This results in low conversion efficiency and in a syngas with
a poor hydrogen fraction, because nitrogen contained in the
air dilutes the syngas and its purification requires higher energy
consumption. A possible solution to reduce the amount
of N2 in the product gas is biomass gasification with oxygen
and steam [18]. Nevertheless, cost of oxygen etoday especially
used in coal gasification [19] e is still too high for a feasible
application in small scale plants [20e23]. A steam blown indirect
heated biomass gasifier, as the one analysed in this
work, avoids problems caused by air producing a gas with high
calorific value (12e14 MJ/Nm3) and high content of hydrogen
[22,23], although the plant complexity increases owing to the
additional combustor and the additional heat recirculation
system between combustor and gasifier. Since particulate,
organic and inorganic impurities are undesirable and noxious
by-products, gasification is followed by gas cleaning processes
as filtration, scrubbing, reforming, cracking, etc.